Merge `package:markdown` (#1208) - [x] Move and fix workflow files, labeler.yaml, and badges in the README.md - [x] Rev the version of the package, so that pub.dev points to the correct site - [x] Add a line to the changelog: ``` * Move to `dart-lang/tools` monorepo. ``` - [x] Add the package to the top-level readme of the monorepo: ``` | [markdown](pkgs/markdown/) | A portable Markdown library written in Dart that can parse Markdown into HTML. | [![pub package](https://img.shields.io/pub/v/markdown.svg)](https://pub.dev/packages/markdown) | ``` - [ ] **Important!** Merge the PR with 'Create a merge commit' (enabling then disabling the `Allow merge commits` admin setting) - [x] Update the auto-publishing settings on https://pub.dev/packages/markdown/admin - [x] Add the following text to https://github.com/dart-lang/markdown/:' ``` > [!IMPORTANT] > This repo has moved to https://github.com/dart-lang/tools/tree/main/pkgs/markdown ``` - [ ] Publish using the autopublish workflow - [ ] Push tags to GitHub using ```git tag --list 'markdown*' | xargs git push origin``` - [x] Close open PRs in dart-lang/markdown with the following message: ``` Closing as the [dart-lang/markdown](https://github.com/dart-lang/markdown) repository is merged into the [dart-lang/tools](https://github.com/dart-lang/tools) monorepo. Please re-open this PR there! ``` - [x] Transfer issues by running ```dart run pkgs/repo_manage/bin/report.dart transfer-issues --source-repo dart-lang/markdown --target-repo dart-lang/tools --add-label package:markdown --apply-changes``` - [ ] Archive https://github.com/dart-lang/markdown/ --- - [x] I’ve reviewed the contributor guide and applied the relevant portions to this PR. <details> <summary>Contribution guidelines:</summary><br> - See our [contributor guide](https://github.com/dart-lang/.github/blob/main/CONTRIBUTING.md) for general expectations for PRs. - Larger or significant changes should be discussed in an issue before creating a PR. - Contributions to our repos should follow the [Dart style guide](https://dart.dev/guides/language/effective-dart) and use `dart format`. - Most changes should add an entry to the changelog and may need to [rev the pubspec package version](https://github.com/dart-lang/sdk/blob/main/docs/External-Package-Maintenance.md#making-a-change). - Changes to packages require [corresponding tests](https://github.com/dart-lang/.github/blob/main/CONTRIBUTING.md#Testing). Note that many Dart repos have a weekly cadence for reviewing PRs - please allow for some latency before initial review feedback. </details>

commit: d785fbb4c08f368f312f02744f2e3b63009630d9 [log] [tgz]
author: Moritz <mosum@google.com> Mon Jan 13 09:24:45 2025 +0100
committer: GitHub <noreply@github.com> Mon Jan 13 09:24:45 2025 +0100
tree: b2ce928425d3be58faceed72700081ed0c22023d
parent: 54b89986ce979324476b5c0ff4b6c0231d7c7c55 [diff]
parent: a8abbfb306f035bfc80ecb337a46cd3c9513f28c [diff]
diff --git a/.github/ISSUE_TEMPLATE/io.md b/.github/ISSUE_TEMPLATE/io.md
new file mode 100644
index 0000000..5646f0f
--- /dev/null
+++ b/.github/ISSUE_TEMPLATE/io.md

@@ -0,0 +1,5 @@
+---
+name: "package:io"
+about: "Create a bug or file a feature request against package:io."
+labels: "package:io"
+---
\ No newline at end of file

diff --git a/.github/ISSUE_TEMPLATE/package_config.md b/.github/ISSUE_TEMPLATE/package_config.md
new file mode 100644
index 0000000..f6322d0
--- /dev/null
+++ b/.github/ISSUE_TEMPLATE/package_config.md

@@ -0,0 +1,5 @@
+---
+name: "package:package_config"
+about: "Create a bug or file a feature request against package:package_config."
+labels: "package:package_config"
+---
\ No newline at end of file

diff --git a/.github/ISSUE_TEMPLATE/pool.md b/.github/ISSUE_TEMPLATE/pool.md
new file mode 100644
index 0000000..7af32c4
--- /dev/null
+++ b/.github/ISSUE_TEMPLATE/pool.md

@@ -0,0 +1,5 @@
+---
+name: "package:pool"
+about: "Create a bug or file a feature request against package:pool."
+labels: "package:pool"
+---
\ No newline at end of file

diff --git a/.github/ISSUE_TEMPLATE/pub_semver.md b/.github/ISSUE_TEMPLATE/pub_semver.md
new file mode 100644
index 0000000..c7db9b5
--- /dev/null
+++ b/.github/ISSUE_TEMPLATE/pub_semver.md

@@ -0,0 +1,5 @@
+---
+name: "package:pub_semver"
+about: "Create a bug or file a feature request against package:pub_semver."
+labels: "package:pub_semver"
+---
\ No newline at end of file

diff --git a/.github/ISSUE_TEMPLATE/pubspec_parse.md b/.github/ISSUE_TEMPLATE/pubspec_parse.md
new file mode 100644
index 0000000..2d65881
--- /dev/null
+++ b/.github/ISSUE_TEMPLATE/pubspec_parse.md

@@ -0,0 +1,5 @@
+---
+name: "package:pubspec_parse"
+about: "Create a bug or file a feature request against package:pubspec_parse."
+labels: "package:pubspec_parse"
+---
\ No newline at end of file

diff --git a/.github/ISSUE_TEMPLATE/source_maps.md b/.github/ISSUE_TEMPLATE/source_maps.md
new file mode 100644
index 0000000..a1e390a
--- /dev/null
+++ b/.github/ISSUE_TEMPLATE/source_maps.md

@@ -0,0 +1,5 @@
+---
+name: "package:source_maps"
+about: "Create a bug or file a feature request against package:source_maps."
+labels: "package:source_maps"
+---
\ No newline at end of file

diff --git a/.github/ISSUE_TEMPLATE/source_span.md b/.github/ISSUE_TEMPLATE/source_span.md
new file mode 100644
index 0000000..7dbb3c4
--- /dev/null
+++ b/.github/ISSUE_TEMPLATE/source_span.md

@@ -0,0 +1,5 @@
+---
+name: "package:source_span"
+about: "Create a bug or file a feature request against package:source_span."
+labels: "package:source_span"
+---
\ No newline at end of file

diff --git a/.github/ISSUE_TEMPLATE/sse.md b/.github/ISSUE_TEMPLATE/sse.md
new file mode 100644
index 0000000..17cc488
--- /dev/null
+++ b/.github/ISSUE_TEMPLATE/sse.md

@@ -0,0 +1,5 @@
+---
+name: "package:sse"
+about: "Create a bug or file a feature request against package:sse."
+labels: "package:sse"
+---
\ No newline at end of file

diff --git a/.github/ISSUE_TEMPLATE/stack_trace.md b/.github/ISSUE_TEMPLATE/stack_trace.md
new file mode 100644
index 0000000..417362b
--- /dev/null
+++ b/.github/ISSUE_TEMPLATE/stack_trace.md

@@ -0,0 +1,5 @@
+---
+name: "package:stack_trace"
+about: "Create a bug or file a feature request against package:stack_trace."
+labels: "package:stack_trace"
+---
\ No newline at end of file

diff --git a/.github/ISSUE_TEMPLATE/stream_channel.md b/.github/ISSUE_TEMPLATE/stream_channel.md
new file mode 100644
index 0000000..76b5994
--- /dev/null
+++ b/.github/ISSUE_TEMPLATE/stream_channel.md

@@ -0,0 +1,5 @@
+---
+name: "package:stream_channel"
+about: "Create a bug or file a feature request against package:stream_channel."
+labels: "package:stream_channel"
+---
\ No newline at end of file

diff --git a/.github/ISSUE_TEMPLATE/stream_transform.md b/.github/ISSUE_TEMPLATE/stream_transform.md
new file mode 100644
index 0000000..475bd83
--- /dev/null
+++ b/.github/ISSUE_TEMPLATE/stream_transform.md

@@ -0,0 +1,5 @@
+---
+name: "package:stream_transform"
+about: "Create a bug or file a feature request against package:stream_transform."
+labels: "package:stream_transform"
+---
\ No newline at end of file

diff --git a/.github/ISSUE_TEMPLATE/string_scanner.md b/.github/ISSUE_TEMPLATE/string_scanner.md
new file mode 100644
index 0000000..ad89f1b
--- /dev/null
+++ b/.github/ISSUE_TEMPLATE/string_scanner.md

@@ -0,0 +1,5 @@
+---
+name: "package:string_scanner"
+about: "Create a bug or file a feature request against package:string_scanner."
+labels: "package:string_scanner"
+---
\ No newline at end of file

diff --git a/.github/ISSUE_TEMPLATE/term_glyph.md b/.github/ISSUE_TEMPLATE/term_glyph.md
new file mode 100644
index 0000000..b6a4766
--- /dev/null
+++ b/.github/ISSUE_TEMPLATE/term_glyph.md

@@ -0,0 +1,5 @@
+---
+name: "package:term_glyph"
+about: "Create a bug or file a feature request against package:term_glyph."
+labels: "package:term_glyph"
+---
\ No newline at end of file

diff --git a/.github/ISSUE_TEMPLATE/test_reflective_loader.md b/.github/ISSUE_TEMPLATE/test_reflective_loader.md
new file mode 100644
index 0000000..bde03fe
--- /dev/null
+++ b/.github/ISSUE_TEMPLATE/test_reflective_loader.md

@@ -0,0 +1,5 @@
+---
+name: "package:test_reflective_loader"
+about: "Create a bug or file a feature request against package:test_reflective_loader."
+labels: "package:test_reflective_loader"
+---
\ No newline at end of file

diff --git a/.github/ISSUE_TEMPLATE/timing.md b/.github/ISSUE_TEMPLATE/timing.md
new file mode 100644
index 0000000..38a0015
--- /dev/null
+++ b/.github/ISSUE_TEMPLATE/timing.md

@@ -0,0 +1,5 @@
+---
+name: "package:timing"
+about: "Create a bug or file a feature request against package:timing."
+labels: "package:timing"
+---
\ No newline at end of file

diff --git a/.github/ISSUE_TEMPLATE/watcher.md b/.github/ISSUE_TEMPLATE/watcher.md
new file mode 100644
index 0000000..2578819
--- /dev/null
+++ b/.github/ISSUE_TEMPLATE/watcher.md

@@ -0,0 +1,5 @@
+---
+name: "package:watcher"
+about: "Create a bug or file a feature request against package:watcher."
+labels: "package:watcher"
+---
\ No newline at end of file

diff --git a/.github/ISSUE_TEMPLATE/yaml.md b/.github/ISSUE_TEMPLATE/yaml.md
new file mode 100644
index 0000000..d6a7c7f
--- /dev/null
+++ b/.github/ISSUE_TEMPLATE/yaml.md

@@ -0,0 +1,5 @@
+---
+name: "package:yaml"
+about: "Create a bug or file a feature request against package:yaml."
+labels: "package:yaml"
+---
\ No newline at end of file

diff --git a/.github/ISSUE_TEMPLATE/yaml_edit.md b/.github/ISSUE_TEMPLATE/yaml_edit.md
new file mode 100644
index 0000000..d1122a9
--- /dev/null
+++ b/.github/ISSUE_TEMPLATE/yaml_edit.md

@@ -0,0 +1,5 @@
+---
+name: "package:yaml_edit"
+about: "Create a bug or file a feature request against package:yaml_edit."
+labels: "package:yaml_edit"
+---
\ No newline at end of file

diff --git a/.github/labeler.yml b/.github/labeler.yml
index e158737..0bb7feb 100644
--- a/.github/labeler.yml
+++ b/.github/labeler.yml

@@ -64,6 +64,10 @@
   - changed-files:
     - any-glob-to-any-file: 'pkgs/html/**'
 
+'package:io':
+  - changed-files:
+    - any-glob-to-any-file: 'pkgs/io/**'
+
 'package:json_rpc_2':
   - changed-files:
     - any-glob-to-any-file: 'pkgs/json_rpc_2/**'
@@ -80,10 +84,74 @@
   - changed-files:
     - any-glob-to-any-file: 'pkgs/oauth2/**'
 
+'package:package_config':
+  - changed-files:
+    - any-glob-to-any-file: 'pkgs/package_config/**'
+
+'package:pool':
+  - changed-files:
+    - any-glob-to-any-file: 'pkgs/pool/**'
+
+'package:pub_semver':
+  - changed-files:
+    - any-glob-to-any-file: 'pkgs/pub_semver/**'
+
+'package:pubspec_parse':
+  - changed-files:
+    - any-glob-to-any-file: 'pkgs/pubspec_parse/**'
+
 'package:source_map_stack_trace':
   - changed-files:
     - any-glob-to-any-file: 'pkgs/source_map_stack_trace/**'
 
+'package:source_maps':
+  - changed-files:
+    - any-glob-to-any-file: 'pkgs/source_maps/**'
+
+'package:source_span':
+  - changed-files:
+    - any-glob-to-any-file: 'pkgs/source_span/**'
+
+'package:sse':
+  - changed-files:
+    - any-glob-to-any-file: 'pkgs/sse/**'
+
+'package:stack_trace':
+  - changed-files:
+    - any-glob-to-any-file: 'pkgs/stack_trace/**'
+
+'package:stream_channel':
+  - changed-files:
+    - any-glob-to-any-file: 'pkgs/stream_channel/**'
+
+'package:stream_transform':
+  - changed-files:
+    - any-glob-to-any-file: 'pkgs/stream_transform/**'
+
+'package:term_glyph':
+  - changed-files:
+    - any-glob-to-any-file: 'pkgs/term_glyph/**'
+
+'package:test_reflective_loader':
+  - changed-files:
+    - any-glob-to-any-file: 'pkgs/test_reflective_loader/**'
+
+'package:timing':
+  - changed-files:
+    - any-glob-to-any-file: 'pkgs/timing/**'
+
 'package:unified_analytics':
   - changed-files:
     - any-glob-to-any-file: 'pkgs/unified_analytics/**'
+
+'package:watcher':
+  - changed-files:
+    - any-glob-to-any-file: 'pkgs/watcher/**'
+
+'package:yaml':
+  - changed-files:
+    - any-glob-to-any-file: 'pkgs/yaml/**'
+
+'package:yaml_edit':
+  - changed-files:
+    - any-glob-to-any-file: 'pkgs/yaml_edit/**'

diff --git a/.github/workflows/bazel_worker.yaml b/.github/workflows/bazel_worker.yaml
index 0eb06da..b448219 100644
--- a/.github/workflows/bazel_worker.yaml
+++ b/.github/workflows/bazel_worker.yaml

@@ -36,6 +36,8 @@
       - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
         with:
           sdk: ${{ matrix.sdk }}
+      - run: dart pub get
       - run: "dart format --output=none --set-exit-if-changed ."
+        if: ${{ matrix.sdk == 'dev' }}
       - name: Test
         run: ./tool/travis.sh

diff --git a/.github/workflows/io.yaml b/.github/workflows/io.yaml
new file mode 100644
index 0000000..0c719a6
--- /dev/null
+++ b/.github/workflows/io.yaml

@@ -0,0 +1,72 @@
+name: package:io
+
+on:
+  # Run on PRs and pushes to the default branch.
+  push:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/io.yml'
+      - 'pkgs/io/**'
+  pull_request:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/io.yml'
+      - 'pkgs/io/**'
+  schedule:
+    - cron: "0 0 * * 0"
+
+env:
+  PUB_ENVIRONMENT: bot.github
+
+
+defaults:
+  run:
+    working-directory: pkgs/io/
+
+
+jobs:
+  # Check code formatting and static analysis on a single OS (linux)
+  # against Dart dev and stable.
+  analyze:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        sdk: [dev, 3.4]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Check formatting
+        run: dart format --output=none --set-exit-if-changed .
+        if: always() && steps.install.outcome == 'success'
+      - name: Analyze code
+        run: dart analyze --fatal-infos
+        if: always() && steps.install.outcome == 'success'
+
+  # Run tests on a matrix consisting of two dimensions:
+  # 1. OS: ubuntu-latest, (macos-latest, windows-latest)
+  # 2. release channel: dev, stable
+  test:
+    needs: analyze
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        # Add macos-latest and/or windows-latest if relevant for this package.
+        os: [ubuntu-latest]
+        sdk: [dev, 3.4]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - run: dart test
+        if: always() && steps.install.outcome == 'success'

diff --git a/.github/workflows/package_config.yaml b/.github/workflows/package_config.yaml
new file mode 100644
index 0000000..416ea1a
--- /dev/null
+++ b/.github/workflows/package_config.yaml

@@ -0,0 +1,71 @@
+name: package:package_config
+
+on:
+  # Run on PRs and pushes to the default branch.
+  push:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/package_config.yml'
+      - 'pkgs/package_config/**'
+  pull_request:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/package_config.yml'
+      - 'pkgs/package_config/**'
+  schedule:
+    - cron: "0 0 * * 0"
+
+env:
+  PUB_ENVIRONMENT: bot.github
+
+
+defaults:
+  run:
+    working-directory: pkgs/package_config/
+
+jobs:
+  # Check code formatting and static analysis on a single OS (linux)
+  # against Dart dev.
+  analyze:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        sdk: [dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Check formatting
+        run: dart format --output=none --set-exit-if-changed .
+        if: always() && steps.install.outcome == 'success'
+      - name: Analyze code
+        run: dart analyze --fatal-infos
+        if: always() && steps.install.outcome == 'success'
+
+  # Run tests on a matrix consisting of two dimensions:
+  # 1. OS: ubuntu-latest, (macos-latest, windows-latest)
+  # 2. release channel: dev
+  test:
+    needs: analyze
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, windows-latest]
+        sdk: [3.4, dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Run tests
+        run: dart test -p chrome,vm
+        if: always() && steps.install.outcome == 'success'

diff --git a/.github/workflows/pool.yaml b/.github/workflows/pool.yaml
new file mode 100644
index 0000000..6d64062
--- /dev/null
+++ b/.github/workflows/pool.yaml

@@ -0,0 +1,78 @@
+name: package:pool
+
+on:
+  # Run on PRs and pushes to the default branch.
+  push:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/pool.yaml'
+      - 'pkgs/pool/**'
+  pull_request:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/pool.yaml'
+      - 'pkgs/pool/**'
+  schedule:
+    - cron: "0 0 * * 0"
+
+env:
+  PUB_ENVIRONMENT: bot.github
+
+
+defaults:
+  run:
+    working-directory: pkgs/pool/
+
+jobs:
+  # Check code formatting and static analysis on a single OS (linux)
+  # against Dart dev.
+  analyze:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        sdk: [dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Check formatting
+        run: dart format --output=none --set-exit-if-changed .
+        if: always() && steps.install.outcome == 'success'
+      - name: Analyze code
+        run: dart analyze --fatal-infos
+        if: always() && steps.install.outcome == 'success'
+
+  # Run tests on a matrix consisting of two dimensions:
+  # 1. OS: ubuntu-latest, (macos-latest, windows-latest)
+  # 2. release channel: dev
+  test:
+    needs: analyze
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        # Add macos-latest and/or windows-latest if relevant for this package.
+        os: [ubuntu-latest]
+        sdk: [3.4, dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Run VM tests
+        run: dart test --platform vm
+        if: always() && steps.install.outcome == 'success'
+      - name: Run Chrome tests
+        run: dart test --platform chrome
+        if: always() && steps.install.outcome == 'success'
+      - name: Run Chrome tests - wasm
+        run: dart test --platform chrome -c dart2wasm
+        if: always() && steps.install.outcome == 'success' && matrix.sdk == 'dev'

diff --git a/.github/workflows/pub_semver.yaml b/.github/workflows/pub_semver.yaml
new file mode 100644
index 0000000..ba0db18
--- /dev/null
+++ b/.github/workflows/pub_semver.yaml

@@ -0,0 +1,75 @@
+name: package:pub_semver
+
+on:
+  # Run on PRs and pushes to the default branch.
+  push:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/pub_semver.yaml'
+      - 'pkgs/pub_semver/**'
+  pull_request:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/pub_semver.yaml'
+      - 'pkgs/pub_semver/**'
+  schedule:
+    - cron: "0 0 * * 0"
+
+env:
+  PUB_ENVIRONMENT: bot.github
+
+
+defaults:
+  run:
+    working-directory: pkgs/pub_semver/
+
+jobs:
+  # Check code formatting and static analysis on a single OS (linux)
+  # against Dart dev.
+  analyze:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        sdk: [dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Check formatting
+        run: dart format --output=none --set-exit-if-changed .
+        if: always() && steps.install.outcome == 'success'
+      - name: Analyze code
+        run: dart analyze --fatal-infos
+        if: always() && steps.install.outcome == 'success'
+
+  # Run tests on a matrix consisting of two dimensions:
+  # 1. OS: ubuntu-latest, (macos-latest, windows-latest)
+  # 2. release channel: dev
+  test:
+    needs: analyze
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        # Add macos-latest and/or windows-latest if relevant for this package.
+        os: [ubuntu-latest]
+        sdk: [3.4, dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Run VM tests
+        run: dart test --platform vm
+        if: always() && steps.install.outcome == 'success'
+      - name: Run Chrome tests
+        run: dart test --platform chrome --compiler dart2js,dart2wasm
+        if: always() && steps.install.outcome == 'success'

diff --git a/.github/workflows/pubspec_parse.yaml b/.github/workflows/pubspec_parse.yaml
new file mode 100644
index 0000000..9cf6257
--- /dev/null
+++ b/.github/workflows/pubspec_parse.yaml

@@ -0,0 +1,71 @@
+name: package:pubspec_parse
+
+on:
+  # Run on PRs and pushes to the default branch.
+  push:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/pubspec_parse.yaml'
+      - 'pkgs/pubspec_parse/**'
+  pull_request:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/pubspec_parse.yaml'
+      - 'pkgs/pubspec_parse/**'
+  schedule:
+    - cron: "0 0 * * 0"
+
+env:
+  PUB_ENVIRONMENT: bot.github
+
+
+defaults:
+  run:
+    working-directory: pkgs/pubspec_parse/
+
+jobs:
+  # Check code formatting and static analysis on a single OS (linux)
+  # against Dart dev.
+  analyze:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        sdk: [dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Check formatting
+        run: dart format --output=none --set-exit-if-changed .
+        if: always() && steps.install.outcome == 'success'
+      - name: Analyze code
+        run: dart analyze --fatal-infos
+        if: always() && steps.install.outcome == 'success'
+
+  # Run tests on a matrix consisting of two dimensions:
+  # 1. OS: ubuntu-latest, (macos-latest, windows-latest)
+  # 2. release channel: dev
+  test:
+    needs: analyze
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest]
+        sdk: [3.6, dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Run VM tests
+        run: dart test --platform vm --run-skipped
+        if: always() && steps.install.outcome == 'success'

diff --git a/.github/workflows/source_maps.yaml b/.github/workflows/source_maps.yaml
new file mode 100644
index 0000000..2ae0f20
--- /dev/null
+++ b/.github/workflows/source_maps.yaml

@@ -0,0 +1,72 @@
+name: package:source_maps
+
+on:
+  # Run on PRs and pushes to the default branch.
+  push:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/source_maps.yaml'
+      - 'pkgs/source_maps/**'
+  pull_request:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/source_maps.yaml'
+      - 'pkgs/source_maps/**'
+  schedule:
+    - cron: "0 0 * * 0"
+
+env:
+  PUB_ENVIRONMENT: bot.github
+
+
+defaults:
+  run:
+    working-directory: pkgs/source_maps/
+
+jobs:
+  # Check code formatting and static analysis on a single OS (linux)
+  # against Dart dev.
+  analyze:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        sdk: [dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Check formatting
+        run: dart format --output=none --set-exit-if-changed .
+        if: always() && steps.install.outcome == 'success'
+      - name: Analyze code
+        run: dart analyze --fatal-infos
+        if: always() && steps.install.outcome == 'success'
+
+  # Run tests on a matrix consisting of two dimensions:
+  # 1. OS: ubuntu-latest, (macos-latest, windows-latest)
+  # 2. release channel: dev
+  test:
+    needs: analyze
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        # Add macos-latest and/or windows-latest if relevant for this package.
+        os: [ubuntu-latest]
+        sdk: [3.3.0, dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Run VM tests
+        run: dart test --platform vm
+        if: always() && steps.install.outcome == 'success'

diff --git a/.github/workflows/source_span.yaml b/.github/workflows/source_span.yaml
new file mode 100644
index 0000000..2c2ba05
--- /dev/null
+++ b/.github/workflows/source_span.yaml

@@ -0,0 +1,75 @@
+name: package:source_span
+
+on:
+  # Run on PRs and pushes to the default branch.
+  push:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/source_span.yml'
+      - 'pkgs/source_span/**'
+  pull_request:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/source_span.yml'
+      - 'pkgs/source_span/**'
+  schedule:
+    - cron: "0 0 * * 0"
+
+env:
+  PUB_ENVIRONMENT: bot.github
+
+
+defaults:
+  run:
+    working-directory: pkgs/source_span/
+
+jobs:
+  # Check code formatting and static analysis on a single OS (linux)
+  # against Dart dev.
+  analyze:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        sdk: [dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Check formatting
+        run: dart format --output=none --set-exit-if-changed .
+        if: always() && steps.install.outcome == 'success'
+      - name: Analyze code
+        run: dart analyze --fatal-infos
+        if: always() && steps.install.outcome == 'success'
+
+  # Run tests on a matrix consisting of two dimensions:
+  # 1. OS: ubuntu-latest, (macos-latest, windows-latest)
+  # 2. release channel: dev
+  test:
+    needs: analyze
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        # Add macos-latest and/or windows-latest if relevant for this package.
+        os: [ubuntu-latest]
+        sdk: [3.1.0, dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Run VM tests
+        run: dart test --platform vm
+        if: always() && steps.install.outcome == 'success'
+      - name: Run Chrome tests
+        run: dart test --platform chrome
+        if: always() && steps.install.outcome == 'success'

diff --git a/.github/workflows/sse.yaml b/.github/workflows/sse.yaml
new file mode 100644
index 0000000..9e2f212
--- /dev/null
+++ b/.github/workflows/sse.yaml

@@ -0,0 +1,73 @@
+name: package:sse
+
+on:
+  # Run on PRs and pushes to the default branch.
+  push:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/sse.yaml'
+      - 'pkgs/sse/**'
+  pull_request:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/sse.yaml'
+      - 'pkgs/sse/**'
+  schedule:
+    - cron: "0 0 * * 0"
+
+env:
+  PUB_ENVIRONMENT: bot.github
+
+
+defaults:
+  run:
+    working-directory: pkgs/sse/
+
+jobs:
+  # Check code formatting and static analysis on a single OS (linux)
+  # against Dart dev.
+  analyze:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        sdk: [dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Check formatting
+        run: dart format --output=none --set-exit-if-changed .
+        if: always() && steps.install.outcome == 'success'
+      - name: Analyze code
+        run: dart analyze --fatal-infos
+        if: always() && steps.install.outcome == 'success'
+
+  # Run tests on a matrix consisting of two dimensions:
+  # 1. OS: ubuntu-latest, (macos-latest, windows-latest)
+  # 2. release channel: dev
+  test:
+    needs: analyze
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        # Add macos-latest and/or windows-latest if relevant for this package.
+        os: [ubuntu-latest]
+        sdk: [3.3, dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - uses: nanasess/setup-chromedriver@42cc2998329f041de87dc3cfa33a930eacd57eaa
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Run VM tests
+        run: dart test --platform vm --test-randomize-ordering-seed=random -j 1
+        if: always() && steps.install.outcome == 'success'

diff --git a/.github/workflows/stack_trace.yaml b/.github/workflows/stack_trace.yaml
new file mode 100644
index 0000000..7435967
--- /dev/null
+++ b/.github/workflows/stack_trace.yaml

@@ -0,0 +1,75 @@
+name: package:stack_trace
+
+on:
+  # Run on PRs and pushes to the default branch.
+  push:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/stack_trace.yaml'
+      - 'pkgs/stack_trace/**'
+  pull_request:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/stack_trace.yaml'
+      - 'pkgs/stack_trace/**'
+  schedule:
+    - cron: "0 0 * * 0"
+
+env:
+  PUB_ENVIRONMENT: bot.github
+
+
+defaults:
+  run:
+    working-directory: pkgs/stack_trace/
+
+jobs:
+  # Check code formatting and static analysis on a single OS (linux)
+  # against Dart dev.
+  analyze:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        sdk: [dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Check formatting
+        run: dart format --output=none --set-exit-if-changed .
+        if: always() && steps.install.outcome == 'success'
+      - name: Analyze code
+        run: dart analyze --fatal-infos
+        if: always() && steps.install.outcome == 'success'
+
+  # Run tests on a matrix consisting of two dimensions:
+  # 1. OS: ubuntu-latest, (macos-latest, windows-latest)
+  # 2. release channel: dev
+  test:
+    needs: analyze
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        # Add macos-latest and/or windows-latest if relevant for this package.
+        os: [ubuntu-latest]
+        sdk: [3.4, dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Run VM tests
+        run: dart test --platform vm
+        if: always() && steps.install.outcome == 'success'
+      - name: Run browser tests
+        run: dart test --platform chrome
+        if: always() && steps.install.outcome == 'success'

diff --git a/.github/workflows/stream_channel.yaml b/.github/workflows/stream_channel.yaml
new file mode 100644
index 0000000..c39424d
--- /dev/null
+++ b/.github/workflows/stream_channel.yaml

@@ -0,0 +1,74 @@
+name: package:stream_channel
+
+on:
+  # Run on PRs and pushes to the default branch.
+  push:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/stream_channel.yaml'
+      - 'pkgs/stream_channel/**'
+  pull_request:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/stream_channel.yaml'
+      - 'pkgs/stream_channel/**'
+  schedule:
+    - cron: "0 0 * * 0"
+
+env:
+  PUB_ENVIRONMENT: bot.github
+
+defaults:
+  run:
+    working-directory: pkgs/stream_channel/
+
+jobs:
+  # Check code formatting and static analysis on a single OS (linux)
+  # against Dart dev.
+  analyze:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        sdk: [dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Check formatting
+        run: dart format --output=none --set-exit-if-changed .
+        if: always() && steps.install.outcome == 'success'
+      - name: Analyze code
+        run: dart analyze --fatal-infos
+        if: always() && steps.install.outcome == 'success'
+
+  # Run tests on a matrix consisting of two dimensions:
+  # 1. OS: ubuntu-latest, (macos-latest, windows-latest)
+  # 2. release channel: dev
+  test:
+    needs: analyze
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        # Add macos-latest and/or windows-latest if relevant for this package.
+        os: [ubuntu-latest]
+        sdk: [3.3, dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Run VM tests
+        run: dart test --platform vm
+        if: always() && steps.install.outcome == 'success'
+      - name: Run Chrome tests
+        run: dart test --platform chrome
+        if: always() && steps.install.outcome == 'success'

diff --git a/.github/workflows/stream_transform.yaml b/.github/workflows/stream_transform.yaml
new file mode 100644
index 0000000..38be5cc
--- /dev/null
+++ b/.github/workflows/stream_transform.yaml

@@ -0,0 +1,73 @@
+name: package:stream_transform
+
+on:
+  # Run on PRs and pushes to the default branch.
+  push:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/stream_transform.yaml'
+      - 'pkgs/stream_transform/**'
+  pull_request:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/stream_transform.yaml'
+      - 'pkgs/stream_transform/**'
+  schedule:
+    - cron: "0 0 * * 0"
+
+env:
+  PUB_ENVIRONMENT: bot.github
+
+
+defaults:
+  run:
+    working-directory: pkgs/stream_transform/
+
+jobs:
+  # Check code formatting and static analysis on a single OS (linux)
+  # against Dart dev.
+  analyze:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        sdk: [dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Check formatting
+        run: dart format --output=none --set-exit-if-changed .
+        if: always() && steps.install.outcome == 'success'
+      - name: Analyze code
+        run: dart analyze --fatal-infos
+        if: always() && steps.install.outcome == 'success'
+
+  # Run tests on a matrix consisting of two dimensions:
+  # 1. OS: ubuntu-latest, (macos-latest, windows-latest)
+  # 2. release channel: dev
+  test:
+    needs: analyze
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        # Add macos-latest and/or windows-latest if relevant for this package.
+        os: [ubuntu-latest]
+        # Bump SDK for Legacy tests when changing min SDK.
+        sdk: [3.4, dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Run tests
+        run: dart test -p chrome,vm --test-randomize-ordering-seed=random
+        if: always() && steps.install.outcome == 'success'

diff --git a/.github/workflows/term_glyph.yaml b/.github/workflows/term_glyph.yaml
new file mode 100644
index 0000000..5b3b320
--- /dev/null
+++ b/.github/workflows/term_glyph.yaml

@@ -0,0 +1,72 @@
+name: package:term_glyph
+
+on:
+  # Run on PRs and pushes to the default branch.
+  push:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/term_glyph.yaml'
+      - 'pkgs/term_glyph/**'
+  pull_request:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/term_glyph.yaml'
+      - 'pkgs/term_glyph/**'
+  schedule:
+    - cron: "0 0 * * 0"
+
+env:
+  PUB_ENVIRONMENT: bot.github
+
+
+defaults:
+  run:
+    working-directory: pkgs/term_glyph/
+
+jobs:
+  # Check code formatting and static analysis on a single OS (linux)
+  # against Dart dev.
+  analyze:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        sdk: [dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Check formatting
+        run: dart format --output=none --set-exit-if-changed .
+        if: always() && steps.install.outcome == 'success'
+      - name: Analyze code
+        run: dart analyze --fatal-infos
+        if: always() && steps.install.outcome == 'success'
+
+  # Run tests on a matrix consisting of two dimensions:
+  # 1. OS: ubuntu-latest, (macos-latest, windows-latest)
+  # 2. release channel: dev
+  test:
+    needs: analyze
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        # Add macos-latest and/or windows-latest if relevant for this package.
+        os: [ubuntu-latest]
+        sdk: [3.1, dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Run VM tests
+        run: dart test --platform vm
+        if: always() && steps.install.outcome == 'success'

diff --git a/.github/workflows/test_reflective_loader.yaml b/.github/workflows/test_reflective_loader.yaml
new file mode 100644
index 0000000..975c970
--- /dev/null
+++ b/.github/workflows/test_reflective_loader.yaml

@@ -0,0 +1,43 @@
+name: package:test_reflective_loader
+
+on:
+  # Run on PRs and pushes to the default branch.
+  push:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/test_reflective_loader.yaml'
+      - 'pkgs/test_reflective_loader/**'
+  pull_request:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/test_reflective_loader.yaml'
+      - 'pkgs/test_reflective_loader/**'
+  schedule:
+    - cron: "0 0 * * 0"
+
+env:
+  PUB_ENVIRONMENT: bot.github
+
+defaults:
+  run:
+    working-directory: pkgs/test_reflective_loader/
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        sdk: [dev, 3.1]
+
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+          
+      - run: dart pub get
+      - name: dart format
+        run: dart format --output=none --set-exit-if-changed .
+      - run: dart analyze --fatal-infos
+      - run: dart test

diff --git a/.github/workflows/timing.yaml b/.github/workflows/timing.yaml
new file mode 100644
index 0000000..df77b13
--- /dev/null
+++ b/.github/workflows/timing.yaml

@@ -0,0 +1,67 @@
+name: package:timing
+
+on:
+  # Run on PRs and pushes to the default branch.
+  push:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/timing.yaml'
+      - 'pkgs/timing/**'
+  pull_request:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/timing.yaml'
+      - 'pkgs/timing/**'
+  schedule:
+    - cron: "0 0 * * 0"
+
+env:
+  PUB_ENVIRONMENT: bot.github
+
+
+defaults:
+  run:
+    working-directory: pkgs/timing/
+
+jobs:
+  # Check code formatting and static analysis on a single OS (linux)
+  # against Dart dev.
+  analyze:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        sdk: [3.4, dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        run: dart pub get
+      - run: dart format --output=none --set-exit-if-changed .
+        if: always() && steps.install.outcome == 'success'
+      - run: dart analyze --fatal-infos
+        if: always() && steps.install.outcome == 'success'
+
+  # Run tests on a matrix consisting of two dimensions:
+  # 1. OS: ubuntu-latest, (macos-latest, windows-latest)
+  # 2. release channel: dev, 2.2.0
+  test:
+    needs: analyze
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        # Add macos-latest and/or windows-latest if relevant for this package.
+        os: [ubuntu-latest]
+        sdk: [3.4, dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        run: dart pub get
+      - run: dart test --platform vm
+        if: always() && steps.install.outcome == 'success'

diff --git a/.github/workflows/watcher.yaml b/.github/workflows/watcher.yaml
new file mode 100644
index 0000000..a04483c
--- /dev/null
+++ b/.github/workflows/watcher.yaml

@@ -0,0 +1,71 @@
+name: package:watcher
+
+on:
+  # Run on PRs and pushes to the default branch.
+  push:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/watcher.yaml'
+      - 'pkgs/watcher/**'
+  pull_request:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/watcher.yaml'
+      - 'pkgs/watcher/**'
+  schedule:
+    - cron: "0 0 * * 0"
+
+env:
+  PUB_ENVIRONMENT: bot.github
+
+
+defaults:
+  run:
+    working-directory: pkgs/watcher/
+
+jobs:
+  # Check code formatting and static analysis on a single OS (linux)
+  # against Dart dev.
+  analyze:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        sdk: [dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Check formatting
+        run: dart format --output=none --set-exit-if-changed .
+        if: always() && steps.install.outcome == 'success'
+      - name: Analyze code
+        run: dart analyze --fatal-infos
+        if: always() && steps.install.outcome == 'success'
+
+  # Run tests on a matrix consisting of two dimensions:
+  # 1. OS: ubuntu-latest, macos-latest, windows-latest
+  # 2. release channel: dev
+  test:
+    needs: analyze
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+        sdk: [3.1, dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Run VM tests
+        run: dart test --platform vm
+        if: always() && steps.install.outcome == 'success'

diff --git a/.github/workflows/yaml.yaml b/.github/workflows/yaml.yaml
new file mode 100644
index 0000000..735461e
--- /dev/null
+++ b/.github/workflows/yaml.yaml

@@ -0,0 +1,75 @@
+name: package:yaml
+
+on:
+  # Run on PRs and pushes to the default branch.
+  push:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/yaml.yaml'
+      - 'pkgs/yaml/**'
+  pull_request:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/yaml.yaml'
+      - 'pkgs/yaml/**'
+  schedule:
+    - cron: "0 0 * * 0"
+
+env:
+  PUB_ENVIRONMENT: bot.github
+
+
+defaults:
+  run:
+    working-directory: pkgs/yaml/
+
+jobs:
+  # Check code formatting and static analysis on a single OS (linux)
+  # against Dart dev.
+  analyze:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        sdk: [dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Check formatting
+        run: dart format --output=none --set-exit-if-changed .
+        if: always() && steps.install.outcome == 'success'
+      - name: Analyze code
+        run: dart analyze --fatal-infos
+        if: always() && steps.install.outcome == 'success'
+
+  # Run tests on a matrix consisting of two dimensions:
+  # 1. OS: ubuntu-latest, (macos-latest, windows-latest)
+  # 2. release channel: dev
+  test:
+    needs: analyze
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        # Add macos-latest and/or windows-latest if relevant for this package.
+        os: [ubuntu-latest]
+        sdk: [3.4, dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Run VM tests
+        run: dart test --platform vm
+        if: always() && steps.install.outcome == 'success'
+      - name: Run Chrome tests
+        run: dart test --platform chrome
+        if: always() && steps.install.outcome == 'success'

diff --git a/.github/workflows/yaml_edit.yaml b/.github/workflows/yaml_edit.yaml
new file mode 100644
index 0000000..ffea62c
--- /dev/null
+++ b/.github/workflows/yaml_edit.yaml

@@ -0,0 +1,91 @@
+name: package:yaml_edit
+
+on:
+  # Run on PRs and pushes to the default branch.
+  push:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/yaml_edit.yaml'
+      - 'pkgs/yaml_edit/**'
+  pull_request:
+    branches: [ main ]
+    paths:
+      - '.github/workflows/yaml_edit.yaml'
+      - 'pkgs/yaml_edit/**'
+  schedule:
+    - cron: "0 0 * * 0"
+
+env:
+  PUB_ENVIRONMENT: bot.github
+
+
+defaults:
+  run:
+    working-directory: pkgs/yaml_edit/
+
+jobs:
+  # Check code formatting and static analysis on a single OS (linux)
+  # against Dart dev.
+  analyze:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        sdk: [dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Check formatting
+        run: dart format --output=none --set-exit-if-changed .
+        if: always() && steps.install.outcome == 'success'
+      - name: Analyze code
+        run: dart analyze --fatal-infos
+        if: always() && steps.install.outcome == 'success'
+
+  # Run tests on a matrix consisting of two dimensions:
+  # 1. OS: ubuntu-latest, (macos-latest, windows-latest)
+  # 2. release channel: dev
+  test:
+    needs: analyze
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        # Add macos-latest and/or windows-latest if relevant for this package.
+        os: [ubuntu-latest]
+        sdk: ['3.1', stable, dev]
+        platform: [vm, chrome]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Run tests on ${{ matrix.platform }}
+        run: dart test --platform ${{ matrix.platform }} --coverage=./coverage
+        if: always() && steps.install.outcome == 'success'
+      # We don't collect code coverage from 2.12.0, because it doesn't work
+      - name: Convert coverage to lcov
+        run: dart run coverage:format_coverage -i ./coverage -o ./coverage/lcov.info --lcov --report-on lib/
+        if: always() && steps.install.outcome == 'success' && matrix.sdk != '2.12.0'
+      - uses: coverallsapp/github-action@cfd0633edbd2411b532b808ba7a8b5e04f76d2c8
+        if: always() && steps.install.outcome == 'success' && matrix.sdk != '2.12.0'
+        with:
+          flag-name: os:${{ matrix.os }}/dart:${{ matrix.sdk }}/platform:${{ matrix.platform }}
+          parallel: true
+
+  report-coverage:
+    needs: test
+    if: ${{ always() }}
+    runs-on: ubuntu-latest
+    steps:
+    - uses: coverallsapp/github-action@cfd0633edbd2411b532b808ba7a8b5e04f76d2c8
+      with:
+        parallel-finished: true

diff --git a/README.md b/README.md
index 91c85e5..f3281a8 100644
--- a/README.md
+++ b/README.md

@@ -29,12 +29,29 @@
 | [file_testing](pkgs/file_testing/) | Testing utilities for package:file. | [![package issues](https://img.shields.io/badge/package:file_testing-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Afile_testing) | [![pub package](https://img.shields.io/pub/v/file_testing.svg)](https://pub.dev/packages/file_testing) |
 | [graphs](pkgs/graphs/) | Graph algorithms that operate on graphs in any representation. | [![package issues](https://img.shields.io/badge/package:graphs-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Agraphs) | [![pub package](https://img.shields.io/pub/v/graphs.svg)](https://pub.dev/packages/graphs) |
 | [html](pkgs/html/) | APIs for parsing and manipulating HTML content outside the browser. | [![package issues](https://img.shields.io/badge/package:html-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Ahtml) | [![pub package](https://img.shields.io/pub/v/html.svg)](https://pub.dev/packages/html) |
+| [io](pkgs/io/) | Utilities for the Dart VM Runtime including support for ANSI colors, file copying, and standard exit code values. | [![pub package](https://img.shields.io/pub/v/io.svg)](https://pub.dev/packages/io) |
 | [json_rpc_2](pkgs/json_rpc_2/) | Utilities to write a client or server using the JSON-RPC 2.0 spec. | [![package issues](https://img.shields.io/badge/package:json_rpc_2-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Ajson_rpc_2) | [![pub package](https://img.shields.io/pub/v/json_rpc_2.svg)](https://pub.dev/packages/json_rpc_2) |
 | [markdown](pkgs/markdown/) | A portable Markdown library written in Dart that can parse Markdown into HTML. | [![pub package](https://img.shields.io/pub/v/markdown.svg)](https://pub.dev/packages/markdown) |
 | [mime](pkgs/mime/) | Utilities for handling media (MIME) types, including determining a type from a file extension and file contents. | [![package issues](https://img.shields.io/badge/package:mime-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Amime) | [![pub package](https://img.shields.io/pub/v/mime.svg)](https://pub.dev/packages/mime) |
 | [oauth2](pkgs/oauth2/) | A client library for authenticating with a remote service via OAuth2 on behalf of a user, and making authorized HTTP requests with the user's OAuth2 credentials. | [![package issues](https://img.shields.io/badge/package:oauth2-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Aoauth2) | [![pub package](https://img.shields.io/pub/v/oauth2.svg)](https://pub.dev/packages/oauth2) |
+| [package_config](pkgs/package_config/) | Support for reading and writing Dart Package Configuration files. | [![package issues](https://img.shields.io/badge/package:package_config-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Apackage_config) | [![pub package](https://img.shields.io/pub/v/package_config.svg)](https://pub.dev/packages/package_config) |
+| [pool](pkgs/pool/) | Manage a finite pool of resources. Useful for controlling concurrent file system or network requests. | [![package issues](https://img.shields.io/badge/package:pool-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Apool) | [![pub package](https://img.shields.io/pub/v/pool.svg)](https://pub.dev/packages/pool) |
+| [pub_semver](pkgs/pub_semver/) | Versions and version constraints implementing pub's versioning policy. This is very similar to vanilla semver, with a few corner cases. | [![package issues](https://img.shields.io/badge/package:pub_semver-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Apub_semver) | [![pub package](https://img.shields.io/pub/v/pub_semver.svg)](https://pub.dev/packages/pub_semver) |
+| [pubspec_parse](pkgs/pubspec_parse/) | Simple package for parsing pubspec.yaml files with a type-safe API and rich error reporting. | [![package issues](https://img.shields.io/badge/package:pubspec_parse-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Apubspec_parse) | [![pub package](https://img.shields.io/pub/v/pubspec_parse.svg)](https://pub.dev/packages/pubspec_parse) |
 | [source_map_stack_trace](pkgs/source_map_stack_trace/) | A package for applying source maps to stack traces. | [![package issues](https://img.shields.io/badge/package:source_map_stack_trace-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Asource_map_stack_trace) | [![pub package](https://img.shields.io/pub/v/source_map_stack_trace.svg)](https://pub.dev/packages/source_map_stack_trace) |
+| [source_maps](pkgs/source_maps/) | A library to programmatically manipulate source map files. | [![package issues](https://img.shields.io/badge/package:source_maps-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Asource_maps) | [![pub package](https://img.shields.io/pub/v/source_maps.svg)](https://pub.dev/packages/source_maps) |
+| [source_span](pkgs/source_span/) | Provides a standard representation for source code locations and spans. | [![package issues](https://img.shields.io/badge/package:source_span-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Asource_span) | [![pub package](https://img.shields.io/pub/v/source_span.svg)](https://pub.dev/packages/source_span) |
+| [sse](pkgs/sse/) | Provides client and server functionality for setting up bi-directional communication through Server Sent Events (SSE) and corresponding POST requests. | [![package issues](https://img.shields.io/badge/package:sse-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Asse) | [![pub package](https://img.shields.io/pub/v/sse.svg)](https://pub.dev/packages/sse) |
+| [stack_trace](pkgs/stack_trace/) | A package for manipulating stack traces and printing them readably. | [![package issues](https://img.shields.io/badge/package:stack_trace-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Astack_trace) | [![pub package](https://img.shields.io/pub/v/stack_trace.svg)](https://pub.dev/packages/stack_trace) |
+| [stream_channel](pkgs/stream_channel/) | An abstraction for two-way communication channels based on the Dart Stream class. | [![package issues](https://img.shields.io/badge/package:stream_channel-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Astream_channel) | [![pub package](https://img.shields.io/pub/v/stream_channel.svg)](https://pub.dev/packages/stream_channel) |
+| [stream_transform](pkgs/stream_transform/) | A collection of utilities to transform and manipulate streams. | [![package issues](https://img.shields.io/badge/package:stream_transform-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Astream_transform) | [![pub package](https://img.shields.io/pub/v/stream_transform.svg)](https://pub.dev/packages/stream_transform) |
+| [term_glyph](pkgs/term_glyph/) | Useful Unicode glyphs and ASCII substitutes. | [![package issues](https://img.shields.io/badge/package:term_glyph-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Aterm_glyph) | [![pub package](https://img.shields.io/pub/v/term_glyph.svg)](https://pub.dev/packages/term_glyph) |
+| [test_reflective_loader](pkgs/test_reflective_loader/) | Support for discovering tests and test suites using reflection. | [![package issues](https://img.shields.io/badge/package:test_reflective_loader-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Atest_reflective_loader) | [![pub package](https://img.shields.io/pub/v/test_reflective_loader.svg)](https://pub.dev/packages/test_reflective_loader) |
+| [timing](pkgs/timing/) | A simple package for tracking the performance of synchronous and asynchronous actions. | [![package issues](https://img.shields.io/badge/package:timing-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Atiming) | [![pub package](https://img.shields.io/pub/v/timing.svg)](https://pub.dev/packages/timing) |
 | [unified_analytics](pkgs/unified_analytics/) | A package for logging analytics for all Dart and Flutter related tooling to Google Analytics. | [![package issues](https://img.shields.io/badge/package:unified_analytics-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Aunified_analytics) | [![pub package](https://img.shields.io/pub/v/unified_analytics.svg)](https://pub.dev/packages/unified_analytics) |
+| [watcher](pkgs/watcher/) | Monitor directories and send notifications when the contents change. | [![package issues](https://img.shields.io/badge/package:watcher-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Awatcher) | [![pub package](https://img.shields.io/pub/v/watcher.svg)](https://pub.dev/packages/watcher) |
+| [yaml](pkgs/yaml/) | A parser for YAML, a human-friendly data serialization standard | [![package issues](https://img.shields.io/badge/package:yaml-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Ayaml) | [![pub package](https://img.shields.io/pub/v/yaml.svg)](https://pub.dev/packages/yaml) |
+| [yaml_edit](pkgs/yaml_edit/) | A library for YAML manipulation with comment and whitespace preservation. | [![package issues](https://img.shields.io/badge/package:yaml_edit-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Ayaml_edit) | [![pub package](https://img.shields.io/pub/v/yaml_edit.svg)](https://pub.dev/packages/yaml_edit) |
 
 ## Publishing automation
 

diff --git a/pkgs/bazel_worker/benchmark/benchmark.dart b/pkgs/bazel_worker/benchmark/benchmark.dart
index 035e2b8..0a03122 100644
--- a/pkgs/bazel_worker/benchmark/benchmark.dart
+++ b/pkgs/bazel_worker/benchmark/benchmark.dart

@@ -12,10 +12,7 @@
     var path = 'blaze-bin/some/path/to/a/file/that/is/an/input/$i';
     workRequest
       ..arguments.add('--input=$path')
-      ..inputs.add(Input(
-        path: '',
-        digest: List.filled(70, 0x11),
-      ));
+      ..inputs.add(Input(path: '', digest: List.filled(70, 0x11)));
   }
 
   // Serialize it.
@@ -24,14 +21,20 @@
   print('Request has $length requestBytes.');
 
   // Add the length in front base 128 encoded as in the worker protocol.
-  requestBytes =
-      Uint8List.fromList(requestBytes.toList()..insertAll(0, _varInt(length)));
+  requestBytes = Uint8List.fromList(
+    requestBytes.toList()..insertAll(0, _varInt(length)),
+  );
 
   // Split into 10000 byte chunks.
   var lists = <Uint8List>[];
   for (var i = 0; i < requestBytes.length; i += 10000) {
-    lists.add(Uint8List.sublistView(
-        requestBytes, i, min(i + 10000, requestBytes.length)));
+    lists.add(
+      Uint8List.sublistView(
+        requestBytes,
+        i,
+        min(i + 10000, requestBytes.length),
+      ),
+    );
   }
 
   // Time `AsyncMessageGrouper` and deserialization.

diff --git a/pkgs/bazel_worker/e2e_test/bin/async_worker_in_isolate.dart b/pkgs/bazel_worker/e2e_test/bin/async_worker_in_isolate.dart
index a94875d..285b03d 100644
--- a/pkgs/bazel_worker/e2e_test/bin/async_worker_in_isolate.dart
+++ b/pkgs/bazel_worker/e2e_test/bin/async_worker_in_isolate.dart

@@ -17,7 +17,10 @@
 Future main(List<String> args, [SendPort? message]) async {
   var receivePort = ReceivePort();
   await Isolate.spawnUri(
-      Uri.file('async_worker.dart'), [], receivePort.sendPort);
+    Uri.file('async_worker.dart'),
+    [],
+    receivePort.sendPort,
+  );
 
   var worker = await ForwardsToIsolateAsyncWorker.create(receivePort);
   await worker.run();

diff --git a/pkgs/bazel_worker/e2e_test/lib/async_worker.dart b/pkgs/bazel_worker/e2e_test/lib/async_worker.dart
index d48d87c..55f5171 100644
--- a/pkgs/bazel_worker/e2e_test/lib/async_worker.dart
+++ b/pkgs/bazel_worker/e2e_test/lib/async_worker.dart

@@ -16,9 +16,6 @@
 
   @override
   Future<WorkResponse> performRequest(WorkRequest request) async {
-    return WorkResponse(
-      exitCode: 0,
-      output: request.arguments.join('\n'),
-    );
+    return WorkResponse(exitCode: 0, output: request.arguments.join('\n'));
   }
 }

diff --git a/pkgs/bazel_worker/e2e_test/lib/forwards_to_isolate_async_worker.dart b/pkgs/bazel_worker/e2e_test/lib/forwards_to_isolate_async_worker.dart
index bb937b2..a4845cf 100644
--- a/pkgs/bazel_worker/e2e_test/lib/forwards_to_isolate_async_worker.dart
+++ b/pkgs/bazel_worker/e2e_test/lib/forwards_to_isolate_async_worker.dart

@@ -13,9 +13,11 @@
   final IsolateDriverConnection _isolateDriverConnection;
 
   static Future<ForwardsToIsolateAsyncWorker> create(
-      ReceivePort receivePort) async {
+    ReceivePort receivePort,
+  ) async {
     return ForwardsToIsolateAsyncWorker(
-        await IsolateDriverConnection.create(receivePort));
+      await IsolateDriverConnection.create(receivePort),
+    );
   }
 
   ForwardsToIsolateAsyncWorker(this._isolateDriverConnection);

diff --git a/pkgs/bazel_worker/e2e_test/pubspec.yaml b/pkgs/bazel_worker/e2e_test/pubspec.yaml
index 56f00cd..7eaa89a 100644
--- a/pkgs/bazel_worker/e2e_test/pubspec.yaml
+++ b/pkgs/bazel_worker/e2e_test/pubspec.yaml

@@ -10,6 +10,6 @@
 
 dev_dependencies:
   cli_util: ^0.4.2
-  dart_flutter_team_lints: ^1.0.0
+  dart_flutter_team_lints: ^3.0.0
   path: ^1.8.0
   test: ^1.16.0

diff --git a/pkgs/bazel_worker/e2e_test/test/e2e_test.dart b/pkgs/bazel_worker/e2e_test/test/e2e_test.dart
index caa813a..6b79b5e 100644
--- a/pkgs/bazel_worker/e2e_test/test/e2e_test.dart
+++ b/pkgs/bazel_worker/e2e_test/test/e2e_test.dart

@@ -12,14 +12,18 @@
 
 void main() {
   var dart = p.join(sdkPath, 'bin', 'dart');
-  runE2eTestForWorker('sync worker',
-      () => Process.start(dart, [p.join('bin', 'sync_worker.dart')]));
-  runE2eTestForWorker('async worker',
-      () => Process.start(dart, [p.join('bin', 'async_worker.dart')]));
   runE2eTestForWorker(
-      'async worker in isolate',
-      () =>
-          Process.start(dart, [p.join('bin', 'async_worker_in_isolate.dart')]));
+    'sync worker',
+    () => Process.start(dart, [p.join('bin', 'sync_worker.dart')]),
+  );
+  runE2eTestForWorker(
+    'async worker',
+    () => Process.start(dart, [p.join('bin', 'async_worker.dart')]),
+  );
+  runE2eTestForWorker(
+    'async worker in isolate',
+    () => Process.start(dart, [p.join('bin', 'async_worker_in_isolate.dart')]),
+  );
 }
 
 void runE2eTestForWorker(String groupName, SpawnWorker spawnWorker) {

diff --git a/pkgs/bazel_worker/example/client.dart b/pkgs/bazel_worker/example/client.dart
index 7147fcb..326bb18 100644
--- a/pkgs/bazel_worker/example/client.dart
+++ b/pkgs/bazel_worker/example/client.dart

@@ -5,10 +5,14 @@
 void main() async {
   var scratchSpace = await Directory.systemTemp.createTemp();
   var driver = BazelWorkerDriver(
-      () => Process.start(Platform.resolvedExecutable,
-          [Platform.script.resolve('worker.dart').toFilePath()],
-          workingDirectory: scratchSpace.path),
-      maxWorkers: 4);
+    () => Process.start(
+        Platform.resolvedExecutable,
+        [
+          Platform.script.resolve('worker.dart').toFilePath(),
+        ],
+        workingDirectory: scratchSpace.path),
+    maxWorkers: 4,
+  );
   var response = await driver.doWork(WorkRequest(arguments: ['foo']));
   if (response.exitCode != EXIT_CODE_OK) {
     print('Worker request failed');

diff --git a/pkgs/bazel_worker/lib/src/async_message_grouper.dart b/pkgs/bazel_worker/lib/src/async_message_grouper.dart
index e1f0dea..8fc4778 100644
--- a/pkgs/bazel_worker/lib/src/async_message_grouper.dart
+++ b/pkgs/bazel_worker/lib/src/async_message_grouper.dart

@@ -86,13 +86,18 @@
             // Copy as much as possible from the input buffer. Limit is the
             // smaller of the remaining length to fill in the message and the
             // remaining length in the buffer.
-            var lengthToCopy = min(_message.length - _messagePos,
-                _inputBuffer.length - _inputBufferPos);
+            var lengthToCopy = min(
+              _message.length - _messagePos,
+              _inputBuffer.length - _inputBufferPos,
+            );
             _message.setRange(
-                _messagePos,
-                _messagePos + lengthToCopy,
-                _inputBuffer.sublist(
-                    _inputBufferPos, _inputBufferPos + lengthToCopy));
+              _messagePos,
+              _messagePos + lengthToCopy,
+              _inputBuffer.sublist(
+                _inputBufferPos,
+                _inputBufferPos + lengthToCopy,
+              ),
+            );
             _messagePos += lengthToCopy;
             _inputBufferPos += lengthToCopy;
 

diff --git a/pkgs/bazel_worker/lib/src/driver/driver.dart b/pkgs/bazel_worker/lib/src/driver/driver.dart
index 4a78020..06cf0fe 100644
--- a/pkgs/bazel_worker/lib/src/driver/driver.dart
+++ b/pkgs/bazel_worker/lib/src/driver/driver.dart

@@ -44,9 +44,12 @@
   /// Factory method that spawns a worker process.
   final SpawnWorker _spawnWorker;
 
-  BazelWorkerDriver(this._spawnWorker,
-      {int? maxIdleWorkers, int? maxWorkers, int? maxRetries})
-      : _maxIdleWorkers = maxIdleWorkers ?? 4,
+  BazelWorkerDriver(
+    this._spawnWorker, {
+    int? maxIdleWorkers,
+    int? maxWorkers,
+    int? maxRetries,
+  })  : _maxIdleWorkers = maxIdleWorkers ?? 4,
         _maxWorkers = maxWorkers ?? 4,
         _maxRetries = maxRetries ?? 4;
 
@@ -56,8 +59,10 @@
   /// [request] has been actually sent to the worker. This allows the caller
   /// to determine when actual work is being done versus just waiting for an
   /// available worker.
-  Future<WorkResponse> doWork(WorkRequest request,
-      {void Function(Future<WorkResponse?>)? trackWork}) {
+  Future<WorkResponse> doWork(
+    WorkRequest request, {
+    void Function(Future<WorkResponse?>)? trackWork,
+  }) {
     var attempt = _WorkAttempt(request, trackWork: trackWork);
     _workQueue.add(attempt);
     _runWorkQueue();
@@ -69,9 +74,11 @@
     for (var worker in _readyWorkers.toList()) {
       _killWorker(worker);
     }
-    await Future.wait(_spawningWorkers.map((worker) async {
-      _killWorker(await worker);
-    }));
+    await Future.wait(
+      _spawningWorkers.map((worker) async {
+        _killWorker(await worker);
+      }),
+    );
   }
 
   /// Runs as many items in [_workQueue] as possible given the number of
@@ -88,8 +95,10 @@
     if (_workQueue.isEmpty) return;
     if (_numWorkers == _maxWorkers && _idleWorkers.isEmpty) return;
     if (_numWorkers > _maxWorkers) {
-      throw StateError('Internal error, created to many workers. Please '
-          'file a bug at https://github.com/dart-lang/bazel_worker/issues/new');
+      throw StateError(
+        'Internal error, created to many workers. Please '
+        'file a bug at https://github.com/dart-lang/bazel_worker/issues/new',
+      );
     }
 
     // At this point we definitely want to run a task, we just need to decide
@@ -137,48 +146,51 @@
   void _runWorker(Process worker, _WorkAttempt attempt) {
     var rescheduled = false;
 
-    runZonedGuarded(() async {
-      var connection = _workerConnections[worker]!;
+    runZonedGuarded(
+      () async {
+        var connection = _workerConnections[worker]!;
 
-      connection.writeRequest(attempt.request);
-      var responseFuture = connection.readResponse();
-      if (attempt.trackWork != null) {
-        attempt.trackWork!(responseFuture);
-      }
-      var response = await responseFuture;
+        connection.writeRequest(attempt.request);
+        var responseFuture = connection.readResponse();
+        if (attempt.trackWork != null) {
+          attempt.trackWork!(responseFuture);
+        }
+        var response = await responseFuture;
 
-      // It is possible for us to complete with an error response due to an
-      // unhandled async error before we get here.
-      if (!attempt.responseCompleter.isCompleted) {
-        if (response.exitCode == EXIT_CODE_BROKEN_PIPE) {
+        // It is possible for us to complete with an error response due to an
+        // unhandled async error before we get here.
+        if (!attempt.responseCompleter.isCompleted) {
+          if (response.exitCode == EXIT_CODE_BROKEN_PIPE) {
+            rescheduled = _tryReschedule(attempt);
+            if (rescheduled) return;
+            stderr.writeln('Failed to run request ${attempt.request}');
+            response = WorkResponse(
+              exitCode: EXIT_CODE_ERROR,
+              output:
+                  'Invalid response from worker, this probably means it wrote '
+                  'invalid output or died.',
+            );
+          }
+          attempt.responseCompleter.complete(response);
+          _cleanUp(worker);
+        }
+      },
+      (e, s) {
+        // Note that we don't need to do additional cleanup here on failures. If
+        // the worker dies that is already handled in a generic fashion, we just
+        // need to make sure we complete with a valid response.
+        if (!attempt.responseCompleter.isCompleted) {
           rescheduled = _tryReschedule(attempt);
           if (rescheduled) return;
-          stderr.writeln('Failed to run request ${attempt.request}');
-          response = WorkResponse(
+          var response = WorkResponse(
             exitCode: EXIT_CODE_ERROR,
-            output:
-                'Invalid response from worker, this probably means it wrote '
-                'invalid output or died.',
+            output: 'Error running worker:\n$e\n$s',
           );
+          attempt.responseCompleter.complete(response);
+          _cleanUp(worker);
         }
-        attempt.responseCompleter.complete(response);
-        _cleanUp(worker);
-      }
-    }, (e, s) {
-      // Note that we don't need to do additional cleanup here on failures. If
-      // the worker dies that is already handled in a generic fashion, we just
-      // need to make sure we complete with a valid response.
-      if (!attempt.responseCompleter.isCompleted) {
-        rescheduled = _tryReschedule(attempt);
-        if (rescheduled) return;
-        var response = WorkResponse(
-          exitCode: EXIT_CODE_ERROR,
-          output: 'Error running worker:\n$e\n$s',
-        );
-        attempt.responseCompleter.complete(response);
-        _cleanUp(worker);
-      }
-    });
+      },
+    );
   }
 
   /// Performs post-work cleanup for [worker].

diff --git a/pkgs/bazel_worker/lib/src/driver/driver_connection.dart b/pkgs/bazel_worker/lib/src/driver/driver_connection.dart
index b419deb..80d5c98 100644
--- a/pkgs/bazel_worker/lib/src/driver/driver_connection.dart
+++ b/pkgs/bazel_worker/lib/src/driver/driver_connection.dart

@@ -34,13 +34,16 @@
 
   Future<void> get done => _messageGrouper.done;
 
-  StdDriverConnection(
-      {Stream<List<int>>? inputStream, StreamSink<List<int>>? outputStream})
-      : _messageGrouper = AsyncMessageGrouper(inputStream ?? stdin),
+  StdDriverConnection({
+    Stream<List<int>>? inputStream,
+    StreamSink<List<int>>? outputStream,
+  })  : _messageGrouper = AsyncMessageGrouper(inputStream ?? stdin),
         _outputStream = outputStream ?? stdout;
 
   factory StdDriverConnection.forWorker(Process worker) => StdDriverConnection(
-      inputStream: worker.stdout, outputStream: worker.stdin);
+        inputStream: worker.stdout,
+        outputStream: worker.stdin,
+      );
 
   /// Note: This will attempts to recover from invalid proto messages by parsing
   /// them as strings. This is a common error case for workers (they print a

diff --git a/pkgs/bazel_worker/lib/src/utils.dart b/pkgs/bazel_worker/lib/src/utils.dart
index 609b435..f67bbac 100644
--- a/pkgs/bazel_worker/lib/src/utils.dart
+++ b/pkgs/bazel_worker/lib/src/utils.dart

@@ -13,8 +13,9 @@
   var delimiterBuffer = CodedBufferWriter();
   delimiterBuffer.writeInt32NoTag(messageBuffer.lengthInBytes);
 
-  var result =
-      Uint8List(messageBuffer.lengthInBytes + delimiterBuffer.lengthInBytes);
+  var result = Uint8List(
+    messageBuffer.lengthInBytes + delimiterBuffer.lengthInBytes,
+  );
 
   delimiterBuffer.writeTo(result);
   messageBuffer.writeTo(result, delimiterBuffer.lengthInBytes);

diff --git a/pkgs/bazel_worker/lib/src/worker/async_worker_loop.dart b/pkgs/bazel_worker/lib/src/worker/async_worker_loop.dart
index 5182b55..a95d09a 100644
--- a/pkgs/bazel_worker/lib/src/worker/async_worker_loop.dart
+++ b/pkgs/bazel_worker/lib/src/worker/async_worker_loop.dart

@@ -32,20 +32,20 @@
         var request = await connection.readRequest();
         if (request == null) break;
         var printMessages = StringBuffer();
-        response = await runZoned(() => performRequest(request),
-            zoneSpecification:
-                ZoneSpecification(print: (self, parent, zone, message) {
-          printMessages.writeln();
-          printMessages.write(message);
-        }));
+        response = await runZoned(
+          () => performRequest(request),
+          zoneSpecification: ZoneSpecification(
+            print: (self, parent, zone, message) {
+              printMessages.writeln();
+              printMessages.write(message);
+            },
+          ),
+        );
         if (printMessages.isNotEmpty) {
           response.output = '${response.output}$printMessages';
         }
       } catch (e, s) {
-        response = WorkResponse(
-          exitCode: EXIT_CODE_ERROR,
-          output: '$e\n$s',
-        );
+        response = WorkResponse(exitCode: EXIT_CODE_ERROR, output: '$e\n$s');
       }
 
       connection.writeResponse(response);

diff --git a/pkgs/bazel_worker/lib/src/worker/sync_worker_loop.dart b/pkgs/bazel_worker/lib/src/worker/sync_worker_loop.dart
index a857105..51da684 100644
--- a/pkgs/bazel_worker/lib/src/worker/sync_worker_loop.dart
+++ b/pkgs/bazel_worker/lib/src/worker/sync_worker_loop.dart

@@ -30,19 +30,20 @@
         var request = connection.readRequest();
         if (request == null) break;
         var printMessages = StringBuffer();
-        response = runZoned(() => performRequest(request), zoneSpecification:
-            ZoneSpecification(print: (self, parent, zone, message) {
-          printMessages.writeln();
-          printMessages.write(message);
-        }));
+        response = runZoned(
+          () => performRequest(request),
+          zoneSpecification: ZoneSpecification(
+            print: (self, parent, zone, message) {
+              printMessages.writeln();
+              printMessages.write(message);
+            },
+          ),
+        );
         if (printMessages.isNotEmpty) {
           response.output = '${response.output}$printMessages';
         }
       } catch (e, s) {
-        response = WorkResponse(
-          exitCode: EXIT_CODE_ERROR,
-          output: '$e\n$s',
-        );
+        response = WorkResponse(exitCode: EXIT_CODE_ERROR, output: '$e\n$s');
       }
 
       connection.writeResponse(response);

diff --git a/pkgs/bazel_worker/lib/src/worker/worker_connection.dart b/pkgs/bazel_worker/lib/src/worker/worker_connection.dart
index b395316..fd5508e 100644
--- a/pkgs/bazel_worker/lib/src/worker/worker_connection.dart
+++ b/pkgs/bazel_worker/lib/src/worker/worker_connection.dart

@@ -29,13 +29,16 @@
   /// Creates a [StdAsyncWorkerConnection] with the specified [inputStream]
   /// and [outputStream], unless [sendPort] is specified, in which case
   /// creates a [SendPortAsyncWorkerConnection].
-  factory AsyncWorkerConnection(
-          {Stream<List<int>>? inputStream,
-          StreamSink<List<int>>? outputStream,
-          SendPort? sendPort}) =>
+  factory AsyncWorkerConnection({
+    Stream<List<int>>? inputStream,
+    StreamSink<List<int>>? outputStream,
+    SendPort? sendPort,
+  }) =>
       sendPort == null
           ? StdAsyncWorkerConnection(
-              inputStream: inputStream, outputStream: outputStream)
+              inputStream: inputStream,
+              outputStream: outputStream,
+            )
           : SendPortAsyncWorkerConnection(sendPort);
 
   @override
@@ -53,9 +56,10 @@
   final AsyncMessageGrouper _messageGrouper;
   final StreamSink<List<int>> _outputStream;
 
-  StdAsyncWorkerConnection(
-      {Stream<List<int>>? inputStream, StreamSink<List<int>>? outputStream})
-      : _messageGrouper = AsyncMessageGrouper(inputStream ?? stdin),
+  StdAsyncWorkerConnection({
+    Stream<List<int>>? inputStream,
+    StreamSink<List<int>>? outputStream,
+  })  : _messageGrouper = AsyncMessageGrouper(inputStream ?? stdin),
         _outputStream = outputStream ?? stdout;
 
   @override

diff --git a/pkgs/bazel_worker/lib/testing.dart b/pkgs/bazel_worker/lib/testing.dart
index 3ae4c1f..7aefabb 100644
--- a/pkgs/bazel_worker/lib/testing.dart
+++ b/pkgs/bazel_worker/lib/testing.dart

@@ -72,10 +72,18 @@
   }
 
   @override
-  StreamSubscription<Uint8List> listen(void Function(Uint8List bytes)? onData,
-      {Function? onError, void Function()? onDone, bool? cancelOnError}) {
-    return _controller.stream.listen(onData,
-        onError: onError, onDone: onDone, cancelOnError: cancelOnError);
+  StreamSubscription<Uint8List> listen(
+    void Function(Uint8List bytes)? onData, {
+    Function? onError,
+    void Function()? onDone,
+    bool? cancelOnError,
+  }) {
+    return _controller.stream.listen(
+      onData,
+      onError: onError,
+      onDone: onDone,
+      cancelOnError: cancelOnError,
+    );
   }
 
   @override
@@ -165,8 +173,9 @@
   final List<WorkResponse> responses = <WorkResponse>[];
 
   TestAsyncWorkerConnection(
-      Stream<List<int>> inputStream, StreamSink<List<int>> outputStream)
-      : super(inputStream: inputStream, outputStream: outputStream);
+    Stream<List<int>> inputStream,
+    StreamSink<List<int>> outputStream,
+  ) : super(inputStream: inputStream, outputStream: outputStream);
 
   @override
   void writeResponse(WorkResponse response) {

diff --git a/pkgs/bazel_worker/test/driver_test.dart b/pkgs/bazel_worker/test/driver_test.dart
index c397830..c3db55c 100644
--- a/pkgs/bazel_worker/test/driver_test.dart
+++ b/pkgs/bazel_worker/test/driver_test.dart

@@ -23,27 +23,37 @@
       await _doRequests(count: 1);
     });
 
-    test('can run multiple batches of requests through multiple workers',
-        () async {
-      var maxWorkers = 4;
-      var maxIdleWorkers = 2;
-      driver = BazelWorkerDriver(MockWorker.spawn,
-          maxWorkers: maxWorkers, maxIdleWorkers: maxIdleWorkers);
-      for (var i = 0; i < 10; i++) {
-        await _doRequests(driver: driver);
-        expect(MockWorker.liveWorkers.length, maxIdleWorkers);
-        // No workers should be killed while there is ongoing work, but they
-        // should be cleaned up once there isn't any more work to do.
-        expect(MockWorker.deadWorkers.length,
-            (maxWorkers - maxIdleWorkers) * (i + 1));
-      }
-    });
+    test(
+      'can run multiple batches of requests through multiple workers',
+      () async {
+        var maxWorkers = 4;
+        var maxIdleWorkers = 2;
+        driver = BazelWorkerDriver(
+          MockWorker.spawn,
+          maxWorkers: maxWorkers,
+          maxIdleWorkers: maxIdleWorkers,
+        );
+        for (var i = 0; i < 10; i++) {
+          await _doRequests(driver: driver);
+          expect(MockWorker.liveWorkers.length, maxIdleWorkers);
+          // No workers should be killed while there is ongoing work, but they
+          // should be cleaned up once there isn't any more work to do.
+          expect(
+            MockWorker.deadWorkers.length,
+            (maxWorkers - maxIdleWorkers) * (i + 1),
+          );
+        }
+      },
+    );
 
     test('can run multiple requests through one worker', () async {
       var maxWorkers = 1;
       var maxIdleWorkers = 1;
-      driver = BazelWorkerDriver(MockWorker.spawn,
-          maxWorkers: maxWorkers, maxIdleWorkers: maxIdleWorkers);
+      driver = BazelWorkerDriver(
+        MockWorker.spawn,
+        maxWorkers: maxWorkers,
+        maxIdleWorkers: maxIdleWorkers,
+      );
       for (var i = 0; i < 10; i++) {
         await _doRequests(driver: driver);
         expect(MockWorker.liveWorkers.length, 1);
@@ -52,8 +62,11 @@
     });
 
     test('can run one request through multiple workers', () async {
-      driver =
-          BazelWorkerDriver(MockWorker.spawn, maxWorkers: 4, maxIdleWorkers: 4);
+      driver = BazelWorkerDriver(
+        MockWorker.spawn,
+        maxWorkers: 4,
+        maxIdleWorkers: 4,
+      );
       for (var i = 0; i < 10; i++) {
         await _doRequests(driver: driver, count: 1);
         expect(MockWorker.liveWorkers.length, 1);
@@ -63,8 +76,11 @@
 
     test('can run with maxIdleWorkers == 0', () async {
       var maxWorkers = 4;
-      driver = BazelWorkerDriver(MockWorker.spawn,
-          maxWorkers: maxWorkers, maxIdleWorkers: 0);
+      driver = BazelWorkerDriver(
+        MockWorker.spawn,
+        maxWorkers: maxWorkers,
+        maxIdleWorkers: 0,
+      );
       for (var i = 0; i < 10; i++) {
         await _doRequests(driver: driver);
         expect(MockWorker.liveWorkers.length, 0);
@@ -77,14 +93,15 @@
       driver = BazelWorkerDriver(MockWorker.spawn, maxWorkers: maxWorkers);
       var tracking = <Future>[];
       await _doRequests(
-          driver: driver,
-          count: 10,
-          trackWork: (Future response) {
-            // We should never be tracking more than `maxWorkers` jobs at a time.
-            expect(tracking.length, lessThan(maxWorkers));
-            tracking.add(response);
-            response.then((_) => tracking.remove(response));
-          });
+        driver: driver,
+        count: 10,
+        trackWork: (Future response) {
+          // We should never be tracking more than `maxWorkers` jobs at a time.
+          expect(tracking.length, lessThan(maxWorkers));
+          tracking.add(response);
+          response.then((_) => tracking.remove(response));
+        },
+      );
     });
 
     group('failing workers', () {
@@ -93,27 +110,39 @@
       void createDriver({int maxRetries = 2, int numBadWorkers = 2}) {
         var numSpawned = 0;
         driver = BazelWorkerDriver(
-            () async => MockWorker(workerLoopFactory: (MockWorker worker) {
-                  var connection = StdAsyncWorkerConnection(
-                      inputStream: worker._stdinController.stream,
-                      outputStream: worker._stdoutController.sink);
-                  if (numSpawned < numBadWorkers) {
-                    numSpawned++;
-                    return ThrowingMockWorkerLoop(
-                        worker, MockWorker.responseQueue, connection);
-                  } else {
-                    return MockWorkerLoop(MockWorker.responseQueue,
-                        connection: connection);
-                  }
-                }),
-            maxRetries: maxRetries);
+          () async => MockWorker(
+            workerLoopFactory: (MockWorker worker) {
+              var connection = StdAsyncWorkerConnection(
+                inputStream: worker._stdinController.stream,
+                outputStream: worker._stdoutController.sink,
+              );
+              if (numSpawned < numBadWorkers) {
+                numSpawned++;
+                return ThrowingMockWorkerLoop(
+                  worker,
+                  MockWorker.responseQueue,
+                  connection,
+                );
+              } else {
+                return MockWorkerLoop(
+                  MockWorker.responseQueue,
+                  connection: connection,
+                );
+              }
+            },
+          ),
+          maxRetries: maxRetries,
+        );
       }
 
       test('should retry up to maxRetries times', () async {
         createDriver();
         var expectedResponse = WorkResponse();
-        MockWorker.responseQueue.addAll(
-            [disconnectedResponse, disconnectedResponse, expectedResponse]);
+        MockWorker.responseQueue.addAll([
+          disconnectedResponse,
+          disconnectedResponse,
+          expectedResponse,
+        ]);
         var actualResponse = await driver!.doWork(WorkRequest());
         // The first 2 null responses are thrown away, and we should get the
         // third one.
@@ -125,23 +154,29 @@
 
       test('should fail if it exceeds maxRetries failures', () async {
         createDriver(maxRetries: 2, numBadWorkers: 3);
-        MockWorker.responseQueue.addAll(
-            [disconnectedResponse, disconnectedResponse, WorkResponse()]);
+        MockWorker.responseQueue.addAll([
+          disconnectedResponse,
+          disconnectedResponse,
+          WorkResponse(),
+        ]);
         var actualResponse = await driver!.doWork(WorkRequest());
         // Should actually get a bad response.
         expect(actualResponse.exitCode, 15);
         expect(
-            actualResponse.output,
-            'Invalid response from worker, this probably means it wrote '
-            'invalid output or died.');
+          actualResponse.output,
+          'Invalid response from worker, this probably means it wrote '
+          'invalid output or died.',
+        );
 
         expect(MockWorker.deadWorkers.length, 3);
       });
     });
 
     test('handles spawnWorker failures', () async {
-      driver = BazelWorkerDriver(() async => throw StateError('oh no!'),
-          maxRetries: 0);
+      driver = BazelWorkerDriver(
+        () async => throw StateError('oh no!'),
+        maxRetries: 0,
+      );
       expect(driver!.doWork(WorkRequest()), throwsA(isA<StateError>()));
     });
 
@@ -156,10 +191,11 @@
 
 /// Runs [count] of fake work requests through [driver], and asserts that they
 /// all completed.
-Future _doRequests(
-    {BazelWorkerDriver? driver,
-    int count = 100,
-    void Function(Future<WorkResponse?>)? trackWork}) async {
+Future _doRequests({
+  BazelWorkerDriver? driver,
+  int count = 100,
+  void Function(Future<WorkResponse?>)? trackWork,
+}) async {
   // If we create a driver, we need to make sure and terminate it.
   var terminateDriver = driver == null;
   driver ??= BazelWorkerDriver(MockWorker.spawn);
@@ -167,7 +203,8 @@
   var responses = List.generate(count, (_) => WorkResponse());
   MockWorker.responseQueue.addAll(responses);
   var actualResponses = await Future.wait(
-      requests.map((request) => driver!.doWork(request, trackWork: trackWork)));
+    requests.map((request) => driver!.doWork(request, trackWork: trackWork)),
+  );
   expect(actualResponses, unorderedEquals(responses));
   if (terminateDriver) await driver.terminateWorkers();
 }
@@ -191,9 +228,11 @@
 class ThrowingMockWorkerLoop extends MockWorkerLoop {
   final MockWorker _mockWorker;
 
-  ThrowingMockWorkerLoop(this._mockWorker, Queue<WorkResponse> responseQueue,
-      AsyncWorkerConnection connection)
-      : super(responseQueue, connection: connection);
+  ThrowingMockWorkerLoop(
+    this._mockWorker,
+    Queue<WorkResponse> responseQueue,
+    AsyncWorkerConnection connection,
+  ) : super(responseQueue, connection: connection);
 
   /// Run the worker loop. The returned [Future] doesn't complete until
   /// [connection#readRequest] returns `null`.
@@ -234,10 +273,13 @@
     liveWorkers.add(this);
     var workerLoop = workerLoopFactory != null
         ? workerLoopFactory(this)
-        : MockWorkerLoop(responseQueue,
+        : MockWorkerLoop(
+            responseQueue,
             connection: StdAsyncWorkerConnection(
-                inputStream: _stdinController.stream,
-                outputStream: _stdoutController.sink));
+              inputStream: _stdinController.stream,
+              outputStream: _stdoutController.sink,
+            ),
+          );
     workerLoop.run();
   }
 
@@ -260,8 +302,10 @@
   int get pid => throw UnsupportedError('Not needed.');
 
   @override
-  bool kill(
-      [ProcessSignal processSignal = ProcessSignal.sigterm, int exitCode = 0]) {
+  bool kill([
+    ProcessSignal processSignal = ProcessSignal.sigterm,
+    int exitCode = 0,
+  ]) {
     if (_killed) return false;
     () async {
       await _stdoutController.close();

diff --git a/pkgs/bazel_worker/test/message_grouper_test.dart b/pkgs/bazel_worker/test/message_grouper_test.dart
index 475190e..fd99911 100644
--- a/pkgs/bazel_worker/test/message_grouper_test.dart
+++ b/pkgs/bazel_worker/test/message_grouper_test.dart

@@ -18,8 +18,10 @@
   });
 }
 
-void runTests(TestStdin Function() stdinFactory,
-    MessageGrouper Function(Stdin) messageGrouperFactory) {
+void runTests(
+  TestStdin Function() stdinFactory,
+  MessageGrouper Function(Stdin) messageGrouperFactory,
+) {
   late MessageGrouper messageGrouper;
 
   late TestStdin stdinStream;
@@ -52,16 +54,12 @@
   });
 
   test('Short message', () async {
-    await check([
-      5,
-      10,
-      20,
-      30,
-      40,
-      50
-    ], [
-      [10, 20, 30, 40, 50]
-    ]);
+    await check(
+      [5, 10, 20, 30, 40, 50],
+      [
+        [10, 20, 30, 40, 50],
+      ],
+    );
   });
 
   test('Message with 2-byte length', () async {
@@ -79,57 +77,44 @@
   });
 
   test('Multiple messages', () async {
-    await check([
-      2,
-      10,
-      20,
-      2,
-      30,
-      40
-    ], [
-      [10, 20],
-      [30, 40]
-    ]);
+    await check(
+      [2, 10, 20, 2, 30, 40],
+      [
+        [10, 20],
+        [30, 40],
+      ],
+    );
   });
 
   test('Empty message at start', () async {
-    await check([
-      0,
-      2,
-      10,
-      20
-    ], [
-      [],
-      [10, 20]
-    ]);
+    await check(
+      [0, 2, 10, 20],
+      [
+        [],
+        [10, 20],
+      ],
+    );
   });
 
   test('Empty message at end', () async {
-    await check([
-      2,
-      10,
-      20,
-      0
-    ], [
-      [10, 20],
-      []
-    ]);
+    await check(
+      [2, 10, 20, 0],
+      [
+        [10, 20],
+        [],
+      ],
+    );
   });
 
   test('Empty message in the middle', () async {
-    await check([
-      2,
-      10,
-      20,
-      0,
-      2,
-      30,
-      40
-    ], [
-      [10, 20],
-      [],
-      [30, 40]
-    ]);
+    await check(
+      [2, 10, 20, 0, 2, 30, 40],
+      [
+        [10, 20],
+        [],
+        [30, 40],
+      ],
+    );
   });
 
   test('Handles the case when stdin gives an error instead of EOF', () async {

diff --git a/pkgs/bazel_worker/test/worker_loop_test.dart b/pkgs/bazel_worker/test/worker_loop_test.dart
index 50d2151..24068b1 100644
--- a/pkgs/bazel_worker/test/worker_loop_test.dart
+++ b/pkgs/bazel_worker/test/worker_loop_test.dart

@@ -11,36 +11,45 @@
 
 void main() {
   group('SyncWorkerLoop', () {
-    runTests(TestStdinSync.new, TestSyncWorkerConnection.new,
-        TestSyncWorkerLoop.new);
+    runTests(
+      TestStdinSync.new,
+      TestSyncWorkerConnection.new,
+      TestSyncWorkerLoop.new,
+    );
   });
 
   group('AsyncWorkerLoop', () {
-    runTests(TestStdinAsync.new, TestAsyncWorkerConnection.new,
-        TestAsyncWorkerLoop.new);
+    runTests(
+      TestStdinAsync.new,
+      TestAsyncWorkerConnection.new,
+      TestAsyncWorkerLoop.new,
+    );
   });
 
   group('SyncWorkerLoopWithPrint', () {
     runTests(
-        TestStdinSync.new,
-        TestSyncWorkerConnection.new,
-        (TestSyncWorkerConnection connection) =>
-            TestSyncWorkerLoop(connection, printMessage: 'Goodbye!'));
+      TestStdinSync.new,
+      TestSyncWorkerConnection.new,
+      (TestSyncWorkerConnection connection) =>
+          TestSyncWorkerLoop(connection, printMessage: 'Goodbye!'),
+    );
   });
 
   group('AsyncWorkerLoopWithPrint', () {
     runTests(
-        TestStdinAsync.new,
-        TestAsyncWorkerConnection.new,
-        (TestAsyncWorkerConnection connection) =>
-            TestAsyncWorkerLoop(connection, printMessage: 'Goodbye!'));
+      TestStdinAsync.new,
+      TestAsyncWorkerConnection.new,
+      (TestAsyncWorkerConnection connection) =>
+          TestAsyncWorkerLoop(connection, printMessage: 'Goodbye!'),
+    );
   });
 }
 
 void runTests<T extends TestWorkerConnection>(
-    TestStdin Function() stdinFactory,
-    T Function(Stdin, Stdout) workerConnectionFactory,
-    TestWorkerLoop Function(T) workerLoopFactory) {
+  TestStdin Function() stdinFactory,
+  T Function(Stdin, Stdout) workerConnectionFactory,
+  TestWorkerLoop Function(T) workerLoopFactory,
+) {
   late TestStdin stdinStream;
   late TestStdoutStream stdoutStream;
   late T connection;
@@ -63,19 +72,29 @@
 
     // Make sure `print` never gets called in the parent zone.
     var printMessages = <String>[];
-    await runZoned(() => workerLoop.run(), zoneSpecification:
-        ZoneSpecification(print: (self, parent, zone, message) {
-      printMessages.add(message);
-    }));
-    expect(printMessages, isEmpty,
-        reason: 'The worker loop should hide all print calls from the parent '
-            'zone.');
+    await runZoned(
+      () => workerLoop.run(),
+      zoneSpecification: ZoneSpecification(
+        print: (self, parent, zone, message) {
+          printMessages.add(message);
+        },
+      ),
+    );
+    expect(
+      printMessages,
+      isEmpty,
+      reason: 'The worker loop should hide all print calls from the parent '
+          'zone.',
+    );
 
     expect(connection.responses, hasLength(1));
     expect(connection.responses[0], response);
     if (workerLoop.printMessage != null) {
-      expect(response.output, endsWith(workerLoop.printMessage!),
-          reason: 'Print messages should get appended to the response output.');
+      expect(
+        response.output,
+        endsWith(workerLoop.printMessage!),
+        reason: 'Print messages should get appended to the response output.',
+      );
     }
 
     // Check that a serialized version was written to std out.

diff --git a/pkgs/clock/analysis_options.yaml b/pkgs/clock/analysis_options.yaml
index 9ee7c2b..db6072d 100644
--- a/pkgs/clock/analysis_options.yaml
+++ b/pkgs/clock/analysis_options.yaml

@@ -11,4 +11,3 @@
   rules:
     - avoid_private_typedef_functions
     - avoid_redundant_argument_values
-    - use_super_parameters

diff --git a/pkgs/coverage/analysis_options.yaml b/pkgs/coverage/analysis_options.yaml
index 82ce5e0..bb1afe0 100644
--- a/pkgs/coverage/analysis_options.yaml
+++ b/pkgs/coverage/analysis_options.yaml

@@ -9,14 +9,9 @@
 
 linter:
   rules:
-    - always_declare_return_types
     - avoid_slow_async_io
     - cancel_subscriptions
-    - comment_references
     - literal_only_boolean_expressions
     - prefer_final_locals
     - sort_constructors_first
     - sort_unnamed_constructors_first
-    - test_types_in_equals
-    - throw_in_finally
-    - type_annotate_public_apis

diff --git a/pkgs/file/CHANGELOG.md b/pkgs/file/CHANGELOG.md
index 50c96c4..3a3969c 100644
--- a/pkgs/file/CHANGELOG.md
+++ b/pkgs/file/CHANGELOG.md

@@ -1,3 +1,5 @@
+## 7.0.2-wip
+
 ## 7.0.1
 
 * Update the pubspec repository field to reflect the new package repository.

diff --git a/pkgs/file/analysis_options.yaml b/pkgs/file/analysis_options.yaml
index 8fbd2e4..d978f81 100644
--- a/pkgs/file/analysis_options.yaml
+++ b/pkgs/file/analysis_options.yaml

@@ -1,6 +1 @@
-include: package:lints/recommended.yaml
-
-analyzer:
-  errors:
-    # Allow having TODOs in the code
-    todo: ignore
+include: package:dart_flutter_team_lints/analysis_options.yaml

diff --git a/pkgs/file/example/main.dart b/pkgs/file/example/main.dart
index 7ca0bc7..b03b363 100644
--- a/pkgs/file/example/main.dart
+++ b/pkgs/file/example/main.dart

@@ -7,8 +7,8 @@
 
 Future<void> main() async {
   final FileSystem fs = MemoryFileSystem();
-  final Directory tmp = await fs.systemTempDirectory.createTemp('example_');
-  final File outputFile = tmp.childFile('output');
+  final tmp = await fs.systemTempDirectory.createTemp('example_');
+  final outputFile = tmp.childFile('output');
   await outputFile.writeAsString('Hello world!');
   print(outputFile.readAsStringSync());
 }

diff --git a/pkgs/file/lib/chroot.dart b/pkgs/file/lib/chroot.dart
index 56d2bd5..6992ad0 100644
--- a/pkgs/file/lib/chroot.dart
+++ b/pkgs/file/lib/chroot.dart

@@ -3,4 +3,6 @@
 // BSD-style license that can be found in the LICENSE file.
 
 /// A file system that provides a view into _another_ `FileSystem` via a path.
+library;
+
 export 'src/backends/chroot.dart';

diff --git a/pkgs/file/lib/file.dart b/pkgs/file/lib/file.dart
index cdde9fe..c2e97b2 100644
--- a/pkgs/file/lib/file.dart
+++ b/pkgs/file/lib/file.dart

@@ -4,5 +4,7 @@
 
 /// Core interfaces containing the abstract `FileSystem` interface definition
 /// and all associated types used by `FileSystem`.
+library;
+
 export 'src/forwarding.dart';
 export 'src/interface.dart';

diff --git a/pkgs/file/lib/local.dart b/pkgs/file/lib/local.dart
index 74f506e..5b1e3cd 100644
--- a/pkgs/file/lib/local.dart
+++ b/pkgs/file/lib/local.dart

@@ -4,4 +4,6 @@
 
 /// A local file system implementation. This relies on the use of `dart:io`
 /// and is thus not suitable for use in the browser.
+library;
+
 export 'src/backends/local.dart';

diff --git a/pkgs/file/lib/memory.dart b/pkgs/file/lib/memory.dart
index c5705ef..690b65f 100644
--- a/pkgs/file/lib/memory.dart
+++ b/pkgs/file/lib/memory.dart

@@ -4,5 +4,7 @@
 
 /// An implementation of `FileSystem` that exists entirely in memory with an
 /// internal representation loosely based on the Filesystem Hierarchy Standard.
+library;
+
 export 'src/backends/memory.dart';
 export 'src/backends/memory/operations.dart';

diff --git a/pkgs/file/lib/src/backends/chroot.dart b/pkgs/file/lib/src/backends/chroot.dart
index 6082e80..402dbec 100644
--- a/pkgs/file/lib/src/backends/chroot.dart
+++ b/pkgs/file/lib/src/backends/chroot.dart

@@ -2,16 +2,16 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-library file.src.backends.chroot;
-
 import 'dart:convert';
 import 'dart:typed_data';
 
-import 'package:file/file.dart';
-import 'package:file/src/common.dart' as common;
-import 'package:file/src/io.dart' as io;
 import 'package:path/path.dart' as p;
 
+import '../common.dart' as common;
+import '../forwarding.dart';
+import '../interface.dart';
+import '../io.dart' as io;
+
 part 'chroot/chroot_directory.dart';
 part 'chroot/chroot_file.dart';
 part 'chroot/chroot_file_system.dart';

diff --git a/pkgs/file/lib/src/backends/chroot/chroot_directory.dart b/pkgs/file/lib/src/backends/chroot/chroot_directory.dart
index 8fec7b1..e094193 100644
--- a/pkgs/file/lib/src/backends/chroot/chroot_directory.dart
+++ b/pkgs/file/lib/src/backends/chroot/chroot_directory.dart

@@ -2,18 +2,18 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-part of file.src.backends.chroot;
+part of '../chroot.dart';
 
 class _ChrootDirectory extends _ChrootFileSystemEntity<Directory, io.Directory>
     with ForwardingDirectory<Directory>, common.DirectoryAddOnsMixin {
-  _ChrootDirectory(ChrootFileSystem fs, String path) : super(fs, path);
+  _ChrootDirectory(super.fs, super.path);
 
   factory _ChrootDirectory.wrapped(
     ChrootFileSystem fs,
     Directory delegate, {
     bool relative = false,
   }) {
-    String localPath = fs._local(delegate.path, relative: relative);
+    var localPath = fs._local(delegate.path, relative: relative);
     return _ChrootDirectory(fs, localPath);
   }
 
@@ -32,7 +32,7 @@
       if (await fileSystem.type(path) != expectedType) {
         throw common.notADirectory(path);
       }
-      FileSystemEntityType type = await fileSystem.type(newPath);
+      var type = await fileSystem.type(newPath);
       if (type != FileSystemEntityType.notFound) {
         if (type != expectedType) {
           throw common.notADirectory(newPath);
@@ -44,7 +44,7 @@
           throw common.directoryNotEmpty(newPath);
         }
       }
-      String target = await fileSystem.link(path).target();
+      var target = await fileSystem.link(path).target();
       await fileSystem.link(path).delete();
       await fileSystem.link(newPath).create(target);
       return fileSystem.directory(newPath);
@@ -60,7 +60,7 @@
       if (fileSystem.typeSync(path) != expectedType) {
         throw common.notADirectory(path);
       }
-      FileSystemEntityType type = fileSystem.typeSync(newPath);
+      var type = fileSystem.typeSync(newPath);
       if (type != FileSystemEntityType.notFound) {
         if (type != expectedType) {
           throw common.notADirectory(newPath);
@@ -72,7 +72,7 @@
           throw common.directoryNotEmpty(newPath);
         }
       }
-      String target = fileSystem.link(path).targetSync();
+      var target = fileSystem.link(path).targetSync();
       fileSystem.link(path).deleteSync();
       fileSystem.link(newPath).createSync(target);
       return fileSystem.directory(newPath);
@@ -97,17 +97,15 @@
   @override
   Future<Directory> create({bool recursive = false}) async {
     if (_isLink) {
-      switch (await fileSystem.type(path)) {
-        case FileSystemEntityType.notFound:
-          throw common.noSuchFileOrDirectory(path);
-        case FileSystemEntityType.file:
-          throw common.fileExists(path);
-        case FileSystemEntityType.directory:
+      return switch (await fileSystem.type(path)) {
+        FileSystemEntityType.notFound =>
+          throw common.noSuchFileOrDirectory(path),
+        FileSystemEntityType.file => throw common.fileExists(path),
+        FileSystemEntityType.directory =>
           // Nothing to do.
-          return this;
-        default:
-          throw AssertionError();
-      }
+          this,
+        _ => throw AssertionError()
+      };
     } else {
       return wrap(await delegate.create(recursive: recursive));
     }
@@ -137,8 +135,8 @@
     bool recursive = false,
     bool followLinks = true,
   }) {
-    Directory delegate = this.delegate as Directory;
-    String dirname = delegate.path;
+    var delegate = this.delegate as Directory;
+    var dirname = delegate.path;
     return delegate
         .list(recursive: recursive, followLinks: followLinks)
         .map((io.FileSystemEntity entity) => _denormalize(entity, dirname));
@@ -149,8 +147,8 @@
     bool recursive = false,
     bool followLinks = true,
   }) {
-    Directory delegate = this.delegate as Directory;
-    String dirname = delegate.path;
+    var delegate = this.delegate as Directory;
+    var dirname = delegate.path;
     return delegate
         .listSync(recursive: recursive, followLinks: followLinks)
         .map((io.FileSystemEntity entity) => _denormalize(entity, dirname))
@@ -158,9 +156,9 @@
   }
 
   FileSystemEntity _denormalize(io.FileSystemEntity entity, String dirname) {
-    p.Context ctx = fileSystem.path;
-    String relativePart = ctx.relative(entity.path, from: dirname);
-    String entityPath = ctx.join(path, relativePart);
+    var ctx = fileSystem.path;
+    var relativePart = ctx.relative(entity.path, from: dirname);
+    var entityPath = ctx.join(path, relativePart);
     if (entity is io.File) {
       return _ChrootFile(fileSystem, entityPath);
     } else if (entity is io.Directory) {

diff --git a/pkgs/file/lib/src/backends/chroot/chroot_file.dart b/pkgs/file/lib/src/backends/chroot/chroot_file.dart
index 4b67bc1..d6c29fc 100644
--- a/pkgs/file/lib/src/backends/chroot/chroot_file.dart
+++ b/pkgs/file/lib/src/backends/chroot/chroot_file.dart

@@ -2,20 +2,20 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-part of file.src.backends.chroot;
+part of '../chroot.dart';
 
 typedef _SetupCallback = dynamic Function();
 
 class _ChrootFile extends _ChrootFileSystemEntity<File, io.File>
     with ForwardingFile {
-  _ChrootFile(ChrootFileSystem fs, String path) : super(fs, path);
+  _ChrootFile(super.fs, super.path);
 
   factory _ChrootFile.wrapped(
     ChrootFileSystem fs,
     io.File delegate, {
     bool relative = false,
   }) {
-    String localPath = fs._local(delegate.path, relative: relative);
+    var localPath = fs._local(delegate.path, relative: relative);
     return _ChrootFile(fs, localPath);
   }
 
@@ -126,7 +126,7 @@
 
   @override
   Future<File> create({bool recursive = false, bool exclusive = false}) async {
-    String path = fileSystem._resolve(
+    var path = fileSystem._resolve(
       this.path,
       followLinks: false,
       notFound: recursive ? _NotFoundBehavior.mkdir : _NotFoundBehavior.allow,
@@ -158,7 +158,7 @@
 
   @override
   void createSync({bool recursive = false, bool exclusive = false}) {
-    String path = fileSystem._resolve(
+    var path = fileSystem._resolve(
       this.path,
       followLinks: false,
       notFound: recursive ? _NotFoundBehavior.mkdir : _NotFoundBehavior.allow,

diff --git a/pkgs/file/lib/src/backends/chroot/chroot_file_system.dart b/pkgs/file/lib/src/backends/chroot/chroot_file_system.dart
index 6889c98..503821f 100644
--- a/pkgs/file/lib/src/backends/chroot/chroot_file_system.dart
+++ b/pkgs/file/lib/src/backends/chroot/chroot_file_system.dart

@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-part of file.src.backends.chroot;
+part of '../chroot.dart';
 
 const String _thisDir = '.';
 const String _parentDir = '..';
@@ -107,7 +107,7 @@
     }
 
     value = _resolve(value, notFound: _NotFoundBehavior.throwError);
-    String realPath = _real(value, resolve: false);
+    var realPath = _real(value, resolve: false);
     switch (delegate.typeSync(realPath, followLinks: false)) {
       case FileSystemEntityType.directory:
         break;
@@ -117,7 +117,7 @@
         throw common.notADirectory(path as String);
     }
     assert(() {
-      p.Context ctx = delegate.path;
+      var ctx = delegate.path;
       return ctx.isAbsolute(value) && value == ctx.canonicalize(value);
     }());
     _cwd = value;
@@ -201,7 +201,7 @@
       throw _ChrootJailException();
     }
     // TODO(tvolkert): See if _context.relative() works here
-    String result = realPath.substring(root.length);
+    var result = realPath.substring(root.length);
     if (result.isEmpty) {
       result = _localRoot;
     }
@@ -263,8 +263,8 @@
       throw common.noSuchFileOrDirectory(path);
     }
 
-    p.Context ctx = this.path;
-    String root = _localRoot;
+    var ctx = this.path;
+    var root = _localRoot;
     List<String> parts, ledger;
     if (ctx.isAbsolute(path)) {
       parts = ctx.split(path).sublist(1);
@@ -277,9 +277,9 @@
     }
 
     String getCurrentPath() => root + ctx.joinAll(ledger);
-    Set<String> breadcrumbs = <String>{};
+    var breadcrumbs = <String>{};
     while (parts.isNotEmpty) {
-      String segment = parts.removeAt(0);
+      var segment = parts.removeAt(0);
       if (segment == _thisDir) {
         continue;
       } else if (segment == _parentDir) {
@@ -290,8 +290,8 @@
       }
 
       ledger.add(segment);
-      String currentPath = getCurrentPath();
-      String realPath = _real(currentPath, resolve: false);
+      var currentPath = getCurrentPath();
+      var realPath = _real(currentPath, resolve: false);
 
       switch (delegate.typeSync(realPath, followLinks: false)) {
         case FileSystemEntityType.directory:
@@ -333,7 +333,7 @@
           if (!breadcrumbs.add(currentPath)) {
             throw common.tooManyLevelsOfSymbolicLinks(path);
           }
-          String target = delegate.link(realPath).targetSync();
+          var target = delegate.link(realPath).targetSync();
           if (ctx.isAbsolute(target)) {
             ledger.clear();
             parts.insertAll(0, ctx.split(target).sublist(1));

diff --git a/pkgs/file/lib/src/backends/chroot/chroot_file_system_entity.dart b/pkgs/file/lib/src/backends/chroot/chroot_file_system_entity.dart
index 8e859ac..18e37cd 100644
--- a/pkgs/file/lib/src/backends/chroot/chroot_file_system_entity.dart
+++ b/pkgs/file/lib/src/backends/chroot/chroot_file_system_entity.dart

@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-part of file.src.backends.chroot;
+part of '../chroot.dart';
 
 abstract class _ChrootFileSystemEntity<T extends FileSystemEntity,
     D extends io.FileSystemEntity> extends ForwardingFileSystemEntity<T, D> {
@@ -103,7 +103,7 @@
 
   @override
   Future<T> delete({bool recursive = false}) async {
-    String path = fileSystem._resolve(this.path,
+    var path = fileSystem._resolve(this.path,
         followLinks: false, notFound: _NotFoundBehavior.throwError);
 
     String real(String path) => fileSystem._real(path, resolve: false);
@@ -114,7 +114,7 @@
       if (expectedType == FileSystemEntityType.link) {
         await fileSystem.delegate.link(real(path)).delete();
       } else {
-        String resolvedPath = fileSystem._resolve(p.basename(path),
+        var resolvedPath = fileSystem._resolve(p.basename(path),
             from: p.dirname(path), notFound: _NotFoundBehavior.allowAtTail);
         if (!recursive && await type(resolvedPath) != expectedType) {
           throw expectedType == FileSystemEntityType.file
@@ -132,7 +132,7 @@
 
   @override
   void deleteSync({bool recursive = false}) {
-    String path = fileSystem._resolve(this.path,
+    var path = fileSystem._resolve(this.path,
         followLinks: false, notFound: _NotFoundBehavior.throwError);
 
     String real(String path) => fileSystem._real(path, resolve: false);
@@ -143,7 +143,7 @@
       if (expectedType == FileSystemEntityType.link) {
         fileSystem.delegate.link(real(path)).deleteSync();
       } else {
-        String resolvedPath = fileSystem._resolve(p.basename(path),
+        var resolvedPath = fileSystem._resolve(p.basename(path),
             from: p.dirname(path), notFound: _NotFoundBehavior.allowAtTail);
         if (!recursive && type(resolvedPath) != expectedType) {
           throw expectedType == FileSystemEntityType.file

diff --git a/pkgs/file/lib/src/backends/chroot/chroot_link.dart b/pkgs/file/lib/src/backends/chroot/chroot_link.dart
index acbeda6..1620df9 100644
--- a/pkgs/file/lib/src/backends/chroot/chroot_link.dart
+++ b/pkgs/file/lib/src/backends/chroot/chroot_link.dart

@@ -2,18 +2,18 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-part of file.src.backends.chroot;
+part of '../chroot.dart';
 
 class _ChrootLink extends _ChrootFileSystemEntity<Link, io.Link>
     with ForwardingLink {
-  _ChrootLink(ChrootFileSystem fs, String path) : super(fs, path);
+  _ChrootLink(super.fs, super.path);
 
   factory _ChrootLink.wrapped(
     ChrootFileSystem fs,
     io.Link delegate, {
     bool relative = false,
   }) {
-    String localPath = fs._local(delegate.path, relative: relative);
+    var localPath = fs._local(delegate.path, relative: relative);
     return _ChrootLink(fs, localPath);
   }
 

diff --git a/pkgs/file/lib/src/backends/chroot/chroot_random_access_file.dart b/pkgs/file/lib/src/backends/chroot/chroot_random_access_file.dart
index 4105ac8..10bbd70 100644
--- a/pkgs/file/lib/src/backends/chroot/chroot_random_access_file.dart
+++ b/pkgs/file/lib/src/backends/chroot/chroot_random_access_file.dart

@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-part of file.src.backends.chroot;
+part of '../chroot.dart';
 
 class _ChrootRandomAccessFile with ForwardingRandomAccessFile {
   _ChrootRandomAccessFile(this.path, this.delegate);

diff --git a/pkgs/file/lib/src/backends/local/local_directory.dart b/pkgs/file/lib/src/backends/local/local_directory.dart
index e23e68f..3e1db61 100644
--- a/pkgs/file/lib/src/backends/local/local_directory.dart
+++ b/pkgs/file/lib/src/backends/local/local_directory.dart

@@ -2,10 +2,10 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:file/file.dart';
-import 'package:file/src/common.dart' as common;
-import 'package:file/src/io.dart' as io;
-
+import '../../common.dart' as common;
+import '../../forwarding.dart';
+import '../../interface.dart';
+import '../../io.dart' as io;
 import 'local_file_system_entity.dart';
 
 /// [Directory] implementation that forwards all calls to `dart:io`.
@@ -13,7 +13,7 @@
     with ForwardingDirectory<LocalDirectory>, common.DirectoryAddOnsMixin {
   /// Instantiates a new [LocalDirectory] tied to the specified file system
   /// and delegating to the specified [delegate].
-  LocalDirectory(FileSystem fs, io.Directory delegate) : super(fs, delegate);
+  LocalDirectory(super.fs, super.delegate);
 
   @override
   String toString() => "LocalDirectory: '$path'";

diff --git a/pkgs/file/lib/src/backends/local/local_file.dart b/pkgs/file/lib/src/backends/local/local_file.dart
index 36293ba..a4bc106 100644
--- a/pkgs/file/lib/src/backends/local/local_file.dart
+++ b/pkgs/file/lib/src/backends/local/local_file.dart

@@ -2,9 +2,9 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:file/file.dart';
-import 'package:file/src/io.dart' as io;
-
+import '../../forwarding.dart';
+import '../../interface.dart';
+import '../../io.dart' as io;
 import 'local_file_system_entity.dart';
 
 /// [File] implementation that forwards all calls to `dart:io`.
@@ -12,7 +12,7 @@
     with ForwardingFile {
   /// Instantiates a new [LocalFile] tied to the specified file system
   /// and delegating to the specified [delegate].
-  LocalFile(FileSystem fs, io.File delegate) : super(fs, delegate);
+  LocalFile(super.fs, super.delegate);
 
   @override
   String toString() => "LocalFile: '$path'";

diff --git a/pkgs/file/lib/src/backends/local/local_file_system.dart b/pkgs/file/lib/src/backends/local/local_file_system.dart
index 635998e..7541c37 100644
--- a/pkgs/file/lib/src/backends/local/local_file_system.dart
+++ b/pkgs/file/lib/src/backends/local/local_file_system.dart

@@ -2,10 +2,10 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:file/src/io.dart' as io;
-import 'package:file/file.dart';
 import 'package:path/path.dart' as p;
 
+import '../../interface.dart';
+import '../../io.dart' as io;
 import 'local_directory.dart';
 import 'local_file.dart';
 import 'local_link.dart';

diff --git a/pkgs/file/lib/src/backends/local/local_file_system_entity.dart b/pkgs/file/lib/src/backends/local/local_file_system_entity.dart
index ca4617b..d0da559 100644
--- a/pkgs/file/lib/src/backends/local/local_file_system_entity.dart
+++ b/pkgs/file/lib/src/backends/local/local_file_system_entity.dart

@@ -2,9 +2,9 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:file/file.dart';
-import 'package:file/src/io.dart' as io;
-
+import '../../forwarding.dart';
+import '../../interface.dart';
+import '../../io.dart' as io;
 import 'local_directory.dart';
 import 'local_file.dart';
 import 'local_link.dart';

diff --git a/pkgs/file/lib/src/backends/local/local_link.dart b/pkgs/file/lib/src/backends/local/local_link.dart
index fc67d5e..2ce4791 100644
--- a/pkgs/file/lib/src/backends/local/local_link.dart
+++ b/pkgs/file/lib/src/backends/local/local_link.dart

@@ -2,9 +2,9 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:file/file.dart';
-import 'package:file/src/io.dart' as io;
-
+import '../../forwarding.dart';
+import '../../interface.dart';
+import '../../io.dart' as io;
 import 'local_file_system_entity.dart';
 
 /// [Link] implementation that forwards all calls to `dart:io`.
@@ -12,7 +12,7 @@
     with ForwardingLink {
   /// Instantiates a new [LocalLink] tied to the specified file system
   /// and delegating to the specified [delegate].
-  LocalLink(FileSystem fs, io.Link delegate) : super(fs, delegate);
+  LocalLink(super.fs, super.delegate);
 
   @override
   String toString() => "LocalLink: '$path'";

diff --git a/pkgs/file/lib/src/backends/memory/clock.dart b/pkgs/file/lib/src/backends/memory/clock.dart
index 98d5434..57c1b72 100644
--- a/pkgs/file/lib/src/backends/memory/clock.dart
+++ b/pkgs/file/lib/src/backends/memory/clock.dart

@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// ignore_for_file: comment_references
+
 /// Interface describing clocks used by the [MemoryFileSystem].
 ///
 /// The [MemoryFileSystem] uses a clock to determine the modification times of

diff --git a/pkgs/file/lib/src/backends/memory/common.dart b/pkgs/file/lib/src/backends/memory/common.dart
index 80e3c38..eb4ca43 100644
--- a/pkgs/file/lib/src/backends/memory/common.dart
+++ b/pkgs/file/lib/src/backends/memory/common.dart

@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:file/src/common.dart' as common;
+import '../../common.dart' as common;
 
 /// Generates a path to use in error messages.
 typedef PathGenerator = dynamic Function();

diff --git a/pkgs/file/lib/src/backends/memory/memory_directory.dart b/pkgs/file/lib/src/backends/memory/memory_directory.dart
index 95fe542..e73b967 100644
--- a/pkgs/file/lib/src/backends/memory/memory_directory.dart
+++ b/pkgs/file/lib/src/backends/memory/memory_directory.dart

@@ -2,11 +2,11 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:file/file.dart';
-import 'package:file/src/common.dart' as common;
-import 'package:file/src/io.dart' as io;
 import 'package:meta/meta.dart';
 
+import '../../common.dart' as common;
+import '../../interface.dart';
+import '../../io.dart' as io;
 import 'common.dart';
 import 'memory_file.dart';
 import 'memory_file_system_entity.dart';
@@ -25,8 +25,7 @@
     with common.DirectoryAddOnsMixin
     implements Directory {
   /// Instantiates a new [MemoryDirectory].
-  MemoryDirectory(NodeBasedFileSystem fileSystem, String path)
-      : super(fileSystem, path);
+  MemoryDirectory(super.fileSystem, super.path);
 
   @override
   io.FileSystemEntityType get expectedType => io.FileSystemEntityType.directory;
@@ -52,7 +51,7 @@
   @override
   void createSync({bool recursive = false}) {
     fileSystem.opHandle(path, FileSystemOp.create);
-    Node? node = internalCreateSync(
+    var node = internalCreateSync(
       followTailLink: true,
       visitLinks: true,
       createChild: (DirectoryNode parent, bool isFinalSegment) {
@@ -75,19 +74,19 @@
   @override
   Directory createTempSync([String? prefix]) {
     prefix = '${prefix ?? ''}rand';
-    String fullPath = fileSystem.path.join(path, prefix);
-    String dirname = fileSystem.path.dirname(fullPath);
-    String basename = fileSystem.path.basename(fullPath);
-    DirectoryNode? node = fileSystem.findNode(dirname) as DirectoryNode?;
+    var fullPath = fileSystem.path.join(path, prefix);
+    var dirname = fileSystem.path.dirname(fullPath);
+    var basename = fileSystem.path.basename(fullPath);
+    var node = fileSystem.findNode(dirname) as DirectoryNode?;
     checkExists(node, () => dirname);
     utils.checkIsDir(node!, () => dirname);
-    int tempCounter = _systemTempCounter[fileSystem] ?? 0;
+    var tempCounter = _systemTempCounter[fileSystem] ?? 0;
     String name() => '$basename$tempCounter';
     while (node.children.containsKey(name())) {
       tempCounter++;
     }
     _systemTempCounter[fileSystem] = tempCounter;
-    DirectoryNode tempDir = DirectoryNode(node);
+    var tempDir = DirectoryNode(node);
     node.children[name()] = tempDir;
     return MemoryDirectory(fileSystem, fileSystem.path.join(dirname, name()))
       ..createSync();
@@ -128,9 +127,9 @@
     bool recursive = false,
     bool followLinks = true,
   }) {
-    DirectoryNode node = backing as DirectoryNode;
-    List<FileSystemEntity> listing = <FileSystemEntity>[];
-    List<_PendingListTask> tasks = <_PendingListTask>[
+    var node = backing as DirectoryNode;
+    var listing = <FileSystemEntity>[];
+    var tasks = <_PendingListTask>[
       _PendingListTask(
         node,
         path.endsWith(fileSystem.path.separator)
@@ -140,14 +139,14 @@
       ),
     ];
     while (tasks.isNotEmpty) {
-      _PendingListTask task = tasks.removeLast();
+      var task = tasks.removeLast();
       task.dir.children.forEach((String name, Node child) {
-        Set<LinkNode> breadcrumbs = Set<LinkNode>.from(task.breadcrumbs);
-        String childPath = fileSystem.path.join(task.path, name);
+        var breadcrumbs = Set<LinkNode>.from(task.breadcrumbs);
+        var childPath = fileSystem.path.join(task.path, name);
         while (followLinks &&
             utils.isLink(child) &&
             breadcrumbs.add(child as LinkNode)) {
-          Node? referent = child.referentOrNull;
+          var referent = child.referentOrNull;
           if (referent != null) {
             child = referent;
           }

diff --git a/pkgs/file/lib/src/backends/memory/memory_file.dart b/pkgs/file/lib/src/backends/memory/memory_file.dart
index ba4faab..1a8f5f9 100644
--- a/pkgs/file/lib/src/backends/memory/memory_file.dart
+++ b/pkgs/file/lib/src/backends/memory/memory_file.dart

@@ -7,26 +7,25 @@
 import 'dart:math' as math show min;
 import 'dart:typed_data';
 
-import 'package:file/file.dart';
-import 'package:file/src/backends/memory/operations.dart';
-import 'package:file/src/common.dart' as common;
-import 'package:file/src/io.dart' as io;
 import 'package:meta/meta.dart';
 
+import '../../common.dart' as common;
+import '../../interface.dart';
+import '../../io.dart' as io;
 import 'common.dart';
 import 'memory_file_system_entity.dart';
 import 'memory_random_access_file.dart';
 import 'node.dart';
+import 'operations.dart';
 import 'utils.dart' as utils;
 
 /// Internal implementation of [File].
 class MemoryFile extends MemoryFileSystemEntity implements File {
   /// Instantiates a new [MemoryFile].
-  const MemoryFile(NodeBasedFileSystem fileSystem, String path)
-      : super(fileSystem, path);
+  const MemoryFile(super.fileSystem, super.path);
 
   FileNode get _resolvedBackingOrCreate {
-    Node? node = backingOrNull;
+    var node = backingOrNull;
     if (node == null) {
       node = _doCreate();
     } else {
@@ -61,7 +60,7 @@
   }
 
   Node? _doCreate({bool recursive = false}) {
-    Node? node = internalCreateSync(
+    var node = internalCreateSync(
       followTailLink: true,
       createChild: (DirectoryNode parent, bool isFinalSegment) {
         if (isFinalSegment) {
@@ -88,7 +87,7 @@
         newPath,
         followTailLink: true,
         checkType: (Node node) {
-          FileSystemEntityType actualType = node.stat.type;
+          var actualType = node.stat.type;
           if (actualType != expectedType) {
             throw actualType == FileSystemEntityType.notFound
                 ? common.noSuchFileOrDirectory(path)
@@ -103,7 +102,7 @@
   @override
   File copySync(String newPath) {
     fileSystem.opHandle(path, FileSystemOp.copy);
-    FileNode sourceNode = resolvedBacking as FileNode;
+    var sourceNode = resolvedBacking as FileNode;
     fileSystem.findNode(
       newPath,
       segmentVisitor: (
@@ -116,7 +115,7 @@
         if (currentSegment == finalSegment) {
           if (child != null) {
             if (utils.isLink(child)) {
-              List<String> ledger = <String>[];
+              var ledger = <String>[];
               child = utils.resolveLinks(child as LinkNode, () => newPath,
                   ledger: ledger);
               checkExists(child, () => newPath);
@@ -127,7 +126,7 @@
             utils.checkType(expectedType, child.type, () => newPath);
             parent.children.remove(childName);
           }
-          FileNode newNode = FileNode(parent);
+          var newNode = FileNode(parent);
           newNode.copyFrom(sourceNode);
           parent.children[childName] = newNode;
         }
@@ -158,7 +157,7 @@
 
   @override
   void setLastAccessedSync(DateTime time) {
-    FileNode node = resolvedBacking as FileNode;
+    var node = resolvedBacking as FileNode;
     node.accessed = time.millisecondsSinceEpoch;
   }
 
@@ -174,7 +173,7 @@
 
   @override
   void setLastModifiedSync(DateTime time) {
-    FileNode node = resolvedBacking as FileNode;
+    var node = resolvedBacking as FileNode;
     node.modified = time.millisecondsSinceEpoch;
   }
 
@@ -199,8 +198,8 @@
   Stream<List<int>> openRead([int? start, int? end]) {
     fileSystem.opHandle(path, FileSystemOp.open);
     try {
-      FileNode node = resolvedBacking as FileNode;
-      Uint8List content = node.content;
+      var node = resolvedBacking as FileNode;
+      var content = node.content;
       if (start != null) {
         content = end == null
             ? content.sublist(start)
@@ -253,13 +252,13 @@
 
   @override
   List<String> readAsLinesSync({Encoding encoding = utf8}) {
-    String str = readAsStringSync(encoding: encoding);
+    var str = readAsStringSync(encoding: encoding);
 
     if (str.isEmpty) {
       return <String>[];
     }
 
-    final List<String> lines = str.split('\n');
+    final lines = str.split('\n');
     if (str.endsWith('\n')) {
       // A final newline should not create an additional line.
       lines.removeLast();
@@ -287,7 +286,7 @@
     if (!utils.isWriteMode(mode)) {
       throw common.badFileDescriptor(path);
     }
-    FileNode node = _resolvedBackingOrCreate;
+    var node = _resolvedBackingOrCreate;
     _truncateIfNecessary(node, mode);
     fileSystem.opHandle(path, FileSystemOp.write);
     node.write(bytes);
@@ -349,7 +348,7 @@
       deferredException = e;
     }
 
-    Future<FileNode> future = Future<FileNode>.microtask(() {
+    var future = Future<FileNode>.microtask(() {
       if (deferredException != null) {
         throw deferredException;
       }
@@ -387,7 +386,7 @@
 
   @override
   void writeAll(Iterable<dynamic> objects, [String separator = '']) {
-    bool firstIter = true;
+    var firstIter = true;
     for (dynamic obj in objects) {
       if (!firstIter) {
         write(separator);
@@ -418,7 +417,7 @@
     _streamCompleter = Completer<void>();
 
     stream.listen(
-      (List<int> data) => _addData(data),
+      _addData,
       cancelOnError: true,
       onError: (Object error, StackTrace stackTrace) {
         _streamCompleter!.completeError(error, stackTrace);
@@ -445,8 +444,7 @@
       _isClosed = true;
       _pendingWrites.then(
         (_) => _completer.complete(),
-        onError: (Object error, StackTrace stackTrace) =>
-            _completer.completeError(error, stackTrace),
+        onError: _completer.completeError,
       );
     }
     return _completer.future;

diff --git a/pkgs/file/lib/src/backends/memory/memory_file_stat.dart b/pkgs/file/lib/src/backends/memory/memory_file_stat.dart
index 94f86d1..ce6beda 100644
--- a/pkgs/file/lib/src/backends/memory/memory_file_stat.dart
+++ b/pkgs/file/lib/src/backends/memory/memory_file_stat.dart

@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:file/src/io.dart' as io;
+import '../../io.dart' as io;
 
 /// Internal implementation of [io.FileStat].
 class MemoryFileStat implements io.FileStat {
@@ -47,8 +47,8 @@
 
   @override
   String modeString() {
-    int permissions = mode & 0xFFF;
-    List<String> codes = const <String>[
+    var permissions = mode & 0xFFF;
+    var codes = const <String>[
       '---',
       '--x',
       '-w-',
@@ -58,7 +58,7 @@
       'rw-',
       'rwx',
     ];
-    List<String> result = <String>[];
+    var result = <String>[];
     result
       ..add(codes[(permissions >> 6) & 0x7])
       ..add(codes[(permissions >> 3) & 0x7])

diff --git a/pkgs/file/lib/src/backends/memory/memory_file_system.dart b/pkgs/file/lib/src/backends/memory/memory_file_system.dart
index f3cdaee..dd359f0 100644
--- a/pkgs/file/lib/src/backends/memory/memory_file_system.dart
+++ b/pkgs/file/lib/src/backends/memory/memory_file_system.dart

@@ -2,11 +2,10 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:file/file.dart';
-import 'package:file/src/backends/memory/operations.dart';
-import 'package:file/src/io.dart' as io;
 import 'package:path/path.dart' as p;
 
+import '../../interface.dart';
+import '../../io.dart' as io;
 import 'clock.dart';
 import 'common.dart';
 import 'memory_directory.dart';
@@ -14,6 +13,7 @@
 import 'memory_file_stat.dart';
 import 'memory_link.dart';
 import 'node.dart';
+import 'operations.dart';
 import 'style.dart';
 import 'utils.dart' as utils;
 
@@ -91,7 +91,7 @@
   p.Context _context;
 
   @override
-  final Function(String context, FileSystemOp operation) opHandle;
+  final void Function(String context, FileSystemOp operation) opHandle;
 
   @override
   final Clock clock;
@@ -141,7 +141,7 @@
     }
 
     value = directory(value).resolveSymbolicLinksSync();
-    Node? node = findNode(value);
+    var node = findNode(value);
     checkExists(node, () => value);
     utils.checkIsDir(node!, () => value);
     assert(_context.isAbsolute(value));
@@ -166,9 +166,9 @@
 
   @override
   bool identicalSync(String path1, String path2) {
-    Node? node1 = findNode(path1);
+    var node1 = findNode(path1);
     checkExists(node1, () => path1);
-    Node? node2 = findNode(path2);
+    var node2 = findNode(path2);
     checkExists(node2, () => path2);
     return node1 != null && node1 == node2;
   }
@@ -220,14 +220,13 @@
       reference ??= _current;
     }
 
-    List<String> parts = path.split(style.separator)
-      ..removeWhere(utils.isEmpty);
-    DirectoryNode? directory = reference?.directory;
+    var parts = path.split(style.separator)..removeWhere(utils.isEmpty);
+    var directory = reference?.directory;
     Node? child = directory;
 
-    int finalSegment = parts.length - 1;
-    for (int i = 0; i <= finalSegment; i++) {
-      String basename = parts[i];
+    var finalSegment = parts.length - 1;
+    for (var i = 0; i <= finalSegment; i++) {
+      var basename = parts[i];
       assert(basename.isNotEmpty);
 
       switch (basename) {

diff --git a/pkgs/file/lib/src/backends/memory/memory_file_system_entity.dart b/pkgs/file/lib/src/backends/memory/memory_file_system_entity.dart
index ad987d7..1990abc 100644
--- a/pkgs/file/lib/src/backends/memory/memory_file_system_entity.dart
+++ b/pkgs/file/lib/src/backends/memory/memory_file_system_entity.dart

@@ -2,11 +2,11 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:file/file.dart';
-import 'package:file/src/common.dart' as common;
-import 'package:file/src/io.dart' as io;
 import 'package:meta/meta.dart';
 
+import '../../common.dart' as common;
+import '../../interface.dart';
+import '../../io.dart' as io;
 import 'common.dart';
 import 'memory_directory.dart';
 import 'node.dart';
@@ -60,7 +60,7 @@
   /// The type of the node is not guaranteed to match [expectedType].
   @protected
   Node get backing {
-    Node? node = fileSystem.findNode(path);
+    var node = fileSystem.findNode(path);
     checkExists(node, () => path);
     return node!;
   }
@@ -71,7 +71,7 @@
   /// doesn't match, this will throw a [io.FileSystemException].
   @protected
   Node get resolvedBacking {
-    Node node = backing;
+    var node = backing;
     node = utils.isLink(node)
         ? utils.resolveLinks(node as LinkNode, () => path)
         : node;
@@ -107,14 +107,14 @@
     if (path.isEmpty) {
       throw common.noSuchFileOrDirectory(path);
     }
-    List<String> ledger = <String>[];
+    var ledger = <String>[];
     if (isAbsolute) {
       ledger.add(fileSystem.style.drive);
     }
-    Node? node = fileSystem.findNode(path,
+    var node = fileSystem.findNode(path,
         pathWithSymlinks: ledger, followTailLink: true);
     checkExists(node, () => path);
-    String resolved = ledger.join(fileSystem.path.separator);
+    var resolved = ledger.join(fileSystem.path.separator);
     if (resolved == fileSystem.style.drive) {
       resolved = fileSystem.style.root;
     } else if (!fileSystem.path.isAbsolute(resolved)) {
@@ -151,7 +151,7 @@
 
   @override
   FileSystemEntity get absolute {
-    String absolutePath = path;
+    var absolutePath = path;
     if (!fileSystem.path.isAbsolute(absolutePath)) {
       absolutePath = fileSystem.path.join(fileSystem.cwd, absolutePath);
     }
@@ -242,7 +242,7 @@
     bool followTailLink = false,
     utils.TypeChecker? checkType,
   }) {
-    Node node = backing;
+    var node = backing;
     (checkType ?? defaultCheckType)(node);
     fileSystem.findNode(
       newPath,
@@ -256,7 +256,7 @@
         if (currentSegment == finalSegment) {
           if (child != null) {
             if (followTailLink) {
-              FileSystemEntityType childType = child.stat.type;
+              var childType = child.stat.type;
               if (childType != FileSystemEntityType.notFound) {
                 utils.checkType(expectedType, child.stat.type, () => newPath);
               }
@@ -289,7 +289,7 @@
     utils.TypeChecker? checkType,
   }) {
     fileSystem.opHandle(path, FileSystemOp.delete);
-    Node node = backing;
+    var node = backing;
     if (!recursive) {
       if (node is DirectoryNode && node.children.isNotEmpty) {
         throw common.directoryNotEmpty(path);

diff --git a/pkgs/file/lib/src/backends/memory/memory_link.dart b/pkgs/file/lib/src/backends/memory/memory_link.dart
index 7d5afb4..a599fe8 100644
--- a/pkgs/file/lib/src/backends/memory/memory_link.dart
+++ b/pkgs/file/lib/src/backends/memory/memory_link.dart

@@ -2,11 +2,11 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:file/file.dart';
-import 'package:file/src/common.dart' as common;
-import 'package:file/src/io.dart' as io;
 import 'package:meta/meta.dart';
 
+import '../../common.dart' as common;
+import '../../interface.dart';
+import '../../io.dart' as io;
 import 'memory_file_system_entity.dart';
 import 'node.dart';
 import 'operations.dart';
@@ -15,8 +15,7 @@
 /// Internal implementation of [Link].
 class MemoryLink extends MemoryFileSystemEntity implements Link {
   /// Instantiates a new [MemoryLink].
-  const MemoryLink(NodeBasedFileSystem fileSystem, String path)
-      : super(fileSystem, path);
+  const MemoryLink(super.fileSystem, super.path);
 
   @override
   io.FileSystemEntityType get expectedType => io.FileSystemEntityType.link;
@@ -50,7 +49,7 @@
 
   @override
   void createSync(String target, {bool recursive = false}) {
-    bool preexisting = true;
+    var preexisting = true;
     fileSystem.opHandle(path, FileSystemOp.create);
     internalCreateSync(
         createChild: (DirectoryNode parent, bool isFinalSegment) {
@@ -76,7 +75,7 @@
 
   @override
   void updateSync(String target) {
-    Node node = backing;
+    var node = backing;
     utils.checkType(expectedType, node.type, () => path);
     (node as LinkNode).target = target;
   }
@@ -93,7 +92,7 @@
 
   @override
   String targetSync() {
-    Node node = backing;
+    var node = backing;
     if (node.type != expectedType) {
       // Note: this may change; https://github.com/dart-lang/sdk/issues/28204
       throw common.noSuchFileOrDirectory(path);

diff --git a/pkgs/file/lib/src/backends/memory/memory_random_access_file.dart b/pkgs/file/lib/src/backends/memory/memory_random_access_file.dart
index d4fe73d..190f0a1 100644
--- a/pkgs/file/lib/src/backends/memory/memory_random_access_file.dart
+++ b/pkgs/file/lib/src/backends/memory/memory_random_access_file.dart

@@ -6,10 +6,11 @@
 import 'dart:math' as math show min;
 import 'dart:typed_data';
 
-import 'package:file/src/common.dart' as common;
-import 'package:file/src/io.dart' as io;
-
+import '../../common.dart' as common;
+import '../../io.dart' as io;
+import '../memory.dart' show MemoryFileSystem;
 import 'memory_file.dart';
+import 'memory_file_system.dart' show MemoryFileSystem;
 import 'node.dart';
 import 'utils.dart' as utils;
 
@@ -106,8 +107,8 @@
   /// Wraps a synchronous function to make it appear asynchronous.
   ///
   /// [_asyncOperationPending], [_checkAsync], and [_asyncWrapper] are used to
-  /// mimic [RandomAccessFile]'s enforcement that only one asynchronous
-  /// operation is pending for a [RandomAccessFile] instance.  Since
+  /// mimic [io.RandomAccessFile]'s enforcement that only one asynchronous
+  /// operation is pending for a [io.RandomAccessFile] instance.  Since
   /// [MemoryFileSystem]-based classes are likely to be used in tests, fidelity
   /// is important to catch errors that might occur in production.
   ///
@@ -211,7 +212,7 @@
     _checkReadable('read');
     // TODO(jamesderlin): Check for integer overflow.
     final int end = math.min(_position + bytes, lengthSync());
-    final Uint8List copy = _node.content.sublist(_position, end);
+    final copy = _node.content.sublist(_position, end);
     _position = end;
     return copy;
   }
@@ -243,7 +244,7 @@
 
     end = RangeError.checkValidRange(start, end, buffer.length);
 
-    final int length = lengthSync();
+    final length = lengthSync();
     int i;
     for (i = start; i < end && _position < length; i += 1, _position += 1) {
       buffer[i] = _node.content[_position];
@@ -288,7 +289,7 @@
           'truncate failed', path, common.invalidArgument(path).osError);
     }
 
-    final int oldLength = lengthSync();
+    final oldLength = lengthSync();
     if (length < oldLength) {
       _node.truncate(length);
 
@@ -329,7 +330,7 @@
     // [Uint8List] will truncate values to 8-bits automatically, so we don't
     // need to check [value].
 
-    int length = lengthSync();
+    var length = lengthSync();
     if (_position >= length) {
       // If [_position] is out of bounds, [RandomAccessFile] zero-fills the
       // file.
@@ -363,8 +364,8 @@
 
     end = RangeError.checkValidRange(start, end, buffer.length);
 
-    final int writeByteCount = end - start;
-    final int endPosition = _position + writeByteCount;
+    final writeByteCount = end - start;
+    final endPosition = _position + writeByteCount;
 
     if (endPosition > lengthSync()) {
       truncateSync(endPosition);

diff --git a/pkgs/file/lib/src/backends/memory/node.dart b/pkgs/file/lib/src/backends/memory/node.dart
index ae4d3f7..eea72b5 100644
--- a/pkgs/file/lib/src/backends/memory/node.dart
+++ b/pkgs/file/lib/src/backends/memory/node.dart

@@ -4,13 +4,12 @@
 
 import 'dart:typed_data';
 
-import 'package:file/file.dart';
-import 'package:file/src/backends/memory/operations.dart';
-import 'package:file/src/io.dart' as io;
-
+import '../../interface.dart';
+import '../../io.dart' as io;
 import 'clock.dart';
 import 'common.dart';
 import 'memory_file_stat.dart';
+import 'operations.dart';
 import 'style.dart';
 
 /// Visitor callback for use with [NodeBasedFileSystem.findNode].
@@ -115,7 +114,7 @@
 
   /// Reparents this node to live in the specified directory.
   set parent(DirectoryNode parent) {
-    DirectoryNode ancestor = parent;
+    var ancestor = parent;
     while (!ancestor.isRoot) {
       if (ancestor == this) {
         throw const io.FileSystemException(
@@ -149,8 +148,8 @@
 /// you call [stat] on them).
 abstract class RealNode extends Node {
   /// Constructs a new [RealNode] as a child of the specified [parent].
-  RealNode(DirectoryNode? parent) : super(parent) {
-    int now = clock.now.millisecondsSinceEpoch;
+  RealNode(super.parent) {
+    var now = clock.now.millisecondsSinceEpoch;
     changed = now;
     modified = now;
     accessed = now;
@@ -195,7 +194,7 @@
 /// Class that represents the backing for an in-memory directory.
 class DirectoryNode extends RealNode {
   /// Constructs a new [DirectoryNode] as a child of the specified [parent].
-  DirectoryNode(DirectoryNode? parent) : super(parent);
+  DirectoryNode(super.parent);
 
   /// Child nodes, indexed by their basename.
   final Map<String, Node> children = <String, Node>{};
@@ -237,7 +236,7 @@
 /// Class that represents the backing for an in-memory regular file.
 class FileNode extends RealNode {
   /// Constructs a new [FileNode] as a child of the specified [parent].
-  FileNode(DirectoryNode parent) : super(parent);
+  FileNode(DirectoryNode super.parent);
 
   /// File contents in bytes.
   Uint8List get content => _content;
@@ -251,7 +250,7 @@
 
   /// Appends the specified bytes to the end of this node's [content].
   void write(List<int> bytes) {
-    Uint8List existing = _content;
+    var existing = _content;
     _content = Uint8List(existing.length + bytes.length);
     _content.setRange(0, existing.length, existing);
     _content.setRange(existing.length, _content.length, bytes);
@@ -286,9 +285,7 @@
 class LinkNode extends Node {
   /// Constructs a new [LinkNode] as a child of the specified [parent] and
   /// linking to the specified [target] path.
-  LinkNode(DirectoryNode parent, this.target)
-      : assert(target.isNotEmpty),
-        super(parent);
+  LinkNode(DirectoryNode super.parent, this.target) : assert(target.isNotEmpty);
 
   /// The path to which this link points.
   String target;
@@ -309,7 +306,7 @@
     Node? Function(DirectoryNode parent, String childName, Node? child)?
         tailVisitor,
   }) {
-    Node? referent = fs.findNode(
+    var referent = fs.findNode(
       target,
       reference: this,
       segmentVisitor: (
@@ -349,7 +346,7 @@
     }
     _reentrant = true;
     try {
-      Node? node = referentOrNull;
+      var node = referentOrNull;
       return node == null ? MemoryFileStat.notFound : node.stat;
     } finally {
       _reentrant = false;

diff --git a/pkgs/file/lib/src/backends/memory/operations.dart b/pkgs/file/lib/src/backends/memory/operations.dart
index 9fc7462..57d118b 100644
--- a/pkgs/file/lib/src/backends/memory/operations.dart
+++ b/pkgs/file/lib/src/backends/memory/operations.dart

@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// ignore_for_file: comment_references
+
 /// A file system operation used by the [MemoryFileSytem] to allow
 /// tests to insert errors for certain operations.
 ///
@@ -64,23 +66,15 @@
 
   @override
   String toString() {
-    switch (_value) {
-      case 0:
-        return 'FileSystemOp.read';
-      case 1:
-        return 'FileSystemOp.write';
-      case 2:
-        return 'FileSystemOp.delete';
-      case 3:
-        return 'FileSystemOp.create';
-      case 4:
-        return 'FileSystemOp.open';
-      case 5:
-        return 'FileSystemOp.copy';
-      case 6:
-        return 'FileSystemOp.exists';
-      default:
-        throw StateError('Invalid FileSytemOp type: $this');
-    }
+    return switch (_value) {
+      0 => 'FileSystemOp.read',
+      1 => 'FileSystemOp.write',
+      2 => 'FileSystemOp.delete',
+      3 => 'FileSystemOp.create',
+      4 => 'FileSystemOp.open',
+      5 => 'FileSystemOp.copy',
+      6 => 'FileSystemOp.exists',
+      _ => throw StateError('Invalid FileSytemOp type: $this')
+    };
   }
 }

diff --git a/pkgs/file/lib/src/backends/memory/style.dart b/pkgs/file/lib/src/backends/memory/style.dart
index 701c9d0..f4bd33f 100644
--- a/pkgs/file/lib/src/backends/memory/style.dart
+++ b/pkgs/file/lib/src/backends/memory/style.dart

@@ -2,9 +2,10 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:file/file.dart';
 import 'package:path/path.dart' as p;
 
+import '../../interface.dart';
+
 /// Class that represents the path style that a memory file system should
 /// adopt.
 ///

diff --git a/pkgs/file/lib/src/backends/memory/utils.dart b/pkgs/file/lib/src/backends/memory/utils.dart
index eec9980..aa24cfb 100644
--- a/pkgs/file/lib/src/backends/memory/utils.dart
+++ b/pkgs/file/lib/src/backends/memory/utils.dart

@@ -2,20 +2,19 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:file/file.dart';
-import 'package:file/src/common.dart' as common;
-import 'package:file/src/io.dart' as io;
-
+import '../../common.dart' as common;
+import '../../interface.dart';
+import '../../io.dart' as io;
 import 'common.dart';
 import 'node.dart';
 
-/// Checks if `node.type` returns [io.FileSystemEntityType.FILE].
+/// Checks if `node.type` returns [io.FileSystemEntityType.file].
 bool isFile(Node? node) => node?.type == io.FileSystemEntityType.file;
 
-/// Checks if `node.type` returns [io.FileSystemEntityType.DIRECTORY].
+/// Checks if `node.type` returns [io.FileSystemEntityType.directory].
 bool isDirectory(Node? node) => node?.type == io.FileSystemEntityType.directory;
 
-/// Checks if `node.type` returns [io.FileSystemEntityType.LINK].
+/// Checks if `node.type` returns [io.FileSystemEntityType.link].
 bool isLink(Node? node) => node?.type == io.FileSystemEntityType.link;
 
 /// Validator function that is expected to throw a [FileSystemException] if
@@ -86,7 +85,7 @@
       tailVisitor,
 }) {
   // Record a breadcrumb trail to guard against symlink loops.
-  Set<LinkNode> breadcrumbs = <LinkNode>{};
+  var breadcrumbs = <LinkNode>{};
 
   Node node = link;
   while (isLink(node)) {

diff --git a/pkgs/file/lib/src/forwarding/forwarding_directory.dart b/pkgs/file/lib/src/forwarding/forwarding_directory.dart
index dba0c8e..ad1c548 100644
--- a/pkgs/file/lib/src/forwarding/forwarding_directory.dart
+++ b/pkgs/file/lib/src/forwarding/forwarding_directory.dart

@@ -2,8 +2,9 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:file/src/io.dart' as io;
-import 'package:file/file.dart';
+import '../forwarding.dart';
+import '../interface.dart';
+import '../io.dart' as io;
 
 /// A directory that forwards all methods and properties to a delegate.
 mixin ForwardingDirectory<T extends Directory>

diff --git a/pkgs/file/lib/src/forwarding/forwarding_file.dart b/pkgs/file/lib/src/forwarding/forwarding_file.dart
index 49c211d..d6cfe3b 100644
--- a/pkgs/file/lib/src/forwarding/forwarding_file.dart
+++ b/pkgs/file/lib/src/forwarding/forwarding_file.dart

@@ -5,8 +5,9 @@
 import 'dart:convert';
 import 'dart:typed_data';
 
-import 'package:file/src/io.dart' as io;
-import 'package:file/file.dart';
+import '../forwarding.dart';
+import '../interface.dart';
+import '../io.dart' as io;
 
 /// A file that forwards all methods and properties to a delegate.
 mixin ForwardingFile

diff --git a/pkgs/file/lib/src/forwarding/forwarding_file_system.dart b/pkgs/file/lib/src/forwarding/forwarding_file_system.dart
index d864db9..885fdb6 100644
--- a/pkgs/file/lib/src/forwarding/forwarding_file_system.dart
+++ b/pkgs/file/lib/src/forwarding/forwarding_file_system.dart

@@ -2,11 +2,12 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:file/src/io.dart' as io;
-import 'package:file/file.dart';
 import 'package:meta/meta.dart';
 import 'package:path/path.dart' as p;
 
+import '../interface.dart';
+import '../io.dart' as io;
+
 /// A file system that forwards all methods and properties to a delegate.
 abstract class ForwardingFileSystem extends FileSystem {
   /// Creates a new [ForwardingFileSystem] that forwards all methods and

diff --git a/pkgs/file/lib/src/forwarding/forwarding_file_system_entity.dart b/pkgs/file/lib/src/forwarding/forwarding_file_system_entity.dart
index 3c41b39..1c0628e 100644
--- a/pkgs/file/lib/src/forwarding/forwarding_file_system_entity.dart
+++ b/pkgs/file/lib/src/forwarding/forwarding_file_system_entity.dart

@@ -2,10 +2,11 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:file/src/io.dart' as io;
-import 'package:file/file.dart';
 import 'package:meta/meta.dart';
 
+import '../interface.dart';
+import '../io.dart' as io;
+
 /// A file system entity that forwards all methods and properties to a delegate.
 abstract class ForwardingFileSystemEntity<T extends FileSystemEntity,
     D extends io.FileSystemEntity> implements FileSystemEntity {

diff --git a/pkgs/file/lib/src/forwarding/forwarding_link.dart b/pkgs/file/lib/src/forwarding/forwarding_link.dart
index 7a60ecb..915e710 100644
--- a/pkgs/file/lib/src/forwarding/forwarding_link.dart
+++ b/pkgs/file/lib/src/forwarding/forwarding_link.dart

@@ -2,8 +2,9 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:file/src/io.dart' as io;
-import 'package:file/file.dart';
+import '../forwarding.dart';
+import '../interface.dart';
+import '../io.dart' as io;
 
 /// A link that forwards all methods and properties to a delegate.
 mixin ForwardingLink

diff --git a/pkgs/file/lib/src/forwarding/forwarding_random_access_file.dart b/pkgs/file/lib/src/forwarding/forwarding_random_access_file.dart
index 9dd4079..3847b91 100644
--- a/pkgs/file/lib/src/forwarding/forwarding_random_access_file.dart
+++ b/pkgs/file/lib/src/forwarding/forwarding_random_access_file.dart

@@ -5,11 +5,12 @@
 import 'dart:convert';
 import 'dart:typed_data';
 
-import 'package:file/src/io.dart' as io;
 import 'package:meta/meta.dart';
 
-/// A [RandomAccessFile] implementation that forwards all methods and properties
-/// to a delegate.
+import '../io.dart' as io;
+
+/// A [io.RandomAccessFile] implementation that forwards all methods and
+/// properties to a delegate.
 mixin ForwardingRandomAccessFile implements io.RandomAccessFile {
   /// The entity to which this entity will forward all methods and properties.
   @protected

diff --git a/pkgs/file/lib/src/interface.dart b/pkgs/file/lib/src/interface.dart
index 4662e35..d9b7ed5 100644
--- a/pkgs/file/lib/src/interface.dart
+++ b/pkgs/file/lib/src/interface.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-library file.src.interface;
-
 export 'interface/directory.dart';
 export 'interface/error_codes.dart';
 export 'interface/file.dart';

diff --git a/pkgs/file/lib/src/interface/error_codes.dart b/pkgs/file/lib/src/interface/error_codes.dart
index 8943538..4836b56 100644
--- a/pkgs/file/lib/src/interface/error_codes.dart
+++ b/pkgs/file/lib/src/interface/error_codes.dart

@@ -168,7 +168,7 @@
   static int get EXDEV => _platform((_Codes codes) => codes.exdev);
 
   static int _platform(int Function(_Codes codes) getCode) {
-    _Codes codes = (_platforms[operatingSystem] ?? _platforms['linux'])!;
+    var codes = (_platforms[operatingSystem] ?? _platforms['linux'])!;
     return getCode(codes);
   }
 }

diff --git a/pkgs/file/lib/src/interface/file_system.dart b/pkgs/file/lib/src/interface/file_system.dart
index ecc01a8..2d4e4aa 100644
--- a/pkgs/file/lib/src/interface/file_system.dart
+++ b/pkgs/file/lib/src/interface/file_system.dart

@@ -6,7 +6,6 @@
 import 'package:path/path.dart' as p;
 
 import '../io.dart' as io;
-
 import 'directory.dart';
 import 'file.dart';
 import 'file_system_entity.dart';
@@ -99,9 +98,9 @@
   bool get isWatchSupported;
 
   /// Finds the type of file system object that a [path] points to. Returns
-  /// a Future<FileSystemEntityType> that completes with the result.
+  /// a `Future<FileSystemEntityType>` that completes with the result.
   ///
-  /// [io.FileSystemEntityType.LINK] will only be returned if [followLinks] is
+  /// [io.FileSystemEntityType.link] will only be returned if [followLinks] is
   /// `false`, and [path] points to a link
   ///
   /// If the [path] does not point to a file system object or an error occurs
@@ -111,37 +110,38 @@
   /// Syncronously finds the type of file system object that a [path] points
   /// to. Returns a [io.FileSystemEntityType].
   ///
-  /// [io.FileSystemEntityType.LINK] will only be returned if [followLinks] is
+  /// [io.FileSystemEntityType.link] will only be returned if [followLinks] is
   /// `false`, and [path] points to a link
   ///
   /// If the [path] does not point to a file system object or an error occurs
   /// then [io.FileSystemEntityType.notFound] is returned.
   io.FileSystemEntityType typeSync(String path, {bool followLinks = true});
 
-  /// Checks if [`type(path)`](type) returns [io.FileSystemEntityType.FILE].
+  /// Checks if [`type(path)`](type) returns [io.FileSystemEntityType.file].
   Future<bool> isFile(String path) async =>
       await type(path) == io.FileSystemEntityType.file;
 
   /// Synchronously checks if [`type(path)`](type) returns
-  /// [io.FileSystemEntityType.FILE].
+  /// [io.FileSystemEntityType.file].
   bool isFileSync(String path) =>
       typeSync(path) == io.FileSystemEntityType.file;
 
-  /// Checks if [`type(path)`](type) returns [io.FileSystemEntityType.DIRECTORY].
+  /// Checks if [`type(path)`](type) returns
+  /// [io.FileSystemEntityType.directory].
   Future<bool> isDirectory(String path) async =>
       await type(path) == io.FileSystemEntityType.directory;
 
   /// Synchronously checks if [`type(path)`](type) returns
-  /// [io.FileSystemEntityType.DIRECTORY].
+  /// [io.FileSystemEntityType.directory].
   bool isDirectorySync(String path) =>
       typeSync(path) == io.FileSystemEntityType.directory;
 
-  /// Checks if [`type(path)`](type) returns [io.FileSystemEntityType.LINK].
+  /// Checks if [`type(path)`](type) returns [io.FileSystemEntityType.link].
   Future<bool> isLink(String path) async =>
       await type(path, followLinks: false) == io.FileSystemEntityType.link;
 
   /// Synchronously checks if [`type(path)`](type) returns
-  /// [io.FileSystemEntityType.LINK].
+  /// [io.FileSystemEntityType.link].
   bool isLinkSync(String path) =>
       typeSync(path, followLinks: false) == io.FileSystemEntityType.link;
 

diff --git a/pkgs/file/lib/src/io.dart b/pkgs/file/lib/src/io.dart
index 9d57e78..28c1d6d 100644
--- a/pkgs/file/lib/src/io.dart
+++ b/pkgs/file/lib/src/io.dart

@@ -8,6 +8,8 @@
 /// the `file` package. The `file` package re-exports these interfaces (or in
 /// some cases, implementations of these interfaces by the same name), so this
 /// file need not be exposes publicly and exists for internal use only.
+library;
+
 export 'dart:io'
     show
         Directory,

diff --git a/pkgs/file/pubspec.yaml b/pkgs/file/pubspec.yaml
index 5de5d37..0ad65b0 100644
--- a/pkgs/file/pubspec.yaml
+++ b/pkgs/file/pubspec.yaml

@@ -1,5 +1,5 @@
 name: file
-version: 7.0.1
+version: 7.0.2-wip
 description: A pluggable, mockable file system abstraction for Dart.
 repository: https://github.com/dart-lang/tools/tree/main/pkgs/file
 issue_tracker: https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Afile
@@ -12,6 +12,10 @@
   path: ^1.8.3
 
 dev_dependencies:
+  dart_flutter_team_lints: ^3.0.0
   file_testing: ^3.0.0
-  lints: ^2.0.1
   test: ^1.23.1
+
+dependency_overrides:
+  file_testing:
+    path: ../file_testing

diff --git a/pkgs/file/test/chroot_test.dart b/pkgs/file/test/chroot_test.dart
index 6c34ff2..cf23f47 100644
--- a/pkgs/file/test/chroot_test.dart
+++ b/pkgs/file/test/chroot_test.dart

@@ -3,6 +3,8 @@
 // BSD-style license that can be found in the LICENSE file.
 
 @TestOn('vm')
+library;
+
 import 'dart:io' as io;
 
 import 'package:file/chroot.dart';
@@ -17,14 +19,15 @@
 void main() {
   group('ChrootFileSystem', () {
     ChrootFileSystem createMemoryBackedChrootFileSystem() {
-      MemoryFileSystem fs = MemoryFileSystem();
+      var fs = MemoryFileSystem();
       fs.directory('/tmp').createSync();
       return ChrootFileSystem(fs, '/tmp');
     }
 
     // TODO(jamesderlin): Make ChrootFile.openSync return a delegating
     // RandomAccessFile that uses the chroot'd path.
-    List<String> skipCommon = <String>[
+    var skipCommon = <String>[
+      // ignore: lines_longer_than_80_chars
       'File > open > .* > RandomAccessFile > read > openReadHandleDoesNotChange',
       'File > open > .* > RandomAccessFile > openWriteHandleDoesNotChange',
     ];
@@ -137,6 +140,7 @@
           test('referencesRootEntityForJailbreakPath', () {
             mem.file('/foo').createSync();
             dynamic f = fs.file('../foo');
+            // ignore: avoid_dynamic_calls
             expect(f.delegate.path, '/tmp/foo');
           });
         });
@@ -151,7 +155,7 @@
 
         group('copy', () {
           test('copiesToRootDirectoryIfDestinationIsJailbreakPath', () {
-            File f = fs.file('/foo')..createSync();
+            var f = fs.file('/foo')..createSync();
             f.copySync('../bar');
             expect(mem.file('/bar'), isNot(exists));
             expect(mem.file('/tmp/bar'), exists);

diff --git a/pkgs/file/test/common_tests.dart b/pkgs/file/test/common_tests.dart
index 6028c77..491d4f9 100644
--- a/pkgs/file/test/common_tests.dart
+++ b/pkgs/file/test/common_tests.dart

@@ -3,6 +3,8 @@
 // BSD-style license that can be found in the LICENSE file.
 
 @TestOn('vm')
+library;
+
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io' as io;
@@ -10,8 +12,8 @@
 import 'package:file/file.dart';
 import 'package:file_testing/file_testing.dart';
 import 'package:path/path.dart' as p;
-import 'package:test/test.dart';
 import 'package:test/test.dart' as testpkg show group, setUp, tearDown, test;
+import 'package:test/test.dart';
 
 import 'utils.dart';
 
@@ -54,7 +56,7 @@
   List<String> skip = const <String>[],
   FileSystemGenerator? replay,
 }) {
-  RootPathGenerator? rootfn = root;
+  var rootfn = root;
 
   group('common', () {
     late FileSystemGenerator createFs;
@@ -62,7 +64,7 @@
     late List<SetUpTearDown> tearDowns;
     late FileSystem fs;
     late String root;
-    List<String> stack = <String>[];
+    var stack = <String>[];
 
     void skipIfNecessary(String description, void Function() callback) {
       stack.add(description);
@@ -105,7 +107,7 @@
               testpkg.setUp(() async {
                 await Future.forEach(setUps, (SetUpTearDown setUp) => setUp());
                 await body();
-                for (SetUpTearDown tearDown in tearDowns) {
+                for (var tearDown in tearDowns) {
                   await tearDown();
                 }
                 createFs = replay;
@@ -115,7 +117,7 @@
               testpkg.test(description, body, skip: skip);
 
               testpkg.tearDown(() async {
-                for (SetUpTearDown tearDown in tearDowns) {
+                for (var tearDown in tearDowns) {
                   await tearDown();
                 }
               });
@@ -126,13 +128,13 @@
     /// Returns [path] prefixed by the [root] namespace.
     /// This is only intended for absolute paths.
     String ns(String path) {
-      p.Context posix = p.Context(style: p.Style.posix);
-      List<String> parts = posix.split(path);
+      var posix = p.Context(style: p.Style.posix);
+      var parts = posix.split(path);
       parts[0] = root;
       path = fs.path.joinAll(parts);
-      String rootPrefix = fs.path.rootPrefix(path);
+      var rootPrefix = fs.path.rootPrefix(path);
       assert(rootPrefix.isNotEmpty);
-      String result = root == rootPrefix
+      var result = root == rootPrefix
           ? path
           : (path == rootPrefix
               ? root
@@ -160,7 +162,7 @@
 
         test('succeedsWithUriArgument', () {
           fs.directory(ns('/foo')).createSync();
-          Uri uri = fs.path.toUri(ns('/foo'));
+          var uri = fs.path.toUri(ns('/foo'));
           expect(fs.directory(uri), exists);
         });
 
@@ -173,11 +175,11 @@
         });
 
         // Fails due to
-        // https://github.com/google/file.dart/issues/112
+        // https://github.com/dart-lang/tools/issues/632
         test('considersBothSlashesEquivalent', () {
           fs.directory(r'foo\bar_dir').createSync(recursive: true);
           expect(fs.directory(r'foo/bar_dir'), exists);
-        }, skip: 'Fails due to https://github.com/google/file.dart/issues/112');
+        }, skip: 'Fails due to https://github.com/dart-lang/tools/issues/632');
       });
 
       group('file', () {
@@ -191,7 +193,7 @@
 
         test('succeedsWithUriArgument', () {
           fs.file(ns('/foo')).createSync();
-          Uri uri = fs.path.toUri(ns('/foo'));
+          var uri = fs.path.toUri(ns('/foo'));
           expect(fs.file(uri), exists);
         });
 
@@ -204,11 +206,11 @@
         });
 
         // Fails due to
-        // https://github.com/google/file.dart/issues/112
+        // https://github.com/dart-lang/tools/issues/632
         test('considersBothSlashesEquivalent', () {
           fs.file(r'foo\bar_file').createSync(recursive: true);
           expect(fs.file(r'foo/bar_file'), exists);
-        }, skip: 'Fails due to https://github.com/google/file.dart/issues/112');
+        }, skip: 'Fails due to https://github.com/dart-lang/tools/issues/632');
       });
 
       group('link', () {
@@ -223,7 +225,7 @@
         test('succeedsWithUriArgument', () {
           fs.file(ns('/foo')).createSync();
           fs.link(ns('/bar')).createSync(ns('/foo'));
-          Uri uri = fs.path.toUri(ns('/bar'));
+          var uri = fs.path.toUri(ns('/bar'));
           expect(fs.link(uri), exists);
         });
 
@@ -248,7 +250,7 @@
 
       group('systemTempDirectory', () {
         test('existsAsDirectory', () {
-          Directory tmp = fs.systemTempDirectory;
+          var tmp = fs.systemTempDirectory;
           expect(tmp, isDirectory);
           expect(tmp, exists);
         });
@@ -318,7 +320,7 @@
         test('staysAtRootIfSetToParentOfRoot', () {
           fs.currentDirectory =
               List<String>.filled(20, '..').join(fs.path.separator);
-          String cwd = fs.currentDirectory.path;
+          var cwd = fs.currentDirectory.path;
           expect(cwd, fs.path.rootPrefix(cwd));
         });
 
@@ -371,36 +373,36 @@
 
       group('stat', () {
         test('isNotFoundForEmptyPath', () {
-          FileStat stat = fs.statSync('');
+          var stat = fs.statSync('');
           expect(stat.type, FileSystemEntityType.notFound);
         });
 
         test('isNotFoundForPathToNonExistentEntityAtTail', () {
-          FileStat stat = fs.statSync(ns('/foo'));
+          var stat = fs.statSync(ns('/foo'));
           expect(stat.type, FileSystemEntityType.notFound);
         });
 
         test('isNotFoundForPathToNonExistentEntityInTraversal', () {
-          FileStat stat = fs.statSync(ns('/foo/bar'));
+          var stat = fs.statSync(ns('/foo/bar'));
           expect(stat.type, FileSystemEntityType.notFound);
         });
 
         test('isDirectoryForDirectory', () {
           fs.directory(ns('/foo')).createSync();
-          FileStat stat = fs.statSync(ns('/foo'));
+          var stat = fs.statSync(ns('/foo'));
           expect(stat.type, FileSystemEntityType.directory);
         });
 
         test('isFileForFile', () {
           fs.file(ns('/foo')).createSync();
-          FileStat stat = fs.statSync(ns('/foo'));
+          var stat = fs.statSync(ns('/foo'));
           expect(stat.type, FileSystemEntityType.file);
         });
 
         test('isFileForLinkToFile', () {
           fs.file(ns('/foo')).createSync();
           fs.link(ns('/bar')).createSync(ns('/foo'));
-          FileStat stat = fs.statSync(ns('/bar'));
+          var stat = fs.statSync(ns('/bar'));
           expect(stat.type, FileSystemEntityType.file);
         });
 
@@ -408,7 +410,7 @@
           fs.link(ns('/foo')).createSync(ns('/bar'));
           fs.link(ns('/bar')).createSync(ns('/baz'));
           fs.link(ns('/baz')).createSync(ns('/foo'));
-          FileStat stat = fs.statSync(ns('/foo'));
+          var stat = fs.statSync(ns('/foo'));
           expect(stat.type, FileSystemEntityType.notFound);
         });
       });
@@ -454,18 +456,18 @@
       group('type', () {
         test('isFileForFile', () {
           fs.file(ns('/foo')).createSync();
-          FileSystemEntityType type = fs.typeSync(ns('/foo'));
+          var type = fs.typeSync(ns('/foo'));
           expect(type, FileSystemEntityType.file);
         });
 
         test('isDirectoryForDirectory', () {
           fs.directory(ns('/foo')).createSync();
-          FileSystemEntityType type = fs.typeSync(ns('/foo'));
+          var type = fs.typeSync(ns('/foo'));
           expect(type, FileSystemEntityType.directory);
         });
 
         test('isDirectoryForAncestorOfRoot', () {
-          FileSystemEntityType type = fs
+          var type = fs
               .typeSync(List<String>.filled(20, '..').join(fs.path.separator));
           expect(type, FileSystemEntityType.directory);
         });
@@ -473,15 +475,14 @@
         test('isFileForLinkToFileAndFollowLinksTrue', () {
           fs.file(ns('/foo')).createSync();
           fs.link(ns('/bar')).createSync(ns('/foo'));
-          FileSystemEntityType type = fs.typeSync(ns('/bar'));
+          var type = fs.typeSync(ns('/bar'));
           expect(type, FileSystemEntityType.file);
         });
 
         test('isLinkForLinkToFileAndFollowLinksFalse', () {
           fs.file(ns('/foo')).createSync();
           fs.link(ns('/bar')).createSync(ns('/foo'));
-          FileSystemEntityType type =
-              fs.typeSync(ns('/bar'), followLinks: false);
+          var type = fs.typeSync(ns('/bar'), followLinks: false);
           expect(type, FileSystemEntityType.link);
         });
 
@@ -489,17 +490,17 @@
           fs.link(ns('/foo')).createSync(ns('/bar'));
           fs.link(ns('/bar')).createSync(ns('/baz'));
           fs.link(ns('/baz')).createSync(ns('/foo'));
-          FileSystemEntityType type = fs.typeSync(ns('/foo'));
+          var type = fs.typeSync(ns('/foo'));
           expect(type, FileSystemEntityType.notFound);
         });
 
         test('isNotFoundForNoEntityAtTail', () {
-          FileSystemEntityType type = fs.typeSync(ns('/foo'));
+          var type = fs.typeSync(ns('/foo'));
           expect(type, FileSystemEntityType.notFound);
         });
 
         test('isNotFoundForNoDirectoryInTraversal', () {
-          FileSystemEntityType type = fs.typeSync(ns('/foo/bar/baz'));
+          var type = fs.typeSync(ns('/foo/bar/baz'));
           expect(type, FileSystemEntityType.notFound);
         });
       });
@@ -676,8 +677,8 @@
         });
 
         test('succeedsIfDestinationDoesntExist', () {
-          Directory src = fs.directory(ns('/foo'))..createSync();
-          Directory dest = src.renameSync(ns('/bar'));
+          var src = fs.directory(ns('/foo'))..createSync();
+          var dest = src.renameSync(ns('/bar'));
           expect(dest.path, ns('/bar'));
           expect(dest, exists);
         });
@@ -686,8 +687,8 @@
           'succeedsIfDestinationIsEmptyDirectory',
           () {
             fs.directory(ns('/bar')).createSync();
-            Directory src = fs.directory(ns('/foo'))..createSync();
-            Directory dest = src.renameSync(ns('/bar'));
+            var src = fs.directory(ns('/foo'))..createSync();
+            var dest = src.renameSync(ns('/bar'));
             expect(src, isNot(exists));
             expect(dest, exists);
           },
@@ -697,14 +698,14 @@
 
         test('throwsIfDestinationIsFile', () {
           fs.file(ns('/bar')).createSync();
-          Directory src = fs.directory(ns('/foo'))..createSync();
+          var src = fs.directory(ns('/foo'))..createSync();
           expectFileSystemException(ErrorCodes.ENOTDIR, () {
             src.renameSync(ns('/bar'));
           });
         });
 
         test('throwsIfDestinationParentFolderDoesntExist', () {
-          Directory src = fs.directory(ns('/foo'))..createSync();
+          var src = fs.directory(ns('/foo'))..createSync();
           expectFileSystemException(ErrorCodes.ENOENT, () {
             src.renameSync(ns('/bar/baz'));
           });
@@ -712,7 +713,7 @@
 
         test('throwsIfDestinationIsNonEmptyDirectory', () {
           fs.file(ns('/bar/baz')).createSync(recursive: true);
-          Directory src = fs.directory(ns('/foo'))..createSync();
+          var src = fs.directory(ns('/foo'))..createSync();
           // The error will be 'Directory not empty' on OS X, but it will be
           // 'File exists' on Linux.
           expectFileSystemException(
@@ -749,7 +750,7 @@
         });
 
         test('throwsIfDestinationIsLinkToNotFound', () {
-          Directory src = fs.directory(ns('/foo'))..createSync();
+          var src = fs.directory(ns('/foo'))..createSync();
           fs.link(ns('/bar')).createSync(ns('/baz'));
           expectFileSystemException(ErrorCodes.ENOTDIR, () {
             src.renameSync(ns('/bar'));
@@ -757,7 +758,7 @@
         });
 
         test('throwsIfDestinationIsLinkToEmptyDirectory', () {
-          Directory src = fs.directory(ns('/foo'))..createSync();
+          var src = fs.directory(ns('/foo'))..createSync();
           fs.directory(ns('/bar')).createSync();
           fs.link(ns('/baz')).createSync(ns('/bar'));
           expectFileSystemException(ErrorCodes.ENOTDIR, () {
@@ -766,7 +767,7 @@
         });
 
         test('succeedsIfDestinationIsInDifferentDirectory', () {
-          Directory src = fs.directory(ns('/foo'))..createSync();
+          var src = fs.directory(ns('/foo'))..createSync();
           fs.directory(ns('/bar')).createSync();
           src.renameSync(ns('/bar/baz'));
           expect(fs.typeSync(ns('/foo')), FileSystemEntityType.notFound);
@@ -790,24 +791,24 @@
 
       group('delete', () {
         test('returnsCovariantType', () async {
-          Directory dir = fs.directory(ns('/foo'))..createSync();
+          var dir = fs.directory(ns('/foo'))..createSync();
           expect(await dir.delete(), isDirectory);
         });
 
         test('succeedsIfEmptyDirectoryExistsAndRecursiveFalse', () {
-          Directory dir = fs.directory(ns('/foo'))..createSync();
+          var dir = fs.directory(ns('/foo'))..createSync();
           dir.deleteSync();
           expect(dir, isNot(exists));
         });
 
         test('succeedsIfEmptyDirectoryExistsAndRecursiveTrue', () {
-          Directory dir = fs.directory(ns('/foo'))..createSync();
+          var dir = fs.directory(ns('/foo'))..createSync();
           dir.deleteSync(recursive: true);
           expect(dir, isNot(exists));
         });
 
         test('throwsIfNonEmptyDirectoryExistsAndRecursiveFalse', () {
-          Directory dir = fs.directory(ns('/foo'))..createSync();
+          var dir = fs.directory(ns('/foo'))..createSync();
           fs.file(ns('/foo/bar')).createSync();
           expectFileSystemException(ErrorCodes.ENOTEMPTY, () {
             dir.deleteSync();
@@ -815,7 +816,7 @@
         });
 
         test('succeedsIfNonEmptyDirectoryExistsAndRecursiveTrue', () {
-          Directory dir = fs.directory(ns('/foo'))..createSync();
+          var dir = fs.directory(ns('/foo'))..createSync();
           fs.file(ns('/foo/bar')).createSync();
           dir.deleteSync(recursive: true);
           expect(fs.directory(ns('/foo')), isNot(exists));
@@ -997,7 +998,7 @@
         test('handlesParentAndThisFolderReferences', () {
           fs.directory(ns('/foo/bar/baz')).createSync(recursive: true);
           fs.link(ns('/foo/bar/baz/qux')).createSync(fs.path.join('..', '..'));
-          String resolved = fs
+          var resolved = fs
               .directory(ns('/foo/./bar/baz/../baz/qux/bar'))
               .resolveSymbolicLinksSync();
           expect(resolved, ns('/foo/bar'));
@@ -1015,7 +1016,7 @@
               .createSync(fs.path.join('..', '..', 'qux'), recursive: true);
           fs.link(ns('/qux')).createSync('quux');
           fs.link(ns('/quux/quuz')).createSync(ns('/foo'), recursive: true);
-          String resolved = fs
+          var resolved = fs
               .directory(ns('/foo//bar/./baz/quuz/bar/..///bar/baz/'))
               .resolveSymbolicLinksSync();
           expect(resolved, ns('/quux'));
@@ -1069,29 +1070,29 @@
 
         test('resolvesNameCollisions', () {
           fs.directory(ns('/foo/bar')).createSync(recursive: true);
-          Directory tmp = fs.directory(ns('/foo')).createTempSync('bar');
+          var tmp = fs.directory(ns('/foo')).createTempSync('bar');
           expect(tmp.path,
               allOf(isNot(ns('/foo/bar')), startsWith(ns('/foo/bar'))));
         });
 
         test('succeedsWithoutPrefix', () {
-          Directory dir = fs.directory(ns('/foo'))..createSync();
+          var dir = fs.directory(ns('/foo'))..createSync();
           expect(dir.createTempSync().path, startsWith(ns('/foo/')));
         });
 
         test('succeedsWithPrefix', () {
-          Directory dir = fs.directory(ns('/foo'))..createSync();
+          var dir = fs.directory(ns('/foo'))..createSync();
           expect(dir.createTempSync('bar').path, startsWith(ns('/foo/bar')));
         });
 
         test('succeedsWithNestedPathPrefixThatExists', () {
           fs.directory(ns('/foo/bar')).createSync(recursive: true);
-          Directory tmp = fs.directory(ns('/foo')).createTempSync('bar/baz');
+          var tmp = fs.directory(ns('/foo')).createTempSync('bar/baz');
           expect(tmp.path, startsWith(ns('/foo/bar/baz')));
         });
 
         test('throwsWithNestedPathPrefixThatDoesntExist', () {
-          Directory dir = fs.directory(ns('/foo'))..createSync();
+          var dir = fs.directory(ns('/foo'))..createSync();
           expectFileSystemException(ErrorCodes.ENOENT, () {
             dir.createTempSync('bar/baz');
           });
@@ -1123,7 +1124,7 @@
         });
 
         test('returnsEmptyListForEmptyDirectory', () {
-          Directory empty = fs.directory(ns('/bar'))..createSync();
+          var empty = fs.directory(ns('/bar'))..createSync();
           expect(empty.listSync(), isEmpty);
         });
 
@@ -1134,7 +1135,7 @@
         });
 
         test('returnsLinkObjectsIfFollowLinksFalse', () {
-          List<FileSystemEntity> list = dir.listSync(followLinks: false);
+          var list = dir.listSync(followLinks: false);
           expect(list, hasLength(3));
           expect(list, contains(allOf(isFile, hasPath(ns('/foo/bar')))));
           expect(list, contains(allOf(isDirectory, hasPath(ns('/foo/baz')))));
@@ -1142,7 +1143,7 @@
         });
 
         test('followsLinksIfFollowLinksTrue', () {
-          List<FileSystemEntity> list = dir.listSync();
+          var list = dir.listSync();
           expect(list, hasLength(3));
           expect(list, contains(allOf(isFile, hasPath(ns('/foo/bar')))));
           expect(list, contains(allOf(isDirectory, hasPath(ns('/foo/baz')))));
@@ -1189,8 +1190,7 @@
         test('childEntriesNotNormalized', () {
           dir = fs.directory(ns('/bar/baz'))..createSync(recursive: true);
           fs.file(ns('/bar/baz/qux')).createSync();
-          List<FileSystemEntity> list =
-              fs.directory(ns('/bar//../bar/./baz')).listSync();
+          var list = fs.directory(ns('/bar//../bar/./baz')).listSync();
           expect(list, hasLength(1));
           expect(list[0], allOf(isFile, hasPath(ns('/bar//../bar/./baz/qux'))));
         });
@@ -1198,9 +1198,8 @@
         test('symlinksToNotFoundAlwaysReturnedAsLinks', () {
           dir = fs.directory(ns('/bar'))..createSync();
           fs.link(ns('/bar/baz')).createSync('qux');
-          for (bool followLinks in const <bool>[true, false]) {
-            List<FileSystemEntity> list =
-                dir.listSync(followLinks: followLinks);
+          for (var followLinks in const <bool>[true, false]) {
+            var list = dir.listSync(followLinks: followLinks);
             expect(list, hasLength(1));
             expect(list[0], allOf(isLink, hasPath(ns('/bar/baz'))));
           }
@@ -1208,7 +1207,7 @@
       });
 
       test('childEntities', () {
-        Directory dir = fs.directory(ns('/foo'))..createSync();
+        var dir = fs.directory(ns('/foo'))..createSync();
         dir.childDirectory('bar').createSync();
         dir.childFile('baz').createSync();
         dir.childLink('qux').createSync('bar');
@@ -1321,22 +1320,22 @@
         });
 
         test('succeedsIfDestinationDoesntExistAtTail', () {
-          File src = fs.file(ns('/foo'))..createSync();
-          File dest = src.renameSync(ns('/bar'));
+          var src = fs.file(ns('/foo'))..createSync();
+          var dest = src.renameSync(ns('/bar'));
           expect(fs.file(ns('/foo')), isNot(exists));
           expect(fs.file(ns('/bar')), exists);
           expect(dest.path, ns('/bar'));
         });
 
         test('throwsIfDestinationDoesntExistViaTraversal', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           expectFileSystemException(ErrorCodes.ENOENT, () {
             f.renameSync(ns('/bar/baz'));
           });
         });
 
         test('succeedsIfDestinationExistsAsFile', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           fs.file(ns('/bar')).createSync();
           f.renameSync(ns('/bar'));
           expect(fs.file(ns('/foo')), isNot(exists));
@@ -1344,7 +1343,7 @@
         });
 
         test('throwsIfDestinationExistsAsDirectory', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           fs.directory(ns('/bar')).createSync();
           expectFileSystemException(ErrorCodes.EISDIR, () {
             f.renameSync(ns('/bar'));
@@ -1352,7 +1351,7 @@
         });
 
         test('succeedsIfDestinationExistsAsLinkToFile', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           fs.file(ns('/bar')).createSync();
           fs.link(ns('/baz')).createSync(ns('/bar'));
           f.renameSync(ns('/baz'));
@@ -1364,7 +1363,7 @@
         });
 
         test('throwsIfDestinationExistsAsLinkToDirectory', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           fs.directory(ns('/bar')).createSync();
           fs.link(ns('/baz')).createSync(ns('/bar'));
           expectFileSystemException(ErrorCodes.EISDIR, () {
@@ -1373,7 +1372,7 @@
         });
 
         test('succeedsIfDestinationExistsAsLinkToNotFound', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           fs.link(ns('/bar')).createSync(ns('/baz'));
           f.renameSync(ns('/bar'));
           expect(fs.typeSync(ns('/foo')), FileSystemEntityType.notFound);
@@ -1429,7 +1428,7 @@
         });
 
         test('succeedsIfDestinationDoesntExistAtTail', () {
-          File f = fs.file(ns('/foo'))
+          var f = fs.file(ns('/foo'))
             ..createSync()
             ..writeAsStringSync('foo');
           f.copySync(ns('/bar'));
@@ -1439,14 +1438,14 @@
         });
 
         test('throwsIfDestinationDoesntExistViaTraversal', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           expectFileSystemException(ErrorCodes.ENOENT, () {
             f.copySync(ns('/bar/baz'));
           });
         });
 
         test('succeedsIfDestinationExistsAsFile', () {
-          File f = fs.file(ns('/foo'))
+          var f = fs.file(ns('/foo'))
             ..createSync()
             ..writeAsStringSync('foo');
           fs.file(ns('/bar'))
@@ -1460,7 +1459,7 @@
         });
 
         test('throwsIfDestinationExistsAsDirectory', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           fs.directory(ns('/bar')).createSync();
           expectFileSystemException(ErrorCodes.EISDIR, () {
             f.copySync(ns('/bar'));
@@ -1468,7 +1467,7 @@
         });
 
         test('succeedsIfDestinationExistsAsLinkToFile', () {
-          File f = fs.file(ns('/foo'))
+          var f = fs.file(ns('/foo'))
             ..createSync()
             ..writeAsStringSync('foo');
           fs.file(ns('/bar'))
@@ -1487,7 +1486,7 @@
         }, skip: io.Platform.isWindows /* No links on Windows */);
 
         test('throwsIfDestinationExistsAsLinkToDirectory', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           fs.directory(ns('/bar')).createSync();
           fs.link(ns('/baz')).createSync(ns('/bar'));
           expectFileSystemException(ErrorCodes.EISDIR, () {
@@ -1525,7 +1524,7 @@
         });
 
         test('succeedsIfDestinationIsInDifferentDirectoryThanSource', () {
-          File f = fs.file(ns('/foo/bar'))
+          var f = fs.file(ns('/foo/bar'))
             ..createSync(recursive: true)
             ..writeAsStringSync('foo');
           fs.directory(ns('/baz')).createSync();
@@ -1587,12 +1586,12 @@
         });
 
         test('returnsZeroForNewlyCreatedFile', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           expect(f.lengthSync(), 0);
         });
 
         test('writeNBytesReturnsLengthN', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           f.writeAsBytesSync(<int>[1, 2, 3, 4], flush: true);
           expect(f.lengthSync(), 4);
         });
@@ -1616,10 +1615,10 @@
 
       group('lastAccessed', () {
         test('isNowForNewlyCreatedFile', () {
-          DateTime before = downstairs();
-          File f = fs.file(ns('/foo'))..createSync();
-          DateTime after = ceil();
-          DateTime accessed = f.lastAccessedSync();
+          var before = downstairs();
+          var f = fs.file(ns('/foo'))..createSync();
+          var after = ceil();
+          var accessed = f.lastAccessedSync();
           expect(accessed, isSameOrAfter(before));
           expect(accessed, isSameOrBefore(after));
         });
@@ -1638,18 +1637,18 @@
         });
 
         test('succeedsIfExistsAsLinkToFile', () {
-          DateTime before = downstairs();
+          var before = downstairs();
           fs.file(ns('/foo')).createSync();
           fs.link(ns('/bar')).createSync(ns('/foo'));
-          DateTime after = ceil();
-          DateTime accessed = fs.file(ns('/bar')).lastAccessedSync();
+          var after = ceil();
+          var accessed = fs.file(ns('/bar')).lastAccessedSync();
           expect(accessed, isSameOrAfter(before));
           expect(accessed, isSameOrBefore(after));
         });
       });
 
       group('setLastAccessed', () {
-        final DateTime time = DateTime(1999);
+        final time = DateTime(1999);
 
         test('throwsIfDoesntExist', () {
           expectFileSystemException(ErrorCodes.ENOENT, () {
@@ -1665,13 +1664,13 @@
         });
 
         test('succeedsIfExistsAsFile', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           f.setLastAccessedSync(time);
           expect(fs.file(ns('/foo')).lastAccessedSync(), time);
         });
 
         test('succeedsIfExistsAsLinkToFile', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           fs.link(ns('/bar')).createSync(ns('/foo'));
           f.setLastAccessedSync(time);
           expect(fs.file(ns('/bar')).lastAccessedSync(), time);
@@ -1680,10 +1679,10 @@
 
       group('lastModified', () {
         test('isNowForNewlyCreatedFile', () {
-          DateTime before = downstairs();
-          File f = fs.file(ns('/foo'))..createSync();
-          DateTime after = ceil();
-          DateTime modified = f.lastModifiedSync();
+          var before = downstairs();
+          var f = fs.file(ns('/foo'))..createSync();
+          var after = ceil();
+          var modified = f.lastModifiedSync();
           expect(modified, isSameOrAfter(before));
           expect(modified, isSameOrBefore(after));
         });
@@ -1702,18 +1701,18 @@
         });
 
         test('succeedsIfExistsAsLinkToFile', () {
-          DateTime before = downstairs();
+          var before = downstairs();
           fs.file(ns('/foo')).createSync();
           fs.link(ns('/bar')).createSync(ns('/foo'));
-          DateTime after = ceil();
-          DateTime modified = fs.file(ns('/bar')).lastModifiedSync();
+          var after = ceil();
+          var modified = fs.file(ns('/bar')).lastModifiedSync();
           expect(modified, isSameOrAfter(before));
           expect(modified, isSameOrBefore(after));
         });
       });
 
       group('setLastModified', () {
-        final DateTime time = DateTime(1999);
+        final time = DateTime(1999);
 
         test('throwsIfDoesntExist', () {
           expectFileSystemException(ErrorCodes.ENOENT, () {
@@ -1729,13 +1728,13 @@
         });
 
         test('succeedsIfExistsAsFile', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           f.setLastModifiedSync(time);
           expect(fs.file(ns('/foo')).lastModifiedSync(), time);
         });
 
         test('succeedsIfExistsAsLinkToFile', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           fs.link(ns('/bar')).createSync(ns('/foo'));
           f.setLastModifiedSync(time);
           expect(fs.file(ns('/bar')).lastModifiedSync(), time);
@@ -1752,7 +1751,7 @@
             });
           } else {
             test('createsFileIfDoesntExistAtTail', () {
-              RandomAccessFile raf = fs.file(ns('/bar')).openSync(mode: mode);
+              var raf = fs.file(ns('/bar')).openSync(mode: mode);
               raf.closeSync();
               expect(fs.file(ns('/bar')), exists);
             });
@@ -1877,39 +1876,39 @@
                 });
 
                 test('readIntoWithBufferLargerThanContent', () {
-                  List<int> buffer = List<int>.filled(1024, 0);
-                  int numRead = raf.readIntoSync(buffer);
+                  var buffer = List<int>.filled(1024, 0);
+                  var numRead = raf.readIntoSync(buffer);
                   expect(numRead, 21);
                   expect(utf8.decode(buffer.sublist(0, 21)),
                       'pre-existing content\n');
                 });
 
                 test('readIntoWithBufferSmallerThanContent', () {
-                  List<int> buffer = List<int>.filled(10, 0);
-                  int numRead = raf.readIntoSync(buffer);
+                  var buffer = List<int>.filled(10, 0);
+                  var numRead = raf.readIntoSync(buffer);
                   expect(numRead, 10);
                   expect(utf8.decode(buffer), 'pre-existi');
                 });
 
                 test('readIntoWithStart', () {
-                  List<int> buffer = List<int>.filled(10, 0);
-                  int numRead = raf.readIntoSync(buffer, 2);
+                  var buffer = List<int>.filled(10, 0);
+                  var numRead = raf.readIntoSync(buffer, 2);
                   expect(numRead, 8);
                   expect(utf8.decode(buffer.sublist(2)), 'pre-exis');
                 });
 
                 test('readIntoWithStartAndEnd', () {
-                  List<int> buffer = List<int>.filled(10, 0);
-                  int numRead = raf.readIntoSync(buffer, 2, 5);
+                  var buffer = List<int>.filled(10, 0);
+                  var numRead = raf.readIntoSync(buffer, 2, 5);
                   expect(numRead, 3);
                   expect(utf8.decode(buffer.sublist(2, 5)), 'pre');
                 });
 
                 test('openReadHandleDoesNotChange', () {
-                  final String initial = utf8.decode(raf.readSync(4));
+                  final initial = utf8.decode(raf.readSync(4));
                   expect(initial, 'pre-');
-                  final File newFile = f.renameSync(ns('/bar'));
-                  String rest = utf8.decode(raf.readSync(1024));
+                  final newFile = f.renameSync(ns('/bar'));
+                  var rest = utf8.decode(raf.readSync(1024));
                   expect(rest, 'existing content\n');
 
                   assert(newFile.path != f.path);
@@ -1942,13 +1941,13 @@
               });
             } else {
               test('lengthGrowsAsDataIsWritten', () {
-                int lengthBefore = f.lengthSync();
+                var lengthBefore = f.lengthSync();
                 raf.writeByteSync(0xFACE);
                 expect(raf.lengthSync(), lengthBefore + 1);
               });
 
               test('flush', () {
-                int lengthBefore = f.lengthSync();
+                var lengthBefore = f.lengthSync();
                 raf.writeByteSync(0xFACE);
                 raf.flushSync();
                 expect(f.lengthSync(), lengthBefore + 1);
@@ -2009,10 +2008,10 @@
 
               test('openWriteHandleDoesNotChange', () {
                 raf.writeStringSync('Hello ');
-                final File newFile = f.renameSync(ns('/bar'));
+                final newFile = f.renameSync(ns('/bar'));
                 raf.writeStringSync('world');
 
-                final String contents = newFile.readAsStringSync();
+                final contents = newFile.readAsStringSync();
                 if (mode == FileMode.write || mode == FileMode.writeOnly) {
                   expect(contents, 'Hello world');
                 } else {
@@ -2067,7 +2066,7 @@
                 });
               } else {
                 test('growsAfterWrite', () {
-                  int positionBefore = raf.positionSync();
+                  var positionBefore = raf.positionSync();
                   raf.writeStringSync('Hello world');
                   expect(raf.positionSync(), positionBefore + 11);
                 });
@@ -2165,42 +2164,42 @@
 
       group('openRead', () {
         test('throwsIfDoesntExist', () {
-          Stream<List<int>> stream = fs.file(ns('/foo')).openRead();
+          var stream = fs.file(ns('/foo')).openRead();
           expect(stream.drain<void>(),
               throwsFileSystemException(ErrorCodes.ENOENT));
         });
 
         test('succeedsIfExistsAsFile', () async {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           f.writeAsStringSync('Hello world', flush: true);
-          Stream<List<int>> stream = f.openRead();
-          List<List<int>> data = await stream.toList();
+          var stream = f.openRead();
+          var data = await stream.toList();
           expect(data, hasLength(1));
           expect(utf8.decode(data[0]), 'Hello world');
         });
 
         test('throwsIfExistsAsDirectory', () {
           fs.directory(ns('/foo')).createSync();
-          Stream<List<int>> stream = fs.file(ns('/foo')).openRead();
+          var stream = fs.file(ns('/foo')).openRead();
           expect(stream.drain<void>(),
               throwsFileSystemException(ErrorCodes.EISDIR));
         });
 
         test('succeedsIfExistsAsLinkToFile', () async {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           fs.link(ns('/bar')).createSync(ns('/foo'));
           f.writeAsStringSync('Hello world', flush: true);
-          Stream<List<int>> stream = fs.file(ns('/bar')).openRead();
-          List<List<int>> data = await stream.toList();
+          var stream = fs.file(ns('/bar')).openRead();
+          var data = await stream.toList();
           expect(data, hasLength(1));
           expect(utf8.decode(data[0]), 'Hello world');
         });
 
         test('respectsStartAndEndParameters', () async {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           f.writeAsStringSync('Hello world', flush: true);
-          Stream<List<int>> stream = f.openRead(2);
-          List<List<int>> data = await stream.toList();
+          var stream = f.openRead(2);
+          var data = await stream.toList();
           expect(data, hasLength(1));
           expect(utf8.decode(data[0]), 'llo world');
           stream = f.openRead(2, 5);
@@ -2210,24 +2209,24 @@
         });
 
         test('throwsIfStartParameterIsNegative', () async {
-          File f = fs.file(ns('/foo'))..createSync();
-          Stream<List<int>> stream = f.openRead(-2);
+          var f = fs.file(ns('/foo'))..createSync();
+          var stream = f.openRead(-2);
           expect(stream.drain<void>(), throwsRangeError);
         });
 
         test('stopsAtEndOfFileIfEndParameterIsPastEndOfFile', () async {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           f.writeAsStringSync('Hello world', flush: true);
-          Stream<List<int>> stream = f.openRead(2, 1024);
-          List<List<int>> data = await stream.toList();
+          var stream = f.openRead(2, 1024);
+          var data = await stream.toList();
           expect(data, hasLength(1));
           expect(utf8.decode(data[0]), 'llo world');
         });
 
         test('providesSingleSubscriptionStream', () async {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           f.writeAsStringSync('Hello world', flush: true);
-          Stream<List<int>> stream = f.openRead();
+          var stream = f.openRead();
           expect(stream.isBroadcast, isFalse);
           await stream.drain<void>();
         });
@@ -2237,20 +2236,20 @@
           // split across multiple chunks in the [Stream].  However, there
           // doesn't seem to be a good way to determine the chunk size used by
           // [io.File].
-          final List<int> data = List<int>.generate(
+          final data = List<int>.generate(
             1024 * 256,
             (int index) => index & 0xFF,
             growable: false,
           );
 
-          final File f = fs.file(ns('/foo'))..createSync();
+          final f = fs.file(ns('/foo'))..createSync();
 
           f.writeAsBytesSync(data, flush: true);
-          final Stream<List<int>> stream = f.openRead();
+          final stream = f.openRead();
 
           File? newFile;
           List<int>? initialChunk;
-          final List<int> remainingChunks = <int>[];
+          final remainingChunks = <int>[];
 
           await for (List<int> chunk in stream) {
             if (initialChunk == null) {
@@ -2276,7 +2275,7 @@
 
         test('openReadCompatibleWithUtf8Decoder', () async {
           const content = 'Hello world!';
-          File file = fs.file(ns('/foo'))
+          var file = fs.file(ns('/foo'))
             ..createSync()
             ..writeAsStringSync(content);
           expect(
@@ -2315,8 +2314,8 @@
         });
 
         test('succeedsIfExistsAsEmptyFile', () async {
-          File f = fs.file(ns('/foo'))..createSync();
-          IOSink sink = f.openWrite();
+          var f = fs.file(ns('/foo'))..createSync();
+          var sink = f.openWrite();
           sink.write('Hello world');
           await sink.flush();
           await sink.close();
@@ -2326,7 +2325,7 @@
         test('succeedsIfExistsAsLinkToFile', () async {
           fs.file(ns('/foo')).createSync();
           fs.link(ns('/bar')).createSync(ns('/foo'));
-          IOSink sink = fs.file(ns('/bar')).openWrite();
+          var sink = fs.file(ns('/bar')).openWrite();
           sink.write('Hello world');
           await sink.flush();
           await sink.close();
@@ -2334,9 +2333,9 @@
         });
 
         test('overwritesContentInWriteMode', () async {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           f.writeAsStringSync('Hello');
-          IOSink sink = f.openWrite();
+          var sink = f.openWrite();
           sink.write('Goodbye');
           await sink.flush();
           await sink.close();
@@ -2344,9 +2343,9 @@
         });
 
         test('appendsContentInAppendMode', () async {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           f.writeAsStringSync('Hello');
-          IOSink sink = f.openWrite(mode: FileMode.append);
+          var sink = f.openWrite(mode: FileMode.append);
           sink.write('Goodbye');
           await sink.flush();
           await sink.close();
@@ -2354,12 +2353,12 @@
         });
 
         test('openWriteHandleDoesNotChange', () async {
-          File f = fs.file(ns('/foo'))..createSync();
-          IOSink sink = f.openWrite();
+          var f = fs.file(ns('/foo'))..createSync();
+          var sink = f.openWrite();
           sink.write('Hello');
           await sink.flush();
 
-          final File newFile = f.renameSync(ns('/bar'));
+          final newFile = f.renameSync(ns('/bar'));
           sink.write('Goodbye');
           await sink.flush();
           await sink.close();
@@ -2377,7 +2376,7 @@
           late bool isSinkClosed;
 
           Future<dynamic> closeSink() {
-            Future<dynamic> future = sink.close();
+            var future = sink.close();
             isSinkClosed = true;
             return future;
           }
@@ -2448,13 +2447,13 @@
 
           test('ignoresCloseAfterAlreadyClosed', () async {
             sink.write('Hello world');
-            Future<dynamic> f1 = closeSink();
-            Future<dynamic> f2 = closeSink();
+            var f1 = closeSink();
+            var f2 = closeSink();
             await Future.wait<dynamic>(<Future<dynamic>>[f1, f2]);
           });
 
           test('returnsAccurateDoneFuture', () async {
-            bool done = false;
+            var done = false;
             // ignore: unawaited_futures
             sink.done.then((dynamic _) => done = true);
             expect(done, isFalse);
@@ -2469,7 +2468,7 @@
             late bool isControllerClosed;
 
             Future<dynamic> closeController() {
-              Future<dynamic> future = controller.close();
+              var future = controller.close();
               isControllerClosed = true;
               return future;
             }
@@ -2543,7 +2542,7 @@
         });
 
         test('succeedsIfExistsAsFile', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           f.writeAsBytesSync(<int>[1, 2, 3, 4]);
           expect(f.readAsBytesSync(), <int>[1, 2, 3, 4]);
         });
@@ -2556,12 +2555,12 @@
         });
 
         test('returnsEmptyListForZeroByteFile', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           expect(f.readAsBytesSync(), isEmpty);
         });
 
         test('returns a copy, not a view, of the file content', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           f.writeAsBytesSync(<int>[1, 2, 3, 4]);
           List<int> result = f.readAsBytesSync();
           expect(result, <int>[1, 2, 3, 4]);
@@ -2593,7 +2592,7 @@
         });
 
         test('succeedsIfExistsAsFile', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           f.writeAsStringSync('Hello world');
           expect(f.readAsStringSync(), 'Hello world');
         });
@@ -2606,14 +2605,14 @@
         });
 
         test('returnsEmptyStringForZeroByteFile', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           expect(f.readAsStringSync(), isEmpty);
         });
       });
 
       group('readAsLines', () {
-        const String testString = 'Hello world\nHow are you?\nI am fine';
-        final List<String> expectedLines = <String>[
+        const testString = 'Hello world\nHow are you?\nI am fine';
+        final expectedLines = <String>[
           'Hello world',
           'How are you?',
           'I am fine',
@@ -2641,25 +2640,25 @@
         });
 
         test('succeedsIfExistsAsFile', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           f.writeAsStringSync(testString);
           expect(f.readAsLinesSync(), expectedLines);
         });
 
         test('succeedsIfExistsAsLinkToFile', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           fs.link(ns('/bar')).createSync(ns('/foo'));
           f.writeAsStringSync(testString);
           expect(f.readAsLinesSync(), expectedLines);
         });
 
         test('returnsEmptyListForZeroByteFile', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           expect(f.readAsLinesSync(), isEmpty);
         });
 
         test('isTrailingNewlineAgnostic', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           f.writeAsStringSync('$testString\n');
           expect(f.readAsLinesSync(), expectedLines);
 
@@ -2677,7 +2676,7 @@
         });
 
         test('createsFileIfDoesntExist', () {
-          File f = fs.file(ns('/foo'));
+          var f = fs.file(ns('/foo'));
           expect(f, isNot(exists));
           f.writeAsBytesSync(<int>[1, 2, 3, 4]);
           expect(f, exists);
@@ -2699,21 +2698,21 @@
         });
 
         test('succeedsIfExistsAsLinkToFile', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           fs.link(ns('/bar')).createSync(ns('/foo'));
           fs.file(ns('/bar')).writeAsBytesSync(<int>[1, 2, 3, 4]);
           expect(f.readAsBytesSync(), <int>[1, 2, 3, 4]);
         });
 
         test('throwsIfFileModeRead', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           expectFileSystemException(ErrorCodes.EBADF, () {
             f.writeAsBytesSync(<int>[1], mode: FileMode.read);
           });
         });
 
         test('overwritesContentIfFileModeWrite', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           f.writeAsBytesSync(<int>[1, 2]);
           expect(f.readAsBytesSync(), <int>[1, 2]);
           f.writeAsBytesSync(<int>[3, 4]);
@@ -2721,7 +2720,7 @@
         });
 
         test('appendsContentIfFileModeAppend', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           f.writeAsBytesSync(<int>[1, 2], mode: FileMode.append);
           expect(f.readAsBytesSync(), <int>[1, 2]);
           f.writeAsBytesSync(<int>[3, 4], mode: FileMode.append);
@@ -2729,17 +2728,17 @@
         });
 
         test('acceptsEmptyBytesList', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           f.writeAsBytesSync(<int>[]);
           expect(f.readAsBytesSync(), <int>[]);
         });
 
         test('updatesLastModifiedTime', () async {
-          File f = fs.file(ns('/foo'))..createSync();
-          DateTime before = f.statSync().modified;
+          var f = fs.file(ns('/foo'))..createSync();
+          var before = f.statSync().modified;
           await Future<void>.delayed(const Duration(seconds: 2));
           f.writeAsBytesSync(<int>[1, 2, 3]);
-          DateTime after = f.statSync().modified;
+          var after = f.statSync().modified;
           expect(after, isAfter(before));
         });
       });
@@ -2750,7 +2749,7 @@
         });
 
         test('createsFileIfDoesntExist', () {
-          File f = fs.file(ns('/foo'));
+          var f = fs.file(ns('/foo'));
           expect(f, isNot(exists));
           f.writeAsStringSync('Hello world');
           expect(f, exists);
@@ -2772,21 +2771,21 @@
         });
 
         test('succeedsIfExistsAsLinkToFile', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           fs.link(ns('/bar')).createSync(ns('/foo'));
           fs.file(ns('/bar')).writeAsStringSync('Hello world');
           expect(f.readAsStringSync(), 'Hello world');
         });
 
         test('throwsIfFileModeRead', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           expectFileSystemException(ErrorCodes.EBADF, () {
             f.writeAsStringSync('Hello world', mode: FileMode.read);
           });
         });
 
         test('overwritesContentIfFileModeWrite', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           f.writeAsStringSync('Hello world');
           expect(f.readAsStringSync(), 'Hello world');
           f.writeAsStringSync('Goodbye cruel world');
@@ -2794,7 +2793,7 @@
         });
 
         test('appendsContentIfFileModeAppend', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           f.writeAsStringSync('Hello', mode: FileMode.append);
           expect(f.readAsStringSync(), 'Hello');
           f.writeAsStringSync('Goodbye', mode: FileMode.append);
@@ -2802,7 +2801,7 @@
         });
 
         test('acceptsEmptyString', () {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           f.writeAsStringSync('');
           expect(f.readAsStringSync(), isEmpty);
         });
@@ -2847,38 +2846,38 @@
 
       group('stat', () {
         test('isNotFoundIfDoesntExistAtTail', () {
-          FileStat stat = fs.file(ns('/foo')).statSync();
+          var stat = fs.file(ns('/foo')).statSync();
           expect(stat.type, FileSystemEntityType.notFound);
         });
 
         test('isNotFoundIfDoesntExistViaTraversal', () {
-          FileStat stat = fs.file(ns('/foo/bar')).statSync();
+          var stat = fs.file(ns('/foo/bar')).statSync();
           expect(stat.type, FileSystemEntityType.notFound);
         });
 
         test('isDirectoryIfExistsAsDirectory', () {
           fs.directory(ns('/foo')).createSync();
-          FileStat stat = fs.file(ns('/foo')).statSync();
+          var stat = fs.file(ns('/foo')).statSync();
           expect(stat.type, FileSystemEntityType.directory);
         });
 
         test('isFileIfExistsAsFile', () {
           fs.file(ns('/foo')).createSync();
-          FileStat stat = fs.file(ns('/foo')).statSync();
+          var stat = fs.file(ns('/foo')).statSync();
           expect(stat.type, FileSystemEntityType.file);
         });
 
         test('isFileIfExistsAsLinkToFile', () {
           fs.file(ns('/foo')).createSync();
           fs.link(ns('/bar')).createSync(ns('/foo'));
-          FileStat stat = fs.file(ns('/bar')).statSync();
+          var stat = fs.file(ns('/bar')).statSync();
           expect(stat.type, FileSystemEntityType.file);
         });
       });
 
       group('delete', () {
         test('returnsCovariantType', () async {
-          File f = fs.file(ns('/foo'))..createSync();
+          var f = fs.file(ns('/foo'))..createSync();
           expect(await f.delete(), isFile);
         });
 
@@ -2953,14 +2952,14 @@
       group('uri', () {
         test('whenTargetIsDirectory', () {
           fs.directory(ns('/foo')).createSync();
-          Link l = fs.link(ns('/bar'))..createSync(ns('/foo'));
+          var l = fs.link(ns('/bar'))..createSync(ns('/foo'));
           expect(l.uri, fs.path.toUri(ns('/bar')));
           expect(fs.link('bar').uri.toString(), 'bar');
         });
 
         test('whenTargetIsFile', () {
           fs.file(ns('/foo')).createSync();
-          Link l = fs.link(ns('/bar'))..createSync(ns('/foo'));
+          var l = fs.link(ns('/bar'))..createSync(ns('/foo'));
           expect(l.uri, fs.path.toUri(ns('/bar')));
           expect(fs.link('bar').uri.toString(), 'bar');
         });
@@ -2991,24 +2990,24 @@
         });
 
         test('isTrueIfTargetIsNotFound', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
           expect(l, exists);
         });
 
         test('isTrueIfTargetIsFile', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
           fs.file(ns('/bar')).createSync();
           expect(l, exists);
         });
 
         test('isTrueIfTargetIsDirectory', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
           fs.directory(ns('/bar')).createSync();
           expect(l, exists);
         });
 
         test('isTrueIfTargetIsLinkLoop', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
           fs.link(ns('/bar')).createSync(ns('/foo'));
           expect(l, exists);
         });
@@ -3038,29 +3037,29 @@
         });
 
         test('isNotFoundIfTargetNotFoundAtTail', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
           expect(l.statSync().type, FileSystemEntityType.notFound);
         });
 
         test('isNotFoundIfTargetNotFoundViaTraversal', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar/baz'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar/baz'));
           expect(l.statSync().type, FileSystemEntityType.notFound);
         });
 
         test('isNotFoundIfTargetIsLinkLoop', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
           fs.link(ns('/bar')).createSync(ns('/foo'));
           expect(l.statSync().type, FileSystemEntityType.notFound);
         });
 
         test('isFileIfTargetIsFile', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
           fs.file(ns('/bar')).createSync();
           expect(l.statSync().type, FileSystemEntityType.file);
         });
 
         test('isDirectoryIfTargetIsDirectory', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
           fs.directory(ns('/bar')).createSync();
           expect(l.statSync().type, FileSystemEntityType.directory);
         });
@@ -3068,7 +3067,7 @@
 
       group('delete', () {
         test('returnsCovariantType', () async {
-          Link link = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var link = fs.link(ns('/foo'))..createSync(ns('/bar'));
           expect(await link.delete(), isLink);
         });
 
@@ -3118,7 +3117,7 @@
         });
 
         test('unlinksIfTargetIsFileAndRecursiveFalse', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
           fs.file(ns('/bar')).createSync();
           l.deleteSync();
           expect(fs.typeSync(ns('/foo'), followLinks: false),
@@ -3128,7 +3127,7 @@
         });
 
         test('unlinksIfTargetIsFileAndRecursiveTrue', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
           fs.file(ns('/bar')).createSync();
           l.deleteSync(recursive: true);
           expect(fs.typeSync(ns('/foo'), followLinks: false),
@@ -3138,7 +3137,7 @@
         });
 
         test('unlinksIfTargetIsDirectoryAndRecursiveFalse', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
           fs.directory(ns('/bar')).createSync();
           l.deleteSync();
           expect(fs.typeSync(ns('/foo'), followLinks: false),
@@ -3148,7 +3147,7 @@
         });
 
         test('unlinksIfTargetIsDirectoryAndRecursiveTrue', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
           fs.directory(ns('/bar')).createSync();
           l.deleteSync(recursive: true);
           expect(fs.typeSync(ns('/foo'), followLinks: false),
@@ -3158,7 +3157,7 @@
         });
 
         test('unlinksIfTargetIsLinkLoop', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
           fs.link(ns('/bar')).createSync(ns('/foo'));
           l.deleteSync();
           expect(fs.typeSync(ns('/foo'), followLinks: false),
@@ -3178,7 +3177,7 @@
         });
 
         test('ignoresLinkTarget', () {
-          Link l = fs.link(ns('/foo/bar'))
+          var l = fs.link(ns('/foo/bar'))
             ..createSync(ns('/baz/qux'), recursive: true);
           expect(l.parent.path, ns('/foo'));
         });
@@ -3190,7 +3189,7 @@
         });
 
         test('succeedsIfLinkDoesntExistAtTail', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
           expect(fs.typeSync(ns('/foo'), followLinks: false),
               FileSystemEntityType.link);
           expect(l.targetSync(), ns('/bar'));
@@ -3203,7 +3202,7 @@
         });
 
         test('succeedsIfLinkDoesntExistViaTraversalAndRecursiveTrue', () {
-          Link l = fs.link(ns('/foo/bar'))..createSync('baz', recursive: true);
+          var l = fs.link(ns('/foo/bar'))..createSync('baz', recursive: true);
           expect(fs.typeSync(ns('/foo'), followLinks: false),
               FileSystemEntityType.directory);
           expect(fs.typeSync(ns('/foo/bar'), followLinks: false),
@@ -3242,7 +3241,7 @@
 
       group('update', () {
         test('returnsCovariantType', () async {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
           expect(await l.update(ns('/baz')), isLink);
         });
 
@@ -3336,24 +3335,24 @@
         });
 
         test('succeedsIfTargetIsNotFound', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
           expect(l.targetSync(), ns('/bar'));
         });
 
         test('succeedsIfTargetIsFile', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
           fs.file(ns('/bar')).createSync();
           expect(l.targetSync(), ns('/bar'));
         });
 
         test('succeedsIfTargetIsDirectory', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
           fs.directory(ns('/bar')).createSync();
           expect(l.targetSync(), ns('/bar'));
         });
 
         test('succeedsIfTargetIsLinkLoop', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
           fs.link(ns('/bar')).createSync(ns('/foo'));
           expect(l.targetSync(), ns('/bar'));
         });
@@ -3393,9 +3392,9 @@
         });
 
         test('succeedsIfSourceIsLinkToFile', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
           fs.file(ns('/bar')).createSync();
-          Link renamed = l.renameSync(ns('/baz'));
+          var renamed = l.renameSync(ns('/baz'));
           expect(renamed.path, ns('/baz'));
           expect(fs.typeSync(ns('/foo'), followLinks: false),
               FileSystemEntityType.notFound);
@@ -3407,8 +3406,8 @@
         });
 
         test('succeedsIfSourceIsLinkToNotFound', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
-          Link renamed = l.renameSync(ns('/baz'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var renamed = l.renameSync(ns('/baz'));
           expect(renamed.path, ns('/baz'));
           expect(fs.typeSync(ns('/foo'), followLinks: false),
               FileSystemEntityType.notFound);
@@ -3418,9 +3417,9 @@
         });
 
         test('succeedsIfSourceIsLinkToDirectory', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
           fs.directory(ns('/bar')).createSync();
-          Link renamed = l.renameSync(ns('/baz'));
+          var renamed = l.renameSync(ns('/baz'));
           expect(renamed.path, ns('/baz'));
           expect(fs.typeSync(ns('/foo'), followLinks: false),
               FileSystemEntityType.notFound);
@@ -3432,9 +3431,9 @@
         });
 
         test('succeedsIfSourceIsLinkLoop', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
           fs.link(ns('/bar')).createSync(ns('/foo'));
-          Link renamed = l.renameSync(ns('/baz'));
+          var renamed = l.renameSync(ns('/baz'));
           expect(renamed.path, ns('/baz'));
           expect(fs.typeSync(ns('/foo'), followLinks: false),
               FileSystemEntityType.notFound);
@@ -3446,22 +3445,22 @@
         });
 
         test('succeedsIfDestinationDoesntExistAtTail', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
-          Link renamed = l.renameSync(ns('/baz'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var renamed = l.renameSync(ns('/baz'));
           expect(renamed.path, ns('/baz'));
           expect(fs.link(ns('/foo')), isNot(exists));
           expect(fs.link(ns('/baz')), exists);
         });
 
         test('throwsIfDestinationDoesntExistViaTraversal', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
           expectFileSystemException(ErrorCodes.ENOENT, () {
             l.renameSync(ns('/baz/qux'));
           });
         });
 
         test('throwsIfDestinationExistsAsFile', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
           fs.file(ns('/baz')).createSync();
           expectFileSystemException(ErrorCodes.EINVAL, () {
             l.renameSync(ns('/baz'));
@@ -3469,7 +3468,7 @@
         });
 
         test('throwsIfDestinationExistsAsDirectory', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
           fs.directory(ns('/baz')).createSync();
           expectFileSystemException(ErrorCodes.EINVAL, () {
             l.renameSync(ns('/baz'));
@@ -3477,7 +3476,7 @@
         });
 
         test('succeedsIfDestinationExistsAsLinkToFile', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
           fs.file(ns('/baz')).createSync();
           fs.link(ns('/qux')).createSync(ns('/baz'));
           l.renameSync(ns('/qux'));
@@ -3490,7 +3489,7 @@
         });
 
         test('throwsIfDestinationExistsAsLinkToDirectory', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
           fs.directory(ns('/baz')).createSync();
           fs.link(ns('/qux')).createSync(ns('/baz'));
           l.renameSync(ns('/qux'));
@@ -3503,7 +3502,7 @@
         });
 
         test('succeedsIfDestinationExistsAsLinkToNotFound', () {
-          Link l = fs.link(ns('/foo'))..createSync(ns('/bar'));
+          var l = fs.link(ns('/foo'))..createSync(ns('/bar'));
           fs.link(ns('/baz')).createSync(ns('/qux'));
           l.renameSync(ns('/baz'));
           expect(fs.typeSync(ns('/foo')), FileSystemEntityType.notFound);

diff --git a/pkgs/file/test/local_test.dart b/pkgs/file/test/local_test.dart
index e1618d2..b794ccd 100644
--- a/pkgs/file/test/local_test.dart
+++ b/pkgs/file/test/local_test.dart

@@ -2,7 +2,11 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// ignore_for_file: lines_longer_than_80_chars
+
 @TestOn('vm')
+library;
+
 import 'dart:io' as io;
 
 import 'package:file/local.dart';
@@ -33,7 +37,7 @@
     setUpAll(() {
       if (io.Platform.isWindows) {
         // TODO(tvolkert): Remove once all more serious test failures are fixed
-        // https://github.com/google/file.dart/issues/56
+        // https://github.com/dart-lang/tools/issues/618
         ignoreOsErrorCodes = true;
       }
     });
@@ -42,7 +46,7 @@
       ignoreOsErrorCodes = false;
     });
 
-    Map<String, List<String>> skipOnPlatform = <String, List<String>>{
+    var skipOnPlatform = <String, List<String>>{
       'windows': <String>[
         'FileSystem > currentDirectory > throwsIfHasNonExistentPathInComplexChain',
         'FileSystem > currentDirectory > resolvesLinksIfEncountered',

diff --git a/pkgs/file/test/memory_operations_test.dart b/pkgs/file/test/memory_operations_test.dart
index 5e27843..916707c 100644
--- a/pkgs/file/test/memory_operations_test.dart
+++ b/pkgs/file/test/memory_operations_test.dart

@@ -2,22 +2,21 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:file/file.dart';
 import 'package:file/memory.dart';
 import 'package:test/test.dart';
 
 void main() {
   test('Read operations invoke opHandle', () async {
-    List<String> contexts = <String>[];
-    List<FileSystemOp> operations = <FileSystemOp>[];
-    MemoryFileSystem fs = MemoryFileSystem.test(
+    var contexts = <String>[];
+    var operations = <FileSystemOp>[];
+    var fs = MemoryFileSystem.test(
         opHandle: (String context, FileSystemOp operation) {
       if (operation == FileSystemOp.read) {
         contexts.add(context);
         operations.add(operation);
       }
     });
-    final File file = fs.file('test')..createSync();
+    final file = fs.file('test')..createSync();
 
     await file.readAsBytes();
     file.readAsBytesSync();
@@ -34,16 +33,16 @@
   });
 
   test('Write operations invoke opHandle', () async {
-    List<String> contexts = <String>[];
-    List<FileSystemOp> operations = <FileSystemOp>[];
-    MemoryFileSystem fs = MemoryFileSystem.test(
+    var contexts = <String>[];
+    var operations = <FileSystemOp>[];
+    var fs = MemoryFileSystem.test(
         opHandle: (String context, FileSystemOp operation) {
       if (operation == FileSystemOp.write) {
         contexts.add(context);
         operations.add(operation);
       }
     });
-    final File file = fs.file('test')..createSync();
+    final file = fs.file('test')..createSync();
 
     await file.writeAsBytes(<int>[]);
     file.writeAsBytesSync(<int>[]);
@@ -60,18 +59,18 @@
   });
 
   test('Delete operations invoke opHandle', () async {
-    List<String> contexts = <String>[];
-    List<FileSystemOp> operations = <FileSystemOp>[];
-    MemoryFileSystem fs = MemoryFileSystem.test(
+    var contexts = <String>[];
+    var operations = <FileSystemOp>[];
+    var fs = MemoryFileSystem.test(
         opHandle: (String context, FileSystemOp operation) {
       if (operation == FileSystemOp.delete) {
         contexts.add(context);
         operations.add(operation);
       }
     });
-    final File file = fs.file('test')..createSync();
-    final Directory directory = fs.directory('testDir')..createSync();
-    final Link link = fs.link('testLink')..createSync('foo');
+    final file = fs.file('test')..createSync();
+    final directory = fs.directory('testDir')..createSync();
+    final link = fs.link('testLink')..createSync('foo');
 
     await file.delete();
     file.createSync();
@@ -98,9 +97,9 @@
   });
 
   test('Create operations invoke opHandle', () async {
-    List<String> contexts = <String>[];
-    List<FileSystemOp> operations = <FileSystemOp>[];
-    MemoryFileSystem fs = MemoryFileSystem.test(
+    var contexts = <String>[];
+    var operations = <FileSystemOp>[];
+    var fs = MemoryFileSystem.test(
         opHandle: (String context, FileSystemOp operation) {
       if (operation == FileSystemOp.create) {
         contexts.add(context);
@@ -139,16 +138,16 @@
   });
 
   test('Open operations invoke opHandle', () async {
-    List<String> contexts = <String>[];
-    List<FileSystemOp> operations = <FileSystemOp>[];
-    MemoryFileSystem fs = MemoryFileSystem.test(
+    var contexts = <String>[];
+    var operations = <FileSystemOp>[];
+    var fs = MemoryFileSystem.test(
         opHandle: (String context, FileSystemOp operation) {
       if (operation == FileSystemOp.open) {
         contexts.add(context);
         operations.add(operation);
       }
     });
-    final File file = fs.file('test')..createSync();
+    final file = fs.file('test')..createSync();
 
     await file.open();
     file.openSync();
@@ -165,16 +164,16 @@
   });
 
   test('Copy operations invoke opHandle', () async {
-    List<String> contexts = <String>[];
-    List<FileSystemOp> operations = <FileSystemOp>[];
-    MemoryFileSystem fs = MemoryFileSystem.test(
+    var contexts = <String>[];
+    var operations = <FileSystemOp>[];
+    var fs = MemoryFileSystem.test(
         opHandle: (String context, FileSystemOp operation) {
       if (operation == FileSystemOp.copy) {
         contexts.add(context);
         operations.add(operation);
       }
     });
-    final File file = fs.file('test')..createSync();
+    final file = fs.file('test')..createSync();
 
     await file.copy('A');
     file.copySync('B');
@@ -187,9 +186,9 @@
   });
 
   test('Exists operations invoke opHandle', () async {
-    List<String> contexts = <String>[];
-    List<FileSystemOp> operations = <FileSystemOp>[];
-    MemoryFileSystem fs = MemoryFileSystem.test(
+    var contexts = <String>[];
+    var operations = <FileSystemOp>[];
+    var fs = MemoryFileSystem.test(
         opHandle: (String context, FileSystemOp operation) {
       if (operation == FileSystemOp.exists) {
         contexts.add(context);

diff --git a/pkgs/file/test/memory_test.dart b/pkgs/file/test/memory_test.dart
index f3b324e..ce8675f 100644
--- a/pkgs/file/test/memory_test.dart
+++ b/pkgs/file/test/memory_test.dart

@@ -66,8 +66,7 @@
   });
 
   test('MemoryFileSystem.test', () {
-    final MemoryFileSystem fs =
-        MemoryFileSystem.test(); // creates root directory
+    final fs = MemoryFileSystem.test(); // creates root directory
     fs.file('/test1.txt').createSync(); // creates file
     fs.file('/test2.txt').createSync(); // creates file
     expect(fs.directory('/').statSync().modified, DateTime(2000, 1, 1, 0, 1));
@@ -95,10 +94,10 @@
   });
 
   test('MemoryFile.openSync returns a MemoryRandomAccessFile', () async {
-    final MemoryFileSystem fs = MemoryFileSystem.test();
+    final fs = MemoryFileSystem.test();
     final io.File file = fs.file('/test1')..createSync();
 
-    io.RandomAccessFile raf = file.openSync();
+    var raf = file.openSync();
     try {
       expect(raf, isA<MemoryRandomAccessFile>());
     } finally {
@@ -114,7 +113,7 @@
   });
 
   test('MemoryFileSystem.systemTempDirectory test', () {
-    final MemoryFileSystem fs = MemoryFileSystem.test();
+    final fs = MemoryFileSystem.test();
 
     final io.Directory fooA = fs.systemTempDirectory.createTempSync('foo');
     final io.Directory fooB = fs.systemTempDirectory.createTempSync('foo');
@@ -122,7 +121,7 @@
     expect(fooA.path, '/.tmp_rand0/foorand0');
     expect(fooB.path, '/.tmp_rand0/foorand1');
 
-    final MemoryFileSystem secondFs = MemoryFileSystem.test();
+    final secondFs = MemoryFileSystem.test();
 
     final io.Directory fooAA =
         secondFs.systemTempDirectory.createTempSync('foo');
@@ -136,16 +135,16 @@
 
   test('Failed UTF8 decoding in MemoryFileSystem throws a FileSystemException',
       () {
-    final MemoryFileSystem fileSystem = MemoryFileSystem.test();
-    final File file = fileSystem.file('foo')
+    final fileSystem = MemoryFileSystem.test();
+    final file = fileSystem.file('foo')
       ..writeAsBytesSync(<int>[0xFFFE]); // Invalid UTF8
 
     expect(file.readAsStringSync, throwsA(isA<FileSystemException>()));
   });
 
   test('Creating a temporary directory actually creates the directory', () {
-    final MemoryFileSystem fileSystem = MemoryFileSystem.test();
-    final Directory tempDir = fileSystem.currentDirectory.createTempSync('foo');
+    final fileSystem = MemoryFileSystem.test();
+    final tempDir = fileSystem.currentDirectory.createTempSync('foo');
 
     expect(tempDir.existsSync(), true);
   });

diff --git a/pkgs/file/test/utils.dart b/pkgs/file/test/utils.dart
index 231312f..797ec9d 100644
--- a/pkgs/file/test/utils.dart
+++ b/pkgs/file/test/utils.dart

@@ -25,7 +25,7 @@
 /// If [time] is not specified, it will default to the current time.
 DateTime ceil([DateTime? time]) {
   time ??= DateTime.now();
-  int microseconds = (1000 * time.millisecond) + time.microsecond;
+  var microseconds = (1000 * time.millisecond) + time.microsecond;
   return (microseconds == 0)
       ? time
       // Add just enough milliseconds and microseconds to reach the next second.
@@ -78,7 +78,7 @@
     bool verbose,
   ) {
     if (item is DateTime) {
-      Duration diff = item.difference(_time).abs();
+      var diff = item.difference(_time).abs();
       return description.add('is $mismatchAdjective $_time by $diff');
     } else {
       return description.add('is not a DateTime');

diff --git a/pkgs/file/test/utils_test.dart b/pkgs/file/test/utils_test.dart
index 75293bf..23788e9 100644
--- a/pkgs/file/test/utils_test.dart
+++ b/pkgs/file/test/utils_test.dart

@@ -8,9 +8,9 @@
 
 void main() {
   test('floorAndCeilProduceExactSecondDateTime', () {
-    DateTime time = DateTime.fromMicrosecondsSinceEpoch(1001);
-    DateTime lower = floor(time);
-    DateTime upper = ceil(time);
+    var time = DateTime.fromMicrosecondsSinceEpoch(1001);
+    var lower = floor(time);
+    var upper = ceil(time);
     expect(lower.millisecond, 0);
     expect(upper.millisecond, 0);
     expect(lower.microsecond, 0);
@@ -18,26 +18,26 @@
   });
 
   test('floorAndCeilWorkWithNow', () {
-    DateTime time = DateTime.now();
-    int lower = time.difference(floor(time)).inMicroseconds;
-    int upper = ceil(time).difference(time).inMicroseconds;
+    var time = DateTime.now();
+    var lower = time.difference(floor(time)).inMicroseconds;
+    var upper = ceil(time).difference(time).inMicroseconds;
     expect(lower, lessThan(1000000));
     expect(upper, lessThanOrEqualTo(1000000));
   });
 
   test('floorAndCeilWorkWithExactSecondDateTime', () {
-    DateTime time = DateTime.parse('1999-12-31 23:59:59');
-    DateTime lower = floor(time);
-    DateTime upper = ceil(time);
+    var time = DateTime.parse('1999-12-31 23:59:59');
+    var lower = floor(time);
+    var upper = ceil(time);
     expect(lower, time);
     expect(upper, time);
   });
 
   test('floorAndCeilWorkWithInexactSecondDateTime', () {
-    DateTime time = DateTime.parse('1999-12-31 23:59:59.500');
-    DateTime lower = floor(time);
-    DateTime upper = ceil(time);
-    Duration difference = upper.difference(lower);
+    var time = DateTime.parse('1999-12-31 23:59:59.500');
+    var lower = floor(time);
+    var upper = ceil(time);
+    var difference = upper.difference(lower);
     expect(difference.inMicroseconds, 1000000);
   });
 }

diff --git a/pkgs/file_testing/CHANGELOG.md b/pkgs/file_testing/CHANGELOG.md
index 0af779d..17039ee 100644
--- a/pkgs/file_testing/CHANGELOG.md
+++ b/pkgs/file_testing/CHANGELOG.md

@@ -1,3 +1,8 @@
+## 3.1.0-wip
+
+* Changed the type of several matchers to `TypeMatcher` which allows cascading
+  their usage with `.having` and similar. 
+
 ## 3.0.2
 
 * Require Dart 3.1.

diff --git a/pkgs/file_testing/analysis_options.yaml b/pkgs/file_testing/analysis_options.yaml
index 8fbd2e4..d978f81 100644
--- a/pkgs/file_testing/analysis_options.yaml
+++ b/pkgs/file_testing/analysis_options.yaml

@@ -1,6 +1 @@
-include: package:lints/recommended.yaml
-
-analyzer:
-  errors:
-    # Allow having TODOs in the code
-    todo: ignore
+include: package:dart_flutter_team_lints/analysis_options.yaml

diff --git a/pkgs/file_testing/lib/src/testing/core_matchers.dart b/pkgs/file_testing/lib/src/testing/core_matchers.dart
index f58539f..801209e 100644
--- a/pkgs/file_testing/lib/src/testing/core_matchers.dart
+++ b/pkgs/file_testing/lib/src/testing/core_matchers.dart

@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// ignore_for_file: comment_references
+
 import 'dart:io';
 
 import 'package:test/test.dart';
@@ -9,26 +11,27 @@
 import 'internal.dart';
 
 /// Matcher that successfully matches against any instance of [Directory].
-const Matcher isDirectory = TypeMatcher<Directory>();
+const isDirectory = TypeMatcher<Directory>();
 
 /// Matcher that successfully matches against any instance of [File].
-const Matcher isFile = TypeMatcher<File>();
+const isFile = TypeMatcher<File>();
 
 /// Matcher that successfully matches against any instance of [Link].
-const Matcher isLink = TypeMatcher<Link>();
+const isLink = TypeMatcher<Link>();
 
 /// Matcher that successfully matches against any instance of
 /// [FileSystemEntity].
-const Matcher isFileSystemEntity = TypeMatcher<FileSystemEntity>();
+const isFileSystemEntity = TypeMatcher<FileSystemEntity>();
 
 /// Matcher that successfully matches against any instance of [FileStat].
-const Matcher isFileStat = TypeMatcher<FileStat>();
+const isFileStat = TypeMatcher<FileStat>();
 
 /// Returns a [Matcher] that matches [path] against an entity's path.
 ///
 /// [path] may be a String, a predicate function, or a [Matcher]. If it is
 /// a String, it will be wrapped in an equality matcher.
-Matcher hasPath(dynamic path) => _HasPath(path);
+TypeMatcher<FileSystemEntity> hasPath(dynamic path) =>
+    isFileSystemEntity.having((e) => e.path, 'path', path);
 
 /// Returns a [Matcher] that successfully matches against an instance of
 /// [FileSystemException].
@@ -39,7 +42,8 @@
 /// [osErrorCode] may be an `int`, a predicate function, or a [Matcher]. If it
 /// is an `int`, it will be wrapped in an equality matcher.
 Matcher isFileSystemException([dynamic osErrorCode]) =>
-    _FileSystemException(osErrorCode);
+    const TypeMatcher<FileSystemException>().having((e) => e.osError?.errorCode,
+        'osError.errorCode', _fileExceptionWrapMatcher(osErrorCode));
 
 /// Returns a matcher that successfully matches against a future or function
 /// that throws a [FileSystemException].
@@ -67,89 +71,10 @@
 
 /// Matcher that successfully matches against a [FileSystemEntity] that
 /// exists ([FileSystemEntity.existsSync] returns true).
-const Matcher exists = _Exists();
+final TypeMatcher<FileSystemEntity> exists =
+    isFileSystemEntity.having((e) => e.existsSync(), 'existsSync', true);
 
-class _FileSystemException extends Matcher {
-  _FileSystemException(dynamic osErrorCode)
-      : _matcher = _wrapMatcher(osErrorCode);
-
-  final Matcher? _matcher;
-
-  static Matcher? _wrapMatcher(dynamic osErrorCode) {
-    if (osErrorCode == null) {
-      return null;
-    }
-    return ignoreOsErrorCodes ? anything : wrapMatcher(osErrorCode);
-  }
-
-  @override
-  bool matches(dynamic item, Map<dynamic, dynamic> matchState) {
-    if (item is FileSystemException) {
-      return _matcher == null ||
-          _matcher!.matches(item.osError?.errorCode, matchState);
-    }
-    return false;
-  }
-
-  @override
-  Description describe(Description desc) {
-    if (_matcher == null) {
-      return desc.add('FileSystemException');
-    } else {
-      desc.add('FileSystemException with osError.errorCode: ');
-      return _matcher!.describe(desc);
-    }
-  }
-}
-
-class _HasPath extends Matcher {
-  _HasPath(dynamic path) : _matcher = wrapMatcher(path);
-
-  final Matcher _matcher;
-
-  @override
-  bool matches(dynamic item, Map<dynamic, dynamic> matchState) =>
-      _matcher.matches(item.path, matchState);
-
-  @override
-  Description describe(Description desc) {
-    desc.add('has path: ');
-    return _matcher.describe(desc);
-  }
-
-  @override
-  Description describeMismatch(
-    dynamic item,
-    Description desc,
-    Map<dynamic, dynamic> matchState,
-    bool verbose,
-  ) {
-    desc.add('has path: \'${item.path}\'').add('\n   Which: ');
-    final Description pathDesc = StringDescription();
-    _matcher.describeMismatch(item.path, pathDesc, matchState, verbose);
-    desc.add(pathDesc.toString());
-    return desc;
-  }
-}
-
-class _Exists extends Matcher {
-  const _Exists();
-
-  @override
-  bool matches(dynamic item, Map<dynamic, dynamic> matchState) =>
-      item is FileSystemEntity && item.existsSync();
-
-  @override
-  Description describe(Description description) =>
-      description.add('a file system entity that exists');
-
-  @override
-  Description describeMismatch(
-    dynamic item,
-    Description description,
-    Map<dynamic, dynamic> matchState,
-    bool verbose,
-  ) {
-    return description.add('does not exist');
-  }
-}
+Matcher? _fileExceptionWrapMatcher(dynamic osErrorCode) =>
+    (osErrorCode == null || ignoreOsErrorCodes)
+        ? anything
+        : wrapMatcher(osErrorCode);

diff --git a/pkgs/file_testing/pubspec.yaml b/pkgs/file_testing/pubspec.yaml
index 691efa0..895826a 100644
--- a/pkgs/file_testing/pubspec.yaml
+++ b/pkgs/file_testing/pubspec.yaml

@@ -1,5 +1,5 @@
 name: file_testing
-version: 3.0.2
+version: 3.1.0-wip
 description: Testing utilities for package:file.
 repository: https://github.com/dart-lang/tools/tree/main/pkgs/file_testing
 issue_tracker: https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Afile_testing
@@ -10,5 +10,5 @@
 dependencies:
   test: ^1.23.1
 
-dev_dependencies: 
-  lints: ^5.0.0
+dev_dependencies:
+  dart_flutter_team_lints: ^3.0.0

diff --git a/pkgs/graphs/pubspec.yaml b/pkgs/graphs/pubspec.yaml
index bdbda2f..e25ee85 100644
--- a/pkgs/graphs/pubspec.yaml
+++ b/pkgs/graphs/pubspec.yaml

@@ -15,6 +15,6 @@
   test: ^1.21.6
 
   # For examples
-  analyzer: '>=5.2.0 <7.0.0'
+  analyzer: '>=5.2.0 <8.0.0'
   path: ^1.8.0
   pool: ^1.5.0

diff --git a/pkgs/io/.gitignore b/pkgs/io/.gitignore
new file mode 100644
index 0000000..01d42c0
--- /dev/null
+++ b/pkgs/io/.gitignore

@@ -0,0 +1,4 @@
+.dart_tool/
+.pub/
+.packages
+pubspec.lock

diff --git a/pkgs/io/AUTHORS b/pkgs/io/AUTHORS
new file mode 100644
index 0000000..ff09364
--- /dev/null
+++ b/pkgs/io/AUTHORS

@@ -0,0 +1,7 @@
+# Below is a list of people and organizations that have contributed
+# to the project. Names should be added to the list like so:
+#
+#   Name/Organization <email address>
+
+Google Inc.
+

diff --git a/pkgs/io/CHANGELOG.md b/pkgs/io/CHANGELOG.md
new file mode 100644
index 0000000..e0631fa
--- /dev/null
+++ b/pkgs/io/CHANGELOG.md

@@ -0,0 +1,119 @@
+## 1.0.5
+
+* Require Dart 3.4.
+* Move to `dart-lang/tools` monorepo.
+
+## 1.0.4
+
+* Updates to the readme.
+
+## 1.0.3
+
+* Revert `meta` constraint to `^1.3.0`.
+
+## 1.0.2
+
+* Update `meta` constraint to `>=1.3.0 <3.0.0`.
+
+## 1.0.1
+
+* Update code examples to call the unified `dart` developer tool.
+
+## 1.0.0
+
+* Migrate this package to null-safety.
+* Require Dart >=2.12.
+
+## 0.3.5
+
+* Require Dart >=2.1.
+* Remove dependency on `package:charcode`.
+
+## 0.3.4
+
+* Fix a number of issues affecting the package score on `pub.dev`.
+
+## 0.3.3
+
+* Updates for Dart 2 constants. Require at least Dart `2.0.0-dev.54`.
+
+* Fix the type of `StartProcess` typedef to match `Process.start` from
+  `dart:io`.
+
+## 0.3.2+1
+
+* `ansi.dart`
+
+  * The "forScript" code paths now ignore the `ansiOutputEnabled` value. Affects
+    the `escapeForScript` property on `AnsiCode` and the `wrap` and `wrapWith`
+    functions when `forScript` is true.
+
+## 0.3.2
+
+* `ansi.dart`
+
+  * Added `forScript` named argument to top-level `wrapWith` function.
+
+  * `AnsiCode`
+
+    * Added `String get escapeForScript` property.
+
+    * Added `forScript` named argument to `wrap` function.
+
+## 0.3.1
+
+- Added `SharedStdIn.nextLine` (similar to `readLineSync`) and `lines`:
+
+```dart
+main() async {
+  // Prints the first line entered on stdin.
+  print(await sharedStdIn.nextLine());
+
+  // Prints all remaining lines.
+  await for (final line in sharedStdIn.lines) {
+    print(line);
+  }
+}
+```
+
+- Added a `copyPath` and `copyPathSync` function, similar to `cp -R`.
+
+- Added a dependency on `package:path`.
+
+- Added the remaining missing arguments to `ProcessManager.spawnX` which
+  forward to `Process.start`. It is now an interchangeable function for running
+  a process.
+
+## 0.3.0
+
+- **BREAKING CHANGE**: The `arguments` argument to `ProcessManager.spawn` is
+  now positional (not named) and required. This makes it more similar to the
+  built-in `Process.start`, and easier to use as a drop in replacement:
+
+```dart
+main() {
+  processManager.spawn('dart', ['--version']);
+}
+```
+
+- Fixed a bug where processes created from `ProcessManager.spawn` could not
+  have their `stdout`/`stderr` read through their respective getters (a runtime
+  error was always thrown).
+
+- Added `ProcessMangaer#spawnBackground`, which does not forward `stdin`.
+
+- Added `ProcessManager#spawnDetached`, which does not forward any I/O.
+
+- Added the `shellSplit()` function, which parses a list of arguments in the
+  same manner as [the POSIX shell][what_is_posix_shell].
+
+[what_is_posix_shell]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/contents.html
+
+## 0.2.0
+
+- Initial commit of...
+   - `FutureOr<bool> String isExecutable(path)`.
+   - `ExitCode`
+   - `ProcessManager` and `Spawn`
+   - `sharedStdIn` and `SharedStdIn`
+   - `ansi.dart` library with support for formatting terminal output

diff --git a/pkgs/io/LICENSE b/pkgs/io/LICENSE
new file mode 100644
index 0000000..03af64a
--- /dev/null
+++ b/pkgs/io/LICENSE

@@ -0,0 +1,27 @@
+Copyright 2017, the Dart project authors. 
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+    * Neither the name of Google LLC nor the names of its
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

diff --git a/pkgs/io/README.md b/pkgs/io/README.md
new file mode 100644
index 0000000..adbc941
--- /dev/null
+++ b/pkgs/io/README.md

@@ -0,0 +1,104 @@
+[![Build Status](https://github.com/dart-lang/tools/actions/workflows/io.yaml/badge.svg)](https://github.com/dart-lang/tools/actions/workflows/io.yaml)
+[![pub package](https://img.shields.io/pub/v/io.svg)](https://pub.dev/packages/io)
+[![package publisher](https://img.shields.io/pub/publisher/io.svg)](https://pub.dev/packages/io/publisher)
+
+Contains utilities for the Dart VM's `dart:io`.
+
+## Usage - `io.dart`
+
+### Files
+
+#### `isExecutable`
+ 
+Returns whether a provided file path is considered _executable_ on the host
+operating system.
+
+### Processes
+
+#### `ExitCode`
+
+An `enum`-like class that contains known exit codes.
+
+#### `ProcessManager`
+
+A higher-level service for spawning and communicating with processes.
+
+##### Use `spawn` to create a process with std[in|out|err] forwarded by default
+
+```dart
+Future<void> main() async {
+  final manager = ProcessManager();
+
+  // Print `dart` tool version to stdout.
+  print('** Running `dart --version`');
+  var spawn = await manager.spawn('dart', ['--version']);
+  await spawn.exitCode;
+
+  // Check formatting and print the result to stdout.
+  print('** Running `dart format --output=none .`');
+  spawn = await manager.spawn('dart', ['format', '--output=none', '.']);
+  await spawn.exitCode;
+
+  // Check if a package is ready for publishing.
+  // Upon hitting a blocking stdin state, you may directly
+  // output to the processes's stdin via your own, similar to how a bash or
+  // shell script would spawn a process.
+  print('** Running pub publish');
+  spawn = await manager.spawn('dart', ['pub', 'publish', '--dry-run']);
+  await spawn.exitCode;
+
+  // Closes stdin for the entire program.
+  await sharedStdIn.terminate();
+}
+```
+
+#### `sharedStdIn`
+
+A safer version of the default `stdin` stream from `dart:io` that allows a
+subscriber to cancel their subscription, and then allows a _new_ subscriber to
+start listening. This differs from the default behavior where only a single
+listener is ever allowed in the application lifecycle:
+
+```dart
+test('should allow multiple subscribers', () async {
+  final logs = <String>[];
+  final asUtf8 = sharedStdIn.transform(UTF8.decoder);
+  // Wait for input for the user.
+  logs.add(await asUtf8.first);
+  // Wait for more input for the user.
+  logs.add(await asUtf8.first);
+  expect(logs, ['Hello World', 'Goodbye World']);
+});
+```
+
+For testing, an instance of `SharedStdIn` may be created directly.
+
+## Usage - `ansi.dart`
+
+```dart
+import 'dart:io' as io;
+import 'package:io/ansi.dart';
+
+void main() {
+  // To use one style, call the `wrap` method on one of the provided top-level
+  // values.
+  io.stderr.writeln(red.wrap("Bad error!"));
+
+  // To use multiple styles, call `wrapWith`.
+  print(wrapWith('** Important **', [red, styleBold, styleUnderlined]));
+
+  // The wrap functions will simply return the provided value unchanged if
+  // `ansiOutputEnabled` is false.
+  //
+  // You can override the value `ansiOutputEnabled` by wrapping code in
+  // `overrideAnsiOutput`.
+  overrideAnsiOutput(false, () {
+    assert('Normal text' == green.wrap('Normal text'));
+  });
+}
+```
+
+## Publishing automation
+
+For information about our publishing automation and release process, see
+https://github.com/dart-lang/ecosystem/wiki/Publishing-automation.

diff --git a/pkgs/io/analysis_options.yaml b/pkgs/io/analysis_options.yaml
new file mode 100644
index 0000000..6d74ee9
--- /dev/null
+++ b/pkgs/io/analysis_options.yaml

@@ -0,0 +1,32 @@
+# https://dart.dev/guides/language/analysis-options
+include: package:dart_flutter_team_lints/analysis_options.yaml
+
+analyzer:
+  language:
+    strict-casts: true
+    strict-inference: true
+    strict-raw-types: true
+
+linter:
+  rules:
+    - avoid_bool_literals_in_conditional_expressions
+    - avoid_classes_with_only_static_members
+    - avoid_private_typedef_functions
+    - avoid_redundant_argument_values
+    - avoid_returning_this
+    - avoid_unused_constructor_parameters
+    - avoid_void_async
+    - cancel_subscriptions
+    - join_return_with_assignment
+    - literal_only_boolean_expressions
+    - missing_whitespace_between_adjacent_strings
+    - no_adjacent_strings_in_list
+    - no_runtimeType_toString
+    - prefer_const_declarations
+    - prefer_expression_function_bodies
+    - prefer_final_locals
+    - unnecessary_await_in_return
+    - unnecessary_breaks
+    - use_if_null_to_convert_nulls_to_bools
+    - use_raw_strings
+    - use_string_buffers

diff --git a/pkgs/io/example/example.dart b/pkgs/io/example/example.dart
new file mode 100644
index 0000000..8e358fd
--- /dev/null
+++ b/pkgs/io/example/example.dart

@@ -0,0 +1,33 @@
+// Copyright (c) 2017, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:math';
+
+import 'package:io/ansi.dart';
+
+/// Prints a sample of all of the `AnsiCode` values.
+void main(List<String> args) {
+  final forScript = args.contains('--for-script');
+
+  if (!ansiOutputEnabled) {
+    print('`ansiOutputEnabled` is `false`.');
+    print("Don't expect pretty output.");
+  }
+  _preview('Foreground', foregroundColors, forScript);
+  _preview('Background', backgroundColors, forScript);
+  _preview('Styles', styles, forScript);
+}
+
+void _preview(String name, List<AnsiCode> values, bool forScript) {
+  print('');
+  final longest = values.map((ac) => ac.name.length).reduce(max);
+
+  print(wrapWith('** $name **', [styleBold, styleUnderlined]));
+  for (var code in values) {
+    final header =
+        '${code.name.padRight(longest)} ${code.code.toString().padLeft(3)}';
+
+    print("$header: ${code.wrap('Sample', forScript: forScript)}");
+  }
+}

diff --git a/pkgs/io/example/spawn_process_example.dart b/pkgs/io/example/spawn_process_example.dart
new file mode 100644
index 0000000..b7ba247
--- /dev/null
+++ b/pkgs/io/example/spawn_process_example.dart

@@ -0,0 +1,33 @@
+// Copyright (c) 2017, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:io/io.dart';
+
+/// Runs a few subcommands in the `dart` command.
+Future<void> main() async {
+  final manager = ProcessManager();
+
+  // Print `dart` tool version to stdout.
+  print('** Running `dart --version`');
+  var spawn = await manager.spawn('dart', ['--version']);
+  await spawn.exitCode;
+
+  // Check formatting and print the result to stdout.
+  print('** Running `dart format --output=none .`');
+  spawn = await manager.spawn('dart', ['format', '--output=none', '.']);
+  await spawn.exitCode;
+
+  // Check if a package is ready for publishing.
+  // Upon hitting a blocking stdin state, you may directly
+  // output to the processes's stdin via your own, similar to how a bash or
+  // shell script would spawn a process.
+  print('** Running pub publish');
+  spawn = await manager.spawn('dart', ['pub', 'publish', '--dry-run']);
+  await spawn.exitCode;
+
+  // Closes stdin for the entire program.
+  await sharedStdIn.terminate();
+}

diff --git a/pkgs/io/lib/ansi.dart b/pkgs/io/lib/ansi.dart
new file mode 100644
index 0000000..a2adbe7
--- /dev/null
+++ b/pkgs/io/lib/ansi.dart

@@ -0,0 +1,5 @@
+// Copyright (c) 2017, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+export 'src/ansi_code.dart';

diff --git a/pkgs/io/lib/io.dart b/pkgs/io/lib/io.dart
new file mode 100644
index 0000000..8ee0843
--- /dev/null
+++ b/pkgs/io/lib/io.dart

@@ -0,0 +1,10 @@
+// Copyright (c) 2017, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+export 'src/copy_path.dart' show copyPath, copyPathSync;
+export 'src/exit_code.dart' show ExitCode;
+export 'src/permissions.dart' show isExecutable;
+export 'src/process_manager.dart' show ProcessManager, Spawn, StartProcess;
+export 'src/shared_stdin.dart' show SharedStdIn, sharedStdIn;
+export 'src/shell_words.dart' show shellSplit;

diff --git a/pkgs/io/lib/src/ansi_code.dart b/pkgs/io/lib/src/ansi_code.dart
new file mode 100644
index 0000000..c9a22c5
--- /dev/null
+++ b/pkgs/io/lib/src/ansi_code.dart

@@ -0,0 +1,316 @@
+// Copyright (c) 2017, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+import 'dart:io' as io;
+
+const _ansiEscapeLiteral = '\x1B';
+const _ansiEscapeForScript = r'\033';
+
+/// Whether formatted ANSI output is enabled for [wrapWith] and [AnsiCode.wrap].
+///
+/// By default, returns `true` if both `stdout.supportsAnsiEscapes` and
+/// `stderr.supportsAnsiEscapes` from `dart:io` are `true`.
+///
+/// The default can be overridden by setting the [Zone] variable [AnsiCode] to
+/// either `true` or `false`.
+///
+/// [overrideAnsiOutput] is provided to make this easy.
+bool get ansiOutputEnabled =>
+    Zone.current[AnsiCode] as bool? ??
+    (io.stdout.supportsAnsiEscapes && io.stderr.supportsAnsiEscapes);
+
+/// Returns `true` no formatting is required for [input].
+bool _isNoop(bool skip, String? input, bool? forScript) =>
+    skip ||
+    input == null ||
+    input.isEmpty ||
+    !((forScript ?? false) || ansiOutputEnabled);
+
+/// Allows overriding [ansiOutputEnabled] to [enableAnsiOutput] for the code run
+/// within [body].
+T overrideAnsiOutput<T>(bool enableAnsiOutput, T Function() body) =>
+    runZoned(body, zoneValues: <Object, Object>{AnsiCode: enableAnsiOutput});
+
+/// The type of code represented by [AnsiCode].
+class AnsiCodeType {
+  final String _name;
+
+  /// A foreground color.
+  static const AnsiCodeType foreground = AnsiCodeType._('foreground');
+
+  /// A style.
+  static const AnsiCodeType style = AnsiCodeType._('style');
+
+  /// A background color.
+  static const AnsiCodeType background = AnsiCodeType._('background');
+
+  /// A reset value.
+  static const AnsiCodeType reset = AnsiCodeType._('reset');
+
+  const AnsiCodeType._(this._name);
+
+  @override
+  String toString() => 'AnsiType.$_name';
+}
+
+/// Standard ANSI escape code for customizing terminal text output.
+///
+/// [Source](https://en.wikipedia.org/wiki/ANSI_escape_code#Colors)
+class AnsiCode {
+  /// The numeric value associated with this code.
+  final int code;
+
+  /// The [AnsiCode] that resets this value, if one exists.
+  ///
+  /// Otherwise, `null`.
+  final AnsiCode? reset;
+
+  /// A description of this code.
+  final String name;
+
+  /// The type of code that is represented.
+  final AnsiCodeType type;
+
+  const AnsiCode._(this.name, this.type, this.code, this.reset);
+
+  /// Represents the value escaped for use in terminal output.
+  String get escape => '$_ansiEscapeLiteral[${code}m';
+
+  /// Represents the value as an unescaped literal suitable for scripts.
+  String get escapeForScript => '$_ansiEscapeForScript[${code}m';
+
+  String _escapeValue({bool forScript = false}) =>
+      forScript ? escapeForScript : escape;
+
+  /// Wraps [value] with the [escape] value for this code, followed by
+  /// [resetAll].
+  ///
+  /// If [forScript] is `true`, the return value is an unescaped literal. The
+  /// value of [ansiOutputEnabled] is also ignored.
+  ///
+  /// Returns `value` unchanged if
+  ///   * [value] is `null` or empty
+  ///   * both [ansiOutputEnabled] and [forScript] are `false`.
+  ///   * [type] is [AnsiCodeType.reset]
+  String? wrap(String? value, {bool forScript = false}) =>
+      _isNoop(type == AnsiCodeType.reset, value, forScript)
+          ? value
+          : '${_escapeValue(forScript: forScript)}$value'
+              '${reset!._escapeValue(forScript: forScript)}';
+
+  @override
+  String toString() => '$name ${type._name} ($code)';
+}
+
+/// Returns a [String] formatted with [codes].
+///
+/// If [forScript] is `true`, the return value is an unescaped literal. The
+/// value of [ansiOutputEnabled] is also ignored.
+///
+/// Returns `value` unchanged if
+///   * [value] is `null` or empty.
+///   * both [ansiOutputEnabled] and [forScript] are `false`.
+///   * [codes] is empty.
+///
+/// Throws an [ArgumentError] if
+///   * [codes] contains more than one value of type [AnsiCodeType.foreground].
+///   * [codes] contains more than one value of type [AnsiCodeType.background].
+///   * [codes] contains any value of type [AnsiCodeType.reset].
+String? wrapWith(String? value, Iterable<AnsiCode> codes,
+    {bool forScript = false}) {
+  // Eliminate duplicates
+  final myCodes = codes.toSet();
+
+  if (_isNoop(myCodes.isEmpty, value, forScript)) {
+    return value;
+  }
+
+  var foreground = 0, background = 0;
+  for (var code in myCodes) {
+    switch (code.type) {
+      case AnsiCodeType.foreground:
+        foreground++;
+        if (foreground > 1) {
+          throw ArgumentError.value(codes, 'codes',
+              'Cannot contain more than one foreground color code.');
+        }
+      case AnsiCodeType.background:
+        background++;
+        if (background > 1) {
+          throw ArgumentError.value(codes, 'codes',
+              'Cannot contain more than one foreground color code.');
+        }
+      case AnsiCodeType.reset:
+        throw ArgumentError.value(
+            codes, 'codes', 'Cannot contain reset codes.');
+      case AnsiCodeType.style:
+        // Ignore.
+        break;
+    }
+  }
+
+  final sortedCodes = myCodes.map((ac) => ac.code).toList()..sort();
+  final escapeValue = forScript ? _ansiEscapeForScript : _ansiEscapeLiteral;
+
+  return "$escapeValue[${sortedCodes.join(';')}m$value"
+      '${resetAll._escapeValue(forScript: forScript)}';
+}
+
+//
+// Style values
+//
+
+const styleBold = AnsiCode._('bold', AnsiCodeType.style, 1, resetBold);
+const styleDim = AnsiCode._('dim', AnsiCodeType.style, 2, resetDim);
+const styleItalic = AnsiCode._('italic', AnsiCodeType.style, 3, resetItalic);
+const styleUnderlined =
+    AnsiCode._('underlined', AnsiCodeType.style, 4, resetUnderlined);
+const styleBlink = AnsiCode._('blink', AnsiCodeType.style, 5, resetBlink);
+const styleReverse = AnsiCode._('reverse', AnsiCodeType.style, 7, resetReverse);
+
+/// Not widely supported.
+const styleHidden = AnsiCode._('hidden', AnsiCodeType.style, 8, resetHidden);
+
+/// Not widely supported.
+const styleCrossedOut =
+    AnsiCode._('crossed out', AnsiCodeType.style, 9, resetCrossedOut);
+
+//
+// Reset values
+//
+
+const resetAll = AnsiCode._('all', AnsiCodeType.reset, 0, null);
+
+// NOTE: bold is weird. The reset code seems to be 22 sometimes – not 21
+// See https://gitlab.com/gnachman/iterm2/issues/3208
+const resetBold = AnsiCode._('bold', AnsiCodeType.reset, 22, null);
+const resetDim = AnsiCode._('dim', AnsiCodeType.reset, 22, null);
+const resetItalic = AnsiCode._('italic', AnsiCodeType.reset, 23, null);
+const resetUnderlined = AnsiCode._('underlined', AnsiCodeType.reset, 24, null);
+const resetBlink = AnsiCode._('blink', AnsiCodeType.reset, 25, null);
+const resetReverse = AnsiCode._('reverse', AnsiCodeType.reset, 27, null);
+const resetHidden = AnsiCode._('hidden', AnsiCodeType.reset, 28, null);
+const resetCrossedOut = AnsiCode._('crossed out', AnsiCodeType.reset, 29, null);
+
+//
+// Foreground values
+//
+
+const black = AnsiCode._('black', AnsiCodeType.foreground, 30, resetAll);
+const red = AnsiCode._('red', AnsiCodeType.foreground, 31, resetAll);
+const green = AnsiCode._('green', AnsiCodeType.foreground, 32, resetAll);
+const yellow = AnsiCode._('yellow', AnsiCodeType.foreground, 33, resetAll);
+const blue = AnsiCode._('blue', AnsiCodeType.foreground, 34, resetAll);
+const magenta = AnsiCode._('magenta', AnsiCodeType.foreground, 35, resetAll);
+const cyan = AnsiCode._('cyan', AnsiCodeType.foreground, 36, resetAll);
+const lightGray =
+    AnsiCode._('light gray', AnsiCodeType.foreground, 37, resetAll);
+const defaultForeground =
+    AnsiCode._('default', AnsiCodeType.foreground, 39, resetAll);
+const darkGray = AnsiCode._('dark gray', AnsiCodeType.foreground, 90, resetAll);
+const lightRed = AnsiCode._('light red', AnsiCodeType.foreground, 91, resetAll);
+const lightGreen =
+    AnsiCode._('light green', AnsiCodeType.foreground, 92, resetAll);
+const lightYellow =
+    AnsiCode._('light yellow', AnsiCodeType.foreground, 93, resetAll);
+const lightBlue =
+    AnsiCode._('light blue', AnsiCodeType.foreground, 94, resetAll);
+const lightMagenta =
+    AnsiCode._('light magenta', AnsiCodeType.foreground, 95, resetAll);
+const lightCyan =
+    AnsiCode._('light cyan', AnsiCodeType.foreground, 96, resetAll);
+const white = AnsiCode._('white', AnsiCodeType.foreground, 97, resetAll);
+
+//
+// Background values
+//
+
+const backgroundBlack =
+    AnsiCode._('black', AnsiCodeType.background, 40, resetAll);
+const backgroundRed = AnsiCode._('red', AnsiCodeType.background, 41, resetAll);
+const backgroundGreen =
+    AnsiCode._('green', AnsiCodeType.background, 42, resetAll);
+const backgroundYellow =
+    AnsiCode._('yellow', AnsiCodeType.background, 43, resetAll);
+const backgroundBlue =
+    AnsiCode._('blue', AnsiCodeType.background, 44, resetAll);
+const backgroundMagenta =
+    AnsiCode._('magenta', AnsiCodeType.background, 45, resetAll);
+const backgroundCyan =
+    AnsiCode._('cyan', AnsiCodeType.background, 46, resetAll);
+const backgroundLightGray =
+    AnsiCode._('light gray', AnsiCodeType.background, 47, resetAll);
+const backgroundDefault =
+    AnsiCode._('default', AnsiCodeType.background, 49, resetAll);
+const backgroundDarkGray =
+    AnsiCode._('dark gray', AnsiCodeType.background, 100, resetAll);
+const backgroundLightRed =
+    AnsiCode._('light red', AnsiCodeType.background, 101, resetAll);
+const backgroundLightGreen =
+    AnsiCode._('light green', AnsiCodeType.background, 102, resetAll);
+const backgroundLightYellow =
+    AnsiCode._('light yellow', AnsiCodeType.background, 103, resetAll);
+const backgroundLightBlue =
+    AnsiCode._('light blue', AnsiCodeType.background, 104, resetAll);
+const backgroundLightMagenta =
+    AnsiCode._('light magenta', AnsiCodeType.background, 105, resetAll);
+const backgroundLightCyan =
+    AnsiCode._('light cyan', AnsiCodeType.background, 106, resetAll);
+const backgroundWhite =
+    AnsiCode._('white', AnsiCodeType.background, 107, resetAll);
+
+/// All of the [AnsiCode] values that represent [AnsiCodeType.style].
+const List<AnsiCode> styles = [
+  styleBold,
+  styleDim,
+  styleItalic,
+  styleUnderlined,
+  styleBlink,
+  styleReverse,
+  styleHidden,
+  styleCrossedOut
+];
+
+/// All of the [AnsiCode] values that represent [AnsiCodeType.foreground].
+const List<AnsiCode> foregroundColors = [
+  black,
+  red,
+  green,
+  yellow,
+  blue,
+  magenta,
+  cyan,
+  lightGray,
+  defaultForeground,
+  darkGray,
+  lightRed,
+  lightGreen,
+  lightYellow,
+  lightBlue,
+  lightMagenta,
+  lightCyan,
+  white
+];
+
+/// All of the [AnsiCode] values that represent [AnsiCodeType.background].
+const List<AnsiCode> backgroundColors = [
+  backgroundBlack,
+  backgroundRed,
+  backgroundGreen,
+  backgroundYellow,
+  backgroundBlue,
+  backgroundMagenta,
+  backgroundCyan,
+  backgroundLightGray,
+  backgroundDefault,
+  backgroundDarkGray,
+  backgroundLightRed,
+  backgroundLightGreen,
+  backgroundLightYellow,
+  backgroundLightBlue,
+  backgroundLightMagenta,
+  backgroundLightCyan,
+  backgroundWhite
+];

diff --git a/pkgs/io/lib/src/charcodes.dart b/pkgs/io/lib/src/charcodes.dart
new file mode 100644
index 0000000..4acaf0a
--- /dev/null
+++ b/pkgs/io/lib/src/charcodes.dart

@@ -0,0 +1,34 @@
+// Copyright (c) 2021, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Generated using:
+//  pub global run charcode \$=dollar \'=single_quote \"=double_quote \
+//      \' '\\\n"$`# \t'
+
+/// "Horizontal Tab" control character, common name.
+const int $tab = 0x09;
+
+/// "Line feed" control character.
+const int $lf = 0x0a;
+
+/// Space character.
+const int $space = 0x20;
+
+/// Character `"`, short name.
+const int $doubleQuote = 0x22;
+
+/// Character `#`.
+const int $hash = 0x23;
+
+/// Character `$`.
+const int $dollar = 0x24;
+
+/// Character "'".
+const int $singleQuote = 0x27;
+
+/// Character `\`.
+const int $backslash = 0x5c;
+
+/// Character `` ` ``.
+const int $backquote = 0x60;

diff --git a/pkgs/io/lib/src/copy_path.dart b/pkgs/io/lib/src/copy_path.dart
new file mode 100644
index 0000000..3a999b6
--- /dev/null
+++ b/pkgs/io/lib/src/copy_path.dart

@@ -0,0 +1,69 @@
+// Copyright (c) 2017, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:io';
+
+import 'package:path/path.dart' as p;
+
+bool _doNothing(String from, String to) {
+  if (p.canonicalize(from) == p.canonicalize(to)) {
+    return true;
+  }
+  if (p.isWithin(from, to)) {
+    throw ArgumentError('Cannot copy from $from to $to');
+  }
+  return false;
+}
+
+/// Copies all of the files in the [from] directory to [to].
+///
+/// This is similar to `cp -R <from> <to>`:
+/// * Symlinks are supported.
+/// * Existing files are over-written, if any.
+/// * If [to] is within [from], throws [ArgumentError] (an infinite operation).
+/// * If [from] and [to] are canonically the same, no operation occurs.
+///
+/// Returns a future that completes when complete.
+Future<void> copyPath(String from, String to) async {
+  if (_doNothing(from, to)) {
+    return;
+  }
+  await Directory(to).create(recursive: true);
+  await for (final file in Directory(from).list(recursive: true)) {
+    final copyTo = p.join(to, p.relative(file.path, from: from));
+    if (file is Directory) {
+      await Directory(copyTo).create(recursive: true);
+    } else if (file is File) {
+      await File(file.path).copy(copyTo);
+    } else if (file is Link) {
+      await Link(copyTo).create(await file.target(), recursive: true);
+    }
+  }
+}
+
+/// Copies all of the files in the [from] directory to [to].
+///
+/// This is similar to `cp -R <from> <to>`:
+/// * Symlinks are supported.
+/// * Existing files are over-written, if any.
+/// * If [to] is within [from], throws [ArgumentError] (an infinite operation).
+/// * If [from] and [to] are canonically the same, no operation occurs.
+///
+/// This action is performed synchronously (blocking I/O).
+void copyPathSync(String from, String to) {
+  if (_doNothing(from, to)) {
+    return;
+  }
+  Directory(to).createSync(recursive: true);
+  for (final file in Directory(from).listSync(recursive: true)) {
+    final copyTo = p.join(to, p.relative(file.path, from: from));
+    if (file is Directory) {
+      Directory(copyTo).createSync(recursive: true);
+    } else if (file is File) {
+      File(file.path).copySync(copyTo);
+    } else if (file is Link) {
+      Link(copyTo).createSync(file.targetSync(), recursive: true);
+    }
+  }
+}

diff --git a/pkgs/io/lib/src/exit_code.dart b/pkgs/io/lib/src/exit_code.dart
new file mode 100644
index 0000000..d405558
--- /dev/null
+++ b/pkgs/io/lib/src/exit_code.dart

@@ -0,0 +1,82 @@
+// Copyright (c) 2017, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Exit code constants.
+///
+/// [Source](https://www.freebsd.org/cgi/man.cgi?query=sysexits).
+class ExitCode {
+  /// Command completed successfully.
+  static const success = ExitCode._(0, 'success');
+
+  /// Command was used incorrectly.
+  ///
+  /// This may occur if the wrong number of arguments was used, a bad flag, or
+  /// bad syntax in a parameter.
+  static const usage = ExitCode._(64, 'usage');
+
+  /// Input data was used incorrectly.
+  ///
+  /// This should occur only for user data (not system files).
+  static const data = ExitCode._(65, 'data');
+
+  /// An input file (not a system file) did not exist or was not readable.
+  static const noInput = ExitCode._(66, 'noInput');
+
+  /// User specified did not exist.
+  static const noUser = ExitCode._(67, 'noUser');
+
+  /// Host specified did not exist.
+  static const noHost = ExitCode._(68, 'noHost');
+
+  /// A service is unavailable.
+  ///
+  /// This may occur if a support program or file does not exist. This may also
+  /// be used as a catch-all error when something you wanted to do does not
+  /// work, but you do not know why.
+  static const unavailable = ExitCode._(69, 'unavailable');
+
+  /// An internal software error has been detected.
+  ///
+  /// This should be limited to non-operating system related errors as possible.
+  static const software = ExitCode._(70, 'software');
+
+  /// An operating system error has been detected.
+  ///
+  /// This intended to be used for such thing as `cannot fork` or `cannot pipe`.
+  static const osError = ExitCode._(71, 'osError');
+
+  /// Some system file (e.g. `/etc/passwd`) does not exist or could not be read.
+  static const osFile = ExitCode._(72, 'osFile');
+
+  /// A (user specified) output file cannot be created.
+  static const cantCreate = ExitCode._(73, 'cantCreate');
+
+  /// An error occurred doing I/O on some file.
+  static const ioError = ExitCode._(74, 'ioError');
+
+  /// Temporary failure, indicating something is not really an error.
+  ///
+  /// In some cases, this can be re-attempted and will succeed later.
+  static const tempFail = ExitCode._(75, 'tempFail');
+
+  /// You did not have sufficient permissions to perform the operation.
+  ///
+  /// This is not intended for file system problems, which should use [noInput]
+  /// or [cantCreate], but rather for higher-level permissions.
+  static const noPerm = ExitCode._(77, 'noPerm');
+
+  /// Something was found in an unconfigured or misconfigured state.
+  static const config = ExitCode._(78, 'config');
+
+  /// Exit code value.
+  final int code;
+
+  /// Name of the exit code.
+  final String _name;
+
+  const ExitCode._(this.code, this._name);
+
+  @override
+  String toString() => '$_name: $code';
+}

diff --git a/pkgs/io/lib/src/permissions.dart b/pkgs/io/lib/src/permissions.dart
new file mode 100644
index 0000000..c516943
--- /dev/null
+++ b/pkgs/io/lib/src/permissions.dart

@@ -0,0 +1,69 @@
+// Copyright (c) 2017, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+import 'dart:io';
+
+/// What type of permission is granted to a file based on file permission roles.
+enum _FilePermission {
+  execute,
+  // Although these two values are unused, their positions in the enum are
+  // meaningful.
+  write, // ignore: unused_field
+  read, // ignore: unused_field
+  setGid,
+  setUid,
+  sticky,
+}
+
+/// What type of role is assigned to a file.
+enum _FilePermissionRole {
+  world,
+  group,
+  user,
+}
+
+/// Returns whether file [stat] has [permission] for a [role] type.
+bool _hasPermission(
+  FileStat stat,
+  _FilePermission permission, {
+  _FilePermissionRole role = _FilePermissionRole.world,
+}) {
+  final index = _permissionBitIndex(permission, role);
+  return (stat.mode & (1 << index)) != 0;
+}
+
+int _permissionBitIndex(_FilePermission permission, _FilePermissionRole role) =>
+    switch (permission) {
+      _FilePermission.setUid => 11,
+      _FilePermission.setGid => 10,
+      _FilePermission.sticky => 9,
+      _ => (role.index * 3) + permission.index
+    };
+
+/// Returns whether [path] is considered an executable file on this OS.
+///
+/// May optionally define how to implement [getStat] or whether to execute based
+/// on whether this is the windows platform ([isWindows]) - if not set it is
+/// automatically extracted from `dart:io#Platform`.
+///
+/// **NOTE**: On windows this always returns `true`.
+FutureOr<bool> isExecutable(
+  String path, {
+  bool? isWindows,
+  FutureOr<FileStat> Function(String path) getStat = FileStat.stat,
+}) {
+  // Windows has no concept of executable.
+  if (isWindows ?? Platform.isWindows) return true;
+  final stat = getStat(path);
+  if (stat is FileStat) {
+    return _isExecutable(stat);
+  }
+  return stat.then(_isExecutable);
+}
+
+bool _isExecutable(FileStat stat) =>
+    stat.type == FileSystemEntityType.file &&
+    _FilePermissionRole.values.any(
+        (role) => _hasPermission(stat, _FilePermission.execute, role: role));

diff --git a/pkgs/io/lib/src/process_manager.dart b/pkgs/io/lib/src/process_manager.dart
new file mode 100644
index 0000000..84d22ec
--- /dev/null
+++ b/pkgs/io/lib/src/process_manager.dart

@@ -0,0 +1,255 @@
+// Copyright (c) 2017, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// ignore_for_file: close_sinks,cancel_subscriptions
+
+import 'dart:async';
+import 'dart:io' as io;
+
+import 'package:meta/meta.dart';
+
+import 'shared_stdin.dart';
+
+/// Type definition for both [io.Process.start] and [ProcessManager.spawn].
+///
+/// Useful for taking different implementations of this base functionality.
+typedef StartProcess = Future<io.Process> Function(
+  String executable,
+  List<String> arguments, {
+  String workingDirectory,
+  Map<String, String> environment,
+  bool includeParentEnvironment,
+  bool runInShell,
+  io.ProcessStartMode mode,
+});
+
+/// A high-level abstraction around using and managing processes on the system.
+abstract class ProcessManager {
+  /// Terminates the global `stdin` listener, making future listens impossible.
+  ///
+  /// This method should be invoked only at the _end_ of a program's execution.
+  static Future<void> terminateStdIn() async {
+    await sharedStdIn.terminate();
+  }
+
+  /// Create a new instance of [ProcessManager] for the current platform.
+  ///
+  /// May manually specify whether the current platform [isWindows], otherwise
+  /// this is derived from the Dart runtime (i.e. [io.Platform.isWindows]).
+  factory ProcessManager({
+    Stream<List<int>>? stdin,
+    io.IOSink? stdout,
+    io.IOSink? stderr,
+    bool? isWindows,
+  }) {
+    stdin ??= sharedStdIn;
+    stdout ??= io.stdout;
+    stderr ??= io.stderr;
+    isWindows ??= io.Platform.isWindows;
+    if (isWindows) {
+      return _WindowsProcessManager(stdin, stdout, stderr);
+    }
+    return _UnixProcessManager(stdin, stdout, stderr);
+  }
+
+  final Stream<List<int>> _stdin;
+  final io.IOSink _stdout;
+  final io.IOSink _stderr;
+
+  const ProcessManager._(this._stdin, this._stdout, this._stderr);
+
+  /// Spawns a process by invoking [executable] with [arguments].
+  ///
+  /// This is _similar_ to [io.Process.start], but all standard input and output
+  /// is forwarded/routed between the process and the host, similar to how a
+  /// shell script works.
+  ///
+  /// Returns a future that completes with a handle to the spawned process.
+  Future<io.Process> spawn(
+    String executable,
+    Iterable<String> arguments, {
+    String? workingDirectory,
+    Map<String, String>? environment,
+    bool includeParentEnvironment = true,
+    bool runInShell = false,
+    io.ProcessStartMode mode = io.ProcessStartMode.normal,
+  }) async {
+    final process = io.Process.start(
+      executable,
+      arguments.toList(),
+      workingDirectory: workingDirectory,
+      environment: environment,
+      includeParentEnvironment: includeParentEnvironment,
+      runInShell: runInShell,
+      mode: mode,
+    );
+    return _ForwardingSpawn(await process, _stdin, _stdout, _stderr);
+  }
+
+  /// Spawns a process by invoking [executable] with [arguments].
+  ///
+  /// This is _similar_ to [io.Process.start], but `stdout` and `stderr` is
+  /// forwarded/routed between the process and host, similar to how a shell
+  /// script works.
+  ///
+  /// Returns a future that completes with a handle to the spawned process.
+  Future<io.Process> spawnBackground(
+    String executable,
+    Iterable<String> arguments, {
+    String? workingDirectory,
+    Map<String, String>? environment,
+    bool includeParentEnvironment = true,
+    bool runInShell = false,
+    io.ProcessStartMode mode = io.ProcessStartMode.normal,
+  }) async {
+    final process = io.Process.start(
+      executable,
+      arguments.toList(),
+      workingDirectory: workingDirectory,
+      environment: environment,
+      includeParentEnvironment: includeParentEnvironment,
+      runInShell: runInShell,
+      mode: mode,
+    );
+    return _ForwardingSpawn(
+      await process,
+      const Stream.empty(),
+      _stdout,
+      _stderr,
+    );
+  }
+
+  /// Spawns a process by invoking [executable] with [arguments].
+  ///
+  /// This is _identical to [io.Process.start] (no forwarding of I/O).
+  ///
+  /// Returns a future that completes with a handle to the spawned process.
+  Future<io.Process> spawnDetached(
+    String executable,
+    Iterable<String> arguments, {
+    String? workingDirectory,
+    Map<String, String>? environment,
+    bool includeParentEnvironment = true,
+    bool runInShell = false,
+    io.ProcessStartMode mode = io.ProcessStartMode.normal,
+  }) async =>
+      io.Process.start(
+        executable,
+        arguments.toList(),
+        workingDirectory: workingDirectory,
+        environment: environment,
+        includeParentEnvironment: includeParentEnvironment,
+        runInShell: runInShell,
+        mode: mode,
+      );
+}
+
+/// A process instance created and managed through [ProcessManager].
+///
+/// Unlike one created directly by [io.Process.start] or [io.Process.run], a
+/// spawned process works more like executing a command in a shell script.
+class Spawn implements io.Process {
+  final io.Process _delegate;
+
+  Spawn._(this._delegate) {
+    _delegate.exitCode.then((_) => _onClosed());
+  }
+
+  @mustCallSuper
+  void _onClosed() {}
+
+  @override
+  bool kill([io.ProcessSignal signal = io.ProcessSignal.sigterm]) =>
+      _delegate.kill(signal);
+
+  @override
+  Future<int> get exitCode => _delegate.exitCode;
+
+  @override
+  int get pid => _delegate.pid;
+
+  @override
+  Stream<List<int>> get stderr => _delegate.stderr;
+
+  @override
+  io.IOSink get stdin => _delegate.stdin;
+
+  @override
+  Stream<List<int>> get stdout => _delegate.stdout;
+}
+
+/// Forwards `stdin`/`stdout`/`stderr` to/from the host.
+class _ForwardingSpawn extends Spawn {
+  final StreamSubscription<List<int>> _stdInSub;
+  final StreamSubscription<List<int>> _stdOutSub;
+  final StreamSubscription<List<int>> _stdErrSub;
+  final StreamController<List<int>> _stdOut;
+  final StreamController<List<int>> _stdErr;
+
+  factory _ForwardingSpawn(
+    io.Process delegate,
+    Stream<List<int>> stdin,
+    io.IOSink stdout,
+    io.IOSink stderr,
+  ) {
+    final stdoutSelf = StreamController<List<int>>();
+    final stderrSelf = StreamController<List<int>>();
+    final stdInSub = stdin.listen(delegate.stdin.add);
+    final stdOutSub = delegate.stdout.listen((event) {
+      stdout.add(event);
+      stdoutSelf.add(event);
+    });
+    final stdErrSub = delegate.stderr.listen((event) {
+      stderr.add(event);
+      stderrSelf.add(event);
+    });
+    return _ForwardingSpawn._delegate(
+      delegate,
+      stdInSub,
+      stdOutSub,
+      stdErrSub,
+      stdoutSelf,
+      stderrSelf,
+    );
+  }
+
+  _ForwardingSpawn._delegate(
+    super.delegate,
+    this._stdInSub,
+    this._stdOutSub,
+    this._stdErrSub,
+    this._stdOut,
+    this._stdErr,
+  ) : super._();
+
+  @override
+  void _onClosed() {
+    _stdInSub.cancel();
+    _stdOutSub.cancel();
+    _stdErrSub.cancel();
+    super._onClosed();
+  }
+
+  @override
+  Stream<List<int>> get stdout => _stdOut.stream;
+
+  @override
+  Stream<List<int>> get stderr => _stdErr.stream;
+}
+
+class _UnixProcessManager extends ProcessManager {
+  const _UnixProcessManager(
+    super.stdin,
+    super.stdout,
+    super.stderr,
+  ) : super._();
+}
+
+class _WindowsProcessManager extends ProcessManager {
+  const _WindowsProcessManager(
+    super.stdin,
+    super.stdout,
+    super.stderr,
+  ) : super._();
+}

diff --git a/pkgs/io/lib/src/shared_stdin.dart b/pkgs/io/lib/src/shared_stdin.dart
new file mode 100644
index 0000000..72bb50c
--- /dev/null
+++ b/pkgs/io/lib/src/shared_stdin.dart

@@ -0,0 +1,99 @@
+// Copyright (c) 2017, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+import 'dart:convert';
+import 'dart:io';
+
+import 'package:meta/meta.dart';
+
+/// A shared singleton instance of `dart:io`'s [stdin] stream.
+///
+/// _Unlike_ the normal [stdin] stream, [sharedStdIn] may switch subscribers
+/// as long as the previous subscriber cancels before the new subscriber starts
+/// listening.
+///
+/// [SharedStdIn.terminate] *must* be invoked in order to close the underlying
+/// connection to [stdin], allowing your program to close automatically without
+/// hanging.
+final SharedStdIn sharedStdIn = SharedStdIn(stdin);
+
+/// A singleton wrapper around `stdin` that allows new subscribers.
+///
+/// This class is visible in order to be used as a test harness for mock
+/// implementations of `stdin`. In normal programs, [sharedStdIn] should be
+/// used directly.
+@visibleForTesting
+class SharedStdIn extends Stream<List<int>> {
+  StreamController<List<int>>? _current;
+  StreamSubscription<List<int>>? _sub;
+
+  SharedStdIn([Stream<List<int>>? stream]) {
+    _sub = (stream ??= stdin).listen(_onInput);
+  }
+
+  /// Returns a future that completes with the next line.
+  ///
+  /// This is similar to the standard [Stdin.readLineSync], but asynchronous.
+  Future<String> nextLine({Encoding encoding = systemEncoding}) =>
+      lines(encoding: encoding).first;
+
+  /// Returns the stream transformed as UTF8 strings separated by line breaks.
+  ///
+  /// This is similar to synchronous code using [Stdin.readLineSync]:
+  /// ```dart
+  /// while (true) {
+  ///   var line = stdin.readLineSync();
+  ///   // ...
+  /// }
+  /// ```
+  ///
+  /// ... but asynchronous.
+  Stream<String> lines({Encoding encoding = systemEncoding}) =>
+      transform(utf8.decoder).transform(const LineSplitter());
+
+  void _onInput(List<int> event) => _getCurrent().add(event);
+
+  StreamController<List<int>> _getCurrent() =>
+      _current ??= StreamController<List<int>>(
+          onCancel: () {
+            _current = null;
+          },
+          sync: true);
+
+  @override
+  StreamSubscription<List<int>> listen(
+    void Function(List<int> event)? onData, {
+    Function? onError,
+    void Function()? onDone,
+    bool? cancelOnError,
+  }) {
+    if (_sub == null) {
+      throw StateError('Stdin has already been terminated.');
+    }
+    // ignore: close_sinks
+    final controller = _getCurrent();
+    if (controller.hasListener) {
+      throw StateError(''
+          'Subscriber already listening. The existing subscriber must cancel '
+          'before another may be added.');
+    }
+    return controller.stream.listen(
+      onData,
+      onDone: onDone,
+      onError: onError,
+      cancelOnError: cancelOnError,
+    );
+  }
+
+  /// Terminates the connection to `stdin`, closing all subscription.
+  Future<void> terminate() async {
+    if (_sub == null) {
+      throw StateError('Stdin has already been terminated.');
+    }
+    await _sub?.cancel();
+    await _current?.close();
+    _sub = null;
+  }
+}

diff --git a/pkgs/io/lib/src/shell_words.dart b/pkgs/io/lib/src/shell_words.dart
new file mode 100644
index 0000000..5fca6d9
--- /dev/null
+++ b/pkgs/io/lib/src/shell_words.dart

@@ -0,0 +1,142 @@
+// Copyright (c) 2017, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// ignore_for_file: comment_references
+
+import 'package:string_scanner/string_scanner.dart';
+
+import 'charcodes.dart';
+
+/// Splits [command] into tokens according to [the POSIX shell
+/// specification][spec].
+///
+/// [spec]: http://pubs.opengroup.org/onlinepubs/9699919799/utilities/contents.html
+///
+/// This returns the unquoted values of quoted tokens. For example,
+/// `shellSplit('foo "bar baz"')` returns `["foo", "bar baz"]`. It does not
+/// currently support here-documents. It does *not* treat dynamic features such
+/// as parameter expansion specially. For example, `shellSplit("foo $(bar
+/// baz)")` returns `["foo", "$(bar", "baz)"]`.
+///
+/// This will discard any comments at the end of [command].
+///
+/// Throws a [FormatException] if [command] isn't a valid shell command.
+List<String> shellSplit(String command) {
+  final scanner = StringScanner(command);
+  final results = <String>[];
+  final token = StringBuffer();
+
+  // Whether a token is being parsed, as opposed to a separator character. This
+  // is different than just [token.isEmpty], because empty quoted tokens can
+  // exist.
+  var hasToken = false;
+
+  while (!scanner.isDone) {
+    final next = scanner.readChar();
+    switch (next) {
+      case $backslash:
+        // Section 2.2.1: A <backslash> that is not quoted shall preserve the
+        // literal value of the following character, with the exception of a
+        // <newline>. If a <newline> follows the <backslash>, the shell shall
+        // interpret this as line continuation. The <backslash> and <newline>
+        // shall be removed before splitting the input into tokens. Since the
+        // escaped <newline> is removed entirely from the input and is not
+        // replaced by any white space, it cannot serve as a token separator.
+        if (scanner.scanChar($lf)) break;
+
+        hasToken = true;
+        token.writeCharCode(scanner.readChar());
+
+      case $singleQuote:
+        hasToken = true;
+        // Section 2.2.2: Enclosing characters in single-quotes ( '' ) shall
+        // preserve the literal value of each character within the
+        // single-quotes. A single-quote cannot occur within single-quotes.
+        final firstQuote = scanner.position - 1;
+        while (!scanner.scanChar($singleQuote)) {
+          _checkUnmatchedQuote(scanner, firstQuote);
+          token.writeCharCode(scanner.readChar());
+        }
+
+      case $doubleQuote:
+        hasToken = true;
+        // Section 2.2.3: Enclosing characters in double-quotes ( "" ) shall
+        // preserve the literal value of all characters within the
+        // double-quotes, with the exception of the characters backquote,
+        // <dollar-sign>, and <backslash>.
+        //
+        // (Note that this code doesn't preserve special behavior of backquote
+        // or dollar sign within double quotes, since those are dynamic
+        // features.)
+        final firstQuote = scanner.position - 1;
+        while (!scanner.scanChar($doubleQuote)) {
+          _checkUnmatchedQuote(scanner, firstQuote);
+
+          if (scanner.scanChar($backslash)) {
+            _checkUnmatchedQuote(scanner, firstQuote);
+
+            // The <backslash> shall retain its special meaning as an escape
+            // character (see Escape Character (Backslash)) only when followed
+            // by one of the following characters when considered special:
+            //
+            //     $ ` " \ <newline>
+            final next = scanner.readChar();
+            if (next == $lf) continue;
+            if (next == $dollar ||
+                next == $backquote ||
+                next == $doubleQuote ||
+                next == $backslash) {
+              token.writeCharCode(next);
+            } else {
+              token
+                ..writeCharCode($backslash)
+                ..writeCharCode(next);
+            }
+          } else {
+            token.writeCharCode(scanner.readChar());
+          }
+        }
+
+      case $hash:
+        // Section 2.3: If the current character is a '#' [and the previous
+        // characters was not part of a word], it and all subsequent characters
+        // up to, but excluding, the next <newline> shall be discarded as a
+        // comment. The <newline> that ends the line is not considered part of
+        // the comment.
+        if (hasToken) {
+          token.writeCharCode($hash);
+          break;
+        }
+
+        while (!scanner.isDone && scanner.peekChar() != $lf) {
+          scanner.readChar();
+        }
+
+      case $space:
+      case $tab:
+      case $lf:
+        // ignore: invariant_booleans
+        if (hasToken) results.add(token.toString());
+        hasToken = false;
+        token.clear();
+
+      default:
+        hasToken = true;
+        token.writeCharCode(next);
+    }
+  }
+
+  if (hasToken) results.add(token.toString());
+  return results;
+}
+
+/// Throws a [FormatException] if [scanner] is done indicating that a closing
+/// quote matching the one at position [openingQuote] is missing.
+void _checkUnmatchedQuote(StringScanner scanner, int openingQuote) {
+  if (!scanner.isDone) return;
+  final type = scanner.substring(openingQuote, openingQuote + 1) == '"'
+      ? 'double'
+      : 'single';
+  scanner.error('Unmatched $type quote.', position: openingQuote, length: 1);
+}

diff --git a/pkgs/io/pubspec.yaml b/pkgs/io/pubspec.yaml
new file mode 100644
index 0000000..7e00d99
--- /dev/null
+++ b/pkgs/io/pubspec.yaml

@@ -0,0 +1,19 @@
+name: io
+description: >-
+  Utilities for the Dart VM Runtime including support for ANSI colors, file
+  copying, and standard exit code values.
+version: 1.0.5
+repository: https://github.com/dart-lang/tools/tree/main/pkgs/io
+
+environment:
+  sdk: ^3.4.0
+
+dependencies:
+  meta: ^1.3.0
+  path: ^1.8.0
+  string_scanner: ^1.1.0
+
+dev_dependencies:
+  dart_flutter_team_lints: ^3.0.0
+  test: ^1.16.6
+  test_descriptor: ^2.0.0

diff --git a/pkgs/io/test/_files/is_executable.sh b/pkgs/io/test/_files/is_executable.sh
new file mode 100755
index 0000000..f1f641a
--- /dev/null
+++ b/pkgs/io/test/_files/is_executable.sh

@@ -0,0 +1 @@
+#!/usr/bin/env bash

diff --git a/pkgs/io/test/_files/is_not_executable.sh b/pkgs/io/test/_files/is_not_executable.sh
new file mode 100644
index 0000000..f1f641a
--- /dev/null
+++ b/pkgs/io/test/_files/is_not_executable.sh

@@ -0,0 +1 @@
+#!/usr/bin/env bash

diff --git a/pkgs/io/test/_files/stderr_hello.dart b/pkgs/io/test/_files/stderr_hello.dart
new file mode 100644
index 0000000..ac7a7d3
--- /dev/null
+++ b/pkgs/io/test/_files/stderr_hello.dart

@@ -0,0 +1,7 @@
+// Copyright (c) 2017, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:io';
+
+void main() => stderr.write('Hello');

diff --git a/pkgs/io/test/_files/stdin_echo.dart b/pkgs/io/test/_files/stdin_echo.dart
new file mode 100644
index 0000000..256e0ee
--- /dev/null
+++ b/pkgs/io/test/_files/stdin_echo.dart

@@ -0,0 +1,7 @@
+// Copyright (c) 2017, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:io';
+
+void main() => stdout.writeln('You said: ${stdin.readLineSync()}');

diff --git a/pkgs/io/test/_files/stdout_hello.dart b/pkgs/io/test/_files/stdout_hello.dart
new file mode 100644
index 0000000..af3bf51
--- /dev/null
+++ b/pkgs/io/test/_files/stdout_hello.dart

@@ -0,0 +1,7 @@
+// Copyright (c) 2017, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:io';
+
+void main() => stdout.write('Hello');

diff --git a/pkgs/io/test/ansi_code_test.dart b/pkgs/io/test/ansi_code_test.dart
new file mode 100644
index 0000000..98ae68b
--- /dev/null
+++ b/pkgs/io/test/ansi_code_test.dart

@@ -0,0 +1,187 @@
+// Copyright (c) 2017, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+@TestOn('vm')
+library;
+
+import 'dart:io';
+
+import 'package:io/ansi.dart';
+import 'package:test/test.dart';
+
+const _ansiEscapeLiteral = '\x1B';
+const _ansiEscapeForScript = r'\033';
+const sampleInput = 'sample input';
+
+void main() {
+  group('ansiOutputEnabled', () {
+    test('default value matches dart:io', () {
+      expect(ansiOutputEnabled,
+          stdout.supportsAnsiEscapes && stderr.supportsAnsiEscapes);
+    });
+
+    test('override true', () {
+      overrideAnsiOutput(true, () {
+        expect(ansiOutputEnabled, isTrue);
+      });
+    });
+
+    test('override false', () {
+      overrideAnsiOutput(false, () {
+        expect(ansiOutputEnabled, isFalse);
+      });
+    });
+
+    test('forScript variaents ignore `ansiOutputEnabled`', () {
+      const expected =
+          '$_ansiEscapeForScript[34m$sampleInput$_ansiEscapeForScript[0m';
+
+      for (var override in [true, false]) {
+        overrideAnsiOutput(override, () {
+          expect(blue.escapeForScript, '$_ansiEscapeForScript[34m');
+          expect(blue.wrap(sampleInput, forScript: true), expected);
+          expect(wrapWith(sampleInput, [blue], forScript: true), expected);
+        });
+      }
+    });
+  });
+
+  test('foreground and background colors match', () {
+    expect(foregroundColors, hasLength(backgroundColors.length));
+
+    for (var i = 0; i < foregroundColors.length; i++) {
+      final foreground = foregroundColors[i];
+      expect(foreground.type, AnsiCodeType.foreground);
+      expect(foreground.name.toLowerCase(), foreground.name,
+          reason: 'All names should be lower case');
+      final background = backgroundColors[i];
+      expect(background.type, AnsiCodeType.background);
+      expect(background.name.toLowerCase(), background.name,
+          reason: 'All names should be lower case');
+
+      expect(foreground.name, background.name);
+
+      // The last base-10 digit also matches – good to sanity check
+      expect(foreground.code % 10, background.code % 10);
+    }
+  });
+
+  test('all styles are styles', () {
+    for (var style in styles) {
+      expect(style.type, AnsiCodeType.style);
+      expect(style.name.toLowerCase(), style.name,
+          reason: 'All names should be lower case');
+      if (style == styleBold) {
+        expect(style.reset, resetBold);
+      } else {
+        expect(style.reset!.code, equals(style.code + 20));
+      }
+      expect(style.name, equals(style.reset!.name));
+    }
+  });
+
+  for (var forScript in [true, false]) {
+    group(forScript ? 'forScript' : 'escaped', () {
+      final escapeLiteral =
+          forScript ? _ansiEscapeForScript : _ansiEscapeLiteral;
+
+      group('wrap', () {
+        _test('color', () {
+          final expected = '$escapeLiteral[34m$sampleInput$escapeLiteral[0m';
+
+          expect(blue.wrap(sampleInput, forScript: forScript), expected);
+        });
+
+        _test('style', () {
+          final expected = '$escapeLiteral[1m$sampleInput$escapeLiteral[22m';
+
+          expect(styleBold.wrap(sampleInput, forScript: forScript), expected);
+        });
+
+        _test('style', () {
+          final expected = '$escapeLiteral[34m$sampleInput$escapeLiteral[0m';
+
+          expect(blue.wrap(sampleInput, forScript: forScript), expected);
+        });
+
+        test('empty', () {
+          expect(blue.wrap('', forScript: forScript), '');
+        });
+
+        test(null, () {
+          expect(blue.wrap(null, forScript: forScript), isNull);
+        });
+      });
+
+      group('wrapWith', () {
+        _test('foreground', () {
+          final expected = '$escapeLiteral[34m$sampleInput$escapeLiteral[0m';
+
+          expect(wrapWith(sampleInput, [blue], forScript: forScript), expected);
+        });
+
+        _test('background', () {
+          final expected = '$escapeLiteral[44m$sampleInput$escapeLiteral[0m';
+
+          expect(wrapWith(sampleInput, [backgroundBlue], forScript: forScript),
+              expected);
+        });
+
+        _test('style', () {
+          final expected = '$escapeLiteral[1m$sampleInput$escapeLiteral[0m';
+
+          expect(wrapWith(sampleInput, [styleBold], forScript: forScript),
+              expected);
+        });
+
+        _test('2 styles', () {
+          final expected = '$escapeLiteral[1;3m$sampleInput$escapeLiteral[0m';
+
+          expect(
+              wrapWith(sampleInput, [styleBold, styleItalic],
+                  forScript: forScript),
+              expected);
+        });
+
+        _test('2 foregrounds', () {
+          expect(
+              () => wrapWith(sampleInput, [blue, white], forScript: forScript),
+              throwsArgumentError);
+        });
+
+        _test('multi', () {
+          final expected =
+              '$escapeLiteral[1;4;34;107m$sampleInput$escapeLiteral[0m';
+
+          expect(
+              wrapWith(sampleInput,
+                  [blue, backgroundWhite, styleBold, styleUnderlined],
+                  forScript: forScript),
+              expected);
+        });
+
+        test('no codes', () {
+          expect(wrapWith(sampleInput, []), sampleInput);
+        });
+
+        _test('empty', () {
+          expect(
+              wrapWith('', [blue, backgroundWhite, styleBold],
+                  forScript: forScript),
+              '');
+        });
+
+        _test('null', () {
+          expect(
+              wrapWith(null, [blue, backgroundWhite, styleBold],
+                  forScript: forScript),
+              isNull);
+        });
+      });
+    });
+  }
+}
+
+void _test<T>(String name, T Function() body) =>
+    test(name, () => overrideAnsiOutput<T>(true, body));

diff --git a/pkgs/io/test/copy_path_test.dart b/pkgs/io/test/copy_path_test.dart
new file mode 100644
index 0000000..fd1e9ce
--- /dev/null
+++ b/pkgs/io/test/copy_path_test.dart

@@ -0,0 +1,45 @@
+// Copyright (c) 2017, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+@TestOn('vm')
+library;
+
+import 'package:io/io.dart';
+import 'package:path/path.dart' as p;
+import 'package:test/test.dart';
+import 'package:test_descriptor/test_descriptor.dart' as d;
+
+void main() {
+  test('should copy a directory (async)', () async {
+    await _create();
+    await copyPath(p.join(d.sandbox, 'parent'), p.join(d.sandbox, 'copy'));
+    await _validate();
+  });
+
+  test('should copy a directory (sync)', () async {
+    await _create();
+    copyPathSync(p.join(d.sandbox, 'parent'), p.join(d.sandbox, 'copy'));
+    await _validate();
+  });
+
+  test('should catch an infinite operation', () async {
+    await _create();
+    expect(
+      copyPath(
+        p.join(d.sandbox, 'parent'),
+        p.join(d.sandbox, 'parent', 'child'),
+      ),
+      throwsArgumentError,
+    );
+  });
+}
+
+d.DirectoryDescriptor _struct() => d.dir('parent', [
+      d.dir('child', [
+        d.file('foo.txt'),
+      ]),
+    ]);
+
+Future<void> _create() => _struct().create();
+Future<void> _validate() => _struct().validate();

diff --git a/pkgs/io/test/permissions_test.dart b/pkgs/io/test/permissions_test.dart
new file mode 100644
index 0000000..478e8df
--- /dev/null
+++ b/pkgs/io/test/permissions_test.dart

@@ -0,0 +1,37 @@
+// Copyright (c) 2017, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+@TestOn('vm')
+library;
+
+import 'package:io/io.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('isExecutable', () {
+    const files = 'test/_files';
+    const shellIsExec = '$files/is_executable.sh';
+    const shellNotExec = '$files/is_not_executable.sh';
+
+    group('on shell scripts', () {
+      test('should return true for "is_executable.sh"', () async {
+        expect(await isExecutable(shellIsExec), isTrue);
+      });
+
+      test('should return false for "is_not_executable.sh"', () async {
+        expect(await isExecutable(shellNotExec), isFalse);
+      });
+    }, testOn: '!windows');
+
+    group('on shell scripts [windows]', () {
+      test('should return true for "is_executable.sh"', () async {
+        expect(await isExecutable(shellIsExec, isWindows: true), isTrue);
+      });
+
+      test('should return true for "is_not_executable.sh"', () async {
+        expect(await isExecutable(shellNotExec, isWindows: true), isTrue);
+      });
+    });
+  });
+}

diff --git a/pkgs/io/test/process_manager_test.dart b/pkgs/io/test/process_manager_test.dart
new file mode 100644
index 0000000..9871a77
--- /dev/null
+++ b/pkgs/io/test/process_manager_test.dart

@@ -0,0 +1,100 @@
+// Copyright (c) 2017, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// ignore_for_file: close_sinks
+
+import 'dart:async';
+import 'dart:convert';
+import 'dart:io';
+
+import 'package:io/io.dart' hide sharedStdIn;
+import 'package:path/path.dart' as p;
+import 'package:test/test.dart';
+
+void main() {
+  StreamController<String> fakeStdIn;
+  late ProcessManager processManager;
+  SharedStdIn sharedStdIn;
+  late List<String> stdoutLog;
+  late List<String> stderrLog;
+
+  test('spawn functions should match the type definition of Process.start', () {
+    const isStartProcess = TypeMatcher<StartProcess>();
+    expect(Process.start, isStartProcess);
+    final manager = ProcessManager();
+    expect(manager.spawn, isStartProcess);
+    expect(manager.spawnBackground, isStartProcess);
+    expect(manager.spawnDetached, isStartProcess);
+  });
+
+  group('spawn', () {
+    setUp(() async {
+      fakeStdIn = StreamController<String>(sync: true);
+      sharedStdIn = SharedStdIn(fakeStdIn.stream.map((s) => s.codeUnits));
+      stdoutLog = <String>[];
+      stderrLog = <String>[];
+
+      final stdoutController = StreamController<List<int>>(sync: true);
+      stdoutController.stream.map(utf8.decode).listen(stdoutLog.add);
+      final stdout = IOSink(stdoutController);
+      final stderrController = StreamController<List<int>>(sync: true);
+      stderrController.stream.map(utf8.decode).listen(stderrLog.add);
+      final stderr = IOSink(stderrController);
+
+      processManager = ProcessManager(
+        stdin: sharedStdIn,
+        stdout: stdout,
+        stderr: stderr,
+      );
+    });
+
+    final dart = Platform.executable;
+
+    test('should output Hello from another process [via stdout]', () async {
+      final spawn = await processManager.spawn(
+        dart,
+        [p.join('test', '_files', 'stdout_hello.dart')],
+      );
+      await spawn.exitCode;
+      expect(stdoutLog, ['Hello']);
+    });
+
+    test('should output Hello from another process [via stderr]', () async {
+      final spawn = await processManager.spawn(
+        dart,
+        [p.join('test', '_files', 'stderr_hello.dart')],
+      );
+      await spawn.exitCode;
+      expect(stderrLog, ['Hello']);
+    });
+
+    test('should forward stdin to another process', () async {
+      final spawn = await processManager.spawn(
+        dart,
+        [p.join('test', '_files', 'stdin_echo.dart')],
+      );
+      spawn.stdin.writeln('Ping');
+      await spawn.exitCode;
+      expect(stdoutLog.join(), contains('You said: Ping'));
+    });
+
+    group('should return a Process where', () {
+      test('.stdout is readable', () async {
+        final spawn = await processManager.spawn(
+          dart,
+          [p.join('test', '_files', 'stdout_hello.dart')],
+        );
+        expect(await spawn.stdout.transform(utf8.decoder).first, 'Hello');
+      });
+
+      test('.stderr is readable', () async {
+        final spawn = await processManager.spawn(
+          dart,
+          [p.join('test', '_files', 'stderr_hello.dart')],
+        );
+        expect(await spawn.stderr.transform(utf8.decoder).first, 'Hello');
+      });
+    });
+  });
+}

diff --git a/pkgs/io/test/shared_stdin_test.dart b/pkgs/io/test/shared_stdin_test.dart
new file mode 100644
index 0000000..71629ec
--- /dev/null
+++ b/pkgs/io/test/shared_stdin_test.dart

@@ -0,0 +1,80 @@
+// Copyright (c) 2017, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+import 'dart:convert';
+
+import 'package:io/io.dart' hide sharedStdIn;
+import 'package:test/test.dart';
+
+void main() {
+  // ignore: close_sinks
+  late StreamController<String> fakeStdIn;
+  late SharedStdIn sharedStdIn;
+
+  setUp(() {
+    fakeStdIn = StreamController<String>(sync: true);
+    sharedStdIn = SharedStdIn(fakeStdIn.stream.map((s) => s.codeUnits));
+  });
+
+  test('should allow a single subscriber', () async {
+    final logs = <String>[];
+    final sub = sharedStdIn.transform(utf8.decoder).listen(logs.add);
+    fakeStdIn.add('Hello World');
+    await sub.cancel();
+    expect(logs, ['Hello World']);
+  });
+
+  test('should allow multiple subscribers', () async {
+    final logs = <String>[];
+    final asUtf8 = sharedStdIn.transform(utf8.decoder);
+    var sub = asUtf8.listen(logs.add);
+    fakeStdIn.add('Hello World');
+    await sub.cancel();
+    sub = asUtf8.listen(logs.add);
+    fakeStdIn.add('Goodbye World');
+    await sub.cancel();
+    expect(logs, ['Hello World', 'Goodbye World']);
+  });
+
+  test('should throw if a subscriber is still active', () async {
+    final active = sharedStdIn.listen((_) {});
+    expect(() => sharedStdIn.listen((_) {}), throwsStateError);
+    await active.cancel();
+    expect(() => sharedStdIn.listen((_) {}), returnsNormally);
+  });
+
+  test('should return a stream of lines', () async {
+    expect(
+      sharedStdIn.lines(),
+      emitsInOrder(<dynamic>[
+        'I',
+        'Think',
+        'Therefore',
+        'I',
+        'Am',
+      ]),
+    );
+    [
+      'I\nThink\n',
+      'Therefore\n',
+      'I\n',
+      'Am\n',
+    ].forEach(fakeStdIn.add);
+  });
+
+  test('should return the next line', () {
+    expect(sharedStdIn.nextLine(), completion('Hello World'));
+    fakeStdIn.add('Hello World\n');
+  });
+
+  test('should allow listening for new lines multiple times', () async {
+    expect(sharedStdIn.nextLine(), completion('Hello World'));
+    fakeStdIn.add('Hello World\n');
+    await Future<void>.value();
+
+    expect(sharedStdIn.nextLine(), completion('Hello World'));
+    fakeStdIn.add('Hello World\n');
+  });
+}

diff --git a/pkgs/io/test/shell_words_test.dart b/pkgs/io/test/shell_words_test.dart
new file mode 100644
index 0000000..dc4441c
--- /dev/null
+++ b/pkgs/io/test/shell_words_test.dart

@@ -0,0 +1,185 @@
+// Copyright (c) 2017, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:io/io.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('shellSplit()', () {
+    group('returns an empty list for', () {
+      test('an empty string', () {
+        expect(shellSplit(''), isEmpty);
+      });
+
+      test('spaces', () {
+        expect(shellSplit('    '), isEmpty);
+      });
+
+      test('tabs', () {
+        expect(shellSplit('\t\t\t'), isEmpty);
+      });
+
+      test('newlines', () {
+        expect(shellSplit('\n\n\n'), isEmpty);
+      });
+
+      test('a comment', () {
+        expect(shellSplit('#foo bar baz'), isEmpty);
+      });
+
+      test('a mix', () {
+        expect(shellSplit(' \t\n# foo'), isEmpty);
+      });
+    });
+
+    group('parses unquoted', () {
+      test('a single token', () {
+        expect(shellSplit('foo'), equals(['foo']));
+      });
+
+      test('multiple tokens', () {
+        expect(shellSplit('foo bar baz'), equals(['foo', 'bar', 'baz']));
+      });
+
+      test('tokens separated by tabs', () {
+        expect(shellSplit('foo\tbar\tbaz'), equals(['foo', 'bar', 'baz']));
+      });
+
+      test('tokens separated by newlines', () {
+        expect(shellSplit('foo\nbar\nbaz'), equals(['foo', 'bar', 'baz']));
+      });
+
+      test('a token after whitespace', () {
+        expect(shellSplit(' \t\nfoo'), equals(['foo']));
+      });
+
+      test('a token before whitespace', () {
+        expect(shellSplit('foo \t\n'), equals(['foo']));
+      });
+
+      test('a token with a hash', () {
+        expect(shellSplit('foo#bar'), equals(['foo#bar']));
+      });
+
+      test('a token before a comment', () {
+        expect(shellSplit('foo #bar'), equals(['foo']));
+      });
+
+      test('dynamic shell features', () {
+        expect(
+            shellSplit(r'foo $(bar baz)'), equals(['foo', r'$(bar', 'baz)']));
+        expect(shellSplit('foo `bar baz`'), equals(['foo', '`bar', 'baz`']));
+        expect(shellSplit(r'foo $bar | baz'),
+            equals(['foo', r'$bar', '|', 'baz']));
+      });
+    });
+
+    group('parses a backslash', () {
+      test('before a normal character', () {
+        expect(shellSplit(r'foo\bar'), equals(['foobar']));
+      });
+
+      test('before a dynamic shell feature', () {
+        expect(shellSplit(r'foo\$bar'), equals([r'foo$bar']));
+      });
+
+      test('before a single quote', () {
+        expect(shellSplit(r"foo\'bar"), equals(["foo'bar"]));
+      });
+
+      test('before a double quote', () {
+        expect(shellSplit(r'foo\"bar'), equals(['foo"bar']));
+      });
+
+      test('before a space', () {
+        expect(shellSplit(r'foo\ bar'), equals(['foo bar']));
+      });
+
+      test('at the beginning of a token', () {
+        expect(shellSplit(r'\ foo'), equals([' foo']));
+      });
+
+      test('before whitespace followed by a hash', () {
+        expect(shellSplit(r'\ #foo'), equals([' #foo']));
+      });
+
+      test('before a newline in a token', () {
+        expect(shellSplit('foo\\\nbar'), equals(['foobar']));
+      });
+
+      test('before a newline outside a token', () {
+        expect(shellSplit('foo \\\n bar'), equals(['foo', 'bar']));
+      });
+
+      test('before a backslash', () {
+        expect(shellSplit(r'foo\\bar'), equals([r'foo\bar']));
+      });
+    });
+
+    group('parses single quotes', () {
+      test('that are empty', () {
+        expect(shellSplit("''"), equals(['']));
+      });
+
+      test('that contain normal characters', () {
+        expect(shellSplit("'foo'"), equals(['foo']));
+      });
+
+      test('that contain active characters', () {
+        expect(shellSplit("'\" \\#'"), equals([r'" \#']));
+      });
+
+      test('before a hash', () {
+        expect(shellSplit("''#foo"), equals([r'#foo']));
+      });
+
+      test('inside a token', () {
+        expect(shellSplit("foo'bar baz'qux"), equals([r'foobar bazqux']));
+      });
+
+      test('without a closing quote', () {
+        expect(() => shellSplit("'foo bar"), throwsFormatException);
+      });
+    });
+
+    group('parses double quotes', () {
+      test('that are empty', () {
+        expect(shellSplit('""'), equals(['']));
+      });
+
+      test('that contain normal characters', () {
+        expect(shellSplit('"foo"'), equals(['foo']));
+      });
+
+      test('that contain otherwise-active characters', () {
+        expect(shellSplit('"\' #"'), equals(["' #"]));
+      });
+
+      test('that contain escaped characters', () {
+        expect(shellSplit(r'"\$\`\"\\"'), equals([r'$`"\']));
+      });
+
+      test('that contain an escaped newline', () {
+        expect(shellSplit('"\\\n"'), equals(['']));
+      });
+
+      test("that contain a backslash that's not an escape", () {
+        expect(shellSplit(r'"f\oo"'), equals([r'f\oo']));
+      });
+
+      test('before a hash', () {
+        expect(shellSplit('""#foo'), equals([r'#foo']));
+      });
+
+      test('inside a token', () {
+        expect(shellSplit('foo"bar baz"qux'), equals([r'foobar bazqux']));
+      });
+
+      test('without a closing quote', () {
+        expect(() => shellSplit('"foo bar'), throwsFormatException);
+        expect(() => shellSplit(r'"foo bar\'), throwsFormatException);
+      });
+    });
+  });
+}

diff --git a/pkgs/package_config/.gitignore b/pkgs/package_config/.gitignore
new file mode 100644
index 0000000..7b888b8
--- /dev/null
+++ b/pkgs/package_config/.gitignore

@@ -0,0 +1,7 @@
+.packages
+.pub
+.dart_tool/
+.vscode/
+packages
+pubspec.lock
+doc/api/

diff --git a/pkgs/package_config/AUTHORS b/pkgs/package_config/AUTHORS
new file mode 100644
index 0000000..e8063a8
--- /dev/null
+++ b/pkgs/package_config/AUTHORS

@@ -0,0 +1,6 @@
+# Below is a list of people and organizations that have contributed
+# to the project. Names should be added to the list like so:
+#
+#   Name/Organization <email address>
+
+Google Inc.

diff --git a/pkgs/package_config/CHANGELOG.md b/pkgs/package_config/CHANGELOG.md
new file mode 100644
index 0000000..101a0fe
--- /dev/null
+++ b/pkgs/package_config/CHANGELOG.md

@@ -0,0 +1,108 @@
+## 2.1.1
+
+- Require Dart 3.4
+- Move to `dart-lang/tools` monorepo.
+
+## 2.1.0
+
+- Adds `minVersion` to `findPackageConfig` and `findPackageConfigVersion`
+  which allows ignoring earlier versions (which currently only means
+  ignoring version 1, aka. `.packages` files.)
+
+- Changes the version number of `SimplePackageConfig.empty` to the
+  current maximum version.
+
+- Improve file read performance; improve lookup performance.
+- Emit an error when a package is inside the package root of another package.
+- Fix a link in the readme.
+
+## 2.0.2
+
+- Update package description and README.
+- Change to package:lints for style checking.
+- Add an example.
+
+## 2.0.1
+
+- Use unique library names to correct docs issue.
+
+## 2.0.0
+
+- Migrate to null safety.
+- Remove legacy APIs.
+- Adds `relativeRoot` property to `Package` which controls whether to
+  make the root URI relative when writing a configuration file.
+
+## 1.9.3
+
+- Fix `Package` constructor not accepting relative `packageUriRoot`.
+
+## 1.9.2
+
+- Updated to support new rules for picking `package_config.json` over
+  a specified `.packages`.
+- Deduce package root from `.packages` derived package configuration,
+  and default all such packages to language version 2.7.
+
+## 1.9.1
+
+- Remove accidental transitive import of `dart:io` from entrypoints that are
+  supposed to be cross-platform compatible.
+
+## 1.9.0
+
+- Based on new JSON file format with more content.
+- This version includes all the new functionality intended for a 2.0.0
+  version, as well as the, now deprecated, version 1 functionality.
+  When we release 2.0.0, the deprecated functionality will be removed.
+
+## 1.1.0
+
+- Allow parsing files with default-package entries and metadata.
+  A default-package entry has an empty key and a valid package name
+  as value.
+  Metadata is attached as fragments to base URIs.
+
+## 1.0.5
+
+- Fix usage of SDK constants.
+
+## 1.0.4
+
+- Set max SDK version to <3.0.0.
+
+## 1.0.3
+
+- Removed unneeded dependency constraint on SDK.
+
+## 1.0.2
+
+- Update SDK constraint to be 2.0.0 dev friendly.
+
+## 1.0.1
+
+- Fix test to not write to sink after it's closed.
+
+## 1.0.0
+
+- Public API marked stable.
+
+## 0.1.5
+
+- `FilePackagesDirectoryPackages.getBase(..)` performance improvements.
+
+## 0.1.4
+
+- Strong mode fixes.
+
+## 0.1.3
+
+- Invalid test cleanup (to keep up with changes in `Uri`).
+
+## 0.1.1
+
+- Syntax updates.
+
+## 0.1.0
+
+- Initial implementation.

diff --git a/pkgs/package_config/LICENSE b/pkgs/package_config/LICENSE
new file mode 100644
index 0000000..7670007
--- /dev/null
+++ b/pkgs/package_config/LICENSE

@@ -0,0 +1,27 @@
+Copyright 2019, the Dart project authors. 
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+    * Neither the name of Google LLC nor the names of its
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

diff --git a/pkgs/package_config/README.md b/pkgs/package_config/README.md
new file mode 100644
index 0000000..76fd3cb
--- /dev/null
+++ b/pkgs/package_config/README.md

@@ -0,0 +1,26 @@
+[![Build Status](https://github.com/dart-lang/tools/actions/workflows/package_config.yaml/badge.svg)](https://github.com/dart-lang/tools/actions/workflows/package_config.yaml)
+[![pub package](https://img.shields.io/pub/v/package_config.svg)](https://pub.dev/packages/package_config)
+[![package publisher](https://img.shields.io/pub/publisher/package_config.svg)](https://pub.dev/packages/package_config/publisher)
+
+Support for working with **Package Configuration** files as described
+in the Package Configuration v2 [design document](https://github.com/dart-lang/language/blob/master/accepted/2.8/language-versioning/package-config-file-v2.md).
+
+A Dart package configuration file is used to resolve Dart package names (e.g.
+`foobar`) to Dart files containing the source code for that package (e.g.
+`file:///Users/myuser/.pub-cache/hosted/pub.dartlang.org/foobar-1.1.0`). The
+standard package configuration file is `.dart_tool/package_config.json`, and is
+written by the Dart tool when the command `dart pub get` is run.
+
+The primary libraries of this package are
+* `package_config.dart`:
+    Defines the `PackageConfig` class and other types needed to use
+    package configurations, and provides functions to find, read and
+    write package configuration files.
+
+* `package_config_types.dart`:
+    Just the `PackageConfig` class and other types needed to use
+    package configurations. This library does not depend on `dart:io`.
+
+The package includes deprecated backwards compatible functionality to
+work with the `.packages` file. This functionality will not be maintained,
+and will be removed in a future version of this package.

diff --git a/pkgs/package_config/analysis_options.yaml b/pkgs/package_config/analysis_options.yaml
new file mode 100644
index 0000000..c0249e5
--- /dev/null
+++ b/pkgs/package_config/analysis_options.yaml

@@ -0,0 +1,5 @@
+# Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+# for details. All rights reserved. Use of this source code is governed by a
+# BSD-style license that can be found in the LICENSE file.
+
+include: package:dart_flutter_team_lints/analysis_options.yaml

diff --git a/pkgs/package_config/example/main.dart b/pkgs/package_config/example/main.dart
new file mode 100644
index 0000000..db137ca
--- /dev/null
+++ b/pkgs/package_config/example/main.dart

@@ -0,0 +1,19 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:io' show Directory;
+
+import 'package:package_config/package_config.dart';
+
+void main() async {
+  var packageConfig = await findPackageConfig(Directory.current);
+  if (packageConfig == null) {
+    print('Failed to locate or read package config.');
+  } else {
+    print('This package depends on ${packageConfig.packages.length} packages:');
+    for (var package in packageConfig.packages) {
+      print('- ${package.name}');
+    }
+  }
+}

diff --git a/pkgs/package_config/lib/package_config.dart b/pkgs/package_config/lib/package_config.dart
new file mode 100644
index 0000000..074c977
--- /dev/null
+++ b/pkgs/package_config/lib/package_config.dart

@@ -0,0 +1,199 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// A package configuration is a way to assign file paths to package URIs,
+/// and vice-versa.
+///
+/// This package provides functionality to find, read and write package
+/// configurations in the [specified format](https://github.com/dart-lang/language/blob/master/accepted/future-releases/language-versioning/package-config-file-v2.md).
+library;
+
+import 'dart:io' show Directory, File;
+import 'dart:typed_data' show Uint8List;
+
+import 'src/discovery.dart' as discover;
+import 'src/errors.dart' show throwError;
+import 'src/package_config.dart';
+import 'src/package_config_io.dart';
+
+export 'package_config_types.dart';
+
+/// Reads a specific package configuration file.
+///
+/// The file must exist and be readable.
+/// It must be either a valid `package_config.json` file
+/// or a valid `.packages` file.
+/// It is considered a `package_config.json` file if its first character
+/// is a `{`.
+///
+/// If the file is a `.packages` file (the file name is `.packages`)
+/// and [preferNewest] is true, the default, also checks if there is
+/// a `.dart_tool/package_config.json` file next
+/// to the original file, and if so, loads that instead.
+/// If [preferNewest] is set to false, a directly specified `.packages` file
+/// is loaded even if there is an available `package_config.json` file.
+/// The caller can determine this from the [PackageConfig.version]
+/// being 1 and look for a `package_config.json` file themselves.
+///
+/// If [onError] is provided, the configuration file parsing will report errors
+/// by calling that function, and then try to recover.
+/// The returned package configuration is a *best effort* attempt to create
+/// a valid configuration from the invalid configuration file.
+/// If no [onError] is provided, errors are thrown immediately.
+Future<PackageConfig> loadPackageConfig(File file,
+        {bool preferNewest = true, void Function(Object error)? onError}) =>
+    readAnyConfigFile(file, preferNewest, onError ?? throwError);
+
+/// Reads a specific package configuration URI.
+///
+/// The file of the URI must exist and be readable.
+/// It must be either a valid `package_config.json` file
+/// or a valid `.packages` file.
+/// It is considered a `package_config.json` file if its first
+/// non-whitespace character is a `{`.
+///
+/// If [preferNewest] is true, the default, and the file is a `.packages` file,
+/// as determined by its file name being `.packages`,
+/// first checks if there is a `.dart_tool/package_config.json` file
+/// next to the original file, and if so, loads that instead.
+/// The [file] *must not* be a `package:` URI.
+/// If [preferNewest] is set to false, a directly specified `.packages` file
+/// is loaded even if there is an available `package_config.json` file.
+/// The caller can determine this from the [PackageConfig.version]
+/// being 1 and look for a `package_config.json` file themselves.
+///
+/// If [loader] is provided, URIs are loaded using that function.
+/// The future returned by the loader must complete with a [Uint8List]
+/// containing the entire file content encoded as UTF-8,
+/// or with `null` if the file does not exist.
+/// The loader may throw at its own discretion, for situations where
+/// it determines that an error might be need user attention,
+/// but it is always allowed to return `null`.
+/// This function makes no attempt to catch such errors.
+/// As such, it may throw any error that [loader] throws.
+///
+/// If no [loader] is supplied, a default loader is used which
+/// only accepts `file:`,  `http:` and `https:` URIs,
+/// and which uses the platform file system and HTTP requests to
+/// fetch file content. The default loader never throws because
+/// of an I/O issue, as long as the location URIs are valid.
+/// As such, it does not distinguish between a file not existing,
+/// and it being temporarily locked or unreachable.
+///
+/// If [onError] is provided, the configuration file parsing will report errors
+/// by calling that function, and then try to recover.
+/// The returned package configuration is a *best effort* attempt to create
+/// a valid configuration from the invalid configuration file.
+/// If no [onError] is provided, errors are thrown immediately.
+Future<PackageConfig> loadPackageConfigUri(Uri file,
+        {Future<Uint8List?> Function(Uri uri)? loader,
+        bool preferNewest = true,
+        void Function(Object error)? onError}) =>
+    readAnyConfigFileUri(file, loader, onError ?? throwError, preferNewest);
+
+/// Finds a package configuration relative to [directory].
+///
+/// If [directory] contains a package configuration,
+/// either a `.dart_tool/package_config.json` file or,
+/// if not, a `.packages`, then that file is loaded.
+///
+/// If no file is found in the current directory,
+/// then the parent directories are checked recursively,
+/// all the way to the root directory, to check if those contains
+/// a package configuration.
+/// If [recurse] is set to `false`, this parent directory check is not
+/// performed.
+///
+/// If [onError] is provided, the configuration file parsing will report errors
+/// by calling that function, and then try to recover.
+/// The returned package configuration is a *best effort* attempt to create
+/// a valid configuration from the invalid configuration file.
+/// If no [onError] is provided, errors are thrown immediately.
+///
+/// If [minVersion] is set to something greater than its default,
+/// any lower-version configuration files are ignored in the search.
+///
+/// Returns `null` if no configuration file is found.
+Future<PackageConfig?> findPackageConfig(Directory directory,
+    {bool recurse = true,
+    void Function(Object error)? onError,
+    int minVersion = 1}) {
+  if (minVersion > PackageConfig.maxVersion) {
+    throw ArgumentError.value(minVersion, 'minVersion',
+        'Maximum known version is ${PackageConfig.maxVersion}');
+  }
+  return discover.findPackageConfig(
+      directory, minVersion, recurse, onError ?? throwError);
+}
+
+/// Finds a package configuration relative to [location].
+///
+/// If [location] contains a package configuration,
+/// either a `.dart_tool/package_config.json` file or,
+/// if not, a `.packages`, then that file is loaded.
+/// The [location] URI *must not* be a `package:` URI.
+/// It should be a hierarchical URI which is supported
+/// by [loader].
+///
+/// If no file is found in the current directory,
+/// then the parent directories are checked recursively,
+/// all the way to the root directory, to check if those contains
+/// a package configuration.
+/// If [recurse] is set to `false`, this parent directory check is not
+/// performed.
+///
+/// If [loader] is provided, URIs are loaded using that function.
+/// The future returned by the loader must complete with a [Uint8List]
+/// containing the entire file content,
+/// or with `null` if the file does not exist.
+/// The loader may throw at its own discretion, for situations where
+/// it determines that an error might be need user attention,
+/// but it is always allowed to return `null`.
+/// This function makes no attempt to catch such errors.
+///
+/// If no [loader] is supplied, a default loader is used which
+/// only accepts `file:`,  `http:` and `https:` URIs,
+/// and which uses the platform file system and HTTP requests to
+/// fetch file content. The default loader never throws because
+/// of an I/O issue, as long as the location URIs are valid.
+/// As such, it does not distinguish between a file not existing,
+/// and it being temporarily locked or unreachable.
+///
+/// If [onError] is provided, the configuration file parsing will report errors
+/// by calling that function, and then try to recover.
+/// The returned package configuration is a *best effort* attempt to create
+/// a valid configuration from the invalid configuration file.
+/// If no [onError] is provided, errors are thrown immediately.
+///
+/// If [minVersion] is set to something greater than its default,
+/// any lower-version configuration files are ignored in the search.
+///
+/// Returns `null` if no configuration file is found.
+Future<PackageConfig?> findPackageConfigUri(Uri location,
+    {bool recurse = true,
+    int minVersion = 1,
+    Future<Uint8List?> Function(Uri uri)? loader,
+    void Function(Object error)? onError}) {
+  if (minVersion > PackageConfig.maxVersion) {
+    throw ArgumentError.value(minVersion, 'minVersion',
+        'Maximum known version is ${PackageConfig.maxVersion}');
+  }
+  return discover.findPackageConfigUri(
+      location, minVersion, loader, onError ?? throwError, recurse);
+}
+
+/// Writes a package configuration to the provided directory.
+///
+/// Writes `.dart_tool/package_config.json` relative to [directory].
+/// If the `.dart_tool/` directory does not exist, it is created.
+/// If it cannot be created, this operation fails.
+///
+/// Also writes a `.packages` file in [directory].
+/// This will stop happening eventually as the `.packages` file becomes
+/// discontinued.
+/// A comment is generated if `[PackageConfig.extraData]` contains a
+/// `"generator"` entry.
+Future<void> savePackageConfig(
+        PackageConfig configuration, Directory directory) =>
+    writePackageConfigJsonFile(configuration, directory);

diff --git a/pkgs/package_config/lib/package_config_types.dart b/pkgs/package_config/lib/package_config_types.dart
new file mode 100644
index 0000000..825f7ac
--- /dev/null
+++ b/pkgs/package_config/lib/package_config_types.dart

@@ -0,0 +1,17 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// A package configuration is a way to assign file paths to package URIs,
+/// and vice-versa.
+///
+/// {@canonicalFor package_config.InvalidLanguageVersion}
+/// {@canonicalFor package_config.LanguageVersion}
+/// {@canonicalFor package_config.Package}
+/// {@canonicalFor package_config.PackageConfig}
+/// {@canonicalFor errors.PackageConfigError}
+library;
+
+export 'src/errors.dart' show PackageConfigError;
+export 'src/package_config.dart'
+    show InvalidLanguageVersion, LanguageVersion, Package, PackageConfig;

diff --git a/pkgs/package_config/lib/src/discovery.dart b/pkgs/package_config/lib/src/discovery.dart
new file mode 100644
index 0000000..b678410
--- /dev/null
+++ b/pkgs/package_config/lib/src/discovery.dart

@@ -0,0 +1,148 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:io';
+import 'dart:typed_data';
+
+import 'errors.dart';
+import 'package_config_impl.dart';
+import 'package_config_io.dart';
+import 'package_config_json.dart';
+import 'packages_file.dart' as packages_file;
+import 'util_io.dart' show defaultLoader, pathJoin;
+
+final Uri packageConfigJsonPath = Uri(path: '.dart_tool/package_config.json');
+final Uri dotPackagesPath = Uri(path: '.packages');
+final Uri currentPath = Uri(path: '.');
+final Uri parentPath = Uri(path: '..');
+
+/// Discover the package configuration for a Dart script.
+///
+/// The [baseDirectory] points to the directory of the Dart script.
+/// A package resolution strategy is found by going through the following steps,
+/// and stopping when something is found.
+///
+/// * Check if a `.dart_tool/package_config.json` file exists in the directory.
+/// * Check if a `.packages` file exists in the directory
+///   (if `minVersion <= 1`).
+/// * Repeat these checks for the parent directories until reaching the
+///   root directory if [recursive] is true.
+///
+/// If any of these tests succeed, a `PackageConfig` class is returned.
+/// Returns `null` if no configuration was found. If a configuration
+/// is needed, then the caller can supply [PackageConfig.empty].
+///
+/// If [minVersion] is greater than 1, `.packages` files are ignored.
+/// If [minVersion] is greater than the version read from the
+/// `package_config.json` file, it too is ignored.
+Future<PackageConfig?> findPackageConfig(Directory baseDirectory,
+    int minVersion, bool recursive, void Function(Object error) onError) async {
+  var directory = baseDirectory;
+  if (!directory.isAbsolute) directory = directory.absolute;
+  if (!await directory.exists()) {
+    return null;
+  }
+  do {
+    // Check for $cwd/.packages
+    var packageConfig =
+        await findPackageConfigInDirectory(directory, minVersion, onError);
+    if (packageConfig != null) return packageConfig;
+    if (!recursive) break;
+    // Check in parent directories.
+    var parentDirectory = directory.parent;
+    if (parentDirectory.path == directory.path) break;
+    directory = parentDirectory;
+  } while (true);
+  return null;
+}
+
+/// Similar to [findPackageConfig] but based on a URI.
+Future<PackageConfig?> findPackageConfigUri(
+    Uri location,
+    int minVersion,
+    Future<Uint8List?> Function(Uri uri)? loader,
+    void Function(Object error) onError,
+    bool recursive) async {
+  if (location.isScheme('package')) {
+    onError(PackageConfigArgumentError(
+        location, 'location', 'Must not be a package: URI'));
+    return null;
+  }
+  if (loader == null) {
+    if (location.isScheme('file')) {
+      return findPackageConfig(
+          Directory.fromUri(location.resolveUri(currentPath)),
+          minVersion,
+          recursive,
+          onError);
+    }
+    loader = defaultLoader;
+  }
+  if (!location.path.endsWith('/')) location = location.resolveUri(currentPath);
+  while (true) {
+    var file = location.resolveUri(packageConfigJsonPath);
+    var bytes = await loader(file);
+    if (bytes != null) {
+      var config = parsePackageConfigBytes(bytes, file, onError);
+      if (config.version >= minVersion) return config;
+    }
+    if (minVersion <= 1) {
+      file = location.resolveUri(dotPackagesPath);
+      bytes = await loader(file);
+      if (bytes != null) {
+        return packages_file.parse(bytes, file, onError);
+      }
+    }
+    if (!recursive) break;
+    var parent = location.resolveUri(parentPath);
+    if (parent == location) break;
+    location = parent;
+  }
+  return null;
+}
+
+/// Finds a `.packages` or `.dart_tool/package_config.json` file in [directory].
+///
+/// Loads the file, if it is there, and returns the resulting [PackageConfig].
+/// Returns `null` if the file isn't there.
+/// Reports a [FormatException] if a file is there but the content is not valid.
+/// If the file exists, but fails to be read, the file system error is reported.
+///
+/// If [onError] is supplied, parsing errors are reported using that, and
+/// a best-effort attempt is made to return a package configuration.
+/// This may be the empty package configuration.
+///
+/// If [minVersion] is greater than 1, `.packages` files are ignored.
+/// If [minVersion] is greater than the version read from the
+/// `package_config.json` file, it too is ignored.
+Future<PackageConfig?> findPackageConfigInDirectory(Directory directory,
+    int minVersion, void Function(Object error) onError) async {
+  var packageConfigFile = await checkForPackageConfigJsonFile(directory);
+  if (packageConfigFile != null) {
+    var config = await readPackageConfigJsonFile(packageConfigFile, onError);
+    if (config.version < minVersion) return null;
+    return config;
+  }
+  if (minVersion <= 1) {
+    packageConfigFile = await checkForDotPackagesFile(directory);
+    if (packageConfigFile != null) {
+      return await readDotPackagesFile(packageConfigFile, onError);
+    }
+  }
+  return null;
+}
+
+Future<File?> checkForPackageConfigJsonFile(Directory directory) async {
+  assert(directory.isAbsolute);
+  var file =
+      File(pathJoin(directory.path, '.dart_tool', 'package_config.json'));
+  if (await file.exists()) return file;
+  return null;
+}
+
+Future<File?> checkForDotPackagesFile(Directory directory) async {
+  var file = File(pathJoin(directory.path, '.packages'));
+  if (await file.exists()) return file;
+  return null;
+}

diff --git a/pkgs/package_config/lib/src/errors.dart b/pkgs/package_config/lib/src/errors.dart
new file mode 100644
index 0000000..a66fef7
--- /dev/null
+++ b/pkgs/package_config/lib/src/errors.dart

@@ -0,0 +1,34 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// General superclass of most errors and exceptions thrown by this package.
+///
+/// Only covers errors thrown while parsing package configuration files.
+/// Programming errors and I/O exceptions are not covered.
+abstract class PackageConfigError {
+  PackageConfigError._();
+}
+
+class PackageConfigArgumentError extends ArgumentError
+    implements PackageConfigError {
+  PackageConfigArgumentError(
+      Object? super.value, String super.name, String super.message)
+      : super.value();
+
+  PackageConfigArgumentError.from(ArgumentError error)
+      : super.value(error.invalidValue, error.name, error.message);
+}
+
+class PackageConfigFormatException extends FormatException
+    implements PackageConfigError {
+  PackageConfigFormatException(super.message, Object? super.source,
+      [super.offset]);
+
+  PackageConfigFormatException.from(FormatException exception)
+      : super(exception.message, exception.source, exception.offset);
+}
+
+/// The default `onError` handler.
+// ignore: only_throw_errors
+Never throwError(Object error) => throw error;

diff --git a/pkgs/package_config/lib/src/package_config.dart b/pkgs/package_config/lib/src/package_config.dart
new file mode 100644
index 0000000..155dfc5
--- /dev/null
+++ b/pkgs/package_config/lib/src/package_config.dart

@@ -0,0 +1,402 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:typed_data';
+
+import 'errors.dart';
+import 'package_config_impl.dart';
+import 'package_config_json.dart';
+
+/// A package configuration.
+///
+/// Associates configuration data to packages and files in packages.
+///
+/// More members may be added to this class in the future,
+/// so classes outside of this package must not implement [PackageConfig]
+/// or any subclass of it.
+abstract class PackageConfig {
+  /// The largest configuration version currently recognized.
+  static const int maxVersion = 2;
+
+  /// An empty package configuration.
+  ///
+  /// A package configuration with no available packages.
+  /// Is used as a default value where a package configuration
+  /// is expected, but none have been specified or found.
+  static const PackageConfig empty = SimplePackageConfig.empty();
+
+  /// Creates a package configuration with the provided available [packages].
+  ///
+  /// The packages must be valid packages (valid package name, valid
+  /// absolute directory URIs, valid language version, if any),
+  /// and there must not be two packages with the same name.
+  ///
+  /// The package's root ([Package.root]) and package-root
+  /// ([Package.packageUriRoot]) paths must satisfy a number of constraints
+  /// We say that one path (which we know ends with a `/` character)
+  /// is inside another path, if the latter path is a prefix of the former path,
+  /// including the two paths being the same.
+  ///
+  /// * No package's root must be the same as another package's root.
+  /// * The package-root of a package must be inside the package's root.
+  /// * If one package's package-root is inside another package's root,
+  ///   then the latter package's package root must not be inside the former
+  ///   package's root. (No getting between a package and its package root!)
+  ///   This also disallows a package's root being the same as another
+  ///   package's package root.
+  ///
+  /// If supplied, the [extraData] will be available as the
+  /// [PackageConfig.extraData] of the created configuration.
+  ///
+  /// The version of the resulting configuration is always [maxVersion].
+  factory PackageConfig(Iterable<Package> packages, {Object? extraData}) =>
+      SimplePackageConfig(maxVersion, packages, extraData);
+
+  /// Parses a package configuration file.
+  ///
+  /// The [bytes] must be an UTF-8 encoded JSON object
+  /// containing a valid package configuration.
+  ///
+  /// The [baseUri] is used as the base for resolving relative
+  /// URI references in the configuration file. If the configuration
+  /// has been read from a file, the [baseUri] can be the URI of that
+  /// file, or of the directory it occurs in.
+  ///
+  /// If [onError] is provided, errors found during parsing or building
+  /// the configuration are reported by calling [onError] instead of
+  /// throwing, and parser makes a *best effort* attempt to continue
+  /// despite the error. The input must still be valid JSON.
+  /// The result may be [PackageConfig.empty] if there is no way to
+  /// extract useful information from the bytes.
+  static PackageConfig parseBytes(Uint8List bytes, Uri baseUri,
+          {void Function(Object error)? onError}) =>
+      parsePackageConfigBytes(bytes, baseUri, onError ?? throwError);
+
+  /// Parses a package configuration file.
+  ///
+  /// The [configuration] must be a JSON object
+  /// containing a valid package configuration.
+  ///
+  /// The [baseUri] is used as the base for resolving relative
+  /// URI references in the configuration file. If the configuration
+  /// has been read from a file, the [baseUri] can be the URI of that
+  /// file, or of the directory it occurs in.
+  ///
+  /// If [onError] is provided, errors found during parsing or building
+  /// the configuration are reported by calling [onError] instead of
+  /// throwing, and parser makes a *best effort* attempt to continue
+  /// despite the error. The input must still be valid JSON.
+  /// The result may be [PackageConfig.empty] if there is no way to
+  /// extract useful information from the bytes.
+  static PackageConfig parseString(String configuration, Uri baseUri,
+          {void Function(Object error)? onError}) =>
+      parsePackageConfigString(configuration, baseUri, onError ?? throwError);
+
+  /// Parses the JSON data of a package configuration file.
+  ///
+  /// The [jsonData] must be a JSON-like Dart data structure,
+  /// like the one provided by parsing JSON text using `dart:convert`,
+  /// containing a valid package configuration.
+  ///
+  /// The [baseUri] is used as the base for resolving relative
+  /// URI references in the configuration file. If the configuration
+  /// has been read from a file, the [baseUri] can be the URI of that
+  /// file, or of the directory it occurs in.
+  ///
+  /// If [onError] is provided, errors found during parsing or building
+  /// the configuration are reported by calling [onError] instead of
+  /// throwing, and parser makes a *best effort* attempt to continue
+  /// despite the error. The input must still be valid JSON.
+  /// The result may be [PackageConfig.empty] if there is no way to
+  /// extract useful information from the bytes.
+  static PackageConfig parseJson(Object? jsonData, Uri baseUri,
+          {void Function(Object error)? onError}) =>
+      parsePackageConfigJson(jsonData, baseUri, onError ?? throwError);
+
+  /// Writes a configuration file for this configuration on [output].
+  ///
+  /// If [baseUri] is provided, URI references in the generated file
+  /// will be made relative to [baseUri] where possible.
+  static void writeBytes(PackageConfig configuration, Sink<Uint8List> output,
+      [Uri? baseUri]) {
+    writePackageConfigJsonUtf8(configuration, baseUri, output);
+  }
+
+  /// Writes a configuration JSON text for this configuration on [output].
+  ///
+  /// If [baseUri] is provided, URI references in the generated file
+  /// will be made relative to [baseUri] where possible.
+  static void writeString(PackageConfig configuration, StringSink output,
+      [Uri? baseUri]) {
+    writePackageConfigJsonString(configuration, baseUri, output);
+  }
+
+  /// Converts a configuration to a JSON-like data structure.
+  ///
+  /// If [baseUri] is provided, URI references in the generated data
+  /// will be made relative to [baseUri] where possible.
+  static Map<String, Object?> toJson(PackageConfig configuration,
+          [Uri? baseUri]) =>
+      packageConfigToJson(configuration, baseUri);
+
+  /// The configuration version number.
+  ///
+  /// Currently this is 1 or 2, where
+  /// * Version one is the `.packages` file format and
+  /// * Version two is the first `package_config.json` format.
+  ///
+  /// Instances of this class supports both, and the version
+  /// is only useful for detecting which kind of file the configuration
+  /// was read from.
+  int get version;
+
+  /// All the available packages of this configuration.
+  ///
+  /// No two of these packages have the same name,
+  /// and no two [Package.root] directories overlap.
+  Iterable<Package> get packages;
+
+  /// Look up a package by name.
+  ///
+  /// Returns the [Package] from [packages] with [packageName] as
+  /// [Package.name]. Returns `null` if the package is not available in the
+  /// current configuration.
+  Package? operator [](String packageName);
+
+  /// Provides the associated package for a specific [file] (or directory).
+  ///
+  /// Returns a [Package] which contains the [file]'s path, if any.
+  /// That is, the [Package.root] directory is a parent directory
+  /// of the [file]'s location.
+  ///
+  /// Returns `null` if the file does not belong to any package.
+  Package? packageOf(Uri file);
+
+  /// Resolves a `package:` URI to a non-package URI
+  ///
+  /// The [packageUri] must be a valid package URI. That means:
+  /// * A URI with `package` as scheme,
+  /// * with no authority part (`package://...`),
+  /// * with a path starting with a valid package name followed by a slash, and
+  /// * with no query or fragment part.
+  ///
+  /// Throws an [ArgumentError] (which also implements [PackageConfigError])
+  /// if the package URI is not valid.
+  ///
+  /// Returns `null` if the package name of [packageUri] is not available
+  /// in this package configuration.
+  /// Returns the remaining path of the package URI resolved relative to the
+  /// [Package.packageUriRoot] of the corresponding package.
+  Uri? resolve(Uri packageUri);
+
+  /// The package URI which resolves to [nonPackageUri].
+  ///
+  /// The [nonPackageUri] must not have any query or fragment part,
+  /// and it must not have `package` as scheme.
+  /// Throws an [ArgumentError] (which also implements [PackageConfigError])
+  /// if the non-package URI is not valid.
+  ///
+  /// Returns a package URI which [resolve] will convert to [nonPackageUri],
+  /// if any such URI exists. Returns `null` if no such package URI exists.
+  Uri? toPackageUri(Uri nonPackageUri);
+
+  /// Extra data associated with the package configuration.
+  ///
+  /// The data may be in any format, depending on who introduced it.
+  /// The standard `package_config.json` file storage will only store
+  /// JSON-like list/map data structures.
+  Object? get extraData;
+}
+
+/// Configuration data for a single package.
+abstract class Package {
+  /// Creates a package with the provided properties.
+  ///
+  /// The [name] must be a valid package name.
+  /// The [root] must be an absolute directory URI, meaning an absolute URI
+  /// with no query or fragment path and a path starting and ending with `/`.
+  /// The [packageUriRoot], if provided, must be either an absolute
+  /// directory URI or a relative URI reference which is then resolved
+  /// relative to [root]. It must then also be a subdirectory of [root],
+  /// or the same directory, and must end with `/`.
+  /// If [languageVersion] is supplied, it must be a valid Dart language
+  /// version, which means two decimal integer literals separated by a `.`,
+  /// where the integer literals have no leading zeros unless they are
+  /// a single zero digit.
+  ///
+  /// The [relativeRoot] controls whether the [root] is written as
+  /// relative to the `package_config.json` file when the package
+  /// configuration is written to a file. It defaults to being relative.
+  ///
+  /// If [extraData] is supplied, it will be available as the
+  /// [Package.extraData] of the created package.
+  factory Package(String name, Uri root,
+          {Uri? packageUriRoot,
+          LanguageVersion? languageVersion,
+          Object? extraData,
+          bool relativeRoot = true}) =>
+      SimplePackage.validate(name, root, packageUriRoot, languageVersion,
+          extraData, relativeRoot, throwError)!;
+
+  /// The package-name of the package.
+  String get name;
+
+  /// The location of the root of the package.
+  ///
+  /// Is always an absolute URI with no query or fragment parts,
+  /// and with a path ending in `/`.
+  ///
+  /// All files in the [root] directory are considered
+  /// part of the package for purposes where that that matters.
+  Uri get root;
+
+  /// The root of the files available through `package:` URIs.
+  ///
+  /// A `package:` URI with [name] as the package name is
+  /// resolved relative to this location.
+  ///
+  /// Is always an absolute URI with no query or fragment part
+  /// with a path ending in `/`,
+  /// and with a location which is a subdirectory
+  /// of the [root], or the same as the [root].
+  Uri get packageUriRoot;
+
+  /// The default language version associated with this package.
+  ///
+  /// Each package may have a default language version associated,
+  /// which is the language version used to parse and compile
+  /// Dart files in the package.
+  /// A package version is defined by two non-negative numbers,
+  /// the *major* and *minor* version numbers.
+  ///
+  /// A package may have no language version associated with it
+  /// in the package configuration, in which case tools should
+  /// use a default behavior for the package.
+  LanguageVersion? get languageVersion;
+
+  /// Extra data associated with the specific package.
+  ///
+  /// The data may be in any format, depending on who introduced it.
+  /// The standard `package_config.json` file storage will only store
+  /// JSON-like list/map data structures.
+  Object? get extraData;
+
+  /// Whether the [root] URI should be written as relative.
+  ///
+  /// When the configuration is written to a `package_config.json`
+  /// file, the [root] URI can be either relative to the file
+  /// location or absolute, controller by this value.
+  bool get relativeRoot;
+}
+
+/// A language version.
+///
+/// A language version is represented by two non-negative integers,
+/// the [major] and [minor] version numbers.
+///
+/// If errors during parsing are handled using an `onError` handler,
+/// then an *invalid* language version may be represented by an
+/// [InvalidLanguageVersion] object.
+abstract class LanguageVersion implements Comparable<LanguageVersion> {
+  /// The maximal value allowed by [major] and [minor] values;
+  static const int maxValue = 0x7FFFFFFF;
+  factory LanguageVersion(int major, int minor) {
+    RangeError.checkValueInInterval(major, 0, maxValue, 'major');
+    RangeError.checkValueInInterval(minor, 0, maxValue, 'major');
+    return SimpleLanguageVersion(major, minor, null);
+  }
+
+  /// Parses a language version string.
+  ///
+  /// A valid language version string has the form
+  ///
+  /// > *decimalNumber* `.` *decimalNumber*
+  ///
+  /// where a *decimalNumber* is a non-empty sequence of decimal digits
+  /// with no unnecessary leading zeros (the decimal number only starts
+  /// with a zero digit if that digit is the entire number).
+  /// No spaces are allowed in the string.
+  ///
+  /// If the [source] is valid then it is parsed into a valid
+  /// [LanguageVersion] object.
+  /// If not, then the [onError] is called with a [FormatException].
+  /// If [onError] is not supplied, it defaults to throwing the exception.
+  /// If the call does not throw, then an [InvalidLanguageVersion] is returned
+  /// containing the original [source].
+  static LanguageVersion parse(String source,
+          {void Function(Object error)? onError}) =>
+      parseLanguageVersion(source, onError ?? throwError);
+
+  /// The major language version.
+  ///
+  /// A non-negative integer less than 2<sup>31</sup>.
+  ///
+  /// The value is negative for objects representing *invalid* language
+  /// versions ([InvalidLanguageVersion]).
+  int get major;
+
+  /// The minor language version.
+  ///
+  /// A non-negative integer less than 2<sup>31</sup>.
+  ///
+  /// The value is negative for objects representing *invalid* language
+  /// versions ([InvalidLanguageVersion]).
+  int get minor;
+
+  /// Compares language versions.
+  ///
+  /// Two language versions are considered equal if they have the
+  /// same major and minor version numbers.
+  ///
+  /// A language version is greater then another if the former's major version
+  /// is greater than the latter's major version, or if they have
+  /// the same major version and the former's minor version is greater than
+  /// the latter's.
+  @override
+  int compareTo(LanguageVersion other);
+
+  /// Valid language versions with the same [major] and [minor] values are
+  /// equal.
+  ///
+  /// Invalid language versions ([InvalidLanguageVersion]) are not equal to
+  /// any other object.
+  @override
+  bool operator ==(Object other);
+
+  @override
+  int get hashCode;
+
+  /// A string representation of the language version.
+  ///
+  /// A valid language version is represented as
+  /// `"${version.major}.${version.minor}"`.
+  @override
+  String toString();
+}
+
+/// An *invalid* language version.
+///
+/// Stored in a [Package] when the original language version string
+/// was invalid and a `onError` handler was passed to the parser
+/// which did not throw on an error.
+abstract class InvalidLanguageVersion implements LanguageVersion {
+  /// The value -1 for an invalid language version.
+  @override
+  int get major;
+
+  /// The value -1 for an invalid language version.
+  @override
+  int get minor;
+
+  /// An invalid language version is only equal to itself.
+  @override
+  bool operator ==(Object other);
+
+  @override
+  int get hashCode;
+
+  /// The original invalid version string.
+  @override
+  String toString();
+}

diff --git a/pkgs/package_config/lib/src/package_config_impl.dart b/pkgs/package_config/lib/src/package_config_impl.dart
new file mode 100644
index 0000000..865e99a
--- /dev/null
+++ b/pkgs/package_config/lib/src/package_config_impl.dart

@@ -0,0 +1,568 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'errors.dart';
+import 'package_config.dart';
+import 'util.dart';
+
+export 'package_config.dart';
+
+const bool _disallowPackagesInsidePackageUriRoot = false;
+
+// Implementations of the main data types exposed by the API of this package.
+
+class SimplePackageConfig implements PackageConfig {
+  @override
+  final int version;
+  final Map<String, Package> _packages;
+  final PackageTree _packageTree;
+  @override
+  final Object? extraData;
+
+  factory SimplePackageConfig(int version, Iterable<Package> packages,
+      [Object? extraData, void Function(Object error)? onError]) {
+    onError ??= throwError;
+    var validVersion = _validateVersion(version, onError);
+    var sortedPackages = [...packages]..sort(_compareRoot);
+    var packageTree = _validatePackages(packages, sortedPackages, onError);
+    return SimplePackageConfig._(validVersion, packageTree,
+        {for (var p in packageTree.allPackages) p.name: p}, extraData);
+  }
+
+  SimplePackageConfig._(
+      this.version, this._packageTree, this._packages, this.extraData);
+
+  /// Creates empty configuration.
+  ///
+  /// The empty configuration can be used in cases where no configuration is
+  /// found, but code expects a non-null configuration.
+  ///
+  /// The version number is [PackageConfig.maxVersion] to avoid
+  /// minimum-version filters discarding the configuration.
+  const SimplePackageConfig.empty()
+      : version = PackageConfig.maxVersion,
+        _packageTree = const EmptyPackageTree(),
+        _packages = const <String, Package>{},
+        extraData = null;
+
+  static int _validateVersion(
+      int version, void Function(Object error) onError) {
+    if (version < 0 || version > PackageConfig.maxVersion) {
+      onError(PackageConfigArgumentError(version, 'version',
+          'Must be in the range 1 to ${PackageConfig.maxVersion}'));
+      return 2; // The minimal version supporting a SimplePackageConfig.
+    }
+    return version;
+  }
+
+  static PackageTree _validatePackages(Iterable<Package> originalPackages,
+      List<Package> packages, void Function(Object error) onError) {
+    var packageNames = <String>{};
+    var tree = TriePackageTree();
+    for (var originalPackage in packages) {
+      SimplePackage? newPackage;
+      if (originalPackage is! SimplePackage) {
+        // SimplePackage validates these properties.
+        newPackage = SimplePackage.validate(
+            originalPackage.name,
+            originalPackage.root,
+            originalPackage.packageUriRoot,
+            originalPackage.languageVersion,
+            originalPackage.extraData,
+            originalPackage.relativeRoot, (error) {
+          if (error is PackageConfigArgumentError) {
+            onError(PackageConfigArgumentError(packages, 'packages',
+                'Package ${newPackage!.name}: ${error.message}'));
+          } else {
+            onError(error);
+          }
+        });
+        if (newPackage == null) continue;
+      } else {
+        newPackage = originalPackage;
+      }
+      var name = newPackage.name;
+      if (packageNames.contains(name)) {
+        onError(PackageConfigArgumentError(
+            name, 'packages', "Duplicate package name '$name'"));
+        continue;
+      }
+      packageNames.add(name);
+      tree.add(newPackage, (error) {
+        if (error is ConflictException) {
+          // There is a conflict with an existing package.
+          var existingPackage = error.existingPackage;
+          switch (error.conflictType) {
+            case ConflictType.sameRoots:
+              onError(PackageConfigArgumentError(
+                  originalPackages,
+                  'packages',
+                  'Packages ${newPackage!.name} and ${existingPackage.name} '
+                      'have the same root directory: ${newPackage.root}.\n'));
+              break;
+            case ConflictType.interleaving:
+              // The new package is inside the package URI root of the existing
+              // package.
+              onError(PackageConfigArgumentError(
+                  originalPackages,
+                  'packages',
+                  'Package ${newPackage!.name} is inside the root of '
+                      'package ${existingPackage.name}, and the package root '
+                      'of ${existingPackage.name} is inside the root of '
+                      '${newPackage.name}.\n'
+                      '${existingPackage.name} package root: '
+                      '${existingPackage.packageUriRoot}\n'
+                      '${newPackage.name} root: ${newPackage.root}\n'));
+              break;
+            case ConflictType.insidePackageRoot:
+              onError(PackageConfigArgumentError(
+                  originalPackages,
+                  'packages',
+                  'Package ${newPackage!.name} is inside the package root of '
+                      'package ${existingPackage.name}.\n'
+                      '${existingPackage.name} package root: '
+                      '${existingPackage.packageUriRoot}\n'
+                      '${newPackage.name} root: ${newPackage.root}\n'));
+              break;
+          }
+        } else {
+          // Any other error.
+          onError(error);
+        }
+      });
+    }
+    return tree;
+  }
+
+  @override
+  Iterable<Package> get packages => _packages.values;
+
+  @override
+  Package? operator [](String packageName) => _packages[packageName];
+
+  @override
+  Package? packageOf(Uri file) => _packageTree.packageOf(file);
+
+  @override
+  Uri? resolve(Uri packageUri) {
+    var packageName = checkValidPackageUri(packageUri, 'packageUri');
+    return _packages[packageName]?.packageUriRoot.resolveUri(
+        Uri(path: packageUri.path.substring(packageName.length + 1)));
+  }
+
+  @override
+  Uri? toPackageUri(Uri nonPackageUri) {
+    if (nonPackageUri.isScheme('package')) {
+      throw PackageConfigArgumentError(
+          nonPackageUri, 'nonPackageUri', 'Must not be a package URI');
+    }
+    if (nonPackageUri.hasQuery || nonPackageUri.hasFragment) {
+      throw PackageConfigArgumentError(nonPackageUri, 'nonPackageUri',
+          'Must not have query or fragment part');
+    }
+    // Find package that file belongs to.
+    var package = _packageTree.packageOf(nonPackageUri);
+    if (package == null) return null;
+    // Check if it is inside the package URI root.
+    var path = nonPackageUri.toString();
+    var root = package.packageUriRoot.toString();
+    if (_beginsWith(package.root.toString().length, root, path)) {
+      var rest = path.substring(root.length);
+      return Uri(scheme: 'package', path: '${package.name}/$rest');
+    }
+    return null;
+  }
+}
+
+/// Configuration data for a single package.
+class SimplePackage implements Package {
+  @override
+  final String name;
+  @override
+  final Uri root;
+  @override
+  final Uri packageUriRoot;
+  @override
+  final LanguageVersion? languageVersion;
+  @override
+  final Object? extraData;
+  @override
+  final bool relativeRoot;
+
+  SimplePackage._(this.name, this.root, this.packageUriRoot,
+      this.languageVersion, this.extraData, this.relativeRoot);
+
+  /// Creates a [SimplePackage] with the provided content.
+  ///
+  /// The provided arguments must be valid.
+  ///
+  /// If the arguments are invalid then the error is reported by
+  /// calling [onError], then the erroneous entry is ignored.
+  ///
+  /// If [onError] is provided, the user is expected to be able to handle
+  /// errors themselves. An invalid [languageVersion] string
+  /// will be replaced with the string `"invalid"`. This allows
+  /// users to detect the difference between an absent version and
+  /// an invalid one.
+  ///
+  /// Returns `null` if the input is invalid and an approximately valid package
+  /// cannot be salvaged from the input.
+  static SimplePackage? validate(
+      String name,
+      Uri root,
+      Uri? packageUriRoot,
+      LanguageVersion? languageVersion,
+      Object? extraData,
+      bool relativeRoot,
+      void Function(Object error) onError) {
+    var fatalError = false;
+    var invalidIndex = checkPackageName(name);
+    if (invalidIndex >= 0) {
+      onError(PackageConfigFormatException(
+          'Not a valid package name', name, invalidIndex));
+      fatalError = true;
+    }
+    if (root.isScheme('package')) {
+      onError(PackageConfigArgumentError(
+          '$root', 'root', 'Must not be a package URI'));
+      fatalError = true;
+    } else if (!isAbsoluteDirectoryUri(root)) {
+      onError(PackageConfigArgumentError(
+          '$root',
+          'root',
+          'In package $name: Not an absolute URI with no query or fragment '
+              'with a path ending in /'));
+      // Try to recover. If the URI has a scheme,
+      // then ensure that the path ends with `/`.
+      if (!root.hasScheme) {
+        fatalError = true;
+      } else if (!root.path.endsWith('/')) {
+        root = root.replace(path: '${root.path}/');
+      }
+    }
+    if (packageUriRoot == null) {
+      packageUriRoot = root;
+    } else if (!fatalError) {
+      packageUriRoot = root.resolveUri(packageUriRoot);
+      if (!isAbsoluteDirectoryUri(packageUriRoot)) {
+        onError(PackageConfigArgumentError(
+            packageUriRoot,
+            'packageUriRoot',
+            'In package $name: Not an absolute URI with no query or fragment '
+                'with a path ending in /'));
+        packageUriRoot = root;
+      } else if (!isUriPrefix(root, packageUriRoot)) {
+        onError(PackageConfigArgumentError(packageUriRoot, 'packageUriRoot',
+            'The package URI root is not below the package root'));
+        packageUriRoot = root;
+      }
+    }
+    if (fatalError) return null;
+    return SimplePackage._(
+        name, root, packageUriRoot, languageVersion, extraData, relativeRoot);
+  }
+}
+
+/// Checks whether [source] is a valid Dart language version string.
+///
+/// The format is (as RegExp) `^(0|[1-9]\d+)\.(0|[1-9]\d+)$`.
+///
+/// Reports a format exception on [onError] if not, or if the numbers
+/// are too large (at most 32-bit signed integers).
+LanguageVersion parseLanguageVersion(
+    String? source, void Function(Object error) onError) {
+  var index = 0;
+  // Reads a positive decimal numeral. Returns the value of the numeral,
+  // or a negative number in case of an error.
+  // Starts at [index] and increments the index to the position after
+  // the numeral.
+  // It is an error if the numeral value is greater than 0x7FFFFFFFF.
+  // It is a recoverable error if the numeral starts with leading zeros.
+  int readNumeral() {
+    const maxValue = 0x7FFFFFFF;
+    if (index == source!.length) {
+      onError(PackageConfigFormatException('Missing number', source, index));
+      return -1;
+    }
+    var start = index;
+
+    var char = source.codeUnitAt(index);
+    var digit = char ^ 0x30;
+    if (digit > 9) {
+      onError(PackageConfigFormatException('Missing number', source, index));
+      return -1;
+    }
+    var firstDigit = digit;
+    var value = 0;
+    do {
+      value = value * 10 + digit;
+      if (value > maxValue) {
+        onError(
+            PackageConfigFormatException('Number too large', source, start));
+        return -1;
+      }
+      index++;
+      if (index == source.length) break;
+      char = source.codeUnitAt(index);
+      digit = char ^ 0x30;
+    } while (digit <= 9);
+    if (firstDigit == 0 && index > start + 1) {
+      onError(PackageConfigFormatException(
+          'Leading zero not allowed', source, start));
+    }
+    return value;
+  }
+
+  var major = readNumeral();
+  if (major < 0) {
+    return SimpleInvalidLanguageVersion(source);
+  }
+  if (index == source!.length || source.codeUnitAt(index) != $dot) {
+    onError(PackageConfigFormatException("Missing '.'", source, index));
+    return SimpleInvalidLanguageVersion(source);
+  }
+  index++;
+  var minor = readNumeral();
+  if (minor < 0) {
+    return SimpleInvalidLanguageVersion(source);
+  }
+  if (index != source.length) {
+    onError(PackageConfigFormatException(
+        'Unexpected trailing character', source, index));
+    return SimpleInvalidLanguageVersion(source);
+  }
+  return SimpleLanguageVersion(major, minor, source);
+}
+
+abstract class _SimpleLanguageVersionBase implements LanguageVersion {
+  @override
+  int compareTo(LanguageVersion other) {
+    var result = major.compareTo(other.major);
+    if (result != 0) return result;
+    return minor.compareTo(other.minor);
+  }
+}
+
+class SimpleLanguageVersion extends _SimpleLanguageVersionBase {
+  @override
+  final int major;
+  @override
+  final int minor;
+  String? _source;
+  SimpleLanguageVersion(this.major, this.minor, this._source);
+
+  @override
+  bool operator ==(Object other) =>
+      other is LanguageVersion && major == other.major && minor == other.minor;
+
+  @override
+  int get hashCode => (major * 17 ^ minor * 37) & 0x3FFFFFFF;
+
+  @override
+  String toString() => _source ??= '$major.$minor';
+}
+
+class SimpleInvalidLanguageVersion extends _SimpleLanguageVersionBase
+    implements InvalidLanguageVersion {
+  final String? _source;
+  SimpleInvalidLanguageVersion(this._source);
+  @override
+  int get major => -1;
+  @override
+  int get minor => -1;
+
+  @override
+  String toString() => _source!;
+}
+
+abstract class PackageTree {
+  Iterable<Package> get allPackages;
+  SimplePackage? packageOf(Uri file);
+}
+
+class _PackageTrieNode {
+  SimplePackage? package;
+
+  /// Indexed by path segment.
+  Map<String, _PackageTrieNode> map = {};
+}
+
+/// Packages of a package configuration ordered by root path.
+///
+/// A package has a root path and a package root path, where the latter
+/// contains the files exposed by `package:` URIs.
+///
+/// A package is said to be inside another package if the root path URI of
+/// the latter is a prefix of the root path URI of the former.
+///
+/// No two packages of a package may have the same root path.
+/// The package root path of a package must not be inside another package's
+/// root path.
+/// Entire other packages are allowed inside a package's root.
+class TriePackageTree implements PackageTree {
+  /// Indexed by URI scheme.
+  final Map<String, _PackageTrieNode> _map = {};
+
+  /// A list of all packages.
+  final List<SimplePackage> _packages = [];
+
+  @override
+  Iterable<Package> get allPackages sync* {
+    for (var package in _packages) {
+      yield package;
+    }
+  }
+
+  bool _checkConflict(_PackageTrieNode node, SimplePackage newPackage,
+      void Function(Object error) onError) {
+    var existingPackage = node.package;
+    if (existingPackage != null) {
+      // Trying to add package that is inside the existing package.
+      // 1) If it's an exact match it's not allowed (i.e. the roots can't be
+      //    the same).
+      if (newPackage.root.path.length == existingPackage.root.path.length) {
+        onError(ConflictException(
+            newPackage, existingPackage, ConflictType.sameRoots));
+        return true;
+      }
+      // 2) The existing package has a packageUriRoot thats inside the
+      //    root of the new package.
+      if (_beginsWith(0, newPackage.root.toString(),
+          existingPackage.packageUriRoot.toString())) {
+        onError(ConflictException(
+            newPackage, existingPackage, ConflictType.interleaving));
+        return true;
+      }
+
+      // For internal reasons we allow this (for now). One should still never do
+      // it though.
+      // 3) The new package is inside the packageUriRoot of existing package.
+      if (_disallowPackagesInsidePackageUriRoot) {
+        if (_beginsWith(0, existingPackage.packageUriRoot.toString(),
+            newPackage.root.toString())) {
+          onError(ConflictException(
+              newPackage, existingPackage, ConflictType.insidePackageRoot));
+          return true;
+        }
+      }
+    }
+    return false;
+  }
+
+  /// Tries to add `newPackage` to the tree.
+  ///
+  /// Reports a [ConflictException] if the added package conflicts with an
+  /// existing package.
+  /// It conflicts if its root or package root is the same as an existing
+  /// package's root or package root, is between the two, or if it's inside the
+  /// package root of an existing package.
+  ///
+  /// If a conflict is detected between [newPackage] and a previous package,
+  /// then [onError] is called with a [ConflictException] object
+  /// and the [newPackage] is not added to the tree.
+  ///
+  /// The packages are added in order of their root path.
+  void add(SimplePackage newPackage, void Function(Object error) onError) {
+    var root = newPackage.root;
+    var node = _map[root.scheme] ??= _PackageTrieNode();
+    if (_checkConflict(node, newPackage, onError)) return;
+    var segments = root.pathSegments;
+    // Notice that we're skipping the last segment as it's always the empty
+    // string because roots are directories.
+    for (var i = 0; i < segments.length - 1; i++) {
+      var path = segments[i];
+      node = node.map[path] ??= _PackageTrieNode();
+      if (_checkConflict(node, newPackage, onError)) return;
+    }
+    node.package = newPackage;
+    _packages.add(newPackage);
+  }
+
+  bool _isMatch(
+      String path, _PackageTrieNode node, List<SimplePackage> potential) {
+    var currentPackage = node.package;
+    if (currentPackage != null) {
+      var currentPackageRootLength = currentPackage.root.toString().length;
+      if (path.length == currentPackageRootLength) return true;
+      var currentPackageUriRoot = currentPackage.packageUriRoot.toString();
+      // Is [file] inside the package root of [currentPackage]?
+      if (currentPackageUriRoot.length == currentPackageRootLength ||
+          _beginsWith(currentPackageRootLength, currentPackageUriRoot, path)) {
+        return true;
+      }
+      potential.add(currentPackage);
+    }
+    return false;
+  }
+
+  @override
+  SimplePackage? packageOf(Uri file) {
+    var currentTrieNode = _map[file.scheme];
+    if (currentTrieNode == null) return null;
+    var path = file.toString();
+    var potential = <SimplePackage>[];
+    if (_isMatch(path, currentTrieNode, potential)) {
+      return currentTrieNode.package;
+    }
+    var segments = file.pathSegments;
+
+    for (var i = 0; i < segments.length - 1; i++) {
+      var segment = segments[i];
+      currentTrieNode = currentTrieNode!.map[segment];
+      if (currentTrieNode == null) break;
+      if (_isMatch(path, currentTrieNode, potential)) {
+        return currentTrieNode.package;
+      }
+    }
+    if (potential.isEmpty) return null;
+    return potential.last;
+  }
+}
+
+class EmptyPackageTree implements PackageTree {
+  const EmptyPackageTree();
+
+  @override
+  Iterable<Package> get allPackages => const Iterable<Package>.empty();
+
+  @override
+  SimplePackage? packageOf(Uri file) => null;
+}
+
+/// Checks whether [longerPath] begins with [parentPath].
+///
+/// Skips checking the [start] first characters which are assumed to
+/// already have been matched.
+bool _beginsWith(int start, String parentPath, String longerPath) {
+  if (longerPath.length < parentPath.length) return false;
+  for (var i = start; i < parentPath.length; i++) {
+    if (longerPath.codeUnitAt(i) != parentPath.codeUnitAt(i)) return false;
+  }
+  return true;
+}
+
+enum ConflictType { sameRoots, interleaving, insidePackageRoot }
+
+/// Conflict between packages added to the same configuration.
+///
+/// The [package] conflicts with [existingPackage] if it has
+/// the same root path or the package URI root path
+/// of [existingPackage] is inside the root path of [package].
+class ConflictException {
+  /// The existing package that [package] conflicts with.
+  final SimplePackage existingPackage;
+
+  /// The package that could not be added without a conflict.
+  final SimplePackage package;
+
+  /// Whether the conflict is with the package URI root of [existingPackage].
+  final ConflictType conflictType;
+
+  /// Creates a root conflict between [package] and [existingPackage].
+  ConflictException(this.package, this.existingPackage, this.conflictType);
+}
+
+/// Used for sorting packages by root path.
+int _compareRoot(Package p1, Package p2) =>
+    p1.root.toString().compareTo(p2.root.toString());

diff --git a/pkgs/package_config/lib/src/package_config_io.dart b/pkgs/package_config/lib/src/package_config_io.dart
new file mode 100644
index 0000000..8c5773b
--- /dev/null
+++ b/pkgs/package_config/lib/src/package_config_io.dart

@@ -0,0 +1,166 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// dart:io dependent functionality for reading and writing configuration files.
+
+import 'dart:convert';
+import 'dart:io';
+import 'dart:typed_data';
+
+import 'errors.dart';
+import 'package_config_impl.dart';
+import 'package_config_json.dart';
+import 'packages_file.dart' as packages_file;
+import 'util.dart';
+import 'util_io.dart';
+
+/// Name of directory where Dart tools store their configuration.
+///
+/// Directory is created in the package root directory.
+const dartToolDirName = '.dart_tool';
+
+/// Name of file containing new package configuration data.
+///
+/// File is stored in the dart tool directory.
+const packageConfigFileName = 'package_config.json';
+
+/// Name of file containing legacy package configuration data.
+///
+/// File is stored in the package root directory.
+const packagesFileName = '.packages';
+
+/// Reads a package configuration file.
+///
+/// Detects whether the [file] is a version one `.packages` file or
+/// a version two `package_config.json` file.
+///
+/// If the [file] is a `.packages` file and [preferNewest] is true,
+/// first checks whether there is an adjacent `.dart_tool/package_config.json`
+/// file, and if so, reads that instead.
+/// If [preferNewest] is false, the specified file is loaded even if it is
+/// a `.packages` file and there is an available `package_config.json` file.
+///
+/// The file must exist and be a normal file.
+Future<PackageConfig> readAnyConfigFile(
+    File file, bool preferNewest, void Function(Object error) onError) async {
+  if (preferNewest && fileName(file.path) == packagesFileName) {
+    var alternateFile = File(
+        pathJoin(dirName(file.path), dartToolDirName, packageConfigFileName));
+    if (alternateFile.existsSync()) {
+      return await readPackageConfigJsonFile(alternateFile, onError);
+    }
+  }
+  Uint8List bytes;
+  try {
+    bytes = await file.readAsBytes();
+  } catch (e) {
+    onError(e);
+    return const SimplePackageConfig.empty();
+  }
+  return parseAnyConfigFile(bytes, file.uri, onError);
+}
+
+/// Like [readAnyConfigFile] but uses a URI and an optional loader.
+Future<PackageConfig> readAnyConfigFileUri(
+    Uri file,
+    Future<Uint8List?> Function(Uri uri)? loader,
+    void Function(Object error) onError,
+    bool preferNewest) async {
+  if (file.isScheme('package')) {
+    throw PackageConfigArgumentError(
+        file, 'file', 'Must not be a package: URI');
+  }
+  if (loader == null) {
+    if (file.isScheme('file')) {
+      return await readAnyConfigFile(File.fromUri(file), preferNewest, onError);
+    }
+    loader = defaultLoader;
+  }
+  if (preferNewest && file.pathSegments.last == packagesFileName) {
+    var alternateFile = file.resolve('$dartToolDirName/$packageConfigFileName');
+    Uint8List? bytes;
+    try {
+      bytes = await loader(alternateFile);
+    } catch (e) {
+      onError(e);
+      return const SimplePackageConfig.empty();
+    }
+    if (bytes != null) {
+      return parsePackageConfigBytes(bytes, alternateFile, onError);
+    }
+  }
+  Uint8List? bytes;
+  try {
+    bytes = await loader(file);
+  } catch (e) {
+    onError(e);
+    return const SimplePackageConfig.empty();
+  }
+  if (bytes == null) {
+    onError(PackageConfigArgumentError(
+        file.toString(), 'file', 'File cannot be read'));
+    return const SimplePackageConfig.empty();
+  }
+  return parseAnyConfigFile(bytes, file, onError);
+}
+
+/// Parses a `.packages` or `package_config.json` file's contents.
+///
+/// Assumes it's a JSON file if the first non-whitespace character
+/// is `{`, otherwise assumes it's a `.packages` file.
+PackageConfig parseAnyConfigFile(
+    Uint8List bytes, Uri file, void Function(Object error) onError) {
+  var firstChar = firstNonWhitespaceChar(bytes);
+  if (firstChar != $lbrace) {
+    // Definitely not a JSON object, probably a .packages.
+    return packages_file.parse(bytes, file, onError);
+  }
+  return parsePackageConfigBytes(bytes, file, onError);
+}
+
+Future<PackageConfig> readPackageConfigJsonFile(
+    File file, void Function(Object error) onError) async {
+  Uint8List bytes;
+  try {
+    bytes = await file.readAsBytes();
+  } catch (error) {
+    onError(error);
+    return const SimplePackageConfig.empty();
+  }
+  return parsePackageConfigBytes(bytes, file.uri, onError);
+}
+
+Future<PackageConfig> readDotPackagesFile(
+    File file, void Function(Object error) onError) async {
+  Uint8List bytes;
+  try {
+    bytes = await file.readAsBytes();
+  } catch (error) {
+    onError(error);
+    return const SimplePackageConfig.empty();
+  }
+  return packages_file.parse(bytes, file.uri, onError);
+}
+
+Future<void> writePackageConfigJsonFile(
+    PackageConfig config, Directory targetDirectory) async {
+  // Write .dart_tool/package_config.json first.
+  var dartToolDir = Directory(pathJoin(targetDirectory.path, dartToolDirName));
+  await dartToolDir.create(recursive: true);
+  var file = File(pathJoin(dartToolDir.path, packageConfigFileName));
+  var baseUri = file.uri;
+
+  var sink = file.openWrite(encoding: utf8);
+  writePackageConfigJsonUtf8(config, baseUri, sink);
+  var doneJson = sink.close();
+
+  // Write .packages too.
+  file = File(pathJoin(targetDirectory.path, packagesFileName));
+  baseUri = file.uri;
+  sink = file.openWrite(encoding: utf8);
+  writeDotPackages(config, baseUri, sink);
+  var donePackages = sink.close();
+
+  await Future.wait([doneJson, donePackages]);
+}

diff --git a/pkgs/package_config/lib/src/package_config_json.dart b/pkgs/package_config/lib/src/package_config_json.dart
new file mode 100644
index 0000000..65560a0
--- /dev/null
+++ b/pkgs/package_config/lib/src/package_config_json.dart

@@ -0,0 +1,321 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Parsing and serialization of package configurations.
+
+import 'dart:convert';
+import 'dart:typed_data';
+
+import 'errors.dart';
+import 'package_config_impl.dart';
+import 'packages_file.dart' as packages_file;
+import 'util.dart';
+
+const String _configVersionKey = 'configVersion';
+const String _packagesKey = 'packages';
+const List<String> _topNames = [_configVersionKey, _packagesKey];
+const String _nameKey = 'name';
+const String _rootUriKey = 'rootUri';
+const String _packageUriKey = 'packageUri';
+const String _languageVersionKey = 'languageVersion';
+const List<String> _packageNames = [
+  _nameKey,
+  _rootUriKey,
+  _packageUriKey,
+  _languageVersionKey
+];
+
+const String _generatedKey = 'generated';
+const String _generatorKey = 'generator';
+const String _generatorVersionKey = 'generatorVersion';
+
+final _jsonUtf8Decoder = json.fuse(utf8).decoder;
+
+PackageConfig parsePackageConfigBytes(
+    Uint8List bytes, Uri file, void Function(Object error) onError) {
+  // TODO(lrn): Make this simpler. Maybe parse directly from bytes.
+  Object? jsonObject;
+  try {
+    jsonObject = _jsonUtf8Decoder.convert(bytes);
+  } on FormatException catch (e) {
+    onError(PackageConfigFormatException.from(e));
+    return const SimplePackageConfig.empty();
+  }
+  return parsePackageConfigJson(jsonObject, file, onError);
+}
+
+PackageConfig parsePackageConfigString(
+    String source, Uri file, void Function(Object error) onError) {
+  Object? jsonObject;
+  try {
+    jsonObject = jsonDecode(source);
+  } on FormatException catch (e) {
+    onError(PackageConfigFormatException.from(e));
+    return const SimplePackageConfig.empty();
+  }
+  return parsePackageConfigJson(jsonObject, file, onError);
+}
+
+/// Creates a [PackageConfig] from a parsed JSON-like object structure.
+///
+/// The [json] argument must be a JSON object (`Map<String, Object?>`)
+/// containing a `"configVersion"` entry with an integer value in the range
+/// 1 to [PackageConfig.maxVersion],
+/// and with a `"packages"` entry which is a JSON array (`List<Object?>`)
+/// containing JSON objects which each has the following properties:
+///
+/// * `"name"`: The package name as a string.
+/// * `"rootUri"`: The root of the package as a URI stored as a string.
+/// * `"packageUri"`: Optionally the root of for `package:` URI resolution
+///     for the package, as a relative URI below the root URI
+///     stored as a string.
+/// * `"languageVersion"`: Optionally a language version string which is a
+///     an integer numeral, a decimal point (`.`) and another integer numeral,
+///     where the integer numeral cannot have a sign, and can only have a
+///     leading zero if the entire numeral is a single zero.
+///
+/// The [baseLocation] is used as base URI to resolve the "rootUri"
+/// URI reference string.
+PackageConfig parsePackageConfigJson(
+    Object? json, Uri baseLocation, void Function(Object error) onError) {
+  if (!baseLocation.hasScheme || baseLocation.isScheme('package')) {
+    throw PackageConfigArgumentError(baseLocation.toString(), 'baseLocation',
+        'Must be an absolute non-package: URI');
+  }
+
+  if (!baseLocation.path.endsWith('/')) {
+    baseLocation = baseLocation.resolveUri(Uri(path: '.'));
+  }
+
+  String typeName<T>() {
+    if (0 is T) return 'int';
+    if ('' is T) return 'string';
+    if (const <Object?>[] is T) return 'array';
+    return 'object';
+  }
+
+  T? checkType<T>(Object? value, String name, [String? packageName]) {
+    if (value is T) return value;
+    // The only types we are called with are [int], [String], [List<Object?>]
+    // and Map<String, Object?>. Recognize which to give a better error message.
+    var message =
+        "$name${packageName != null ? " of package $packageName" : ""}"
+        ' is not a JSON ${typeName<T>()}';
+    onError(PackageConfigFormatException(message, value));
+    return null;
+  }
+
+  Package? parsePackage(Map<String, Object?> entry) {
+    String? name;
+    String? rootUri;
+    String? packageUri;
+    String? languageVersion;
+    Map<String, Object?>? extraData;
+    var hasName = false;
+    var hasRoot = false;
+    var hasVersion = false;
+    entry.forEach((key, value) {
+      switch (key) {
+        case _nameKey:
+          hasName = true;
+          name = checkType<String>(value, _nameKey);
+          break;
+        case _rootUriKey:
+          hasRoot = true;
+          rootUri = checkType<String>(value, _rootUriKey, name);
+          break;
+        case _packageUriKey:
+          packageUri = checkType<String>(value, _packageUriKey, name);
+          break;
+        case _languageVersionKey:
+          hasVersion = true;
+          languageVersion = checkType<String>(value, _languageVersionKey, name);
+          break;
+        default:
+          (extraData ??= {})[key] = value;
+          break;
+      }
+    });
+    if (!hasName) {
+      onError(PackageConfigFormatException('Missing name entry', entry));
+    }
+    if (!hasRoot) {
+      onError(PackageConfigFormatException('Missing rootUri entry', entry));
+    }
+    if (name == null || rootUri == null) return null;
+    var parsedRootUri = Uri.parse(rootUri!);
+    var relativeRoot = !hasAbsolutePath(parsedRootUri);
+    var root = baseLocation.resolveUri(parsedRootUri);
+    if (!root.path.endsWith('/')) root = root.replace(path: '${root.path}/');
+    var packageRoot = root;
+    if (packageUri != null) packageRoot = root.resolve(packageUri!);
+    if (!packageRoot.path.endsWith('/')) {
+      packageRoot = packageRoot.replace(path: '${packageRoot.path}/');
+    }
+
+    LanguageVersion? version;
+    if (languageVersion != null) {
+      version = parseLanguageVersion(languageVersion, onError);
+    } else if (hasVersion) {
+      version = SimpleInvalidLanguageVersion('invalid');
+    }
+
+    return SimplePackage.validate(
+        name!, root, packageRoot, version, extraData, relativeRoot, (error) {
+      if (error is ArgumentError) {
+        onError(
+          PackageConfigFormatException(
+              error.message.toString(), error.invalidValue),
+        );
+      } else {
+        onError(error);
+      }
+    });
+  }
+
+  var map = checkType<Map<String, Object?>>(json, 'value');
+  if (map == null) return const SimplePackageConfig.empty();
+  Map<String, Object?>? extraData;
+  List<Package>? packageList;
+  int? configVersion;
+  map.forEach((key, value) {
+    switch (key) {
+      case _configVersionKey:
+        configVersion = checkType<int>(value, _configVersionKey) ?? 2;
+        break;
+      case _packagesKey:
+        var packageArray = checkType<List<Object?>>(value, _packagesKey) ?? [];
+        var packages = <Package>[];
+        for (var package in packageArray) {
+          var packageMap =
+              checkType<Map<String, Object?>>(package, 'package entry');
+          if (packageMap != null) {
+            var entry = parsePackage(packageMap);
+            if (entry != null) {
+              packages.add(entry);
+            }
+          }
+        }
+        packageList = packages;
+        break;
+      default:
+        (extraData ??= {})[key] = value;
+        break;
+    }
+  });
+  if (configVersion == null) {
+    onError(PackageConfigFormatException('Missing configVersion entry', json));
+    configVersion = 2;
+  }
+  if (packageList == null) {
+    onError(PackageConfigFormatException('Missing packages list', json));
+    packageList = [];
+  }
+  return SimplePackageConfig(configVersion!, packageList!, extraData, (error) {
+    if (error is ArgumentError) {
+      onError(
+        PackageConfigFormatException(
+            error.message.toString(), error.invalidValue),
+      );
+    } else {
+      onError(error);
+    }
+  });
+}
+
+final _jsonUtf8Encoder = JsonUtf8Encoder('  ');
+
+void writePackageConfigJsonUtf8(
+    PackageConfig config, Uri? baseUri, Sink<List<int>> output) {
+  // Can be optimized.
+  var data = packageConfigToJson(config, baseUri);
+  output.add(_jsonUtf8Encoder.convert(data) as Uint8List);
+}
+
+void writePackageConfigJsonString(
+    PackageConfig config, Uri? baseUri, StringSink output) {
+  // Can be optimized.
+  var data = packageConfigToJson(config, baseUri);
+  output.write(const JsonEncoder.withIndent('  ').convert(data));
+}
+
+Map<String, Object?> packageConfigToJson(PackageConfig config, Uri? baseUri) =>
+    <String, Object?>{
+      ...?_extractExtraData(config.extraData, _topNames),
+      _configVersionKey: PackageConfig.maxVersion,
+      _packagesKey: [
+        for (var package in config.packages)
+          <String, Object?>{
+            _nameKey: package.name,
+            _rootUriKey: trailingSlash((package.relativeRoot
+                    ? relativizeUri(package.root, baseUri)
+                    : package.root)
+                .toString()),
+            if (package.root != package.packageUriRoot)
+              _packageUriKey: trailingSlash(
+                  relativizeUri(package.packageUriRoot, package.root)
+                      .toString()),
+            if (package.languageVersion != null &&
+                package.languageVersion is! InvalidLanguageVersion)
+              _languageVersionKey: package.languageVersion.toString(),
+            ...?_extractExtraData(package.extraData, _packageNames),
+          }
+      ],
+    };
+
+void writeDotPackages(PackageConfig config, Uri baseUri, StringSink output) {
+  var extraData = config.extraData;
+  // Write .packages too.
+  String? comment;
+  if (extraData is Map<String, Object?>) {
+    var generator = extraData[_generatorKey];
+    if (generator is String) {
+      var generated = extraData[_generatedKey];
+      var generatorVersion = extraData[_generatorVersionKey];
+      comment = 'Generated by $generator'
+          "${generatorVersion is String ? " $generatorVersion" : ""}"
+          "${generated is String ? " on $generated" : ""}.";
+    }
+  }
+  packages_file.write(output, config, baseUri: baseUri, comment: comment);
+}
+
+/// If "extraData" is a JSON map, then return it, otherwise return null.
+///
+/// If the value contains any of the [reservedNames] for the current context,
+/// entries with that name in the extra data are dropped.
+Map<String, Object?>? _extractExtraData(
+    Object? data, Iterable<String> reservedNames) {
+  if (data is Map<String, Object?>) {
+    if (data.isEmpty) return null;
+    for (var name in reservedNames) {
+      if (data.containsKey(name)) {
+        var filteredData = {
+          for (var key in data.keys)
+            if (!reservedNames.contains(key)) key: data[key]
+        };
+        if (filteredData.isEmpty) return null;
+        for (var value in filteredData.values) {
+          if (!_validateJson(value)) return null;
+        }
+        return filteredData;
+      }
+    }
+    return data;
+  }
+  return null;
+}
+
+/// Checks that the object is a valid JSON-like data structure.
+bool _validateJson(Object? object) {
+  if (object == null || true == object || false == object) return true;
+  if (object is num || object is String) return true;
+  if (object is List<Object?>) {
+    return object.every(_validateJson);
+  }
+  if (object is Map<String, Object?>) {
+    return object.values.every(_validateJson);
+  }
+  return false;
+}

diff --git a/pkgs/package_config/lib/src/packages_file.dart b/pkgs/package_config/lib/src/packages_file.dart
new file mode 100644
index 0000000..bf68f2c
--- /dev/null
+++ b/pkgs/package_config/lib/src/packages_file.dart

@@ -0,0 +1,193 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'errors.dart';
+import 'package_config_impl.dart';
+import 'util.dart';
+
+/// The language version prior to the release of language versioning.
+///
+/// This is the default language version used by all packages from a
+/// `.packages` file.
+final LanguageVersion _languageVersion = LanguageVersion(2, 7);
+
+/// Parses a `.packages` file into a [PackageConfig].
+///
+/// The [source] is the byte content of a `.packages` file, assumed to be
+/// UTF-8 encoded. In practice, all significant parts of the file must be ASCII,
+/// so Latin-1 or Windows-1252 encoding will also work fine.
+///
+/// If the file content is available as a string, its [String.codeUnits] can
+/// be used as the `source` argument of this function.
+///
+/// The [baseLocation] is used as a base URI to resolve all relative
+/// URI references against.
+/// If the content was read from a file, `baseLocation` should be the
+/// location of that file.
+///
+/// Returns a simple package configuration where each package's
+/// [Package.packageUriRoot] is the same as its [Package.root]
+/// and it has no [Package.languageVersion].
+PackageConfig parse(
+    List<int> source, Uri baseLocation, void Function(Object error) onError) {
+  if (baseLocation.isScheme('package')) {
+    onError(PackageConfigArgumentError(
+        baseLocation, 'baseLocation', 'Must not be a package: URI'));
+    return PackageConfig.empty;
+  }
+  var index = 0;
+  var packages = <Package>[];
+  var packageNames = <String>{};
+  while (index < source.length) {
+    var ignoreLine = false;
+    var start = index;
+    var separatorIndex = -1;
+    var end = source.length;
+    var char = source[index++];
+    if (char == $cr || char == $lf) {
+      continue;
+    }
+    if (char == $colon) {
+      onError(PackageConfigFormatException(
+          'Missing package name', source, index - 1));
+      ignoreLine = true; // Ignore if package name is invalid.
+    } else {
+      ignoreLine = char == $hash; // Ignore if comment.
+    }
+    var queryStart = -1;
+    var fragmentStart = -1;
+    while (index < source.length) {
+      char = source[index++];
+      if (char == $colon && separatorIndex < 0) {
+        separatorIndex = index - 1;
+      } else if (char == $cr || char == $lf) {
+        end = index - 1;
+        break;
+      } else if (char == $question && queryStart < 0 && fragmentStart < 0) {
+        queryStart = index - 1;
+      } else if (char == $hash && fragmentStart < 0) {
+        fragmentStart = index - 1;
+      }
+    }
+    if (ignoreLine) continue;
+    if (separatorIndex < 0) {
+      onError(
+          PackageConfigFormatException("No ':' on line", source, index - 1));
+      continue;
+    }
+    var packageName = String.fromCharCodes(source, start, separatorIndex);
+    var invalidIndex = checkPackageName(packageName);
+    if (invalidIndex >= 0) {
+      onError(PackageConfigFormatException(
+          'Not a valid package name', source, start + invalidIndex));
+      continue;
+    }
+    if (queryStart >= 0) {
+      onError(PackageConfigFormatException(
+          'Location URI must not have query', source, queryStart));
+      end = queryStart;
+    } else if (fragmentStart >= 0) {
+      onError(PackageConfigFormatException(
+          'Location URI must not have fragment', source, fragmentStart));
+      end = fragmentStart;
+    }
+    var packageValue = String.fromCharCodes(source, separatorIndex + 1, end);
+    Uri packageLocation;
+    try {
+      packageLocation = Uri.parse(packageValue);
+    } on FormatException catch (e) {
+      onError(PackageConfigFormatException.from(e));
+      continue;
+    }
+    var relativeRoot = !hasAbsolutePath(packageLocation);
+    packageLocation = baseLocation.resolveUri(packageLocation);
+    if (packageLocation.isScheme('package')) {
+      onError(PackageConfigFormatException(
+          'Package URI as location for package', source, separatorIndex + 1));
+      continue;
+    }
+    var path = packageLocation.path;
+    if (!path.endsWith('/')) {
+      path += '/';
+      packageLocation = packageLocation.replace(path: path);
+    }
+    if (packageNames.contains(packageName)) {
+      onError(PackageConfigFormatException(
+          'Same package name occurred more than once', source, start));
+      continue;
+    }
+    var rootUri = packageLocation;
+    if (path.endsWith('/lib/')) {
+      // Assume default Pub package layout. Include package itself in root.
+      rootUri =
+          packageLocation.replace(path: path.substring(0, path.length - 4));
+    }
+    var package = SimplePackage.validate(packageName, rootUri, packageLocation,
+        _languageVersion, null, relativeRoot, (error) {
+      if (error is ArgumentError) {
+        onError(PackageConfigFormatException(error.message.toString(), source));
+      } else {
+        onError(error);
+      }
+    });
+    if (package != null) {
+      packages.add(package);
+      packageNames.add(packageName);
+    }
+  }
+  return SimplePackageConfig(1, packages, null, onError);
+}
+
+/// Writes the configuration to a [StringSink].
+///
+/// If [comment] is provided, the output will contain this comment
+/// with `# ` in front of each line.
+/// Lines are defined as ending in line feed (`'\n'`). If the final
+/// line of the comment doesn't end in a line feed, one will be added.
+///
+/// If [baseUri] is provided, package locations will be made relative
+/// to the base URI, if possible, before writing.
+void write(StringSink output, PackageConfig config,
+    {Uri? baseUri, String? comment}) {
+  if (baseUri != null && !baseUri.isAbsolute) {
+    throw PackageConfigArgumentError(baseUri, 'baseUri', 'Must be absolute');
+  }
+
+  if (comment != null) {
+    var lines = comment.split('\n');
+    if (lines.last.isEmpty) lines.removeLast();
+    for (var commentLine in lines) {
+      output.write('# ');
+      output.writeln(commentLine);
+    }
+  } else {
+    output.write('# generated by package:package_config at ');
+    output.write(DateTime.now());
+    output.writeln();
+  }
+  for (var package in config.packages) {
+    var packageName = package.name;
+    var uri = package.packageUriRoot;
+    // Validate packageName.
+    if (!isValidPackageName(packageName)) {
+      throw PackageConfigArgumentError(
+          config, 'config', '"$packageName" is not a valid package name');
+    }
+    if (uri.scheme == 'package') {
+      throw PackageConfigArgumentError(
+          config, 'config', 'Package location must not be a package URI: $uri');
+    }
+    output.write(packageName);
+    output.write(':');
+    // If baseUri is provided, make the URI relative to baseUri.
+    if (baseUri != null) {
+      uri = relativizeUri(uri, baseUri)!;
+    }
+    if (!uri.path.endsWith('/')) {
+      uri = uri.replace(path: '${uri.path}/');
+    }
+    output.write(uri);
+    output.writeln();
+  }
+}

diff --git a/pkgs/package_config/lib/src/util.dart b/pkgs/package_config/lib/src/util.dart
new file mode 100644
index 0000000..4f0210c
--- /dev/null
+++ b/pkgs/package_config/lib/src/util.dart

@@ -0,0 +1,253 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Utility methods used by more than one library in the package.
+library;
+
+import 'errors.dart';
+
+// All ASCII characters that are valid in a package name, with space
+// for all the invalid ones (including space).
+const String _validPackageNameCharacters =
+    r"                                 !  $ &'()*+,-. 0123456789 ; =  "
+    r'@ABCDEFGHIJKLMNOPQRSTUVWXYZ    _ abcdefghijklmnopqrstuvwxyz   ~ ';
+
+/// Tests whether something is a valid Dart package name.
+bool isValidPackageName(String string) {
+  return checkPackageName(string) < 0;
+}
+
+/// Check if a string is a valid package name.
+///
+/// Valid package names contain only characters in [_validPackageNameCharacters]
+/// and must contain at least one non-'.' character.
+///
+/// Returns `-1` if the string is valid.
+/// Otherwise returns the index of the first invalid character,
+/// or `string.length` if the string contains no non-'.' character.
+int checkPackageName(String string) {
+  // Becomes non-zero if any non-'.' character is encountered.
+  var nonDot = 0;
+  for (var i = 0; i < string.length; i++) {
+    var c = string.codeUnitAt(i);
+    if (c > 0x7f || _validPackageNameCharacters.codeUnitAt(c) <= $space) {
+      return i;
+    }
+    nonDot += c ^ $dot;
+  }
+  if (nonDot == 0) return string.length;
+  return -1;
+}
+
+/// Validate that a [Uri] is a valid `package:` URI.
+///
+/// Used to validate user input.
+///
+/// Returns the package name extracted from the package URI,
+/// which is the path segment between `package:` and the first `/`.
+String checkValidPackageUri(Uri packageUri, String name) {
+  if (packageUri.scheme != 'package') {
+    throw PackageConfigArgumentError(packageUri, name, 'Not a package: URI');
+  }
+  if (packageUri.hasAuthority) {
+    throw PackageConfigArgumentError(
+        packageUri, name, 'Package URIs must not have a host part');
+  }
+  if (packageUri.hasQuery) {
+    // A query makes no sense if resolved to a file: URI.
+    throw PackageConfigArgumentError(
+        packageUri, name, 'Package URIs must not have a query part');
+  }
+  if (packageUri.hasFragment) {
+    // We could leave the fragment after the URL when resolving,
+    // but it would be odd if "package:foo/foo.dart#1" and
+    // "package:foo/foo.dart#2" were considered different libraries.
+    // Keep the syntax open in case we ever get multiple libraries in one file.
+    throw PackageConfigArgumentError(
+        packageUri, name, 'Package URIs must not have a fragment part');
+  }
+  if (packageUri.path.startsWith('/')) {
+    throw PackageConfigArgumentError(
+        packageUri, name, "Package URIs must not start with a '/'");
+  }
+  var firstSlash = packageUri.path.indexOf('/');
+  if (firstSlash == -1) {
+    throw PackageConfigArgumentError(packageUri, name,
+        "Package URIs must start with the package name followed by a '/'");
+  }
+  var packageName = packageUri.path.substring(0, firstSlash);
+  var badIndex = checkPackageName(packageName);
+  if (badIndex >= 0) {
+    if (packageName.isEmpty) {
+      throw PackageConfigArgumentError(
+          packageUri, name, 'Package names mus be non-empty');
+    }
+    if (badIndex == packageName.length) {
+      throw PackageConfigArgumentError(packageUri, name,
+          "Package names must contain at least one non-'.' character");
+    }
+    assert(badIndex < packageName.length);
+    var badCharCode = packageName.codeUnitAt(badIndex);
+    var badChar = 'U+${badCharCode.toRadixString(16).padLeft(4, '0')}';
+    if (badCharCode >= 0x20 && badCharCode <= 0x7e) {
+      // Printable character.
+      badChar = "'${packageName[badIndex]}' ($badChar)";
+    }
+    throw PackageConfigArgumentError(
+        packageUri, name, 'Package names must not contain $badChar');
+  }
+  return packageName;
+}
+
+/// Checks whether URI is just an absolute directory.
+///
+/// * It must have a scheme.
+/// * It must not have a query or fragment.
+/// * The path must end with `/`.
+bool isAbsoluteDirectoryUri(Uri uri) {
+  if (uri.hasQuery) return false;
+  if (uri.hasFragment) return false;
+  if (!uri.hasScheme) return false;
+  var path = uri.path;
+  if (!path.endsWith('/')) return false;
+  return true;
+}
+
+/// Whether the former URI is a prefix of the latter.
+bool isUriPrefix(Uri prefix, Uri path) {
+  assert(!prefix.hasFragment);
+  assert(!prefix.hasQuery);
+  assert(!path.hasQuery);
+  assert(!path.hasFragment);
+  assert(prefix.path.endsWith('/'));
+  return path.toString().startsWith(prefix.toString());
+}
+
+/// Finds the first non-JSON-whitespace character in a file.
+///
+/// Used to heuristically detect whether a file is a JSON file or an .ini file.
+int firstNonWhitespaceChar(List<int> bytes) {
+  for (var i = 0; i < bytes.length; i++) {
+    var char = bytes[i];
+    if (char != 0x20 && char != 0x09 && char != 0x0a && char != 0x0d) {
+      return char;
+    }
+  }
+  return -1;
+}
+
+/// Appends a trailing `/` if the path doesn't end with one.
+String trailingSlash(String path) {
+  if (path.isEmpty || path.endsWith('/')) return path;
+  return '$path/';
+}
+
+/// Whether a URI should not be considered relative to the base URI.
+///
+/// Used to determine whether a parsed root URI is relative
+/// to the configuration file or not.
+/// If it is relative, then it's rewritten as relative when
+/// output again later. If not, it's output as absolute.
+bool hasAbsolutePath(Uri uri) =>
+    uri.hasScheme || uri.hasAuthority || uri.hasAbsolutePath;
+
+/// Attempts to return a relative path-only URI for [uri].
+///
+/// First removes any query or fragment part from [uri].
+///
+/// If [uri] is already relative (has no scheme), it's returned as-is.
+/// If that is not desired, the caller can pass `baseUri.resolveUri(uri)`
+/// as the [uri] instead.
+///
+/// If the [uri] has a scheme or authority part which differs from
+/// the [baseUri], or if there is no overlap in the paths of the
+/// two URIs at all, the [uri] is returned as-is.
+///
+/// Otherwise the result is a path-only URI which satisfies
+/// `baseUri.resolveUri(result) == uri`,
+///
+/// The `baseUri` must be absolute.
+Uri? relativizeUri(Uri? uri, Uri? baseUri) {
+  if (baseUri == null) return uri;
+  assert(baseUri.isAbsolute);
+  if (uri!.hasQuery || uri.hasFragment) {
+    uri = Uri(
+        scheme: uri.scheme,
+        userInfo: uri.hasAuthority ? uri.userInfo : null,
+        host: uri.hasAuthority ? uri.host : null,
+        port: uri.hasAuthority ? uri.port : null,
+        path: uri.path);
+  }
+
+  // Already relative. We assume the caller knows what they are doing.
+  if (!uri.isAbsolute) return uri;
+
+  if (baseUri.scheme != uri.scheme) {
+    return uri;
+  }
+
+  // If authority differs, we could remove the scheme, but it's not worth it.
+  if (uri.hasAuthority != baseUri.hasAuthority) return uri;
+  if (uri.hasAuthority) {
+    if (uri.userInfo != baseUri.userInfo ||
+        uri.host.toLowerCase() != baseUri.host.toLowerCase() ||
+        uri.port != baseUri.port) {
+      return uri;
+    }
+  }
+
+  baseUri = baseUri.normalizePath();
+  var base = [...baseUri.pathSegments];
+  if (base.isNotEmpty) base.removeLast();
+  uri = uri.normalizePath();
+  var target = [...uri.pathSegments];
+  if (target.isNotEmpty && target.last.isEmpty) target.removeLast();
+  var index = 0;
+  while (index < base.length && index < target.length) {
+    if (base[index] != target[index]) {
+      break;
+    }
+    index++;
+  }
+  if (index == base.length) {
+    if (index == target.length) {
+      return Uri(path: './');
+    }
+    return Uri(path: target.skip(index).join('/'));
+  } else if (index > 0) {
+    var buffer = StringBuffer();
+    for (var n = base.length - index; n > 0; --n) {
+      buffer.write('../');
+    }
+    buffer.writeAll(target.skip(index), '/');
+    return Uri(path: buffer.toString());
+  } else {
+    return uri;
+  }
+}
+
+// Character constants used by this package.
+/// "Line feed" control character.
+const int $lf = 0x0a;
+
+/// "Carriage return" control character.
+const int $cr = 0x0d;
+
+/// Space character.
+const int $space = 0x20;
+
+/// Character `#`.
+const int $hash = 0x23;
+
+/// Character `.`.
+const int $dot = 0x2e;
+
+/// Character `:`.
+const int $colon = 0x3a;
+
+/// Character `?`.
+const int $question = 0x3f;
+
+/// Character `{`.
+const int $lbrace = 0x7b;

diff --git a/pkgs/package_config/lib/src/util_io.dart b/pkgs/package_config/lib/src/util_io.dart
new file mode 100644
index 0000000..4680eef
--- /dev/null
+++ b/pkgs/package_config/lib/src/util_io.dart

@@ -0,0 +1,108 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Utility methods requiring dart:io and used by more than one library in the
+/// package.
+library;
+
+import 'dart:io';
+import 'dart:typed_data';
+
+Future<Uint8List?> defaultLoader(Uri uri) async {
+  if (uri.isScheme('file')) {
+    var file = File.fromUri(uri);
+    try {
+      return await file.readAsBytes();
+    } catch (_) {
+      return null;
+    }
+  }
+  if (uri.isScheme('http') || uri.isScheme('https')) {
+    return _httpGet(uri);
+  }
+  throw UnsupportedError('Default URI unsupported scheme: $uri');
+}
+
+Future<Uint8List?> _httpGet(Uri uri) async {
+  assert(uri.isScheme('http') || uri.isScheme('https'));
+  var client = HttpClient();
+  var request = await client.getUrl(uri);
+  var response = await request.close();
+  if (response.statusCode != HttpStatus.ok) {
+    return null;
+  }
+  var splitContent = await response.toList();
+  var totalLength = 0;
+  if (splitContent.length == 1) {
+    var part = splitContent[0];
+    if (part is Uint8List) {
+      return part;
+    }
+  }
+  for (var list in splitContent) {
+    totalLength += list.length;
+  }
+  var result = Uint8List(totalLength);
+  var offset = 0;
+  for (var contentPart in splitContent as Iterable<Uint8List>) {
+    result.setRange(offset, offset + contentPart.length, contentPart);
+    offset += contentPart.length;
+  }
+  return result;
+}
+
+/// The file name of a path.
+///
+/// The file name is everything after the last occurrence of
+/// [Platform.pathSeparator], or the entire string if no
+/// path separator occurs in the string.
+String fileName(String path) {
+  var separator = Platform.pathSeparator;
+  var lastSeparator = path.lastIndexOf(separator);
+  if (lastSeparator < 0) return path;
+  return path.substring(lastSeparator + separator.length);
+}
+
+/// The directory name of a path.
+///
+/// The directory name is everything before the last occurrence of
+/// [Platform.pathSeparator], or the empty string if no
+/// path separator occurs in the string.
+String dirName(String path) {
+  var separator = Platform.pathSeparator;
+  var lastSeparator = path.lastIndexOf(separator);
+  if (lastSeparator < 0) return '';
+  return path.substring(0, lastSeparator);
+}
+
+/// Join path parts with the [Platform.pathSeparator].
+///
+/// If a part ends with a path separator, then no extra separator is
+/// inserted.
+String pathJoin(String part1, String part2, [String? part3]) {
+  var separator = Platform.pathSeparator;
+  var separator1 = part1.endsWith(separator) ? '' : separator;
+  if (part3 == null) {
+    return '$part1$separator1$part2';
+  }
+  var separator2 = part2.endsWith(separator) ? '' : separator;
+  return '$part1$separator1$part2$separator2$part3';
+}
+
+/// Join an unknown number of path parts with [Platform.pathSeparator].
+///
+/// If a part ends with a path separator, then no extra separator is
+/// inserted.
+String pathJoinAll(Iterable<String> parts) {
+  var buffer = StringBuffer();
+  var separator = '';
+  for (var part in parts) {
+    buffer
+      ..write(separator)
+      ..write(part);
+    separator =
+        part.endsWith(Platform.pathSeparator) ? '' : Platform.pathSeparator;
+  }
+  return buffer.toString();
+}

diff --git a/pkgs/package_config/pubspec.yaml b/pkgs/package_config/pubspec.yaml
new file mode 100644
index 0000000..28f3e13
--- /dev/null
+++ b/pkgs/package_config/pubspec.yaml

@@ -0,0 +1,14 @@
+name: package_config
+version: 2.1.1
+description: Support for reading and writing Dart Package Configuration files.
+repository: https://github.com/dart-lang/tools/tree/main/pkgs/package_config
+
+environment:
+  sdk: ^3.4.0
+
+dependencies:
+  path: ^1.8.0
+
+dev_dependencies:
+  dart_flutter_team_lints: ^3.0.0
+  test: ^1.16.0

diff --git a/pkgs/package_config/test/bench.dart b/pkgs/package_config/test/bench.dart
new file mode 100644
index 0000000..8428481
--- /dev/null
+++ b/pkgs/package_config/test/bench.dart

@@ -0,0 +1,71 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:convert';
+import 'dart:typed_data';
+
+import 'package:package_config/src/errors.dart';
+import 'package:package_config/src/package_config_json.dart';
+
+void bench(final int size, final bool doPrint) {
+  var sb = StringBuffer();
+  sb.writeln('{');
+  sb.writeln('"configVersion": 2,');
+  sb.writeln('"packages": [');
+  for (var i = 0; i < size; i++) {
+    if (i != 0) {
+      sb.writeln(',');
+    }
+    sb.writeln('{');
+    sb.writeln('  "name": "p_$i",');
+    sb.writeln('  "rootUri": "file:///p_$i/",');
+    sb.writeln('  "packageUri": "lib/",');
+    sb.writeln('  "languageVersion": "2.5",');
+    sb.writeln('  "nonstandard": true');
+    sb.writeln('}');
+  }
+  sb.writeln('],');
+  sb.writeln('"generator": "pub",');
+  sb.writeln('"other": [42]');
+  sb.writeln('}');
+  var stopwatch = Stopwatch()..start();
+  var config = parsePackageConfigBytes(
+    // ignore: unnecessary_cast
+    utf8.encode(sb.toString()) as Uint8List,
+    Uri.parse('file:///tmp/.dart_tool/file.dart'),
+    throwError,
+  );
+  final read = stopwatch.elapsedMilliseconds;
+
+  stopwatch.reset();
+  for (var i = 0; i < size; i++) {
+    if (config.packageOf(Uri.parse('file:///p_$i/lib/src/foo.dart'))!.name !=
+        'p_$i') {
+      throw StateError('Unexpected result!');
+    }
+  }
+  final lookup = stopwatch.elapsedMilliseconds;
+
+  if (doPrint) {
+    print('Read file with $size packages in $read ms, '
+        'looked up all packages in $lookup ms');
+  }
+}
+
+void main(List<String> args) {
+  if (args.length != 1 && args.length != 2) {
+    throw ArgumentError('Expects arguments: <size> <warmup iterations>?');
+  }
+  final size = int.parse(args[0]);
+  if (args.length > 1) {
+    final warmups = int.parse(args[1]);
+    print('Performing $warmups warmup iterations.');
+    for (var i = 0; i < warmups; i++) {
+      bench(10, false);
+    }
+  }
+
+  // Benchmark.
+  bench(size, true);
+}

diff --git a/pkgs/package_config/test/discovery_test.dart b/pkgs/package_config/test/discovery_test.dart
new file mode 100644
index 0000000..6d1b655
--- /dev/null
+++ b/pkgs/package_config/test/discovery_test.dart

@@ -0,0 +1,346 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+@TestOn('vm')
+library;
+
+import 'dart:io';
+
+import 'package:package_config/package_config.dart';
+import 'package:test/test.dart';
+
+import 'src/util.dart';
+import 'src/util_io.dart';
+
+const packagesFile = '''
+# A comment
+foo:file:///dart/packages/foo/
+bar:/dart/packages/bar/
+baz:packages/baz/
+''';
+
+const packageConfigFile = '''
+{
+  "configVersion": 2,
+  "packages": [
+    {
+      "name": "foo",
+      "rootUri": "file:///dart/packages/foo/"
+    },
+    {
+      "name": "bar",
+      "rootUri": "/dart/packages/bar/"
+    },
+    {
+      "name": "baz",
+      "rootUri": "../packages/baz/"
+    }
+  ],
+  "extra": [42]
+}
+''';
+
+void validatePackagesFile(PackageConfig resolver, Directory directory) {
+  expect(resolver, isNotNull);
+  expect(resolver.resolve(pkg('foo', 'bar/baz')),
+      equals(Uri.parse('file:///dart/packages/foo/bar/baz')));
+  expect(resolver.resolve(pkg('bar', 'baz/qux')),
+      equals(Uri.parse('file:///dart/packages/bar/baz/qux')));
+  expect(resolver.resolve(pkg('baz', 'qux/foo')),
+      equals(Uri.directory(directory.path).resolve('packages/baz/qux/foo')));
+  expect([for (var p in resolver.packages) p.name],
+      unorderedEquals(['foo', 'bar', 'baz']));
+}
+
+void main() {
+  group('findPackages', () {
+    // Finds package_config.json if there.
+    fileTest('package_config.json', {
+      '.packages': 'invalid .packages file',
+      'script.dart': 'main(){}',
+      'packages': {'shouldNotBeFound': <Never, Never>{}},
+      '.dart_tool': {
+        'package_config.json': packageConfigFile,
+      }
+    }, (Directory directory) async {
+      var config = (await findPackageConfig(directory))!;
+      expect(config.version, 2); // Found package_config.json file.
+      validatePackagesFile(config, directory);
+    });
+
+    // Finds .packages if no package_config.json.
+    fileTest('.packages', {
+      '.packages': packagesFile,
+      'script.dart': 'main(){}',
+      'packages': {'shouldNotBeFound': <Object, Object>{}}
+    }, (Directory directory) async {
+      var config = (await findPackageConfig(directory))!;
+      expect(config.version, 1); // Found .packages file.
+      validatePackagesFile(config, directory);
+    });
+
+    // Finds package_config.json in super-directory.
+    fileTest('package_config.json recursive', {
+      '.packages': packagesFile,
+      '.dart_tool': {
+        'package_config.json': packageConfigFile,
+      },
+      'subdir': {
+        'script.dart': 'main(){}',
+      }
+    }, (Directory directory) async {
+      var config = (await findPackageConfig(subdir(directory, 'subdir/')))!;
+      expect(config.version, 2);
+      validatePackagesFile(config, directory);
+    });
+
+    // Finds .packages in super-directory.
+    fileTest('.packages recursive', {
+      '.packages': packagesFile,
+      'subdir': {'script.dart': 'main(){}'}
+    }, (Directory directory) async {
+      var config = (await findPackageConfig(subdir(directory, 'subdir/')))!;
+      expect(config.version, 1);
+      validatePackagesFile(config, directory);
+    });
+
+    // Does not find a packages/ directory, and returns null if nothing found.
+    fileTest('package directory packages not supported', {
+      'packages': {
+        'foo': <String, dynamic>{},
+      }
+    }, (Directory directory) async {
+      var config = await findPackageConfig(directory);
+      expect(config, null);
+    });
+
+    group('throws', () {
+      fileTest('invalid .packages', {
+        '.packages': 'not a .packages file',
+      }, (Directory directory) {
+        expect(findPackageConfig(directory), throwsA(isA<FormatException>()));
+      });
+
+      fileTest('invalid .packages as JSON', {
+        '.packages': packageConfigFile,
+      }, (Directory directory) {
+        expect(findPackageConfig(directory), throwsA(isA<FormatException>()));
+      });
+
+      fileTest('invalid .packages', {
+        '.dart_tool': {
+          'package_config.json': 'not a JSON file',
+        }
+      }, (Directory directory) {
+        expect(findPackageConfig(directory), throwsA(isA<FormatException>()));
+      });
+
+      fileTest('invalid .packages as INI', {
+        '.dart_tool': {
+          'package_config.json': packagesFile,
+        }
+      }, (Directory directory) {
+        expect(findPackageConfig(directory), throwsA(isA<FormatException>()));
+      });
+    });
+
+    group('handles error', () {
+      fileTest('invalid .packages', {
+        '.packages': 'not a .packages file',
+      }, (Directory directory) async {
+        var hadError = false;
+        await findPackageConfig(directory,
+            onError: expectAsync1((error) {
+              hadError = true;
+              expect(error, isA<FormatException>());
+            }, max: -1));
+        expect(hadError, true);
+      });
+
+      fileTest('invalid .packages as JSON', {
+        '.packages': packageConfigFile,
+      }, (Directory directory) async {
+        var hadError = false;
+        await findPackageConfig(directory,
+            onError: expectAsync1((error) {
+              hadError = true;
+              expect(error, isA<FormatException>());
+            }, max: -1));
+        expect(hadError, true);
+      });
+
+      fileTest('invalid package_config not JSON', {
+        '.dart_tool': {
+          'package_config.json': 'not a JSON file',
+        }
+      }, (Directory directory) async {
+        var hadError = false;
+        await findPackageConfig(directory,
+            onError: expectAsync1((error) {
+              hadError = true;
+              expect(error, isA<FormatException>());
+            }, max: -1));
+        expect(hadError, true);
+      });
+
+      fileTest('invalid package config as INI', {
+        '.dart_tool': {
+          'package_config.json': packagesFile,
+        }
+      }, (Directory directory) async {
+        var hadError = false;
+        await findPackageConfig(directory,
+            onError: expectAsync1((error) {
+              hadError = true;
+              expect(error, isA<FormatException>());
+            }, max: -1));
+        expect(hadError, true);
+      });
+    });
+
+    // Does not find .packages if no package_config.json and minVersion > 1.
+    fileTest('.packages ignored', {
+      '.packages': packagesFile,
+      'script.dart': 'main(){}'
+    }, (Directory directory) async {
+      var config = await findPackageConfig(directory, minVersion: 2);
+      expect(config, null);
+    });
+
+    // Finds package_config.json in super-directory, with .packages in
+    // subdir and minVersion > 1.
+    fileTest('package_config.json recursive .packages ignored', {
+      '.dart_tool': {
+        'package_config.json': packageConfigFile,
+      },
+      'subdir': {
+        '.packages': packagesFile,
+        'script.dart': 'main(){}',
+      }
+    }, (Directory directory) async {
+      var config = (await findPackageConfig(subdir(directory, 'subdir/'),
+          minVersion: 2))!;
+      expect(config.version, 2);
+      validatePackagesFile(config, directory);
+    });
+  });
+
+  group('loadPackageConfig', () {
+    // Load a specific files
+    group('package_config.json', () {
+      var files = {
+        '.packages': packagesFile,
+        '.dart_tool': {
+          'package_config.json': packageConfigFile,
+        },
+      };
+      fileTest('directly', files, (Directory directory) async {
+        var file =
+            dirFile(subdir(directory, '.dart_tool'), 'package_config.json');
+        var config = await loadPackageConfig(file);
+        expect(config.version, 2);
+        validatePackagesFile(config, directory);
+      });
+      fileTest('indirectly through .packages', files,
+          (Directory directory) async {
+        var file = dirFile(directory, '.packages');
+        var config = await loadPackageConfig(file);
+        expect(config.version, 2);
+        validatePackagesFile(config, directory);
+      });
+      fileTest('prefer .packages', files, (Directory directory) async {
+        var file = dirFile(directory, '.packages');
+        var config = await loadPackageConfig(file, preferNewest: false);
+        expect(config.version, 1);
+        validatePackagesFile(config, directory);
+      });
+    });
+
+    fileTest('package_config.json non-default name', {
+      '.packages': packagesFile,
+      'subdir': {
+        'pheldagriff': packageConfigFile,
+      },
+    }, (Directory directory) async {
+      var file = dirFile(directory, 'subdir/pheldagriff');
+      var config = await loadPackageConfig(file);
+      expect(config.version, 2);
+      validatePackagesFile(config, directory);
+    });
+
+    fileTest('package_config.json named .packages', {
+      'subdir': {
+        '.packages': packageConfigFile,
+      },
+    }, (Directory directory) async {
+      var file = dirFile(directory, 'subdir/.packages');
+      var config = await loadPackageConfig(file);
+      expect(config.version, 2);
+      validatePackagesFile(config, directory);
+    });
+
+    fileTest('.packages', {
+      '.packages': packagesFile,
+    }, (Directory directory) async {
+      var file = dirFile(directory, '.packages');
+      var config = await loadPackageConfig(file);
+      expect(config.version, 1);
+      validatePackagesFile(config, directory);
+    });
+
+    fileTest('.packages non-default name', {
+      'pheldagriff': packagesFile,
+    }, (Directory directory) async {
+      var file = dirFile(directory, 'pheldagriff');
+      var config = await loadPackageConfig(file);
+      expect(config.version, 1);
+      validatePackagesFile(config, directory);
+    });
+
+    fileTest('no config found', {}, (Directory directory) {
+      var file = dirFile(directory, 'anyname');
+      expect(
+          () => loadPackageConfig(file), throwsA(isA<FileSystemException>()));
+    });
+
+    fileTest('no config found, handled', {}, (Directory directory) async {
+      var file = dirFile(directory, 'anyname');
+      var hadError = false;
+      await loadPackageConfig(file,
+          onError: expectAsync1((error) {
+            hadError = true;
+            expect(error, isA<FileSystemException>());
+          }, max: -1));
+      expect(hadError, true);
+    });
+
+    fileTest('specified file syntax error', {
+      'anyname': 'syntax error',
+    }, (Directory directory) {
+      var file = dirFile(directory, 'anyname');
+      expect(() => loadPackageConfig(file), throwsFormatException);
+    });
+
+    // Find package_config.json in subdir even if initial file syntax error.
+    fileTest('specified file syntax onError', {
+      '.packages': 'syntax error',
+      '.dart_tool': {
+        'package_config.json': packageConfigFile,
+      },
+    }, (Directory directory) async {
+      var file = dirFile(directory, '.packages');
+      var config = await loadPackageConfig(file);
+      expect(config.version, 2);
+      validatePackagesFile(config, directory);
+    });
+
+    // A file starting with `{` is a package_config.json file.
+    fileTest('file syntax error with {', {
+      '.packages': '{syntax error',
+    }, (Directory directory) {
+      var file = dirFile(directory, '.packages');
+      expect(() => loadPackageConfig(file), throwsFormatException);
+    });
+  });
+}

diff --git a/pkgs/package_config/test/discovery_uri_test.dart b/pkgs/package_config/test/discovery_uri_test.dart
new file mode 100644
index 0000000..542bf0a
--- /dev/null
+++ b/pkgs/package_config/test/discovery_uri_test.dart

@@ -0,0 +1,310 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+@TestOn('vm')
+library;
+
+import 'package:package_config/package_config.dart';
+import 'package:test/test.dart';
+
+import 'src/util.dart';
+
+const packagesFile = '''
+# A comment
+foo:file:///dart/packages/foo/
+bar:/dart/packages/bar/
+baz:packages/baz/
+''';
+
+const packageConfigFile = '''
+{
+  "configVersion": 2,
+  "packages": [
+    {
+      "name": "foo",
+      "rootUri": "file:///dart/packages/foo/"
+    },
+    {
+      "name": "bar",
+      "rootUri": "/dart/packages/bar/"
+    },
+    {
+      "name": "baz",
+      "rootUri": "../packages/baz/"
+    }
+  ],
+  "extra": [42]
+}
+''';
+
+void validatePackagesFile(PackageConfig resolver, Uri directory) {
+  expect(resolver, isNotNull);
+  expect(resolver.resolve(pkg('foo', 'bar/baz')),
+      equals(Uri.parse('file:///dart/packages/foo/bar/baz')));
+  expect(resolver.resolve(pkg('bar', 'baz/qux')),
+      equals(directory.resolve('/dart/packages/bar/baz/qux')));
+  expect(resolver.resolve(pkg('baz', 'qux/foo')),
+      equals(directory.resolve('packages/baz/qux/foo')));
+  expect([for (var p in resolver.packages) p.name],
+      unorderedEquals(['foo', 'bar', 'baz']));
+}
+
+void main() {
+  group('findPackages', () {
+    // Finds package_config.json if there.
+    loaderTest('package_config.json', {
+      '.packages': 'invalid .packages file',
+      'script.dart': 'main(){}',
+      'packages': {'shouldNotBeFound': <String, dynamic>{}},
+      '.dart_tool': {
+        'package_config.json': packageConfigFile,
+      }
+    }, (directory, loader) async {
+      var config = (await findPackageConfigUri(directory, loader: loader))!;
+      expect(config.version, 2); // Found package_config.json file.
+      validatePackagesFile(config, directory);
+    });
+
+    // Finds .packages if no package_config.json.
+    loaderTest('.packages', {
+      '.packages': packagesFile,
+      'script.dart': 'main(){}',
+      'packages': {'shouldNotBeFound': <String, dynamic>{}}
+    }, (directory, loader) async {
+      var config = (await findPackageConfigUri(directory, loader: loader))!;
+      expect(config.version, 1); // Found .packages file.
+      validatePackagesFile(config, directory);
+    });
+
+    // Finds package_config.json in super-directory.
+    loaderTest('package_config.json recursive', {
+      '.packages': packagesFile,
+      '.dart_tool': {
+        'package_config.json': packageConfigFile,
+      },
+      'subdir': {
+        'script.dart': 'main(){}',
+      }
+    }, (directory, loader) async {
+      var config = (await findPackageConfigUri(directory.resolve('subdir/'),
+          loader: loader))!;
+      expect(config.version, 2);
+      validatePackagesFile(config, directory);
+    });
+
+    // Finds .packages in super-directory.
+    loaderTest('.packages recursive', {
+      '.packages': packagesFile,
+      'subdir': {'script.dart': 'main(){}'}
+    }, (directory, loader) async {
+      var config = (await findPackageConfigUri(directory.resolve('subdir/'),
+          loader: loader))!;
+      expect(config.version, 1);
+      validatePackagesFile(config, directory);
+    });
+
+    // Does not find a packages/ directory, and returns null if nothing found.
+    loaderTest('package directory packages not supported', {
+      'packages': {
+        'foo': <String, dynamic>{},
+      }
+    }, (Uri directory, loader) async {
+      var config = await findPackageConfigUri(directory, loader: loader);
+      expect(config, null);
+    });
+
+    loaderTest('invalid .packages', {
+      '.packages': 'not a .packages file',
+    }, (Uri directory, loader) {
+      expect(() => findPackageConfigUri(directory, loader: loader),
+          throwsA(isA<FormatException>()));
+    });
+
+    loaderTest('invalid .packages as JSON', {
+      '.packages': packageConfigFile,
+    }, (Uri directory, loader) {
+      expect(() => findPackageConfigUri(directory, loader: loader),
+          throwsA(isA<FormatException>()));
+    });
+
+    loaderTest('invalid .packages', {
+      '.dart_tool': {
+        'package_config.json': 'not a JSON file',
+      }
+    }, (Uri directory, loader) {
+      expect(() => findPackageConfigUri(directory, loader: loader),
+          throwsA(isA<FormatException>()));
+    });
+
+    loaderTest('invalid .packages as INI', {
+      '.dart_tool': {
+        'package_config.json': packagesFile,
+      }
+    }, (Uri directory, loader) {
+      expect(() => findPackageConfigUri(directory, loader: loader),
+          throwsA(isA<FormatException>()));
+    });
+
+    // Does not find .packages if no package_config.json and minVersion > 1.
+    loaderTest('.packages ignored', {
+      '.packages': packagesFile,
+      'script.dart': 'main(){}'
+    }, (directory, loader) async {
+      var config =
+          await findPackageConfigUri(directory, minVersion: 2, loader: loader);
+      expect(config, null);
+    });
+
+    // Finds package_config.json in super-directory, with .packages in
+    // subdir and minVersion > 1.
+    loaderTest('package_config.json recursive ignores .packages', {
+      '.dart_tool': {
+        'package_config.json': packageConfigFile,
+      },
+      'subdir': {
+        '.packages': packagesFile,
+        'script.dart': 'main(){}',
+      }
+    }, (directory, loader) async {
+      var config = (await findPackageConfigUri(directory.resolve('subdir/'),
+          minVersion: 2, loader: loader))!;
+      expect(config.version, 2);
+      validatePackagesFile(config, directory);
+    });
+  });
+
+  group('loadPackageConfig', () {
+    // Load a specific files
+    group('package_config.json', () {
+      var files = {
+        '.packages': packagesFile,
+        '.dart_tool': {
+          'package_config.json': packageConfigFile,
+        },
+      };
+      loaderTest('directly', files, (Uri directory, loader) async {
+        var file = directory.resolve('.dart_tool/package_config.json');
+        var config = await loadPackageConfigUri(file, loader: loader);
+        expect(config.version, 2);
+        validatePackagesFile(config, directory);
+      });
+      loaderTest('indirectly through .packages', files,
+          (Uri directory, loader) async {
+        var file = directory.resolve('.packages');
+        var config = await loadPackageConfigUri(file, loader: loader);
+        expect(config.version, 2);
+        validatePackagesFile(config, directory);
+      });
+    });
+
+    loaderTest('package_config.json non-default name', {
+      '.packages': packagesFile,
+      'subdir': {
+        'pheldagriff': packageConfigFile,
+      },
+    }, (Uri directory, loader) async {
+      var file = directory.resolve('subdir/pheldagriff');
+      var config = await loadPackageConfigUri(file, loader: loader);
+      expect(config.version, 2);
+      validatePackagesFile(config, directory);
+    });
+
+    loaderTest('package_config.json named .packages', {
+      'subdir': {
+        '.packages': packageConfigFile,
+      },
+    }, (Uri directory, loader) async {
+      var file = directory.resolve('subdir/.packages');
+      var config = await loadPackageConfigUri(file, loader: loader);
+      expect(config.version, 2);
+      validatePackagesFile(config, directory);
+    });
+
+    loaderTest('.packages', {
+      '.packages': packagesFile,
+    }, (Uri directory, loader) async {
+      var file = directory.resolve('.packages');
+      var config = await loadPackageConfigUri(file, loader: loader);
+      expect(config.version, 1);
+      validatePackagesFile(config, directory);
+    });
+
+    loaderTest('.packages non-default name', {
+      'pheldagriff': packagesFile,
+    }, (Uri directory, loader) async {
+      var file = directory.resolve('pheldagriff');
+      var config = await loadPackageConfigUri(file, loader: loader);
+      expect(config.version, 1);
+      validatePackagesFile(config, directory);
+    });
+
+    loaderTest('no config found', {}, (Uri directory, loader) {
+      var file = directory.resolve('anyname');
+      expect(() => loadPackageConfigUri(file, loader: loader),
+          throwsA(isA<ArgumentError>()));
+    });
+
+    loaderTest('no config found, handle error', {},
+        (Uri directory, loader) async {
+      var file = directory.resolve('anyname');
+      var hadError = false;
+      await loadPackageConfigUri(file,
+          loader: loader,
+          onError: expectAsync1((error) {
+            hadError = true;
+            expect(error, isA<ArgumentError>());
+          }, max: -1));
+      expect(hadError, true);
+    });
+
+    loaderTest('specified file syntax error', {
+      'anyname': 'syntax error',
+    }, (Uri directory, loader) {
+      var file = directory.resolve('anyname');
+      expect(() => loadPackageConfigUri(file, loader: loader),
+          throwsFormatException);
+    });
+
+    loaderTest('specified file syntax onError', {
+      'anyname': 'syntax error',
+    }, (directory, loader) async {
+      var file = directory.resolve('anyname');
+      var hadError = false;
+      await loadPackageConfigUri(file,
+          loader: loader,
+          onError: expectAsync1((error) {
+            hadError = true;
+            expect(error, isA<FormatException>());
+          }, max: -1));
+      expect(hadError, true);
+    });
+
+    // Don't look for package_config.json if original file not named .packages.
+    loaderTest('specified file syntax error with alternative', {
+      'anyname': 'syntax error',
+      '.dart_tool': {
+        'package_config.json': packageConfigFile,
+      },
+    }, (directory, loader) async {
+      var file = directory.resolve('anyname');
+      expect(() => loadPackageConfigUri(file, loader: loader),
+          throwsFormatException);
+    });
+
+    // A file starting with `{` is a package_config.json file.
+    loaderTest('file syntax error with {', {
+      '.packages': '{syntax error',
+    }, (directory, loader) async {
+      var file = directory.resolve('.packages');
+      var hadError = false;
+      await loadPackageConfigUri(file,
+          loader: loader,
+          onError: expectAsync1((error) {
+            hadError = true;
+            expect(error, isA<FormatException>());
+          }, max: -1));
+      expect(hadError, true);
+    });
+  });
+}

diff --git a/pkgs/package_config/test/package_config_impl_test.dart b/pkgs/package_config/test/package_config_impl_test.dart
new file mode 100644
index 0000000..0f39963
--- /dev/null
+++ b/pkgs/package_config/test/package_config_impl_test.dart

@@ -0,0 +1,188 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:convert' show jsonDecode;
+
+import 'package:package_config/package_config_types.dart';
+import 'package:test/test.dart';
+import 'src/util.dart';
+
+void main() {
+  var unique = Object();
+  var root = Uri.file('/tmp/root/');
+
+  group('LanguageVersion', () {
+    test('minimal', () {
+      var version = LanguageVersion(3, 5);
+      expect(version.major, 3);
+      expect(version.minor, 5);
+    });
+
+    test('negative major', () {
+      expect(() => LanguageVersion(-1, 1), throwsArgumentError);
+    });
+
+    test('negative minor', () {
+      expect(() => LanguageVersion(1, -1), throwsArgumentError);
+    });
+
+    test('minimal parse', () {
+      var version = LanguageVersion.parse('3.5');
+      expect(version.major, 3);
+      expect(version.minor, 5);
+    });
+
+    void failParse(String name, String input) {
+      test('$name - error', () {
+        expect(() => LanguageVersion.parse(input),
+            throwsA(isA<PackageConfigError>()));
+        expect(() => LanguageVersion.parse(input), throwsFormatException);
+        var failed = false;
+        var actual = LanguageVersion.parse(input, onError: (_) {
+          failed = true;
+        });
+        expect(failed, true);
+        expect(actual, isA<LanguageVersion>());
+      });
+    }
+
+    failParse('Leading zero major', '01.1');
+    failParse('Leading zero minor', '1.01');
+    failParse('Sign+ major', '+1.1');
+    failParse('Sign- major', '-1.1');
+    failParse('Sign+ minor', '1.+1');
+    failParse('Sign- minor', '1.-1');
+    failParse('WhiteSpace 1', ' 1.1');
+    failParse('WhiteSpace 2', '1 .1');
+    failParse('WhiteSpace 3', '1. 1');
+    failParse('WhiteSpace 4', '1.1 ');
+  });
+
+  group('Package', () {
+    test('minimal', () {
+      var package = Package('name', root, extraData: unique);
+      expect(package.name, 'name');
+      expect(package.root, root);
+      expect(package.packageUriRoot, root);
+      expect(package.languageVersion, null);
+      expect(package.extraData, same(unique));
+    });
+
+    test('absolute package root', () {
+      var version = LanguageVersion(1, 1);
+      var absolute = root.resolve('foo/bar/');
+      var package = Package('name', root,
+          packageUriRoot: absolute,
+          relativeRoot: false,
+          languageVersion: version,
+          extraData: unique);
+      expect(package.name, 'name');
+      expect(package.root, root);
+      expect(package.packageUriRoot, absolute);
+      expect(package.languageVersion, version);
+      expect(package.extraData, same(unique));
+      expect(package.relativeRoot, false);
+    });
+
+    test('relative package root', () {
+      var relative = Uri.parse('foo/bar/');
+      var absolute = root.resolveUri(relative);
+      var package = Package('name', root,
+          packageUriRoot: relative, relativeRoot: true, extraData: unique);
+      expect(package.name, 'name');
+      expect(package.root, root);
+      expect(package.packageUriRoot, absolute);
+      expect(package.relativeRoot, true);
+      expect(package.languageVersion, null);
+      expect(package.extraData, same(unique));
+    });
+
+    for (var badName in ['a/z', 'a:z', '', '...']) {
+      test("Invalid name '$badName'", () {
+        expect(() => Package(badName, root), throwsPackageConfigError);
+      });
+    }
+
+    test('Invalid root, not absolute', () {
+      expect(
+          () => Package('name', Uri.parse('/foo/')), throwsPackageConfigError);
+    });
+
+    test('Invalid root, not ending in slash', () {
+      expect(() => Package('name', Uri.parse('file:///foo')),
+          throwsPackageConfigError);
+    });
+
+    test('invalid package root, not ending in slash', () {
+      expect(() => Package('name', root, packageUriRoot: Uri.parse('foo')),
+          throwsPackageConfigError);
+    });
+
+    test('invalid package root, not inside root', () {
+      expect(() => Package('name', root, packageUriRoot: Uri.parse('../baz/')),
+          throwsPackageConfigError);
+    });
+  });
+
+  group('package config', () {
+    test('empty', () {
+      var empty = PackageConfig([], extraData: unique);
+      expect(empty.version, 2);
+      expect(empty.packages, isEmpty);
+      expect(empty.extraData, same(unique));
+      expect(empty.resolve(pkg('a', 'b')), isNull);
+    });
+
+    test('single', () {
+      var package = Package('name', root);
+      var single = PackageConfig([package], extraData: unique);
+      expect(single.version, 2);
+      expect(single.packages, hasLength(1));
+      expect(single.extraData, same(unique));
+      expect(single.resolve(pkg('a', 'b')), isNull);
+      var resolved = single.resolve(pkg('name', 'a/b'));
+      expect(resolved, root.resolve('a/b'));
+    });
+  });
+  test('writeString', () {
+    var config = PackageConfig([
+      Package('foo', Uri.parse('file:///pkg/foo/'),
+          packageUriRoot: Uri.parse('file:///pkg/foo/lib/'),
+          relativeRoot: false,
+          languageVersion: LanguageVersion(2, 4),
+          extraData: {'foo': 'foo!'}),
+      Package('bar', Uri.parse('file:///pkg/bar/'),
+          packageUriRoot: Uri.parse('file:///pkg/bar/lib/'),
+          relativeRoot: true,
+          extraData: {'bar': 'bar!'}),
+    ], extraData: {
+      'extra': 'data'
+    });
+    var buffer = StringBuffer();
+    PackageConfig.writeString(config, buffer, Uri.parse('file:///pkg/'));
+    var text = buffer.toString();
+    var json = jsonDecode(text); // Is valid JSON.
+    expect(json, {
+      'configVersion': 2,
+      'packages': unorderedEquals([
+        {
+          'name': 'foo',
+          'rootUri': 'file:///pkg/foo/',
+          'packageUri': 'lib/',
+          'languageVersion': '2.4',
+          'foo': 'foo!',
+        },
+        {
+          'name': 'bar',
+          'rootUri': 'bar/',
+          'packageUri': 'lib/',
+          'bar': 'bar!',
+        },
+      ]),
+      'extra': 'data',
+    });
+  });
+}
+
+final Matcher throwsPackageConfigError = throwsA(isA<PackageConfigError>());

diff --git a/pkgs/package_config/test/parse_test.dart b/pkgs/package_config/test/parse_test.dart
new file mode 100644
index 0000000..a92b9bf
--- /dev/null
+++ b/pkgs/package_config/test/parse_test.dart

@@ -0,0 +1,552 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:convert';
+import 'dart:typed_data';
+
+import 'package:package_config/package_config_types.dart';
+import 'package:package_config/src/errors.dart';
+import 'package:package_config/src/package_config_json.dart';
+import 'package:package_config/src/packages_file.dart' as packages;
+import 'package:test/test.dart';
+
+import 'src/util.dart';
+
+void main() {
+  group('.packages', () {
+    test('valid', () {
+      var packagesFile = '# Generated by pub yadda yadda\n'
+          'foo:file:///foo/lib/\n'
+          'bar:/bar/lib/\n'
+          'baz:lib/\n';
+      var result = packages.parse(utf8.encode(packagesFile),
+          Uri.parse('file:///tmp/file.dart'), throwError);
+      expect(result.version, 1);
+      expect({for (var p in result.packages) p.name}, {'foo', 'bar', 'baz'});
+      expect(result.resolve(pkg('foo', 'foo.dart')),
+          Uri.parse('file:///foo/lib/foo.dart'));
+      expect(result.resolve(pkg('bar', 'bar.dart')),
+          Uri.parse('file:///bar/lib/bar.dart'));
+      expect(result.resolve(pkg('baz', 'baz.dart')),
+          Uri.parse('file:///tmp/lib/baz.dart'));
+
+      var foo = result['foo']!;
+      expect(foo, isNotNull);
+      expect(foo.root, Uri.parse('file:///foo/'));
+      expect(foo.packageUriRoot, Uri.parse('file:///foo/lib/'));
+      expect(foo.languageVersion, LanguageVersion(2, 7));
+      expect(foo.relativeRoot, false);
+    });
+
+    test('valid empty', () {
+      var packagesFile = '# Generated by pub yadda yadda\n';
+      var result = packages.parse(
+          utf8.encode(packagesFile), Uri.file('/tmp/file.dart'), throwError);
+      expect(result.version, 1);
+      expect({for (var p in result.packages) p.name}, <String>{});
+    });
+
+    group('invalid', () {
+      var baseFile = Uri.file('/tmp/file.dart');
+      void testThrows(String name, String content) {
+        test(name, () {
+          expect(
+              () => packages.parse(utf8.encode(content), baseFile, throwError),
+              throwsA(isA<FormatException>()));
+        });
+        test('$name, handle error', () {
+          var hadError = false;
+          packages.parse(utf8.encode(content), baseFile, (error) {
+            hadError = true;
+            expect(error, isA<FormatException>());
+          });
+          expect(hadError, true);
+        });
+      }
+
+      testThrows('repeated package name', 'foo:lib/\nfoo:lib\n');
+      testThrows('no colon', 'foo\n');
+      testThrows('empty package name', ':lib/\n');
+      testThrows('dot only package name', '.:lib/\n');
+      testThrows('dot only package name', '..:lib/\n');
+      testThrows('invalid package name character', 'f\\o:lib/\n');
+      testThrows('package URI', 'foo:package:bar/lib/');
+      testThrows('location with query', 'f\\o:lib/?\n');
+      testThrows('location with fragment', 'f\\o:lib/#\n');
+    });
+  });
+
+  group('package_config.json', () {
+    test('valid', () {
+      var packageConfigFile = '''
+        {
+          "configVersion": 2,
+          "packages": [
+            {
+              "name": "foo",
+              "rootUri": "file:///foo/",
+              "packageUri": "lib/",
+              "languageVersion": "2.5",
+              "nonstandard": true
+            },
+            {
+              "name": "bar",
+              "rootUri": "/bar/",
+              "packageUri": "lib/",
+              "languageVersion": "9999.9999"
+            },
+            {
+              "name": "baz",
+              "rootUri": "../",
+              "packageUri": "lib/"
+            },
+            {
+              "name": "noslash",
+              "rootUri": "../noslash",
+              "packageUri": "lib"
+            }
+          ],
+          "generator": "pub",
+          "other": [42]
+        }
+        ''';
+      var config = parsePackageConfigBytes(
+          // ignore: unnecessary_cast
+          utf8.encode(packageConfigFile) as Uint8List,
+          Uri.parse('file:///tmp/.dart_tool/file.dart'),
+          throwError);
+      expect(config.version, 2);
+      expect({for (var p in config.packages) p.name},
+          {'foo', 'bar', 'baz', 'noslash'});
+
+      expect(config.resolve(pkg('foo', 'foo.dart')),
+          Uri.parse('file:///foo/lib/foo.dart'));
+      expect(config.resolve(pkg('bar', 'bar.dart')),
+          Uri.parse('file:///bar/lib/bar.dart'));
+      expect(config.resolve(pkg('baz', 'baz.dart')),
+          Uri.parse('file:///tmp/lib/baz.dart'));
+
+      var foo = config['foo']!;
+      expect(foo, isNotNull);
+      expect(foo.root, Uri.parse('file:///foo/'));
+      expect(foo.packageUriRoot, Uri.parse('file:///foo/lib/'));
+      expect(foo.languageVersion, LanguageVersion(2, 5));
+      expect(foo.extraData, {'nonstandard': true});
+      expect(foo.relativeRoot, false);
+
+      var bar = config['bar']!;
+      expect(bar, isNotNull);
+      expect(bar.root, Uri.parse('file:///bar/'));
+      expect(bar.packageUriRoot, Uri.parse('file:///bar/lib/'));
+      expect(bar.languageVersion, LanguageVersion(9999, 9999));
+      expect(bar.extraData, null);
+      expect(bar.relativeRoot, false);
+
+      var baz = config['baz']!;
+      expect(baz, isNotNull);
+      expect(baz.root, Uri.parse('file:///tmp/'));
+      expect(baz.packageUriRoot, Uri.parse('file:///tmp/lib/'));
+      expect(baz.languageVersion, null);
+      expect(baz.relativeRoot, true);
+
+      // No slash after root or package root. One is inserted.
+      var noslash = config['noslash']!;
+      expect(noslash, isNotNull);
+      expect(noslash.root, Uri.parse('file:///tmp/noslash/'));
+      expect(noslash.packageUriRoot, Uri.parse('file:///tmp/noslash/lib/'));
+      expect(noslash.languageVersion, null);
+      expect(noslash.relativeRoot, true);
+
+      expect(config.extraData, {
+        'generator': 'pub',
+        'other': [42]
+      });
+    });
+
+    test('valid other order', () {
+      // The ordering in the file is not important.
+      var packageConfigFile = '''
+        {
+          "generator": "pub",
+          "other": [42],
+          "packages": [
+            {
+              "languageVersion": "2.5",
+              "packageUri": "lib/",
+              "rootUri": "file:///foo/",
+              "name": "foo"
+            },
+            {
+              "packageUri": "lib/",
+              "languageVersion": "9999.9999",
+              "rootUri": "/bar/",
+              "name": "bar"
+            },
+            {
+              "packageUri": "lib/",
+              "name": "baz",
+              "rootUri": "../"
+            }
+          ],
+          "configVersion": 2
+        }
+        ''';
+      var config = parsePackageConfigBytes(
+          // ignore: unnecessary_cast
+          utf8.encode(packageConfigFile) as Uint8List,
+          Uri.parse('file:///tmp/.dart_tool/file.dart'),
+          throwError);
+      expect(config.version, 2);
+      expect({for (var p in config.packages) p.name}, {'foo', 'bar', 'baz'});
+
+      expect(config.resolve(pkg('foo', 'foo.dart')),
+          Uri.parse('file:///foo/lib/foo.dart'));
+      expect(config.resolve(pkg('bar', 'bar.dart')),
+          Uri.parse('file:///bar/lib/bar.dart'));
+      expect(config.resolve(pkg('baz', 'baz.dart')),
+          Uri.parse('file:///tmp/lib/baz.dart'));
+      expect(config.extraData, {
+        'generator': 'pub',
+        'other': [42]
+      });
+    });
+
+    // Check that a few minimal configurations are valid.
+    // These form the basis of invalid tests below.
+    var cfg = '"configVersion":2';
+    var pkgs = '"packages":[]';
+    var name = '"name":"foo"';
+    var root = '"rootUri":"/foo/"';
+    test('minimal', () {
+      var config = parsePackageConfigBytes(
+          // ignore: unnecessary_cast
+          utf8.encode('{$cfg,$pkgs}') as Uint8List,
+          Uri.parse('file:///tmp/.dart_tool/file.dart'),
+          throwError);
+      expect(config.version, 2);
+      expect(config.packages, isEmpty);
+    });
+    test('minimal package', () {
+      // A package must have a name and a rootUri, the remaining properties
+      // are optional.
+      var config = parsePackageConfigBytes(
+          // ignore: unnecessary_cast
+          utf8.encode('{$cfg,"packages":[{$name,$root}]}') as Uint8List,
+          Uri.parse('file:///tmp/.dart_tool/file.dart'),
+          throwError);
+      expect(config.version, 2);
+      expect(config.packages.first.name, 'foo');
+    });
+
+    test('nested packages', () {
+      var configBytes = utf8.encode(json.encode({
+        'configVersion': 2,
+        'packages': [
+          {'name': 'foo', 'rootUri': '/foo/', 'packageUri': 'lib/'},
+          {'name': 'bar', 'rootUri': '/foo/bar/', 'packageUri': 'lib/'},
+          {'name': 'baz', 'rootUri': '/foo/bar/baz/', 'packageUri': 'lib/'},
+          {'name': 'qux', 'rootUri': '/foo/qux/', 'packageUri': 'lib/'},
+        ]
+      }));
+      // ignore: unnecessary_cast
+      var config = parsePackageConfigBytes(configBytes as Uint8List,
+          Uri.parse('file:///tmp/.dart_tool/file.dart'), throwError);
+      expect(config.version, 2);
+      expect(config.packageOf(Uri.parse('file:///foo/lala/lala.dart'))!.name,
+          'foo');
+      expect(config.packageOf(Uri.parse('file:///foo/bar/lala.dart'))!.name,
+          'bar');
+      expect(config.packageOf(Uri.parse('file:///foo/bar/baz/lala.dart'))!.name,
+          'baz');
+      expect(config.packageOf(Uri.parse('file:///foo/qux/lala.dart'))!.name,
+          'qux');
+      expect(config.toPackageUri(Uri.parse('file:///foo/lib/diz')),
+          Uri.parse('package:foo/diz'));
+      expect(config.toPackageUri(Uri.parse('file:///foo/bar/lib/diz')),
+          Uri.parse('package:bar/diz'));
+      expect(config.toPackageUri(Uri.parse('file:///foo/bar/baz/lib/diz')),
+          Uri.parse('package:baz/diz'));
+      expect(config.toPackageUri(Uri.parse('file:///foo/qux/lib/diz')),
+          Uri.parse('package:qux/diz'));
+    });
+
+    test('nested packages 2', () {
+      var configBytes = utf8.encode(json.encode({
+        'configVersion': 2,
+        'packages': [
+          {'name': 'foo', 'rootUri': '/', 'packageUri': 'lib/'},
+          {'name': 'bar', 'rootUri': '/bar/', 'packageUri': 'lib/'},
+          {'name': 'baz', 'rootUri': '/bar/baz/', 'packageUri': 'lib/'},
+          {'name': 'qux', 'rootUri': '/qux/', 'packageUri': 'lib/'},
+        ]
+      }));
+      // ignore: unnecessary_cast
+      var config = parsePackageConfigBytes(configBytes as Uint8List,
+          Uri.parse('file:///tmp/.dart_tool/file.dart'), throwError);
+      expect(config.version, 2);
+      expect(
+          config.packageOf(Uri.parse('file:///lala/lala.dart'))!.name, 'foo');
+      expect(config.packageOf(Uri.parse('file:///bar/lala.dart'))!.name, 'bar');
+      expect(config.packageOf(Uri.parse('file:///bar/baz/lala.dart'))!.name,
+          'baz');
+      expect(config.packageOf(Uri.parse('file:///qux/lala.dart'))!.name, 'qux');
+      expect(config.toPackageUri(Uri.parse('file:///lib/diz')),
+          Uri.parse('package:foo/diz'));
+      expect(config.toPackageUri(Uri.parse('file:///bar/lib/diz')),
+          Uri.parse('package:bar/diz'));
+      expect(config.toPackageUri(Uri.parse('file:///bar/baz/lib/diz')),
+          Uri.parse('package:baz/diz'));
+      expect(config.toPackageUri(Uri.parse('file:///qux/lib/diz')),
+          Uri.parse('package:qux/diz'));
+    });
+
+    test('packageOf is case sensitive on windows', () {
+      var configBytes = utf8.encode(json.encode({
+        'configVersion': 2,
+        'packages': [
+          {'name': 'foo', 'rootUri': 'file:///C:/Foo/', 'packageUri': 'lib/'},
+        ]
+      }));
+      var config = parsePackageConfigBytes(
+          // ignore: unnecessary_cast
+          configBytes as Uint8List,
+          Uri.parse('file:///C:/tmp/.dart_tool/file.dart'),
+          throwError);
+      expect(config.version, 2);
+      expect(
+          config.packageOf(Uri.parse('file:///C:/foo/lala/lala.dart')), null);
+      expect(config.packageOf(Uri.parse('file:///C:/Foo/lala/lala.dart'))!.name,
+          'foo');
+    });
+
+    group('invalid', () {
+      void testThrows(String name, String source) {
+        test(name, () {
+          expect(
+              // ignore: unnecessary_cast
+              () => parsePackageConfigBytes(utf8.encode(source) as Uint8List,
+                  Uri.parse('file:///tmp/.dart_tool/file.dart'), throwError),
+              throwsA(isA<FormatException>()));
+        });
+      }
+
+      void testThrowsContains(
+          String name, String source, String containsString) {
+        test(name, () {
+          dynamic exception;
+          try {
+            parsePackageConfigBytes(
+              // ignore: unnecessary_cast
+              utf8.encode(source) as Uint8List,
+              Uri.parse('file:///tmp/.dart_tool/file.dart'),
+              throwError,
+            );
+          } catch (e) {
+            exception = e;
+          }
+          if (exception == null) fail("Didn't get exception");
+          expect('$exception', contains(containsString));
+        });
+      }
+
+      testThrows('comment', '# comment\n {$cfg,$pkgs}');
+      testThrows('.packages file', 'foo:/foo\n');
+      testThrows('no configVersion', '{$pkgs}');
+      testThrows('no packages', '{$cfg}');
+      group('config version:', () {
+        testThrows('null', '{"configVersion":null,$pkgs}');
+        testThrows('string', '{"configVersion":"2",$pkgs}');
+        testThrows('array', '{"configVersion":[2],$pkgs}');
+      });
+      group('packages:', () {
+        testThrows('null', '{$cfg,"packages":null}');
+        testThrows('string', '{$cfg,"packages":"foo"}');
+        testThrows('object', '{$cfg,"packages":{}}');
+      });
+      group('packages entry:', () {
+        testThrows('null', '{$cfg,"packages":[null]}');
+        testThrows('string', '{$cfg,"packages":["foo"]}');
+        testThrows('array', '{$cfg,"packages":[[]]}');
+      });
+      group('package', () {
+        testThrows('no name', '{$cfg,"packages":[{$root}]}');
+        group('name:', () {
+          testThrows('null', '{$cfg,"packages":[{"name":null,$root}]}');
+          testThrows('num', '{$cfg,"packages":[{"name":1,$root}]}');
+          testThrows('object', '{$cfg,"packages":[{"name":{},$root}]}');
+          testThrows('empty', '{$cfg,"packages":[{"name":"",$root}]}');
+          testThrows('one-dot', '{$cfg,"packages":[{"name":".",$root}]}');
+          testThrows('two-dot', '{$cfg,"packages":[{"name":"..",$root}]}');
+          testThrows(
+              "invalid char '\\'", '{$cfg,"packages":[{"name":"\\",$root}]}');
+          testThrows(
+              "invalid char ':'", '{$cfg,"packages":[{"name":":",$root}]}');
+          testThrows(
+              "invalid char ' '", '{$cfg,"packages":[{"name":" ",$root}]}');
+        });
+
+        testThrows('no root', '{$cfg,"packages":[{$name}]}');
+        group('root:', () {
+          testThrows('null', '{$cfg,"packages":[{$name,"rootUri":null}]}');
+          testThrows('num', '{$cfg,"packages":[{$name,"rootUri":1}]}');
+          testThrows('object', '{$cfg,"packages":[{$name,"rootUri":{}}]}');
+          testThrows('fragment', '{$cfg,"packages":[{$name,"rootUri":"x/#"}]}');
+          testThrows('query', '{$cfg,"packages":[{$name,"rootUri":"x/?"}]}');
+          testThrows('package-URI',
+              '{$cfg,"packages":[{$name,"rootUri":"package:x/x/"}]}');
+        });
+        group('package-URI root:', () {
+          testThrows(
+              'null', '{$cfg,"packages":[{$name,$root,"packageUri":null}]}');
+          testThrows('num', '{$cfg,"packages":[{$name,$root,"packageUri":1}]}');
+          testThrows(
+              'object', '{$cfg,"packages":[{$name,$root,"packageUri":{}}]}');
+          testThrows('fragment',
+              '{$cfg,"packages":[{$name,$root,"packageUri":"x/#"}]}');
+          testThrows(
+              'query', '{$cfg,"packages":[{$name,$root,"packageUri":"x/?"}]}');
+          testThrows('package: URI',
+              '{$cfg,"packages":[{$name,$root,"packageUri":"package:x/x/"}]}');
+          testThrows('not inside root',
+              '{$cfg,"packages":[{$name,$root,"packageUri":"../other/"}]}');
+        });
+        group('language version', () {
+          testThrows('null',
+              '{$cfg,"packages":[{$name,$root,"languageVersion":null}]}');
+          testThrows(
+              'num', '{$cfg,"packages":[{$name,$root,"languageVersion":1}]}');
+          testThrows('object',
+              '{$cfg,"packages":[{$name,$root,"languageVersion":{}}]}');
+          testThrows('empty',
+              '{$cfg,"packages":[{$name,$root,"languageVersion":""}]}');
+          testThrows('non number.number',
+              '{$cfg,"packages":[{$name,$root,"languageVersion":"x.1"}]}');
+          testThrows('number.non number',
+              '{$cfg,"packages":[{$name,$root,"languageVersion":"1.x"}]}');
+          testThrows('non number',
+              '{$cfg,"packages":[{$name,$root,"languageVersion":"x"}]}');
+          testThrows('one number',
+              '{$cfg,"packages":[{$name,$root,"languageVersion":"1"}]}');
+          testThrows('three numbers',
+              '{$cfg,"packages":[{$name,$root,"languageVersion":"1.2.3"}]}');
+          testThrows('leading zero first',
+              '{$cfg,"packages":[{$name,$root,"languageVersion":"01.1"}]}');
+          testThrows('leading zero second',
+              '{$cfg,"packages":[{$name,$root,"languageVersion":"1.01"}]}');
+          testThrows('trailing-',
+              '{$cfg,"packages":[{$name,$root,"languageVersion":"1.1-1"}]}');
+          testThrows('trailing+',
+              '{$cfg,"packages":[{$name,$root,"languageVersion":"1.1+1"}]}');
+        });
+      });
+      testThrows('duplicate package name',
+          '{$cfg,"packages":[{$name,$root},{$name,"rootUri":"/other/"}]}');
+      testThrowsContains(
+          // The roots of foo and bar are the same.
+          'same roots',
+          '{$cfg,"packages":[{$name,$root},{"name":"bar",$root}]}',
+          'the same root directory');
+      testThrowsContains(
+          // The roots of foo and bar are the same.
+          'same roots 2',
+          '{$cfg,"packages":[{$name,"rootUri":"/"},{"name":"bar","rootUri":"/"}]}',
+          'the same root directory');
+      testThrowsContains(
+          // The root of bar is inside the root of foo,
+          // but the package root of foo is inside the root of bar.
+          'between root and lib',
+          '{$cfg,"packages":['
+              '{"name":"foo","rootUri":"/foo/","packageUri":"bar/lib/"},'
+              '{"name":"bar","rootUri":"/foo/bar/","packageUri":"baz/lib"}]}',
+          'package root of foo is inside the root of bar');
+
+      // This shouldn't be allowed, but for internal reasons it is.
+      test('package inside package root', () {
+        var config = parsePackageConfigBytes(
+            // ignore: unnecessary_cast
+            utf8.encode(
+              '{$cfg,"packages":['
+              '{"name":"foo","rootUri":"/foo/","packageUri":"lib/"},'
+              '{"name":"bar","rootUri":"/foo/lib/bar/","packageUri":"lib"}]}',
+            ) as Uint8List,
+            Uri.parse('file:///tmp/.dart_tool/file.dart'),
+            throwError);
+        expect(
+            config
+                .packageOf(Uri.parse('file:///foo/lib/bar/lib/lala.dart'))!
+                .name,
+            'foo'); // why not bar?
+        expect(config.toPackageUri(Uri.parse('file:///foo/lib/bar/lib/diz')),
+            Uri.parse('package:foo/bar/lib/diz')); // why not package:bar/diz?
+      });
+    });
+  });
+
+  group('factories', () {
+    void testConfig(String name, PackageConfig config, PackageConfig expected) {
+      group(name, () {
+        test('structure', () {
+          expect(config.version, expected.version);
+          var expectedPackages = {for (var p in expected.packages) p.name};
+          var actualPackages = {for (var p in config.packages) p.name};
+          expect(actualPackages, expectedPackages);
+        });
+        for (var package in config.packages) {
+          var name = package.name;
+          test('package $name', () {
+            var expectedPackage = expected[name]!;
+            expect(expectedPackage, isNotNull);
+            expect(package.root, expectedPackage.root, reason: 'root');
+            expect(package.packageUriRoot, expectedPackage.packageUriRoot,
+                reason: 'package root');
+            expect(package.languageVersion, expectedPackage.languageVersion,
+                reason: 'languageVersion');
+          });
+        }
+      });
+    }
+
+    var configText = '''
+     {"configVersion": 2, "packages": [
+       {
+         "name": "foo",
+         "rootUri": "foo/",
+         "packageUri": "bar/",
+         "languageVersion": "1.2"
+       }
+     ]}
+    ''';
+    var baseUri = Uri.parse('file:///start/');
+    var config = PackageConfig([
+      Package('foo', Uri.parse('file:///start/foo/'),
+          packageUriRoot: Uri.parse('file:///start/foo/bar/'),
+          languageVersion: LanguageVersion(1, 2))
+    ]);
+    testConfig(
+        'string', PackageConfig.parseString(configText, baseUri), config);
+    testConfig(
+        'bytes',
+        PackageConfig.parseBytes(
+            Uint8List.fromList(configText.codeUnits), baseUri),
+        config);
+    testConfig('json', PackageConfig.parseJson(jsonDecode(configText), baseUri),
+        config);
+
+    baseUri = Uri.parse('file:///start2/');
+    config = PackageConfig([
+      Package('foo', Uri.parse('file:///start2/foo/'),
+          packageUriRoot: Uri.parse('file:///start2/foo/bar/'),
+          languageVersion: LanguageVersion(1, 2))
+    ]);
+    testConfig(
+        'string2', PackageConfig.parseString(configText, baseUri), config);
+    testConfig(
+        'bytes2',
+        PackageConfig.parseBytes(
+            Uint8List.fromList(configText.codeUnits), baseUri),
+        config);
+    testConfig('json2',
+        PackageConfig.parseJson(jsonDecode(configText), baseUri), config);
+  });
+}

diff --git a/pkgs/package_config/test/src/util.dart b/pkgs/package_config/test/src/util.dart
new file mode 100644
index 0000000..780ee80
--- /dev/null
+++ b/pkgs/package_config/test/src/util.dart

@@ -0,0 +1,57 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:convert';
+import 'dart:typed_data';
+
+import 'package:test/test.dart';
+
+/// Creates a package: URI.
+Uri pkg(String packageName, String packagePath) {
+  var path =
+      "$packageName${packagePath.startsWith('/') ? "" : "/"}$packagePath";
+  return Uri(scheme: 'package', path: path);
+}
+
+// Remove if not used.
+String configFromPackages(List<List<String>> packages) => """
+{
+  "configVersion": 2,
+  "packages": [
+${packages.map((nu) => """
+    {
+      "name": "${nu[0]}",
+      "rootUri": "${nu[1]}"
+    }""").join(",\n")}
+  ]
+}
+""";
+
+/// Mimics a directory structure of [description] and runs [loaderTest].
+///
+/// Description is a map, each key is a file entry. If the value is a map,
+/// it's a subdirectory, otherwise it's a file and the value is the content
+/// as a string.
+void loaderTest(
+  String name,
+  Map<String, Object> description,
+  void Function(Uri root, Future<Uint8List?> Function(Uri) loader) loaderTest,
+) {
+  var root = Uri(scheme: 'test', path: '/');
+  Future<Uint8List?> loader(Uri uri) async {
+    var path = uri.path;
+    if (!uri.isScheme('test') || !path.startsWith('/')) return null;
+    var parts = path.split('/');
+    Object? value = description;
+    for (var i = 1; i < parts.length; i++) {
+      if (value is! Map<String, Object?>) return null;
+      value = value[parts[i]];
+    }
+    // ignore: unnecessary_cast
+    if (value is String) return utf8.encode(value) as Uint8List;
+    return null;
+  }
+
+  test(name, () => loaderTest(root, loader));
+}

diff --git a/pkgs/package_config/test/src/util_io.dart b/pkgs/package_config/test/src/util_io.dart
new file mode 100644
index 0000000..e032556
--- /dev/null
+++ b/pkgs/package_config/test/src/util_io.dart

@@ -0,0 +1,62 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:io';
+
+import 'package:package_config/src/util_io.dart';
+import 'package:test/test.dart';
+
+/// Creates a directory structure from [description] and runs [fileTest].
+///
+/// Description is a map, each key is a file entry. If the value is a map,
+/// it's a subdirectory, otherwise it's a file and the value is the content
+/// as a string.
+/// Introduces a group to hold the [setUp]/[tearDown] logic.
+void fileTest(String name, Map<String, Object> description,
+    void Function(Directory directory) fileTest) {
+  group('file-test', () {
+    var tempDir = Directory.systemTemp.createTempSync('pkgcfgtest');
+    setUp(() {
+      _createFiles(tempDir, description);
+    });
+    tearDown(() {
+      tempDir.deleteSync(recursive: true);
+    });
+    test(name, () => fileTest(tempDir));
+  });
+}
+
+/// Creates a set of files under a new temporary directory.
+/// Returns the temporary directory.
+///
+/// The [description] is a map from file names to content.
+/// If the content is again a map, it represents a subdirectory
+/// with the content as description.
+/// Otherwise the content should be a string,
+/// which is written to the file as UTF-8.
+// Directory createTestFiles(Map<String, Object> description) {
+//   var target = Directory.systemTemp.createTempSync("pkgcfgtest");
+//   _createFiles(target, description);
+//   return target;
+// }
+
+// Creates temporary files in the target directory.
+void _createFiles(Directory target, Map<Object?, Object?> description) {
+  description.forEach((name, content) {
+    var entryName = pathJoin(target.path, '$name');
+    if (content is Map<Object?, Object?>) {
+      _createFiles(Directory(entryName)..createSync(), content);
+    } else {
+      File(entryName).writeAsStringSync(content as String, flush: true);
+    }
+  });
+}
+
+/// Creates a [Directory] for a subdirectory of [parent].
+Directory subdir(Directory parent, String dirName) =>
+    Directory(pathJoinAll([parent.path, ...dirName.split('/')]));
+
+/// Creates a [File] for an entry in the [directory] directory.
+File dirFile(Directory directory, String fileName) =>
+    File(pathJoin(directory.path, fileName));

diff --git a/pkgs/pool/.gitignore b/pkgs/pool/.gitignore
new file mode 100644
index 0000000..e450c83
--- /dev/null
+++ b/pkgs/pool/.gitignore

@@ -0,0 +1,5 @@
+# Don’t commit the following directories created by pub.
+.dart_tool/
+.packages
+.pub/
+pubspec.lock

diff --git a/pkgs/pool/CHANGELOG.md b/pkgs/pool/CHANGELOG.md
new file mode 100644
index 0000000..56424fc
--- /dev/null
+++ b/pkgs/pool/CHANGELOG.md

@@ -0,0 +1,105 @@
+## 1.5.2-wip
+
+* Require Dart 3.4.
+* Move to `dart-lang/tools` monorepo.
+
+## 1.5.1
+
+* Populate the pubspec `repository` field.
+
+## 1.5.0
+
+* Stable release for null safety.
+
+## 1.5.0-nullsafety.3
+
+* Update SDK constraints to `>=2.12.0-0 <3.0.0` based on beta release
+  guidelines.
+
+## 1.5.0-nullsafety.2
+
+* Allow prerelease versions of the 2.12 sdk.
+
+## 1.5.0-nullsafety.1
+
+* Allow 2.10 stable and 2.11.0 dev SDK versions.
+
+## 1.5.0-nullsafety
+
+* Migrate to null safety.
+* `forEach`: Avoid `await null` if the `Stream` is not paused.
+  Improves trivial benchmark by 40%.
+
+## 1.4.0
+
+* Add `forEach` to `Pool` to support efficient async processing of an
+  `Iterable`.
+
+* Throw ArgumentError if poolSize <= 0
+
+## 1.3.6
+
+* Set max SDK version to `<3.0.0`, and adjust other dependencies.
+
+## 1.3.5
+
+- Updated SDK version to 2.0.0-dev.17.0
+
+## 1.3.4
+
+* Modify code to eliminate Future flattening.
+
+## 1.3.3
+
+* Declare support for `async` 2.0.0.
+
+## 1.3.2
+
+* Update to make the code work with strong-mode clean Zone API.
+
+* Required minimum SDK of 1.23.0.
+
+## 1.3.1
+
+* Fix the type annotation of `Pool.withResource()` to indicate that it takes
+  `() -> FutureOr<T>`.
+
+## 1.3.0
+
+* Add a `Pool.done` getter that returns the same future returned by
+  `Pool.close()`.
+
+## 1.2.4
+
+* Fix a strong-mode error.
+
+## 1.2.3
+
+* Fix a bug in which `Pool.withResource()` could throw a `StateError` when
+  called immediately before closing the pool.
+
+## 1.2.2
+
+* Fix strong mode warnings and add generic method annotations.
+
+## 1.2.1
+
+* Internal changes only.
+
+## 1.2.0
+
+* Add `Pool.close()`, which forbids new resource requests and releases all
+  releasable resources.
+
+## 1.1.0
+
+* Add `PoolResource.allowRelease()`, which allows a resource to indicate that it
+  can be released without forcing it to deallocate immediately.
+
+## 1.0.2
+
+* Fixed the homepage.
+
+## 1.0.1
+
+* A `TimeoutException` is now correctly thrown if the pool detects a deadlock.

diff --git a/pkgs/pool/LICENSE b/pkgs/pool/LICENSE
new file mode 100644
index 0000000..000cd7b
--- /dev/null
+++ b/pkgs/pool/LICENSE

@@ -0,0 +1,27 @@
+Copyright 2014, the Dart project authors. 
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+    * Neither the name of Google LLC nor the names of its
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

diff --git a/pkgs/pool/README.md b/pkgs/pool/README.md
new file mode 100644
index 0000000..461e872
--- /dev/null
+++ b/pkgs/pool/README.md

@@ -0,0 +1,57 @@
+[![Build Status](https://github.com/dart-lang/tools/actions/workflows/pool.yaml/badge.svg)](https://github.com/dart-lang/tools/actions/workflows/pool.yaml)
+[![pub package](https://img.shields.io/pub/v/pool.svg)](https://pub.dev/packages/pool)
+[![package publisher](https://img.shields.io/pub/publisher/pool.svg)](https://pub.dev/packages/pool/publisher)
+
+The pool package exposes a `Pool` class which makes it easy to manage a limited
+pool of resources.
+
+The easiest way to use a pool is by calling `withResource`. This runs a callback
+and returns its result, but only once there aren't too many other callbacks
+currently running.
+
+```dart
+// Create a Pool that will only allocate 10 resources at once. After 30 seconds
+// of inactivity with all resources checked out, the pool will throw an error.
+final pool = new Pool(10, timeout: new Duration(seconds: 30));
+
+Future<String> readFile(String path) {
+  // Since the call to [File.readAsString] is within [withResource], no more
+  // than ten files will be open at once.
+  return pool.withResource(() => new File(path).readAsString());
+}
+```
+
+For more fine-grained control, the user can also explicitly request generic
+`PoolResource` objects that can later be released back into the pool. This is
+what `withResource` does under the covers: requests a resource, then releases it
+once the callback completes.
+
+`Pool` ensures that only a limited number of resources are allocated at once.
+It's the caller's responsibility to ensure that the corresponding physical
+resource is only consumed when a `PoolResource` is allocated.
+
+```dart
+class PooledFile implements RandomAccessFile {
+  final RandomAccessFile _file;
+  final PoolResource _resource;
+
+  static Future<PooledFile> open(String path) {
+    return pool.request().then((resource) {
+      return new File(path).open().then((file) {
+        return new PooledFile._(file, resource);
+      });
+    });
+  }
+
+  PooledFile(this._file, this._resource);
+
+  // ...
+
+  Future<RandomAccessFile> close() {
+    return _file.close.then((_) {
+      _resource.release();
+      return this;
+    });
+  }
+}
+```

diff --git a/pkgs/pool/analysis_options.yaml b/pkgs/pool/analysis_options.yaml
new file mode 100644
index 0000000..44cda4d
--- /dev/null
+++ b/pkgs/pool/analysis_options.yaml

@@ -0,0 +1,5 @@
+include: package:dart_flutter_team_lints/analysis_options.yaml
+
+analyzer:
+  language:
+    strict-casts: true

diff --git a/pkgs/pool/benchmark/for_each_benchmark.dart b/pkgs/pool/benchmark/for_each_benchmark.dart
new file mode 100644
index 0000000..0cd2543
--- /dev/null
+++ b/pkgs/pool/benchmark/for_each_benchmark.dart

@@ -0,0 +1,55 @@
+// Copyright (c) 2024, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:pool/pool.dart';
+
+void main(List<String> args) async {
+  var poolSize = args.isEmpty ? 5 : int.parse(args.first);
+  print('Pool size: $poolSize');
+
+  final pool = Pool(poolSize);
+  final watch = Stopwatch()..start();
+  final start = DateTime.now();
+
+  DateTime? lastLog;
+  Duration? fastest;
+  late int fastestIteration;
+  var i = 1;
+
+  void log(bool force) {
+    var now = DateTime.now();
+    if (force ||
+        lastLog == null ||
+        now.difference(lastLog!) > const Duration(seconds: 1)) {
+      lastLog = now;
+      print([
+        now.difference(start),
+        i.toString().padLeft(10),
+        fastestIteration.toString().padLeft(7),
+        fastest!.inMicroseconds.toString().padLeft(9)
+      ].join('   '));
+    }
+  }
+
+  print(['Elapsed       ', 'Iterations', 'Fastest', 'Time (us)'].join('   '));
+
+  for (;; i++) {
+    watch.reset();
+
+    var sum = await pool
+        .forEach<int, int>(Iterable<int>.generate(100000), (i) => i)
+        .reduce((a, b) => a + b);
+
+    assert(sum == 4999950000, 'was $sum');
+
+    var elapsed = watch.elapsed;
+    if (fastest == null || fastest > elapsed) {
+      fastest = elapsed;
+      fastestIteration = i;
+      log(true);
+    } else {
+      log(false);
+    }
+  }
+}

diff --git a/pkgs/pool/lib/pool.dart b/pkgs/pool/lib/pool.dart
new file mode 100644
index 0000000..70e9df1
--- /dev/null
+++ b/pkgs/pool/lib/pool.dart

@@ -0,0 +1,380 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+import 'dart:collection';
+
+import 'package:async/async.dart';
+import 'package:stack_trace/stack_trace.dart';
+
+/// Manages an abstract pool of resources with a limit on how many may be in use
+/// at once.
+///
+/// When a resource is needed, the user should call [request]. When the returned
+/// future completes with a [PoolResource], the resource may be allocated. Once
+/// the resource has been released, the user should call [PoolResource.release].
+/// The pool will ensure that only a certain number of [PoolResource]s may be
+/// allocated at once.
+class Pool {
+  /// Completers for requests beyond the first [_maxAllocatedResources].
+  ///
+  /// When an item is released, the next element of [_requestedResources] will
+  /// be completed.
+  final _requestedResources = Queue<Completer<PoolResource>>();
+
+  /// Callbacks that must be called before additional resources can be
+  /// allocated.
+  ///
+  /// See [PoolResource.allowRelease].
+  final _onReleaseCallbacks = Queue<void Function()>();
+
+  /// Completers that will be completed once `onRelease` callbacks are done
+  /// running.
+  ///
+  /// These are kept in a queue to ensure that the earliest request completes
+  /// first regardless of what order the `onRelease` callbacks complete in.
+  final _onReleaseCompleters = Queue<Completer<PoolResource>>();
+
+  /// The maximum number of resources that may be allocated at once.
+  final int _maxAllocatedResources;
+
+  /// The number of resources that are currently allocated.
+  int _allocatedResources = 0;
+
+  /// The timeout timer.
+  ///
+  /// This timer is canceled as long as the pool is below the resource limit.
+  /// It's reset once the resource limit is reached and again every time an
+  /// resource is released or a new resource is requested. If it fires, that
+  /// indicates that the caller became deadlocked, likely due to files waiting
+  /// for additional files to be read before they could be closed.
+  ///
+  /// This is `null` if this pool shouldn't time out.
+  RestartableTimer? _timer;
+
+  /// The amount of time to wait before timing out the pending resources.
+  final Duration? _timeout;
+
+  /// A [FutureGroup] that tracks all the `onRelease` callbacks for resources
+  /// that have been marked releasable.
+  ///
+  /// This is `null` until [close] is called.
+  FutureGroup? _closeGroup;
+
+  /// Whether [close] has been called.
+  bool get isClosed => _closeMemo.hasRun;
+
+  /// A future that completes once the pool is closed and all its outstanding
+  /// resources have been released.
+  ///
+  /// If any [PoolResource.allowRelease] callback throws an exception after the
+  /// pool is closed, this completes with that exception.
+  Future get done => _closeMemo.future;
+
+  /// Creates a new pool with the given limit on how many resources may be
+  /// allocated at once.
+  ///
+  /// If [timeout] is passed, then if that much time passes without any activity
+  /// all pending [request] futures will throw a [TimeoutException]. This is
+  /// intended to avoid deadlocks.
+  Pool(this._maxAllocatedResources, {Duration? timeout}) : _timeout = timeout {
+    if (_maxAllocatedResources <= 0) {
+      throw ArgumentError.value(_maxAllocatedResources, 'maxAllocatedResources',
+          'Must be greater than zero.');
+    }
+
+    if (timeout != null) {
+      // Start the timer canceled since we only want to start counting down once
+      // we've run out of available resources.
+      _timer = RestartableTimer(timeout, _onTimeout)..cancel();
+    }
+  }
+
+  /// Request a [PoolResource].
+  ///
+  /// If the maximum number of resources is already allocated, this will delay
+  /// until one of them is released.
+  Future<PoolResource> request() {
+    if (isClosed) {
+      throw StateError('request() may not be called on a closed Pool.');
+    }
+
+    if (_allocatedResources < _maxAllocatedResources) {
+      _allocatedResources++;
+      return Future.value(PoolResource._(this));
+    } else if (_onReleaseCallbacks.isNotEmpty) {
+      return _runOnRelease(_onReleaseCallbacks.removeFirst());
+    } else {
+      var completer = Completer<PoolResource>();
+      _requestedResources.add(completer);
+      _resetTimer();
+      return completer.future;
+    }
+  }
+
+  /// Requests a resource for the duration of [callback], which may return a
+  /// Future.
+  ///
+  /// The return value of [callback] is piped to the returned Future.
+  Future<T> withResource<T>(FutureOr<T> Function() callback) async {
+    if (isClosed) {
+      throw StateError('withResource() may not be called on a closed Pool.');
+    }
+
+    var resource = await request();
+    try {
+      return await callback();
+    } finally {
+      resource.release();
+    }
+  }
+
+  /// Returns a [Stream] containing the result of [action] applied to each
+  /// element of [elements].
+  ///
+  /// While [action] is invoked on each element of [elements] in order,
+  /// it's possible the return [Stream] may have items out-of-order – especially
+  /// if the completion time of [action] varies.
+  ///
+  /// If [action] throws an error the source item along with the error object
+  /// and [StackTrace] are passed to [onError], if it is provided. If [onError]
+  /// returns `true`, the error is added to the returned [Stream], otherwise
+  /// it is ignored.
+  ///
+  /// Errors thrown from iterating [elements] will not be passed to
+  /// [onError]. They will always be added to the returned stream as an error.
+  ///
+  /// Note: all of the resources of the this [Pool] will be used when the
+  /// returned [Stream] is listened to until it is completed or canceled.
+  ///
+  /// Note: if this [Pool] is closed before the returned [Stream] is listened
+  /// to, a [StateError] is thrown.
+  Stream<T> forEach<S, T>(
+      Iterable<S> elements, FutureOr<T> Function(S source) action,
+      {bool Function(S item, Object error, StackTrace stack)? onError}) {
+    onError ??= (item, e, s) => true;
+
+    var cancelPending = false;
+
+    Completer? resumeCompleter;
+    late StreamController<T> controller;
+
+    late Iterator<S> iterator;
+
+    Future<void> run(int _) async {
+      while (iterator.moveNext()) {
+        // caching `current` is necessary because there are async breaks
+        // in this code and `iterator` is shared across many workers
+        final current = iterator.current;
+
+        _resetTimer();
+
+        if (resumeCompleter != null) {
+          await resumeCompleter!.future;
+        }
+
+        if (cancelPending) {
+          break;
+        }
+
+        T value;
+        try {
+          value = await action(current);
+        } catch (e, stack) {
+          if (onError!(current, e, stack)) {
+            controller.addError(e, stack);
+          }
+          continue;
+        }
+        controller.add(value);
+      }
+    }
+
+    Future<void>? doneFuture;
+
+    void onListen() {
+      iterator = elements.iterator;
+
+      assert(doneFuture == null);
+      var futures = Iterable<Future<void>>.generate(
+          _maxAllocatedResources, (i) => withResource(() => run(i)));
+      doneFuture = Future.wait(futures, eagerError: true)
+          .then<void>((_) {})
+          .catchError(controller.addError);
+
+      doneFuture!.whenComplete(controller.close);
+    }
+
+    controller = StreamController<T>(
+      sync: true,
+      onListen: onListen,
+      onCancel: () async {
+        assert(!cancelPending);
+        cancelPending = true;
+        await doneFuture;
+      },
+      onPause: () {
+        assert(resumeCompleter == null);
+        resumeCompleter = Completer<void>();
+      },
+      onResume: () {
+        assert(resumeCompleter != null);
+        resumeCompleter!.complete();
+        resumeCompleter = null;
+      },
+    );
+
+    return controller.stream;
+  }
+
+  /// Closes the pool so that no more resources are requested.
+  ///
+  /// Existing resource requests remain unchanged.
+  ///
+  /// Any resources that are marked as releasable using
+  /// [PoolResource.allowRelease] are released immediately. Once all resources
+  /// have been released and any `onRelease` callbacks have completed, the
+  /// returned future completes successfully. If any `onRelease` callback throws
+  /// an error, the returned future completes with that error.
+  ///
+  /// This may be called more than once; it returns the same [Future] each time.
+  Future close() => _closeMemo.runOnce(_close);
+
+  Future<void> _close() {
+    if (_closeGroup != null) return _closeGroup!.future;
+
+    _resetTimer();
+
+    _closeGroup = FutureGroup();
+    for (var callback in _onReleaseCallbacks) {
+      _closeGroup!.add(Future.sync(callback));
+    }
+
+    _allocatedResources -= _onReleaseCallbacks.length;
+    _onReleaseCallbacks.clear();
+
+    if (_allocatedResources == 0) _closeGroup!.close();
+    return _closeGroup!.future;
+  }
+
+  final _closeMemo = AsyncMemoizer<void>();
+
+  /// If there are any pending requests, this will fire the oldest one.
+  void _onResourceReleased() {
+    _resetTimer();
+
+    if (_requestedResources.isNotEmpty) {
+      var pending = _requestedResources.removeFirst();
+      pending.complete(PoolResource._(this));
+    } else {
+      _allocatedResources--;
+      if (isClosed && _allocatedResources == 0) _closeGroup!.close();
+    }
+  }
+
+  /// If there are any pending requests, this will fire the oldest one after
+  /// running [onRelease].
+  void _onResourceReleaseAllowed(void Function() onRelease) {
+    _resetTimer();
+
+    if (_requestedResources.isNotEmpty) {
+      var pending = _requestedResources.removeFirst();
+      pending.complete(_runOnRelease(onRelease));
+    } else if (isClosed) {
+      _closeGroup!.add(Future.sync(onRelease));
+      _allocatedResources--;
+      if (_allocatedResources == 0) _closeGroup!.close();
+    } else {
+      var zone = Zone.current;
+      var registered = zone.registerCallback(onRelease);
+      _onReleaseCallbacks.add(() => zone.run(registered));
+    }
+  }
+
+  /// Runs [onRelease] and returns a Future that completes to a resource once an
+  /// [onRelease] callback completes.
+  ///
+  /// Futures returned by [_runOnRelease] always complete in the order they were
+  /// created, even if earlier [onRelease] callbacks take longer to run.
+  Future<PoolResource> _runOnRelease(void Function() onRelease) {
+    Future.sync(onRelease).then((value) {
+      _onReleaseCompleters.removeFirst().complete(PoolResource._(this));
+    }).catchError((Object error, StackTrace stackTrace) {
+      _onReleaseCompleters.removeFirst().completeError(error, stackTrace);
+    });
+
+    var completer = Completer<PoolResource>.sync();
+    _onReleaseCompleters.add(completer);
+    return completer.future;
+  }
+
+  /// A resource has been requested, allocated, or released.
+  void _resetTimer() {
+    if (_timer == null) return;
+
+    if (_requestedResources.isEmpty) {
+      _timer!.cancel();
+    } else {
+      _timer!.reset();
+    }
+  }
+
+  /// Handles [_timer] timing out by causing all pending resource completers to
+  /// emit exceptions.
+  void _onTimeout() {
+    for (var completer in _requestedResources) {
+      completer.completeError(
+          TimeoutException(
+              'Pool deadlock: all resources have been '
+              'allocated for too long.',
+              _timeout),
+          Chain.current());
+    }
+    _requestedResources.clear();
+    _timer = null;
+  }
+}
+
+/// A member of a [Pool].
+///
+/// A [PoolResource] is a token that indicates that a resource is allocated.
+/// When the associated resource is released, the user should call [release].
+class PoolResource {
+  final Pool _pool;
+
+  /// Whether `this` has been released yet.
+  bool _released = false;
+
+  PoolResource._(this._pool);
+
+  /// Tells the parent [Pool] that the resource associated with this resource is
+  /// no longer allocated, and that a new [PoolResource] may be allocated.
+  void release() {
+    if (_released) {
+      throw StateError('A PoolResource may only be released once.');
+    }
+    _released = true;
+    _pool._onResourceReleased();
+  }
+
+  /// Tells the parent [Pool] that the resource associated with this resource is
+  /// no longer necessary, but should remain allocated until more resources are
+  /// needed.
+  ///
+  /// When [Pool.request] is called and there are no remaining available
+  /// resources, the [onRelease] callback is called. It should free the
+  /// resource, and it may return a Future or `null`. Once that completes, the
+  /// [Pool.request] call will complete to a new [PoolResource].
+  ///
+  /// This is useful when a resource's main function is complete, but it may
+  /// produce additional information later on. For example, an isolate's task
+  /// may be complete, but it could still emit asynchronous errors.
+  void allowRelease(FutureOr<void> Function() onRelease) {
+    if (_released) {
+      throw StateError('A PoolResource may only be released once.');
+    }
+    _released = true;
+    _pool._onResourceReleaseAllowed(onRelease);
+  }
+}

diff --git a/pkgs/pool/pubspec.yaml b/pkgs/pool/pubspec.yaml
new file mode 100644
index 0000000..a205b74
--- /dev/null
+++ b/pkgs/pool/pubspec.yaml

@@ -0,0 +1,18 @@
+name: pool
+version: 1.5.2-wip
+description: >-
+  Manage a finite pool of resources.
+  Useful for controlling concurrent file system or network requests.
+repository: https://github.com/dart-lang/tools/tree/main/pkgs/pool
+
+environment:
+  sdk: ^3.4.0
+
+dependencies:
+  async: ^2.5.0
+  stack_trace: ^1.10.0
+
+dev_dependencies:
+  dart_flutter_team_lints: ^3.0.0
+  fake_async: ^1.2.0
+  test: ^1.16.6

diff --git a/pkgs/pool/test/pool_test.dart b/pkgs/pool/test/pool_test.dart
new file mode 100644
index 0000000..6334a8a
--- /dev/null
+++ b/pkgs/pool/test/pool_test.dart

@@ -0,0 +1,745 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:fake_async/fake_async.dart';
+import 'package:pool/pool.dart';
+import 'package:stack_trace/stack_trace.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('request()', () {
+    test('resources can be requested freely up to the limit', () {
+      var pool = Pool(50);
+      for (var i = 0; i < 50; i++) {
+        expect(pool.request(), completes);
+      }
+    });
+
+    test('resources block past the limit', () {
+      FakeAsync().run((async) {
+        var pool = Pool(50);
+        for (var i = 0; i < 50; i++) {
+          expect(pool.request(), completes);
+        }
+        expect(pool.request(), doesNotComplete);
+
+        async.elapse(const Duration(seconds: 1));
+      });
+    });
+
+    test('a blocked resource is allocated when another is released', () {
+      FakeAsync().run((async) {
+        var pool = Pool(50);
+        for (var i = 0; i < 49; i++) {
+          expect(pool.request(), completes);
+        }
+
+        pool.request().then((lastAllocatedResource) {
+          // This will only complete once [lastAllocatedResource] is released.
+          expect(pool.request(), completes);
+
+          Future<void>.delayed(const Duration(microseconds: 1)).then((_) {
+            lastAllocatedResource.release();
+          });
+        });
+
+        async.elapse(const Duration(seconds: 1));
+      });
+    });
+  });
+
+  group('withResource()', () {
+    test('can be called freely up to the limit', () {
+      var pool = Pool(50);
+      for (var i = 0; i < 50; i++) {
+        pool.withResource(expectAsync0(() => Completer<void>().future));
+      }
+    });
+
+    test('blocks the callback past the limit', () {
+      FakeAsync().run((async) {
+        var pool = Pool(50);
+        for (var i = 0; i < 50; i++) {
+          pool.withResource(expectAsync0(() => Completer<void>().future));
+        }
+        pool.withResource(expectNoAsync());
+
+        async.elapse(const Duration(seconds: 1));
+      });
+    });
+
+    test('a blocked resource is allocated when another is released', () {
+      FakeAsync().run((async) {
+        var pool = Pool(50);
+        for (var i = 0; i < 49; i++) {
+          pool.withResource(expectAsync0(() => Completer<void>().future));
+        }
+
+        var completer = Completer<void>();
+        pool.withResource(() => completer.future);
+        var blockedResourceAllocated = false;
+        pool.withResource(() {
+          blockedResourceAllocated = true;
+        });
+
+        Future<void>.delayed(const Duration(microseconds: 1)).then((_) {
+          expect(blockedResourceAllocated, isFalse);
+          completer.complete();
+          return Future<void>.delayed(const Duration(microseconds: 1));
+        }).then((_) {
+          expect(blockedResourceAllocated, isTrue);
+        });
+
+        async.elapse(const Duration(seconds: 1));
+      });
+    });
+
+    // Regression test for #3.
+    test('can be called immediately before close()', () async {
+      var pool = Pool(1);
+      unawaited(pool.withResource(expectAsync0(() {})));
+      await pool.close();
+    });
+  });
+
+  group('with a timeout', () {
+    test("doesn't time out if there are no pending requests", () {
+      FakeAsync().run((async) {
+        var pool = Pool(50, timeout: const Duration(seconds: 5));
+        for (var i = 0; i < 50; i++) {
+          expect(pool.request(), completes);
+        }
+
+        async.elapse(const Duration(seconds: 6));
+      });
+    });
+
+    test('resets the timer if a resource is returned', () {
+      FakeAsync().run((async) {
+        var pool = Pool(50, timeout: const Duration(seconds: 5));
+        for (var i = 0; i < 49; i++) {
+          expect(pool.request(), completes);
+        }
+
+        pool.request().then((lastAllocatedResource) {
+          // This will only complete once [lastAllocatedResource] is released.
+          expect(pool.request(), completes);
+
+          Future<void>.delayed(const Duration(seconds: 3)).then((_) {
+            lastAllocatedResource.release();
+            expect(pool.request(), doesNotComplete);
+          });
+        });
+
+        async.elapse(const Duration(seconds: 6));
+      });
+    });
+
+    test('resets the timer if a resource is requested', () {
+      FakeAsync().run((async) {
+        var pool = Pool(50, timeout: const Duration(seconds: 5));
+        for (var i = 0; i < 50; i++) {
+          expect(pool.request(), completes);
+        }
+        expect(pool.request(), doesNotComplete);
+
+        Future<void>.delayed(const Duration(seconds: 3)).then((_) {
+          expect(pool.request(), doesNotComplete);
+        });
+
+        async.elapse(const Duration(seconds: 6));
+      });
+    });
+
+    test('times out if nothing happens', () {
+      FakeAsync().run((async) {
+        var pool = Pool(50, timeout: const Duration(seconds: 5));
+        for (var i = 0; i < 50; i++) {
+          expect(pool.request(), completes);
+        }
+        expect(pool.request(), throwsA(const TypeMatcher<TimeoutException>()));
+
+        async.elapse(const Duration(seconds: 6));
+      });
+    });
+  });
+
+  group('allowRelease()', () {
+    test('runs the callback once the resource limit is exceeded', () async {
+      var pool = Pool(50);
+      for (var i = 0; i < 49; i++) {
+        expect(pool.request(), completes);
+      }
+
+      var resource = await pool.request();
+      var onReleaseCalled = false;
+      resource.allowRelease(() => onReleaseCalled = true);
+      await Future<void>.delayed(Duration.zero);
+      expect(onReleaseCalled, isFalse);
+
+      expect(pool.request(), completes);
+      await Future<void>.delayed(Duration.zero);
+      expect(onReleaseCalled, isTrue);
+    });
+
+    test('runs the callback immediately if there are blocked requests',
+        () async {
+      var pool = Pool(1);
+      var resource = await pool.request();
+
+      // This will be blocked until [resource.allowRelease] is called.
+      expect(pool.request(), completes);
+
+      var onReleaseCalled = false;
+      resource.allowRelease(() => onReleaseCalled = true);
+      await Future<void>.delayed(Duration.zero);
+      expect(onReleaseCalled, isTrue);
+    });
+
+    test('blocks the request until the callback completes', () async {
+      var pool = Pool(1);
+      var resource = await pool.request();
+
+      var requestComplete = false;
+      unawaited(pool.request().then((_) => requestComplete = true));
+
+      var completer = Completer<void>();
+      resource.allowRelease(() => completer.future);
+      await Future<void>.delayed(Duration.zero);
+      expect(requestComplete, isFalse);
+
+      completer.complete();
+      await Future<void>.delayed(Duration.zero);
+      expect(requestComplete, isTrue);
+    });
+
+    test('completes requests in request order regardless of callback order',
+        () async {
+      var pool = Pool(2);
+      var resource1 = await pool.request();
+      var resource2 = await pool.request();
+
+      var request1Complete = false;
+      unawaited(pool.request().then((_) => request1Complete = true));
+      var request2Complete = false;
+      unawaited(pool.request().then((_) => request2Complete = true));
+
+      var onRelease1Called = false;
+      var completer1 = Completer<void>();
+      resource1.allowRelease(() {
+        onRelease1Called = true;
+        return completer1.future;
+      });
+      await Future<void>.delayed(Duration.zero);
+      expect(onRelease1Called, isTrue);
+
+      var onRelease2Called = false;
+      var completer2 = Completer<void>();
+      resource2.allowRelease(() {
+        onRelease2Called = true;
+        return completer2.future;
+      });
+      await Future<void>.delayed(Duration.zero);
+      expect(onRelease2Called, isTrue);
+      expect(request1Complete, isFalse);
+      expect(request2Complete, isFalse);
+
+      // Complete the second resource's onRelease callback first. Even though it
+      // was triggered by the second blocking request, it should complete the
+      // first one to preserve ordering.
+      completer2.complete();
+      await Future<void>.delayed(Duration.zero);
+      expect(request1Complete, isTrue);
+      expect(request2Complete, isFalse);
+
+      completer1.complete();
+      await Future<void>.delayed(Duration.zero);
+      expect(request1Complete, isTrue);
+      expect(request2Complete, isTrue);
+    });
+
+    test('runs onRequest in the zone it was created', () async {
+      var pool = Pool(1);
+      var resource = await pool.request();
+
+      var outerZone = Zone.current;
+      runZoned(() {
+        var innerZone = Zone.current;
+        expect(innerZone, isNot(equals(outerZone)));
+
+        resource.allowRelease(expectAsync0(() {
+          expect(Zone.current, equals(innerZone));
+        }));
+      });
+
+      await pool.request();
+    });
+  });
+
+  test("done doesn't complete without close", () async {
+    var pool = Pool(1);
+    unawaited(pool.done.then(expectAsync1((_) {}, count: 0)));
+
+    var resource = await pool.request();
+    resource.release();
+
+    await Future<void>.delayed(Duration.zero);
+  });
+
+  group('close()', () {
+    test('disallows request() and withResource()', () {
+      var pool = Pool(1)..close();
+      expect(pool.request, throwsStateError);
+      expect(() => pool.withResource(() {}), throwsStateError);
+    });
+
+    test('pending requests are fulfilled', () async {
+      var pool = Pool(1);
+      var resource1 = await pool.request();
+      expect(
+          pool.request().then((resource2) {
+            resource2.release();
+          }),
+          completes);
+      expect(pool.done, completes);
+      expect(pool.close(), completes);
+      resource1.release();
+    });
+
+    test('pending requests are fulfilled with allowRelease', () async {
+      var pool = Pool(1);
+      var resource1 = await pool.request();
+
+      var completer = Completer<void>();
+      expect(
+          pool.request().then((resource2) {
+            expect(completer.isCompleted, isTrue);
+            resource2.release();
+          }),
+          completes);
+      expect(pool.close(), completes);
+
+      resource1.allowRelease(() => completer.future);
+      await Future<void>.delayed(Duration.zero);
+
+      completer.complete();
+    });
+
+    test("doesn't complete until all resources are released", () async {
+      var pool = Pool(2);
+      var resource1 = await pool.request();
+      var resource2 = await pool.request();
+      var resource3Future = pool.request();
+
+      var resource1Released = false;
+      var resource2Released = false;
+      var resource3Released = false;
+      expect(
+          pool.close().then((_) {
+            expect(resource1Released, isTrue);
+            expect(resource2Released, isTrue);
+            expect(resource3Released, isTrue);
+          }),
+          completes);
+
+      resource1Released = true;
+      resource1.release();
+      await Future<void>.delayed(Duration.zero);
+
+      resource2Released = true;
+      resource2.release();
+      await Future<void>.delayed(Duration.zero);
+
+      var resource3 = await resource3Future;
+      resource3Released = true;
+      resource3.release();
+    });
+
+    test('active onReleases complete as usual', () async {
+      var pool = Pool(1);
+      var resource = await pool.request();
+
+      // Set up an onRelease callback whose completion is controlled by
+      // [completer].
+      var completer = Completer<void>();
+      resource.allowRelease(() => completer.future);
+      expect(
+          pool.request().then((_) {
+            expect(completer.isCompleted, isTrue);
+          }),
+          completes);
+
+      await Future<void>.delayed(Duration.zero);
+      unawaited(pool.close());
+
+      await Future<void>.delayed(Duration.zero);
+      completer.complete();
+    });
+
+    test('inactive onReleases fire', () async {
+      var pool = Pool(2);
+      var resource1 = await pool.request();
+      var resource2 = await pool.request();
+
+      var completer1 = Completer<void>();
+      resource1.allowRelease(() => completer1.future);
+      var completer2 = Completer<void>();
+      resource2.allowRelease(() => completer2.future);
+
+      expect(
+          pool.close().then((_) {
+            expect(completer1.isCompleted, isTrue);
+            expect(completer2.isCompleted, isTrue);
+          }),
+          completes);
+
+      await Future<void>.delayed(Duration.zero);
+      completer1.complete();
+
+      await Future<void>.delayed(Duration.zero);
+      completer2.complete();
+    });
+
+    test('new allowReleases fire immediately', () async {
+      var pool = Pool(1);
+      var resource = await pool.request();
+
+      var completer = Completer<void>();
+      expect(
+          pool.close().then((_) {
+            expect(completer.isCompleted, isTrue);
+          }),
+          completes);
+
+      await Future<void>.delayed(Duration.zero);
+      resource.allowRelease(() => completer.future);
+
+      await Future<void>.delayed(Duration.zero);
+      completer.complete();
+    });
+
+    test('an onRelease error is piped to the return value', () async {
+      var pool = Pool(1);
+      var resource = await pool.request();
+
+      var completer = Completer<void>();
+      resource.allowRelease(() => completer.future);
+
+      expect(pool.done, throwsA('oh no!'));
+      expect(pool.close(), throwsA('oh no!'));
+
+      await Future<void>.delayed(Duration.zero);
+      completer.completeError('oh no!');
+    });
+  });
+
+  group('forEach', () {
+    late Pool pool;
+
+    tearDown(() async {
+      await pool.close();
+    });
+
+    const delayedToStringDuration = Duration(milliseconds: 10);
+
+    Future<String> delayedToString(int i) =>
+        Future<String>.delayed(delayedToStringDuration, () => i.toString());
+
+    for (var itemCount in [0, 5]) {
+      for (var poolSize in [1, 5, 6]) {
+        test('poolSize: $poolSize, itemCount: $itemCount', () async {
+          pool = Pool(poolSize);
+
+          var finishedItems = 0;
+
+          await for (var item in pool.forEach(
+              Iterable.generate(itemCount, (i) {
+                expect(i, lessThanOrEqualTo(finishedItems + poolSize),
+                    reason: 'the iterator should be called lazily');
+                return i;
+              }),
+              delayedToString)) {
+            expect(int.parse(item), lessThan(itemCount));
+            finishedItems++;
+          }
+
+          expect(finishedItems, itemCount);
+        });
+      }
+    }
+
+    test('pool closed before listen', () async {
+      pool = Pool(2);
+
+      var stream = pool.forEach(Iterable<int>.generate(5), delayedToString);
+
+      await pool.close();
+
+      expect(stream.toList(), throwsStateError);
+    });
+
+    test('completes even if the pool is partially used', () async {
+      pool = Pool(2);
+
+      var resource = await pool.request();
+
+      var stream = pool.forEach(<int>[], delayedToString);
+
+      expect(await stream.length, 0);
+
+      resource.release();
+    });
+
+    test('stream paused longer than timeout', () async {
+      pool = Pool(2, timeout: delayedToStringDuration);
+
+      var resource = await pool.request();
+
+      var stream = pool.forEach<int, int>(
+          Iterable.generate(100, (i) {
+            expect(i, lessThan(20),
+                reason: 'The timeout should happen '
+                    'before the entire iterable is iterated.');
+            return i;
+          }), (i) async {
+        await Future<void>.delayed(Duration(milliseconds: i));
+        return i;
+      });
+
+      await expectLater(
+          stream.toList,
+          throwsA(const TypeMatcher<TimeoutException>().having(
+              (te) => te.message,
+              'message',
+              contains('Pool deadlock: '
+                  'all resources have been allocated for too long.'))));
+
+      resource.release();
+    });
+
+    group('timing and timeout', () {
+      for (var poolSize in [2, 8, 64]) {
+        for (var otherTaskCount
+            in [0, 1, 7, 63].where((otc) => otc < poolSize)) {
+          test('poolSize: $poolSize, otherTaskCount: $otherTaskCount',
+              () async {
+            final itemCount = 128;
+            pool = Pool(poolSize, timeout: const Duration(milliseconds: 20));
+
+            var otherTasks = await Future.wait(
+                Iterable<int>.generate(otherTaskCount)
+                    .map((i) => pool.request()));
+
+            try {
+              var finishedItems = 0;
+
+              var watch = Stopwatch()..start();
+
+              await for (var item in pool.forEach(
+                  Iterable.generate(itemCount, (i) {
+                    expect(i, lessThanOrEqualTo(finishedItems + poolSize),
+                        reason: 'the iterator should be called lazily');
+                    return i;
+                  }),
+                  delayedToString)) {
+                expect(int.parse(item), lessThan(itemCount));
+                finishedItems++;
+              }
+
+              expect(finishedItems, itemCount);
+
+              final expectedElapsed =
+                  delayedToStringDuration.inMicroseconds * 4;
+
+              expect((watch.elapsed ~/ itemCount).inMicroseconds,
+                  lessThan(expectedElapsed / (poolSize - otherTaskCount)),
+                  reason: 'Average time per task should be '
+                      'proportionate to the available pool resources.');
+            } finally {
+              for (var task in otherTasks) {
+                task.release();
+              }
+            }
+          });
+        }
+      }
+    }, testOn: 'vm');
+
+    test('partial iteration', () async {
+      pool = Pool(5);
+      var stream = pool.forEach(Iterable<int>.generate(100), delayedToString);
+      expect(await stream.take(10).toList(), hasLength(10));
+    });
+
+    test('pool close during data with waiting to be done', () async {
+      pool = Pool(5);
+
+      var stream = pool.forEach(Iterable<int>.generate(100), delayedToString);
+
+      var dataCount = 0;
+      var subscription = stream.listen((data) {
+        dataCount++;
+        pool.close();
+      });
+
+      await subscription.asFuture<void>();
+      expect(dataCount, 100);
+      await subscription.cancel();
+    });
+
+    test('pause and resume ', () async {
+      var generatedCount = 0;
+      var dataCount = 0;
+      final poolSize = 5;
+
+      pool = Pool(poolSize);
+
+      var stream = pool.forEach(
+          Iterable<int>.generate(40, (i) {
+            expect(generatedCount, lessThanOrEqualTo(dataCount + 2 * poolSize),
+                reason: 'The iterator should not be called '
+                    'much faster than the data is consumed.');
+            generatedCount++;
+            return i;
+          }),
+          delayedToString);
+
+      // ignore: cancel_subscriptions
+      late StreamSubscription subscription;
+
+      subscription = stream.listen(
+        (data) {
+          dataCount++;
+
+          if (int.parse(data) % 3 == 1) {
+            subscription.pause(Future(() async {
+              await Future<void>.delayed(const Duration(milliseconds: 100));
+            }));
+          }
+        },
+        onError: registerException,
+        onDone: expectAsync0(() {
+          expect(dataCount, 40);
+        }),
+      );
+    });
+
+    group('cancel', () {
+      final dataSize = 32;
+      for (var i = 1; i < 5; i++) {
+        test('with pool size $i', () async {
+          pool = Pool(i);
+
+          var stream =
+              pool.forEach(Iterable<int>.generate(dataSize), delayedToString);
+
+          var cancelCompleter = Completer<void>();
+
+          StreamSubscription subscription;
+
+          var eventCount = 0;
+          subscription = stream.listen((data) {
+            eventCount++;
+            if (int.parse(data) == dataSize ~/ 2) {
+              cancelCompleter.complete();
+            }
+          }, onError: registerException);
+
+          await cancelCompleter.future;
+
+          await subscription.cancel();
+
+          expect(eventCount, 1 + dataSize ~/ 2);
+        });
+      }
+    });
+
+    group('errors', () {
+      Future<void> errorInIterator({
+        bool Function(int item, Object error, StackTrace stack)? onError,
+      }) async {
+        pool = Pool(20);
+
+        var listFuture = pool
+            .forEach(
+                Iterable.generate(100, (i) {
+                  if (i == 50) {
+                    throw StateError('error while generating item in iterator');
+                  }
+
+                  return i;
+                }),
+                delayedToString,
+                onError: onError)
+            .toList();
+
+        await expectLater(() async => listFuture, throwsStateError);
+      }
+
+      test('iteration, no onError', () async {
+        await errorInIterator();
+      });
+      test('iteration, with onError', () async {
+        await errorInIterator(onError: (i, e, s) => false);
+      });
+
+      test('error in action, no onError', () async {
+        pool = Pool(20);
+
+        var listFuture = pool.forEach(Iterable<int>.generate(100), (i) async {
+          await Future<void>.delayed(const Duration(milliseconds: 10));
+          if (i == 10) {
+            throw UnsupportedError('10 is not supported');
+          }
+          return i.toString();
+        }).toList();
+
+        await expectLater(() async => listFuture, throwsUnsupportedError);
+      });
+
+      test('error in action, no onError', () async {
+        pool = Pool(20);
+
+        var list = await pool.forEach(Iterable<int>.generate(100),
+            (int i) async {
+          await Future<void>.delayed(const Duration(milliseconds: 10));
+          if (i % 10 == 0) {
+            throw UnsupportedError('Multiples of 10 not supported');
+          }
+          return i.toString();
+        },
+            onError: (item, error, stack) =>
+                error is! UnsupportedError).toList();
+
+        expect(list, hasLength(90));
+      });
+    });
+  });
+
+  test('throw error when pool limit <= 0', () {
+    expect(() => Pool(-1), throwsArgumentError);
+    expect(() => Pool(0), throwsArgumentError);
+  });
+}
+
+/// Returns a function that will cause the test to fail if it's called.
+///
+/// This should only be called within a [FakeAsync.run] zone.
+void Function() expectNoAsync() {
+  var stack = Trace.current(1);
+  return () => registerException(
+      TestFailure('Expected function not to be called.'), stack);
+}
+
+/// A matcher for Futures that asserts that they don't complete.
+///
+/// This should only be called within a [FakeAsync.run] zone.
+Matcher get doesNotComplete => predicate((Future future) {
+      var stack = Trace.current(1);
+      future.then((_) => registerException(
+          TestFailure('Expected future not to complete.'), stack));
+      return true;
+    });

diff --git a/pkgs/pub_semver/.gitignore b/pkgs/pub_semver/.gitignore
new file mode 100644
index 0000000..49ce72d
--- /dev/null
+++ b/pkgs/pub_semver/.gitignore

@@ -0,0 +1,3 @@
+.dart_tool/
+.packages
+pubspec.lock

diff --git a/pkgs/pub_semver/CHANGELOG.md b/pkgs/pub_semver/CHANGELOG.md
new file mode 100644
index 0000000..a31fbb2
--- /dev/null
+++ b/pkgs/pub_semver/CHANGELOG.md

@@ -0,0 +1,177 @@
+## 2.1.5
+
+- Require Dart `3.4.0`.
+- Move to `dart-lang/tools` monorepo.
+
+## 2.1.4
+
+- Added topics to `pubspec.yaml`.
+
+## 2.1.3
+
+- Add type parameters to the signatures of the `Version.preRelease` and
+  `Version.build` fields (`List` ==> `List<Object>`).
+  [#74](https://github.com/dart-lang/pub_semver/pull/74).
+- Require Dart 2.17.
+
+## 2.1.2
+
+- Add markdown badges to the readme.
+
+## 2.1.1
+
+- Fixed the version parsing pattern to only accept dots between version
+  components.
+
+## 2.1.0
+
+- Added `Version.canonicalizedVersion` to help scrub leading zeros and highlight
+  that `Version.toString()` preserves leading zeros.
+- Annotated `Version` with `@sealed` to discourage users from implementing the
+  interface.
+
+## 2.0.0
+
+- Stable null safety release.
+- `Version.primary` now throws `StateError` if the `versions` argument is empty.
+
+## 1.4.4
+
+- Fix a bug of `VersionRange.union` where ranges bounded at infinity would get
+  combined wrongly.
+
+# 1.4.3
+
+- Update Dart SDK constraint to `>=2.0.0 <3.0.0`.
+- Update `package:collection` constraint to `^1.0.0`.
+
+## 1.4.2
+
+* Set max SDK version to `<3.0.0`.
+
+## 1.4.1
+
+* Fix a bug where there upper bound of a version range with a build identifier
+  could accidentally be rewritten.
+
+## 1.4.0
+
+* Add a `Version.firstPreRelease` getter that returns the first possible
+  pre-release of a version.
+
+* Add a `Version.isFirstPreRelease` getter that returns whether a version is the
+  first possible pre-release.
+
+* `new VersionRange()` with an exclusive maximum now replaces the maximum with
+  its first pre-release version. This matches the existing semantics, where an
+  exclusive maximum would exclude pre-release versions of that maximum.
+
+  Explicitly representing this by changing the maximum version ensures that all
+  operations behave correctly with respect to the special pre-release semantics.
+  In particular, it fixes bugs where, for example,
+  `(>=1.0.0 <2.0.0-dev).union(>=2.0.0-dev <2.0.0)` and
+  `(>=1.0.0 <3.0.0).difference(^1.0.0)` wouldn't include `2.0.0-dev`.
+
+* Add an `alwaysIncludeMaxPreRelease` parameter to `new VersionRange()`, which
+  disables the replacement described above and allows users to create ranges
+  that do include the pre-release versions of an exclusive max version.
+
+## 1.3.7
+
+* Fix more bugs with `VersionRange.intersect()`, `VersionRange.difference()`,
+  and `VersionRange.union()` involving version ranges with pre-release maximums.
+
+## 1.3.6
+
+* Fix a bug where constraints that only allowed pre-release versions would be
+  parsed as empty constraints.
+
+## 1.3.5
+
+* Fix a bug where `VersionRange.intersect()` would return incorrect results for
+  pre-release versions with the same base version number as release versions.
+
+## 1.3.4
+
+* Fix a bug where `VersionRange.allowsAll()`, `VersionRange.allowsAny()`, and
+  `VersionRange.difference()` would return incorrect results for pre-release
+  versions with the same base version number as release versions.
+
+## 1.3.3
+
+* Fix a bug where `VersionRange.difference()` with a union constraint that
+  covered the entire range would crash.
+
+## 1.3.2
+
+* Fix a checked-mode error in `VersionRange.difference()`.
+
+## 1.3.1
+
+* Fix a new strong mode error.
+
+## 1.3.0
+
+* Make the `VersionUnion` class public. This was previously used internally to
+  implement `new VersionConstraint.unionOf()` and `VersionConstraint.union()`.
+  Now it's public so you can use it too.
+
+* Added `VersionConstraint.difference()`. This returns a constraint matching all
+  versions matched by one constraint but not another.
+
+* Make `VersionRange` implement `Comparable<VersionRange>`. Ranges are ordered
+  first by lower bound, then by upper bound.
+
+## 1.2.4
+
+* Fix all remaining strong mode warnings.
+
+## 1.2.3
+
+* Addressed three strong mode warnings.
+
+## 1.2.2
+
+* Make the package analyze under strong mode and compile with the DDC (Dart Dev
+  Compiler). Fix two issues with a private subclass of `VersionConstraint`
+  having different types for overridden methods.
+
+## 1.2.1
+
+* Allow version ranges like `>=1.2.3-dev.1 <1.2.3` to match pre-release versions
+  of `1.2.3`. Previously, these didn't match, since the pre-release versions had
+  the same major, minor, and patch numbers as the max; now an exception has been
+  added if they also have the same major, minor, and patch numbers as the min
+  *and* the min is also a pre-release version.
+
+## 1.2.0
+
+* Add a `VersionConstraint.union()` method and a `new
+  VersionConstraint.unionOf()` constructor. These each return a constraint that
+  matches multiple existing constraints.
+
+* Add a `VersionConstraint.allowsAll()` method, which returns whether one
+  constraint is a superset of another.
+
+* Add a `VersionConstraint.allowsAny()` method, which returns whether one
+  constraint overlaps another.
+
+* `Version` now implements `VersionRange`.
+
+## 1.1.0
+
+* Add support for the `^` operator for compatible versions according to pub's
+  notion of compatibility. `^1.2.3` is equivalent to `>=1.2.3 <2.0.0`; `^0.1.2`
+  is equivalent to `>=0.1.2 <0.2.0`.
+
+* Add `Version.nextBreaking`, which returns the next version that introduces
+  breaking changes after a given version.
+
+* Add `new VersionConstraint.compatibleWith()`, which returns a range covering
+  all versions compatible with a given version.
+
+* Add a custom `VersionRange.hashCode` to make it properly hashable.
+
+## 1.0.0
+
+* Initial release.

diff --git a/pkgs/pub_semver/LICENSE b/pkgs/pub_semver/LICENSE
new file mode 100644
index 0000000..000cd7b
--- /dev/null
+++ b/pkgs/pub_semver/LICENSE

@@ -0,0 +1,27 @@
+Copyright 2014, the Dart project authors. 
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+    * Neither the name of Google LLC nor the names of its
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

diff --git a/pkgs/pub_semver/README.md b/pkgs/pub_semver/README.md
new file mode 100644
index 0000000..03c92a3
--- /dev/null
+++ b/pkgs/pub_semver/README.md

@@ -0,0 +1,107 @@
+[![Build Status](https://github.com/dart-lang/tools/actions/workflows/pub_semver.yaml/badge.svg)](https://github.com/dart-lang/tools/actions/workflows/pub_semver.yaml)
+[![pub package](https://img.shields.io/pub/v/pub_semver.svg)](https://pub.dev/packages/pub_semver)
+[![package publisher](https://img.shields.io/pub/publisher/pub_semver.svg)](https://pub.dev/packages/pub_semver/publisher)
+
+Handles version numbers and version constraints in the same way that [pub][]
+does.
+
+## Semantics
+
+The semantics here very closely follow the
+[Semantic Versioning spec version 2.0.0-rc.1][semver]. It differs from semver
+in a few corner cases:
+
+ *  **Version ordering does take build suffixes into account.** This is unlike
+    semver 2.0.0 but like earlier versions of semver. Version `1.2.3+1` is
+    considered a lower number than `1.2.3+2`.
+
+    Since a package may have published multiple versions that differ only by
+    build suffix, pub still has to pick one of them *somehow*. Semver leaves
+    that issue unresolved, so we just say that build numbers are sorted like
+    pre-release suffixes.
+
+ *  **Pre-release versions are excluded from most max ranges.** Let's say a
+    user is depending on "foo" with constraint `>=1.0.0 <2.0.0` and that "foo"
+    has published these versions:
+
+     *  `1.0.0`
+     *  `1.1.0`
+     *  `1.2.0`
+     *  `2.0.0-alpha`
+     *  `2.0.0-beta`
+     *  `2.0.0`
+     *  `2.1.0`
+
+    Versions `2.0.0` and `2.1.0` are excluded by the constraint since neither
+    matches `<2.0.0`. However, since semver specifies that pre-release versions
+    are lower than the non-prerelease version (i.e. `2.0.0-beta < 2.0.0`, then
+    the `<2.0.0` constraint does technically allow those.
+
+    But that's almost never what the user wants. If their package doesn't work
+    with foo `2.0.0`, it's certainly not likely to work with experimental,
+    unstable versions of `2.0.0`'s API, which is what pre-release versions
+    represent.
+
+    To handle that, `<` version ranges don't allow pre-release versions of the
+    maximum unless the max is itself a pre-release, or the min is a pre-release
+    of the same version. In other words, a `<2.0.0` constraint will prohibit not
+    just `2.0.0` but any pre-release of `2.0.0`. However, `<2.0.0-beta` will
+    exclude `2.0.0-beta` but allow `2.0.0-alpha`. Likewise, `>2.0.0-alpha
+    <2.0.0` will exclude `2.0.0-alpha` but allow `2.0.0-beta`.
+
+ *  **Pre-release versions are avoided when possible.** The above case
+    handles pre-release versions at the top of the range, but what about in
+    the middle? What if "foo" has these versions:
+
+     *  `1.0.0`
+     *  `1.2.0-alpha`
+     *  `1.2.0`
+     *  `1.3.0-experimental`
+
+    When a number of versions are valid, pub chooses the best one where "best"
+    usually means "highest numbered". That follows the user's intuition that,
+    all else being equal, they want the latest and greatest. Here, that would
+    mean `1.3.0-experimental`. However, most users don't want to use unstable
+    versions of their dependencies.
+
+    We want pre-releases to be explicitly opt-in so that package consumers
+    don't get unpleasant surprises and so that package maintainers are free to
+    put out pre-releases and get feedback without dragging all of their users
+    onto the bleeding edge.
+
+    To accommodate that, when pub is choosing a version, it uses *priority*
+    order which is different from strict comparison ordering. Any stable
+    version is considered higher priority than any unstable version. The above
+    versions, in priority order, are:
+
+     *  `1.2.0-alpha`
+     *  `1.3.0-experimental`
+     *  `1.0.0`
+     *  `1.2.0`
+
+    This ensures that users only end up with an unstable version when there are
+    no alternatives. Usually this means they've picked a constraint that
+    specifically selects that unstable version -- they've deliberately opted
+    into it.
+
+ *  **There is a notion of compatibility between pre-1.0.0 versions.** Semver
+    deems all pre-1.0.0 versions to be incompatible.  This means that the only
+    way to ensure compatibility when depending on a pre-1.0.0 package is to
+    pin the dependency to an exact version. Pinned version constraints prevent
+    automatic patch and pre-release updates. To avoid this situation, pub
+    defines the "next breaking" version as the version which increments the
+    major version if it's greater than zero, and the minor version otherwise,
+    resets subsequent digits to zero, and strips any pre-release or build
+    suffix.  For example, here are some versions along with their next breaking
+    ones:
+
+    `0.0.3` -> `0.1.0`
+    `0.7.2-alpha` -> `0.8.0`
+    `1.2.3` -> `2.0.0`
+
+    To make use of this, pub defines a "^" operator which yields a version
+    constraint greater than or equal to a given version, but less than its next
+    breaking one.
+
+[pub]: https://pub.dev
+[semver]: https://semver.org/spec/v2.0.0-rc.1.html

diff --git a/pkgs/pub_semver/analysis_options.yaml b/pkgs/pub_semver/analysis_options.yaml
new file mode 100644
index 0000000..76380a0
--- /dev/null
+++ b/pkgs/pub_semver/analysis_options.yaml

@@ -0,0 +1,31 @@
+# https://dart.dev/guides/language/analysis-options
+include: package:dart_flutter_team_lints/analysis_options.yaml
+
+analyzer:
+  language:
+    strict-casts: true
+    strict-inference: true
+    strict-raw-types: true
+
+linter:
+  rules:
+    - avoid_bool_literals_in_conditional_expressions
+    - avoid_classes_with_only_static_members
+    - avoid_private_typedef_functions
+    - avoid_redundant_argument_values
+    - avoid_returning_this
+    - avoid_unused_constructor_parameters
+    - avoid_void_async
+    - cancel_subscriptions
+    - cascade_invocations
+    - join_return_with_assignment
+    - literal_only_boolean_expressions
+    - missing_whitespace_between_adjacent_strings
+    - no_adjacent_strings_in_list
+    - no_runtimeType_toString
+    - prefer_const_declarations
+    - prefer_expression_function_bodies
+    - unnecessary_await_in_return
+    - use_if_null_to_convert_nulls_to_bools
+    - use_raw_strings
+    - use_string_buffers

diff --git a/pkgs/pub_semver/example/example.dart b/pkgs/pub_semver/example/example.dart
new file mode 100644
index 0000000..890343c
--- /dev/null
+++ b/pkgs/pub_semver/example/example.dart

@@ -0,0 +1,17 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:pub_semver/pub_semver.dart';
+
+void main() {
+  final range = VersionConstraint.parse('^2.0.0');
+
+  for (var version in [
+    Version.parse('1.2.3-pre'),
+    Version.parse('2.0.0+123'),
+    Version.parse('3.0.0-dev'),
+  ]) {
+    print('$version ${version.isPreRelease} ${range.allows(version)}');
+  }
+}

diff --git a/pkgs/pub_semver/lib/pub_semver.dart b/pkgs/pub_semver/lib/pub_semver.dart
new file mode 100644
index 0000000..4b6487c
--- /dev/null
+++ b/pkgs/pub_semver/lib/pub_semver.dart

@@ -0,0 +1,8 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+export 'src/version.dart';
+export 'src/version_constraint.dart';
+export 'src/version_range.dart' hide CompatibleWithVersionRange;
+export 'src/version_union.dart';

diff --git a/pkgs/pub_semver/lib/src/patterns.dart b/pkgs/pub_semver/lib/src/patterns.dart
new file mode 100644
index 0000000..03119ac
--- /dev/null
+++ b/pkgs/pub_semver/lib/src/patterns.dart

@@ -0,0 +1,19 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Regex that matches a version number at the beginning of a string.
+final startVersion = RegExp(r'^' // Start at beginning.
+    r'(\d+)\.(\d+)\.(\d+)' // Version number.
+    r'(-([0-9A-Za-z-]+(\.[0-9A-Za-z-]+)*))?' // Pre-release.
+    r'(\+([0-9A-Za-z-]+(\.[0-9A-Za-z-]+)*))?'); // Build.
+
+/// Like [startVersion] but matches the entire string.
+final completeVersion = RegExp('${startVersion.pattern}\$');
+
+/// Parses a comparison operator ("<", ">", "<=", or ">=") at the beginning of
+/// a string.
+final startComparison = RegExp(r'^[<>]=?');
+
+/// The "compatible with" operator.
+const compatibleWithChar = '^';

diff --git a/pkgs/pub_semver/lib/src/utils.dart b/pkgs/pub_semver/lib/src/utils.dart
new file mode 100644
index 0000000..a9f714f
--- /dev/null
+++ b/pkgs/pub_semver/lib/src/utils.dart

@@ -0,0 +1,58 @@
+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'version.dart';
+import 'version_range.dart';
+
+/// Returns whether [range1] is immediately next to, but not overlapping,
+/// [range2].
+bool areAdjacent(VersionRange range1, VersionRange range2) {
+  if (range1.max != range2.min) return false;
+
+  return (range1.includeMax && !range2.includeMin) ||
+      (!range1.includeMax && range2.includeMin);
+}
+
+/// Returns whether [range1] allows lower versions than [range2].
+bool allowsLower(VersionRange range1, VersionRange range2) {
+  if (range1.min == null) return range2.min != null;
+  if (range2.min == null) return false;
+
+  var comparison = range1.min!.compareTo(range2.min!);
+  if (comparison == -1) return true;
+  if (comparison == 1) return false;
+  return range1.includeMin && !range2.includeMin;
+}
+
+/// Returns whether [range1] allows higher versions than [range2].
+bool allowsHigher(VersionRange range1, VersionRange range2) {
+  if (range1.max == null) return range2.max != null;
+  if (range2.max == null) return false;
+
+  var comparison = range1.max!.compareTo(range2.max!);
+  if (comparison == 1) return true;
+  if (comparison == -1) return false;
+  return range1.includeMax && !range2.includeMax;
+}
+
+/// Returns whether [range1] allows only versions lower than those allowed by
+/// [range2].
+bool strictlyLower(VersionRange range1, VersionRange range2) {
+  if (range1.max == null || range2.min == null) return false;
+
+  var comparison = range1.max!.compareTo(range2.min!);
+  if (comparison == -1) return true;
+  if (comparison == 1) return false;
+  return !range1.includeMax || !range2.includeMin;
+}
+
+/// Returns whether [range1] allows only versions higher than those allowed by
+/// [range2].
+bool strictlyHigher(VersionRange range1, VersionRange range2) =>
+    strictlyLower(range2, range1);
+
+bool equalsWithoutPreRelease(Version version1, Version version2) =>
+    version1.major == version2.major &&
+    version1.minor == version2.minor &&
+    version1.patch == version2.patch;

diff --git a/pkgs/pub_semver/lib/src/version.dart b/pkgs/pub_semver/lib/src/version.dart
new file mode 100644
index 0000000..90f3d53
--- /dev/null
+++ b/pkgs/pub_semver/lib/src/version.dart

@@ -0,0 +1,391 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:math' as math;
+
+import 'package:collection/collection.dart';
+import 'package:meta/meta.dart' show sealed;
+
+import 'patterns.dart';
+import 'version_constraint.dart';
+import 'version_range.dart';
+
+/// The equality operator to use for comparing version components.
+const _equality = IterableEquality<Object>();
+
+/// A parsed semantic version number.
+@sealed
+class Version implements VersionConstraint, VersionRange {
+  /// No released version: i.e. "0.0.0".
+  static Version get none => Version(0, 0, 0);
+
+  /// Compares [a] and [b] to see which takes priority over the other.
+  ///
+  /// Returns `1` if [a] takes priority over [b] and `-1` if vice versa. If
+  /// [a] and [b] are equivalent, returns `0`.
+  ///
+  /// Unlike [compareTo], which *orders* versions, this determines which
+  /// version a user is likely to prefer. In particular, it prioritizes
+  /// pre-release versions lower than stable versions, regardless of their
+  /// version numbers. Pub uses this when determining which version to prefer
+  /// when a number of versions are allowed. In that case, it will always
+  /// choose a stable version when possible.
+  ///
+  /// When used to sort a list, orders in ascending priority so that the
+  /// highest priority version is *last* in the result.
+  static int prioritize(Version a, Version b) {
+    // Sort all prerelease versions after all normal versions. This way
+    // the solver will prefer stable packages over unstable ones.
+    if (a.isPreRelease && !b.isPreRelease) return -1;
+    if (!a.isPreRelease && b.isPreRelease) return 1;
+
+    return a.compareTo(b);
+  }
+
+  /// Like [prioritize], but lower version numbers are considered greater than
+  /// higher version numbers.
+  ///
+  /// This still considers prerelease versions to be lower than non-prerelease
+  /// versions. Pub uses this when downgrading -- it chooses the lowest version
+  /// but still excludes pre-release versions when possible.
+  static int antiprioritize(Version a, Version b) {
+    if (a.isPreRelease && !b.isPreRelease) return -1;
+    if (!a.isPreRelease && b.isPreRelease) return 1;
+
+    return b.compareTo(a);
+  }
+
+  /// The major version number: "1" in "1.2.3".
+  final int major;
+
+  /// The minor version number: "2" in "1.2.3".
+  final int minor;
+
+  /// The patch version number: "3" in "1.2.3".
+  final int patch;
+
+  /// The pre-release identifier: "foo" in "1.2.3-foo".
+  ///
+  /// This is split into a list of components, each of which may be either a
+  /// string or a non-negative integer. It may also be empty, indicating that
+  /// this version has no pre-release identifier.
+  final List<Object> preRelease;
+
+  /// The build identifier: "foo" in "1.2.3+foo".
+  ///
+  /// This is split into a list of components, each of which may be either a
+  /// string or a non-negative integer. It may also be empty, indicating that
+  /// this version has no build identifier.
+  final List<Object> build;
+
+  /// The original string representation of the version number.
+  ///
+  /// This preserves textual artifacts like leading zeros that may be left out
+  /// of the parsed version.
+  final String _text;
+
+  @override
+  Version get min => this;
+  @override
+  Version get max => this;
+  @override
+  bool get includeMin => true;
+  @override
+  bool get includeMax => true;
+
+  Version._(this.major, this.minor, this.patch, String? preRelease,
+      String? build, this._text)
+      : preRelease = preRelease == null ? <Object>[] : _splitParts(preRelease),
+        build = build == null ? [] : _splitParts(build) {
+    if (major < 0) throw ArgumentError('Major version must be non-negative.');
+    if (minor < 0) throw ArgumentError('Minor version must be non-negative.');
+    if (patch < 0) throw ArgumentError('Patch version must be non-negative.');
+  }
+
+  /// Creates a new [Version] object.
+  factory Version(int major, int minor, int patch,
+      {String? pre, String? build}) {
+    var text = '$major.$minor.$patch';
+    if (pre != null) text += '-$pre';
+    if (build != null) text += '+$build';
+
+    return Version._(major, minor, patch, pre, build, text);
+  }
+
+  /// Creates a new [Version] by parsing [text].
+  factory Version.parse(String text) {
+    final match = completeVersion.firstMatch(text);
+    if (match == null) {
+      throw FormatException('Could not parse "$text".');
+    }
+
+    try {
+      var major = int.parse(match[1]!);
+      var minor = int.parse(match[2]!);
+      var patch = int.parse(match[3]!);
+
+      var preRelease = match[5];
+      var build = match[8];
+
+      return Version._(major, minor, patch, preRelease, build, text);
+    } on FormatException {
+      throw FormatException('Could not parse "$text".');
+    }
+  }
+
+  /// Returns the primary version out of [versions].
+  ///
+  /// This is the highest-numbered stable (non-prerelease) version. If there
+  /// are no stable versions, it's just the highest-numbered version.
+  ///
+  /// If [versions] is empty, throws a [StateError].
+  static Version primary(List<Version> versions) {
+    var primary = versions.first;
+    for (var version in versions.skip(1)) {
+      if ((!version.isPreRelease && primary.isPreRelease) ||
+          (version.isPreRelease == primary.isPreRelease && version > primary)) {
+        primary = version;
+      }
+    }
+    return primary;
+  }
+
+  /// Splits a string of dot-delimited identifiers into their component parts.
+  ///
+  /// Identifiers that are numeric are converted to numbers.
+  static List<Object> _splitParts(String text) => text
+      .split('.')
+      .map((part) =>
+          // Return an integer part if possible, otherwise return the string
+          // as-is
+          int.tryParse(part) ?? part)
+      .toList();
+
+  @override
+  bool operator ==(Object other) =>
+      other is Version &&
+      major == other.major &&
+      minor == other.minor &&
+      patch == other.patch &&
+      _equality.equals(preRelease, other.preRelease) &&
+      _equality.equals(build, other.build);
+
+  @override
+  int get hashCode =>
+      major ^
+      minor ^
+      patch ^
+      _equality.hash(preRelease) ^
+      _equality.hash(build);
+
+  bool operator <(Version other) => compareTo(other) < 0;
+  bool operator >(Version other) => compareTo(other) > 0;
+  bool operator <=(Version other) => compareTo(other) <= 0;
+  bool operator >=(Version other) => compareTo(other) >= 0;
+
+  @override
+  bool get isAny => false;
+  @override
+  bool get isEmpty => false;
+
+  /// Whether or not this is a pre-release version.
+  bool get isPreRelease => preRelease.isNotEmpty;
+
+  /// Gets the next major version number that follows this one.
+  ///
+  /// If this version is a pre-release of a major version release (i.e. the
+  /// minor and patch versions are zero), then it just strips the pre-release
+  /// suffix. Otherwise, it increments the major version and resets the minor
+  /// and patch.
+  Version get nextMajor {
+    if (isPreRelease && minor == 0 && patch == 0) {
+      return Version(major, minor, patch);
+    }
+
+    return _incrementMajor();
+  }
+
+  /// Gets the next minor version number that follows this one.
+  ///
+  /// If this version is a pre-release of a minor version release (i.e. the
+  /// patch version is zero), then it just strips the pre-release suffix.
+  /// Otherwise, it increments the minor version and resets the patch.
+  Version get nextMinor {
+    if (isPreRelease && patch == 0) {
+      return Version(major, minor, patch);
+    }
+
+    return _incrementMinor();
+  }
+
+  /// Gets the next patch version number that follows this one.
+  ///
+  /// If this version is a pre-release, then it just strips the pre-release
+  /// suffix. Otherwise, it increments the patch version.
+  Version get nextPatch {
+    if (isPreRelease) {
+      return Version(major, minor, patch);
+    }
+
+    return _incrementPatch();
+  }
+
+  /// Gets the next breaking version number that follows this one.
+  ///
+  /// Increments [major] if it's greater than zero, otherwise [minor], resets
+  /// subsequent digits to zero, and strips any [preRelease] or [build]
+  /// suffix.
+  Version get nextBreaking {
+    if (major == 0) {
+      return _incrementMinor();
+    }
+
+    return _incrementMajor();
+  }
+
+  /// Returns the first possible pre-release of this version.
+  Version get firstPreRelease => Version(major, minor, patch, pre: '0');
+
+  /// Returns whether this is the first possible pre-release of its version.
+  bool get isFirstPreRelease => preRelease.length == 1 && preRelease.first == 0;
+
+  Version _incrementMajor() => Version(major + 1, 0, 0);
+  Version _incrementMinor() => Version(major, minor + 1, 0);
+  Version _incrementPatch() => Version(major, minor, patch + 1);
+
+  /// Tests if [other] matches this version exactly.
+  @override
+  bool allows(Version other) => this == other;
+
+  @override
+  bool allowsAll(VersionConstraint other) => other.isEmpty || other == this;
+
+  @override
+  bool allowsAny(VersionConstraint other) => other.allows(this);
+
+  @override
+  VersionConstraint intersect(VersionConstraint other) =>
+      other.allows(this) ? this : VersionConstraint.empty;
+
+  @override
+  VersionConstraint union(VersionConstraint other) {
+    if (other.allows(this)) return other;
+
+    if (other is VersionRange) {
+      if (other.min == this) {
+        return VersionRange(
+            min: other.min,
+            max: other.max,
+            includeMin: true,
+            includeMax: other.includeMax,
+            alwaysIncludeMaxPreRelease: true);
+      }
+
+      if (other.max == this) {
+        return VersionRange(
+            min: other.min,
+            max: other.max,
+            includeMin: other.includeMin,
+            includeMax: true,
+            alwaysIncludeMaxPreRelease: true);
+      }
+    }
+
+    return VersionConstraint.unionOf([this, other]);
+  }
+
+  @override
+  VersionConstraint difference(VersionConstraint other) =>
+      other.allows(this) ? VersionConstraint.empty : this;
+
+  @override
+  int compareTo(VersionRange other) {
+    if (other is Version) {
+      if (major != other.major) return major.compareTo(other.major);
+      if (minor != other.minor) return minor.compareTo(other.minor);
+      if (patch != other.patch) return patch.compareTo(other.patch);
+
+      // Pre-releases always come before no pre-release string.
+      if (!isPreRelease && other.isPreRelease) return 1;
+      if (!other.isPreRelease && isPreRelease) return -1;
+
+      var comparison = _compareLists(preRelease, other.preRelease);
+      if (comparison != 0) return comparison;
+
+      // Builds always come after no build string.
+      if (build.isEmpty && other.build.isNotEmpty) return -1;
+      if (other.build.isEmpty && build.isNotEmpty) return 1;
+      return _compareLists(build, other.build);
+    } else {
+      return -other.compareTo(this);
+    }
+  }
+
+  /// Get non-canonical string representation of this [Version].
+  ///
+  /// If created with [Version.parse], the string from which the version was
+  /// parsed is returned. Unlike the [canonicalizedVersion] this preserves
+  /// artifacts such as leading zeros.
+  @override
+  String toString() => _text;
+
+  /// Get a canonicalized string representation of this [Version].
+  ///
+  /// Unlike [Version.toString()] this always returns a canonical string
+  /// representation of this [Version].
+  ///
+  /// **Example**
+  /// ```dart
+  /// final v = Version.parse('01.02.03-01.dev+pre.02');
+  ///
+  /// assert(v.toString() == '01.02.03-01.dev+pre.02');
+  /// assert(v.canonicalizedVersion == '1.2.3-1.dev+pre.2');
+  /// assert(Version.parse(v.canonicalizedVersion) == v);
+  /// ```
+  String get canonicalizedVersion => Version(
+        major,
+        minor,
+        patch,
+        pre: preRelease.isNotEmpty ? preRelease.join('.') : null,
+        build: build.isNotEmpty ? build.join('.') : null,
+      ).toString();
+
+  /// Compares a dot-separated component of two versions.
+  ///
+  /// This is used for the pre-release and build version parts. This follows
+  /// Rule 12 of the Semantic Versioning spec (v2.0.0-rc.1).
+  int _compareLists(List<Object> a, List<Object> b) {
+    for (var i = 0; i < math.max(a.length, b.length); i++) {
+      var aPart = (i < a.length) ? a[i] : null;
+      var bPart = (i < b.length) ? b[i] : null;
+
+      if (aPart == bPart) continue;
+
+      // Missing parts come before present ones.
+      if (aPart == null) return -1;
+      if (bPart == null) return 1;
+
+      if (aPart is num) {
+        if (bPart is num) {
+          // Compare two numbers.
+          return aPart.compareTo(bPart);
+        } else {
+          // Numbers come before strings.
+          return -1;
+        }
+      } else {
+        if (bPart is num) {
+          // Strings come after numbers.
+          return 1;
+        } else {
+          // Compare two strings.
+          return (aPart as String).compareTo(bPart as String);
+        }
+      }
+    }
+
+    // The lists are entirely equal.
+    return 0;
+  }
+}

diff --git a/pkgs/pub_semver/lib/src/version_constraint.dart b/pkgs/pub_semver/lib/src/version_constraint.dart
new file mode 100644
index 0000000..948118e
--- /dev/null
+++ b/pkgs/pub_semver/lib/src/version_constraint.dart

@@ -0,0 +1,287 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'patterns.dart';
+import 'utils.dart';
+import 'version.dart';
+import 'version_range.dart';
+import 'version_union.dart';
+
+/// A [VersionConstraint] is a predicate that can determine whether a given
+/// version is valid or not.
+///
+/// For example, a ">= 2.0.0" constraint allows any version that is "2.0.0" or
+/// greater. Version objects themselves implement this to match a specific
+/// version.
+abstract class VersionConstraint {
+  /// A [VersionConstraint] that allows all versions.
+  static VersionConstraint any = VersionRange();
+
+  /// A [VersionConstraint] that allows no versions -- the empty set.
+  static VersionConstraint empty = const _EmptyVersion();
+
+  /// Parses a version constraint.
+  ///
+  /// This string is one of:
+  ///
+  ///   * "any". [any] version.
+  ///   * "^" followed by a version string. Versions compatible with
+  ///     ([VersionConstraint.compatibleWith]) the version.
+  ///   * a series of version parts. Each part can be one of:
+  ///     * A version string like `1.2.3`. In other words, anything that can be
+  ///       parsed by [Version.parse()].
+  ///     * A comparison operator (`<`, `>`, `<=`, or `>=`) followed by a
+  ///       version string.
+  ///
+  /// Whitespace is ignored.
+  ///
+  /// Examples:
+  ///
+  ///     any
+  ///     ^0.7.2
+  ///     ^1.0.0-alpha
+  ///     1.2.3-alpha
+  ///     <=5.1.4
+  ///     >2.0.4 <= 2.4.6
+  factory VersionConstraint.parse(String text) {
+    var originalText = text;
+
+    void skipWhitespace() {
+      text = text.trim();
+    }
+
+    skipWhitespace();
+
+    // Handle the "any" constraint.
+    if (text == 'any') return any;
+
+    // Try to parse and consume a version number.
+    Version? matchVersion() {
+      var version = startVersion.firstMatch(text);
+      if (version == null) return null;
+
+      text = text.substring(version.end);
+      return Version.parse(version[0]!);
+    }
+
+    // Try to parse and consume a comparison operator followed by a version.
+    VersionRange? matchComparison() {
+      var comparison = startComparison.firstMatch(text);
+      if (comparison == null) return null;
+
+      var op = comparison[0]!;
+      text = text.substring(comparison.end);
+      skipWhitespace();
+
+      var version = matchVersion();
+      if (version == null) {
+        throw FormatException('Expected version number after "$op" in '
+            '"$originalText", got "$text".');
+      }
+
+      return switch (op) {
+        '<=' => VersionRange(max: version, includeMax: true),
+        '<' => VersionRange(max: version, alwaysIncludeMaxPreRelease: true),
+        '>=' => VersionRange(min: version, includeMin: true),
+        '>' => VersionRange(min: version),
+        _ => throw UnsupportedError(op),
+      };
+    }
+
+    // Try to parse the "^" operator followed by a version.
+    VersionConstraint? matchCompatibleWith() {
+      if (!text.startsWith(compatibleWithChar)) return null;
+
+      text = text.substring(compatibleWithChar.length);
+      skipWhitespace();
+
+      var version = matchVersion();
+      if (version == null) {
+        throw FormatException('Expected version number after '
+            '"$compatibleWithChar" in "$originalText", got "$text".');
+      }
+
+      if (text.isNotEmpty) {
+        throw FormatException('Cannot include other constraints with '
+            '"$compatibleWithChar" constraint in "$originalText".');
+      }
+
+      return VersionConstraint.compatibleWith(version);
+    }
+
+    var compatibleWith = matchCompatibleWith();
+    if (compatibleWith != null) return compatibleWith;
+
+    Version? min;
+    var includeMin = false;
+    Version? max;
+    var includeMax = false;
+
+    for (;;) {
+      skipWhitespace();
+
+      if (text.isEmpty) break;
+
+      var newRange = matchVersion() ?? matchComparison();
+      if (newRange == null) {
+        throw FormatException('Could not parse version "$originalText". '
+            'Unknown text at "$text".');
+      }
+
+      if (newRange.min != null) {
+        if (min == null || newRange.min! > min) {
+          min = newRange.min;
+          includeMin = newRange.includeMin;
+        } else if (newRange.min == min && !newRange.includeMin) {
+          includeMin = false;
+        }
+      }
+
+      if (newRange.max != null) {
+        if (max == null || newRange.max! < max) {
+          max = newRange.max;
+          includeMax = newRange.includeMax;
+        } else if (newRange.max == max && !newRange.includeMax) {
+          includeMax = false;
+        }
+      }
+    }
+
+    if (min == null && max == null) {
+      throw const FormatException('Cannot parse an empty string.');
+    }
+
+    if (min != null && max != null) {
+      if (min > max) return VersionConstraint.empty;
+      if (min == max) {
+        if (includeMin && includeMax) return min;
+        return VersionConstraint.empty;
+      }
+    }
+
+    return VersionRange(
+        min: min, includeMin: includeMin, max: max, includeMax: includeMax);
+  }
+
+  /// Creates a version constraint which allows all versions that are
+  /// backward compatible with [version].
+  ///
+  /// Versions are considered backward compatible with [version] if they
+  /// are greater than or equal to [version], but less than the next breaking
+  /// version ([Version.nextBreaking]) of [version].
+  factory VersionConstraint.compatibleWith(Version version) =>
+      CompatibleWithVersionRange(version);
+
+  /// Creates a new version constraint that is the intersection of
+  /// [constraints].
+  ///
+  /// It only allows versions that all of those constraints allow. If
+  /// constraints is empty, then it returns a VersionConstraint that allows
+  /// all versions.
+  factory VersionConstraint.intersection(
+      Iterable<VersionConstraint> constraints) {
+    var constraint = VersionRange();
+    for (var other in constraints) {
+      constraint = constraint.intersect(other) as VersionRange;
+    }
+    return constraint;
+  }
+
+  /// Creates a new version constraint that is the union of [constraints].
+  ///
+  /// It allows any versions that any of those constraints allows. If
+  /// [constraints] is empty, this returns a constraint that allows no versions.
+  factory VersionConstraint.unionOf(Iterable<VersionConstraint> constraints) {
+    var flattened = constraints.expand((constraint) {
+      if (constraint.isEmpty) return <VersionRange>[];
+      if (constraint is VersionUnion) return constraint.ranges;
+      if (constraint is VersionRange) return [constraint];
+      throw ArgumentError('Unknown VersionConstraint type $constraint.');
+    }).toList();
+
+    if (flattened.isEmpty) return VersionConstraint.empty;
+
+    if (flattened.any((constraint) => constraint.isAny)) {
+      return VersionConstraint.any;
+    }
+
+    flattened.sort();
+
+    var merged = <VersionRange>[];
+    for (var constraint in flattened) {
+      // Merge this constraint with the previous one, but only if they touch.
+      if (merged.isEmpty ||
+          (!merged.last.allowsAny(constraint) &&
+              !areAdjacent(merged.last, constraint))) {
+        merged.add(constraint);
+      } else {
+        merged[merged.length - 1] =
+            merged.last.union(constraint) as VersionRange;
+      }
+    }
+
+    if (merged.length == 1) return merged.single;
+    return VersionUnion.fromRanges(merged);
+  }
+
+  /// Returns `true` if this constraint allows no versions.
+  bool get isEmpty;
+
+  /// Returns `true` if this constraint allows all versions.
+  bool get isAny;
+
+  /// Returns `true` if this constraint allows [version].
+  bool allows(Version version);
+
+  /// Returns `true` if this constraint allows all the versions that [other]
+  /// allows.
+  bool allowsAll(VersionConstraint other);
+
+  /// Returns `true` if this constraint allows any of the versions that [other]
+  /// allows.
+  bool allowsAny(VersionConstraint other);
+
+  /// Returns a [VersionConstraint] that only allows [Version]s allowed by both
+  /// this and [other].
+  VersionConstraint intersect(VersionConstraint other);
+
+  /// Returns a [VersionConstraint] that allows [Version]s allowed by either
+  /// this or [other].
+  VersionConstraint union(VersionConstraint other);
+
+  /// Returns a [VersionConstraint] that allows [Version]s allowed by this but
+  /// not [other].
+  VersionConstraint difference(VersionConstraint other);
+}
+
+class _EmptyVersion implements VersionConstraint {
+  const _EmptyVersion();
+
+  @override
+  bool get isEmpty => true;
+
+  @override
+  bool get isAny => false;
+
+  @override
+  bool allows(Version other) => false;
+
+  @override
+  bool allowsAll(VersionConstraint other) => other.isEmpty;
+
+  @override
+  bool allowsAny(VersionConstraint other) => false;
+
+  @override
+  VersionConstraint intersect(VersionConstraint other) => this;
+
+  @override
+  VersionConstraint union(VersionConstraint other) => other;
+
+  @override
+  VersionConstraint difference(VersionConstraint other) => this;
+
+  @override
+  String toString() => '<empty>';
+}

diff --git a/pkgs/pub_semver/lib/src/version_range.dart b/pkgs/pub_semver/lib/src/version_range.dart
new file mode 100644
index 0000000..6f2ed54
--- /dev/null
+++ b/pkgs/pub_semver/lib/src/version_range.dart

@@ -0,0 +1,476 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'utils.dart';
+import 'version.dart';
+import 'version_constraint.dart';
+import 'version_union.dart';
+
+/// Constrains versions to a fall within a given range.
+///
+/// If there is a minimum, then this only allows versions that are at that
+/// minimum or greater. If there is a maximum, then only versions less than
+/// that are allowed. In other words, this allows `>= min, < max`.
+///
+/// Version ranges are ordered first by their lower bounds, then by their upper
+/// bounds. For example, `>=1.0.0 <2.0.0` is before `>=1.5.0 <2.0.0` is before
+/// `>=1.5.0 <3.0.0`.
+class VersionRange implements Comparable<VersionRange>, VersionConstraint {
+  /// The minimum end of the range.
+  ///
+  /// If [includeMin] is `true`, this will be the minimum allowed version.
+  /// Otherwise, it will be the highest version below the range that is not
+  /// allowed.
+  ///
+  /// This may be `null` in which case the range has no minimum end and allows
+  /// any version less than the maximum.
+  final Version? min;
+
+  /// The maximum end of the range.
+  ///
+  /// If [includeMax] is `true`, this will be the maximum allowed version.
+  /// Otherwise, it will be the lowest version above the range that is not
+  /// allowed.
+  ///
+  /// This may be `null` in which case the range has no maximum end and allows
+  /// any version greater than the minimum.
+  final Version? max;
+
+  /// If `true` then [min] is allowed by the range.
+  final bool includeMin;
+
+  /// If `true`, then [max] is allowed by the range.
+  final bool includeMax;
+
+  /// Creates a new version range from [min] to [max], either inclusive or
+  /// exclusive.
+  ///
+  /// If it is an error if [min] is greater than [max].
+  ///
+  /// Either [max] or [min] may be omitted to not clamp the range at that end.
+  /// If both are omitted, the range allows all versions.
+  ///
+  /// If [includeMin] is `true`, then the minimum end of the range is inclusive.
+  /// Likewise, passing [includeMax] as `true` makes the upper end inclusive.
+  ///
+  /// If [alwaysIncludeMaxPreRelease] is `true`, this will always include
+  /// pre-release versions of an exclusive [max]. Otherwise, it will use the
+  /// default behavior for pre-release versions of [max].
+  factory VersionRange(
+      {Version? min,
+      Version? max,
+      bool includeMin = false,
+      bool includeMax = false,
+      bool alwaysIncludeMaxPreRelease = false}) {
+    if (min != null && max != null && min > max) {
+      throw ArgumentError(
+          'Minimum version ("$min") must be less than maximum ("$max").');
+    }
+
+    if (!alwaysIncludeMaxPreRelease &&
+        !includeMax &&
+        max != null &&
+        !max.isPreRelease &&
+        max.build.isEmpty &&
+        (min == null ||
+            !min.isPreRelease ||
+            !equalsWithoutPreRelease(min, max))) {
+      max = max.firstPreRelease;
+    }
+
+    return VersionRange._(min, max, includeMin, includeMax);
+  }
+
+  VersionRange._(this.min, this.max, this.includeMin, this.includeMax);
+
+  @override
+  bool operator ==(Object other) {
+    if (other is! VersionRange) return false;
+
+    return min == other.min &&
+        max == other.max &&
+        includeMin == other.includeMin &&
+        includeMax == other.includeMax;
+  }
+
+  @override
+  int get hashCode =>
+      min.hashCode ^
+      (max.hashCode * 3) ^
+      (includeMin.hashCode * 5) ^
+      (includeMax.hashCode * 7);
+
+  @override
+  bool get isEmpty => false;
+
+  @override
+  bool get isAny => min == null && max == null;
+
+  /// Tests if [other] falls within this version range.
+  @override
+  bool allows(Version other) {
+    if (min != null) {
+      if (other < min!) return false;
+      if (!includeMin && other == min) return false;
+    }
+
+    if (max != null) {
+      if (other > max!) return false;
+      if (!includeMax && other == max) return false;
+    }
+
+    return true;
+  }
+
+  @override
+  bool allowsAll(VersionConstraint other) {
+    if (other.isEmpty) return true;
+    if (other is Version) return allows(other);
+
+    if (other is VersionUnion) {
+      return other.ranges.every(allowsAll);
+    }
+
+    if (other is VersionRange) {
+      return !allowsLower(other, this) && !allowsHigher(other, this);
+    }
+
+    throw ArgumentError('Unknown VersionConstraint type $other.');
+  }
+
+  @override
+  bool allowsAny(VersionConstraint other) {
+    if (other.isEmpty) return false;
+    if (other is Version) return allows(other);
+
+    if (other is VersionUnion) {
+      return other.ranges.any(allowsAny);
+    }
+
+    if (other is VersionRange) {
+      return !strictlyLower(other, this) && !strictlyHigher(other, this);
+    }
+
+    throw ArgumentError('Unknown VersionConstraint type $other.');
+  }
+
+  @override
+  VersionConstraint intersect(VersionConstraint other) {
+    if (other.isEmpty) return other;
+    if (other is VersionUnion) return other.intersect(this);
+
+    // A range and a Version just yields the version if it's in the range.
+    if (other is Version) {
+      return allows(other) ? other : VersionConstraint.empty;
+    }
+
+    if (other is VersionRange) {
+      // Intersect the two ranges.
+      Version? intersectMin;
+      bool intersectIncludeMin;
+      if (allowsLower(this, other)) {
+        if (strictlyLower(this, other)) return VersionConstraint.empty;
+        intersectMin = other.min;
+        intersectIncludeMin = other.includeMin;
+      } else {
+        if (strictlyLower(other, this)) return VersionConstraint.empty;
+        intersectMin = min;
+        intersectIncludeMin = includeMin;
+      }
+
+      Version? intersectMax;
+      bool intersectIncludeMax;
+      if (allowsHigher(this, other)) {
+        intersectMax = other.max;
+        intersectIncludeMax = other.includeMax;
+      } else {
+        intersectMax = max;
+        intersectIncludeMax = includeMax;
+      }
+
+      if (intersectMin == null && intersectMax == null) {
+        // Open range.
+        return VersionRange();
+      }
+
+      // If the range is just a single version.
+      if (intersectMin == intersectMax) {
+        // Because we already verified that the lower range isn't strictly
+        // lower, there must be some overlap.
+        assert(intersectIncludeMin && intersectIncludeMax);
+        return intersectMin!;
+      }
+
+      // If we got here, there is an actual range.
+      return VersionRange(
+          min: intersectMin,
+          max: intersectMax,
+          includeMin: intersectIncludeMin,
+          includeMax: intersectIncludeMax,
+          alwaysIncludeMaxPreRelease: true);
+    }
+
+    throw ArgumentError('Unknown VersionConstraint type $other.');
+  }
+
+  @override
+  VersionConstraint union(VersionConstraint other) {
+    if (other is Version) {
+      if (allows(other)) return this;
+
+      if (other == min) {
+        return VersionRange(
+            min: min,
+            max: max,
+            includeMin: true,
+            includeMax: includeMax,
+            alwaysIncludeMaxPreRelease: true);
+      }
+
+      if (other == max) {
+        return VersionRange(
+            min: min,
+            max: max,
+            includeMin: includeMin,
+            includeMax: true,
+            alwaysIncludeMaxPreRelease: true);
+      }
+
+      return VersionConstraint.unionOf([this, other]);
+    }
+
+    if (other is VersionRange) {
+      // If the two ranges don't overlap, we won't be able to create a single
+      // VersionRange for both of them.
+      var edgesTouch = (max != null &&
+              max == other.min &&
+              (includeMax || other.includeMin)) ||
+          (min != null && min == other.max && (includeMin || other.includeMax));
+      if (!edgesTouch && !allowsAny(other)) {
+        return VersionConstraint.unionOf([this, other]);
+      }
+
+      Version? unionMin;
+      bool unionIncludeMin;
+      if (allowsLower(this, other)) {
+        unionMin = min;
+        unionIncludeMin = includeMin;
+      } else {
+        unionMin = other.min;
+        unionIncludeMin = other.includeMin;
+      }
+
+      Version? unionMax;
+      bool unionIncludeMax;
+      if (allowsHigher(this, other)) {
+        unionMax = max;
+        unionIncludeMax = includeMax;
+      } else {
+        unionMax = other.max;
+        unionIncludeMax = other.includeMax;
+      }
+
+      return VersionRange(
+          min: unionMin,
+          max: unionMax,
+          includeMin: unionIncludeMin,
+          includeMax: unionIncludeMax,
+          alwaysIncludeMaxPreRelease: true);
+    }
+
+    return VersionConstraint.unionOf([this, other]);
+  }
+
+  @override
+  VersionConstraint difference(VersionConstraint other) {
+    if (other.isEmpty) return this;
+
+    if (other is Version) {
+      if (!allows(other)) return this;
+
+      if (other == min) {
+        if (!includeMin) return this;
+        return VersionRange(
+            min: min,
+            max: max,
+            includeMax: includeMax,
+            alwaysIncludeMaxPreRelease: true);
+      }
+
+      if (other == max) {
+        if (!includeMax) return this;
+        return VersionRange(
+            min: min,
+            max: max,
+            includeMin: includeMin,
+            alwaysIncludeMaxPreRelease: true);
+      }
+
+      return VersionUnion.fromRanges([
+        VersionRange(
+            min: min,
+            max: other,
+            includeMin: includeMin,
+            alwaysIncludeMaxPreRelease: true),
+        VersionRange(
+            min: other,
+            max: max,
+            includeMax: includeMax,
+            alwaysIncludeMaxPreRelease: true)
+      ]);
+    } else if (other is VersionRange) {
+      if (!allowsAny(other)) return this;
+
+      VersionRange? before;
+      if (!allowsLower(this, other)) {
+        before = null;
+      } else if (min == other.min) {
+        assert(includeMin && !other.includeMin);
+        assert(min != null);
+        before = min;
+      } else {
+        before = VersionRange(
+            min: min,
+            max: other.min,
+            includeMin: includeMin,
+            includeMax: !other.includeMin,
+            alwaysIncludeMaxPreRelease: true);
+      }
+
+      VersionRange? after;
+      if (!allowsHigher(this, other)) {
+        after = null;
+      } else if (max == other.max) {
+        assert(includeMax && !other.includeMax);
+        assert(max != null);
+        after = max;
+      } else {
+        after = VersionRange(
+            min: other.max,
+            max: max,
+            includeMin: !other.includeMax,
+            includeMax: includeMax,
+            alwaysIncludeMaxPreRelease: true);
+      }
+
+      if (before == null && after == null) return VersionConstraint.empty;
+      if (before == null) return after!;
+      if (after == null) return before;
+      return VersionUnion.fromRanges([before, after]);
+    } else if (other is VersionUnion) {
+      var ranges = <VersionRange>[];
+      var current = this;
+
+      for (var range in other.ranges) {
+        // Skip any ranges that are strictly lower than [current].
+        if (strictlyLower(range, current)) continue;
+
+        // If we reach a range strictly higher than [current], no more ranges
+        // will be relevant so we can bail early.
+        if (strictlyHigher(range, current)) break;
+
+        var difference = current.difference(range);
+        if (difference.isEmpty) {
+          return VersionConstraint.empty;
+        } else if (difference is VersionUnion) {
+          // If [range] split [current] in half, we only need to continue
+          // checking future ranges against the latter half.
+          assert(difference.ranges.length == 2);
+          ranges.add(difference.ranges.first);
+          current = difference.ranges.last;
+        } else {
+          current = difference as VersionRange;
+        }
+      }
+
+      if (ranges.isEmpty) return current;
+      return VersionUnion.fromRanges(ranges..add(current));
+    }
+
+    throw ArgumentError('Unknown VersionConstraint type $other.');
+  }
+
+  @override
+  int compareTo(VersionRange other) {
+    if (min == null) {
+      if (other.min == null) return _compareMax(other);
+      return -1;
+    } else if (other.min == null) {
+      return 1;
+    }
+
+    var result = min!.compareTo(other.min!);
+    if (result != 0) return result;
+    if (includeMin != other.includeMin) return includeMin ? -1 : 1;
+
+    return _compareMax(other);
+  }
+
+  /// Compares the maximum values of `this` and [other].
+  int _compareMax(VersionRange other) {
+    if (max == null) {
+      if (other.max == null) return 0;
+      return 1;
+    } else if (other.max == null) {
+      return -1;
+    }
+
+    var result = max!.compareTo(other.max!);
+    if (result != 0) return result;
+    if (includeMax != other.includeMax) return includeMax ? 1 : -1;
+    return 0;
+  }
+
+  @override
+  String toString() {
+    var buffer = StringBuffer();
+
+    final min = this.min;
+    if (min != null) {
+      buffer
+        ..write(includeMin ? '>=' : '>')
+        ..write(min);
+    }
+
+    final max = this.max;
+
+    if (max != null) {
+      if (min != null) buffer.write(' ');
+      if (includeMax) {
+        buffer
+          ..write('<=')
+          ..write(max);
+      } else {
+        buffer.write('<');
+        if (max.isFirstPreRelease) {
+          // Since `"<$max"` would parse the same as `"<$max-0"`, we just emit
+          // `<$max` to avoid confusing "-0" suffixes.
+          buffer.write('${max.major}.${max.minor}.${max.patch}');
+        } else {
+          buffer.write(max);
+
+          // If `">=$min <$max"` would parse as `">=$min <$max-0"`, add `-*` to
+          // indicate that actually does allow pre-release versions.
+          var minIsPreReleaseOfMax = min != null &&
+              min.isPreRelease &&
+              equalsWithoutPreRelease(min, max);
+          if (!max.isPreRelease && max.build.isEmpty && !minIsPreReleaseOfMax) {
+            buffer.write('-∞');
+          }
+        }
+      }
+    }
+
+    if (min == null && max == null) buffer.write('any');
+    return buffer.toString();
+  }
+}
+
+class CompatibleWithVersionRange extends VersionRange {
+  CompatibleWithVersionRange(Version version)
+      : super._(version, version.nextBreaking.firstPreRelease, true, false);
+
+  @override
+  String toString() => '^$min';
+}

diff --git a/pkgs/pub_semver/lib/src/version_union.dart b/pkgs/pub_semver/lib/src/version_union.dart
new file mode 100644
index 0000000..844d3b8
--- /dev/null
+++ b/pkgs/pub_semver/lib/src/version_union.dart

@@ -0,0 +1,224 @@
+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:collection/collection.dart';
+
+import 'utils.dart';
+import 'version.dart';
+import 'version_constraint.dart';
+import 'version_range.dart';
+
+/// A version constraint representing a union of multiple disjoint version
+/// ranges.
+///
+/// An instance of this will only be created if the version can't be represented
+/// as a non-compound value.
+class VersionUnion implements VersionConstraint {
+  /// The constraints that compose this union.
+  ///
+  /// This list has two invariants:
+  ///
+  /// * Its contents are sorted using the standard ordering of [VersionRange]s.
+  /// * Its contents are disjoint and non-adjacent. In other words, for any two
+  ///   constraints next to each other in the list, there's some version between
+  ///   those constraints that they don't match.
+  final List<VersionRange> ranges;
+
+  @override
+  bool get isEmpty => false;
+
+  @override
+  bool get isAny => false;
+
+  /// Creates a union from a list of ranges with no pre-processing.
+  ///
+  /// It's up to the caller to ensure that the invariants described in [ranges]
+  /// are maintained. They are not verified by this constructor. To
+  /// automatically ensure that they're maintained, use
+  /// [VersionConstraint.unionOf] instead.
+  VersionUnion.fromRanges(this.ranges);
+
+  @override
+  bool allows(Version version) =>
+      ranges.any((constraint) => constraint.allows(version));
+
+  @override
+  bool allowsAll(VersionConstraint other) {
+    var ourRanges = ranges.iterator;
+    var theirRanges = _rangesFor(other).iterator;
+
+    // Because both lists of ranges are ordered by minimum version, we can
+    // safely move through them linearly here.
+    var ourRangesMoved = ourRanges.moveNext();
+    var theirRangesMoved = theirRanges.moveNext();
+    while (ourRangesMoved && theirRangesMoved) {
+      if (ourRanges.current.allowsAll(theirRanges.current)) {
+        theirRangesMoved = theirRanges.moveNext();
+      } else {
+        ourRangesMoved = ourRanges.moveNext();
+      }
+    }
+
+    // If our ranges have allowed all of their ranges, we'll have consumed all
+    // of them.
+    return !theirRangesMoved;
+  }
+
+  @override
+  bool allowsAny(VersionConstraint other) {
+    var ourRanges = ranges.iterator;
+    var theirRanges = _rangesFor(other).iterator;
+
+    // Because both lists of ranges are ordered by minimum version, we can
+    // safely move through them linearly here.
+    var ourRangesMoved = ourRanges.moveNext();
+    var theirRangesMoved = theirRanges.moveNext();
+    while (ourRangesMoved && theirRangesMoved) {
+      if (ourRanges.current.allowsAny(theirRanges.current)) {
+        return true;
+      }
+
+      // Move the constraint with the lower max value forward. This ensures that
+      // we keep both lists in sync as much as possible.
+      if (allowsHigher(theirRanges.current, ourRanges.current)) {
+        ourRangesMoved = ourRanges.moveNext();
+      } else {
+        theirRangesMoved = theirRanges.moveNext();
+      }
+    }
+
+    return false;
+  }
+
+  @override
+  VersionConstraint intersect(VersionConstraint other) {
+    var ourRanges = ranges.iterator;
+    var theirRanges = _rangesFor(other).iterator;
+
+    // Because both lists of ranges are ordered by minimum version, we can
+    // safely move through them linearly here.
+    var newRanges = <VersionRange>[];
+    var ourRangesMoved = ourRanges.moveNext();
+    var theirRangesMoved = theirRanges.moveNext();
+    while (ourRangesMoved && theirRangesMoved) {
+      var intersection = ourRanges.current.intersect(theirRanges.current);
+
+      if (!intersection.isEmpty) newRanges.add(intersection as VersionRange);
+
+      // Move the constraint with the lower max value forward. This ensures that
+      // we keep both lists in sync as much as possible, and that large ranges
+      // have a chance to match multiple small ranges that they contain.
+      if (allowsHigher(theirRanges.current, ourRanges.current)) {
+        ourRangesMoved = ourRanges.moveNext();
+      } else {
+        theirRangesMoved = theirRanges.moveNext();
+      }
+    }
+
+    if (newRanges.isEmpty) return VersionConstraint.empty;
+    if (newRanges.length == 1) return newRanges.single;
+
+    return VersionUnion.fromRanges(newRanges);
+  }
+
+  @override
+  VersionConstraint difference(VersionConstraint other) {
+    var ourRanges = ranges.iterator;
+    var theirRanges = _rangesFor(other).iterator;
+
+    var newRanges = <VersionRange>[];
+    ourRanges.moveNext();
+    theirRanges.moveNext();
+    var current = ourRanges.current;
+
+    bool theirNextRange() {
+      if (theirRanges.moveNext()) return true;
+
+      // If there are no more of their ranges, none of the rest of our ranges
+      // need to be subtracted so we can add them as-is.
+      newRanges.add(current);
+      while (ourRanges.moveNext()) {
+        newRanges.add(ourRanges.current);
+      }
+      return false;
+    }
+
+    bool ourNextRange({bool includeCurrent = true}) {
+      if (includeCurrent) newRanges.add(current);
+      if (!ourRanges.moveNext()) return false;
+      current = ourRanges.current;
+      return true;
+    }
+
+    for (;;) {
+      // If the current ranges are disjoint, move the lowest one forward.
+      if (strictlyLower(theirRanges.current, current)) {
+        if (!theirNextRange()) break;
+        continue;
+      }
+
+      if (strictlyHigher(theirRanges.current, current)) {
+        if (!ourNextRange()) break;
+        continue;
+      }
+
+      // If we're here, we know [theirRanges.current] overlaps [current].
+      var difference = current.difference(theirRanges.current);
+      if (difference is VersionUnion) {
+        // If their range split [current] in half, we only need to continue
+        // checking future ranges against the latter half.
+        assert(difference.ranges.length == 2);
+        newRanges.add(difference.ranges.first);
+        current = difference.ranges.last;
+
+        // Since their range split [current], it definitely doesn't allow higher
+        // versions, so we should move their ranges forward.
+        if (!theirNextRange()) break;
+      } else if (difference.isEmpty) {
+        if (!ourNextRange(includeCurrent: false)) break;
+      } else {
+        current = difference as VersionRange;
+
+        // Move the constraint with the lower max value forward. This ensures
+        // that we keep both lists in sync as much as possible, and that large
+        // ranges have a chance to subtract or be subtracted by multiple small
+        // ranges that they contain.
+        if (allowsHigher(current, theirRanges.current)) {
+          if (!theirNextRange()) break;
+        } else {
+          if (!ourNextRange()) break;
+        }
+      }
+    }
+
+    if (newRanges.isEmpty) return VersionConstraint.empty;
+    if (newRanges.length == 1) return newRanges.single;
+    return VersionUnion.fromRanges(newRanges);
+  }
+
+  /// Returns [constraint] as a list of ranges.
+  ///
+  /// This is used to normalize ranges of various types.
+  List<VersionRange> _rangesFor(VersionConstraint constraint) {
+    if (constraint.isEmpty) return [];
+    if (constraint is VersionUnion) return constraint.ranges;
+    if (constraint is VersionRange) return [constraint];
+    throw ArgumentError('Unknown VersionConstraint type $constraint.');
+  }
+
+  @override
+  VersionConstraint union(VersionConstraint other) =>
+      VersionConstraint.unionOf([this, other]);
+
+  @override
+  bool operator ==(Object other) =>
+      other is VersionUnion &&
+      const ListEquality<VersionRange>().equals(ranges, other.ranges);
+
+  @override
+  int get hashCode => const ListEquality<VersionRange>().hash(ranges);
+
+  @override
+  String toString() => ranges.join(' or ');
+}

diff --git a/pkgs/pub_semver/pubspec.yaml b/pkgs/pub_semver/pubspec.yaml
new file mode 100644
index 0000000..290fb92
--- /dev/null
+++ b/pkgs/pub_semver/pubspec.yaml

@@ -0,0 +1,20 @@
+name: pub_semver
+version: 2.1.5
+description: >-
+ Versions and version constraints implementing pub's versioning policy. This
+ is very similar to vanilla semver, with a few corner cases.
+repository: https://github.com/dart-lang/tools/tree/main/pkgs/pub_semver
+topics:
+ - dart-pub
+ - semver
+
+environment:
+  sdk: ^3.4.0
+
+dependencies:
+  collection: ^1.15.0
+  meta: ^1.3.0
+
+dev_dependencies:
+  dart_flutter_team_lints: ^3.0.0
+  test: ^1.16.0

diff --git a/pkgs/pub_semver/test/utils.dart b/pkgs/pub_semver/test/utils.dart
new file mode 100644
index 0000000..bd7aa8f
--- /dev/null
+++ b/pkgs/pub_semver/test/utils.dart

@@ -0,0 +1,123 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:pub_semver/pub_semver.dart';
+import 'package:test/test.dart';
+
+/// Some stock example versions to use in tests.
+final v003 = Version.parse('0.0.3');
+final v010 = Version.parse('0.1.0');
+final v072 = Version.parse('0.7.2');
+final v080 = Version.parse('0.8.0');
+final v114 = Version.parse('1.1.4');
+final v123 = Version.parse('1.2.3');
+final v124 = Version.parse('1.2.4');
+final v130 = Version.parse('1.3.0');
+final v140 = Version.parse('1.4.0');
+final v200 = Version.parse('2.0.0');
+final v201 = Version.parse('2.0.1');
+final v234 = Version.parse('2.3.4');
+final v250 = Version.parse('2.5.0');
+final v300 = Version.parse('3.0.0');
+
+/// A range that allows pre-release versions of its max version.
+final includeMaxPreReleaseRange =
+    VersionRange(max: v200, alwaysIncludeMaxPreRelease: true);
+
+/// A [Matcher] that tests if a [VersionConstraint] allows or does not allow a
+/// given list of [Version]s.
+class _VersionConstraintMatcher implements Matcher {
+  final List<Version> _expected;
+  final bool _allow;
+
+  _VersionConstraintMatcher(this._expected, this._allow);
+
+  @override
+  bool matches(dynamic item, Map<dynamic, dynamic> matchState) =>
+      (item is VersionConstraint) &&
+      _expected.every((version) => item.allows(version) == _allow);
+
+  @override
+  Description describe(Description description) {
+    description.addAll(' ${_allow ? "allows" : "does not allow"} versions ',
+        ', ', '', _expected);
+    return description;
+  }
+
+  @override
+  Description describeMismatch(dynamic item, Description mismatchDescription,
+      Map<dynamic, dynamic> matchState, bool verbose) {
+    if (item is! VersionConstraint) {
+      mismatchDescription.add('was not a VersionConstraint');
+      return mismatchDescription;
+    }
+
+    var first = true;
+    for (var version in _expected) {
+      if (item.allows(version) != _allow) {
+        if (first) {
+          if (_allow) {
+            mismatchDescription.addDescriptionOf(item).add(' did not allow ');
+          } else {
+            mismatchDescription.addDescriptionOf(item).add(' allowed ');
+          }
+        } else {
+          mismatchDescription.add(' and ');
+        }
+        first = false;
+
+        mismatchDescription.add(version.toString());
+      }
+    }
+
+    return mismatchDescription;
+  }
+}
+
+/// Gets a [Matcher] that validates that a [VersionConstraint] allows all
+/// given versions.
+Matcher allows(Version v1,
+    [Version? v2,
+    Version? v3,
+    Version? v4,
+    Version? v5,
+    Version? v6,
+    Version? v7,
+    Version? v8]) {
+  var versions = _makeVersionList(v1, v2, v3, v4, v5, v6, v7, v8);
+  return _VersionConstraintMatcher(versions, true);
+}
+
+/// Gets a [Matcher] that validates that a [VersionConstraint] allows none of
+/// the given versions.
+Matcher doesNotAllow(Version v1,
+    [Version? v2,
+    Version? v3,
+    Version? v4,
+    Version? v5,
+    Version? v6,
+    Version? v7,
+    Version? v8]) {
+  var versions = _makeVersionList(v1, v2, v3, v4, v5, v6, v7, v8);
+  return _VersionConstraintMatcher(versions, false);
+}
+
+List<Version> _makeVersionList(Version v1,
+    [Version? v2,
+    Version? v3,
+    Version? v4,
+    Version? v5,
+    Version? v6,
+    Version? v7,
+    Version? v8]) {
+  var versions = [v1];
+  if (v2 != null) versions.add(v2);
+  if (v3 != null) versions.add(v3);
+  if (v4 != null) versions.add(v4);
+  if (v5 != null) versions.add(v5);
+  if (v6 != null) versions.add(v6);
+  if (v7 != null) versions.add(v7);
+  if (v8 != null) versions.add(v8);
+  return versions;
+}

diff --git a/pkgs/pub_semver/test/version_constraint_test.dart b/pkgs/pub_semver/test/version_constraint_test.dart
new file mode 100644
index 0000000..4fbcbe0
--- /dev/null
+++ b/pkgs/pub_semver/test/version_constraint_test.dart

@@ -0,0 +1,185 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:pub_semver/pub_semver.dart';
+import 'package:test/test.dart';
+
+import 'utils.dart';
+
+void main() {
+  test('any', () {
+    expect(VersionConstraint.any.isAny, isTrue);
+    expect(
+        VersionConstraint.any,
+        allows(Version.parse('0.0.0-blah'), Version.parse('1.2.3'),
+            Version.parse('12345.678.90')));
+  });
+
+  test('empty', () {
+    expect(VersionConstraint.empty.isEmpty, isTrue);
+    expect(VersionConstraint.empty.isAny, isFalse);
+    expect(
+        VersionConstraint.empty,
+        doesNotAllow(Version.parse('0.0.0-blah'), Version.parse('1.2.3'),
+            Version.parse('12345.678.90')));
+  });
+
+  group('parse()', () {
+    test('parses an exact version', () {
+      var constraint = VersionConstraint.parse('1.2.3-alpha');
+
+      expect(constraint is Version, isTrue);
+      expect(constraint, equals(Version(1, 2, 3, pre: 'alpha')));
+    });
+
+    test('parses "any"', () {
+      var constraint = VersionConstraint.parse('any');
+
+      expect(
+          constraint,
+          allows(Version.parse('0.0.0'), Version.parse('1.2.3'),
+              Version.parse('12345.678.90')));
+    });
+
+    test('parses a ">" minimum version', () {
+      var constraint = VersionConstraint.parse('>1.2.3');
+
+      expect(constraint,
+          allows(Version.parse('1.2.3+foo'), Version.parse('1.2.4')));
+      expect(
+          constraint,
+          doesNotAllow(Version.parse('1.2.1'), Version.parse('1.2.3-build'),
+              Version.parse('1.2.3')));
+    });
+
+    test('parses a ">=" minimum version', () {
+      var constraint = VersionConstraint.parse('>=1.2.3');
+
+      expect(
+          constraint,
+          allows(Version.parse('1.2.3'), Version.parse('1.2.3+foo'),
+              Version.parse('1.2.4')));
+      expect(constraint,
+          doesNotAllow(Version.parse('1.2.1'), Version.parse('1.2.3-build')));
+    });
+
+    test('parses a "<" maximum version', () {
+      var constraint = VersionConstraint.parse('<1.2.3');
+
+      expect(constraint,
+          allows(Version.parse('1.2.1'), Version.parse('1.2.2+foo')));
+      expect(
+          constraint,
+          doesNotAllow(Version.parse('1.2.3'), Version.parse('1.2.3+foo'),
+              Version.parse('1.2.4')));
+    });
+
+    test('parses a "<=" maximum version', () {
+      var constraint = VersionConstraint.parse('<=1.2.3');
+
+      expect(
+          constraint,
+          allows(Version.parse('1.2.1'), Version.parse('1.2.3-build'),
+              Version.parse('1.2.3')));
+      expect(constraint,
+          doesNotAllow(Version.parse('1.2.3+foo'), Version.parse('1.2.4')));
+    });
+
+    test('parses a series of space-separated constraints', () {
+      var constraint = VersionConstraint.parse('>1.0.0 >=1.2.3 <1.3.0');
+
+      expect(
+          constraint, allows(Version.parse('1.2.3'), Version.parse('1.2.5')));
+      expect(
+          constraint,
+          doesNotAllow(Version.parse('1.2.3-pre'), Version.parse('1.3.0'),
+              Version.parse('3.4.5')));
+    });
+
+    test('parses a pre-release-only constraint', () {
+      var constraint = VersionConstraint.parse('>=1.0.0-dev.2 <1.0.0');
+      expect(constraint,
+          allows(Version.parse('1.0.0-dev.2'), Version.parse('1.0.0-dev.3')));
+      expect(constraint,
+          doesNotAllow(Version.parse('1.0.0-dev.1'), Version.parse('1.0.0')));
+    });
+
+    test('ignores whitespace around comparison operators', () {
+      var constraint = VersionConstraint.parse(' >1.0.0>=1.2.3 < 1.3.0');
+
+      expect(
+          constraint, allows(Version.parse('1.2.3'), Version.parse('1.2.5')));
+      expect(
+          constraint,
+          doesNotAllow(Version.parse('1.2.3-pre'), Version.parse('1.3.0'),
+              Version.parse('3.4.5')));
+    });
+
+    test('does not allow "any" to be mixed with other constraints', () {
+      expect(() => VersionConstraint.parse('any 1.0.0'), throwsFormatException);
+    });
+
+    test('parses a "^" version', () {
+      expect(VersionConstraint.parse('^0.0.3'),
+          equals(VersionConstraint.compatibleWith(v003)));
+
+      expect(VersionConstraint.parse('^0.7.2'),
+          equals(VersionConstraint.compatibleWith(v072)));
+
+      expect(VersionConstraint.parse('^1.2.3'),
+          equals(VersionConstraint.compatibleWith(v123)));
+
+      var min = Version.parse('0.7.2-pre+1');
+      expect(VersionConstraint.parse('^0.7.2-pre+1'),
+          equals(VersionConstraint.compatibleWith(min)));
+    });
+
+    test('does not allow "^" to be mixed with other constraints', () {
+      expect(() => VersionConstraint.parse('>=1.2.3 ^1.0.0'),
+          throwsFormatException);
+      expect(() => VersionConstraint.parse('^1.0.0 <1.2.3'),
+          throwsFormatException);
+    });
+
+    test('ignores whitespace around "^"', () {
+      var constraint = VersionConstraint.parse(' ^ 1.2.3 ');
+
+      expect(constraint, equals(VersionConstraint.compatibleWith(v123)));
+    });
+
+    test('throws FormatException on a bad string', () {
+      var bad = [
+        '', '   ', // Empty string.
+        'foo', // Bad text.
+        '>foo', // Bad text after operator.
+        '^foo', // Bad text after "^".
+        '1.0.0 foo', '1.0.0foo', // Bad text after version.
+        'anything', // Bad text after "any".
+        '<>1.0.0', // Multiple operators.
+        '1.0.0<' // Trailing operator.
+      ];
+
+      for (var text in bad) {
+        expect(() => VersionConstraint.parse(text), throwsFormatException);
+      }
+    });
+  });
+
+  group('compatibleWith()', () {
+    test('returns the range of compatible versions', () {
+      var constraint = VersionConstraint.compatibleWith(v072);
+
+      expect(
+          constraint,
+          equals(VersionRange(
+              min: v072, includeMin: true, max: v072.nextBreaking)));
+    });
+
+    test('toString() uses "^"', () {
+      var constraint = VersionConstraint.compatibleWith(v072);
+
+      expect(constraint.toString(), equals('^0.7.2'));
+    });
+  });
+}

diff --git a/pkgs/pub_semver/test/version_range_test.dart b/pkgs/pub_semver/test/version_range_test.dart
new file mode 100644
index 0000000..5978df0
--- /dev/null
+++ b/pkgs/pub_semver/test/version_range_test.dart

@@ -0,0 +1,998 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:pub_semver/pub_semver.dart';
+import 'package:test/test.dart';
+
+import 'utils.dart';
+
+void main() {
+  group('constructor', () {
+    test('takes a min and max', () {
+      var range = VersionRange(min: v123, max: v124);
+      expect(range.isAny, isFalse);
+      expect(range.min, equals(v123));
+      expect(range.max, equals(v124.firstPreRelease));
+    });
+
+    group("doesn't make the max a pre-release if", () {
+      test("it's already a pre-release", () {
+        expect(VersionRange(max: Version.parse('1.2.4-pre')).max,
+            equals(Version.parse('1.2.4-pre')));
+      });
+
+      test('includeMax is true', () {
+        expect(VersionRange(max: v124, includeMax: true).max, equals(v124));
+      });
+
+      test('min is a prerelease of max', () {
+        expect(VersionRange(min: Version.parse('1.2.4-pre'), max: v124).max,
+            equals(v124));
+      });
+
+      test('max has a build identifier', () {
+        expect(VersionRange(max: Version.parse('1.2.4+1')).max,
+            equals(Version.parse('1.2.4+1')));
+      });
+    });
+
+    test('allows omitting max', () {
+      var range = VersionRange(min: v123);
+      expect(range.isAny, isFalse);
+      expect(range.min, equals(v123));
+      expect(range.max, isNull);
+    });
+
+    test('allows omitting min and max', () {
+      var range = VersionRange();
+      expect(range.isAny, isTrue);
+      expect(range.min, isNull);
+      expect(range.max, isNull);
+    });
+
+    test('takes includeMin', () {
+      var range = VersionRange(min: v123, includeMin: true);
+      expect(range.includeMin, isTrue);
+    });
+
+    test('includeMin defaults to false if omitted', () {
+      var range = VersionRange(min: v123);
+      expect(range.includeMin, isFalse);
+    });
+
+    test('takes includeMax', () {
+      var range = VersionRange(max: v123, includeMax: true);
+      expect(range.includeMax, isTrue);
+    });
+
+    test('includeMax defaults to false if omitted', () {
+      var range = VersionRange(max: v123);
+      expect(range.includeMax, isFalse);
+    });
+
+    test('throws if min > max', () {
+      expect(() => VersionRange(min: v124, max: v123), throwsArgumentError);
+    });
+  });
+
+  group('allows()', () {
+    test('version must be greater than min', () {
+      var range = VersionRange(min: v123);
+
+      expect(range, allows(Version.parse('1.3.3'), Version.parse('2.3.3')));
+      expect(
+          range, doesNotAllow(Version.parse('1.2.2'), Version.parse('1.2.3')));
+    });
+
+    test('version must be min or greater if includeMin', () {
+      var range = VersionRange(min: v123, includeMin: true);
+
+      expect(
+          range,
+          allows(Version.parse('1.2.3'), Version.parse('1.3.3'),
+              Version.parse('2.3.3')));
+      expect(range, doesNotAllow(Version.parse('1.2.2')));
+    });
+
+    test('pre-release versions of inclusive min are excluded', () {
+      var range = VersionRange(min: v123, includeMin: true);
+
+      expect(range, allows(Version.parse('1.2.4-dev')));
+      expect(range, doesNotAllow(Version.parse('1.2.3-dev')));
+    });
+
+    test('version must be less than max', () {
+      var range = VersionRange(max: v234);
+
+      expect(range, allows(Version.parse('2.3.3')));
+      expect(
+          range, doesNotAllow(Version.parse('2.3.4'), Version.parse('2.4.3')));
+    });
+
+    test('pre-release versions of non-pre-release max are excluded', () {
+      var range = VersionRange(max: v234);
+
+      expect(range, allows(Version.parse('2.3.3')));
+      expect(range,
+          doesNotAllow(Version.parse('2.3.4-dev'), Version.parse('2.3.4')));
+    });
+
+    test(
+        'pre-release versions of non-pre-release max are included if min is a '
+        'pre-release of the same version', () {
+      var range = VersionRange(min: Version.parse('2.3.4-dev.0'), max: v234);
+
+      expect(range, allows(Version.parse('2.3.4-dev.1')));
+      expect(
+          range,
+          doesNotAllow(Version.parse('2.3.3'), Version.parse('2.3.4-dev'),
+              Version.parse('2.3.4')));
+    });
+
+    test('pre-release versions of pre-release max are included', () {
+      var range = VersionRange(max: Version.parse('2.3.4-dev.2'));
+
+      expect(range, allows(Version.parse('2.3.4-dev.1')));
+      expect(
+          range,
+          doesNotAllow(
+              Version.parse('2.3.4-dev.2'), Version.parse('2.3.4-dev.3')));
+    });
+
+    test('version must be max or less if includeMax', () {
+      var range = VersionRange(min: v123, max: v234, includeMax: true);
+
+      expect(
+          range,
+          allows(
+              Version.parse('2.3.3'),
+              Version.parse('2.3.4'),
+              // Pre-releases of the max are allowed.
+              Version.parse('2.3.4-dev')));
+      expect(range, doesNotAllow(Version.parse('2.4.3')));
+    });
+
+    test('has no min if one was not set', () {
+      var range = VersionRange(max: v123);
+
+      expect(range, allows(Version.parse('0.0.0')));
+      expect(range, doesNotAllow(Version.parse('1.2.3')));
+    });
+
+    test('has no max if one was not set', () {
+      var range = VersionRange(min: v123);
+
+      expect(range, allows(Version.parse('1.3.3'), Version.parse('999.3.3')));
+      expect(range, doesNotAllow(Version.parse('1.2.3')));
+    });
+
+    test('allows any version if there is no min or max', () {
+      var range = VersionRange();
+
+      expect(range, allows(Version.parse('0.0.0'), Version.parse('999.99.9')));
+    });
+
+    test('allows pre-releases of the max with includeMaxPreRelease', () {
+      expect(includeMaxPreReleaseRange, allows(Version.parse('2.0.0-dev')));
+    });
+  });
+
+  group('allowsAll()', () {
+    test('allows an empty constraint', () {
+      expect(
+          VersionRange(min: v123, max: v250).allowsAll(VersionConstraint.empty),
+          isTrue);
+    });
+
+    test('allows allowed versions', () {
+      var range = VersionRange(min: v123, max: v250, includeMax: true);
+      expect(range.allowsAll(v123), isFalse);
+      expect(range.allowsAll(v124), isTrue);
+      expect(range.allowsAll(v250), isTrue);
+      expect(range.allowsAll(v300), isFalse);
+    });
+
+    test('with no min', () {
+      var range = VersionRange(max: v250);
+      expect(range.allowsAll(VersionRange(min: v080, max: v140)), isTrue);
+      expect(range.allowsAll(VersionRange(min: v080, max: v300)), isFalse);
+      expect(range.allowsAll(VersionRange(max: v140)), isTrue);
+      expect(range.allowsAll(VersionRange(max: v300)), isFalse);
+      expect(range.allowsAll(range), isTrue);
+      expect(range.allowsAll(VersionConstraint.any), isFalse);
+    });
+
+    test('with no max', () {
+      var range = VersionRange(min: v010);
+      expect(range.allowsAll(VersionRange(min: v080, max: v140)), isTrue);
+      expect(range.allowsAll(VersionRange(min: v003, max: v140)), isFalse);
+      expect(range.allowsAll(VersionRange(min: v080)), isTrue);
+      expect(range.allowsAll(VersionRange(min: v003)), isFalse);
+      expect(range.allowsAll(range), isTrue);
+      expect(range.allowsAll(VersionConstraint.any), isFalse);
+    });
+
+    test('with a min and max', () {
+      var range = VersionRange(min: v010, max: v250);
+      expect(range.allowsAll(VersionRange(min: v080, max: v140)), isTrue);
+      expect(range.allowsAll(VersionRange(min: v080, max: v300)), isFalse);
+      expect(range.allowsAll(VersionRange(min: v003, max: v140)), isFalse);
+      expect(range.allowsAll(VersionRange(min: v080)), isFalse);
+      expect(range.allowsAll(VersionRange(max: v140)), isFalse);
+      expect(range.allowsAll(range), isTrue);
+    });
+
+    test("allows a bordering range that's not more inclusive", () {
+      var exclusive = VersionRange(min: v010, max: v250);
+      var inclusive = VersionRange(
+          min: v010, includeMin: true, max: v250, includeMax: true);
+      expect(inclusive.allowsAll(exclusive), isTrue);
+      expect(inclusive.allowsAll(inclusive), isTrue);
+      expect(exclusive.allowsAll(inclusive), isFalse);
+      expect(exclusive.allowsAll(exclusive), isTrue);
+    });
+
+    test('allows unions that are completely contained', () {
+      var range = VersionRange(min: v114, max: v200);
+      expect(range.allowsAll(VersionRange(min: v123, max: v124).union(v140)),
+          isTrue);
+      expect(range.allowsAll(VersionRange(min: v010, max: v124).union(v140)),
+          isFalse);
+      expect(range.allowsAll(VersionRange(min: v123, max: v234).union(v140)),
+          isFalse);
+    });
+
+    group('pre-release versions', () {
+      test('of inclusive min are excluded', () {
+        var range = VersionRange(min: v123, includeMin: true);
+
+        expect(range.allowsAll(VersionConstraint.parse('>1.2.4-dev')), isTrue);
+        expect(range.allowsAll(VersionConstraint.parse('>1.2.3-dev')), isFalse);
+      });
+
+      test('of non-pre-release max are excluded', () {
+        var range = VersionRange(max: v234);
+
+        expect(range.allowsAll(VersionConstraint.parse('<2.3.3')), isTrue);
+        expect(range.allowsAll(VersionConstraint.parse('<2.3.4-dev')), isFalse);
+      });
+
+      test('of non-pre-release max are included with includeMaxPreRelease', () {
+        expect(
+            includeMaxPreReleaseRange
+                .allowsAll(VersionConstraint.parse('<2.0.0-dev')),
+            isTrue);
+      });
+
+      test(
+          'of non-pre-release max are included if min is a pre-release of the '
+          'same version', () {
+        var range = VersionRange(min: Version.parse('2.3.4-dev.0'), max: v234);
+
+        expect(
+            range.allowsAll(
+                VersionConstraint.parse('>2.3.4-dev.0 <2.3.4-dev.1')),
+            isTrue);
+      });
+
+      test('of pre-release max are included', () {
+        var range = VersionRange(max: Version.parse('2.3.4-dev.2'));
+
+        expect(
+            range.allowsAll(VersionConstraint.parse('<2.3.4-dev.1')), isTrue);
+        expect(
+            range.allowsAll(VersionConstraint.parse('<2.3.4-dev.2')), isTrue);
+        expect(
+            range.allowsAll(VersionConstraint.parse('<=2.3.4-dev.2')), isFalse);
+        expect(
+            range.allowsAll(VersionConstraint.parse('<2.3.4-dev.3')), isFalse);
+      });
+    });
+  });
+
+  group('allowsAny()', () {
+    test('disallows an empty constraint', () {
+      expect(
+          VersionRange(min: v123, max: v250).allowsAny(VersionConstraint.empty),
+          isFalse);
+    });
+
+    test('allows allowed versions', () {
+      var range = VersionRange(min: v123, max: v250, includeMax: true);
+      expect(range.allowsAny(v123), isFalse);
+      expect(range.allowsAny(v124), isTrue);
+      expect(range.allowsAny(v250), isTrue);
+      expect(range.allowsAny(v300), isFalse);
+    });
+
+    test('with no min', () {
+      var range = VersionRange(max: v200);
+      expect(range.allowsAny(VersionRange(min: v140, max: v300)), isTrue);
+      expect(range.allowsAny(VersionRange(min: v234, max: v300)), isFalse);
+      expect(range.allowsAny(VersionRange(min: v140)), isTrue);
+      expect(range.allowsAny(VersionRange(min: v234)), isFalse);
+      expect(range.allowsAny(range), isTrue);
+    });
+
+    test('with no max', () {
+      var range = VersionRange(min: v072);
+      expect(range.allowsAny(VersionRange(min: v003, max: v140)), isTrue);
+      expect(range.allowsAny(VersionRange(min: v003, max: v010)), isFalse);
+      expect(range.allowsAny(VersionRange(max: v080)), isTrue);
+      expect(range.allowsAny(VersionRange(max: v003)), isFalse);
+      expect(range.allowsAny(range), isTrue);
+    });
+
+    test('with a min and max', () {
+      var range = VersionRange(min: v072, max: v200);
+      expect(range.allowsAny(VersionRange(min: v003, max: v140)), isTrue);
+      expect(range.allowsAny(VersionRange(min: v140, max: v300)), isTrue);
+      expect(range.allowsAny(VersionRange(min: v003, max: v010)), isFalse);
+      expect(range.allowsAny(VersionRange(min: v234, max: v300)), isFalse);
+      expect(range.allowsAny(VersionRange(max: v010)), isFalse);
+      expect(range.allowsAny(VersionRange(min: v234)), isFalse);
+      expect(range.allowsAny(range), isTrue);
+    });
+
+    test('allows a bordering range when both are inclusive', () {
+      expect(
+          VersionRange(max: v250).allowsAny(VersionRange(min: v250)), isFalse);
+
+      expect(
+          VersionRange(max: v250, includeMax: true)
+              .allowsAny(VersionRange(min: v250)),
+          isFalse);
+
+      expect(
+          VersionRange(max: v250)
+              .allowsAny(VersionRange(min: v250, includeMin: true)),
+          isFalse);
+
+      expect(
+          VersionRange(max: v250, includeMax: true)
+              .allowsAny(VersionRange(min: v250, includeMin: true)),
+          isTrue);
+
+      expect(
+          VersionRange(min: v250).allowsAny(VersionRange(max: v250)), isFalse);
+
+      expect(
+          VersionRange(min: v250, includeMin: true)
+              .allowsAny(VersionRange(max: v250)),
+          isFalse);
+
+      expect(
+          VersionRange(min: v250)
+              .allowsAny(VersionRange(max: v250, includeMax: true)),
+          isFalse);
+
+      expect(
+          VersionRange(min: v250, includeMin: true)
+              .allowsAny(VersionRange(max: v250, includeMax: true)),
+          isTrue);
+    });
+
+    test('allows unions that are partially contained', () {
+      var range = VersionRange(min: v114, max: v200);
+      expect(range.allowsAny(VersionRange(min: v010, max: v080).union(v140)),
+          isTrue);
+      expect(range.allowsAny(VersionRange(min: v123, max: v234).union(v300)),
+          isTrue);
+      expect(range.allowsAny(VersionRange(min: v234, max: v300).union(v010)),
+          isFalse);
+    });
+
+    group('pre-release versions', () {
+      test('of inclusive min are excluded', () {
+        var range = VersionRange(min: v123, includeMin: true);
+
+        expect(range.allowsAny(VersionConstraint.parse('<1.2.4-dev')), isTrue);
+        expect(range.allowsAny(VersionConstraint.parse('<1.2.3-dev')), isFalse);
+      });
+
+      test('of non-pre-release max are excluded', () {
+        var range = VersionRange(max: v234);
+
+        expect(range.allowsAny(VersionConstraint.parse('>2.3.3')), isTrue);
+        expect(range.allowsAny(VersionConstraint.parse('>2.3.4-dev')), isFalse);
+      });
+
+      test('of non-pre-release max are included with includeMaxPreRelease', () {
+        expect(
+            includeMaxPreReleaseRange
+                .allowsAny(VersionConstraint.parse('>2.0.0-dev')),
+            isTrue);
+      });
+
+      test(
+          'of non-pre-release max are included if min is a pre-release of the '
+          'same version', () {
+        var range = VersionRange(min: Version.parse('2.3.4-dev.0'), max: v234);
+
+        expect(
+            range.allowsAny(VersionConstraint.parse('>2.3.4-dev.1')), isTrue);
+        expect(range.allowsAny(VersionConstraint.parse('>2.3.4')), isFalse);
+
+        expect(
+            range.allowsAny(VersionConstraint.parse('<2.3.4-dev.1')), isTrue);
+        expect(range.allowsAny(VersionConstraint.parse('<2.3.4-dev')), isFalse);
+      });
+
+      test('of pre-release max are included', () {
+        var range = VersionConstraint.parse('<2.3.4-dev.2');
+
+        expect(
+            range.allowsAny(VersionConstraint.parse('>2.3.4-dev.1')), isTrue);
+        expect(
+            range.allowsAny(VersionConstraint.parse('>2.3.4-dev.2')), isFalse);
+        expect(
+            range.allowsAny(VersionConstraint.parse('>2.3.4-dev.3')), isFalse);
+      });
+    });
+  });
+
+  group('intersect()', () {
+    test('two overlapping ranges', () {
+      expect(
+          VersionRange(min: v123, max: v250)
+              .intersect(VersionRange(min: v200, max: v300)),
+          equals(VersionRange(min: v200, max: v250)));
+    });
+
+    test('a non-overlapping range allows no versions', () {
+      var a = VersionRange(min: v114, max: v124);
+      var b = VersionRange(min: v200, max: v250);
+      expect(a.intersect(b).isEmpty, isTrue);
+    });
+
+    test('adjacent ranges allow no versions if exclusive', () {
+      var a = VersionRange(min: v114, max: v124);
+      var b = VersionRange(min: v124, max: v200);
+      expect(a.intersect(b).isEmpty, isTrue);
+    });
+
+    test('adjacent ranges allow version if inclusive', () {
+      var a = VersionRange(min: v114, max: v124, includeMax: true);
+      var b = VersionRange(min: v124, max: v200, includeMin: true);
+      expect(a.intersect(b), equals(v124));
+    });
+
+    test('with an open range', () {
+      var open = VersionRange();
+      var a = VersionRange(min: v114, max: v124);
+      expect(open.intersect(open), equals(open));
+      expect(a.intersect(open), equals(a));
+    });
+
+    test('returns the version if the range allows it', () {
+      expect(VersionRange(min: v114, max: v124).intersect(v123), equals(v123));
+      expect(
+          VersionRange(min: v123, max: v124).intersect(v114).isEmpty, isTrue);
+    });
+
+    test('with a range with a pre-release min, returns an empty constraint',
+        () {
+      expect(
+          VersionRange(max: v200)
+              .intersect(VersionConstraint.parse('>=2.0.0-dev')),
+          equals(VersionConstraint.empty));
+    });
+
+    test('with a range with a pre-release max, returns the original', () {
+      expect(
+          VersionRange(max: v200)
+              .intersect(VersionConstraint.parse('<2.0.0-dev')),
+          equals(VersionRange(max: v200)));
+    });
+
+    group('with includeMaxPreRelease', () {
+      test('preserves includeMaxPreRelease if the max version is included', () {
+        expect(
+            includeMaxPreReleaseRange
+                .intersect(VersionConstraint.parse('<1.0.0')),
+            equals(VersionConstraint.parse('<1.0.0')));
+        expect(
+            includeMaxPreReleaseRange
+                .intersect(VersionConstraint.parse('<2.0.0')),
+            equals(VersionConstraint.parse('<2.0.0')));
+        expect(includeMaxPreReleaseRange.intersect(includeMaxPreReleaseRange),
+            equals(includeMaxPreReleaseRange));
+        expect(
+            includeMaxPreReleaseRange
+                .intersect(VersionConstraint.parse('<3.0.0')),
+            equals(includeMaxPreReleaseRange));
+        expect(
+            includeMaxPreReleaseRange
+                .intersect(VersionConstraint.parse('>1.1.4')),
+            equals(VersionRange(
+                min: v114, max: v200, alwaysIncludeMaxPreRelease: true)));
+      });
+
+      test(
+          'and a range with a pre-release min, returns '
+          'an intersection', () {
+        expect(
+            includeMaxPreReleaseRange
+                .intersect(VersionConstraint.parse('>=2.0.0-dev')),
+            equals(VersionConstraint.parse('>=2.0.0-dev <2.0.0')));
+      });
+
+      test(
+          'and a range with a pre-release max, returns '
+          'the narrower constraint', () {
+        expect(
+            includeMaxPreReleaseRange
+                .intersect(VersionConstraint.parse('<2.0.0-dev')),
+            equals(VersionConstraint.parse('<2.0.0-dev')));
+      });
+    });
+  });
+
+  group('union()', () {
+    test('with a version returns the range if it contains the version', () {
+      var range = VersionRange(min: v114, max: v124);
+      expect(range.union(v123), equals(range));
+    });
+
+    test('with a version on the edge of the range, expands the range', () {
+      expect(
+          VersionRange(min: v114, max: v124, alwaysIncludeMaxPreRelease: true)
+              .union(v124),
+          equals(VersionRange(min: v114, max: v124, includeMax: true)));
+      expect(VersionRange(min: v114, max: v124).union(v114),
+          equals(VersionRange(min: v114, max: v124, includeMin: true)));
+    });
+
+    test(
+        'with a version allows both the range and the version if the range '
+        "doesn't contain the version", () {
+      var result = VersionRange(min: v003, max: v114).union(v124);
+      expect(result, allows(v010));
+      expect(result, doesNotAllow(v123));
+      expect(result, allows(v124));
+    });
+
+    test('returns a VersionUnion for a disjoint range', () {
+      var result = VersionRange(min: v003, max: v114)
+          .union(VersionRange(min: v130, max: v200));
+      expect(result, allows(v080));
+      expect(result, doesNotAllow(v123));
+      expect(result, allows(v140));
+    });
+
+    test('returns a VersionUnion for a disjoint range with infinite end', () {
+      void isVersionUnion(VersionConstraint constraint) {
+        expect(constraint, allows(v080));
+        expect(constraint, doesNotAllow(v123));
+        expect(constraint, allows(v140));
+      }
+
+      for (final includeAMin in [true, false]) {
+        for (final includeAMax in [true, false]) {
+          for (final includeBMin in [true, false]) {
+            for (final includeBMax in [true, false]) {
+              final a = VersionRange(
+                  min: v130, includeMin: includeAMin, includeMax: includeAMax);
+              final b = VersionRange(
+                  max: v114, includeMin: includeBMin, includeMax: includeBMax);
+              isVersionUnion(a.union(b));
+              isVersionUnion(b.union(a));
+            }
+          }
+        }
+      }
+    });
+
+    test('considers open ranges disjoint', () {
+      var result = VersionRange(min: v003, max: v114)
+          .union(VersionRange(min: v114, max: v200));
+      expect(result, allows(v080));
+      expect(result, doesNotAllow(v114));
+      expect(result, allows(v140));
+
+      result = VersionRange(min: v114, max: v200)
+          .union(VersionRange(min: v003, max: v114));
+      expect(result, allows(v080));
+      expect(result, doesNotAllow(v114));
+      expect(result, allows(v140));
+    });
+
+    test('returns a merged range for an overlapping range', () {
+      var result = VersionRange(min: v003, max: v114)
+          .union(VersionRange(min: v080, max: v200));
+      expect(result, equals(VersionRange(min: v003, max: v200)));
+    });
+
+    test('considers closed ranges overlapping', () {
+      var result = VersionRange(min: v003, max: v114, includeMax: true)
+          .union(VersionRange(min: v114, max: v200));
+      expect(result, equals(VersionRange(min: v003, max: v200)));
+
+      result =
+          VersionRange(min: v003, max: v114, alwaysIncludeMaxPreRelease: true)
+              .union(VersionRange(min: v114, max: v200, includeMin: true));
+      expect(result, equals(VersionRange(min: v003, max: v200)));
+
+      result = VersionRange(min: v114, max: v200)
+          .union(VersionRange(min: v003, max: v114, includeMax: true));
+      expect(result, equals(VersionRange(min: v003, max: v200)));
+
+      result = VersionRange(min: v114, max: v200, includeMin: true).union(
+          VersionRange(min: v003, max: v114, alwaysIncludeMaxPreRelease: true));
+      expect(result, equals(VersionRange(min: v003, max: v200)));
+    });
+
+    test('includes edges if either range does', () {
+      var result = VersionRange(min: v003, max: v114, includeMin: true)
+          .union(VersionRange(min: v003, max: v114, includeMax: true));
+      expect(
+          result,
+          equals(VersionRange(
+              min: v003, max: v114, includeMin: true, includeMax: true)));
+    });
+
+    test('with a range with a pre-release min, returns a constraint with a gap',
+        () {
+      var result =
+          VersionRange(max: v200).union(VersionConstraint.parse('>=2.0.0-dev'));
+      expect(result, allows(v140));
+      expect(result, doesNotAllow(Version.parse('2.0.0-alpha')));
+      expect(result, allows(Version.parse('2.0.0-dev')));
+      expect(result, allows(Version.parse('2.0.0-dev.1')));
+      expect(result, allows(Version.parse('2.0.0')));
+    });
+
+    test('with a range with a pre-release max, returns the larger constraint',
+        () {
+      expect(
+          VersionRange(max: v200).union(VersionConstraint.parse('<2.0.0-dev')),
+          equals(VersionConstraint.parse('<2.0.0-dev')));
+    });
+
+    group('with includeMaxPreRelease', () {
+      test('adds includeMaxPreRelease if the max version is included', () {
+        expect(
+            includeMaxPreReleaseRange.union(VersionConstraint.parse('<1.0.0')),
+            equals(includeMaxPreReleaseRange));
+        expect(includeMaxPreReleaseRange.union(includeMaxPreReleaseRange),
+            equals(includeMaxPreReleaseRange));
+        expect(
+            includeMaxPreReleaseRange.union(VersionConstraint.parse('<2.0.0')),
+            equals(includeMaxPreReleaseRange));
+        expect(
+            includeMaxPreReleaseRange.union(VersionConstraint.parse('<3.0.0')),
+            equals(VersionConstraint.parse('<3.0.0')));
+      });
+
+      test('and a range with a pre-release min, returns any', () {
+        expect(
+            includeMaxPreReleaseRange
+                .union(VersionConstraint.parse('>=2.0.0-dev')),
+            equals(VersionConstraint.any));
+      });
+
+      test('and a range with a pre-release max, returns the original', () {
+        expect(
+            includeMaxPreReleaseRange
+                .union(VersionConstraint.parse('<2.0.0-dev')),
+            equals(includeMaxPreReleaseRange));
+      });
+    });
+  });
+
+  group('difference()', () {
+    test('with an empty range returns the original range', () {
+      expect(
+          VersionRange(min: v003, max: v114)
+              .difference(VersionConstraint.empty),
+          equals(VersionRange(min: v003, max: v114)));
+    });
+
+    test('with a version outside the range returns the original range', () {
+      expect(VersionRange(min: v003, max: v114).difference(v200),
+          equals(VersionRange(min: v003, max: v114)));
+    });
+
+    test('with a version in the range splits the range', () {
+      expect(
+          VersionRange(min: v003, max: v114).difference(v072),
+          equals(VersionConstraint.unionOf([
+            VersionRange(
+                min: v003, max: v072, alwaysIncludeMaxPreRelease: true),
+            VersionRange(min: v072, max: v114)
+          ])));
+    });
+
+    test('with the max version makes the max exclusive', () {
+      expect(
+          VersionRange(min: v003, max: v114, includeMax: true).difference(v114),
+          equals(VersionRange(
+              min: v003, max: v114, alwaysIncludeMaxPreRelease: true)));
+    });
+
+    test('with the min version makes the min exclusive', () {
+      expect(
+          VersionRange(min: v003, max: v114, includeMin: true).difference(v003),
+          equals(VersionRange(min: v003, max: v114)));
+    });
+
+    test('with a disjoint range returns the original', () {
+      expect(
+          VersionRange(min: v003, max: v114)
+              .difference(VersionRange(min: v123, max: v140)),
+          equals(VersionRange(min: v003, max: v114)));
+    });
+
+    test('with an adjacent range returns the original', () {
+      expect(
+          VersionRange(min: v003, max: v114, includeMax: true)
+              .difference(VersionRange(min: v114, max: v140)),
+          equals(VersionRange(min: v003, max: v114, includeMax: true)));
+    });
+
+    test('with a range at the beginning cuts off the beginning of the range',
+        () {
+      expect(
+          VersionRange(min: v080, max: v130)
+              .difference(VersionRange(min: v010, max: v114)),
+          equals(VersionConstraint.parse('>=1.1.4-0 <1.3.0')));
+      expect(
+          VersionRange(min: v080, max: v130)
+              .difference(VersionRange(max: v114)),
+          equals(VersionConstraint.parse('>=1.1.4-0 <1.3.0')));
+      expect(
+          VersionRange(min: v080, max: v130)
+              .difference(VersionRange(min: v010, max: v114, includeMax: true)),
+          equals(VersionRange(min: v114, max: v130)));
+      expect(
+          VersionRange(min: v080, max: v130, includeMin: true)
+              .difference(VersionRange(min: v010, max: v080, includeMax: true)),
+          equals(VersionRange(min: v080, max: v130)));
+      expect(
+          VersionRange(min: v080, max: v130, includeMax: true)
+              .difference(VersionRange(min: v080, max: v130)),
+          equals(VersionConstraint.parse('>=1.3.0-0 <=1.3.0')));
+    });
+
+    test('with a range at the end cuts off the end of the range', () {
+      expect(
+          VersionRange(min: v080, max: v130)
+              .difference(VersionRange(min: v114, max: v140)),
+          equals(VersionRange(min: v080, max: v114, includeMax: true)));
+      expect(
+          VersionRange(min: v080, max: v130)
+              .difference(VersionRange(min: v114)),
+          equals(VersionRange(min: v080, max: v114, includeMax: true)));
+      expect(
+          VersionRange(min: v080, max: v130)
+              .difference(VersionRange(min: v114, max: v140, includeMin: true)),
+          equals(VersionRange(
+              min: v080, max: v114, alwaysIncludeMaxPreRelease: true)));
+      expect(
+          VersionRange(min: v080, max: v130, includeMax: true)
+              .difference(VersionRange(min: v130, max: v140, includeMin: true)),
+          equals(VersionRange(
+              min: v080, max: v130, alwaysIncludeMaxPreRelease: true)));
+      expect(
+          VersionRange(min: v080, max: v130, includeMin: true)
+              .difference(VersionRange(min: v080, max: v130)),
+          equals(v080));
+    });
+
+    test('with a range in the middle cuts the range in half', () {
+      expect(
+          VersionRange(min: v003, max: v130)
+              .difference(VersionRange(min: v072, max: v114)),
+          equals(VersionConstraint.unionOf([
+            VersionRange(min: v003, max: v072, includeMax: true),
+            VersionConstraint.parse('>=1.1.4-0 <1.3.0')
+          ])));
+    });
+
+    test('with a totally covering range returns empty', () {
+      expect(
+          VersionRange(min: v114, max: v200)
+              .difference(VersionRange(min: v072, max: v300)),
+          isEmpty);
+      expect(
+          VersionRange(min: v003, max: v114)
+              .difference(VersionRange(min: v003, max: v114)),
+          isEmpty);
+      expect(
+          VersionRange(min: v003, max: v114, includeMin: true, includeMax: true)
+              .difference(VersionRange(
+                  min: v003, max: v114, includeMin: true, includeMax: true)),
+          isEmpty);
+    });
+
+    test(
+        "with a version union that doesn't cover the range, returns the "
+        'original', () {
+      expect(
+          VersionRange(min: v114, max: v140)
+              .difference(VersionConstraint.unionOf([v010, v200])),
+          equals(VersionRange(min: v114, max: v140)));
+    });
+
+    test('with a version union that intersects the ends, chops them off', () {
+      expect(
+          VersionRange(min: v114, max: v140).difference(
+              VersionConstraint.unionOf([
+            VersionRange(min: v080, max: v123),
+            VersionRange(min: v130, max: v200)
+          ])),
+          equals(VersionConstraint.parse('>=1.2.3-0 <=1.3.0')));
+    });
+
+    test('with a version union that intersects the middle, chops it up', () {
+      expect(
+          VersionRange(min: v114, max: v140)
+              .difference(VersionConstraint.unionOf([v123, v124, v130])),
+          equals(VersionConstraint.unionOf([
+            VersionRange(
+                min: v114, max: v123, alwaysIncludeMaxPreRelease: true),
+            VersionRange(
+                min: v123, max: v124, alwaysIncludeMaxPreRelease: true),
+            VersionRange(
+                min: v124, max: v130, alwaysIncludeMaxPreRelease: true),
+            VersionRange(min: v130, max: v140)
+          ])));
+    });
+
+    test('with a version union that covers the whole range, returns empty', () {
+      expect(
+          VersionRange(min: v114, max: v140).difference(
+              VersionConstraint.unionOf([v003, VersionRange(min: v010)])),
+          equals(VersionConstraint.empty));
+    });
+
+    test('with a range with a pre-release min, returns the original', () {
+      expect(
+          VersionRange(max: v200)
+              .difference(VersionConstraint.parse('>=2.0.0-dev')),
+          equals(VersionRange(max: v200)));
+    });
+
+    test('with a range with a pre-release max, returns null', () {
+      expect(
+          VersionRange(max: v200)
+              .difference(VersionConstraint.parse('<2.0.0-dev')),
+          equals(VersionConstraint.empty));
+    });
+
+    group('with includeMaxPreRelease', () {
+      group('for the minuend', () {
+        test('preserves includeMaxPreRelease if the max version is included',
+            () {
+          expect(
+              includeMaxPreReleaseRange
+                  .difference(VersionConstraint.parse('<1.0.0')),
+              equals(VersionRange(
+                  min: Version.parse('1.0.0-0'),
+                  max: v200,
+                  includeMin: true,
+                  alwaysIncludeMaxPreRelease: true)));
+          expect(
+              includeMaxPreReleaseRange
+                  .difference(VersionConstraint.parse('<2.0.0')),
+              equals(VersionRange(
+                  min: v200.firstPreRelease,
+                  max: v200,
+                  includeMin: true,
+                  alwaysIncludeMaxPreRelease: true)));
+          expect(
+              includeMaxPreReleaseRange.difference(includeMaxPreReleaseRange),
+              equals(VersionConstraint.empty));
+          expect(
+              includeMaxPreReleaseRange
+                  .difference(VersionConstraint.parse('<3.0.0')),
+              equals(VersionConstraint.empty));
+        });
+
+        test('with a range with a pre-release min, adjusts the max', () {
+          expect(
+              includeMaxPreReleaseRange
+                  .difference(VersionConstraint.parse('>=2.0.0-dev')),
+              equals(VersionConstraint.parse('<2.0.0-dev')));
+        });
+
+        test('with a range with a pre-release max, adjusts the min', () {
+          expect(
+              includeMaxPreReleaseRange
+                  .difference(VersionConstraint.parse('<2.0.0-dev')),
+              equals(VersionConstraint.parse('>=2.0.0-dev <2.0.0')));
+        });
+      });
+
+      group('for the subtrahend', () {
+        group("doesn't create a pre-release minimum", () {
+          test('when cutting off the bottom', () {
+            expect(
+                VersionConstraint.parse('<3.0.0')
+                    .difference(includeMaxPreReleaseRange),
+                equals(VersionRange(min: v200, max: v300, includeMin: true)));
+          });
+
+          test('with splitting down the middle', () {
+            expect(
+                VersionConstraint.parse('<4.0.0').difference(VersionRange(
+                    min: v200,
+                    max: v300,
+                    includeMin: true,
+                    alwaysIncludeMaxPreRelease: true)),
+                equals(VersionConstraint.unionOf([
+                  VersionRange(max: v200, alwaysIncludeMaxPreRelease: true),
+                  VersionConstraint.parse('>=3.0.0 <4.0.0')
+                ])));
+          });
+
+          test('can leave a single version', () {
+            expect(
+                VersionConstraint.parse('<=2.0.0')
+                    .difference(includeMaxPreReleaseRange),
+                equals(v200));
+          });
+        });
+      });
+    });
+  });
+
+  test('isEmpty', () {
+    expect(VersionRange().isEmpty, isFalse);
+    expect(VersionRange(min: v123, max: v124).isEmpty, isFalse);
+  });
+
+  group('compareTo()', () {
+    test('orders by minimum first', () {
+      _expectComparesSmaller(VersionRange(min: v003, max: v080),
+          VersionRange(min: v010, max: v072));
+      _expectComparesSmaller(VersionRange(min: v003, max: v080),
+          VersionRange(min: v010, max: v080));
+      _expectComparesSmaller(VersionRange(min: v003, max: v080),
+          VersionRange(min: v010, max: v114));
+    });
+
+    test('orders by maximum second', () {
+      _expectComparesSmaller(VersionRange(min: v003, max: v010),
+          VersionRange(min: v003, max: v072));
+    });
+
+    test('includeMin comes before !includeMin', () {
+      _expectComparesSmaller(
+          VersionRange(min: v003, max: v080, includeMin: true),
+          VersionRange(min: v003, max: v080));
+    });
+
+    test('includeMax comes after !includeMax', () {
+      _expectComparesSmaller(VersionRange(min: v003, max: v080),
+          VersionRange(min: v003, max: v080, includeMax: true));
+    });
+
+    test('includeMaxPreRelease comes after !includeMaxPreRelease', () {
+      _expectComparesSmaller(
+          VersionRange(max: v200), includeMaxPreReleaseRange);
+    });
+
+    test('no minimum comes before small minimum', () {
+      _expectComparesSmaller(
+          VersionRange(max: v010), VersionRange(min: v003, max: v010));
+      _expectComparesSmaller(VersionRange(max: v010, includeMin: true),
+          VersionRange(min: v003, max: v010));
+    });
+
+    test('no maximium comes after large maximum', () {
+      _expectComparesSmaller(
+          VersionRange(min: v003, max: v300), VersionRange(min: v003));
+      _expectComparesSmaller(VersionRange(min: v003, max: v300),
+          VersionRange(min: v003, includeMax: true));
+    });
+  });
+}
+
+void _expectComparesSmaller(VersionRange smaller, VersionRange larger) {
+  expect(smaller.compareTo(larger), lessThan(0),
+      reason: 'expected $smaller to sort below $larger');
+  expect(larger.compareTo(smaller), greaterThan(0),
+      reason: 'expected $larger to sort above $smaller');
+}

diff --git a/pkgs/pub_semver/test/version_test.dart b/pkgs/pub_semver/test/version_test.dart
new file mode 100644
index 0000000..d7f1197
--- /dev/null
+++ b/pkgs/pub_semver/test/version_test.dart

@@ -0,0 +1,411 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:pub_semver/pub_semver.dart';
+import 'package:test/test.dart';
+
+import 'utils.dart';
+
+void main() {
+  test('none', () {
+    expect(Version.none.toString(), equals('0.0.0'));
+  });
+
+  test('prioritize()', () {
+    // A correctly sorted list of versions in order of increasing priority.
+    var versions = [
+      '1.0.0-alpha',
+      '2.0.0-alpha',
+      '1.0.0',
+      '1.0.0+build',
+      '1.0.1',
+      '1.1.0',
+      '2.0.0'
+    ];
+
+    // Ensure that every pair of versions is prioritized in the order that it
+    // appears in the list.
+    for (var i = 0; i < versions.length; i++) {
+      for (var j = 0; j < versions.length; j++) {
+        var a = Version.parse(versions[i]);
+        var b = Version.parse(versions[j]);
+        expect(Version.prioritize(a, b), equals(i.compareTo(j)));
+      }
+    }
+  });
+
+  test('antiprioritize()', () {
+    // A correctly sorted list of versions in order of increasing antipriority.
+    var versions = [
+      '2.0.0-alpha',
+      '1.0.0-alpha',
+      '2.0.0',
+      '1.1.0',
+      '1.0.1',
+      '1.0.0+build',
+      '1.0.0'
+    ];
+
+    // Ensure that every pair of versions is prioritized in the order that it
+    // appears in the list.
+    for (var i = 0; i < versions.length; i++) {
+      for (var j = 0; j < versions.length; j++) {
+        var a = Version.parse(versions[i]);
+        var b = Version.parse(versions[j]);
+        expect(Version.antiprioritize(a, b), equals(i.compareTo(j)));
+      }
+    }
+  });
+
+  group('constructor', () {
+    test('throws on negative numbers', () {
+      expect(() => Version(-1, 1, 1), throwsArgumentError);
+      expect(() => Version(1, -1, 1), throwsArgumentError);
+      expect(() => Version(1, 1, -1), throwsArgumentError);
+    });
+  });
+
+  group('comparison', () {
+    // A correctly sorted list of versions.
+    var versions = [
+      '1.0.0-alpha',
+      '1.0.0-alpha.1',
+      '1.0.0-beta.2',
+      '1.0.0-beta.11',
+      '1.0.0-rc.1',
+      '1.0.0-rc.1+build.1',
+      '1.0.0',
+      '1.0.0+0.3.7',
+      '1.3.7+build',
+      '1.3.7+build.2.b8f12d7',
+      '1.3.7+build.11.e0f985a',
+      '2.0.0',
+      '2.1.0',
+      '2.2.0',
+      '2.11.0',
+      '2.11.1'
+    ];
+
+    test('compareTo()', () {
+      // Ensure that every pair of versions compares in the order that it
+      // appears in the list.
+      for (var i = 0; i < versions.length; i++) {
+        for (var j = 0; j < versions.length; j++) {
+          var a = Version.parse(versions[i]);
+          var b = Version.parse(versions[j]);
+          expect(a.compareTo(b), equals(i.compareTo(j)));
+        }
+      }
+    });
+
+    test('operators', () {
+      for (var i = 0; i < versions.length; i++) {
+        for (var j = 0; j < versions.length; j++) {
+          var a = Version.parse(versions[i]);
+          var b = Version.parse(versions[j]);
+          expect(a < b, equals(i < j));
+          expect(a > b, equals(i > j));
+          expect(a <= b, equals(i <= j));
+          expect(a >= b, equals(i >= j));
+          expect(a == b, equals(i == j));
+          expect(a != b, equals(i != j));
+        }
+      }
+    });
+
+    test('equality', () {
+      expect(Version.parse('01.2.3'), equals(Version.parse('1.2.3')));
+      expect(Version.parse('1.02.3'), equals(Version.parse('1.2.3')));
+      expect(Version.parse('1.2.03'), equals(Version.parse('1.2.3')));
+      expect(Version.parse('1.2.3-01'), equals(Version.parse('1.2.3-1')));
+      expect(Version.parse('1.2.3+01'), equals(Version.parse('1.2.3+1')));
+    });
+  });
+
+  test('allows()', () {
+    expect(v123, allows(v123));
+    expect(
+        v123,
+        doesNotAllow(
+            Version.parse('2.2.3'),
+            Version.parse('1.3.3'),
+            Version.parse('1.2.4'),
+            Version.parse('1.2.3-dev'),
+            Version.parse('1.2.3+build')));
+  });
+
+  test('allowsAll()', () {
+    expect(v123.allowsAll(v123), isTrue);
+    expect(v123.allowsAll(v003), isFalse);
+    expect(v123.allowsAll(VersionRange(min: v114, max: v124)), isFalse);
+    expect(v123.allowsAll(VersionConstraint.any), isFalse);
+    expect(v123.allowsAll(VersionConstraint.empty), isTrue);
+  });
+
+  test('allowsAny()', () {
+    expect(v123.allowsAny(v123), isTrue);
+    expect(v123.allowsAny(v003), isFalse);
+    expect(v123.allowsAny(VersionRange(min: v114, max: v124)), isTrue);
+    expect(v123.allowsAny(VersionConstraint.any), isTrue);
+    expect(v123.allowsAny(VersionConstraint.empty), isFalse);
+  });
+
+  test('intersect()', () {
+    // Intersecting the same version returns the version.
+    expect(v123.intersect(v123), equals(v123));
+
+    // Intersecting a different version allows no versions.
+    expect(v123.intersect(v114).isEmpty, isTrue);
+
+    // Intersecting a range returns the version if the range allows it.
+    expect(v123.intersect(VersionRange(min: v114, max: v124)), equals(v123));
+
+    // Intersecting a range allows no versions if the range doesn't allow it.
+    expect(v114.intersect(VersionRange(min: v123, max: v124)).isEmpty, isTrue);
+  });
+
+  group('union()', () {
+    test('with the same version returns the version', () {
+      expect(v123.union(v123), equals(v123));
+    });
+
+    test('with a different version returns a version that matches both', () {
+      var result = v123.union(v080);
+      expect(result, allows(v123));
+      expect(result, allows(v080));
+
+      // Nothing in between should match.
+      expect(result, doesNotAllow(v114));
+    });
+
+    test('with a range returns the range if it contains the version', () {
+      var range = VersionRange(min: v114, max: v124);
+      expect(v123.union(range), equals(range));
+    });
+
+    test('with a range with the version on the edge, expands the range', () {
+      expect(
+          v124.union(VersionRange(
+              min: v114, max: v124, alwaysIncludeMaxPreRelease: true)),
+          equals(VersionRange(min: v114, max: v124, includeMax: true)));
+      expect(
+          v124.firstPreRelease.union(VersionRange(min: v114, max: v124)),
+          equals(VersionRange(
+              min: v114, max: v124.firstPreRelease, includeMax: true)));
+      expect(v114.union(VersionRange(min: v114, max: v124)),
+          equals(VersionRange(min: v114, max: v124, includeMin: true)));
+    });
+
+    test(
+        'with a range allows both the range and the version if the range '
+        "doesn't contain the version", () {
+      var result = v123.union(VersionRange(min: v003, max: v114));
+      expect(result, allows(v123));
+      expect(result, allows(v010));
+    });
+  });
+
+  group('difference()', () {
+    test('with the same version returns an empty constraint', () {
+      expect(v123.difference(v123), isEmpty);
+    });
+
+    test('with a different version returns the original version', () {
+      expect(v123.difference(v080), equals(v123));
+    });
+
+    test('returns an empty constraint with a range that contains the version',
+        () {
+      expect(v123.difference(VersionRange(min: v114, max: v124)), isEmpty);
+    });
+
+    test("returns the version constraint with a range that doesn't contain it",
+        () {
+      expect(v123.difference(VersionRange(min: v140, max: v300)), equals(v123));
+    });
+  });
+
+  test('isEmpty', () {
+    expect(v123.isEmpty, isFalse);
+  });
+
+  test('nextMajor', () {
+    expect(v123.nextMajor, equals(v200));
+    expect(v114.nextMajor, equals(v200));
+    expect(v200.nextMajor, equals(v300));
+
+    // Ignores pre-release if not on a major version.
+    expect(Version.parse('1.2.3-dev').nextMajor, equals(v200));
+
+    // Just removes it if on a major version.
+    expect(Version.parse('2.0.0-dev').nextMajor, equals(v200));
+
+    // Strips build suffix.
+    expect(Version.parse('1.2.3+patch').nextMajor, equals(v200));
+  });
+
+  test('nextMinor', () {
+    expect(v123.nextMinor, equals(v130));
+    expect(v130.nextMinor, equals(v140));
+
+    // Ignores pre-release if not on a minor version.
+    expect(Version.parse('1.2.3-dev').nextMinor, equals(v130));
+
+    // Just removes it if on a minor version.
+    expect(Version.parse('1.3.0-dev').nextMinor, equals(v130));
+
+    // Strips build suffix.
+    expect(Version.parse('1.2.3+patch').nextMinor, equals(v130));
+  });
+
+  test('nextPatch', () {
+    expect(v123.nextPatch, equals(v124));
+    expect(v200.nextPatch, equals(v201));
+
+    // Just removes pre-release version if present.
+    expect(Version.parse('1.2.4-dev').nextPatch, equals(v124));
+
+    // Strips build suffix.
+    expect(Version.parse('1.2.3+patch').nextPatch, equals(v124));
+  });
+
+  test('nextBreaking', () {
+    expect(v123.nextBreaking, equals(v200));
+    expect(v072.nextBreaking, equals(v080));
+    expect(v003.nextBreaking, equals(v010));
+
+    // Removes pre-release version if present.
+    expect(Version.parse('1.2.3-dev').nextBreaking, equals(v200));
+
+    // Strips build suffix.
+    expect(Version.parse('1.2.3+patch').nextBreaking, equals(v200));
+  });
+
+  test('parse()', () {
+    expect(Version.parse('0.0.0'), equals(Version(0, 0, 0)));
+    expect(Version.parse('12.34.56'), equals(Version(12, 34, 56)));
+
+    expect(Version.parse('1.2.3-alpha.1'),
+        equals(Version(1, 2, 3, pre: 'alpha.1')));
+    expect(Version.parse('1.2.3-x.7.z-92'),
+        equals(Version(1, 2, 3, pre: 'x.7.z-92')));
+
+    expect(Version.parse('1.2.3+build.1'),
+        equals(Version(1, 2, 3, build: 'build.1')));
+    expect(Version.parse('1.2.3+x.7.z-92'),
+        equals(Version(1, 2, 3, build: 'x.7.z-92')));
+
+    expect(Version.parse('1.0.0-rc-1+build-1'),
+        equals(Version(1, 0, 0, pre: 'rc-1', build: 'build-1')));
+
+    expect(() => Version.parse('1.0'), throwsFormatException);
+    expect(() => Version.parse('1a2b3'), throwsFormatException);
+    expect(() => Version.parse('1.2.3.4'), throwsFormatException);
+    expect(() => Version.parse('1234'), throwsFormatException);
+    expect(() => Version.parse('-2.3.4'), throwsFormatException);
+    expect(() => Version.parse('1.3-pre'), throwsFormatException);
+    expect(() => Version.parse('1.3+build'), throwsFormatException);
+    expect(() => Version.parse('1.3+bu?!3ild'), throwsFormatException);
+  });
+
+  group('toString()', () {
+    test('returns the version string', () {
+      expect(Version(0, 0, 0).toString(), equals('0.0.0'));
+      expect(Version(12, 34, 56).toString(), equals('12.34.56'));
+
+      expect(
+          Version(1, 2, 3, pre: 'alpha.1').toString(), equals('1.2.3-alpha.1'));
+      expect(Version(1, 2, 3, pre: 'x.7.z-92').toString(),
+          equals('1.2.3-x.7.z-92'));
+
+      expect(Version(1, 2, 3, build: 'build.1').toString(),
+          equals('1.2.3+build.1'));
+      expect(Version(1, 2, 3, pre: 'pre', build: 'bui').toString(),
+          equals('1.2.3-pre+bui'));
+    });
+
+    test('preserves leading zeroes', () {
+      expect(Version.parse('001.02.0003-01.dev+pre.002').toString(),
+          equals('001.02.0003-01.dev+pre.002'));
+    });
+  });
+
+  group('canonicalizedVersion', () {
+    test('returns version string', () {
+      expect(Version(0, 0, 0).canonicalizedVersion, equals('0.0.0'));
+      expect(Version(12, 34, 56).canonicalizedVersion, equals('12.34.56'));
+
+      expect(Version(1, 2, 3, pre: 'alpha.1').canonicalizedVersion,
+          equals('1.2.3-alpha.1'));
+      expect(Version(1, 2, 3, pre: 'x.7.z-92').canonicalizedVersion,
+          equals('1.2.3-x.7.z-92'));
+
+      expect(Version(1, 2, 3, build: 'build.1').canonicalizedVersion,
+          equals('1.2.3+build.1'));
+      expect(Version(1, 2, 3, pre: 'pre', build: 'bui').canonicalizedVersion,
+          equals('1.2.3-pre+bui'));
+    });
+
+    test('discards leading zeroes', () {
+      expect(Version.parse('001.02.0003-01.dev+pre.002').canonicalizedVersion,
+          equals('1.2.3-1.dev+pre.2'));
+    });
+
+    test('example from documentation', () {
+      final v = Version.parse('01.02.03-01.dev+pre.02');
+
+      assert(v.toString() == '01.02.03-01.dev+pre.02');
+      assert(v.canonicalizedVersion == '1.2.3-1.dev+pre.2');
+      assert(Version.parse(v.canonicalizedVersion) == v);
+    });
+  });
+
+  group('primary', () {
+    test('single', () {
+      expect(
+        _primary([
+          '1.2.3',
+        ]).toString(),
+        '1.2.3',
+      );
+    });
+
+    test('normal', () {
+      expect(
+        _primary([
+          '1.2.3',
+          '1.2.2',
+        ]).toString(),
+        '1.2.3',
+      );
+    });
+
+    test('all prerelease', () {
+      expect(
+        _primary([
+          '1.2.2-dev.1',
+          '1.2.2-dev.2',
+        ]).toString(),
+        '1.2.2-dev.2',
+      );
+    });
+
+    test('later prerelease', () {
+      expect(
+        _primary([
+          '1.2.3',
+          '1.2.3-dev',
+        ]).toString(),
+        '1.2.3',
+      );
+    });
+
+    test('empty', () {
+      expect(() => Version.primary([]), throwsStateError);
+    });
+  });
+}
+
+Version _primary(List<String> input) =>
+    Version.primary(input.map(Version.parse).toList());

diff --git a/pkgs/pub_semver/test/version_union_test.dart b/pkgs/pub_semver/test/version_union_test.dart
new file mode 100644
index 0000000..857f10e
--- /dev/null
+++ b/pkgs/pub_semver/test/version_union_test.dart

@@ -0,0 +1,482 @@
+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:pub_semver/pub_semver.dart';
+import 'package:test/test.dart';
+
+import 'utils.dart';
+
+void main() {
+  group('factory', () {
+    test('ignores empty constraints', () {
+      expect(
+          VersionConstraint.unionOf([
+            VersionConstraint.empty,
+            VersionConstraint.empty,
+            v123,
+            VersionConstraint.empty
+          ]),
+          equals(v123));
+
+      expect(
+          VersionConstraint.unionOf(
+              [VersionConstraint.empty, VersionConstraint.empty]),
+          isEmpty);
+    });
+
+    test('returns an empty constraint for an empty list', () {
+      expect(VersionConstraint.unionOf([]), isEmpty);
+    });
+
+    test('any constraints override everything', () {
+      expect(
+          VersionConstraint.unionOf([
+            v123,
+            VersionConstraint.any,
+            v200,
+            VersionRange(min: v234, max: v250)
+          ]),
+          equals(VersionConstraint.any));
+    });
+
+    test('flattens other unions', () {
+      expect(
+          VersionConstraint.unionOf([
+            v072,
+            VersionConstraint.unionOf([v123, v124]),
+            v250
+          ]),
+          equals(VersionConstraint.unionOf([v072, v123, v124, v250])));
+    });
+
+    test('returns a single merged range as-is', () {
+      expect(
+          VersionConstraint.unionOf([
+            VersionRange(min: v080, max: v140),
+            VersionRange(min: v123, max: v200)
+          ]),
+          equals(VersionRange(min: v080, max: v200)));
+    });
+  });
+
+  group('equality', () {
+    test("doesn't depend on original order", () {
+      expect(
+          VersionConstraint.unionOf([
+            v250,
+            VersionRange(min: v201, max: v234),
+            v124,
+            v072,
+            VersionRange(min: v080, max: v114),
+            v123
+          ]),
+          equals(VersionConstraint.unionOf([
+            v072,
+            VersionRange(min: v080, max: v114),
+            v123,
+            v124,
+            VersionRange(min: v201, max: v234),
+            v250
+          ])));
+    });
+
+    test('merges overlapping ranges', () {
+      expect(
+          VersionConstraint.unionOf([
+            VersionRange(min: v003, max: v072),
+            VersionRange(min: v010, max: v080),
+            VersionRange(min: v114, max: v124),
+            VersionRange(min: v123, max: v130)
+          ]),
+          equals(VersionConstraint.unionOf([
+            VersionRange(min: v003, max: v080),
+            VersionRange(min: v114, max: v130)
+          ])));
+    });
+
+    test('merges adjacent ranges', () {
+      expect(
+          VersionConstraint.unionOf([
+            VersionRange(min: v003, max: v072, includeMax: true),
+            VersionRange(min: v072, max: v080),
+            VersionRange(
+                min: v114, max: v124, alwaysIncludeMaxPreRelease: true),
+            VersionRange(min: v124, max: v130, includeMin: true),
+            VersionRange(min: v130.firstPreRelease, max: v200, includeMin: true)
+          ]),
+          equals(VersionConstraint.unionOf([
+            VersionRange(min: v003, max: v080),
+            VersionRange(min: v114, max: v200)
+          ])));
+    });
+
+    test("doesn't merge not-quite-adjacent ranges", () {
+      expect(
+          VersionConstraint.unionOf([
+            VersionRange(min: v114, max: v124),
+            VersionRange(min: v124, max: v130, includeMin: true)
+          ]),
+          isNot(equals(VersionRange(min: v114, max: v130))));
+
+      expect(
+          VersionConstraint.unionOf([
+            VersionRange(min: v003, max: v072),
+            VersionRange(min: v072, max: v080)
+          ]),
+          isNot(equals(VersionRange(min: v003, max: v080))));
+    });
+
+    test('merges version numbers into ranges', () {
+      expect(
+          VersionConstraint.unionOf([
+            VersionRange(min: v003, max: v072),
+            v010,
+            VersionRange(min: v114, max: v124),
+            v123
+          ]),
+          equals(VersionConstraint.unionOf([
+            VersionRange(min: v003, max: v072),
+            VersionRange(min: v114, max: v124)
+          ])));
+    });
+
+    test('merges adjacent version numbers into ranges', () {
+      expect(
+          VersionConstraint.unionOf([
+            VersionRange(
+                min: v003, max: v072, alwaysIncludeMaxPreRelease: true),
+            v072,
+            v114,
+            VersionRange(min: v114, max: v124),
+            v124.firstPreRelease
+          ]),
+          equals(VersionConstraint.unionOf([
+            VersionRange(min: v003, max: v072, includeMax: true),
+            VersionRange(
+                min: v114,
+                max: v124.firstPreRelease,
+                includeMin: true,
+                includeMax: true)
+          ])));
+    });
+
+    test("doesn't merge not-quite-adjacent version numbers into ranges", () {
+      expect(
+          VersionConstraint.unionOf([VersionRange(min: v003, max: v072), v072]),
+          isNot(equals(VersionRange(min: v003, max: v072, includeMax: true))));
+    });
+  });
+
+  test('isEmpty returns false', () {
+    expect(
+        VersionConstraint.unionOf([
+          VersionRange(min: v003, max: v080),
+          VersionRange(min: v123, max: v130),
+        ]),
+        isNot(isEmpty));
+  });
+
+  test('isAny returns false', () {
+    expect(
+        VersionConstraint.unionOf([
+          VersionRange(min: v003, max: v080),
+          VersionRange(min: v123, max: v130),
+        ]).isAny,
+        isFalse);
+  });
+
+  test('allows() allows anything the components allow', () {
+    var union = VersionConstraint.unionOf([
+      VersionRange(min: v003, max: v080),
+      VersionRange(min: v123, max: v130),
+      v200
+    ]);
+
+    expect(union, allows(v010));
+    expect(union, doesNotAllow(v080));
+    expect(union, allows(v124));
+    expect(union, doesNotAllow(v140));
+    expect(union, allows(v200));
+  });
+
+  group('allowsAll()', () {
+    test('for a version, returns true if any component allows the version', () {
+      var union = VersionConstraint.unionOf([
+        VersionRange(min: v003, max: v080),
+        VersionRange(min: v123, max: v130),
+        v200
+      ]);
+
+      expect(union.allowsAll(v010), isTrue);
+      expect(union.allowsAll(v080), isFalse);
+      expect(union.allowsAll(v124), isTrue);
+      expect(union.allowsAll(v140), isFalse);
+      expect(union.allowsAll(v200), isTrue);
+    });
+
+    test(
+        'for a version range, returns true if any component allows the whole '
+        'range', () {
+      var union = VersionConstraint.unionOf([
+        VersionRange(min: v003, max: v080),
+        VersionRange(min: v123, max: v130)
+      ]);
+
+      expect(union.allowsAll(VersionRange(min: v003, max: v080)), isTrue);
+      expect(union.allowsAll(VersionRange(min: v010, max: v072)), isTrue);
+      expect(union.allowsAll(VersionRange(min: v010, max: v124)), isFalse);
+    });
+
+    group('for a union,', () {
+      var union = VersionConstraint.unionOf([
+        VersionRange(min: v003, max: v080),
+        VersionRange(min: v123, max: v130)
+      ]);
+
+      test('returns true if every constraint matches a different constraint',
+          () {
+        expect(
+            union.allowsAll(VersionConstraint.unionOf([
+              VersionRange(min: v010, max: v072),
+              VersionRange(min: v124, max: v130)
+            ])),
+            isTrue);
+      });
+
+      test('returns true if every constraint matches the same constraint', () {
+        expect(
+            union.allowsAll(VersionConstraint.unionOf([
+              VersionRange(min: v003, max: v010),
+              VersionRange(min: v072, max: v080)
+            ])),
+            isTrue);
+      });
+
+      test("returns false if there's an unmatched constraint", () {
+        expect(
+            union.allowsAll(VersionConstraint.unionOf([
+              VersionRange(min: v010, max: v072),
+              VersionRange(min: v124, max: v130),
+              VersionRange(min: v140, max: v200)
+            ])),
+            isFalse);
+      });
+
+      test("returns false if a constraint isn't fully matched", () {
+        expect(
+            union.allowsAll(VersionConstraint.unionOf([
+              VersionRange(min: v010, max: v114),
+              VersionRange(min: v124, max: v130)
+            ])),
+            isFalse);
+      });
+    });
+  });
+
+  group('allowsAny()', () {
+    test('for a version, returns true if any component allows the version', () {
+      var union = VersionConstraint.unionOf([
+        VersionRange(min: v003, max: v080),
+        VersionRange(min: v123, max: v130),
+        v200
+      ]);
+
+      expect(union.allowsAny(v010), isTrue);
+      expect(union.allowsAny(v080), isFalse);
+      expect(union.allowsAny(v124), isTrue);
+      expect(union.allowsAny(v140), isFalse);
+      expect(union.allowsAny(v200), isTrue);
+    });
+
+    test(
+        'for a version range, returns true if any component allows part of '
+        'the range', () {
+      var union =
+          VersionConstraint.unionOf([VersionRange(min: v003, max: v080), v123]);
+
+      expect(union.allowsAny(VersionRange(min: v010, max: v114)), isTrue);
+      expect(union.allowsAny(VersionRange(min: v114, max: v124)), isTrue);
+      expect(union.allowsAny(VersionRange(min: v124, max: v130)), isFalse);
+    });
+
+    group('for a union,', () {
+      var union = VersionConstraint.unionOf([
+        VersionRange(min: v010, max: v080),
+        VersionRange(min: v123, max: v130)
+      ]);
+
+      test('returns true if any constraint matches', () {
+        expect(
+            union.allowsAny(VersionConstraint.unionOf(
+                [v072, VersionRange(min: v200, max: v300)])),
+            isTrue);
+
+        expect(
+            union.allowsAny(VersionConstraint.unionOf(
+                [v003, VersionRange(min: v124, max: v300)])),
+            isTrue);
+      });
+
+      test('returns false if no constraint matches', () {
+        expect(
+            union.allowsAny(VersionConstraint.unionOf([
+              v003,
+              VersionRange(min: v130, max: v140),
+              VersionRange(min: v140, max: v200)
+            ])),
+            isFalse);
+      });
+    });
+  });
+
+  group('intersect()', () {
+    test('with an overlapping version, returns that version', () {
+      expect(
+          VersionConstraint.unionOf([
+            VersionRange(min: v010, max: v080),
+            VersionRange(min: v123, max: v140)
+          ]).intersect(v072),
+          equals(v072));
+    });
+
+    test('with a non-overlapping version, returns an empty constraint', () {
+      expect(
+          VersionConstraint.unionOf([
+            VersionRange(min: v010, max: v080),
+            VersionRange(min: v123, max: v140)
+          ]).intersect(v300),
+          isEmpty);
+    });
+
+    test('with an overlapping range, returns that range', () {
+      var range = VersionRange(min: v072, max: v080);
+      expect(
+          VersionConstraint.unionOf([
+            VersionRange(min: v010, max: v080),
+            VersionRange(min: v123, max: v140)
+          ]).intersect(range),
+          equals(range));
+    });
+
+    test('with a non-overlapping range, returns an empty constraint', () {
+      expect(
+          VersionConstraint.unionOf([
+            VersionRange(min: v010, max: v080),
+            VersionRange(min: v123, max: v140)
+          ]).intersect(VersionRange(min: v080, max: v123)),
+          isEmpty);
+    });
+
+    test('with a parially-overlapping range, returns the overlapping parts',
+        () {
+      expect(
+          VersionConstraint.unionOf([
+            VersionRange(min: v010, max: v080),
+            VersionRange(min: v123, max: v140)
+          ]).intersect(VersionRange(min: v072, max: v130)),
+          equals(VersionConstraint.unionOf([
+            VersionRange(min: v072, max: v080),
+            VersionRange(min: v123, max: v130)
+          ])));
+    });
+
+    group('for a union,', () {
+      var union = VersionConstraint.unionOf([
+        VersionRange(min: v003, max: v080),
+        VersionRange(min: v123, max: v130)
+      ]);
+
+      test('returns the overlapping parts', () {
+        expect(
+            union.intersect(VersionConstraint.unionOf([
+              v010,
+              VersionRange(min: v072, max: v124),
+              VersionRange(min: v124, max: v130)
+            ])),
+            equals(VersionConstraint.unionOf([
+              v010,
+              VersionRange(min: v072, max: v080),
+              VersionRange(min: v123, max: v124),
+              VersionRange(min: v124, max: v130)
+            ])));
+      });
+
+      test("drops parts that don't match", () {
+        expect(
+            union.intersect(VersionConstraint.unionOf([
+              v003,
+              VersionRange(min: v072, max: v080),
+              VersionRange(min: v080, max: v123)
+            ])),
+            equals(VersionRange(min: v072, max: v080)));
+      });
+    });
+  });
+
+  group('difference()', () {
+    test("ignores ranges that don't intersect", () {
+      expect(
+          VersionConstraint.unionOf([
+            VersionRange(min: v072, max: v080),
+            VersionRange(min: v123, max: v130)
+          ]).difference(VersionConstraint.unionOf([
+            VersionRange(min: v003, max: v010),
+            VersionRange(min: v080, max: v123),
+            VersionRange(min: v140)
+          ])),
+          equals(VersionConstraint.unionOf([
+            VersionRange(min: v072, max: v080),
+            VersionRange(min: v123, max: v130)
+          ])));
+    });
+
+    test('removes overlapping portions', () {
+      expect(
+          VersionConstraint.unionOf([
+            VersionRange(min: v010, max: v080),
+            VersionRange(min: v123, max: v130)
+          ]).difference(VersionConstraint.unionOf(
+              [VersionRange(min: v003, max: v072), VersionRange(min: v124)])),
+          equals(VersionConstraint.unionOf([
+            VersionRange(
+                min: v072.firstPreRelease, max: v080, includeMin: true),
+            VersionRange(min: v123, max: v124, includeMax: true)
+          ])));
+    });
+
+    test('removes multiple portions from the same range', () {
+      expect(
+          VersionConstraint.unionOf([
+            VersionRange(min: v010, max: v114),
+            VersionRange(min: v130, max: v200)
+          ]).difference(VersionConstraint.unionOf([v072, v080])),
+          equals(VersionConstraint.unionOf([
+            VersionRange(
+                min: v010, max: v072, alwaysIncludeMaxPreRelease: true),
+            VersionRange(
+                min: v072, max: v080, alwaysIncludeMaxPreRelease: true),
+            VersionRange(min: v080, max: v114),
+            VersionRange(min: v130, max: v200)
+          ])));
+    });
+
+    test('removes the same range from multiple ranges', () {
+      expect(
+          VersionConstraint.unionOf([
+            VersionRange(min: v010, max: v072),
+            VersionRange(min: v080, max: v123),
+            VersionRange(min: v124, max: v130),
+            VersionRange(min: v200, max: v234),
+            VersionRange(min: v250, max: v300)
+          ]).difference(VersionRange(min: v114, max: v201)),
+          equals(VersionConstraint.unionOf([
+            VersionRange(min: v010, max: v072),
+            VersionRange(min: v080, max: v114, includeMax: true),
+            VersionRange(
+                min: v201.firstPreRelease, max: v234, includeMin: true),
+            VersionRange(min: v250, max: v300)
+          ])));
+    });
+  });
+}

diff --git a/pkgs/pubspec_parse/.gitignore b/pkgs/pubspec_parse/.gitignore
new file mode 100644
index 0000000..ec8eae3
--- /dev/null
+++ b/pkgs/pubspec_parse/.gitignore

@@ -0,0 +1,4 @@
+# Don’t commit the following directories created by pub.
+.dart_tool/
+.packages
+pubspec.lock

diff --git a/pkgs/pubspec_parse/CHANGELOG.md b/pkgs/pubspec_parse/CHANGELOG.md
new file mode 100644
index 0000000..5aeb498
--- /dev/null
+++ b/pkgs/pubspec_parse/CHANGELOG.md

@@ -0,0 +1,110 @@
+## 1.5.0
+
+- Added fields to `Pubspec`: `executables`, `resolution`, `workspace`.
+- Require Dart 3.6
+- Update dependencies.
+
+## 1.4.0
+
+- Require Dart 3.2
+- Seal the `Dependency` class.
+- Set `Pubspec.environment` to non-nullable.
+- Remove deprecated package_api_docs rule
+- Move to `dart-lang/tools` monorepo.
+
+## 1.3.0
+
+- Require Dart 3.0
+- Added support for `ignored_advisories` field.
+- Added structural equality for `Dependency` subclasses and `HostedDetails`.
+
+## 1.2.3
+
+- Added topics to `pubspec.yaml`.
+
+## 1.2.2
+
+- Require Dart SDK >= 2.18.0
+- Required `json_annotation: ^4.8.0`
+- Added support for `topics` field.
+
+## 1.2.1
+
+- Added support for `funding` field.
+
+## 1.2.0
+
+- Added support for `screenshots` field.
+- Update `HostedDetails` to reflect how `hosted` dependencies are parsed in
+  Dart 2.15:
+   - Add `HostedDetails.declaredName` as the (optional) `name` property in a
+     `hosted` block.
+   - `HostedDetails.name` now falls back to the name of the dependency if no
+      name is declared in the block.
+- Require Dart SDK >= 2.14.0
+
+## 1.1.0
+
+- Export `HostedDetails` publicly.
+
+## 1.0.0
+
+- Migrate to null-safety.
+- Pubspec: `author` and `authors` are both now deprecated.
+  See https://dart.dev/tools/pub/pubspec#authorauthors
+
+## 0.1.8
+
+- Allow the latest `package:pub_semver`.
+
+## 0.1.7
+
+- Allow `package:yaml` `v3.x`.
+
+## 0.1.6
+
+- Update SDK requirement to `>=2.7.0 <3.0.0`.
+- Allow `package:json_annotation` `v4.x`.
+
+## 0.1.5
+
+- Update SDK requirement to `>=2.2.0 <3.0.0`.
+- Support the latest `package:json_annotation`.
+
+## 0.1.4
+
+- Added `lenient` named argument to `Pubspec.fromJson` to ignore format and type errors.
+
+## 0.1.3
+
+- Added support for `flutter`, `issue_tracker`, `publish_to`, and `repository`
+  fields.
+
+## 0.1.2+3
+
+- Support the latest version of `package:json_annotation`.
+
+## 0.1.2+2
+
+- Support `package:json_annotation` v1.
+
+## 0.1.2+1
+
+- Support the Dart 2 stable release.
+
+## 0.1.2
+
+- Allow superfluous `version` keys with `git` and `path` dependencies.
+- Improve errors when unsupported keys are provided in dependencies.
+- Provide better errors with invalid `sdk` dependency values.
+- Support "scp-like syntax" for Git SSH URIs in the form
+  `[user@]host.xz:path/to/repo.git/`.
+
+## 0.1.1
+
+- Fixed name collision with error type in latest `package:json_annotation`.
+- Improved parsing of hosted dependencies and environment constraints.
+
+## 0.1.0
+
+- Initial release.

diff --git a/pkgs/pubspec_parse/LICENSE b/pkgs/pubspec_parse/LICENSE
new file mode 100644
index 0000000..4d1ad40
--- /dev/null
+++ b/pkgs/pubspec_parse/LICENSE

@@ -0,0 +1,27 @@
+Copyright 2018, the Dart project authors.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+    * Neither the name of Google LLC nor the names of its
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

diff --git a/pkgs/pubspec_parse/README.md b/pkgs/pubspec_parse/README.md
new file mode 100644
index 0000000..1d04aa4
--- /dev/null
+++ b/pkgs/pubspec_parse/README.md

@@ -0,0 +1,12 @@
+[![Build Status](https://github.com/dart-lang/tools/actions/workflows/pubspec_parse.yaml/badge.svg)](https://github.com/dart-lang/tools/actions/workflows/pubspec_parse.yaml)
+[![pub package](https://img.shields.io/pub/v/pubspec_parse.svg)](https://pub.dev/packages/pubspec_parse)
+[![package publisher](https://img.shields.io/pub/publisher/pubspec_parse.svg)](https://pub.dev/packages/pubspec_parse/publisher)
+
+## What's this?
+
+Supports parsing `pubspec.yaml` files with robust error reporting and support
+for most of the documented features.
+
+## More information
+
+Read more about the [pubspec format](https://dart.dev/tools/pub/pubspec).

diff --git a/pkgs/pubspec_parse/analysis_options.yaml b/pkgs/pubspec_parse/analysis_options.yaml
new file mode 100644
index 0000000..93eeebf
--- /dev/null
+++ b/pkgs/pubspec_parse/analysis_options.yaml

@@ -0,0 +1,30 @@
+# https://dart.dev/guides/language/analysis-options
+include: package:dart_flutter_team_lints/analysis_options.yaml
+
+analyzer:
+  language:
+    strict-casts: true
+    strict-inference: true
+
+linter:
+  rules:
+    - avoid_bool_literals_in_conditional_expressions
+    - avoid_classes_with_only_static_members
+    - avoid_private_typedef_functions
+    - avoid_redundant_argument_values
+    - avoid_returning_this
+    - avoid_unused_constructor_parameters
+    - avoid_void_async
+    - cancel_subscriptions
+    - cascade_invocations
+    - join_return_with_assignment
+    - literal_only_boolean_expressions
+    - missing_whitespace_between_adjacent_strings
+    - no_adjacent_strings_in_list
+    - no_runtimeType_toString
+    - prefer_const_declarations
+    - prefer_expression_function_bodies
+    - prefer_final_locals
+    - require_trailing_commas
+    - unnecessary_await_in_return
+    - use_string_buffers

diff --git a/pkgs/pubspec_parse/build.yaml b/pkgs/pubspec_parse/build.yaml
new file mode 100644
index 0000000..2003bc2
--- /dev/null
+++ b/pkgs/pubspec_parse/build.yaml

@@ -0,0 +1,25 @@
+# Read about `build.yaml` at https://pub.dev/packages/build_config
+# To update generated code, run `pub run build_runner build`
+targets:
+  $default:
+    builders:
+      json_serializable:
+        generate_for:
+          - lib/src/pubspec.dart
+          - lib/src/dependency.dart
+        options:
+          any_map: true
+          checked: true
+          create_to_json: false
+          field_rename: snake
+
+      # The end-user of a builder which applies "source_gen|combining_builder"
+      # may configure the builder to ignore specific lints for their project
+      source_gen|combining_builder:
+        options:
+          ignore_for_file:
+          - deprecated_member_use_from_same_package
+          - lines_longer_than_80_chars
+          - require_trailing_commas
+          # https://github.com/google/json_serializable.dart/issues/945
+          - unnecessary_cast

diff --git a/pkgs/pubspec_parse/dart_test.yaml b/pkgs/pubspec_parse/dart_test.yaml
new file mode 100644
index 0000000..1d7ac69
--- /dev/null
+++ b/pkgs/pubspec_parse/dart_test.yaml

@@ -0,0 +1,3 @@
+tags:
+  presubmit-only:
+    skip: "Should only be run during presubmit"

diff --git a/pkgs/pubspec_parse/lib/pubspec_parse.dart b/pkgs/pubspec_parse/lib/pubspec_parse.dart
new file mode 100644
index 0000000..b5c12e4
--- /dev/null
+++ b/pkgs/pubspec_parse/lib/pubspec_parse.dart

@@ -0,0 +1,14 @@
+// Copyright (c) 2018, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+export 'src/dependency.dart'
+    show
+        Dependency,
+        GitDependency,
+        HostedDependency,
+        HostedDetails,
+        PathDependency,
+        SdkDependency;
+export 'src/pubspec.dart' show Pubspec;
+export 'src/screenshot.dart' show Screenshot;

diff --git a/pkgs/pubspec_parse/lib/src/dependency.dart b/pkgs/pubspec_parse/lib/src/dependency.dart
new file mode 100644
index 0000000..24c65ea
--- /dev/null
+++ b/pkgs/pubspec_parse/lib/src/dependency.dart

@@ -0,0 +1,277 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:collection/collection.dart';
+import 'package:json_annotation/json_annotation.dart';
+import 'package:pub_semver/pub_semver.dart';
+import 'package:yaml/yaml.dart';
+
+part 'dependency.g.dart';
+
+Map<String, Dependency> parseDeps(Map? source) =>
+    source?.map((k, v) {
+      final key = k as String;
+      Dependency? value;
+      try {
+        value = _fromJson(v, k);
+      } on CheckedFromJsonException catch (e) {
+        if (e.map is! YamlMap) {
+          // This is likely a "synthetic" map created from a String value
+          // Use `source` to throw this exception with an actual YamlMap and
+          // extract the associated error information.
+          throw CheckedFromJsonException(source, key, e.className!, e.message);
+        }
+        rethrow;
+      }
+
+      if (value == null) {
+        throw CheckedFromJsonException(
+          source,
+          key,
+          'Pubspec',
+          'Not a valid dependency value.',
+        );
+      }
+      return MapEntry(key, value);
+    }) ??
+    {};
+
+const _sourceKeys = ['sdk', 'git', 'path', 'hosted'];
+
+/// Returns `null` if the data could not be parsed.
+Dependency? _fromJson(Object? data, String name) {
+  if (data is String || data == null) {
+    return _$HostedDependencyFromJson({'version': data});
+  }
+
+  if (data is Map) {
+    final matchedKeys =
+        data.keys.cast<String>().where((key) => key != 'version').toList();
+
+    if (data.isEmpty || (matchedKeys.isEmpty && data.containsKey('version'))) {
+      return _$HostedDependencyFromJson(data);
+    } else {
+      final firstUnrecognizedKey =
+          matchedKeys.firstWhereOrNull((k) => !_sourceKeys.contains(k));
+
+      return $checkedNew<Dependency>('Dependency', data, () {
+        if (firstUnrecognizedKey != null) {
+          throw UnrecognizedKeysException(
+            [firstUnrecognizedKey],
+            data,
+            _sourceKeys,
+          );
+        }
+        if (matchedKeys.length > 1) {
+          throw CheckedFromJsonException(
+            data,
+            matchedKeys[1],
+            'Dependency',
+            'A dependency may only have one source.',
+          );
+        }
+
+        final key = matchedKeys.single;
+
+        return switch (key) {
+          'git' => GitDependency.fromData(data[key]),
+          'path' => PathDependency.fromData(data[key]),
+          'sdk' => _$SdkDependencyFromJson(data),
+          'hosted' => _$HostedDependencyFromJson(data)
+            ..hosted?._nameOfPackage = name,
+          _ => throw StateError('There is a bug in pubspec_parse.'),
+        };
+      });
+    }
+  }
+
+  // Not a String or a Map – return null so parent logic can throw proper error
+  return null;
+}
+
+sealed class Dependency {}
+
+@JsonSerializable()
+class SdkDependency extends Dependency {
+  final String sdk;
+  @JsonKey(fromJson: _constraintFromString)
+  final VersionConstraint version;
+
+  SdkDependency(this.sdk, {VersionConstraint? version})
+      : version = version ?? VersionConstraint.any;
+
+  @override
+  bool operator ==(Object other) =>
+      other is SdkDependency && other.sdk == sdk && other.version == version;
+
+  @override
+  int get hashCode => Object.hash(sdk, version);
+
+  @override
+  String toString() => 'SdkDependency: $sdk';
+}
+
+@JsonSerializable()
+class GitDependency extends Dependency {
+  @JsonKey(fromJson: parseGitUri)
+  final Uri url;
+  final String? ref;
+  final String? path;
+
+  GitDependency(this.url, {this.ref, this.path});
+
+  factory GitDependency.fromData(Object? data) {
+    if (data is String) {
+      data = {'url': data};
+    }
+
+    if (data is Map) {
+      return _$GitDependencyFromJson(data);
+    }
+
+    throw ArgumentError.value(data, 'git', 'Must be a String or a Map.');
+  }
+
+  @override
+  bool operator ==(Object other) =>
+      other is GitDependency &&
+      other.url == url &&
+      other.ref == ref &&
+      other.path == path;
+
+  @override
+  int get hashCode => Object.hash(url, ref, path);
+
+  @override
+  String toString() => 'GitDependency: url@$url';
+}
+
+Uri? parseGitUriOrNull(String? value) =>
+    value == null ? null : parseGitUri(value);
+
+Uri parseGitUri(String value) => _tryParseScpUri(value) ?? Uri.parse(value);
+
+/// Supports URIs like `[user@]host.xz:path/to/repo.git/`
+/// See https://git-scm.com/docs/git-clone#_git_urls_a_id_urls_a
+Uri? _tryParseScpUri(String value) {
+  final colonIndex = value.indexOf(':');
+
+  if (colonIndex < 0) {
+    return null;
+  } else if (colonIndex == value.indexOf('://')) {
+    // If the first colon is part of a scheme, it's not an scp-like URI
+    return null;
+  }
+  final slashIndex = value.indexOf('/');
+
+  if (slashIndex >= 0 && slashIndex < colonIndex) {
+    // Per docs: This syntax is only recognized if there are no slashes before
+    // the first colon. This helps differentiate a local path that contains a
+    // colon. For example the local path foo:bar could be specified as an
+    // absolute path or ./foo:bar to avoid being misinterpreted as an ssh url.
+    return null;
+  }
+
+  final atIndex = value.indexOf('@');
+  if (colonIndex > atIndex) {
+    final user = atIndex >= 0 ? value.substring(0, atIndex) : null;
+    final host = value.substring(atIndex + 1, colonIndex);
+    final path = value.substring(colonIndex + 1);
+    return Uri(scheme: 'ssh', userInfo: user, host: host, path: path);
+  }
+  return null;
+}
+
+class PathDependency extends Dependency {
+  final String path;
+
+  PathDependency(this.path);
+
+  factory PathDependency.fromData(Object? data) {
+    if (data is String) {
+      return PathDependency(data);
+    }
+    throw ArgumentError.value(data, 'path', 'Must be a String.');
+  }
+
+  @override
+  bool operator ==(Object other) =>
+      other is PathDependency && other.path == path;
+
+  @override
+  int get hashCode => path.hashCode;
+
+  @override
+  String toString() => 'PathDependency: path@$path';
+}
+
+@JsonSerializable(disallowUnrecognizedKeys: true)
+class HostedDependency extends Dependency {
+  @JsonKey(fromJson: _constraintFromString)
+  final VersionConstraint version;
+
+  @JsonKey(disallowNullValue: true)
+  final HostedDetails? hosted;
+
+  HostedDependency({VersionConstraint? version, this.hosted})
+      : version = version ?? VersionConstraint.any;
+
+  @override
+  bool operator ==(Object other) =>
+      other is HostedDependency &&
+      other.version == version &&
+      other.hosted == hosted;
+
+  @override
+  int get hashCode => Object.hash(version, hosted);
+
+  @override
+  String toString() => 'HostedDependency: $version';
+}
+
+@JsonSerializable(disallowUnrecognizedKeys: true)
+class HostedDetails {
+  /// The name of the target dependency as declared in a `hosted` block.
+  ///
+  /// This may be null if no explicit name is present, for instance because the
+  /// hosted dependency was declared as a string (`hosted: pub.example.org`).
+  @JsonKey(name: 'name')
+  final String? declaredName;
+
+  @JsonKey(fromJson: parseGitUriOrNull, disallowNullValue: true)
+  final Uri? url;
+
+  @JsonKey(includeFromJson: false, includeToJson: false)
+  String? _nameOfPackage;
+
+  /// The name of this package on the package repository.
+  ///
+  /// If this hosted block has a [declaredName], that one will be used.
+  /// Otherwise, the name will be inferred from the surrounding package name.
+  String get name => declaredName ?? _nameOfPackage!;
+
+  HostedDetails(this.declaredName, this.url);
+
+  factory HostedDetails.fromJson(Object data) {
+    if (data is String) {
+      data = {'url': data};
+    }
+
+    if (data is Map) {
+      return _$HostedDetailsFromJson(data);
+    }
+
+    throw ArgumentError.value(data, 'hosted', 'Must be a Map or String.');
+  }
+
+  @override
+  bool operator ==(Object other) =>
+      other is HostedDetails && other.name == name && other.url == url;
+
+  @override
+  int get hashCode => Object.hash(name, url);
+}
+
+VersionConstraint _constraintFromString(String? input) =>
+    input == null ? VersionConstraint.any : VersionConstraint.parse(input);

diff --git a/pkgs/pubspec_parse/lib/src/dependency.g.dart b/pkgs/pubspec_parse/lib/src/dependency.g.dart
new file mode 100644
index 0000000..1a504f1
--- /dev/null
+++ b/pkgs/pubspec_parse/lib/src/dependency.g.dart

@@ -0,0 +1,72 @@
+// GENERATED CODE - DO NOT MODIFY BY HAND
+
+// ignore_for_file: deprecated_member_use_from_same_package, lines_longer_than_80_chars, require_trailing_commas, unnecessary_cast
+
+part of 'dependency.dart';
+
+// **************************************************************************
+// JsonSerializableGenerator
+// **************************************************************************
+
+SdkDependency _$SdkDependencyFromJson(Map json) => $checkedCreate(
+      'SdkDependency',
+      json,
+      ($checkedConvert) {
+        final val = SdkDependency(
+          $checkedConvert('sdk', (v) => v as String),
+          version: $checkedConvert(
+              'version', (v) => _constraintFromString(v as String?)),
+        );
+        return val;
+      },
+    );
+
+GitDependency _$GitDependencyFromJson(Map json) => $checkedCreate(
+      'GitDependency',
+      json,
+      ($checkedConvert) {
+        final val = GitDependency(
+          $checkedConvert('url', (v) => parseGitUri(v as String)),
+          ref: $checkedConvert('ref', (v) => v as String?),
+          path: $checkedConvert('path', (v) => v as String?),
+        );
+        return val;
+      },
+    );
+
+HostedDependency _$HostedDependencyFromJson(Map json) => $checkedCreate(
+      'HostedDependency',
+      json,
+      ($checkedConvert) {
+        $checkKeys(
+          json,
+          allowedKeys: const ['version', 'hosted'],
+          disallowNullValues: const ['hosted'],
+        );
+        final val = HostedDependency(
+          version: $checkedConvert(
+              'version', (v) => _constraintFromString(v as String?)),
+          hosted: $checkedConvert('hosted',
+              (v) => v == null ? null : HostedDetails.fromJson(v as Object)),
+        );
+        return val;
+      },
+    );
+
+HostedDetails _$HostedDetailsFromJson(Map json) => $checkedCreate(
+      'HostedDetails',
+      json,
+      ($checkedConvert) {
+        $checkKeys(
+          json,
+          allowedKeys: const ['name', 'url'],
+          disallowNullValues: const ['url'],
+        );
+        final val = HostedDetails(
+          $checkedConvert('name', (v) => v as String?),
+          $checkedConvert('url', (v) => parseGitUriOrNull(v as String?)),
+        );
+        return val;
+      },
+      fieldKeyMap: const {'declaredName': 'name'},
+    );

diff --git a/pkgs/pubspec_parse/lib/src/pubspec.dart b/pkgs/pubspec_parse/lib/src/pubspec.dart
new file mode 100644
index 0000000..eb77908
--- /dev/null
+++ b/pkgs/pubspec_parse/lib/src/pubspec.dart

@@ -0,0 +1,258 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:checked_yaml/checked_yaml.dart';
+import 'package:json_annotation/json_annotation.dart';
+import 'package:pub_semver/pub_semver.dart';
+
+import 'dependency.dart';
+import 'screenshot.dart';
+
+part 'pubspec.g.dart';
+
+@JsonSerializable()
+class Pubspec {
+  // TODO: executables
+
+  final String name;
+
+  @JsonKey(fromJson: _versionFromString)
+  final Version? version;
+
+  final String? description;
+
+  /// This should be a URL pointing to the website for the package.
+  final String? homepage;
+
+  /// Specifies where to publish this package.
+  ///
+  /// Accepted values: `null`, `'none'` or an `http` or `https` URL.
+  ///
+  /// [More information](https://dart.dev/tools/pub/pubspec#publish_to).
+  final String? publishTo;
+
+  /// Optional field to specify the source code repository of the package.
+  /// Useful when a package has both a home page and a repository.
+  final Uri? repository;
+
+  /// Optional field to a web page where developers can report new issues or
+  /// view existing ones.
+  final Uri? issueTracker;
+
+  /// Optional field to list the URLs where the package authors accept
+  /// support or funding.
+  final List<Uri>? funding;
+
+  /// Optional field to list the topics that this packages belongs to.
+  final List<String>? topics;
+
+  /// Optional field to list advisories to be ignored by the client.
+  final List<String>? ignoredAdvisories;
+
+  /// Optional field for specifying included screenshot files.
+  @JsonKey(fromJson: parseScreenshots)
+  final List<Screenshot>? screenshots;
+
+  /// If there is exactly 1 value in [authors], returns it.
+  ///
+  /// If there are 0 or more than 1, returns `null`.
+  @Deprecated(
+    'See https://dart.dev/tools/pub/pubspec#authorauthors',
+  )
+  String? get author {
+    if (authors.length == 1) {
+      return authors.single;
+    }
+    return null;
+  }
+
+  @Deprecated(
+    'See https://dart.dev/tools/pub/pubspec#authorauthors',
+  )
+  final List<String> authors;
+  final String? documentation;
+
+  @JsonKey(fromJson: _environmentMap)
+  final Map<String, VersionConstraint?> environment;
+
+  @JsonKey(fromJson: parseDeps)
+  final Map<String, Dependency> dependencies;
+
+  @JsonKey(fromJson: parseDeps)
+  final Map<String, Dependency> devDependencies;
+
+  @JsonKey(fromJson: parseDeps)
+  final Map<String, Dependency> dependencyOverrides;
+
+  /// Optional configuration specific to [Flutter](https://flutter.io/)
+  /// packages.
+  ///
+  /// May include
+  /// [assets](https://flutter.io/docs/development/ui/assets-and-images)
+  /// and other settings.
+  final Map<String, dynamic>? flutter;
+
+  /// Optional field to specify executables
+  @JsonKey(fromJson: _executablesMap)
+  final Map<String, String?> executables;
+
+  /// If this package is a Pub Workspace, this field lists the sub-packages.
+  final List<String>? workspace;
+
+  /// Specifies how to resolve dependencies with the surrounding Pub Workspace.
+  final String? resolution;
+
+  /// If [author] and [authors] are both provided, their values are combined
+  /// with duplicates eliminated.
+  Pubspec(
+    this.name, {
+    this.version,
+    this.publishTo,
+    @Deprecated(
+      'See https://dart.dev/tools/pub/pubspec#authorauthors',
+    )
+    String? author,
+    @Deprecated(
+      'See https://dart.dev/tools/pub/pubspec#authorauthors',
+    )
+    List<String>? authors,
+    Map<String, VersionConstraint?>? environment,
+    this.homepage,
+    this.repository,
+    this.issueTracker,
+    this.funding,
+    this.topics,
+    this.ignoredAdvisories,
+    this.screenshots,
+    this.documentation,
+    this.description,
+    this.workspace,
+    this.resolution,
+    Map<String, Dependency>? dependencies,
+    Map<String, Dependency>? devDependencies,
+    Map<String, Dependency>? dependencyOverrides,
+    this.flutter,
+    Map<String, String?>? executables,
+  })  :
+        // ignore: deprecated_member_use_from_same_package
+        authors = _normalizeAuthors(author, authors),
+        environment = environment ?? const {},
+        dependencies = dependencies ?? const {},
+        devDependencies = devDependencies ?? const {},
+        executables = executables ?? const {},
+        dependencyOverrides = dependencyOverrides ?? const {} {
+    if (name.isEmpty) {
+      throw ArgumentError.value(name, 'name', '"name" cannot be empty.');
+    }
+
+    if (publishTo != null && publishTo != 'none') {
+      try {
+        final targetUri = Uri.parse(publishTo!);
+        if (!(targetUri.isScheme('http') || targetUri.isScheme('https'))) {
+          throw const FormatException('Must be an http or https URL.');
+        }
+      } on FormatException catch (e) {
+        throw ArgumentError.value(publishTo, 'publishTo', e.message);
+      }
+    }
+  }
+
+  factory Pubspec.fromJson(Map json, {bool lenient = false}) {
+    if (lenient) {
+      while (json.isNotEmpty) {
+        // Attempting to remove top-level properties that cause parsing errors.
+        try {
+          return _$PubspecFromJson(json);
+        } on CheckedFromJsonException catch (e) {
+          if (e.map == json && json.containsKey(e.key)) {
+            json = Map.from(json)..remove(e.key);
+            continue;
+          }
+          rethrow;
+        }
+      }
+    }
+
+    return _$PubspecFromJson(json);
+  }
+
+  /// Parses source [yaml] into [Pubspec].
+  ///
+  /// When [lenient] is set, top-level property-parsing or type cast errors are
+  /// ignored and `null` values are returned.
+  factory Pubspec.parse(String yaml, {Uri? sourceUrl, bool lenient = false}) =>
+      checkedYamlDecode(
+        yaml,
+        (map) => Pubspec.fromJson(map!, lenient: lenient),
+        sourceUrl: sourceUrl,
+      );
+
+  static List<String> _normalizeAuthors(String? author, List<String>? authors) {
+    final value = <String>{
+      if (author != null) author,
+      ...?authors,
+    };
+    return value.toList();
+  }
+}
+
+Version? _versionFromString(String? input) =>
+    input == null ? null : Version.parse(input);
+
+Map<String, VersionConstraint?> _environmentMap(Map? source) =>
+    source?.map((k, value) {
+      final key = k as String;
+      if (key == 'dart') {
+        // github.com/dart-lang/pub/blob/d84173eeb03c3/lib/src/pubspec.dart#L342
+        // 'dart' is not allowed as a key!
+        throw CheckedFromJsonException(
+          source,
+          'dart',
+          'VersionConstraint',
+          'Use "sdk" to for Dart SDK constraints.',
+          badKey: true,
+        );
+      }
+
+      VersionConstraint? constraint;
+      if (value == null) {
+        constraint = null;
+      } else if (value is String) {
+        try {
+          constraint = VersionConstraint.parse(value);
+        } on FormatException catch (e) {
+          throw CheckedFromJsonException(source, key, 'Pubspec', e.message);
+        }
+
+        return MapEntry(key, constraint);
+      } else {
+        throw CheckedFromJsonException(
+          source,
+          key,
+          'VersionConstraint',
+          '`$value` is not a String.',
+        );
+      }
+
+      return MapEntry(key, constraint);
+    }) ??
+    {};
+
+Map<String, String?> _executablesMap(Map? source) =>
+    source?.map((k, value) {
+      final key = k as String;
+      if (value == null) {
+        return MapEntry(key, null);
+      } else if (value is String) {
+        return MapEntry(key, value);
+      } else {
+        throw CheckedFromJsonException(
+          source,
+          key,
+          'String',
+          '`$value` is not a String.',
+        );
+      }
+    }) ??
+    {};

diff --git a/pkgs/pubspec_parse/lib/src/pubspec.g.dart b/pkgs/pubspec_parse/lib/src/pubspec.g.dart
new file mode 100644
index 0000000..58e015a
--- /dev/null
+++ b/pkgs/pubspec_parse/lib/src/pubspec.g.dart

@@ -0,0 +1,69 @@
+// GENERATED CODE - DO NOT MODIFY BY HAND
+
+// ignore_for_file: deprecated_member_use_from_same_package, lines_longer_than_80_chars, require_trailing_commas, unnecessary_cast
+
+part of 'pubspec.dart';
+
+// **************************************************************************
+// JsonSerializableGenerator
+// **************************************************************************
+
+Pubspec _$PubspecFromJson(Map json) => $checkedCreate(
+      'Pubspec',
+      json,
+      ($checkedConvert) {
+        final val = Pubspec(
+          $checkedConvert('name', (v) => v as String),
+          version: $checkedConvert(
+              'version', (v) => _versionFromString(v as String?)),
+          publishTo: $checkedConvert('publish_to', (v) => v as String?),
+          author: $checkedConvert('author', (v) => v as String?),
+          authors: $checkedConvert('authors',
+              (v) => (v as List<dynamic>?)?.map((e) => e as String).toList()),
+          environment:
+              $checkedConvert('environment', (v) => _environmentMap(v as Map?)),
+          homepage: $checkedConvert('homepage', (v) => v as String?),
+          repository: $checkedConvert(
+              'repository', (v) => v == null ? null : Uri.parse(v as String)),
+          issueTracker: $checkedConvert('issue_tracker',
+              (v) => v == null ? null : Uri.parse(v as String)),
+          funding: $checkedConvert(
+              'funding',
+              (v) => (v as List<dynamic>?)
+                  ?.map((e) => Uri.parse(e as String))
+                  .toList()),
+          topics: $checkedConvert('topics',
+              (v) => (v as List<dynamic>?)?.map((e) => e as String).toList()),
+          ignoredAdvisories: $checkedConvert('ignored_advisories',
+              (v) => (v as List<dynamic>?)?.map((e) => e as String).toList()),
+          screenshots: $checkedConvert(
+              'screenshots', (v) => parseScreenshots(v as List?)),
+          documentation: $checkedConvert('documentation', (v) => v as String?),
+          description: $checkedConvert('description', (v) => v as String?),
+          workspace: $checkedConvert('workspace',
+              (v) => (v as List<dynamic>?)?.map((e) => e as String).toList()),
+          resolution: $checkedConvert('resolution', (v) => v as String?),
+          dependencies:
+              $checkedConvert('dependencies', (v) => parseDeps(v as Map?)),
+          devDependencies:
+              $checkedConvert('dev_dependencies', (v) => parseDeps(v as Map?)),
+          dependencyOverrides: $checkedConvert(
+              'dependency_overrides', (v) => parseDeps(v as Map?)),
+          flutter: $checkedConvert(
+              'flutter',
+              (v) => (v as Map?)?.map(
+                    (k, e) => MapEntry(k as String, e),
+                  )),
+          executables:
+              $checkedConvert('executables', (v) => _executablesMap(v as Map?)),
+        );
+        return val;
+      },
+      fieldKeyMap: const {
+        'publishTo': 'publish_to',
+        'issueTracker': 'issue_tracker',
+        'ignoredAdvisories': 'ignored_advisories',
+        'devDependencies': 'dev_dependencies',
+        'dependencyOverrides': 'dependency_overrides'
+      },
+    );

diff --git a/pkgs/pubspec_parse/lib/src/screenshot.dart b/pkgs/pubspec_parse/lib/src/screenshot.dart
new file mode 100644
index 0000000..f5f0be2
--- /dev/null
+++ b/pkgs/pubspec_parse/lib/src/screenshot.dart

@@ -0,0 +1,65 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:json_annotation/json_annotation.dart';
+
+@JsonSerializable()
+class Screenshot {
+  final String description;
+  final String path;
+
+  Screenshot(this.description, this.path);
+}
+
+List<Screenshot> parseScreenshots(List? input) {
+  final res = <Screenshot>[];
+  if (input == null) {
+    return res;
+  }
+
+  for (final e in input) {
+    if (e is! Map) continue;
+
+    final description = e['description'];
+    if (description == null) {
+      throw CheckedFromJsonException(
+        e,
+        'description',
+        'Screenshot',
+        'Missing required key `description`',
+      );
+    }
+
+    if (description is! String) {
+      throw CheckedFromJsonException(
+        e,
+        'description',
+        'Screenshot',
+        '`$description` is not a String',
+      );
+    }
+
+    final path = e['path'];
+    if (path == null) {
+      throw CheckedFromJsonException(
+        e,
+        'path',
+        'Screenshot',
+        'Missing required key `path`',
+      );
+    }
+
+    if (path is! String) {
+      throw CheckedFromJsonException(
+        e,
+        'path',
+        'Screenshot',
+        '`$path` is not a String',
+      );
+    }
+
+    res.add(Screenshot(description, path));
+  }
+  return res;
+}

diff --git a/pkgs/pubspec_parse/pubspec.yaml b/pkgs/pubspec_parse/pubspec.yaml
new file mode 100644
index 0000000..73a1117
--- /dev/null
+++ b/pkgs/pubspec_parse/pubspec.yaml

@@ -0,0 +1,32 @@
+name: pubspec_parse
+version: 1.5.0
+description: >-
+  Simple package for parsing pubspec.yaml files with a type-safe API and rich
+  error reporting.
+repository: https://github.com/dart-lang/tools/tree/main/pkgs/pubspec_parse
+
+topics:
+- dart-pub
+
+environment:
+  sdk: ^3.6.0
+
+dependencies:
+  checked_yaml: ^2.0.1
+  collection: ^1.19.0
+  json_annotation: ^4.9.0
+  pub_semver: ^2.1.4
+  yaml: ^3.0.0
+
+dev_dependencies:
+  build_runner: ^2.4.6
+  build_verify: ^3.0.0
+  dart_flutter_team_lints: ^3.0.0
+  json_serializable: ^6.9.1
+  path: ^1.9.0
+  # Needed because we are configuring `combining_builder`
+  source_gen: ^2.0.0
+  stack_trace: ^1.10.0
+  test: ^1.24.4
+  test_descriptor: ^2.0.0
+  test_process: ^2.0.0

diff --git a/pkgs/pubspec_parse/test/dependency_test.dart b/pkgs/pubspec_parse/test/dependency_test.dart
new file mode 100644
index 0000000..f1e4f57
--- /dev/null
+++ b/pkgs/pubspec_parse/test/dependency_test.dart

@@ -0,0 +1,446 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:io';
+
+import 'package:pub_semver/pub_semver.dart';
+import 'package:pubspec_parse/pubspec_parse.dart';
+import 'package:test/test.dart';
+
+import 'test_utils.dart';
+
+void main() {
+  group('hosted', _hostedDependency);
+  group('git', _gitDependency);
+  group('sdk', _sdkDependency);
+  group('path', _pathDependency);
+
+  group('errors', () {
+    test('List', () {
+      _expectThrows(
+        [],
+        r'''
+line 4, column 10: Unsupported value for "dep". Not a valid dependency value.
+  ╷
+4 │   "dep": []
+  │          ^^
+  ╵''',
+      );
+    });
+
+    test('int', () {
+      _expectThrows(
+        42,
+        r'''
+line 4, column 10: Unsupported value for "dep". Not a valid dependency value.
+  ╷
+4 │     "dep": 42
+  │ ┌──────────^
+5 │ │  }
+  │ └─^
+  ╵''',
+      );
+    });
+
+    test('map with too many keys', () {
+      _expectThrows(
+        {'path': 'a', 'git': 'b'},
+        r'''
+line 6, column 11: Unsupported value for "git". A dependency may only have one source.
+  ╷
+6 │    "git": "b"
+  │           ^^^
+  ╵''',
+      );
+    });
+
+    test('map with unsupported keys', () {
+      _expectThrows(
+        {'bob': 'a', 'jones': 'b'},
+        r'''
+line 5, column 4: Unrecognized keys: [bob]; supported keys: [sdk, git, path, hosted]
+  ╷
+5 │    "bob": "a",
+  │    ^^^^^
+  ╵''',
+      );
+    });
+  });
+}
+
+void _hostedDependency() {
+  test('null', () async {
+    final dep = await _dependency<HostedDependency>(null);
+    expect(dep.version.toString(), 'any');
+    expect(dep.hosted, isNull);
+    expect(dep.toString(), 'HostedDependency: any');
+  });
+
+  test('empty map', () async {
+    final dep = await _dependency<HostedDependency>({});
+    expect(dep.hosted, isNull);
+    expect(dep.toString(), 'HostedDependency: any');
+  });
+
+  test('string version', () async {
+    final dep = await _dependency<HostedDependency>('^1.0.0');
+    expect(dep.version.toString(), '^1.0.0');
+    expect(dep.hosted, isNull);
+    expect(dep.toString(), 'HostedDependency: ^1.0.0');
+  });
+
+  test('bad string version', () {
+    _expectThrows(
+      'not a version',
+      r'''
+line 4, column 10: Unsupported value for "dep". Could not parse version "not a version". Unknown text at "not a version".
+  ╷
+4 │   "dep": "not a version"
+  │          ^^^^^^^^^^^^^^^
+  ╵''',
+    );
+  });
+
+  test('map w/ just version', () async {
+    final dep = await _dependency<HostedDependency>({'version': '^1.0.0'});
+    expect(dep.version.toString(), '^1.0.0');
+    expect(dep.hosted, isNull);
+    expect(dep.toString(), 'HostedDependency: ^1.0.0');
+  });
+
+  test('map w/ version and hosted as Map', () async {
+    final dep = await _dependency<HostedDependency>({
+      'version': '^1.0.0',
+      'hosted': {'name': 'hosted_name', 'url': 'https://hosted_url'},
+    });
+    expect(dep.version.toString(), '^1.0.0');
+    expect(dep.hosted!.name, 'hosted_name');
+    expect(dep.hosted!.url.toString(), 'https://hosted_url');
+    expect(dep.toString(), 'HostedDependency: ^1.0.0');
+  });
+
+  test('map /w hosted as a map without name', () async {
+    final dep = await _dependency<HostedDependency>(
+      {
+        'version': '^1.0.0',
+        'hosted': {'url': 'https://hosted_url'},
+      },
+      skipTryPub: true, // todo: Unskip once pub supports this syntax
+    );
+    expect(dep.version.toString(), '^1.0.0');
+    expect(dep.hosted!.declaredName, isNull);
+    expect(dep.hosted!.name, 'dep');
+    expect(dep.hosted!.url.toString(), 'https://hosted_url');
+    expect(dep.toString(), 'HostedDependency: ^1.0.0');
+  });
+
+  test('map w/ bad version value', () {
+    _expectThrows(
+      {
+        'version': 'not a version',
+        'hosted': {'name': 'hosted_name', 'url': 'hosted_url'},
+      },
+      r'''
+line 5, column 15: Unsupported value for "version". Could not parse version "not a version". Unknown text at "not a version".
+  ╷
+5 │    "version": "not a version",
+  │               ^^^^^^^^^^^^^^^
+  ╵''',
+    );
+  });
+
+  test('map w/ extra keys should fail', () {
+    _expectThrows(
+      {
+        'version': '^1.0.0',
+        'hosted': {'name': 'hosted_name', 'url': 'hosted_url'},
+        'not_supported': null,
+      },
+      r'''
+line 10, column 4: Unrecognized keys: [not_supported]; supported keys: [sdk, git, path, hosted]
+   ╷
+10 │    "not_supported": null
+   │    ^^^^^^^^^^^^^^^
+   ╵''',
+    );
+  });
+
+  test('map w/ version and hosted as String', () async {
+    final dep = await _dependency<HostedDependency>(
+      {'version': '^1.0.0', 'hosted': 'hosted_url'},
+      skipTryPub: true, // todo: Unskip once put supports this
+    );
+    expect(dep.version.toString(), '^1.0.0');
+    expect(dep.hosted!.declaredName, isNull);
+    expect(dep.hosted!.name, 'dep');
+    expect(dep.hosted!.url, Uri.parse('hosted_url'));
+    expect(dep.toString(), 'HostedDependency: ^1.0.0');
+  });
+
+  test('map w/ hosted as String', () async {
+    final dep = await _dependency<HostedDependency>({'hosted': 'hosted_url'});
+    expect(dep.version, VersionConstraint.any);
+    expect(dep.hosted!.declaredName, isNull);
+    expect(dep.hosted!.name, 'dep');
+    expect(dep.hosted!.url, Uri.parse('hosted_url'));
+    expect(dep.toString(), 'HostedDependency: any');
+  });
+
+  test('map w/ null hosted should error', () {
+    _expectThrows(
+      {'hosted': null},
+      r'''
+line 5, column 4: These keys had `null` values, which is not allowed: [hosted]
+  ╷
+5 │    "hosted": null
+  │    ^^^^^^^^
+  ╵''',
+    );
+  });
+
+  test('map w/ null version is fine', () async {
+    final dep = await _dependency<HostedDependency>({'version': null});
+    expect(dep.version, VersionConstraint.any);
+    expect(dep.hosted, isNull);
+    expect(dep.toString(), 'HostedDependency: any');
+  });
+}
+
+void _sdkDependency() {
+  test('without version', () async {
+    final dep = await _dependency<SdkDependency>({'sdk': 'flutter'});
+    expect(dep.sdk, 'flutter');
+    expect(dep.version, VersionConstraint.any);
+    expect(dep.toString(), 'SdkDependency: flutter');
+  });
+
+  test('with version', () async {
+    final dep = await _dependency<SdkDependency>(
+      {'sdk': 'flutter', 'version': '>=1.2.3 <2.0.0'},
+    );
+    expect(dep.sdk, 'flutter');
+    expect(dep.version.toString(), '>=1.2.3 <2.0.0');
+    expect(dep.toString(), 'SdkDependency: flutter');
+  });
+
+  test('null content', () {
+    _expectThrowsContaining(
+      {'sdk': null},
+      r"type 'Null' is not a subtype of type 'String'",
+    );
+  });
+
+  test('number content', () {
+    _expectThrowsContaining(
+      {'sdk': 42},
+      r"type 'int' is not a subtype of type 'String'",
+    );
+  });
+}
+
+void _gitDependency() {
+  test('string', () async {
+    final dep = await _dependency<GitDependency>({'git': 'url'});
+    expect(dep.url.toString(), 'url');
+    expect(dep.path, isNull);
+    expect(dep.ref, isNull);
+    expect(dep.toString(), 'GitDependency: url@url');
+  });
+
+  test('string with version key is ignored', () async {
+    // Regression test for https://github.com/dart-lang/pubspec_parse/issues/13
+    final dep =
+        await _dependency<GitDependency>({'git': 'url', 'version': '^1.2.3'});
+    expect(dep.url.toString(), 'url');
+    expect(dep.path, isNull);
+    expect(dep.ref, isNull);
+    expect(dep.toString(), 'GitDependency: url@url');
+  });
+
+  test('string with user@ URL', () async {
+    final skipTryParse = Platform.environment.containsKey('TRAVIS');
+    if (skipTryParse) {
+      print('FYI: not validating git@ URI on travis due to failure');
+    }
+    final dep = await _dependency<GitDependency>(
+      {'git': 'git@localhost:dep.git'},
+      skipTryPub: skipTryParse,
+    );
+    expect(dep.url.toString(), 'ssh://git@localhost/dep.git');
+    expect(dep.path, isNull);
+    expect(dep.ref, isNull);
+    expect(dep.toString(), 'GitDependency: url@ssh://git@localhost/dep.git');
+  });
+
+  test('string with random extra key fails', () {
+    _expectThrows(
+      {'git': 'url', 'bob': '^1.2.3'},
+      r'''
+line 6, column 4: Unrecognized keys: [bob]; supported keys: [sdk, git, path, hosted]
+  ╷
+6 │    "bob": "^1.2.3"
+  │    ^^^^^
+  ╵''',
+    );
+  });
+
+  test('map', () async {
+    final dep = await _dependency<GitDependency>({
+      'git': {'url': 'url', 'path': 'path', 'ref': 'ref'},
+    });
+    expect(dep.url.toString(), 'url');
+    expect(dep.path, 'path');
+    expect(dep.ref, 'ref');
+    expect(dep.toString(), 'GitDependency: url@url');
+  });
+
+  test('git - null content', () {
+    _expectThrows(
+      {'git': null},
+      r'''
+line 5, column 11: Unsupported value for "git". Must be a String or a Map.
+  ╷
+5 │      "git": null
+  │ ┌───────────^
+6 │ │   }
+  │ └──^
+  ╵''',
+    );
+  });
+
+  test('git - int content', () {
+    _expectThrows(
+      {'git': 42},
+      r'''
+line 5, column 11: Unsupported value for "git". Must be a String or a Map.
+  ╷
+5 │      "git": 42
+  │ ┌───────────^
+6 │ │   }
+  │ └──^
+  ╵''',
+    );
+  });
+
+  test('git - empty map', () {
+    _expectThrowsContaining(
+      {'git': <String, dynamic>{}},
+      r"type 'Null' is not a subtype of type 'String'",
+    );
+  });
+
+  test('git - null url', () {
+    _expectThrowsContaining(
+      {
+        'git': {'url': null},
+      },
+      r"type 'Null' is not a subtype of type 'String'",
+    );
+  });
+
+  test('git - int url', () {
+    _expectThrowsContaining(
+      {
+        'git': {'url': 42},
+      },
+      r"type 'int' is not a subtype of type 'String'",
+    );
+  });
+}
+
+void _pathDependency() {
+  test('valid', () async {
+    final dep = await _dependency<PathDependency>({'path': '../path'});
+    expect(dep.path, '../path');
+    expect(dep.toString(), 'PathDependency: path@../path');
+  });
+
+  test('valid with version key is ignored', () async {
+    final dep = await _dependency<PathDependency>(
+      {'path': '../path', 'version': '^1.2.3'},
+    );
+    expect(dep.path, '../path');
+    expect(dep.toString(), 'PathDependency: path@../path');
+  });
+
+  test('valid with random extra key fails', () {
+    _expectThrows(
+      {'path': '../path', 'bob': '^1.2.3'},
+      r'''
+line 6, column 4: Unrecognized keys: [bob]; supported keys: [sdk, git, path, hosted]
+  ╷
+6 │    "bob": "^1.2.3"
+  │    ^^^^^
+  ╵''',
+    );
+  });
+
+  test('null content', () {
+    _expectThrows(
+      {'path': null},
+      r'''
+line 5, column 12: Unsupported value for "path". Must be a String.
+  ╷
+5 │      "path": null
+  │ ┌────────────^
+6 │ │   }
+  │ └──^
+  ╵''',
+    );
+  });
+
+  test('int content', () {
+    _expectThrows(
+      {'path': 42},
+      r'''
+line 5, column 12: Unsupported value for "path". Must be a String.
+  ╷
+5 │      "path": 42
+  │ ┌────────────^
+6 │ │   }
+  │ └──^
+  ╵''',
+    );
+  });
+}
+
+void _expectThrows(Object content, String expectedError) {
+  expectParseThrows(
+    {
+      'name': 'sample',
+      'dependencies': {'dep': content},
+    },
+    expectedError,
+  );
+}
+
+void _expectThrowsContaining(Object content, String errorText) {
+  expectParseThrowsContaining(
+    {
+      'name': 'sample',
+      'dependencies': {'dep': content},
+    },
+    errorText,
+  );
+}
+
+Future<T> _dependency<T extends Dependency>(
+  Object? content, {
+  bool skipTryPub = false,
+}) async {
+  final value = await parse(
+    {
+      ...defaultPubspec,
+      'dependencies': {'dep': content},
+    },
+    skipTryPub: skipTryPub,
+  );
+  expect(value.name, 'sample');
+  expect(value.dependencies, hasLength(1));
+
+  final entry = value.dependencies.entries.single;
+  expect(entry.key, 'dep');
+
+  return entry.value as T;
+}

diff --git a/pkgs/pubspec_parse/test/ensure_build_test.dart b/pkgs/pubspec_parse/test/ensure_build_test.dart
new file mode 100644
index 0000000..0e4371c
--- /dev/null
+++ b/pkgs/pubspec_parse/test/ensure_build_test.dart

@@ -0,0 +1,18 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+@Timeout.factor(2)
+@TestOn('vm')
+@Tags(['presubmit-only'])
+library;
+
+import 'package:build_verify/build_verify.dart';
+import 'package:test/test.dart';
+
+void main() {
+  test(
+    'ensure_build',
+    () => expectBuildClean(packageRelativeDirectory: 'pkgs/pubspec_parse/'),
+  );
+}

diff --git a/pkgs/pubspec_parse/test/git_uri_test.dart b/pkgs/pubspec_parse/test/git_uri_test.dart
new file mode 100644
index 0000000..be89ba8
--- /dev/null
+++ b/pkgs/pubspec_parse/test/git_uri_test.dart

@@ -0,0 +1,25 @@
+import 'package:pubspec_parse/src/dependency.dart';
+import 'package:test/test.dart';
+
+void main() {
+  for (var item in {
+    'git@github.com:google/grinder.dart.git':
+        'ssh://git@github.com/google/grinder.dart.git',
+    'host.xz:path/to/repo.git/': 'ssh://host.xz/path/to/repo.git/',
+    'http:path/to/repo.git/': 'ssh://http/path/to/repo.git/',
+    'file:path/to/repo.git/': 'ssh://file/path/to/repo.git/',
+    './foo:bar': 'foo%3Abar',
+    '/path/to/repo.git/': '/path/to/repo.git/',
+    'file:///path/to/repo.git/': 'file:///path/to/repo.git/',
+  }.entries) {
+    test(item.key, () {
+      final uri = parseGitUri(item.key);
+
+      printOnFailure(
+        [uri.scheme, uri.userInfo, uri.host, uri.port, uri.path].join('\n'),
+      );
+
+      expect(uri, Uri.parse(item.value));
+    });
+  }
+}

diff --git a/pkgs/pubspec_parse/test/parse_test.dart b/pkgs/pubspec_parse/test/parse_test.dart
new file mode 100644
index 0000000..e0698af
--- /dev/null
+++ b/pkgs/pubspec_parse/test/parse_test.dart

@@ -0,0 +1,827 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// ignore_for_file: deprecated_member_use_from_same_package
+// ignore_for_file: lines_longer_than_80_chars
+
+import 'package:pub_semver/pub_semver.dart';
+import 'package:test/test.dart';
+
+import 'test_utils.dart';
+
+void main() {
+  test('minimal set values', () async {
+    final value = await parse(defaultPubspec);
+    expect(value.name, 'sample');
+    expect(value.version, isNull);
+    expect(value.publishTo, isNull);
+    expect(value.description, isNull);
+    expect(value.homepage, isNull);
+    expect(value.author, isNull);
+    expect(value.authors, isEmpty);
+    expect(
+      value.environment,
+      {'sdk': VersionConstraint.parse('>=2.12.0 <3.0.0')},
+    );
+    expect(value.documentation, isNull);
+    expect(value.dependencies, isEmpty);
+    expect(value.devDependencies, isEmpty);
+    expect(value.dependencyOverrides, isEmpty);
+    expect(value.flutter, isNull);
+    expect(value.repository, isNull);
+    expect(value.issueTracker, isNull);
+    expect(value.screenshots, isEmpty);
+    expect(value.workspace, isNull);
+    expect(value.resolution, isNull);
+    expect(value.executables, isEmpty);
+  });
+
+  test('all fields set', () async {
+    final version = Version.parse('1.2.3');
+    final sdkConstraint = VersionConstraint.parse('>=3.6.0 <4.0.0');
+    final value = await parse(
+      {
+        'name': 'sample',
+        'version': version.toString(),
+        'publish_to': 'none',
+        'author': 'name@example.com',
+        'environment': {'sdk': sdkConstraint.toString()},
+        'description': 'description',
+        'homepage': 'homepage',
+        'documentation': 'documentation',
+        'repository': 'https://github.com/example/repo',
+        'issue_tracker': 'https://github.com/example/repo/issues',
+        'funding': [
+          'https://patreon.com/example',
+        ],
+        'topics': ['widget', 'button'],
+        'ignored_advisories': ['111', '222'],
+        'screenshots': [
+          {'description': 'my screenshot', 'path': 'path/to/screenshot'},
+        ],
+        'workspace': [
+          'pkg1',
+          'pkg2',
+        ],
+        'resolution': 'workspace',
+        'executables': {
+          'my_script': 'bin/my_script.dart',
+          'my_script2': 'bin/my_script2.dart',
+        },
+      },
+      skipTryPub: true,
+    );
+    expect(value.name, 'sample');
+    expect(value.version, version);
+    expect(value.publishTo, 'none');
+    expect(value.description, 'description');
+    expect(value.homepage, 'homepage');
+    expect(value.author, 'name@example.com');
+    expect(value.authors, ['name@example.com']);
+    expect(value.environment, hasLength(1));
+    expect(value.environment, containsPair('sdk', sdkConstraint));
+    expect(value.documentation, 'documentation');
+    expect(value.dependencies, isEmpty);
+    expect(value.devDependencies, isEmpty);
+    expect(value.dependencyOverrides, isEmpty);
+    expect(value.repository, Uri.parse('https://github.com/example/repo'));
+    expect(
+      value.issueTracker,
+      Uri.parse('https://github.com/example/repo/issues'),
+    );
+    expect(value.funding, hasLength(1));
+    expect(value.funding!.single.toString(), 'https://patreon.com/example');
+    expect(value.topics, hasLength(2));
+    expect(value.topics!.first, 'widget');
+    expect(value.topics!.last, 'button');
+    expect(value.ignoredAdvisories, hasLength(2));
+    expect(value.ignoredAdvisories!.first, '111');
+    expect(value.ignoredAdvisories!.last, '222');
+    expect(value.screenshots, hasLength(1));
+    expect(value.screenshots!.first.description, 'my screenshot');
+    expect(value.screenshots!.first.path, 'path/to/screenshot');
+    expect(value.executables, hasLength(2));
+    expect(value.executables.keys, contains('my_script'));
+    expect(value.executables.keys, contains('my_script2'));
+    expect(value.executables['my_script'], 'bin/my_script.dart');
+    expect(value.executables['my_script2'], 'bin/my_script2.dart');
+    expect(value.workspace, hasLength(2));
+    expect(value.workspace!.first, 'pkg1');
+    expect(value.workspace!.last, 'pkg2');
+    expect(value.resolution, 'workspace');
+  });
+
+  test('environment values can be null', () async {
+    final value = await parse(
+      {
+        'name': 'sample',
+        'environment': {
+          'sdk': '>=2.12.0 <3.0.0',
+          'bob': null,
+        },
+      },
+      skipTryPub: true,
+    );
+    expect(value.name, 'sample');
+    expect(value.environment, hasLength(2));
+    expect(value.environment, containsPair('bob', isNull));
+  });
+
+  group('publish_to', () {
+    for (var entry in {
+      42: "Unsupported value for \"publish_to\". type 'int' is not a subtype of type 'String?'",
+      '##not a uri!': r'''
+line 3, column 16: Unsupported value for "publish_to". Must be an http or https URL.
+  ╷
+3 │  "publish_to": "##not a uri!"
+  │                ^^^^^^^^^^^^^^
+  ╵''',
+      '/cool/beans': r'''
+line 3, column 16: Unsupported value for "publish_to". Must be an http or https URL.
+  ╷
+3 │  "publish_to": "/cool/beans"
+  │                ^^^^^^^^^^^^^
+  ╵''',
+      'file:///Users/kevmoo/': r'''
+line 3, column 16: Unsupported value for "publish_to". Must be an http or https URL.
+  ╷
+3 │  "publish_to": "file:///Users/kevmoo/"
+  │                ^^^^^^^^^^^^^^^^^^^^^^^
+  ╵''',
+    }.entries) {
+      test('cannot be `${entry.key}`', () {
+        expectParseThrowsContaining(
+          {'name': 'sample', 'publish_to': entry.key},
+          entry.value,
+          skipTryPub: true,
+        );
+      });
+    }
+
+    for (var entry in {
+      null: null,
+      'http': 'http://example.com',
+      'https': 'https://example.com',
+      'none': 'none',
+    }.entries) {
+      test('can be ${entry.key}', () async {
+        final value = await parse({
+          ...defaultPubspec,
+          'publish_to': entry.value,
+        });
+        expect(value.publishTo, entry.value);
+      });
+    }
+  });
+
+  group('author, authors', () {
+    test('one author', () async {
+      final value = await parse({
+        ...defaultPubspec,
+        'author': 'name@example.com',
+      });
+      expect(value.author, 'name@example.com');
+      expect(value.authors, ['name@example.com']);
+    });
+
+    test('one author, via authors', () async {
+      final value = await parse({
+        ...defaultPubspec,
+        'authors': ['name@example.com'],
+      });
+      expect(value.author, 'name@example.com');
+      expect(value.authors, ['name@example.com']);
+    });
+
+    test('many authors', () async {
+      final value = await parse({
+        ...defaultPubspec,
+        'authors': ['name@example.com', 'name2@example.com'],
+      });
+      expect(value.author, isNull);
+      expect(value.authors, ['name@example.com', 'name2@example.com']);
+    });
+
+    test('author and authors', () async {
+      final value = await parse({
+        ...defaultPubspec,
+        'author': 'name@example.com',
+        'authors': ['name2@example.com'],
+      });
+      expect(value.author, isNull);
+      expect(value.authors, ['name@example.com', 'name2@example.com']);
+    });
+
+    test('duplicate author values', () async {
+      final value = await parse({
+        ...defaultPubspec,
+        'author': 'name@example.com',
+        'authors': ['name@example.com', 'name@example.com'],
+      });
+      expect(value.author, 'name@example.com');
+      expect(value.authors, ['name@example.com']);
+    });
+
+    test('flutter', () async {
+      final value = await parse({
+        ...defaultPubspec,
+        'flutter': {'key': 'value'},
+      });
+      expect(value.flutter, {'key': 'value'});
+    });
+  });
+
+  group('executables', () {
+    test('one executable', () async {
+      final value = await parse({
+        ...defaultPubspec,
+        'executables': {'my_script': 'bin/my_script.dart'},
+      });
+      expect(value.executables, hasLength(1));
+      expect(value.executables.keys, contains('my_script'));
+      expect(value.executables['my_script'], 'bin/my_script.dart');
+    });
+
+    test('many executables', () async {
+      final value = await parse({
+        ...defaultPubspec,
+        'executables': {
+          'my_script': 'bin/my_script.dart',
+          'my_script2': 'bin/my_script2.dart',
+        },
+      });
+      expect(value.executables, hasLength(2));
+      expect(value.executables.keys, contains('my_script'));
+      expect(value.executables.keys, contains('my_script2'));
+      expect(value.executables['my_script'], 'bin/my_script.dart');
+      expect(value.executables['my_script2'], 'bin/my_script2.dart');
+    });
+
+    test('invalid value', () async {
+      expectParseThrowsContaining(
+        {
+          ...defaultPubspec,
+          'executables': {
+            'script': 32,
+          },
+        },
+        'Unsupported value for "script". `32` is not a String.',
+        skipTryPub: true,
+      );
+    });
+
+    test('invalid executable - lenient', () async {
+      final value = await parse(
+        {
+          ...defaultPubspec,
+          'executables': 'Invalid value',
+        },
+        lenient: true,
+      );
+      expect(value.name, 'sample');
+      expect(value.executables, isEmpty);
+    });
+  });
+
+  group('invalid', () {
+    test('null', () {
+      expectParseThrows(
+        null,
+        r'''
+line 1, column 1: Not a map
+  ╷
+1 │ null
+  │ ^^^^
+  ╵''',
+      );
+    });
+    test('empty string', () {
+      expectParseThrows(
+        '',
+        r'''
+line 1, column 1: Not a map
+  ╷
+1 │ ""
+  │ ^^
+  ╵''',
+      );
+    });
+    test('array', () {
+      expectParseThrows(
+        [],
+        r'''
+line 1, column 1: Not a map
+  ╷
+1 │ []
+  │ ^^
+  ╵''',
+      );
+    });
+
+    test('missing name', () {
+      expectParseThrowsContaining(
+        {},
+        "Missing key \"name\". type 'Null' is not a subtype of type 'String'",
+      );
+    });
+
+    test('null name value', () {
+      expectParseThrowsContaining(
+        {'name': null},
+        "Unsupported value for \"name\". type 'Null' is not a subtype of type 'String'",
+      );
+    });
+
+    test('empty name value', () {
+      expectParseThrows(
+        {'name': ''},
+        r'''
+line 2, column 10: Unsupported value for "name". "name" cannot be empty.
+  ╷
+2 │  "name": ""
+  │          ^^
+  ╵''',
+      );
+    });
+
+    test('"dart" is an invalid environment key', () {
+      expectParseThrows(
+        {
+          'name': 'sample',
+          'environment': {'dart': 'cool'},
+        },
+        r'''
+line 4, column 3: Use "sdk" to for Dart SDK constraints.
+  ╷
+4 │   "dart": "cool"
+  │   ^^^^^^
+  ╵''',
+      );
+    });
+
+    test('environment values cannot be int', () {
+      expectParseThrows(
+        {
+          'name': 'sample',
+          'environment': {'sdk': 42},
+        },
+        r'''
+line 4, column 10: Unsupported value for "sdk". `42` is not a String.
+  ╷
+4 │     "sdk": 42
+  │ ┌──────────^
+5 │ │  }
+  │ └─^
+  ╵''',
+      );
+    });
+
+    test('version', () {
+      expectParseThrows(
+        {'name': 'sample', 'version': 'invalid'},
+        r'''
+line 3, column 13: Unsupported value for "version". Could not parse "invalid".
+  ╷
+3 │  "version": "invalid"
+  │             ^^^^^^^^^
+  ╵''',
+      );
+    });
+
+    test('invalid environment value', () {
+      expectParseThrows(
+        {
+          'name': 'sample',
+          'environment': {'sdk': 'silly'},
+        },
+        r'''
+line 4, column 10: Unsupported value for "sdk". Could not parse version "silly". Unknown text at "silly".
+  ╷
+4 │   "sdk": "silly"
+  │          ^^^^^^^
+  ╵''',
+      );
+    });
+
+    test('bad repository url', () {
+      expectParseThrowsContaining(
+        {
+          ...defaultPubspec,
+          'repository': {'x': 'y'},
+        },
+        "Unsupported value for \"repository\". type 'YamlMap' is not a subtype of type 'String'",
+        skipTryPub: true,
+      );
+    });
+
+    test('bad issue_tracker url', () {
+      expectParseThrowsContaining(
+        {
+          'name': 'sample',
+          'issue_tracker': {'x': 'y'},
+        },
+        "Unsupported value for \"issue_tracker\". type 'YamlMap' is not a subtype of type 'String'",
+        skipTryPub: true,
+      );
+    });
+  });
+
+  group('funding', () {
+    test('not a list', () {
+      expectParseThrowsContaining(
+        {
+          ...defaultPubspec,
+          'funding': 1,
+        },
+        "Unsupported value for \"funding\". type 'int' is not a subtype of type 'List<dynamic>?'",
+        skipTryPub: true,
+      );
+    });
+
+    test('not an uri', () {
+      expectParseThrowsContaining(
+        {
+          ...defaultPubspec,
+          'funding': [1],
+        },
+        "Unsupported value for \"funding\". type 'int' is not a subtype of type 'String'",
+        skipTryPub: true,
+      );
+    });
+
+    test('not an uri', () {
+      expectParseThrows(
+        {
+          ...defaultPubspec,
+          'funding': ['ht tps://example.com/'],
+        },
+        r'''
+line 6, column 13: Unsupported value for "funding". Illegal scheme character at offset 2.
+  ╷
+6 │    "funding": [
+  │ ┌─────────────^
+7 │ │   "ht tps://example.com/"
+8 │ └  ]
+  ╵''',
+        skipTryPub: true,
+      );
+    });
+  });
+  group('topics', () {
+    test('not a list', () {
+      expectParseThrowsContaining(
+        {
+          ...defaultPubspec,
+          'topics': 1,
+        },
+        "Unsupported value for \"topics\". type 'int' is not a subtype of type 'List<dynamic>?'",
+        skipTryPub: true,
+      );
+    });
+
+    test('not a string', () {
+      expectParseThrowsContaining(
+        {
+          ...defaultPubspec,
+          'topics': [1],
+        },
+        "Unsupported value for \"topics\". type 'int' is not a subtype of type 'String'",
+        skipTryPub: true,
+      );
+    });
+
+    test('invalid data - lenient', () async {
+      final value = await parse(
+        {
+          ...defaultPubspec,
+          'topics': [1],
+        },
+        skipTryPub: true,
+        lenient: true,
+      );
+      expect(value.name, 'sample');
+      expect(value.topics, isNull);
+    });
+  });
+
+  group('ignored_advisories', () {
+    test('not a list', () {
+      expectParseThrowsContaining(
+        {
+          ...defaultPubspec,
+          'ignored_advisories': 1,
+        },
+        "Unsupported value for \"ignored_advisories\". type 'int' is not a subtype of type 'List<dynamic>?'",
+        skipTryPub: true,
+      );
+    });
+
+    test('not a string', () {
+      expectParseThrowsContaining(
+        {
+          ...defaultPubspec,
+          'ignored_advisories': [1],
+        },
+        "Unsupported value for \"ignored_advisories\". type 'int' is not a subtype of type 'String'",
+        skipTryPub: true,
+      );
+    });
+
+    test('invalid data - lenient', () async {
+      final value = await parse(
+        {
+          ...defaultPubspec,
+          'ignored_advisories': [1],
+        },
+        skipTryPub: true,
+        lenient: true,
+      );
+      expect(value.name, 'sample');
+      expect(value.ignoredAdvisories, isNull);
+    });
+  });
+
+  group('screenshots', () {
+    test('one screenshot', () async {
+      final value = await parse({
+        ...defaultPubspec,
+        'screenshots': [
+          {'description': 'my screenshot', 'path': 'path/to/screenshot'},
+        ],
+      });
+      expect(value.screenshots, hasLength(1));
+      expect(value.screenshots!.first.description, 'my screenshot');
+      expect(value.screenshots!.first.path, 'path/to/screenshot');
+    });
+
+    test('many screenshots', () async {
+      final value = await parse({
+        ...defaultPubspec,
+        'screenshots': [
+          {'description': 'my screenshot', 'path': 'path/to/screenshot'},
+          {
+            'description': 'my second screenshot',
+            'path': 'path/to/screenshot2',
+          },
+        ],
+      });
+      expect(value.screenshots, hasLength(2));
+      expect(value.screenshots!.first.description, 'my screenshot');
+      expect(value.screenshots!.first.path, 'path/to/screenshot');
+      expect(value.screenshots!.last.description, 'my second screenshot');
+      expect(value.screenshots!.last.path, 'path/to/screenshot2');
+    });
+
+    test('one screenshot plus invalid entries', () async {
+      final value = await parse({
+        ...defaultPubspec,
+        'screenshots': [
+          42,
+          {
+            'description': 'my screenshot',
+            'path': 'path/to/screenshot',
+            'extraKey': 'not important',
+          },
+          'not a screenshot',
+        ],
+      });
+      expect(value.screenshots, hasLength(1));
+      expect(value.screenshots!.first.description, 'my screenshot');
+      expect(value.screenshots!.first.path, 'path/to/screenshot');
+    });
+
+    test('invalid entries', () async {
+      final value = await parse({
+        ...defaultPubspec,
+        'screenshots': [
+          42,
+          'not a screenshot',
+        ],
+      });
+      expect(value.screenshots, isEmpty);
+    });
+
+    test('missing key `dessription', () {
+      expectParseThrows(
+        {
+          ...defaultPubspec,
+          'screenshots': [
+            {'path': 'my/path'},
+          ],
+        },
+        r'''
+line 7, column 3: Missing key "description". Missing required key `description`
+  ╷
+7 │ ┌   {
+8 │ │    "path": "my/path"
+9 │ └   }
+  ╵''',
+        skipTryPub: true,
+      );
+    });
+
+    test('missing key `path`', () {
+      expectParseThrows(
+        {
+          ...defaultPubspec,
+          'screenshots': [
+            {'description': 'my screenshot'},
+          ],
+        },
+        r'''
+line 7, column 3: Missing key "path". Missing required key `path`
+  ╷
+7 │ ┌   {
+8 │ │    "description": "my screenshot"
+9 │ └   }
+  ╵''',
+        skipTryPub: true,
+      );
+    });
+
+    test('Value of description not a String`', () {
+      expectParseThrows(
+        {
+          ...defaultPubspec,
+          'screenshots': [
+            {'description': 42},
+          ],
+        },
+        r'''
+line 8, column 19: Unsupported value for "description". `42` is not a String
+  ╷
+8 │      "description": 42
+  │ ┌───────────────────^
+9 │ │   }
+  │ └──^
+  ╵''',
+        skipTryPub: true,
+      );
+    });
+
+    test('Value of path not a String`', () {
+      expectParseThrows(
+        {
+          ...defaultPubspec,
+          'screenshots': [
+            {
+              'description': '',
+              'path': 42,
+            },
+          ],
+        },
+        r'''
+line 9, column 12: Unsupported value for "path". `42` is not a String
+   ╷
+9  │      "path": 42
+   │ ┌────────────^
+10 │ │   }
+   │ └──^
+   ╵''',
+        skipTryPub: true,
+      );
+    });
+
+    test('invalid screenshot - lenient', () async {
+      final value = await parse(
+        {
+          ...defaultPubspec,
+          'screenshots': 'Invalid value',
+        },
+        lenient: true,
+      );
+      expect(value.name, 'sample');
+      expect(value.screenshots, isEmpty);
+    });
+  });
+
+  group('lenient', () {
+    test('null', () {
+      expectParseThrows(
+        null,
+        r'''
+line 1, column 1: Not a map
+  ╷
+1 │ null
+  │ ^^^^
+  ╵''',
+        lenient: true,
+      );
+    });
+
+    test('empty string', () {
+      expectParseThrows(
+        '',
+        r'''
+line 1, column 1: Not a map
+  ╷
+1 │ ""
+  │ ^^
+  ╵''',
+        lenient: true,
+      );
+    });
+
+    test('name cannot be empty', () {
+      expectParseThrowsContaining(
+        {},
+        "Missing key \"name\". type 'Null' is not a subtype of type 'String'",
+        lenient: true,
+      );
+    });
+
+    test('bad repository url', () async {
+      final value = await parse(
+        {
+          ...defaultPubspec,
+          'repository': {'x': 'y'},
+        },
+        lenient: true,
+      );
+      expect(value.name, 'sample');
+      expect(value.repository, isNull);
+    });
+
+    test('bad issue_tracker url', () async {
+      final value = await parse(
+        {
+          ...defaultPubspec,
+          'issue_tracker': {'x': 'y'},
+        },
+        lenient: true,
+      );
+      expect(value.name, 'sample');
+      expect(value.issueTracker, isNull);
+    });
+
+    test('multiple bad values', () async {
+      final value = await parse(
+        {
+          ...defaultPubspec,
+          'repository': {'x': 'y'},
+          'issue_tracker': {'x': 'y'},
+        },
+        lenient: true,
+      );
+      expect(value.name, 'sample');
+      expect(value.repository, isNull);
+      expect(value.issueTracker, isNull);
+    });
+
+    test('deep error throws with lenient', () {
+      expect(
+        () => parse(
+          {
+            'name': 'sample',
+            'dependencies': {
+              'foo': {
+                'git': {'url': 1},
+              },
+            },
+            'issue_tracker': {'x': 'y'},
+          },
+          skipTryPub: true,
+          lenient: true,
+        ),
+        throwsException,
+      );
+    });
+  });
+
+  group('workspaces', () {
+    test('workspace key must be a list', () {
+      expectParseThrowsContaining(
+        {
+          ...defaultPubspec,
+          'workspace': 42,
+        },
+        'Unsupported value for "workspace". type \'int\' is not a subtype of type \'List<dynamic>?\' in type cast',
+        skipTryPub: true,
+      );
+    });
+
+    test('workspace key must be a list of strings', () {
+      expectParseThrowsContaining(
+        {
+          ...defaultPubspec,
+          'workspace': [42],
+        },
+        'Unsupported value for "workspace". type \'int\' is not a subtype of type \'String\' in type cast',
+        skipTryPub: true,
+      );
+    });
+
+    test('resolution key must be a string', () {
+      expectParseThrowsContaining(
+        {
+          'name': 'sample',
+          'environment': {'sdk': '^3.6.0'},
+          'resolution': 42,
+        },
+        'Unsupported value for "resolution". type \'int\' is not a subtype of type \'String?\' in type cast',
+        skipTryPub: true,
+      );
+    });
+  });
+}

diff --git a/pkgs/pubspec_parse/test/pub_utils.dart b/pkgs/pubspec_parse/test/pub_utils.dart
new file mode 100644
index 0000000..a60aa2a
--- /dev/null
+++ b/pkgs/pubspec_parse/test/pub_utils.dart

@@ -0,0 +1,88 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+import 'dart:io';
+
+import 'package:path/path.dart' as p;
+import 'package:test/test.dart';
+import 'package:test_descriptor/test_descriptor.dart' as d;
+import 'package:test_process/test_process.dart';
+
+Future<ProcResult> tryPub(String content) async {
+  await d.file('pubspec.yaml', content).create();
+
+  final proc = await TestProcess.start(
+    Platform.resolvedExecutable,
+    ['pub', 'get', '--offline'],
+    workingDirectory: d.sandbox,
+    // Don't pass current process VM options to child
+    environment: Map.from(Platform.environment)..remove('DART_VM_OPTIONS'),
+  );
+
+  final result = await ProcResult.fromTestProcess(proc);
+
+  printOnFailure(
+    [
+      '-----BEGIN pub output-----',
+      result.toString().trim(),
+      '-----END pub output-----',
+    ].join('\n'),
+  );
+
+  if (result.exitCode == 0) {
+    final lockContent =
+        File(p.join(d.sandbox, 'pubspec.lock')).readAsStringSync();
+
+    printOnFailure(
+      [
+        '-----BEGIN pubspec.lock-----',
+        lockContent.trim(),
+        '-----END pubspec.lock-----',
+      ].join('\n'),
+    );
+  }
+
+  return result;
+}
+
+class ProcResult {
+  final int exitCode;
+  final List<ProcLine> lines;
+
+  bool get cleanParse => exitCode == 0 || exitCode == 66 || exitCode == 69;
+
+  ProcResult(this.exitCode, this.lines);
+
+  static Future<ProcResult> fromTestProcess(TestProcess proc) async {
+    final items = <ProcLine>[];
+
+    final values = await Future.wait([
+      proc.exitCode,
+      proc.stdoutStream().forEach((line) => items.add(ProcLine(false, line))),
+      proc.stderrStream().forEach((line) => items.add(ProcLine(true, line))),
+    ]);
+
+    return ProcResult(values[0] as int, items);
+  }
+
+  @override
+  String toString() {
+    final buffer = StringBuffer('Exit code: $exitCode');
+    for (var line in lines) {
+      buffer.write('\n$line');
+    }
+    return buffer.toString();
+  }
+}
+
+class ProcLine {
+  final bool isError;
+  final String line;
+
+  ProcLine(this.isError, this.line);
+
+  @override
+  String toString() => '${isError ? 'err' : 'out'}  $line';
+}

diff --git a/pkgs/pubspec_parse/test/test_utils.dart b/pkgs/pubspec_parse/test/test_utils.dart
new file mode 100644
index 0000000..cc46522
--- /dev/null
+++ b/pkgs/pubspec_parse/test/test_utils.dart

@@ -0,0 +1,157 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:convert';
+
+import 'package:checked_yaml/checked_yaml.dart';
+import 'package:json_annotation/json_annotation.dart';
+import 'package:pubspec_parse/pubspec_parse.dart';
+import 'package:stack_trace/stack_trace.dart';
+import 'package:test/test.dart';
+
+import 'pub_utils.dart';
+
+const defaultPubspec = {
+  'name': 'sample',
+  'environment': {'sdk': '>=2.12.0 <3.0.0'},
+};
+
+String _encodeJson(Object? input) =>
+    const JsonEncoder.withIndent(' ').convert(input);
+
+Matcher _throwsParsedYamlException(String prettyValue) => throwsA(
+      const TypeMatcher<ParsedYamlException>().having(
+        (e) {
+          final message = e.formattedMessage;
+          printOnFailure("Actual error format:\nr'''\n$message'''");
+          _printDebugParsedYamlException(e);
+          return message;
+        },
+        'formattedMessage',
+        prettyValue,
+      ),
+    );
+
+void _printDebugParsedYamlException(ParsedYamlException e) {
+  var innerError = e.innerError;
+  StackTrace? innerStack;
+
+  if (innerError is CheckedFromJsonException) {
+    final cfje = innerError;
+
+    if (cfje.innerError != null) {
+      innerError = cfje.innerError;
+      innerStack = cfje.innerStack;
+    }
+  }
+
+  if (innerError != null) {
+    final items = [innerError];
+    if (innerStack != null) {
+      items.add(Trace.format(innerStack));
+    }
+
+    final content =
+        LineSplitter.split(items.join('\n')).map((e) => '  $e').join('\n');
+
+    printOnFailure('Inner error details:\n$content');
+  }
+}
+
+Future<Pubspec> parse(
+  Object? content, {
+  bool quietOnError = false,
+  bool skipTryPub = false,
+  bool lenient = false,
+}) async {
+  final encoded = _encodeJson(content);
+
+  ProcResult? pubResult;
+  if (!skipTryPub) {
+    // ignore: deprecated_member_use
+    pubResult = await tryPub(encoded);
+    expect(pubResult, isNotNull);
+  }
+
+  try {
+    final value = Pubspec.parse(encoded, lenient: lenient);
+
+    if (pubResult != null) {
+      addTearDown(() {
+        expect(
+          pubResult!.cleanParse,
+          isTrue,
+          reason:
+              'On success, parsing from the pub client should also succeed.',
+        );
+      });
+    }
+    return value;
+  } catch (e) {
+    if (pubResult != null) {
+      addTearDown(() {
+        expect(
+          pubResult!.cleanParse,
+          isFalse,
+          reason: 'On failure, parsing from the pub client should also fail.',
+        );
+      });
+    }
+    if (e is ParsedYamlException) {
+      if (!quietOnError) {
+        _printDebugParsedYamlException(e);
+      }
+    }
+    rethrow;
+  }
+}
+
+void expectParseThrows(
+  Object? content,
+  String expectedError, {
+  bool skipTryPub = false,
+  bool lenient = false,
+}) =>
+    expect(
+      () => parse(
+        content,
+        lenient: lenient,
+        quietOnError: true,
+        skipTryPub: skipTryPub,
+      ),
+      _throwsParsedYamlException(expectedError),
+    );
+
+void expectParseThrowsContaining(
+  Object? content,
+  String errorFragment, {
+  bool skipTryPub = false,
+  bool lenient = false,
+}) {
+  expect(
+    () => parse(
+      content,
+      lenient: lenient,
+      quietOnError: true,
+      skipTryPub: skipTryPub,
+    ),
+    _throwsParsedYamlExceptionContaining(errorFragment),
+  );
+}
+
+// ignore: prefer_expression_function_bodies
+Matcher _throwsParsedYamlExceptionContaining(String errorFragment) {
+  return throwsA(
+    const TypeMatcher<ParsedYamlException>().having(
+      (e) {
+        final message = e.formattedMessage;
+        printOnFailure("Actual error format:\nr'''\n$message'''");
+        _printDebugParsedYamlException(e);
+        return message;
+      },
+      'formattedMessage',
+      contains(errorFragment),
+    ),
+  );
+}

diff --git a/pkgs/source_maps/.gitignore b/pkgs/source_maps/.gitignore
new file mode 100644
index 0000000..f73b2f9
--- /dev/null
+++ b/pkgs/source_maps/.gitignore

@@ -0,0 +1,4 @@
+.dart_tool/
+.packages
+.pub/
+pubspec.lock

diff --git a/pkgs/source_maps/CHANGELOG.md b/pkgs/source_maps/CHANGELOG.md
new file mode 100644
index 0000000..b06ac72
--- /dev/null
+++ b/pkgs/source_maps/CHANGELOG.md

@@ -0,0 +1,133 @@
+## 0.10.14-wip
+
+## 0.10.13
+
+* Require Dart 3.3
+* Move to `dart-lang/tools` monorepo.
+
+## 0.10.12
+
+* Add additional types at API boundaries.
+
+## 0.10.11
+
+* Populate the pubspec `repository` field.
+* Update the source map documentation link in the readme.
+
+## 0.10.10
+
+* Stable release for null safety.
+
+## 0.10.9
+
+* Fix a number of document comment issues.
+* Allow parsing source map files with a missing `names` field.
+
+## 0.10.8
+
+* Preserve source-map extensions in `SingleMapping`. Extensions are keys in the
+  json map that start with `"x_"`.
+
+## 0.10.7
+
+* Set max SDK version to `<3.0.0`, and adjust other dependencies.
+
+## 0.10.6
+
+* Require version 2.0.0 of the Dart SDK.
+
+## 0.10.5
+
+* Add a `SingleMapping.files` field which provides access to `SourceFile`s
+  representing the `"sourcesContent"` fields in the source map.
+
+* Add an `includeSourceContents` flag to `SingleMapping.toJson()` which
+  indicates whether to include source file contents in the source map.
+
+## 0.10.4
+* Implement `highlight` in `SourceMapFileSpan`.
+* Require version `^1.3.0` of `source_span`.
+
+## 0.10.3
+ * Add `addMapping` and `containsMapping` members to `MappingBundle`.
+
+## 0.10.2
+ * Support for extended source map format.
+ * Polish `MappingBundle.spanFor` handling of URIs that have a suffix that
+   exactly match a source map in the MappingBundle.
+
+## 0.10.1+5
+ * Fix strong mode warning in test.
+
+## 0.10.1+4
+
+* Extend `MappingBundle.spanFor` to accept requests for output files that
+  don't have source maps.
+
+## 0.10.1+3
+
+* Add `MappingBundle` class that handles extended source map format that
+  supports source maps for multiple output files in a single mapper.
+  Extend `Mapping.spanFor` API to accept a uri parameter that is optional
+  for normal source maps but required for MappingBundle source maps.
+
+## 0.10.1+2
+
+* Fix more strong mode warnings.
+
+## 0.10.1+1
+
+* Fix all strong mode warnings.
+
+## 0.10.1
+
+* Add a `mapUrl` named argument to `parse` and `parseJson`. This argument is
+  used to resolve source URLs for source spans.
+
+## 0.10.0+2
+
+* Fix analyzer error (FileSpan has a new field since `source_span` 1.1.1)
+
+## 0.10.0+1
+
+* Remove an unnecessary warning printed when the "file" field is missing from a
+  Json formatted source map. This field is optional and its absence is not
+  unusual.
+
+## 0.10.0
+
+* Remove the `Span`, `Location` and `SourceFile` classes. Use the
+  corresponding `source_span` classes instead.
+
+## 0.9.4
+
+* Update `SpanFormatException` with `source` and `offset`.
+
+* All methods that take `Span`s, `Location`s, and `SourceFile`s as inputs now
+  also accept the corresponding `source_span` classes as well. Using the old
+  classes is now deprecated and will be unsupported in version 0.10.0.
+
+## 0.9.3
+
+* Support writing SingleMapping objects to source map version 3 format.
+* Support the `sourceRoot` field in the SingleMapping class.
+* Support updating the `targetUrl` field in the SingleMapping class.
+
+## 0.9.2+2
+
+* Fix a bug in `FixedSpan.getLocationMessage`.
+
+## 0.9.2+1
+
+* Minor readability improvements to `FixedSpan.getLocationMessage` and
+  `SpanException.toString`.
+
+## 0.9.2
+
+* Add `SpanException` and `SpanFormatException` classes.
+
+## 0.9.1
+
+* Support unmapped areas in source maps.
+
+* Increase the readability of location messages.

diff --git a/pkgs/source_maps/LICENSE b/pkgs/source_maps/LICENSE
new file mode 100644
index 0000000..162572a
--- /dev/null
+++ b/pkgs/source_maps/LICENSE

@@ -0,0 +1,27 @@
+Copyright 2014, the Dart project authors.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+    * Neither the name of Google LLC nor the names of its
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

diff --git a/pkgs/source_maps/README.md b/pkgs/source_maps/README.md
new file mode 100644
index 0000000..cf80291
--- /dev/null
+++ b/pkgs/source_maps/README.md

@@ -0,0 +1,25 @@
+[![Build Status](https://github.com/dart-lang/tools/actions/workflows/source_maps.yaml/badge.svg)](https://github.com/dart-lang/tools/actions/workflows/source_maps.yaml)
+[![pub package](https://img.shields.io/pub/v/source_maps.svg)](https://pub.dev/packages/source_maps)
+[![package publisher](https://img.shields.io/pub/publisher/source_maps.svg)](https://pub.dev/packages/source_maps/publisher)
+
+This project implements a Dart pub package to work with source maps.
+
+## Docs and usage
+
+The implementation is based on the [source map version 3 spec][spec] which was
+originated from the [Closure Compiler][closure] and has been implemented in
+Chrome and Firefox.
+
+In this package we provide:
+
+  * Data types defining file locations and spans: these are not part of the
+    original source map specification. These data types are great for tracking
+    source locations on source maps, but they can also be used by tools to
+    reporting useful error messages that include on source locations.
+  * A builder that creates a source map programmatically and produces the encoded
+    source map format.
+  * A parser that reads the source map format and provides APIs to read the
+    mapping information.
+
+[closure]: https://github.com/google/closure-compiler/wiki/Source-Maps
+[spec]: https://docs.google.com/a/google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k/edit

diff --git a/pkgs/source_maps/analysis_options.yaml b/pkgs/source_maps/analysis_options.yaml
new file mode 100644
index 0000000..d978f81
--- /dev/null
+++ b/pkgs/source_maps/analysis_options.yaml

@@ -0,0 +1 @@
+include: package:dart_flutter_team_lints/analysis_options.yaml

diff --git a/pkgs/source_maps/lib/builder.dart b/pkgs/source_maps/lib/builder.dart
new file mode 100644
index 0000000..9043c63
--- /dev/null
+++ b/pkgs/source_maps/lib/builder.dart

@@ -0,0 +1,84 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Contains a builder object useful for creating source maps programatically.
+library;
+
+// TODO(sigmund): add a builder for multi-section mappings.
+
+import 'dart:convert';
+
+import 'package:source_span/source_span.dart';
+
+import 'parser.dart';
+import 'src/source_map_span.dart';
+
+/// Builds a source map given a set of mappings.
+class SourceMapBuilder {
+  final List<Entry> _entries = <Entry>[];
+
+  /// Adds an entry mapping the [targetOffset] to [source].
+  void addFromOffset(SourceLocation source, SourceFile targetFile,
+      int targetOffset, String identifier) {
+    ArgumentError.checkNotNull(targetFile, 'targetFile');
+    _entries.add(Entry(source, targetFile.location(targetOffset), identifier));
+  }
+
+  /// Adds an entry mapping [target] to [source].
+  ///
+  /// If [isIdentifier] is true or if [target] is a [SourceMapSpan] with
+  /// `isIdentifier` set to true, this entry is considered to represent an
+  /// identifier whose value will be stored in the source map. [isIdentifier]
+  /// takes precedence over [target]'s `isIdentifier` value.
+  void addSpan(SourceSpan source, SourceSpan target, {bool? isIdentifier}) {
+    isIdentifier ??= source is SourceMapSpan ? source.isIdentifier : false;
+
+    var name = isIdentifier ? source.text : null;
+    _entries.add(Entry(source.start, target.start, name));
+  }
+
+  /// Adds an entry mapping [target] to [source].
+  void addLocation(
+      SourceLocation source, SourceLocation target, String? identifier) {
+    _entries.add(Entry(source, target, identifier));
+  }
+
+  /// Encodes all mappings added to this builder as a json map.
+  Map<String, dynamic> build(String fileUrl) {
+    return SingleMapping.fromEntries(_entries, fileUrl).toJson();
+  }
+
+  /// Encodes all mappings added to this builder as a json string.
+  String toJson(String fileUrl) => jsonEncode(build(fileUrl));
+}
+
+/// An entry in the source map builder.
+class Entry implements Comparable<Entry> {
+  /// Span denoting the original location in the input source file
+  final SourceLocation source;
+
+  /// Span indicating the corresponding location in the target file.
+  final SourceLocation target;
+
+  /// An identifier name, when this location is the start of an identifier.
+  final String? identifierName;
+
+  /// Creates a new [Entry] mapping [target] to [source].
+  Entry(this.source, this.target, this.identifierName);
+
+  /// Implements [Comparable] to ensure that entries are ordered by their
+  /// location in the target file. We sort primarily by the target offset
+  /// because source map files are encoded by printing each mapping in order as
+  /// they appear in the target file.
+  @override
+  int compareTo(Entry other) {
+    var res = target.compareTo(other.target);
+    if (res != 0) return res;
+    res = source.sourceUrl
+        .toString()
+        .compareTo(other.source.sourceUrl.toString());
+    if (res != 0) return res;
+    return source.compareTo(other.source);
+  }
+}

diff --git a/pkgs/source_maps/lib/parser.dart b/pkgs/source_maps/lib/parser.dart
new file mode 100644
index 0000000..590dfc6
--- /dev/null
+++ b/pkgs/source_maps/lib/parser.dart

@@ -0,0 +1,718 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Contains the top-level function to parse source maps version 3.
+library;
+
+import 'dart:convert';
+
+import 'package:source_span/source_span.dart';
+
+import 'builder.dart' as builder;
+import 'src/source_map_span.dart';
+import 'src/utils.dart';
+import 'src/vlq.dart';
+
+/// Parses a source map directly from a json string.
+///
+/// [mapUrl], which may be either a [String] or a [Uri], indicates the URL of
+/// the source map file itself. If it's passed, any URLs in the source
+/// map will be interpreted as relative to this URL when generating spans.
+// TODO(sigmund): evaluate whether other maps should have the json parsed, or
+// the string represenation.
+// TODO(tjblasi): Ignore the first line of [jsonMap] if the JSON safety string
+// `)]}'` begins the string representation of the map.
+Mapping parse(String jsonMap,
+        {Map<String, Map>? otherMaps, /*String|Uri*/ Object? mapUrl}) =>
+    parseJson(jsonDecode(jsonMap) as Map, otherMaps: otherMaps, mapUrl: mapUrl);
+
+/// Parses a source map or source map bundle directly from a json string.
+///
+/// [mapUrl], which may be either a [String] or a [Uri], indicates the URL of
+/// the source map file itself. If it's passed, any URLs in the source
+/// map will be interpreted as relative to this URL when generating spans.
+Mapping parseExtended(String jsonMap,
+        {Map<String, Map>? otherMaps, /*String|Uri*/ Object? mapUrl}) =>
+    parseJsonExtended(jsonDecode(jsonMap),
+        otherMaps: otherMaps, mapUrl: mapUrl);
+
+/// Parses a source map or source map bundle.
+///
+/// [mapUrl], which may be either a [String] or a [Uri], indicates the URL of
+/// the source map file itself. If it's passed, any URLs in the source
+/// map will be interpreted as relative to this URL when generating spans.
+Mapping parseJsonExtended(/*List|Map*/ Object? json,
+    {Map<String, Map>? otherMaps, /*String|Uri*/ Object? mapUrl}) {
+  if (json is List) {
+    return MappingBundle.fromJson(json, mapUrl: mapUrl);
+  }
+  return parseJson(json as Map);
+}
+
+/// Parses a source map.
+///
+/// [mapUrl], which may be either a [String] or a [Uri], indicates the URL of
+/// the source map file itself. If it's passed, any URLs in the source
+/// map will be interpreted as relative to this URL when generating spans.
+Mapping parseJson(Map map,
+    {Map<String, Map>? otherMaps, /*String|Uri*/ Object? mapUrl}) {
+  if (map['version'] != 3) {
+    throw ArgumentError('unexpected source map version: ${map["version"]}. '
+        'Only version 3 is supported.');
+  }
+
+  if (map.containsKey('sections')) {
+    if (map.containsKey('mappings') ||
+        map.containsKey('sources') ||
+        map.containsKey('names')) {
+      throw const FormatException('map containing "sections" '
+          'cannot contain "mappings", "sources", or "names".');
+    }
+    return MultiSectionMapping.fromJson(map['sections'] as List, otherMaps,
+        mapUrl: mapUrl);
+  }
+  return SingleMapping.fromJson(map.cast<String, dynamic>(), mapUrl: mapUrl);
+}
+
+/// A mapping parsed out of a source map.
+abstract class Mapping {
+  /// Returns the span associated with [line] and [column].
+  ///
+  /// [uri] is the optional location of the output file to find the span for
+  /// to disambiguate cases where a mapping may have different mappings for
+  /// different output files.
+  SourceMapSpan? spanFor(int line, int column,
+      {Map<String, SourceFile>? files, String? uri});
+
+  /// Returns the span associated with [location].
+  SourceMapSpan? spanForLocation(SourceLocation location,
+      {Map<String, SourceFile>? files}) {
+    return spanFor(location.line, location.column,
+        uri: location.sourceUrl?.toString(), files: files);
+  }
+}
+
+/// A meta-level map containing sections.
+class MultiSectionMapping extends Mapping {
+  /// For each section, the start line offset.
+  final List<int> _lineStart = <int>[];
+
+  /// For each section, the start column offset.
+  final List<int> _columnStart = <int>[];
+
+  /// For each section, the actual source map information, which is not adjusted
+  /// for offsets.
+  final List<Mapping> _maps = <Mapping>[];
+
+  /// Creates a section mapping from json.
+  MultiSectionMapping.fromJson(List sections, Map<String, Map>? otherMaps,
+      {/*String|Uri*/ Object? mapUrl}) {
+    for (var section in sections.cast<Map>()) {
+      var offset = section['offset'] as Map?;
+      if (offset == null) throw const FormatException('section missing offset');
+
+      var line = offset['line'] as int?;
+      if (line == null) throw const FormatException('offset missing line');
+
+      var column = offset['column'] as int?;
+      if (column == null) throw const FormatException('offset missing column');
+
+      _lineStart.add(line);
+      _columnStart.add(column);
+
+      var url = section['url'] as String?;
+      var map = section['map'] as Map?;
+
+      if (url != null && map != null) {
+        throw const FormatException(
+            "section can't use both url and map entries");
+      } else if (url != null) {
+        var other = otherMaps?[url];
+        if (otherMaps == null || other == null) {
+          throw FormatException(
+              'section contains refers to $url, but no map was '
+              'given for it. Make sure a map is passed in "otherMaps"');
+        }
+        _maps.add(parseJson(other, otherMaps: otherMaps, mapUrl: url));
+      } else if (map != null) {
+        _maps.add(parseJson(map, otherMaps: otherMaps, mapUrl: mapUrl));
+      } else {
+        throw const FormatException('section missing url or map');
+      }
+    }
+    if (_lineStart.isEmpty) {
+      throw const FormatException('expected at least one section');
+    }
+  }
+
+  int _indexFor(int line, int column) {
+    for (var i = 0; i < _lineStart.length; i++) {
+      if (line < _lineStart[i]) return i - 1;
+      if (line == _lineStart[i] && column < _columnStart[i]) return i - 1;
+    }
+    return _lineStart.length - 1;
+  }
+
+  @override
+  SourceMapSpan? spanFor(int line, int column,
+      {Map<String, SourceFile>? files, String? uri}) {
+    // TODO(jacobr): perhaps verify that targetUrl matches the actual uri
+    // or at least ends in the same file name.
+    var index = _indexFor(line, column);
+    return _maps[index].spanFor(
+        line - _lineStart[index], column - _columnStart[index],
+        files: files);
+  }
+
+  @override
+  String toString() {
+    var buff = StringBuffer('$runtimeType : [');
+    for (var i = 0; i < _lineStart.length; i++) {
+      buff
+        ..write('(')
+        ..write(_lineStart[i])
+        ..write(',')
+        ..write(_columnStart[i])
+        ..write(':')
+        ..write(_maps[i])
+        ..write(')');
+    }
+    buff.write(']');
+    return buff.toString();
+  }
+}
+
+class MappingBundle extends Mapping {
+  final Map<String, SingleMapping> _mappings = {};
+
+  MappingBundle();
+
+  MappingBundle.fromJson(List json, {/*String|Uri*/ Object? mapUrl}) {
+    for (var map in json) {
+      addMapping(parseJson(map as Map, mapUrl: mapUrl) as SingleMapping);
+    }
+  }
+
+  void addMapping(SingleMapping mapping) {
+    // TODO(jacobr): verify that targetUrl is valid uri instead of a windows
+    // path.
+    // TODO: Remove type arg https://github.com/dart-lang/sdk/issues/42227
+    var targetUrl = ArgumentError.checkNotNull<String>(
+        mapping.targetUrl, 'mapping.targetUrl');
+    _mappings[targetUrl] = mapping;
+  }
+
+  /// Encodes the Mapping mappings as a json map.
+  List toJson() => _mappings.values.map((v) => v.toJson()).toList();
+
+  @override
+  String toString() {
+    var buff = StringBuffer();
+    for (var map in _mappings.values) {
+      buff.write(map.toString());
+    }
+    return buff.toString();
+  }
+
+  bool containsMapping(String url) => _mappings.containsKey(url);
+
+  @override
+  SourceMapSpan? spanFor(int line, int column,
+      {Map<String, SourceFile>? files, String? uri}) {
+    // TODO: Remove type arg https://github.com/dart-lang/sdk/issues/42227
+    uri = ArgumentError.checkNotNull<String>(uri, 'uri');
+
+    // Find the longest suffix of the uri that matches the sourcemap
+    // where the suffix starts after a path segment boundary.
+    // We consider ":" and "/" as path segment boundaries so that
+    // "package:" uris can be handled with minimal special casing. Having a
+    // few false positive path segment boundaries is not a significant issue
+    // as we prefer the longest matching prefix.
+    // Using package:path `path.split` to find path segment boundaries would
+    // not generate all of the path segment boundaries we want for "package:"
+    // urls as "package:package_name" would be one path segment when we want
+    // "package" and "package_name" to be sepearate path segments.
+
+    var onBoundary = true;
+    var separatorCodeUnits = ['/'.codeUnitAt(0), ':'.codeUnitAt(0)];
+    for (var i = 0; i < uri.length; ++i) {
+      if (onBoundary) {
+        var candidate = uri.substring(i);
+        var candidateMapping = _mappings[candidate];
+        if (candidateMapping != null) {
+          return candidateMapping.spanFor(line, column,
+              files: files, uri: candidate);
+        }
+      }
+      onBoundary = separatorCodeUnits.contains(uri.codeUnitAt(i));
+    }
+
+    // Note: when there is no source map for an uri, this behaves like an
+    // identity function, returning the requested location as the result.
+
+    // Create a mock offset for the output location. We compute it in terms
+    // of the input line and column to minimize the chances that two different
+    // line and column locations are mapped to the same offset.
+    var offset = line * 1000000 + column;
+    var location = SourceLocation(offset,
+        line: line, column: column, sourceUrl: Uri.parse(uri));
+    return SourceMapSpan(location, location, '');
+  }
+}
+
+/// A map containing direct source mappings.
+class SingleMapping extends Mapping {
+  /// Source urls used in the mapping, indexed by id.
+  final List<String> urls;
+
+  /// Source names used in the mapping, indexed by id.
+  final List<String> names;
+
+  /// The [SourceFile]s to which the entries in [lines] refer.
+  ///
+  /// This is in the same order as [urls]. If this was constructed using
+  /// [SingleMapping.fromEntries], this contains files from any [FileLocation]s
+  /// used to build the mapping. If it was parsed from JSON, it contains files
+  /// for any sources whose contents were provided via the `"sourcesContent"`
+  /// field.
+  ///
+  /// Files whose contents aren't available are `null`.
+  final List<SourceFile?> files;
+
+  /// Entries indicating the beginning of each span.
+  final List<TargetLineEntry> lines;
+
+  /// Url of the target file.
+  String? targetUrl;
+
+  /// Source root prepended to all entries in [urls].
+  String? sourceRoot;
+
+  final Uri? _mapUrl;
+
+  final Map<String, dynamic> extensions;
+
+  SingleMapping._(this.targetUrl, this.files, this.urls, this.names, this.lines)
+      : _mapUrl = null,
+        extensions = {};
+
+  factory SingleMapping.fromEntries(Iterable<builder.Entry> entries,
+      [String? fileUrl]) {
+    // The entries needs to be sorted by the target offsets.
+    var sourceEntries = entries.toList()..sort();
+    var lines = <TargetLineEntry>[];
+
+    // Indices associated with file urls that will be part of the source map. We
+    // rely on map order so that `urls.keys[urls[u]] == u`
+    var urls = <String, int>{};
+
+    // Indices associated with identifiers that will be part of the source map.
+    // We rely on map order so that `names.keys[names[n]] == n`
+    var names = <String, int>{};
+
+    /// The file for each URL, indexed by [urls]' values.
+    var files = <int, SourceFile>{};
+
+    int? lineNum;
+    late List<TargetEntry> targetEntries;
+    for (var sourceEntry in sourceEntries) {
+      if (lineNum == null || sourceEntry.target.line > lineNum) {
+        lineNum = sourceEntry.target.line;
+        targetEntries = <TargetEntry>[];
+        lines.add(TargetLineEntry(lineNum, targetEntries));
+      }
+
+      var sourceUrl = sourceEntry.source.sourceUrl;
+      var urlId = urls.putIfAbsent(
+          sourceUrl == null ? '' : sourceUrl.toString(), () => urls.length);
+
+      if (sourceEntry.source is FileLocation) {
+        files.putIfAbsent(
+            urlId, () => (sourceEntry.source as FileLocation).file);
+      }
+
+      var sourceEntryIdentifierName = sourceEntry.identifierName;
+      var srcNameId = sourceEntryIdentifierName == null
+          ? null
+          : names.putIfAbsent(sourceEntryIdentifierName, () => names.length);
+      targetEntries.add(TargetEntry(sourceEntry.target.column, urlId,
+          sourceEntry.source.line, sourceEntry.source.column, srcNameId));
+    }
+    return SingleMapping._(fileUrl, urls.values.map((i) => files[i]).toList(),
+        urls.keys.toList(), names.keys.toList(), lines);
+  }
+
+  SingleMapping.fromJson(Map<String, dynamic> map, {Object? mapUrl})
+      : targetUrl = map['file'] as String?,
+        urls = List<String>.from(map['sources'] as List),
+        names = List<String>.from((map['names'] as List?) ?? []),
+        files = List.filled((map['sources'] as List).length, null),
+        sourceRoot = map['sourceRoot'] as String?,
+        lines = <TargetLineEntry>[],
+        _mapUrl = mapUrl is String ? Uri.parse(mapUrl) : (mapUrl as Uri?),
+        extensions = {} {
+    var sourcesContent = map['sourcesContent'] == null
+        ? const <String?>[]
+        : List<String?>.from(map['sourcesContent'] as List);
+    for (var i = 0; i < urls.length && i < sourcesContent.length; i++) {
+      var source = sourcesContent[i];
+      if (source == null) continue;
+      files[i] = SourceFile.fromString(source, url: urls[i]);
+    }
+
+    var line = 0;
+    var column = 0;
+    var srcUrlId = 0;
+    var srcLine = 0;
+    var srcColumn = 0;
+    var srcNameId = 0;
+    var tokenizer = _MappingTokenizer(map['mappings'] as String);
+    var entries = <TargetEntry>[];
+
+    while (tokenizer.hasTokens) {
+      if (tokenizer.nextKind.isNewLine) {
+        if (entries.isNotEmpty) {
+          lines.add(TargetLineEntry(line, entries));
+          entries = <TargetEntry>[];
+        }
+        line++;
+        column = 0;
+        tokenizer._consumeNewLine();
+        continue;
+      }
+
+      // Decode the next entry, using the previous encountered values to
+      // decode the relative values.
+      //
+      // We expect 1, 4, or 5 values. If present, values are expected in the
+      // following order:
+      //   0: the starting column in the current line of the generated file
+      //   1: the id of the original source file
+      //   2: the starting line in the original source
+      //   3: the starting column in the original source
+      //   4: the id of the original symbol name
+      // The values are relative to the previous encountered values.
+      if (tokenizer.nextKind.isNewSegment) throw _segmentError(0, line);
+      column += tokenizer._consumeValue();
+      if (!tokenizer.nextKind.isValue) {
+        entries.add(TargetEntry(column));
+      } else {
+        srcUrlId += tokenizer._consumeValue();
+        if (srcUrlId >= urls.length) {
+          throw StateError(
+              'Invalid source url id. $targetUrl, $line, $srcUrlId');
+        }
+        if (!tokenizer.nextKind.isValue) throw _segmentError(2, line);
+        srcLine += tokenizer._consumeValue();
+        if (!tokenizer.nextKind.isValue) throw _segmentError(3, line);
+        srcColumn += tokenizer._consumeValue();
+        if (!tokenizer.nextKind.isValue) {
+          entries.add(TargetEntry(column, srcUrlId, srcLine, srcColumn));
+        } else {
+          srcNameId += tokenizer._consumeValue();
+          if (srcNameId >= names.length) {
+            throw StateError('Invalid name id: $targetUrl, $line, $srcNameId');
+          }
+          entries.add(
+              TargetEntry(column, srcUrlId, srcLine, srcColumn, srcNameId));
+        }
+      }
+      if (tokenizer.nextKind.isNewSegment) tokenizer._consumeNewSegment();
+    }
+    if (entries.isNotEmpty) {
+      lines.add(TargetLineEntry(line, entries));
+    }
+
+    map.forEach((name, value) {
+      if (name.startsWith('x_')) extensions[name] = value;
+    });
+  }
+
+  /// Encodes the Mapping mappings as a json map.
+  ///
+  /// If [includeSourceContents] is `true`, this includes the source file
+  /// contents from [files] in the map if possible.
+  Map<String, dynamic> toJson({bool includeSourceContents = false}) {
+    var buff = StringBuffer();
+    var line = 0;
+    var column = 0;
+    var srcLine = 0;
+    var srcColumn = 0;
+    var srcUrlId = 0;
+    var srcNameId = 0;
+    var first = true;
+
+    for (var entry in lines) {
+      var nextLine = entry.line;
+      if (nextLine > line) {
+        for (var i = line; i < nextLine; ++i) {
+          buff.write(';');
+        }
+        line = nextLine;
+        column = 0;
+        first = true;
+      }
+
+      for (var segment in entry.entries) {
+        if (!first) buff.write(',');
+        first = false;
+        column = _append(buff, column, segment.column);
+
+        // Encoding can be just the column offset if there is no source
+        // information.
+        var newUrlId = segment.sourceUrlId;
+        if (newUrlId == null) continue;
+        srcUrlId = _append(buff, srcUrlId, newUrlId);
+        srcLine = _append(buff, srcLine, segment.sourceLine!);
+        srcColumn = _append(buff, srcColumn, segment.sourceColumn!);
+
+        if (segment.sourceNameId == null) continue;
+        srcNameId = _append(buff, srcNameId, segment.sourceNameId!);
+      }
+    }
+
+    var result = <String, dynamic>{
+      'version': 3,
+      'sourceRoot': sourceRoot ?? '',
+      'sources': urls,
+      'names': names,
+      'mappings': buff.toString(),
+    };
+    if (targetUrl != null) result['file'] = targetUrl!;
+
+    if (includeSourceContents) {
+      result['sourcesContent'] = files.map((file) => file?.getText(0)).toList();
+    }
+    extensions.forEach((name, value) => result[name] = value);
+
+    return result;
+  }
+
+  /// Appends to [buff] a VLQ encoding of [newValue] using the difference
+  /// between [oldValue] and [newValue]
+  static int _append(StringBuffer buff, int oldValue, int newValue) {
+    buff.writeAll(encodeVlq(newValue - oldValue));
+    return newValue;
+  }
+
+  StateError _segmentError(int seen, int line) =>
+      StateError('Invalid entry in sourcemap, expected 1, 4, or 5'
+          ' values, but got $seen.\ntargeturl: $targetUrl, line: $line');
+
+  /// Returns [TargetLineEntry] which includes the location in the target [line]
+  /// number. In particular, the resulting entry is the last entry whose line
+  /// number is lower or equal to [line].
+  TargetLineEntry? _findLine(int line) {
+    var index = binarySearch(lines, (e) => e.line > line);
+    return (index <= 0) ? null : lines[index - 1];
+  }
+
+  /// Returns [TargetEntry] which includes the location denoted by
+  /// [line], [column]. If [lineEntry] corresponds to [line], then this will be
+  /// the last entry whose column is lower or equal than [column]. If
+  /// [lineEntry] corresponds to a line prior to [line], then the result will be
+  /// the very last entry on that line.
+  TargetEntry? _findColumn(int line, int column, TargetLineEntry? lineEntry) {
+    if (lineEntry == null || lineEntry.entries.isEmpty) return null;
+    if (lineEntry.line != line) return lineEntry.entries.last;
+    var entries = lineEntry.entries;
+    var index = binarySearch(entries, (e) => e.column > column);
+    return (index <= 0) ? null : entries[index - 1];
+  }
+
+  @override
+  SourceMapSpan? spanFor(int line, int column,
+      {Map<String, SourceFile>? files, String? uri}) {
+    var entry = _findColumn(line, column, _findLine(line));
+    if (entry == null) return null;
+
+    var sourceUrlId = entry.sourceUrlId;
+    if (sourceUrlId == null) return null;
+
+    var url = urls[sourceUrlId];
+    if (sourceRoot != null) {
+      url = '$sourceRoot$url';
+    }
+
+    var sourceNameId = entry.sourceNameId;
+    var file = files?[url];
+    if (file != null) {
+      var start = file.getOffset(entry.sourceLine!, entry.sourceColumn);
+      if (sourceNameId != null) {
+        var text = names[sourceNameId];
+        return SourceMapFileSpan(file.span(start, start + text.length),
+            isIdentifier: true);
+      } else {
+        return SourceMapFileSpan(file.location(start).pointSpan());
+      }
+    } else {
+      var start = SourceLocation(0,
+          sourceUrl: _mapUrl?.resolve(url) ?? url,
+          line: entry.sourceLine,
+          column: entry.sourceColumn);
+
+      // Offset and other context is not available.
+      if (sourceNameId != null) {
+        return SourceMapSpan.identifier(start, names[sourceNameId]);
+      } else {
+        return SourceMapSpan(start, start, '');
+      }
+    }
+  }
+
+  @override
+  String toString() {
+    return (StringBuffer('$runtimeType : [')
+          ..write('targetUrl: ')
+          ..write(targetUrl)
+          ..write(', sourceRoot: ')
+          ..write(sourceRoot)
+          ..write(', urls: ')
+          ..write(urls)
+          ..write(', names: ')
+          ..write(names)
+          ..write(', lines: ')
+          ..write(lines)
+          ..write(']'))
+        .toString();
+  }
+
+  String get debugString {
+    var buff = StringBuffer();
+    for (var lineEntry in lines) {
+      var line = lineEntry.line;
+      for (var entry in lineEntry.entries) {
+        buff
+          ..write(targetUrl)
+          ..write(': ')
+          ..write(line)
+          ..write(':')
+          ..write(entry.column);
+        var sourceUrlId = entry.sourceUrlId;
+        if (sourceUrlId != null) {
+          buff
+            ..write('   -->   ')
+            ..write(sourceRoot)
+            ..write(urls[sourceUrlId])
+            ..write(': ')
+            ..write(entry.sourceLine)
+            ..write(':')
+            ..write(entry.sourceColumn);
+        }
+        var sourceNameId = entry.sourceNameId;
+        if (sourceNameId != null) {
+          buff
+            ..write(' (')
+            ..write(names[sourceNameId])
+            ..write(')');
+        }
+        buff.write('\n');
+      }
+    }
+    return buff.toString();
+  }
+}
+
+/// A line entry read from a source map.
+class TargetLineEntry {
+  final int line;
+  List<TargetEntry> entries;
+  TargetLineEntry(this.line, this.entries);
+
+  @override
+  String toString() => '$runtimeType: $line $entries';
+}
+
+/// A target segment entry read from a source map
+class TargetEntry {
+  final int column;
+  final int? sourceUrlId;
+  final int? sourceLine;
+  final int? sourceColumn;
+  final int? sourceNameId;
+
+  TargetEntry(this.column,
+      [this.sourceUrlId,
+      this.sourceLine,
+      this.sourceColumn,
+      this.sourceNameId]);
+
+  @override
+  String toString() => '$runtimeType: '
+      '($column, $sourceUrlId, $sourceLine, $sourceColumn, $sourceNameId)';
+}
+
+/// A character iterator over a string that can peek one character ahead.
+class _MappingTokenizer implements Iterator<String> {
+  final String _internal;
+  final int _length;
+  int index = -1;
+  _MappingTokenizer(String internal)
+      : _internal = internal,
+        _length = internal.length;
+
+  // Iterator API is used by decodeVlq to consume VLQ entries.
+  @override
+  bool moveNext() => ++index < _length;
+
+  @override
+  String get current => (index >= 0 && index < _length)
+      ? _internal[index]
+      : throw RangeError.index(index, _internal);
+
+  bool get hasTokens => index < _length - 1 && _length > 0;
+
+  _TokenKind get nextKind {
+    if (!hasTokens) return _TokenKind.eof;
+    var next = _internal[index + 1];
+    if (next == ';') return _TokenKind.line;
+    if (next == ',') return _TokenKind.segment;
+    return _TokenKind.value;
+  }
+
+  int _consumeValue() => decodeVlq(this);
+  void _consumeNewLine() {
+    ++index;
+  }
+
+  void _consumeNewSegment() {
+    ++index;
+  }
+
+  // Print the state of the iterator, with colors indicating the current
+  // position.
+  @override
+  String toString() {
+    var buff = StringBuffer();
+    for (var i = 0; i < index; i++) {
+      buff.write(_internal[i]);
+    }
+    buff.write('[31m');
+    try {
+      buff.write(current);
+      // TODO: Determine whether this try / catch can be removed.
+      // ignore: avoid_catching_errors
+    } on RangeError catch (_) {}
+    buff.write('[0m');
+    for (var i = index + 1; i < _internal.length; i++) {
+      buff.write(_internal[i]);
+    }
+    buff.write(' ($index)');
+    return buff.toString();
+  }
+}
+
+class _TokenKind {
+  static const _TokenKind line = _TokenKind(isNewLine: true);
+  static const _TokenKind segment = _TokenKind(isNewSegment: true);
+  static const _TokenKind eof = _TokenKind(isEof: true);
+  static const _TokenKind value = _TokenKind();
+  final bool isNewLine;
+  final bool isNewSegment;
+  final bool isEof;
+  bool get isValue => !isNewLine && !isNewSegment && !isEof;
+
+  const _TokenKind(
+      {this.isNewLine = false, this.isNewSegment = false, this.isEof = false});
+}

diff --git a/pkgs/source_maps/lib/printer.dart b/pkgs/source_maps/lib/printer.dart
new file mode 100644
index 0000000..32523d6
--- /dev/null
+++ b/pkgs/source_maps/lib/printer.dart

@@ -0,0 +1,262 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Contains a code printer that generates code by recording the source maps.
+library;
+
+import 'package:source_span/source_span.dart';
+
+import 'builder.dart';
+import 'src/source_map_span.dart';
+import 'src/utils.dart';
+
+/// A simple printer that keeps track of offset locations and records source
+/// maps locations.
+class Printer {
+  final String filename;
+  final StringBuffer _buff = StringBuffer();
+  final SourceMapBuilder _maps = SourceMapBuilder();
+  String get text => _buff.toString();
+  String get map => _maps.toJson(filename);
+
+  /// Current source location mapping.
+  SourceLocation? _loc;
+
+  /// Current line in the buffer;
+  int _line = 0;
+
+  /// Current column in the buffer.
+  int _column = 0;
+
+  Printer(this.filename);
+
+  /// Add [str] contents to the output, tracking new lines to track correct
+  /// positions for span locations. When [projectMarks] is true, this method
+  /// adds a source map location on each new line, projecting that every new
+  /// line in the target file (printed here) corresponds to a new line in the
+  /// source file.
+  void add(String str, {bool projectMarks = false}) {
+    var chars = str.runes.toList();
+    var length = chars.length;
+    for (var i = 0; i < length; i++) {
+      var c = chars[i];
+      if (c == lineFeed ||
+          (c == carriageReturn &&
+              (i + 1 == length || chars[i + 1] != lineFeed))) {
+        // Return not followed by line-feed is treated as a new line.
+        _line++;
+        _column = 0;
+        {
+          // **Warning**: Any calls to `mark` will change the value of `_loc`,
+          // so this local variable is no longer up to date after that point.
+          //
+          // This is why it has been put inside its own block to limit the
+          // scope in which it is available.
+          var loc = _loc;
+          if (projectMarks && loc != null) {
+            if (loc is FileLocation) {
+              var file = loc.file;
+              mark(file.location(file.getOffset(loc.line + 1)));
+            } else {
+              mark(SourceLocation(0,
+                  sourceUrl: loc.sourceUrl, line: loc.line + 1, column: 0));
+            }
+          }
+        }
+      } else {
+        _column++;
+      }
+    }
+    _buff.write(str);
+  }
+
+  /// Append a [total] number of spaces in the target file. Typically used for
+  /// formatting indentation.
+  void addSpaces(int total) {
+    for (var i = 0; i < total; i++) {
+      _buff.write(' ');
+    }
+    _column += total;
+  }
+
+  /// Marks that the current point in the target file corresponds to the [mark]
+  /// in the source file, which can be either a [SourceLocation] or a
+  /// [SourceSpan]. When the mark is a [SourceMapSpan] with `isIdentifier` set,
+  /// this also records the name of the identifier in the source map
+  /// information.
+  void mark(Object mark) {
+    late final SourceLocation loc;
+    String? identifier;
+    if (mark is SourceLocation) {
+      loc = mark;
+    } else if (mark is SourceSpan) {
+      loc = mark.start;
+      if (mark is SourceMapSpan && mark.isIdentifier) identifier = mark.text;
+    }
+    _maps.addLocation(loc,
+        SourceLocation(_buff.length, line: _line, column: _column), identifier);
+    _loc = loc;
+  }
+}
+
+/// A more advanced printer that keeps track of offset locations to record
+/// source maps, but additionally allows nesting of different kind of items,
+/// including [NestedPrinter]s, and it let's you automatically indent text.
+///
+/// This class is especially useful when doing code generation, where different
+/// pieces of the code are generated independently on separate printers, and are
+/// finally put together in the end.
+class NestedPrinter implements NestedItem {
+  /// Items recoded by this printer, which can be [String] literals,
+  /// [NestedItem]s, and source map information like [SourceLocation] and
+  /// [SourceSpan].
+  final List<Object> _items = [];
+
+  /// Internal buffer to merge consecutive strings added to this printer.
+  StringBuffer? _buff;
+
+  /// Current indentation, which can be updated from outside this class.
+  int indent;
+
+  /// [Printer] used during the last call to [build], if any.
+  Printer? printer;
+
+  /// Returns the text produced after calling [build].
+  String? get text => printer?.text;
+
+  /// Returns the source-map information produced after calling [build].
+  String? get map => printer?.map;
+
+  /// Item used to indicate that the following item is copied from the original
+  /// source code, and hence we should preserve source-maps on every new line.
+  static final _original = Object();
+
+  NestedPrinter([this.indent = 0]);
+
+  /// Adds [object] to this printer. [object] can be a [String],
+  /// [NestedPrinter], or anything implementing [NestedItem]. If [object] is a
+  /// [String], the value is appended directly, without doing any formatting
+  /// changes. If you wish to add a line of code with automatic indentation, use
+  /// [addLine] instead.  [NestedPrinter]s and [NestedItem]s are not processed
+  /// until [build] gets called later on. We ensure that [build] emits every
+  /// object in the order that they were added to this printer.
+  ///
+  /// The [location] and [span] parameters indicate the corresponding source map
+  /// location of [object] in the original input. Only one, [location] or
+  /// [span], should be provided at a time.
+  ///
+  /// Indicate [isOriginal] when [object] is copied directly from the user code.
+  /// Setting [isOriginal] will make this printer propagate source map locations
+  /// on every line-break.
+  void add(Object object,
+      {SourceLocation? location, SourceSpan? span, bool isOriginal = false}) {
+    if (object is! String || location != null || span != null || isOriginal) {
+      _flush();
+      assert(location == null || span == null);
+      if (location != null) _items.add(location);
+      if (span != null) _items.add(span);
+      if (isOriginal) _items.add(_original);
+    }
+
+    if (object is String) {
+      _appendString(object);
+    } else {
+      _items.add(object);
+    }
+  }
+
+  /// Append `2 * indent` spaces to this printer.
+  void insertIndent() => _indent(indent);
+
+  /// Add a [line], autoindenting to the current value of [indent]. Note,
+  /// indentation is not inferred from the contents added to this printer. If a
+  /// line starts or ends an indentation block, you need to also update [indent]
+  /// accordingly. Also, indentation is not adapted for nested printers. If
+  /// you add a [NestedPrinter] to this printer, its indentation is set
+  /// separately and will not include any the indentation set here.
+  ///
+  /// The [location] and [span] parameters indicate the corresponding source map
+  /// location of [line] in the original input. Only one, [location] or
+  /// [span], should be provided at a time.
+  void addLine(String? line, {SourceLocation? location, SourceSpan? span}) {
+    if (location != null || span != null) {
+      _flush();
+      assert(location == null || span == null);
+      if (location != null) _items.add(location);
+      if (span != null) _items.add(span);
+    }
+    if (line == null) return;
+    if (line != '') {
+      // We don't indent empty lines.
+      _indent(indent);
+      _appendString(line);
+    }
+    _appendString('\n');
+  }
+
+  /// Appends a string merging it with any previous strings, if possible.
+  void _appendString(String s) {
+    var buf = _buff ??= StringBuffer();
+    buf.write(s);
+  }
+
+  /// Adds all of the current [_buff] contents as a string item.
+  void _flush() {
+    if (_buff != null) {
+      _items.add(_buff.toString());
+      _buff = null;
+    }
+  }
+
+  void _indent(int indent) {
+    for (var i = 0; i < indent; i++) {
+      _appendString('  ');
+    }
+  }
+
+  /// Returns a string representation of all the contents appended to this
+  /// printer, including source map location tokens.
+  @override
+  String toString() {
+    _flush();
+    return (StringBuffer()..writeAll(_items)).toString();
+  }
+
+  /// Builds the output of this printer and source map information. After
+  /// calling this function, you can use [text] and [map] to retrieve the
+  /// geenrated code and source map information, respectively.
+  void build(String filename) {
+    writeTo(printer = Printer(filename));
+  }
+
+  /// Implements the [NestedItem] interface.
+  @override
+  void writeTo(Printer printer) {
+    _flush();
+    var propagate = false;
+    for (var item in _items) {
+      if (item is NestedItem) {
+        item.writeTo(printer);
+      } else if (item is String) {
+        printer.add(item, projectMarks: propagate);
+        propagate = false;
+      } else if (item is SourceLocation || item is SourceSpan) {
+        printer.mark(item);
+      } else if (item == _original) {
+        // we insert booleans when we are about to quote text that was copied
+        // from the original source. In such case, we will propagate marks on
+        // every new-line.
+        propagate = true;
+      } else {
+        throw UnsupportedError('Unknown item type: $item');
+      }
+    }
+  }
+}
+
+/// An item added to a [NestedPrinter].
+abstract class NestedItem {
+  /// Write the contents of this item into [printer].
+  void writeTo(Printer printer);
+}

diff --git a/pkgs/source_maps/lib/refactor.dart b/pkgs/source_maps/lib/refactor.dart
new file mode 100644
index 0000000..a518a0c
--- /dev/null
+++ b/pkgs/source_maps/lib/refactor.dart

@@ -0,0 +1,140 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Tools to help implement refactoring like transformations to Dart code.
+///
+/// [TextEditTransaction] supports making a series of changes to a text buffer.
+/// [guessIndent] helps to guess the appropriate indentiation for the new code.
+library;
+
+import 'package:source_span/source_span.dart';
+
+import 'printer.dart';
+import 'src/utils.dart';
+
+/// Editable text transaction.
+///
+/// Applies a series of edits using original location
+/// information, and composes them into the edited string.
+class TextEditTransaction {
+  final SourceFile? file;
+  final String original;
+  final _edits = <_TextEdit>[];
+
+  /// Creates a new transaction.
+  TextEditTransaction(this.original, this.file);
+
+  bool get hasEdits => _edits.isNotEmpty;
+
+  /// Edit the original text, replacing text on the range [begin] and [end]
+  /// with the [replacement]. [replacement] can be either a string or a
+  /// [NestedPrinter].
+  void edit(int begin, int end, Object replacement) {
+    _edits.add(_TextEdit(begin, end, replacement));
+  }
+
+  /// Create a source map [SourceLocation] for [offset], if [file] is not
+  /// `null`.
+  SourceLocation? _loc(int offset) => file?.location(offset);
+
+  /// Applies all pending [edit]s and returns a [NestedPrinter] containing the
+  /// rewritten string and source map information. [file]`.location` is given to
+  /// the underlying printer to indicate the name of the generated file that
+  /// will contains the source map information.
+  ///
+  /// Throws [UnsupportedError] if the edits were overlapping. If no edits were
+  /// made, the printer simply contains the original string.
+  NestedPrinter commit() {
+    var printer = NestedPrinter();
+    if (_edits.isEmpty) {
+      return printer..add(original, location: _loc(0), isOriginal: true);
+    }
+
+    // Sort edits by start location.
+    _edits.sort();
+
+    var consumed = 0;
+    for (var edit in _edits) {
+      if (consumed > edit.begin) {
+        var sb = StringBuffer();
+        sb
+          ..write(file?.location(edit.begin).toolString)
+          ..write(': overlapping edits. Insert at offset ')
+          ..write(edit.begin)
+          ..write(' but have consumed ')
+          ..write(consumed)
+          ..write(' input characters. List of edits:');
+        for (var e in _edits) {
+          sb
+            ..write('\n    ')
+            ..write(e);
+        }
+        throw UnsupportedError(sb.toString());
+      }
+
+      // Add characters from the original string between this edit and the last
+      // one, if any.
+      var betweenEdits = original.substring(consumed, edit.begin);
+      printer
+        ..add(betweenEdits, location: _loc(consumed), isOriginal: true)
+        ..add(edit.replace, location: _loc(edit.begin));
+      consumed = edit.end;
+    }
+
+    // Add any text from the end of the original string that was not replaced.
+    printer.add(original.substring(consumed),
+        location: _loc(consumed), isOriginal: true);
+    return printer;
+  }
+}
+
+class _TextEdit implements Comparable<_TextEdit> {
+  final int begin;
+  final int end;
+
+  /// The replacement used by the edit, can be a string or a [NestedPrinter].
+  final Object replace;
+
+  _TextEdit(this.begin, this.end, this.replace);
+
+  int get length => end - begin;
+
+  @override
+  String toString() => '(Edit @ $begin,$end: "$replace")';
+
+  @override
+  int compareTo(_TextEdit other) {
+    var diff = begin - other.begin;
+    if (diff != 0) return diff;
+    return end - other.end;
+  }
+}
+
+/// Returns all whitespace characters at the start of [charOffset]'s line.
+String guessIndent(String code, int charOffset) {
+  // Find the beginning of the line
+  var lineStart = 0;
+  for (var i = charOffset - 1; i >= 0; i--) {
+    var c = code.codeUnitAt(i);
+    if (c == lineFeed || c == carriageReturn) {
+      lineStart = i + 1;
+      break;
+    }
+  }
+
+  // Grab all the whitespace
+  var whitespaceEnd = code.length;
+  for (var i = lineStart; i < code.length; i++) {
+    var c = code.codeUnitAt(i);
+    if (c != _space && c != _tab) {
+      whitespaceEnd = i;
+      break;
+    }
+  }
+
+  return code.substring(lineStart, whitespaceEnd);
+}
+
+const int _tab = 9;
+const int _space = 32;

diff --git a/pkgs/source_maps/lib/source_maps.dart b/pkgs/source_maps/lib/source_maps.dart
new file mode 100644
index 0000000..244dee7
--- /dev/null
+++ b/pkgs/source_maps/lib/source_maps.dart

@@ -0,0 +1,38 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Library to create and parse source maps.
+///
+/// Create a source map using [SourceMapBuilder]. For example:
+///
+/// ```dart
+/// var json = (new SourceMapBuilder()
+///     ..add(inputSpan1, outputSpan1)
+///     ..add(inputSpan2, outputSpan2)
+///     ..add(inputSpan3, outputSpan3)
+///     .toJson(outputFile);
+/// ```
+///
+/// Use the source_span package's [SourceSpan] and [SourceFile] classes to
+/// specify span locations.
+///
+/// Parse a source map using [parse], and call `spanFor` on the returned mapping
+/// object. For example:
+///
+/// ```dart
+/// var mapping = parse(json);
+/// mapping.spanFor(outputSpan1.line, outputSpan1.column)
+/// ```
+library;
+
+import 'package:source_span/source_span.dart';
+
+import 'builder.dart';
+import 'parser.dart';
+
+export 'builder.dart';
+export 'parser.dart';
+export 'printer.dart';
+export 'refactor.dart';
+export 'src/source_map_span.dart';

diff --git a/pkgs/source_maps/lib/src/source_map_span.dart b/pkgs/source_maps/lib/src/source_map_span.dart
new file mode 100644
index 0000000..aad8a32
--- /dev/null
+++ b/pkgs/source_maps/lib/src/source_map_span.dart

@@ -0,0 +1,72 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:source_span/source_span.dart';
+
+/// A [SourceSpan] for spans coming from or being written to source maps.
+///
+/// These spans have an extra piece of metadata: whether or not they represent
+/// an identifier (see [isIdentifier]).
+class SourceMapSpan extends SourceSpanBase {
+  /// Whether this span represents an identifier.
+  ///
+  /// If this is `true`, [text] is the value of the identifier.
+  final bool isIdentifier;
+
+  SourceMapSpan(super.start, super.end, super.text,
+      {this.isIdentifier = false});
+
+  /// Creates a [SourceMapSpan] for an identifier with value [text] starting at
+  /// [start].
+  ///
+  /// The [end] location is determined by adding [text] to [start].
+  SourceMapSpan.identifier(SourceLocation start, String text)
+      : this(
+            start,
+            SourceLocation(start.offset + text.length,
+                sourceUrl: start.sourceUrl,
+                line: start.line,
+                column: start.column + text.length),
+            text,
+            isIdentifier: true);
+}
+
+/// A wrapper aruond a [FileSpan] that implements [SourceMapSpan].
+class SourceMapFileSpan implements SourceMapSpan, FileSpan {
+  final FileSpan _inner;
+  @override
+  final bool isIdentifier;
+
+  @override
+  SourceFile get file => _inner.file;
+  @override
+  FileLocation get start => _inner.start;
+  @override
+  FileLocation get end => _inner.end;
+  @override
+  String get text => _inner.text;
+  @override
+  String get context => _inner.context;
+  @override
+  Uri? get sourceUrl => _inner.sourceUrl;
+  @override
+  int get length => _inner.length;
+
+  SourceMapFileSpan(this._inner, {this.isIdentifier = false});
+
+  @override
+  int compareTo(SourceSpan other) => _inner.compareTo(other);
+  @override
+  String highlight({Object? color}) => _inner.highlight(color: color);
+  @override
+  SourceSpan union(SourceSpan other) => _inner.union(other);
+  @override
+  FileSpan expand(FileSpan other) => _inner.expand(other);
+  @override
+  String message(String message, {Object? color}) =>
+      _inner.message(message, color: color);
+  @override
+  String toString() =>
+      _inner.toString().replaceAll('FileSpan', 'SourceMapFileSpan');
+}

diff --git a/pkgs/source_maps/lib/src/utils.dart b/pkgs/source_maps/lib/src/utils.dart
new file mode 100644
index 0000000..ba04fbb
--- /dev/null
+++ b/pkgs/source_maps/lib/src/utils.dart

@@ -0,0 +1,32 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Utilities that shouldn't be in this package.
+library;
+
+/// Find the first entry in a sorted [list] that matches a monotonic predicate.
+/// Given a result `n`, that all items before `n` will not match, `n` matches,
+/// and all items after `n` match too. The result is -1 when there are no
+/// items, 0 when all items match, and list.length when none does.
+// TODO(sigmund): remove this function after dartbug.com/5624 is fixed.
+int binarySearch<T>(List<T> list, bool Function(T) matches) {
+  if (list.isEmpty) return -1;
+  if (matches(list.first)) return 0;
+  if (!matches(list.last)) return list.length;
+
+  var min = 0;
+  var max = list.length - 1;
+  while (min < max) {
+    var half = min + ((max - min) ~/ 2);
+    if (matches(list[half])) {
+      max = half;
+    } else {
+      min = half + 1;
+    }
+  }
+  return max;
+}
+
+const int lineFeed = 10;
+const int carriageReturn = 13;

diff --git a/pkgs/source_maps/lib/src/vlq.dart b/pkgs/source_maps/lib/src/vlq.dart
new file mode 100644
index 0000000..3b0562d
--- /dev/null
+++ b/pkgs/source_maps/lib/src/vlq.dart

@@ -0,0 +1,101 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Utilities to encode and decode VLQ values used in source maps.
+///
+/// Sourcemaps are encoded with variable length numbers as base64 encoded
+/// strings with the least significant digit coming first. Each base64 digit
+/// encodes a 5-bit value (0-31) and a continuation bit. Signed values can be
+/// represented by using the least significant bit of the value as the sign bit.
+///
+/// For more details see the source map [version 3 documentation](https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k/edit?usp=sharing).
+library;
+
+import 'dart:math';
+
+const int vlqBaseShift = 5;
+
+const int vlqBaseMask = (1 << 5) - 1;
+
+const int vlqContinuationBit = 1 << 5;
+
+const int vlqContinuationMask = 1 << 5;
+
+const String base64Digits =
+    'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
+
+final Map<String, int> _digits = () {
+  var map = <String, int>{};
+  for (var i = 0; i < 64; i++) {
+    map[base64Digits[i]] = i;
+  }
+  return map;
+}();
+
+final int maxInt32 = (pow(2, 31) as int) - 1;
+final int minInt32 = -(pow(2, 31) as int);
+
+/// Creates the VLQ encoding of [value] as a sequence of characters
+Iterable<String> encodeVlq(int value) {
+  if (value < minInt32 || value > maxInt32) {
+    throw ArgumentError('expected 32 bit int, got: $value');
+  }
+  var res = <String>[];
+  var signBit = 0;
+  if (value < 0) {
+    signBit = 1;
+    value = -value;
+  }
+  value = (value << 1) | signBit;
+  do {
+    var digit = value & vlqBaseMask;
+    value >>= vlqBaseShift;
+    if (value > 0) {
+      digit |= vlqContinuationBit;
+    }
+    res.add(base64Digits[digit]);
+  } while (value > 0);
+  return res;
+}
+
+/// Decodes a value written as a sequence of VLQ characters. The first input
+/// character will be `chars.current` after calling `chars.moveNext` once. The
+/// iterator is advanced until a stop character is found (a character without
+/// the [vlqContinuationBit]).
+int decodeVlq(Iterator<String> chars) {
+  var result = 0;
+  var stop = false;
+  var shift = 0;
+  while (!stop) {
+    if (!chars.moveNext()) throw StateError('incomplete VLQ value');
+    var char = chars.current;
+    var digit = _digits[char];
+    if (digit == null) {
+      throw FormatException('invalid character in VLQ encoding: $char');
+    }
+    stop = (digit & vlqContinuationBit) == 0;
+    digit &= vlqBaseMask;
+    result += digit << shift;
+    shift += vlqBaseShift;
+  }
+
+  // Result uses the least significant bit as a sign bit. We convert it into a
+  // two-complement value. For example,
+  //   2 (10 binary) becomes 1
+  //   3 (11 binary) becomes -1
+  //   4 (100 binary) becomes 2
+  //   5 (101 binary) becomes -2
+  //   6 (110 binary) becomes 3
+  //   7 (111 binary) becomes -3
+  var negate = (result & 1) == 1;
+  result = result >> 1;
+  result = negate ? -result : result;
+
+  // TODO(sigmund): can we detect this earlier?
+  if (result < minInt32 || result > maxInt32) {
+    throw FormatException(
+        'expected an encoded 32 bit int, but we got: $result');
+  }
+  return result;
+}

diff --git a/pkgs/source_maps/pubspec.yaml b/pkgs/source_maps/pubspec.yaml
new file mode 100644
index 0000000..32cbf4f
--- /dev/null
+++ b/pkgs/source_maps/pubspec.yaml

@@ -0,0 +1,15 @@
+name: source_maps
+version: 0.10.14-wip
+description: A library to programmatically manipulate source map files.
+repository: https://github.com/dart-lang/tools/tree/main/pkgs/source_maps
+
+environment:
+  sdk: ^3.3.0
+
+dependencies:
+  source_span: ^1.8.0
+
+dev_dependencies:
+  dart_flutter_team_lints: ^3.0.0
+  term_glyph: ^1.2.0
+  test: ^1.16.0

diff --git a/pkgs/source_maps/test/builder_test.dart b/pkgs/source_maps/test/builder_test.dart
new file mode 100644
index 0000000..4f773e7
--- /dev/null
+++ b/pkgs/source_maps/test/builder_test.dart

@@ -0,0 +1,32 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:convert';
+
+import 'package:source_maps/source_maps.dart';
+import 'package:test/test.dart';
+
+import 'common.dart';
+
+void main() {
+  test('builder - with span', () {
+    var map = (SourceMapBuilder()
+          ..addSpan(inputVar1, outputVar1)
+          ..addSpan(inputFunction, outputFunction)
+          ..addSpan(inputVar2, outputVar2)
+          ..addSpan(inputExpr, outputExpr))
+        .build(output.url.toString());
+    expect(map, equals(expectedMap));
+  });
+
+  test('builder - with location', () {
+    var str = (SourceMapBuilder()
+          ..addLocation(inputVar1.start, outputVar1.start, 'longVar1')
+          ..addLocation(inputFunction.start, outputFunction.start, 'longName')
+          ..addLocation(inputVar2.start, outputVar2.start, 'longVar2')
+          ..addLocation(inputExpr.start, outputExpr.start, null))
+        .toJson(output.url.toString());
+    expect(str, jsonEncode(expectedMap));
+  });
+}

diff --git a/pkgs/source_maps/test/common.dart b/pkgs/source_maps/test/common.dart
new file mode 100644
index 0000000..e225ff5
--- /dev/null
+++ b/pkgs/source_maps/test/common.dart

@@ -0,0 +1,107 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Common input/output used by builder, parser and end2end tests
+library;
+
+import 'package:source_maps/source_maps.dart';
+import 'package:source_span/source_span.dart';
+import 'package:test/test.dart';
+
+/// Content of the source file
+const String inputContent = '''
+/** this is a comment. */
+int longVar1 = 3;
+
+// this is a comment too
+int longName(int longVar2) {
+  return longVar1 + longVar2;
+}
+''';
+final input = SourceFile.fromString(inputContent, url: 'input.dart');
+
+/// A span in the input file
+SourceMapSpan ispan(int start, int end, [bool isIdentifier = false]) =>
+    SourceMapFileSpan(input.span(start, end), isIdentifier: isIdentifier);
+
+SourceMapSpan inputVar1 = ispan(30, 38, true);
+SourceMapSpan inputFunction = ispan(74, 82, true);
+SourceMapSpan inputVar2 = ispan(87, 95, true);
+
+SourceMapSpan inputVar1NoSymbol = ispan(30, 38);
+SourceMapSpan inputFunctionNoSymbol = ispan(74, 82);
+SourceMapSpan inputVar2NoSymbol = ispan(87, 95);
+
+SourceMapSpan inputExpr = ispan(108, 127);
+
+/// Content of the target file
+const String outputContent = '''
+var x = 3;
+f(y) => x + y;
+''';
+final output = SourceFile.fromString(outputContent, url: 'output.dart');
+
+/// A span in the output file
+SourceMapSpan ospan(int start, int end, [bool isIdentifier = false]) =>
+    SourceMapFileSpan(output.span(start, end), isIdentifier: isIdentifier);
+
+SourceMapSpan outputVar1 = ospan(4, 5, true);
+SourceMapSpan outputFunction = ospan(11, 12, true);
+SourceMapSpan outputVar2 = ospan(13, 14, true);
+SourceMapSpan outputVar1NoSymbol = ospan(4, 5);
+SourceMapSpan outputFunctionNoSymbol = ospan(11, 12);
+SourceMapSpan outputVar2NoSymbol = ospan(13, 14);
+SourceMapSpan outputExpr = ospan(19, 24);
+
+/// Expected output mapping when recording the following four mappings:
+///      inputVar1       <=   outputVar1
+///      inputFunction   <=   outputFunction
+///      inputVar2       <=   outputVar2
+///      inputExpr       <=   outputExpr
+///
+/// This mapping is stored in the tests so we can independently test the builder
+/// and parser algorithms without relying entirely on end2end tests.
+const Map<String, dynamic> expectedMap = {
+  'version': 3,
+  'sourceRoot': '',
+  'sources': ['input.dart'],
+  'names': ['longVar1', 'longName', 'longVar2'],
+  'mappings': 'IACIA;AAGAC,EAAaC,MACR',
+  'file': 'output.dart'
+};
+
+void check(SourceSpan outputSpan, Mapping mapping, SourceMapSpan inputSpan,
+    bool realOffsets) {
+  var line = outputSpan.start.line;
+  var column = outputSpan.start.column;
+  var files = realOffsets ? {'input.dart': input} : null;
+  var span = mapping.spanFor(line, column, files: files)!;
+  var span2 = mapping.spanForLocation(outputSpan.start, files: files)!;
+
+  // Both mapping APIs are equivalent.
+  expect(span.start.offset, span2.start.offset);
+  expect(span.start.line, span2.start.line);
+  expect(span.start.column, span2.start.column);
+  expect(span.end.offset, span2.end.offset);
+  expect(span.end.line, span2.end.line);
+  expect(span.end.column, span2.end.column);
+
+  // Mapping matches our input location (modulo using real offsets)
+  expect(span.start.line, inputSpan.start.line);
+  expect(span.start.column, inputSpan.start.column);
+  expect(span.sourceUrl, inputSpan.sourceUrl);
+  expect(span.start.offset, realOffsets ? inputSpan.start.offset : 0);
+
+  // Mapping includes the identifier, if any
+  if (inputSpan.isIdentifier) {
+    expect(span.end.line, inputSpan.end.line);
+    expect(span.end.column, inputSpan.end.column);
+    expect(span.end.offset, span.start.offset + inputSpan.text.length);
+    if (realOffsets) expect(span.end.offset, inputSpan.end.offset);
+  } else {
+    expect(span.end.offset, span.start.offset);
+    expect(span.end.line, span.start.line);
+    expect(span.end.column, span.start.column);
+  }
+}

diff --git a/pkgs/source_maps/test/end2end_test.dart b/pkgs/source_maps/test/end2end_test.dart
new file mode 100644
index 0000000..84dd5ba
--- /dev/null
+++ b/pkgs/source_maps/test/end2end_test.dart

@@ -0,0 +1,160 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:source_maps/source_maps.dart';
+import 'package:source_span/source_span.dart';
+import 'package:test/test.dart';
+
+import 'common.dart';
+
+void main() {
+  test('end-to-end setup', () {
+    expect(inputVar1.text, 'longVar1');
+    expect(inputFunction.text, 'longName');
+    expect(inputVar2.text, 'longVar2');
+    expect(inputVar1NoSymbol.text, 'longVar1');
+    expect(inputFunctionNoSymbol.text, 'longName');
+    expect(inputVar2NoSymbol.text, 'longVar2');
+    expect(inputExpr.text, 'longVar1 + longVar2');
+
+    expect(outputVar1.text, 'x');
+    expect(outputFunction.text, 'f');
+    expect(outputVar2.text, 'y');
+    expect(outputVar1NoSymbol.text, 'x');
+    expect(outputFunctionNoSymbol.text, 'f');
+    expect(outputVar2NoSymbol.text, 'y');
+    expect(outputExpr.text, 'x + y');
+  });
+
+  test('build + parse', () {
+    var map = (SourceMapBuilder()
+          ..addSpan(inputVar1, outputVar1)
+          ..addSpan(inputFunction, outputFunction)
+          ..addSpan(inputVar2, outputVar2)
+          ..addSpan(inputExpr, outputExpr))
+        .build(output.url.toString());
+    var mapping = parseJson(map);
+    check(outputVar1, mapping, inputVar1, false);
+    check(outputVar2, mapping, inputVar2, false);
+    check(outputFunction, mapping, inputFunction, false);
+    check(outputExpr, mapping, inputExpr, false);
+  });
+
+  test('build + parse - no symbols', () {
+    var map = (SourceMapBuilder()
+          ..addSpan(inputVar1NoSymbol, outputVar1NoSymbol)
+          ..addSpan(inputFunctionNoSymbol, outputFunctionNoSymbol)
+          ..addSpan(inputVar2NoSymbol, outputVar2NoSymbol)
+          ..addSpan(inputExpr, outputExpr))
+        .build(output.url.toString());
+    var mapping = parseJson(map);
+    check(outputVar1NoSymbol, mapping, inputVar1NoSymbol, false);
+    check(outputVar2NoSymbol, mapping, inputVar2NoSymbol, false);
+    check(outputFunctionNoSymbol, mapping, inputFunctionNoSymbol, false);
+    check(outputExpr, mapping, inputExpr, false);
+  });
+
+  test('build + parse, repeated entries', () {
+    var map = (SourceMapBuilder()
+          ..addSpan(inputVar1, outputVar1)
+          ..addSpan(inputVar1, outputVar1)
+          ..addSpan(inputFunction, outputFunction)
+          ..addSpan(inputFunction, outputFunction)
+          ..addSpan(inputVar2, outputVar2)
+          ..addSpan(inputVar2, outputVar2)
+          ..addSpan(inputExpr, outputExpr)
+          ..addSpan(inputExpr, outputExpr))
+        .build(output.url.toString());
+    var mapping = parseJson(map);
+    check(outputVar1, mapping, inputVar1, false);
+    check(outputVar2, mapping, inputVar2, false);
+    check(outputFunction, mapping, inputFunction, false);
+    check(outputExpr, mapping, inputExpr, false);
+  });
+
+  test('build + parse - no symbols, repeated entries', () {
+    var map = (SourceMapBuilder()
+          ..addSpan(inputVar1NoSymbol, outputVar1NoSymbol)
+          ..addSpan(inputVar1NoSymbol, outputVar1NoSymbol)
+          ..addSpan(inputFunctionNoSymbol, outputFunctionNoSymbol)
+          ..addSpan(inputFunctionNoSymbol, outputFunctionNoSymbol)
+          ..addSpan(inputVar2NoSymbol, outputVar2NoSymbol)
+          ..addSpan(inputVar2NoSymbol, outputVar2NoSymbol)
+          ..addSpan(inputExpr, outputExpr))
+        .build(output.url.toString());
+    var mapping = parseJson(map);
+    check(outputVar1NoSymbol, mapping, inputVar1NoSymbol, false);
+    check(outputVar2NoSymbol, mapping, inputVar2NoSymbol, false);
+    check(outputFunctionNoSymbol, mapping, inputFunctionNoSymbol, false);
+    check(outputExpr, mapping, inputExpr, false);
+  });
+
+  test('build + parse with file', () {
+    var json = (SourceMapBuilder()
+          ..addSpan(inputVar1, outputVar1)
+          ..addSpan(inputFunction, outputFunction)
+          ..addSpan(inputVar2, outputVar2)
+          ..addSpan(inputExpr, outputExpr))
+        .toJson(output.url.toString());
+    var mapping = parse(json);
+    check(outputVar1, mapping, inputVar1, true);
+    check(outputVar2, mapping, inputVar2, true);
+    check(outputFunction, mapping, inputFunction, true);
+    check(outputExpr, mapping, inputExpr, true);
+  });
+
+  test('printer projecting marks + parse', () {
+    var out = inputContent.replaceAll('long', '_s');
+    var file = SourceFile.fromString(out, url: 'output2.dart');
+    var printer = Printer('output2.dart');
+    printer.mark(ispan(0, 0));
+
+    var segments = inputContent.split('long');
+    expect(segments.length, 6);
+    printer.add(segments[0], projectMarks: true);
+    printer.mark(inputVar1);
+    printer.add('_s');
+    printer.add(segments[1], projectMarks: true);
+    printer.mark(inputFunction);
+    printer.add('_s');
+    printer.add(segments[2], projectMarks: true);
+    printer.mark(inputVar2);
+    printer.add('_s');
+    printer.add(segments[3], projectMarks: true);
+    printer.mark(inputExpr);
+    printer.add('_s');
+    printer.add(segments[4], projectMarks: true);
+    printer.add('_s');
+    printer.add(segments[5], projectMarks: true);
+
+    expect(printer.text, out);
+
+    var mapping = parse(printer.map);
+    void checkHelper(SourceMapSpan inputSpan, int adjustment) {
+      var start = inputSpan.start.offset - adjustment;
+      var end = (inputSpan.end.offset - adjustment) - 2;
+      var span = SourceMapFileSpan(file.span(start, end),
+          isIdentifier: inputSpan.isIdentifier);
+      check(span, mapping, inputSpan, true);
+    }
+
+    checkHelper(inputVar1, 0);
+    checkHelper(inputFunction, 2);
+    checkHelper(inputVar2, 4);
+    checkHelper(inputExpr, 6);
+
+    // We projected correctly lines that have no mappings
+    check(file.span(66, 66), mapping, ispan(45, 45), true);
+    check(file.span(63, 64), mapping, ispan(45, 45), true);
+    check(file.span(68, 68), mapping, ispan(70, 70), true);
+    check(file.span(71, 71), mapping, ispan(70, 70), true);
+
+    // Start of the last line
+    var oOffset = out.length - 2;
+    var iOffset = inputContent.length - 2;
+    check(file.span(oOffset, oOffset), mapping, ispan(iOffset, iOffset), true);
+    check(file.span(oOffset + 1, oOffset + 1), mapping, ispan(iOffset, iOffset),
+        true);
+  });
+}

diff --git a/pkgs/source_maps/test/parser_test.dart b/pkgs/source_maps/test/parser_test.dart
new file mode 100644
index 0000000..6cfe928
--- /dev/null
+++ b/pkgs/source_maps/test/parser_test.dart

@@ -0,0 +1,431 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// ignore_for_file: inference_failure_on_collection_literal
+// ignore_for_file: inference_failure_on_instance_creation
+
+import 'dart:convert';
+
+import 'package:source_maps/source_maps.dart';
+import 'package:source_span/source_span.dart';
+import 'package:test/test.dart';
+
+import 'common.dart';
+
+const Map<String, dynamic> _mapWithNoSourceLocation = {
+  'version': 3,
+  'sourceRoot': '',
+  'sources': ['input.dart'],
+  'names': [],
+  'mappings': 'A',
+  'file': 'output.dart'
+};
+
+const Map<String, dynamic> _mapWithSourceLocation = {
+  'version': 3,
+  'sourceRoot': '',
+  'sources': ['input.dart'],
+  'names': [],
+  'mappings': 'AAAA',
+  'file': 'output.dart'
+};
+
+const Map<String, dynamic> _mapWithSourceLocationAndMissingNames = {
+  'version': 3,
+  'sourceRoot': '',
+  'sources': ['input.dart'],
+  'mappings': 'AAAA',
+  'file': 'output.dart'
+};
+
+const Map<String, dynamic> _mapWithSourceLocationAndName = {
+  'version': 3,
+  'sourceRoot': '',
+  'sources': ['input.dart'],
+  'names': ['var'],
+  'mappings': 'AAAAA',
+  'file': 'output.dart'
+};
+
+const Map<String, dynamic> _mapWithSourceLocationAndName1 = {
+  'version': 3,
+  'sourceRoot': 'pkg/',
+  'sources': ['input1.dart'],
+  'names': ['var1'],
+  'mappings': 'AAAAA',
+  'file': 'output.dart'
+};
+
+const Map<String, dynamic> _mapWithSourceLocationAndName2 = {
+  'version': 3,
+  'sourceRoot': 'pkg/',
+  'sources': ['input2.dart'],
+  'names': ['var2'],
+  'mappings': 'AAAAA',
+  'file': 'output2.dart'
+};
+
+const Map<String, dynamic> _mapWithSourceLocationAndName3 = {
+  'version': 3,
+  'sourceRoot': 'pkg/',
+  'sources': ['input3.dart'],
+  'names': ['var3'],
+  'mappings': 'AAAAA',
+  'file': '3/output.dart'
+};
+
+const _sourceMapBundle = [
+  _mapWithSourceLocationAndName1,
+  _mapWithSourceLocationAndName2,
+  _mapWithSourceLocationAndName3,
+];
+
+void main() {
+  test('parse', () {
+    var mapping = parseJson(expectedMap);
+    check(outputVar1, mapping, inputVar1, false);
+    check(outputVar2, mapping, inputVar2, false);
+    check(outputFunction, mapping, inputFunction, false);
+    check(outputExpr, mapping, inputExpr, false);
+  });
+
+  test('parse + json', () {
+    var mapping = parse(jsonEncode(expectedMap));
+    check(outputVar1, mapping, inputVar1, false);
+    check(outputVar2, mapping, inputVar2, false);
+    check(outputFunction, mapping, inputFunction, false);
+    check(outputExpr, mapping, inputExpr, false);
+  });
+
+  test('parse with file', () {
+    var mapping = parseJson(expectedMap);
+    check(outputVar1, mapping, inputVar1, true);
+    check(outputVar2, mapping, inputVar2, true);
+    check(outputFunction, mapping, inputFunction, true);
+    check(outputExpr, mapping, inputExpr, true);
+  });
+
+  test('parse with no source location', () {
+    var map = parse(jsonEncode(_mapWithNoSourceLocation)) as SingleMapping;
+    expect(map.lines.length, 1);
+    expect(map.lines.first.entries.length, 1);
+    var entry = map.lines.first.entries.first;
+
+    expect(entry.column, 0);
+    expect(entry.sourceUrlId, null);
+    expect(entry.sourceColumn, null);
+    expect(entry.sourceLine, null);
+    expect(entry.sourceNameId, null);
+  });
+
+  test('parse with source location and no name', () {
+    var map = parse(jsonEncode(_mapWithSourceLocation)) as SingleMapping;
+    expect(map.lines.length, 1);
+    expect(map.lines.first.entries.length, 1);
+    var entry = map.lines.first.entries.first;
+
+    expect(entry.column, 0);
+    expect(entry.sourceUrlId, 0);
+    expect(entry.sourceColumn, 0);
+    expect(entry.sourceLine, 0);
+    expect(entry.sourceNameId, null);
+  });
+
+  test('parse with source location and missing names entry', () {
+    var map = parse(jsonEncode(_mapWithSourceLocationAndMissingNames))
+        as SingleMapping;
+    expect(map.lines.length, 1);
+    expect(map.lines.first.entries.length, 1);
+    var entry = map.lines.first.entries.first;
+
+    expect(entry.column, 0);
+    expect(entry.sourceUrlId, 0);
+    expect(entry.sourceColumn, 0);
+    expect(entry.sourceLine, 0);
+    expect(entry.sourceNameId, null);
+  });
+
+  test('parse with source location and name', () {
+    var map = parse(jsonEncode(_mapWithSourceLocationAndName)) as SingleMapping;
+    expect(map.lines.length, 1);
+    expect(map.lines.first.entries.length, 1);
+    var entry = map.lines.first.entries.first;
+
+    expect(entry.sourceUrlId, 0);
+    expect(entry.sourceUrlId, 0);
+    expect(entry.sourceColumn, 0);
+    expect(entry.sourceLine, 0);
+    expect(entry.sourceNameId, 0);
+  });
+
+  test('parse with source root', () {
+    var inputMap = Map.from(_mapWithSourceLocation);
+    inputMap['sourceRoot'] = '/pkg/';
+    var mapping = parseJson(inputMap) as SingleMapping;
+    expect(mapping.spanFor(0, 0)?.sourceUrl, Uri.parse('/pkg/input.dart'));
+    expect(
+        mapping
+            .spanForLocation(
+                SourceLocation(0, sourceUrl: Uri.parse('ignored.dart')))
+            ?.sourceUrl,
+        Uri.parse('/pkg/input.dart'));
+
+    var newSourceRoot = '/new/';
+
+    mapping.sourceRoot = newSourceRoot;
+    inputMap['sourceRoot'] = newSourceRoot;
+
+    expect(mapping.toJson(), equals(inputMap));
+  });
+
+  test('parse with map URL', () {
+    var inputMap = Map.from(_mapWithSourceLocation);
+    inputMap['sourceRoot'] = 'pkg/';
+    var mapping = parseJson(inputMap, mapUrl: 'file:///path/to/map');
+    expect(mapping.spanFor(0, 0)?.sourceUrl,
+        Uri.parse('file:///path/to/pkg/input.dart'));
+  });
+
+  group('parse with bundle', () {
+    var mapping =
+        parseJsonExtended(_sourceMapBundle, mapUrl: 'file:///path/to/map');
+
+    test('simple', () {
+      expect(
+          mapping
+              .spanForLocation(SourceLocation(0,
+                  sourceUrl: Uri.file('/path/to/output.dart')))
+              ?.sourceUrl,
+          Uri.parse('file:///path/to/pkg/input1.dart'));
+      expect(
+          mapping
+              .spanForLocation(SourceLocation(0,
+                  sourceUrl: Uri.file('/path/to/output2.dart')))
+              ?.sourceUrl,
+          Uri.parse('file:///path/to/pkg/input2.dart'));
+      expect(
+          mapping
+              .spanForLocation(SourceLocation(0,
+                  sourceUrl: Uri.file('/path/to/3/output.dart')))
+              ?.sourceUrl,
+          Uri.parse('file:///path/to/pkg/input3.dart'));
+
+      expect(
+          mapping.spanFor(0, 0, uri: 'file:///path/to/output.dart')?.sourceUrl,
+          Uri.parse('file:///path/to/pkg/input1.dart'));
+      expect(
+          mapping.spanFor(0, 0, uri: 'file:///path/to/output2.dart')?.sourceUrl,
+          Uri.parse('file:///path/to/pkg/input2.dart'));
+      expect(
+          mapping
+              .spanFor(0, 0, uri: 'file:///path/to/3/output.dart')
+              ?.sourceUrl,
+          Uri.parse('file:///path/to/pkg/input3.dart'));
+    });
+
+    test('package uris', () {
+      expect(
+          mapping
+              .spanForLocation(SourceLocation(0,
+                  sourceUrl: Uri.parse('package:1/output.dart')))
+              ?.sourceUrl,
+          Uri.parse('file:///path/to/pkg/input1.dart'));
+      expect(
+          mapping
+              .spanForLocation(SourceLocation(0,
+                  sourceUrl: Uri.parse('package:2/output2.dart')))
+              ?.sourceUrl,
+          Uri.parse('file:///path/to/pkg/input2.dart'));
+      expect(
+          mapping
+              .spanForLocation(SourceLocation(0,
+                  sourceUrl: Uri.parse('package:3/output.dart')))
+              ?.sourceUrl,
+          Uri.parse('file:///path/to/pkg/input3.dart'));
+
+      expect(mapping.spanFor(0, 0, uri: 'package:1/output.dart')?.sourceUrl,
+          Uri.parse('file:///path/to/pkg/input1.dart'));
+      expect(mapping.spanFor(0, 0, uri: 'package:2/output2.dart')?.sourceUrl,
+          Uri.parse('file:///path/to/pkg/input2.dart'));
+      expect(mapping.spanFor(0, 0, uri: 'package:3/output.dart')?.sourceUrl,
+          Uri.parse('file:///path/to/pkg/input3.dart'));
+    });
+
+    test('unmapped path', () {
+      var span = mapping.spanFor(0, 0, uri: 'unmapped_output.dart')!;
+      expect(span.sourceUrl, Uri.parse('unmapped_output.dart'));
+      expect(span.start.line, equals(0));
+      expect(span.start.column, equals(0));
+
+      span = mapping.spanFor(10, 5, uri: 'unmapped_output.dart')!;
+      expect(span.sourceUrl, Uri.parse('unmapped_output.dart'));
+      expect(span.start.line, equals(10));
+      expect(span.start.column, equals(5));
+    });
+
+    test('missing path', () {
+      expect(() => mapping.spanFor(0, 0), throwsA(anything));
+    });
+
+    test('incomplete paths', () {
+      expect(mapping.spanFor(0, 0, uri: 'output.dart')?.sourceUrl,
+          Uri.parse('file:///path/to/pkg/input1.dart'));
+      expect(mapping.spanFor(0, 0, uri: 'output2.dart')?.sourceUrl,
+          Uri.parse('file:///path/to/pkg/input2.dart'));
+      expect(mapping.spanFor(0, 0, uri: '3/output.dart')?.sourceUrl,
+          Uri.parse('file:///path/to/pkg/input3.dart'));
+    });
+
+    test('parseExtended', () {
+      var mapping = parseExtended(jsonEncode(_sourceMapBundle),
+          mapUrl: 'file:///path/to/map');
+
+      expect(mapping.spanFor(0, 0, uri: 'output.dart')?.sourceUrl,
+          Uri.parse('file:///path/to/pkg/input1.dart'));
+      expect(mapping.spanFor(0, 0, uri: 'output2.dart')?.sourceUrl,
+          Uri.parse('file:///path/to/pkg/input2.dart'));
+      expect(mapping.spanFor(0, 0, uri: '3/output.dart')?.sourceUrl,
+          Uri.parse('file:///path/to/pkg/input3.dart'));
+    });
+
+    test('build bundle incrementally', () {
+      var mapping = MappingBundle();
+
+      mapping.addMapping(parseJson(_mapWithSourceLocationAndName1,
+          mapUrl: 'file:///path/to/map') as SingleMapping);
+      expect(mapping.spanFor(0, 0, uri: 'output.dart')?.sourceUrl,
+          Uri.parse('file:///path/to/pkg/input1.dart'));
+
+      expect(mapping.containsMapping('output2.dart'), isFalse);
+      mapping.addMapping(parseJson(_mapWithSourceLocationAndName2,
+          mapUrl: 'file:///path/to/map') as SingleMapping);
+      expect(mapping.containsMapping('output2.dart'), isTrue);
+      expect(mapping.spanFor(0, 0, uri: 'output2.dart')?.sourceUrl,
+          Uri.parse('file:///path/to/pkg/input2.dart'));
+
+      expect(mapping.containsMapping('3/output.dart'), isFalse);
+      mapping.addMapping(parseJson(_mapWithSourceLocationAndName3,
+          mapUrl: 'file:///path/to/map') as SingleMapping);
+      expect(mapping.containsMapping('3/output.dart'), isTrue);
+      expect(mapping.spanFor(0, 0, uri: '3/output.dart')?.sourceUrl,
+          Uri.parse('file:///path/to/pkg/input3.dart'));
+    });
+
+    // Test that the source map can handle cases where the uri passed in is
+    // not from the expected host but it is still unambiguous which source
+    // map should be used.
+    test('different paths', () {
+      expect(
+          mapping
+              .spanForLocation(SourceLocation(0,
+                  sourceUrl: Uri.parse('http://localhost/output.dart')))
+              ?.sourceUrl,
+          Uri.parse('file:///path/to/pkg/input1.dart'));
+      expect(
+          mapping
+              .spanForLocation(SourceLocation(0,
+                  sourceUrl: Uri.parse('http://localhost/output2.dart')))
+              ?.sourceUrl,
+          Uri.parse('file:///path/to/pkg/input2.dart'));
+      expect(
+          mapping
+              .spanForLocation(SourceLocation(0,
+                  sourceUrl: Uri.parse('http://localhost/3/output.dart')))
+              ?.sourceUrl,
+          Uri.parse('file:///path/to/pkg/input3.dart'));
+
+      expect(
+          mapping.spanFor(0, 0, uri: 'http://localhost/output.dart')?.sourceUrl,
+          Uri.parse('file:///path/to/pkg/input1.dart'));
+      expect(
+          mapping
+              .spanFor(0, 0, uri: 'http://localhost/output2.dart')
+              ?.sourceUrl,
+          Uri.parse('file:///path/to/pkg/input2.dart'));
+      expect(
+          mapping
+              .spanFor(0, 0, uri: 'http://localhost/3/output.dart')
+              ?.sourceUrl,
+          Uri.parse('file:///path/to/pkg/input3.dart'));
+    });
+  });
+
+  test('parse and re-emit', () {
+    for (var expected in [
+      expectedMap,
+      _mapWithNoSourceLocation,
+      _mapWithSourceLocation,
+      _mapWithSourceLocationAndName
+    ]) {
+      var mapping = parseJson(expected) as SingleMapping;
+      expect(mapping.toJson(), equals(expected));
+
+      mapping = parseJsonExtended(expected) as SingleMapping;
+      expect(mapping.toJson(), equals(expected));
+    }
+
+    var mapping = parseJsonExtended(_sourceMapBundle) as MappingBundle;
+    expect(mapping.toJson(), equals(_sourceMapBundle));
+  });
+
+  test('parse extensions', () {
+    var map = Map.from(expectedMap);
+    map['x_foo'] = 'a';
+    map['x_bar'] = [3];
+    var mapping = parseJson(map) as SingleMapping;
+    expect(mapping.toJson(), equals(map));
+    expect(mapping.extensions['x_foo'], equals('a'));
+    expect((mapping.extensions['x_bar'] as List).first, equals(3));
+  });
+
+  group('source files', () {
+    group('from fromEntries()', () {
+      test('are null for non-FileLocations', () {
+        var mapping = SingleMapping.fromEntries([
+          Entry(SourceLocation(10, line: 1, column: 8), outputVar1.start, null)
+        ]);
+        expect(mapping.files, equals([null]));
+      });
+
+      test("use a file location's file", () {
+        var mapping = SingleMapping.fromEntries(
+            [Entry(inputVar1.start, outputVar1.start, null)]);
+        expect(mapping.files, equals([input]));
+      });
+    });
+
+    group('from parse()', () {
+      group('are null', () {
+        test('with no sourcesContent field', () {
+          var mapping = parseJson(expectedMap) as SingleMapping;
+          expect(mapping.files, equals([null]));
+        });
+
+        test('with null sourcesContent values', () {
+          var map = Map.from(expectedMap);
+          map['sourcesContent'] = [null];
+          var mapping = parseJson(map) as SingleMapping;
+          expect(mapping.files, equals([null]));
+        });
+
+        test('with a too-short sourcesContent', () {
+          var map = Map.from(expectedMap);
+          map['sourcesContent'] = [];
+          var mapping = parseJson(map) as SingleMapping;
+          expect(mapping.files, equals([null]));
+        });
+      });
+
+      test('are parsed from sourcesContent', () {
+        var map = Map.from(expectedMap);
+        map['sourcesContent'] = ['hello, world!'];
+        var mapping = parseJson(map) as SingleMapping;
+
+        var file = mapping.files[0]!;
+        expect(file.url, equals(Uri.parse('input.dart')));
+        expect(file.getText(0), equals('hello, world!'));
+      });
+    });
+  });
+}

diff --git a/pkgs/source_maps/test/printer_test.dart b/pkgs/source_maps/test/printer_test.dart
new file mode 100644
index 0000000..89265e3
--- /dev/null
+++ b/pkgs/source_maps/test/printer_test.dart

@@ -0,0 +1,126 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:convert';
+
+import 'package:source_maps/source_maps.dart';
+import 'package:source_span/source_span.dart';
+import 'package:test/test.dart';
+
+import 'common.dart';
+
+void main() {
+  test('printer', () {
+    var printer = Printer('output.dart');
+    printer
+      ..add('var ')
+      ..mark(inputVar1)
+      ..add('x = 3;\n')
+      ..mark(inputFunction)
+      ..add('f(')
+      ..mark(inputVar2)
+      ..add('y) => ')
+      ..mark(inputExpr)
+      ..add('x + y;\n');
+    expect(printer.text, outputContent);
+    expect(printer.map, jsonEncode(expectedMap));
+  });
+
+  test('printer projecting marks', () {
+    var out = inputContent.replaceAll('long', '_s');
+    var printer = Printer('output2.dart');
+
+    var segments = inputContent.split('long');
+    expect(segments.length, 6);
+    printer
+      ..mark(ispan(0, 0))
+      ..add(segments[0], projectMarks: true)
+      ..mark(inputVar1)
+      ..add('_s')
+      ..add(segments[1], projectMarks: true)
+      ..mark(inputFunction)
+      ..add('_s')
+      ..add(segments[2], projectMarks: true)
+      ..mark(inputVar2)
+      ..add('_s')
+      ..add(segments[3], projectMarks: true)
+      ..mark(inputExpr)
+      ..add('_s')
+      ..add(segments[4], projectMarks: true)
+      ..add('_s')
+      ..add(segments[5], projectMarks: true);
+
+    expect(printer.text, out);
+    // 8 new lines in the source map:
+    expect(printer.map.split(';').length, 8);
+
+    SourceMapSpan asFixed(SourceMapSpan s) =>
+        SourceMapSpan(s.start, s.end, s.text, isIdentifier: s.isIdentifier);
+
+    // The result is the same if we use fixed positions
+    var printer2 = Printer('output2.dart');
+    printer2
+      ..mark(SourceLocation(0, sourceUrl: 'input.dart').pointSpan())
+      ..add(segments[0], projectMarks: true)
+      ..mark(asFixed(inputVar1))
+      ..add('_s')
+      ..add(segments[1], projectMarks: true)
+      ..mark(asFixed(inputFunction))
+      ..add('_s')
+      ..add(segments[2], projectMarks: true)
+      ..mark(asFixed(inputVar2))
+      ..add('_s')
+      ..add(segments[3], projectMarks: true)
+      ..mark(asFixed(inputExpr))
+      ..add('_s')
+      ..add(segments[4], projectMarks: true)
+      ..add('_s')
+      ..add(segments[5], projectMarks: true);
+
+    expect(printer2.text, out);
+    expect(printer2.map, printer.map);
+  });
+
+  group('nested printer', () {
+    test('simple use', () {
+      var printer = NestedPrinter();
+      printer
+        ..add('var ')
+        ..add('x = 3;\n', span: inputVar1)
+        ..add('f(', span: inputFunction)
+        ..add('y) => ', span: inputVar2)
+        ..add('x + y;\n', span: inputExpr)
+        ..build('output.dart');
+      expect(printer.text, outputContent);
+      expect(printer.map, jsonEncode(expectedMap));
+    });
+
+    test('nested use', () {
+      var printer = NestedPrinter();
+      printer
+        ..add('var ')
+        ..add(NestedPrinter()..add('x = 3;\n', span: inputVar1))
+        ..add('f(', span: inputFunction)
+        ..add(NestedPrinter()..add('y) => ', span: inputVar2))
+        ..add('x + y;\n', span: inputExpr)
+        ..build('output.dart');
+      expect(printer.text, outputContent);
+      expect(printer.map, jsonEncode(expectedMap));
+    });
+
+    test('add indentation', () {
+      var out = inputContent.replaceAll('long', '_s');
+      var lines = inputContent.trim().split('\n');
+      expect(lines.length, 7);
+      var printer = NestedPrinter();
+      for (var i = 0; i < lines.length; i++) {
+        if (i == 5) printer.indent++;
+        printer.addLine(lines[i].replaceAll('long', '_s').trim());
+        if (i == 5) printer.indent--;
+      }
+      printer.build('output.dart');
+      expect(printer.text, out);
+    });
+  });
+}

diff --git a/pkgs/source_maps/test/refactor_test.dart b/pkgs/source_maps/test/refactor_test.dart
new file mode 100644
index 0000000..5bc3818
--- /dev/null
+++ b/pkgs/source_maps/test/refactor_test.dart

@@ -0,0 +1,199 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:source_maps/parser.dart' show Mapping, parse;
+import 'package:source_maps/refactor.dart';
+import 'package:source_span/source_span.dart';
+import 'package:term_glyph/term_glyph.dart' as term_glyph;
+import 'package:test/test.dart';
+
+void main() {
+  setUpAll(() {
+    term_glyph.ascii = true;
+  });
+
+  group('conflict detection', () {
+    var original = '0123456789abcdefghij';
+    var file = SourceFile.fromString(original);
+
+    test('no conflict, in order', () {
+      var txn = TextEditTransaction(original, file);
+      txn.edit(2, 4, '.');
+      txn.edit(5, 5, '|');
+      txn.edit(6, 6, '-');
+      txn.edit(6, 7, '_');
+      expect((txn.commit()..build('')).text, '01.4|5-_789abcdefghij');
+    });
+
+    test('no conflict, out of order', () {
+      var txn = TextEditTransaction(original, file);
+      txn.edit(2, 4, '.');
+      txn.edit(5, 5, '|');
+
+      // Regresion test for issue #404: there is no conflict/overlap for edits
+      // that don't remove any of the original code.
+      txn.edit(6, 7, '_');
+      txn.edit(6, 6, '-');
+      expect((txn.commit()..build('')).text, '01.4|5-_789abcdefghij');
+    });
+
+    test('conflict', () {
+      var txn = TextEditTransaction(original, file);
+      txn.edit(2, 4, '.');
+      txn.edit(3, 3, '-');
+      expect(
+          () => txn.commit(),
+          throwsA(
+              predicate((e) => e.toString().contains('overlapping edits'))));
+    });
+  });
+
+  test('generated source maps', () {
+    var original =
+        '0123456789\n0*23456789\n01*3456789\nabcdefghij\nabcd*fghij\n';
+    var file = SourceFile.fromString(original);
+    var txn = TextEditTransaction(original, file);
+    txn.edit(27, 29, '__\n    ');
+    txn.edit(34, 35, '___');
+    var printer = (txn.commit()..build(''));
+    var output = printer.text;
+    var map = parse(printer.map!);
+    expect(output,
+        '0123456789\n0*23456789\n01*34__\n    789\na___cdefghij\nabcd*fghij\n');
+
+    // Line 1 and 2 are unmodified: mapping any column returns the beginning
+    // of the corresponding line:
+    expect(
+        _span(1, 1, map, file),
+        'line 1, column 1: \n'
+        '  ,\n'
+        '1 | 0123456789\n'
+        '  | ^\n'
+        "  '");
+    expect(
+        _span(1, 5, map, file),
+        'line 1, column 1: \n'
+        '  ,\n'
+        '1 | 0123456789\n'
+        '  | ^\n'
+        "  '");
+    expect(
+        _span(2, 1, map, file),
+        'line 2, column 1: \n'
+        '  ,\n'
+        '2 | 0*23456789\n'
+        '  | ^\n'
+        "  '");
+    expect(
+        _span(2, 8, map, file),
+        'line 2, column 1: \n'
+        '  ,\n'
+        '2 | 0*23456789\n'
+        '  | ^\n'
+        "  '");
+
+    // Line 3 is modified part way: mappings before the edits have the right
+    // mapping, after the edits the mapping is null.
+    expect(
+        _span(3, 1, map, file),
+        'line 3, column 1: \n'
+        '  ,\n'
+        '3 | 01*3456789\n'
+        '  | ^\n'
+        "  '");
+    expect(
+        _span(3, 5, map, file),
+        'line 3, column 1: \n'
+        '  ,\n'
+        '3 | 01*3456789\n'
+        '  | ^\n'
+        "  '");
+
+    // Start of edits map to beginning of the edit secion:
+    expect(
+        _span(3, 6, map, file),
+        'line 3, column 6: \n'
+        '  ,\n'
+        '3 | 01*3456789\n'
+        '  |      ^\n'
+        "  '");
+    expect(
+        _span(3, 7, map, file),
+        'line 3, column 6: \n'
+        '  ,\n'
+        '3 | 01*3456789\n'
+        '  |      ^\n'
+        "  '");
+
+    // Lines added have no mapping (they should inherit the last mapping),
+    // but the end of the edit region continues were we left off:
+    expect(_span(4, 1, map, file), isNull);
+    expect(
+        _span(4, 5, map, file),
+        'line 3, column 8: \n'
+        '  ,\n'
+        '3 | 01*3456789\n'
+        '  |        ^\n'
+        "  '");
+
+    // Subsequent lines are still mapped correctly:
+    // a (in a___cd...)
+    expect(
+        _span(5, 1, map, file),
+        'line 4, column 1: \n'
+        '  ,\n'
+        '4 | abcdefghij\n'
+        '  | ^\n'
+        "  '");
+    // _ (in a___cd...)
+    expect(
+        _span(5, 2, map, file),
+        'line 4, column 2: \n'
+        '  ,\n'
+        '4 | abcdefghij\n'
+        '  |  ^\n'
+        "  '");
+    // _ (in a___cd...)
+    expect(
+        _span(5, 3, map, file),
+        'line 4, column 2: \n'
+        '  ,\n'
+        '4 | abcdefghij\n'
+        '  |  ^\n'
+        "  '");
+    // _ (in a___cd...)
+    expect(
+        _span(5, 4, map, file),
+        'line 4, column 2: \n'
+        '  ,\n'
+        '4 | abcdefghij\n'
+        '  |  ^\n'
+        "  '");
+    // c (in a___cd...)
+    expect(
+        _span(5, 5, map, file),
+        'line 4, column 3: \n'
+        '  ,\n'
+        '4 | abcdefghij\n'
+        '  |   ^\n'
+        "  '");
+    expect(
+        _span(6, 1, map, file),
+        'line 5, column 1: \n'
+        '  ,\n'
+        '5 | abcd*fghij\n'
+        '  | ^\n'
+        "  '");
+    expect(
+        _span(6, 8, map, file),
+        'line 5, column 1: \n'
+        '  ,\n'
+        '5 | abcd*fghij\n'
+        '  | ^\n'
+        "  '");
+  });
+}
+
+String? _span(int line, int column, Mapping map, SourceFile file) =>
+    map.spanFor(line - 1, column - 1, files: {'': file})?.message('').trim();

diff --git a/pkgs/source_maps/test/utils_test.dart b/pkgs/source_maps/test/utils_test.dart
new file mode 100644
index 0000000..2516d1e
--- /dev/null
+++ b/pkgs/source_maps/test/utils_test.dart

@@ -0,0 +1,53 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Tests for the binary search utility algorithm.
+library;
+
+import 'package:source_maps/src/utils.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('binary search', () {
+    test('empty', () {
+      expect(binarySearch([], (x) => true), -1);
+    });
+
+    test('single element', () {
+      expect(binarySearch([1], (x) => true), 0);
+      expect(binarySearch([1], (x) => false), 1);
+    });
+
+    test('no matches', () {
+      var list = [1, 2, 3, 4, 5, 6, 7];
+      expect(binarySearch(list, (x) => false), list.length);
+    });
+
+    test('all match', () {
+      var list = [1, 2, 3, 4, 5, 6, 7];
+      expect(binarySearch(list, (x) => true), 0);
+    });
+
+    test('compare with linear search', () {
+      for (var size = 0; size < 100; size++) {
+        var list = <int>[];
+        for (var i = 0; i < size; i++) {
+          list.add(i);
+        }
+        for (var pos = 0; pos <= size; pos++) {
+          expect(binarySearch(list, (x) => x >= pos),
+              _linearSearch(list, (x) => x >= pos));
+        }
+      }
+    });
+  });
+}
+
+int _linearSearch<T>(List<T> list, bool Function(T) predicate) {
+  if (list.isEmpty) return -1;
+  for (var i = 0; i < list.length; i++) {
+    if (predicate(list[i])) return i;
+  }
+  return list.length;
+}

diff --git a/pkgs/source_maps/test/vlq_test.dart b/pkgs/source_maps/test/vlq_test.dart
new file mode 100644
index 0000000..4568cff
--- /dev/null
+++ b/pkgs/source_maps/test/vlq_test.dart

@@ -0,0 +1,59 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:math';
+
+import 'package:source_maps/src/vlq.dart';
+import 'package:test/test.dart';
+
+void main() {
+  test('encode and decode - simple values', () {
+    expect(encodeVlq(1).join(''), 'C');
+    expect(encodeVlq(2).join(''), 'E');
+    expect(encodeVlq(3).join(''), 'G');
+    expect(encodeVlq(100).join(''), 'oG');
+    expect(decodeVlq('C'.split('').iterator), 1);
+    expect(decodeVlq('E'.split('').iterator), 2);
+    expect(decodeVlq('G'.split('').iterator), 3);
+    expect(decodeVlq('oG'.split('').iterator), 100);
+  });
+
+  test('encode and decode', () {
+    for (var i = -10000; i < 10000; i++) {
+      _checkEncodeDecode(i);
+    }
+  });
+
+  test('only 32-bit ints allowed', () {
+    var maxInt = (pow(2, 31) as int) - 1;
+    var minInt = -(pow(2, 31) as int);
+    _checkEncodeDecode(maxInt - 1);
+    _checkEncodeDecode(minInt + 1);
+    _checkEncodeDecode(maxInt);
+    _checkEncodeDecode(minInt);
+
+    expect(encodeVlq(minInt).join(''), 'hgggggE');
+    expect(decodeVlq('hgggggE'.split('').iterator), minInt);
+
+    expect(() => encodeVlq(maxInt + 1), throwsA(anything));
+    expect(() => encodeVlq(maxInt + 2), throwsA(anything));
+    expect(() => encodeVlq(minInt - 1), throwsA(anything));
+    expect(() => encodeVlq(minInt - 2), throwsA(anything));
+
+    // if we allowed more than 32 bits, these would be the expected encodings
+    // for the large numbers above.
+    expect(() => decodeVlq('ggggggE'.split('').iterator), throwsA(anything));
+    expect(() => decodeVlq('igggggE'.split('').iterator), throwsA(anything));
+    expect(() => decodeVlq('jgggggE'.split('').iterator), throwsA(anything));
+    expect(() => decodeVlq('lgggggE'.split('').iterator), throwsA(anything));
+  },
+      // This test uses integers so large they overflow in JS.
+      testOn: 'dart-vm');
+}
+
+void _checkEncodeDecode(int value) {
+  var encoded = encodeVlq(value);
+  expect(decodeVlq(encoded.iterator), value);
+  expect(decodeVlq(encoded.join('').split('').iterator), value);
+}

diff --git a/pkgs/source_span/.gitignore b/pkgs/source_span/.gitignore
new file mode 100644
index 0000000..ab3cb76
--- /dev/null
+++ b/pkgs/source_span/.gitignore

@@ -0,0 +1,16 @@
+# Don’t commit the following directories created by pub.
+.buildlog
+.dart_tool/
+.pub/
+build/
+packages
+.packages
+
+# Or the files created by dart2js.
+*.dart.js
+*.js_
+*.js.deps
+*.js.map
+
+# Include when developing application packages.
+pubspec.lock

diff --git a/pkgs/source_span/CHANGELOG.md b/pkgs/source_span/CHANGELOG.md
new file mode 100644
index 0000000..b8319d7
--- /dev/null
+++ b/pkgs/source_span/CHANGELOG.md

@@ -0,0 +1,240 @@
+## 1.10.1
+
+* Require Dart 3.1
+* Move to `dart-lang/tools` monorepo.
+
+## 1.10.0
+
+* Add a `SourceFile.codeUnits` property.
+* Require Dart 2.18
+* Add an API usage example in `example/`.
+
+## 1.9.1
+
+* Properly handle multi-line labels for multi-span highlights.
+
+* Populate the pubspec `repository` field.
+
+## 1.9.0
+
+* Add `SourceSpanWithContextExtension.subspan` that returns a
+  `SourceSpanWithContext` rather than a plain `SourceSpan`.
+
+## 1.8.2
+
+* Fix a bug where highlighting multiple spans with `null` URLs could cause an
+  assertion error. Now when multiple spans are passed with `null` URLs, they're
+  highlighted as though they all come from different source files.
+
+## 1.8.1
+
+* Fix a bug where the URL header for the highlights with multiple files would
+  get omitted only one span has a non-null URI.
+
+## 1.8.0
+
+* Stable release for null safety.
+
+## 1.7.0
+
+* Add a `SourceSpan.subspan()` extension method which returns a slice of an
+  existing source span.
+
+## 1.6.0
+
+* Add support for highlighting multiple source spans at once, providing more
+  context for span-based messages. This is exposed through the new APIs
+  `SourceSpan.highlightMultiple()` and `SourceSpan.messageMultiple()` (both
+  extension methods), `MultiSourceSpanException`, and
+  `MultiSourceSpanFormatException`.
+
+## 1.5.6
+
+* Fix padding around line numbers that are powers of 10 in
+  `FileSpan.highlight()`.
+
+## 1.5.5
+
+* Fix a bug where `FileSpan.highlight()` would crash for spans that covered a
+  trailing newline and a single additional empty line.
+
+## 1.5.4
+
+* `FileSpan.highlight()` now properly highlights point spans at the beginning of
+  lines.
+
+## 1.5.3
+
+* Fix an edge case where `FileSpan.highlight()` would put the highlight
+  indicator in the wrong position when highlighting a point span after the end
+  of a file.
+
+## 1.5.2
+
+* `SourceFile.span()` now goes to the end of the file by default, rather than
+  ending one character before the end of the file. This matches the documented
+  behavior.
+
+* `FileSpan.context` now includes the full line on which the span appears for
+  empty spans at the beginning and end of lines.
+
+* Fix an edge case where `FileSpan.highlight()` could crash when highlighting a
+  span that ended with an empty line.
+
+## 1.5.1
+
+* Produce better source span highlights for multi-line spans that cover the
+  entire last line of the span, including the newline.
+
+* Produce better source span highlights for spans that contain Windows-style
+  newlines.
+
+## 1.5.0
+
+* Improve the output of `SourceSpan.highlight()` and `SourceSpan.message()`:
+
+  * They now include line numbers.
+  * They will now print every line of a multiline span.
+  * They will now use Unicode box-drawing characters by default (this can be
+    controlled using [`term_glyph.ascii`][]).
+
+[`term_glyph.ascii`]: https://pub.dartlang.org/documentation/term_glyph/latest/term_glyph/ascii.html
+
+## 1.4.1
+
+* Set max SDK version to `<3.0.0`, and adjust other dependencies.
+
+## 1.4.0
+
+* The `new SourceFile()` constructor is deprecated. This constructed a source
+  file from a string's runes, rather than its code units, which runs counter to
+  the way Dart handles strings otherwise. The `new StringFile.fromString()`
+  constructor (see below) should be used instead.
+
+* The `new SourceFile.fromString()` constructor was added. This works like `new
+  SourceFile()`, except it uses code units rather than runes.
+
+* The current behavior when characters larger than `0xFFFF` are passed to `new
+  SourceFile.decoded()` is now considered deprecated.
+
+## 1.3.1
+
+* Properly highlight spans for lines that include tabs with
+  `SourceSpan.highlight()` and `SourceSpan.message()`.
+
+## 1.3.0
+
+* Add `SourceSpan.highlight()`, which returns just the highlighted text that
+  would be included in `SourceSpan.message()`.
+
+## 1.2.4
+
+* Fix a new strong mode error.
+
+## 1.2.3
+
+* Fix a bug where a point span at the end of a file without a trailing newline
+  would be printed incorrectly.
+
+## 1.2.2
+
+* Allow `SourceSpanException.message`, `SourceSpanFormatException.source`, and
+  `SourceSpanWithContext.context` to be overridden in strong mode.
+
+## 1.2.1
+
+* Fix the declared type of `FileSpan.start` and `FileSpan.end`. In 1.2.0 these
+  were mistakenly changed from `FileLocation` to `SourceLocation`.
+
+## 1.2.0
+
+* **Deprecated:** Extending `SourceLocation` directly is deprecated. Instead,
+  extend the new `SourceLocationBase` class or mix in the new
+  `SourceLocationMixin` mixin.
+
+* Dramatically improve the performance of `FileLocation`.
+
+## 1.1.6
+
+* Optimize `getLine()` in `SourceFile` when repeatedly called.
+
+## 1.1.5
+
+* Fixed another case in which `FileSpan.union` could throw an exception for
+  external implementations of `FileSpan`.
+
+## 1.1.4
+
+* Eliminated dart2js warning about overriding `==`, but not `hashCode`.
+
+## 1.1.3
+
+* `FileSpan.compareTo`, `FileSpan.==`, `FileSpan.union`, and `FileSpan.expand`
+  no longer throw exceptions for external implementations of `FileSpan`.
+
+* `FileSpan.hashCode` now fully agrees with `FileSpan.==`.
+
+## 1.1.2
+
+* Fixed validation in `SourceSpanWithContext` to allow multiple occurrences of
+  `text` within `context`.
+
+## 1.1.1
+
+* Fixed `FileSpan`'s context to include the full span text, not just the first
+  line of it.
+
+## 1.1.0
+
+* Added `SourceSpanWithContext`: a span that also includes the full line of text
+  that contains the span.
+
+## 1.0.3
+
+* Cleanup equality operator to accept any Object rather than just a
+  `SourceLocation`.
+
+## 1.0.2
+
+* Avoid unintentionally allocating extra objects for internal `FileSpan`
+  operations.
+
+* Ensure that `SourceSpan.operator==` works on arbitrary `Object`s.
+
+## 1.0.1
+
+* Use a more compact internal representation for `FileSpan`.
+
+## 1.0.0
+
+This package was extracted from the
+[`source_maps`](https://pub.dev/packages/source_maps) package, but the
+API has many differences. Among them:
+
+* `Span` has been renamed to `SourceSpan` and `Location` has been renamed to
+  `SourceLocation` to clarify their purpose and maintain consistency with the
+  package name. Likewise, `SpanException` is now `SourceSpanException` and
+  `SpanFormatException` is not `SourceSpanFormatException`.
+
+* `FixedSpan` and `FixedLocation` have been rolled into the `Span` and
+  `Location` classes, respectively.
+
+* `SourceFile` is more aggressive about validating its arguments. Out-of-bounds
+  lines, columns, and offsets will now throw errors rather than be silently
+  clamped.
+
+* `SourceSpan.sourceUrl`, `SourceLocation.sourceUrl`, and `SourceFile.url` now
+  return `Uri` objects rather than `String`s. The constructors allow either
+  `String`s or `Uri`s.
+
+* `Span.getLocationMessage` and `SourceFile.getLocationMessage` are now
+  `SourceSpan.message` and `SourceFile.message`, respectively. Rather than
+  taking both a `useColor` and a `color` parameter, they now take a single
+  `color` parameter that controls both whether and which color is used.
+
+* `Span.isIdentifier` has been removed. This property doesn't make sense outside
+  of a source map context.
+
+* `SourceFileSegment` has been removed. This class wasn't widely used and was
+  inconsistent in its choice of which parameters were considered relative and
+  which absolute.

diff --git a/pkgs/source_span/LICENSE b/pkgs/source_span/LICENSE
new file mode 100644
index 0000000..000cd7b
--- /dev/null
+++ b/pkgs/source_span/LICENSE

@@ -0,0 +1,27 @@
+Copyright 2014, the Dart project authors. 
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+    * Neither the name of Google LLC nor the names of its
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

diff --git a/pkgs/source_span/README.md b/pkgs/source_span/README.md
new file mode 100644
index 0000000..b4ce25f
--- /dev/null
+++ b/pkgs/source_span/README.md

@@ -0,0 +1,21 @@
+[![Build Status](https://github.com/dart-lang/tools/actions/workflows/source_span.yaml/badge.svg)](https://github.com/dart-lang/tools/actions/workflows/source_span.yaml)
+[![pub package](https://img.shields.io/pub/v/source_span.svg)](https://pub.dev/packages/source_span)
+[![package publisher](https://img.shields.io/pub/publisher/source_span.svg)](https://pub.dev/packages/source_span/publisher)
+
+## About this package
+
+`source_span` is a library for tracking locations in source code. It's designed
+to provide a standard representation for source code locations and spans so that
+disparate packages can easily pass them among one another, and to make it easy
+to generate human-friendly messages associated with a given piece of code.
+
+The most commonly-used class is the package's namesake, `SourceSpan`. It
+represents a span of characters in some source file, and is often attached to an
+object that has been parsed to indicate where it was parsed from. It provides
+access to the text of the span via `SourceSpan.text` and can be used to produce
+human-friendly messages using `SourceSpan.message()`.
+
+When parsing code from a file, `SourceFile` is useful. Not only does it provide
+an efficient means of computing line and column numbers, `SourceFile.span()`
+returns special `FileSpan`s that are able to provide more context for their
+error messages.

diff --git a/pkgs/source_span/analysis_options.yaml b/pkgs/source_span/analysis_options.yaml
new file mode 100644
index 0000000..d2ebdbf
--- /dev/null
+++ b/pkgs/source_span/analysis_options.yaml

@@ -0,0 +1,32 @@
+# https://dart.dev/guides/language/analysis-options
+include: package:dart_flutter_team_lints/analysis_options.yaml
+
+analyzer:
+  language:
+    strict-casts: true
+    strict-inference: true
+    strict-raw-types: true
+
+linter:
+  rules:
+  - avoid_bool_literals_in_conditional_expressions
+  - avoid_classes_with_only_static_members
+  - avoid_private_typedef_functions
+  - avoid_redundant_argument_values
+  - avoid_returning_this
+  - avoid_unused_constructor_parameters
+  - avoid_void_async
+  - cancel_subscriptions
+  - cascade_invocations
+  - join_return_with_assignment
+  - literal_only_boolean_expressions
+  - missing_whitespace_between_adjacent_strings
+  - no_adjacent_strings_in_list
+  - prefer_const_declarations
+  - prefer_expression_function_bodies
+  - prefer_final_locals
+  - unnecessary_await_in_return
+  - unnecessary_raw_strings
+  - use_if_null_to_convert_nulls_to_bools
+  - use_raw_strings
+  - use_string_buffers

diff --git a/pkgs/source_span/example/main.dart b/pkgs/source_span/example/main.dart
new file mode 100644
index 0000000..e296765
--- /dev/null
+++ b/pkgs/source_span/example/main.dart

@@ -0,0 +1,51 @@
+// Copyright (c) 2023, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:io';
+
+import 'package:source_span/source_span.dart';
+
+void main(List<String> args) {
+  final file = File('README.md');
+  final contents = file.readAsStringSync();
+
+  final sourceFile = SourceFile.fromString(contents, url: file.uri);
+  final spans = _parseFile(contents, sourceFile);
+
+  for (var span in spans.take(30)) {
+    print('[${span.start.line + 1}:${span.start.column + 1}] ${span.text}');
+  }
+}
+
+Iterable<SourceSpan> _parseFile(String contents, SourceFile sourceFile) sync* {
+  var wordStart = 0;
+  var inWhiteSpace = true;
+
+  for (var i = 0; i < contents.length; i++) {
+    final codeUnit = contents.codeUnitAt(i);
+
+    if (codeUnit == _eol || codeUnit == _space) {
+      if (!inWhiteSpace) {
+        inWhiteSpace = true;
+
+        // emit a word
+        yield sourceFile.span(wordStart, i);
+      }
+    } else {
+      if (inWhiteSpace) {
+        inWhiteSpace = false;
+
+        wordStart = i;
+      }
+    }
+  }
+
+  if (!inWhiteSpace) {
+    // emit a word
+    yield sourceFile.span(wordStart, contents.length);
+  }
+}
+
+const int _eol = 10;
+const int _space = 32;

diff --git a/pkgs/source_span/lib/source_span.dart b/pkgs/source_span/lib/source_span.dart
new file mode 100644
index 0000000..534a3a7
--- /dev/null
+++ b/pkgs/source_span/lib/source_span.dart

@@ -0,0 +1,11 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+export 'src/file.dart';
+export 'src/location.dart';
+export 'src/location_mixin.dart';
+export 'src/span.dart';
+export 'src/span_exception.dart';
+export 'src/span_mixin.dart';
+export 'src/span_with_context.dart';

diff --git a/pkgs/source_span/lib/src/charcode.dart b/pkgs/source_span/lib/src/charcode.dart
new file mode 100644
index 0000000..5182638
--- /dev/null
+++ b/pkgs/source_span/lib/src/charcode.dart

@@ -0,0 +1,15 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// "Carriage return" control character.
+const int $cr = 0x0D;
+
+/// "Line feed" control character.
+const int $lf = 0x0A;
+
+/// Space character.
+const int $space = 0x20;
+
+/// "Horizontal Tab" control character, common name.
+const int $tab = 0x09;

diff --git a/pkgs/source_span/lib/src/colors.dart b/pkgs/source_span/lib/src/colors.dart
new file mode 100644
index 0000000..b48d468
--- /dev/null
+++ b/pkgs/source_span/lib/src/colors.dart

@@ -0,0 +1,12 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Color constants used for generating messages.
+const String red = '\u001b[31m';
+
+const String yellow = '\u001b[33m';
+
+const String blue = '\u001b[34m';
+
+const String none = '\u001b[0m';

diff --git a/pkgs/source_span/lib/src/file.dart b/pkgs/source_span/lib/src/file.dart
new file mode 100644
index 0000000..74c9234
--- /dev/null
+++ b/pkgs/source_span/lib/src/file.dart

@@ -0,0 +1,454 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:math' as math;
+import 'dart:typed_data';
+
+import 'location.dart';
+import 'location_mixin.dart';
+import 'span.dart';
+import 'span_mixin.dart';
+import 'span_with_context.dart';
+
+// Constants to determine end-of-lines.
+const int _lf = 10;
+const int _cr = 13;
+
+/// A class representing a source file.
+///
+/// This doesn't necessarily have to correspond to a file on disk, just a chunk
+/// of text usually with a URL associated with it.
+class SourceFile {
+  /// The URL where the source file is located.
+  ///
+  /// This may be null, indicating that the URL is unknown or unavailable.
+  final Uri? url;
+
+  /// An array of offsets for each line beginning in the file.
+  ///
+  /// Each offset refers to the first character *after* the newline. If the
+  /// source file has a trailing newline, the final offset won't actually be in
+  /// the file.
+  final _lineStarts = <int>[0];
+
+  /// The code units of the characters in the file.
+  ///
+  /// If this was constructed with the deprecated `SourceFile()` constructor,
+  /// this will instead contain the code _points_ of the characters in the file
+  /// (so characters above 2^16 are represented as individual integers rather
+  /// than surrogate pairs).
+  List<int> get codeUnits => _decodedChars;
+
+  /// The code units of the characters in this file.
+  final Uint32List _decodedChars;
+
+  /// The length of the file in characters.
+  int get length => _decodedChars.length;
+
+  /// The number of lines in the file.
+  int get lines => _lineStarts.length;
+
+  /// The line that the offset fell on the last time [getLine] was called.
+  ///
+  /// In many cases, sequential calls to getLine() are for nearby, usually
+  /// increasing offsets. In that case, we can find the line for an offset
+  /// quickly by first checking to see if the offset is on the same line as the
+  /// previous result.
+  int? _cachedLine;
+
+  /// This constructor is deprecated.
+  ///
+  /// Use [SourceFile.fromString] instead.
+  @Deprecated('Will be removed in 2.0.0')
+  SourceFile(String text, {Object? url}) : this.decoded(text.runes, url: url);
+
+  /// Creates a new source file from [text].
+  ///
+  /// [url] may be either a [String], a [Uri], or `null`.
+  SourceFile.fromString(String text, {Object? url})
+      : this.decoded(text.codeUnits, url: url);
+
+  /// Creates a new source file from a list of decoded code units.
+  ///
+  /// [url] may be either a [String], a [Uri], or `null`.
+  ///
+  /// Currently, if [decodedChars] contains characters larger than `0xFFFF`,
+  /// they'll be treated as single characters rather than being split into
+  /// surrogate pairs. **This behavior is deprecated**. For
+  /// forwards-compatibility, callers should only pass in characters less than
+  /// or equal to `0xFFFF`.
+  SourceFile.decoded(Iterable<int> decodedChars, {Object? url})
+      : url = url is String ? Uri.parse(url) : url as Uri?,
+        _decodedChars = Uint32List.fromList(decodedChars.toList()) {
+    for (var i = 0; i < _decodedChars.length; i++) {
+      var c = _decodedChars[i];
+      if (c == _cr) {
+        // Return not followed by newline is treated as a newline
+        final j = i + 1;
+        if (j >= _decodedChars.length || _decodedChars[j] != _lf) c = _lf;
+      }
+      if (c == _lf) _lineStarts.add(i + 1);
+    }
+  }
+
+  /// Returns a span from [start] to [end] (exclusive).
+  ///
+  /// If [end] isn't passed, it defaults to the end of the file.
+  FileSpan span(int start, [int? end]) {
+    end ??= length;
+    return _FileSpan(this, start, end);
+  }
+
+  /// Returns a location at [offset].
+  FileLocation location(int offset) => FileLocation._(this, offset);
+
+  /// Gets the 0-based line corresponding to [offset].
+  int getLine(int offset) {
+    if (offset < 0) {
+      throw RangeError('Offset may not be negative, was $offset.');
+    } else if (offset > length) {
+      throw RangeError('Offset $offset must not be greater than the number '
+          'of characters in the file, $length.');
+    }
+
+    if (offset < _lineStarts.first) return -1;
+    if (offset >= _lineStarts.last) return _lineStarts.length - 1;
+
+    if (_isNearCachedLine(offset)) return _cachedLine!;
+
+    _cachedLine = _binarySearch(offset) - 1;
+    return _cachedLine!;
+  }
+
+  /// Returns `true` if [offset] is near [_cachedLine].
+  ///
+  /// Checks on [_cachedLine] and the next line. If it's on the next line, it
+  /// updates [_cachedLine] to point to that.
+  bool _isNearCachedLine(int offset) {
+    if (_cachedLine == null) return false;
+    final cachedLine = _cachedLine!;
+
+    // See if it's before the cached line.
+    if (offset < _lineStarts[cachedLine]) return false;
+
+    // See if it's on the cached line.
+    if (cachedLine >= _lineStarts.length - 1 ||
+        offset < _lineStarts[cachedLine + 1]) {
+      return true;
+    }
+
+    // See if it's on the next line.
+    if (cachedLine >= _lineStarts.length - 2 ||
+        offset < _lineStarts[cachedLine + 2]) {
+      _cachedLine = cachedLine + 1;
+      return true;
+    }
+
+    return false;
+  }
+
+  /// Binary search through [_lineStarts] to find the line containing [offset].
+  ///
+  /// Returns the index of the line in [_lineStarts].
+  int _binarySearch(int offset) {
+    var min = 0;
+    var max = _lineStarts.length - 1;
+    while (min < max) {
+      final half = min + ((max - min) ~/ 2);
+      if (_lineStarts[half] > offset) {
+        max = half;
+      } else {
+        min = half + 1;
+      }
+    }
+
+    return max;
+  }
+
+  /// Gets the 0-based column corresponding to [offset].
+  ///
+  /// If [line] is passed, it's assumed to be the line containing [offset] and
+  /// is used to more efficiently compute the column.
+  int getColumn(int offset, {int? line}) {
+    if (offset < 0) {
+      throw RangeError('Offset may not be negative, was $offset.');
+    } else if (offset > length) {
+      throw RangeError('Offset $offset must be not be greater than the '
+          'number of characters in the file, $length.');
+    }
+
+    if (line == null) {
+      line = getLine(offset);
+    } else if (line < 0) {
+      throw RangeError('Line may not be negative, was $line.');
+    } else if (line >= lines) {
+      throw RangeError('Line $line must be less than the number of '
+          'lines in the file, $lines.');
+    }
+
+    final lineStart = _lineStarts[line];
+    if (lineStart > offset) {
+      throw RangeError('Line $line comes after offset $offset.');
+    }
+
+    return offset - lineStart;
+  }
+
+  /// Gets the offset for a [line] and [column].
+  ///
+  /// [column] defaults to 0.
+  int getOffset(int line, [int? column]) {
+    column ??= 0;
+
+    if (line < 0) {
+      throw RangeError('Line may not be negative, was $line.');
+    } else if (line >= lines) {
+      throw RangeError('Line $line must be less than the number of '
+          'lines in the file, $lines.');
+    } else if (column < 0) {
+      throw RangeError('Column may not be negative, was $column.');
+    }
+
+    final result = _lineStarts[line] + column;
+    if (result > length ||
+        (line + 1 < lines && result >= _lineStarts[line + 1])) {
+      throw RangeError("Line $line doesn't have $column columns.");
+    }
+
+    return result;
+  }
+
+  /// Returns the text of the file from [start] to [end] (exclusive).
+  ///
+  /// If [end] isn't passed, it defaults to the end of the file.
+  String getText(int start, [int? end]) =>
+      String.fromCharCodes(_decodedChars.sublist(start, end));
+}
+
+/// A [SourceLocation] within a [SourceFile].
+///
+/// Unlike the base [SourceLocation], [FileLocation] lazily computes its line
+/// and column values based on its offset and the contents of [file].
+///
+/// A [FileLocation] can be created using [SourceFile.location].
+class FileLocation extends SourceLocationMixin implements SourceLocation {
+  /// The [file] that `this` belongs to.
+  final SourceFile file;
+
+  @override
+  final int offset;
+
+  @override
+  Uri? get sourceUrl => file.url;
+
+  @override
+  int get line => file.getLine(offset);
+
+  @override
+  int get column => file.getColumn(offset);
+
+  FileLocation._(this.file, this.offset) {
+    if (offset < 0) {
+      throw RangeError('Offset may not be negative, was $offset.');
+    } else if (offset > file.length) {
+      throw RangeError('Offset $offset must not be greater than the number '
+          'of characters in the file, ${file.length}.');
+    }
+  }
+
+  @override
+  FileSpan pointSpan() => _FileSpan(file, offset, offset);
+}
+
+/// A [SourceSpan] within a [SourceFile].
+///
+/// Unlike the base [SourceSpan], [FileSpan] lazily computes its line and column
+/// values based on its offset and the contents of [file]. [SourceSpan.message]
+/// is also able to provide more context then [SourceSpan.message], and
+/// [SourceSpan.union] will return a [FileSpan] if possible.
+///
+/// A [FileSpan] can be created using [SourceFile.span].
+abstract class FileSpan implements SourceSpanWithContext {
+  /// The [file] that `this` belongs to.
+  SourceFile get file;
+
+  @override
+  FileLocation get start;
+
+  @override
+  FileLocation get end;
+
+  /// Returns a new span that covers both `this` and [other].
+  ///
+  /// Unlike [union], [other] may be disjoint from `this`. If it is, the text
+  /// between the two will be covered by the returned span.
+  FileSpan expand(FileSpan other);
+}
+
+/// The implementation of [FileSpan].
+///
+/// This is split into a separate class so that `is _FileSpan` checks can be run
+/// to make certain operations more efficient. If we used `is FileSpan`, that
+/// would break if external classes implemented the interface.
+class _FileSpan extends SourceSpanMixin implements FileSpan {
+  @override
+  final SourceFile file;
+
+  /// The offset of the beginning of the span.
+  ///
+  /// [start] is lazily generated from this to avoid allocating unnecessary
+  /// objects.
+  final int _start;
+
+  /// The offset of the end of the span.
+  ///
+  /// [end] is lazily generated from this to avoid allocating unnecessary
+  /// objects.
+  final int _end;
+
+  @override
+  Uri? get sourceUrl => file.url;
+
+  @override
+  int get length => _end - _start;
+
+  @override
+  FileLocation get start => FileLocation._(file, _start);
+
+  @override
+  FileLocation get end => FileLocation._(file, _end);
+
+  @override
+  String get text => file.getText(_start, _end);
+
+  @override
+  String get context {
+    final endLine = file.getLine(_end);
+    final endColumn = file.getColumn(_end);
+
+    int? endOffset;
+    if (endColumn == 0 && endLine != 0) {
+      // If [end] is at the very beginning of the line, the span covers the
+      // previous newline, so we only want to include the previous line in the
+      // context...
+
+      if (length == 0) {
+        // ...unless this is a point span, in which case we want to include the
+        // next line (or the empty string if this is the end of the file).
+        return endLine == file.lines - 1
+            ? ''
+            : file.getText(
+                file.getOffset(endLine), file.getOffset(endLine + 1));
+      }
+
+      endOffset = _end;
+    } else if (endLine == file.lines - 1) {
+      // If the span covers the last line of the file, the context should go all
+      // the way to the end of the file.
+      endOffset = file.length;
+    } else {
+      // Otherwise, the context should cover the full line on which [end]
+      // appears.
+      endOffset = file.getOffset(endLine + 1);
+    }
+
+    return file.getText(file.getOffset(file.getLine(_start)), endOffset);
+  }
+
+  _FileSpan(this.file, this._start, this._end) {
+    if (_end < _start) {
+      throw ArgumentError('End $_end must come after start $_start.');
+    } else if (_end > file.length) {
+      throw RangeError('End $_end must not be greater than the number '
+          'of characters in the file, ${file.length}.');
+    } else if (_start < 0) {
+      throw RangeError('Start may not be negative, was $_start.');
+    }
+  }
+
+  @override
+  int compareTo(SourceSpan other) {
+    if (other is! _FileSpan) return super.compareTo(other);
+
+    final result = _start.compareTo(other._start);
+    return result == 0 ? _end.compareTo(other._end) : result;
+  }
+
+  @override
+  SourceSpan union(SourceSpan other) {
+    if (other is! FileSpan) return super.union(other);
+
+    final span = expand(other);
+
+    if (other is _FileSpan) {
+      if (_start > other._end || other._start > _end) {
+        throw ArgumentError('Spans $this and $other are disjoint.');
+      }
+    } else {
+      if (_start > other.end.offset || other.start.offset > _end) {
+        throw ArgumentError('Spans $this and $other are disjoint.');
+      }
+    }
+
+    return span;
+  }
+
+  @override
+  bool operator ==(Object other) {
+    if (other is! FileSpan) return super == other;
+    if (other is! _FileSpan) {
+      return super == other && sourceUrl == other.sourceUrl;
+    }
+
+    return _start == other._start &&
+        _end == other._end &&
+        sourceUrl == other.sourceUrl;
+  }
+
+  @override
+  int get hashCode => Object.hash(_start, _end, sourceUrl);
+
+  /// Returns a new span that covers both `this` and [other].
+  ///
+  /// Unlike [union], [other] may be disjoint from `this`. If it is, the text
+  /// between the two will be covered by the returned span.
+  @override
+  FileSpan expand(FileSpan other) {
+    if (sourceUrl != other.sourceUrl) {
+      throw ArgumentError('Source URLs "$sourceUrl" and '
+          " \"${other.sourceUrl}\" don't match.");
+    }
+
+    if (other is _FileSpan) {
+      final start = math.min(_start, other._start);
+      final end = math.max(_end, other._end);
+      return _FileSpan(file, start, end);
+    } else {
+      final start = math.min(_start, other.start.offset);
+      final end = math.max(_end, other.end.offset);
+      return _FileSpan(file, start, end);
+    }
+  }
+
+  /// See `SourceSpanExtension.subspan`.
+  FileSpan subspan(int start, [int? end]) {
+    RangeError.checkValidRange(start, end, length);
+    if (start == 0 && (end == null || end == length)) return this;
+    return file.span(_start + start, end == null ? _end : _start + end);
+  }
+}
+
+// TODO(#52): Move these to instance methods in the next breaking release.
+/// Extension methods on the [FileSpan] API.
+extension FileSpanExtension on FileSpan {
+  /// See `SourceSpanExtension.subspan`.
+  FileSpan subspan(int start, [int? end]) {
+    RangeError.checkValidRange(start, end, length);
+    if (start == 0 && (end == null || end == length)) return this;
+
+    final startOffset = this.start.offset;
+    return file.span(
+        startOffset + start, end == null ? this.end.offset : startOffset + end);
+  }
+}

diff --git a/pkgs/source_span/lib/src/highlighter.dart b/pkgs/source_span/lib/src/highlighter.dart
new file mode 100644
index 0000000..19e04d0
--- /dev/null
+++ b/pkgs/source_span/lib/src/highlighter.dart

@@ -0,0 +1,727 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:math' as math;
+
+import 'package:collection/collection.dart';
+import 'package:path/path.dart' as p;
+import 'package:term_glyph/term_glyph.dart' as glyph;
+
+import 'charcode.dart';
+import 'colors.dart' as colors;
+import 'location.dart';
+import 'span.dart';
+import 'span_with_context.dart';
+import 'utils.dart';
+
+/// A class for writing a chunk of text with a particular span highlighted.
+class Highlighter {
+  /// The lines to display, including context around the highlighted spans.
+  final List<_Line> _lines;
+
+  /// The color to highlight the primary [_Highlight] within its context, or
+  /// `null` if it should not be colored.
+  final String? _primaryColor;
+
+  /// The color to highlight the secondary [_Highlight]s within their context,
+  /// or `null` if they should not be colored.
+  final String? _secondaryColor;
+
+  /// The number of characters before the bar in the sidebar.
+  final int _paddingBeforeSidebar;
+
+  /// The maximum number of multiline spans that cover any part of a single
+  /// line in [_lines].
+  final int _maxMultilineSpans;
+
+  /// Whether [_lines] includes lines from multiple different files.
+  final bool _multipleFiles;
+
+  /// The buffer to which to write the result.
+  final _buffer = StringBuffer();
+
+  /// The number of spaces to render for hard tabs that appear in `_span.text`.
+  ///
+  /// We don't want to render raw tabs, because they'll mess up our character
+  /// alignment.
+  static const _spacesPerTab = 4;
+
+  /// Creates a [Highlighter] that will return a string highlighting [span]
+  /// within the text of its file when [highlight] is called.
+  ///
+  /// [color] may either be a [String], a [bool], or `null`. If it's a string,
+  /// it indicates an [ANSI terminal color escape][] that should be used to
+  /// highlight [span]'s text (for example, `"\u001b[31m"` will color red). If
+  /// it's `true`, it indicates that the text should be highlighted using the
+  /// default color. If it's `false` or `null`, it indicates that no color
+  /// should be used.
+  ///
+  /// [ANSI terminal color escape]: https://en.wikipedia.org/wiki/ANSI_escape_code#Colors
+  Highlighter(SourceSpan span, {Object? color})
+      : this._(_collateLines([_Highlight(span, primary: true)]), () {
+          if (color == true) return colors.red;
+          if (color == false) return null;
+          return color as String?;
+        }(), null);
+
+  /// Creates a [Highlighter] that will return a string highlighting
+  /// [primarySpan] as well as all the spans in [secondarySpans] within the text
+  /// of their file when [highlight] is called.
+  ///
+  /// Each span has an associated label that will be written alongside it. For
+  /// [primarySpan] this message is [primaryLabel], and for [secondarySpans] the
+  /// labels are the map values.
+  ///
+  /// If [color] is `true`, this will use [ANSI terminal color escapes][] to
+  /// highlight the text. The [primarySpan] will be highlighted with
+  /// [primaryColor] (which defaults to red), and the [secondarySpans] will be
+  /// highlighted with [secondaryColor] (which defaults to blue). These
+  /// arguments are ignored if [color] is `false`.
+  ///
+  /// [ANSI terminal color escape]: https://en.wikipedia.org/wiki/ANSI_escape_code#Colors
+  Highlighter.multiple(SourceSpan primarySpan, String primaryLabel,
+      Map<SourceSpan, String> secondarySpans,
+      {bool color = false, String? primaryColor, String? secondaryColor})
+      : this._(
+            _collateLines([
+              _Highlight(primarySpan, label: primaryLabel, primary: true),
+              for (var entry in secondarySpans.entries)
+                _Highlight(entry.key, label: entry.value)
+            ]),
+            color ? (primaryColor ?? colors.red) : null,
+            color ? (secondaryColor ?? colors.blue) : null);
+
+  Highlighter._(this._lines, this._primaryColor, this._secondaryColor)
+      : _paddingBeforeSidebar = 1 +
+            math.max<int>(
+              // In a purely mathematical world, floor(log10(n)) would give the
+              // number of digits in n, but floating point errors render that
+              // unreliable in practice.
+              (_lines.last.number + 1).toString().length,
+              // If [_lines] aren't contiguous, we'll write "..." in place of a
+              // line number.
+              _contiguous(_lines) ? 0 : 3,
+            ),
+        _maxMultilineSpans = _lines
+            .map((line) => line.highlights
+                .where((highlight) => isMultiline(highlight.span))
+                .length)
+            .reduce(math.max),
+        _multipleFiles = !isAllTheSame(_lines.map((line) => line.url));
+
+  /// Returns whether [lines] contains any adjacent lines from the same source
+  /// file that aren't adjacent in the original file.
+  static bool _contiguous(List<_Line> lines) {
+    for (var i = 0; i < lines.length - 1; i++) {
+      final thisLine = lines[i];
+      final nextLine = lines[i + 1];
+      if (thisLine.number + 1 != nextLine.number &&
+          thisLine.url == nextLine.url) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  /// Collect all the source lines from the contexts of all spans in
+  /// [highlights], and associates them with the highlights that cover them.
+  static List<_Line> _collateLines(List<_Highlight> highlights) {
+    // Assign spans without URLs opaque Objects as keys. Each such Object will
+    // be different, but they can then be used later on to determine which lines
+    // came from the same span even if they'd all otherwise have `null` URLs.
+    final highlightsByUrl = groupBy<_Highlight, Object>(
+        highlights, (highlight) => highlight.span.sourceUrl ?? Object());
+    for (var list in highlightsByUrl.values) {
+      list.sort((highlight1, highlight2) =>
+          highlight1.span.compareTo(highlight2.span));
+    }
+
+    return highlightsByUrl.entries.expand((entry) {
+      final url = entry.key;
+      final highlightsForFile = entry.value;
+
+      // First, create a list of all the lines in the current file that we have
+      // context for along with their line numbers.
+      final lines = <_Line>[];
+      for (var highlight in highlightsForFile) {
+        final context = highlight.span.context;
+        // If [highlight.span.context] contains lines prior to the one
+        // [highlight.span.text] appears on, write those first.
+        final lineStart = findLineStart(
+            context, highlight.span.text, highlight.span.start.column)!;
+
+        final linesBeforeSpan =
+            '\n'.allMatches(context.substring(0, lineStart)).length;
+
+        var lineNumber = highlight.span.start.line - linesBeforeSpan;
+        for (var line in context.split('\n')) {
+          // Only add a line if it hasn't already been added for a previous span
+          if (lines.isEmpty || lineNumber > lines.last.number) {
+            lines.add(_Line(line, lineNumber, url));
+          }
+          lineNumber++;
+        }
+      }
+
+      // Next, associate each line with each highlights that covers it.
+      final activeHighlights = <_Highlight>[];
+      var highlightIndex = 0;
+      for (var line in lines) {
+        activeHighlights
+            .removeWhere((highlight) => highlight.span.end.line < line.number);
+
+        final oldHighlightLength = activeHighlights.length;
+        for (var highlight in highlightsForFile.skip(highlightIndex)) {
+          if (highlight.span.start.line > line.number) break;
+          activeHighlights.add(highlight);
+        }
+        highlightIndex += activeHighlights.length - oldHighlightLength;
+
+        line.highlights.addAll(activeHighlights);
+      }
+
+      return lines;
+    }).toList();
+  }
+
+  /// Returns the highlighted span text.
+  ///
+  /// This method should only be called once.
+  String highlight() {
+    _writeFileStart(_lines.first.url);
+
+    // Each index of this list represents a column after the sidebar that could
+    // contain a line indicating an active highlight. If it's `null`, that
+    // column is empty; if it contains a highlight, it should be drawn for that
+    // column.
+    final highlightsByColumn =
+        List<_Highlight?>.filled(_maxMultilineSpans, null);
+
+    for (var i = 0; i < _lines.length; i++) {
+      final line = _lines[i];
+      if (i > 0) {
+        final lastLine = _lines[i - 1];
+        if (lastLine.url != line.url) {
+          _writeSidebar(end: glyph.upEnd);
+          _buffer.writeln();
+          _writeFileStart(line.url);
+        } else if (lastLine.number + 1 != line.number) {
+          _writeSidebar(text: '...');
+          _buffer.writeln();
+        }
+      }
+
+      // If a highlight covers the entire first line other than initial
+      // whitespace, don't bother pointing out exactly where it begins. Iterate
+      // in reverse so that longer highlights (which are sorted after shorter
+      // highlights) appear further out, leading to fewer crossed lines.
+      for (var highlight in line.highlights.reversed) {
+        if (isMultiline(highlight.span) &&
+            highlight.span.start.line == line.number &&
+            _isOnlyWhitespace(
+                line.text.substring(0, highlight.span.start.column))) {
+          replaceFirstNull(highlightsByColumn, highlight);
+        }
+      }
+
+      _writeSidebar(line: line.number);
+      _buffer.write(' ');
+      _writeMultilineHighlights(line, highlightsByColumn);
+      if (highlightsByColumn.isNotEmpty) _buffer.write(' ');
+
+      final primaryIdx =
+          line.highlights.indexWhere((highlight) => highlight.isPrimary);
+      final primary = primaryIdx == -1 ? null : line.highlights[primaryIdx];
+
+      if (primary != null) {
+        _writeHighlightedText(
+            line.text,
+            primary.span.start.line == line.number
+                ? primary.span.start.column
+                : 0,
+            primary.span.end.line == line.number
+                ? primary.span.end.column
+                : line.text.length,
+            color: _primaryColor);
+      } else {
+        _writeText(line.text);
+      }
+      _buffer.writeln();
+
+      // Always write the primary span's indicator first so that it's right next
+      // to the highlighted text.
+      if (primary != null) _writeIndicator(line, primary, highlightsByColumn);
+      for (var highlight in line.highlights) {
+        if (highlight.isPrimary) continue;
+        _writeIndicator(line, highlight, highlightsByColumn);
+      }
+    }
+
+    _writeSidebar(end: glyph.upEnd);
+    return _buffer.toString();
+  }
+
+  /// Writes the beginning of the file highlight for the file with the given
+  /// [url] (or opaque object if it comes from a span with a null URL).
+  void _writeFileStart(Object url) {
+    if (!_multipleFiles || url is! Uri) {
+      _writeSidebar(end: glyph.downEnd);
+    } else {
+      _writeSidebar(end: glyph.topLeftCorner);
+      _colorize(() => _buffer.write('${glyph.horizontalLine * 2}>'),
+          color: colors.blue);
+      _buffer.write(' ${p.prettyUri(url)}');
+    }
+    _buffer.writeln();
+  }
+
+  /// Writes the post-sidebar highlight bars for [line] according to
+  /// [highlightsByColumn].
+  ///
+  /// If [current] is passed, it's the highlight for which an indicator is being
+  /// written. If it appears in [highlightsByColumn], a horizontal line is
+  /// written from its column to the rightmost column.
+  void _writeMultilineHighlights(
+      _Line line, List<_Highlight?> highlightsByColumn,
+      {_Highlight? current}) {
+    // Whether we've written a sidebar indicator for opening a new span on this
+    // line, and which color should be used for that indicator's rightward line.
+    var openedOnThisLine = false;
+    String? openedOnThisLineColor;
+
+    final currentColor = current == null
+        ? null
+        : current.isPrimary
+            ? _primaryColor
+            : _secondaryColor;
+    var foundCurrent = false;
+    for (var highlight in highlightsByColumn) {
+      final startLine = highlight?.span.start.line;
+      final endLine = highlight?.span.end.line;
+      if (current != null && highlight == current) {
+        foundCurrent = true;
+        assert(startLine == line.number || endLine == line.number);
+        _colorize(() {
+          _buffer.write(startLine == line.number
+              ? glyph.topLeftCorner
+              : glyph.bottomLeftCorner);
+        }, color: currentColor);
+      } else if (foundCurrent) {
+        _colorize(() {
+          _buffer.write(highlight == null ? glyph.horizontalLine : glyph.cross);
+        }, color: currentColor);
+      } else if (highlight == null) {
+        if (openedOnThisLine) {
+          _colorize(() => _buffer.write(glyph.horizontalLine),
+              color: openedOnThisLineColor);
+        } else {
+          _buffer.write(' ');
+        }
+      } else {
+        _colorize(() {
+          final vertical = openedOnThisLine ? glyph.cross : glyph.verticalLine;
+          if (current != null) {
+            _buffer.write(vertical);
+          } else if (startLine == line.number) {
+            _colorize(() {
+              _buffer
+                  .write(glyph.glyphOrAscii(openedOnThisLine ? '┬' : '┌', '/'));
+            }, color: openedOnThisLineColor);
+            openedOnThisLine = true;
+            openedOnThisLineColor ??=
+                highlight.isPrimary ? _primaryColor : _secondaryColor;
+          } else if (endLine == line.number &&
+              highlight.span.end.column == line.text.length) {
+            _buffer.write(highlight.label == null
+                ? glyph.glyphOrAscii('└', r'\')
+                : vertical);
+          } else {
+            _colorize(() {
+              _buffer.write(vertical);
+            }, color: openedOnThisLineColor);
+          }
+        }, color: highlight.isPrimary ? _primaryColor : _secondaryColor);
+      }
+    }
+  }
+
+  // Writes [text], with text between [startColumn] and [endColumn] colorized in
+  // the same way as [_colorize].
+  void _writeHighlightedText(String text, int startColumn, int endColumn,
+      {required String? color}) {
+    _writeText(text.substring(0, startColumn));
+    _colorize(() => _writeText(text.substring(startColumn, endColumn)),
+        color: color);
+    _writeText(text.substring(endColumn, text.length));
+  }
+
+  /// Writes an indicator for where [highlight] starts, ends, or both below
+  /// [line].
+  ///
+  /// This may either add or remove [highlight] from [highlightsByColumn].
+  void _writeIndicator(
+      _Line line, _Highlight highlight, List<_Highlight?> highlightsByColumn) {
+    final color = highlight.isPrimary ? _primaryColor : _secondaryColor;
+    if (!isMultiline(highlight.span)) {
+      _writeSidebar();
+      _buffer.write(' ');
+      _writeMultilineHighlights(line, highlightsByColumn, current: highlight);
+      if (highlightsByColumn.isNotEmpty) _buffer.write(' ');
+
+      final underlineLength = _colorize(() {
+        final start = _buffer.length;
+        _writeUnderline(line, highlight.span,
+            highlight.isPrimary ? '^' : glyph.horizontalLineBold);
+        return _buffer.length - start;
+      }, color: color);
+      _writeLabel(highlight, highlightsByColumn, underlineLength);
+    } else if (highlight.span.start.line == line.number) {
+      if (highlightsByColumn.contains(highlight)) return;
+      replaceFirstNull(highlightsByColumn, highlight);
+
+      _writeSidebar();
+      _buffer.write(' ');
+      _writeMultilineHighlights(line, highlightsByColumn, current: highlight);
+      _colorize(() => _writeArrow(line, highlight.span.start.column),
+          color: color);
+      _buffer.writeln();
+    } else if (highlight.span.end.line == line.number) {
+      final coversWholeLine = highlight.span.end.column == line.text.length;
+      if (coversWholeLine && highlight.label == null) {
+        replaceWithNull(highlightsByColumn, highlight);
+        return;
+      }
+
+      _writeSidebar();
+      _buffer.write(' ');
+      _writeMultilineHighlights(line, highlightsByColumn, current: highlight);
+
+      final underlineLength = _colorize(() {
+        final start = _buffer.length;
+        if (coversWholeLine) {
+          _buffer.write(glyph.horizontalLine * 3);
+        } else {
+          _writeArrow(line, math.max(highlight.span.end.column - 1, 0),
+              beginning: false);
+        }
+        return _buffer.length - start;
+      }, color: color);
+      _writeLabel(highlight, highlightsByColumn, underlineLength);
+      replaceWithNull(highlightsByColumn, highlight);
+    }
+  }
+
+  /// Underlines the portion of [line] covered by [span] with repeated instances
+  /// of [character].
+  void _writeUnderline(_Line line, SourceSpan span, String character) {
+    assert(!isMultiline(span));
+    assert(line.text.contains(span.text),
+        '"${line.text}" should contain "${span.text}"');
+
+    var startColumn = span.start.column;
+    var endColumn = span.end.column;
+
+    // Adjust the start and end columns to account for any tabs that were
+    // converted to spaces.
+    final tabsBefore = _countTabs(line.text.substring(0, startColumn));
+    final tabsInside = _countTabs(line.text.substring(startColumn, endColumn));
+    startColumn += tabsBefore * (_spacesPerTab - 1);
+    endColumn += (tabsBefore + tabsInside) * (_spacesPerTab - 1);
+
+    _buffer
+      ..write(' ' * startColumn)
+      ..write(character * math.max(endColumn - startColumn, 1));
+  }
+
+  /// Write an arrow pointing to column [column] in [line].
+  ///
+  /// If the arrow points to a tab character, this will point to the beginning
+  /// of the tab if [beginning] is `true` and the end if it's `false`.
+  void _writeArrow(_Line line, int column, {bool beginning = true}) {
+    final tabs =
+        _countTabs(line.text.substring(0, column + (beginning ? 0 : 1)));
+    _buffer
+      ..write(glyph.horizontalLine * (1 + column + tabs * (_spacesPerTab - 1)))
+      ..write('^');
+  }
+
+  /// Writes [highlight]'s label.
+  ///
+  /// The `_buffer` is assumed to be written to the point where the first line
+  /// of `highlight.label` can be written after a space, but this takes care of
+  /// writing indentation and highlight columns for later lines.
+  ///
+  /// The [highlightsByColumn] are used to write ongoing highlight lines if the
+  /// label is more than one line long.
+  ///
+  /// The [underlineLength] is the length of the line written between the
+  /// highlights and the beginning of the first label.
+  void _writeLabel(_Highlight highlight, List<_Highlight?> highlightsByColumn,
+      int underlineLength) {
+    final label = highlight.label;
+    if (label == null) {
+      _buffer.writeln();
+      return;
+    }
+
+    final lines = label.split('\n');
+    final color = highlight.isPrimary ? _primaryColor : _secondaryColor;
+    _colorize(() => _buffer.write(' ${lines.first}'), color: color);
+    _buffer.writeln();
+
+    for (var text in lines.skip(1)) {
+      _writeSidebar();
+      _buffer.write(' ');
+      for (var columnHighlight in highlightsByColumn) {
+        if (columnHighlight == null || columnHighlight == highlight) {
+          _buffer.write(' ');
+        } else {
+          _buffer.write(glyph.verticalLine);
+        }
+      }
+
+      _buffer.write(' ' * underlineLength);
+      _colorize(() => _buffer.write(' $text'), color: color);
+      _buffer.writeln();
+    }
+  }
+
+  /// Writes a snippet from the source text, converting hard tab characters into
+  /// plain indentation.
+  void _writeText(String text) {
+    for (var char in text.codeUnits) {
+      if (char == $tab) {
+        _buffer.write(' ' * _spacesPerTab);
+      } else {
+        _buffer.writeCharCode(char);
+      }
+    }
+  }
+
+  // Writes a sidebar to [buffer] that includes [line] as the line number if
+  // given and writes [end] at the end (defaults to [glyphs.verticalLine]).
+  //
+  // If [text] is given, it's used in place of the line number. It can't be
+  // passed at the same time as [line].
+  void _writeSidebar({int? line, String? text, String? end}) {
+    assert(line == null || text == null);
+
+    // Add 1 to line to convert from computer-friendly 0-indexed line numbers to
+    // human-friendly 1-indexed line numbers.
+    if (line != null) text = (line + 1).toString();
+    _colorize(() {
+      _buffer
+        ..write((text ?? '').padRight(_paddingBeforeSidebar))
+        ..write(end ?? glyph.verticalLine);
+    }, color: colors.blue);
+  }
+
+  /// Returns the number of hard tabs in [text].
+  int _countTabs(String text) {
+    var count = 0;
+    for (var char in text.codeUnits) {
+      if (char == $tab) count++;
+    }
+    return count;
+  }
+
+  /// Returns whether [text] contains only space or tab characters.
+  bool _isOnlyWhitespace(String text) {
+    for (var char in text.codeUnits) {
+      if (char != $space && char != $tab) return false;
+    }
+    return true;
+  }
+
+  /// Colors all text written to [_buffer] during [callback], if colorization is
+  /// enabled and [color] is not `null`.
+  T _colorize<T>(T Function() callback, {required String? color}) {
+    if (_primaryColor != null && color != null) _buffer.write(color);
+    final result = callback();
+    if (_primaryColor != null && color != null) _buffer.write(colors.none);
+    return result;
+  }
+}
+
+/// Information about how to highlight a single section of a source file.
+class _Highlight {
+  /// The section of the source file to highlight.
+  ///
+  /// This is normalized to make it easier for [Highlighter] to work with.
+  final SourceSpanWithContext span;
+
+  /// Whether this is the primary span in the highlight.
+  ///
+  /// The primary span is highlighted with a different character and colored
+  /// differently than non-primary spans.
+  final bool isPrimary;
+
+  /// The label to include inline when highlighting [span].
+  ///
+  /// This helps distinguish clarify what each highlight means when multiple are
+  /// used in the same message.
+  final String? label;
+
+  _Highlight(SourceSpan span, {String? label, bool primary = false})
+      : span = (() {
+          var newSpan = _normalizeContext(span);
+          newSpan = _normalizeNewlines(newSpan);
+          newSpan = _normalizeTrailingNewline(newSpan);
+          return _normalizeEndOfLine(newSpan);
+        })(),
+        isPrimary = primary,
+        label = label?.replaceAll('\r\n', '\n');
+
+  /// Normalizes [span] to ensure that it's a [SourceSpanWithContext] whose
+  /// context actually contains its text at the expected column.
+  ///
+  /// If it's not already a [SourceSpanWithContext], adjust the start and end
+  /// locations' line and column fields so that the highlighter can assume they
+  /// match up with the context.
+  static SourceSpanWithContext _normalizeContext(SourceSpan span) =>
+      span is SourceSpanWithContext &&
+              findLineStart(span.context, span.text, span.start.column) != null
+          ? span
+          : SourceSpanWithContext(
+              SourceLocation(span.start.offset,
+                  sourceUrl: span.sourceUrl, line: 0, column: 0),
+              SourceLocation(span.end.offset,
+                  sourceUrl: span.sourceUrl,
+                  line: countCodeUnits(span.text, $lf),
+                  column: _lastLineLength(span.text)),
+              span.text,
+              span.text);
+
+  /// Normalizes [span] to replace Windows-style newlines with Unix-style
+  /// newlines.
+  static SourceSpanWithContext _normalizeNewlines(SourceSpanWithContext span) {
+    final text = span.text;
+    if (!text.contains('\r\n')) return span;
+
+    var endOffset = span.end.offset;
+    for (var i = 0; i < text.length - 1; i++) {
+      if (text.codeUnitAt(i) == $cr && text.codeUnitAt(i + 1) == $lf) {
+        endOffset--;
+      }
+    }
+
+    return SourceSpanWithContext(
+        span.start,
+        SourceLocation(endOffset,
+            sourceUrl: span.sourceUrl,
+            line: span.end.line,
+            column: span.end.column),
+        text.replaceAll('\r\n', '\n'),
+        span.context.replaceAll('\r\n', '\n'));
+  }
+
+  /// Normalizes [span] to remove a trailing newline from `span.context`.
+  ///
+  /// If necessary, also adjust `span.end` so that it doesn't point past where
+  /// the trailing newline used to be.
+  static SourceSpanWithContext _normalizeTrailingNewline(
+      SourceSpanWithContext span) {
+    if (!span.context.endsWith('\n')) return span;
+
+    // If there's a full blank line on the end of [span.context], it's probably
+    // significant, so we shouldn't trim it.
+    if (span.text.endsWith('\n\n')) return span;
+
+    final context = span.context.substring(0, span.context.length - 1);
+    var text = span.text;
+    var start = span.start;
+    var end = span.end;
+    if (span.text.endsWith('\n') && _isTextAtEndOfContext(span)) {
+      text = span.text.substring(0, span.text.length - 1);
+      if (text.isEmpty) {
+        end = start;
+      } else {
+        end = SourceLocation(span.end.offset - 1,
+            sourceUrl: span.sourceUrl,
+            line: span.end.line - 1,
+            column: _lastLineLength(context));
+        start = span.start.offset == span.end.offset ? end : span.start;
+      }
+    }
+    return SourceSpanWithContext(start, end, text, context);
+  }
+
+  /// Normalizes [span] so that the end location is at the end of a line rather
+  /// than at the beginning of the next line.
+  static SourceSpanWithContext _normalizeEndOfLine(SourceSpanWithContext span) {
+    if (span.end.column != 0) return span;
+    if (span.end.line == span.start.line) return span;
+
+    final text = span.text.substring(0, span.text.length - 1);
+
+    return SourceSpanWithContext(
+        span.start,
+        SourceLocation(span.end.offset - 1,
+            sourceUrl: span.sourceUrl,
+            line: span.end.line - 1,
+            column: text.length - text.lastIndexOf('\n') - 1),
+        text,
+        // If the context also ends with a newline, it's possible that we don't
+        // have the full context for that line, so we shouldn't print it at all.
+        span.context.endsWith('\n')
+            ? span.context.substring(0, span.context.length - 1)
+            : span.context);
+  }
+
+  /// Returns the length of the last line in [text], whether or not it ends in a
+  /// newline.
+  static int _lastLineLength(String text) {
+    if (text.isEmpty) {
+      return 0;
+    } else if (text.codeUnitAt(text.length - 1) == $lf) {
+      return text.length == 1
+          ? 0
+          : text.length - text.lastIndexOf('\n', text.length - 2) - 1;
+    } else {
+      return text.length - text.lastIndexOf('\n') - 1;
+    }
+  }
+
+  /// Returns whether [span]'s text runs all the way to the end of its context.
+  static bool _isTextAtEndOfContext(SourceSpanWithContext span) =>
+      findLineStart(span.context, span.text, span.start.column)! +
+          span.start.column +
+          span.length ==
+      span.context.length;
+
+  @override
+  String toString() {
+    final buffer = StringBuffer();
+    if (isPrimary) buffer.write('primary ');
+    buffer.write('${span.start.line}:${span.start.column}-'
+        '${span.end.line}:${span.end.column}');
+    if (label != null) buffer.write(' ($label)');
+    return buffer.toString();
+  }
+}
+
+/// A single line of the source file being highlighted.
+class _Line {
+  /// The text of the line, not including the trailing newline.
+  final String text;
+
+  /// The 0-based line number in the source file.
+  final int number;
+
+  /// The URL of the source file in which this line appears.
+  ///
+  /// For lines created from spans without an explicit URL, this is an opaque
+  /// object that differs between lines that come from different spans.
+  final Object url;
+
+  /// All highlights that cover any portion of this line, in source span order.
+  ///
+  /// This is populated after the initial line is created.
+  final highlights = <_Highlight>[];
+
+  _Line(this.text, this.number, this.url);
+
+  @override
+  String toString() => '$number: "$text" (${highlights.join(', ')})';
+}

diff --git a/pkgs/source_span/lib/src/location.dart b/pkgs/source_span/lib/src/location.dart
new file mode 100644
index 0000000..8f22d7b
--- /dev/null
+++ b/pkgs/source_span/lib/src/location.dart

@@ -0,0 +1,102 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'span.dart';
+
+// TODO(nweiz): Use SourceLocationMixin once we decide to cut a release with
+// breaking changes. See SourceLocationMixin for details.
+
+/// A class that describes a single location within a source file.
+///
+/// This class should not be extended. Instead, [SourceLocationBase] should be
+/// extended instead.
+class SourceLocation implements Comparable<SourceLocation> {
+  /// URL of the source containing this location.
+  ///
+  /// This may be null, indicating that the source URL is unknown or
+  /// unavailable.
+  final Uri? sourceUrl;
+
+  /// The 0-based offset of this location in the source.
+  final int offset;
+
+  /// The 0-based line of this location in the source.
+  final int line;
+
+  /// The 0-based column of this location in the source
+  final int column;
+
+  /// Returns a representation of this location in the `source:line:column`
+  /// format used by text editors.
+  ///
+  /// This prints 1-based lines and columns.
+  String get toolString {
+    final source = sourceUrl ?? 'unknown source';
+    return '$source:${line + 1}:${column + 1}';
+  }
+
+  /// Creates a new location indicating [offset] within [sourceUrl].
+  ///
+  /// [line] and [column] default to assuming the source is a single line. This
+  /// means that [line] defaults to 0 and [column] defaults to [offset].
+  ///
+  /// [sourceUrl] may be either a [String], a [Uri], or `null`.
+  SourceLocation(this.offset, {Object? sourceUrl, int? line, int? column})
+      : sourceUrl =
+            sourceUrl is String ? Uri.parse(sourceUrl) : sourceUrl as Uri?,
+        line = line ?? 0,
+        column = column ?? offset {
+    if (offset < 0) {
+      throw RangeError('Offset may not be negative, was $offset.');
+    } else if (line != null && line < 0) {
+      throw RangeError('Line may not be negative, was $line.');
+    } else if (column != null && column < 0) {
+      throw RangeError('Column may not be negative, was $column.');
+    }
+  }
+
+  /// Returns the distance in characters between `this` and [other].
+  ///
+  /// This always returns a non-negative value.
+  int distance(SourceLocation other) {
+    if (sourceUrl != other.sourceUrl) {
+      throw ArgumentError('Source URLs "$sourceUrl" and '
+          "\"${other.sourceUrl}\" don't match.");
+    }
+    return (offset - other.offset).abs();
+  }
+
+  /// Returns a span that covers only a single point: this location.
+  SourceSpan pointSpan() => SourceSpan(this, this, '');
+
+  /// Compares two locations.
+  ///
+  /// [other] must have the same source URL as `this`.
+  @override
+  int compareTo(SourceLocation other) {
+    if (sourceUrl != other.sourceUrl) {
+      throw ArgumentError('Source URLs "$sourceUrl" and '
+          "\"${other.sourceUrl}\" don't match.");
+    }
+    return offset - other.offset;
+  }
+
+  @override
+  bool operator ==(Object other) =>
+      other is SourceLocation &&
+      sourceUrl == other.sourceUrl &&
+      offset == other.offset;
+
+  @override
+  int get hashCode => (sourceUrl?.hashCode ?? 0) + offset;
+
+  @override
+  String toString() => '<$runtimeType: $offset $toolString>';
+}
+
+/// A base class for source locations with [offset], [line], and [column] known
+/// at construction time.
+class SourceLocationBase extends SourceLocation {
+  SourceLocationBase(super.offset, {super.sourceUrl, super.line, super.column});
+}

diff --git a/pkgs/source_span/lib/src/location_mixin.dart b/pkgs/source_span/lib/src/location_mixin.dart
new file mode 100644
index 0000000..a44f5e2
--- /dev/null
+++ b/pkgs/source_span/lib/src/location_mixin.dart

@@ -0,0 +1,55 @@
+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'location.dart';
+import 'span.dart';
+
+// Note: this class duplicates a lot of functionality of [SourceLocation]. This
+// is because in order for SourceLocation to use SourceLocationMixin,
+// SourceLocationMixin couldn't implement SourceLocation. In SourceSpan we
+// handle this by making the class itself non-extensible, but that would be a
+// breaking change for SourceLocation. So until we want to endure the pain of
+// cutting a release with breaking changes, we duplicate the code here.
+
+/// A mixin for easily implementing [SourceLocation].
+abstract class SourceLocationMixin implements SourceLocation {
+  @override
+  String get toolString {
+    final source = sourceUrl ?? 'unknown source';
+    return '$source:${line + 1}:${column + 1}';
+  }
+
+  @override
+  int distance(SourceLocation other) {
+    if (sourceUrl != other.sourceUrl) {
+      throw ArgumentError('Source URLs "$sourceUrl" and '
+          "\"${other.sourceUrl}\" don't match.");
+    }
+    return (offset - other.offset).abs();
+  }
+
+  @override
+  SourceSpan pointSpan() => SourceSpan(this, this, '');
+
+  @override
+  int compareTo(SourceLocation other) {
+    if (sourceUrl != other.sourceUrl) {
+      throw ArgumentError('Source URLs "$sourceUrl" and '
+          "\"${other.sourceUrl}\" don't match.");
+    }
+    return offset - other.offset;
+  }
+
+  @override
+  bool operator ==(Object other) =>
+      other is SourceLocation &&
+      sourceUrl == other.sourceUrl &&
+      offset == other.offset;
+
+  @override
+  int get hashCode => (sourceUrl?.hashCode ?? 0) + offset;
+
+  @override
+  String toString() => '<$runtimeType: $offset $toolString>';
+}

diff --git a/pkgs/source_span/lib/src/span.dart b/pkgs/source_span/lib/src/span.dart
new file mode 100644
index 0000000..941dedc
--- /dev/null
+++ b/pkgs/source_span/lib/src/span.dart

@@ -0,0 +1,193 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:path/path.dart' as p;
+import 'package:term_glyph/term_glyph.dart' as glyph;
+
+import 'file.dart';
+import 'highlighter.dart';
+import 'location.dart';
+import 'span_mixin.dart';
+import 'span_with_context.dart';
+import 'utils.dart';
+
+/// A class that describes a segment of source text.
+abstract class SourceSpan implements Comparable<SourceSpan> {
+  /// The start location of this span.
+  SourceLocation get start;
+
+  /// The end location of this span, exclusive.
+  SourceLocation get end;
+
+  /// The source text for this span.
+  String get text;
+
+  /// The URL of the source (typically a file) of this span.
+  ///
+  /// This may be null, indicating that the source URL is unknown or
+  /// unavailable.
+  Uri? get sourceUrl;
+
+  /// The length of this span, in characters.
+  int get length;
+
+  /// Creates a new span from [start] to [end] (exclusive) containing [text].
+  ///
+  /// [start] and [end] must have the same source URL and [start] must come
+  /// before [end]. [text] must have a number of characters equal to the
+  /// distance between [start] and [end].
+  factory SourceSpan(SourceLocation start, SourceLocation end, String text) =>
+      SourceSpanBase(start, end, text);
+
+  /// Creates a new span that's the union of `this` and [other].
+  ///
+  /// The two spans must have the same source URL and may not be disjoint.
+  /// [text] is computed by combining `this.text` and `other.text`.
+  SourceSpan union(SourceSpan other);
+
+  /// Compares two spans.
+  ///
+  /// [other] must have the same source URL as `this`. This orders spans by
+  /// [start] then [length].
+  @override
+  int compareTo(SourceSpan other);
+
+  /// Formats [message] in a human-friendly way associated with this span.
+  ///
+  /// [color] may either be a [String], a [bool], or `null`. If it's a string,
+  /// it indicates an [ANSI terminal color escape][] that should
+  /// be used to highlight the span's text (for example, `"\u001b[31m"` will
+  /// color red). If it's `true`, it indicates that the text should be
+  /// highlighted using the default color. If it's `false` or `null`, it
+  /// indicates that the text shouldn't be highlighted.
+  ///
+  /// This uses the full range of Unicode characters to highlight the source
+  /// span if [glyph.ascii] is `false` (the default), but only uses ASCII
+  /// characters if it's `true`.
+  ///
+  /// [ANSI terminal color escape]: https://en.wikipedia.org/wiki/ANSI_escape_code#Colors
+  String message(String message, {Object? color});
+
+  /// Prints the text associated with this span in a user-friendly way.
+  ///
+  /// This is identical to [message], except that it doesn't print the file
+  /// name, line number, column number, or message. If [length] is 0 and this
+  /// isn't a [SourceSpanWithContext], returns an empty string.
+  ///
+  /// [color] may either be a [String], a [bool], or `null`. If it's a string,
+  /// it indicates an [ANSI terminal color escape][] that should
+  /// be used to highlight the span's text (for example, `"\u001b[31m"` will
+  /// color red). If it's `true`, it indicates that the text should be
+  /// highlighted using the default color. If it's `false` or `null`, it
+  /// indicates that the text shouldn't be highlighted.
+  ///
+  /// This uses the full range of Unicode characters to highlight the source
+  /// span if [glyph.ascii] is `false` (the default), but only uses ASCII
+  /// characters if it's `true`.
+  ///
+  /// [ANSI terminal color escape]: https://en.wikipedia.org/wiki/ANSI_escape_code#Colors
+  String highlight({Object? color});
+}
+
+/// A base class for source spans with [start], [end], and [text] known at
+/// construction time.
+class SourceSpanBase extends SourceSpanMixin {
+  @override
+  final SourceLocation start;
+  @override
+  final SourceLocation end;
+  @override
+  final String text;
+
+  SourceSpanBase(this.start, this.end, this.text) {
+    if (end.sourceUrl != start.sourceUrl) {
+      throw ArgumentError('Source URLs "${start.sourceUrl}" and '
+          " \"${end.sourceUrl}\" don't match.");
+    } else if (end.offset < start.offset) {
+      throw ArgumentError('End $end must come after start $start.');
+    } else if (text.length != start.distance(end)) {
+      throw ArgumentError('Text "$text" must be ${start.distance(end)} '
+          'characters long.');
+    }
+  }
+}
+
+// TODO(#52): Move these to instance methods in the next breaking release.
+/// Extension methods on the base [SourceSpan] API.
+extension SourceSpanExtension on SourceSpan {
+  /// Like [SourceSpan.message], but also highlights [secondarySpans] to provide
+  /// the user with additional context.
+  ///
+  /// Each span takes a label ([label] for this span, and the values of the
+  /// [secondarySpans] map for the secondary spans) that's used to indicate to
+  /// the user what that particular span represents.
+  ///
+  /// If [color] is `true`, [ANSI terminal color escapes][] are used to color
+  /// the resulting string. By default this span is colored red and the
+  /// secondary spans are colored blue, but that can be customized by passing
+  /// ANSI escape strings to [primaryColor] or [secondaryColor].
+  ///
+  /// [ANSI terminal color escapes]: https://en.wikipedia.org/wiki/ANSI_escape_code#Colors
+  ///
+  /// Each span in [secondarySpans] must refer to the same document as this
+  /// span. Throws an [ArgumentError] if any secondary span has a different
+  /// source URL than this span.
+  ///
+  /// Note that while this will work with plain [SourceSpan]s, it will produce
+  /// much more useful output with [SourceSpanWithContext]s (including
+  /// [FileSpan]s).
+  String messageMultiple(
+      String message, String label, Map<SourceSpan, String> secondarySpans,
+      {bool color = false, String? primaryColor, String? secondaryColor}) {
+    final buffer = StringBuffer()
+      ..write('line ${start.line + 1}, column ${start.column + 1}');
+    if (sourceUrl != null) buffer.write(' of ${p.prettyUri(sourceUrl)}');
+    buffer
+      ..writeln(': $message')
+      ..write(highlightMultiple(label, secondarySpans,
+          color: color,
+          primaryColor: primaryColor,
+          secondaryColor: secondaryColor));
+    return buffer.toString();
+  }
+
+  /// Like [SourceSpan.highlight], but also highlights [secondarySpans] to
+  /// provide the user with additional context.
+  ///
+  /// Each span takes a label ([label] for this span, and the values of the
+  /// [secondarySpans] map for the secondary spans) that's used to indicate to
+  /// the user what that particular span represents.
+  ///
+  /// If [color] is `true`, [ANSI terminal color escapes][] are used to color
+  /// the resulting string. By default this span is colored red and the
+  /// secondary spans are colored blue, but that can be customized by passing
+  /// ANSI escape strings to [primaryColor] or [secondaryColor].
+  ///
+  /// [ANSI terminal color escapes]: https://en.wikipedia.org/wiki/ANSI_escape_code#Colors
+  ///
+  /// Each span in [secondarySpans] must refer to the same document as this
+  /// span. Throws an [ArgumentError] if any secondary span has a different
+  /// source URL than this span.
+  ///
+  /// Note that while this will work with plain [SourceSpan]s, it will produce
+  /// much more useful output with [SourceSpanWithContext]s (including
+  /// [FileSpan]s).
+  String highlightMultiple(String label, Map<SourceSpan, String> secondarySpans,
+          {bool color = false, String? primaryColor, String? secondaryColor}) =>
+      Highlighter.multiple(this, label, secondarySpans,
+              color: color,
+              primaryColor: primaryColor,
+              secondaryColor: secondaryColor)
+          .highlight();
+
+  /// Returns a span from [start] code units (inclusive) to [end] code units
+  /// (exclusive) after the beginning of this span.
+  SourceSpan subspan(int start, [int? end]) {
+    RangeError.checkValidRange(start, end, length);
+    if (start == 0 && (end == null || end == length)) return this;
+
+    final locations = subspanLocations(this, start, end);
+    return SourceSpan(locations[0], locations[1], text.substring(start, end));
+  }
+}

diff --git a/pkgs/source_span/lib/src/span_exception.dart b/pkgs/source_span/lib/src/span_exception.dart
new file mode 100644
index 0000000..90ad690
--- /dev/null
+++ b/pkgs/source_span/lib/src/span_exception.dart

@@ -0,0 +1,114 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'span.dart';
+
+/// A class for exceptions that have source span information attached.
+class SourceSpanException implements Exception {
+  // This is a getter so that subclasses can override it.
+  /// A message describing the exception.
+  String get message => _message;
+  final String _message;
+
+  // This is a getter so that subclasses can override it.
+  /// The span associated with this exception.
+  ///
+  /// This may be `null` if the source location can't be determined.
+  SourceSpan? get span => _span;
+  final SourceSpan? _span;
+
+  SourceSpanException(this._message, this._span);
+
+  /// Returns a string representation of `this`.
+  ///
+  /// [color] may either be a [String], a [bool], or `null`. If it's a string,
+  /// it indicates an ANSI terminal color escape that should be used to
+  /// highlight the span's text. If it's `true`, it indicates that the text
+  /// should be highlighted using the default color. If it's `false` or `null`,
+  /// it indicates that the text shouldn't be highlighted.
+  @override
+  String toString({Object? color}) {
+    if (span == null) return message;
+    return 'Error on ${span!.message(message, color: color)}';
+  }
+}
+
+/// A [SourceSpanException] that's also a [FormatException].
+class SourceSpanFormatException extends SourceSpanException
+    implements FormatException {
+  @override
+  final dynamic source;
+
+  @override
+  int? get offset => span?.start.offset;
+
+  SourceSpanFormatException(super.message, super.span, [this.source]);
+}
+
+/// A [SourceSpanException] that also highlights some secondary spans to provide
+/// the user with extra context.
+///
+/// Each span has a label ([primaryLabel] for the primary, and the values of the
+/// [secondarySpans] map for the secondary spans) that's used to indicate to the
+/// user what that particular span represents.
+class MultiSourceSpanException extends SourceSpanException {
+  /// A label to attach to [span] that provides additional information and helps
+  /// distinguish it from [secondarySpans].
+  final String primaryLabel;
+
+  /// A map whose keys are secondary spans that should be highlighted.
+  ///
+  /// Each span's value is a label to attach to that span that provides
+  /// additional information and helps distinguish it from [secondarySpans].
+  final Map<SourceSpan, String> secondarySpans;
+
+  MultiSourceSpanException(super.message, super.span, this.primaryLabel,
+      Map<SourceSpan, String> secondarySpans)
+      : secondarySpans = Map.unmodifiable(secondarySpans);
+
+  /// Returns a string representation of `this`.
+  ///
+  /// [color] may either be a [String], a [bool], or `null`. If it's a string,
+  /// it indicates an ANSI terminal color escape that should be used to
+  /// highlight the primary span's text. If it's `true`, it indicates that the
+  /// text should be highlighted using the default color. If it's `false` or
+  /// `null`, it indicates that the text shouldn't be highlighted.
+  ///
+  /// If [color] is `true` or a string, [secondaryColor] is used to highlight
+  /// [secondarySpans].
+  @override
+  String toString({Object? color, String? secondaryColor}) {
+    if (span == null) return message;
+
+    var useColor = false;
+    String? primaryColor;
+    if (color is String) {
+      useColor = true;
+      primaryColor = color;
+    } else if (color == true) {
+      useColor = true;
+    }
+
+    final formatted = span!.messageMultiple(
+        message, primaryLabel, secondarySpans,
+        color: useColor,
+        primaryColor: primaryColor,
+        secondaryColor: secondaryColor);
+    return 'Error on $formatted';
+  }
+}
+
+/// A [MultiSourceSpanException] that's also a [FormatException].
+class MultiSourceSpanFormatException extends MultiSourceSpanException
+    implements FormatException {
+  @override
+  final dynamic source;
+
+  @override
+  int? get offset => span?.start.offset;
+
+  MultiSourceSpanFormatException(
+      super.message, super.span, super.primaryLabel, super.secondarySpans,
+      [this.source]);
+}

diff --git a/pkgs/source_span/lib/src/span_mixin.dart b/pkgs/source_span/lib/src/span_mixin.dart
new file mode 100644
index 0000000..29b6119
--- /dev/null
+++ b/pkgs/source_span/lib/src/span_mixin.dart

@@ -0,0 +1,84 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:path/path.dart' as p;
+
+import 'highlighter.dart';
+import 'span.dart';
+import 'span_with_context.dart';
+import 'utils.dart';
+
+/// A mixin for easily implementing [SourceSpan].
+///
+/// This implements the [SourceSpan] methods in terms of [start], [end], and
+/// [text]. This assumes that [start] and [end] have the same source URL, that
+/// [start] comes before [end], and that [text] has a number of characters equal
+/// to the distance between [start] and [end].
+abstract class SourceSpanMixin implements SourceSpan {
+  @override
+  Uri? get sourceUrl => start.sourceUrl;
+
+  @override
+  int get length => end.offset - start.offset;
+
+  @override
+  int compareTo(SourceSpan other) {
+    final result = start.compareTo(other.start);
+    return result == 0 ? end.compareTo(other.end) : result;
+  }
+
+  @override
+  SourceSpan union(SourceSpan other) {
+    if (sourceUrl != other.sourceUrl) {
+      throw ArgumentError('Source URLs "$sourceUrl" and '
+          " \"${other.sourceUrl}\" don't match.");
+    }
+
+    final start = min(this.start, other.start);
+    final end = max(this.end, other.end);
+    final beginSpan = start == this.start ? this : other;
+    final endSpan = end == this.end ? this : other;
+
+    if (beginSpan.end.compareTo(endSpan.start) < 0) {
+      throw ArgumentError('Spans $this and $other are disjoint.');
+    }
+
+    final text = beginSpan.text +
+        endSpan.text.substring(beginSpan.end.distance(endSpan.start));
+    return SourceSpan(start, end, text);
+  }
+
+  @override
+  String message(String message, {Object? color}) {
+    final buffer = StringBuffer()
+      ..write('line ${start.line + 1}, column ${start.column + 1}');
+    if (sourceUrl != null) buffer.write(' of ${p.prettyUri(sourceUrl)}');
+    buffer.write(': $message');
+
+    final highlight = this.highlight(color: color);
+    if (highlight.isNotEmpty) {
+      buffer
+        ..writeln()
+        ..write(highlight);
+    }
+
+    return buffer.toString();
+  }
+
+  @override
+  String highlight({Object? color}) {
+    if (this is! SourceSpanWithContext && length == 0) return '';
+    return Highlighter(this, color: color).highlight();
+  }
+
+  @override
+  bool operator ==(Object other) =>
+      other is SourceSpan && start == other.start && end == other.end;
+
+  @override
+  int get hashCode => Object.hash(start, end);
+
+  @override
+  String toString() => '<$runtimeType: from $start to $end "$text">';
+}

diff --git a/pkgs/source_span/lib/src/span_with_context.dart b/pkgs/source_span/lib/src/span_with_context.dart
new file mode 100644
index 0000000..776c789
--- /dev/null
+++ b/pkgs/source_span/lib/src/span_with_context.dart

@@ -0,0 +1,51 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'location.dart';
+import 'span.dart';
+import 'utils.dart';
+
+/// A class that describes a segment of source text with additional context.
+class SourceSpanWithContext extends SourceSpanBase {
+  // This is a getter so that subclasses can override it.
+  /// Text around the span, which includes the line containing this span.
+  String get context => _context;
+  final String _context;
+
+  /// Creates a new span from [start] to [end] (exclusive) containing [text], in
+  /// the given [context].
+  ///
+  /// [start] and [end] must have the same source URL and [start] must come
+  /// before [end]. [text] must have a number of characters equal to the
+  /// distance between [start] and [end]. [context] must contain [text], and
+  /// [text] should start at `start.column` from the beginning of a line in
+  /// [context].
+  SourceSpanWithContext(
+      SourceLocation start, SourceLocation end, String text, this._context)
+      : super(start, end, text) {
+    if (!context.contains(text)) {
+      throw ArgumentError('The context line "$context" must contain "$text".');
+    }
+
+    if (findLineStart(context, text, start.column) == null) {
+      throw ArgumentError('The span text "$text" must start at '
+          'column ${start.column + 1} in a line within "$context".');
+    }
+  }
+}
+
+// TODO(#52): Move these to instance methods in the next breaking release.
+/// Extension methods on the base [SourceSpan] API.
+extension SourceSpanWithContextExtension on SourceSpanWithContext {
+  /// Returns a span from [start] code units (inclusive) to [end] code units
+  /// (exclusive) after the beginning of this span.
+  SourceSpanWithContext subspan(int start, [int? end]) {
+    RangeError.checkValidRange(start, end, length);
+    if (start == 0 && (end == null || end == length)) return this;
+
+    final locations = subspanLocations(this, start, end);
+    return SourceSpanWithContext(
+        locations[0], locations[1], text.substring(start, end), context);
+  }
+}

diff --git a/pkgs/source_span/lib/src/utils.dart b/pkgs/source_span/lib/src/utils.dart
new file mode 100644
index 0000000..aba14ec
--- /dev/null
+++ b/pkgs/source_span/lib/src/utils.dart

@@ -0,0 +1,145 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'charcode.dart';
+import 'location.dart';
+import 'span.dart';
+import 'span_with_context.dart';
+
+/// Returns the minimum of [obj1] and [obj2] according to
+/// [Comparable.compareTo].
+T min<T extends Comparable<T>>(T obj1, T obj2) =>
+    obj1.compareTo(obj2) > 0 ? obj2 : obj1;
+
+/// Returns the maximum of [obj1] and [obj2] according to
+/// [Comparable.compareTo].
+T max<T extends Comparable<T>>(T obj1, T obj2) =>
+    obj1.compareTo(obj2) > 0 ? obj1 : obj2;
+
+/// Returns whether all elements of [iter] are the same value, according to
+/// `==`.
+bool isAllTheSame(Iterable<Object?> iter) {
+  if (iter.isEmpty) return true;
+  final firstValue = iter.first;
+  for (var value in iter.skip(1)) {
+    if (value != firstValue) {
+      return false;
+    }
+  }
+  return true;
+}
+
+/// Returns whether [span] covers multiple lines.
+bool isMultiline(SourceSpan span) => span.start.line != span.end.line;
+
+/// Sets the first `null` element of [list] to [element].
+void replaceFirstNull<E>(List<E?> list, E element) {
+  final index = list.indexOf(null);
+  if (index < 0) throw ArgumentError('$list contains no null elements.');
+  list[index] = element;
+}
+
+/// Sets the element of [list] that currently contains [element] to `null`.
+void replaceWithNull<E>(List<E?> list, E element) {
+  final index = list.indexOf(element);
+  if (index < 0) {
+    throw ArgumentError('$list contains no elements matching $element.');
+  }
+
+  list[index] = null;
+}
+
+/// Returns the number of instances of [codeUnit] in [string].
+int countCodeUnits(String string, int codeUnit) {
+  var count = 0;
+  for (var codeUnitToCheck in string.codeUnits) {
+    if (codeUnitToCheck == codeUnit) count++;
+  }
+  return count;
+}
+
+/// Finds a line in [context] containing [text] at the specified [column].
+///
+/// Returns the index in [context] where that line begins, or null if none
+/// exists.
+int? findLineStart(String context, String text, int column) {
+  // If the text is empty, we just want to find the first line that has at least
+  // [column] characters.
+  if (text.isEmpty) {
+    var beginningOfLine = 0;
+    while (true) {
+      final index = context.indexOf('\n', beginningOfLine);
+      if (index == -1) {
+        return context.length - beginningOfLine >= column
+            ? beginningOfLine
+            : null;
+      }
+
+      if (index - beginningOfLine >= column) return beginningOfLine;
+      beginningOfLine = index + 1;
+    }
+  }
+
+  var index = context.indexOf(text);
+  while (index != -1) {
+    // Start looking before [index] in case [text] starts with a newline.
+    final lineStart = index == 0 ? 0 : context.lastIndexOf('\n', index - 1) + 1;
+    final textColumn = index - lineStart;
+    if (column == textColumn) return lineStart;
+    index = context.indexOf(text, index + 1);
+  }
+  // ignore: avoid_returning_null
+  return null;
+}
+
+/// Returns a two-element list containing the start and end locations of the
+/// span from [start] code units (inclusive) to [end] code units (exclusive)
+/// after the beginning of [span].
+///
+/// This is factored out so it can be shared between
+/// [SourceSpanExtension.subspan] and [SourceSpanWithContextExtension.subspan].
+List<SourceLocation> subspanLocations(SourceSpan span, int start, [int? end]) {
+  final text = span.text;
+  final startLocation = span.start;
+  var line = startLocation.line;
+  var column = startLocation.column;
+
+  // Adjust [line] and [column] as necessary if the character at [i] in [text]
+  // is a newline.
+  void consumeCodePoint(int i) {
+    final codeUnit = text.codeUnitAt(i);
+    if (codeUnit == $lf ||
+        // A carriage return counts as a newline, but only if it's not
+        // followed by a line feed.
+        (codeUnit == $cr &&
+            (i + 1 == text.length || text.codeUnitAt(i + 1) != $lf))) {
+      line += 1;
+      column = 0;
+    } else {
+      column += 1;
+    }
+  }
+
+  for (var i = 0; i < start; i++) {
+    consumeCodePoint(i);
+  }
+
+  final newStartLocation = SourceLocation(startLocation.offset + start,
+      sourceUrl: span.sourceUrl, line: line, column: column);
+
+  SourceLocation newEndLocation;
+  if (end == null || end == span.length) {
+    newEndLocation = span.end;
+  } else if (end == start) {
+    newEndLocation = newStartLocation;
+  } else {
+    for (var i = start; i < end; i++) {
+      consumeCodePoint(i);
+    }
+    newEndLocation = SourceLocation(startLocation.offset + end,
+        sourceUrl: span.sourceUrl, line: line, column: column);
+  }
+
+  return [newStartLocation, newEndLocation];
+}

diff --git a/pkgs/source_span/pubspec.yaml b/pkgs/source_span/pubspec.yaml
new file mode 100644
index 0000000..8757b2d
--- /dev/null
+++ b/pkgs/source_span/pubspec.yaml

@@ -0,0 +1,17 @@
+name: source_span
+version: 1.10.1
+description: >-
+  Provides a standard representation for source code locations and spans.
+repository: https://github.com/dart-lang/tools/tree/main/pkgs/source_span
+
+environment:
+  sdk: ^3.1.0
+
+dependencies:
+  collection: ^1.15.0
+  path: ^1.8.0
+  term_glyph: ^1.2.0
+
+dev_dependencies:
+  dart_flutter_team_lints: ^3.0.0
+  test: ^1.16.0

diff --git a/pkgs/source_span/test/file_test.dart b/pkgs/source_span/test/file_test.dart
new file mode 100644
index 0000000..dff51ee
--- /dev/null
+++ b/pkgs/source_span/test/file_test.dart

@@ -0,0 +1,530 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:source_span/source_span.dart';
+import 'package:test/test.dart';
+
+void main() {
+  late SourceFile file;
+  setUp(() {
+    file = SourceFile.fromString('''
+foo bar baz
+whiz bang boom
+zip zap zop''', url: 'foo.dart');
+  });
+
+  group('errors', () {
+    group('for span()', () {
+      test('end must come after start', () {
+        expect(() => file.span(10, 5), throwsArgumentError);
+      });
+
+      test('start may not be negative', () {
+        expect(() => file.span(-1, 5), throwsRangeError);
+      });
+
+      test('end may not be outside the file', () {
+        expect(() => file.span(10, 100), throwsRangeError);
+      });
+    });
+
+    group('for location()', () {
+      test('offset may not be negative', () {
+        expect(() => file.location(-1), throwsRangeError);
+      });
+
+      test('offset may not be outside the file', () {
+        expect(() => file.location(100), throwsRangeError);
+      });
+    });
+
+    group('for getLine()', () {
+      test('offset may not be negative', () {
+        expect(() => file.getLine(-1), throwsRangeError);
+      });
+
+      test('offset may not be outside the file', () {
+        expect(() => file.getLine(100), throwsRangeError);
+      });
+    });
+
+    group('for getColumn()', () {
+      test('offset may not be negative', () {
+        expect(() => file.getColumn(-1), throwsRangeError);
+      });
+
+      test('offset may not be outside the file', () {
+        expect(() => file.getColumn(100), throwsRangeError);
+      });
+
+      test('line may not be negative', () {
+        expect(() => file.getColumn(1, line: -1), throwsRangeError);
+      });
+
+      test('line may not be outside the file', () {
+        expect(() => file.getColumn(1, line: 100), throwsRangeError);
+      });
+
+      test('line must be accurate', () {
+        expect(() => file.getColumn(1, line: 1), throwsRangeError);
+      });
+    });
+
+    group('getOffset()', () {
+      test('line may not be negative', () {
+        expect(() => file.getOffset(-1), throwsRangeError);
+      });
+
+      test('column may not be negative', () {
+        expect(() => file.getOffset(1, -1), throwsRangeError);
+      });
+
+      test('line may not be outside the file', () {
+        expect(() => file.getOffset(100), throwsRangeError);
+      });
+
+      test('column may not be outside the file', () {
+        expect(() => file.getOffset(2, 100), throwsRangeError);
+      });
+
+      test('column may not be outside the line', () {
+        expect(() => file.getOffset(1, 20), throwsRangeError);
+      });
+    });
+
+    group('for getText()', () {
+      test('end must come after start', () {
+        expect(() => file.getText(10, 5), throwsArgumentError);
+      });
+
+      test('start may not be negative', () {
+        expect(() => file.getText(-1, 5), throwsRangeError);
+      });
+
+      test('end may not be outside the file', () {
+        expect(() => file.getText(10, 100), throwsRangeError);
+      });
+    });
+
+    group('for span().union()', () {
+      test('source URLs must match', () {
+        final other = SourceSpan(SourceLocation(10), SourceLocation(11), '_');
+
+        expect(() => file.span(9, 10).union(other), throwsArgumentError);
+      });
+
+      test('spans may not be disjoint', () {
+        expect(() => file.span(9, 10).union(file.span(11, 12)),
+            throwsArgumentError);
+      });
+    });
+
+    test('for span().expand() source URLs must match', () {
+      final other = SourceFile.fromString('''
+foo bar baz
+whiz bang boom
+zip zap zop''', url: 'bar.dart').span(10, 11);
+
+      expect(() => file.span(9, 10).expand(other), throwsArgumentError);
+    });
+  });
+
+  test('fields work correctly', () {
+    expect(file.url, equals(Uri.parse('foo.dart')));
+    expect(file.lines, equals(3));
+    expect(file.length, equals(38));
+  });
+
+  group('new SourceFile()', () {
+    test('handles CRLF correctly', () {
+      expect(SourceFile.fromString('foo\r\nbar').getLine(6), equals(1));
+    });
+
+    test('handles a lone CR correctly', () {
+      expect(SourceFile.fromString('foo\rbar').getLine(5), equals(1));
+    });
+  });
+
+  group('span()', () {
+    test('returns a span between the given offsets', () {
+      final span = file.span(5, 10);
+      expect(span.start, equals(file.location(5)));
+      expect(span.end, equals(file.location(10)));
+    });
+
+    test('end defaults to the end of the file', () {
+      final span = file.span(5);
+      expect(span.start, equals(file.location(5)));
+      expect(span.end, equals(file.location(file.length)));
+    });
+  });
+
+  group('getLine()', () {
+    test('works for a middle character on the line', () {
+      expect(file.getLine(15), equals(1));
+    });
+
+    test('works for the first character of a line', () {
+      expect(file.getLine(12), equals(1));
+    });
+
+    test('works for a newline character', () {
+      expect(file.getLine(11), equals(0));
+    });
+
+    test('works for the last offset', () {
+      expect(file.getLine(file.length), equals(2));
+    });
+  });
+
+  group('getColumn()', () {
+    test('works for a middle character on the line', () {
+      expect(file.getColumn(15), equals(3));
+    });
+
+    test('works for the first character of a line', () {
+      expect(file.getColumn(12), equals(0));
+    });
+
+    test('works for a newline character', () {
+      expect(file.getColumn(11), equals(11));
+    });
+
+    test('works when line is passed as well', () {
+      expect(file.getColumn(12, line: 1), equals(0));
+    });
+
+    test('works for the last offset', () {
+      expect(file.getColumn(file.length), equals(11));
+    });
+  });
+
+  group('getOffset()', () {
+    test('works for a middle character on the line', () {
+      expect(file.getOffset(1, 3), equals(15));
+    });
+
+    test('works for the first character of a line', () {
+      expect(file.getOffset(1), equals(12));
+    });
+
+    test('works for a newline character', () {
+      expect(file.getOffset(0, 11), equals(11));
+    });
+
+    test('works for the last offset', () {
+      expect(file.getOffset(2, 11), equals(file.length));
+    });
+  });
+
+  group('getText()', () {
+    test('returns a substring of the source', () {
+      expect(file.getText(8, 15), equals('baz\nwhi'));
+    });
+
+    test('end defaults to the end of the file', () {
+      expect(file.getText(20), equals('g boom\nzip zap zop'));
+    });
+  });
+
+  group('FileLocation', () {
+    test('reports the correct line number', () {
+      expect(file.location(15).line, equals(1));
+    });
+
+    test('reports the correct column number', () {
+      expect(file.location(15).column, equals(3));
+    });
+
+    test('pointSpan() returns a FileSpan', () {
+      final location = file.location(15);
+      final span = location.pointSpan();
+      expect(span, isA<FileSpan>());
+      expect(span.start, equals(location));
+      expect(span.end, equals(location));
+      expect(span.text, isEmpty);
+    });
+  });
+
+  group('FileSpan', () {
+    test('text returns a substring of the source', () {
+      expect(file.span(8, 15).text, equals('baz\nwhi'));
+    });
+
+    test('text includes the last char when end is defaulted to EOF', () {
+      expect(file.span(29).text, equals('p zap zop'));
+    });
+
+    group('context', () {
+      test("contains the span's text", () {
+        final span = file.span(8, 15);
+        expect(span.context.contains(span.text), isTrue);
+        expect(span.context, equals('foo bar baz\nwhiz bang boom\n'));
+      });
+
+      test('contains the previous line for a point span at the end of a line',
+          () {
+        final span = file.span(25, 25);
+        expect(span.context, equals('whiz bang boom\n'));
+      });
+
+      test('contains the next line for a point span at the beginning of a line',
+          () {
+        final span = file.span(12, 12);
+        expect(span.context, equals('whiz bang boom\n'));
+      });
+
+      group('for a point span at the end of a file', () {
+        test('without a newline, contains the last line', () {
+          final span = file.span(file.length, file.length);
+          expect(span.context, equals('zip zap zop'));
+        });
+
+        test('with a newline, contains an empty line', () {
+          file = SourceFile.fromString('''
+foo bar baz
+whiz bang boom
+zip zap zop
+''', url: 'foo.dart');
+
+          final span = file.span(file.length, file.length);
+          expect(span.context, isEmpty);
+        });
+      });
+    });
+
+    group('union()', () {
+      late FileSpan span;
+      setUp(() {
+        span = file.span(5, 12);
+      });
+
+      test('works with a preceding adjacent span', () {
+        final other = file.span(0, 5);
+        final result = span.union(other);
+        expect(result.start, equals(other.start));
+        expect(result.end, equals(span.end));
+        expect(result.text, equals('foo bar baz\n'));
+      });
+
+      test('works with a preceding overlapping span', () {
+        final other = file.span(0, 8);
+        final result = span.union(other);
+        expect(result.start, equals(other.start));
+        expect(result.end, equals(span.end));
+        expect(result.text, equals('foo bar baz\n'));
+      });
+
+      test('works with a following adjacent span', () {
+        final other = file.span(12, 16);
+        final result = span.union(other);
+        expect(result.start, equals(span.start));
+        expect(result.end, equals(other.end));
+        expect(result.text, equals('ar baz\nwhiz'));
+      });
+
+      test('works with a following overlapping span', () {
+        final other = file.span(9, 16);
+        final result = span.union(other);
+        expect(result.start, equals(span.start));
+        expect(result.end, equals(other.end));
+        expect(result.text, equals('ar baz\nwhiz'));
+      });
+
+      test('works with an internal overlapping span', () {
+        final other = file.span(7, 10);
+        expect(span.union(other), equals(span));
+      });
+
+      test('works with an external overlapping span', () {
+        final other = file.span(0, 16);
+        expect(span.union(other), equals(other));
+      });
+
+      test('returns a FileSpan for a FileSpan input', () {
+        expect(span.union(file.span(0, 5)), isA<FileSpan>());
+      });
+
+      test('returns a base SourceSpan for a SourceSpan input', () {
+        final other = SourceSpan(SourceLocation(0, sourceUrl: 'foo.dart'),
+            SourceLocation(5, sourceUrl: 'foo.dart'), 'hey, ');
+        final result = span.union(other);
+        expect(result, isNot(isA<FileSpan>()));
+        expect(result.start, equals(other.start));
+        expect(result.end, equals(span.end));
+        expect(result.text, equals('hey, ar baz\n'));
+      });
+    });
+
+    group('expand()', () {
+      late FileSpan span;
+      setUp(() {
+        span = file.span(5, 12);
+      });
+
+      test('works with a preceding nonadjacent span', () {
+        final other = file.span(0, 3);
+        final result = span.expand(other);
+        expect(result.start, equals(other.start));
+        expect(result.end, equals(span.end));
+        expect(result.text, equals('foo bar baz\n'));
+      });
+
+      test('works with a preceding overlapping span', () {
+        final other = file.span(0, 8);
+        final result = span.expand(other);
+        expect(result.start, equals(other.start));
+        expect(result.end, equals(span.end));
+        expect(result.text, equals('foo bar baz\n'));
+      });
+
+      test('works with a following nonadjacent span', () {
+        final other = file.span(14, 16);
+        final result = span.expand(other);
+        expect(result.start, equals(span.start));
+        expect(result.end, equals(other.end));
+        expect(result.text, equals('ar baz\nwhiz'));
+      });
+
+      test('works with a following overlapping span', () {
+        final other = file.span(9, 16);
+        final result = span.expand(other);
+        expect(result.start, equals(span.start));
+        expect(result.end, equals(other.end));
+        expect(result.text, equals('ar baz\nwhiz'));
+      });
+
+      test('works with an internal overlapping span', () {
+        final other = file.span(7, 10);
+        expect(span.expand(other), equals(span));
+      });
+
+      test('works with an external overlapping span', () {
+        final other = file.span(0, 16);
+        expect(span.expand(other), equals(other));
+      });
+    });
+
+    group('subspan()', () {
+      late FileSpan span;
+      setUp(() {
+        span = file.span(5, 11); // "ar baz"
+      });
+
+      group('errors', () {
+        test('start must be greater than zero', () {
+          expect(() => span.subspan(-1), throwsRangeError);
+        });
+
+        test('start must be less than or equal to length', () {
+          expect(() => span.subspan(span.length + 1), throwsRangeError);
+        });
+
+        test('end must be greater than start', () {
+          expect(() => span.subspan(2, 1), throwsRangeError);
+        });
+
+        test('end must be less than or equal to length', () {
+          expect(() => span.subspan(0, span.length + 1), throwsRangeError);
+        });
+      });
+
+      test('preserves the source URL', () {
+        final result = span.subspan(1, 2);
+        expect(result.start.sourceUrl, equals(span.sourceUrl));
+        expect(result.end.sourceUrl, equals(span.sourceUrl));
+      });
+
+      group('returns the original span', () {
+        test('with an implicit end',
+            () => expect(span.subspan(0), equals(span)));
+
+        test('with an explicit end',
+            () => expect(span.subspan(0, span.length), equals(span)));
+      });
+
+      group('within a single line', () {
+        test('returns a strict substring of the original span', () {
+          final result = span.subspan(1, 5);
+          expect(result.text, equals('r ba'));
+          expect(result.start.offset, equals(6));
+          expect(result.start.line, equals(0));
+          expect(result.start.column, equals(6));
+          expect(result.end.offset, equals(10));
+          expect(result.end.line, equals(0));
+          expect(result.end.column, equals(10));
+        });
+
+        test('an implicit end goes to the end of the original span', () {
+          final result = span.subspan(1);
+          expect(result.text, equals('r baz'));
+          expect(result.start.offset, equals(6));
+          expect(result.start.line, equals(0));
+          expect(result.start.column, equals(6));
+          expect(result.end.offset, equals(11));
+          expect(result.end.line, equals(0));
+          expect(result.end.column, equals(11));
+        });
+
+        test('can return an empty span', () {
+          final result = span.subspan(3, 3);
+          expect(result.text, isEmpty);
+          expect(result.start.offset, equals(8));
+          expect(result.start.line, equals(0));
+          expect(result.start.column, equals(8));
+          expect(result.end, equals(result.start));
+        });
+      });
+
+      group('across multiple lines', () {
+        setUp(() {
+          span = file.span(22, 30); // "boom\nzip"
+        });
+
+        test('with start and end in the middle of a line', () {
+          final result = span.subspan(3, 6);
+          expect(result.text, equals('m\nz'));
+          expect(result.start.offset, equals(25));
+          expect(result.start.line, equals(1));
+          expect(result.start.column, equals(13));
+          expect(result.end.offset, equals(28));
+          expect(result.end.line, equals(2));
+          expect(result.end.column, equals(1));
+        });
+
+        test('with start at the end of a line', () {
+          final result = span.subspan(4, 6);
+          expect(result.text, equals('\nz'));
+          expect(result.start.offset, equals(26));
+          expect(result.start.line, equals(1));
+          expect(result.start.column, equals(14));
+        });
+
+        test('with start at the beginning of a line', () {
+          final result = span.subspan(5, 6);
+          expect(result.text, equals('z'));
+          expect(result.start.offset, equals(27));
+          expect(result.start.line, equals(2));
+          expect(result.start.column, equals(0));
+        });
+
+        test('with end at the end of a line', () {
+          final result = span.subspan(3, 4);
+          expect(result.text, equals('m'));
+          expect(result.end.offset, equals(26));
+          expect(result.end.line, equals(1));
+          expect(result.end.column, equals(14));
+        });
+
+        test('with end at the beginning of a line', () {
+          final result = span.subspan(3, 5);
+          expect(result.text, equals('m\n'));
+          expect(result.end.offset, equals(27));
+          expect(result.end.line, equals(2));
+          expect(result.end.column, equals(0));
+        });
+      });
+    });
+  });
+}

diff --git a/pkgs/source_span/test/highlight_test.dart b/pkgs/source_span/test/highlight_test.dart
new file mode 100644
index 0000000..93c42db
--- /dev/null
+++ b/pkgs/source_span/test/highlight_test.dart

@@ -0,0 +1,605 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// ignore_for_file: prefer_interpolation_to_compose_strings
+
+import 'package:source_span/source_span.dart';
+import 'package:source_span/src/colors.dart' as colors;
+import 'package:term_glyph/term_glyph.dart' as glyph;
+import 'package:test/test.dart';
+
+void main() {
+  late bool oldAscii;
+  setUpAll(() {
+    oldAscii = glyph.ascii;
+    glyph.ascii = true;
+  });
+
+  tearDownAll(() {
+    glyph.ascii = oldAscii;
+  });
+
+  late SourceFile file;
+  setUp(() {
+    file = SourceFile.fromString('''
+foo bar baz
+whiz bang boom
+zip zap zop
+''');
+  });
+
+  test('points to the span in the source', () {
+    expect(file.span(4, 7).highlight(), equals("""
+  ,
+1 | foo bar baz
+  |     ^^^
+  '"""));
+  });
+
+  test('gracefully handles a missing source URL', () {
+    final span = SourceFile.fromString('foo bar baz').span(4, 7);
+    expect(span.highlight(), equals("""
+  ,
+1 | foo bar baz
+  |     ^^^
+  '"""));
+  });
+
+  group('highlights a point span', () {
+    test('in the middle of a line', () {
+      expect(file.location(4).pointSpan().highlight(), equals("""
+  ,
+1 | foo bar baz
+  |     ^
+  '"""));
+    });
+
+    test('at the beginning of the file', () {
+      expect(file.location(0).pointSpan().highlight(), equals("""
+  ,
+1 | foo bar baz
+  | ^
+  '"""));
+    });
+
+    test('at the beginning of a line', () {
+      expect(file.location(12).pointSpan().highlight(), equals("""
+  ,
+2 | whiz bang boom
+  | ^
+  '"""));
+    });
+
+    test('at the end of a line', () {
+      expect(file.location(11).pointSpan().highlight(), equals("""
+  ,
+1 | foo bar baz
+  |            ^
+  '"""));
+    });
+
+    test('at the end of the file', () {
+      expect(file.location(38).pointSpan().highlight(), equals("""
+  ,
+3 | zip zap zop
+  |            ^
+  '"""));
+    });
+
+    test('after the end of the file', () {
+      expect(file.location(39).pointSpan().highlight(), equals("""
+  ,
+4 | 
+  | ^
+  '"""));
+    });
+
+    test('at the end of the file with no trailing newline', () {
+      file = SourceFile.fromString('zip zap zop');
+      expect(file.location(10).pointSpan().highlight(), equals("""
+  ,
+1 | zip zap zop
+  |           ^
+  '"""));
+    });
+
+    test('after the end of the file with no trailing newline', () {
+      file = SourceFile.fromString('zip zap zop');
+      expect(file.location(11).pointSpan().highlight(), equals("""
+  ,
+1 | zip zap zop
+  |            ^
+  '"""));
+    });
+
+    test('in an empty file', () {
+      expect(SourceFile.fromString('').location(0).pointSpan().highlight(),
+          equals("""
+  ,
+1 | 
+  | ^
+  '"""));
+    });
+
+    test('on an empty line', () {
+      final file = SourceFile.fromString('foo\n\nbar');
+      expect(file.location(4).pointSpan().highlight(), equals("""
+  ,
+2 | 
+  | ^
+  '"""));
+    });
+  });
+
+  test('highlights a single-line file without a newline', () {
+    expect(SourceFile.fromString('foo bar').span(0, 7).highlight(), equals("""
+  ,
+1 | foo bar
+  | ^^^^^^^
+  '"""));
+  });
+
+  test('highlights text including a trailing newline', () {
+    expect(file.span(8, 12).highlight(), equals("""
+  ,
+1 | foo bar baz
+  |         ^^^
+  '"""));
+  });
+
+  test('highlights a single empty line', () {
+    expect(
+        SourceFile.fromString('foo\n\nbar').span(4, 5).highlight(), equals("""
+  ,
+2 | 
+  | ^
+  '"""));
+  });
+
+  test('highlights a trailing newline', () {
+    expect(file.span(11, 12).highlight(), equals("""
+  ,
+1 | foo bar baz
+  |            ^
+  '"""));
+  });
+
+  group('with a multiline span', () {
+    test('highlights the middle of the first and last lines', () {
+      expect(file.span(4, 34).highlight(), equals("""
+  ,
+1 |   foo bar baz
+  | ,-----^
+2 | | whiz bang boom
+3 | | zip zap zop
+  | '-------^
+  '"""));
+    });
+
+    test('works when it begins at the end of a line', () {
+      expect(file.span(11, 34).highlight(), equals("""
+  ,
+1 |   foo bar baz
+  | ,------------^
+2 | | whiz bang boom
+3 | | zip zap zop
+  | '-------^
+  '"""));
+    });
+
+    test('works when it ends at the beginning of a line', () {
+      expect(file.span(4, 28).highlight(), equals("""
+  ,
+1 |   foo bar baz
+  | ,-----^
+2 | | whiz bang boom
+3 | | zip zap zop
+  | '-^
+  '"""));
+    });
+
+    test('highlights the full first line', () {
+      expect(file.span(0, 34).highlight(), equals("""
+  ,
+1 | / foo bar baz
+2 | | whiz bang boom
+3 | | zip zap zop
+  | '-------^
+  '"""));
+    });
+
+    test("highlights the full first line even if it's indented", () {
+      final file = SourceFile.fromString('''
+  foo bar baz
+  whiz bang boom
+  zip zap zop
+''');
+
+      expect(file.span(2, 38).highlight(), equals("""
+  ,
+1 | /   foo bar baz
+2 | |   whiz bang boom
+3 | |   zip zap zop
+  | '-------^
+  '"""));
+    });
+
+    test("highlights the full first line if it's empty", () {
+      final file = SourceFile.fromString('''
+foo
+
+bar
+''');
+
+      expect(file.span(4, 9).highlight(), equals(r"""
+  ,
+2 | / 
+3 | \ bar
+  '"""));
+    });
+
+    test('highlights the full last line', () {
+      expect(file.span(4, 27).highlight(), equals(r"""
+  ,
+1 |   foo bar baz
+  | ,-----^
+2 | \ whiz bang boom
+  '"""));
+    });
+
+    test('highlights the full last line with no trailing newline', () {
+      expect(file.span(4, 26).highlight(), equals(r"""
+  ,
+1 |   foo bar baz
+  | ,-----^
+2 | \ whiz bang boom
+  '"""));
+    });
+
+    test('highlights the full last line with a trailing Windows newline', () {
+      final file = SourceFile.fromString('''
+foo bar baz\r
+whiz bang boom\r
+zip zap zop\r
+''');
+
+      expect(file.span(4, 29).highlight(), equals(r"""
+  ,
+1 |   foo bar baz
+  | ,-----^
+2 | \ whiz bang boom
+  '"""));
+    });
+
+    test('highlights the full last line at the end of the file', () {
+      expect(file.span(4, 39).highlight(), equals(r"""
+  ,
+1 |   foo bar baz
+  | ,-----^
+2 | | whiz bang boom
+3 | \ zip zap zop
+  '"""));
+    });
+
+    test(
+        'highlights the full last line at the end of the file with no trailing '
+        'newline', () {
+      final file = SourceFile.fromString('''
+foo bar baz
+whiz bang boom
+zip zap zop''');
+
+      expect(file.span(4, 38).highlight(), equals(r"""
+  ,
+1 |   foo bar baz
+  | ,-----^
+2 | | whiz bang boom
+3 | \ zip zap zop
+  '"""));
+    });
+
+    test("highlights the full last line if it's empty", () {
+      final file = SourceFile.fromString('''
+foo
+
+bar
+''');
+
+      expect(file.span(0, 5).highlight(), equals(r"""
+  ,
+1 | / foo
+2 | \ 
+  '"""));
+    });
+
+    test('highlights multiple empty lines', () {
+      final file = SourceFile.fromString('foo\n\n\n\nbar');
+      expect(file.span(4, 7).highlight(), equals(r"""
+  ,
+2 | / 
+3 | | 
+4 | \ 
+  '"""));
+    });
+
+    // Regression test for #32
+    test('highlights the end of a line and an empty line', () {
+      final file = SourceFile.fromString('foo\n\n');
+      expect(file.span(3, 5).highlight(), equals(r"""
+  ,
+1 |   foo
+  | ,----^
+2 | \ 
+  '"""));
+    });
+  });
+
+  group('prints tabs as spaces', () {
+    group('in a single-line span', () {
+      test('before the highlighted section', () {
+        final span = SourceFile.fromString('foo\tbar baz').span(4, 7);
+
+        expect(span.highlight(), equals("""
+  ,
+1 | foo    bar baz
+  |        ^^^
+  '"""));
+      });
+
+      test('within the highlighted section', () {
+        final span = SourceFile.fromString('foo bar\tbaz bang').span(4, 11);
+
+        expect(span.highlight(), equals("""
+  ,
+1 | foo bar    baz bang
+  |     ^^^^^^^^^^
+  '"""));
+      });
+
+      test('after the highlighted section', () {
+        final span = SourceFile.fromString('foo bar\tbaz').span(4, 7);
+
+        expect(span.highlight(), equals("""
+  ,
+1 | foo bar    baz
+  |     ^^^
+  '"""));
+      });
+    });
+
+    group('in a multi-line span', () {
+      test('before the highlighted section', () {
+        final span = SourceFile.fromString('''
+foo\tbar baz
+whiz bang boom
+''').span(4, 21);
+
+        expect(span.highlight(), equals("""
+  ,
+1 |   foo    bar baz
+  | ,--------^
+2 | | whiz bang boom
+  | '---------^
+  '"""));
+      });
+
+      test('within the first highlighted line', () {
+        final span = SourceFile.fromString('''
+foo bar\tbaz
+whiz bang boom
+''').span(4, 21);
+
+        expect(span.highlight(), equals("""
+  ,
+1 |   foo bar    baz
+  | ,-----^
+2 | | whiz bang boom
+  | '---------^
+  '"""));
+      });
+
+      test('at the beginning of the first highlighted line', () {
+        final span = SourceFile.fromString('''
+foo bar\tbaz
+whiz bang boom
+''').span(7, 21);
+
+        expect(span.highlight(), equals("""
+  ,
+1 |   foo bar    baz
+  | ,--------^
+2 | | whiz bang boom
+  | '---------^
+  '"""));
+      });
+
+      test('within a middle highlighted line', () {
+        final span = SourceFile.fromString('''
+foo bar baz
+whiz\tbang boom
+zip zap zop
+''').span(4, 34);
+
+        expect(span.highlight(), equals("""
+  ,
+1 |   foo bar baz
+  | ,-----^
+2 | | whiz    bang boom
+3 | | zip zap zop
+  | '-------^
+  '"""));
+      });
+
+      test('within the last highlighted line', () {
+        final span = SourceFile.fromString('''
+foo bar baz
+whiz\tbang boom
+''').span(4, 21);
+
+        expect(span.highlight(), equals("""
+  ,
+1 |   foo bar baz
+  | ,-----^
+2 | | whiz    bang boom
+  | '------------^
+  '"""));
+      });
+
+      test('at the end of the last highlighted line', () {
+        final span = SourceFile.fromString('''
+foo bar baz
+whiz\tbang boom
+''').span(4, 17);
+
+        expect(span.highlight(), equals("""
+  ,
+1 |   foo bar baz
+  | ,-----^
+2 | | whiz    bang boom
+  | '--------^
+  '"""));
+      });
+
+      test('after the highlighted section', () {
+        final span = SourceFile.fromString('''
+foo bar baz
+whiz bang\tboom
+''').span(4, 21);
+
+        expect(span.highlight(), equals("""
+  ,
+1 |   foo bar baz
+  | ,-----^
+2 | | whiz bang    boom
+  | '---------^
+  '"""));
+      });
+    });
+  });
+
+  group('supports lines of preceding and following context for a span', () {
+    test('within a single line', () {
+      final span = SourceSpanWithContext(
+          SourceLocation(20, line: 2, column: 5, sourceUrl: 'foo.dart'),
+          SourceLocation(27, line: 2, column: 12, sourceUrl: 'foo.dart'),
+          'foo bar',
+          'previous\nlines\n-----foo bar-----\nfollowing line\n');
+
+      expect(span.highlight(), equals("""
+  ,
+1 | previous
+2 | lines
+3 | -----foo bar-----
+  |      ^^^^^^^
+4 | following line
+  '"""));
+    });
+
+    test('covering a full line', () {
+      final span = SourceSpanWithContext(
+          SourceLocation(15, line: 2, column: 0, sourceUrl: 'foo.dart'),
+          SourceLocation(33, line: 3, column: 0, sourceUrl: 'foo.dart'),
+          '-----foo bar-----\n',
+          'previous\nlines\n-----foo bar-----\nfollowing line\n');
+
+      expect(span.highlight(), equals("""
+  ,
+1 | previous
+2 | lines
+3 | -----foo bar-----
+  | ^^^^^^^^^^^^^^^^^
+4 | following line
+  '"""));
+    });
+
+    test('covering multiple full lines', () {
+      final span = SourceSpanWithContext(
+          SourceLocation(15, line: 2, column: 0, sourceUrl: 'foo.dart'),
+          SourceLocation(23, line: 4, column: 0, sourceUrl: 'foo.dart'),
+          'foo\nbar\n',
+          'previous\nlines\nfoo\nbar\nfollowing line\n');
+
+      expect(span.highlight(), equals(r"""
+  ,
+1 |   previous
+2 |   lines
+3 | / foo
+4 | \ bar
+5 |   following line
+  '"""));
+    });
+  });
+
+  group('colors', () {
+    test("doesn't colorize if color is false", () {
+      expect(file.span(4, 7).highlight(color: false), equals("""
+  ,
+1 | foo bar baz
+  |     ^^^
+  '"""));
+    });
+
+    test('colorizes if color is true', () {
+      expect(file.span(4, 7).highlight(color: true), equals('''
+${colors.blue}  ,${colors.none}
+${colors.blue}1 |${colors.none} foo ${colors.red}bar${colors.none} baz
+${colors.blue}  |${colors.none} ${colors.red}    ^^^${colors.none}
+${colors.blue}  '${colors.none}'''));
+    });
+
+    test("uses the given color if it's passed", () {
+      expect(file.span(4, 7).highlight(color: colors.yellow), equals('''
+${colors.blue}  ,${colors.none}
+${colors.blue}1 |${colors.none} foo ${colors.yellow}bar${colors.none} baz
+${colors.blue}  |${colors.none} ${colors.yellow}    ^^^${colors.none}
+${colors.blue}  '${colors.none}'''));
+    });
+
+    test('colorizes a multiline span', () {
+      expect(file.span(4, 34).highlight(color: true), equals('''
+${colors.blue}  ,${colors.none}
+${colors.blue}1 |${colors.none}   foo ${colors.red}bar baz${colors.none}
+${colors.blue}  |${colors.none} ${colors.red},${colors.none}${colors.red}-----^${colors.none}
+${colors.blue}2 |${colors.none} ${colors.red}|${colors.none} ${colors.red}whiz bang boom${colors.none}
+${colors.blue}3 |${colors.none} ${colors.red}|${colors.none} ${colors.red}zip zap${colors.none} zop
+${colors.blue}  |${colors.none} ${colors.red}'${colors.none}${colors.red}-------^${colors.none}
+${colors.blue}  '${colors.none}'''));
+    });
+
+    test('colorizes a multiline span that highlights full lines', () {
+      expect(file.span(0, 39).highlight(color: true), equals('''
+${colors.blue}  ,${colors.none}
+${colors.blue}1 |${colors.none} ${colors.red}/${colors.none} ${colors.red}foo bar baz${colors.none}
+${colors.blue}2 |${colors.none} ${colors.red}|${colors.none} ${colors.red}whiz bang boom${colors.none}
+${colors.blue}3 |${colors.none} ${colors.red}\\${colors.none} ${colors.red}zip zap zop${colors.none}
+${colors.blue}  '${colors.none}'''));
+    });
+  });
+
+  group('line numbers have appropriate padding', () {
+    test('with line number 9', () {
+      expect(
+          SourceFile.fromString('\n' * 8 + 'foo bar baz\n')
+              .span(8, 11)
+              .highlight(),
+          equals("""
+  ,
+9 | foo bar baz
+  | ^^^
+  '"""));
+    });
+
+    test('with line number 10', () {
+      expect(
+          SourceFile.fromString('\n' * 9 + 'foo bar baz\n')
+              .span(9, 12)
+              .highlight(),
+          equals("""
+   ,
+10 | foo bar baz
+   | ^^^
+   '"""));
+    });
+  });
+}

diff --git a/pkgs/source_span/test/location_test.dart b/pkgs/source_span/test/location_test.dart
new file mode 100644
index 0000000..bbe259b
--- /dev/null
+++ b/pkgs/source_span/test/location_test.dart

@@ -0,0 +1,97 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:source_span/source_span.dart';
+import 'package:test/test.dart';
+
+void main() {
+  late SourceLocation location;
+  setUp(() {
+    location = SourceLocation(15, line: 2, column: 6, sourceUrl: 'foo.dart');
+  });
+
+  group('errors', () {
+    group('for new SourceLocation()', () {
+      test('offset may not be negative', () {
+        expect(() => SourceLocation(-1), throwsRangeError);
+      });
+
+      test('line may not be negative', () {
+        expect(() => SourceLocation(0, line: -1), throwsRangeError);
+      });
+
+      test('column may not be negative', () {
+        expect(() => SourceLocation(0, column: -1), throwsRangeError);
+      });
+    });
+
+    test('for distance() source URLs must match', () {
+      expect(() => location.distance(SourceLocation(0)), throwsArgumentError);
+    });
+
+    test('for compareTo() source URLs must match', () {
+      expect(() => location.compareTo(SourceLocation(0)), throwsArgumentError);
+    });
+  });
+
+  test('fields work correctly', () {
+    expect(location.sourceUrl, equals(Uri.parse('foo.dart')));
+    expect(location.offset, equals(15));
+    expect(location.line, equals(2));
+    expect(location.column, equals(6));
+  });
+
+  group('toolString', () {
+    test('returns a computer-readable representation', () {
+      expect(location.toolString, equals('foo.dart:3:7'));
+    });
+
+    test('gracefully handles a missing source URL', () {
+      final location = SourceLocation(15, line: 2, column: 6);
+      expect(location.toolString, equals('unknown source:3:7'));
+    });
+  });
+
+  test('distance returns the absolute distance between locations', () {
+    final other = SourceLocation(10, sourceUrl: 'foo.dart');
+    expect(location.distance(other), equals(5));
+    expect(other.distance(location), equals(5));
+  });
+
+  test('pointSpan returns an empty span at location', () {
+    final span = location.pointSpan();
+    expect(span.start, equals(location));
+    expect(span.end, equals(location));
+    expect(span.text, isEmpty);
+  });
+
+  group('compareTo()', () {
+    test('sorts by offset', () {
+      final other = SourceLocation(20, sourceUrl: 'foo.dart');
+      expect(location.compareTo(other), lessThan(0));
+      expect(other.compareTo(location), greaterThan(0));
+    });
+
+    test('considers equal locations equal', () {
+      expect(location.compareTo(location), equals(0));
+    });
+  });
+
+  group('equality', () {
+    test('two locations with the same offset and source are equal', () {
+      final other = SourceLocation(15, sourceUrl: 'foo.dart');
+      expect(location, equals(other));
+    });
+
+    test("a different offset isn't equal", () {
+      final other = SourceLocation(10, sourceUrl: 'foo.dart');
+      expect(location, isNot(equals(other)));
+    });
+
+    test("a different source isn't equal", () {
+      final other = SourceLocation(15, sourceUrl: 'bar.dart');
+      expect(location, isNot(equals(other)));
+    });
+  });
+}

diff --git a/pkgs/source_span/test/multiple_highlight_test.dart b/pkgs/source_span/test/multiple_highlight_test.dart
new file mode 100644
index 0000000..139d53c
--- /dev/null
+++ b/pkgs/source_span/test/multiple_highlight_test.dart

@@ -0,0 +1,423 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:source_span/source_span.dart';
+import 'package:term_glyph/term_glyph.dart' as glyph;
+import 'package:test/test.dart';
+
+void main() {
+  late bool oldAscii;
+  setUpAll(() {
+    oldAscii = glyph.ascii;
+    glyph.ascii = true;
+  });
+
+  tearDownAll(() {
+    glyph.ascii = oldAscii;
+  });
+
+  late SourceFile file;
+  setUp(() {
+    file = SourceFile.fromString('''
+foo bar baz
+whiz bang boom
+zip zap zop
+fwee fwoo fwip
+argle bargle boo
+gibble bibble bop
+''', url: 'file1.txt');
+  });
+
+  test('highlights spans on separate lines', () {
+    expect(
+        file.span(17, 21).highlightMultiple(
+            'one', {file.span(31, 34): 'two', file.span(4, 7): 'three'}),
+        equals("""
+  ,
+1 | foo bar baz
+  |     === three
+2 | whiz bang boom
+  |      ^^^^ one
+3 | zip zap zop
+  |     === two
+  '"""));
+  });
+
+  test('highlights spans on the same line', () {
+    expect(
+        file.span(17, 21).highlightMultiple(
+            'one', {file.span(22, 26): 'two', file.span(12, 16): 'three'}),
+        equals("""
+  ,
+2 | whiz bang boom
+  |      ^^^^ one
+  | ==== three
+  |           ==== two
+  '"""));
+  });
+
+  test('highlights overlapping spans on the same line', () {
+    expect(
+        file.span(17, 21).highlightMultiple(
+            'one', {file.span(20, 26): 'two', file.span(12, 18): 'three'}),
+        equals("""
+  ,
+2 | whiz bang boom
+  |      ^^^^ one
+  | ====== three
+  |         ====== two
+  '"""));
+  });
+
+  test('highlights multiple multiline spans', () {
+    expect(
+        file.span(27, 54).highlightMultiple(
+            'one', {file.span(54, 89): 'two', file.span(0, 27): 'three'}),
+        equals("""
+  ,
+1 | / foo bar baz
+2 | | whiz bang boom
+  | '--- three
+3 | / zip zap zop
+4 | | fwee fwoo fwip
+  | '--- one
+5 | / argle bargle boo
+6 | | gibble bibble bop
+  | '--- two
+  '"""));
+  });
+
+  test('highlights multiple overlapping multiline spans', () {
+    expect(
+        file.span(12, 70).highlightMultiple(
+            'one', {file.span(54, 89): 'two', file.span(0, 27): 'three'}),
+        equals("""
+  ,
+1 | /- foo bar baz
+2 | |/ whiz bang boom
+  | '+--- three
+3 |  | zip zap zop
+4 |  | fwee fwoo fwip
+5 | /+ argle bargle boo
+  | |'--- one
+6 | |  gibble bibble bop
+  | '---- two
+  '"""));
+  });
+
+  test('highlights many layers of overlaps', () {
+    expect(
+        file.span(0, 54).highlightMultiple('one', {
+          file.span(12, 77): 'two',
+          file.span(27, 84): 'three',
+          file.span(39, 88): 'four'
+        }),
+        equals("""
+  ,
+1 | /--- foo bar baz
+2 | |/-- whiz bang boom
+3 | ||/- zip zap zop
+4 | |||/ fwee fwoo fwip
+  | '+++--- one
+5 |  ||| argle bargle boo
+6 |  ||| gibble bibble bop
+  |  '++------^ two
+  |   '+-------------^ three
+  |    '--- four
+  '"""));
+  });
+
+  group("highlights a multiline span that's a subset", () {
+    test('with no first or last line overlap', () {
+      expect(
+          file
+              .span(27, 53)
+              .highlightMultiple('inner', {file.span(12, 70): 'outer'}),
+          equals("""
+  ,
+2 | /- whiz bang boom
+3 | |/ zip zap zop
+4 | || fwee fwoo fwip
+  | |'--- inner
+5 | |  argle bargle boo
+  | '---- outer
+  '"""));
+    });
+
+    test('overlapping the whole first line', () {
+      expect(
+          file
+              .span(12, 53)
+              .highlightMultiple('inner', {file.span(12, 70): 'outer'}),
+          equals("""
+  ,
+2 | // whiz bang boom
+3 | || zip zap zop
+4 | || fwee fwoo fwip
+  | |'--- inner
+5 | |  argle bargle boo
+  | '---- outer
+  '"""));
+    });
+
+    test('overlapping part of first line', () {
+      expect(
+          file
+              .span(17, 53)
+              .highlightMultiple('inner', {file.span(12, 70): 'outer'}),
+          equals("""
+  ,
+2 | /- whiz bang boom
+  | |,------^
+3 | || zip zap zop
+4 | || fwee fwoo fwip
+  | |'--- inner
+5 | |  argle bargle boo
+  | '---- outer
+  '"""));
+    });
+
+    test('overlapping the whole last line', () {
+      expect(
+          file
+              .span(27, 70)
+              .highlightMultiple('inner', {file.span(12, 70): 'outer'}),
+          equals("""
+  ,
+2 | /- whiz bang boom
+3 | |/ zip zap zop
+4 | || fwee fwoo fwip
+5 | || argle bargle boo
+  | |'--- inner
+  | '---- outer
+  '"""));
+    });
+
+    test('overlapping part of the last line', () {
+      expect(
+          file
+              .span(27, 66)
+              .highlightMultiple('inner', {file.span(12, 70): 'outer'}),
+          equals("""
+  ,
+2 | /- whiz bang boom
+3 | |/ zip zap zop
+4 | || fwee fwoo fwip
+5 | || argle bargle boo
+  | |'------------^ inner
+  | '---- outer
+  '"""));
+    });
+  });
+
+  group('a single-line span in a multiline span', () {
+    test('on the first line', () {
+      expect(
+          file
+              .span(17, 21)
+              .highlightMultiple('inner', {file.span(12, 70): 'outer'}),
+          equals("""
+  ,
+2 | / whiz bang boom
+  | |      ^^^^ inner
+3 | | zip zap zop
+4 | | fwee fwoo fwip
+5 | | argle bargle boo
+  | '--- outer
+  '"""));
+    });
+
+    test('in the middle', () {
+      expect(
+          file
+              .span(31, 34)
+              .highlightMultiple('inner', {file.span(12, 70): 'outer'}),
+          equals("""
+  ,
+2 | / whiz bang boom
+3 | | zip zap zop
+  | |     ^^^ inner
+4 | | fwee fwoo fwip
+5 | | argle bargle boo
+  | '--- outer
+  '"""));
+    });
+
+    test('on the last line', () {
+      expect(
+          file
+              .span(60, 66)
+              .highlightMultiple('inner', {file.span(12, 70): 'outer'}),
+          equals("""
+  ,
+2 | / whiz bang boom
+3 | | zip zap zop
+4 | | fwee fwoo fwip
+5 | | argle bargle boo
+  | |       ^^^^^^ inner
+  | '--- outer
+  '"""));
+    });
+  });
+
+  group('writes headers when highlighting multiple files', () {
+    test('writes all file URLs', () {
+      final span2 = SourceFile.fromString('''
+quibble bibble boop
+''', url: 'file2.txt').span(8, 14);
+
+      expect(
+          file.span(31, 34).highlightMultiple('one', {span2: 'two'}), equals("""
+  ,--> file1.txt
+3 | zip zap zop
+  |     ^^^ one
+  '
+  ,--> file2.txt
+1 | quibble bibble boop
+  |         ====== two
+  '"""));
+    });
+
+    test('allows secondary spans to have null URL', () {
+      final span2 = SourceSpan(SourceLocation(1), SourceLocation(4), 'foo');
+
+      expect(
+          file.span(31, 34).highlightMultiple('one', {span2: 'two'}), equals("""
+  ,--> file1.txt
+3 | zip zap zop
+  |     ^^^ one
+  '
+  ,
+1 | foo
+  | === two
+  '"""));
+    });
+
+    test('allows primary span to have null URL', () {
+      final span1 = SourceSpan(SourceLocation(1), SourceLocation(4), 'foo');
+
+      expect(
+          span1.highlightMultiple('one', {file.span(31, 34): 'two'}), equals("""
+  ,
+1 | foo
+  | ^^^ one
+  '
+  ,--> file1.txt
+3 | zip zap zop
+  |     === two
+  '"""));
+    });
+  });
+
+  test('highlights multiple null URLs as separate files', () {
+    final span1 = SourceSpan(SourceLocation(1), SourceLocation(4), 'foo');
+    final span2 = SourceSpan(SourceLocation(1), SourceLocation(4), 'bar');
+
+    expect(span1.highlightMultiple('one', {span2: 'two'}), equals("""
+  ,
+1 | foo
+  | ^^^ one
+  '
+  ,
+1 | bar
+  | === two
+  '"""));
+  });
+
+  group('indents mutli-line labels', () {
+    test('for the primary label', () {
+      expect(file.span(17, 21).highlightMultiple('line 1\nline 2\nline 3', {}),
+          equals("""
+  ,
+2 | whiz bang boom
+  |      ^^^^ line 1
+  |           line 2
+  |           line 3
+  '"""));
+    });
+
+    group('for a secondary label', () {
+      test('on the same line', () {
+        expect(
+            file.span(17, 21).highlightMultiple(
+                'primary', {file.span(22, 26): 'line 1\nline 2\nline 3'}),
+            equals("""
+  ,
+2 | whiz bang boom
+  |      ^^^^ primary
+  |           ==== line 1
+  |                line 2
+  |                line 3
+  '"""));
+      });
+
+      test('on a different line', () {
+        expect(
+            file.span(17, 21).highlightMultiple(
+                'primary', {file.span(31, 34): 'line 1\nline 2\nline 3'}),
+            equals("""
+  ,
+2 | whiz bang boom
+  |      ^^^^ primary
+3 | zip zap zop
+  |     === line 1
+  |         line 2
+  |         line 3
+  '"""));
+      });
+    });
+
+    group('for a multiline span', () {
+      test('that covers the whole last line', () {
+        expect(
+            file.span(12, 70).highlightMultiple('line 1\nline 2\nline 3', {}),
+            equals("""
+  ,
+2 | / whiz bang boom
+3 | | zip zap zop
+4 | | fwee fwoo fwip
+5 | | argle bargle boo
+  | '--- line 1
+  |      line 2
+  |      line 3
+  '"""));
+      });
+
+      test('that covers part of the last line', () {
+        expect(
+            file.span(12, 66).highlightMultiple('line 1\nline 2\nline 3', {}),
+            equals("""
+  ,
+2 | / whiz bang boom
+3 | | zip zap zop
+4 | | fwee fwoo fwip
+5 | | argle bargle boo
+  | '------------^ line 1
+  |                line 2
+  |                line 3
+  '"""));
+      });
+    });
+
+    test('with an overlapping span', () {
+      expect(
+          file.span(12, 70).highlightMultiple('line 1\nline 2\nline 3',
+              {file.span(54, 89): 'two', file.span(0, 27): 'three'}),
+          equals("""
+  ,
+1 | /- foo bar baz
+2 | |/ whiz bang boom
+  | '+--- three
+3 |  | zip zap zop
+4 |  | fwee fwoo fwip
+5 | /+ argle bargle boo
+  | |'--- line 1
+  | |     line 2
+  | |     line 3
+6 | |  gibble bibble bop
+  | '---- two
+  '"""));
+    });
+  });
+}

diff --git a/pkgs/source_span/test/span_test.dart b/pkgs/source_span/test/span_test.dart
new file mode 100644
index 0000000..22c498e
--- /dev/null
+++ b/pkgs/source_span/test/span_test.dart

@@ -0,0 +1,432 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:source_span/source_span.dart';
+import 'package:source_span/src/colors.dart' as colors;
+import 'package:term_glyph/term_glyph.dart' as glyph;
+import 'package:test/test.dart';
+
+void main() {
+  late bool oldAscii;
+
+  setUpAll(() {
+    oldAscii = glyph.ascii;
+    glyph.ascii = true;
+  });
+
+  tearDownAll(() {
+    glyph.ascii = oldAscii;
+  });
+
+  late SourceSpan span;
+  setUp(() {
+    span = SourceSpan(SourceLocation(5, sourceUrl: 'foo.dart'),
+        SourceLocation(12, sourceUrl: 'foo.dart'), 'foo bar');
+  });
+
+  group('errors', () {
+    group('for new SourceSpan()', () {
+      test('source URLs must match', () {
+        final start = SourceLocation(0, sourceUrl: 'foo.dart');
+        final end = SourceLocation(1, sourceUrl: 'bar.dart');
+        expect(() => SourceSpan(start, end, '_'), throwsArgumentError);
+      });
+
+      test('end must come after start', () {
+        final start = SourceLocation(1);
+        final end = SourceLocation(0);
+        expect(() => SourceSpan(start, end, '_'), throwsArgumentError);
+      });
+
+      test('text must be the right length', () {
+        final start = SourceLocation(0);
+        final end = SourceLocation(1);
+        expect(() => SourceSpan(start, end, 'abc'), throwsArgumentError);
+      });
+    });
+
+    group('for new SourceSpanWithContext()', () {
+      test('context must contain text', () {
+        final start = SourceLocation(2);
+        final end = SourceLocation(5);
+        expect(() => SourceSpanWithContext(start, end, 'abc', '--axc--'),
+            throwsArgumentError);
+      });
+
+      test('text starts at start.column in context', () {
+        final start = SourceLocation(3);
+        final end = SourceLocation(5);
+        expect(() => SourceSpanWithContext(start, end, 'abc', '--abc--'),
+            throwsArgumentError);
+      });
+
+      test('text starts at start.column of line in multi-line context', () {
+        final start = SourceLocation(4, line: 55, column: 3);
+        final end = SourceLocation(7, line: 55, column: 6);
+        expect(() => SourceSpanWithContext(start, end, 'abc', '\n--abc--'),
+            throwsArgumentError);
+        expect(() => SourceSpanWithContext(start, end, 'abc', '\n----abc--'),
+            throwsArgumentError);
+        expect(() => SourceSpanWithContext(start, end, 'abc', '\n\n--abc--'),
+            throwsArgumentError);
+
+        // However, these are valid:
+        SourceSpanWithContext(start, end, 'abc', '\n---abc--');
+        SourceSpanWithContext(start, end, 'abc', '\n\n---abc--');
+      });
+
+      test('text can occur multiple times in context', () {
+        final start1 = SourceLocation(4, line: 55, column: 2);
+        final end1 = SourceLocation(7, line: 55, column: 5);
+        final start2 = SourceLocation(4, line: 55, column: 8);
+        final end2 = SourceLocation(7, line: 55, column: 11);
+        SourceSpanWithContext(start1, end1, 'abc', '--abc---abc--\n');
+        SourceSpanWithContext(start1, end1, 'abc', '--abc--abc--\n');
+        SourceSpanWithContext(start2, end2, 'abc', '--abc---abc--\n');
+        SourceSpanWithContext(start2, end2, 'abc', '---abc--abc--\n');
+        expect(
+            () => SourceSpanWithContext(start1, end1, 'abc', '---abc--abc--\n'),
+            throwsArgumentError);
+        expect(
+            () => SourceSpanWithContext(start2, end2, 'abc', '--abc--abc--\n'),
+            throwsArgumentError);
+      });
+    });
+
+    group('for union()', () {
+      test('source URLs must match', () {
+        final other = SourceSpan(SourceLocation(12, sourceUrl: 'bar.dart'),
+            SourceLocation(13, sourceUrl: 'bar.dart'), '_');
+
+        expect(() => span.union(other), throwsArgumentError);
+      });
+
+      test('spans may not be disjoint', () {
+        final other = SourceSpan(SourceLocation(13, sourceUrl: 'foo.dart'),
+            SourceLocation(14, sourceUrl: 'foo.dart'), '_');
+
+        expect(() => span.union(other), throwsArgumentError);
+      });
+    });
+
+    test('for compareTo() source URLs must match', () {
+      final other = SourceSpan(SourceLocation(12, sourceUrl: 'bar.dart'),
+          SourceLocation(13, sourceUrl: 'bar.dart'), '_');
+
+      expect(() => span.compareTo(other), throwsArgumentError);
+    });
+  });
+
+  test('fields work correctly', () {
+    expect(span.start, equals(SourceLocation(5, sourceUrl: 'foo.dart')));
+    expect(span.end, equals(SourceLocation(12, sourceUrl: 'foo.dart')));
+    expect(span.sourceUrl, equals(Uri.parse('foo.dart')));
+    expect(span.length, equals(7));
+  });
+
+  group('union()', () {
+    test('works with a preceding adjacent span', () {
+      final other = SourceSpan(SourceLocation(0, sourceUrl: 'foo.dart'),
+          SourceLocation(5, sourceUrl: 'foo.dart'), 'hey, ');
+
+      final result = span.union(other);
+      expect(result.start, equals(other.start));
+      expect(result.end, equals(span.end));
+      expect(result.text, equals('hey, foo bar'));
+    });
+
+    test('works with a preceding overlapping span', () {
+      final other = SourceSpan(SourceLocation(0, sourceUrl: 'foo.dart'),
+          SourceLocation(8, sourceUrl: 'foo.dart'), 'hey, foo');
+
+      final result = span.union(other);
+      expect(result.start, equals(other.start));
+      expect(result.end, equals(span.end));
+      expect(result.text, equals('hey, foo bar'));
+    });
+
+    test('works with a following adjacent span', () {
+      final other = SourceSpan(SourceLocation(12, sourceUrl: 'foo.dart'),
+          SourceLocation(16, sourceUrl: 'foo.dart'), ' baz');
+
+      final result = span.union(other);
+      expect(result.start, equals(span.start));
+      expect(result.end, equals(other.end));
+      expect(result.text, equals('foo bar baz'));
+    });
+
+    test('works with a following overlapping span', () {
+      final other = SourceSpan(SourceLocation(9, sourceUrl: 'foo.dart'),
+          SourceLocation(16, sourceUrl: 'foo.dart'), 'bar baz');
+
+      final result = span.union(other);
+      expect(result.start, equals(span.start));
+      expect(result.end, equals(other.end));
+      expect(result.text, equals('foo bar baz'));
+    });
+
+    test('works with an internal overlapping span', () {
+      final other = SourceSpan(SourceLocation(7, sourceUrl: 'foo.dart'),
+          SourceLocation(10, sourceUrl: 'foo.dart'), 'o b');
+
+      expect(span.union(other), equals(span));
+    });
+
+    test('works with an external overlapping span', () {
+      final other = SourceSpan(SourceLocation(0, sourceUrl: 'foo.dart'),
+          SourceLocation(16, sourceUrl: 'foo.dart'), 'hey, foo bar baz');
+
+      expect(span.union(other), equals(other));
+    });
+  });
+
+  group('subspan()', () {
+    group('errors', () {
+      test('start must be greater than zero', () {
+        expect(() => span.subspan(-1), throwsRangeError);
+      });
+
+      test('start must be less than or equal to length', () {
+        expect(() => span.subspan(span.length + 1), throwsRangeError);
+      });
+
+      test('end must be greater than start', () {
+        expect(() => span.subspan(2, 1), throwsRangeError);
+      });
+
+      test('end must be less than or equal to length', () {
+        expect(() => span.subspan(0, span.length + 1), throwsRangeError);
+      });
+    });
+
+    test('preserves the source URL', () {
+      final result = span.subspan(1, 2);
+      expect(result.start.sourceUrl, equals(span.sourceUrl));
+      expect(result.end.sourceUrl, equals(span.sourceUrl));
+    });
+
+    test('preserves the context', () {
+      final start = SourceLocation(2);
+      final end = SourceLocation(5);
+      final span = SourceSpanWithContext(start, end, 'abc', '--abc--');
+      expect(span.subspan(1, 2).context, equals('--abc--'));
+    });
+
+    group('returns the original span', () {
+      test('with an implicit end', () => expect(span.subspan(0), equals(span)));
+
+      test('with an explicit end',
+          () => expect(span.subspan(0, span.length), equals(span)));
+    });
+
+    group('within a single line', () {
+      test('returns a strict substring of the original span', () {
+        final result = span.subspan(1, 5);
+        expect(result.text, equals('oo b'));
+        expect(result.start.offset, equals(6));
+        expect(result.start.line, equals(0));
+        expect(result.start.column, equals(6));
+        expect(result.end.offset, equals(10));
+        expect(result.end.line, equals(0));
+        expect(result.end.column, equals(10));
+      });
+
+      test('an implicit end goes to the end of the original span', () {
+        final result = span.subspan(1);
+        expect(result.text, equals('oo bar'));
+        expect(result.start.offset, equals(6));
+        expect(result.start.line, equals(0));
+        expect(result.start.column, equals(6));
+        expect(result.end.offset, equals(12));
+        expect(result.end.line, equals(0));
+        expect(result.end.column, equals(12));
+      });
+
+      test('can return an empty span', () {
+        final result = span.subspan(3, 3);
+        expect(result.text, isEmpty);
+        expect(result.start.offset, equals(8));
+        expect(result.start.line, equals(0));
+        expect(result.start.column, equals(8));
+        expect(result.end, equals(result.start));
+      });
+    });
+
+    group('across multiple lines', () {
+      setUp(() {
+        span = SourceSpan(
+            SourceLocation(5, line: 2, column: 0),
+            SourceLocation(16, line: 4, column: 3),
+            'foo\n'
+            'bar\n'
+            'baz');
+      });
+
+      test('with start and end in the middle of a line', () {
+        final result = span.subspan(2, 5);
+        expect(result.text, equals('o\nb'));
+        expect(result.start.offset, equals(7));
+        expect(result.start.line, equals(2));
+        expect(result.start.column, equals(2));
+        expect(result.end.offset, equals(10));
+        expect(result.end.line, equals(3));
+        expect(result.end.column, equals(1));
+      });
+
+      test('with start at the end of a line', () {
+        final result = span.subspan(3, 5);
+        expect(result.text, equals('\nb'));
+        expect(result.start.offset, equals(8));
+        expect(result.start.line, equals(2));
+        expect(result.start.column, equals(3));
+      });
+
+      test('with start at the beginning of a line', () {
+        final result = span.subspan(4, 5);
+        expect(result.text, equals('b'));
+        expect(result.start.offset, equals(9));
+        expect(result.start.line, equals(3));
+        expect(result.start.column, equals(0));
+      });
+
+      test('with end at the end of a line', () {
+        final result = span.subspan(2, 3);
+        expect(result.text, equals('o'));
+        expect(result.end.offset, equals(8));
+        expect(result.end.line, equals(2));
+        expect(result.end.column, equals(3));
+      });
+
+      test('with end at the beginning of a line', () {
+        final result = span.subspan(2, 4);
+        expect(result.text, equals('o\n'));
+        expect(result.end.offset, equals(9));
+        expect(result.end.line, equals(3));
+        expect(result.end.column, equals(0));
+      });
+    });
+  });
+
+  group('message()', () {
+    test('prints the text being described', () {
+      expect(span.message('oh no'), equals("""
+line 1, column 6 of foo.dart: oh no
+  ,
+1 | foo bar
+  | ^^^^^^^
+  '"""));
+    });
+
+    test('gracefully handles a missing source URL', () {
+      final span = SourceSpan(SourceLocation(5), SourceLocation(12), 'foo bar');
+
+      expect(span.message('oh no'), equalsIgnoringWhitespace("""
+line 1, column 6: oh no
+  ,
+1 | foo bar
+  | ^^^^^^^
+  '"""));
+    });
+
+    test('gracefully handles empty text', () {
+      final span = SourceSpan(SourceLocation(5), SourceLocation(5), '');
+
+      expect(span.message('oh no'), equals('line 1, column 6: oh no'));
+    });
+
+    test("doesn't colorize if color is false", () {
+      expect(span.message('oh no', color: false), equals("""
+line 1, column 6 of foo.dart: oh no
+  ,
+1 | foo bar
+  | ^^^^^^^
+  '"""));
+    });
+
+    test('colorizes if color is true', () {
+      expect(span.message('oh no', color: true), equals("""
+line 1, column 6 of foo.dart: oh no
+${colors.blue}  ,${colors.none}
+${colors.blue}1 |${colors.none} ${colors.red}foo bar${colors.none}
+${colors.blue}  |${colors.none} ${colors.red}^^^^^^^${colors.none}
+${colors.blue}  '${colors.none}"""));
+    });
+
+    test("uses the given color if it's passed", () {
+      expect(span.message('oh no', color: colors.yellow), equals("""
+line 1, column 6 of foo.dart: oh no
+${colors.blue}  ,${colors.none}
+${colors.blue}1 |${colors.none} ${colors.yellow}foo bar${colors.none}
+${colors.blue}  |${colors.none} ${colors.yellow}^^^^^^^${colors.none}
+${colors.blue}  '${colors.none}"""));
+    });
+
+    test('with context, underlines the right column', () {
+      final spanWithContext = SourceSpanWithContext(
+          SourceLocation(5, sourceUrl: 'foo.dart'),
+          SourceLocation(12, sourceUrl: 'foo.dart'),
+          'foo bar',
+          '-----foo bar-----');
+
+      expect(spanWithContext.message('oh no', color: colors.yellow), equals("""
+line 1, column 6 of foo.dart: oh no
+${colors.blue}  ,${colors.none}
+${colors.blue}1 |${colors.none} -----${colors.yellow}foo bar${colors.none}-----
+${colors.blue}  |${colors.none} ${colors.yellow}     ^^^^^^^${colors.none}
+${colors.blue}  '${colors.none}"""));
+    });
+  });
+
+  group('compareTo()', () {
+    test('sorts by start location first', () {
+      final other = SourceSpan(SourceLocation(6, sourceUrl: 'foo.dart'),
+          SourceLocation(14, sourceUrl: 'foo.dart'), 'oo bar b');
+
+      expect(span.compareTo(other), lessThan(0));
+      expect(other.compareTo(span), greaterThan(0));
+    });
+
+    test('sorts by length second', () {
+      final other = SourceSpan(SourceLocation(5, sourceUrl: 'foo.dart'),
+          SourceLocation(14, sourceUrl: 'foo.dart'), 'foo bar b');
+
+      expect(span.compareTo(other), lessThan(0));
+      expect(other.compareTo(span), greaterThan(0));
+    });
+
+    test('considers equal spans equal', () {
+      expect(span.compareTo(span), equals(0));
+    });
+  });
+
+  group('equality', () {
+    test('two spans with the same locations are equal', () {
+      final other = SourceSpan(SourceLocation(5, sourceUrl: 'foo.dart'),
+          SourceLocation(12, sourceUrl: 'foo.dart'), 'foo bar');
+
+      expect(span, equals(other));
+    });
+
+    test("a different start isn't equal", () {
+      final other = SourceSpan(SourceLocation(0, sourceUrl: 'foo.dart'),
+          SourceLocation(12, sourceUrl: 'foo.dart'), 'hey, foo bar');
+
+      expect(span, isNot(equals(other)));
+    });
+
+    test("a different end isn't equal", () {
+      final other = SourceSpan(SourceLocation(5, sourceUrl: 'foo.dart'),
+          SourceLocation(16, sourceUrl: 'foo.dart'), 'foo bar baz');
+
+      expect(span, isNot(equals(other)));
+    });
+
+    test("a different source URL isn't equal", () {
+      final other = SourceSpan(SourceLocation(5, sourceUrl: 'bar.dart'),
+          SourceLocation(12, sourceUrl: 'bar.dart'), 'foo bar');
+
+      expect(span, isNot(equals(other)));
+    });
+  });
+}

diff --git a/pkgs/source_span/test/utils_test.dart b/pkgs/source_span/test/utils_test.dart
new file mode 100644
index 0000000..91397c0
--- /dev/null
+++ b/pkgs/source_span/test/utils_test.dart

@@ -0,0 +1,58 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:source_span/src/utils.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('find line start', () {
+    test('skip entries in wrong column', () {
+      const context = '0_bb\n1_bbb\n2b____\n3bbb\n';
+      final index = findLineStart(context, 'b', 1)!;
+      expect(index, 11);
+      expect(context.substring(index - 1, index + 3), '\n2b_');
+    });
+
+    test('end of line column for empty text', () {
+      const context = '0123\n56789\nabcdefgh\n';
+      final index = findLineStart(context, '', 5)!;
+      expect(index, 5);
+      expect(context[index], '5');
+    });
+
+    test('column at the end of the file for empty text', () {
+      var context = '0\n2\n45\n';
+      var index = findLineStart(context, '', 2)!;
+      expect(index, 4);
+      expect(context[index], '4');
+
+      context = '0\n2\n45';
+      index = findLineStart(context, '', 2)!;
+      expect(index, 4);
+    });
+
+    test('empty text in empty context', () {
+      final index = findLineStart('', '', 0);
+      expect(index, 0);
+    });
+
+    test('found on the first line', () {
+      const context = '0\n2\n45\n';
+      final index = findLineStart(context, '0', 0);
+      expect(index, 0);
+    });
+
+    test('finds text that starts with a newline', () {
+      const context = '0\n2\n45\n';
+      final index = findLineStart(context, '\n2', 1);
+      expect(index, 0);
+    });
+
+    test('not found', () {
+      const context = '0\n2\n45\n';
+      final index = findLineStart(context, '0', 1);
+      expect(index, isNull);
+    });
+  });
+}

diff --git a/pkgs/sse/.gitignore b/pkgs/sse/.gitignore
new file mode 100644
index 0000000..1467782
--- /dev/null
+++ b/pkgs/sse/.gitignore

@@ -0,0 +1,3 @@
+.dart_tool
+pubspec.lock
+test/web/index.dart.js.deps

diff --git a/pkgs/sse/AUTHORS b/pkgs/sse/AUTHORS
new file mode 100644
index 0000000..7c12ae6
--- /dev/null
+++ b/pkgs/sse/AUTHORS

@@ -0,0 +1,6 @@
+# Below is a list of people and organizations that have contributed
+# to the Dart project. Names should be added to the list like so:
+#
+#   Name/Organization <email address>
+
+Google Inc.

diff --git a/pkgs/sse/CHANGELOG.md b/pkgs/sse/CHANGELOG.md
new file mode 100644
index 0000000..0387ba9
--- /dev/null
+++ b/pkgs/sse/CHANGELOG.md

@@ -0,0 +1,178 @@
+## 4.1.7
+
+- Move to `dart-lang/tools` monorepo.
+
+## 4.1.6
+
+- Require package `web: '>=0.5.0 <2.0.0'`.
+
+## 4.1.5
+
+- Drop unneeded dependency on `package:js`.
+- Update the minimum Dart SDK version to `3.3.0`.
+- Support the latest `package:web`.
+
+## 4.1.4
+
+- Fix incorrect cast causing failure with `dart2wasm`.
+
+## 4.1.3
+
+- Update the minimum Dart SDK version to `3.2.0`.
+
+## 4.1.2
+
+- Send `fetch` requests instead of `XHR` requests.
+- Add an optional `debugKey` parameter to `SseClient` to include in logging.
+- Add a dependency on `package:js`.
+- Update the minimum Dart SDK version to `2.16.0`.
+
+## 4.1.1
+
+- Apply `keepAlive` logic to `SocketException`s.
+- Switch from using `package:pedantic` to `package:lints`
+- Rev the minimum required SDK to 2.15.
+- Populate the pubspec `repository` field.
+
+## 4.1.0
+
+- Limit the number of concurrent requests to prevent Chrome from automatically
+  dropping them on the floor.
+
+## 4.0.0
+
+- Support null safety.
+
+## 3.8.3
+
+- Require the latest shelf and remove dead code.
+
+## 3.8.2
+
+- Complete `onConnected` with an error if the `SseClient` receives an error
+  before the connection is successfully opened.
+
+## 3.8.1
+
+- Fix an issue where closing the `SseConnection` stream would result in an
+  error.
+
+## 3.8.0
+
+- Add `onConnected` to replace `onOpen`.
+- Fix an issue where failed requests would not add a `done` event to the
+  connection `sink`.
+
+## 3.7.0
+
+- Deprecate the client's `onOpen` getter. Messages will now be buffered until a
+  connection is established.
+
+## 3.6.1
+
+- Drop dependency on `package:uuid`.
+
+## 3.6.0
+
+- Improve performance by buffering out of order messages in the server instead
+  of the client.
+
+\*\* Note \*\* This is not modelled as a breaking change as the server can
+handle messages from older clients. However, clients should be using the latest
+server if they require order guarantees.
+
+## 3.5.0
+
+- Add new `shutdown` methods on `SseHandler` and `SseConnection` to allow
+  closing connections immediately, ignoring any keep-alive periods.
+
+## 3.4.0
+
+- Remove `onClose` from `SseConnection` and ensure the corresponding
+  `sink.close` correctly fires.
+
+## 3.3.0
+
+- Add an `onClose` event to the `SseConnection`. This allows consumers to listen
+  to this event in lue of `sseConnection.sink.done` as that is not guaranteed to
+  fire.
+
+## 3.2.2
+
+- Fix an issue where `keepAlive` may cause state errors when attempting to send
+  messages on a closed stream.
+
+## 3.2.1
+
+- Fix an issue where `keepAlive` would only allow a single reconnection.
+
+## 3.2.0
+
+- Re-expose `isInKeepAlivePeriod` flag on `SseConnection`. This flag will be
+  `true` when a connection has been dropped and is in the keep-alive period
+  waiting for a client to reconnect.
+
+## 3.1.2
+
+- Fix an issue where the `SseClient` would not send a `done` event when there
+  was an error with the SSE connection.
+
+## 3.1.1
+
+- Make `isInKeepAlive` on `SseConnection` private.
+
+**Note that this is a breaking change but in actuality no one should be
+depending on this API.**
+
+## 3.1.0
+
+- Add optional `keepAlive` parameter to the `SseHandler`. If `keepAlive` is
+  supplied, the connection will remain active for this period after a disconnect
+  and can be reconnected transparently. If there is no reconnect within that
+  period, the connection will be closed normally.
+
+## 3.0.0
+
+- Add retry logic.
+
+**Possible Breaking Change Error messages may now be delayed up to 5 seconds in
+the client.**
+
+## 2.1.2
+
+- Remove `package:http` dependency.
+
+## 2.1.1
+
+- Use proper headers delimiter.
+
+## 2.1.0
+
+- Support Firefox.
+
+## 2.0.3
+
+- Fix an issue where messages could come out of order.
+
+## 2.0.2
+
+- Support the latest `package:stream_channel`.
+- Require Dart SDK `>=2.1.0 <3.0.0`.
+
+## 2.0.1
+
+- Update to `package:uuid` version 2.0.
+
+## 2.0.0
+
+- No longer expose `close` and `onClose` on an `SseConnection`. This is simply
+  handled by the underlying `stream` / `sink`.
+- Fix a bug where resources of the `SseConnection` were not properly closed.
+
+## 1.0.0
+
+- Internal cleanup.
+
+## 0.0.1
+
+- Initial commit.

diff --git a/pkgs/sse/LICENSE b/pkgs/sse/LICENSE
new file mode 100644
index 0000000..a0d5f54
--- /dev/null
+++ b/pkgs/sse/LICENSE

@@ -0,0 +1,27 @@
+Copyright 2019, the Dart project authors.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+    * Neither the name of Google LLC nor the names of its
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

diff --git a/pkgs/sse/README.md b/pkgs/sse/README.md
new file mode 100644
index 0000000..ef51415
--- /dev/null
+++ b/pkgs/sse/README.md

@@ -0,0 +1,14 @@
+[![Build Status](https://github.com/dart-lang/tools/actions/workflows/sse.yaml/badge.svg)](https://github.com/dart-lang/tools/actions/workflows/sse.yaml)
+[![pub package](https://img.shields.io/pub/v/sse.svg)](https://pub.dev/packages/sse)
+[![package publisher](https://img.shields.io/pub/publisher/sse.svg)](https://pub.dev/packages/sse/publisher)
+
+This package provides support for bi-directional communication through Server
+Sent Events and corresponding POST requests.
+
+This package is not intended to be a general purpose SSE package, but instead is
+a bidirectional protocol for use when Websockets are unavailable. That is, both
+the client and the server expose a `sink` and `stream` on which to send and
+receive messages respectively.
+
+Both the server and client have implicit assumptions on each other and therefore
+a client from this package must be paired with a server from this package.

diff --git a/pkgs/sse/analysis_options.yaml b/pkgs/sse/analysis_options.yaml
new file mode 100644
index 0000000..6729bd9
--- /dev/null
+++ b/pkgs/sse/analysis_options.yaml

@@ -0,0 +1,13 @@
+# https://dart.dev/guides/language/analysis-options
+include: package:dart_flutter_team_lints/analysis_options.yaml
+
+analyzer:
+  language:
+    strict-casts: true
+
+linter:
+  rules:
+    - avoid_unused_constructor_parameters
+    - cancel_subscriptions
+    - literal_only_boolean_expressions
+    - no_adjacent_strings_in_list

diff --git a/pkgs/sse/example/index.dart b/pkgs/sse/example/index.dart
new file mode 100644
index 0000000..0ed7596
--- /dev/null
+++ b/pkgs/sse/example/index.dart

@@ -0,0 +1,15 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:sse/client/sse_client.dart';
+
+/// A basic example which should be used in a browser that supports SSE.
+void main() {
+  var channel = SseClient('/sseHandler');
+
+  channel.stream.listen((s) {
+    // Listen for messages and send them back.
+    channel.sink.add(s);
+  });
+}

diff --git a/pkgs/sse/example/server.dart b/pkgs/sse/example/server.dart
new file mode 100644
index 0000000..b6ee750
--- /dev/null
+++ b/pkgs/sse/example/server.dart

@@ -0,0 +1,21 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:shelf/shelf_io.dart' as io;
+import 'package:sse/server/sse_handler.dart';
+
+/// A basic server which sets up an SSE handler.
+///
+/// When a client connects it will send a simple message and print the
+/// response.
+void main() async {
+  var handler = SseHandler(Uri.parse('/sseHandler'));
+  await io.serve(handler.handler, 'localhost', 0);
+  var connections = handler.connections;
+  while (await connections.hasNext) {
+    var connection = await connections.next;
+    connection.sink.add('foo');
+    connection.stream.listen(print);
+  }
+}

diff --git a/pkgs/sse/lib/client/sse_client.dart b/pkgs/sse/lib/client/sse_client.dart
new file mode 100644
index 0000000..4d3df49
--- /dev/null
+++ b/pkgs/sse/lib/client/sse_client.dart

@@ -0,0 +1,166 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+import 'dart:convert';
+import 'dart:js_interop';
+
+import 'package:logging/logging.dart';
+import 'package:pool/pool.dart';
+import 'package:stream_channel/stream_channel.dart';
+import 'package:web/web.dart';
+
+import '../src/util/uuid.dart';
+
+/// Limit for the number of concurrent outgoing requests.
+///
+/// Chrome drops outgoing requests on the floor after some threshold. To prevent
+/// these errors we buffer outgoing requests with a pool.
+///
+/// Note Chrome's limit is 6000. So this gives us plenty of headroom.
+final _requestPool = Pool(1000);
+
+/// A client for bi-directional sse communication.
+///
+/// The client can send any JSON-encodable messages to the server by adding
+/// them to the [sink] and listen to messages from the server on the [stream].
+class SseClient extends StreamChannelMixin<String?> {
+  final String _clientId;
+
+  final _incomingController = StreamController<String>();
+
+  final _outgoingController = StreamController<String>();
+
+  final _logger = Logger('SseClient');
+
+  final _onConnected = Completer<void>();
+
+  int _lastMessageId = -1;
+
+  late EventSource _eventSource;
+
+  late String _serverUrl;
+
+  Timer? _errorTimer;
+
+  /// [serverUrl] is the URL under which the server is listening for
+  /// incoming bi-directional SSE connections. [debugKey] is an optional key
+  /// that can be used to identify the SSE connection.
+  SseClient(String serverUrl, {String? debugKey})
+      : _clientId = debugKey == null
+            ? generateUuidV4()
+            : '$debugKey-${generateUuidV4()}' {
+    _serverUrl = '$serverUrl?sseClientId=$_clientId';
+    _eventSource =
+        EventSource(_serverUrl, EventSourceInit(withCredentials: true));
+    _eventSource.onOpen.first.whenComplete(() {
+      _onConnected.complete();
+      _outgoingController.stream
+          .listen(_onOutgoingMessage, onDone: _onOutgoingDone);
+    });
+    _eventSource.addEventListener('message', _onIncomingMessage.toJS);
+    _eventSource.addEventListener('control', _onIncomingControlMessage.toJS);
+
+    _eventSource.onOpen.listen((_) {
+      _errorTimer?.cancel();
+    });
+    _eventSource.onError.listen((error) {
+      if (!(_errorTimer?.isActive ?? false)) {
+        // By default the SSE client uses keep-alive.
+        // Allow for a retry to connect before giving up.
+        _errorTimer = Timer(const Duration(seconds: 5), () {
+          _closeWithError(error);
+        });
+      }
+    });
+  }
+
+  @Deprecated('Use onConnected instead.')
+  Stream<Event> get onOpen => _eventSource.onOpen;
+
+  Future<void> get onConnected => _onConnected.future;
+
+  /// Add messages to this [StreamSink] to send them to the server.
+  ///
+  /// The message added to the sink has to be JSON encodable. Messages that fail
+  /// to encode will be logged through a [Logger].
+  @override
+  StreamSink<String> get sink => _outgoingController.sink;
+
+  /// [Stream] of messages sent from the server to this client.
+  ///
+  /// A message is a decoded JSON object.
+  @override
+  Stream<String> get stream => _incomingController.stream;
+
+  void close() {
+    _eventSource.close();
+    // If the initial connection was never established. Add a listener so close
+    // adds a done event to [sink].
+    if (!_onConnected.isCompleted) _outgoingController.stream.drain<void>();
+    _incomingController.close();
+    _outgoingController.close();
+  }
+
+  void _closeWithError(Object error) {
+    _incomingController.addError(error);
+    close();
+    if (!_onConnected.isCompleted) {
+      // This call must happen after the call to close() which checks
+      // whether the completer was completed earlier.
+      _onConnected.completeError(error);
+    }
+  }
+
+  void _onIncomingControlMessage(Event message) {
+    var data = (message as MessageEvent).data;
+    if (data.dartify() == 'close') {
+      close();
+    } else {
+      throw UnsupportedError('[$_clientId] Illegal Control Message "$data"');
+    }
+  }
+
+  void _onIncomingMessage(Event message) {
+    var decoded =
+        jsonDecode(((message as MessageEvent).data as JSString).toDart);
+    _incomingController.add(decoded as String);
+  }
+
+  void _onOutgoingDone() {
+    close();
+  }
+
+  void _onOutgoingMessage(String? message) async {
+    String? encodedMessage;
+    await _requestPool.withResource(() async {
+      try {
+        encodedMessage = jsonEncode(message);
+        // ignore: avoid_catching_errors
+      } on JsonUnsupportedObjectError catch (e) {
+        _logger.warning('[$_clientId] Unable to encode outgoing message: $e');
+        // ignore: avoid_catching_errors
+      } on ArgumentError catch (e) {
+        _logger.warning('[$_clientId] Invalid argument: $e');
+      }
+      try {
+        final url = '$_serverUrl&messageId=${++_lastMessageId}';
+        await _fetch(
+            url,
+            RequestInit(
+                method: 'POST',
+                body: encodedMessage?.toJS,
+                credentials: 'include'));
+      } catch (error) {
+        final augmentedError =
+            '[$_clientId] SSE client failed to send $message:\n $error';
+        _logger.severe(augmentedError);
+        _closeWithError(augmentedError);
+      }
+    });
+  }
+}
+
+Future<void> _fetch(String resourceUrl, RequestInit options) =>
+    window.fetch(resourceUrl.toJS, options).toDart;

diff --git a/pkgs/sse/lib/server/sse_handler.dart b/pkgs/sse/lib/server/sse_handler.dart
new file mode 100644
index 0000000..bfed935
--- /dev/null
+++ b/pkgs/sse/lib/server/sse_handler.dart

@@ -0,0 +1,5 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+export 'package:sse/src/server/sse_handler.dart' show SseConnection, SseHandler;

diff --git a/pkgs/sse/lib/src/server/sse_handler.dart b/pkgs/sse/lib/src/server/sse_handler.dart
new file mode 100644
index 0000000..376fe27
--- /dev/null
+++ b/pkgs/sse/lib/src/server/sse_handler.dart

@@ -0,0 +1,299 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+import 'dart:convert';
+import 'dart:io';
+
+import 'package:async/async.dart';
+import 'package:collection/collection.dart';
+import 'package:logging/logging.dart';
+import 'package:shelf/shelf.dart' as shelf;
+import 'package:stream_channel/stream_channel.dart';
+
+// RFC 2616 requires carriage return delimiters.
+String _sseHeaders(String? origin) => 'HTTP/1.1 200 OK\r\n'
+    'Content-Type: text/event-stream\r\n'
+    'Cache-Control: no-cache\r\n'
+    'Connection: keep-alive\r\n'
+    'Access-Control-Allow-Credentials: true\r\n'
+    "${origin != null ? 'Access-Control-Allow-Origin: $origin\r\n' : ''}"
+    '\r\n\r\n';
+
+class _SseMessage {
+  final int id;
+  final String message;
+  _SseMessage(this.id, this.message);
+}
+
+/// A bi-directional SSE connection between server and browser.
+class SseConnection extends StreamChannelMixin<String> {
+  /// Incoming messages from the Browser client.
+  final _incomingController = StreamController<String>();
+
+  /// Outgoing messages to the Browser client.
+  final _outgoingController = StreamController<String>();
+
+  Sink _sink;
+
+  /// How long to wait after a connection drops before considering it closed.
+  final Duration? _keepAlive;
+
+  /// A timer counting down the KeepAlive period (null if hasn't disconnected).
+  Timer? _keepAliveTimer;
+
+  /// Whether this connection is currently in the KeepAlive timeout period.
+  bool get isInKeepAlivePeriod => _keepAliveTimer?.isActive ?? false;
+
+  /// The id of the last processed incoming message.
+  int _lastProcessedId = -1;
+
+  /// Incoming messages that have yet to be processed.
+  final _pendingMessages =
+      HeapPriorityQueue<_SseMessage>((a, b) => a.id.compareTo(b.id));
+
+  final _closedCompleter = Completer<void>();
+
+  /// Wraps the `_outgoingController.stream` to buffer events to enable keep
+  /// alive.
+  late StreamQueue _outgoingStreamQueue;
+
+  /// Creates an [SseConnection] for the supplied [_sink].
+  ///
+  /// If [keepAlive] is supplied, the connection will remain active for this
+  /// period after a disconnect and can be reconnected transparently. If there
+  /// is no reconnect within that period, the connection will be closed
+  /// normally.
+  ///
+  /// If [keepAlive] is not supplied, the connection will be closed immediately
+  /// after a disconnect.
+  SseConnection(this._sink, {Duration? keepAlive}) : _keepAlive = keepAlive {
+    _outgoingStreamQueue = StreamQueue(_outgoingController.stream);
+    unawaited(_setUpListener());
+    _outgoingController.onCancel = _close;
+    _incomingController.onCancel = _close;
+  }
+
+  Future<void> _setUpListener() async {
+    while (
+        !_outgoingController.isClosed && await _outgoingStreamQueue.hasNext) {
+      // If we're in a KeepAlive timeout, there's nowhere to send messages so
+      // wait a short period and check again.
+      if (isInKeepAlivePeriod) {
+        await Future<void>.delayed(const Duration(milliseconds: 200));
+        continue;
+      }
+
+      // Peek the data so we don't remove it from the stream if we're unable to
+      // send it.
+      final data = await _outgoingStreamQueue.peek;
+
+      // Ignore outgoing messages since the connection may have closed while
+      // waiting for the keep alive.
+      if (_closedCompleter.isCompleted) break;
+
+      try {
+        // JSON encode the message to escape new lines.
+        _sink.add('data: ${json.encode(data)}\n');
+        _sink.add('\n');
+        await _outgoingStreamQueue.next; // Consume from stream if no errors.
+      } catch (e) {
+        if ((e is StateError || e is SocketException) &&
+            (_keepAlive != null && !_closedCompleter.isCompleted)) {
+          // If we got here then the sink may have closed but the stream.onDone
+          // hasn't fired yet, so pause the subscription and skip calling
+          // `next` so the message remains in the queue to try again.
+          _handleDisconnect();
+        } else {
+          rethrow;
+        }
+      }
+    }
+  }
+
+  /// The message added to the sink has to be JSON encodable.
+  @override
+  StreamSink<String> get sink => _outgoingController.sink;
+
+  // Add messages to this [StreamSink] to send them to the server.
+  /// [Stream] of messages sent from the server to this client.
+  ///
+  /// A message is a decoded JSON object.
+  @override
+  Stream<String> get stream => _incomingController.stream;
+
+  /// Adds an incoming [message] to the [stream].
+  ///
+  /// This will buffer messages to guarantee order.
+  void _addIncomingMessage(int id, String message) {
+    _pendingMessages.add(_SseMessage(id, message));
+    while (_pendingMessages.isNotEmpty) {
+      var pendingMessage = _pendingMessages.first;
+      // Only process the next incremental message.
+      if (pendingMessage.id - _lastProcessedId <= 1) {
+        _incomingController.sink.add(pendingMessage.message);
+        _lastProcessedId = pendingMessage.id;
+        _pendingMessages.removeFirst();
+      } else {
+        // A message came out of order. Wait until we receive the previous
+        // messages to process.
+        break;
+      }
+    }
+  }
+
+  void _acceptReconnection(Sink sink) {
+    _keepAliveTimer?.cancel();
+    _sink = sink;
+  }
+
+  void _handleDisconnect() {
+    if (_keepAlive == null) {
+      // Close immediately if we're not keeping alive.
+      _close();
+    } else if (!isInKeepAlivePeriod && !_closedCompleter.isCompleted) {
+      // Otherwise if we didn't already have an active timer and we've not
+      // already been completely closed, set a timer to close after the timeout
+      // period.
+      // If the connection comes back, this will be cancelled and all messages
+      // left in the queue tried again.
+      _keepAliveTimer = Timer(_keepAlive, _close);
+    }
+  }
+
+  void _close() {
+    if (!_closedCompleter.isCompleted) {
+      _closedCompleter.complete();
+      // Cancel any existing timer in case we were told to explicitly shut down
+      // to avoid keeping the process alive.
+      _keepAliveTimer?.cancel();
+      _sink.close();
+      if (!_outgoingController.isClosed) {
+        _outgoingStreamQueue.cancel(immediate: true);
+        _outgoingController.close();
+      }
+      if (!_incomingController.isClosed) _incomingController.close();
+    }
+  }
+
+  /// Immediately close the connection, ignoring any keepAlive period.
+  void shutdown() {
+    _close();
+  }
+}
+
+/// [SseHandler] handles requests on a user defined path to create
+/// two-way communications of JSON encodable data between server and clients.
+///
+/// A server sends messages to a client through an SSE channel, while
+/// a client sends message to a server through HTTP POST requests.
+class SseHandler {
+  final _logger = Logger('SseHandler');
+  final Uri _uri;
+  final Duration? _keepAlive;
+  final _connections = <String?, SseConnection>{};
+  final _connectionController = StreamController<SseConnection>();
+
+  StreamQueue<SseConnection>? _connectionsStream;
+
+  /// [_uri] is the URL under which the server is listening for
+  /// incoming bi-directional SSE connections.
+  ///
+  /// If [keepAlive] is supplied, connections will remain active for this
+  /// period after a disconnect and can be reconnected transparently. If there
+  /// is no reconnect within that period, the connection will be closed
+  /// normally.
+  ///
+  /// If [keepAlive] is not supplied, connections will be closed immediately
+  /// after a disconnect.
+  SseHandler(this._uri, {Duration? keepAlive}) : _keepAlive = keepAlive;
+
+  StreamQueue<SseConnection> get connections =>
+      _connectionsStream ??= StreamQueue(_connectionController.stream);
+
+  shelf.Handler get handler => _handle;
+
+  int get numberOfClients => _connections.length;
+
+  shelf.Response _createSseConnection(shelf.Request req, String path) {
+    req.hijack((channel) async {
+      var sink = utf8.encoder.startChunkedConversion(channel.sink);
+      sink.add(_sseHeaders(req.headers['origin']));
+      var clientId = req.url.queryParameters['sseClientId'];
+
+      // Check if we already have a connection for this ID that is in the
+      // process of timing out
+      // (in which case we can reconnect it transparently).
+      if (_connections[clientId] != null &&
+          _connections[clientId]!.isInKeepAlivePeriod) {
+        _connections[clientId]!._acceptReconnection(sink);
+      } else {
+        var connection = SseConnection(sink, keepAlive: _keepAlive);
+        _connections[clientId] = connection;
+        unawaited(connection._closedCompleter.future.then((_) {
+          _connections.remove(clientId);
+        }));
+        _connectionController.add(connection);
+      }
+      // Remove connection when it is remotely closed or the stream is
+      // cancelled.
+      channel.stream.listen((_) {
+        // SSE is unidirectional. Responses are handled through POST requests.
+      }, onDone: () {
+        _connections[clientId]?._handleDisconnect();
+      });
+    });
+  }
+
+  String _getOriginalPath(shelf.Request req) => req.requestedUri.path;
+
+  Future<shelf.Response> _handle(shelf.Request req) async {
+    var path = _getOriginalPath(req);
+    if (_uri.path != path) {
+      return shelf.Response.notFound('');
+    }
+
+    if (req.headers['accept'] == 'text/event-stream' && req.method == 'GET') {
+      return _createSseConnection(req, path);
+    }
+
+    if (req.headers['accept'] != 'text/event-stream' && req.method == 'POST') {
+      return _handleIncomingMessage(req, path);
+    }
+
+    return shelf.Response.notFound('');
+  }
+
+  Future<shelf.Response> _handleIncomingMessage(
+      shelf.Request req, String path) async {
+    String? clientId;
+    try {
+      clientId = req.url.queryParameters['sseClientId'];
+      var messageId = int.parse(req.url.queryParameters['messageId'] ?? '0');
+      var message = await req.readAsString();
+      var jsonObject = json.decode(message) as String;
+      _connections[clientId]?._addIncomingMessage(messageId, jsonObject);
+    } catch (e, st) {
+      _logger.fine('[$clientId] Failed to handle incoming message. $e $st');
+    }
+    return shelf.Response.ok('', headers: {
+      'access-control-allow-credentials': 'true',
+      'access-control-allow-origin': _originFor(req),
+    });
+  }
+
+  String _originFor(shelf.Request req) =>
+      // Firefox does not set header "origin".
+      // https://bugzilla.mozilla.org/show_bug.cgi?id=1508661
+      req.headers['origin'] ?? req.headers['host']!;
+
+  /// Immediately close all connections, ignoring any keepAlive periods.
+  void shutdown() {
+    for (final connection in _connections.values) {
+      connection.shutdown();
+    }
+  }
+}
+
+void closeSink(SseConnection connection) => connection._sink.close();

diff --git a/pkgs/sse/lib/src/util/uuid.dart b/pkgs/sse/lib/src/util/uuid.dart
new file mode 100644
index 0000000..a1aa398
--- /dev/null
+++ b/pkgs/sse/lib/src/util/uuid.dart

@@ -0,0 +1,32 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:math' show Random;
+
+/// Returns a unique ID in the format:
+///
+///     f47ac10b-58cc-4372-a567-0e02b2c3d479
+///
+/// The generated uuids are 128 bit numbers encoded in a specific string format.
+/// For more information, see
+/// [en.wikipedia.org/wiki/Universally_unique_identifier](http://en.wikipedia.org/wiki/Universally_unique_identifier).
+String generateUuidV4() {
+  final random = Random();
+
+  int generateBits(int bitCount) => random.nextInt(1 << bitCount);
+
+  String printDigits(int value, int count) =>
+      value.toRadixString(16).padLeft(count, '0');
+  String bitsDigits(int bitCount, int digitCount) =>
+      printDigits(generateBits(bitCount), digitCount);
+
+  // Generate xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx / 8-4-4-4-12.
+  var special = 8 + random.nextInt(4);
+
+  return '${bitsDigits(16, 4)}${bitsDigits(16, 4)}-'
+      '${bitsDigits(16, 4)}-'
+      '4${bitsDigits(12, 3)}-'
+      '${printDigits(special, 1)}${bitsDigits(12, 3)}-'
+      '${bitsDigits(16, 4)}${bitsDigits(16, 4)}${bitsDigits(16, 4)}';
+}

diff --git a/pkgs/sse/pubspec.yaml b/pkgs/sse/pubspec.yaml
new file mode 100644
index 0000000..bd70f74
--- /dev/null
+++ b/pkgs/sse/pubspec.yaml

@@ -0,0 +1,25 @@
+name: sse
+version: 4.1.7
+description: >-
+  Provides client and server functionality for setting up bi-directional
+  communication through Server Sent Events (SSE) and corresponding POST
+  requests.
+repository: https://github.com/dart-lang/tools/tree/main/pkgs/sse
+
+environment:
+  sdk: ^3.3.0
+
+dependencies:
+  async: ^2.0.8
+  collection: ^1.0.0
+  logging: ^1.0.0
+  pool: ^1.5.0
+  shelf: ^1.1.0
+  stream_channel: ^2.0.0
+  web: '>=0.5.0 <2.0.0'
+
+dev_dependencies:
+  dart_flutter_team_lints: ^3.0.0
+  shelf_static: ^1.0.0
+  test: ^1.16.6
+  webdriver: ^3.0.0

diff --git a/pkgs/sse/test/sse_test.dart b/pkgs/sse/test/sse_test.dart
new file mode 100644
index 0000000..0455baa
--- /dev/null
+++ b/pkgs/sse/test/sse_test.dart

@@ -0,0 +1,270 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+@TestOn('vm')
+library;
+
+import 'dart:async';
+import 'dart:io';
+
+import 'package:async/async.dart';
+import 'package:shelf/shelf.dart' as shelf;
+import 'package:shelf/shelf_io.dart' as io;
+import 'package:shelf_static/shelf_static.dart';
+import 'package:sse/server/sse_handler.dart';
+import 'package:sse/src/server/sse_handler.dart' show closeSink;
+import 'package:test/test.dart';
+import 'package:webdriver/async_io.dart';
+
+void main() {
+  late HttpServer server;
+  late WebDriver webdriver;
+  late SseHandler handler;
+  late Process chromeDriver;
+
+  setUpAll(() async {
+    try {
+      chromeDriver = await Process.start(
+          'chromedriver', ['--port=4444', '--url-base=wd/hub']);
+    } catch (e) {
+      throw StateError(
+          'Could not start ChromeDriver. Is it installed?\nError: $e');
+    }
+  });
+
+  tearDownAll(() {
+    chromeDriver.kill();
+  });
+
+  group('SSE', () {
+    setUp(() async {
+      handler = SseHandler(Uri.parse('/test'));
+
+      var cascade = shelf.Cascade()
+          .add(handler.handler)
+          .add(_faviconHandler)
+          .add(createStaticHandler('test/web',
+              listDirectories: true, defaultDocument: 'index.html'));
+
+      server = await io.serve(cascade.handler, 'localhost', 0);
+      var capabilities = Capabilities.chrome
+        ..addAll({
+          Capabilities.chromeOptions: {
+            'args': ['--headless']
+          }
+        });
+      webdriver = await createDriver(desired: capabilities);
+    });
+
+    tearDown(() async {
+      await webdriver.quit();
+      await server.close();
+    });
+
+    test('can round trip messages', () async {
+      await webdriver.get('http://localhost:${server.port}');
+      var connection = await handler.connections.next;
+      connection.sink.add('blah');
+      expect(await connection.stream.first, 'blah');
+    });
+
+    test('can send a significant number of requests', () async {
+      await webdriver.get('http://localhost:${server.port}');
+      var connection = await handler.connections.next;
+      var limit = 7000;
+      for (var i = 0; i < limit; i++) {
+        connection.sink.add('$i');
+      }
+      await connection.stream.take(limit).drain<void>();
+    });
+
+    test('messages arrive in-order', () async {
+      expect(handler.numberOfClients, 0);
+      await webdriver.get('http://localhost:${server.port}');
+      var connection = await handler.connections.next;
+      expect(handler.numberOfClients, 1);
+
+      var expected = <String>[];
+      var count = 100;
+      for (var i = 0; i < count; i++) {
+        expected.add(i.toString());
+      }
+      connection.sink.add('send $count');
+
+      expect(await connection.stream.take(count).toList(), equals(expected));
+    });
+
+    test('multiple clients can connect', () async {
+      var connections = handler.connections;
+      await webdriver.get('http://localhost:${server.port}');
+      await connections.next;
+      await webdriver.get('http://localhost:${server.port}');
+      await connections.next;
+    });
+
+    test('routes data correctly', () async {
+      var connections = handler.connections;
+      await webdriver.get('http://localhost:${server.port}');
+      var connectionA = await connections.next;
+      connectionA.sink.add('foo');
+      expect(await connectionA.stream.first, 'foo');
+
+      await webdriver.get('http://localhost:${server.port}');
+      var connectionB = await connections.next;
+      connectionB.sink.add('bar');
+      expect(await connectionB.stream.first, 'bar');
+    });
+
+    test('can close from the server', () async {
+      expect(handler.numberOfClients, 0);
+      await webdriver.get('http://localhost:${server.port}');
+      var connection = await handler.connections.next;
+      expect(handler.numberOfClients, 1);
+      await connection.sink.close();
+      await pumpEventQueue();
+      expect(handler.numberOfClients, 0);
+    });
+
+    test('client reconnects after being disconnected', () async {
+      expect(handler.numberOfClients, 0);
+      await webdriver.get('http://localhost:${server.port}');
+      var connection = await handler.connections.next;
+      expect(handler.numberOfClients, 1);
+      await connection.sink.close();
+      await pumpEventQueue();
+      expect(handler.numberOfClients, 0);
+
+      // Ensure the client reconnects
+      await handler.connections.next;
+    });
+
+    test('can close from the client-side', () async {
+      expect(handler.numberOfClients, 0);
+      await webdriver.get('http://localhost:${server.port}');
+      var connection = await handler.connections.next;
+      expect(handler.numberOfClients, 1);
+
+      var closeButton = await webdriver.findElement(const By.tagName('button'));
+      await closeButton.click();
+
+      // Should complete since the connection is closed.
+      await connection.stream.drain<void>();
+      expect(handler.numberOfClients, 0);
+    });
+
+    test('cancelling the listener closes the connection', () async {
+      expect(handler.numberOfClients, 0);
+      await webdriver.get('http://localhost:${server.port}');
+      var connection = await handler.connections.next;
+      expect(handler.numberOfClients, 1);
+
+      var sub = connection.stream.listen((_) {});
+      await sub.cancel();
+      await pumpEventQueue();
+      expect(handler.numberOfClients, 0);
+    });
+
+    test('disconnects when navigating away', () async {
+      await webdriver.get('http://localhost:${server.port}');
+      expect(handler.numberOfClients, 1);
+
+      await webdriver.get('chrome://version/');
+      expect(handler.numberOfClients, 0);
+    });
+  });
+
+  group('SSE with server keep-alive', () {
+    setUp(() async {
+      handler =
+          SseHandler(Uri.parse('/test'), keepAlive: const Duration(seconds: 5));
+
+      var cascade = shelf.Cascade()
+          .add(handler.handler)
+          .add(_faviconHandler)
+          .add(createStaticHandler('test/web',
+              listDirectories: true, defaultDocument: 'index.html'));
+
+      server = await io.serve(cascade.handler, 'localhost', 0);
+      var capabilities = Capabilities.chrome
+        ..addAll({
+          Capabilities.chromeOptions: {
+            'args': ['--headless']
+          }
+        });
+      webdriver = await createDriver(desired: capabilities);
+    });
+
+    tearDown(() async {
+      await webdriver.quit();
+      await server.close();
+    });
+
+    test('client reconnect use the same connection', () async {
+      expect(handler.numberOfClients, 0);
+      await webdriver.get('http://localhost:${server.port}');
+      var connection = await handler.connections.next;
+      expect(handler.numberOfClients, 1);
+
+      // Close the underlying connection.
+      closeSink(connection);
+      // Ensure we can still round-trip data on the original connection and that
+      // the connection is no longer marked keep-alive once it's reconnected.
+      connection.sink.add('bar');
+      var queue = StreamQueue(connection.stream);
+      expect(await queue.next, 'bar');
+
+      // Now check that we can reconnect multiple times.
+      closeSink(connection);
+      connection.sink.add('bar');
+      expect(await queue.next, 'bar');
+      expect(handler.numberOfClients, 1);
+    });
+
+    test('messages sent during disconnect arrive in-order', () async {
+      expect(handler.numberOfClients, 0);
+      await webdriver.get('http://localhost:${server.port}');
+      var connection = await handler.connections.next;
+      expect(handler.numberOfClients, 1);
+
+      // Close the underlying connection.
+      closeSink(connection);
+      connection.sink.add('one');
+      connection.sink.add('two');
+      await pumpEventQueue();
+
+      // Ensure there's still a connection.
+      expect(handler.numberOfClients, 1);
+
+      // Ensure messages arrive in the same order
+      expect(await connection.stream.take(2).toList(), equals(['one', 'two']));
+    });
+
+    test('explicit shutdown does not wait for keepAlive', () async {
+      expect(handler.numberOfClients, 0);
+      await webdriver.get('http://localhost:${server.port}');
+      await handler.connections.next;
+      expect(handler.numberOfClients, 1);
+
+      // Close the underlying connection.
+      handler.shutdown();
+
+      // Wait for a short period to allow the connection to close, but not
+      // long enough that the 30second keep-alive may have expired.
+      var maxPumps = 50;
+      while (handler.numberOfClients > 0 && maxPumps-- > 0) {
+        await pumpEventQueue(times: 1);
+      }
+
+      // Ensure there are not connected clients.
+      expect(handler.numberOfClients, 0);
+    });
+  }, timeout: const Timeout(Duration(seconds: 120)));
+}
+
+FutureOr<shelf.Response> _faviconHandler(shelf.Request request) {
+  if (request.url.path.endsWith('favicon.ico')) {
+    return shelf.Response.ok('');
+  }
+  return shelf.Response.notFound('');
+}

diff --git a/pkgs/sse/test/web/index.dart b/pkgs/sse/test/web/index.dart
new file mode 100644
index 0000000..c4d78cd
--- /dev/null
+++ b/pkgs/sse/test/web/index.dart

@@ -0,0 +1,25 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:sse/client/sse_client.dart';
+import 'package:web/web.dart';
+
+void main() {
+  var channel = SseClient('/test');
+
+  document.querySelector('button')!.onClick.listen((_) {
+    channel.sink.close();
+  });
+
+  channel.stream.listen((s) {
+    if (s.startsWith('send ')) {
+      var count = int.parse(s.split(' ').last);
+      for (var i = 0; i < count; i++) {
+        channel.sink.add('$i');
+      }
+    } else {
+      channel.sink.add(s);
+    }
+  });
+}

diff --git a/pkgs/sse/test/web/index.dart.js b/pkgs/sse/test/web/index.dart.js
new file mode 100644
index 0000000..e1b37b9
--- /dev/null
+++ b/pkgs/sse/test/web/index.dart.js

@@ -0,0 +1,8851 @@
+// Generated by dart2js (NullSafetyMode.sound, csp, intern-composite-values), the Dart to JavaScript compiler version: 3.4.0-157.0.dev.
+// The code supports the following hooks:
+// dartPrint(message):
+//    if this function is defined it is called instead of the Dart [print]
+//    method.
+//
+// dartMainRunner(main, args):
+//    if this function is defined, the Dart [main] method will not be invoked
+//    directly. Instead, a closure that will invoke [main], and its arguments
+//    [args] is passed to [dartMainRunner].
+//
+// dartDeferredLibraryLoader(uri, successCallback, errorCallback, loadId, loadPriority):
+//    if this function is defined, it will be called when a deferred library
+//    is loaded. It should load and eval the javascript of `uri`, and call
+//    successCallback. If it fails to do so, it should call errorCallback with
+//    an error. The loadId argument is the deferred import that resulted in
+//    this uri being loaded. The loadPriority argument is the priority the
+//    library should be loaded with as specified in the code via the
+//    load-priority annotation (0: normal, 1: high).
+// dartDeferredLibraryMultiLoader(uris, successCallback, errorCallback, loadId, loadPriority):
+//    if this function is defined, it will be called when a deferred library
+//    is loaded. It should load and eval the javascript of every URI in `uris`,
+//    and call successCallback. If it fails to do so, it should call
+//    errorCallback with an error. The loadId argument is the deferred import
+//    that resulted in this uri being loaded. The loadPriority argument is the
+//    priority the library should be loaded with as specified in the code via
+//    the load-priority annotation (0: normal, 1: high).
+//
+// dartCallInstrumentation(id, qualifiedName):
+//    if this function is defined, it will be called at each entry of a
+//    method or constructor. Used only when compiling programs with
+//    --experiment-call-instrumentation.
+(function dartProgram() {
+  function copyProperties(from, to) {
+    var keys = Object.keys(from);
+    for (var i = 0; i < keys.length; i++) {
+      var key = keys[i];
+      to[key] = from[key];
+    }
+  }
+  function mixinPropertiesHard(from, to) {
+    var keys = Object.keys(from);
+    for (var i = 0; i < keys.length; i++) {
+      var key = keys[i];
+      if (!to.hasOwnProperty(key)) {
+        to[key] = from[key];
+      }
+    }
+  }
+  function mixinPropertiesEasy(from, to) {
+    Object.assign(to, from);
+  }
+  var supportsDirectProtoAccess = function() {
+    var cls = function() {
+    };
+    cls.prototype = {p: {}};
+    var object = new cls();
+    if (!(Object.getPrototypeOf(object) && Object.getPrototypeOf(object).p === cls.prototype.p))
+      return false;
+    try {
+      if (typeof navigator != "undefined" && typeof navigator.userAgent == "string" && navigator.userAgent.indexOf("Chrome/") >= 0)
+        return true;
+      if (typeof version == "function" && version.length == 0) {
+        var v = version();
+        if (/^\d+\.\d+\.\d+\.\d+$/.test(v))
+          return true;
+      }
+    } catch (_) {
+    }
+    return false;
+  }();
+  function inherit(cls, sup) {
+    cls.prototype.constructor = cls;
+    cls.prototype["$is" + cls.name] = cls;
+    if (sup != null) {
+      if (supportsDirectProtoAccess) {
+        Object.setPrototypeOf(cls.prototype, sup.prototype);
+        return;
+      }
+      var clsPrototype = Object.create(sup.prototype);
+      copyProperties(cls.prototype, clsPrototype);
+      cls.prototype = clsPrototype;
+    }
+  }
+  function inheritMany(sup, classes) {
+    for (var i = 0; i < classes.length; i++) {
+      inherit(classes[i], sup);
+    }
+  }
+  function mixinEasy(cls, mixin) {
+    mixinPropertiesEasy(mixin.prototype, cls.prototype);
+    cls.prototype.constructor = cls;
+  }
+  function mixinHard(cls, mixin) {
+    mixinPropertiesHard(mixin.prototype, cls.prototype);
+    cls.prototype.constructor = cls;
+  }
+  function lazy(holder, name, getterName, initializer) {
+    var uninitializedSentinel = holder;
+    holder[name] = uninitializedSentinel;
+    holder[getterName] = function() {
+      if (holder[name] === uninitializedSentinel) {
+        holder[name] = initializer();
+      }
+      holder[getterName] = function() {
+        return this[name];
+      };
+      return holder[name];
+    };
+  }
+  function lazyFinal(holder, name, getterName, initializer) {
+    var uninitializedSentinel = holder;
+    holder[name] = uninitializedSentinel;
+    holder[getterName] = function() {
+      if (holder[name] === uninitializedSentinel) {
+        var value = initializer();
+        if (holder[name] !== uninitializedSentinel) {
+          A.throwLateFieldADI(name);
+        }
+        holder[name] = value;
+      }
+      var finalValue = holder[name];
+      holder[getterName] = function() {
+        return finalValue;
+      };
+      return finalValue;
+    };
+  }
+  function makeConstList(list) {
+    list.immutable$list = Array;
+    list.fixed$length = Array;
+    return list;
+  }
+  function convertToFastObject(properties) {
+    function t() {
+    }
+    t.prototype = properties;
+    new t();
+    return properties;
+  }
+  function convertAllToFastObject(arrayOfObjects) {
+    for (var i = 0; i < arrayOfObjects.length; ++i) {
+      convertToFastObject(arrayOfObjects[i]);
+    }
+  }
+  var functionCounter = 0;
+  function instanceTearOffGetter(isIntercepted, parameters) {
+    var cache = null;
+    return isIntercepted ? function(receiver) {
+      if (cache === null)
+        cache = A.closureFromTearOff(parameters);
+      return new cache(receiver, this);
+    } : function() {
+      if (cache === null)
+        cache = A.closureFromTearOff(parameters);
+      return new cache(this, null);
+    };
+  }
+  function staticTearOffGetter(parameters) {
+    var cache = null;
+    return function() {
+      if (cache === null)
+        cache = A.closureFromTearOff(parameters).prototype;
+      return cache;
+    };
+  }
+  var typesOffset = 0;
+  function tearOffParameters(container, isStatic, isIntercepted, requiredParameterCount, optionalParameterDefaultValues, callNames, funsOrNames, funType, applyIndex, needsDirectAccess) {
+    if (typeof funType == "number") {
+      funType += typesOffset;
+    }
+    return {co: container, iS: isStatic, iI: isIntercepted, rC: requiredParameterCount, dV: optionalParameterDefaultValues, cs: callNames, fs: funsOrNames, fT: funType, aI: applyIndex || 0, nDA: needsDirectAccess};
+  }
+  function installStaticTearOff(holder, getterName, requiredParameterCount, optionalParameterDefaultValues, callNames, funsOrNames, funType, applyIndex) {
+    var parameters = tearOffParameters(holder, true, false, requiredParameterCount, optionalParameterDefaultValues, callNames, funsOrNames, funType, applyIndex, false);
+    var getterFunction = staticTearOffGetter(parameters);
+    holder[getterName] = getterFunction;
+  }
+  function installInstanceTearOff(prototype, getterName, isIntercepted, requiredParameterCount, optionalParameterDefaultValues, callNames, funsOrNames, funType, applyIndex, needsDirectAccess) {
+    isIntercepted = !!isIntercepted;
+    var parameters = tearOffParameters(prototype, false, isIntercepted, requiredParameterCount, optionalParameterDefaultValues, callNames, funsOrNames, funType, applyIndex, !!needsDirectAccess);
+    var getterFunction = instanceTearOffGetter(isIntercepted, parameters);
+    prototype[getterName] = getterFunction;
+  }
+  function setOrUpdateInterceptorsByTag(newTags) {
+    var tags = init.interceptorsByTag;
+    if (!tags) {
+      init.interceptorsByTag = newTags;
+      return;
+    }
+    copyProperties(newTags, tags);
+  }
+  function setOrUpdateLeafTags(newTags) {
+    var tags = init.leafTags;
+    if (!tags) {
+      init.leafTags = newTags;
+      return;
+    }
+    copyProperties(newTags, tags);
+  }
+  function updateTypes(newTypes) {
+    var types = init.types;
+    var length = types.length;
+    types.push.apply(types, newTypes);
+    return length;
+  }
+  function updateHolder(holder, newHolder) {
+    copyProperties(newHolder, holder);
+    return holder;
+  }
+  var hunkHelpers = function() {
+    var mkInstance = function(isIntercepted, requiredParameterCount, optionalParameterDefaultValues, callNames, applyIndex) {
+        return function(container, getterName, name, funType) {
+          return installInstanceTearOff(container, getterName, isIntercepted, requiredParameterCount, optionalParameterDefaultValues, callNames, [name], funType, applyIndex, false);
+        };
+      },
+      mkStatic = function(requiredParameterCount, optionalParameterDefaultValues, callNames, applyIndex) {
+        return function(container, getterName, name, funType) {
+          return installStaticTearOff(container, getterName, requiredParameterCount, optionalParameterDefaultValues, callNames, [name], funType, applyIndex);
+        };
+      };
+    return {inherit: inherit, inheritMany: inheritMany, mixin: mixinEasy, mixinHard: mixinHard, installStaticTearOff: installStaticTearOff, installInstanceTearOff: installInstanceTearOff, _instance_0u: mkInstance(0, 0, null, ["call$0"], 0), _instance_1u: mkInstance(0, 1, null, ["call$1"], 0), _instance_2u: mkInstance(0, 2, null, ["call$2"], 0), _instance_0i: mkInstance(1, 0, null, ["call$0"], 0), _instance_1i: mkInstance(1, 1, null, ["call$1"], 0), _instance_2i: mkInstance(1, 2, null, ["call$2"], 0), _static_0: mkStatic(0, null, ["call$0"], 0), _static_1: mkStatic(1, null, ["call$1"], 0), _static_2: mkStatic(2, null, ["call$2"], 0), makeConstList: makeConstList, lazy: lazy, lazyFinal: lazyFinal, updateHolder: updateHolder, convertToFastObject: convertToFastObject, updateTypes: updateTypes, setOrUpdateInterceptorsByTag: setOrUpdateInterceptorsByTag, setOrUpdateLeafTags: setOrUpdateLeafTags};
+  }();
+  function initializeDeferredHunk(hunk) {
+    typesOffset = init.types.length;
+    hunk(hunkHelpers, init, holders, $);
+  }
+  var J = {
+    makeDispatchRecord(interceptor, proto, extension, indexability) {
+      return {i: interceptor, p: proto, e: extension, x: indexability};
+    },
+    getNativeInterceptor(object) {
+      var proto, objectProto, $constructor, interceptor, t1,
+        record = object[init.dispatchPropertyName];
+      if (record == null)
+        if ($.initNativeDispatchFlag == null) {
+          A.initNativeDispatch();
+          record = object[init.dispatchPropertyName];
+        }
+      if (record != null) {
+        proto = record.p;
+        if (false === proto)
+          return record.i;
+        if (true === proto)
+          return object;
+        objectProto = Object.getPrototypeOf(object);
+        if (proto === objectProto)
+          return record.i;
+        if (record.e === objectProto)
+          throw A.wrapException(A.UnimplementedError$("Return interceptor for " + A.S(proto(object, record))));
+      }
+      $constructor = object.constructor;
+      if ($constructor == null)
+        interceptor = null;
+      else {
+        t1 = $._JS_INTEROP_INTERCEPTOR_TAG;
+        if (t1 == null)
+          t1 = $._JS_INTEROP_INTERCEPTOR_TAG = init.getIsolateTag("_$dart_js");
+        interceptor = $constructor[t1];
+      }
+      if (interceptor != null)
+        return interceptor;
+      interceptor = A.lookupAndCacheInterceptor(object);
+      if (interceptor != null)
+        return interceptor;
+      if (typeof object == "function")
+        return B.JavaScriptFunction_methods;
+      proto = Object.getPrototypeOf(object);
+      if (proto == null)
+        return B.PlainJavaScriptObject_methods;
+      if (proto === Object.prototype)
+        return B.PlainJavaScriptObject_methods;
+      if (typeof $constructor == "function") {
+        t1 = $._JS_INTEROP_INTERCEPTOR_TAG;
+        if (t1 == null)
+          t1 = $._JS_INTEROP_INTERCEPTOR_TAG = init.getIsolateTag("_$dart_js");
+        Object.defineProperty($constructor, t1, {value: B.UnknownJavaScriptObject_methods, enumerable: false, writable: true, configurable: true});
+        return B.UnknownJavaScriptObject_methods;
+      }
+      return B.UnknownJavaScriptObject_methods;
+    },
+    JSArray_JSArray$fixed($length, $E) {
+      if ($length < 0 || $length > 4294967295)
+        throw A.wrapException(A.RangeError$range($length, 0, 4294967295, "length", null));
+      return J.JSArray_JSArray$markFixed(new Array($length), $E);
+    },
+    JSArray_JSArray$growable($length, $E) {
+      if ($length < 0)
+        throw A.wrapException(A.ArgumentError$("Length must be a non-negative integer: " + $length, null));
+      return A._setArrayType(new Array($length), $E._eval$1("JSArray<0>"));
+    },
+    JSArray_JSArray$markFixed(allocation, $E) {
+      return J.JSArray_markFixedList(A._setArrayType(allocation, $E._eval$1("JSArray<0>")), $E);
+    },
+    JSArray_markFixedList(list, $T) {
+      list.fixed$length = Array;
+      return list;
+    },
+    JSArray_markUnmodifiableList(list) {
+      list.fixed$length = Array;
+      list.immutable$list = Array;
+      return list;
+    },
+    getInterceptor$(receiver) {
+      if (typeof receiver == "number") {
+        if (Math.floor(receiver) == receiver)
+          return J.JSInt.prototype;
+        return J.JSNumNotInt.prototype;
+      }
+      if (typeof receiver == "string")
+        return J.JSString.prototype;
+      if (receiver == null)
+        return J.JSNull.prototype;
+      if (typeof receiver == "boolean")
+        return J.JSBool.prototype;
+      if (Array.isArray(receiver))
+        return J.JSArray.prototype;
+      if (typeof receiver != "object") {
+        if (typeof receiver == "function")
+          return J.JavaScriptFunction.prototype;
+        if (typeof receiver == "symbol")
+          return J.JavaScriptSymbol.prototype;
+        if (typeof receiver == "bigint")
+          return J.JavaScriptBigInt.prototype;
+        return receiver;
+      }
+      if (receiver instanceof A.Object)
+        return receiver;
+      return J.getNativeInterceptor(receiver);
+    },
+    getInterceptor$asx(receiver) {
+      if (typeof receiver == "string")
+        return J.JSString.prototype;
+      if (receiver == null)
+        return receiver;
+      if (Array.isArray(receiver))
+        return J.JSArray.prototype;
+      if (typeof receiver != "object") {
+        if (typeof receiver == "function")
+          return J.JavaScriptFunction.prototype;
+        if (typeof receiver == "symbol")
+          return J.JavaScriptSymbol.prototype;
+        if (typeof receiver == "bigint")
+          return J.JavaScriptBigInt.prototype;
+        return receiver;
+      }
+      if (receiver instanceof A.Object)
+        return receiver;
+      return J.getNativeInterceptor(receiver);
+    },
+    getInterceptor$ax(receiver) {
+      if (receiver == null)
+        return receiver;
+      if (Array.isArray(receiver))
+        return J.JSArray.prototype;
+      if (typeof receiver != "object") {
+        if (typeof receiver == "function")
+          return J.JavaScriptFunction.prototype;
+        if (typeof receiver == "symbol")
+          return J.JavaScriptSymbol.prototype;
+        if (typeof receiver == "bigint")
+          return J.JavaScriptBigInt.prototype;
+        return receiver;
+      }
+      if (receiver instanceof A.Object)
+        return receiver;
+      return J.getNativeInterceptor(receiver);
+    },
+    getInterceptor$s(receiver) {
+      if (typeof receiver == "string")
+        return J.JSString.prototype;
+      if (receiver == null)
+        return receiver;
+      if (!(receiver instanceof A.Object))
+        return J.UnknownJavaScriptObject.prototype;
+      return receiver;
+    },
+    get$hashCode$(receiver) {
+      return J.getInterceptor$(receiver).get$hashCode(receiver);
+    },
+    get$iterator$ax(receiver) {
+      return J.getInterceptor$ax(receiver).get$iterator(receiver);
+    },
+    get$length$asx(receiver) {
+      return J.getInterceptor$asx(receiver).get$length(receiver);
+    },
+    get$runtimeType$(receiver) {
+      return J.getInterceptor$(receiver).get$runtimeType(receiver);
+    },
+    $eq$(receiver, a0) {
+      if (receiver == null)
+        return a0 == null;
+      if (typeof receiver != "object")
+        return a0 != null && receiver === a0;
+      return J.getInterceptor$(receiver).$eq(receiver, a0);
+    },
+    matchAsPrefix$2$s(receiver, a0, a1) {
+      return J.getInterceptor$s(receiver).matchAsPrefix$2(receiver, a0, a1);
+    },
+    noSuchMethod$1$(receiver, a0) {
+      return J.getInterceptor$(receiver).noSuchMethod$1(receiver, a0);
+    },
+    toString$0$(receiver) {
+      return J.getInterceptor$(receiver).toString$0(receiver);
+    },
+    Interceptor: function Interceptor() {
+    },
+    JSBool: function JSBool() {
+    },
+    JSNull: function JSNull() {
+    },
+    JavaScriptObject: function JavaScriptObject() {
+    },
+    LegacyJavaScriptObject: function LegacyJavaScriptObject() {
+    },
+    PlainJavaScriptObject: function PlainJavaScriptObject() {
+    },
+    UnknownJavaScriptObject: function UnknownJavaScriptObject() {
+    },
+    JavaScriptFunction: function JavaScriptFunction() {
+    },
+    JavaScriptBigInt: function JavaScriptBigInt() {
+    },
+    JavaScriptSymbol: function JavaScriptSymbol() {
+    },
+    JSArray: function JSArray(t0) {
+      this.$ti = t0;
+    },
+    JSUnmodifiableArray: function JSUnmodifiableArray(t0) {
+      this.$ti = t0;
+    },
+    ArrayIterator: function ArrayIterator(t0, t1, t2) {
+      var _ = this;
+      _._iterable = t0;
+      _._length = t1;
+      _._index = 0;
+      _._current = null;
+      _.$ti = t2;
+    },
+    JSNumber: function JSNumber() {
+    },
+    JSInt: function JSInt() {
+    },
+    JSNumNotInt: function JSNumNotInt() {
+    },
+    JSString: function JSString() {
+    }
+  },
+  A = {JS_CONST: function JS_CONST() {
+    },
+    checkNotNullable(value, $name, $T) {
+      return value;
+    },
+    isToStringVisiting(object) {
+      var t1, i;
+      for (t1 = $.toStringVisiting.length, i = 0; i < t1; ++i)
+        if (object === $.toStringVisiting[i])
+          return true;
+      return false;
+    },
+    IterableElementError_noElement() {
+      return new A.StateError("No element");
+    },
+    IterableElementError_tooFew() {
+      return new A.StateError("Too few elements");
+    },
+    LateError: function LateError(t0) {
+      this._message = t0;
+    },
+    nullFuture_closure: function nullFuture_closure() {
+    },
+    EfficientLengthIterable: function EfficientLengthIterable() {
+    },
+    ListIterable: function ListIterable() {
+    },
+    ListIterator: function ListIterator(t0, t1, t2) {
+      var _ = this;
+      _.__internal$_iterable = t0;
+      _.__internal$_length = t1;
+      _.__internal$_index = 0;
+      _.__internal$_current = null;
+      _.$ti = t2;
+    },
+    FixedLengthListMixin: function FixedLengthListMixin() {
+    },
+    Symbol: function Symbol(t0) {
+      this._name = t0;
+    },
+    unminifyOrTag(rawClassName) {
+      var preserved = init.mangledGlobalNames[rawClassName];
+      if (preserved != null)
+        return preserved;
+      return rawClassName;
+    },
+    isJsIndexable(object, record) {
+      var result;
+      if (record != null) {
+        result = record.x;
+        if (result != null)
+          return result;
+      }
+      return type$.JavaScriptIndexingBehavior_dynamic._is(object);
+    },
+    S(value) {
+      var result;
+      if (typeof value == "string")
+        return value;
+      if (typeof value == "number") {
+        if (value !== 0)
+          return "" + value;
+      } else if (true === value)
+        return "true";
+      else if (false === value)
+        return "false";
+      else if (value == null)
+        return "null";
+      result = J.toString$0$(value);
+      return result;
+    },
+    Primitives_objectHashCode(object) {
+      var hash,
+        property = $.Primitives__identityHashCodeProperty;
+      if (property == null)
+        property = $.Primitives__identityHashCodeProperty = Symbol("identityHashCode");
+      hash = object[property];
+      if (hash == null) {
+        hash = Math.random() * 0x3fffffff | 0;
+        object[property] = hash;
+      }
+      return hash;
+    },
+    Primitives_parseInt(source, radix) {
+      var decimalMatch, maxCharCode, digitsPart, t1, i, _null = null,
+        match = /^\s*[+-]?((0x[a-f0-9]+)|(\d+)|([a-z0-9]+))\s*$/i.exec(source);
+      if (match == null)
+        return _null;
+      if (3 >= match.length)
+        return A.ioore(match, 3);
+      decimalMatch = match[3];
+      if (radix == null) {
+        if (decimalMatch != null)
+          return parseInt(source, 10);
+        if (match[2] != null)
+          return parseInt(source, 16);
+        return _null;
+      }
+      if (radix < 2 || radix > 36)
+        throw A.wrapException(A.RangeError$range(radix, 2, 36, "radix", _null));
+      if (radix === 10 && decimalMatch != null)
+        return parseInt(source, 10);
+      if (radix < 10 || decimalMatch == null) {
+        maxCharCode = radix <= 10 ? 47 + radix : 86 + radix;
+        digitsPart = match[1];
+        for (t1 = digitsPart.length, i = 0; i < t1; ++i)
+          if ((digitsPart.charCodeAt(i) | 32) > maxCharCode)
+            return _null;
+      }
+      return parseInt(source, radix);
+    },
+    Primitives_objectTypeName(object) {
+      return A.Primitives__objectTypeNameNewRti(object);
+    },
+    Primitives__objectTypeNameNewRti(object) {
+      var interceptor, dispatchName, $constructor, constructorName;
+      if (object instanceof A.Object)
+        return A._rtiToString(A.instanceType(object), null);
+      interceptor = J.getInterceptor$(object);
+      if (interceptor === B.Interceptor_methods || interceptor === B.JavaScriptObject_methods || type$.UnknownJavaScriptObject._is(object)) {
+        dispatchName = B.C_JS_CONST(object);
+        if (dispatchName !== "Object" && dispatchName !== "")
+          return dispatchName;
+        $constructor = object.constructor;
+        if (typeof $constructor == "function") {
+          constructorName = $constructor.name;
+          if (typeof constructorName == "string" && constructorName !== "Object" && constructorName !== "")
+            return constructorName;
+        }
+      }
+      return A._rtiToString(A.instanceType(object), null);
+    },
+    Primitives_safeToString(object) {
+      if (typeof object == "number" || A._isBool(object))
+        return J.toString$0$(object);
+      if (typeof object == "string")
+        return JSON.stringify(object);
+      if (object instanceof A.Closure)
+        return object.toString$0(0);
+      return "Instance of '" + A.Primitives_objectTypeName(object) + "'";
+    },
+    Primitives_stringFromCharCode(charCode) {
+      var bits;
+      if (0 <= charCode) {
+        if (charCode <= 65535)
+          return String.fromCharCode(charCode);
+        if (charCode <= 1114111) {
+          bits = charCode - 65536;
+          return String.fromCharCode((B.JSInt_methods._shrOtherPositive$1(bits, 10) | 55296) >>> 0, bits & 1023 | 56320);
+        }
+      }
+      throw A.wrapException(A.RangeError$range(charCode, 0, 1114111, null, null));
+    },
+    Primitives_lazyAsJsDate(receiver) {
+      if (receiver.date === void 0)
+        receiver.date = new Date(receiver._value);
+      return receiver.date;
+    },
+    Primitives_getYear(receiver) {
+      return receiver.isUtc ? A.Primitives_lazyAsJsDate(receiver).getUTCFullYear() + 0 : A.Primitives_lazyAsJsDate(receiver).getFullYear() + 0;
+    },
+    Primitives_getMonth(receiver) {
+      return receiver.isUtc ? A.Primitives_lazyAsJsDate(receiver).getUTCMonth() + 1 : A.Primitives_lazyAsJsDate(receiver).getMonth() + 1;
+    },
+    Primitives_getDay(receiver) {
+      return receiver.isUtc ? A.Primitives_lazyAsJsDate(receiver).getUTCDate() + 0 : A.Primitives_lazyAsJsDate(receiver).getDate() + 0;
+    },
+    Primitives_getHours(receiver) {
+      return receiver.isUtc ? A.Primitives_lazyAsJsDate(receiver).getUTCHours() + 0 : A.Primitives_lazyAsJsDate(receiver).getHours() + 0;
+    },
+    Primitives_getMinutes(receiver) {
+      return receiver.isUtc ? A.Primitives_lazyAsJsDate(receiver).getUTCMinutes() + 0 : A.Primitives_lazyAsJsDate(receiver).getMinutes() + 0;
+    },
+    Primitives_getSeconds(receiver) {
+      return receiver.isUtc ? A.Primitives_lazyAsJsDate(receiver).getUTCSeconds() + 0 : A.Primitives_lazyAsJsDate(receiver).getSeconds() + 0;
+    },
+    Primitives_getMilliseconds(receiver) {
+      return receiver.isUtc ? A.Primitives_lazyAsJsDate(receiver).getUTCMilliseconds() + 0 : A.Primitives_lazyAsJsDate(receiver).getMilliseconds() + 0;
+    },
+    Primitives_functionNoSuchMethod($function, positionalArguments, namedArguments) {
+      var $arguments, namedArgumentList, t1 = {};
+      t1.argumentCount = 0;
+      $arguments = [];
+      namedArgumentList = [];
+      t1.argumentCount = positionalArguments.length;
+      B.JSArray_methods.addAll$1($arguments, positionalArguments);
+      t1.names = "";
+      if (namedArguments != null && namedArguments.__js_helper$_length !== 0)
+        namedArguments.forEach$1(0, new A.Primitives_functionNoSuchMethod_closure(t1, namedArgumentList, $arguments));
+      return J.noSuchMethod$1$($function, new A.JSInvocationMirror(B.Symbol_call, 0, $arguments, namedArgumentList, 0));
+    },
+    Primitives_applyFunction($function, positionalArguments, namedArguments) {
+      var t1, argumentCount, jsStub;
+      if (Array.isArray(positionalArguments))
+        t1 = namedArguments == null || namedArguments.__js_helper$_length === 0;
+      else
+        t1 = false;
+      if (t1) {
+        argumentCount = positionalArguments.length;
+        if (argumentCount === 0) {
+          if (!!$function.call$0)
+            return $function.call$0();
+        } else if (argumentCount === 1) {
+          if (!!$function.call$1)
+            return $function.call$1(positionalArguments[0]);
+        } else if (argumentCount === 2) {
+          if (!!$function.call$2)
+            return $function.call$2(positionalArguments[0], positionalArguments[1]);
+        } else if (argumentCount === 3) {
+          if (!!$function.call$3)
+            return $function.call$3(positionalArguments[0], positionalArguments[1], positionalArguments[2]);
+        } else if (argumentCount === 4) {
+          if (!!$function.call$4)
+            return $function.call$4(positionalArguments[0], positionalArguments[1], positionalArguments[2], positionalArguments[3]);
+        } else if (argumentCount === 5)
+          if (!!$function.call$5)
+            return $function.call$5(positionalArguments[0], positionalArguments[1], positionalArguments[2], positionalArguments[3], positionalArguments[4]);
+        jsStub = $function["call" + "$" + argumentCount];
+        if (jsStub != null)
+          return jsStub.apply($function, positionalArguments);
+      }
+      return A.Primitives__generalApplyFunction($function, positionalArguments, namedArguments);
+    },
+    Primitives__generalApplyFunction($function, positionalArguments, namedArguments) {
+      var defaultValuesClosure, t1, defaultValues, interceptor, jsFunction, maxArguments, missingDefaults, keys, _i, defaultValue, used, key,
+        $arguments = Array.isArray(positionalArguments) ? positionalArguments : A.List_List$of(positionalArguments, true, type$.dynamic),
+        argumentCount = $arguments.length,
+        requiredParameterCount = $function.$requiredArgCount;
+      if (argumentCount < requiredParameterCount)
+        return A.Primitives_functionNoSuchMethod($function, $arguments, namedArguments);
+      defaultValuesClosure = $function.$defaultValues;
+      t1 = defaultValuesClosure == null;
+      defaultValues = !t1 ? defaultValuesClosure() : null;
+      interceptor = J.getInterceptor$($function);
+      jsFunction = interceptor["call*"];
+      if (typeof jsFunction == "string")
+        jsFunction = interceptor[jsFunction];
+      if (t1) {
+        if (namedArguments != null && namedArguments.__js_helper$_length !== 0)
+          return A.Primitives_functionNoSuchMethod($function, $arguments, namedArguments);
+        if (argumentCount === requiredParameterCount)
+          return jsFunction.apply($function, $arguments);
+        return A.Primitives_functionNoSuchMethod($function, $arguments, namedArguments);
+      }
+      if (Array.isArray(defaultValues)) {
+        if (namedArguments != null && namedArguments.__js_helper$_length !== 0)
+          return A.Primitives_functionNoSuchMethod($function, $arguments, namedArguments);
+        maxArguments = requiredParameterCount + defaultValues.length;
+        if (argumentCount > maxArguments)
+          return A.Primitives_functionNoSuchMethod($function, $arguments, null);
+        if (argumentCount < maxArguments) {
+          missingDefaults = defaultValues.slice(argumentCount - requiredParameterCount);
+          if ($arguments === positionalArguments)
+            $arguments = A.List_List$of($arguments, true, type$.dynamic);
+          B.JSArray_methods.addAll$1($arguments, missingDefaults);
+        }
+        return jsFunction.apply($function, $arguments);
+      } else {
+        if (argumentCount > requiredParameterCount)
+          return A.Primitives_functionNoSuchMethod($function, $arguments, namedArguments);
+        if ($arguments === positionalArguments)
+          $arguments = A.List_List$of($arguments, true, type$.dynamic);
+        keys = Object.keys(defaultValues);
+        if (namedArguments == null)
+          for (t1 = keys.length, _i = 0; _i < keys.length; keys.length === t1 || (0, A.throwConcurrentModificationError)(keys), ++_i) {
+            defaultValue = defaultValues[A._asString(keys[_i])];
+            if (B.C__Required === defaultValue)
+              return A.Primitives_functionNoSuchMethod($function, $arguments, namedArguments);
+            B.JSArray_methods.add$1($arguments, defaultValue);
+          }
+        else {
+          for (t1 = keys.length, used = 0, _i = 0; _i < keys.length; keys.length === t1 || (0, A.throwConcurrentModificationError)(keys), ++_i) {
+            key = A._asString(keys[_i]);
+            if (namedArguments.containsKey$1(key)) {
+              ++used;
+              B.JSArray_methods.add$1($arguments, namedArguments.$index(0, key));
+            } else {
+              defaultValue = defaultValues[key];
+              if (B.C__Required === defaultValue)
+                return A.Primitives_functionNoSuchMethod($function, $arguments, namedArguments);
+              B.JSArray_methods.add$1($arguments, defaultValue);
+            }
+          }
+          if (used !== namedArguments.__js_helper$_length)
+            return A.Primitives_functionNoSuchMethod($function, $arguments, namedArguments);
+        }
+        return jsFunction.apply($function, $arguments);
+      }
+    },
+    ioore(receiver, index) {
+      if (receiver == null)
+        J.get$length$asx(receiver);
+      throw A.wrapException(A.diagnoseIndexError(receiver, index));
+    },
+    diagnoseIndexError(indexable, index) {
+      var $length, _s5_ = "index";
+      if (!A._isInt(index))
+        return new A.ArgumentError(true, index, _s5_, null);
+      $length = A._asInt(J.get$length$asx(indexable));
+      if (index < 0 || index >= $length)
+        return A.IndexError$withLength(index, $length, indexable, null, _s5_);
+      return A.RangeError$value(index, _s5_);
+    },
+    wrapException(ex) {
+      return A.initializeExceptionWrapper(new Error(), ex);
+    },
+    initializeExceptionWrapper(wrapper, ex) {
+      var t1;
+      if (ex == null)
+        ex = new A.TypeError();
+      wrapper.dartException = ex;
+      t1 = A.toStringWrapper;
+      if ("defineProperty" in Object) {
+        Object.defineProperty(wrapper, "message", {get: t1});
+        wrapper.name = "";
+      } else
+        wrapper.toString = t1;
+      return wrapper;
+    },
+    toStringWrapper() {
+      return J.toString$0$(this.dartException);
+    },
+    throwExpression(ex) {
+      throw A.wrapException(ex);
+    },
+    throwExpressionWithWrapper(ex, wrapper) {
+      throw A.initializeExceptionWrapper(wrapper, ex);
+    },
+    throwConcurrentModificationError(collection) {
+      throw A.wrapException(A.ConcurrentModificationError$(collection));
+    },
+    TypeErrorDecoder_extractPattern(message) {
+      var match, $arguments, argumentsExpr, expr, method, receiver;
+      message = A.quoteStringForRegExp(message.replace(String({}), "$receiver$"));
+      match = message.match(/\\\$[a-zA-Z]+\\\$/g);
+      if (match == null)
+        match = A._setArrayType([], type$.JSArray_String);
+      $arguments = match.indexOf("\\$arguments\\$");
+      argumentsExpr = match.indexOf("\\$argumentsExpr\\$");
+      expr = match.indexOf("\\$expr\\$");
+      method = match.indexOf("\\$method\\$");
+      receiver = match.indexOf("\\$receiver\\$");
+      return new A.TypeErrorDecoder(message.replace(new RegExp("\\\\\\$arguments\\\\\\$", "g"), "((?:x|[^x])*)").replace(new RegExp("\\\\\\$argumentsExpr\\\\\\$", "g"), "((?:x|[^x])*)").replace(new RegExp("\\\\\\$expr\\\\\\$", "g"), "((?:x|[^x])*)").replace(new RegExp("\\\\\\$method\\\\\\$", "g"), "((?:x|[^x])*)").replace(new RegExp("\\\\\\$receiver\\\\\\$", "g"), "((?:x|[^x])*)"), $arguments, argumentsExpr, expr, method, receiver);
+    },
+    TypeErrorDecoder_provokeCallErrorOn(expression) {
+      return function($expr$) {
+        var $argumentsExpr$ = "$arguments$";
+        try {
+          $expr$.$method$($argumentsExpr$);
+        } catch (e) {
+          return e.message;
+        }
+      }(expression);
+    },
+    TypeErrorDecoder_provokePropertyErrorOn(expression) {
+      return function($expr$) {
+        try {
+          $expr$.$method$;
+        } catch (e) {
+          return e.message;
+        }
+      }(expression);
+    },
+    JsNoSuchMethodError$(_message, match) {
+      var t1 = match == null,
+        t2 = t1 ? null : match.method;
+      return new A.JsNoSuchMethodError(_message, t2, t1 ? null : match.receiver);
+    },
+    unwrapException(ex) {
+      var t1;
+      if (ex == null)
+        return new A.NullThrownFromJavaScriptException(ex);
+      if (ex instanceof A.ExceptionAndStackTrace) {
+        t1 = ex.dartException;
+        return A.saveStackTrace(ex, t1 == null ? type$.Object._as(t1) : t1);
+      }
+      if (typeof ex !== "object")
+        return ex;
+      if ("dartException" in ex)
+        return A.saveStackTrace(ex, ex.dartException);
+      return A._unwrapNonDartException(ex);
+    },
+    saveStackTrace(ex, error) {
+      if (type$.Error._is(error))
+        if (error.$thrownJsError == null)
+          error.$thrownJsError = ex;
+      return error;
+    },
+    _unwrapNonDartException(ex) {
+      var message, number, ieErrorCode, nsme, notClosure, nullCall, nullLiteralCall, undefCall, undefLiteralCall, nullProperty, undefProperty, undefLiteralProperty, match;
+      if (!("message" in ex))
+        return ex;
+      message = ex.message;
+      if ("number" in ex && typeof ex.number == "number") {
+        number = ex.number;
+        ieErrorCode = number & 65535;
+        if ((B.JSInt_methods._shrOtherPositive$1(number, 16) & 8191) === 10)
+          switch (ieErrorCode) {
+            case 438:
+              return A.saveStackTrace(ex, A.JsNoSuchMethodError$(A.S(message) + " (Error " + ieErrorCode + ")", null));
+            case 445:
+            case 5007:
+              A.S(message);
+              return A.saveStackTrace(ex, new A.NullError());
+          }
+      }
+      if (ex instanceof TypeError) {
+        nsme = $.$get$TypeErrorDecoder_noSuchMethodPattern();
+        notClosure = $.$get$TypeErrorDecoder_notClosurePattern();
+        nullCall = $.$get$TypeErrorDecoder_nullCallPattern();
+        nullLiteralCall = $.$get$TypeErrorDecoder_nullLiteralCallPattern();
+        undefCall = $.$get$TypeErrorDecoder_undefinedCallPattern();
+        undefLiteralCall = $.$get$TypeErrorDecoder_undefinedLiteralCallPattern();
+        nullProperty = $.$get$TypeErrorDecoder_nullPropertyPattern();
+        $.$get$TypeErrorDecoder_nullLiteralPropertyPattern();
+        undefProperty = $.$get$TypeErrorDecoder_undefinedPropertyPattern();
+        undefLiteralProperty = $.$get$TypeErrorDecoder_undefinedLiteralPropertyPattern();
+        match = nsme.matchTypeError$1(message);
+        if (match != null)
+          return A.saveStackTrace(ex, A.JsNoSuchMethodError$(A._asString(message), match));
+        else {
+          match = notClosure.matchTypeError$1(message);
+          if (match != null) {
+            match.method = "call";
+            return A.saveStackTrace(ex, A.JsNoSuchMethodError$(A._asString(message), match));
+          } else if (nullCall.matchTypeError$1(message) != null || nullLiteralCall.matchTypeError$1(message) != null || undefCall.matchTypeError$1(message) != null || undefLiteralCall.matchTypeError$1(message) != null || nullProperty.matchTypeError$1(message) != null || nullLiteralCall.matchTypeError$1(message) != null || undefProperty.matchTypeError$1(message) != null || undefLiteralProperty.matchTypeError$1(message) != null) {
+            A._asString(message);
+            return A.saveStackTrace(ex, new A.NullError());
+          }
+        }
+        return A.saveStackTrace(ex, new A.UnknownJsTypeError(typeof message == "string" ? message : ""));
+      }
+      if (ex instanceof RangeError) {
+        if (typeof message == "string" && message.indexOf("call stack") !== -1)
+          return new A.StackOverflowError();
+        message = function(ex) {
+          try {
+            return String(ex);
+          } catch (e) {
+          }
+          return null;
+        }(ex);
+        return A.saveStackTrace(ex, new A.ArgumentError(false, null, null, typeof message == "string" ? message.replace(/^RangeError:\s*/, "") : message));
+      }
+      if (typeof InternalError == "function" && ex instanceof InternalError)
+        if (typeof message == "string" && message === "too much recursion")
+          return new A.StackOverflowError();
+      return ex;
+    },
+    getTraceFromException(exception) {
+      var trace;
+      if (exception instanceof A.ExceptionAndStackTrace)
+        return exception.stackTrace;
+      if (exception == null)
+        return new A._StackTrace(exception);
+      trace = exception.$cachedTrace;
+      if (trace != null)
+        return trace;
+      trace = new A._StackTrace(exception);
+      if (typeof exception === "object")
+        exception.$cachedTrace = trace;
+      return trace;
+    },
+    objectHashCode(object) {
+      if (object == null)
+        return J.get$hashCode$(object);
+      if (typeof object == "object")
+        return A.Primitives_objectHashCode(object);
+      return J.get$hashCode$(object);
+    },
+    _invokeClosure(closure, numberOfArguments, arg1, arg2, arg3, arg4) {
+      type$.Function._as(closure);
+      switch (A._asInt(numberOfArguments)) {
+        case 0:
+          return closure.call$0();
+        case 1:
+          return closure.call$1(arg1);
+        case 2:
+          return closure.call$2(arg1, arg2);
+        case 3:
+          return closure.call$3(arg1, arg2, arg3);
+        case 4:
+          return closure.call$4(arg1, arg2, arg3, arg4);
+      }
+      throw A.wrapException(new A._Exception("Unsupported number of arguments for wrapped closure"));
+    },
+    convertDartClosureToJS(closure, arity) {
+      var $function = closure.$identity;
+      if (!!$function)
+        return $function;
+      $function = A.convertDartClosureToJSUncached(closure, arity);
+      closure.$identity = $function;
+      return $function;
+    },
+    convertDartClosureToJSUncached(closure, arity) {
+      var entry;
+      switch (arity) {
+        case 0:
+          entry = closure.call$0;
+          break;
+        case 1:
+          entry = closure.call$1;
+          break;
+        case 2:
+          entry = closure.call$2;
+          break;
+        case 3:
+          entry = closure.call$3;
+          break;
+        case 4:
+          entry = closure.call$4;
+          break;
+        default:
+          entry = null;
+      }
+      if (entry != null)
+        return entry.bind(closure);
+      return function(closure, arity, invoke) {
+        return function(a1, a2, a3, a4) {
+          return invoke(closure, arity, a1, a2, a3, a4);
+        };
+      }(closure, arity, A._invokeClosure);
+    },
+    Closure_fromTearOff(parameters) {
+      var $prototype, $constructor, t2, trampoline, applyTrampoline, i, stub, stub0, stubName, stubCallName,
+        container = parameters.co,
+        isStatic = parameters.iS,
+        isIntercepted = parameters.iI,
+        needsDirectAccess = parameters.nDA,
+        applyTrampolineIndex = parameters.aI,
+        funsOrNames = parameters.fs,
+        callNames = parameters.cs,
+        $name = funsOrNames[0],
+        callName = callNames[0],
+        $function = container[$name],
+        t1 = parameters.fT;
+      t1.toString;
+      $prototype = isStatic ? Object.create(new A.StaticClosure().constructor.prototype) : Object.create(new A.BoundClosure(null, null).constructor.prototype);
+      $prototype.$initialize = $prototype.constructor;
+      $constructor = isStatic ? function static_tear_off() {
+        this.$initialize();
+      } : function tear_off(a, b) {
+        this.$initialize(a, b);
+      };
+      $prototype.constructor = $constructor;
+      $constructor.prototype = $prototype;
+      $prototype.$_name = $name;
+      $prototype.$_target = $function;
+      t2 = !isStatic;
+      if (t2)
+        trampoline = A.Closure_forwardCallTo($name, $function, isIntercepted, needsDirectAccess);
+      else {
+        $prototype.$static_name = $name;
+        trampoline = $function;
+      }
+      $prototype.$signature = A.Closure__computeSignatureFunctionNewRti(t1, isStatic, isIntercepted);
+      $prototype[callName] = trampoline;
+      for (applyTrampoline = trampoline, i = 1; i < funsOrNames.length; ++i) {
+        stub = funsOrNames[i];
+        if (typeof stub == "string") {
+          stub0 = container[stub];
+          stubName = stub;
+          stub = stub0;
+        } else
+          stubName = "";
+        stubCallName = callNames[i];
+        if (stubCallName != null) {
+          if (t2)
+            stub = A.Closure_forwardCallTo(stubName, stub, isIntercepted, needsDirectAccess);
+          $prototype[stubCallName] = stub;
+        }
+        if (i === applyTrampolineIndex)
+          applyTrampoline = stub;
+      }
+      $prototype["call*"] = applyTrampoline;
+      $prototype.$requiredArgCount = parameters.rC;
+      $prototype.$defaultValues = parameters.dV;
+      return $constructor;
+    },
+    Closure__computeSignatureFunctionNewRti(functionType, isStatic, isIntercepted) {
+      if (typeof functionType == "number")
+        return functionType;
+      if (typeof functionType == "string") {
+        if (isStatic)
+          throw A.wrapException("Cannot compute signature for static tearoff.");
+        return function(recipe, evalOnReceiver) {
+          return function() {
+            return evalOnReceiver(this, recipe);
+          };
+        }(functionType, A.BoundClosure_evalRecipe);
+      }
+      throw A.wrapException("Error in functionType of tearoff");
+    },
+    Closure_cspForwardCall(arity, needsDirectAccess, stubName, $function) {
+      var getReceiver = A.BoundClosure_receiverOf;
+      switch (needsDirectAccess ? -1 : arity) {
+        case 0:
+          return function(entry, receiverOf) {
+            return function() {
+              return receiverOf(this)[entry]();
+            };
+          }(stubName, getReceiver);
+        case 1:
+          return function(entry, receiverOf) {
+            return function(a) {
+              return receiverOf(this)[entry](a);
+            };
+          }(stubName, getReceiver);
+        case 2:
+          return function(entry, receiverOf) {
+            return function(a, b) {
+              return receiverOf(this)[entry](a, b);
+            };
+          }(stubName, getReceiver);
+        case 3:
+          return function(entry, receiverOf) {
+            return function(a, b, c) {
+              return receiverOf(this)[entry](a, b, c);
+            };
+          }(stubName, getReceiver);
+        case 4:
+          return function(entry, receiverOf) {
+            return function(a, b, c, d) {
+              return receiverOf(this)[entry](a, b, c, d);
+            };
+          }(stubName, getReceiver);
+        case 5:
+          return function(entry, receiverOf) {
+            return function(a, b, c, d, e) {
+              return receiverOf(this)[entry](a, b, c, d, e);
+            };
+          }(stubName, getReceiver);
+        default:
+          return function(f, receiverOf) {
+            return function() {
+              return f.apply(receiverOf(this), arguments);
+            };
+          }($function, getReceiver);
+      }
+    },
+    Closure_forwardCallTo(stubName, $function, isIntercepted, needsDirectAccess) {
+      if (isIntercepted)
+        return A.Closure_forwardInterceptedCallTo(stubName, $function, needsDirectAccess);
+      return A.Closure_cspForwardCall($function.length, needsDirectAccess, stubName, $function);
+    },
+    Closure_cspForwardInterceptedCall(arity, needsDirectAccess, stubName, $function) {
+      var getReceiver = A.BoundClosure_receiverOf,
+        getInterceptor = A.BoundClosure_interceptorOf;
+      switch (needsDirectAccess ? -1 : arity) {
+        case 0:
+          throw A.wrapException(new A.RuntimeError("Intercepted function with no arguments."));
+        case 1:
+          return function(entry, interceptorOf, receiverOf) {
+            return function() {
+              return interceptorOf(this)[entry](receiverOf(this));
+            };
+          }(stubName, getInterceptor, getReceiver);
+        case 2:
+          return function(entry, interceptorOf, receiverOf) {
+            return function(a) {
+              return interceptorOf(this)[entry](receiverOf(this), a);
+            };
+          }(stubName, getInterceptor, getReceiver);
+        case 3:
+          return function(entry, interceptorOf, receiverOf) {
+            return function(a, b) {
+              return interceptorOf(this)[entry](receiverOf(this), a, b);
+            };
+          }(stubName, getInterceptor, getReceiver);
+        case 4:
+          return function(entry, interceptorOf, receiverOf) {
+            return function(a, b, c) {
+              return interceptorOf(this)[entry](receiverOf(this), a, b, c);
+            };
+          }(stubName, getInterceptor, getReceiver);
+        case 5:
+          return function(entry, interceptorOf, receiverOf) {
+            return function(a, b, c, d) {
+              return interceptorOf(this)[entry](receiverOf(this), a, b, c, d);
+            };
+          }(stubName, getInterceptor, getReceiver);
+        case 6:
+          return function(entry, interceptorOf, receiverOf) {
+            return function(a, b, c, d, e) {
+              return interceptorOf(this)[entry](receiverOf(this), a, b, c, d, e);
+            };
+          }(stubName, getInterceptor, getReceiver);
+        default:
+          return function(f, interceptorOf, receiverOf) {
+            return function() {
+              var a = [receiverOf(this)];
+              Array.prototype.push.apply(a, arguments);
+              return f.apply(interceptorOf(this), a);
+            };
+          }($function, getInterceptor, getReceiver);
+      }
+    },
+    Closure_forwardInterceptedCallTo(stubName, $function, needsDirectAccess) {
+      var arity, t1;
+      if ($.BoundClosure__interceptorFieldNameCache == null)
+        $.BoundClosure__interceptorFieldNameCache = A.BoundClosure__computeFieldNamed("interceptor");
+      if ($.BoundClosure__receiverFieldNameCache == null)
+        $.BoundClosure__receiverFieldNameCache = A.BoundClosure__computeFieldNamed("receiver");
+      arity = $function.length;
+      t1 = A.Closure_cspForwardInterceptedCall(arity, needsDirectAccess, stubName, $function);
+      return t1;
+    },
+    closureFromTearOff(parameters) {
+      return A.Closure_fromTearOff(parameters);
+    },
+    BoundClosure_evalRecipe(closure, recipe) {
+      return A._Universe_evalInEnvironment(init.typeUniverse, A.instanceType(closure._receiver), recipe);
+    },
+    BoundClosure_receiverOf(closure) {
+      return closure._receiver;
+    },
+    BoundClosure_interceptorOf(closure) {
+      return closure._interceptor;
+    },
+    BoundClosure__computeFieldNamed(fieldName) {
+      var t1, i, $name,
+        template = new A.BoundClosure("receiver", "interceptor"),
+        names = J.JSArray_markFixedList(Object.getOwnPropertyNames(template), type$.nullable_Object);
+      for (t1 = names.length, i = 0; i < t1; ++i) {
+        $name = names[i];
+        if (template[$name] === fieldName)
+          return $name;
+      }
+      throw A.wrapException(A.ArgumentError$("Field name " + fieldName + " not found.", null));
+    },
+    throwCyclicInit(staticName) {
+      throw A.wrapException(new A._CyclicInitializationError(staticName));
+    },
+    getIsolateAffinityTag($name) {
+      return init.getIsolateTag($name);
+    },
+    lookupAndCacheInterceptor(obj) {
+      var interceptor, interceptorClass, altTag, mark, t1,
+        tag = A._asString($.getTagFunction.call$1(obj)),
+        record = $.dispatchRecordsForInstanceTags[tag];
+      if (record != null) {
+        Object.defineProperty(obj, init.dispatchPropertyName, {value: record, enumerable: false, writable: true, configurable: true});
+        return record.i;
+      }
+      interceptor = $.interceptorsForUncacheableTags[tag];
+      if (interceptor != null)
+        return interceptor;
+      interceptorClass = init.interceptorsByTag[tag];
+      if (interceptorClass == null) {
+        altTag = A._asStringQ($.alternateTagFunction.call$2(obj, tag));
+        if (altTag != null) {
+          record = $.dispatchRecordsForInstanceTags[altTag];
+          if (record != null) {
+            Object.defineProperty(obj, init.dispatchPropertyName, {value: record, enumerable: false, writable: true, configurable: true});
+            return record.i;
+          }
+          interceptor = $.interceptorsForUncacheableTags[altTag];
+          if (interceptor != null)
+            return interceptor;
+          interceptorClass = init.interceptorsByTag[altTag];
+          tag = altTag;
+        }
+      }
+      if (interceptorClass == null)
+        return null;
+      interceptor = interceptorClass.prototype;
+      mark = tag[0];
+      if (mark === "!") {
+        record = A.makeLeafDispatchRecord(interceptor);
+        $.dispatchRecordsForInstanceTags[tag] = record;
+        Object.defineProperty(obj, init.dispatchPropertyName, {value: record, enumerable: false, writable: true, configurable: true});
+        return record.i;
+      }
+      if (mark === "~") {
+        $.interceptorsForUncacheableTags[tag] = interceptor;
+        return interceptor;
+      }
+      if (mark === "-") {
+        t1 = A.makeLeafDispatchRecord(interceptor);
+        Object.defineProperty(Object.getPrototypeOf(obj), init.dispatchPropertyName, {value: t1, enumerable: false, writable: true, configurable: true});
+        return t1.i;
+      }
+      if (mark === "+")
+        return A.patchInteriorProto(obj, interceptor);
+      if (mark === "*")
+        throw A.wrapException(A.UnimplementedError$(tag));
+      if (init.leafTags[tag] === true) {
+        t1 = A.makeLeafDispatchRecord(interceptor);
+        Object.defineProperty(Object.getPrototypeOf(obj), init.dispatchPropertyName, {value: t1, enumerable: false, writable: true, configurable: true});
+        return t1.i;
+      } else
+        return A.patchInteriorProto(obj, interceptor);
+    },
+    patchInteriorProto(obj, interceptor) {
+      var proto = Object.getPrototypeOf(obj);
+      Object.defineProperty(proto, init.dispatchPropertyName, {value: J.makeDispatchRecord(interceptor, proto, null, null), enumerable: false, writable: true, configurable: true});
+      return interceptor;
+    },
+    makeLeafDispatchRecord(interceptor) {
+      return J.makeDispatchRecord(interceptor, false, null, !!interceptor.$isJavaScriptIndexingBehavior);
+    },
+    makeDefaultDispatchRecord(tag, interceptorClass, proto) {
+      var interceptor = interceptorClass.prototype;
+      if (init.leafTags[tag] === true)
+        return A.makeLeafDispatchRecord(interceptor);
+      else
+        return J.makeDispatchRecord(interceptor, proto, null, null);
+    },
+    initNativeDispatch() {
+      if (true === $.initNativeDispatchFlag)
+        return;
+      $.initNativeDispatchFlag = true;
+      A.initNativeDispatchContinue();
+    },
+    initNativeDispatchContinue() {
+      var map, tags, fun, i, tag, proto, record, interceptorClass;
+      $.dispatchRecordsForInstanceTags = Object.create(null);
+      $.interceptorsForUncacheableTags = Object.create(null);
+      A.initHooks();
+      map = init.interceptorsByTag;
+      tags = Object.getOwnPropertyNames(map);
+      if (typeof window != "undefined") {
+        window;
+        fun = function() {
+        };
+        for (i = 0; i < tags.length; ++i) {
+          tag = tags[i];
+          proto = $.prototypeForTagFunction.call$1(tag);
+          if (proto != null) {
+            record = A.makeDefaultDispatchRecord(tag, map[tag], proto);
+            if (record != null) {
+              Object.defineProperty(proto, init.dispatchPropertyName, {value: record, enumerable: false, writable: true, configurable: true});
+              fun.prototype = proto;
+            }
+          }
+        }
+      }
+      for (i = 0; i < tags.length; ++i) {
+        tag = tags[i];
+        if (/^[A-Za-z_]/.test(tag)) {
+          interceptorClass = map[tag];
+          map["!" + tag] = interceptorClass;
+          map["~" + tag] = interceptorClass;
+          map["-" + tag] = interceptorClass;
+          map["+" + tag] = interceptorClass;
+          map["*" + tag] = interceptorClass;
+        }
+      }
+    },
+    initHooks() {
+      var transformers, i, transformer, getTag, getUnknownTag, prototypeForTag,
+        hooks = B.C_JS_CONST0();
+      hooks = A.applyHooksTransformer(B.C_JS_CONST1, A.applyHooksTransformer(B.C_JS_CONST2, A.applyHooksTransformer(B.C_JS_CONST3, A.applyHooksTransformer(B.C_JS_CONST3, A.applyHooksTransformer(B.C_JS_CONST4, A.applyHooksTransformer(B.C_JS_CONST5, A.applyHooksTransformer(B.C_JS_CONST6(B.C_JS_CONST), hooks)))))));
+      if (typeof dartNativeDispatchHooksTransformer != "undefined") {
+        transformers = dartNativeDispatchHooksTransformer;
+        if (typeof transformers == "function")
+          transformers = [transformers];
+        if (Array.isArray(transformers))
+          for (i = 0; i < transformers.length; ++i) {
+            transformer = transformers[i];
+            if (typeof transformer == "function")
+              hooks = transformer(hooks) || hooks;
+          }
+      }
+      getTag = hooks.getTag;
+      getUnknownTag = hooks.getUnknownTag;
+      prototypeForTag = hooks.prototypeForTag;
+      $.getTagFunction = new A.initHooks_closure(getTag);
+      $.alternateTagFunction = new A.initHooks_closure0(getUnknownTag);
+      $.prototypeForTagFunction = new A.initHooks_closure1(prototypeForTag);
+    },
+    applyHooksTransformer(transformer, hooks) {
+      return transformer(hooks) || hooks;
+    },
+    createRecordTypePredicate(shape, fieldRtis) {
+      var $length = fieldRtis.length,
+        $function = init.rttc["" + $length + ";" + shape];
+      if ($function == null)
+        return null;
+      if ($length === 0)
+        return $function;
+      if ($length === $function.length)
+        return $function.apply(null, fieldRtis);
+      return $function(fieldRtis);
+    },
+    quoteStringForRegExp(string) {
+      if (/[[\]{}()*+?.\\^$|]/.test(string))
+        return string.replace(/[[\]{}()*+?.\\^$|]/g, "\\$&");
+      return string;
+    },
+    ConstantMapView: function ConstantMapView(t0, t1) {
+      this._collection$_map = t0;
+      this.$ti = t1;
+    },
+    ConstantMap: function ConstantMap() {
+    },
+    ConstantStringMap: function ConstantStringMap(t0, t1, t2) {
+      this._jsIndex = t0;
+      this._values = t1;
+      this.$ti = t2;
+    },
+    JSInvocationMirror: function JSInvocationMirror(t0, t1, t2, t3, t4) {
+      var _ = this;
+      _._memberName = t0;
+      _.__js_helper$_kind = t1;
+      _._arguments = t2;
+      _._namedArgumentNames = t3;
+      _._typeArgumentCount = t4;
+    },
+    Primitives_functionNoSuchMethod_closure: function Primitives_functionNoSuchMethod_closure(t0, t1, t2) {
+      this._box_0 = t0;
+      this.namedArgumentList = t1;
+      this.$arguments = t2;
+    },
+    TypeErrorDecoder: function TypeErrorDecoder(t0, t1, t2, t3, t4, t5) {
+      var _ = this;
+      _._pattern = t0;
+      _._arguments = t1;
+      _._argumentsExpr = t2;
+      _._expr = t3;
+      _._method = t4;
+      _._receiver = t5;
+    },
+    NullError: function NullError() {
+    },
+    JsNoSuchMethodError: function JsNoSuchMethodError(t0, t1, t2) {
+      this.__js_helper$_message = t0;
+      this._method = t1;
+      this._receiver = t2;
+    },
+    UnknownJsTypeError: function UnknownJsTypeError(t0) {
+      this.__js_helper$_message = t0;
+    },
+    NullThrownFromJavaScriptException: function NullThrownFromJavaScriptException(t0) {
+      this._irritant = t0;
+    },
+    ExceptionAndStackTrace: function ExceptionAndStackTrace(t0, t1) {
+      this.dartException = t0;
+      this.stackTrace = t1;
+    },
+    _StackTrace: function _StackTrace(t0) {
+      this._exception = t0;
+      this._trace = null;
+    },
+    Closure: function Closure() {
+    },
+    Closure0Args: function Closure0Args() {
+    },
+    Closure2Args: function Closure2Args() {
+    },
+    TearOffClosure: function TearOffClosure() {
+    },
+    StaticClosure: function StaticClosure() {
+    },
+    BoundClosure: function BoundClosure(t0, t1) {
+      this._receiver = t0;
+      this._interceptor = t1;
+    },
+    _CyclicInitializationError: function _CyclicInitializationError(t0) {
+      this.variableName = t0;
+    },
+    RuntimeError: function RuntimeError(t0) {
+      this.message = t0;
+    },
+    _Required: function _Required() {
+    },
+    JsLinkedHashMap: function JsLinkedHashMap(t0) {
+      var _ = this;
+      _.__js_helper$_length = 0;
+      _._last = _._first = _.__js_helper$_rest = _._nums = _._strings = null;
+      _._modifications = 0;
+      _.$ti = t0;
+    },
+    LinkedHashMapCell: function LinkedHashMapCell(t0, t1) {
+      this.hashMapCellKey = t0;
+      this.hashMapCellValue = t1;
+      this._next = null;
+    },
+    LinkedHashMapKeyIterable: function LinkedHashMapKeyIterable(t0, t1) {
+      this._map = t0;
+      this.$ti = t1;
+    },
+    LinkedHashMapKeyIterator: function LinkedHashMapKeyIterator(t0, t1, t2) {
+      var _ = this;
+      _._map = t0;
+      _._modifications = t1;
+      _.__js_helper$_current = _._cell = null;
+      _.$ti = t2;
+    },
+    initHooks_closure: function initHooks_closure(t0) {
+      this.getTag = t0;
+    },
+    initHooks_closure0: function initHooks_closure0(t0) {
+      this.getUnknownTag = t0;
+    },
+    initHooks_closure1: function initHooks_closure1(t0) {
+      this.prototypeForTag = t0;
+    },
+    StringMatch: function StringMatch(t0, t1) {
+      this.start = t0;
+      this.pattern = t1;
+    },
+    _checkValidIndex(index, list, $length) {
+      if (index >>> 0 !== index || index >= $length)
+        throw A.wrapException(A.diagnoseIndexError(list, index));
+    },
+    NativeByteBuffer: function NativeByteBuffer() {
+    },
+    NativeTypedData: function NativeTypedData() {
+    },
+    NativeByteData: function NativeByteData() {
+    },
+    NativeTypedArray: function NativeTypedArray() {
+    },
+    NativeTypedArrayOfDouble: function NativeTypedArrayOfDouble() {
+    },
+    NativeTypedArrayOfInt: function NativeTypedArrayOfInt() {
+    },
+    NativeFloat32List: function NativeFloat32List() {
+    },
+    NativeFloat64List: function NativeFloat64List() {
+    },
+    NativeInt16List: function NativeInt16List() {
+    },
+    NativeInt32List: function NativeInt32List() {
+    },
+    NativeInt8List: function NativeInt8List() {
+    },
+    NativeUint16List: function NativeUint16List() {
+    },
+    NativeUint32List: function NativeUint32List() {
+    },
+    NativeUint8ClampedList: function NativeUint8ClampedList() {
+    },
+    NativeUint8List: function NativeUint8List() {
+    },
+    _NativeTypedArrayOfDouble_NativeTypedArray_ListMixin: function _NativeTypedArrayOfDouble_NativeTypedArray_ListMixin() {
+    },
+    _NativeTypedArrayOfDouble_NativeTypedArray_ListMixin_FixedLengthListMixin: function _NativeTypedArrayOfDouble_NativeTypedArray_ListMixin_FixedLengthListMixin() {
+    },
+    _NativeTypedArrayOfInt_NativeTypedArray_ListMixin: function _NativeTypedArrayOfInt_NativeTypedArray_ListMixin() {
+    },
+    _NativeTypedArrayOfInt_NativeTypedArray_ListMixin_FixedLengthListMixin: function _NativeTypedArrayOfInt_NativeTypedArray_ListMixin_FixedLengthListMixin() {
+    },
+    Rti__getQuestionFromStar(universe, rti) {
+      var question = rti._precomputed1;
+      return question == null ? rti._precomputed1 = A._Universe__lookupQuestionRti(universe, rti._primary, true) : question;
+    },
+    Rti__getFutureFromFutureOr(universe, rti) {
+      var future = rti._precomputed1;
+      return future == null ? rti._precomputed1 = A._Universe__lookupInterfaceRti(universe, "Future", [rti._primary]) : future;
+    },
+    Rti__isUnionOfFunctionType(rti) {
+      var kind = rti._kind;
+      if (kind === 6 || kind === 7 || kind === 8)
+        return A.Rti__isUnionOfFunctionType(rti._primary);
+      return kind === 12 || kind === 13;
+    },
+    Rti__getCanonicalRecipe(rti) {
+      return rti._canonicalRecipe;
+    },
+    findType(recipe) {
+      return A._Universe_eval(init.typeUniverse, recipe, false);
+    },
+    _substitute(universe, rti, typeArguments, depth) {
+      var baseType, substitutedBaseType, interfaceTypeArguments, substitutedInterfaceTypeArguments, base, substitutedBase, $arguments, substitutedArguments, t1, fields, substitutedFields, returnType, substitutedReturnType, functionParameters, substitutedFunctionParameters, bounds, substitutedBounds, index, argument,
+        kind = rti._kind;
+      switch (kind) {
+        case 5:
+        case 1:
+        case 2:
+        case 3:
+        case 4:
+          return rti;
+        case 6:
+          baseType = rti._primary;
+          substitutedBaseType = A._substitute(universe, baseType, typeArguments, depth);
+          if (substitutedBaseType === baseType)
+            return rti;
+          return A._Universe__lookupStarRti(universe, substitutedBaseType, true);
+        case 7:
+          baseType = rti._primary;
+          substitutedBaseType = A._substitute(universe, baseType, typeArguments, depth);
+          if (substitutedBaseType === baseType)
+            return rti;
+          return A._Universe__lookupQuestionRti(universe, substitutedBaseType, true);
+        case 8:
+          baseType = rti._primary;
+          substitutedBaseType = A._substitute(universe, baseType, typeArguments, depth);
+          if (substitutedBaseType === baseType)
+            return rti;
+          return A._Universe__lookupFutureOrRti(universe, substitutedBaseType, true);
+        case 9:
+          interfaceTypeArguments = rti._rest;
+          substitutedInterfaceTypeArguments = A._substituteArray(universe, interfaceTypeArguments, typeArguments, depth);
+          if (substitutedInterfaceTypeArguments === interfaceTypeArguments)
+            return rti;
+          return A._Universe__lookupInterfaceRti(universe, rti._primary, substitutedInterfaceTypeArguments);
+        case 10:
+          base = rti._primary;
+          substitutedBase = A._substitute(universe, base, typeArguments, depth);
+          $arguments = rti._rest;
+          substitutedArguments = A._substituteArray(universe, $arguments, typeArguments, depth);
+          if (substitutedBase === base && substitutedArguments === $arguments)
+            return rti;
+          return A._Universe__lookupBindingRti(universe, substitutedBase, substitutedArguments);
+        case 11:
+          t1 = rti._primary;
+          fields = rti._rest;
+          substitutedFields = A._substituteArray(universe, fields, typeArguments, depth);
+          if (substitutedFields === fields)
+            return rti;
+          return A._Universe__lookupRecordRti(universe, t1, substitutedFields);
+        case 12:
+          returnType = rti._primary;
+          substitutedReturnType = A._substitute(universe, returnType, typeArguments, depth);
+          functionParameters = rti._rest;
+          substitutedFunctionParameters = A._substituteFunctionParameters(universe, functionParameters, typeArguments, depth);
+          if (substitutedReturnType === returnType && substitutedFunctionParameters === functionParameters)
+            return rti;
+          return A._Universe__lookupFunctionRti(universe, substitutedReturnType, substitutedFunctionParameters);
+        case 13:
+          bounds = rti._rest;
+          depth += bounds.length;
+          substitutedBounds = A._substituteArray(universe, bounds, typeArguments, depth);
+          base = rti._primary;
+          substitutedBase = A._substitute(universe, base, typeArguments, depth);
+          if (substitutedBounds === bounds && substitutedBase === base)
+            return rti;
+          return A._Universe__lookupGenericFunctionRti(universe, substitutedBase, substitutedBounds, true);
+        case 14:
+          index = rti._primary;
+          if (index < depth)
+            return rti;
+          argument = typeArguments[index - depth];
+          if (argument == null)
+            return rti;
+          return argument;
+        default:
+          throw A.wrapException(A.AssertionError$("Attempted to substitute unexpected RTI kind " + kind));
+      }
+    },
+    _substituteArray(universe, rtiArray, typeArguments, depth) {
+      var changed, i, rti, substitutedRti,
+        $length = rtiArray.length,
+        result = A._Utils_newArrayOrEmpty($length);
+      for (changed = false, i = 0; i < $length; ++i) {
+        rti = rtiArray[i];
+        substitutedRti = A._substitute(universe, rti, typeArguments, depth);
+        if (substitutedRti !== rti)
+          changed = true;
+        result[i] = substitutedRti;
+      }
+      return changed ? result : rtiArray;
+    },
+    _substituteNamed(universe, namedArray, typeArguments, depth) {
+      var changed, i, t1, t2, rti, substitutedRti,
+        $length = namedArray.length,
+        result = A._Utils_newArrayOrEmpty($length);
+      for (changed = false, i = 0; i < $length; i += 3) {
+        t1 = namedArray[i];
+        t2 = namedArray[i + 1];
+        rti = namedArray[i + 2];
+        substitutedRti = A._substitute(universe, rti, typeArguments, depth);
+        if (substitutedRti !== rti)
+          changed = true;
+        result.splice(i, 3, t1, t2, substitutedRti);
+      }
+      return changed ? result : namedArray;
+    },
+    _substituteFunctionParameters(universe, functionParameters, typeArguments, depth) {
+      var result,
+        requiredPositional = functionParameters._requiredPositional,
+        substitutedRequiredPositional = A._substituteArray(universe, requiredPositional, typeArguments, depth),
+        optionalPositional = functionParameters._optionalPositional,
+        substitutedOptionalPositional = A._substituteArray(universe, optionalPositional, typeArguments, depth),
+        named = functionParameters._named,
+        substitutedNamed = A._substituteNamed(universe, named, typeArguments, depth);
+      if (substitutedRequiredPositional === requiredPositional && substitutedOptionalPositional === optionalPositional && substitutedNamed === named)
+        return functionParameters;
+      result = new A._FunctionParameters();
+      result._requiredPositional = substitutedRequiredPositional;
+      result._optionalPositional = substitutedOptionalPositional;
+      result._named = substitutedNamed;
+      return result;
+    },
+    _setArrayType(target, rti) {
+      target[init.arrayRti] = rti;
+      return target;
+    },
+    closureFunctionType(closure) {
+      var signature = closure.$signature;
+      if (signature != null) {
+        if (typeof signature == "number")
+          return A.getTypeFromTypesTable(signature);
+        return closure.$signature();
+      }
+      return null;
+    },
+    instanceOrFunctionType(object, testRti) {
+      var rti;
+      if (A.Rti__isUnionOfFunctionType(testRti))
+        if (object instanceof A.Closure) {
+          rti = A.closureFunctionType(object);
+          if (rti != null)
+            return rti;
+        }
+      return A.instanceType(object);
+    },
+    instanceType(object) {
+      if (object instanceof A.Object)
+        return A._instanceType(object);
+      if (Array.isArray(object))
+        return A._arrayInstanceType(object);
+      return A._instanceTypeFromConstructor(J.getInterceptor$(object));
+    },
+    _arrayInstanceType(object) {
+      var rti = object[init.arrayRti],
+        defaultRti = type$.JSArray_dynamic;
+      if (rti == null)
+        return defaultRti;
+      if (rti.constructor !== defaultRti.constructor)
+        return defaultRti;
+      return rti;
+    },
+    _instanceType(object) {
+      var rti = object.$ti;
+      return rti != null ? rti : A._instanceTypeFromConstructor(object);
+    },
+    _instanceTypeFromConstructor(instance) {
+      var $constructor = instance.constructor,
+        probe = $constructor.$ccache;
+      if (probe != null)
+        return probe;
+      return A._instanceTypeFromConstructorMiss(instance, $constructor);
+    },
+    _instanceTypeFromConstructorMiss(instance, $constructor) {
+      var effectiveConstructor = instance instanceof A.Closure ? Object.getPrototypeOf(Object.getPrototypeOf(instance)).constructor : $constructor,
+        rti = A._Universe_findErasedType(init.typeUniverse, effectiveConstructor.name);
+      $constructor.$ccache = rti;
+      return rti;
+    },
+    getTypeFromTypesTable(index) {
+      var rti,
+        table = init.types,
+        type = table[index];
+      if (typeof type == "string") {
+        rti = A._Universe_eval(init.typeUniverse, type, false);
+        table[index] = rti;
+        return rti;
+      }
+      return type;
+    },
+    getRuntimeTypeOfDartObject(object) {
+      return A.createRuntimeType(A._instanceType(object));
+    },
+    _structuralTypeOf(object) {
+      var functionRti = object instanceof A.Closure ? A.closureFunctionType(object) : null;
+      if (functionRti != null)
+        return functionRti;
+      if (type$.TrustedGetRuntimeType._is(object))
+        return J.get$runtimeType$(object)._rti;
+      if (Array.isArray(object))
+        return A._arrayInstanceType(object);
+      return A.instanceType(object);
+    },
+    createRuntimeType(rti) {
+      var t1 = rti._cachedRuntimeType;
+      return t1 == null ? rti._cachedRuntimeType = A._createRuntimeType(rti) : t1;
+    },
+    _createRuntimeType(rti) {
+      var starErasedRti, t1,
+        s = rti._canonicalRecipe,
+        starErasedRecipe = s.replace(/\*/g, "");
+      if (starErasedRecipe === s)
+        return rti._cachedRuntimeType = new A._Type(rti);
+      starErasedRti = A._Universe_eval(init.typeUniverse, starErasedRecipe, true);
+      t1 = starErasedRti._cachedRuntimeType;
+      return t1 == null ? starErasedRti._cachedRuntimeType = A._createRuntimeType(starErasedRti) : t1;
+    },
+    typeLiteral(recipe) {
+      return A.createRuntimeType(A._Universe_eval(init.typeUniverse, recipe, false));
+    },
+    _installSpecializedIsTest(object) {
+      var t1, unstarred, unstarredKind, isFn, $name, predicate, testRti = this;
+      if (testRti === type$.Object)
+        return A._finishIsFn(testRti, object, A._isObject);
+      if (!A.isSoundTopType(testRti))
+        t1 = testRti === type$.legacy_Object;
+      else
+        t1 = true;
+      if (t1)
+        return A._finishIsFn(testRti, object, A._isTop);
+      t1 = testRti._kind;
+      if (t1 === 7)
+        return A._finishIsFn(testRti, object, A._generalNullableIsTestImplementation);
+      if (t1 === 1)
+        return A._finishIsFn(testRti, object, A._isNever);
+      unstarred = t1 === 6 ? testRti._primary : testRti;
+      unstarredKind = unstarred._kind;
+      if (unstarredKind === 8)
+        return A._finishIsFn(testRti, object, A._isFutureOr);
+      if (unstarred === type$.int)
+        isFn = A._isInt;
+      else if (unstarred === type$.double || unstarred === type$.num)
+        isFn = A._isNum;
+      else if (unstarred === type$.String)
+        isFn = A._isString;
+      else
+        isFn = unstarred === type$.bool ? A._isBool : null;
+      if (isFn != null)
+        return A._finishIsFn(testRti, object, isFn);
+      if (unstarredKind === 9) {
+        $name = unstarred._primary;
+        if (unstarred._rest.every(A.isDefinitelyTopType)) {
+          testRti._specializedTestResource = "$is" + $name;
+          if ($name === "List")
+            return A._finishIsFn(testRti, object, A._isListTestViaProperty);
+          return A._finishIsFn(testRti, object, A._isTestViaProperty);
+        }
+      } else if (unstarredKind === 11) {
+        predicate = A.createRecordTypePredicate(unstarred._primary, unstarred._rest);
+        return A._finishIsFn(testRti, object, predicate == null ? A._isNever : predicate);
+      }
+      return A._finishIsFn(testRti, object, A._generalIsTestImplementation);
+    },
+    _finishIsFn(testRti, object, isFn) {
+      testRti._is = isFn;
+      return testRti._is(object);
+    },
+    _installSpecializedAsCheck(object) {
+      var t1, testRti = this,
+        asFn = A._generalAsCheckImplementation;
+      if (!A.isSoundTopType(testRti))
+        t1 = testRti === type$.legacy_Object;
+      else
+        t1 = true;
+      if (t1)
+        asFn = A._asTop;
+      else if (testRti === type$.Object)
+        asFn = A._asObject;
+      else {
+        t1 = A.isNullable(testRti);
+        if (t1)
+          asFn = A._generalNullableAsCheckImplementation;
+      }
+      testRti._as = asFn;
+      return testRti._as(object);
+    },
+    _nullIs(testRti) {
+      var t1,
+        kind = testRti._kind;
+      if (!A.isSoundTopType(testRti))
+        if (!(testRti === type$.legacy_Object))
+          if (!(testRti === type$.legacy_Never))
+            if (kind !== 7)
+              if (!(kind === 6 && A._nullIs(testRti._primary)))
+                t1 = kind === 8 && A._nullIs(testRti._primary) || testRti === type$.Null || testRti === type$.JSNull;
+              else
+                t1 = true;
+            else
+              t1 = true;
+          else
+            t1 = true;
+        else
+          t1 = true;
+      else
+        t1 = true;
+      return t1;
+    },
+    _generalIsTestImplementation(object) {
+      var testRti = this;
+      if (object == null)
+        return A._nullIs(testRti);
+      return A.isSubtype(init.typeUniverse, A.instanceOrFunctionType(object, testRti), testRti);
+    },
+    _generalNullableIsTestImplementation(object) {
+      if (object == null)
+        return true;
+      return this._primary._is(object);
+    },
+    _isTestViaProperty(object) {
+      var tag, testRti = this;
+      if (object == null)
+        return A._nullIs(testRti);
+      tag = testRti._specializedTestResource;
+      if (object instanceof A.Object)
+        return !!object[tag];
+      return !!J.getInterceptor$(object)[tag];
+    },
+    _isListTestViaProperty(object) {
+      var tag, testRti = this;
+      if (object == null)
+        return A._nullIs(testRti);
+      if (typeof object != "object")
+        return false;
+      if (Array.isArray(object))
+        return true;
+      tag = testRti._specializedTestResource;
+      if (object instanceof A.Object)
+        return !!object[tag];
+      return !!J.getInterceptor$(object)[tag];
+    },
+    _generalAsCheckImplementation(object) {
+      var testRti = this;
+      if (object == null) {
+        if (A.isNullable(testRti))
+          return object;
+      } else if (testRti._is(object))
+        return object;
+      A._failedAsCheck(object, testRti);
+    },
+    _generalNullableAsCheckImplementation(object) {
+      var testRti = this;
+      if (object == null)
+        return object;
+      else if (testRti._is(object))
+        return object;
+      A._failedAsCheck(object, testRti);
+    },
+    _failedAsCheck(object, testRti) {
+      throw A.wrapException(A._TypeError$fromMessage(A._Error_compose(object, A._rtiToString(testRti, null))));
+    },
+    _Error_compose(object, checkedTypeDescription) {
+      return A.Error_safeToString(object) + ": type '" + A._rtiToString(A._structuralTypeOf(object), null) + "' is not a subtype of type '" + checkedTypeDescription + "'";
+    },
+    _TypeError$fromMessage(message) {
+      return new A._TypeError("TypeError: " + message);
+    },
+    _TypeError__TypeError$forType(object, type) {
+      return new A._TypeError("TypeError: " + A._Error_compose(object, type));
+    },
+    _isFutureOr(object) {
+      var testRti = this,
+        unstarred = testRti._kind === 6 ? testRti._primary : testRti;
+      return unstarred._primary._is(object) || A.Rti__getFutureFromFutureOr(init.typeUniverse, unstarred)._is(object);
+    },
+    _isObject(object) {
+      return object != null;
+    },
+    _asObject(object) {
+      if (object != null)
+        return object;
+      throw A.wrapException(A._TypeError__TypeError$forType(object, "Object"));
+    },
+    _isTop(object) {
+      return true;
+    },
+    _asTop(object) {
+      return object;
+    },
+    _isNever(object) {
+      return false;
+    },
+    _isBool(object) {
+      return true === object || false === object;
+    },
+    _asBool(object) {
+      if (true === object)
+        return true;
+      if (false === object)
+        return false;
+      throw A.wrapException(A._TypeError__TypeError$forType(object, "bool"));
+    },
+    _asBoolS(object) {
+      if (true === object)
+        return true;
+      if (false === object)
+        return false;
+      if (object == null)
+        return object;
+      throw A.wrapException(A._TypeError__TypeError$forType(object, "bool"));
+    },
+    _asBoolQ(object) {
+      if (true === object)
+        return true;
+      if (false === object)
+        return false;
+      if (object == null)
+        return object;
+      throw A.wrapException(A._TypeError__TypeError$forType(object, "bool?"));
+    },
+    _asDouble(object) {
+      if (typeof object == "number")
+        return object;
+      throw A.wrapException(A._TypeError__TypeError$forType(object, "double"));
+    },
+    _asDoubleS(object) {
+      if (typeof object == "number")
+        return object;
+      if (object == null)
+        return object;
+      throw A.wrapException(A._TypeError__TypeError$forType(object, "double"));
+    },
+    _asDoubleQ(object) {
+      if (typeof object == "number")
+        return object;
+      if (object == null)
+        return object;
+      throw A.wrapException(A._TypeError__TypeError$forType(object, "double?"));
+    },
+    _isInt(object) {
+      return typeof object == "number" && Math.floor(object) === object;
+    },
+    _asInt(object) {
+      if (typeof object == "number" && Math.floor(object) === object)
+        return object;
+      throw A.wrapException(A._TypeError__TypeError$forType(object, "int"));
+    },
+    _asIntS(object) {
+      if (typeof object == "number" && Math.floor(object) === object)
+        return object;
+      if (object == null)
+        return object;
+      throw A.wrapException(A._TypeError__TypeError$forType(object, "int"));
+    },
+    _asIntQ(object) {
+      if (typeof object == "number" && Math.floor(object) === object)
+        return object;
+      if (object == null)
+        return object;
+      throw A.wrapException(A._TypeError__TypeError$forType(object, "int?"));
+    },
+    _isNum(object) {
+      return typeof object == "number";
+    },
+    _asNum(object) {
+      if (typeof object == "number")
+        return object;
+      throw A.wrapException(A._TypeError__TypeError$forType(object, "num"));
+    },
+    _asNumS(object) {
+      if (typeof object == "number")
+        return object;
+      if (object == null)
+        return object;
+      throw A.wrapException(A._TypeError__TypeError$forType(object, "num"));
+    },
+    _asNumQ(object) {
+      if (typeof object == "number")
+        return object;
+      if (object == null)
+        return object;
+      throw A.wrapException(A._TypeError__TypeError$forType(object, "num?"));
+    },
+    _isString(object) {
+      return typeof object == "string";
+    },
+    _asString(object) {
+      if (typeof object == "string")
+        return object;
+      throw A.wrapException(A._TypeError__TypeError$forType(object, "String"));
+    },
+    _asStringS(object) {
+      if (typeof object == "string")
+        return object;
+      if (object == null)
+        return object;
+      throw A.wrapException(A._TypeError__TypeError$forType(object, "String"));
+    },
+    _asStringQ(object) {
+      if (typeof object == "string")
+        return object;
+      if (object == null)
+        return object;
+      throw A.wrapException(A._TypeError__TypeError$forType(object, "String?"));
+    },
+    _rtiArrayToString(array, genericContext) {
+      var s, sep, i;
+      for (s = "", sep = "", i = 0; i < array.length; ++i, sep = ", ")
+        s += sep + A._rtiToString(array[i], genericContext);
+      return s;
+    },
+    _recordRtiToString(recordType, genericContext) {
+      var fieldCount, names, namesIndex, s, comma, i,
+        partialShape = recordType._primary,
+        fields = recordType._rest;
+      if ("" === partialShape)
+        return "(" + A._rtiArrayToString(fields, genericContext) + ")";
+      fieldCount = fields.length;
+      names = partialShape.split(",");
+      namesIndex = names.length - fieldCount;
+      for (s = "(", comma = "", i = 0; i < fieldCount; ++i, comma = ", ") {
+        s += comma;
+        if (namesIndex === 0)
+          s += "{";
+        s += A._rtiToString(fields[i], genericContext);
+        if (namesIndex >= 0)
+          s += " " + names[namesIndex];
+        ++namesIndex;
+      }
+      return s + "})";
+    },
+    _functionRtiToString(functionType, genericContext, bounds) {
+      var boundsLength, outerContextLength, offset, i, t1, t2, typeParametersText, typeSep, t3, t4, boundRti, kind, parameters, requiredPositional, requiredPositionalLength, optionalPositional, optionalPositionalLength, named, namedLength, returnTypeText, argumentsText, sep, _s2_ = ", ";
+      if (bounds != null) {
+        boundsLength = bounds.length;
+        if (genericContext == null) {
+          genericContext = A._setArrayType([], type$.JSArray_String);
+          outerContextLength = null;
+        } else
+          outerContextLength = genericContext.length;
+        offset = genericContext.length;
+        for (i = boundsLength; i > 0; --i)
+          B.JSArray_methods.add$1(genericContext, "T" + (offset + i));
+        for (t1 = type$.nullable_Object, t2 = type$.legacy_Object, typeParametersText = "<", typeSep = "", i = 0; i < boundsLength; ++i, typeSep = _s2_) {
+          t3 = genericContext.length;
+          t4 = t3 - 1 - i;
+          if (!(t4 >= 0))
+            return A.ioore(genericContext, t4);
+          typeParametersText = B.JSString_methods.$add(typeParametersText + typeSep, genericContext[t4]);
+          boundRti = bounds[i];
+          kind = boundRti._kind;
+          if (!(kind === 2 || kind === 3 || kind === 4 || kind === 5 || boundRti === t1))
+            t3 = boundRti === t2;
+          else
+            t3 = true;
+          if (!t3)
+            typeParametersText += " extends " + A._rtiToString(boundRti, genericContext);
+        }
+        typeParametersText += ">";
+      } else {
+        typeParametersText = "";
+        outerContextLength = null;
+      }
+      t1 = functionType._primary;
+      parameters = functionType._rest;
+      requiredPositional = parameters._requiredPositional;
+      requiredPositionalLength = requiredPositional.length;
+      optionalPositional = parameters._optionalPositional;
+      optionalPositionalLength = optionalPositional.length;
+      named = parameters._named;
+      namedLength = named.length;
+      returnTypeText = A._rtiToString(t1, genericContext);
+      for (argumentsText = "", sep = "", i = 0; i < requiredPositionalLength; ++i, sep = _s2_)
+        argumentsText += sep + A._rtiToString(requiredPositional[i], genericContext);
+      if (optionalPositionalLength > 0) {
+        argumentsText += sep + "[";
+        for (sep = "", i = 0; i < optionalPositionalLength; ++i, sep = _s2_)
+          argumentsText += sep + A._rtiToString(optionalPositional[i], genericContext);
+        argumentsText += "]";
+      }
+      if (namedLength > 0) {
+        argumentsText += sep + "{";
+        for (sep = "", i = 0; i < namedLength; i += 3, sep = _s2_) {
+          argumentsText += sep;
+          if (named[i + 1])
+            argumentsText += "required ";
+          argumentsText += A._rtiToString(named[i + 2], genericContext) + " " + named[i];
+        }
+        argumentsText += "}";
+      }
+      if (outerContextLength != null) {
+        genericContext.toString;
+        genericContext.length = outerContextLength;
+      }
+      return typeParametersText + "(" + argumentsText + ") => " + returnTypeText;
+    },
+    _rtiToString(rti, genericContext) {
+      var questionArgument, s, argumentKind, $name, $arguments, t1, t2,
+        kind = rti._kind;
+      if (kind === 5)
+        return "erased";
+      if (kind === 2)
+        return "dynamic";
+      if (kind === 3)
+        return "void";
+      if (kind === 1)
+        return "Never";
+      if (kind === 4)
+        return "any";
+      if (kind === 6)
+        return A._rtiToString(rti._primary, genericContext);
+      if (kind === 7) {
+        questionArgument = rti._primary;
+        s = A._rtiToString(questionArgument, genericContext);
+        argumentKind = questionArgument._kind;
+        return (argumentKind === 12 || argumentKind === 13 ? "(" + s + ")" : s) + "?";
+      }
+      if (kind === 8)
+        return "FutureOr<" + A._rtiToString(rti._primary, genericContext) + ">";
+      if (kind === 9) {
+        $name = A._unminifyOrTag(rti._primary);
+        $arguments = rti._rest;
+        return $arguments.length > 0 ? $name + ("<" + A._rtiArrayToString($arguments, genericContext) + ">") : $name;
+      }
+      if (kind === 11)
+        return A._recordRtiToString(rti, genericContext);
+      if (kind === 12)
+        return A._functionRtiToString(rti, genericContext, null);
+      if (kind === 13)
+        return A._functionRtiToString(rti._primary, genericContext, rti._rest);
+      if (kind === 14) {
+        t1 = rti._primary;
+        t2 = genericContext.length;
+        t1 = t2 - 1 - t1;
+        if (!(t1 >= 0 && t1 < t2))
+          return A.ioore(genericContext, t1);
+        return genericContext[t1];
+      }
+      return "?";
+    },
+    _unminifyOrTag(rawClassName) {
+      var preserved = init.mangledGlobalNames[rawClassName];
+      if (preserved != null)
+        return preserved;
+      return rawClassName;
+    },
+    _Universe_findRule(universe, targetType) {
+      var rule = universe.tR[targetType];
+      for (; typeof rule == "string";)
+        rule = universe.tR[rule];
+      return rule;
+    },
+    _Universe_findErasedType(universe, cls) {
+      var $length, erased, $arguments, i, $interface,
+        t1 = universe.eT,
+        probe = t1[cls];
+      if (probe == null)
+        return A._Universe_eval(universe, cls, false);
+      else if (typeof probe == "number") {
+        $length = probe;
+        erased = A._Universe__lookupTerminalRti(universe, 5, "#");
+        $arguments = A._Utils_newArrayOrEmpty($length);
+        for (i = 0; i < $length; ++i)
+          $arguments[i] = erased;
+        $interface = A._Universe__lookupInterfaceRti(universe, cls, $arguments);
+        t1[cls] = $interface;
+        return $interface;
+      } else
+        return probe;
+    },
+    _Universe_addRules(universe, rules) {
+      return A._Utils_objectAssign(universe.tR, rules);
+    },
+    _Universe_addErasedTypes(universe, types) {
+      return A._Utils_objectAssign(universe.eT, types);
+    },
+    _Universe_eval(universe, recipe, normalize) {
+      var rti,
+        t1 = universe.eC,
+        probe = t1.get(recipe);
+      if (probe != null)
+        return probe;
+      rti = A._Parser_parse(A._Parser_create(universe, null, recipe, normalize));
+      t1.set(recipe, rti);
+      return rti;
+    },
+    _Universe_evalInEnvironment(universe, environment, recipe) {
+      var probe, rti,
+        cache = environment._evalCache;
+      if (cache == null)
+        cache = environment._evalCache = new Map();
+      probe = cache.get(recipe);
+      if (probe != null)
+        return probe;
+      rti = A._Parser_parse(A._Parser_create(universe, environment, recipe, true));
+      cache.set(recipe, rti);
+      return rti;
+    },
+    _Universe_bind(universe, environment, argumentsRti) {
+      var argumentsRecipe, probe, rti,
+        cache = environment._bindCache;
+      if (cache == null)
+        cache = environment._bindCache = new Map();
+      argumentsRecipe = argumentsRti._canonicalRecipe;
+      probe = cache.get(argumentsRecipe);
+      if (probe != null)
+        return probe;
+      rti = A._Universe__lookupBindingRti(universe, environment, argumentsRti._kind === 10 ? argumentsRti._rest : [argumentsRti]);
+      cache.set(argumentsRecipe, rti);
+      return rti;
+    },
+    _Universe__installTypeTests(universe, rti) {
+      rti._as = A._installSpecializedAsCheck;
+      rti._is = A._installSpecializedIsTest;
+      return rti;
+    },
+    _Universe__lookupTerminalRti(universe, kind, key) {
+      var rti, t1,
+        probe = universe.eC.get(key);
+      if (probe != null)
+        return probe;
+      rti = new A.Rti(null, null);
+      rti._kind = kind;
+      rti._canonicalRecipe = key;
+      t1 = A._Universe__installTypeTests(universe, rti);
+      universe.eC.set(key, t1);
+      return t1;
+    },
+    _Universe__lookupStarRti(universe, baseType, normalize) {
+      var t1,
+        key = baseType._canonicalRecipe + "*",
+        probe = universe.eC.get(key);
+      if (probe != null)
+        return probe;
+      t1 = A._Universe__createStarRti(universe, baseType, key, normalize);
+      universe.eC.set(key, t1);
+      return t1;
+    },
+    _Universe__createStarRti(universe, baseType, key, normalize) {
+      var baseKind, t1, rti;
+      if (normalize) {
+        baseKind = baseType._kind;
+        if (!A.isSoundTopType(baseType))
+          t1 = baseType === type$.Null || baseType === type$.JSNull || baseKind === 7 || baseKind === 6;
+        else
+          t1 = true;
+        if (t1)
+          return baseType;
+      }
+      rti = new A.Rti(null, null);
+      rti._kind = 6;
+      rti._primary = baseType;
+      rti._canonicalRecipe = key;
+      return A._Universe__installTypeTests(universe, rti);
+    },
+    _Universe__lookupQuestionRti(universe, baseType, normalize) {
+      var t1,
+        key = baseType._canonicalRecipe + "?",
+        probe = universe.eC.get(key);
+      if (probe != null)
+        return probe;
+      t1 = A._Universe__createQuestionRti(universe, baseType, key, normalize);
+      universe.eC.set(key, t1);
+      return t1;
+    },
+    _Universe__createQuestionRti(universe, baseType, key, normalize) {
+      var baseKind, t1, starArgument, rti;
+      if (normalize) {
+        baseKind = baseType._kind;
+        if (!A.isSoundTopType(baseType))
+          if (!(baseType === type$.Null || baseType === type$.JSNull))
+            if (baseKind !== 7)
+              t1 = baseKind === 8 && A.isNullable(baseType._primary);
+            else
+              t1 = true;
+          else
+            t1 = true;
+        else
+          t1 = true;
+        if (t1)
+          return baseType;
+        else if (baseKind === 1 || baseType === type$.legacy_Never)
+          return type$.Null;
+        else if (baseKind === 6) {
+          starArgument = baseType._primary;
+          if (starArgument._kind === 8 && A.isNullable(starArgument._primary))
+            return starArgument;
+          else
+            return A.Rti__getQuestionFromStar(universe, baseType);
+        }
+      }
+      rti = new A.Rti(null, null);
+      rti._kind = 7;
+      rti._primary = baseType;
+      rti._canonicalRecipe = key;
+      return A._Universe__installTypeTests(universe, rti);
+    },
+    _Universe__lookupFutureOrRti(universe, baseType, normalize) {
+      var t1,
+        key = baseType._canonicalRecipe + "/",
+        probe = universe.eC.get(key);
+      if (probe != null)
+        return probe;
+      t1 = A._Universe__createFutureOrRti(universe, baseType, key, normalize);
+      universe.eC.set(key, t1);
+      return t1;
+    },
+    _Universe__createFutureOrRti(universe, baseType, key, normalize) {
+      var t1, rti;
+      if (normalize) {
+        t1 = baseType._kind;
+        if (A.isSoundTopType(baseType) || baseType === type$.Object || baseType === type$.legacy_Object)
+          return baseType;
+        else if (t1 === 1)
+          return A._Universe__lookupInterfaceRti(universe, "Future", [baseType]);
+        else if (baseType === type$.Null || baseType === type$.JSNull)
+          return type$.nullable_Future_Null;
+      }
+      rti = new A.Rti(null, null);
+      rti._kind = 8;
+      rti._primary = baseType;
+      rti._canonicalRecipe = key;
+      return A._Universe__installTypeTests(universe, rti);
+    },
+    _Universe__lookupGenericFunctionParameterRti(universe, index) {
+      var rti, t1,
+        key = "" + index + "^",
+        probe = universe.eC.get(key);
+      if (probe != null)
+        return probe;
+      rti = new A.Rti(null, null);
+      rti._kind = 14;
+      rti._primary = index;
+      rti._canonicalRecipe = key;
+      t1 = A._Universe__installTypeTests(universe, rti);
+      universe.eC.set(key, t1);
+      return t1;
+    },
+    _Universe__canonicalRecipeJoin($arguments) {
+      var s, sep, i,
+        $length = $arguments.length;
+      for (s = "", sep = "", i = 0; i < $length; ++i, sep = ",")
+        s += sep + $arguments[i]._canonicalRecipe;
+      return s;
+    },
+    _Universe__canonicalRecipeJoinNamed($arguments) {
+      var s, sep, i, t1, nameSep,
+        $length = $arguments.length;
+      for (s = "", sep = "", i = 0; i < $length; i += 3, sep = ",") {
+        t1 = $arguments[i];
+        nameSep = $arguments[i + 1] ? "!" : ":";
+        s += sep + t1 + nameSep + $arguments[i + 2]._canonicalRecipe;
+      }
+      return s;
+    },
+    _Universe__lookupInterfaceRti(universe, $name, $arguments) {
+      var probe, rti, t1,
+        s = $name;
+      if ($arguments.length > 0)
+        s += "<" + A._Universe__canonicalRecipeJoin($arguments) + ">";
+      probe = universe.eC.get(s);
+      if (probe != null)
+        return probe;
+      rti = new A.Rti(null, null);
+      rti._kind = 9;
+      rti._primary = $name;
+      rti._rest = $arguments;
+      if ($arguments.length > 0)
+        rti._precomputed1 = $arguments[0];
+      rti._canonicalRecipe = s;
+      t1 = A._Universe__installTypeTests(universe, rti);
+      universe.eC.set(s, t1);
+      return t1;
+    },
+    _Universe__lookupBindingRti(universe, base, $arguments) {
+      var newBase, newArguments, key, probe, rti, t1;
+      if (base._kind === 10) {
+        newBase = base._primary;
+        newArguments = base._rest.concat($arguments);
+      } else {
+        newArguments = $arguments;
+        newBase = base;
+      }
+      key = newBase._canonicalRecipe + (";<" + A._Universe__canonicalRecipeJoin(newArguments) + ">");
+      probe = universe.eC.get(key);
+      if (probe != null)
+        return probe;
+      rti = new A.Rti(null, null);
+      rti._kind = 10;
+      rti._primary = newBase;
+      rti._rest = newArguments;
+      rti._canonicalRecipe = key;
+      t1 = A._Universe__installTypeTests(universe, rti);
+      universe.eC.set(key, t1);
+      return t1;
+    },
+    _Universe__lookupRecordRti(universe, partialShapeTag, fields) {
+      var rti, t1,
+        key = "+" + (partialShapeTag + "(" + A._Universe__canonicalRecipeJoin(fields) + ")"),
+        probe = universe.eC.get(key);
+      if (probe != null)
+        return probe;
+      rti = new A.Rti(null, null);
+      rti._kind = 11;
+      rti._primary = partialShapeTag;
+      rti._rest = fields;
+      rti._canonicalRecipe = key;
+      t1 = A._Universe__installTypeTests(universe, rti);
+      universe.eC.set(key, t1);
+      return t1;
+    },
+    _Universe__lookupFunctionRti(universe, returnType, parameters) {
+      var sep, key, probe, rti, t1,
+        s = returnType._canonicalRecipe,
+        requiredPositional = parameters._requiredPositional,
+        requiredPositionalLength = requiredPositional.length,
+        optionalPositional = parameters._optionalPositional,
+        optionalPositionalLength = optionalPositional.length,
+        named = parameters._named,
+        namedLength = named.length,
+        recipe = "(" + A._Universe__canonicalRecipeJoin(requiredPositional);
+      if (optionalPositionalLength > 0) {
+        sep = requiredPositionalLength > 0 ? "," : "";
+        recipe += sep + "[" + A._Universe__canonicalRecipeJoin(optionalPositional) + "]";
+      }
+      if (namedLength > 0) {
+        sep = requiredPositionalLength > 0 ? "," : "";
+        recipe += sep + "{" + A._Universe__canonicalRecipeJoinNamed(named) + "}";
+      }
+      key = s + (recipe + ")");
+      probe = universe.eC.get(key);
+      if (probe != null)
+        return probe;
+      rti = new A.Rti(null, null);
+      rti._kind = 12;
+      rti._primary = returnType;
+      rti._rest = parameters;
+      rti._canonicalRecipe = key;
+      t1 = A._Universe__installTypeTests(universe, rti);
+      universe.eC.set(key, t1);
+      return t1;
+    },
+    _Universe__lookupGenericFunctionRti(universe, baseFunctionType, bounds, normalize) {
+      var t1,
+        key = baseFunctionType._canonicalRecipe + ("<" + A._Universe__canonicalRecipeJoin(bounds) + ">"),
+        probe = universe.eC.get(key);
+      if (probe != null)
+        return probe;
+      t1 = A._Universe__createGenericFunctionRti(universe, baseFunctionType, bounds, key, normalize);
+      universe.eC.set(key, t1);
+      return t1;
+    },
+    _Universe__createGenericFunctionRti(universe, baseFunctionType, bounds, key, normalize) {
+      var $length, typeArguments, count, i, bound, substitutedBase, substitutedBounds, rti;
+      if (normalize) {
+        $length = bounds.length;
+        typeArguments = A._Utils_newArrayOrEmpty($length);
+        for (count = 0, i = 0; i < $length; ++i) {
+          bound = bounds[i];
+          if (bound._kind === 1) {
+            typeArguments[i] = bound;
+            ++count;
+          }
+        }
+        if (count > 0) {
+          substitutedBase = A._substitute(universe, baseFunctionType, typeArguments, 0);
+          substitutedBounds = A._substituteArray(universe, bounds, typeArguments, 0);
+          return A._Universe__lookupGenericFunctionRti(universe, substitutedBase, substitutedBounds, bounds !== substitutedBounds);
+        }
+      }
+      rti = new A.Rti(null, null);
+      rti._kind = 13;
+      rti._primary = baseFunctionType;
+      rti._rest = bounds;
+      rti._canonicalRecipe = key;
+      return A._Universe__installTypeTests(universe, rti);
+    },
+    _Parser_create(universe, environment, recipe, normalize) {
+      return {u: universe, e: environment, r: recipe, s: [], p: 0, n: normalize};
+    },
+    _Parser_parse(parser) {
+      var t2, i, ch, t3, array, end, item,
+        source = parser.r,
+        t1 = parser.s;
+      for (t2 = source.length, i = 0; i < t2;) {
+        ch = source.charCodeAt(i);
+        if (ch >= 48 && ch <= 57)
+          i = A._Parser_handleDigit(i + 1, ch, source, t1);
+        else if ((((ch | 32) >>> 0) - 97 & 65535) < 26 || ch === 95 || ch === 36 || ch === 124)
+          i = A._Parser_handleIdentifier(parser, i, source, t1, false);
+        else if (ch === 46)
+          i = A._Parser_handleIdentifier(parser, i, source, t1, true);
+        else {
+          ++i;
+          switch (ch) {
+            case 44:
+              break;
+            case 58:
+              t1.push(false);
+              break;
+            case 33:
+              t1.push(true);
+              break;
+            case 59:
+              t1.push(A._Parser_toType(parser.u, parser.e, t1.pop()));
+              break;
+            case 94:
+              t1.push(A._Universe__lookupGenericFunctionParameterRti(parser.u, t1.pop()));
+              break;
+            case 35:
+              t1.push(A._Universe__lookupTerminalRti(parser.u, 5, "#"));
+              break;
+            case 64:
+              t1.push(A._Universe__lookupTerminalRti(parser.u, 2, "@"));
+              break;
+            case 126:
+              t1.push(A._Universe__lookupTerminalRti(parser.u, 3, "~"));
+              break;
+            case 60:
+              t1.push(parser.p);
+              parser.p = t1.length;
+              break;
+            case 62:
+              A._Parser_handleTypeArguments(parser, t1);
+              break;
+            case 38:
+              A._Parser_handleExtendedOperations(parser, t1);
+              break;
+            case 42:
+              t3 = parser.u;
+              t1.push(A._Universe__lookupStarRti(t3, A._Parser_toType(t3, parser.e, t1.pop()), parser.n));
+              break;
+            case 63:
+              t3 = parser.u;
+              t1.push(A._Universe__lookupQuestionRti(t3, A._Parser_toType(t3, parser.e, t1.pop()), parser.n));
+              break;
+            case 47:
+              t3 = parser.u;
+              t1.push(A._Universe__lookupFutureOrRti(t3, A._Parser_toType(t3, parser.e, t1.pop()), parser.n));
+              break;
+            case 40:
+              t1.push(-3);
+              t1.push(parser.p);
+              parser.p = t1.length;
+              break;
+            case 41:
+              A._Parser_handleArguments(parser, t1);
+              break;
+            case 91:
+              t1.push(parser.p);
+              parser.p = t1.length;
+              break;
+            case 93:
+              array = t1.splice(parser.p);
+              A._Parser_toTypes(parser.u, parser.e, array);
+              parser.p = t1.pop();
+              t1.push(array);
+              t1.push(-1);
+              break;
+            case 123:
+              t1.push(parser.p);
+              parser.p = t1.length;
+              break;
+            case 125:
+              array = t1.splice(parser.p);
+              A._Parser_toTypesNamed(parser.u, parser.e, array);
+              parser.p = t1.pop();
+              t1.push(array);
+              t1.push(-2);
+              break;
+            case 43:
+              end = source.indexOf("(", i);
+              t1.push(source.substring(i, end));
+              t1.push(-4);
+              t1.push(parser.p);
+              parser.p = t1.length;
+              i = end + 1;
+              break;
+            default:
+              throw "Bad character " + ch;
+          }
+        }
+      }
+      item = t1.pop();
+      return A._Parser_toType(parser.u, parser.e, item);
+    },
+    _Parser_handleDigit(i, digit, source, stack) {
+      var t1, ch,
+        value = digit - 48;
+      for (t1 = source.length; i < t1; ++i) {
+        ch = source.charCodeAt(i);
+        if (!(ch >= 48 && ch <= 57))
+          break;
+        value = value * 10 + (ch - 48);
+      }
+      stack.push(value);
+      return i;
+    },
+    _Parser_handleIdentifier(parser, start, source, stack, hasPeriod) {
+      var t1, ch, t2, string, environment, recipe,
+        i = start + 1;
+      for (t1 = source.length; i < t1; ++i) {
+        ch = source.charCodeAt(i);
+        if (ch === 46) {
+          if (hasPeriod)
+            break;
+          hasPeriod = true;
+        } else {
+          if (!((((ch | 32) >>> 0) - 97 & 65535) < 26 || ch === 95 || ch === 36 || ch === 124))
+            t2 = ch >= 48 && ch <= 57;
+          else
+            t2 = true;
+          if (!t2)
+            break;
+        }
+      }
+      string = source.substring(start, i);
+      if (hasPeriod) {
+        t1 = parser.u;
+        environment = parser.e;
+        if (environment._kind === 10)
+          environment = environment._primary;
+        recipe = A._Universe_findRule(t1, environment._primary)[string];
+        if (recipe == null)
+          A.throwExpression('No "' + string + '" in "' + A.Rti__getCanonicalRecipe(environment) + '"');
+        stack.push(A._Universe_evalInEnvironment(t1, environment, recipe));
+      } else
+        stack.push(string);
+      return i;
+    },
+    _Parser_handleTypeArguments(parser, stack) {
+      var base,
+        t1 = parser.u,
+        $arguments = A._Parser_collectArray(parser, stack),
+        head = stack.pop();
+      if (typeof head == "string")
+        stack.push(A._Universe__lookupInterfaceRti(t1, head, $arguments));
+      else {
+        base = A._Parser_toType(t1, parser.e, head);
+        switch (base._kind) {
+          case 12:
+            stack.push(A._Universe__lookupGenericFunctionRti(t1, base, $arguments, parser.n));
+            break;
+          default:
+            stack.push(A._Universe__lookupBindingRti(t1, base, $arguments));
+            break;
+        }
+      }
+    },
+    _Parser_handleArguments(parser, stack) {
+      var optionalPositional, named, requiredPositional, returnType, parameters, _null = null,
+        t1 = parser.u,
+        head = stack.pop();
+      if (typeof head == "number")
+        switch (head) {
+          case -1:
+            optionalPositional = stack.pop();
+            named = _null;
+            break;
+          case -2:
+            named = stack.pop();
+            optionalPositional = _null;
+            break;
+          default:
+            stack.push(head);
+            named = _null;
+            optionalPositional = named;
+            break;
+        }
+      else {
+        stack.push(head);
+        named = _null;
+        optionalPositional = named;
+      }
+      requiredPositional = A._Parser_collectArray(parser, stack);
+      head = stack.pop();
+      switch (head) {
+        case -3:
+          head = stack.pop();
+          if (optionalPositional == null)
+            optionalPositional = t1.sEA;
+          if (named == null)
+            named = t1.sEA;
+          returnType = A._Parser_toType(t1, parser.e, head);
+          parameters = new A._FunctionParameters();
+          parameters._requiredPositional = requiredPositional;
+          parameters._optionalPositional = optionalPositional;
+          parameters._named = named;
+          stack.push(A._Universe__lookupFunctionRti(t1, returnType, parameters));
+          return;
+        case -4:
+          stack.push(A._Universe__lookupRecordRti(t1, stack.pop(), requiredPositional));
+          return;
+        default:
+          throw A.wrapException(A.AssertionError$("Unexpected state under `()`: " + A.S(head)));
+      }
+    },
+    _Parser_handleExtendedOperations(parser, stack) {
+      var $top = stack.pop();
+      if (0 === $top) {
+        stack.push(A._Universe__lookupTerminalRti(parser.u, 1, "0&"));
+        return;
+      }
+      if (1 === $top) {
+        stack.push(A._Universe__lookupTerminalRti(parser.u, 4, "1&"));
+        return;
+      }
+      throw A.wrapException(A.AssertionError$("Unexpected extended operation " + A.S($top)));
+    },
+    _Parser_collectArray(parser, stack) {
+      var array = stack.splice(parser.p);
+      A._Parser_toTypes(parser.u, parser.e, array);
+      parser.p = stack.pop();
+      return array;
+    },
+    _Parser_toType(universe, environment, item) {
+      if (typeof item == "string")
+        return A._Universe__lookupInterfaceRti(universe, item, universe.sEA);
+      else if (typeof item == "number") {
+        environment.toString;
+        return A._Parser_indexToType(universe, environment, item);
+      } else
+        return item;
+    },
+    _Parser_toTypes(universe, environment, items) {
+      var i,
+        $length = items.length;
+      for (i = 0; i < $length; ++i)
+        items[i] = A._Parser_toType(universe, environment, items[i]);
+    },
+    _Parser_toTypesNamed(universe, environment, items) {
+      var i,
+        $length = items.length;
+      for (i = 2; i < $length; i += 3)
+        items[i] = A._Parser_toType(universe, environment, items[i]);
+    },
+    _Parser_indexToType(universe, environment, index) {
+      var typeArguments, len,
+        kind = environment._kind;
+      if (kind === 10) {
+        if (index === 0)
+          return environment._primary;
+        typeArguments = environment._rest;
+        len = typeArguments.length;
+        if (index <= len)
+          return typeArguments[index - 1];
+        index -= len;
+        environment = environment._primary;
+        kind = environment._kind;
+      } else if (index === 0)
+        return environment;
+      if (kind !== 9)
+        throw A.wrapException(A.AssertionError$("Indexed base must be an interface type"));
+      typeArguments = environment._rest;
+      if (index <= typeArguments.length)
+        return typeArguments[index - 1];
+      throw A.wrapException(A.AssertionError$("Bad index " + index + " for " + environment.toString$0(0)));
+    },
+    isSubtype(universe, s, t) {
+      var result,
+        sCache = s._isSubtypeCache;
+      if (sCache == null)
+        sCache = s._isSubtypeCache = new Map();
+      result = sCache.get(t);
+      if (result == null) {
+        result = A._isSubtype(universe, s, null, t, null, false) ? 1 : 0;
+        sCache.set(t, result);
+      }
+      if (0 === result)
+        return false;
+      if (1 === result)
+        return true;
+      return true;
+    },
+    _isSubtype(universe, s, sEnv, t, tEnv, isLegacy) {
+      var t1, sKind, leftTypeVariable, tKind, t2, sBounds, tBounds, sLength, i, sBound, tBound;
+      if (s === t)
+        return true;
+      if (!A.isSoundTopType(t))
+        t1 = t === type$.legacy_Object;
+      else
+        t1 = true;
+      if (t1)
+        return true;
+      sKind = s._kind;
+      if (sKind === 4)
+        return true;
+      if (A.isSoundTopType(s))
+        return false;
+      t1 = s._kind;
+      if (t1 === 1)
+        return true;
+      leftTypeVariable = sKind === 14;
+      if (leftTypeVariable)
+        if (A._isSubtype(universe, sEnv[s._primary], sEnv, t, tEnv, false))
+          return true;
+      tKind = t._kind;
+      t1 = s === type$.Null || s === type$.JSNull;
+      if (t1) {
+        if (tKind === 8)
+          return A._isSubtype(universe, s, sEnv, t._primary, tEnv, false);
+        return t === type$.Null || t === type$.JSNull || tKind === 7 || tKind === 6;
+      }
+      if (t === type$.Object) {
+        if (sKind === 8)
+          return A._isSubtype(universe, s._primary, sEnv, t, tEnv, false);
+        if (sKind === 6)
+          return A._isSubtype(universe, s._primary, sEnv, t, tEnv, false);
+        return sKind !== 7;
+      }
+      if (sKind === 6)
+        return A._isSubtype(universe, s._primary, sEnv, t, tEnv, false);
+      if (tKind === 6) {
+        t1 = A.Rti__getQuestionFromStar(universe, t);
+        return A._isSubtype(universe, s, sEnv, t1, tEnv, false);
+      }
+      if (sKind === 8) {
+        if (!A._isSubtype(universe, s._primary, sEnv, t, tEnv, false))
+          return false;
+        return A._isSubtype(universe, A.Rti__getFutureFromFutureOr(universe, s), sEnv, t, tEnv, false);
+      }
+      if (sKind === 7) {
+        t1 = A._isSubtype(universe, type$.Null, sEnv, t, tEnv, false);
+        return t1 && A._isSubtype(universe, s._primary, sEnv, t, tEnv, false);
+      }
+      if (tKind === 8) {
+        if (A._isSubtype(universe, s, sEnv, t._primary, tEnv, false))
+          return true;
+        return A._isSubtype(universe, s, sEnv, A.Rti__getFutureFromFutureOr(universe, t), tEnv, false);
+      }
+      if (tKind === 7) {
+        t1 = A._isSubtype(universe, s, sEnv, type$.Null, tEnv, false);
+        return t1 || A._isSubtype(universe, s, sEnv, t._primary, tEnv, false);
+      }
+      if (leftTypeVariable)
+        return false;
+      t1 = sKind !== 12;
+      if ((!t1 || sKind === 13) && t === type$.Function)
+        return true;
+      t2 = sKind === 11;
+      if (t2 && t === type$.Record)
+        return true;
+      if (tKind === 13) {
+        if (s === type$.JavaScriptFunction)
+          return true;
+        if (sKind !== 13)
+          return false;
+        sBounds = s._rest;
+        tBounds = t._rest;
+        sLength = sBounds.length;
+        if (sLength !== tBounds.length)
+          return false;
+        sEnv = sEnv == null ? sBounds : sBounds.concat(sEnv);
+        tEnv = tEnv == null ? tBounds : tBounds.concat(tEnv);
+        for (i = 0; i < sLength; ++i) {
+          sBound = sBounds[i];
+          tBound = tBounds[i];
+          if (!A._isSubtype(universe, sBound, sEnv, tBound, tEnv, false) || !A._isSubtype(universe, tBound, tEnv, sBound, sEnv, false))
+            return false;
+        }
+        return A._isFunctionSubtype(universe, s._primary, sEnv, t._primary, tEnv, false);
+      }
+      if (tKind === 12) {
+        if (s === type$.JavaScriptFunction)
+          return true;
+        if (t1)
+          return false;
+        return A._isFunctionSubtype(universe, s, sEnv, t, tEnv, false);
+      }
+      if (sKind === 9) {
+        if (tKind !== 9)
+          return false;
+        return A._isInterfaceSubtype(universe, s, sEnv, t, tEnv, false);
+      }
+      if (t2 && tKind === 11)
+        return A._isRecordSubtype(universe, s, sEnv, t, tEnv, false);
+      return false;
+    },
+    _isFunctionSubtype(universe, s, sEnv, t, tEnv, isLegacy) {
+      var sParameters, tParameters, sRequiredPositional, tRequiredPositional, sRequiredPositionalLength, tRequiredPositionalLength, requiredPositionalDelta, sOptionalPositional, tOptionalPositional, sOptionalPositionalLength, tOptionalPositionalLength, i, t1, sNamed, tNamed, sNamedLength, tNamedLength, sIndex, tIndex, tName, sName, sIsRequired;
+      if (!A._isSubtype(universe, s._primary, sEnv, t._primary, tEnv, false))
+        return false;
+      sParameters = s._rest;
+      tParameters = t._rest;
+      sRequiredPositional = sParameters._requiredPositional;
+      tRequiredPositional = tParameters._requiredPositional;
+      sRequiredPositionalLength = sRequiredPositional.length;
+      tRequiredPositionalLength = tRequiredPositional.length;
+      if (sRequiredPositionalLength > tRequiredPositionalLength)
+        return false;
+      requiredPositionalDelta = tRequiredPositionalLength - sRequiredPositionalLength;
+      sOptionalPositional = sParameters._optionalPositional;
+      tOptionalPositional = tParameters._optionalPositional;
+      sOptionalPositionalLength = sOptionalPositional.length;
+      tOptionalPositionalLength = tOptionalPositional.length;
+      if (sRequiredPositionalLength + sOptionalPositionalLength < tRequiredPositionalLength + tOptionalPositionalLength)
+        return false;
+      for (i = 0; i < sRequiredPositionalLength; ++i) {
+        t1 = sRequiredPositional[i];
+        if (!A._isSubtype(universe, tRequiredPositional[i], tEnv, t1, sEnv, false))
+          return false;
+      }
+      for (i = 0; i < requiredPositionalDelta; ++i) {
+        t1 = sOptionalPositional[i];
+        if (!A._isSubtype(universe, tRequiredPositional[sRequiredPositionalLength + i], tEnv, t1, sEnv, false))
+          return false;
+      }
+      for (i = 0; i < tOptionalPositionalLength; ++i) {
+        t1 = sOptionalPositional[requiredPositionalDelta + i];
+        if (!A._isSubtype(universe, tOptionalPositional[i], tEnv, t1, sEnv, false))
+          return false;
+      }
+      sNamed = sParameters._named;
+      tNamed = tParameters._named;
+      sNamedLength = sNamed.length;
+      tNamedLength = tNamed.length;
+      for (sIndex = 0, tIndex = 0; tIndex < tNamedLength; tIndex += 3) {
+        tName = tNamed[tIndex];
+        for (; true;) {
+          if (sIndex >= sNamedLength)
+            return false;
+          sName = sNamed[sIndex];
+          sIndex += 3;
+          if (tName < sName)
+            return false;
+          sIsRequired = sNamed[sIndex - 2];
+          if (sName < tName) {
+            if (sIsRequired)
+              return false;
+            continue;
+          }
+          t1 = tNamed[tIndex + 1];
+          if (sIsRequired && !t1)
+            return false;
+          t1 = sNamed[sIndex - 1];
+          if (!A._isSubtype(universe, tNamed[tIndex + 2], tEnv, t1, sEnv, false))
+            return false;
+          break;
+        }
+      }
+      for (; sIndex < sNamedLength;) {
+        if (sNamed[sIndex + 1])
+          return false;
+        sIndex += 3;
+      }
+      return true;
+    },
+    _isInterfaceSubtype(universe, s, sEnv, t, tEnv, isLegacy) {
+      var rule, recipes, $length, supertypeArgs, i,
+        sName = s._primary,
+        tName = t._primary;
+      for (; sName !== tName;) {
+        rule = universe.tR[sName];
+        if (rule == null)
+          return false;
+        if (typeof rule == "string") {
+          sName = rule;
+          continue;
+        }
+        recipes = rule[tName];
+        if (recipes == null)
+          return false;
+        $length = recipes.length;
+        supertypeArgs = $length > 0 ? new Array($length) : init.typeUniverse.sEA;
+        for (i = 0; i < $length; ++i)
+          supertypeArgs[i] = A._Universe_evalInEnvironment(universe, s, recipes[i]);
+        return A._areArgumentsSubtypes(universe, supertypeArgs, null, sEnv, t._rest, tEnv, false);
+      }
+      return A._areArgumentsSubtypes(universe, s._rest, null, sEnv, t._rest, tEnv, false);
+    },
+    _areArgumentsSubtypes(universe, sArgs, sVariances, sEnv, tArgs, tEnv, isLegacy) {
+      var i,
+        $length = sArgs.length;
+      for (i = 0; i < $length; ++i)
+        if (!A._isSubtype(universe, sArgs[i], sEnv, tArgs[i], tEnv, false))
+          return false;
+      return true;
+    },
+    _isRecordSubtype(universe, s, sEnv, t, tEnv, isLegacy) {
+      var i,
+        sFields = s._rest,
+        tFields = t._rest,
+        sCount = sFields.length;
+      if (sCount !== tFields.length)
+        return false;
+      if (s._primary !== t._primary)
+        return false;
+      for (i = 0; i < sCount; ++i)
+        if (!A._isSubtype(universe, sFields[i], sEnv, tFields[i], tEnv, false))
+          return false;
+      return true;
+    },
+    isNullable(t) {
+      var t1,
+        kind = t._kind;
+      if (!(t === type$.Null || t === type$.JSNull))
+        if (!A.isSoundTopType(t))
+          if (kind !== 7)
+            if (!(kind === 6 && A.isNullable(t._primary)))
+              t1 = kind === 8 && A.isNullable(t._primary);
+            else
+              t1 = true;
+          else
+            t1 = true;
+        else
+          t1 = true;
+      else
+        t1 = true;
+      return t1;
+    },
+    isDefinitelyTopType(t) {
+      var t1;
+      if (!A.isSoundTopType(t))
+        t1 = t === type$.legacy_Object;
+      else
+        t1 = true;
+      return t1;
+    },
+    isSoundTopType(t) {
+      var kind = t._kind;
+      return kind === 2 || kind === 3 || kind === 4 || kind === 5 || t === type$.nullable_Object;
+    },
+    _Utils_objectAssign(o, other) {
+      var i, key,
+        keys = Object.keys(other),
+        $length = keys.length;
+      for (i = 0; i < $length; ++i) {
+        key = keys[i];
+        o[key] = other[key];
+      }
+    },
+    _Utils_newArrayOrEmpty($length) {
+      return $length > 0 ? new Array($length) : init.typeUniverse.sEA;
+    },
+    Rti: function Rti(t0, t1) {
+      var _ = this;
+      _._as = t0;
+      _._is = t1;
+      _._cachedRuntimeType = _._specializedTestResource = _._isSubtypeCache = _._precomputed1 = null;
+      _._kind = 0;
+      _._canonicalRecipe = _._bindCache = _._evalCache = _._rest = _._primary = null;
+    },
+    _FunctionParameters: function _FunctionParameters() {
+      this._named = this._optionalPositional = this._requiredPositional = null;
+    },
+    _Type: function _Type(t0) {
+      this._rti = t0;
+    },
+    _Error: function _Error() {
+    },
+    _TypeError: function _TypeError(t0) {
+      this.__rti$_message = t0;
+    },
+    _AsyncRun__initializeScheduleImmediate() {
+      var div, span, t1 = {};
+      if (self.scheduleImmediate != null)
+        return A.async__AsyncRun__scheduleImmediateJsOverride$closure();
+      if (self.MutationObserver != null && self.document != null) {
+        div = self.document.createElement("div");
+        span = self.document.createElement("span");
+        t1.storedCallback = null;
+        new self.MutationObserver(A.convertDartClosureToJS(new A._AsyncRun__initializeScheduleImmediate_internalCallback(t1), 1)).observe(div, {childList: true});
+        return new A._AsyncRun__initializeScheduleImmediate_closure(t1, div, span);
+      } else if (self.setImmediate != null)
+        return A.async__AsyncRun__scheduleImmediateWithSetImmediate$closure();
+      return A.async__AsyncRun__scheduleImmediateWithTimer$closure();
+    },
+    _AsyncRun__scheduleImmediateJsOverride(callback) {
+      self.scheduleImmediate(A.convertDartClosureToJS(new A._AsyncRun__scheduleImmediateJsOverride_internalCallback(type$.void_Function._as(callback)), 0));
+    },
+    _AsyncRun__scheduleImmediateWithSetImmediate(callback) {
+      self.setImmediate(A.convertDartClosureToJS(new A._AsyncRun__scheduleImmediateWithSetImmediate_internalCallback(type$.void_Function._as(callback)), 0));
+    },
+    _AsyncRun__scheduleImmediateWithTimer(callback) {
+      A.Timer__createTimer(B.Duration_0, type$.void_Function._as(callback));
+    },
+    Timer__createTimer(duration, callback) {
+      return A._TimerImpl$(duration._duration / 1000 | 0, callback);
+    },
+    _TimerImpl$(milliseconds, callback) {
+      var t1 = new A._TimerImpl();
+      t1._TimerImpl$2(milliseconds, callback);
+      return t1;
+    },
+    _makeAsyncAwaitCompleter($T) {
+      return new A._AsyncAwaitCompleter(new A._Future($.Zone__current, $T._eval$1("_Future<0>")), $T._eval$1("_AsyncAwaitCompleter<0>"));
+    },
+    _asyncStartSync(bodyFunction, completer) {
+      bodyFunction.call$2(0, null);
+      completer.isSync = true;
+      return completer._future;
+    },
+    _asyncAwait(object, bodyFunction) {
+      A._awaitOnObject(object, bodyFunction);
+    },
+    _asyncReturn(object, completer) {
+      completer.complete$1(object);
+    },
+    _asyncRethrow(object, completer) {
+      completer.completeError$2(A.unwrapException(object), A.getTraceFromException(object));
+    },
+    _awaitOnObject(object, bodyFunction) {
+      var t1, future,
+        thenCallback = new A._awaitOnObject_closure(bodyFunction),
+        errorCallback = new A._awaitOnObject_closure0(bodyFunction);
+      if (object instanceof A._Future)
+        object._thenAwait$1$2(thenCallback, errorCallback, type$.dynamic);
+      else {
+        t1 = type$.dynamic;
+        if (object instanceof A._Future)
+          object.then$1$2$onError(thenCallback, errorCallback, t1);
+        else {
+          future = new A._Future($.Zone__current, type$._Future_dynamic);
+          future._state = 8;
+          future._resultOrListeners = object;
+          future._thenAwait$1$2(thenCallback, errorCallback, t1);
+        }
+      }
+    },
+    _wrapJsFunctionForAsync($function) {
+      var $protected = function(fn, ERROR) {
+        return function(errorCode, result) {
+          while (true) {
+            try {
+              fn(errorCode, result);
+              break;
+            } catch (error) {
+              result = error;
+              errorCode = ERROR;
+            }
+          }
+        };
+      }($function, 1);
+      return $.Zone__current.registerBinaryCallback$3$1(new A._wrapJsFunctionForAsync_closure($protected), type$.void, type$.int, type$.dynamic);
+    },
+    AsyncError$(error, stackTrace) {
+      var t1 = A.checkNotNullable(error, "error", type$.Object);
+      return new A.AsyncError(t1, stackTrace == null ? A.AsyncError_defaultStackTrace(error) : stackTrace);
+    },
+    AsyncError_defaultStackTrace(error) {
+      var stackTrace;
+      if (type$.Error._is(error)) {
+        stackTrace = error.get$stackTrace();
+        if (stackTrace != null)
+          return stackTrace;
+      }
+      return B._StringStackTrace_3uE;
+    },
+    Future_Future$sync(computation, $T) {
+      var result, error, stackTrace, future, replacement, t1, exception;
+      try {
+        result = computation.call$0();
+        t1 = $T._eval$1("Future<0>")._is(result) ? result : A._Future$value(result, $T);
+        return t1;
+      } catch (exception) {
+        error = A.unwrapException(exception);
+        stackTrace = A.getTraceFromException(exception);
+        future = new A._Future($.Zone__current, $T._eval$1("_Future<0>"));
+        type$.Object._as(error);
+        type$.nullable_StackTrace._as(stackTrace);
+        replacement = null;
+        if (replacement != null)
+          future._asyncCompleteError$2(replacement.get$error(), replacement.get$stackTrace());
+        else
+          future._asyncCompleteError$2(error, stackTrace);
+        return future;
+      }
+    },
+    Future_Future$value(value, $T) {
+      var t1 = value == null ? $T._as(value) : value,
+        t2 = new A._Future($.Zone__current, $T._eval$1("_Future<0>"));
+      t2._asyncComplete$1(t1);
+      return t2;
+    },
+    Completer_Completer($T) {
+      return new A._AsyncCompleter(new A._Future($.Zone__current, $T._eval$1("_Future<0>")), $T._eval$1("_AsyncCompleter<0>"));
+    },
+    _Future$value(value, $T) {
+      var t1 = new A._Future($.Zone__current, $T._eval$1("_Future<0>"));
+      $T._as(value);
+      t1._state = 8;
+      t1._resultOrListeners = value;
+      return t1;
+    },
+    _Future__chainCoreFutureSync(source, target) {
+      var t1, t2, listeners;
+      for (t1 = type$._Future_dynamic; t2 = source._state, (t2 & 4) !== 0;)
+        source = t1._as(source._resultOrListeners);
+      if ((t2 & 24) !== 0) {
+        listeners = target._removeListeners$0();
+        target._cloneResult$1(source);
+        A._Future__propagateToListeners(target, listeners);
+      } else {
+        listeners = type$.nullable__FutureListener_dynamic_dynamic._as(target._resultOrListeners);
+        target._setChained$1(source);
+        source._prependListeners$1(listeners);
+      }
+    },
+    _Future__chainCoreFutureAsync(source, target) {
+      var t2, t3, listeners, _box_0 = {},
+        t1 = _box_0.source = source;
+      for (t2 = type$._Future_dynamic; t3 = t1._state, (t3 & 4) !== 0; t1 = source) {
+        source = t2._as(t1._resultOrListeners);
+        _box_0.source = source;
+      }
+      if ((t3 & 24) === 0) {
+        listeners = type$.nullable__FutureListener_dynamic_dynamic._as(target._resultOrListeners);
+        target._setChained$1(t1);
+        _box_0.source._prependListeners$1(listeners);
+        return;
+      }
+      if ((t3 & 16) === 0 && target._resultOrListeners == null) {
+        target._cloneResult$1(t1);
+        return;
+      }
+      target._state ^= 2;
+      A._rootScheduleMicrotask(null, null, target._zone, type$.void_Function._as(new A._Future__chainCoreFutureAsync_closure(_box_0, target)));
+    },
+    _Future__propagateToListeners(source, listeners) {
+      var t2, t3, t4, _box_0, t5, t6, hasError, asyncError, nextListener, nextListener0, sourceResult, t7, zone, oldZone, result, current, _box_1 = {},
+        t1 = _box_1.source = source;
+      for (t2 = type$.AsyncError, t3 = type$.nullable__FutureListener_dynamic_dynamic, t4 = type$.Future_dynamic; true;) {
+        _box_0 = {};
+        t5 = t1._state;
+        t6 = (t5 & 16) === 0;
+        hasError = !t6;
+        if (listeners == null) {
+          if (hasError && (t5 & 1) === 0) {
+            asyncError = t2._as(t1._resultOrListeners);
+            A._rootHandleError(asyncError.error, asyncError.stackTrace);
+          }
+          return;
+        }
+        _box_0.listener = listeners;
+        nextListener = listeners._nextListener;
+        for (t1 = listeners; nextListener != null; t1 = nextListener, nextListener = nextListener0) {
+          t1._nextListener = null;
+          A._Future__propagateToListeners(_box_1.source, t1);
+          _box_0.listener = nextListener;
+          nextListener0 = nextListener._nextListener;
+        }
+        t5 = _box_1.source;
+        sourceResult = t5._resultOrListeners;
+        _box_0.listenerHasError = hasError;
+        _box_0.listenerValueOrError = sourceResult;
+        if (t6) {
+          t7 = t1.state;
+          t7 = (t7 & 1) !== 0 || (t7 & 15) === 8;
+        } else
+          t7 = true;
+        if (t7) {
+          zone = t1.result._zone;
+          if (hasError) {
+            t5 = t5._zone === zone;
+            t5 = !(t5 || t5);
+          } else
+            t5 = false;
+          if (t5) {
+            t2._as(sourceResult);
+            A._rootHandleError(sourceResult.error, sourceResult.stackTrace);
+            return;
+          }
+          oldZone = $.Zone__current;
+          if (oldZone !== zone)
+            $.Zone__current = zone;
+          else
+            oldZone = null;
+          t1 = t1.state;
+          if ((t1 & 15) === 8)
+            new A._Future__propagateToListeners_handleWhenCompleteCallback(_box_0, _box_1, hasError).call$0();
+          else if (t6) {
+            if ((t1 & 1) !== 0)
+              new A._Future__propagateToListeners_handleValueCallback(_box_0, sourceResult).call$0();
+          } else if ((t1 & 2) !== 0)
+            new A._Future__propagateToListeners_handleError(_box_1, _box_0).call$0();
+          if (oldZone != null)
+            $.Zone__current = oldZone;
+          t1 = _box_0.listenerValueOrError;
+          if (t1 instanceof A._Future) {
+            t5 = _box_0.listener.$ti;
+            t5 = t5._eval$1("Future<2>")._is(t1) || !t5._rest[1]._is(t1);
+          } else
+            t5 = false;
+          if (t5) {
+            t4._as(t1);
+            result = _box_0.listener.result;
+            if ((t1._state & 24) !== 0) {
+              current = t3._as(result._resultOrListeners);
+              result._resultOrListeners = null;
+              listeners = result._reverseListeners$1(current);
+              result._state = t1._state & 30 | result._state & 1;
+              result._resultOrListeners = t1._resultOrListeners;
+              _box_1.source = t1;
+              continue;
+            } else
+              A._Future__chainCoreFutureSync(t1, result);
+            return;
+          }
+        }
+        result = _box_0.listener.result;
+        current = t3._as(result._resultOrListeners);
+        result._resultOrListeners = null;
+        listeners = result._reverseListeners$1(current);
+        t1 = _box_0.listenerHasError;
+        t5 = _box_0.listenerValueOrError;
+        if (!t1) {
+          result.$ti._precomputed1._as(t5);
+          result._state = 8;
+          result._resultOrListeners = t5;
+        } else {
+          t2._as(t5);
+          result._state = result._state & 1 | 16;
+          result._resultOrListeners = t5;
+        }
+        _box_1.source = result;
+        t1 = result;
+      }
+    },
+    _registerErrorHandler(errorHandler, zone) {
+      var t1;
+      if (type$.dynamic_Function_Object_StackTrace._is(errorHandler))
+        return zone.registerBinaryCallback$3$1(errorHandler, type$.dynamic, type$.Object, type$.StackTrace);
+      t1 = type$.dynamic_Function_Object;
+      if (t1._is(errorHandler))
+        return t1._as(errorHandler);
+      throw A.wrapException(A.ArgumentError$value(errorHandler, "onError", string$.Error_));
+    },
+    _microtaskLoop() {
+      var entry, next;
+      for (entry = $._nextCallback; entry != null; entry = $._nextCallback) {
+        $._lastPriorityCallback = null;
+        next = entry.next;
+        $._nextCallback = next;
+        if (next == null)
+          $._lastCallback = null;
+        entry.callback.call$0();
+      }
+    },
+    _startMicrotaskLoop() {
+      $._isInCallbackLoop = true;
+      try {
+        A._microtaskLoop();
+      } finally {
+        $._lastPriorityCallback = null;
+        $._isInCallbackLoop = false;
+        if ($._nextCallback != null)
+          $.$get$_AsyncRun__scheduleImmediateClosure().call$1(A.async___startMicrotaskLoop$closure());
+      }
+    },
+    _scheduleAsyncCallback(callback) {
+      var newEntry = new A._AsyncCallbackEntry(callback),
+        lastCallback = $._lastCallback;
+      if (lastCallback == null) {
+        $._nextCallback = $._lastCallback = newEntry;
+        if (!$._isInCallbackLoop)
+          $.$get$_AsyncRun__scheduleImmediateClosure().call$1(A.async___startMicrotaskLoop$closure());
+      } else
+        $._lastCallback = lastCallback.next = newEntry;
+    },
+    _schedulePriorityAsyncCallback(callback) {
+      var entry, lastPriorityCallback, next,
+        t1 = $._nextCallback;
+      if (t1 == null) {
+        A._scheduleAsyncCallback(callback);
+        $._lastPriorityCallback = $._lastCallback;
+        return;
+      }
+      entry = new A._AsyncCallbackEntry(callback);
+      lastPriorityCallback = $._lastPriorityCallback;
+      if (lastPriorityCallback == null) {
+        entry.next = t1;
+        $._nextCallback = $._lastPriorityCallback = entry;
+      } else {
+        next = lastPriorityCallback.next;
+        entry.next = next;
+        $._lastPriorityCallback = lastPriorityCallback.next = entry;
+        if (next == null)
+          $._lastCallback = entry;
+      }
+    },
+    scheduleMicrotask(callback) {
+      var _null = null,
+        currentZone = $.Zone__current;
+      if (B.C__RootZone === currentZone) {
+        A._rootScheduleMicrotask(_null, _null, B.C__RootZone, callback);
+        return;
+      }
+      A._rootScheduleMicrotask(_null, _null, currentZone, type$.void_Function._as(currentZone.bindCallbackGuarded$1(callback)));
+    },
+    StreamIterator_StreamIterator(stream, $T) {
+      A.checkNotNullable(stream, "stream", type$.Object);
+      return new A._StreamIterator($T._eval$1("_StreamIterator<0>"));
+    },
+    StreamController_StreamController($T) {
+      var _null = null;
+      return new A._AsyncStreamController(_null, _null, _null, _null, $T._eval$1("_AsyncStreamController<0>"));
+    },
+    _runGuarded(notificationHandler) {
+      return;
+    },
+    _BufferingStreamSubscription__registerDataHandler(zone, handleData, $T) {
+      var t1 = handleData == null ? A.async___nullDataHandler$closure() : handleData;
+      return type$.$env_1_1_void._bind$1($T)._eval$1("1(2)")._as(t1);
+    },
+    _BufferingStreamSubscription__registerErrorHandler(zone, handleError) {
+      if (handleError == null)
+        handleError = A.async___nullErrorHandler$closure();
+      if (type$.void_Function_Object_StackTrace._is(handleError))
+        return zone.registerBinaryCallback$3$1(handleError, type$.dynamic, type$.Object, type$.StackTrace);
+      if (type$.void_Function_Object._is(handleError))
+        return type$.dynamic_Function_Object._as(handleError);
+      throw A.wrapException(A.ArgumentError$("handleError callback must take either an Object (the error), or both an Object (the error) and a StackTrace.", null));
+    },
+    _nullDataHandler(value) {
+    },
+    _nullErrorHandler(error, stackTrace) {
+      A._rootHandleError(type$.Object._as(error), type$.StackTrace._as(stackTrace));
+    },
+    _nullDoneHandler() {
+    },
+    _cancelAndValue(subscription, future, value) {
+      var cancelFuture = subscription.cancel$0(),
+        t1 = $.$get$Future__nullFuture();
+      if (cancelFuture !== t1)
+        cancelFuture.whenComplete$1(new A._cancelAndValue_closure(future, value));
+      else
+        future._complete$1(value);
+    },
+    Timer_Timer(duration, callback) {
+      var t1 = $.Zone__current;
+      if (t1 === B.C__RootZone)
+        return A.Timer__createTimer(duration, type$.void_Function._as(callback));
+      return A.Timer__createTimer(duration, type$.void_Function._as(t1.bindCallbackGuarded$1(callback)));
+    },
+    _rootHandleError(error, stackTrace) {
+      A._schedulePriorityAsyncCallback(new A._rootHandleError_closure(error, stackTrace));
+    },
+    _rootRun($self, $parent, zone, f, $R) {
+      var old,
+        t1 = $.Zone__current;
+      if (t1 === zone)
+        return f.call$0();
+      $.Zone__current = zone;
+      old = t1;
+      try {
+        t1 = f.call$0();
+        return t1;
+      } finally {
+        $.Zone__current = old;
+      }
+    },
+    _rootRunUnary($self, $parent, zone, f, arg, $R, $T) {
+      var old,
+        t1 = $.Zone__current;
+      if (t1 === zone)
+        return f.call$1(arg);
+      $.Zone__current = zone;
+      old = t1;
+      try {
+        t1 = f.call$1(arg);
+        return t1;
+      } finally {
+        $.Zone__current = old;
+      }
+    },
+    _rootRunBinary($self, $parent, zone, f, arg1, arg2, $R, T1, T2) {
+      var old,
+        t1 = $.Zone__current;
+      if (t1 === zone)
+        return f.call$2(arg1, arg2);
+      $.Zone__current = zone;
+      old = t1;
+      try {
+        t1 = f.call$2(arg1, arg2);
+        return t1;
+      } finally {
+        $.Zone__current = old;
+      }
+    },
+    _rootScheduleMicrotask($self, $parent, zone, f) {
+      type$.void_Function._as(f);
+      if (B.C__RootZone !== zone)
+        f = zone.bindCallbackGuarded$1(f);
+      A._scheduleAsyncCallback(f);
+    },
+    _AsyncRun__initializeScheduleImmediate_internalCallback: function _AsyncRun__initializeScheduleImmediate_internalCallback(t0) {
+      this._box_0 = t0;
+    },
+    _AsyncRun__initializeScheduleImmediate_closure: function _AsyncRun__initializeScheduleImmediate_closure(t0, t1, t2) {
+      this._box_0 = t0;
+      this.div = t1;
+      this.span = t2;
+    },
+    _AsyncRun__scheduleImmediateJsOverride_internalCallback: function _AsyncRun__scheduleImmediateJsOverride_internalCallback(t0) {
+      this.callback = t0;
+    },
+    _AsyncRun__scheduleImmediateWithSetImmediate_internalCallback: function _AsyncRun__scheduleImmediateWithSetImmediate_internalCallback(t0) {
+      this.callback = t0;
+    },
+    _TimerImpl: function _TimerImpl() {
+      this._handle = null;
+    },
+    _TimerImpl_internalCallback: function _TimerImpl_internalCallback(t0, t1) {
+      this.$this = t0;
+      this.callback = t1;
+    },
+    _AsyncAwaitCompleter: function _AsyncAwaitCompleter(t0, t1) {
+      this._future = t0;
+      this.isSync = false;
+      this.$ti = t1;
+    },
+    _awaitOnObject_closure: function _awaitOnObject_closure(t0) {
+      this.bodyFunction = t0;
+    },
+    _awaitOnObject_closure0: function _awaitOnObject_closure0(t0) {
+      this.bodyFunction = t0;
+    },
+    _wrapJsFunctionForAsync_closure: function _wrapJsFunctionForAsync_closure(t0) {
+      this.$protected = t0;
+    },
+    AsyncError: function AsyncError(t0, t1) {
+      this.error = t0;
+      this.stackTrace = t1;
+    },
+    _Completer: function _Completer() {
+    },
+    _AsyncCompleter: function _AsyncCompleter(t0, t1) {
+      this.future = t0;
+      this.$ti = t1;
+    },
+    _SyncCompleter: function _SyncCompleter(t0, t1) {
+      this.future = t0;
+      this.$ti = t1;
+    },
+    _FutureListener: function _FutureListener(t0, t1, t2, t3, t4) {
+      var _ = this;
+      _._nextListener = null;
+      _.result = t0;
+      _.state = t1;
+      _.callback = t2;
+      _.errorCallback = t3;
+      _.$ti = t4;
+    },
+    _Future: function _Future(t0, t1) {
+      var _ = this;
+      _._state = 0;
+      _._zone = t0;
+      _._resultOrListeners = null;
+      _.$ti = t1;
+    },
+    _Future__addListener_closure: function _Future__addListener_closure(t0, t1) {
+      this.$this = t0;
+      this.listener = t1;
+    },
+    _Future__prependListeners_closure: function _Future__prependListeners_closure(t0, t1) {
+      this._box_0 = t0;
+      this.$this = t1;
+    },
+    _Future__chainForeignFuture_closure: function _Future__chainForeignFuture_closure(t0) {
+      this.$this = t0;
+    },
+    _Future__chainForeignFuture_closure0: function _Future__chainForeignFuture_closure0(t0) {
+      this.$this = t0;
+    },
+    _Future__chainForeignFuture_closure1: function _Future__chainForeignFuture_closure1(t0, t1, t2) {
+      this.$this = t0;
+      this.e = t1;
+      this.s = t2;
+    },
+    _Future__chainCoreFutureAsync_closure: function _Future__chainCoreFutureAsync_closure(t0, t1) {
+      this._box_0 = t0;
+      this.target = t1;
+    },
+    _Future__asyncCompleteWithValue_closure: function _Future__asyncCompleteWithValue_closure(t0, t1) {
+      this.$this = t0;
+      this.value = t1;
+    },
+    _Future__asyncCompleteError_closure: function _Future__asyncCompleteError_closure(t0, t1, t2) {
+      this.$this = t0;
+      this.error = t1;
+      this.stackTrace = t2;
+    },
+    _Future__propagateToListeners_handleWhenCompleteCallback: function _Future__propagateToListeners_handleWhenCompleteCallback(t0, t1, t2) {
+      this._box_0 = t0;
+      this._box_1 = t1;
+      this.hasError = t2;
+    },
+    _Future__propagateToListeners_handleWhenCompleteCallback_closure: function _Future__propagateToListeners_handleWhenCompleteCallback_closure(t0) {
+      this.originalSource = t0;
+    },
+    _Future__propagateToListeners_handleValueCallback: function _Future__propagateToListeners_handleValueCallback(t0, t1) {
+      this._box_0 = t0;
+      this.sourceResult = t1;
+    },
+    _Future__propagateToListeners_handleError: function _Future__propagateToListeners_handleError(t0, t1) {
+      this._box_1 = t0;
+      this._box_0 = t1;
+    },
+    _AsyncCallbackEntry: function _AsyncCallbackEntry(t0) {
+      this.callback = t0;
+      this.next = null;
+    },
+    Stream: function Stream() {
+    },
+    Stream_length_closure: function Stream_length_closure(t0, t1) {
+      this._box_0 = t0;
+      this.$this = t1;
+    },
+    Stream_length_closure0: function Stream_length_closure0(t0, t1) {
+      this._box_0 = t0;
+      this.future = t1;
+    },
+    Stream_first_closure: function Stream_first_closure(t0) {
+      this.future = t0;
+    },
+    Stream_first_closure0: function Stream_first_closure0(t0, t1, t2) {
+      this.$this = t0;
+      this.subscription = t1;
+      this.future = t2;
+    },
+    _StreamController: function _StreamController() {
+    },
+    _StreamController__subscribe_closure: function _StreamController__subscribe_closure(t0) {
+      this.$this = t0;
+    },
+    _StreamController__recordCancel_complete: function _StreamController__recordCancel_complete(t0) {
+      this.$this = t0;
+    },
+    _AsyncStreamControllerDispatch: function _AsyncStreamControllerDispatch() {
+    },
+    _AsyncStreamController: function _AsyncStreamController(t0, t1, t2, t3, t4) {
+      var _ = this;
+      _._varData = null;
+      _._state = 0;
+      _._doneFuture = null;
+      _.onListen = t0;
+      _.onPause = t1;
+      _.onResume = t2;
+      _.onCancel = t3;
+      _.$ti = t4;
+    },
+    _ControllerStream: function _ControllerStream(t0, t1) {
+      this._controller = t0;
+      this.$ti = t1;
+    },
+    _ControllerSubscription: function _ControllerSubscription(t0, t1, t2, t3, t4, t5, t6) {
+      var _ = this;
+      _._controller = t0;
+      _._onData = t1;
+      _._onError = t2;
+      _._onDone = t3;
+      _._zone = t4;
+      _._state = t5;
+      _._pending = _._cancelFuture = null;
+      _.$ti = t6;
+    },
+    _StreamSinkWrapper: function _StreamSinkWrapper(t0, t1) {
+      this._async$_target = t0;
+      this.$ti = t1;
+    },
+    _BufferingStreamSubscription: function _BufferingStreamSubscription() {
+    },
+    _BufferingStreamSubscription_asFuture_closure: function _BufferingStreamSubscription_asFuture_closure(t0, t1) {
+      this._box_0 = t0;
+      this.result = t1;
+    },
+    _BufferingStreamSubscription_asFuture_closure0: function _BufferingStreamSubscription_asFuture_closure0(t0, t1) {
+      this.$this = t0;
+      this.result = t1;
+    },
+    _BufferingStreamSubscription_asFuture__closure: function _BufferingStreamSubscription_asFuture__closure(t0, t1, t2) {
+      this.result = t0;
+      this.error = t1;
+      this.stackTrace = t2;
+    },
+    _BufferingStreamSubscription__sendError_sendError: function _BufferingStreamSubscription__sendError_sendError(t0, t1, t2) {
+      this.$this = t0;
+      this.error = t1;
+      this.stackTrace = t2;
+    },
+    _BufferingStreamSubscription__sendDone_sendDone: function _BufferingStreamSubscription__sendDone_sendDone(t0) {
+      this.$this = t0;
+    },
+    _StreamImpl: function _StreamImpl() {
+    },
+    _DelayedEvent: function _DelayedEvent() {
+    },
+    _DelayedData: function _DelayedData(t0, t1) {
+      this.value = t0;
+      this.next = null;
+      this.$ti = t1;
+    },
+    _DelayedError: function _DelayedError(t0, t1) {
+      this.error = t0;
+      this.stackTrace = t1;
+      this.next = null;
+    },
+    _DelayedDone: function _DelayedDone() {
+    },
+    _PendingEvents: function _PendingEvents(t0) {
+      var _ = this;
+      _._state = 0;
+      _.lastPendingEvent = _.firstPendingEvent = null;
+      _.$ti = t0;
+    },
+    _PendingEvents_schedule_closure: function _PendingEvents_schedule_closure(t0, t1) {
+      this.$this = t0;
+      this.dispatch = t1;
+    },
+    _StreamIterator: function _StreamIterator(t0) {
+      this.$ti = t0;
+    },
+    _cancelAndValue_closure: function _cancelAndValue_closure(t0, t1) {
+      this.future = t0;
+      this.value = t1;
+    },
+    _Zone: function _Zone() {
+    },
+    _rootHandleError_closure: function _rootHandleError_closure(t0, t1) {
+      this.error = t0;
+      this.stackTrace = t1;
+    },
+    _RootZone: function _RootZone() {
+    },
+    _RootZone_bindCallbackGuarded_closure: function _RootZone_bindCallbackGuarded_closure(t0, t1) {
+      this.$this = t0;
+      this.f = t1;
+    },
+    _RootZone_bindUnaryCallbackGuarded_closure: function _RootZone_bindUnaryCallbackGuarded_closure(t0, t1, t2) {
+      this.$this = t0;
+      this.f = t1;
+      this.T = t2;
+    },
+    _HashMap__getTableEntry(table, key) {
+      var entry = table[key];
+      return entry === table ? null : entry;
+    },
+    _HashMap__setTableEntry(table, key, value) {
+      if (value == null)
+        table[key] = table;
+      else
+        table[key] = value;
+    },
+    _HashMap__newHashTable() {
+      var table = Object.create(null);
+      A._HashMap__setTableEntry(table, "<non-identifier-key>", table);
+      delete table["<non-identifier-key>"];
+      return table;
+    },
+    LinkedHashMap_LinkedHashMap$_empty($K, $V) {
+      return new A.JsLinkedHashMap($K._eval$1("@<0>")._bind$1($V)._eval$1("JsLinkedHashMap<1,2>"));
+    },
+    MapBase_mapToString(m) {
+      var result, t1 = {};
+      if (A.isToStringVisiting(m))
+        return "{...}";
+      result = new A.StringBuffer("");
+      try {
+        B.JSArray_methods.add$1($.toStringVisiting, m);
+        result._contents += "{";
+        t1.first = true;
+        m.forEach$1(0, new A.MapBase_mapToString_closure(t1, result));
+        result._contents += "}";
+      } finally {
+        if (0 >= $.toStringVisiting.length)
+          return A.ioore($.toStringVisiting, -1);
+        $.toStringVisiting.pop();
+      }
+      t1 = result._contents;
+      return t1.charCodeAt(0) == 0 ? t1 : t1;
+    },
+    ListQueue$($E) {
+      return new A.ListQueue(A.List_List$filled(A.ListQueue__calculateCapacity(null), null, false, $E._eval$1("0?")), $E._eval$1("ListQueue<0>"));
+    },
+    ListQueue__calculateCapacity(initialCapacity) {
+      return 8;
+    },
+    _HashMap: function _HashMap() {
+    },
+    _IdentityHashMap: function _IdentityHashMap(t0) {
+      var _ = this;
+      _._collection$_length = 0;
+      _._collection$_keys = _._collection$_rest = _._collection$_nums = _._collection$_strings = null;
+      _.$ti = t0;
+    },
+    _HashMapKeyIterable: function _HashMapKeyIterable(t0, t1) {
+      this._collection$_map = t0;
+      this.$ti = t1;
+    },
+    _HashMapKeyIterator: function _HashMapKeyIterator(t0, t1, t2) {
+      var _ = this;
+      _._collection$_map = t0;
+      _._collection$_keys = t1;
+      _._offset = 0;
+      _._collection$_current = null;
+      _.$ti = t2;
+    },
+    ListBase: function ListBase() {
+    },
+    MapBase: function MapBase() {
+    },
+    MapBase_mapToString_closure: function MapBase_mapToString_closure(t0, t1) {
+      this._box_0 = t0;
+      this.result = t1;
+    },
+    _UnmodifiableMapMixin: function _UnmodifiableMapMixin() {
+    },
+    MapView: function MapView() {
+    },
+    UnmodifiableMapView: function UnmodifiableMapView() {
+    },
+    ListQueue: function ListQueue(t0, t1) {
+      var _ = this;
+      _._table = t0;
+      _._modificationCount = _._tail = _._head = 0;
+      _.$ti = t1;
+    },
+    _ListQueueIterator: function _ListQueueIterator(t0, t1, t2, t3, t4) {
+      var _ = this;
+      _._queue = t0;
+      _._end = t1;
+      _._modificationCount = t2;
+      _._position = t3;
+      _._collection$_current = null;
+      _.$ti = t4;
+    },
+    _UnmodifiableMapView_MapView__UnmodifiableMapMixin: function _UnmodifiableMapView_MapView__UnmodifiableMapMixin() {
+    },
+    _parseJson(source, reviver) {
+      var e, exception, t1, parsed = null;
+      try {
+        parsed = JSON.parse(source);
+      } catch (exception) {
+        e = A.unwrapException(exception);
+        t1 = A.FormatException$(String(e), null, null);
+        throw A.wrapException(t1);
+      }
+      t1 = A._convertJsonToDartLazy(parsed);
+      return t1;
+    },
+    _convertJsonToDartLazy(object) {
+      var i;
+      if (object == null)
+        return null;
+      if (typeof object != "object")
+        return object;
+      if (Object.getPrototypeOf(object) !== Array.prototype)
+        return new A._JsonMap(object, Object.create(null));
+      for (i = 0; i < object.length; ++i)
+        object[i] = A._convertJsonToDartLazy(object[i]);
+      return object;
+    },
+    JsonUnsupportedObjectError$(unsupportedObject, cause, partialResult) {
+      return new A.JsonUnsupportedObjectError(unsupportedObject, cause);
+    },
+    _defaultToEncodable(object) {
+      return object.toJson$0();
+    },
+    _JsonStringStringifier$(_sink, _toEncodable) {
+      return new A._JsonStringStringifier(_sink, [], A.convert___defaultToEncodable$closure());
+    },
+    _JsonStringStringifier_stringify(object, toEncodable, indent) {
+      var t1,
+        output = new A.StringBuffer(""),
+        stringifier = A._JsonStringStringifier$(output, toEncodable);
+      stringifier.writeObject$1(object);
+      t1 = output._contents;
+      return t1.charCodeAt(0) == 0 ? t1 : t1;
+    },
+    _JsonMap: function _JsonMap(t0, t1) {
+      this._original = t0;
+      this._processed = t1;
+      this._data = null;
+    },
+    _JsonMapKeyIterable: function _JsonMapKeyIterable(t0) {
+      this._parent = t0;
+    },
+    Codec: function Codec() {
+    },
+    Converter: function Converter() {
+    },
+    JsonUnsupportedObjectError: function JsonUnsupportedObjectError(t0, t1) {
+      this.unsupportedObject = t0;
+      this.cause = t1;
+    },
+    JsonCyclicError: function JsonCyclicError(t0, t1) {
+      this.unsupportedObject = t0;
+      this.cause = t1;
+    },
+    JsonCodec: function JsonCodec() {
+    },
+    JsonEncoder: function JsonEncoder(t0) {
+      this._toEncodable = t0;
+    },
+    JsonDecoder: function JsonDecoder(t0) {
+      this._reviver = t0;
+    },
+    _JsonStringifier: function _JsonStringifier() {
+    },
+    _JsonStringifier_writeMap_closure: function _JsonStringifier_writeMap_closure(t0, t1) {
+      this._box_0 = t0;
+      this.keyValueList = t1;
+    },
+    _JsonStringStringifier: function _JsonStringStringifier(t0, t1, t2) {
+      this._sink = t0;
+      this._seen = t1;
+      this._toEncodable = t2;
+    },
+    int_parse(source, radix) {
+      var value = A.Primitives_parseInt(source, radix);
+      if (value != null)
+        return value;
+      throw A.wrapException(A.FormatException$(source, null, null));
+    },
+    Error__throw(error, stackTrace) {
+      error = A.wrapException(error);
+      if (error == null)
+        error = type$.Object._as(error);
+      error.stack = stackTrace.toString$0(0);
+      throw error;
+      throw A.wrapException("unreachable");
+    },
+    List_List$filled($length, fill, growable, $E) {
+      var i,
+        result = growable ? J.JSArray_JSArray$growable($length, $E) : J.JSArray_JSArray$fixed($length, $E);
+      if ($length !== 0 && fill != null)
+        for (i = 0; i < result.length; ++i)
+          result[i] = fill;
+      return result;
+    },
+    List_List$of(elements, growable, $E) {
+      var t1 = A.List_List$_of(elements, $E);
+      return t1;
+    },
+    List_List$_of(elements, $E) {
+      var list, t1;
+      if (Array.isArray(elements))
+        return A._setArrayType(elements.slice(0), $E._eval$1("JSArray<0>"));
+      list = A._setArrayType([], $E._eval$1("JSArray<0>"));
+      for (t1 = J.get$iterator$ax(elements); t1.moveNext$0();)
+        B.JSArray_methods.add$1(list, t1.get$current());
+      return list;
+    },
+    StringBuffer__writeAll(string, objects, separator) {
+      var iterator = J.get$iterator$ax(objects);
+      if (!iterator.moveNext$0())
+        return string;
+      if (separator.length === 0) {
+        do
+          string += A.S(iterator.get$current());
+        while (iterator.moveNext$0());
+      } else {
+        string += A.S(iterator.get$current());
+        for (; iterator.moveNext$0();)
+          string = string + separator + A.S(iterator.get$current());
+      }
+      return string;
+    },
+    NoSuchMethodError_NoSuchMethodError$withInvocation(receiver, invocation) {
+      return new A.NoSuchMethodError(receiver, invocation.get$memberName(), invocation.get$positionalArguments(), invocation.get$namedArguments());
+    },
+    StackTrace_current() {
+      return A.getTraceFromException(new Error());
+    },
+    DateTime__fourDigits(n) {
+      var absN = Math.abs(n),
+        sign = n < 0 ? "-" : "";
+      if (absN >= 1000)
+        return "" + n;
+      if (absN >= 100)
+        return sign + "0" + absN;
+      if (absN >= 10)
+        return sign + "00" + absN;
+      return sign + "000" + absN;
+    },
+    DateTime__threeDigits(n) {
+      if (n >= 100)
+        return "" + n;
+      if (n >= 10)
+        return "0" + n;
+      return "00" + n;
+    },
+    DateTime__twoDigits(n) {
+      if (n >= 10)
+        return "" + n;
+      return "0" + n;
+    },
+    Error_safeToString(object) {
+      if (typeof object == "number" || A._isBool(object) || object == null)
+        return J.toString$0$(object);
+      if (typeof object == "string")
+        return JSON.stringify(object);
+      return A.Primitives_safeToString(object);
+    },
+    Error_throwWithStackTrace(error, stackTrace) {
+      A.checkNotNullable(error, "error", type$.Object);
+      A.checkNotNullable(stackTrace, "stackTrace", type$.StackTrace);
+      A.Error__throw(error, stackTrace);
+    },
+    AssertionError$(message) {
+      return new A.AssertionError(message);
+    },
+    ArgumentError$(message, $name) {
+      return new A.ArgumentError(false, null, $name, message);
+    },
+    ArgumentError$value(value, $name, message) {
+      return new A.ArgumentError(true, value, $name, message);
+    },
+    ArgumentError$notNull($name) {
+      return new A.ArgumentError(false, null, $name, "Must not be null");
+    },
+    RangeError$(message) {
+      var _null = null;
+      return new A.RangeError(_null, _null, false, _null, _null, message);
+    },
+    RangeError$value(value, $name) {
+      return new A.RangeError(null, null, true, value, $name, "Value not in range");
+    },
+    RangeError$range(invalidValue, minValue, maxValue, $name, message) {
+      return new A.RangeError(minValue, maxValue, true, invalidValue, $name, "Invalid value");
+    },
+    RangeError_checkValidRange(start, end, $length) {
+      if (0 > start || start > $length)
+        throw A.wrapException(A.RangeError$range(start, 0, $length, "start", null));
+      if (end != null) {
+        if (start > end || end > $length)
+          throw A.wrapException(A.RangeError$range(end, start, $length, "end", null));
+        return end;
+      }
+      return $length;
+    },
+    RangeError_checkNotNegative(value, $name) {
+      if (value < 0)
+        throw A.wrapException(A.RangeError$range(value, 0, null, $name, null));
+      return value;
+    },
+    IndexError$withLength(invalidValue, $length, indexable, message, $name) {
+      return new A.IndexError($length, true, invalidValue, $name, "Index out of range");
+    },
+    UnsupportedError$(message) {
+      return new A.UnsupportedError(message);
+    },
+    UnimplementedError$(message) {
+      return new A.UnimplementedError(message);
+    },
+    StateError$(message) {
+      return new A.StateError(message);
+    },
+    ConcurrentModificationError$(modifiedObject) {
+      return new A.ConcurrentModificationError(modifiedObject);
+    },
+    FormatException$(message, source, offset) {
+      return new A.FormatException(message, source, offset);
+    },
+    Iterable_iterableToShortString(iterable, leftDelimiter, rightDelimiter) {
+      var parts, t1;
+      if (A.isToStringVisiting(iterable)) {
+        if (leftDelimiter === "(" && rightDelimiter === ")")
+          return "(...)";
+        return leftDelimiter + "..." + rightDelimiter;
+      }
+      parts = A._setArrayType([], type$.JSArray_String);
+      B.JSArray_methods.add$1($.toStringVisiting, iterable);
+      try {
+        A._iterablePartsToStrings(iterable, parts);
+      } finally {
+        if (0 >= $.toStringVisiting.length)
+          return A.ioore($.toStringVisiting, -1);
+        $.toStringVisiting.pop();
+      }
+      t1 = A.StringBuffer__writeAll(leftDelimiter, type$.Iterable_dynamic._as(parts), ", ") + rightDelimiter;
+      return t1.charCodeAt(0) == 0 ? t1 : t1;
+    },
+    Iterable_iterableToFullString(iterable, leftDelimiter, rightDelimiter) {
+      var buffer, t1;
+      if (A.isToStringVisiting(iterable))
+        return leftDelimiter + "..." + rightDelimiter;
+      buffer = new A.StringBuffer(leftDelimiter);
+      B.JSArray_methods.add$1($.toStringVisiting, iterable);
+      try {
+        t1 = buffer;
+        t1._contents = A.StringBuffer__writeAll(t1._contents, iterable, ", ");
+      } finally {
+        if (0 >= $.toStringVisiting.length)
+          return A.ioore($.toStringVisiting, -1);
+        $.toStringVisiting.pop();
+      }
+      buffer._contents += rightDelimiter;
+      t1 = buffer._contents;
+      return t1.charCodeAt(0) == 0 ? t1 : t1;
+    },
+    _iterablePartsToStrings(iterable, parts) {
+      var next, ultimateString, penultimateString, penultimate, ultimate, ultimate0, elision,
+        it = iterable.get$iterator(iterable),
+        $length = 0, count = 0;
+      while (true) {
+        if (!($length < 80 || count < 3))
+          break;
+        if (!it.moveNext$0())
+          return;
+        next = A.S(it.get$current());
+        B.JSArray_methods.add$1(parts, next);
+        $length += next.length + 2;
+        ++count;
+      }
+      if (!it.moveNext$0()) {
+        if (count <= 5)
+          return;
+        if (0 >= parts.length)
+          return A.ioore(parts, -1);
+        ultimateString = parts.pop();
+        if (0 >= parts.length)
+          return A.ioore(parts, -1);
+        penultimateString = parts.pop();
+      } else {
+        penultimate = it.get$current();
+        ++count;
+        if (!it.moveNext$0()) {
+          if (count <= 4) {
+            B.JSArray_methods.add$1(parts, A.S(penultimate));
+            return;
+          }
+          ultimateString = A.S(penultimate);
+          if (0 >= parts.length)
+            return A.ioore(parts, -1);
+          penultimateString = parts.pop();
+          $length += ultimateString.length + 2;
+        } else {
+          ultimate = it.get$current();
+          ++count;
+          for (; it.moveNext$0(); penultimate = ultimate, ultimate = ultimate0) {
+            ultimate0 = it.get$current();
+            ++count;
+            if (count > 100) {
+              while (true) {
+                if (!($length > 75 && count > 3))
+                  break;
+                if (0 >= parts.length)
+                  return A.ioore(parts, -1);
+                $length -= parts.pop().length + 2;
+                --count;
+              }
+              B.JSArray_methods.add$1(parts, "...");
+              return;
+            }
+          }
+          penultimateString = A.S(penultimate);
+          ultimateString = A.S(ultimate);
+          $length += ultimateString.length + penultimateString.length + 4;
+        }
+      }
+      if (count > parts.length + 2) {
+        $length += 5;
+        elision = "...";
+      } else
+        elision = null;
+      while (true) {
+        if (!($length > 80 && parts.length > 3))
+          break;
+        if (0 >= parts.length)
+          return A.ioore(parts, -1);
+        $length -= parts.pop().length + 2;
+        if (elision == null) {
+          $length += 5;
+          elision = "...";
+        }
+      }
+      if (elision != null)
+        B.JSArray_methods.add$1(parts, elision);
+      B.JSArray_methods.add$1(parts, penultimateString);
+      B.JSArray_methods.add$1(parts, ultimateString);
+    },
+    NoSuchMethodError_toString_closure: function NoSuchMethodError_toString_closure(t0, t1) {
+      this._box_0 = t0;
+      this.sb = t1;
+    },
+    DateTime: function DateTime(t0, t1) {
+      this._value = t0;
+      this.isUtc = t1;
+    },
+    Duration: function Duration(t0) {
+      this._duration = t0;
+    },
+    Error: function Error() {
+    },
+    AssertionError: function AssertionError(t0) {
+      this.message = t0;
+    },
+    TypeError: function TypeError() {
+    },
+    ArgumentError: function ArgumentError(t0, t1, t2, t3) {
+      var _ = this;
+      _._hasValue = t0;
+      _.invalidValue = t1;
+      _.name = t2;
+      _.message = t3;
+    },
+    RangeError: function RangeError(t0, t1, t2, t3, t4, t5) {
+      var _ = this;
+      _.start = t0;
+      _.end = t1;
+      _._hasValue = t2;
+      _.invalidValue = t3;
+      _.name = t4;
+      _.message = t5;
+    },
+    IndexError: function IndexError(t0, t1, t2, t3, t4) {
+      var _ = this;
+      _.length = t0;
+      _._hasValue = t1;
+      _.invalidValue = t2;
+      _.name = t3;
+      _.message = t4;
+    },
+    NoSuchMethodError: function NoSuchMethodError(t0, t1, t2, t3) {
+      var _ = this;
+      _._core$_receiver = t0;
+      _._core$_memberName = t1;
+      _._core$_arguments = t2;
+      _._namedArguments = t3;
+    },
+    UnsupportedError: function UnsupportedError(t0) {
+      this.message = t0;
+    },
+    UnimplementedError: function UnimplementedError(t0) {
+      this.message = t0;
+    },
+    StateError: function StateError(t0) {
+      this.message = t0;
+    },
+    ConcurrentModificationError: function ConcurrentModificationError(t0) {
+      this.modifiedObject = t0;
+    },
+    OutOfMemoryError: function OutOfMemoryError() {
+    },
+    StackOverflowError: function StackOverflowError() {
+    },
+    _Exception: function _Exception(t0) {
+      this.message = t0;
+    },
+    FormatException: function FormatException(t0, t1, t2) {
+      this.message = t0;
+      this.source = t1;
+      this.offset = t2;
+    },
+    Iterable: function Iterable() {
+    },
+    Null: function Null() {
+    },
+    Object: function Object() {
+    },
+    _StringStackTrace: function _StringStackTrace(t0) {
+      this._stackTrace = t0;
+    },
+    StringBuffer: function StringBuffer(t0) {
+      this._contents = t0;
+    },
+    _convertDartFunctionFast(f) {
+      var ret,
+        existing = f.$dart_jsFunction;
+      if (existing != null)
+        return existing;
+      ret = function(_call, f) {
+        return function() {
+          return _call(f, Array.prototype.slice.apply(arguments));
+        };
+      }(A._callDartFunctionFast, f);
+      ret[$.$get$DART_CLOSURE_PROPERTY_NAME()] = f;
+      f.$dart_jsFunction = ret;
+      return ret;
+    },
+    _callDartFunctionFast(callback, $arguments) {
+      type$.List_dynamic._as($arguments);
+      type$.Function._as(callback);
+      return A.Primitives_applyFunction(callback, $arguments, null);
+    },
+    allowInterop(f, $F) {
+      if (typeof f == "function")
+        return f;
+      else
+        return $F._as(A._convertDartFunctionFast(f));
+    },
+    promiseToFuture(jsPromise, $T) {
+      var t1 = new A._Future($.Zone__current, $T._eval$1("_Future<0>")),
+        completer = new A._AsyncCompleter(t1, $T._eval$1("_AsyncCompleter<0>"));
+      jsPromise.then(A.convertDartClosureToJS(new A.promiseToFuture_closure(completer, $T), 1), A.convertDartClosureToJS(new A.promiseToFuture_closure0(completer), 1));
+      return t1;
+    },
+    _noDartifyRequired(o) {
+      return o == null || typeof o === "boolean" || typeof o === "number" || typeof o === "string" || o instanceof Int8Array || o instanceof Uint8Array || o instanceof Uint8ClampedArray || o instanceof Int16Array || o instanceof Uint16Array || o instanceof Int32Array || o instanceof Uint32Array || o instanceof Float32Array || o instanceof Float64Array || o instanceof ArrayBuffer || o instanceof DataView;
+    },
+    dartify(o) {
+      if (A._noDartifyRequired(o))
+        return o;
+      return new A.dartify_convert(new A._IdentityHashMap(type$._IdentityHashMap_of_nullable_Object_and_nullable_Object)).call$1(o);
+    },
+    promiseToFuture_closure: function promiseToFuture_closure(t0, t1) {
+      this.completer = t0;
+      this.T = t1;
+    },
+    promiseToFuture_closure0: function promiseToFuture_closure0(t0) {
+      this.completer = t0;
+    },
+    dartify_convert: function dartify_convert(t0) {
+      this._convertedObjects = t0;
+    },
+    NullRejectionException: function NullRejectionException(t0) {
+      this.isUndefined = t0;
+    },
+    _JSRandom: function _JSRandom() {
+    },
+    AsyncMemoizer: function AsyncMemoizer(t0, t1) {
+      this._completer = t0;
+      this.$ti = t1;
+    },
+    Level: function Level(t0, t1) {
+      this.name = t0;
+      this.value = t1;
+    },
+    LogRecord: function LogRecord(t0, t1, t2) {
+      this.level = t0;
+      this.message = t1;
+      this.loggerName = t2;
+    },
+    Logger_Logger($name) {
+      return $.Logger__loggers.putIfAbsent$2($name, new A.Logger_Logger_closure($name));
+    },
+    Logger: function Logger(t0, t1, t2) {
+      var _ = this;
+      _.name = t0;
+      _.parent = t1;
+      _._level = null;
+      _._children = t2;
+    },
+    Logger_Logger_closure: function Logger_Logger_closure(t0) {
+      this.name = t0;
+    },
+    Pool: function Pool(t0, t1, t2, t3, t4) {
+      var _ = this;
+      _._requestedResources = t0;
+      _._onReleaseCallbacks = t1;
+      _._onReleaseCompleters = t2;
+      _._maxAllocatedResources = t3;
+      _._allocatedResources = 0;
+      _._timer = null;
+      _._closeMemo = t4;
+    },
+    Pool__runOnRelease_closure: function Pool__runOnRelease_closure(t0) {
+      this.$this = t0;
+    },
+    Pool__runOnRelease_closure0: function Pool__runOnRelease_closure0(t0) {
+      this.$this = t0;
+    },
+    PoolResource: function PoolResource(t0) {
+      this._pool = t0;
+      this._released = false;
+    },
+    SseClient$(serverUrl) {
+      var t3, t4, t5,
+        t1 = type$.String,
+        t2 = A.StreamController_StreamController(t1);
+      t1 = A.StreamController_StreamController(t1);
+      t3 = A.Logger_Logger("SseClient");
+      t4 = $.Zone__current;
+      t5 = A.generateUuidV4();
+      t1 = new A.SseClient(t5, t2, t1, t3, new A._AsyncCompleter(new A._Future(t4, type$._Future_void), type$._AsyncCompleter_void));
+      t1.SseClient$2$debugKey(serverUrl, null);
+      return t1;
+    },
+    SseClient: function SseClient(t0, t1, t2, t3, t4) {
+      var _ = this;
+      _._clientId = t0;
+      _._incomingController = t1;
+      _._outgoingController = t2;
+      _._logger = t3;
+      _._onConnected = t4;
+      _._lastMessageId = -1;
+      _.__SseClient__serverUrl_A = _.__SseClient__eventSource_A = $;
+      _._errorTimer = null;
+    },
+    SseClient_closure: function SseClient_closure(t0) {
+      this.$this = t0;
+    },
+    SseClient_closure0: function SseClient_closure0(t0) {
+      this.$this = t0;
+    },
+    SseClient_closure1: function SseClient_closure1(t0) {
+      this.$this = t0;
+    },
+    SseClient__closure: function SseClient__closure(t0, t1) {
+      this.$this = t0;
+      this.error = t1;
+    },
+    SseClient__onOutgoingMessage_closure: function SseClient__onOutgoingMessage_closure(t0, t1, t2) {
+      this._box_0 = t0;
+      this.$this = t1;
+      this.message = t2;
+    },
+    generateUuidV4() {
+      var t1 = new A.generateUuidV4_printDigits(),
+        t2 = new A.generateUuidV4_bitsDigits(t1, new A.generateUuidV4_generateBits(B.C__JSRandom)),
+        t3 = B.C__JSRandom.nextInt$1(4);
+      return A.S(t2.call$2(16, 4)) + A.S(t2.call$2(16, 4)) + "-" + A.S(t2.call$2(16, 4)) + "-4" + A.S(t2.call$2(12, 3)) + "-" + A.S(t1.call$2(8 + t3, 1)) + A.S(t2.call$2(12, 3)) + "-" + A.S(t2.call$2(16, 4)) + A.S(t2.call$2(16, 4)) + A.S(t2.call$2(16, 4));
+    },
+    generateUuidV4_generateBits: function generateUuidV4_generateBits(t0) {
+      this.random = t0;
+    },
+    generateUuidV4_printDigits: function generateUuidV4_printDigits() {
+    },
+    generateUuidV4_bitsDigits: function generateUuidV4_bitsDigits(t0, t1) {
+      this.printDigits = t0;
+      this.generateBits = t1;
+    },
+    StreamChannelMixin: function StreamChannelMixin() {
+    },
+    _EventStreamSubscription$(_target, _eventType, onData, _useCapture, $T) {
+      var t1;
+      if (onData == null)
+        t1 = null;
+      else {
+        t1 = A._wrapZone(new A._EventStreamSubscription_closure(onData), type$.JSObject);
+        t1 = t1 == null ? null : type$.JavaScriptFunction._as(A.allowInterop(t1, type$.Function));
+      }
+      t1 = new A._EventStreamSubscription(_target, _eventType, t1, false, $T._eval$1("_EventStreamSubscription<0>"));
+      t1._tryResume$0();
+      return t1;
+    },
+    _wrapZone(callback, $T) {
+      var t1 = $.Zone__current;
+      if (t1 === B.C__RootZone)
+        return callback;
+      return t1.bindUnaryCallbackGuarded$1$1(callback, $T);
+    },
+    EventStreamProvider: function EventStreamProvider(t0, t1) {
+      this._eventType = t0;
+      this.$ti = t1;
+    },
+    _EventStream: function _EventStream(t0, t1, t2, t3) {
+      var _ = this;
+      _._target = t0;
+      _._eventType = t1;
+      _._useCapture = t2;
+      _.$ti = t3;
+    },
+    _ElementEventStreamImpl: function _ElementEventStreamImpl(t0, t1, t2, t3) {
+      var _ = this;
+      _._target = t0;
+      _._eventType = t1;
+      _._useCapture = t2;
+      _.$ti = t3;
+    },
+    _EventStreamSubscription: function _EventStreamSubscription(t0, t1, t2, t3, t4) {
+      var _ = this;
+      _._target = t0;
+      _._eventType = t1;
+      _._streams$_onData = t2;
+      _._useCapture = t3;
+      _.$ti = t4;
+    },
+    _EventStreamSubscription_closure: function _EventStreamSubscription_closure(t0) {
+      this.onData = t0;
+    },
+    _EventStreamSubscription_onData_closure: function _EventStreamSubscription_onData_closure(t0) {
+      this.handleData = t0;
+    },
+    main() {
+      var t2,
+        channel = A.SseClient$("/test"),
+        t1 = type$.nullable_JSObject._as(type$.JSObject._as(self.document).querySelector("button"));
+      t1.toString;
+      t2 = type$._ElementEventStreamImpl_JSObject;
+      A._EventStreamSubscription$(t1, "click", t2._eval$1("~(1)?")._as(new A.main_closure(channel)), false, t2._precomputed1);
+      t2 = channel._incomingController;
+      new A._ControllerStream(t2, A._instanceType(t2)._eval$1("_ControllerStream<1>")).listen$1(new A.main_closure0(channel));
+    },
+    main_closure: function main_closure(t0) {
+      this.channel = t0;
+    },
+    main_closure0: function main_closure0(t0) {
+      this.channel = t0;
+    },
+    throwLateFieldNI(fieldName) {
+      A.throwExpressionWithWrapper(new A.LateError("Field '" + fieldName + "' has not been initialized."), new Error());
+    },
+    throwLateFieldADI(fieldName) {
+      A.throwExpressionWithWrapper(new A.LateError("Field '" + fieldName + "' has been assigned during initialization."), new Error());
+    }
+  },
+  B = {};
+  var holders = [A, J, B];
+  var $ = {};
+  A.JS_CONST.prototype = {};
+  J.Interceptor.prototype = {
+    $eq(receiver, other) {
+      return receiver === other;
+    },
+    get$hashCode(receiver) {
+      return A.Primitives_objectHashCode(receiver);
+    },
+    toString$0(receiver) {
+      return "Instance of '" + A.Primitives_objectTypeName(receiver) + "'";
+    },
+    noSuchMethod$1(receiver, invocation) {
+      throw A.wrapException(A.NoSuchMethodError_NoSuchMethodError$withInvocation(receiver, type$.Invocation._as(invocation)));
+    },
+    get$runtimeType(receiver) {
+      return A.createRuntimeType(A._instanceTypeFromConstructor(this));
+    }
+  };
+  J.JSBool.prototype = {
+    toString$0(receiver) {
+      return String(receiver);
+    },
+    get$hashCode(receiver) {
+      return receiver ? 519018 : 218159;
+    },
+    get$runtimeType(receiver) {
+      return A.createRuntimeType(type$.bool);
+    },
+    $isTrustedGetRuntimeType: 1,
+    $isbool: 1
+  };
+  J.JSNull.prototype = {
+    $eq(receiver, other) {
+      return null == other;
+    },
+    toString$0(receiver) {
+      return "null";
+    },
+    get$hashCode(receiver) {
+      return 0;
+    },
+    $isTrustedGetRuntimeType: 1,
+    $isNull: 1
+  };
+  J.JavaScriptObject.prototype = {$isJSObject: 1};
+  J.LegacyJavaScriptObject.prototype = {
+    get$hashCode(receiver) {
+      return 0;
+    },
+    toString$0(receiver) {
+      return String(receiver);
+    }
+  };
+  J.PlainJavaScriptObject.prototype = {};
+  J.UnknownJavaScriptObject.prototype = {};
+  J.JavaScriptFunction.prototype = {
+    toString$0(receiver) {
+      var dartClosure = receiver[$.$get$DART_CLOSURE_PROPERTY_NAME()];
+      if (dartClosure == null)
+        return this.super$LegacyJavaScriptObject$toString(receiver);
+      return "JavaScript function for " + J.toString$0$(dartClosure);
+    },
+    $isFunction: 1
+  };
+  J.JavaScriptBigInt.prototype = {
+    get$hashCode(receiver) {
+      return 0;
+    },
+    toString$0(receiver) {
+      return String(receiver);
+    }
+  };
+  J.JavaScriptSymbol.prototype = {
+    get$hashCode(receiver) {
+      return 0;
+    },
+    toString$0(receiver) {
+      return String(receiver);
+    }
+  };
+  J.JSArray.prototype = {
+    add$1(receiver, value) {
+      A._arrayInstanceType(receiver)._precomputed1._as(value);
+      if (!!receiver.fixed$length)
+        A.throwExpression(A.UnsupportedError$("add"));
+      receiver.push(value);
+    },
+    addAll$1(receiver, collection) {
+      var t1;
+      A._arrayInstanceType(receiver)._eval$1("Iterable<1>")._as(collection);
+      if (!!receiver.fixed$length)
+        A.throwExpression(A.UnsupportedError$("addAll"));
+      if (Array.isArray(collection)) {
+        this._addAllFromArray$1(receiver, collection);
+        return;
+      }
+      for (t1 = J.get$iterator$ax(collection); t1.moveNext$0();)
+        receiver.push(t1.get$current());
+    },
+    _addAllFromArray$1(receiver, array) {
+      var len, i;
+      type$.JSArray_dynamic._as(array);
+      len = array.length;
+      if (len === 0)
+        return;
+      if (receiver === array)
+        throw A.wrapException(A.ConcurrentModificationError$(receiver));
+      for (i = 0; i < len; ++i)
+        receiver.push(array[i]);
+    },
+    get$last(receiver) {
+      var t1 = receiver.length;
+      if (t1 > 0)
+        return receiver[t1 - 1];
+      throw A.wrapException(A.IterableElementError_noElement());
+    },
+    setRange$4(receiver, start, end, iterable, skipCount) {
+      var $length, otherList, t1, i;
+      A._arrayInstanceType(receiver)._eval$1("Iterable<1>")._as(iterable);
+      if (!!receiver.immutable$list)
+        A.throwExpression(A.UnsupportedError$("setRange"));
+      A.RangeError_checkValidRange(start, end, receiver.length);
+      $length = end - start;
+      if ($length === 0)
+        return;
+      A.RangeError_checkNotNegative(skipCount, "skipCount");
+      otherList = iterable;
+      t1 = J.getInterceptor$asx(otherList);
+      if (skipCount + $length > t1.get$length(otherList))
+        throw A.wrapException(A.IterableElementError_tooFew());
+      if (skipCount < start)
+        for (i = $length - 1; i >= 0; --i)
+          receiver[start + i] = t1.$index(otherList, skipCount + i);
+      else
+        for (i = 0; i < $length; ++i)
+          receiver[start + i] = t1.$index(otherList, skipCount + i);
+    },
+    get$isNotEmpty(receiver) {
+      return receiver.length !== 0;
+    },
+    toString$0(receiver) {
+      return A.Iterable_iterableToFullString(receiver, "[", "]");
+    },
+    get$iterator(receiver) {
+      return new J.ArrayIterator(receiver, receiver.length, A._arrayInstanceType(receiver)._eval$1("ArrayIterator<1>"));
+    },
+    get$hashCode(receiver) {
+      return A.Primitives_objectHashCode(receiver);
+    },
+    get$length(receiver) {
+      return receiver.length;
+    },
+    $index(receiver, index) {
+      if (!(index >= 0 && index < receiver.length))
+        throw A.wrapException(A.diagnoseIndexError(receiver, index));
+      return receiver[index];
+    },
+    $indexSet(receiver, index, value) {
+      A._arrayInstanceType(receiver)._precomputed1._as(value);
+      if (!!receiver.immutable$list)
+        A.throwExpression(A.UnsupportedError$("indexed set"));
+      if (!(index >= 0 && index < receiver.length))
+        throw A.wrapException(A.diagnoseIndexError(receiver, index));
+      receiver[index] = value;
+    },
+    $isIterable: 1,
+    $isList: 1
+  };
+  J.JSUnmodifiableArray.prototype = {};
+  J.ArrayIterator.prototype = {
+    get$current() {
+      var t1 = this._current;
+      return t1 == null ? this.$ti._precomputed1._as(t1) : t1;
+    },
+    moveNext$0() {
+      var t2, _this = this,
+        t1 = _this._iterable,
+        $length = t1.length;
+      if (_this._length !== $length) {
+        t1 = A.throwConcurrentModificationError(t1);
+        throw A.wrapException(t1);
+      }
+      t2 = _this._index;
+      if (t2 >= $length) {
+        _this.set$_current(null);
+        return false;
+      }
+      _this.set$_current(t1[t2]);
+      ++_this._index;
+      return true;
+    },
+    set$_current(_current) {
+      this._current = this.$ti._eval$1("1?")._as(_current);
+    }
+  };
+  J.JSNumber.prototype = {
+    toRadixString$1(receiver, radix) {
+      var result, t1, t2, match, exponent;
+      if (radix < 2 || radix > 36)
+        throw A.wrapException(A.RangeError$range(radix, 2, 36, "radix", null));
+      result = receiver.toString(radix);
+      t1 = result.length;
+      t2 = t1 - 1;
+      if (!(t2 >= 0))
+        return A.ioore(result, t2);
+      if (result.charCodeAt(t2) !== 41)
+        return result;
+      match = /^([\da-z]+)(?:\.([\da-z]+))?\(e\+(\d+)\)$/.exec(result);
+      if (match == null)
+        A.throwExpression(A.UnsupportedError$("Unexpected toString result: " + result));
+      t1 = match.length;
+      if (1 >= t1)
+        return A.ioore(match, 1);
+      result = match[1];
+      if (3 >= t1)
+        return A.ioore(match, 3);
+      exponent = +match[3];
+      t1 = match[2];
+      if (t1 != null) {
+        result += t1;
+        exponent -= t1.length;
+      }
+      return result + B.JSString_methods.$mul("0", exponent);
+    },
+    toString$0(receiver) {
+      if (receiver === 0 && 1 / receiver < 0)
+        return "-0.0";
+      else
+        return "" + receiver;
+    },
+    get$hashCode(receiver) {
+      var absolute, floorLog2, factor, scaled,
+        intValue = receiver | 0;
+      if (receiver === intValue)
+        return intValue & 536870911;
+      absolute = Math.abs(receiver);
+      floorLog2 = Math.log(absolute) / 0.6931471805599453 | 0;
+      factor = Math.pow(2, floorLog2);
+      scaled = absolute < 1 ? absolute / factor : factor / absolute;
+      return ((scaled * 9007199254740992 | 0) + (scaled * 3542243181176521 | 0)) * 599197 + floorLog2 * 1259 & 536870911;
+    },
+    _tdivFast$1(receiver, other) {
+      return (receiver | 0) === receiver ? receiver / other | 0 : this._tdivSlow$1(receiver, other);
+    },
+    _tdivSlow$1(receiver, other) {
+      var quotient = receiver / other;
+      if (quotient >= -2147483648 && quotient <= 2147483647)
+        return quotient | 0;
+      if (quotient > 0) {
+        if (quotient !== 1 / 0)
+          return Math.floor(quotient);
+      } else if (quotient > -1 / 0)
+        return Math.ceil(quotient);
+      throw A.wrapException(A.UnsupportedError$("Result of truncating division is " + A.S(quotient) + ": " + A.S(receiver) + " ~/ " + other));
+    },
+    _shlPositive$1(receiver, other) {
+      return other > 31 ? 0 : receiver << other >>> 0;
+    },
+    _shrOtherPositive$1(receiver, other) {
+      var t1;
+      if (receiver > 0)
+        t1 = this._shrBothPositive$1(receiver, other);
+      else {
+        t1 = other > 31 ? 31 : other;
+        t1 = receiver >> t1 >>> 0;
+      }
+      return t1;
+    },
+    _shrBothPositive$1(receiver, other) {
+      return other > 31 ? 0 : receiver >>> other;
+    },
+    get$runtimeType(receiver) {
+      return A.createRuntimeType(type$.num);
+    },
+    $isdouble: 1,
+    $isnum: 1
+  };
+  J.JSInt.prototype = {
+    get$runtimeType(receiver) {
+      return A.createRuntimeType(type$.int);
+    },
+    $isTrustedGetRuntimeType: 1,
+    $isint: 1
+  };
+  J.JSNumNotInt.prototype = {
+    get$runtimeType(receiver) {
+      return A.createRuntimeType(type$.double);
+    },
+    $isTrustedGetRuntimeType: 1
+  };
+  J.JSString.prototype = {
+    matchAsPrefix$2(receiver, string, start) {
+      var t1, t2, i, t3, _null = null;
+      if (start < 0 || start > string.length)
+        throw A.wrapException(A.RangeError$range(start, 0, string.length, _null, _null));
+      t1 = receiver.length;
+      t2 = string.length;
+      if (start + t1 > t2)
+        return _null;
+      for (i = 0; i < t1; ++i) {
+        t3 = start + i;
+        if (!(t3 >= 0 && t3 < t2))
+          return A.ioore(string, t3);
+        if (string.charCodeAt(t3) !== receiver.charCodeAt(i))
+          return _null;
+      }
+      return new A.StringMatch(start, receiver);
+    },
+    $add(receiver, other) {
+      return receiver + other;
+    },
+    endsWith$1(receiver, other) {
+      var otherLength = other.length,
+        t1 = receiver.length;
+      if (otherLength > t1)
+        return false;
+      return other === this.substring$1(receiver, t1 - otherLength);
+    },
+    startsWith$2(receiver, pattern, index) {
+      var endIndex;
+      if (index < 0 || index > receiver.length)
+        throw A.wrapException(A.RangeError$range(index, 0, receiver.length, null, null));
+      if (typeof pattern == "string") {
+        endIndex = index + pattern.length;
+        if (endIndex > receiver.length)
+          return false;
+        return pattern === receiver.substring(index, endIndex);
+      }
+      return J.matchAsPrefix$2$s(pattern, receiver, index) != null;
+    },
+    startsWith$1(receiver, pattern) {
+      return this.startsWith$2(receiver, pattern, 0);
+    },
+    substring$2(receiver, start, end) {
+      return receiver.substring(start, A.RangeError_checkValidRange(start, end, receiver.length));
+    },
+    substring$1(receiver, start) {
+      return this.substring$2(receiver, start, null);
+    },
+    $mul(receiver, times) {
+      var s, result;
+      if (0 >= times)
+        return "";
+      if (times === 1 || receiver.length === 0)
+        return receiver;
+      if (times !== times >>> 0)
+        throw A.wrapException(B.C_OutOfMemoryError);
+      for (s = receiver, result = ""; true;) {
+        if ((times & 1) === 1)
+          result = s + result;
+        times = times >>> 1;
+        if (times === 0)
+          break;
+        s += s;
+      }
+      return result;
+    },
+    padLeft$2(receiver, width, padding) {
+      var delta = width - receiver.length;
+      if (delta <= 0)
+        return receiver;
+      return this.$mul(padding, delta) + receiver;
+    },
+    lastIndexOf$2(receiver, pattern, start) {
+      var t1, t2;
+      if (start == null)
+        start = receiver.length;
+      else if (start < 0 || start > receiver.length)
+        throw A.wrapException(A.RangeError$range(start, 0, receiver.length, null, null));
+      t1 = pattern.length;
+      t2 = receiver.length;
+      if (start + t1 > t2)
+        start = t2 - t1;
+      return receiver.lastIndexOf(pattern, start);
+    },
+    lastIndexOf$1(receiver, pattern) {
+      return this.lastIndexOf$2(receiver, pattern, null);
+    },
+    toString$0(receiver) {
+      return receiver;
+    },
+    get$hashCode(receiver) {
+      var t1, hash, i;
+      for (t1 = receiver.length, hash = 0, i = 0; i < t1; ++i) {
+        hash = hash + receiver.charCodeAt(i) & 536870911;
+        hash = hash + ((hash & 524287) << 10) & 536870911;
+        hash ^= hash >> 6;
+      }
+      hash = hash + ((hash & 67108863) << 3) & 536870911;
+      hash ^= hash >> 11;
+      return hash + ((hash & 16383) << 15) & 536870911;
+    },
+    get$runtimeType(receiver) {
+      return A.createRuntimeType(type$.String);
+    },
+    get$length(receiver) {
+      return receiver.length;
+    },
+    $isTrustedGetRuntimeType: 1,
+    $isPattern: 1,
+    $isString: 1
+  };
+  A.LateError.prototype = {
+    toString$0(_) {
+      return "LateInitializationError: " + this._message;
+    }
+  };
+  A.nullFuture_closure.prototype = {
+    call$0() {
+      return A.Future_Future$value(null, type$.Null);
+    },
+    $signature: 7
+  };
+  A.EfficientLengthIterable.prototype = {};
+  A.ListIterable.prototype = {
+    get$iterator(_) {
+      var _this = this;
+      return new A.ListIterator(_this, _this.get$length(_this), A._instanceType(_this)._eval$1("ListIterator<ListIterable.E>"));
+    },
+    get$isEmpty(_) {
+      return this.get$length(this) === 0;
+    }
+  };
+  A.ListIterator.prototype = {
+    get$current() {
+      var t1 = this.__internal$_current;
+      return t1 == null ? this.$ti._precomputed1._as(t1) : t1;
+    },
+    moveNext$0() {
+      var t3, _this = this,
+        t1 = _this.__internal$_iterable,
+        t2 = J.getInterceptor$asx(t1),
+        $length = t2.get$length(t1);
+      if (_this.__internal$_length !== $length)
+        throw A.wrapException(A.ConcurrentModificationError$(t1));
+      t3 = _this.__internal$_index;
+      if (t3 >= $length) {
+        _this.set$__internal$_current(null);
+        return false;
+      }
+      _this.set$__internal$_current(t2.elementAt$1(t1, t3));
+      ++_this.__internal$_index;
+      return true;
+    },
+    set$__internal$_current(_current) {
+      this.__internal$_current = this.$ti._eval$1("1?")._as(_current);
+    }
+  };
+  A.FixedLengthListMixin.prototype = {};
+  A.Symbol.prototype = {
+    get$hashCode(_) {
+      var hash = this._hashCode;
+      if (hash != null)
+        return hash;
+      hash = 664597 * B.JSString_methods.get$hashCode(this._name) & 536870911;
+      this._hashCode = hash;
+      return hash;
+    },
+    toString$0(_) {
+      return 'Symbol("' + this._name + '")';
+    },
+    $eq(_, other) {
+      if (other == null)
+        return false;
+      return other instanceof A.Symbol && this._name === other._name;
+    },
+    $isSymbol0: 1
+  };
+  A.ConstantMapView.prototype = {};
+  A.ConstantMap.prototype = {
+    get$isEmpty(_) {
+      return this.get$length(this) === 0;
+    },
+    toString$0(_) {
+      return A.MapBase_mapToString(this);
+    },
+    $isMap: 1
+  };
+  A.ConstantStringMap.prototype = {
+    get$length(_) {
+      return this._values.length;
+    },
+    get$_keys() {
+      var keys = this.$keys;
+      if (keys == null) {
+        keys = Object.keys(this._jsIndex);
+        this.$keys = keys;
+      }
+      return keys;
+    },
+    forEach$1(_, f) {
+      var keys, values, t1, i;
+      this.$ti._eval$1("~(1,2)")._as(f);
+      keys = this.get$_keys();
+      values = this._values;
+      for (t1 = keys.length, i = 0; i < t1; ++i)
+        f.call$2(keys[i], values[i]);
+    }
+  };
+  A.JSInvocationMirror.prototype = {
+    get$memberName() {
+      var t1 = this._memberName;
+      if (t1 instanceof A.Symbol)
+        return t1;
+      return this._memberName = new A.Symbol(A._asString(t1));
+    },
+    get$positionalArguments() {
+      var t1, t2, argumentCount, list, index, _this = this;
+      if (_this.__js_helper$_kind === 1)
+        return B.List_empty;
+      t1 = _this._arguments;
+      t2 = J.getInterceptor$asx(t1);
+      argumentCount = t2.get$length(t1) - J.get$length$asx(_this._namedArgumentNames) - _this._typeArgumentCount;
+      if (argumentCount === 0)
+        return B.List_empty;
+      list = [];
+      for (index = 0; index < argumentCount; ++index)
+        list.push(t2.$index(t1, index));
+      return J.JSArray_markUnmodifiableList(list);
+    },
+    get$namedArguments() {
+      var t1, t2, namedArgumentCount, t3, t4, namedArgumentsStartIndex, map, i, _this = this;
+      if (_this.__js_helper$_kind !== 0)
+        return B.Map_empty;
+      t1 = _this._namedArgumentNames;
+      t2 = J.getInterceptor$asx(t1);
+      namedArgumentCount = t2.get$length(t1);
+      t3 = _this._arguments;
+      t4 = J.getInterceptor$asx(t3);
+      namedArgumentsStartIndex = t4.get$length(t3) - namedArgumentCount - _this._typeArgumentCount;
+      if (namedArgumentCount === 0)
+        return B.Map_empty;
+      map = new A.JsLinkedHashMap(type$.JsLinkedHashMap_Symbol_dynamic);
+      for (i = 0; i < namedArgumentCount; ++i)
+        map.$indexSet(0, new A.Symbol(A._asString(t2.$index(t1, i))), t4.$index(t3, namedArgumentsStartIndex + i));
+      return new A.ConstantMapView(map, type$.ConstantMapView_Symbol_dynamic);
+    },
+    $isInvocation: 1
+  };
+  A.Primitives_functionNoSuchMethod_closure.prototype = {
+    call$2($name, argument) {
+      var t1;
+      A._asString($name);
+      t1 = this._box_0;
+      t1.names = t1.names + "$" + $name;
+      B.JSArray_methods.add$1(this.namedArgumentList, $name);
+      B.JSArray_methods.add$1(this.$arguments, argument);
+      ++t1.argumentCount;
+    },
+    $signature: 12
+  };
+  A.TypeErrorDecoder.prototype = {
+    matchTypeError$1(message) {
+      var result, t1, _this = this,
+        match = new RegExp(_this._pattern).exec(message);
+      if (match == null)
+        return null;
+      result = Object.create(null);
+      t1 = _this._arguments;
+      if (t1 !== -1)
+        result.arguments = match[t1 + 1];
+      t1 = _this._argumentsExpr;
+      if (t1 !== -1)
+        result.argumentsExpr = match[t1 + 1];
+      t1 = _this._expr;
+      if (t1 !== -1)
+        result.expr = match[t1 + 1];
+      t1 = _this._method;
+      if (t1 !== -1)
+        result.method = match[t1 + 1];
+      t1 = _this._receiver;
+      if (t1 !== -1)
+        result.receiver = match[t1 + 1];
+      return result;
+    }
+  };
+  A.NullError.prototype = {
+    toString$0(_) {
+      return "Null check operator used on a null value";
+    }
+  };
+  A.JsNoSuchMethodError.prototype = {
+    toString$0(_) {
+      var t2, _this = this,
+        _s38_ = "NoSuchMethodError: method not found: '",
+        t1 = _this._method;
+      if (t1 == null)
+        return "NoSuchMethodError: " + _this.__js_helper$_message;
+      t2 = _this._receiver;
+      if (t2 == null)
+        return _s38_ + t1 + "' (" + _this.__js_helper$_message + ")";
+      return _s38_ + t1 + "' on '" + t2 + "' (" + _this.__js_helper$_message + ")";
+    }
+  };
+  A.UnknownJsTypeError.prototype = {
+    toString$0(_) {
+      var t1 = this.__js_helper$_message;
+      return t1.length === 0 ? "Error" : "Error: " + t1;
+    }
+  };
+  A.NullThrownFromJavaScriptException.prototype = {
+    toString$0(_) {
+      return "Throw of null ('" + (this._irritant === null ? "null" : "undefined") + "' from JavaScript)";
+    }
+  };
+  A.ExceptionAndStackTrace.prototype = {};
+  A._StackTrace.prototype = {
+    toString$0(_) {
+      var trace,
+        t1 = this._trace;
+      if (t1 != null)
+        return t1;
+      t1 = this._exception;
+      trace = t1 !== null && typeof t1 === "object" ? t1.stack : null;
+      return this._trace = trace == null ? "" : trace;
+    },
+    $isStackTrace: 1
+  };
+  A.Closure.prototype = {
+    toString$0(_) {
+      var $constructor = this.constructor,
+        $name = $constructor == null ? null : $constructor.name;
+      return "Closure '" + A.unminifyOrTag($name == null ? "unknown" : $name) + "'";
+    },
+    $isFunction: 1,
+    get$$call() {
+      return this;
+    },
+    "call*": "call$1",
+    $requiredArgCount: 1,
+    $defaultValues: null
+  };
+  A.Closure0Args.prototype = {"call*": "call$0", $requiredArgCount: 0};
+  A.Closure2Args.prototype = {"call*": "call$2", $requiredArgCount: 2};
+  A.TearOffClosure.prototype = {};
+  A.StaticClosure.prototype = {
+    toString$0(_) {
+      var $name = this.$static_name;
+      if ($name == null)
+        return "Closure of unknown static method";
+      return "Closure '" + A.unminifyOrTag($name) + "'";
+    }
+  };
+  A.BoundClosure.prototype = {
+    $eq(_, other) {
+      if (other == null)
+        return false;
+      if (this === other)
+        return true;
+      if (!(other instanceof A.BoundClosure))
+        return false;
+      return this.$_target === other.$_target && this._receiver === other._receiver;
+    },
+    get$hashCode(_) {
+      return (A.objectHashCode(this._receiver) ^ A.Primitives_objectHashCode(this.$_target)) >>> 0;
+    },
+    toString$0(_) {
+      return "Closure '" + this.$_name + "' of " + ("Instance of '" + A.Primitives_objectTypeName(this._receiver) + "'");
+    }
+  };
+  A._CyclicInitializationError.prototype = {
+    toString$0(_) {
+      return "Reading static variable '" + this.variableName + "' during its initialization";
+    }
+  };
+  A.RuntimeError.prototype = {
+    toString$0(_) {
+      return "RuntimeError: " + this.message;
+    }
+  };
+  A._Required.prototype = {};
+  A.JsLinkedHashMap.prototype = {
+    get$length(_) {
+      return this.__js_helper$_length;
+    },
+    get$isEmpty(_) {
+      return this.__js_helper$_length === 0;
+    },
+    get$keys() {
+      return new A.LinkedHashMapKeyIterable(this, A._instanceType(this)._eval$1("LinkedHashMapKeyIterable<1>"));
+    },
+    containsKey$1(key) {
+      var strings = this._strings;
+      if (strings == null)
+        return false;
+      return strings[key] != null;
+    },
+    $index(_, key) {
+      var strings, cell, t1, nums, _null = null;
+      if (typeof key == "string") {
+        strings = this._strings;
+        if (strings == null)
+          return _null;
+        cell = strings[key];
+        t1 = cell == null ? _null : cell.hashMapCellValue;
+        return t1;
+      } else if (typeof key == "number" && (key & 0x3fffffff) === key) {
+        nums = this._nums;
+        if (nums == null)
+          return _null;
+        cell = nums[key];
+        t1 = cell == null ? _null : cell.hashMapCellValue;
+        return t1;
+      } else
+        return this.internalGet$1(key);
+    },
+    internalGet$1(key) {
+      var bucket, index,
+        rest = this.__js_helper$_rest;
+      if (rest == null)
+        return null;
+      bucket = rest[this.internalComputeHashCode$1(key)];
+      index = this.internalFindBucketIndex$2(bucket, key);
+      if (index < 0)
+        return null;
+      return bucket[index].hashMapCellValue;
+    },
+    $indexSet(_, key, value) {
+      var strings, nums, rest, hash, bucket, index, _this = this,
+        t1 = A._instanceType(_this);
+      t1._precomputed1._as(key);
+      t1._rest[1]._as(value);
+      if (typeof key == "string") {
+        strings = _this._strings;
+        _this._addHashTableEntry$3(strings == null ? _this._strings = _this._newHashTable$0() : strings, key, value);
+      } else if (typeof key == "number" && (key & 0x3fffffff) === key) {
+        nums = _this._nums;
+        _this._addHashTableEntry$3(nums == null ? _this._nums = _this._newHashTable$0() : nums, key, value);
+      } else {
+        rest = _this.__js_helper$_rest;
+        if (rest == null)
+          rest = _this.__js_helper$_rest = _this._newHashTable$0();
+        hash = _this.internalComputeHashCode$1(key);
+        bucket = rest[hash];
+        if (bucket == null)
+          rest[hash] = [_this._newLinkedCell$2(key, value)];
+        else {
+          index = _this.internalFindBucketIndex$2(bucket, key);
+          if (index >= 0)
+            bucket[index].hashMapCellValue = value;
+          else
+            bucket.push(_this._newLinkedCell$2(key, value));
+        }
+      }
+    },
+    putIfAbsent$2(key, ifAbsent) {
+      var t2, value, _this = this,
+        t1 = A._instanceType(_this);
+      t1._precomputed1._as(key);
+      t1._eval$1("2()")._as(ifAbsent);
+      if (_this.containsKey$1(key)) {
+        t2 = _this.$index(0, key);
+        return t2 == null ? t1._rest[1]._as(t2) : t2;
+      }
+      value = ifAbsent.call$0();
+      _this.$indexSet(0, key, value);
+      return value;
+    },
+    forEach$1(_, action) {
+      var cell, modifications, _this = this;
+      A._instanceType(_this)._eval$1("~(1,2)")._as(action);
+      cell = _this._first;
+      modifications = _this._modifications;
+      for (; cell != null;) {
+        action.call$2(cell.hashMapCellKey, cell.hashMapCellValue);
+        if (modifications !== _this._modifications)
+          throw A.wrapException(A.ConcurrentModificationError$(_this));
+        cell = cell._next;
+      }
+    },
+    _addHashTableEntry$3(table, key, value) {
+      var cell,
+        t1 = A._instanceType(this);
+      t1._precomputed1._as(key);
+      t1._rest[1]._as(value);
+      cell = table[key];
+      if (cell == null)
+        table[key] = this._newLinkedCell$2(key, value);
+      else
+        cell.hashMapCellValue = value;
+    },
+    _newLinkedCell$2(key, value) {
+      var _this = this,
+        t1 = A._instanceType(_this),
+        cell = new A.LinkedHashMapCell(t1._precomputed1._as(key), t1._rest[1]._as(value));
+      if (_this._first == null)
+        _this._first = _this._last = cell;
+      else
+        _this._last = _this._last._next = cell;
+      ++_this.__js_helper$_length;
+      _this._modifications = _this._modifications + 1 & 1073741823;
+      return cell;
+    },
+    internalComputeHashCode$1(key) {
+      return J.get$hashCode$(key) & 1073741823;
+    },
+    internalFindBucketIndex$2(bucket, key) {
+      var $length, i;
+      if (bucket == null)
+        return -1;
+      $length = bucket.length;
+      for (i = 0; i < $length; ++i)
+        if (J.$eq$(bucket[i].hashMapCellKey, key))
+          return i;
+      return -1;
+    },
+    toString$0(_) {
+      return A.MapBase_mapToString(this);
+    },
+    _newHashTable$0() {
+      var table = Object.create(null);
+      table["<non-identifier-key>"] = table;
+      delete table["<non-identifier-key>"];
+      return table;
+    }
+  };
+  A.LinkedHashMapCell.prototype = {};
+  A.LinkedHashMapKeyIterable.prototype = {
+    get$length(_) {
+      return this._map.__js_helper$_length;
+    },
+    get$isEmpty(_) {
+      return this._map.__js_helper$_length === 0;
+    },
+    get$iterator(_) {
+      var t1 = this._map,
+        t2 = new A.LinkedHashMapKeyIterator(t1, t1._modifications, this.$ti._eval$1("LinkedHashMapKeyIterator<1>"));
+      t2._cell = t1._first;
+      return t2;
+    }
+  };
+  A.LinkedHashMapKeyIterator.prototype = {
+    get$current() {
+      return this.__js_helper$_current;
+    },
+    moveNext$0() {
+      var cell, _this = this,
+        t1 = _this._map;
+      if (_this._modifications !== t1._modifications)
+        throw A.wrapException(A.ConcurrentModificationError$(t1));
+      cell = _this._cell;
+      if (cell == null) {
+        _this.set$__js_helper$_current(null);
+        return false;
+      } else {
+        _this.set$__js_helper$_current(cell.hashMapCellKey);
+        _this._cell = cell._next;
+        return true;
+      }
+    },
+    set$__js_helper$_current(_current) {
+      this.__js_helper$_current = this.$ti._eval$1("1?")._as(_current);
+    }
+  };
+  A.initHooks_closure.prototype = {
+    call$1(o) {
+      return this.getTag(o);
+    },
+    $signature: 8
+  };
+  A.initHooks_closure0.prototype = {
+    call$2(o, tag) {
+      return this.getUnknownTag(o, tag);
+    },
+    $signature: 13
+  };
+  A.initHooks_closure1.prototype = {
+    call$1(tag) {
+      return this.prototypeForTag(A._asString(tag));
+    },
+    $signature: 14
+  };
+  A.StringMatch.prototype = {};
+  A.NativeByteBuffer.prototype = {
+    get$runtimeType(receiver) {
+      return B.Type_ByteBuffer_RkP;
+    },
+    $isTrustedGetRuntimeType: 1
+  };
+  A.NativeTypedData.prototype = {};
+  A.NativeByteData.prototype = {
+    get$runtimeType(receiver) {
+      return B.Type_ByteData_zNC;
+    },
+    $isTrustedGetRuntimeType: 1
+  };
+  A.NativeTypedArray.prototype = {
+    get$length(receiver) {
+      return receiver.length;
+    },
+    $isJavaScriptIndexingBehavior: 1
+  };
+  A.NativeTypedArrayOfDouble.prototype = {
+    $index(receiver, index) {
+      A._checkValidIndex(index, receiver, receiver.length);
+      return receiver[index];
+    },
+    $isIterable: 1,
+    $isList: 1
+  };
+  A.NativeTypedArrayOfInt.prototype = {$isIterable: 1, $isList: 1};
+  A.NativeFloat32List.prototype = {
+    get$runtimeType(receiver) {
+      return B.Type_Float32List_LB7;
+    },
+    $isTrustedGetRuntimeType: 1
+  };
+  A.NativeFloat64List.prototype = {
+    get$runtimeType(receiver) {
+      return B.Type_Float64List_LB7;
+    },
+    $isTrustedGetRuntimeType: 1
+  };
+  A.NativeInt16List.prototype = {
+    get$runtimeType(receiver) {
+      return B.Type_Int16List_uXf;
+    },
+    $index(receiver, index) {
+      A._checkValidIndex(index, receiver, receiver.length);
+      return receiver[index];
+    },
+    $isTrustedGetRuntimeType: 1
+  };
+  A.NativeInt32List.prototype = {
+    get$runtimeType(receiver) {
+      return B.Type_Int32List_O50;
+    },
+    $index(receiver, index) {
+      A._checkValidIndex(index, receiver, receiver.length);
+      return receiver[index];
+    },
+    $isTrustedGetRuntimeType: 1
+  };
+  A.NativeInt8List.prototype = {
+    get$runtimeType(receiver) {
+      return B.Type_Int8List_ekJ;
+    },
+    $index(receiver, index) {
+      A._checkValidIndex(index, receiver, receiver.length);
+      return receiver[index];
+    },
+    $isTrustedGetRuntimeType: 1
+  };
+  A.NativeUint16List.prototype = {
+    get$runtimeType(receiver) {
+      return B.Type_Uint16List_2bx;
+    },
+    $index(receiver, index) {
+      A._checkValidIndex(index, receiver, receiver.length);
+      return receiver[index];
+    },
+    $isTrustedGetRuntimeType: 1
+  };
+  A.NativeUint32List.prototype = {
+    get$runtimeType(receiver) {
+      return B.Type_Uint32List_2bx;
+    },
+    $index(receiver, index) {
+      A._checkValidIndex(index, receiver, receiver.length);
+      return receiver[index];
+    },
+    $isTrustedGetRuntimeType: 1
+  };
+  A.NativeUint8ClampedList.prototype = {
+    get$runtimeType(receiver) {
+      return B.Type_Uint8ClampedList_Jik;
+    },
+    get$length(receiver) {
+      return receiver.length;
+    },
+    $index(receiver, index) {
+      A._checkValidIndex(index, receiver, receiver.length);
+      return receiver[index];
+    },
+    $isTrustedGetRuntimeType: 1
+  };
+  A.NativeUint8List.prototype = {
+    get$runtimeType(receiver) {
+      return B.Type_Uint8List_WLA;
+    },
+    get$length(receiver) {
+      return receiver.length;
+    },
+    $index(receiver, index) {
+      A._checkValidIndex(index, receiver, receiver.length);
+      return receiver[index];
+    },
+    $isTrustedGetRuntimeType: 1
+  };
+  A._NativeTypedArrayOfDouble_NativeTypedArray_ListMixin.prototype = {};
+  A._NativeTypedArrayOfDouble_NativeTypedArray_ListMixin_FixedLengthListMixin.prototype = {};
+  A._NativeTypedArrayOfInt_NativeTypedArray_ListMixin.prototype = {};
+  A._NativeTypedArrayOfInt_NativeTypedArray_ListMixin_FixedLengthListMixin.prototype = {};
+  A.Rti.prototype = {
+    _eval$1(recipe) {
+      return A._Universe_evalInEnvironment(init.typeUniverse, this, recipe);
+    },
+    _bind$1(typeOrTuple) {
+      return A._Universe_bind(init.typeUniverse, this, typeOrTuple);
+    }
+  };
+  A._FunctionParameters.prototype = {};
+  A._Type.prototype = {
+    toString$0(_) {
+      return A._rtiToString(this._rti, null);
+    }
+  };
+  A._Error.prototype = {
+    toString$0(_) {
+      return this.__rti$_message;
+    }
+  };
+  A._TypeError.prototype = {$isTypeError: 1};
+  A._AsyncRun__initializeScheduleImmediate_internalCallback.prototype = {
+    call$1(_) {
+      var t1 = this._box_0,
+        f = t1.storedCallback;
+      t1.storedCallback = null;
+      f.call$0();
+    },
+    $signature: 4
+  };
+  A._AsyncRun__initializeScheduleImmediate_closure.prototype = {
+    call$1(callback) {
+      var t1, t2;
+      this._box_0.storedCallback = type$.void_Function._as(callback);
+      t1 = this.div;
+      t2 = this.span;
+      t1.firstChild ? t1.removeChild(t2) : t1.appendChild(t2);
+    },
+    $signature: 15
+  };
+  A._AsyncRun__scheduleImmediateJsOverride_internalCallback.prototype = {
+    call$0() {
+      this.callback.call$0();
+    },
+    $signature: 2
+  };
+  A._AsyncRun__scheduleImmediateWithSetImmediate_internalCallback.prototype = {
+    call$0() {
+      this.callback.call$0();
+    },
+    $signature: 2
+  };
+  A._TimerImpl.prototype = {
+    _TimerImpl$2(milliseconds, callback) {
+      if (self.setTimeout != null)
+        this._handle = self.setTimeout(A.convertDartClosureToJS(new A._TimerImpl_internalCallback(this, callback), 0), milliseconds);
+      else
+        throw A.wrapException(A.UnsupportedError$("`setTimeout()` not found."));
+    },
+    cancel$0() {
+      if (self.setTimeout != null) {
+        var t1 = this._handle;
+        if (t1 == null)
+          return;
+        self.clearTimeout(t1);
+        this._handle = null;
+      } else
+        throw A.wrapException(A.UnsupportedError$("Canceling a timer."));
+    },
+    $isTimer: 1
+  };
+  A._TimerImpl_internalCallback.prototype = {
+    call$0() {
+      this.$this._handle = null;
+      this.callback.call$0();
+    },
+    $signature: 0
+  };
+  A._AsyncAwaitCompleter.prototype = {
+    complete$1(value) {
+      var t2, _this = this,
+        t1 = _this.$ti;
+      t1._eval$1("1/?")._as(value);
+      if (value == null)
+        value = t1._precomputed1._as(value);
+      if (!_this.isSync)
+        _this._future._asyncComplete$1(value);
+      else {
+        t2 = _this._future;
+        if (t1._eval$1("Future<1>")._is(value))
+          t2._chainFuture$1(value);
+        else
+          t2._completeWithValue$1(value);
+      }
+    },
+    completeError$2(e, st) {
+      var t1 = this._future;
+      if (this.isSync)
+        t1._completeError$2(e, st);
+      else
+        t1._asyncCompleteError$2(e, st);
+    },
+    $isCompleter: 1
+  };
+  A._awaitOnObject_closure.prototype = {
+    call$1(result) {
+      return this.bodyFunction.call$2(0, result);
+    },
+    $signature: 3
+  };
+  A._awaitOnObject_closure0.prototype = {
+    call$2(error, stackTrace) {
+      this.bodyFunction.call$2(1, new A.ExceptionAndStackTrace(error, type$.StackTrace._as(stackTrace)));
+    },
+    $signature: 16
+  };
+  A._wrapJsFunctionForAsync_closure.prototype = {
+    call$2(errorCode, result) {
+      this.$protected(A._asInt(errorCode), result);
+    },
+    $signature: 17
+  };
+  A.AsyncError.prototype = {
+    toString$0(_) {
+      return A.S(this.error);
+    },
+    $isError: 1,
+    get$stackTrace() {
+      return this.stackTrace;
+    }
+  };
+  A._Completer.prototype = {
+    completeError$2(error, stackTrace) {
+      A.checkNotNullable(error, "error", type$.Object);
+      if ((this.future._state & 30) !== 0)
+        throw A.wrapException(A.StateError$("Future already completed"));
+      if (stackTrace == null)
+        stackTrace = A.AsyncError_defaultStackTrace(error);
+      this._completeError$2(error, stackTrace);
+    },
+    completeError$1(error) {
+      return this.completeError$2(error, null);
+    },
+    $isCompleter: 1
+  };
+  A._AsyncCompleter.prototype = {
+    complete$1(value) {
+      var t2,
+        t1 = this.$ti;
+      t1._eval$1("1/?")._as(value);
+      t2 = this.future;
+      if ((t2._state & 30) !== 0)
+        throw A.wrapException(A.StateError$("Future already completed"));
+      t2._asyncComplete$1(t1._eval$1("1/")._as(value));
+    },
+    complete$0() {
+      return this.complete$1(null);
+    },
+    _completeError$2(error, stackTrace) {
+      this.future._asyncCompleteError$2(error, stackTrace);
+    }
+  };
+  A._SyncCompleter.prototype = {
+    complete$1(value) {
+      var t2,
+        t1 = this.$ti;
+      t1._eval$1("1/?")._as(value);
+      t2 = this.future;
+      if ((t2._state & 30) !== 0)
+        throw A.wrapException(A.StateError$("Future already completed"));
+      t2._complete$1(t1._eval$1("1/")._as(value));
+    },
+    _completeError$2(error, stackTrace) {
+      this.future._completeError$2(error, stackTrace);
+    }
+  };
+  A._FutureListener.prototype = {
+    matchesErrorTest$1(asyncError) {
+      if ((this.state & 15) !== 6)
+        return true;
+      return this.result._zone.runUnary$2$2(type$.bool_Function_Object._as(this.callback), asyncError.error, type$.bool, type$.Object);
+    },
+    handleError$1(asyncError) {
+      var exception, _this = this,
+        errorCallback = _this.errorCallback,
+        result = null,
+        t1 = type$.dynamic,
+        t2 = type$.Object,
+        t3 = asyncError.error,
+        t4 = _this.result._zone;
+      if (type$.dynamic_Function_Object_StackTrace._is(errorCallback))
+        result = t4.runBinary$3$3(errorCallback, t3, asyncError.stackTrace, t1, t2, type$.StackTrace);
+      else
+        result = t4.runUnary$2$2(type$.dynamic_Function_Object._as(errorCallback), t3, t1, t2);
+      try {
+        t1 = _this.$ti._eval$1("2/")._as(result);
+        return t1;
+      } catch (exception) {
+        if (type$.TypeError._is(A.unwrapException(exception))) {
+          if ((_this.state & 1) !== 0)
+            throw A.wrapException(A.ArgumentError$("The error handler of Future.then must return a value of the returned future's type", "onError"));
+          throw A.wrapException(A.ArgumentError$("The error handler of Future.catchError must return a value of the future's type", "onError"));
+        } else
+          throw exception;
+      }
+    }
+  };
+  A._Future.prototype = {
+    _setChained$1(source) {
+      this._state = this._state & 1 | 4;
+      this._resultOrListeners = source;
+    },
+    then$1$2$onError(f, onError, $R) {
+      var currentZone, result, t2,
+        t1 = this.$ti;
+      t1._bind$1($R)._eval$1("1/(2)")._as(f);
+      currentZone = $.Zone__current;
+      if (currentZone === B.C__RootZone) {
+        if (onError != null && !type$.dynamic_Function_Object_StackTrace._is(onError) && !type$.dynamic_Function_Object._is(onError))
+          throw A.wrapException(A.ArgumentError$value(onError, "onError", string$.Error_));
+      } else {
+        $R._eval$1("@<0/>")._bind$1(t1._precomputed1)._eval$1("1(2)")._as(f);
+        if (onError != null)
+          onError = A._registerErrorHandler(onError, currentZone);
+      }
+      result = new A._Future(currentZone, $R._eval$1("_Future<0>"));
+      t2 = onError == null ? 1 : 3;
+      this._addListener$1(new A._FutureListener(result, t2, f, onError, t1._eval$1("@<1>")._bind$1($R)._eval$1("_FutureListener<1,2>")));
+      return result;
+    },
+    then$1$1(f, $R) {
+      return this.then$1$2$onError(f, null, $R);
+    },
+    _thenAwait$1$2(f, onError, $E) {
+      var result,
+        t1 = this.$ti;
+      t1._bind$1($E)._eval$1("1/(2)")._as(f);
+      result = new A._Future($.Zone__current, $E._eval$1("_Future<0>"));
+      this._addListener$1(new A._FutureListener(result, 19, f, onError, t1._eval$1("@<1>")._bind$1($E)._eval$1("_FutureListener<1,2>")));
+      return result;
+    },
+    whenComplete$1(action) {
+      var t1, result;
+      type$.dynamic_Function._as(action);
+      t1 = this.$ti;
+      result = new A._Future($.Zone__current, t1);
+      this._addListener$1(new A._FutureListener(result, 8, action, null, t1._eval$1("@<1>")._bind$1(t1._precomputed1)._eval$1("_FutureListener<1,2>")));
+      return result;
+    },
+    _setErrorObject$1(error) {
+      this._state = this._state & 1 | 16;
+      this._resultOrListeners = error;
+    },
+    _cloneResult$1(source) {
+      this._state = source._state & 30 | this._state & 1;
+      this._resultOrListeners = source._resultOrListeners;
+    },
+    _addListener$1(listener) {
+      var source, _this = this,
+        t1 = _this._state;
+      if (t1 <= 3) {
+        listener._nextListener = type$.nullable__FutureListener_dynamic_dynamic._as(_this._resultOrListeners);
+        _this._resultOrListeners = listener;
+      } else {
+        if ((t1 & 4) !== 0) {
+          source = type$._Future_dynamic._as(_this._resultOrListeners);
+          if ((source._state & 24) === 0) {
+            source._addListener$1(listener);
+            return;
+          }
+          _this._cloneResult$1(source);
+        }
+        A._rootScheduleMicrotask(null, null, _this._zone, type$.void_Function._as(new A._Future__addListener_closure(_this, listener)));
+      }
+    },
+    _prependListeners$1(listeners) {
+      var t1, existingListeners, next, cursor, next0, source, _this = this, _box_0 = {};
+      _box_0.listeners = listeners;
+      if (listeners == null)
+        return;
+      t1 = _this._state;
+      if (t1 <= 3) {
+        existingListeners = type$.nullable__FutureListener_dynamic_dynamic._as(_this._resultOrListeners);
+        _this._resultOrListeners = listeners;
+        if (existingListeners != null) {
+          next = listeners._nextListener;
+          for (cursor = listeners; next != null; cursor = next, next = next0)
+            next0 = next._nextListener;
+          cursor._nextListener = existingListeners;
+        }
+      } else {
+        if ((t1 & 4) !== 0) {
+          source = type$._Future_dynamic._as(_this._resultOrListeners);
+          if ((source._state & 24) === 0) {
+            source._prependListeners$1(listeners);
+            return;
+          }
+          _this._cloneResult$1(source);
+        }
+        _box_0.listeners = _this._reverseListeners$1(listeners);
+        A._rootScheduleMicrotask(null, null, _this._zone, type$.void_Function._as(new A._Future__prependListeners_closure(_box_0, _this)));
+      }
+    },
+    _removeListeners$0() {
+      var current = type$.nullable__FutureListener_dynamic_dynamic._as(this._resultOrListeners);
+      this._resultOrListeners = null;
+      return this._reverseListeners$1(current);
+    },
+    _reverseListeners$1(listeners) {
+      var current, prev, next;
+      for (current = listeners, prev = null; current != null; prev = current, current = next) {
+        next = current._nextListener;
+        current._nextListener = prev;
+      }
+      return prev;
+    },
+    _chainForeignFuture$1(source) {
+      var e, s, exception, _this = this;
+      _this._state ^= 2;
+      try {
+        source.then$1$2$onError(new A._Future__chainForeignFuture_closure(_this), new A._Future__chainForeignFuture_closure0(_this), type$.Null);
+      } catch (exception) {
+        e = A.unwrapException(exception);
+        s = A.getTraceFromException(exception);
+        A.scheduleMicrotask(new A._Future__chainForeignFuture_closure1(_this, e, s));
+      }
+    },
+    _complete$1(value) {
+      var listeners, _this = this,
+        t1 = _this.$ti;
+      t1._eval$1("1/")._as(value);
+      if (t1._eval$1("Future<1>")._is(value))
+        if (t1._is(value))
+          A._Future__chainCoreFutureSync(value, _this);
+        else
+          _this._chainForeignFuture$1(value);
+      else {
+        listeners = _this._removeListeners$0();
+        t1._precomputed1._as(value);
+        _this._state = 8;
+        _this._resultOrListeners = value;
+        A._Future__propagateToListeners(_this, listeners);
+      }
+    },
+    _completeWithValue$1(value) {
+      var listeners, _this = this;
+      _this.$ti._precomputed1._as(value);
+      listeners = _this._removeListeners$0();
+      _this._state = 8;
+      _this._resultOrListeners = value;
+      A._Future__propagateToListeners(_this, listeners);
+    },
+    _completeError$2(error, stackTrace) {
+      var listeners;
+      type$.Object._as(error);
+      type$.StackTrace._as(stackTrace);
+      listeners = this._removeListeners$0();
+      this._setErrorObject$1(A.AsyncError$(error, stackTrace));
+      A._Future__propagateToListeners(this, listeners);
+    },
+    _asyncComplete$1(value) {
+      var t1 = this.$ti;
+      t1._eval$1("1/")._as(value);
+      if (t1._eval$1("Future<1>")._is(value)) {
+        this._chainFuture$1(value);
+        return;
+      }
+      this._asyncCompleteWithValue$1(value);
+    },
+    _asyncCompleteWithValue$1(value) {
+      var _this = this;
+      _this.$ti._precomputed1._as(value);
+      _this._state ^= 2;
+      A._rootScheduleMicrotask(null, null, _this._zone, type$.void_Function._as(new A._Future__asyncCompleteWithValue_closure(_this, value)));
+    },
+    _chainFuture$1(value) {
+      var t1 = this.$ti;
+      t1._eval$1("Future<1>")._as(value);
+      if (t1._is(value)) {
+        A._Future__chainCoreFutureAsync(value, this);
+        return;
+      }
+      this._chainForeignFuture$1(value);
+    },
+    _asyncCompleteError$2(error, stackTrace) {
+      type$.StackTrace._as(stackTrace);
+      this._state ^= 2;
+      A._rootScheduleMicrotask(null, null, this._zone, type$.void_Function._as(new A._Future__asyncCompleteError_closure(this, error, stackTrace)));
+    },
+    $isFuture: 1
+  };
+  A._Future__addListener_closure.prototype = {
+    call$0() {
+      A._Future__propagateToListeners(this.$this, this.listener);
+    },
+    $signature: 0
+  };
+  A._Future__prependListeners_closure.prototype = {
+    call$0() {
+      A._Future__propagateToListeners(this.$this, this._box_0.listeners);
+    },
+    $signature: 0
+  };
+  A._Future__chainForeignFuture_closure.prototype = {
+    call$1(value) {
+      var error, stackTrace, exception,
+        t1 = this.$this;
+      t1._state ^= 2;
+      try {
+        t1._completeWithValue$1(t1.$ti._precomputed1._as(value));
+      } catch (exception) {
+        error = A.unwrapException(exception);
+        stackTrace = A.getTraceFromException(exception);
+        t1._completeError$2(error, stackTrace);
+      }
+    },
+    $signature: 4
+  };
+  A._Future__chainForeignFuture_closure0.prototype = {
+    call$2(error, stackTrace) {
+      this.$this._completeError$2(type$.Object._as(error), type$.StackTrace._as(stackTrace));
+    },
+    $signature: 5
+  };
+  A._Future__chainForeignFuture_closure1.prototype = {
+    call$0() {
+      this.$this._completeError$2(this.e, this.s);
+    },
+    $signature: 0
+  };
+  A._Future__chainCoreFutureAsync_closure.prototype = {
+    call$0() {
+      A._Future__chainCoreFutureSync(this._box_0.source, this.target);
+    },
+    $signature: 0
+  };
+  A._Future__asyncCompleteWithValue_closure.prototype = {
+    call$0() {
+      this.$this._completeWithValue$1(this.value);
+    },
+    $signature: 0
+  };
+  A._Future__asyncCompleteError_closure.prototype = {
+    call$0() {
+      this.$this._completeError$2(this.error, this.stackTrace);
+    },
+    $signature: 0
+  };
+  A._Future__propagateToListeners_handleWhenCompleteCallback.prototype = {
+    call$0() {
+      var e, s, t1, exception, t2, originalSource, _this = this, completeResult = null;
+      try {
+        t1 = _this._box_0.listener;
+        completeResult = t1.result._zone.run$1$1(type$.dynamic_Function._as(t1.callback), type$.dynamic);
+      } catch (exception) {
+        e = A.unwrapException(exception);
+        s = A.getTraceFromException(exception);
+        t1 = _this.hasError && type$.AsyncError._as(_this._box_1.source._resultOrListeners).error === e;
+        t2 = _this._box_0;
+        if (t1)
+          t2.listenerValueOrError = type$.AsyncError._as(_this._box_1.source._resultOrListeners);
+        else
+          t2.listenerValueOrError = A.AsyncError$(e, s);
+        t2.listenerHasError = true;
+        return;
+      }
+      if (completeResult instanceof A._Future && (completeResult._state & 24) !== 0) {
+        if ((completeResult._state & 16) !== 0) {
+          t1 = _this._box_0;
+          t1.listenerValueOrError = type$.AsyncError._as(completeResult._resultOrListeners);
+          t1.listenerHasError = true;
+        }
+        return;
+      }
+      if (completeResult instanceof A._Future) {
+        originalSource = _this._box_1.source;
+        t1 = _this._box_0;
+        t1.listenerValueOrError = completeResult.then$1$1(new A._Future__propagateToListeners_handleWhenCompleteCallback_closure(originalSource), type$.dynamic);
+        t1.listenerHasError = false;
+      }
+    },
+    $signature: 0
+  };
+  A._Future__propagateToListeners_handleWhenCompleteCallback_closure.prototype = {
+    call$1(_) {
+      return this.originalSource;
+    },
+    $signature: 18
+  };
+  A._Future__propagateToListeners_handleValueCallback.prototype = {
+    call$0() {
+      var e, s, t1, t2, t3, t4, t5, exception;
+      try {
+        t1 = this._box_0;
+        t2 = t1.listener;
+        t3 = t2.$ti;
+        t4 = t3._precomputed1;
+        t5 = t4._as(this.sourceResult);
+        t1.listenerValueOrError = t2.result._zone.runUnary$2$2(t3._eval$1("2/(1)")._as(t2.callback), t5, t3._eval$1("2/"), t4);
+      } catch (exception) {
+        e = A.unwrapException(exception);
+        s = A.getTraceFromException(exception);
+        t1 = this._box_0;
+        t1.listenerValueOrError = A.AsyncError$(e, s);
+        t1.listenerHasError = true;
+      }
+    },
+    $signature: 0
+  };
+  A._Future__propagateToListeners_handleError.prototype = {
+    call$0() {
+      var asyncError, e, s, t1, exception, t2, _this = this;
+      try {
+        asyncError = type$.AsyncError._as(_this._box_1.source._resultOrListeners);
+        t1 = _this._box_0;
+        if (t1.listener.matchesErrorTest$1(asyncError) && t1.listener.errorCallback != null) {
+          t1.listenerValueOrError = t1.listener.handleError$1(asyncError);
+          t1.listenerHasError = false;
+        }
+      } catch (exception) {
+        e = A.unwrapException(exception);
+        s = A.getTraceFromException(exception);
+        t1 = type$.AsyncError._as(_this._box_1.source._resultOrListeners);
+        t2 = _this._box_0;
+        if (t1.error === e)
+          t2.listenerValueOrError = t1;
+        else
+          t2.listenerValueOrError = A.AsyncError$(e, s);
+        t2.listenerHasError = true;
+      }
+    },
+    $signature: 0
+  };
+  A._AsyncCallbackEntry.prototype = {};
+  A.Stream.prototype = {
+    get$length(_) {
+      var t1 = {},
+        future = new A._Future($.Zone__current, type$._Future_int);
+      t1.count = 0;
+      this.listen$4$cancelOnError$onDone$onError(new A.Stream_length_closure(t1, this), true, new A.Stream_length_closure0(t1, future), future.get$_completeError());
+      return future;
+    },
+    get$first(_) {
+      var future = new A._Future($.Zone__current, A._instanceType(this)._eval$1("_Future<1>")),
+        subscription = this.listen$4$cancelOnError$onDone$onError(null, true, new A.Stream_first_closure(future), future.get$_completeError());
+      subscription.onData$1(new A.Stream_first_closure0(this, subscription, future));
+      return future;
+    }
+  };
+  A.Stream_length_closure.prototype = {
+    call$1(_) {
+      A._instanceType(this.$this)._precomputed1._as(_);
+      ++this._box_0.count;
+    },
+    $signature() {
+      return A._instanceType(this.$this)._eval$1("~(1)");
+    }
+  };
+  A.Stream_length_closure0.prototype = {
+    call$0() {
+      this.future._complete$1(this._box_0.count);
+    },
+    $signature: 0
+  };
+  A.Stream_first_closure.prototype = {
+    call$0() {
+      var e, s, t1, exception, stackTrace;
+      try {
+        t1 = A.IterableElementError_noElement();
+        throw A.wrapException(t1);
+      } catch (exception) {
+        e = A.unwrapException(exception);
+        s = A.getTraceFromException(exception);
+        t1 = e;
+        stackTrace = s;
+        if (stackTrace == null)
+          stackTrace = A.AsyncError_defaultStackTrace(t1);
+        this.future._completeError$2(t1, stackTrace);
+      }
+    },
+    $signature: 0
+  };
+  A.Stream_first_closure0.prototype = {
+    call$1(value) {
+      A._cancelAndValue(this.subscription, this.future, A._instanceType(this.$this)._precomputed1._as(value));
+    },
+    $signature() {
+      return A._instanceType(this.$this)._eval$1("~(1)");
+    }
+  };
+  A._StreamController.prototype = {
+    get$_pendingEvents() {
+      var t1, _this = this;
+      if ((_this._state & 8) === 0)
+        return A._instanceType(_this)._eval$1("_PendingEvents<1>?")._as(_this._varData);
+      t1 = A._instanceType(_this);
+      return t1._eval$1("_PendingEvents<1>?")._as(t1._eval$1("_StreamControllerAddStreamState<1>")._as(_this._varData).get$_varData());
+    },
+    _ensurePendingEvents$0() {
+      var events, t1, _this = this;
+      if ((_this._state & 8) === 0) {
+        events = _this._varData;
+        if (events == null)
+          events = _this._varData = new A._PendingEvents(A._instanceType(_this)._eval$1("_PendingEvents<1>"));
+        return A._instanceType(_this)._eval$1("_PendingEvents<1>")._as(events);
+      }
+      t1 = A._instanceType(_this);
+      events = t1._eval$1("_StreamControllerAddStreamState<1>")._as(_this._varData).get$_varData();
+      return t1._eval$1("_PendingEvents<1>")._as(events);
+    },
+    get$_subscription() {
+      var varData = this._varData;
+      if ((this._state & 8) !== 0)
+        varData = type$._StreamControllerAddStreamState_nullable_Object._as(varData).get$_varData();
+      return A._instanceType(this)._eval$1("_ControllerSubscription<1>")._as(varData);
+    },
+    _badEventState$0() {
+      if ((this._state & 4) !== 0)
+        return new A.StateError("Cannot add event after closing");
+      return new A.StateError("Cannot add event while adding a stream");
+    },
+    _ensureDoneFuture$0() {
+      var t1 = this._doneFuture;
+      if (t1 == null)
+        t1 = this._doneFuture = (this._state & 2) !== 0 ? $.$get$Future__nullFuture() : new A._Future($.Zone__current, type$._Future_void);
+      return t1;
+    },
+    add$1(_, value) {
+      var t2, _this = this,
+        t1 = A._instanceType(_this);
+      t1._precomputed1._as(value);
+      t2 = _this._state;
+      if (t2 >= 4)
+        throw A.wrapException(_this._badEventState$0());
+      if ((t2 & 1) !== 0)
+        _this._sendData$1(value);
+      else if ((t2 & 3) === 0)
+        _this._ensurePendingEvents$0().add$1(0, new A._DelayedData(value, t1._eval$1("_DelayedData<1>")));
+    },
+    close$0() {
+      var _this = this,
+        t1 = _this._state;
+      if ((t1 & 4) !== 0)
+        return _this._ensureDoneFuture$0();
+      if (t1 >= 4)
+        throw A.wrapException(_this._badEventState$0());
+      t1 = _this._state = t1 | 4;
+      if ((t1 & 1) !== 0)
+        _this._sendDone$0();
+      else if ((t1 & 3) === 0)
+        _this._ensurePendingEvents$0().add$1(0, B.C__DelayedDone);
+      return _this._ensureDoneFuture$0();
+    },
+    _subscribe$4(onData, onError, onDone, cancelOnError) {
+      var t2, t3, t4, t5, t6, t7, t8, subscription, pendingEvents, addState, _this = this,
+        t1 = A._instanceType(_this);
+      t1._eval$1("~(1)?")._as(onData);
+      type$.nullable_void_Function._as(onDone);
+      if ((_this._state & 3) !== 0)
+        throw A.wrapException(A.StateError$("Stream has already been listened to."));
+      t2 = $.Zone__current;
+      t3 = cancelOnError ? 1 : 0;
+      t4 = onError != null ? 32 : 0;
+      t5 = A._BufferingStreamSubscription__registerDataHandler(t2, onData, t1._precomputed1);
+      t6 = A._BufferingStreamSubscription__registerErrorHandler(t2, onError);
+      t7 = onDone == null ? A.async___nullDoneHandler$closure() : onDone;
+      t8 = type$.void_Function;
+      subscription = new A._ControllerSubscription(_this, t5, t6, t8._as(t7), t2, t3 | t4, t1._eval$1("_ControllerSubscription<1>"));
+      pendingEvents = _this.get$_pendingEvents();
+      t4 = _this._state |= 1;
+      if ((t4 & 8) !== 0) {
+        addState = t1._eval$1("_StreamControllerAddStreamState<1>")._as(_this._varData);
+        addState.set$_varData(subscription);
+        addState.resume$0();
+      } else
+        _this._varData = subscription;
+      subscription._setPendingEvents$1(pendingEvents);
+      t1 = t8._as(new A._StreamController__subscribe_closure(_this));
+      t2 = subscription._state;
+      subscription._state = t2 | 64;
+      t1.call$0();
+      subscription._state &= 4294967231;
+      subscription._checkState$1((t2 & 4) !== 0);
+      return subscription;
+    },
+    _recordCancel$1(subscription) {
+      var result, onCancel, cancelResult, e, s, exception, result0, _this = this,
+        t1 = A._instanceType(_this);
+      t1._eval$1("StreamSubscription<1>")._as(subscription);
+      result = null;
+      if ((_this._state & 8) !== 0)
+        result = t1._eval$1("_StreamControllerAddStreamState<1>")._as(_this._varData).cancel$0();
+      _this._varData = null;
+      _this._state = _this._state & 4294967286 | 2;
+      onCancel = _this.onCancel;
+      if (onCancel != null)
+        if (result == null)
+          try {
+            cancelResult = onCancel.call$0();
+            if (cancelResult instanceof A._Future)
+              result = cancelResult;
+          } catch (exception) {
+            e = A.unwrapException(exception);
+            s = A.getTraceFromException(exception);
+            result0 = new A._Future($.Zone__current, type$._Future_void);
+            result0._asyncCompleteError$2(e, s);
+            result = result0;
+          }
+        else
+          result = result.whenComplete$1(onCancel);
+      t1 = new A._StreamController__recordCancel_complete(_this);
+      if (result != null)
+        result = result.whenComplete$1(t1);
+      else
+        t1.call$0();
+      return result;
+    },
+    $isStreamController: 1,
+    $is_StreamControllerLifecycle: 1,
+    $is_EventDispatch: 1
+  };
+  A._StreamController__subscribe_closure.prototype = {
+    call$0() {
+      A._runGuarded(this.$this.onListen);
+    },
+    $signature: 0
+  };
+  A._StreamController__recordCancel_complete.prototype = {
+    call$0() {
+      var doneFuture = this.$this._doneFuture;
+      if (doneFuture != null && (doneFuture._state & 30) === 0)
+        doneFuture._asyncComplete$1(null);
+    },
+    $signature: 0
+  };
+  A._AsyncStreamControllerDispatch.prototype = {
+    _sendData$1(data) {
+      var t1 = this.$ti;
+      t1._precomputed1._as(data);
+      this.get$_subscription()._addPending$1(new A._DelayedData(data, t1._eval$1("_DelayedData<1>")));
+    },
+    _sendError$2(error, stackTrace) {
+      this.get$_subscription()._addPending$1(new A._DelayedError(error, stackTrace));
+    },
+    _sendDone$0() {
+      this.get$_subscription()._addPending$1(B.C__DelayedDone);
+    }
+  };
+  A._AsyncStreamController.prototype = {};
+  A._ControllerStream.prototype = {
+    get$hashCode(_) {
+      return (A.Primitives_objectHashCode(this._controller) ^ 892482866) >>> 0;
+    },
+    $eq(_, other) {
+      if (other == null)
+        return false;
+      if (this === other)
+        return true;
+      return other instanceof A._ControllerStream && other._controller === this._controller;
+    }
+  };
+  A._ControllerSubscription.prototype = {
+    _onCancel$0() {
+      return this._controller._recordCancel$1(this);
+    },
+    _onPause$0() {
+      var t1 = this._controller,
+        t2 = A._instanceType(t1);
+      t2._eval$1("StreamSubscription<1>")._as(this);
+      if ((t1._state & 8) !== 0)
+        t2._eval$1("_StreamControllerAddStreamState<1>")._as(t1._varData).pause$0();
+      A._runGuarded(t1.onPause);
+    },
+    _onResume$0() {
+      var t1 = this._controller,
+        t2 = A._instanceType(t1);
+      t2._eval$1("StreamSubscription<1>")._as(this);
+      if ((t1._state & 8) !== 0)
+        t2._eval$1("_StreamControllerAddStreamState<1>")._as(t1._varData).resume$0();
+      A._runGuarded(t1.onResume);
+    }
+  };
+  A._StreamSinkWrapper.prototype = {};
+  A._BufferingStreamSubscription.prototype = {
+    _setPendingEvents$1(pendingEvents) {
+      var _this = this;
+      A._instanceType(_this)._eval$1("_PendingEvents<1>?")._as(pendingEvents);
+      if (pendingEvents == null)
+        return;
+      _this.set$_pending(pendingEvents);
+      if (pendingEvents.lastPendingEvent != null) {
+        _this._state |= 128;
+        pendingEvents.schedule$1(_this);
+      }
+    },
+    onData$1(handleData) {
+      var t1 = A._instanceType(this);
+      this.set$_onData(A._BufferingStreamSubscription__registerDataHandler(this._zone, t1._eval$1("~(1)?")._as(handleData), t1._precomputed1));
+    },
+    cancel$0() {
+      var t1 = this._state &= 4294967279;
+      if ((t1 & 8) === 0)
+        this._cancel$0();
+      t1 = this._cancelFuture;
+      return t1 == null ? $.$get$Future__nullFuture() : t1;
+    },
+    asFuture$1$1(futureValue, $E) {
+      var result, _this = this, t1 = {};
+      t1.resultValue = null;
+      if (!$E._is(null))
+        throw A.wrapException(A.ArgumentError$notNull("futureValue"));
+      $E._as(futureValue);
+      t1.resultValue = futureValue;
+      result = new A._Future($.Zone__current, $E._eval$1("_Future<0>"));
+      _this.set$_onDone(new A._BufferingStreamSubscription_asFuture_closure(t1, result));
+      _this._state |= 32;
+      _this._onError = new A._BufferingStreamSubscription_asFuture_closure0(_this, result);
+      return result;
+    },
+    _cancel$0() {
+      var t2, _this = this,
+        t1 = _this._state |= 8;
+      if ((t1 & 128) !== 0) {
+        t2 = _this._pending;
+        if (t2._state === 1)
+          t2._state = 3;
+      }
+      if ((t1 & 64) === 0)
+        _this.set$_pending(null);
+      _this._cancelFuture = _this._onCancel$0();
+    },
+    _onPause$0() {
+    },
+    _onResume$0() {
+    },
+    _onCancel$0() {
+      return null;
+    },
+    _addPending$1($event) {
+      var t1, _this = this,
+        pending = _this._pending;
+      if (pending == null) {
+        pending = new A._PendingEvents(A._instanceType(_this)._eval$1("_PendingEvents<1>"));
+        _this.set$_pending(pending);
+      }
+      pending.add$1(0, $event);
+      t1 = _this._state;
+      if ((t1 & 128) === 0) {
+        t1 |= 128;
+        _this._state = t1;
+        if (t1 < 256)
+          pending.schedule$1(_this);
+      }
+    },
+    _sendData$1(data) {
+      var t2, _this = this,
+        t1 = A._instanceType(_this)._precomputed1;
+      t1._as(data);
+      t2 = _this._state;
+      _this._state = t2 | 64;
+      _this._zone.runUnaryGuarded$1$2(_this._onData, data, t1);
+      _this._state &= 4294967231;
+      _this._checkState$1((t2 & 4) !== 0);
+    },
+    _sendError$2(error, stackTrace) {
+      var cancelFuture, _this = this,
+        t1 = _this._state,
+        t2 = new A._BufferingStreamSubscription__sendError_sendError(_this, error, stackTrace);
+      if ((t1 & 1) !== 0) {
+        _this._state = t1 | 16;
+        _this._cancel$0();
+        cancelFuture = _this._cancelFuture;
+        if (cancelFuture != null && cancelFuture !== $.$get$Future__nullFuture())
+          cancelFuture.whenComplete$1(t2);
+        else
+          t2.call$0();
+      } else {
+        t2.call$0();
+        _this._checkState$1((t1 & 4) !== 0);
+      }
+    },
+    _sendDone$0() {
+      var cancelFuture, _this = this,
+        t1 = new A._BufferingStreamSubscription__sendDone_sendDone(_this);
+      _this._cancel$0();
+      _this._state |= 16;
+      cancelFuture = _this._cancelFuture;
+      if (cancelFuture != null && cancelFuture !== $.$get$Future__nullFuture())
+        cancelFuture.whenComplete$1(t1);
+      else
+        t1.call$0();
+    },
+    _checkState$1(wasInputPaused) {
+      var t2, isInputPaused, _this = this,
+        t1 = _this._state;
+      if ((t1 & 128) !== 0 && _this._pending.lastPendingEvent == null) {
+        t1 = _this._state = t1 & 4294967167;
+        if ((t1 & 4) !== 0)
+          if (t1 < 256) {
+            t2 = _this._pending;
+            t2 = t2 == null ? null : t2.lastPendingEvent == null;
+            t2 = t2 !== false;
+          } else
+            t2 = false;
+        else
+          t2 = false;
+        if (t2) {
+          t1 &= 4294967291;
+          _this._state = t1;
+        }
+      }
+      for (; true; wasInputPaused = isInputPaused) {
+        if ((t1 & 8) !== 0) {
+          _this.set$_pending(null);
+          return;
+        }
+        isInputPaused = (t1 & 4) !== 0;
+        if (wasInputPaused === isInputPaused)
+          break;
+        _this._state = t1 ^ 64;
+        if (isInputPaused)
+          _this._onPause$0();
+        else
+          _this._onResume$0();
+        t1 = _this._state &= 4294967231;
+      }
+      if ((t1 & 128) !== 0 && t1 < 256)
+        _this._pending.schedule$1(_this);
+    },
+    set$_onData(_onData) {
+      this._onData = A._instanceType(this)._eval$1("~(1)")._as(_onData);
+    },
+    set$_onDone(_onDone) {
+      this._onDone = type$.void_Function._as(_onDone);
+    },
+    set$_pending(_pending) {
+      this._pending = A._instanceType(this)._eval$1("_PendingEvents<1>?")._as(_pending);
+    },
+    $isStreamSubscription: 1,
+    $is_EventDispatch: 1
+  };
+  A._BufferingStreamSubscription_asFuture_closure.prototype = {
+    call$0() {
+      this.result._complete$1(this._box_0.resultValue);
+    },
+    $signature: 0
+  };
+  A._BufferingStreamSubscription_asFuture_closure0.prototype = {
+    call$2(error, stackTrace) {
+      var cancelFuture = this.$this.cancel$0(),
+        t1 = this.result;
+      if (cancelFuture !== $.$get$Future__nullFuture())
+        cancelFuture.whenComplete$1(new A._BufferingStreamSubscription_asFuture__closure(t1, error, stackTrace));
+      else
+        t1._completeError$2(error, stackTrace);
+    },
+    $signature: 5
+  };
+  A._BufferingStreamSubscription_asFuture__closure.prototype = {
+    call$0() {
+      this.result._completeError$2(this.error, this.stackTrace);
+    },
+    $signature: 2
+  };
+  A._BufferingStreamSubscription__sendError_sendError.prototype = {
+    call$0() {
+      var onError, t3, t4,
+        t1 = this.$this,
+        t2 = t1._state;
+      if ((t2 & 8) !== 0 && (t2 & 16) === 0)
+        return;
+      t1._state = t2 | 64;
+      onError = t1._onError;
+      t2 = this.error;
+      t3 = type$.Object;
+      t4 = t1._zone;
+      if (type$.void_Function_Object_StackTrace._is(onError))
+        t4.runBinaryGuarded$2$3(onError, t2, this.stackTrace, t3, type$.StackTrace);
+      else
+        t4.runUnaryGuarded$1$2(type$.void_Function_Object._as(onError), t2, t3);
+      t1._state &= 4294967231;
+    },
+    $signature: 0
+  };
+  A._BufferingStreamSubscription__sendDone_sendDone.prototype = {
+    call$0() {
+      var t1 = this.$this,
+        t2 = t1._state;
+      if ((t2 & 16) === 0)
+        return;
+      t1._state = t2 | 74;
+      t1._zone.runGuarded$1(t1._onDone);
+      t1._state &= 4294967231;
+    },
+    $signature: 0
+  };
+  A._StreamImpl.prototype = {
+    listen$4$cancelOnError$onDone$onError(onData, cancelOnError, onDone, onError) {
+      var t1 = this.$ti;
+      t1._eval$1("~(1)?")._as(onData);
+      type$.nullable_void_Function._as(onDone);
+      return this._controller._subscribe$4(t1._eval$1("~(1)?")._as(onData), onError, onDone, cancelOnError === true);
+    },
+    listen$1(onData) {
+      return this.listen$4$cancelOnError$onDone$onError(onData, null, null, null);
+    },
+    listen$2$cancelOnError(onData, cancelOnError) {
+      return this.listen$4$cancelOnError$onDone$onError(onData, cancelOnError, null, null);
+    },
+    listen$2$onDone(onData, onDone) {
+      return this.listen$4$cancelOnError$onDone$onError(onData, null, onDone, null);
+    }
+  };
+  A._DelayedEvent.prototype = {
+    set$next(next) {
+      this.next = type$.nullable__DelayedEvent_dynamic._as(next);
+    },
+    get$next() {
+      return this.next;
+    }
+  };
+  A._DelayedData.prototype = {
+    perform$1(dispatch) {
+      this.$ti._eval$1("_EventDispatch<1>")._as(dispatch)._sendData$1(this.value);
+    }
+  };
+  A._DelayedError.prototype = {
+    perform$1(dispatch) {
+      dispatch._sendError$2(this.error, this.stackTrace);
+    }
+  };
+  A._DelayedDone.prototype = {
+    perform$1(dispatch) {
+      dispatch._sendDone$0();
+    },
+    get$next() {
+      return null;
+    },
+    set$next(_) {
+      throw A.wrapException(A.StateError$("No events after a done."));
+    },
+    $is_DelayedEvent: 1
+  };
+  A._PendingEvents.prototype = {
+    schedule$1(dispatch) {
+      var t1, _this = this;
+      _this.$ti._eval$1("_EventDispatch<1>")._as(dispatch);
+      t1 = _this._state;
+      if (t1 === 1)
+        return;
+      if (t1 >= 1) {
+        _this._state = 1;
+        return;
+      }
+      A.scheduleMicrotask(new A._PendingEvents_schedule_closure(_this, dispatch));
+      _this._state = 1;
+    },
+    add$1(_, $event) {
+      var _this = this,
+        lastEvent = _this.lastPendingEvent;
+      if (lastEvent == null)
+        _this.firstPendingEvent = _this.lastPendingEvent = $event;
+      else {
+        lastEvent.set$next($event);
+        _this.lastPendingEvent = $event;
+      }
+    }
+  };
+  A._PendingEvents_schedule_closure.prototype = {
+    call$0() {
+      var t2, $event, nextEvent,
+        t1 = this.$this,
+        oldState = t1._state;
+      t1._state = 0;
+      if (oldState === 3)
+        return;
+      t2 = t1.$ti._eval$1("_EventDispatch<1>")._as(this.dispatch);
+      $event = t1.firstPendingEvent;
+      nextEvent = $event.get$next();
+      t1.firstPendingEvent = nextEvent;
+      if (nextEvent == null)
+        t1.lastPendingEvent = null;
+      $event.perform$1(t2);
+    },
+    $signature: 0
+  };
+  A._StreamIterator.prototype = {};
+  A._cancelAndValue_closure.prototype = {
+    call$0() {
+      return this.future._complete$1(this.value);
+    },
+    $signature: 0
+  };
+  A._Zone.prototype = {$isZone: 1};
+  A._rootHandleError_closure.prototype = {
+    call$0() {
+      A.Error_throwWithStackTrace(this.error, this.stackTrace);
+    },
+    $signature: 0
+  };
+  A._RootZone.prototype = {
+    runGuarded$1(f) {
+      var e, s, exception;
+      type$.void_Function._as(f);
+      try {
+        if (B.C__RootZone === $.Zone__current) {
+          f.call$0();
+          return;
+        }
+        A._rootRun(null, null, this, f, type$.void);
+      } catch (exception) {
+        e = A.unwrapException(exception);
+        s = A.getTraceFromException(exception);
+        A._rootHandleError(type$.Object._as(e), type$.StackTrace._as(s));
+      }
+    },
+    runUnaryGuarded$1$2(f, arg, $T) {
+      var e, s, exception;
+      $T._eval$1("~(0)")._as(f);
+      $T._as(arg);
+      try {
+        if (B.C__RootZone === $.Zone__current) {
+          f.call$1(arg);
+          return;
+        }
+        A._rootRunUnary(null, null, this, f, arg, type$.void, $T);
+      } catch (exception) {
+        e = A.unwrapException(exception);
+        s = A.getTraceFromException(exception);
+        A._rootHandleError(type$.Object._as(e), type$.StackTrace._as(s));
+      }
+    },
+    runBinaryGuarded$2$3(f, arg1, arg2, T1, T2) {
+      var e, s, exception;
+      T1._eval$1("@<0>")._bind$1(T2)._eval$1("~(1,2)")._as(f);
+      T1._as(arg1);
+      T2._as(arg2);
+      try {
+        if (B.C__RootZone === $.Zone__current) {
+          f.call$2(arg1, arg2);
+          return;
+        }
+        A._rootRunBinary(null, null, this, f, arg1, arg2, type$.void, T1, T2);
+      } catch (exception) {
+        e = A.unwrapException(exception);
+        s = A.getTraceFromException(exception);
+        A._rootHandleError(type$.Object._as(e), type$.StackTrace._as(s));
+      }
+    },
+    bindCallbackGuarded$1(f) {
+      return new A._RootZone_bindCallbackGuarded_closure(this, type$.void_Function._as(f));
+    },
+    bindUnaryCallbackGuarded$1$1(f, $T) {
+      return new A._RootZone_bindUnaryCallbackGuarded_closure(this, $T._eval$1("~(0)")._as(f), $T);
+    },
+    run$1$1(f, $R) {
+      $R._eval$1("0()")._as(f);
+      if ($.Zone__current === B.C__RootZone)
+        return f.call$0();
+      return A._rootRun(null, null, this, f, $R);
+    },
+    runUnary$2$2(f, arg, $R, $T) {
+      $R._eval$1("@<0>")._bind$1($T)._eval$1("1(2)")._as(f);
+      $T._as(arg);
+      if ($.Zone__current === B.C__RootZone)
+        return f.call$1(arg);
+      return A._rootRunUnary(null, null, this, f, arg, $R, $T);
+    },
+    runBinary$3$3(f, arg1, arg2, $R, T1, T2) {
+      $R._eval$1("@<0>")._bind$1(T1)._bind$1(T2)._eval$1("1(2,3)")._as(f);
+      T1._as(arg1);
+      T2._as(arg2);
+      if ($.Zone__current === B.C__RootZone)
+        return f.call$2(arg1, arg2);
+      return A._rootRunBinary(null, null, this, f, arg1, arg2, $R, T1, T2);
+    },
+    registerBinaryCallback$3$1(f, $R, T1, T2) {
+      return $R._eval$1("@<0>")._bind$1(T1)._bind$1(T2)._eval$1("1(2,3)")._as(f);
+    }
+  };
+  A._RootZone_bindCallbackGuarded_closure.prototype = {
+    call$0() {
+      return this.$this.runGuarded$1(this.f);
+    },
+    $signature: 0
+  };
+  A._RootZone_bindUnaryCallbackGuarded_closure.prototype = {
+    call$1(arg) {
+      var t1 = this.T;
+      return this.$this.runUnaryGuarded$1$2(this.f, t1._as(arg), t1);
+    },
+    $signature() {
+      return this.T._eval$1("~(0)");
+    }
+  };
+  A._HashMap.prototype = {
+    get$length(_) {
+      return this._collection$_length;
+    },
+    get$isEmpty(_) {
+      return this._collection$_length === 0;
+    },
+    get$keys() {
+      return new A._HashMapKeyIterable(this, this.$ti._eval$1("_HashMapKeyIterable<1>"));
+    },
+    containsKey$1(key) {
+      var strings, nums;
+      if (typeof key == "string" && key !== "__proto__") {
+        strings = this._collection$_strings;
+        return strings == null ? false : strings[key] != null;
+      } else if (typeof key == "number" && (key & 1073741823) === key) {
+        nums = this._collection$_nums;
+        return nums == null ? false : nums[key] != null;
+      } else
+        return this._containsKey$1(key);
+    },
+    _containsKey$1(key) {
+      var rest = this._collection$_rest;
+      if (rest == null)
+        return false;
+      return this._findBucketIndex$2(this._getBucket$2(rest, key), key) >= 0;
+    },
+    $index(_, key) {
+      var strings, t1, nums;
+      if (typeof key == "string" && key !== "__proto__") {
+        strings = this._collection$_strings;
+        t1 = strings == null ? null : A._HashMap__getTableEntry(strings, key);
+        return t1;
+      } else if (typeof key == "number" && (key & 1073741823) === key) {
+        nums = this._collection$_nums;
+        t1 = nums == null ? null : A._HashMap__getTableEntry(nums, key);
+        return t1;
+      } else
+        return this._get$1(key);
+    },
+    _get$1(key) {
+      var bucket, index,
+        rest = this._collection$_rest;
+      if (rest == null)
+        return null;
+      bucket = this._getBucket$2(rest, key);
+      index = this._findBucketIndex$2(bucket, key);
+      return index < 0 ? null : bucket[index + 1];
+    },
+    $indexSet(_, key, value) {
+      var strings, nums, rest, hash, bucket, index, _this = this,
+        t1 = _this.$ti;
+      t1._precomputed1._as(key);
+      t1._rest[1]._as(value);
+      if (typeof key == "string" && key !== "__proto__") {
+        strings = _this._collection$_strings;
+        _this._collection$_addHashTableEntry$3(strings == null ? _this._collection$_strings = A._HashMap__newHashTable() : strings, key, value);
+      } else if (typeof key == "number" && (key & 1073741823) === key) {
+        nums = _this._collection$_nums;
+        _this._collection$_addHashTableEntry$3(nums == null ? _this._collection$_nums = A._HashMap__newHashTable() : nums, key, value);
+      } else {
+        rest = _this._collection$_rest;
+        if (rest == null)
+          rest = _this._collection$_rest = A._HashMap__newHashTable();
+        hash = A.objectHashCode(key) & 1073741823;
+        bucket = rest[hash];
+        if (bucket == null) {
+          A._HashMap__setTableEntry(rest, hash, [key, value]);
+          ++_this._collection$_length;
+          _this._collection$_keys = null;
+        } else {
+          index = _this._findBucketIndex$2(bucket, key);
+          if (index >= 0)
+            bucket[index + 1] = value;
+          else {
+            bucket.push(key, value);
+            ++_this._collection$_length;
+            _this._collection$_keys = null;
+          }
+        }
+      }
+    },
+    forEach$1(_, action) {
+      var keys, $length, t2, i, key, t3, _this = this,
+        t1 = _this.$ti;
+      t1._eval$1("~(1,2)")._as(action);
+      keys = _this._computeKeys$0();
+      for ($length = keys.length, t2 = t1._precomputed1, t1 = t1._rest[1], i = 0; i < $length; ++i) {
+        key = keys[i];
+        t2._as(key);
+        t3 = _this.$index(0, key);
+        action.call$2(key, t3 == null ? t1._as(t3) : t3);
+        if (keys !== _this._collection$_keys)
+          throw A.wrapException(A.ConcurrentModificationError$(_this));
+      }
+    },
+    _computeKeys$0() {
+      var strings, names, entries, index, i, nums, rest, bucket, $length, i0, _this = this,
+        result = _this._collection$_keys;
+      if (result != null)
+        return result;
+      result = A.List_List$filled(_this._collection$_length, null, false, type$.dynamic);
+      strings = _this._collection$_strings;
+      if (strings != null) {
+        names = Object.getOwnPropertyNames(strings);
+        entries = names.length;
+        for (index = 0, i = 0; i < entries; ++i) {
+          result[index] = names[i];
+          ++index;
+        }
+      } else
+        index = 0;
+      nums = _this._collection$_nums;
+      if (nums != null) {
+        names = Object.getOwnPropertyNames(nums);
+        entries = names.length;
+        for (i = 0; i < entries; ++i) {
+          result[index] = +names[i];
+          ++index;
+        }
+      }
+      rest = _this._collection$_rest;
+      if (rest != null) {
+        names = Object.getOwnPropertyNames(rest);
+        entries = names.length;
+        for (i = 0; i < entries; ++i) {
+          bucket = rest[names[i]];
+          $length = bucket.length;
+          for (i0 = 0; i0 < $length; i0 += 2) {
+            result[index] = bucket[i0];
+            ++index;
+          }
+        }
+      }
+      return _this._collection$_keys = result;
+    },
+    _collection$_addHashTableEntry$3(table, key, value) {
+      var t1 = this.$ti;
+      t1._precomputed1._as(key);
+      t1._rest[1]._as(value);
+      if (table[key] == null) {
+        ++this._collection$_length;
+        this._collection$_keys = null;
+      }
+      A._HashMap__setTableEntry(table, key, value);
+    },
+    _getBucket$2(table, key) {
+      return table[A.objectHashCode(key) & 1073741823];
+    }
+  };
+  A._IdentityHashMap.prototype = {
+    _findBucketIndex$2(bucket, key) {
+      var $length, i, t1;
+      if (bucket == null)
+        return -1;
+      $length = bucket.length;
+      for (i = 0; i < $length; i += 2) {
+        t1 = bucket[i];
+        if (t1 == null ? key == null : t1 === key)
+          return i;
+      }
+      return -1;
+    }
+  };
+  A._HashMapKeyIterable.prototype = {
+    get$length(_) {
+      return this._collection$_map._collection$_length;
+    },
+    get$isEmpty(_) {
+      return this._collection$_map._collection$_length === 0;
+    },
+    get$iterator(_) {
+      var t1 = this._collection$_map;
+      return new A._HashMapKeyIterator(t1, t1._computeKeys$0(), this.$ti._eval$1("_HashMapKeyIterator<1>"));
+    }
+  };
+  A._HashMapKeyIterator.prototype = {
+    get$current() {
+      var t1 = this._collection$_current;
+      return t1 == null ? this.$ti._precomputed1._as(t1) : t1;
+    },
+    moveNext$0() {
+      var _this = this,
+        keys = _this._collection$_keys,
+        offset = _this._offset,
+        t1 = _this._collection$_map;
+      if (keys !== t1._collection$_keys)
+        throw A.wrapException(A.ConcurrentModificationError$(t1));
+      else if (offset >= keys.length) {
+        _this.set$_collection$_current(null);
+        return false;
+      } else {
+        _this.set$_collection$_current(keys[offset]);
+        _this._offset = offset + 1;
+        return true;
+      }
+    },
+    set$_collection$_current(_current) {
+      this._collection$_current = this.$ti._eval$1("1?")._as(_current);
+    }
+  };
+  A.ListBase.prototype = {
+    get$iterator(receiver) {
+      return new A.ListIterator(receiver, this.get$length(receiver), A.instanceType(receiver)._eval$1("ListIterator<ListBase.E>"));
+    },
+    elementAt$1(receiver, index) {
+      return this.$index(receiver, index);
+    },
+    get$isNotEmpty(receiver) {
+      return this.get$length(receiver) !== 0;
+    },
+    toString$0(receiver) {
+      return A.Iterable_iterableToFullString(receiver, "[", "]");
+    }
+  };
+  A.MapBase.prototype = {
+    forEach$1(_, action) {
+      var t2, key, t3,
+        t1 = A._instanceType(this);
+      t1._eval$1("~(MapBase.K,MapBase.V)")._as(action);
+      for (t2 = this.get$keys(), t2 = t2.get$iterator(t2), t1 = t1._eval$1("MapBase.V"); t2.moveNext$0();) {
+        key = t2.get$current();
+        t3 = this.$index(0, key);
+        action.call$2(key, t3 == null ? t1._as(t3) : t3);
+      }
+    },
+    get$length(_) {
+      var t1 = this.get$keys();
+      return t1.get$length(t1);
+    },
+    get$isEmpty(_) {
+      var t1 = this.get$keys();
+      return t1.get$isEmpty(t1);
+    },
+    toString$0(_) {
+      return A.MapBase_mapToString(this);
+    },
+    $isMap: 1
+  };
+  A.MapBase_mapToString_closure.prototype = {
+    call$2(k, v) {
+      var t2,
+        t1 = this._box_0;
+      if (!t1.first)
+        this.result._contents += ", ";
+      t1.first = false;
+      t1 = this.result;
+      t2 = A.S(k);
+      t2 = t1._contents += t2;
+      t1._contents = t2 + ": ";
+      t2 = A.S(v);
+      t1._contents += t2;
+    },
+    $signature: 10
+  };
+  A._UnmodifiableMapMixin.prototype = {};
+  A.MapView.prototype = {
+    forEach$1(_, action) {
+      this._collection$_map.forEach$1(0, A._instanceType(this)._eval$1("~(1,2)")._as(action));
+    },
+    get$isEmpty(_) {
+      return this._collection$_map.__js_helper$_length === 0;
+    },
+    get$length(_) {
+      return this._collection$_map.__js_helper$_length;
+    },
+    toString$0(_) {
+      return A.MapBase_mapToString(this._collection$_map);
+    },
+    $isMap: 1
+  };
+  A.UnmodifiableMapView.prototype = {};
+  A.ListQueue.prototype = {
+    get$iterator(_) {
+      var _this = this;
+      return new A._ListQueueIterator(_this, _this._tail, _this._modificationCount, _this._head, _this.$ti._eval$1("_ListQueueIterator<1>"));
+    },
+    get$isEmpty(_) {
+      return this._head === this._tail;
+    },
+    get$length(_) {
+      return (this._tail - this._head & this._table.length - 1) >>> 0;
+    },
+    elementAt$1(_, index) {
+      var t2, t3, _this = this,
+        t1 = _this.get$length(0);
+      if (0 > index || index >= t1)
+        A.throwExpression(A.IndexError$withLength(index, t1, _this, null, "index"));
+      t1 = _this._table;
+      t2 = t1.length;
+      t3 = (_this._head + index & t2 - 1) >>> 0;
+      if (!(t3 >= 0 && t3 < t2))
+        return A.ioore(t1, t3);
+      t3 = t1[t3];
+      return t3 == null ? _this.$ti._precomputed1._as(t3) : t3;
+    },
+    toString$0(_) {
+      return A.Iterable_iterableToFullString(this, "{", "}");
+    },
+    removeFirst$0() {
+      var t2, result, _this = this,
+        t1 = _this._head;
+      if (t1 === _this._tail)
+        throw A.wrapException(A.IterableElementError_noElement());
+      ++_this._modificationCount;
+      t2 = _this._table;
+      if (!(t1 < t2.length))
+        return A.ioore(t2, t1);
+      result = t2[t1];
+      if (result == null)
+        result = _this.$ti._precomputed1._as(result);
+      B.JSArray_methods.$indexSet(t2, t1, null);
+      _this._head = (_this._head + 1 & _this._table.length - 1) >>> 0;
+      return result;
+    },
+    _add$1(element) {
+      var t2, t3, newTable, split, _this = this,
+        t1 = _this.$ti;
+      t1._precomputed1._as(element);
+      B.JSArray_methods.$indexSet(_this._table, _this._tail, element);
+      t2 = _this._tail;
+      t3 = _this._table.length;
+      t2 = (t2 + 1 & t3 - 1) >>> 0;
+      _this._tail = t2;
+      if (_this._head === t2) {
+        newTable = A.List_List$filled(t3 * 2, null, false, t1._eval$1("1?"));
+        t1 = _this._table;
+        t2 = _this._head;
+        split = t1.length - t2;
+        B.JSArray_methods.setRange$4(newTable, 0, split, t1, t2);
+        B.JSArray_methods.setRange$4(newTable, split, split + _this._head, _this._table, 0);
+        _this._head = 0;
+        _this._tail = _this._table.length;
+        _this.set$_table(newTable);
+      }
+      ++_this._modificationCount;
+    },
+    set$_table(_table) {
+      this._table = this.$ti._eval$1("List<1?>")._as(_table);
+    },
+    $isQueue: 1
+  };
+  A._ListQueueIterator.prototype = {
+    get$current() {
+      var t1 = this._collection$_current;
+      return t1 == null ? this.$ti._precomputed1._as(t1) : t1;
+    },
+    moveNext$0() {
+      var t2, t3, _this = this,
+        t1 = _this._queue;
+      if (_this._modificationCount !== t1._modificationCount)
+        A.throwExpression(A.ConcurrentModificationError$(t1));
+      t2 = _this._position;
+      if (t2 === _this._end) {
+        _this.set$_collection$_current(null);
+        return false;
+      }
+      t3 = t1._table;
+      if (!(t2 < t3.length))
+        return A.ioore(t3, t2);
+      _this.set$_collection$_current(t3[t2]);
+      _this._position = (_this._position + 1 & t1._table.length - 1) >>> 0;
+      return true;
+    },
+    set$_collection$_current(_current) {
+      this._collection$_current = this.$ti._eval$1("1?")._as(_current);
+    }
+  };
+  A._UnmodifiableMapView_MapView__UnmodifiableMapMixin.prototype = {};
+  A._JsonMap.prototype = {
+    $index(_, key) {
+      var result,
+        t1 = this._processed;
+      if (t1 == null)
+        return this._data.$index(0, key);
+      else if (typeof key != "string")
+        return null;
+      else {
+        result = t1[key];
+        return typeof result == "undefined" ? this._process$1(key) : result;
+      }
+    },
+    get$length(_) {
+      return this._processed == null ? this._data.__js_helper$_length : this._convert$_computeKeys$0().length;
+    },
+    get$isEmpty(_) {
+      return this.get$length(0) === 0;
+    },
+    get$keys() {
+      if (this._processed == null) {
+        var t1 = this._data;
+        return new A.LinkedHashMapKeyIterable(t1, A._instanceType(t1)._eval$1("LinkedHashMapKeyIterable<1>"));
+      }
+      return new A._JsonMapKeyIterable(this);
+    },
+    forEach$1(_, f) {
+      var keys, i, key, value, _this = this;
+      type$.void_Function_String_dynamic._as(f);
+      if (_this._processed == null)
+        return _this._data.forEach$1(0, f);
+      keys = _this._convert$_computeKeys$0();
+      for (i = 0; i < keys.length; ++i) {
+        key = keys[i];
+        value = _this._processed[key];
+        if (typeof value == "undefined") {
+          value = A._convertJsonToDartLazy(_this._original[key]);
+          _this._processed[key] = value;
+        }
+        f.call$2(key, value);
+        if (keys !== _this._data)
+          throw A.wrapException(A.ConcurrentModificationError$(_this));
+      }
+    },
+    _convert$_computeKeys$0() {
+      var keys = type$.nullable_List_dynamic._as(this._data);
+      if (keys == null)
+        keys = this._data = A._setArrayType(Object.keys(this._original), type$.JSArray_String);
+      return keys;
+    },
+    _process$1(key) {
+      var result;
+      if (!Object.prototype.hasOwnProperty.call(this._original, key))
+        return null;
+      result = A._convertJsonToDartLazy(this._original[key]);
+      return this._processed[key] = result;
+    }
+  };
+  A._JsonMapKeyIterable.prototype = {
+    get$length(_) {
+      return this._parent.get$length(0);
+    },
+    elementAt$1(_, index) {
+      var t1 = this._parent;
+      if (t1._processed == null)
+        t1 = t1.get$keys().elementAt$1(0, index);
+      else {
+        t1 = t1._convert$_computeKeys$0();
+        if (!(index >= 0 && index < t1.length))
+          return A.ioore(t1, index);
+        t1 = t1[index];
+      }
+      return t1;
+    },
+    get$iterator(_) {
+      var t1 = this._parent;
+      if (t1._processed == null) {
+        t1 = t1.get$keys();
+        t1 = t1.get$iterator(t1);
+      } else {
+        t1 = t1._convert$_computeKeys$0();
+        t1 = new J.ArrayIterator(t1, t1.length, A._arrayInstanceType(t1)._eval$1("ArrayIterator<1>"));
+      }
+      return t1;
+    }
+  };
+  A.Codec.prototype = {};
+  A.Converter.prototype = {};
+  A.JsonUnsupportedObjectError.prototype = {
+    toString$0(_) {
+      var safeString = A.Error_safeToString(this.unsupportedObject);
+      return (this.cause != null ? "Converting object to an encodable object failed:" : "Converting object did not return an encodable object:") + " " + safeString;
+    }
+  };
+  A.JsonCyclicError.prototype = {
+    toString$0(_) {
+      return "Cyclic error in JSON stringify";
+    }
+  };
+  A.JsonCodec.prototype = {
+    decode$2$reviver(source, reviver) {
+      var t1 = A._parseJson(source, this.get$decoder()._reviver);
+      return t1;
+    },
+    encode$2$toEncodable(value, toEncodable) {
+      var t1 = A._JsonStringStringifier_stringify(value, this.get$encoder()._toEncodable, null);
+      return t1;
+    },
+    get$encoder() {
+      return B.JsonEncoder_null;
+    },
+    get$decoder() {
+      return B.JsonDecoder_null;
+    }
+  };
+  A.JsonEncoder.prototype = {};
+  A.JsonDecoder.prototype = {};
+  A._JsonStringifier.prototype = {
+    writeStringContent$1(s) {
+      var offset, i, charCode, t1, t2, _this = this,
+        $length = s.length;
+      for (offset = 0, i = 0; i < $length; ++i) {
+        charCode = s.charCodeAt(i);
+        if (charCode > 92) {
+          if (charCode >= 55296) {
+            t1 = charCode & 64512;
+            if (t1 === 55296) {
+              t2 = i + 1;
+              t2 = !(t2 < $length && (s.charCodeAt(t2) & 64512) === 56320);
+            } else
+              t2 = false;
+            if (!t2)
+              if (t1 === 56320) {
+                t1 = i - 1;
+                t1 = !(t1 >= 0 && (s.charCodeAt(t1) & 64512) === 55296);
+              } else
+                t1 = false;
+            else
+              t1 = true;
+            if (t1) {
+              if (i > offset)
+                _this.writeStringSlice$3(s, offset, i);
+              offset = i + 1;
+              _this.writeCharCode$1(92);
+              _this.writeCharCode$1(117);
+              _this.writeCharCode$1(100);
+              t1 = charCode >>> 8 & 15;
+              _this.writeCharCode$1(t1 < 10 ? 48 + t1 : 87 + t1);
+              t1 = charCode >>> 4 & 15;
+              _this.writeCharCode$1(t1 < 10 ? 48 + t1 : 87 + t1);
+              t1 = charCode & 15;
+              _this.writeCharCode$1(t1 < 10 ? 48 + t1 : 87 + t1);
+            }
+          }
+          continue;
+        }
+        if (charCode < 32) {
+          if (i > offset)
+            _this.writeStringSlice$3(s, offset, i);
+          offset = i + 1;
+          _this.writeCharCode$1(92);
+          switch (charCode) {
+            case 8:
+              _this.writeCharCode$1(98);
+              break;
+            case 9:
+              _this.writeCharCode$1(116);
+              break;
+            case 10:
+              _this.writeCharCode$1(110);
+              break;
+            case 12:
+              _this.writeCharCode$1(102);
+              break;
+            case 13:
+              _this.writeCharCode$1(114);
+              break;
+            default:
+              _this.writeCharCode$1(117);
+              _this.writeCharCode$1(48);
+              _this.writeCharCode$1(48);
+              t1 = charCode >>> 4 & 15;
+              _this.writeCharCode$1(t1 < 10 ? 48 + t1 : 87 + t1);
+              t1 = charCode & 15;
+              _this.writeCharCode$1(t1 < 10 ? 48 + t1 : 87 + t1);
+              break;
+          }
+        } else if (charCode === 34 || charCode === 92) {
+          if (i > offset)
+            _this.writeStringSlice$3(s, offset, i);
+          offset = i + 1;
+          _this.writeCharCode$1(92);
+          _this.writeCharCode$1(charCode);
+        }
+      }
+      if (offset === 0)
+        _this.writeString$1(s);
+      else if (offset < $length)
+        _this.writeStringSlice$3(s, offset, $length);
+    },
+    _checkCycle$1(object) {
+      var t1, t2, i, t3;
+      for (t1 = this._seen, t2 = t1.length, i = 0; i < t2; ++i) {
+        t3 = t1[i];
+        if (object == null ? t3 == null : object === t3)
+          throw A.wrapException(new A.JsonCyclicError(object, null));
+      }
+      B.JSArray_methods.add$1(t1, object);
+    },
+    writeObject$1(object) {
+      var customJson, e, t1, exception, _this = this;
+      if (_this.writeJsonValue$1(object))
+        return;
+      _this._checkCycle$1(object);
+      try {
+        customJson = _this._toEncodable.call$1(object);
+        if (!_this.writeJsonValue$1(customJson)) {
+          t1 = A.JsonUnsupportedObjectError$(object, null, _this.get$_partialResult());
+          throw A.wrapException(t1);
+        }
+        t1 = _this._seen;
+        if (0 >= t1.length)
+          return A.ioore(t1, -1);
+        t1.pop();
+      } catch (exception) {
+        e = A.unwrapException(exception);
+        t1 = A.JsonUnsupportedObjectError$(object, e, _this.get$_partialResult());
+        throw A.wrapException(t1);
+      }
+    },
+    writeJsonValue$1(object) {
+      var t1, success, _this = this;
+      if (typeof object == "number") {
+        if (!isFinite(object))
+          return false;
+        _this.writeNumber$1(object);
+        return true;
+      } else if (object === true) {
+        _this.writeString$1("true");
+        return true;
+      } else if (object === false) {
+        _this.writeString$1("false");
+        return true;
+      } else if (object == null) {
+        _this.writeString$1("null");
+        return true;
+      } else if (typeof object == "string") {
+        _this.writeString$1('"');
+        _this.writeStringContent$1(object);
+        _this.writeString$1('"');
+        return true;
+      } else if (type$.List_dynamic._is(object)) {
+        _this._checkCycle$1(object);
+        _this.writeList$1(object);
+        t1 = _this._seen;
+        if (0 >= t1.length)
+          return A.ioore(t1, -1);
+        t1.pop();
+        return true;
+      } else if (type$.Map_dynamic_dynamic._is(object)) {
+        _this._checkCycle$1(object);
+        success = _this.writeMap$1(object);
+        t1 = _this._seen;
+        if (0 >= t1.length)
+          return A.ioore(t1, -1);
+        t1.pop();
+        return success;
+      } else
+        return false;
+    },
+    writeList$1(list) {
+      var t1, i, _this = this;
+      _this.writeString$1("[");
+      t1 = J.getInterceptor$asx(list);
+      if (t1.get$isNotEmpty(list)) {
+        _this.writeObject$1(t1.$index(list, 0));
+        for (i = 1; i < t1.get$length(list); ++i) {
+          _this.writeString$1(",");
+          _this.writeObject$1(t1.$index(list, i));
+        }
+      }
+      _this.writeString$1("]");
+    },
+    writeMap$1(map) {
+      var t1, keyValueList, i, separator, t2, _this = this, _box_0 = {};
+      if (map.get$isEmpty(map)) {
+        _this.writeString$1("{}");
+        return true;
+      }
+      t1 = map.get$length(map) * 2;
+      keyValueList = A.List_List$filled(t1, null, false, type$.nullable_Object);
+      i = _box_0.i = 0;
+      _box_0.allStringKeys = true;
+      map.forEach$1(0, new A._JsonStringifier_writeMap_closure(_box_0, keyValueList));
+      if (!_box_0.allStringKeys)
+        return false;
+      _this.writeString$1("{");
+      for (separator = '"'; i < t1; i += 2, separator = ',"') {
+        _this.writeString$1(separator);
+        _this.writeStringContent$1(A._asString(keyValueList[i]));
+        _this.writeString$1('":');
+        t2 = i + 1;
+        if (!(t2 < t1))
+          return A.ioore(keyValueList, t2);
+        _this.writeObject$1(keyValueList[t2]);
+      }
+      _this.writeString$1("}");
+      return true;
+    }
+  };
+  A._JsonStringifier_writeMap_closure.prototype = {
+    call$2(key, value) {
+      var t1, t2;
+      if (typeof key != "string")
+        this._box_0.allStringKeys = false;
+      t1 = this.keyValueList;
+      t2 = this._box_0;
+      B.JSArray_methods.$indexSet(t1, t2.i++, key);
+      B.JSArray_methods.$indexSet(t1, t2.i++, value);
+    },
+    $signature: 10
+  };
+  A._JsonStringStringifier.prototype = {
+    get$_partialResult() {
+      var t1 = this._sink._contents;
+      return t1.charCodeAt(0) == 0 ? t1 : t1;
+    },
+    writeNumber$1(number) {
+      var t1 = this._sink,
+        t2 = B.JSNumber_methods.toString$0(number);
+      t1._contents += t2;
+    },
+    writeString$1(string) {
+      this._sink._contents += string;
+    },
+    writeStringSlice$3(string, start, end) {
+      this._sink._contents += B.JSString_methods.substring$2(string, start, end);
+    },
+    writeCharCode$1(charCode) {
+      var t1 = this._sink,
+        t2 = A.Primitives_stringFromCharCode(charCode);
+      t1._contents += t2;
+    }
+  };
+  A.NoSuchMethodError_toString_closure.prototype = {
+    call$2(key, value) {
+      var t1, t2, t3;
+      type$.Symbol._as(key);
+      t1 = this.sb;
+      t2 = this._box_0;
+      t3 = t1._contents += t2.comma;
+      t3 += key._name;
+      t1._contents = t3;
+      t1._contents = t3 + ": ";
+      t3 = A.Error_safeToString(value);
+      t1._contents += t3;
+      t2.comma = ", ";
+    },
+    $signature: 19
+  };
+  A.DateTime.prototype = {
+    $eq(_, other) {
+      if (other == null)
+        return false;
+      return other instanceof A.DateTime && this._value === other._value && this.isUtc === other.isUtc;
+    },
+    get$hashCode(_) {
+      var t1 = this._value;
+      return (t1 ^ B.JSInt_methods._shrOtherPositive$1(t1, 30)) & 1073741823;
+    },
+    toString$0(_) {
+      var _this = this,
+        y = A.DateTime__fourDigits(A.Primitives_getYear(_this)),
+        m = A.DateTime__twoDigits(A.Primitives_getMonth(_this)),
+        d = A.DateTime__twoDigits(A.Primitives_getDay(_this)),
+        h = A.DateTime__twoDigits(A.Primitives_getHours(_this)),
+        min = A.DateTime__twoDigits(A.Primitives_getMinutes(_this)),
+        sec = A.DateTime__twoDigits(A.Primitives_getSeconds(_this)),
+        ms = A.DateTime__threeDigits(A.Primitives_getMilliseconds(_this)),
+        t1 = y + "-" + m;
+      if (_this.isUtc)
+        return t1 + "-" + d + " " + h + ":" + min + ":" + sec + "." + ms + "Z";
+      else
+        return t1 + "-" + d + " " + h + ":" + min + ":" + sec + "." + ms;
+    }
+  };
+  A.Duration.prototype = {
+    $eq(_, other) {
+      if (other == null)
+        return false;
+      return other instanceof A.Duration && this._duration === other._duration;
+    },
+    get$hashCode(_) {
+      return B.JSInt_methods.get$hashCode(this._duration);
+    },
+    toString$0(_) {
+      var minutesPadding, seconds, secondsPadding,
+        microseconds = this._duration,
+        microseconds0 = microseconds % 3600000000,
+        minutes = B.JSInt_methods._tdivFast$1(microseconds0, 60000000);
+      microseconds0 %= 60000000;
+      minutesPadding = minutes < 10 ? "0" : "";
+      seconds = B.JSInt_methods._tdivFast$1(microseconds0, 1000000);
+      secondsPadding = seconds < 10 ? "0" : "";
+      return "" + (microseconds / 3600000000 | 0) + ":" + minutesPadding + minutes + ":" + secondsPadding + seconds + "." + B.JSString_methods.padLeft$2(B.JSInt_methods.toString$0(microseconds0 % 1000000), 6, "0");
+    }
+  };
+  A.Error.prototype = {
+    get$stackTrace() {
+      return A.getTraceFromException(this.$thrownJsError);
+    }
+  };
+  A.AssertionError.prototype = {
+    toString$0(_) {
+      var t1 = this.message;
+      if (t1 != null)
+        return "Assertion failed: " + A.Error_safeToString(t1);
+      return "Assertion failed";
+    }
+  };
+  A.TypeError.prototype = {};
+  A.ArgumentError.prototype = {
+    get$_errorName() {
+      return "Invalid argument" + (!this._hasValue ? "(s)" : "");
+    },
+    get$_errorExplanation() {
+      return "";
+    },
+    toString$0(_) {
+      var _this = this,
+        $name = _this.name,
+        nameString = $name == null ? "" : " (" + $name + ")",
+        message = _this.message,
+        messageString = message == null ? "" : ": " + A.S(message),
+        prefix = _this.get$_errorName() + nameString + messageString;
+      if (!_this._hasValue)
+        return prefix;
+      return prefix + _this.get$_errorExplanation() + ": " + A.Error_safeToString(_this.get$invalidValue());
+    },
+    get$invalidValue() {
+      return this.invalidValue;
+    }
+  };
+  A.RangeError.prototype = {
+    get$invalidValue() {
+      return A._asNumQ(this.invalidValue);
+    },
+    get$_errorName() {
+      return "RangeError";
+    },
+    get$_errorExplanation() {
+      var explanation,
+        start = this.start,
+        end = this.end;
+      if (start == null)
+        explanation = end != null ? ": Not less than or equal to " + A.S(end) : "";
+      else if (end == null)
+        explanation = ": Not greater than or equal to " + A.S(start);
+      else if (end > start)
+        explanation = ": Not in inclusive range " + A.S(start) + ".." + A.S(end);
+      else
+        explanation = end < start ? ": Valid value range is empty" : ": Only valid value is " + A.S(start);
+      return explanation;
+    }
+  };
+  A.IndexError.prototype = {
+    get$invalidValue() {
+      return A._asInt(this.invalidValue);
+    },
+    get$_errorName() {
+      return "RangeError";
+    },
+    get$_errorExplanation() {
+      if (A._asInt(this.invalidValue) < 0)
+        return ": index must not be negative";
+      var t1 = this.length;
+      if (t1 === 0)
+        return ": no indices are valid";
+      return ": index should be less than " + t1;
+    },
+    get$length(receiver) {
+      return this.length;
+    }
+  };
+  A.NoSuchMethodError.prototype = {
+    toString$0(_) {
+      var $arguments, t1, _i, t2, t3, argument, receiverText, actualParameters, _this = this, _box_0 = {},
+        sb = new A.StringBuffer("");
+      _box_0.comma = "";
+      $arguments = _this._core$_arguments;
+      for (t1 = $arguments.length, _i = 0, t2 = "", t3 = ""; _i < t1; ++_i, t3 = ", ") {
+        argument = $arguments[_i];
+        sb._contents = t2 + t3;
+        t2 = A.Error_safeToString(argument);
+        t2 = sb._contents += t2;
+        _box_0.comma = ", ";
+      }
+      _this._namedArguments.forEach$1(0, new A.NoSuchMethodError_toString_closure(_box_0, sb));
+      receiverText = A.Error_safeToString(_this._core$_receiver);
+      actualParameters = sb.toString$0(0);
+      return "NoSuchMethodError: method not found: '" + _this._core$_memberName._name + "'\nReceiver: " + receiverText + "\nArguments: [" + actualParameters + "]";
+    }
+  };
+  A.UnsupportedError.prototype = {
+    toString$0(_) {
+      return "Unsupported operation: " + this.message;
+    }
+  };
+  A.UnimplementedError.prototype = {
+    toString$0(_) {
+      return "UnimplementedError: " + this.message;
+    }
+  };
+  A.StateError.prototype = {
+    toString$0(_) {
+      return "Bad state: " + this.message;
+    }
+  };
+  A.ConcurrentModificationError.prototype = {
+    toString$0(_) {
+      var t1 = this.modifiedObject;
+      if (t1 == null)
+        return "Concurrent modification during iteration.";
+      return "Concurrent modification during iteration: " + A.Error_safeToString(t1) + ".";
+    }
+  };
+  A.OutOfMemoryError.prototype = {
+    toString$0(_) {
+      return "Out of Memory";
+    },
+    get$stackTrace() {
+      return null;
+    },
+    $isError: 1
+  };
+  A.StackOverflowError.prototype = {
+    toString$0(_) {
+      return "Stack Overflow";
+    },
+    get$stackTrace() {
+      return null;
+    },
+    $isError: 1
+  };
+  A._Exception.prototype = {
+    toString$0(_) {
+      return "Exception: " + this.message;
+    }
+  };
+  A.FormatException.prototype = {
+    toString$0(_) {
+      var t1, lineEnd, lineNum, lineStart, previousCharWasCR, i, char, end, start, prefix, postfix,
+        message = this.message,
+        report = "" !== message ? "FormatException: " + message : "FormatException",
+        offset = this.offset,
+        source = this.source;
+      if (typeof source == "string") {
+        if (offset != null)
+          t1 = offset < 0 || offset > source.length;
+        else
+          t1 = false;
+        if (t1)
+          offset = null;
+        if (offset == null) {
+          if (source.length > 78)
+            source = B.JSString_methods.substring$2(source, 0, 75) + "...";
+          return report + "\n" + source;
+        }
+        for (lineEnd = source.length, lineNum = 1, lineStart = 0, previousCharWasCR = false, i = 0; i < offset; ++i) {
+          if (!(i < lineEnd))
+            return A.ioore(source, i);
+          char = source.charCodeAt(i);
+          if (char === 10) {
+            if (lineStart !== i || !previousCharWasCR)
+              ++lineNum;
+            lineStart = i + 1;
+            previousCharWasCR = false;
+          } else if (char === 13) {
+            ++lineNum;
+            lineStart = i + 1;
+            previousCharWasCR = true;
+          }
+        }
+        report = lineNum > 1 ? report + (" (at line " + lineNum + ", character " + (offset - lineStart + 1) + ")\n") : report + (" (at character " + (offset + 1) + ")\n");
+        for (i = offset; i < lineEnd; ++i) {
+          if (!(i >= 0))
+            return A.ioore(source, i);
+          char = source.charCodeAt(i);
+          if (char === 10 || char === 13) {
+            lineEnd = i;
+            break;
+          }
+        }
+        if (lineEnd - lineStart > 78)
+          if (offset - lineStart < 75) {
+            end = lineStart + 75;
+            start = lineStart;
+            prefix = "";
+            postfix = "...";
+          } else {
+            if (lineEnd - offset < 75) {
+              start = lineEnd - 75;
+              end = lineEnd;
+              postfix = "";
+            } else {
+              start = offset - 36;
+              end = offset + 36;
+              postfix = "...";
+            }
+            prefix = "...";
+          }
+        else {
+          end = lineEnd;
+          start = lineStart;
+          prefix = "";
+          postfix = "";
+        }
+        return report + prefix + B.JSString_methods.substring$2(source, start, end) + postfix + "\n" + B.JSString_methods.$mul(" ", offset - start + prefix.length) + "^\n";
+      } else
+        return offset != null ? report + (" (at offset " + A.S(offset) + ")") : report;
+    }
+  };
+  A.Iterable.prototype = {
+    get$length(_) {
+      var count,
+        it = this.get$iterator(this);
+      for (count = 0; it.moveNext$0();)
+        ++count;
+      return count;
+    },
+    elementAt$1(_, index) {
+      var iterator, skipCount;
+      A.RangeError_checkNotNegative(index, "index");
+      iterator = this.get$iterator(this);
+      for (skipCount = index; iterator.moveNext$0();) {
+        if (skipCount === 0)
+          return iterator.get$current();
+        --skipCount;
+      }
+      throw A.wrapException(A.IndexError$withLength(index, index - skipCount, this, null, "index"));
+    },
+    toString$0(_) {
+      return A.Iterable_iterableToShortString(this, "(", ")");
+    }
+  };
+  A.Null.prototype = {
+    get$hashCode(_) {
+      return A.Object.prototype.get$hashCode.call(this, 0);
+    },
+    toString$0(_) {
+      return "null";
+    }
+  };
+  A.Object.prototype = {$isObject: 1,
+    $eq(_, other) {
+      return this === other;
+    },
+    get$hashCode(_) {
+      return A.Primitives_objectHashCode(this);
+    },
+    toString$0(_) {
+      return "Instance of '" + A.Primitives_objectTypeName(this) + "'";
+    },
+    noSuchMethod$1(_, invocation) {
+      throw A.wrapException(A.NoSuchMethodError_NoSuchMethodError$withInvocation(this, type$.Invocation._as(invocation)));
+    },
+    get$runtimeType(_) {
+      return A.getRuntimeTypeOfDartObject(this);
+    },
+    toString() {
+      return this.toString$0(this);
+    }
+  };
+  A._StringStackTrace.prototype = {
+    toString$0(_) {
+      return this._stackTrace;
+    },
+    $isStackTrace: 1
+  };
+  A.StringBuffer.prototype = {
+    get$length(_) {
+      return this._contents.length;
+    },
+    toString$0(_) {
+      var t1 = this._contents;
+      return t1.charCodeAt(0) == 0 ? t1 : t1;
+    },
+    $isStringSink: 1
+  };
+  A.promiseToFuture_closure.prototype = {
+    call$1(r) {
+      return this.completer.complete$1(this.T._eval$1("0/?")._as(r));
+    },
+    $signature: 3
+  };
+  A.promiseToFuture_closure0.prototype = {
+    call$1(e) {
+      if (e == null)
+        return this.completer.completeError$1(new A.NullRejectionException(e === undefined));
+      return this.completer.completeError$1(e);
+    },
+    $signature: 3
+  };
+  A.dartify_convert.prototype = {
+    call$1(o) {
+      var t1, millisSinceEpoch, proto, t2, dartObject, originalKeys, dartKeys, i, jsKey, dartKey, l, $length;
+      if (A._noDartifyRequired(o))
+        return o;
+      t1 = this._convertedObjects;
+      o.toString;
+      if (t1.containsKey$1(o))
+        return t1.$index(0, o);
+      if (o instanceof Date) {
+        millisSinceEpoch = o.getTime();
+        if (Math.abs(millisSinceEpoch) > 864e13)
+          A.throwExpression(A.ArgumentError$("DateTime is outside valid range: " + millisSinceEpoch, null));
+        A.checkNotNullable(true, "isUtc", type$.bool);
+        return new A.DateTime(millisSinceEpoch, true);
+      }
+      if (o instanceof RegExp)
+        throw A.wrapException(A.ArgumentError$("structured clone of RegExp", null));
+      if (typeof Promise != "undefined" && o instanceof Promise)
+        return A.promiseToFuture(o, type$.nullable_Object);
+      proto = Object.getPrototypeOf(o);
+      if (proto === Object.prototype || proto === null) {
+        t2 = type$.nullable_Object;
+        dartObject = A.LinkedHashMap_LinkedHashMap$_empty(t2, t2);
+        t1.$indexSet(0, o, dartObject);
+        originalKeys = Object.keys(o);
+        dartKeys = [];
+        for (t1 = J.getInterceptor$ax(originalKeys), t2 = t1.get$iterator(originalKeys); t2.moveNext$0();)
+          dartKeys.push(A.dartify(t2.get$current()));
+        for (i = 0; i < t1.get$length(originalKeys); ++i) {
+          jsKey = t1.$index(originalKeys, i);
+          if (!(i < dartKeys.length))
+            return A.ioore(dartKeys, i);
+          dartKey = dartKeys[i];
+          if (jsKey != null)
+            dartObject.$indexSet(0, dartKey, this.call$1(o[jsKey]));
+        }
+        return dartObject;
+      }
+      if (o instanceof Array) {
+        l = o;
+        dartObject = [];
+        t1.$indexSet(0, o, dartObject);
+        $length = A._asInt(o.length);
+        for (t1 = J.getInterceptor$asx(l), i = 0; i < $length; ++i)
+          dartObject.push(this.call$1(t1.$index(l, i)));
+        return dartObject;
+      }
+      return o;
+    },
+    $signature: 20
+  };
+  A.NullRejectionException.prototype = {
+    toString$0(_) {
+      return "Promise was rejected with a value of `" + (this.isUndefined ? "undefined" : "null") + "`.";
+    }
+  };
+  A._JSRandom.prototype = {
+    nextInt$1(max) {
+      if (max <= 0 || max > 4294967296)
+        throw A.wrapException(A.RangeError$("max must be in range 0 < max \u2264 2^32, was " + max));
+      return Math.random() * max >>> 0;
+    }
+  };
+  A.AsyncMemoizer.prototype = {};
+  A.Level.prototype = {
+    $eq(_, other) {
+      if (other == null)
+        return false;
+      return other instanceof A.Level && this.value === other.value;
+    },
+    get$hashCode(_) {
+      return this.value;
+    },
+    toString$0(_) {
+      return this.name;
+    }
+  };
+  A.LogRecord.prototype = {
+    toString$0(_) {
+      return "[" + this.level.name + "] " + this.loggerName + ": " + this.message;
+    }
+  };
+  A.Logger.prototype = {
+    get$fullName() {
+      var t1 = this.parent,
+        t2 = t1 == null ? null : t1.name.length !== 0,
+        t3 = this.name;
+      return t2 === true ? t1.get$fullName() + "." + t3 : t3;
+    },
+    get$level() {
+      var t1, effectiveLevel;
+      if (this.parent == null) {
+        t1 = this._level;
+        t1.toString;
+        effectiveLevel = t1;
+      } else {
+        t1 = $.$get$Logger_root()._level;
+        t1.toString;
+        effectiveLevel = t1;
+      }
+      return effectiveLevel;
+    },
+    log$4(logLevel, message, error, stackTrace) {
+      var record, _this = this,
+        t1 = logLevel.value;
+      if (t1 >= _this.get$level().value) {
+        if (t1 >= 2000) {
+          A.StackTrace_current();
+          logLevel.toString$0(0);
+        }
+        t1 = _this.get$fullName();
+        Date.now();
+        $.LogRecord__nextNumber = $.LogRecord__nextNumber + 1;
+        record = new A.LogRecord(logLevel, message, t1);
+        if (_this.parent == null)
+          _this._publish$1(record);
+        else
+          $.$get$Logger_root()._publish$1(record);
+      }
+    },
+    _publish$1(record) {
+      return null;
+    }
+  };
+  A.Logger_Logger_closure.prototype = {
+    call$0() {
+      var dot, $parent, t1,
+        thisName = this.name;
+      if (B.JSString_methods.startsWith$1(thisName, "."))
+        A.throwExpression(A.ArgumentError$("name shouldn't start with a '.'", null));
+      if (B.JSString_methods.endsWith$1(thisName, "."))
+        A.throwExpression(A.ArgumentError$("name shouldn't end with a '.'", null));
+      dot = B.JSString_methods.lastIndexOf$1(thisName, ".");
+      if (dot === -1)
+        $parent = thisName !== "" ? A.Logger_Logger("") : null;
+      else {
+        $parent = A.Logger_Logger(B.JSString_methods.substring$2(thisName, 0, dot));
+        thisName = B.JSString_methods.substring$1(thisName, dot + 1);
+      }
+      t1 = new A.Logger(thisName, $parent, A.LinkedHashMap_LinkedHashMap$_empty(type$.String, type$.Logger));
+      if ($parent == null)
+        t1._level = B.Level_INFO_800;
+      else
+        $parent._children.$indexSet(0, thisName, t1);
+      return t1;
+    },
+    $signature: 21
+  };
+  A.Pool.prototype = {
+    request$0() {
+      var t1, t2, _this = this;
+      if ((_this._closeMemo._completer.future._state & 30) !== 0)
+        throw A.wrapException(A.StateError$("request() may not be called on a closed Pool."));
+      t1 = _this._allocatedResources;
+      if (t1 < _this._maxAllocatedResources) {
+        _this._allocatedResources = t1 + 1;
+        return A.Future_Future$value(new A.PoolResource(_this), type$.PoolResource);
+      } else {
+        t1 = _this._onReleaseCallbacks;
+        if (!t1.get$isEmpty(0))
+          return _this._runOnRelease$1(t1.removeFirst$0());
+        else {
+          t1 = new A._Future($.Zone__current, type$._Future_PoolResource);
+          t2 = _this._requestedResources;
+          t2._add$1(t2.$ti._precomputed1._as(new A._AsyncCompleter(t1, type$._AsyncCompleter_PoolResource)));
+          _this._resetTimer$0();
+          return t1;
+        }
+      }
+    },
+    withResource$1$1(callback, $T) {
+      return this.withResource$body$Pool($T._eval$1("0/()")._as(callback), $T, $T);
+    },
+    withResource$body$Pool(callback, $T, $async$type) {
+      var $async$goto = 0,
+        $async$completer = A._makeAsyncAwaitCompleter($async$type),
+        $async$returnValue, $async$handler = 2, $async$currentError, $async$next = [], $async$self = this, resource, t1, t2;
+      var $async$withResource$1$1 = A._wrapJsFunctionForAsync(function($async$errorCode, $async$result) {
+        if ($async$errorCode === 1) {
+          $async$currentError = $async$result;
+          $async$goto = $async$handler;
+        }
+        while (true)
+          switch ($async$goto) {
+            case 0:
+              // Function start
+              if (($async$self._closeMemo._completer.future._state & 30) !== 0)
+                throw A.wrapException(A.StateError$("withResource() may not be called on a closed Pool."));
+              $async$goto = 3;
+              return A._asyncAwait($async$self.request$0(), $async$withResource$1$1);
+            case 3:
+              // returning from await.
+              resource = $async$result;
+              $async$handler = 4;
+              t1 = callback.call$0();
+              $async$goto = 7;
+              return A._asyncAwait($T._eval$1("Future<0>")._is(t1) ? t1 : A._Future$value($T._as(t1), $T), $async$withResource$1$1);
+            case 7:
+              // returning from await.
+              t1 = $async$result;
+              $async$returnValue = t1;
+              $async$next = [1];
+              // goto finally
+              $async$goto = 5;
+              break;
+              $async$next.push(6);
+              // goto finally
+              $async$goto = 5;
+              break;
+            case 4:
+              // uncaught
+              $async$next = [2];
+            case 5:
+              // finally
+              $async$handler = 2;
+              t1 = resource;
+              if (t1._released)
+                A.throwExpression(A.StateError$("A PoolResource may only be released once."));
+              t1._released = true;
+              t1 = t1._pool;
+              t1._resetTimer$0();
+              t2 = t1._requestedResources;
+              if (!t2.get$isEmpty(0))
+                t2.removeFirst$0().complete$1(new A.PoolResource(t1));
+              else {
+                t2 = --t1._allocatedResources;
+                if ((t1._closeMemo._completer.future._state & 30) !== 0 && t2 === 0)
+                  null.close$0();
+              }
+              // goto the next finally handler
+              $async$goto = $async$next.pop();
+              break;
+            case 6:
+              // after finally
+            case 1:
+              // return
+              return A._asyncReturn($async$returnValue, $async$completer);
+            case 2:
+              // rethrow
+              return A._asyncRethrow($async$currentError, $async$completer);
+          }
+      });
+      return A._asyncStartSync($async$withResource$1$1, $async$completer);
+    },
+    _runOnRelease$1(onRelease) {
+      var t1 = A.Future_Future$sync(type$.dynamic_Function._as(onRelease), type$.dynamic).then$1$1(new A.Pool__runOnRelease_closure(this), type$.Null),
+        onError = new A.Pool__runOnRelease_closure0(this),
+        t2 = t1.$ti,
+        t3 = $.Zone__current;
+      if (t3 !== B.C__RootZone)
+        onError = A._registerErrorHandler(onError, t3);
+      t1._addListener$1(new A._FutureListener(new A._Future(t3, t2), 2, null, onError, t2._eval$1("@<1>")._bind$1(t2._precomputed1)._eval$1("_FutureListener<1,2>")));
+      t1 = new A._Future($.Zone__current, type$._Future_PoolResource);
+      t2 = this._onReleaseCompleters;
+      t2._add$1(t2.$ti._precomputed1._as(new A._SyncCompleter(t1, type$._SyncCompleter_PoolResource)));
+      return t1;
+    },
+    _resetTimer$0() {
+      var t2,
+        t1 = this._timer;
+      if (t1 == null)
+        return;
+      t2 = this._requestedResources;
+      if (t2._head === t2._tail)
+        t1._restartable_timer$_timer.cancel$0();
+      else {
+        t1._restartable_timer$_timer.cancel$0();
+        t1._restartable_timer$_timer = A.Timer_Timer(t1._restartable_timer$_duration, t1._callback);
+      }
+    }
+  };
+  A.Pool__runOnRelease_closure.prototype = {
+    call$1(value) {
+      var t1 = this.$this;
+      t1._onReleaseCompleters.removeFirst$0().complete$1(new A.PoolResource(t1));
+    },
+    $signature: 4
+  };
+  A.Pool__runOnRelease_closure0.prototype = {
+    call$2(error, stackTrace) {
+      type$.Object._as(error);
+      type$.StackTrace._as(stackTrace);
+      this.$this._onReleaseCompleters.removeFirst$0().completeError$2(error, stackTrace);
+    },
+    $signature: 5
+  };
+  A.PoolResource.prototype = {};
+  A.SseClient.prototype = {
+    SseClient$2$debugKey(serverUrl, debugKey) {
+      var t2, t3, _this = this,
+        t1 = serverUrl + "?sseClientId=" + _this._clientId;
+      _this.__SseClient__serverUrl_A = t1;
+      t2 = type$.JSObject;
+      t1 = t2._as(new self.EventSource(t1, {withCredentials: true}));
+      _this.__SseClient__eventSource_A = t1;
+      new A._EventStream(t1, "open", false, type$._EventStream_JSObject).get$first(0).whenComplete$1(new A.SseClient_closure(_this));
+      t1 = type$.Function;
+      t3 = type$.JavaScriptFunction;
+      _this.__SseClient__eventSource_A.addEventListener("message", t3._as(A.allowInterop(_this.get$_onIncomingMessage(), t1)));
+      _this.__SseClient__eventSource_A.addEventListener("control", t3._as(A.allowInterop(_this.get$_onIncomingControlMessage(), t1)));
+      t1 = type$.nullable_void_Function_JSObject;
+      A._EventStreamSubscription$(_this.__SseClient__eventSource_A, "open", t1._as(new A.SseClient_closure0(_this)), false, t2);
+      A._EventStreamSubscription$(_this.__SseClient__eventSource_A, "error", t1._as(new A.SseClient_closure1(_this)), false, t2);
+    },
+    close$0() {
+      var _this = this,
+        t1 = _this.__SseClient__eventSource_A;
+      t1 === $ && A.throwLateFieldNI("_eventSource");
+      t1.close();
+      if ((_this._onConnected.future._state & 30) === 0) {
+        t1 = _this._outgoingController;
+        new A._ControllerStream(t1, A._instanceType(t1)._eval$1("_ControllerStream<1>")).listen$2$cancelOnError(null, true).asFuture$1$1(null, type$.void);
+      }
+      _this._incomingController.close$0();
+      _this._outgoingController.close$0();
+    },
+    _closeWithError$1(error) {
+      var stackTrace, t2,
+        t1 = this._incomingController;
+      A.checkNotNullable(error, "error", type$.Object);
+      if (t1._state >= 4)
+        A.throwExpression(t1._badEventState$0());
+      stackTrace = A.AsyncError_defaultStackTrace(error);
+      t2 = t1._state;
+      if ((t2 & 1) !== 0)
+        t1._sendError$2(error, stackTrace);
+      else if ((t2 & 3) === 0)
+        t1._ensurePendingEvents$0().add$1(0, new A._DelayedError(error, stackTrace));
+      this.close$0();
+      t1 = this._onConnected;
+      if ((t1.future._state & 30) === 0)
+        t1.completeError$1(error);
+    },
+    _onIncomingControlMessage$1(message) {
+      var data = type$.JSObject._as(message).data;
+      if (J.$eq$(A.dartify(data), "close"))
+        this.close$0();
+      else
+        throw A.wrapException(A.UnsupportedError$("[" + this._clientId + '] Illegal Control Message "' + A.S(data) + '"'));
+    },
+    _onIncomingMessage$1(message) {
+      this._incomingController.add$1(0, A._asString(B.C_JsonCodec.decode$2$reviver(A._asString(type$.JSObject._as(message).data), null)));
+    },
+    _onOutgoingDone$0() {
+      this.close$0();
+    },
+    _onOutgoingMessage$1(message) {
+      return this._onOutgoingMessage$body$SseClient(A._asStringQ(message));
+    },
+    _onOutgoingMessage$body$SseClient(message) {
+      var $async$goto = 0,
+        $async$completer = A._makeAsyncAwaitCompleter(type$.void),
+        $async$self = this, t1;
+      var $async$_onOutgoingMessage$1 = A._wrapJsFunctionForAsync(function($async$errorCode, $async$result) {
+        if ($async$errorCode === 1)
+          return A._asyncRethrow($async$result, $async$completer);
+        while (true)
+          switch ($async$goto) {
+            case 0:
+              // Function start
+              t1 = {};
+              t1.encodedMessage = null;
+              $async$goto = 2;
+              return A._asyncAwait($.$get$_requestPool().withResource$1$1(new A.SseClient__onOutgoingMessage_closure(t1, $async$self, message), type$.Null), $async$_onOutgoingMessage$1);
+            case 2:
+              // returning from await.
+              // implicit return
+              return A._asyncReturn(null, $async$completer);
+          }
+      });
+      return A._asyncStartSync($async$_onOutgoingMessage$1, $async$completer);
+    }
+  };
+  A.SseClient_closure.prototype = {
+    call$0() {
+      var t2,
+        t1 = this.$this;
+      t1._onConnected.complete$0();
+      t2 = t1._outgoingController;
+      new A._ControllerStream(t2, A._instanceType(t2)._eval$1("_ControllerStream<1>")).listen$2$onDone(t1.get$_onOutgoingMessage(), t1.get$_onOutgoingDone());
+    },
+    $signature: 2
+  };
+  A.SseClient_closure0.prototype = {
+    call$1(_) {
+      var t1 = this.$this._errorTimer;
+      if (t1 != null)
+        t1.cancel$0();
+    },
+    $signature: 1
+  };
+  A.SseClient_closure1.prototype = {
+    call$1(error) {
+      var t1 = this.$this,
+        t2 = t1._errorTimer;
+      t2 = t2 == null ? null : t2._handle != null;
+      if (t2 !== true)
+        t1._errorTimer = A.Timer_Timer(B.Duration_5000000, new A.SseClient__closure(t1, error));
+    },
+    $signature: 1
+  };
+  A.SseClient__closure.prototype = {
+    call$0() {
+      this.$this._closeWithError$1(this.error);
+    },
+    $signature: 0
+  };
+  A.SseClient__onOutgoingMessage_closure.prototype = {
+    call$0() {
+      var $async$goto = 0,
+        $async$completer = A._makeAsyncAwaitCompleter(type$.Null),
+        $async$handler = 1, $async$currentError, $async$self = this, e, e0, url, error, augmentedError, exception, t1, t2, $async$exception;
+      var $async$call$0 = A._wrapJsFunctionForAsync(function($async$errorCode, $async$result) {
+        if ($async$errorCode === 1) {
+          $async$currentError = $async$result;
+          $async$goto = $async$handler;
+        }
+        while (true)
+          switch ($async$goto) {
+            case 0:
+              // Function start
+              try {
+                $async$self._box_0.encodedMessage = B.C_JsonCodec.encode$2$toEncodable($async$self.message, null);
+              } catch (exception) {
+                t1 = A.unwrapException(exception);
+                if (t1 instanceof A.JsonUnsupportedObjectError) {
+                  e = t1;
+                  t1 = $async$self.$this;
+                  t1._logger.log$4(B.Level_WARNING_900, "[" + t1._clientId + "] Unable to encode outgoing message: " + A.S(e), null, null);
+                } else if (t1 instanceof A.ArgumentError) {
+                  e0 = t1;
+                  t1 = $async$self.$this;
+                  t1._logger.log$4(B.Level_WARNING_900, "[" + t1._clientId + "] Invalid argument: " + A.S(e0), null, null);
+                } else
+                  throw exception;
+              }
+              $async$handler = 3;
+              t1 = $async$self.$this;
+              t2 = t1.__SseClient__serverUrl_A;
+              t2 === $ && A.throwLateFieldNI("_serverUrl");
+              url = t2 + "&messageId=" + ++t1._lastMessageId;
+              t1 = $async$self._box_0.encodedMessage;
+              if (t1 == null)
+                t1 = null;
+              t1 = {method: "POST", body: t1, credentials: "include"};
+              t2 = type$.JSObject;
+              $async$goto = 6;
+              return A._asyncAwait(A.promiseToFuture(t2._as(t2._as(self.window).fetch(url, t1)), t2), $async$call$0);
+            case 6:
+              // returning from await.
+              $async$handler = 1;
+              // goto after finally
+              $async$goto = 5;
+              break;
+            case 3:
+              // catch
+              $async$handler = 2;
+              $async$exception = $async$currentError;
+              error = A.unwrapException($async$exception);
+              t1 = $async$self.$this;
+              augmentedError = "[" + t1._clientId + "] SSE client failed to send " + A.S($async$self.message) + ":\n " + A.S(error);
+              t1._logger.log$4(B.Level_SEVERE_1000, augmentedError, null, null);
+              t1._closeWithError$1(augmentedError);
+              // goto after finally
+              $async$goto = 5;
+              break;
+            case 2:
+              // uncaught
+              // goto rethrow
+              $async$goto = 1;
+              break;
+            case 5:
+              // after finally
+              // implicit return
+              return A._asyncReturn(null, $async$completer);
+            case 1:
+              // rethrow
+              return A._asyncRethrow($async$currentError, $async$completer);
+          }
+      });
+      return A._asyncStartSync($async$call$0, $async$completer);
+    },
+    $signature: 7
+  };
+  A.generateUuidV4_generateBits.prototype = {
+    call$1(bitCount) {
+      return this.random.nextInt$1(B.JSInt_methods._shlPositive$1(1, bitCount));
+    },
+    $signature: 23
+  };
+  A.generateUuidV4_printDigits.prototype = {
+    call$2(value, count) {
+      return B.JSString_methods.padLeft$2(B.JSInt_methods.toRadixString$1(value, 16), count, "0");
+    },
+    $signature: 11
+  };
+  A.generateUuidV4_bitsDigits.prototype = {
+    call$2(bitCount, digitCount) {
+      return this.printDigits.call$2(this.generateBits.call$1(bitCount), digitCount);
+    },
+    $signature: 11
+  };
+  A.StreamChannelMixin.prototype = {};
+  A.EventStreamProvider.prototype = {};
+  A._EventStream.prototype = {
+    listen$4$cancelOnError$onDone$onError(onData, cancelOnError, onDone, onError) {
+      var t1 = A._instanceType(this);
+      t1._eval$1("~(1)?")._as(onData);
+      type$.nullable_void_Function._as(onDone);
+      return A._EventStreamSubscription$(this._target, this._eventType, onData, false, t1._precomputed1);
+    }
+  };
+  A._ElementEventStreamImpl.prototype = {};
+  A._EventStreamSubscription.prototype = {
+    cancel$0() {
+      var _this = this,
+        emptyFuture = A.Future_Future$value(null, type$.void);
+      if (_this._target == null)
+        return emptyFuture;
+      _this._unlisten$0();
+      _this._streams$_onData = _this._target = null;
+      return emptyFuture;
+    },
+    onData$1(handleData) {
+      var t1, _this = this;
+      _this.$ti._eval$1("~(1)?")._as(handleData);
+      if (_this._target == null)
+        throw A.wrapException(A.StateError$("Subscription has been canceled."));
+      _this._unlisten$0();
+      t1 = A._wrapZone(new A._EventStreamSubscription_onData_closure(handleData), type$.JSObject);
+      t1 = t1 == null ? null : type$.JavaScriptFunction._as(A.allowInterop(t1, type$.Function));
+      _this._streams$_onData = t1;
+      _this._tryResume$0();
+    },
+    _tryResume$0() {
+      var t1 = this._streams$_onData;
+      if (t1 != null)
+        this._target.addEventListener(this._eventType, t1, false);
+    },
+    _unlisten$0() {
+      var t1 = this._streams$_onData;
+      if (t1 != null)
+        this._target.removeEventListener(this._eventType, t1, false);
+    },
+    $isStreamSubscription: 1
+  };
+  A._EventStreamSubscription_closure.prototype = {
+    call$1(e) {
+      return this.onData.call$1(type$.JSObject._as(e));
+    },
+    $signature: 1
+  };
+  A._EventStreamSubscription_onData_closure.prototype = {
+    call$1(e) {
+      return this.handleData.call$1(type$.JSObject._as(e));
+    },
+    $signature: 1
+  };
+  A.main_closure.prototype = {
+    call$1(_) {
+      this.channel._outgoingController.close$0();
+    },
+    $signature: 1
+  };
+  A.main_closure0.prototype = {
+    call$1(s) {
+      var count, t1, t2, t3, i, t4, t5, lastEvent;
+      A._asString(s);
+      if (B.JSString_methods.startsWith$1(s, "send ")) {
+        count = A.int_parse(B.JSArray_methods.get$last(s.split(" ")), null);
+        for (t1 = this.channel._outgoingController, t2 = A._instanceType(t1), t3 = t2._precomputed1, t2 = t2._eval$1("_DelayedData<1>"), i = 0; i < count; ++i) {
+          t4 = t3._as("" + i);
+          t5 = t1._state;
+          if (t5 >= 4)
+            A.throwExpression(t1._badEventState$0());
+          if ((t5 & 1) !== 0)
+            t1._sendData$1(t4);
+          else if ((t5 & 3) === 0) {
+            t5 = t1._ensurePendingEvents$0();
+            t4 = new A._DelayedData(t4, t2);
+            lastEvent = t5.lastPendingEvent;
+            if (lastEvent == null)
+              t5.firstPendingEvent = t5.lastPendingEvent = t4;
+            else {
+              lastEvent.set$next(t4);
+              t5.lastPendingEvent = t4;
+            }
+          }
+        }
+      } else {
+        t1 = this.channel._outgoingController;
+        t1.add$1(0, A._instanceType(t1)._precomputed1._as(s));
+      }
+    },
+    $signature: 24
+  };
+  (function aliases() {
+    var _ = J.LegacyJavaScriptObject.prototype;
+    _.super$LegacyJavaScriptObject$toString = _.toString$0;
+  })();
+  (function installTearOffs() {
+    var _static_1 = hunkHelpers._static_1,
+      _static_0 = hunkHelpers._static_0,
+      _static_2 = hunkHelpers._static_2,
+      _instance_2_u = hunkHelpers._instance_2u,
+      _instance_1_u = hunkHelpers._instance_1u,
+      _instance_0_u = hunkHelpers._instance_0u;
+    _static_1(A, "async__AsyncRun__scheduleImmediateJsOverride$closure", "_AsyncRun__scheduleImmediateJsOverride", 6);
+    _static_1(A, "async__AsyncRun__scheduleImmediateWithSetImmediate$closure", "_AsyncRun__scheduleImmediateWithSetImmediate", 6);
+    _static_1(A, "async__AsyncRun__scheduleImmediateWithTimer$closure", "_AsyncRun__scheduleImmediateWithTimer", 6);
+    _static_0(A, "async___startMicrotaskLoop$closure", "_startMicrotaskLoop", 0);
+    _static_1(A, "async___nullDataHandler$closure", "_nullDataHandler", 3);
+    _static_2(A, "async___nullErrorHandler$closure", "_nullErrorHandler", 9);
+    _static_0(A, "async___nullDoneHandler$closure", "_nullDoneHandler", 0);
+    _instance_2_u(A._Future.prototype, "get$_completeError", "_completeError$2", 9);
+    _static_1(A, "convert___defaultToEncodable$closure", "_defaultToEncodable", 8);
+    var _;
+    _instance_1_u(_ = A.SseClient.prototype, "get$_onIncomingControlMessage", "_onIncomingControlMessage$1", 1);
+    _instance_1_u(_, "get$_onIncomingMessage", "_onIncomingMessage$1", 1);
+    _instance_0_u(_, "get$_onOutgoingDone", "_onOutgoingDone$0", 0);
+    _instance_1_u(_, "get$_onOutgoingMessage", "_onOutgoingMessage$1", 22);
+  })();
+  (function inheritance() {
+    var _mixin = hunkHelpers.mixin,
+      _inherit = hunkHelpers.inherit,
+      _inheritMany = hunkHelpers.inheritMany;
+    _inherit(A.Object, null);
+    _inheritMany(A.Object, [A.JS_CONST, J.Interceptor, J.ArrayIterator, A.Error, A.Closure, A.Iterable, A.ListIterator, A.FixedLengthListMixin, A.Symbol, A.MapView, A.ConstantMap, A.JSInvocationMirror, A.TypeErrorDecoder, A.NullThrownFromJavaScriptException, A.ExceptionAndStackTrace, A._StackTrace, A._Required, A.MapBase, A.LinkedHashMapCell, A.LinkedHashMapKeyIterator, A.StringMatch, A.Rti, A._FunctionParameters, A._Type, A._TimerImpl, A._AsyncAwaitCompleter, A.AsyncError, A._Completer, A._FutureListener, A._Future, A._AsyncCallbackEntry, A.Stream, A._StreamController, A._AsyncStreamControllerDispatch, A._BufferingStreamSubscription, A._StreamSinkWrapper, A._DelayedEvent, A._DelayedDone, A._PendingEvents, A._StreamIterator, A._Zone, A._HashMapKeyIterator, A.ListBase, A._UnmodifiableMapMixin, A._ListQueueIterator, A.Codec, A.Converter, A._JsonStringifier, A.DateTime, A.Duration, A.OutOfMemoryError, A.StackOverflowError, A._Exception, A.FormatException, A.Null, A._StringStackTrace, A.StringBuffer, A.NullRejectionException, A._JSRandom, A.AsyncMemoizer, A.Level, A.LogRecord, A.Logger, A.Pool, A.PoolResource, A.StreamChannelMixin, A.EventStreamProvider, A._EventStreamSubscription]);
+    _inheritMany(J.Interceptor, [J.JSBool, J.JSNull, J.JavaScriptObject, J.JavaScriptBigInt, J.JavaScriptSymbol, J.JSNumber, J.JSString]);
+    _inheritMany(J.JavaScriptObject, [J.LegacyJavaScriptObject, J.JSArray, A.NativeByteBuffer, A.NativeTypedData]);
+    _inheritMany(J.LegacyJavaScriptObject, [J.PlainJavaScriptObject, J.UnknownJavaScriptObject, J.JavaScriptFunction]);
+    _inherit(J.JSUnmodifiableArray, J.JSArray);
+    _inheritMany(J.JSNumber, [J.JSInt, J.JSNumNotInt]);
+    _inheritMany(A.Error, [A.LateError, A.TypeError, A.JsNoSuchMethodError, A.UnknownJsTypeError, A._CyclicInitializationError, A.RuntimeError, A._Error, A.JsonUnsupportedObjectError, A.AssertionError, A.ArgumentError, A.NoSuchMethodError, A.UnsupportedError, A.UnimplementedError, A.StateError, A.ConcurrentModificationError]);
+    _inheritMany(A.Closure, [A.Closure0Args, A.Closure2Args, A.TearOffClosure, A.initHooks_closure, A.initHooks_closure1, A._AsyncRun__initializeScheduleImmediate_internalCallback, A._AsyncRun__initializeScheduleImmediate_closure, A._awaitOnObject_closure, A._Future__chainForeignFuture_closure, A._Future__propagateToListeners_handleWhenCompleteCallback_closure, A.Stream_length_closure, A.Stream_first_closure0, A._RootZone_bindUnaryCallbackGuarded_closure, A.promiseToFuture_closure, A.promiseToFuture_closure0, A.dartify_convert, A.Pool__runOnRelease_closure, A.SseClient_closure0, A.SseClient_closure1, A.generateUuidV4_generateBits, A._EventStreamSubscription_closure, A._EventStreamSubscription_onData_closure, A.main_closure, A.main_closure0]);
+    _inheritMany(A.Closure0Args, [A.nullFuture_closure, A._AsyncRun__scheduleImmediateJsOverride_internalCallback, A._AsyncRun__scheduleImmediateWithSetImmediate_internalCallback, A._TimerImpl_internalCallback, A._Future__addListener_closure, A._Future__prependListeners_closure, A._Future__chainForeignFuture_closure1, A._Future__chainCoreFutureAsync_closure, A._Future__asyncCompleteWithValue_closure, A._Future__asyncCompleteError_closure, A._Future__propagateToListeners_handleWhenCompleteCallback, A._Future__propagateToListeners_handleValueCallback, A._Future__propagateToListeners_handleError, A.Stream_length_closure0, A.Stream_first_closure, A._StreamController__subscribe_closure, A._StreamController__recordCancel_complete, A._BufferingStreamSubscription_asFuture_closure, A._BufferingStreamSubscription_asFuture__closure, A._BufferingStreamSubscription__sendError_sendError, A._BufferingStreamSubscription__sendDone_sendDone, A._PendingEvents_schedule_closure, A._cancelAndValue_closure, A._rootHandleError_closure, A._RootZone_bindCallbackGuarded_closure, A.Logger_Logger_closure, A.SseClient_closure, A.SseClient__closure, A.SseClient__onOutgoingMessage_closure]);
+    _inherit(A.EfficientLengthIterable, A.Iterable);
+    _inheritMany(A.EfficientLengthIterable, [A.ListIterable, A.LinkedHashMapKeyIterable, A._HashMapKeyIterable]);
+    _inherit(A._UnmodifiableMapView_MapView__UnmodifiableMapMixin, A.MapView);
+    _inherit(A.UnmodifiableMapView, A._UnmodifiableMapView_MapView__UnmodifiableMapMixin);
+    _inherit(A.ConstantMapView, A.UnmodifiableMapView);
+    _inherit(A.ConstantStringMap, A.ConstantMap);
+    _inheritMany(A.Closure2Args, [A.Primitives_functionNoSuchMethod_closure, A.initHooks_closure0, A._awaitOnObject_closure0, A._wrapJsFunctionForAsync_closure, A._Future__chainForeignFuture_closure0, A._BufferingStreamSubscription_asFuture_closure0, A.MapBase_mapToString_closure, A._JsonStringifier_writeMap_closure, A.NoSuchMethodError_toString_closure, A.Pool__runOnRelease_closure0, A.generateUuidV4_printDigits, A.generateUuidV4_bitsDigits]);
+    _inherit(A.NullError, A.TypeError);
+    _inheritMany(A.TearOffClosure, [A.StaticClosure, A.BoundClosure]);
+    _inheritMany(A.MapBase, [A.JsLinkedHashMap, A._HashMap, A._JsonMap]);
+    _inheritMany(A.NativeTypedData, [A.NativeByteData, A.NativeTypedArray]);
+    _inheritMany(A.NativeTypedArray, [A._NativeTypedArrayOfDouble_NativeTypedArray_ListMixin, A._NativeTypedArrayOfInt_NativeTypedArray_ListMixin]);
+    _inherit(A._NativeTypedArrayOfDouble_NativeTypedArray_ListMixin_FixedLengthListMixin, A._NativeTypedArrayOfDouble_NativeTypedArray_ListMixin);
+    _inherit(A.NativeTypedArrayOfDouble, A._NativeTypedArrayOfDouble_NativeTypedArray_ListMixin_FixedLengthListMixin);
+    _inherit(A._NativeTypedArrayOfInt_NativeTypedArray_ListMixin_FixedLengthListMixin, A._NativeTypedArrayOfInt_NativeTypedArray_ListMixin);
+    _inherit(A.NativeTypedArrayOfInt, A._NativeTypedArrayOfInt_NativeTypedArray_ListMixin_FixedLengthListMixin);
+    _inheritMany(A.NativeTypedArrayOfDouble, [A.NativeFloat32List, A.NativeFloat64List]);
+    _inheritMany(A.NativeTypedArrayOfInt, [A.NativeInt16List, A.NativeInt32List, A.NativeInt8List, A.NativeUint16List, A.NativeUint32List, A.NativeUint8ClampedList, A.NativeUint8List]);
+    _inherit(A._TypeError, A._Error);
+    _inheritMany(A._Completer, [A._AsyncCompleter, A._SyncCompleter]);
+    _inherit(A._AsyncStreamController, A._StreamController);
+    _inheritMany(A.Stream, [A._StreamImpl, A._EventStream]);
+    _inherit(A._ControllerStream, A._StreamImpl);
+    _inherit(A._ControllerSubscription, A._BufferingStreamSubscription);
+    _inheritMany(A._DelayedEvent, [A._DelayedData, A._DelayedError]);
+    _inherit(A._RootZone, A._Zone);
+    _inherit(A._IdentityHashMap, A._HashMap);
+    _inheritMany(A.ListIterable, [A.ListQueue, A._JsonMapKeyIterable]);
+    _inherit(A.JsonCyclicError, A.JsonUnsupportedObjectError);
+    _inherit(A.JsonCodec, A.Codec);
+    _inheritMany(A.Converter, [A.JsonEncoder, A.JsonDecoder]);
+    _inherit(A._JsonStringStringifier, A._JsonStringifier);
+    _inheritMany(A.ArgumentError, [A.RangeError, A.IndexError]);
+    _inherit(A.SseClient, A.StreamChannelMixin);
+    _inherit(A._ElementEventStreamImpl, A._EventStream);
+    _mixin(A._NativeTypedArrayOfDouble_NativeTypedArray_ListMixin, A.ListBase);
+    _mixin(A._NativeTypedArrayOfDouble_NativeTypedArray_ListMixin_FixedLengthListMixin, A.FixedLengthListMixin);
+    _mixin(A._NativeTypedArrayOfInt_NativeTypedArray_ListMixin, A.ListBase);
+    _mixin(A._NativeTypedArrayOfInt_NativeTypedArray_ListMixin_FixedLengthListMixin, A.FixedLengthListMixin);
+    _mixin(A._AsyncStreamController, A._AsyncStreamControllerDispatch);
+    _mixin(A._UnmodifiableMapView_MapView__UnmodifiableMapMixin, A._UnmodifiableMapMixin);
+  })();
+  var init = {
+    typeUniverse: {eC: new Map(), tR: {}, eT: {}, tPV: {}, sEA: []},
+    mangledGlobalNames: {int: "int", double: "double", num: "num", String: "String", bool: "bool", Null: "Null", List: "List", Object: "Object", Map: "Map"},
+    mangledNames: {},
+    types: ["~()", "~(JSObject)", "Null()", "~(@)", "Null(@)", "Null(Object,StackTrace)", "~(~())", "Future<Null>()", "@(@)", "~(Object,StackTrace)", "~(Object?,Object?)", "String(int,int)", "~(String,@)", "@(@,String)", "@(String)", "Null(~())", "Null(@,StackTrace)", "~(int,@)", "_Future<@>(@)", "~(Symbol0,@)", "Object?(Object?)", "Logger()", "~(String?)", "int(int)", "~(String)"],
+    interceptorsByTag: null,
+    leafTags: null,
+    arrayRti: Symbol("$ti")
+  };
+  A._Universe_addRules(init.typeUniverse, JSON.parse('{"PlainJavaScriptObject":"LegacyJavaScriptObject","UnknownJavaScriptObject":"LegacyJavaScriptObject","JavaScriptFunction":"LegacyJavaScriptObject","JSBool":{"bool":[],"TrustedGetRuntimeType":[]},"JSNull":{"Null":[],"TrustedGetRuntimeType":[]},"JavaScriptObject":{"JSObject":[]},"LegacyJavaScriptObject":{"JSObject":[]},"JSArray":{"List":["1"],"JSObject":[],"Iterable":["1"]},"JSUnmodifiableArray":{"JSArray":["1"],"List":["1"],"JSObject":[],"Iterable":["1"]},"JSNumber":{"double":[],"num":[]},"JSInt":{"double":[],"int":[],"num":[],"TrustedGetRuntimeType":[]},"JSNumNotInt":{"double":[],"num":[],"TrustedGetRuntimeType":[]},"JSString":{"String":[],"Pattern":[],"TrustedGetRuntimeType":[]},"LateError":{"Error":[]},"EfficientLengthIterable":{"Iterable":["1"]},"ListIterable":{"Iterable":["1"]},"Symbol":{"Symbol0":[]},"ConstantMapView":{"UnmodifiableMapView":["1","2"],"_UnmodifiableMapView_MapView__UnmodifiableMapMixin":["1","2"],"MapView":["1","2"],"_UnmodifiableMapMixin":["1","2"],"Map":["1","2"]},"ConstantMap":{"Map":["1","2"]},"ConstantStringMap":{"ConstantMap":["1","2"],"Map":["1","2"]},"JSInvocationMirror":{"Invocation":[]},"NullError":{"TypeError":[],"Error":[]},"JsNoSuchMethodError":{"Error":[]},"UnknownJsTypeError":{"Error":[]},"_StackTrace":{"StackTrace":[]},"Closure":{"Function":[]},"Closure0Args":{"Function":[]},"Closure2Args":{"Function":[]},"TearOffClosure":{"Function":[]},"StaticClosure":{"Function":[]},"BoundClosure":{"Function":[]},"_CyclicInitializationError":{"Error":[]},"RuntimeError":{"Error":[]},"JsLinkedHashMap":{"MapBase":["1","2"],"Map":["1","2"],"MapBase.K":"1","MapBase.V":"2"},"LinkedHashMapKeyIterable":{"Iterable":["1"]},"NativeByteBuffer":{"JSObject":[],"TrustedGetRuntimeType":[]},"NativeTypedData":{"JSObject":[]},"NativeByteData":{"JSObject":[],"TrustedGetRuntimeType":[]},"NativeTypedArray":{"JavaScriptIndexingBehavior":["1"],"JSObject":[]},"NativeTypedArrayOfDouble":{"ListBase":["double"],"List":["double"],"JavaScriptIndexingBehavior":["double"],"JSObject":[],"Iterable":["double"],"FixedLengthListMixin":["double"]},"NativeTypedArrayOfInt":{"ListBase":["int"],"List":["int"],"JavaScriptIndexingBehavior":["int"],"JSObject":[],"Iterable":["int"],"FixedLengthListMixin":["int"]},"NativeFloat32List":{"ListBase":["double"],"List":["double"],"JavaScriptIndexingBehavior":["double"],"JSObject":[],"Iterable":["double"],"FixedLengthListMixin":["double"],"TrustedGetRuntimeType":[],"ListBase.E":"double"},"NativeFloat64List":{"ListBase":["double"],"List":["double"],"JavaScriptIndexingBehavior":["double"],"JSObject":[],"Iterable":["double"],"FixedLengthListMixin":["double"],"TrustedGetRuntimeType":[],"ListBase.E":"double"},"NativeInt16List":{"ListBase":["int"],"List":["int"],"JavaScriptIndexingBehavior":["int"],"JSObject":[],"Iterable":["int"],"FixedLengthListMixin":["int"],"TrustedGetRuntimeType":[],"ListBase.E":"int"},"NativeInt32List":{"ListBase":["int"],"List":["int"],"JavaScriptIndexingBehavior":["int"],"JSObject":[],"Iterable":["int"],"FixedLengthListMixin":["int"],"TrustedGetRuntimeType":[],"ListBase.E":"int"},"NativeInt8List":{"ListBase":["int"],"List":["int"],"JavaScriptIndexingBehavior":["int"],"JSObject":[],"Iterable":["int"],"FixedLengthListMixin":["int"],"TrustedGetRuntimeType":[],"ListBase.E":"int"},"NativeUint16List":{"ListBase":["int"],"List":["int"],"JavaScriptIndexingBehavior":["int"],"JSObject":[],"Iterable":["int"],"FixedLengthListMixin":["int"],"TrustedGetRuntimeType":[],"ListBase.E":"int"},"NativeUint32List":{"ListBase":["int"],"List":["int"],"JavaScriptIndexingBehavior":["int"],"JSObject":[],"Iterable":["int"],"FixedLengthListMixin":["int"],"TrustedGetRuntimeType":[],"ListBase.E":"int"},"NativeUint8ClampedList":{"ListBase":["int"],"List":["int"],"JavaScriptIndexingBehavior":["int"],"JSObject":[],"Iterable":["int"],"FixedLengthListMixin":["int"],"TrustedGetRuntimeType":[],"ListBase.E":"int"},"NativeUint8List":{"ListBase":["int"],"List":["int"],"JavaScriptIndexingBehavior":["int"],"JSObject":[],"Iterable":["int"],"FixedLengthListMixin":["int"],"TrustedGetRuntimeType":[],"ListBase.E":"int"},"_Error":{"Error":[]},"_TypeError":{"TypeError":[],"Error":[]},"_Future":{"Future":["1"]},"_TimerImpl":{"Timer":[]},"_AsyncAwaitCompleter":{"Completer":["1"]},"AsyncError":{"Error":[]},"_Completer":{"Completer":["1"]},"_AsyncCompleter":{"_Completer":["1"],"Completer":["1"]},"_SyncCompleter":{"_Completer":["1"],"Completer":["1"]},"_StreamController":{"StreamController":["1"],"_StreamControllerLifecycle":["1"],"_EventDispatch":["1"]},"_AsyncStreamController":{"_AsyncStreamControllerDispatch":["1"],"_StreamController":["1"],"StreamController":["1"],"_StreamControllerLifecycle":["1"],"_EventDispatch":["1"]},"_ControllerStream":{"_StreamImpl":["1"],"Stream":["1"]},"_ControllerSubscription":{"_BufferingStreamSubscription":["1"],"StreamSubscription":["1"],"_EventDispatch":["1"]},"_BufferingStreamSubscription":{"StreamSubscription":["1"],"_EventDispatch":["1"]},"_StreamImpl":{"Stream":["1"]},"_DelayedData":{"_DelayedEvent":["1"]},"_DelayedError":{"_DelayedEvent":["@"]},"_DelayedDone":{"_DelayedEvent":["@"]},"_Zone":{"Zone":[]},"_RootZone":{"_Zone":[],"Zone":[]},"_HashMap":{"MapBase":["1","2"],"Map":["1","2"]},"_IdentityHashMap":{"_HashMap":["1","2"],"MapBase":["1","2"],"Map":["1","2"],"MapBase.K":"1","MapBase.V":"2"},"_HashMapKeyIterable":{"Iterable":["1"]},"MapBase":{"Map":["1","2"]},"MapView":{"Map":["1","2"]},"UnmodifiableMapView":{"_UnmodifiableMapView_MapView__UnmodifiableMapMixin":["1","2"],"MapView":["1","2"],"_UnmodifiableMapMixin":["1","2"],"Map":["1","2"]},"ListQueue":{"Queue":["1"],"ListIterable":["1"],"Iterable":["1"],"ListIterable.E":"1"},"_JsonMap":{"MapBase":["String","@"],"Map":["String","@"],"MapBase.K":"String","MapBase.V":"@"},"_JsonMapKeyIterable":{"ListIterable":["String"],"Iterable":["String"],"ListIterable.E":"String"},"JsonUnsupportedObjectError":{"Error":[]},"JsonCyclicError":{"Error":[]},"JsonCodec":{"Codec":["Object?","String"]},"JsonEncoder":{"Converter":["Object?","String"]},"JsonDecoder":{"Converter":["String","Object?"]},"double":{"num":[]},"int":{"num":[]},"String":{"Pattern":[]},"AssertionError":{"Error":[]},"TypeError":{"Error":[]},"ArgumentError":{"Error":[]},"RangeError":{"Error":[]},"IndexError":{"Error":[]},"NoSuchMethodError":{"Error":[]},"UnsupportedError":{"Error":[]},"UnimplementedError":{"Error":[]},"StateError":{"Error":[]},"ConcurrentModificationError":{"Error":[]},"OutOfMemoryError":{"Error":[]},"StackOverflowError":{"Error":[]},"_StringStackTrace":{"StackTrace":[]},"StringBuffer":{"StringSink":[]},"_EventStream":{"Stream":["1"]},"_ElementEventStreamImpl":{"_EventStream":["1"],"Stream":["1"]},"_EventStreamSubscription":{"StreamSubscription":["1"]},"Int8List":{"List":["int"],"Iterable":["int"]},"Uint8List":{"List":["int"],"Iterable":["int"]},"Uint8ClampedList":{"List":["int"],"Iterable":["int"]},"Int16List":{"List":["int"],"Iterable":["int"]},"Uint16List":{"List":["int"],"Iterable":["int"]},"Int32List":{"List":["int"],"Iterable":["int"]},"Uint32List":{"List":["int"],"Iterable":["int"]},"Float32List":{"List":["double"],"Iterable":["double"]},"Float64List":{"List":["double"],"Iterable":["double"]}}'));
+  A._Universe_addErasedTypes(init.typeUniverse, JSON.parse('{"EfficientLengthIterable":1,"NativeTypedArray":1,"_DelayedEvent":1,"StreamChannelMixin":1}'));
+  var string$ = {
+    Error_: "Error handler must accept one Object or one Object and a StackTrace as arguments, and return a value of the returned future's type"
+  };
+  var type$ = (function rtii() {
+    var findType = A.findType;
+    return {
+      $env_1_1_void: findType("@<~>"),
+      AsyncError: findType("AsyncError"),
+      ConstantMapView_Symbol_dynamic: findType("ConstantMapView<Symbol0,@>"),
+      Error: findType("Error"),
+      Function: findType("Function"),
+      Future_dynamic: findType("Future<@>"),
+      Invocation: findType("Invocation"),
+      Iterable_dynamic: findType("Iterable<@>"),
+      JSArray_String: findType("JSArray<String>"),
+      JSArray_dynamic: findType("JSArray<@>"),
+      JSNull: findType("JSNull"),
+      JSObject: findType("JSObject"),
+      JavaScriptFunction: findType("JavaScriptFunction"),
+      JavaScriptIndexingBehavior_dynamic: findType("JavaScriptIndexingBehavior<@>"),
+      JsLinkedHashMap_Symbol_dynamic: findType("JsLinkedHashMap<Symbol0,@>"),
+      List_dynamic: findType("List<@>"),
+      Logger: findType("Logger"),
+      Map_dynamic_dynamic: findType("Map<@,@>"),
+      Null: findType("Null"),
+      Object: findType("Object"),
+      PoolResource: findType("PoolResource"),
+      Record: findType("Record"),
+      StackTrace: findType("StackTrace"),
+      String: findType("String"),
+      Symbol: findType("Symbol0"),
+      TrustedGetRuntimeType: findType("TrustedGetRuntimeType"),
+      TypeError: findType("TypeError"),
+      UnknownJavaScriptObject: findType("UnknownJavaScriptObject"),
+      _AsyncCompleter_PoolResource: findType("_AsyncCompleter<PoolResource>"),
+      _AsyncCompleter_void: findType("_AsyncCompleter<~>"),
+      _ElementEventStreamImpl_JSObject: findType("_ElementEventStreamImpl<JSObject>"),
+      _EventStream_JSObject: findType("_EventStream<JSObject>"),
+      _Future_PoolResource: findType("_Future<PoolResource>"),
+      _Future_dynamic: findType("_Future<@>"),
+      _Future_int: findType("_Future<int>"),
+      _Future_void: findType("_Future<~>"),
+      _IdentityHashMap_of_nullable_Object_and_nullable_Object: findType("_IdentityHashMap<Object?,Object?>"),
+      _StreamControllerAddStreamState_nullable_Object: findType("_StreamControllerAddStreamState<Object?>"),
+      _SyncCompleter_PoolResource: findType("_SyncCompleter<PoolResource>"),
+      bool: findType("bool"),
+      bool_Function_Object: findType("bool(Object)"),
+      double: findType("double"),
+      dynamic: findType("@"),
+      dynamic_Function: findType("@()"),
+      dynamic_Function_Object: findType("@(Object)"),
+      dynamic_Function_Object_StackTrace: findType("@(Object,StackTrace)"),
+      int: findType("int"),
+      legacy_Never: findType("0&*"),
+      legacy_Object: findType("Object*"),
+      nullable_Future_Null: findType("Future<Null>?"),
+      nullable_JSObject: findType("JSObject?"),
+      nullable_List_dynamic: findType("List<@>?"),
+      nullable_Object: findType("Object?"),
+      nullable_StackTrace: findType("StackTrace?"),
+      nullable__DelayedEvent_dynamic: findType("_DelayedEvent<@>?"),
+      nullable__FutureListener_dynamic_dynamic: findType("_FutureListener<@,@>?"),
+      nullable_void_Function: findType("~()?"),
+      nullable_void_Function_JSObject: findType("~(JSObject)?"),
+      num: findType("num"),
+      void: findType("~"),
+      void_Function: findType("~()"),
+      void_Function_Object: findType("~(Object)"),
+      void_Function_Object_StackTrace: findType("~(Object,StackTrace)"),
+      void_Function_String_dynamic: findType("~(String,@)")
+    };
+  })();
+  (function constants() {
+    var makeConstList = hunkHelpers.makeConstList;
+    B.Interceptor_methods = J.Interceptor.prototype;
+    B.JSArray_methods = J.JSArray.prototype;
+    B.JSInt_methods = J.JSInt.prototype;
+    B.JSNumber_methods = J.JSNumber.prototype;
+    B.JSString_methods = J.JSString.prototype;
+    B.JavaScriptFunction_methods = J.JavaScriptFunction.prototype;
+    B.JavaScriptObject_methods = J.JavaScriptObject.prototype;
+    B.PlainJavaScriptObject_methods = J.PlainJavaScriptObject.prototype;
+    B.UnknownJavaScriptObject_methods = J.UnknownJavaScriptObject.prototype;
+    B.C_JS_CONST = function getTagFallback(o) {
+  var s = Object.prototype.toString.call(o);
+  return s.substring(8, s.length - 1);
+};
+    B.C_JS_CONST0 = function() {
+  var toStringFunction = Object.prototype.toString;
+  function getTag(o) {
+    var s = toStringFunction.call(o);
+    return s.substring(8, s.length - 1);
+  }
+  function getUnknownTag(object, tag) {
+    if (/^HTML[A-Z].*Element$/.test(tag)) {
+      var name = toStringFunction.call(object);
+      if (name == "[object Object]") return null;
+      return "HTMLElement";
+    }
+  }
+  function getUnknownTagGenericBrowser(object, tag) {
+    if (object instanceof HTMLElement) return "HTMLElement";
+    return getUnknownTag(object, tag);
+  }
+  function prototypeForTag(tag) {
+    if (typeof window == "undefined") return null;
+    if (typeof window[tag] == "undefined") return null;
+    var constructor = window[tag];
+    if (typeof constructor != "function") return null;
+    return constructor.prototype;
+  }
+  function discriminator(tag) { return null; }
+  var isBrowser = typeof HTMLElement == "function";
+  return {
+    getTag: getTag,
+    getUnknownTag: isBrowser ? getUnknownTagGenericBrowser : getUnknownTag,
+    prototypeForTag: prototypeForTag,
+    discriminator: discriminator };
+};
+    B.C_JS_CONST6 = function(getTagFallback) {
+  return function(hooks) {
+    if (typeof navigator != "object") return hooks;
+    var userAgent = navigator.userAgent;
+    if (typeof userAgent != "string") return hooks;
+    if (userAgent.indexOf("DumpRenderTree") >= 0) return hooks;
+    if (userAgent.indexOf("Chrome") >= 0) {
+      function confirm(p) {
+        return typeof window == "object" && window[p] && window[p].name == p;
+      }
+      if (confirm("Window") && confirm("HTMLElement")) return hooks;
+    }
+    hooks.getTag = getTagFallback;
+  };
+};
+    B.C_JS_CONST1 = function(hooks) {
+  if (typeof dartExperimentalFixupGetTag != "function") return hooks;
+  hooks.getTag = dartExperimentalFixupGetTag(hooks.getTag);
+};
+    B.C_JS_CONST5 = function(hooks) {
+  if (typeof navigator != "object") return hooks;
+  var userAgent = navigator.userAgent;
+  if (typeof userAgent != "string") return hooks;
+  if (userAgent.indexOf("Firefox") == -1) return hooks;
+  var getTag = hooks.getTag;
+  var quickMap = {
+    "BeforeUnloadEvent": "Event",
+    "DataTransfer": "Clipboard",
+    "GeoGeolocation": "Geolocation",
+    "Location": "!Location",
+    "WorkerMessageEvent": "MessageEvent",
+    "XMLDocument": "!Document"};
+  function getTagFirefox(o) {
+    var tag = getTag(o);
+    return quickMap[tag] || tag;
+  }
+  hooks.getTag = getTagFirefox;
+};
+    B.C_JS_CONST4 = function(hooks) {
+  if (typeof navigator != "object") return hooks;
+  var userAgent = navigator.userAgent;
+  if (typeof userAgent != "string") return hooks;
+  if (userAgent.indexOf("Trident/") == -1) return hooks;
+  var getTag = hooks.getTag;
+  var quickMap = {
+    "BeforeUnloadEvent": "Event",
+    "DataTransfer": "Clipboard",
+    "HTMLDDElement": "HTMLElement",
+    "HTMLDTElement": "HTMLElement",
+    "HTMLPhraseElement": "HTMLElement",
+    "Position": "Geoposition"
+  };
+  function getTagIE(o) {
+    var tag = getTag(o);
+    var newTag = quickMap[tag];
+    if (newTag) return newTag;
+    if (tag == "Object") {
+      if (window.DataView && (o instanceof window.DataView)) return "DataView";
+    }
+    return tag;
+  }
+  function prototypeForTagIE(tag) {
+    var constructor = window[tag];
+    if (constructor == null) return null;
+    return constructor.prototype;
+  }
+  hooks.getTag = getTagIE;
+  hooks.prototypeForTag = prototypeForTagIE;
+};
+    B.C_JS_CONST2 = function(hooks) {
+  var getTag = hooks.getTag;
+  var prototypeForTag = hooks.prototypeForTag;
+  function getTagFixed(o) {
+    var tag = getTag(o);
+    if (tag == "Document") {
+      if (!!o.xmlVersion) return "!Document";
+      return "!HTMLDocument";
+    }
+    return tag;
+  }
+  function prototypeForTagFixed(tag) {
+    if (tag == "Document") return null;
+    return prototypeForTag(tag);
+  }
+  hooks.getTag = getTagFixed;
+  hooks.prototypeForTag = prototypeForTagFixed;
+};
+    B.C_JS_CONST3 = function(hooks) { return hooks; }
+;
+    B.C_JsonCodec = new A.JsonCodec();
+    B.C_OutOfMemoryError = new A.OutOfMemoryError();
+    B.C__DelayedDone = new A._DelayedDone();
+    B.C__JSRandom = new A._JSRandom();
+    B.C__Required = new A._Required();
+    B.C__RootZone = new A._RootZone();
+    B.Duration_0 = new A.Duration(0);
+    B.Duration_5000000 = new A.Duration(5000000);
+    B.JsonDecoder_null = new A.JsonDecoder(null);
+    B.JsonEncoder_null = new A.JsonEncoder(null);
+    B.Level_INFO_800 = new A.Level("INFO", 800);
+    B.Level_SEVERE_1000 = new A.Level("SEVERE", 1000);
+    B.Level_WARNING_900 = new A.Level("WARNING", 900);
+    B.List_empty = A._setArrayType(makeConstList([]), type$.JSArray_dynamic);
+    B.Object_empty = {};
+    B.Map_empty = new A.ConstantStringMap(B.Object_empty, [], A.findType("ConstantStringMap<Symbol0,@>"));
+    B.Symbol_call = new A.Symbol("call");
+    B.Type_ByteBuffer_RkP = A.typeLiteral("ByteBuffer");
+    B.Type_ByteData_zNC = A.typeLiteral("ByteData");
+    B.Type_Float32List_LB7 = A.typeLiteral("Float32List");
+    B.Type_Float64List_LB7 = A.typeLiteral("Float64List");
+    B.Type_Int16List_uXf = A.typeLiteral("Int16List");
+    B.Type_Int32List_O50 = A.typeLiteral("Int32List");
+    B.Type_Int8List_ekJ = A.typeLiteral("Int8List");
+    B.Type_Uint16List_2bx = A.typeLiteral("Uint16List");
+    B.Type_Uint32List_2bx = A.typeLiteral("Uint32List");
+    B.Type_Uint8ClampedList_Jik = A.typeLiteral("Uint8ClampedList");
+    B.Type_Uint8List_WLA = A.typeLiteral("Uint8List");
+    B._StringStackTrace_3uE = new A._StringStackTrace("");
+  })();
+  (function staticFields() {
+    $._JS_INTEROP_INTERCEPTOR_TAG = null;
+    $.toStringVisiting = A._setArrayType([], A.findType("JSArray<Object>"));
+    $.Primitives__identityHashCodeProperty = null;
+    $.BoundClosure__receiverFieldNameCache = null;
+    $.BoundClosure__interceptorFieldNameCache = null;
+    $.getTagFunction = null;
+    $.alternateTagFunction = null;
+    $.prototypeForTagFunction = null;
+    $.dispatchRecordsForInstanceTags = null;
+    $.interceptorsForUncacheableTags = null;
+    $.initNativeDispatchFlag = null;
+    $._nextCallback = null;
+    $._lastCallback = null;
+    $._lastPriorityCallback = null;
+    $._isInCallbackLoop = false;
+    $.Zone__current = B.C__RootZone;
+    $.LogRecord__nextNumber = 0;
+    $.Logger__loggers = A.LinkedHashMap_LinkedHashMap$_empty(type$.String, type$.Logger);
+  })();
+  (function lazyInitializers() {
+    var _lazyFinal = hunkHelpers.lazyFinal;
+    _lazyFinal($, "DART_CLOSURE_PROPERTY_NAME", "$get$DART_CLOSURE_PROPERTY_NAME", () => A.getIsolateAffinityTag("_$dart_dartClosure"));
+    _lazyFinal($, "nullFuture", "$get$nullFuture", () => B.C__RootZone.run$1$1(new A.nullFuture_closure(), A.findType("Future<Null>")));
+    _lazyFinal($, "TypeErrorDecoder_noSuchMethodPattern", "$get$TypeErrorDecoder_noSuchMethodPattern", () => A.TypeErrorDecoder_extractPattern(A.TypeErrorDecoder_provokeCallErrorOn({
+      toString: function() {
+        return "$receiver$";
+      }
+    })));
+    _lazyFinal($, "TypeErrorDecoder_notClosurePattern", "$get$TypeErrorDecoder_notClosurePattern", () => A.TypeErrorDecoder_extractPattern(A.TypeErrorDecoder_provokeCallErrorOn({$method$: null,
+      toString: function() {
+        return "$receiver$";
+      }
+    })));
+    _lazyFinal($, "TypeErrorDecoder_nullCallPattern", "$get$TypeErrorDecoder_nullCallPattern", () => A.TypeErrorDecoder_extractPattern(A.TypeErrorDecoder_provokeCallErrorOn(null)));
+    _lazyFinal($, "TypeErrorDecoder_nullLiteralCallPattern", "$get$TypeErrorDecoder_nullLiteralCallPattern", () => A.TypeErrorDecoder_extractPattern(function() {
+      var $argumentsExpr$ = "$arguments$";
+      try {
+        null.$method$($argumentsExpr$);
+      } catch (e) {
+        return e.message;
+      }
+    }()));
+    _lazyFinal($, "TypeErrorDecoder_undefinedCallPattern", "$get$TypeErrorDecoder_undefinedCallPattern", () => A.TypeErrorDecoder_extractPattern(A.TypeErrorDecoder_provokeCallErrorOn(void 0)));
+    _lazyFinal($, "TypeErrorDecoder_undefinedLiteralCallPattern", "$get$TypeErrorDecoder_undefinedLiteralCallPattern", () => A.TypeErrorDecoder_extractPattern(function() {
+      var $argumentsExpr$ = "$arguments$";
+      try {
+        (void 0).$method$($argumentsExpr$);
+      } catch (e) {
+        return e.message;
+      }
+    }()));
+    _lazyFinal($, "TypeErrorDecoder_nullPropertyPattern", "$get$TypeErrorDecoder_nullPropertyPattern", () => A.TypeErrorDecoder_extractPattern(A.TypeErrorDecoder_provokePropertyErrorOn(null)));
+    _lazyFinal($, "TypeErrorDecoder_nullLiteralPropertyPattern", "$get$TypeErrorDecoder_nullLiteralPropertyPattern", () => A.TypeErrorDecoder_extractPattern(function() {
+      try {
+        null.$method$;
+      } catch (e) {
+        return e.message;
+      }
+    }()));
+    _lazyFinal($, "TypeErrorDecoder_undefinedPropertyPattern", "$get$TypeErrorDecoder_undefinedPropertyPattern", () => A.TypeErrorDecoder_extractPattern(A.TypeErrorDecoder_provokePropertyErrorOn(void 0)));
+    _lazyFinal($, "TypeErrorDecoder_undefinedLiteralPropertyPattern", "$get$TypeErrorDecoder_undefinedLiteralPropertyPattern", () => A.TypeErrorDecoder_extractPattern(function() {
+      try {
+        (void 0).$method$;
+      } catch (e) {
+        return e.message;
+      }
+    }()));
+    _lazyFinal($, "_AsyncRun__scheduleImmediateClosure", "$get$_AsyncRun__scheduleImmediateClosure", () => A._AsyncRun__initializeScheduleImmediate());
+    _lazyFinal($, "Future__nullFuture", "$get$Future__nullFuture", () => A.findType("_Future<Null>")._as($.$get$nullFuture()));
+    _lazyFinal($, "Logger_root", "$get$Logger_root", () => A.Logger_Logger(""));
+    _lazyFinal($, "_requestPool", "$get$_requestPool", () => {
+      var t4,
+        t1 = A.findType("Completer<PoolResource>"),
+        t2 = A.ListQueue$(t1),
+        t3 = A.ListQueue$(type$.void_Function);
+      t1 = A.ListQueue$(t1);
+      t4 = A.Completer_Completer(type$.dynamic);
+      return new A.Pool(t2, t3, t1, 1000, new A.AsyncMemoizer(t4, A.findType("AsyncMemoizer<@>")));
+    });
+  })();
+  (function nativeSupport() {
+    !function() {
+      var intern = function(s) {
+        var o = {};
+        o[s] = 1;
+        return Object.keys(hunkHelpers.convertToFastObject(o))[0];
+      };
+      init.getIsolateTag = function(name) {
+        return intern("___dart_" + name + init.isolateTag);
+      };
+      var tableProperty = "___dart_isolate_tags_";
+      var usedProperties = Object[tableProperty] || (Object[tableProperty] = Object.create(null));
+      var rootProperty = "_ZxYxX";
+      for (var i = 0;; i++) {
+        var property = intern(rootProperty + "_" + i + "_");
+        if (!(property in usedProperties)) {
+          usedProperties[property] = 1;
+          init.isolateTag = property;
+          break;
+        }
+      }
+      init.dispatchPropertyName = init.getIsolateTag("dispatch_record");
+    }();
+    hunkHelpers.setOrUpdateInterceptorsByTag({ArrayBuffer: A.NativeByteBuffer, ArrayBufferView: A.NativeTypedData, DataView: A.NativeByteData, Float32Array: A.NativeFloat32List, Float64Array: A.NativeFloat64List, Int16Array: A.NativeInt16List, Int32Array: A.NativeInt32List, Int8Array: A.NativeInt8List, Uint16Array: A.NativeUint16List, Uint32Array: A.NativeUint32List, Uint8ClampedArray: A.NativeUint8ClampedList, CanvasPixelArray: A.NativeUint8ClampedList, Uint8Array: A.NativeUint8List});
+    hunkHelpers.setOrUpdateLeafTags({ArrayBuffer: true, ArrayBufferView: false, DataView: true, Float32Array: true, Float64Array: true, Int16Array: true, Int32Array: true, Int8Array: true, Uint16Array: true, Uint32Array: true, Uint8ClampedArray: true, CanvasPixelArray: true, Uint8Array: false});
+    A.NativeTypedArray.$nativeSuperclassTag = "ArrayBufferView";
+    A._NativeTypedArrayOfDouble_NativeTypedArray_ListMixin.$nativeSuperclassTag = "ArrayBufferView";
+    A._NativeTypedArrayOfDouble_NativeTypedArray_ListMixin_FixedLengthListMixin.$nativeSuperclassTag = "ArrayBufferView";
+    A.NativeTypedArrayOfDouble.$nativeSuperclassTag = "ArrayBufferView";
+    A._NativeTypedArrayOfInt_NativeTypedArray_ListMixin.$nativeSuperclassTag = "ArrayBufferView";
+    A._NativeTypedArrayOfInt_NativeTypedArray_ListMixin_FixedLengthListMixin.$nativeSuperclassTag = "ArrayBufferView";
+    A.NativeTypedArrayOfInt.$nativeSuperclassTag = "ArrayBufferView";
+  })();
+  Function.prototype.call$1 = function(a) {
+    return this(a);
+  };
+  Function.prototype.call$0 = function() {
+    return this();
+  };
+  Function.prototype.call$2 = function(a, b) {
+    return this(a, b);
+  };
+  Function.prototype.call$3 = function(a, b, c) {
+    return this(a, b, c);
+  };
+  Function.prototype.call$4 = function(a, b, c, d) {
+    return this(a, b, c, d);
+  };
+  Function.prototype.call$1$1 = function(a) {
+    return this(a);
+  };
+  convertAllToFastObject(holders);
+  convertToFastObject($);
+  (function(callback) {
+    if (typeof document === "undefined") {
+      callback(null);
+      return;
+    }
+    if (typeof document.currentScript != "undefined") {
+      callback(document.currentScript);
+      return;
+    }
+    var scripts = document.scripts;
+    function onLoad(event) {
+      for (var i = 0; i < scripts.length; ++i) {
+        scripts[i].removeEventListener("load", onLoad, false);
+      }
+      callback(event.target);
+    }
+    for (var i = 0; i < scripts.length; ++i) {
+      scripts[i].addEventListener("load", onLoad, false);
+    }
+  })(function(currentScript) {
+    init.currentScript = currentScript;
+    var callMain = A.main;
+    if (typeof dartMainRunner === "function") {
+      dartMainRunner(callMain, []);
+    } else {
+      callMain([]);
+    }
+  });
+})();

diff --git a/pkgs/sse/test/web/index.html b/pkgs/sse/test/web/index.html
new file mode 100644
index 0000000..be26763
--- /dev/null
+++ b/pkgs/sse/test/web/index.html

@@ -0,0 +1,13 @@
+<!DOCTYPE html>
+<html>
+
+<head>
+    <title>SSE Broadcast Channel Test</title>
+</head>
+
+<body>
+    <button type="button">Close Sink</button>
+    <script type="application/javascript" src="index.dart.js"></script>
+</body>
+
+</html>

diff --git a/pkgs/sse/tool/build_js.sh b/pkgs/sse/tool/build_js.sh
new file mode 100755
index 0000000..ef29b70
--- /dev/null
+++ b/pkgs/sse/tool/build_js.sh

@@ -0,0 +1,2 @@
+#!/bin/bash
+dart compile js --no-source-maps test/web/index.dart -o test/web/index.dart.js

diff --git a/pkgs/stack_trace/.gitignore b/pkgs/stack_trace/.gitignore
new file mode 100644
index 0000000..f023015
--- /dev/null
+++ b/pkgs/stack_trace/.gitignore

@@ -0,0 +1,6 @@
+# See https://dart.dev/guides/libraries/private-files
+# Don’t commit the following directories created by pub.
+.dart_tool/
+.packages
+.pub/
+pubspec.lock

diff --git a/pkgs/stack_trace/CHANGELOG.md b/pkgs/stack_trace/CHANGELOG.md
new file mode 100644
index 0000000..e92cf9c
--- /dev/null
+++ b/pkgs/stack_trace/CHANGELOG.md

@@ -0,0 +1,363 @@
+## 1.12.1
+
+* Move to `dart-lang/tools` monorepo.
+
+## 1.12.0
+
+* Added support for parsing Wasm frames of Chrome (V8), Firefox, Safari.
+* Require Dart 3.4 or greater
+
+## 1.11.1
+
+* Make use of `@pragma('vm:awaiter-link')` to make package work better with
+  Dart VM's builtin awaiter stack unwinding. No other changes.
+
+## 1.11.0
+
+* Added the parameter `zoneValues` to `Chain.capture` to be able to use custom
+  zone values with the `runZoned` internal calls.
+* Populate the pubspec `repository` field.
+* Require Dart 2.18 or greater
+
+## 1.10.0
+
+* Stable release for null safety.
+* Fix broken test, `test/chain/vm_test.dart`, which incorrectly handles
+  asynchronous suspension gap markers at the end of stack traces.
+
+## 1.10.0-nullsafety.6
+
+* Fix bug parsing asynchronous suspension gap markers at the end of stack
+  traces, when parsing with `Trace.parse` and `Chain.parse`.
+* Update SDK constraints to `>=2.12.0-0 <3.0.0` based on beta release
+  guidelines.
+
+## 1.10.0-nullsafety.5
+
+* Allow prerelease versions of the 2.12 sdk.
+
+## 1.10.0-nullsafety.4
+
+* Allow the `2.10.0` stable and dev SDKs.
+
+## 1.10.0-nullsafety.3
+
+* Fix bug parsing asynchronous suspension gap markers at the end of stack
+  traces.
+
+## 1.10.0-nullsafety.2
+
+* Forward fix for a change in SDK type promotion behavior.
+
+## 1.10.0-nullsafety.1
+
+* Allow 2.10 stable and 2.11.0 dev SDK versions.
+
+## 1.10.0-nullsafety
+
+* Opt in to null safety.
+
+## 1.9.6 (backpublish)
+
+* Fix bug parsing asynchronous suspension gap markers at the end of stack
+  traces. (Also fixed separately in 1.10.0-nullsafety.3)
+* Fix bug parsing asynchronous suspension gap markers at the end of stack
+  traces, when parsing with `Trace.parse` and `Chain.parse`. (Also fixed
+  separately in 1.10.0-nullsafety.6)
+
+## 1.9.5
+
+* Parse the format for `data:` URIs that the Dart VM has used since `2.2.0`.
+
+## 1.9.4
+
+* Add support for firefox anonymous stack traces.
+* Add support for chrome eval stack traces without a column.
+* Change the argument type to `Chain.capture` from `Function(dynamic, Chain)` to
+  `Function(Object, Chain)`. Existing functions which take `dynamic` are still
+  fine, but new uses can have a safer type.
+
+## 1.9.3
+
+* Set max SDK version to `<3.0.0`.
+
+## 1.9.2
+
+* Fix Dart 2.0 runtime cast failure in test.
+
+## 1.9.1
+
+* Preserve the original chain for a trace to handle cases where an
+  error is rethrown.
+
+## 1.9.0
+
+* Add an `errorZone` parameter to `Chain.capture()` that makes it avoid creating
+  an error zone.
+
+## 1.8.3
+
+* `Chain.forTrace()` now returns a full stack chain for *all* `StackTrace`s
+  within `Chain.capture()`, even those that haven't been processed by
+  `dart:async` yet.
+
+* `Chain.forTrace()` now uses the Dart VM's stack chain information when called
+  synchronously within `Chain.capture()`. This matches the existing behavior
+  outside `Chain.capture()`.
+
+* `Chain.forTrace()` now trims the VM's stack chains for the innermost stack
+  trace within `Chain.capture()` (unless it's called synchronously, as above).
+  This avoids duplicated frames and makes the format of the innermost traces
+  consistent with the other traces in the chain.
+
+## 1.8.2
+
+* Update to use strong-mode clean Zone API.
+
+## 1.8.1
+
+* Use official generic function syntax.
+
+* Updated minimum SDK to 1.23.0.
+
+## 1.8.0
+
+* Add a `Trace.original` field to provide access to the original `StackTrace`s
+  from which the `Trace` was created, and a matching constructor parameter to
+  `new Trace()`.
+
+## 1.7.4
+
+* Always run `onError` callbacks for `Chain.capture()` in the parent zone.
+
+## 1.7.3
+
+* Fix broken links in the README.
+
+## 1.7.2
+
+* `Trace.foldFrames()` and `Chain.foldFrames()` now remove the outermost folded
+  frame. This matches the behavior of `.terse` with core frames.
+
+* Fix bug parsing a friendly frame with spaces in the member name.
+
+* Fix bug parsing a friendly frame where the location is a data url.
+
+## 1.7.1
+
+* Make `Trace.parse()`, `Chain.parse()`, treat the VM's new causal asynchronous
+  stack traces as chains. Outside of a `Chain.capture()` block, `new
+  Chain.current()` will return a stack chain constructed from the asynchronous
+  stack traces.
+
+## 1.7.0
+
+* Add a `Chain.disable()` function that disables stack-chain tracking.
+
+* Fix a bug where `Chain.capture(..., when: false)` would throw if an error was
+  emitted without a stack trace.
+
+## 1.6.8
+
+* Add a note to the documentation of `Chain.terse` and `Trace.terse`.
+
+## 1.6.7
+
+* Fix a bug where `new Frame.caller()` returned the wrong depth of frame on
+  Dartium.
+
+## 1.6.6
+
+* `new Trace.current()` and `new Chain.current()` now skip an extra frame when
+  run in a JS context. This makes their return values match the VM context.
+
+## 1.6.5
+
+* Really fix strong mode warnings.
+
+## 1.6.4
+
+* Fix a syntax error introduced in 1.6.3.
+
+## 1.6.3
+
+* Make `Chain.capture()` generic. Its signature is now `T Chain.capture<T>(T
+  callback(), ...)`.
+
+## 1.6.2
+
+* Fix all strong mode warnings.
+
+## 1.6.1
+
+* Use `StackTrace.current` in Dart SDK 1.14 to get the current stack trace.
+
+## 1.6.0
+
+* Add a `when` parameter to `Chain.capture()`. This allows capturing to be
+  easily enabled and disabled based on whether the application is running in
+  debug/development mode or not.
+
+* Deprecate the `ChainHandler` typedef. This didn't provide any value over
+  directly annotating the function argument, and it made the documentation less
+  clear.
+
+## 1.5.1
+
+* Fix a crash in `Chain.foldFrames()` and `Chain.terse` when one of the chain's
+  traces has no frames.
+
+## 1.5.0
+
+* `new Chain.parse()` now parses all the stack trace formats supported by `new
+  Trace.parse()`. Formats other than that emitted by `Chain.toString()` will
+  produce single-element chains.
+
+* `new Trace.parse()` now parses the output of `Chain.toString()`. It produces
+  the same result as `Chain.parse().toTrace()`.
+
+## 1.4.2
+
+* Improve the display of `data:` URIs in stack traces.
+
+## 1.4.1
+
+* Fix a crashing bug in `UnparsedFrame.toString()`.
+
+## 1.4.0
+
+* `new Trace.parse()` and related constructors will no longer throw an exception
+  if they encounter an unparseable stack frame. Instead, they will generate an
+  `UnparsedFrame`, which exposes no metadata but preserves the frame's original
+  text.
+
+* Properly parse native-code V8 frames.
+
+## 1.3.5
+
+* Properly shorten library names for pathnames of folded frames on Windows.
+
+## 1.3.4
+
+* No longer say that stack chains aren't supported on dart2js now that
+  [sdk#15171][] is fixed. Note that this fix only applies to Dart 1.12.
+
+[sdk#15171]: https://github.com/dart-lang/sdk/issues/15171
+
+## 1.3.3
+
+* When a `null` stack trace is passed to a completer or stream controller in
+  nested `Chain.capture()` blocks, substitute the inner block's chain rather
+  than the outer block's.
+
+* Add support for empty chains and chains of empty traces to `Chain.parse()`.
+
+* Don't crash when parsing stack traces from Dart VM stack overflows.
+
+## 1.3.2
+
+* Don't crash when running `Trace.terse` on empty stack traces.
+
+## 1.3.1
+
+* Support more types of JavaScriptCore stack frames.
+
+## 1.3.0
+
+* Support stack traces generated by JavaScriptCore. They can be explicitly
+  parsed via `new Trace.parseJSCore` and `new Frame.parseJSCore`.
+
+## 1.2.4
+
+* Fix a type annotation in `LazyTrace`.
+
+## 1.2.3
+
+* Fix a crash in `Chain.parse`.
+
+## 1.2.2
+
+* Don't print the first folded frame of terse stack traces. This frame
+  is always just an internal isolate message handler anyway. This
+  improves the readability of stack traces, especially in stack chains.
+
+* Remove the line numbers and specific files in all terse folded frames, not
+  just those from core libraries.
+
+* Make padding consistent across all stack traces for `Chain.toString()`.
+
+## 1.2.1
+
+* Add `terse` to `LazyTrace.foldFrames()`.
+
+* Further improve stack chains when using the VM's async/await implementation.
+
+## 1.2.0
+
+* Add a `terse` argument to `Trace.foldFrames()` and `Chain.foldFrames()`. This
+  allows them to inherit the behavior of `Trace.terse` and `Chain.terse` without
+  having to duplicate the logic.
+
+## 1.1.3
+
+* Produce nicer-looking stack chains when using the VM's async/await
+  implementation.
+
+## 1.1.2
+
+* Support VM frames without line *or* column numbers, which async/await programs
+  occasionally generate.
+
+* Replace `<<anonymous closure>_async_body>` in VM frames' members with the
+  terser `<async>`.
+
+## 1.1.1
+
+* Widen the SDK constraint to include 1.7.0-dev.4.0.
+
+## 1.1.0
+
+* Unify the parsing of Safari and Firefox stack traces. This fixes an error in
+  Firefox trace parsing.
+
+* Deprecate `Trace.parseSafari6_0`, `Trace.parseSafari6_1`,
+  `Frame.parseSafari6_0`, and `Frame.parseSafari6_1`.
+
+* Add `Frame.parseSafari`.
+
+## 1.0.3
+
+* Use `Zone.errorCallback` to attach stack chains to all errors without the need
+  for `Chain.track`, which is now deprecated.
+
+## 1.0.2
+
+* Remove a workaround for [issue 17083][].
+
+[issue 17083]: https://github.com/dart-lang/sdk/issues/17083
+
+## 1.0.1
+
+* Synchronous errors in the [Chain.capture] callback are now handled correctly.
+
+## 1.0.0
+
+* No API changes, just declared stable.
+
+## 0.9.3+2
+
+* Update the dependency on path.
+
+* Improve the formatting of library URIs in stack traces.
+
+## 0.9.3+1
+
+* If an error is thrown in `Chain.capture`'s `onError` handler, that error is
+  handled by the parent zone. This matches the behavior of `runZoned` in
+  `dart:async`.
+
+## 0.9.3
+
+* Add a `Chain.foldFrames` method that parallels `Trace.foldFrames`.
+
+* Record anonymous method frames in IE10 as "<fn>".

diff --git a/pkgs/stack_trace/LICENSE b/pkgs/stack_trace/LICENSE
new file mode 100644
index 0000000..162572a
--- /dev/null
+++ b/pkgs/stack_trace/LICENSE

@@ -0,0 +1,27 @@
+Copyright 2014, the Dart project authors.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+    * Neither the name of Google LLC nor the names of its
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

diff --git a/pkgs/stack_trace/README.md b/pkgs/stack_trace/README.md
new file mode 100644
index 0000000..b10a556
--- /dev/null
+++ b/pkgs/stack_trace/README.md

@@ -0,0 +1,169 @@
+[![Build Status](https://github.com/dart-lang/tools/actions/workflows/stack_trace.yaml/badge.svg)](https://github.com/dart-lang/tools/actions/workflows/stack_trace.yaml)
+[![pub package](https://img.shields.io/pub/v/stack_trace.svg)](https://pub.dev/packages/stack_trace)
+[![package publisher](https://img.shields.io/pub/publisher/stack_trace.svg)](https://pub.dev/packages/stack_trace/publisher)
+
+This library provides the ability to parse, inspect, and manipulate stack traces
+produced by the underlying Dart implementation. It also provides functions to
+produce string representations of stack traces in a more readable format than
+the native [StackTrace] implementation.
+
+`Trace`s can be parsed from native [StackTrace]s using `Trace.from`, or captured
+using `Trace.current`. Native [StackTrace]s can also be directly converted to
+human-readable strings using `Trace.format`.
+
+[StackTrace]: https://api.dart.dev/stable/dart-core/StackTrace-class.html
+
+Here's an example native stack trace from debugging this library:
+
+    #0      Object.noSuchMethod (dart:core-patch:1884:25)
+    #1      Trace.terse.<anonymous closure> (file:///usr/local/google-old/home/goog/dart/dart/pkg/stack_trace/lib/src/trace.dart:47:21)
+    #2      IterableMixinWorkaround.reduce (dart:collection:29:29)
+    #3      List.reduce (dart:core-patch:1247:42)
+    #4      Trace.terse (file:///usr/local/google-old/home/goog/dart/dart/pkg/stack_trace/lib/src/trace.dart:40:35)
+    #5      format (file:///usr/local/google-old/home/goog/dart/dart/pkg/stack_trace/lib/stack_trace.dart:24:28)
+    #6      main.<anonymous closure> (file:///usr/local/google-old/home/goog/dart/dart/test.dart:21:29)
+    #7      _CatchErrorFuture._sendError (dart:async:525:24)
+    #8      _FutureImpl._setErrorWithoutAsyncTrace (dart:async:393:26)
+    #9      _FutureImpl._setError (dart:async:378:31)
+    #10     _ThenFuture._sendValue (dart:async:490:16)
+    #11     _FutureImpl._handleValue.<anonymous closure> (dart:async:349:28)
+    #12     Timer.run.<anonymous closure> (dart:async:2402:21)
+    #13     Timer.Timer.<anonymous closure> (dart:async-patch:15:15)
+
+and its human-readable representation:
+
+    dart:core-patch 1884:25                     Object.noSuchMethod
+    pkg/stack_trace/lib/src/trace.dart 47:21    Trace.terse.<fn>
+    dart:collection 29:29                       IterableMixinWorkaround.reduce
+    dart:core-patch 1247:42                     List.reduce
+    pkg/stack_trace/lib/src/trace.dart 40:35    Trace.terse
+    pkg/stack_trace/lib/stack_trace.dart 24:28  format
+    test.dart 21:29                             main.<fn>
+    dart:async 525:24                           _CatchErrorFuture._sendError
+    dart:async 393:26                           _FutureImpl._setErrorWithoutAsyncTrace
+    dart:async 378:31                           _FutureImpl._setError
+    dart:async 490:16                           _ThenFuture._sendValue
+    dart:async 349:28                           _FutureImpl._handleValue.<fn>
+    dart:async 2402:21                          Timer.run.<fn>
+    dart:async-patch 15:15                      Timer.Timer.<fn>
+
+You can further clean up the stack trace using `Trace.terse`. This folds
+together multiple stack frames from the Dart core libraries, so that only the
+core library method that was directly called from user code is visible. For
+example:
+
+    dart:core                                   Object.noSuchMethod
+    pkg/stack_trace/lib/src/trace.dart 47:21    Trace.terse.<fn>
+    dart:core                                   List.reduce
+    pkg/stack_trace/lib/src/trace.dart 40:35    Trace.terse
+    pkg/stack_trace/lib/stack_trace.dart 24:28  format
+    test.dart 21:29                             main.<fn>
+
+## Stack Chains
+
+This library also provides the ability to capture "stack chains" with the
+`Chain` class. When writing asynchronous code, a single stack trace isn't very
+useful, since the call stack is unwound every time something async happens. A
+stack chain tracks stack traces through asynchronous calls, so that you can see
+the full path from `main` down to the error.
+
+To use stack chains, just wrap the code that you want to track in
+`Chain.capture`. This will create a new [Zone][] in which stack traces are
+recorded and woven into chains every time an asynchronous call occurs. Zones are
+sticky, too, so any asynchronous operations started in the `Chain.capture`
+callback will have their chains tracked, as will asynchronous operations they
+start and so on.
+
+Here's an example of some code that doesn't capture its stack chains:
+
+```dart
+import 'dart:async';
+
+void main() {
+  _scheduleAsync();
+}
+
+void _scheduleAsync() {
+  Future.delayed(Duration(seconds: 1)).then((_) => _runAsync());
+}
+
+void _runAsync() {
+  throw 'oh no!';
+}
+```
+
+If we run this, it prints the following:
+
+    Unhandled exception:
+    oh no!
+    #0      _runAsync (file:///Users/kevmoo/github/stack_trace/example/example.dart:12:3)
+    #1      _scheduleAsync.<anonymous closure> (file:///Users/kevmoo/github/stack_trace/example/example.dart:8:52)
+    <asynchronous suspension>
+
+Notice how there's no mention of `main` in that stack trace. All we know is that
+the error was in `runAsync`; we don't know why `runAsync` was called.
+
+Now let's look at the same code with stack chains captured:
+
+```dart
+import 'dart:async';
+
+import 'package:stack_trace/stack_trace.dart';
+
+void main() {
+  Chain.capture(_scheduleAsync);
+}
+
+void _scheduleAsync() {
+  Future.delayed(Duration(seconds: 1)).then((_) => _runAsync());
+}
+
+void _runAsync() {
+  throw 'oh no!';
+}
+```
+
+Now if we run it, it prints this:
+
+    Unhandled exception:
+    oh no!
+    example/example.dart 14:3                                     _runAsync
+    example/example.dart 10:52                                    _scheduleAsync.<fn>
+    package:stack_trace/src/stack_zone_specification.dart 126:26  StackZoneSpecification._registerUnaryCallback.<fn>.<fn>
+    package:stack_trace/src/stack_zone_specification.dart 208:15  StackZoneSpecification._run
+    package:stack_trace/src/stack_zone_specification.dart 126:14  StackZoneSpecification._registerUnaryCallback.<fn>
+    dart:async/zone.dart 1406:47                                  _rootRunUnary
+    dart:async/zone.dart 1307:19                                  _CustomZone.runUnary
+    ===== asynchronous gap ===========================
+    dart:async/zone.dart 1328:19                                  _CustomZone.registerUnaryCallback
+    dart:async/future_impl.dart 315:23                            Future.then
+    example/example.dart 10:40                                    _scheduleAsync
+    package:stack_trace/src/chain.dart 97:24                      Chain.capture.<fn>
+    dart:async/zone.dart 1398:13                                  _rootRun
+    dart:async/zone.dart 1300:19                                  _CustomZone.run
+    dart:async/zone.dart 1803:10                                  _runZoned
+    dart:async/zone.dart 1746:10                                  runZoned
+    package:stack_trace/src/chain.dart 95:12                      Chain.capture
+    example/example.dart 6:9                                      main
+    dart:isolate-patch/isolate_patch.dart 297:19                  _delayEntrypointInvocation.<fn>
+    dart:isolate-patch/isolate_patch.dart 192:12                  _RawReceivePortImpl._handleMessage
+
+That's a lot of text! If you look closely, though, you can see that `main` is
+listed in the first trace in the chain.
+
+Thankfully, you can call `Chain.terse` just like `Trace.terse` to get rid of all
+the frames you don't care about. The terse version of the stack chain above is
+this:
+
+    test.dart 17:3       runAsync
+    test.dart 13:28      scheduleAsync.<fn>
+    ===== asynchronous gap ===========================
+    dart:async           _Future.then
+    test.dart 13:12      scheduleAsync
+    test.dart 7:18       main.<fn>
+    package:stack_trace  Chain.capture
+    test.dart 6:16       main
+
+That's a lot easier to understand!
+
+[Zone]: https://api.dart.dev/stable/dart-async/Zone-class.html

diff --git a/pkgs/stack_trace/analysis_options.yaml b/pkgs/stack_trace/analysis_options.yaml
new file mode 100644
index 0000000..4eb82ce
--- /dev/null
+++ b/pkgs/stack_trace/analysis_options.yaml

@@ -0,0 +1,22 @@
+# https://dart.dev/tools/analysis#the-analysis-options-file
+include: package:dart_flutter_team_lints/analysis_options.yaml
+
+analyzer:
+  language:
+    strict-casts: true
+    strict-raw-types: true
+
+linter:
+  rules:
+    - avoid_private_typedef_functions
+    - avoid_redundant_argument_values
+    - avoid_unused_constructor_parameters
+    - avoid_void_async
+    - cancel_subscriptions
+    - literal_only_boolean_expressions
+    - missing_whitespace_between_adjacent_strings
+    - no_adjacent_strings_in_list
+    - no_runtimeType_toString
+    - prefer_const_declarations
+    - unnecessary_await_in_return
+    - use_string_buffers

diff --git a/pkgs/stack_trace/example/example.dart b/pkgs/stack_trace/example/example.dart
new file mode 100644
index 0000000..d601ca4
--- /dev/null
+++ b/pkgs/stack_trace/example/example.dart

@@ -0,0 +1,15 @@
+import 'dart:async';
+
+import 'package:stack_trace/stack_trace.dart';
+
+void main() {
+  Chain.capture(_scheduleAsync);
+}
+
+void _scheduleAsync() {
+  Future<void>.delayed(const Duration(seconds: 1)).then((_) => _runAsync());
+}
+
+void _runAsync() {
+  throw StateError('oh no!');
+}

diff --git a/pkgs/stack_trace/lib/src/chain.dart b/pkgs/stack_trace/lib/src/chain.dart
new file mode 100644
index 0000000..6a815c6
--- /dev/null
+++ b/pkgs/stack_trace/lib/src/chain.dart

@@ -0,0 +1,264 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+import 'dart:math' as math;
+
+import 'frame.dart';
+import 'lazy_chain.dart';
+import 'stack_zone_specification.dart';
+import 'trace.dart';
+import 'utils.dart';
+
+/// A function that handles errors in the zone wrapped by [Chain.capture].
+@Deprecated('Will be removed in stack_trace 2.0.0.')
+typedef ChainHandler = void Function(dynamic error, Chain chain);
+
+/// An opaque key used to track the current [StackZoneSpecification].
+final _specKey = Object();
+
+/// A chain of stack traces.
+///
+/// A stack chain is a collection of one or more stack traces that collectively
+/// represent the path from `main` through nested function calls to a particular
+/// code location, usually where an error was thrown. Multiple stack traces are
+/// necessary when using asynchronous functions, since the program's stack is
+/// reset before each asynchronous callback is run.
+///
+/// Stack chains can be automatically tracked using [Chain.capture]. This sets
+/// up a new [Zone] in which the current stack chain is tracked and can be
+/// accessed using [Chain.current]. Any errors that would be top-leveled in
+/// the zone can be handled, along with their associated chains, with the
+/// `onError` callback. For example:
+///
+///     Chain.capture(() {
+///       // ...
+///     }, onError: (error, stackChain) {
+///       print("Caught error $error\n"
+///             "$stackChain");
+///     });
+class Chain implements StackTrace {
+  /// The stack traces that make up this chain.
+  ///
+  /// Like the frames in a stack trace, the traces are ordered from most local
+  /// to least local. The first one is the trace where the actual exception was
+  /// raised, the second one is where that callback was scheduled, and so on.
+  final List<Trace> traces;
+
+  /// The [StackZoneSpecification] for the current zone.
+  static StackZoneSpecification? get _currentSpec =>
+      Zone.current[_specKey] as StackZoneSpecification?;
+
+  /// If [when] is `true`, runs [callback] in a [Zone] in which the current
+  /// stack chain is tracked and automatically associated with (most) errors.
+  ///
+  /// If [when] is `false`, this does not track stack chains. Instead, it's
+  /// identical to [runZoned], except that it wraps any errors in
+  /// [Chain.forTrace]—which will only wrap the trace unless there's a different
+  /// [Chain.capture] active. This makes it easy for the caller to only capture
+  /// stack chains in debug mode or during development.
+  ///
+  /// If [onError] is passed, any error in the zone that would otherwise go
+  /// unhandled is passed to it, along with the [Chain] associated with that
+  /// error. Note that if [callback] produces multiple unhandled errors,
+  /// [onError] may be called more than once. If [onError] isn't passed, the
+  /// parent Zone's `unhandledErrorHandler` will be called with the error and
+  /// its chain.
+  ///
+  /// The zone this creates will be an error zone if either [onError] is
+  /// not `null` and [when] is false,
+  /// or if both [when] and [errorZone] are `true`.
+  ///  If [errorZone] is `false`, [onError] must be `null`.
+  ///
+  /// If [callback] returns a value, it will be returned by [capture] as well.
+  ///
+  /// [zoneValues] is added to the [runZoned] calls.
+  static T capture<T>(T Function() callback,
+      {void Function(Object error, Chain)? onError,
+      bool when = true,
+      bool errorZone = true,
+      Map<Object?, Object?>? zoneValues}) {
+    if (!errorZone && onError != null) {
+      throw ArgumentError.value(
+          onError, 'onError', 'must be null if errorZone is false');
+    }
+
+    if (!when) {
+      if (onError == null) return runZoned(callback, zoneValues: zoneValues);
+      return runZonedGuarded(callback, (error, stackTrace) {
+        onError(error, Chain.forTrace(stackTrace));
+      }, zoneValues: zoneValues) as T;
+    }
+
+    var spec = StackZoneSpecification(onError, errorZone: errorZone);
+    return runZoned(() {
+      try {
+        return callback();
+      } on Object catch (error, stackTrace) {
+        // Forward synchronous errors through the async error path to match the
+        // behavior of `runZonedGuarded`.
+        Zone.current.handleUncaughtError(error, stackTrace);
+
+        // If the expected return type of capture() is not nullable, this will
+        // throw a cast exception. But the only other alternative is to throw
+        // some other exception. Casting null to T at least lets existing uses
+        // where T is a nullable type continue to work.
+        return null as T;
+      }
+    }, zoneSpecification: spec.toSpec(), zoneValues: {
+      ...?zoneValues,
+      _specKey: spec,
+      StackZoneSpecification.disableKey: false
+    });
+  }
+
+  /// If [when] is `true` and this is called within a [Chain.capture] zone, runs
+  /// [callback] in a [Zone] in which chain capturing is disabled.
+  ///
+  /// If [callback] returns a value, it will be returned by [disable] as well.
+  static T disable<T>(T Function() callback, {bool when = true}) {
+    var zoneValues =
+        when ? {_specKey: null, StackZoneSpecification.disableKey: true} : null;
+
+    return runZoned(callback, zoneValues: zoneValues);
+  }
+
+  /// Returns [futureOrStream] unmodified.
+  ///
+  /// Prior to Dart 1.7, this was necessary to ensure that stack traces for
+  /// exceptions reported with [Completer.completeError] and
+  /// [StreamController.addError] were tracked correctly.
+  @Deprecated('Chain.track is not necessary in Dart 1.7+.')
+  static dynamic track(Object? futureOrStream) => futureOrStream;
+
+  /// Returns the current stack chain.
+  ///
+  /// By default, the first frame of the first trace will be the line where
+  /// [Chain.current] is called. If [level] is passed, the first trace will
+  /// start that many frames up instead.
+  ///
+  /// If this is called outside of a [capture] zone, it just returns a
+  /// single-trace chain.
+  factory Chain.current([int level = 0]) {
+    if (_currentSpec != null) return _currentSpec!.currentChain(level + 1);
+
+    var chain = Chain.forTrace(StackTrace.current);
+    return LazyChain(() {
+      // JS includes a frame for the call to StackTrace.current, but the VM
+      // doesn't, so we skip an extra frame in a JS context.
+      var first = Trace(chain.traces.first.frames.skip(level + (inJS ? 2 : 1)),
+          original: chain.traces.first.original.toString());
+      return Chain([first, ...chain.traces.skip(1)]);
+    });
+  }
+
+  /// Returns the stack chain associated with [trace].
+  ///
+  /// The first stack trace in the returned chain will always be [trace]
+  /// (converted to a [Trace] if necessary). If there is no chain associated
+  /// with [trace] or if this is called outside of a [capture] zone, this just
+  /// returns a single-trace chain containing [trace].
+  ///
+  /// If [trace] is already a [Chain], it will be returned as-is.
+  factory Chain.forTrace(StackTrace trace) {
+    if (trace is Chain) return trace;
+    if (_currentSpec != null) return _currentSpec!.chainFor(trace);
+    if (trace is Trace) return Chain([trace]);
+    return LazyChain(() => Chain.parse(trace.toString()));
+  }
+
+  /// Parses a string representation of a stack chain.
+  ///
+  /// If [chain] is the output of a call to [Chain.toString], it will be parsed
+  /// as a full stack chain. Otherwise, it will be parsed as in [Trace.parse]
+  /// and returned as a single-trace chain.
+  factory Chain.parse(String chain) {
+    if (chain.isEmpty) return Chain([]);
+    if (chain.contains(vmChainGap)) {
+      return Chain(chain
+          .split(vmChainGap)
+          .where((line) => line.isNotEmpty)
+          .map(Trace.parseVM));
+    }
+    if (!chain.contains(chainGap)) return Chain([Trace.parse(chain)]);
+
+    return Chain(chain.split(chainGap).map(Trace.parseFriendly));
+  }
+
+  /// Returns a new [Chain] comprised of [traces].
+  Chain(Iterable<Trace> traces) : traces = List<Trace>.unmodifiable(traces);
+
+  /// Returns a terser version of this chain.
+  ///
+  /// This calls [Trace.terse] on every trace in [traces], and discards any
+  /// trace that contain only internal frames.
+  ///
+  /// This won't do anything with a raw JavaScript trace, since there's no way
+  /// to determine which frames come from which Dart libraries. However, the
+  /// [`source_map_stack_trace`](https://pub.dev/packages/source_map_stack_trace)
+  /// package can be used to convert JavaScript traces into Dart-style traces.
+  Chain get terse => foldFrames((_) => false, terse: true);
+
+  /// Returns a new [Chain] based on this chain where multiple stack frames
+  /// matching [predicate] are folded together.
+  ///
+  /// This means that whenever there are multiple frames in a row that match
+  /// [predicate], only the last one is kept. In addition, traces that are
+  /// composed entirely of frames matching [predicate] are omitted.
+  ///
+  /// This is useful for limiting the amount of library code that appears in a
+  /// stack trace by only showing user code and code that's called by user code.
+  ///
+  /// If [terse] is true, this will also fold together frames from the core
+  /// library or from this package, and simplify core library frames as in
+  /// [Trace.terse].
+  Chain foldFrames(bool Function(Frame) predicate, {bool terse = false}) {
+    var foldedTraces =
+        traces.map((trace) => trace.foldFrames(predicate, terse: terse));
+    var nonEmptyTraces = foldedTraces.where((trace) {
+      // Ignore traces that contain only folded frames.
+      if (trace.frames.length > 1) return true;
+      if (trace.frames.isEmpty) return false;
+
+      // In terse mode, the trace may have removed an outer folded frame,
+      // leaving a single non-folded frame. We can detect a folded frame because
+      // it has no line information.
+      if (!terse) return false;
+      return trace.frames.single.line != null;
+    });
+
+    // If all the traces contain only internal processing, preserve the last
+    // (top-most) one so that the chain isn't empty.
+    if (nonEmptyTraces.isEmpty && foldedTraces.isNotEmpty) {
+      return Chain([foldedTraces.last]);
+    }
+
+    return Chain(nonEmptyTraces);
+  }
+
+  /// Converts this chain to a [Trace].
+  ///
+  /// The trace version of a chain is just the concatenation of all the traces
+  /// in the chain.
+  Trace toTrace() => Trace(traces.expand((trace) => trace.frames));
+
+  @override
+  String toString() {
+    // Figure out the longest path so we know how much to pad.
+    var longest = traces
+        .map((trace) => trace.frames
+            .map((frame) => frame.location.length)
+            .fold(0, math.max))
+        .fold(0, math.max);
+
+    // Don't call out to [Trace.toString] here because that doesn't ensure that
+    // padding is consistent across all traces.
+    return traces
+        .map((trace) => trace.frames
+            .map((frame) =>
+                '${frame.location.padRight(longest)}  ${frame.member}\n')
+            .join())
+        .join(chainGap);
+  }
+}

diff --git a/pkgs/stack_trace/lib/src/frame.dart b/pkgs/stack_trace/lib/src/frame.dart
new file mode 100644
index 0000000..d4043b7
--- /dev/null
+++ b/pkgs/stack_trace/lib/src/frame.dart

@@ -0,0 +1,458 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:path/path.dart' as path;
+
+import 'trace.dart';
+import 'unparsed_frame.dart';
+
+// #1      Foo._bar (file:///home/nweiz/code/stuff.dart:42:21)
+// #1      Foo._bar (file:///home/nweiz/code/stuff.dart:42)
+// #1      Foo._bar (file:///home/nweiz/code/stuff.dart)
+final _vmFrame = RegExp(r'^#\d+\s+(\S.*) \((.+?)((?::\d+){0,2})\)$');
+
+//     at Object.stringify (native)
+//     at VW.call$0 (https://example.com/stuff.dart.js:560:28)
+//     at VW.call$0 (eval as fn
+//         (https://example.com/stuff.dart.js:560:28), efn:3:28)
+//     at https://example.com/stuff.dart.js:560:28
+final _v8JsFrame =
+    RegExp(r'^\s*at (?:(\S.*?)(?: \[as [^\]]+\])? \((.*)\)|(.*))$');
+
+// https://example.com/stuff.dart.js:560:28
+// https://example.com/stuff.dart.js:560
+//
+// Group 1: URI, required
+// Group 2: line number, required
+// Group 3: column number, optional
+final _v8JsUrlLocation = RegExp(r'^(.*?):(\d+)(?::(\d+))?$|native$');
+
+// With names:
+//
+//     at Error.f (wasm://wasm/0006d966:wasm-function[119]:0xbb13)
+//     at g (wasm://wasm/0006d966:wasm-function[796]:0x143b4)
+//
+// Without names:
+//
+//     at wasm://wasm/0005168a:wasm-function[119]:0xbb13
+//     at wasm://wasm/0005168a:wasm-function[796]:0x143b4
+//
+// Matches named groups:
+//
+// - "member": optional, `Error.f` in the first example, NA in the second.
+// - "uri":  `wasm://wasm/0006d966`.
+// - "index": `119`.
+// - "offset": (hex number) `bb13`.
+//
+// To avoid having multiple groups for the same part of the frame, this regex
+// matches unmatched parentheses after the member name.
+final _v8WasmFrame = RegExp(r'^\s*at (?:(?<member>.+) )?'
+    r'(?:\(?(?:(?<uri>\S+):wasm-function\[(?<index>\d+)\]'
+    r'\:0x(?<offset>[0-9a-fA-F]+))\)?)$');
+
+// eval as function (https://example.com/stuff.dart.js:560:28), efn:3:28
+// eval as function (https://example.com/stuff.dart.js:560:28)
+// eval as function (eval as otherFunction
+//     (https://example.com/stuff.dart.js:560:28))
+final _v8EvalLocation =
+    RegExp(r'^eval at (?:\S.*?) \((.*)\)(?:, .*?:\d+:\d+)?$');
+
+// anonymous/<@https://example.com/stuff.js line 693 > Function:3:40
+// anonymous/<@https://example.com/stuff.js line 693 > eval:3:40
+final _firefoxEvalLocation =
+    RegExp(r'(\S+)@(\S+) line (\d+) >.* (Function|eval):\d+:\d+');
+
+// .VW.call$0@https://example.com/stuff.dart.js:560
+// .VW.call$0("arg")@https://example.com/stuff.dart.js:560
+// .VW.call$0/name<@https://example.com/stuff.dart.js:560
+// .VW.call$0@https://example.com/stuff.dart.js:560:36
+// https://example.com/stuff.dart.js:560
+final _firefoxSafariJSFrame = RegExp(r'^'
+    r'(?:' // Member description. Not present in some Safari frames.
+    r'([^@(/]*)' // The actual name of the member.
+    r'(?:\(.*\))?' // Arguments to the member, sometimes captured by Firefox.
+    r'((?:/[^/]*)*)' // Extra characters indicating a nested closure.
+    r'(?:\(.*\))?' // Arguments to the closure.
+    r'@'
+    r')?'
+    r'(.*?)' // The frame's URL.
+    r':'
+    r'(\d*)' // The line number. Empty in Safari if it's unknown.
+    r'(?::(\d*))?' // The column number. Not present in older browsers and
+    // empty in Safari if it's unknown.
+    r'$');
+
+// With names:
+//
+// g@http://localhost:8080/test.wasm:wasm-function[796]:0x143b4
+// f@http://localhost:8080/test.wasm:wasm-function[795]:0x143a8
+// main@http://localhost:8080/test.wasm:wasm-function[792]:0x14390
+//
+// Without names:
+//
+// @http://localhost:8080/test.wasm:wasm-function[796]:0x143b4
+// @http://localhost:8080/test.wasm:wasm-function[795]:0x143a8
+// @http://localhost:8080/test.wasm:wasm-function[792]:0x14390
+//
+// JSShell in the command line uses a different format, which this regex also
+// parses.
+//
+// With names:
+//
+// main@/home/user/test.mjs line 29 > WebAssembly.compile:wasm-function[792]:0x14378
+//
+// Without names:
+//
+// @/home/user/test.mjs line 29 > WebAssembly.compile:wasm-function[792]:0x14378
+//
+// Matches named groups:
+//
+// - "member": Function name, may be empty: `g`.
+// - "uri": `http://localhost:8080/test.wasm`.
+// - "index": `796`.
+// - "offset": (in hex) `143b4`.
+final _firefoxWasmFrame =
+    RegExp(r'^(?<member>.*?)@(?:(?<uri>\S+).*?:wasm-function'
+        r'\[(?<index>\d+)\]:0x(?<offset>[0-9a-fA-F]+))$');
+
+// With names:
+//
+// (Note: Lines below are literal text, e.g. <?> is not a placeholder, it's a
+// part of the stack frame.)
+//
+// <?>.wasm-function[g]@[wasm code]
+// <?>.wasm-function[f]@[wasm code]
+// <?>.wasm-function[main]@[wasm code]
+//
+// Without names:
+//
+// <?>.wasm-function[796]@[wasm code]
+// <?>.wasm-function[795]@[wasm code]
+// <?>.wasm-function[792]@[wasm code]
+//
+// Matches named group "member": `g` or `796`.
+final _safariWasmFrame =
+    RegExp(r'^.*?wasm-function\[(?<member>.*)\]@\[wasm code\]$');
+
+// foo/bar.dart 10:11 Foo._bar
+// foo/bar.dart 10:11 (anonymous function).dart.fn
+// https://dart.dev/foo/bar.dart Foo._bar
+// data:... 10:11 Foo._bar
+final _friendlyFrame = RegExp(r'^(\S+)(?: (\d+)(?::(\d+))?)?\s+([^\d].*)$');
+
+/// A regular expression that matches asynchronous member names generated by the
+/// VM.
+final _asyncBody = RegExp(r'<(<anonymous closure>|[^>]+)_async_body>');
+
+final _initialDot = RegExp(r'^\.');
+
+/// A single stack frame. Each frame points to a precise location in Dart code.
+class Frame {
+  /// The URI of the file in which the code is located.
+  ///
+  /// This URI will usually have the scheme `dart`, `file`, `http`, or `https`.
+  final Uri uri;
+
+  /// The line number on which the code location is located.
+  ///
+  /// This can be null, indicating that the line number is unknown or
+  /// unimportant.
+  final int? line;
+
+  /// The column number of the code location.
+  ///
+  /// This can be null, indicating that the column number is unknown or
+  /// unimportant.
+  final int? column;
+
+  /// The name of the member in which the code location occurs.
+  ///
+  /// Anonymous closures are represented as `<fn>` in this member string.
+  final String? member;
+
+  /// Whether this stack frame comes from the Dart core libraries.
+  bool get isCore => uri.scheme == 'dart';
+
+  /// Returns a human-friendly description of the library that this stack frame
+  /// comes from.
+  ///
+  /// This will usually be the string form of [uri], but a relative URI will be
+  /// used if possible. Data URIs will be truncated.
+  String get library {
+    if (uri.scheme == 'data') return 'data:...';
+    return path.prettyUri(uri);
+  }
+
+  /// Returns the name of the package this stack frame comes from, or `null` if
+  /// this stack frame doesn't come from a `package:` URL.
+  String? get package {
+    if (uri.scheme != 'package') return null;
+    return uri.path.split('/').first;
+  }
+
+  /// A human-friendly description of the code location.
+  String get location {
+    if (line == null) return library;
+    if (column == null) return '$library $line';
+    return '$library $line:$column';
+  }
+
+  /// Returns a single frame of the current stack.
+  ///
+  /// By default, this will return the frame above the current method. If
+  /// [level] is `0`, it will return the current method's frame; if [level] is
+  /// higher than `1`, it will return higher frames.
+  factory Frame.caller([int level = 1]) {
+    if (level < 0) {
+      throw ArgumentError('Argument [level] must be greater than or equal '
+          'to 0.');
+    }
+
+    return Trace.current(level + 1).frames.first;
+  }
+
+  /// Parses a string representation of a Dart VM stack frame.
+  factory Frame.parseVM(String frame) => _catchFormatException(frame, () {
+        // The VM sometimes folds multiple stack frames together and replaces
+        // them with "...".
+        if (frame == '...') {
+          return Frame(Uri(), null, null, '...');
+        }
+
+        var match = _vmFrame.firstMatch(frame);
+        if (match == null) return UnparsedFrame(frame);
+
+        // Get the pieces out of the regexp match. Function, URI and line should
+        // always be found. The column is optional.
+        var member = match[1]!
+            .replaceAll(_asyncBody, '<async>')
+            .replaceAll('<anonymous closure>', '<fn>');
+        var uri = match[2]!.startsWith('<data:')
+            ? Uri.dataFromString('')
+            : Uri.parse(match[2]!);
+
+        var lineAndColumn = match[3]!.split(':');
+        var line =
+            lineAndColumn.length > 1 ? int.parse(lineAndColumn[1]) : null;
+        var column =
+            lineAndColumn.length > 2 ? int.parse(lineAndColumn[2]) : null;
+        return Frame(uri, line, column, member);
+      });
+
+  /// Parses a string representation of a Chrome/V8 stack frame.
+  factory Frame.parseV8(String frame) => _catchFormatException(frame, () {
+        // Try to match a Wasm frame first: the Wasm frame regex won't match a
+        // JS frame but the JS frame regex may match a Wasm frame.
+        var match = _v8WasmFrame.firstMatch(frame);
+        if (match != null) {
+          final member = match.namedGroup('member');
+          final uri = _uriOrPathToUri(match.namedGroup('uri')!);
+          final functionIndex = match.namedGroup('index')!;
+          final functionOffset =
+              int.parse(match.namedGroup('offset')!, radix: 16);
+          return Frame(uri, 1, functionOffset + 1, member ?? functionIndex);
+        }
+
+        match = _v8JsFrame.firstMatch(frame);
+        if (match != null) {
+          // v8 location strings can be arbitrarily-nested, since it adds a
+          // layer of nesting for each eval performed on that line.
+          Frame parseJsLocation(String location, String member) {
+            var evalMatch = _v8EvalLocation.firstMatch(location);
+            while (evalMatch != null) {
+              location = evalMatch[1]!;
+              evalMatch = _v8EvalLocation.firstMatch(location);
+            }
+
+            if (location == 'native') {
+              return Frame(Uri.parse('native'), null, null, member);
+            }
+
+            var urlMatch = _v8JsUrlLocation.firstMatch(location);
+            if (urlMatch == null) return UnparsedFrame(frame);
+
+            final uri = _uriOrPathToUri(urlMatch[1]!);
+            final line = int.parse(urlMatch[2]!);
+            final columnMatch = urlMatch[3];
+            final column = columnMatch != null ? int.parse(columnMatch) : null;
+            return Frame(uri, line, column, member);
+          }
+
+          // V8 stack frames can be in two forms.
+          if (match[2] != null) {
+            // The first form looks like " at FUNCTION (LOCATION)". V8 proper
+            // lists anonymous functions within eval as "<anonymous>", while
+            // IE10 lists them as "Anonymous function".
+            return parseJsLocation(
+                match[2]!,
+                match[1]!
+                    .replaceAll('<anonymous>', '<fn>')
+                    .replaceAll('Anonymous function', '<fn>')
+                    .replaceAll('(anonymous function)', '<fn>'));
+          } else {
+            // The second form looks like " at LOCATION", and is used for
+            // anonymous functions.
+            return parseJsLocation(match[3]!, '<fn>');
+          }
+        }
+
+        return UnparsedFrame(frame);
+      });
+
+  /// Parses a string representation of a JavaScriptCore stack trace.
+  factory Frame.parseJSCore(String frame) => Frame.parseV8(frame);
+
+  /// Parses a string representation of an IE stack frame.
+  ///
+  /// IE10+ frames look just like V8 frames. Prior to IE10, stack traces can't
+  /// be retrieved.
+  factory Frame.parseIE(String frame) => Frame.parseV8(frame);
+
+  /// Parses a Firefox 'eval' or 'function' stack frame.
+  ///
+  /// For example:
+  ///
+  /// ```
+  /// anonymous/<@https://example.com/stuff.js line 693 > Function:3:40
+  /// anonymous/<@https://example.com/stuff.js line 693 > eval:3:40
+  /// ```
+  factory Frame._parseFirefoxEval(String frame) =>
+      _catchFormatException(frame, () {
+        final match = _firefoxEvalLocation.firstMatch(frame);
+        if (match == null) return UnparsedFrame(frame);
+        var member = match[1]!.replaceAll('/<', '');
+        final uri = _uriOrPathToUri(match[2]!);
+        final line = int.parse(match[3]!);
+        if (member.isEmpty || member == 'anonymous') {
+          member = '<fn>';
+        }
+        return Frame(uri, line, null, member);
+      });
+
+  /// Parses a string representation of a Firefox or Safari stack frame.
+  factory Frame.parseFirefox(String frame) => _catchFormatException(frame, () {
+        var match = _firefoxSafariJSFrame.firstMatch(frame);
+        if (match != null) {
+          if (match[3]!.contains(' line ')) {
+            return Frame._parseFirefoxEval(frame);
+          }
+
+          // Normally this is a URI, but in a jsshell trace it can be a path.
+          var uri = _uriOrPathToUri(match[3]!);
+
+          var member = match[1];
+          if (member != null) {
+            member +=
+                List.filled('/'.allMatches(match[2]!).length, '.<fn>').join();
+            if (member == '') member = '<fn>';
+
+            // Some Firefox members have initial dots. We remove them for
+            // consistency with other platforms.
+            member = member.replaceFirst(_initialDot, '');
+          } else {
+            member = '<fn>';
+          }
+
+          var line = match[4] == '' ? null : int.parse(match[4]!);
+          var column =
+              match[5] == null || match[5] == '' ? null : int.parse(match[5]!);
+          return Frame(uri, line, column, member);
+        }
+
+        match = _firefoxWasmFrame.firstMatch(frame);
+        if (match != null) {
+          final member = match.namedGroup('member')!;
+          final uri = _uriOrPathToUri(match.namedGroup('uri')!);
+          final functionIndex = match.namedGroup('index')!;
+          final functionOffset =
+              int.parse(match.namedGroup('offset')!, radix: 16);
+          return Frame(uri, 1, functionOffset + 1,
+              member.isNotEmpty ? member : functionIndex);
+        }
+
+        match = _safariWasmFrame.firstMatch(frame);
+        if (match != null) {
+          final member = match.namedGroup('member')!;
+          return Frame(Uri(path: 'wasm code'), null, null, member);
+        }
+
+        return UnparsedFrame(frame);
+      });
+
+  /// Parses a string representation of a Safari 6.0 stack frame.
+  @Deprecated('Use Frame.parseSafari instead.')
+  factory Frame.parseSafari6_0(String frame) => Frame.parseFirefox(frame);
+
+  /// Parses a string representation of a Safari 6.1+ stack frame.
+  @Deprecated('Use Frame.parseSafari instead.')
+  factory Frame.parseSafari6_1(String frame) => Frame.parseFirefox(frame);
+
+  /// Parses a string representation of a Safari stack frame.
+  factory Frame.parseSafari(String frame) => Frame.parseFirefox(frame);
+
+  /// Parses this package's string representation of a stack frame.
+  factory Frame.parseFriendly(String frame) => _catchFormatException(frame, () {
+        var match = _friendlyFrame.firstMatch(frame);
+        if (match == null) {
+          throw FormatException(
+              "Couldn't parse package:stack_trace stack trace line '$frame'.");
+        }
+        // Fake truncated data urls generated by the friendly stack trace format
+        // cause Uri.parse to throw an exception so we have to special case
+        // them.
+        var uri = match[1] == 'data:...'
+            ? Uri.dataFromString('')
+            : Uri.parse(match[1]!);
+        // If there's no scheme, this is a relative URI. We should interpret it
+        // as relative to the current working directory.
+        if (uri.scheme == '') {
+          uri = path.toUri(path.absolute(path.fromUri(uri)));
+        }
+
+        var line = match[2] == null ? null : int.parse(match[2]!);
+        var column = match[3] == null ? null : int.parse(match[3]!);
+        return Frame(uri, line, column, match[4]);
+      });
+
+  /// A regular expression matching an absolute URI.
+  static final _uriRegExp = RegExp(r'^[a-zA-Z][-+.a-zA-Z\d]*://');
+
+  /// A regular expression matching a Windows path.
+  static final _windowsRegExp = RegExp(r'^([a-zA-Z]:[\\/]|\\\\)');
+
+  /// Converts [uriOrPath], which can be a URI, a Windows path, or a Posix path,
+  /// to a URI (absolute if possible).
+  static Uri _uriOrPathToUri(String uriOrPath) {
+    if (uriOrPath.contains(_uriRegExp)) {
+      return Uri.parse(uriOrPath);
+    } else if (uriOrPath.contains(_windowsRegExp)) {
+      return Uri.file(uriOrPath, windows: true);
+    } else if (uriOrPath.startsWith('/')) {
+      return Uri.file(uriOrPath, windows: false);
+    }
+
+    // As far as I've seen, Firefox and V8 both always report absolute paths in
+    // their stack frames. However, if we do get a relative path, we should
+    // handle it gracefully.
+    if (uriOrPath.contains('\\')) return path.windows.toUri(uriOrPath);
+    return Uri.parse(uriOrPath);
+  }
+
+  /// Runs [body] and returns its result.
+  ///
+  /// If [body] throws a [FormatException], returns an [UnparsedFrame] with
+  /// [text] instead.
+  static Frame _catchFormatException(String text, Frame Function() body) {
+    try {
+      return body();
+    } on FormatException catch (_) {
+      return UnparsedFrame(text);
+    }
+  }
+
+  Frame(this.uri, this.line, this.column, this.member);
+
+  @override
+  String toString() => '$location in $member';
+}

diff --git a/pkgs/stack_trace/lib/src/lazy_chain.dart b/pkgs/stack_trace/lib/src/lazy_chain.dart
new file mode 100644
index 0000000..063ed59
--- /dev/null
+++ b/pkgs/stack_trace/lib/src/lazy_chain.dart

@@ -0,0 +1,33 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'chain.dart';
+import 'frame.dart';
+import 'lazy_trace.dart';
+import 'trace.dart';
+
+/// A thunk for lazily constructing a [Chain].
+typedef ChainThunk = Chain Function();
+
+/// A wrapper around a [ChainThunk]. This works around issue 9579 by avoiding
+/// the conversion of native [StackTrace]s to strings until it's absolutely
+/// necessary.
+class LazyChain implements Chain {
+  final ChainThunk _thunk;
+  late final Chain _chain = _thunk();
+
+  LazyChain(this._thunk);
+
+  @override
+  List<Trace> get traces => _chain.traces;
+  @override
+  Chain get terse => _chain.terse;
+  @override
+  Chain foldFrames(bool Function(Frame) predicate, {bool terse = false}) =>
+      LazyChain(() => _chain.foldFrames(predicate, terse: terse));
+  @override
+  Trace toTrace() => LazyTrace(_chain.toTrace);
+  @override
+  String toString() => _chain.toString();
+}

diff --git a/pkgs/stack_trace/lib/src/lazy_trace.dart b/pkgs/stack_trace/lib/src/lazy_trace.dart
new file mode 100644
index 0000000..3ecaa2d
--- /dev/null
+++ b/pkgs/stack_trace/lib/src/lazy_trace.dart

@@ -0,0 +1,33 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'frame.dart';
+import 'trace.dart';
+
+/// A thunk for lazily constructing a [Trace].
+typedef TraceThunk = Trace Function();
+
+/// A wrapper around a [TraceThunk]. This works around issue 9579 by avoiding
+/// the conversion of native [StackTrace]s to strings until it's absolutely
+/// necessary.
+class LazyTrace implements Trace {
+  final TraceThunk _thunk;
+  late final Trace _trace = _thunk();
+
+  LazyTrace(this._thunk);
+
+  @override
+  List<Frame> get frames => _trace.frames;
+  @override
+  StackTrace get original => _trace.original;
+  @override
+  StackTrace get vmTrace => _trace.vmTrace;
+  @override
+  Trace get terse => LazyTrace(() => _trace.terse);
+  @override
+  Trace foldFrames(bool Function(Frame) predicate, {bool terse = false}) =>
+      LazyTrace(() => _trace.foldFrames(predicate, terse: terse));
+  @override
+  String toString() => _trace.toString();
+}

diff --git a/pkgs/stack_trace/lib/src/stack_zone_specification.dart b/pkgs/stack_trace/lib/src/stack_zone_specification.dart
new file mode 100644
index 0000000..901a5ee
--- /dev/null
+++ b/pkgs/stack_trace/lib/src/stack_zone_specification.dart

@@ -0,0 +1,262 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'chain.dart';
+import 'lazy_chain.dart';
+import 'lazy_trace.dart';
+import 'trace.dart';
+import 'utils.dart';
+
+/// A class encapsulating the zone specification for a [Chain.capture] zone.
+///
+/// Until they're materialized and exposed to the user, stack chains are tracked
+/// as linked lists of [Trace]s using the [_Node] class. These nodes are stored
+/// in three distinct ways:
+///
+/// * When a callback is registered, a node is created and stored as a captured
+///   local variable until the callback is run.
+///
+/// * When a callback is run, its captured node is set as the [_currentNode] so
+///   it can be available to [Chain.current] and to be linked into additional
+///   chains when more callbacks are scheduled.
+///
+/// * When a callback throws an error or a Future or Stream emits an error, the
+///   current node is associated with that error's stack trace using the
+///   [_chains] expando.
+///
+/// Since [ZoneSpecification] can't be extended or even implemented, in order to
+/// get a real [ZoneSpecification] instance it's necessary to call [toSpec].
+class StackZoneSpecification {
+  /// An opaque object used as a zone value to disable chain tracking in a given
+  /// zone.
+  ///
+  /// If `Zone.current[disableKey]` is `true`, no stack chains will be tracked.
+  static final disableKey = Object();
+
+  /// Whether chain-tracking is disabled in the current zone.
+  bool get _disabled => Zone.current[disableKey] == true;
+
+  /// The expando that associates stack chains with [StackTrace]s.
+  ///
+  /// The chains are associated with stack traces rather than errors themselves
+  /// because it's a common practice to throw strings as errors, which can't be
+  /// used with expandos.
+  ///
+  /// The chain associated with a given stack trace doesn't contain a node for
+  /// that stack trace.
+  final _chains = Expando<_Node>('stack chains');
+
+  /// The error handler for the zone.
+  ///
+  /// If this is null, that indicates that any unhandled errors should be passed
+  /// to the parent zone.
+  final void Function(Object error, Chain)? _onError;
+
+  /// The most recent node of the current stack chain.
+  _Node? _currentNode;
+
+  /// Whether this is an error zone.
+  final bool _errorZone;
+
+  StackZoneSpecification(this._onError, {bool errorZone = true})
+      : _errorZone = errorZone;
+
+  /// Converts this specification to a real [ZoneSpecification].
+  ZoneSpecification toSpec() => ZoneSpecification(
+      handleUncaughtError: _errorZone ? _handleUncaughtError : null,
+      registerCallback: _registerCallback,
+      registerUnaryCallback: _registerUnaryCallback,
+      registerBinaryCallback: _registerBinaryCallback,
+      errorCallback: _errorCallback);
+
+  /// Returns the current stack chain.
+  ///
+  /// By default, the first frame of the first trace will be the line where
+  /// [currentChain] is called. If [level] is passed, the first trace will start
+  /// that many frames up instead.
+  Chain currentChain([int level = 0]) => _createNode(level + 1).toChain();
+
+  /// Returns the stack chain associated with [trace], if one exists.
+  ///
+  /// The first stack trace in the returned chain will always be [trace]
+  /// (converted to a [Trace] if necessary). If there is no chain associated
+  /// with [trace], this just returns a single-trace chain containing [trace].
+  Chain chainFor(StackTrace? trace) {
+    if (trace is Chain) return trace;
+    trace ??= StackTrace.current;
+
+    var previous = _chains[trace] ?? _currentNode;
+    if (previous == null) {
+      // If there's no [_currentNode], we're running synchronously beneath
+      // [Chain.capture] and we should fall back to the VM's stack chaining. We
+      // can't use [Chain.from] here because it'll just call [chainFor] again.
+      if (trace is Trace) return Chain([trace]);
+      return LazyChain(() => Chain.parse(trace!.toString()));
+    } else {
+      if (trace is! Trace) {
+        var original = trace;
+        trace = LazyTrace(() => Trace.parse(_trimVMChain(original)));
+      }
+
+      return _Node(trace, previous).toChain();
+    }
+  }
+
+  /// Tracks the current stack chain so it can be set to [_currentNode] when
+  /// [f] is run.
+  ZoneCallback<R> _registerCallback<R>(
+      Zone self, ZoneDelegate parent, Zone zone, R Function() f) {
+    if (_disabled) return parent.registerCallback(zone, f);
+    var node = _createNode(1);
+    return parent.registerCallback(zone, () => _run(f, node));
+  }
+
+  /// Tracks the current stack chain so it can be set to [_currentNode] when
+  /// [f] is run.
+  ZoneUnaryCallback<R, T> _registerUnaryCallback<R, T>(
+      Zone self,
+      ZoneDelegate parent,
+      Zone zone,
+      @pragma('vm:awaiter-link') R Function(T) f) {
+    if (_disabled) return parent.registerUnaryCallback(zone, f);
+    var node = _createNode(1);
+    return parent.registerUnaryCallback(
+        zone, (arg) => _run(() => f(arg), node));
+  }
+
+  /// Tracks the current stack chain so it can be set to [_currentNode] when
+  /// [f] is run.
+  ZoneBinaryCallback<R, T1, T2> _registerBinaryCallback<R, T1, T2>(
+      Zone self, ZoneDelegate parent, Zone zone, R Function(T1, T2) f) {
+    if (_disabled) return parent.registerBinaryCallback(zone, f);
+
+    var node = _createNode(1);
+    return parent.registerBinaryCallback(
+        zone, (arg1, arg2) => _run(() => f(arg1, arg2), node));
+  }
+
+  /// Looks up the chain associated with [stackTrace] and passes it either to
+  /// [_onError] or [parent]'s error handler.
+  void _handleUncaughtError(Zone self, ZoneDelegate parent, Zone zone,
+      Object error, StackTrace stackTrace) {
+    if (_disabled) {
+      parent.handleUncaughtError(zone, error, stackTrace);
+      return;
+    }
+
+    var stackChain = chainFor(stackTrace);
+    if (_onError == null) {
+      parent.handleUncaughtError(zone, error, stackChain);
+      return;
+    }
+
+    // TODO(nweiz): Currently this copies a lot of logic from [runZoned]. Just
+    // allow [runBinary] to throw instead once issue 18134 is fixed.
+    try {
+      // TODO(rnystrom): Is the null-assertion correct here? It is nullable in
+      // Zone. Should we check for that here?
+      self.parent!.runBinary(_onError, error, stackChain);
+    } on Object catch (newError, newStackTrace) {
+      if (identical(newError, error)) {
+        parent.handleUncaughtError(zone, error, stackChain);
+      } else {
+        parent.handleUncaughtError(zone, newError, newStackTrace);
+      }
+    }
+  }
+
+  /// Attaches the current stack chain to [stackTrace], replacing it if
+  /// necessary.
+  AsyncError? _errorCallback(Zone self, ZoneDelegate parent, Zone zone,
+      Object error, StackTrace? stackTrace) {
+    if (_disabled) return parent.errorCallback(zone, error, stackTrace);
+
+    // Go up two levels to get through [_CustomZone.errorCallback].
+    if (stackTrace == null) {
+      stackTrace = _createNode(2).toChain();
+    } else {
+      if (_chains[stackTrace] == null) _chains[stackTrace] = _createNode(2);
+    }
+
+    var asyncError = parent.errorCallback(zone, error, stackTrace);
+    return asyncError ?? AsyncError(error, stackTrace);
+  }
+
+  /// Creates a [_Node] with the current stack trace and linked to
+  /// [_currentNode].
+  ///
+  /// By default, the first frame of the first trace will be the line where
+  /// [_createNode] is called. If [level] is passed, the first trace will start
+  /// that many frames up instead.
+  _Node _createNode([int level = 0]) =>
+      _Node(_currentTrace(level + 1), _currentNode);
+
+  // TODO(nweiz): use a more robust way of detecting and tracking errors when
+  // issue 15105 is fixed.
+  /// Runs [f] with [_currentNode] set to [node].
+  ///
+  /// If [f] throws an error, this associates [node] with that error's stack
+  /// trace.
+  T _run<T>(T Function() f, _Node node) {
+    var previousNode = _currentNode;
+    _currentNode = node;
+    try {
+      return f();
+    } catch (e, stackTrace) {
+      // We can see the same stack trace multiple times if it's rethrown through
+      // guarded callbacks.  The innermost chain will have the most
+      // information so it should take precedence.
+      _chains[stackTrace] ??= node;
+      rethrow;
+    } finally {
+      _currentNode = previousNode;
+    }
+  }
+
+  /// Like [Trace.current], but if the current stack trace has VM chaining
+  /// enabled, this only returns the innermost sub-trace.
+  Trace _currentTrace([int? level]) {
+    var stackTrace = StackTrace.current;
+    return LazyTrace(() {
+      var text = _trimVMChain(stackTrace);
+      var trace = Trace.parse(text);
+      // JS includes a frame for the call to StackTrace.current, but the VM
+      // doesn't, so we skip an extra frame in a JS context.
+      return Trace(trace.frames.skip((level ?? 0) + (inJS ? 2 : 1)),
+          original: text);
+    });
+  }
+
+  /// Removes the VM's stack chains from the native [trace], since we're
+  /// generating our own and we don't want duplicate frames.
+  String _trimVMChain(StackTrace trace) {
+    var text = trace.toString();
+    var index = text.indexOf(vmChainGap);
+    return index == -1 ? text : text.substring(0, index);
+  }
+}
+
+/// A linked list node representing a single entry in a stack chain.
+class _Node {
+  /// The stack trace for this link of the chain.
+  final Trace trace;
+
+  /// The previous node in the chain.
+  final _Node? previous;
+
+  _Node(StackTrace trace, [this.previous]) : trace = Trace.from(trace);
+
+  /// Converts this to a [Chain].
+  Chain toChain() {
+    var nodes = <Trace>[];
+    _Node? node = this;
+    while (node != null) {
+      nodes.add(node.trace);
+      node = node.previous;
+    }
+    return Chain(nodes);
+  }
+}

diff --git a/pkgs/stack_trace/lib/src/trace.dart b/pkgs/stack_trace/lib/src/trace.dart
new file mode 100644
index 0000000..b8c62f5
--- /dev/null
+++ b/pkgs/stack_trace/lib/src/trace.dart

@@ -0,0 +1,341 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:math' as math;
+
+import 'chain.dart';
+import 'frame.dart';
+import 'lazy_trace.dart';
+import 'unparsed_frame.dart';
+import 'utils.dart';
+import 'vm_trace.dart';
+
+final _terseRegExp = RegExp(r'(-patch)?([/\\].*)?$');
+
+/// A RegExp to match V8's stack traces.
+///
+/// V8's traces start with a line that's either just "Error" or else is a
+/// description of the exception that occurred. That description can be multiple
+/// lines, so we just look for any line other than the first that begins with
+/// three or four spaces and "at".
+final _v8Trace = RegExp(r'\n    ?at ');
+
+/// A RegExp to match indidual lines of V8's stack traces.
+///
+/// This is intended to filter out the leading exception details of the trace
+/// though it is possible for the message to match this as well.
+final _v8TraceLine = RegExp(r'    ?at ');
+
+/// A RegExp to match Firefox's eval and Function stack traces.
+///
+/// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/stack
+///
+/// These stack traces look like:
+///
+/// ````
+/// anonymous/<@https://example.com/stuff.js line 693 > Function:3:40
+/// anonymous/<@https://example.com/stuff.js line 693 > eval:3:40
+/// ````
+final _firefoxEvalTrace = RegExp(r'@\S+ line \d+ >.* (Function|eval):\d+:\d+');
+
+/// A RegExp to match Firefox and Safari's stack traces.
+///
+/// Firefox and Safari have very similar stack trace formats, so we use the same
+/// logic for parsing them.
+///
+/// Firefox's trace frames start with the name of the function in which the
+/// error occurred, possibly including its parameters inside `()`. For example,
+/// `.VW.call$0("arg")@https://example.com/stuff.dart.js:560`.
+///
+/// Safari traces occasionally don't include the initial method name followed by
+/// "@", and they always have both the line and column number (or just a
+/// trailing colon if no column number is available). They can also contain
+/// empty lines or lines consisting only of `[native code]`.
+final _firefoxSafariTrace = RegExp(
+    r'^'
+    r'(' // Member description. Not present in some Safari frames.
+    r'([.0-9A-Za-z_$/<]|\(.*\))*' // Member name and arguments.
+    r'@'
+    r')?'
+    r'[^\s]*' // Frame URL.
+    r':\d*' // Line or column number. Some older frames only have a line number.
+    r'$',
+    multiLine: true);
+
+/// A RegExp to match this package's stack traces.
+final _friendlyTrace =
+    RegExp(r'^[^\s<][^\s]*( \d+(:\d+)?)?[ \t]+[^\s]+$', multiLine: true);
+
+/// A stack trace, comprised of a list of stack frames.
+class Trace implements StackTrace {
+  /// The stack frames that comprise this stack trace.
+  final List<Frame> frames;
+
+  /// The original stack trace from which this trace was parsed.
+  final StackTrace original;
+
+  /// Returns a human-readable representation of [stackTrace]. If [terse] is
+  /// set, this folds together multiple stack frames from the Dart core
+  /// libraries, so that only the core library method directly called from user
+  /// code is visible (see [Trace.terse]).
+  static String format(StackTrace stackTrace, {bool terse = true}) {
+    var trace = Trace.from(stackTrace);
+    if (terse) trace = trace.terse;
+    return trace.toString();
+  }
+
+  /// Returns the current stack trace.
+  ///
+  /// By default, the first frame of this trace will be the line where
+  /// [Trace.current] is called. If [level] is passed, the trace will start that
+  /// many frames up instead.
+  factory Trace.current([int level = 0]) {
+    if (level < 0) {
+      throw ArgumentError('Argument [level] must be greater than or equal '
+          'to 0.');
+    }
+
+    var trace = Trace.from(StackTrace.current);
+    return LazyTrace(
+      () =>
+          // JS includes a frame for the call to StackTrace.current, but the VM
+          // doesn't, so we skip an extra frame in a JS context.
+          Trace(trace.frames.skip(level + (inJS ? 2 : 1)),
+              original: trace.original.toString()),
+    );
+  }
+
+  /// Returns a new stack trace containing the same data as [trace].
+  ///
+  /// If [trace] is a native [StackTrace], its data will be parsed out; if it's
+  /// a [Trace], it will be returned as-is.
+  factory Trace.from(StackTrace trace) {
+    if (trace is Trace) return trace;
+    if (trace is Chain) return trace.toTrace();
+    return LazyTrace(() => Trace.parse(trace.toString()));
+  }
+
+  /// Parses a string representation of a stack trace.
+  ///
+  /// [trace] should be formatted in the same way as a Dart VM or browser stack
+  /// trace. If it's formatted as a stack chain, this will return the equivalent
+  /// of [Chain.toTrace].
+  factory Trace.parse(String trace) {
+    try {
+      if (trace.isEmpty) return Trace(<Frame>[]);
+      if (trace.contains(_v8Trace)) return Trace.parseV8(trace);
+      if (trace.contains('\tat ')) return Trace.parseJSCore(trace);
+      if (trace.contains(_firefoxSafariTrace) ||
+          trace.contains(_firefoxEvalTrace)) {
+        return Trace.parseFirefox(trace);
+      }
+      if (trace.contains(chainGap)) return Chain.parse(trace).toTrace();
+      if (trace.contains(_friendlyTrace)) {
+        return Trace.parseFriendly(trace);
+      }
+
+      // Default to parsing the stack trace as a VM trace. This is also hit on
+      // IE and Safari, where the stack trace is just an empty string (issue
+      // 11257).
+      return Trace.parseVM(trace);
+    } on FormatException catch (error) {
+      throw FormatException('${error.message}\nStack trace:\n$trace');
+    }
+  }
+
+  /// Parses a string representation of a Dart VM stack trace.
+  Trace.parseVM(String trace) : this(_parseVM(trace), original: trace);
+
+  static List<Frame> _parseVM(String trace) {
+    // Ignore [vmChainGap]. This matches the behavior of
+    // `Chain.parse().toTrace()`.
+    var lines = trace
+        .trim()
+        .replaceAll(vmChainGap, '')
+        .split('\n')
+        .where((line) => line.isNotEmpty);
+
+    if (lines.isEmpty) {
+      return [];
+    }
+
+    var frames = lines.take(lines.length - 1).map(Frame.parseVM).toList();
+
+    // TODO(nweiz): Remove this when issue 23614 is fixed.
+    if (!lines.last.endsWith('.da')) {
+      frames.add(Frame.parseVM(lines.last));
+    }
+
+    return frames;
+  }
+
+  /// Parses a string representation of a Chrome/V8 stack trace.
+  Trace.parseV8(String trace)
+      : this(
+            trace
+                .split('\n')
+                .skip(1)
+                // It's possible that an Exception's description contains a line
+                // that looks like a V8 trace line, which will screw this up.
+                // Unfortunately, that's impossible to detect.
+                .skipWhile((line) => !line.startsWith(_v8TraceLine))
+                .map(Frame.parseV8),
+            original: trace);
+
+  /// Parses a string representation of a JavaScriptCore stack trace.
+  Trace.parseJSCore(String trace)
+      : this(
+            trace
+                .split('\n')
+                .where((line) => line != '\tat ')
+                .map(Frame.parseV8),
+            original: trace);
+
+  /// Parses a string representation of an Internet Explorer stack trace.
+  ///
+  /// IE10+ traces look just like V8 traces. Prior to IE10, stack traces can't
+  /// be retrieved.
+  Trace.parseIE(String trace) : this.parseV8(trace);
+
+  /// Parses a string representation of a Firefox stack trace.
+  Trace.parseFirefox(String trace)
+      : this(
+            trace
+                .trim()
+                .split('\n')
+                .where((line) => line.isNotEmpty && line != '[native code]')
+                .map(Frame.parseFirefox),
+            original: trace);
+
+  /// Parses a string representation of a Safari stack trace.
+  Trace.parseSafari(String trace) : this.parseFirefox(trace);
+
+  /// Parses a string representation of a Safari 6.1+ stack trace.
+  @Deprecated('Use Trace.parseSafari instead.')
+  Trace.parseSafari6_1(String trace) : this.parseSafari(trace);
+
+  /// Parses a string representation of a Safari 6.0 stack trace.
+  @Deprecated('Use Trace.parseSafari instead.')
+  Trace.parseSafari6_0(String trace)
+      : this(
+            trace
+                .trim()
+                .split('\n')
+                .where((line) => line != '[native code]')
+                .map(Frame.parseFirefox),
+            original: trace);
+
+  /// Parses this package's string representation of a stack trace.
+  ///
+  /// This also parses string representations of [Chain]s. They parse to the
+  /// same trace that [Chain.toTrace] would return.
+  Trace.parseFriendly(String trace)
+      : this(
+            trace.isEmpty
+                ? []
+                : trace
+                    .trim()
+                    .split('\n')
+                    // Filter out asynchronous gaps from [Chain]s.
+                    .where((line) => !line.startsWith('====='))
+                    .map(Frame.parseFriendly),
+            original: trace);
+
+  /// Returns a new [Trace] comprised of [frames].
+  Trace(Iterable<Frame> frames, {String? original})
+      : frames = List<Frame>.unmodifiable(frames),
+        original = StackTrace.fromString(original ?? '');
+
+  /// Returns a VM-style [StackTrace] object.
+  ///
+  /// The return value's [toString] method will always return a string
+  /// representation in the Dart VM's stack trace format, regardless of what
+  /// platform is being used.
+  StackTrace get vmTrace => VMTrace(frames);
+
+  /// Returns a terser version of this trace.
+  ///
+  /// This is accomplished by folding together multiple stack frames from the
+  /// core library or from this package, as in [foldFrames]. Remaining core
+  /// library frames have their libraries, "-patch" suffixes, and line numbers
+  /// removed. If the outermost frame of the stack trace is a core library
+  /// frame, it's removed entirely.
+  ///
+  /// This won't do anything with a raw JavaScript trace, since there's no way
+  /// to determine which frames come from which Dart libraries. However, the
+  /// [`source_map_stack_trace`][https://pub.dev/packages/source_map_stack_trace]
+  /// package can be used to convert JavaScript traces into Dart-style traces.
+  ///
+  /// For custom folding, see [foldFrames].
+  Trace get terse => foldFrames((_) => false, terse: true);
+
+  /// Returns a new [Trace] based on `this` where multiple stack frames matching
+  /// [predicate] are folded together.
+  ///
+  /// This means that whenever there are multiple frames in a row that match
+  /// [predicate], only the last one is kept. This is useful for limiting the
+  /// amount of library code that appears in a stack trace by only showing user
+  /// code and code that's called by user code.
+  ///
+  /// If [terse] is true, this will also fold together frames from the core
+  /// library or from this package, simplify core library frames, and
+  /// potentially remove the outermost frame as in [Trace.terse].
+  Trace foldFrames(bool Function(Frame) predicate, {bool terse = false}) {
+    if (terse) {
+      var oldPredicate = predicate;
+      predicate = (frame) {
+        if (oldPredicate(frame)) return true;
+
+        if (frame.isCore) return true;
+        if (frame.package == 'stack_trace') return true;
+
+        // Ignore async stack frames without any line or column information.
+        // These come from the VM's async/await implementation and represent
+        // internal frames. They only ever show up in stack chains and are
+        // always surrounded by other traces that are actually useful, so we can
+        // just get rid of them.
+        // TODO(nweiz): Get rid of this logic some time after issue 22009 is
+        // fixed.
+        if (!frame.member!.contains('<async>')) return false;
+        return frame.line == null;
+      };
+    }
+
+    var newFrames = <Frame>[];
+    for (var frame in frames.reversed) {
+      if (frame is UnparsedFrame || !predicate(frame)) {
+        newFrames.add(frame);
+      } else if (newFrames.isEmpty || !predicate(newFrames.last)) {
+        newFrames.add(Frame(frame.uri, frame.line, frame.column, frame.member));
+      }
+    }
+
+    if (terse) {
+      newFrames = newFrames.map((frame) {
+        if (frame is UnparsedFrame || !predicate(frame)) return frame;
+        var library = frame.library.replaceAll(_terseRegExp, '');
+        return Frame(Uri.parse(library), null, null, frame.member);
+      }).toList();
+
+      if (newFrames.length > 1 && predicate(newFrames.first)) {
+        newFrames.removeAt(0);
+      }
+    }
+
+    return Trace(newFrames.reversed, original: original.toString());
+  }
+
+  @override
+  String toString() {
+    // Figure out the longest path so we know how much to pad.
+    var longest =
+        frames.map((frame) => frame.location.length).fold(0, math.max);
+
+    // Print out the stack trace nicely formatted.
+    return frames.map((frame) {
+      if (frame is UnparsedFrame) return '$frame\n';
+      return '${frame.location.padRight(longest)}  ${frame.member}\n';
+    }).join();
+  }
+}

diff --git a/pkgs/stack_trace/lib/src/unparsed_frame.dart b/pkgs/stack_trace/lib/src/unparsed_frame.dart
new file mode 100644
index 0000000..27e97f6
--- /dev/null
+++ b/pkgs/stack_trace/lib/src/unparsed_frame.dart

@@ -0,0 +1,33 @@
+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'frame.dart';
+
+/// A frame that failed to parse.
+///
+/// The [member] property contains the original frame's contents.
+class UnparsedFrame implements Frame {
+  @override
+  final Uri uri = Uri(path: 'unparsed');
+  @override
+  final int? line = null;
+  @override
+  final int? column = null;
+  @override
+  final bool isCore = false;
+  @override
+  final String library = 'unparsed';
+  @override
+  final String? package = null;
+  @override
+  final String location = 'unparsed';
+
+  @override
+  final String member;
+
+  UnparsedFrame(this.member);
+
+  @override
+  String toString() => member;
+}

diff --git a/pkgs/stack_trace/lib/src/utils.dart b/pkgs/stack_trace/lib/src/utils.dart
new file mode 100644
index 0000000..bd971fe
--- /dev/null
+++ b/pkgs/stack_trace/lib/src/utils.dart

@@ -0,0 +1,15 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// The line used in the string representation of stack chains to represent
+/// the gap between traces.
+const chainGap = '===== asynchronous gap ===========================\n';
+
+/// The line used in the string representation of VM stack chains to represent
+/// the gap between traces.
+final vmChainGap = RegExp(r'^<asynchronous suspension>\n?$', multiLine: true);
+
+// TODO(nweiz): When cross-platform imports work, use them to set this.
+/// Whether we're running in a JS context.
+const bool inJS = 0.0 is int;

diff --git a/pkgs/stack_trace/lib/src/vm_trace.dart b/pkgs/stack_trace/lib/src/vm_trace.dart
new file mode 100644
index 0000000..005b7af
--- /dev/null
+++ b/pkgs/stack_trace/lib/src/vm_trace.dart

@@ -0,0 +1,32 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'frame.dart';
+
+/// An implementation of [StackTrace] that emulates the behavior of the VM's
+/// implementation.
+///
+/// In particular, when [toString] is called, this returns a string in the VM's
+/// stack trace format.
+class VMTrace implements StackTrace {
+  /// The stack frames that comprise this stack trace.
+  final List<Frame> frames;
+
+  VMTrace(this.frames);
+
+  @override
+  String toString() {
+    var i = 1;
+    return frames.map((frame) {
+      var number = '#${i++}'.padRight(8);
+      var member = frame.member!
+          .replaceAllMapped(RegExp(r'[^.]+\.<async>'),
+              (match) => '${match[1]}.<${match[1]}_async_body>')
+          .replaceAll('<fn>', '<anonymous closure>');
+      var line = frame.line ?? 0;
+      var column = frame.column ?? 0;
+      return '$number$member (${frame.uri}:$line:$column)\n';
+    }).join();
+  }
+}

diff --git a/pkgs/stack_trace/lib/stack_trace.dart b/pkgs/stack_trace/lib/stack_trace.dart
new file mode 100644
index 0000000..fad30ce
--- /dev/null
+++ b/pkgs/stack_trace/lib/stack_trace.dart

@@ -0,0 +1,8 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+export 'src/chain.dart';
+export 'src/frame.dart';
+export 'src/trace.dart';
+export 'src/unparsed_frame.dart';

diff --git a/pkgs/stack_trace/pubspec.yaml b/pkgs/stack_trace/pubspec.yaml
new file mode 100644
index 0000000..4f387b1
--- /dev/null
+++ b/pkgs/stack_trace/pubspec.yaml

@@ -0,0 +1,14 @@
+name: stack_trace
+version: 1.12.1
+description: A package for manipulating stack traces and printing them readably.
+repository: https://github.com/dart-lang/tools/tree/main/pkgs/stack_trace
+
+environment:
+  sdk: ^3.4.0
+
+dependencies:
+  path: ^1.8.0
+
+dev_dependencies:
+  dart_flutter_team_lints: ^3.0.0
+  test: ^1.16.6

diff --git a/pkgs/stack_trace/test/chain/chain_test.dart b/pkgs/stack_trace/test/chain/chain_test.dart
new file mode 100644
index 0000000..d5426dd
--- /dev/null
+++ b/pkgs/stack_trace/test/chain/chain_test.dart

@@ -0,0 +1,375 @@
+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:path/path.dart' as p;
+import 'package:stack_trace/stack_trace.dart';
+import 'package:test/test.dart';
+
+import 'utils.dart';
+
+void main() {
+  group('Chain.parse()', () {
+    test('parses a real Chain', () async {
+      // ignore: only_throw_errors
+      final chain = await captureFuture(() => inMicrotask(() => throw 'error'));
+
+      expect(
+        Chain.parse(chain.toString()).toString(),
+        equals(chain.toString()),
+      );
+    });
+
+    test('parses an empty string', () {
+      var chain = Chain.parse('');
+      expect(chain.traces, isEmpty);
+    });
+
+    test('parses a chain containing empty traces', () {
+      var chain =
+          Chain.parse('===== asynchronous gap ===========================\n'
+              '===== asynchronous gap ===========================\n');
+      expect(chain.traces, hasLength(3));
+      expect(chain.traces[0].frames, isEmpty);
+      expect(chain.traces[1].frames, isEmpty);
+      expect(chain.traces[2].frames, isEmpty);
+    });
+
+    test('parses a chain with VM gaps', () {
+      final chain =
+          Chain.parse('#1      MyClass.run (package:my_lib.dart:134:5)\n'
+              '<asynchronous suspension>\n'
+              '#2      main (file:///my_app.dart:9:3)\n'
+              '<asynchronous suspension>\n');
+      expect(chain.traces, hasLength(2));
+      expect(chain.traces[0].frames, hasLength(1));
+      expect(chain.traces[0].frames[0].toString(),
+          equals('package:my_lib.dart 134:5 in MyClass.run'));
+      expect(chain.traces[1].frames, hasLength(1));
+      expect(
+        chain.traces[1].frames[0].toString(),
+        anyOf(
+          equals('/my_app.dart 9:3 in main'), // VM
+          equals('file:///my_app.dart 9:3 in main'), // Browser
+        ),
+      );
+    });
+  });
+
+  group('Chain.capture()', () {
+    test('with onError blocks errors', () {
+      Chain.capture(() {
+        return Future<void>.error('oh no');
+      }, onError: expectAsync2((error, chain) {
+        expect(error, equals('oh no'));
+        expect(chain, isA<Chain>());
+      })).then(expectAsync1((_) {}, count: 0),
+          onError: expectAsync2((_, __) {}, count: 0));
+    });
+
+    test('with no onError blocks errors', () {
+      runZonedGuarded(() {
+        Chain.capture(() => Future<void>.error('oh no')).then(
+            expectAsync1((_) {}, count: 0),
+            onError: expectAsync2((_, __) {}, count: 0));
+      }, expectAsync2((error, chain) {
+        expect(error, equals('oh no'));
+        expect(chain, isA<Chain>());
+      }));
+    });
+
+    test("with errorZone: false doesn't block errors", () {
+      expect(Chain.capture(() => Future<void>.error('oh no'), errorZone: false),
+          throwsA('oh no'));
+    });
+
+    test("doesn't allow onError and errorZone: false", () {
+      expect(() => Chain.capture(() {}, onError: (_, __) {}, errorZone: false),
+          throwsArgumentError);
+    });
+
+    group('with when: false', () {
+      test("with no onError doesn't block errors", () {
+        expect(Chain.capture(() => Future<void>.error('oh no'), when: false),
+            throwsA('oh no'));
+      });
+
+      test('with onError blocks errors', () {
+        Chain.capture(() {
+          return Future<void>.error('oh no');
+        }, onError: expectAsync2((error, chain) {
+          expect(error, equals('oh no'));
+          expect(chain, isA<Chain>());
+        }), when: false);
+      });
+
+      test("doesn't enable chain-tracking", () {
+        return Chain.disable(() {
+          return Chain.capture(() {
+            var completer = Completer<Chain>();
+            inMicrotask(() {
+              completer.complete(Chain.current());
+            });
+
+            return completer.future.then((chain) {
+              expect(chain.traces, hasLength(1));
+            });
+          }, when: false);
+        });
+      });
+    });
+  });
+
+  test('Chain.capture() with custom zoneValues', () {
+    return Chain.capture(() {
+      expect(Zone.current[#enabled], true);
+    }, zoneValues: {#enabled: true});
+  });
+
+  group('Chain.disable()', () {
+    test('disables chain-tracking', () {
+      return Chain.disable(() {
+        var completer = Completer<Chain>();
+        inMicrotask(() => completer.complete(Chain.current()));
+
+        return completer.future.then((chain) {
+          expect(chain.traces, hasLength(1));
+        });
+      });
+    });
+
+    test('Chain.capture() re-enables chain-tracking', () {
+      return Chain.disable(() {
+        return Chain.capture(() {
+          var completer = Completer<Chain>();
+          inMicrotask(() => completer.complete(Chain.current()));
+
+          return completer.future.then((chain) {
+            expect(chain.traces, hasLength(2));
+          });
+        });
+      });
+    });
+
+    test('preserves parent zones of the capture zone', () {
+      // The outer disable call turns off the test package's chain-tracking.
+      return Chain.disable(() {
+        return runZoned(() {
+          return Chain.capture(() {
+            expect(Chain.disable(() => Zone.current[#enabled]), isTrue);
+          });
+        }, zoneValues: {#enabled: true});
+      });
+    });
+
+    test('preserves child zones of the capture zone', () {
+      // The outer disable call turns off the test package's chain-tracking.
+      return Chain.disable(() {
+        return Chain.capture(() {
+          return runZoned(() {
+            expect(Chain.disable(() => Zone.current[#enabled]), isTrue);
+          }, zoneValues: {#enabled: true});
+        });
+      });
+    });
+
+    test("with when: false doesn't disable", () {
+      return Chain.capture(() {
+        return Chain.disable(() {
+          var completer = Completer<Chain>();
+          inMicrotask(() => completer.complete(Chain.current()));
+
+          return completer.future.then((chain) {
+            expect(chain.traces, hasLength(2));
+          });
+        }, when: false);
+      });
+    });
+  });
+
+  test('toString() ensures that all traces are aligned', () {
+    var chain = Chain([
+      Trace.parse('short 10:11  Foo.bar\n'),
+      Trace.parse('loooooooooooong 10:11  Zop.zoop')
+    ]);
+
+    expect(
+        chain.toString(),
+        equals('short 10:11            Foo.bar\n'
+            '===== asynchronous gap ===========================\n'
+            'loooooooooooong 10:11  Zop.zoop\n'));
+  });
+
+  var userSlashCode = p.join('user', 'code.dart');
+  group('Chain.terse', () {
+    test('makes each trace terse', () {
+      var chain = Chain([
+        Trace.parse('dart:core 10:11       Foo.bar\n'
+            'dart:core 10:11       Bar.baz\n'
+            'user/code.dart 10:11  Bang.qux\n'
+            'dart:core 10:11       Zip.zap\n'
+            'dart:core 10:11       Zop.zoop'),
+        Trace.parse('user/code.dart 10:11                        Bang.qux\n'
+            'dart:core 10:11                             Foo.bar\n'
+            'package:stack_trace/stack_trace.dart 10:11  Bar.baz\n'
+            'dart:core 10:11                             Zip.zap\n'
+            'user/code.dart 10:11                        Zop.zoop')
+      ]);
+
+      expect(
+          chain.terse.toString(),
+          equals('dart:core             Bar.baz\n'
+              '$userSlashCode 10:11  Bang.qux\n'
+              '===== asynchronous gap ===========================\n'
+              '$userSlashCode 10:11  Bang.qux\n'
+              'dart:core             Zip.zap\n'
+              '$userSlashCode 10:11  Zop.zoop\n'));
+    });
+
+    test('eliminates internal-only traces', () {
+      var chain = Chain([
+        Trace.parse('user/code.dart 10:11  Foo.bar\n'
+            'dart:core 10:11       Bar.baz'),
+        Trace.parse('dart:core 10:11                             Foo.bar\n'
+            'package:stack_trace/stack_trace.dart 10:11  Bar.baz\n'
+            'dart:core 10:11                             Zip.zap'),
+        Trace.parse('user/code.dart 10:11  Foo.bar\n'
+            'dart:core 10:11       Bar.baz')
+      ]);
+
+      expect(
+          chain.terse.toString(),
+          equals('$userSlashCode 10:11  Foo.bar\n'
+              '===== asynchronous gap ===========================\n'
+              '$userSlashCode 10:11  Foo.bar\n'));
+    });
+
+    test("doesn't return an empty chain", () {
+      var chain = Chain([
+        Trace.parse('dart:core 10:11                             Foo.bar\n'
+            'package:stack_trace/stack_trace.dart 10:11  Bar.baz\n'
+            'dart:core 10:11                             Zip.zap'),
+        Trace.parse('dart:core 10:11                             A.b\n'
+            'package:stack_trace/stack_trace.dart 10:11  C.d\n'
+            'dart:core 10:11                             E.f')
+      ]);
+
+      expect(chain.terse.toString(), equals('dart:core  E.f\n'));
+    });
+
+    // Regression test for #9
+    test("doesn't crash on empty traces", () {
+      var chain = Chain([
+        Trace.parse('user/code.dart 10:11  Bang.qux'),
+        Trace([]),
+        Trace.parse('user/code.dart 10:11  Bang.qux')
+      ]);
+
+      expect(
+          chain.terse.toString(),
+          equals('$userSlashCode 10:11  Bang.qux\n'
+              '===== asynchronous gap ===========================\n'
+              '$userSlashCode 10:11  Bang.qux\n'));
+    });
+  });
+
+  group('Chain.foldFrames', () {
+    test('folds each trace', () {
+      var chain = Chain([
+        Trace.parse('a.dart 10:11  Foo.bar\n'
+            'a.dart 10:11  Bar.baz\n'
+            'b.dart 10:11  Bang.qux\n'
+            'a.dart 10:11  Zip.zap\n'
+            'a.dart 10:11  Zop.zoop'),
+        Trace.parse('a.dart 10:11  Foo.bar\n'
+            'a.dart 10:11  Bar.baz\n'
+            'a.dart 10:11  Bang.qux\n'
+            'a.dart 10:11  Zip.zap\n'
+            'b.dart 10:11  Zop.zoop')
+      ]);
+
+      var folded = chain.foldFrames((frame) => frame.library == 'a.dart');
+      expect(
+          folded.toString(),
+          equals('a.dart 10:11  Bar.baz\n'
+              'b.dart 10:11  Bang.qux\n'
+              'a.dart 10:11  Zop.zoop\n'
+              '===== asynchronous gap ===========================\n'
+              'a.dart 10:11  Zip.zap\n'
+              'b.dart 10:11  Zop.zoop\n'));
+    });
+
+    test('with terse: true, folds core frames as well', () {
+      var chain = Chain([
+        Trace.parse('a.dart 10:11                        Foo.bar\n'
+            'dart:async-patch/future.dart 10:11  Zip.zap\n'
+            'b.dart 10:11                        Bang.qux\n'
+            'dart:core 10:11                     Bar.baz\n'
+            'a.dart 10:11                        Zop.zoop'),
+        Trace.parse('a.dart 10:11  Foo.bar\n'
+            'a.dart 10:11  Bar.baz\n'
+            'a.dart 10:11  Bang.qux\n'
+            'a.dart 10:11  Zip.zap\n'
+            'b.dart 10:11  Zop.zoop')
+      ]);
+
+      var folded =
+          chain.foldFrames((frame) => frame.library == 'a.dart', terse: true);
+      expect(
+          folded.toString(),
+          equals('dart:async    Zip.zap\n'
+              'b.dart 10:11  Bang.qux\n'
+              '===== asynchronous gap ===========================\n'
+              'a.dart        Zip.zap\n'
+              'b.dart 10:11  Zop.zoop\n'));
+    });
+
+    test('eliminates completely-folded traces', () {
+      var chain = Chain([
+        Trace.parse('a.dart 10:11  Foo.bar\n'
+            'b.dart 10:11  Bang.qux'),
+        Trace.parse('a.dart 10:11  Foo.bar\n'
+            'a.dart 10:11  Bang.qux'),
+        Trace.parse('a.dart 10:11  Zip.zap\n'
+            'b.dart 10:11  Zop.zoop')
+      ]);
+
+      var folded = chain.foldFrames((frame) => frame.library == 'a.dart');
+      expect(
+          folded.toString(),
+          equals('a.dart 10:11  Foo.bar\n'
+              'b.dart 10:11  Bang.qux\n'
+              '===== asynchronous gap ===========================\n'
+              'a.dart 10:11  Zip.zap\n'
+              'b.dart 10:11  Zop.zoop\n'));
+    });
+
+    test("doesn't return an empty trace", () {
+      var chain = Chain([
+        Trace.parse('a.dart 10:11  Foo.bar\n'
+            'a.dart 10:11  Bang.qux')
+      ]);
+
+      var folded = chain.foldFrames((frame) => frame.library == 'a.dart');
+      expect(folded.toString(), equals('a.dart 10:11  Bang.qux\n'));
+    });
+  });
+
+  test('Chain.toTrace eliminates asynchronous gaps', () {
+    var trace = Chain([
+      Trace.parse('user/code.dart 10:11  Foo.bar\n'
+          'dart:core 10:11       Bar.baz'),
+      Trace.parse('user/code.dart 10:11  Foo.bar\n'
+          'dart:core 10:11       Bar.baz')
+    ]).toTrace();
+
+    expect(
+        trace.toString(),
+        equals('$userSlashCode 10:11  Foo.bar\n'
+            'dart:core 10:11       Bar.baz\n'
+            '$userSlashCode 10:11  Foo.bar\n'
+            'dart:core 10:11       Bar.baz\n'));
+  });
+}

diff --git a/pkgs/stack_trace/test/chain/dart2js_test.dart b/pkgs/stack_trace/test/chain/dart2js_test.dart
new file mode 100644
index 0000000..abb842d
--- /dev/null
+++ b/pkgs/stack_trace/test/chain/dart2js_test.dart

@@ -0,0 +1,337 @@
+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// ignore_for_file: only_throw_errors
+
+// dart2js chain tests are separated out because dart2js stack traces are
+// inconsistent due to inlining and browser differences. These tests don't
+// assert anything about the content of the traces, just the number of traces in
+// a chain.
+@TestOn('js')
+library;
+
+import 'dart:async';
+
+import 'package:stack_trace/stack_trace.dart';
+import 'package:test/test.dart';
+
+import 'utils.dart';
+
+void main() {
+  group('capture() with onError catches exceptions', () {
+    test('thrown synchronously', () async {
+      var chain = await captureFuture(() => throw 'error');
+      expect(chain.traces, hasLength(1));
+    });
+
+    test('thrown in a microtask', () async {
+      var chain = await captureFuture(() => inMicrotask(() => throw 'error'));
+      expect(chain.traces, hasLength(2));
+    });
+
+    test('thrown in a one-shot timer', () async {
+      var chain =
+          await captureFuture(() => inOneShotTimer(() => throw 'error'));
+      expect(chain.traces, hasLength(2));
+    });
+
+    test('thrown in a periodic timer', () async {
+      var chain =
+          await captureFuture(() => inPeriodicTimer(() => throw 'error'));
+      expect(chain.traces, hasLength(2));
+    });
+
+    test('thrown in a nested series of asynchronous operations', () async {
+      var chain = await captureFuture(() {
+        inPeriodicTimer(() {
+          inOneShotTimer(() => inMicrotask(() => throw 'error'));
+        });
+      });
+
+      expect(chain.traces, hasLength(4));
+    });
+
+    test('thrown in a long future chain', () async {
+      var chain = await captureFuture(() => inFutureChain(() => throw 'error'));
+
+      // Despite many asynchronous operations, there's only one level of
+      // nested calls, so there should be only two traces in the chain. This
+      // is important; programmers expect stack trace memory consumption to be
+      // O(depth of program), not O(length of program).
+      expect(chain.traces, hasLength(2));
+    });
+
+    test('thrown in new Future()', () async {
+      var chain = await captureFuture(() => inNewFuture(() => throw 'error'));
+      expect(chain.traces, hasLength(3));
+    });
+
+    test('thrown in new Future.sync()', () async {
+      var chain = await captureFuture(() {
+        inMicrotask(() => inSyncFuture(() => throw 'error'));
+      });
+
+      expect(chain.traces, hasLength(3));
+    });
+
+    test('multiple times', () {
+      var completer = Completer<void>();
+      var first = true;
+
+      Chain.capture(() {
+        inMicrotask(() => throw 'first error');
+        inPeriodicTimer(() => throw 'second error');
+      }, onError: (error, chain) {
+        try {
+          if (first) {
+            expect(error, equals('first error'));
+            expect(chain.traces, hasLength(2));
+            first = false;
+          } else {
+            expect(error, equals('second error'));
+            expect(chain.traces, hasLength(2));
+            completer.complete();
+          }
+        } on Object catch (error, stackTrace) {
+          completer.completeError(error, stackTrace);
+        }
+      });
+
+      return completer.future;
+    });
+
+    test('passed to a completer', () async {
+      var trace = Trace.current();
+      var chain = await captureFuture(() {
+        inMicrotask(() => completerErrorFuture(trace));
+      });
+
+      expect(chain.traces, hasLength(3));
+
+      // The first trace is the trace that was manually reported for the
+      // error.
+      expect(chain.traces.first.toString(), equals(trace.toString()));
+    });
+
+    test('passed to a completer with no stack trace', () async {
+      var chain = await captureFuture(() {
+        inMicrotask(completerErrorFuture);
+      });
+
+      expect(chain.traces, hasLength(2));
+    });
+
+    test('passed to a stream controller', () async {
+      var trace = Trace.current();
+      var chain = await captureFuture(() {
+        inMicrotask(() => controllerErrorStream(trace).listen(null));
+      });
+
+      expect(chain.traces, hasLength(3));
+      expect(chain.traces.first.toString(), equals(trace.toString()));
+    });
+
+    test('passed to a stream controller with no stack trace', () async {
+      var chain = await captureFuture(() {
+        inMicrotask(() => controllerErrorStream().listen(null));
+      });
+
+      expect(chain.traces, hasLength(2));
+    });
+
+    test('and relays them to the parent zone', () {
+      var completer = Completer<void>();
+
+      runZonedGuarded(() {
+        Chain.capture(() {
+          inMicrotask(() => throw 'error');
+        }, onError: (error, chain) {
+          expect(error, equals('error'));
+          expect(chain.traces, hasLength(2));
+          throw error;
+        });
+      }, (error, chain) {
+        try {
+          expect(error, equals('error'));
+          expect(chain,
+              isA<Chain>().having((c) => c.traces, 'traces', hasLength(2)));
+          completer.complete();
+        } on Object catch (error, stackTrace) {
+          completer.completeError(error, stackTrace);
+        }
+      });
+
+      return completer.future;
+    });
+  });
+
+  test('capture() without onError passes exceptions to parent zone', () {
+    var completer = Completer<void>();
+
+    runZonedGuarded(() {
+      Chain.capture(() => inMicrotask(() => throw 'error'));
+    }, (error, chain) {
+      try {
+        expect(error, equals('error'));
+        expect(chain,
+            isA<Chain>().having((c) => c.traces, 'traces', hasLength(2)));
+        completer.complete();
+      } on Object catch (error, stackTrace) {
+        completer.completeError(error, stackTrace);
+      }
+    });
+
+    return completer.future;
+  });
+
+  group('current() within capture()', () {
+    test('called in a microtask', () async {
+      var completer = Completer<Chain>();
+      Chain.capture(() {
+        inMicrotask(() => completer.complete(Chain.current()));
+      });
+
+      var chain = await completer.future;
+      expect(chain.traces, hasLength(2));
+    });
+
+    test('called in a one-shot timer', () async {
+      var completer = Completer<Chain>();
+      Chain.capture(() {
+        inOneShotTimer(() => completer.complete(Chain.current()));
+      });
+
+      var chain = await completer.future;
+      expect(chain.traces, hasLength(2));
+    });
+
+    test('called in a periodic timer', () async {
+      var completer = Completer<Chain>();
+      Chain.capture(() {
+        inPeriodicTimer(() => completer.complete(Chain.current()));
+      });
+
+      var chain = await completer.future;
+      expect(chain.traces, hasLength(2));
+    });
+
+    test('called in a nested series of asynchronous operations', () async {
+      var completer = Completer<Chain>();
+      Chain.capture(() {
+        inPeriodicTimer(() {
+          inOneShotTimer(() {
+            inMicrotask(() => completer.complete(Chain.current()));
+          });
+        });
+      });
+
+      var chain = await completer.future;
+      expect(chain.traces, hasLength(4));
+    });
+
+    test('called in a long future chain', () async {
+      var completer = Completer<Chain>();
+      Chain.capture(() {
+        inFutureChain(() => completer.complete(Chain.current()));
+      });
+
+      var chain = await completer.future;
+      expect(chain.traces, hasLength(2));
+    });
+  });
+
+  test(
+    'current() outside of capture() returns a chain wrapping the current trace',
+    () =>
+        // The test runner runs all tests with chains enabled.
+        Chain.disable(() async {
+      var completer = Completer<Chain>();
+      inMicrotask(() => completer.complete(Chain.current()));
+
+      var chain = await completer.future;
+      // Since the chain wasn't loaded within [Chain.capture], the full stack
+      // chain isn't available and it just returns the current stack when
+      // called.
+      expect(chain.traces, hasLength(1));
+    }),
+  );
+
+  group('forTrace() within capture()', () {
+    test('called for a stack trace from a microtask', () async {
+      var chain = await Chain.capture(
+          () => chainForTrace(inMicrotask, () => throw 'error'));
+
+      // Because [chainForTrace] has to set up a future chain to capture the
+      // stack trace while still showing it to the zone specification, it adds
+      // an additional level of async nesting and so an additional trace.
+      expect(chain.traces, hasLength(3));
+    });
+
+    test('called for a stack trace from a one-shot timer', () async {
+      var chain = await Chain.capture(
+          () => chainForTrace(inOneShotTimer, () => throw 'error'));
+
+      expect(chain.traces, hasLength(3));
+    });
+
+    test('called for a stack trace from a periodic timer', () async {
+      var chain = await Chain.capture(
+          () => chainForTrace(inPeriodicTimer, () => throw 'error'));
+
+      expect(chain.traces, hasLength(3));
+    });
+
+    test(
+        'called for a stack trace from a nested series of asynchronous '
+        'operations', () async {
+      var chain = await Chain.capture(() => chainForTrace((callback) {
+            inPeriodicTimer(() => inOneShotTimer(() => inMicrotask(callback)));
+          }, () => throw 'error'));
+
+      expect(chain.traces, hasLength(5));
+    });
+
+    test('called for a stack trace from a long future chain', () async {
+      var chain = await Chain.capture(
+          () => chainForTrace(inFutureChain, () => throw 'error'));
+
+      expect(chain.traces, hasLength(3));
+    });
+
+    test(
+        'called for an unregistered stack trace returns a chain wrapping that '
+        'trace', () {
+      late StackTrace trace;
+      var chain = Chain.capture(() {
+        try {
+          throw 'error';
+        } catch (_, stackTrace) {
+          trace = stackTrace;
+          return Chain.forTrace(stackTrace);
+        }
+      });
+
+      expect(chain.traces, hasLength(1));
+      expect(
+          chain.traces.first.toString(), equals(Trace.from(trace).toString()));
+    });
+  });
+
+  test(
+      'forTrace() outside of capture() returns a chain wrapping the given '
+      'trace', () {
+    late StackTrace trace;
+    var chain = Chain.capture(() {
+      try {
+        throw 'error';
+      } catch (_, stackTrace) {
+        trace = stackTrace;
+        return Chain.forTrace(stackTrace);
+      }
+    });
+
+    expect(chain.traces, hasLength(1));
+    expect(chain.traces.first.toString(), equals(Trace.from(trace).toString()));
+  });
+}

diff --git a/pkgs/stack_trace/test/chain/utils.dart b/pkgs/stack_trace/test/chain/utils.dart
new file mode 100644
index 0000000..27fb0e6
--- /dev/null
+++ b/pkgs/stack_trace/test/chain/utils.dart

@@ -0,0 +1,94 @@
+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:stack_trace/stack_trace.dart';
+import 'package:test/test.dart';
+
+/// Runs [callback] in a microtask callback.
+void inMicrotask(void Function() callback) => scheduleMicrotask(callback);
+
+/// Runs [callback] in a one-shot timer callback.
+void inOneShotTimer(void Function() callback) => Timer.run(callback);
+
+/// Runs [callback] once in a periodic timer callback.
+void inPeriodicTimer(void Function() callback) {
+  var count = 0;
+  Timer.periodic(const Duration(milliseconds: 1), (timer) {
+    count++;
+    if (count != 5) return;
+    timer.cancel();
+    callback();
+  });
+}
+
+/// Runs [callback] within a long asynchronous Future chain.
+void inFutureChain(void Function() callback) {
+  Future(() {})
+      .then((_) => Future(() {}))
+      .then((_) => Future(() {}))
+      .then((_) => Future(() {}))
+      .then((_) => Future(() {}))
+      .then((_) => callback())
+      .then((_) => Future(() {}));
+}
+
+void inNewFuture(void Function() callback) {
+  Future(callback);
+}
+
+void inSyncFuture(void Function() callback) {
+  Future.sync(callback);
+}
+
+/// Returns a Future that completes to an error using a completer.
+///
+/// If [trace] is passed, it's used as the stack trace for the error.
+Future<void> completerErrorFuture([StackTrace? trace]) {
+  var completer = Completer<void>();
+  completer.completeError('error', trace);
+  return completer.future;
+}
+
+/// Returns a Stream that emits an error using a controller.
+///
+/// If [trace] is passed, it's used as the stack trace for the error.
+Stream<void> controllerErrorStream([StackTrace? trace]) {
+  var controller = StreamController<void>();
+  controller.addError('error', trace);
+  return controller.stream;
+}
+
+/// Runs [callback] within [asyncFn], then converts any errors raised into a
+/// [Chain] with [Chain.forTrace].
+Future<Chain> chainForTrace(
+    void Function(void Function()) asyncFn, void Function() callback) {
+  var completer = Completer<Chain>();
+  asyncFn(() {
+    // We use `new Future.value().then(...)` here as opposed to [new Future] or
+    // [new Future.sync] because those methods don't pass the exception through
+    // the zone specification before propagating it, so there's no chance to
+    // attach a chain to its stack trace. See issue 15105.
+    Future<void>.value()
+        .then((_) => callback())
+        .catchError(completer.completeError);
+  });
+
+  return completer.future
+      .catchError((_, StackTrace stackTrace) => Chain.forTrace(stackTrace));
+}
+
+/// Runs [callback] in a [Chain.capture] zone and returns a Future that
+/// completes to the stack chain for an error thrown by [callback].
+///
+/// [callback] is expected to throw the string `"error"`.
+Future<Chain> captureFuture(void Function() callback) {
+  var completer = Completer<Chain>();
+  Chain.capture(callback, onError: (error, chain) {
+    expect(error, equals('error'));
+    completer.complete(chain);
+  });
+  return completer.future;
+}

diff --git a/pkgs/stack_trace/test/chain/vm_test.dart b/pkgs/stack_trace/test/chain/vm_test.dart
new file mode 100644
index 0000000..5c6c0b7
--- /dev/null
+++ b/pkgs/stack_trace/test/chain/vm_test.dart

@@ -0,0 +1,508 @@
+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// ignore_for_file: only_throw_errors
+
+// VM chain tests can rely on stronger guarantees about the contents of the
+// stack traces than dart2js.
+@TestOn('dart-vm')
+library;
+
+import 'dart:async';
+
+import 'package:stack_trace/src/utils.dart';
+import 'package:stack_trace/stack_trace.dart';
+import 'package:test/test.dart';
+
+import '../utils.dart';
+import 'utils.dart';
+
+void main() {
+  group('capture() with onError catches exceptions', () {
+    test('thrown synchronously', () async {
+      late StackTrace vmTrace;
+      var chain = await captureFuture(() {
+        try {
+          throw 'error';
+        } catch (_, stackTrace) {
+          vmTrace = stackTrace;
+          rethrow;
+        }
+      });
+
+      // Because there's no chain context for a synchronous error, we fall back
+      // on the VM's stack chain tracking.
+      expect(
+          chain.toString(), equals(Chain.parse(vmTrace.toString()).toString()));
+    });
+
+    test('thrown in a microtask', () {
+      return captureFuture(() => inMicrotask(() => throw 'error'))
+          .then((chain) {
+        // Since there was only one asynchronous operation, there should be only
+        // two traces in the chain.
+        expect(chain.traces, hasLength(2));
+
+        // The first frame of the first trace should be the line on which the
+        // actual error was thrown.
+        expect(chain.traces[0].frames.first, frameMember(startsWith('main')));
+
+        // The second trace should describe the stack when the error callback
+        // was scheduled.
+        expect(chain.traces[1].frames,
+            contains(frameMember(startsWith('inMicrotask'))));
+      });
+    });
+
+    test('thrown in a one-shot timer', () {
+      return captureFuture(() => inOneShotTimer(() => throw 'error'))
+          .then((chain) {
+        expect(chain.traces, hasLength(2));
+        expect(chain.traces[0].frames.first, frameMember(startsWith('main')));
+        expect(chain.traces[1].frames,
+            contains(frameMember(startsWith('inOneShotTimer'))));
+      });
+    });
+
+    test('thrown in a periodic timer', () {
+      return captureFuture(() => inPeriodicTimer(() => throw 'error'))
+          .then((chain) {
+        expect(chain.traces, hasLength(2));
+        expect(chain.traces[0].frames.first, frameMember(startsWith('main')));
+        expect(chain.traces[1].frames,
+            contains(frameMember(startsWith('inPeriodicTimer'))));
+      });
+    });
+
+    test('thrown in a nested series of asynchronous operations', () {
+      return captureFuture(() {
+        inPeriodicTimer(() {
+          inOneShotTimer(() => inMicrotask(() => throw 'error'));
+        });
+      }).then((chain) {
+        expect(chain.traces, hasLength(4));
+        expect(chain.traces[0].frames.first, frameMember(startsWith('main')));
+        expect(chain.traces[1].frames,
+            contains(frameMember(startsWith('inMicrotask'))));
+        expect(chain.traces[2].frames,
+            contains(frameMember(startsWith('inOneShotTimer'))));
+        expect(chain.traces[3].frames,
+            contains(frameMember(startsWith('inPeriodicTimer'))));
+      });
+    });
+
+    test('thrown in a long future chain', () {
+      return captureFuture(() => inFutureChain(() => throw 'error'))
+          .then((chain) {
+        // Despite many asynchronous operations, there's only one level of
+        // nested calls, so there should be only two traces in the chain. This
+        // is important; programmers expect stack trace memory consumption to be
+        // O(depth of program), not O(length of program).
+        expect(chain.traces, hasLength(2));
+
+        expect(chain.traces[0].frames.first, frameMember(startsWith('main')));
+        expect(chain.traces[1].frames,
+            contains(frameMember(startsWith('inFutureChain'))));
+      });
+    });
+
+    test('thrown in new Future()', () {
+      return captureFuture(() => inNewFuture(() => throw 'error'))
+          .then((chain) {
+        expect(chain.traces, hasLength(3));
+        expect(chain.traces[0].frames.first, frameMember(startsWith('main')));
+
+        // The second trace is the one captured by
+        // [StackZoneSpecification.errorCallback]. Because that runs
+        // asynchronously within [new Future], it doesn't actually refer to the
+        // source file at all.
+        expect(chain.traces[1].frames,
+            everyElement(frameLibrary(isNot(contains('chain_test')))));
+
+        expect(chain.traces[2].frames,
+            contains(frameMember(startsWith('inNewFuture'))));
+      });
+    });
+
+    test('thrown in new Future.sync()', () {
+      return captureFuture(() {
+        inMicrotask(() => inSyncFuture(() => throw 'error'));
+      }).then((chain) {
+        expect(chain.traces, hasLength(3));
+        expect(chain.traces[0].frames.first, frameMember(startsWith('main')));
+        expect(chain.traces[1].frames,
+            contains(frameMember(startsWith('inSyncFuture'))));
+        expect(chain.traces[2].frames,
+            contains(frameMember(startsWith('inMicrotask'))));
+      });
+    });
+
+    test('multiple times', () {
+      var completer = Completer<void>();
+      var first = true;
+
+      Chain.capture(() {
+        inMicrotask(() => throw 'first error');
+        inPeriodicTimer(() => throw 'second error');
+      }, onError: (error, chain) {
+        try {
+          if (first) {
+            expect(error, equals('first error'));
+            expect(chain.traces[1].frames,
+                contains(frameMember(startsWith('inMicrotask'))));
+            first = false;
+          } else {
+            expect(error, equals('second error'));
+            expect(chain.traces[1].frames,
+                contains(frameMember(startsWith('inPeriodicTimer'))));
+            completer.complete();
+          }
+        } on Object catch (error, stackTrace) {
+          completer.completeError(error, stackTrace);
+        }
+      });
+
+      return completer.future;
+    });
+
+    test('passed to a completer', () {
+      var trace = Trace.current();
+      return captureFuture(() {
+        inMicrotask(() => completerErrorFuture(trace));
+      }).then((chain) {
+        expect(chain.traces, hasLength(3));
+
+        // The first trace is the trace that was manually reported for the
+        // error.
+        expect(chain.traces.first.toString(), equals(trace.toString()));
+
+        // The second trace is the trace that was captured when
+        // [Completer.addError] was called.
+        expect(chain.traces[1].frames,
+            contains(frameMember(startsWith('completerErrorFuture'))));
+
+        // The third trace is the automatically-captured trace from when the
+        // microtask was scheduled.
+        expect(chain.traces[2].frames,
+            contains(frameMember(startsWith('inMicrotask'))));
+      });
+    });
+
+    test('passed to a completer with no stack trace', () {
+      return captureFuture(() {
+        inMicrotask(completerErrorFuture);
+      }).then((chain) {
+        expect(chain.traces, hasLength(2));
+
+        // The first trace is the one captured when [Completer.addError] was
+        // called.
+        expect(chain.traces[0].frames,
+            contains(frameMember(startsWith('completerErrorFuture'))));
+
+        // The second trace is the automatically-captured trace from when the
+        // microtask was scheduled.
+        expect(chain.traces[1].frames,
+            contains(frameMember(startsWith('inMicrotask'))));
+      });
+    });
+
+    test('passed to a stream controller', () {
+      var trace = Trace.current();
+      return captureFuture(() {
+        inMicrotask(() => controllerErrorStream(trace).listen(null));
+      }).then((chain) {
+        expect(chain.traces, hasLength(3));
+        expect(chain.traces.first.toString(), equals(trace.toString()));
+        expect(chain.traces[1].frames,
+            contains(frameMember(startsWith('controllerErrorStream'))));
+        expect(chain.traces[2].frames,
+            contains(frameMember(startsWith('inMicrotask'))));
+      });
+    });
+
+    test('passed to a stream controller with no stack trace', () {
+      return captureFuture(() {
+        inMicrotask(() => controllerErrorStream().listen(null));
+      }).then((chain) {
+        expect(chain.traces, hasLength(2));
+        expect(chain.traces[0].frames,
+            contains(frameMember(startsWith('controllerErrorStream'))));
+        expect(chain.traces[1].frames,
+            contains(frameMember(startsWith('inMicrotask'))));
+      });
+    });
+
+    test('and relays them to the parent zone', () {
+      var completer = Completer<void>();
+
+      runZonedGuarded(() {
+        Chain.capture(() {
+          inMicrotask(() => throw 'error');
+        }, onError: (error, chain) {
+          expect(error, equals('error'));
+          expect(chain.traces[1].frames,
+              contains(frameMember(startsWith('inMicrotask'))));
+          throw error;
+        });
+      }, (error, chain) {
+        try {
+          expect(error, equals('error'));
+          expect(
+              chain,
+              isA<Chain>().having((c) => c.traces[1].frames, 'traces[1].frames',
+                  contains(frameMember(startsWith('inMicrotask')))));
+          completer.complete();
+        } on Object catch (error, stackTrace) {
+          completer.completeError(error, stackTrace);
+        }
+      });
+
+      return completer.future;
+    });
+  });
+
+  test('capture() without onError passes exceptions to parent zone', () {
+    var completer = Completer<void>();
+
+    runZonedGuarded(() {
+      Chain.capture(() => inMicrotask(() => throw 'error'));
+    }, (error, chain) {
+      try {
+        expect(error, equals('error'));
+        expect(
+            chain,
+            isA<Chain>().having((c) => c.traces[1].frames, 'traces[1].frames',
+                contains(frameMember(startsWith('inMicrotask')))));
+        completer.complete();
+      } on Object catch (error, stackTrace) {
+        completer.completeError(error, stackTrace);
+      }
+    });
+
+    return completer.future;
+  });
+
+  group('current() within capture()', () {
+    test('called in a microtask', () {
+      var completer = Completer<Chain>();
+      Chain.capture(() {
+        inMicrotask(() => completer.complete(Chain.current()));
+      });
+
+      return completer.future.then((chain) {
+        expect(chain.traces, hasLength(2));
+        expect(chain.traces[0].frames.first, frameMember(startsWith('main')));
+        expect(chain.traces[1].frames,
+            contains(frameMember(startsWith('inMicrotask'))));
+      });
+    });
+
+    test('called in a one-shot timer', () {
+      var completer = Completer<Chain>();
+      Chain.capture(() {
+        inOneShotTimer(() => completer.complete(Chain.current()));
+      });
+
+      return completer.future.then((chain) {
+        expect(chain.traces, hasLength(2));
+        expect(chain.traces[0].frames.first, frameMember(startsWith('main')));
+        expect(chain.traces[1].frames,
+            contains(frameMember(startsWith('inOneShotTimer'))));
+      });
+    });
+
+    test('called in a periodic timer', () {
+      var completer = Completer<Chain>();
+      Chain.capture(() {
+        inPeriodicTimer(() => completer.complete(Chain.current()));
+      });
+
+      return completer.future.then((chain) {
+        expect(chain.traces, hasLength(2));
+        expect(chain.traces[0].frames.first, frameMember(startsWith('main')));
+        expect(chain.traces[1].frames,
+            contains(frameMember(startsWith('inPeriodicTimer'))));
+      });
+    });
+
+    test('called in a nested series of asynchronous operations', () {
+      var completer = Completer<Chain>();
+      Chain.capture(() {
+        inPeriodicTimer(() {
+          inOneShotTimer(() {
+            inMicrotask(() => completer.complete(Chain.current()));
+          });
+        });
+      });
+
+      return completer.future.then((chain) {
+        expect(chain.traces, hasLength(4));
+        expect(chain.traces[0].frames.first, frameMember(startsWith('main')));
+        expect(chain.traces[1].frames,
+            contains(frameMember(startsWith('inMicrotask'))));
+        expect(chain.traces[2].frames,
+            contains(frameMember(startsWith('inOneShotTimer'))));
+        expect(chain.traces[3].frames,
+            contains(frameMember(startsWith('inPeriodicTimer'))));
+      });
+    });
+
+    test('called in a long future chain', () {
+      var completer = Completer<Chain>();
+      Chain.capture(() {
+        inFutureChain(() => completer.complete(Chain.current()));
+      });
+
+      return completer.future.then((chain) {
+        expect(chain.traces, hasLength(2));
+        expect(chain.traces[0].frames.first, frameMember(startsWith('main')));
+        expect(chain.traces[1].frames,
+            contains(frameMember(startsWith('inFutureChain'))));
+      });
+    });
+  });
+
+  test(
+      'current() outside of capture() returns a chain wrapping the current '
+      'trace', () {
+    // The test runner runs all tests with chains enabled.
+    return Chain.disable(() {
+      var completer = Completer<Chain>();
+      inMicrotask(() => completer.complete(Chain.current()));
+
+      return completer.future.then((chain) {
+        // Since the chain wasn't loaded within [Chain.capture], the full stack
+        // chain isn't available and it just returns the current stack when
+        // called.
+        expect(chain.traces, hasLength(1));
+        expect(
+            chain.traces.first.frames.first, frameMember(startsWith('main')));
+      });
+    });
+  });
+
+  group('forTrace() within capture()', () {
+    test('called for a stack trace from a microtask', () {
+      return Chain.capture(() {
+        return chainForTrace(inMicrotask, () => throw 'error');
+      }).then((chain) {
+        // Because [chainForTrace] has to set up a future chain to capture the
+        // stack trace while still showing it to the zone specification, it adds
+        // an additional level of async nesting and so an additional trace.
+        expect(chain.traces, hasLength(3));
+        expect(chain.traces[0].frames.first, frameMember(startsWith('main')));
+        expect(chain.traces[1].frames,
+            contains(frameMember(startsWith('chainForTrace'))));
+        expect(chain.traces[2].frames,
+            contains(frameMember(startsWith('inMicrotask'))));
+      });
+    });
+
+    test('called for a stack trace from a one-shot timer', () {
+      return Chain.capture(() {
+        return chainForTrace(inOneShotTimer, () => throw 'error');
+      }).then((chain) {
+        expect(chain.traces, hasLength(3));
+        expect(chain.traces[0].frames.first, frameMember(startsWith('main')));
+        expect(chain.traces[1].frames,
+            contains(frameMember(startsWith('chainForTrace'))));
+        expect(chain.traces[2].frames,
+            contains(frameMember(startsWith('inOneShotTimer'))));
+      });
+    });
+
+    test('called for a stack trace from a periodic timer', () {
+      return Chain.capture(() {
+        return chainForTrace(inPeriodicTimer, () => throw 'error');
+      }).then((chain) {
+        expect(chain.traces, hasLength(3));
+        expect(chain.traces[0].frames.first, frameMember(startsWith('main')));
+        expect(chain.traces[1].frames,
+            contains(frameMember(startsWith('chainForTrace'))));
+        expect(chain.traces[2].frames,
+            contains(frameMember(startsWith('inPeriodicTimer'))));
+      });
+    });
+
+    test(
+        'called for a stack trace from a nested series of asynchronous '
+        'operations', () {
+      return Chain.capture(() {
+        return chainForTrace((callback) {
+          inPeriodicTimer(() => inOneShotTimer(() => inMicrotask(callback)));
+        }, () => throw 'error');
+      }).then((chain) {
+        expect(chain.traces, hasLength(5));
+        expect(chain.traces[0].frames.first, frameMember(startsWith('main')));
+        expect(chain.traces[1].frames,
+            contains(frameMember(startsWith('chainForTrace'))));
+        expect(chain.traces[2].frames,
+            contains(frameMember(startsWith('inMicrotask'))));
+        expect(chain.traces[3].frames,
+            contains(frameMember(startsWith('inOneShotTimer'))));
+        expect(chain.traces[4].frames,
+            contains(frameMember(startsWith('inPeriodicTimer'))));
+      });
+    });
+
+    test('called for a stack trace from a long future chain', () {
+      return Chain.capture(() {
+        return chainForTrace(inFutureChain, () => throw 'error');
+      }).then((chain) {
+        expect(chain.traces, hasLength(3));
+        expect(chain.traces[0].frames.first, frameMember(startsWith('main')));
+        expect(chain.traces[1].frames,
+            contains(frameMember(startsWith('chainForTrace'))));
+        expect(chain.traces[2].frames,
+            contains(frameMember(startsWith('inFutureChain'))));
+      });
+    });
+
+    test('called for an unregistered stack trace uses the current chain',
+        () async {
+      late StackTrace trace;
+      var chain = await Chain.capture(() async {
+        try {
+          throw 'error';
+        } catch (_, stackTrace) {
+          trace = stackTrace;
+          return Chain.forTrace(stackTrace);
+        }
+      });
+
+      expect(chain.traces, hasLength(greaterThan(1)));
+
+      // Assert that we've trimmed the VM's stack chains here to avoid
+      // duplication.
+      expect(chain.traces.first.toString(),
+          equals(Chain.parse(trace.toString()).traces.first.toString()));
+    });
+  });
+
+  test(
+      'forTrace() outside of capture() returns a chain describing the VM stack '
+      'chain', () {
+    // Disable the test package's chain-tracking.
+    return Chain.disable(() async {
+      late StackTrace trace;
+      await Chain.capture(() async {
+        try {
+          throw 'error';
+        } catch (_, stackTrace) {
+          trace = stackTrace;
+        }
+      });
+
+      final chain = Chain.forTrace(trace);
+      final traceStr = trace.toString();
+      final gaps = vmChainGap.allMatches(traceStr);
+      // If the trace ends on a gap, there's no sub-trace following the gap.
+      final expectedLength =
+          (gaps.last.end == traceStr.length) ? gaps.length : gaps.length + 1;
+      expect(chain.traces, hasLength(expectedLength));
+      expect(
+          chain.traces.first.frames, contains(frameMember(startsWith('main'))));
+    });
+  });
+}

diff --git a/pkgs/stack_trace/test/frame_test.dart b/pkgs/stack_trace/test/frame_test.dart
new file mode 100644
index 0000000..a5dfc20
--- /dev/null
+++ b/pkgs/stack_trace/test/frame_test.dart

@@ -0,0 +1,729 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:path/path.dart' as path;
+import 'package:stack_trace/stack_trace.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('.parseVM', () {
+    test('parses a stack frame with column correctly', () {
+      var frame = Frame.parseVM('#1      Foo._bar '
+          '(file:///home/nweiz/code/stuff.dart:42:21)');
+      expect(
+          frame.uri, equals(Uri.parse('file:///home/nweiz/code/stuff.dart')));
+      expect(frame.line, equals(42));
+      expect(frame.column, equals(21));
+      expect(frame.member, equals('Foo._bar'));
+    });
+
+    test('parses a stack frame without column correctly', () {
+      var frame = Frame.parseVM('#1      Foo._bar '
+          '(file:///home/nweiz/code/stuff.dart:24)');
+      expect(
+          frame.uri, equals(Uri.parse('file:///home/nweiz/code/stuff.dart')));
+      expect(frame.line, equals(24));
+      expect(frame.column, null);
+      expect(frame.member, equals('Foo._bar'));
+    });
+
+    // This can happen with async stack traces. See issue 22009.
+    test('parses a stack frame without line or column correctly', () {
+      var frame = Frame.parseVM('#1      Foo._bar '
+          '(file:///home/nweiz/code/stuff.dart)');
+      expect(
+          frame.uri, equals(Uri.parse('file:///home/nweiz/code/stuff.dart')));
+      expect(frame.line, isNull);
+      expect(frame.column, isNull);
+      expect(frame.member, equals('Foo._bar'));
+    });
+
+    test('converts "<anonymous closure>" to "<fn>"', () {
+      String? parsedMember(String member) =>
+          Frame.parseVM('#0 $member (foo:0:0)').member;
+
+      expect(parsedMember('Foo.<anonymous closure>'), equals('Foo.<fn>'));
+      expect(parsedMember('<anonymous closure>.<anonymous closure>.bar'),
+          equals('<fn>.<fn>.bar'));
+    });
+
+    test('converts "<<anonymous closure>_async_body>" to "<async>"', () {
+      var frame =
+          Frame.parseVM('#0 Foo.<<anonymous closure>_async_body> (foo:0:0)');
+      expect(frame.member, equals('Foo.<async>'));
+    });
+
+    test('converts "<function_name_async_body>" to "<async>"', () {
+      var frame = Frame.parseVM('#0 Foo.<function_name_async_body> (foo:0:0)');
+      expect(frame.member, equals('Foo.<async>'));
+    });
+
+    test('parses a folded frame correctly', () {
+      var frame = Frame.parseVM('...');
+
+      expect(frame.member, equals('...'));
+      expect(frame.uri, equals(Uri()));
+      expect(frame.line, isNull);
+      expect(frame.column, isNull);
+    });
+  });
+
+  group('.parseV8', () {
+    test('returns an UnparsedFrame for malformed frames', () {
+      expectIsUnparsed(Frame.parseV8, '');
+      expectIsUnparsed(Frame.parseV8, '#1');
+      expectIsUnparsed(Frame.parseV8, '#1      Foo');
+      expectIsUnparsed(Frame.parseV8, '#1      (dart:async/future.dart:10:15)');
+      expectIsUnparsed(Frame.parseV8, 'Foo (dart:async/future.dart:10:15)');
+    });
+
+    test('parses a stack frame correctly', () {
+      var frame = Frame.parseV8('    at VW.call\$0 '
+          '(https://example.com/stuff.dart.js:560:28)');
+      expect(frame.uri, equals(Uri.parse('https://example.com/stuff.dart.js')));
+      expect(frame.line, equals(560));
+      expect(frame.column, equals(28));
+      expect(frame.member, equals('VW.call\$0'));
+    });
+
+    test('parses a stack frame with a : in the authority', () {
+      var frame = Frame.parseV8('    at VW.call\$0 '
+          '(http://localhost:8080/stuff.dart.js:560:28)');
+      expect(
+          frame.uri, equals(Uri.parse('http://localhost:8080/stuff.dart.js')));
+      expect(frame.line, equals(560));
+      expect(frame.column, equals(28));
+      expect(frame.member, equals('VW.call\$0'));
+    });
+
+    test('parses a stack frame with an absolute POSIX path correctly', () {
+      var frame = Frame.parseV8('    at VW.call\$0 '
+          '(/path/to/stuff.dart.js:560:28)');
+      expect(frame.uri, equals(Uri.parse('file:///path/to/stuff.dart.js')));
+      expect(frame.line, equals(560));
+      expect(frame.column, equals(28));
+      expect(frame.member, equals('VW.call\$0'));
+    });
+
+    test('parses a stack frame with an absolute Windows path correctly', () {
+      var frame = Frame.parseV8('    at VW.call\$0 '
+          r'(C:\path\to\stuff.dart.js:560:28)');
+      expect(frame.uri, equals(Uri.parse('file:///C:/path/to/stuff.dart.js')));
+      expect(frame.line, equals(560));
+      expect(frame.column, equals(28));
+      expect(frame.member, equals('VW.call\$0'));
+    });
+
+    test('parses a stack frame with a Windows UNC path correctly', () {
+      var frame = Frame.parseV8('    at VW.call\$0 '
+          r'(\\mount\path\to\stuff.dart.js:560:28)');
+      expect(
+          frame.uri, equals(Uri.parse('file://mount/path/to/stuff.dart.js')));
+      expect(frame.line, equals(560));
+      expect(frame.column, equals(28));
+      expect(frame.member, equals('VW.call\$0'));
+    });
+
+    test('parses a stack frame with a relative POSIX path correctly', () {
+      var frame = Frame.parseV8('    at VW.call\$0 '
+          '(path/to/stuff.dart.js:560:28)');
+      expect(frame.uri, equals(Uri.parse('path/to/stuff.dart.js')));
+      expect(frame.line, equals(560));
+      expect(frame.column, equals(28));
+      expect(frame.member, equals('VW.call\$0'));
+    });
+
+    test('parses a stack frame with a relative Windows path correctly', () {
+      var frame = Frame.parseV8('    at VW.call\$0 '
+          r'(path\to\stuff.dart.js:560:28)');
+      expect(frame.uri, equals(Uri.parse('path/to/stuff.dart.js')));
+      expect(frame.line, equals(560));
+      expect(frame.column, equals(28));
+      expect(frame.member, equals('VW.call\$0'));
+    });
+
+    test('parses an anonymous stack frame correctly', () {
+      var frame =
+          Frame.parseV8('    at https://example.com/stuff.dart.js:560:28');
+      expect(frame.uri, equals(Uri.parse('https://example.com/stuff.dart.js')));
+      expect(frame.line, equals(560));
+      expect(frame.column, equals(28));
+      expect(frame.member, equals('<fn>'));
+    });
+
+    test('parses a native stack frame correctly', () {
+      var frame = Frame.parseV8('    at Object.stringify (native)');
+      expect(frame.uri, Uri.parse('native'));
+      expect(frame.line, isNull);
+      expect(frame.column, isNull);
+      expect(frame.member, equals('Object.stringify'));
+    });
+
+    test('parses a stack frame with [as ...] correctly', () {
+      // Ignore "[as ...]", since other stack trace formats don't support a
+      // similar construct.
+      var frame = Frame.parseV8('    at VW.call\$0 [as call\$4] '
+          '(https://example.com/stuff.dart.js:560:28)');
+      expect(frame.uri, equals(Uri.parse('https://example.com/stuff.dart.js')));
+      expect(frame.line, equals(560));
+      expect(frame.column, equals(28));
+      expect(frame.member, equals('VW.call\$0'));
+    });
+
+    test('parses a basic eval stack frame correctly', () {
+      var frame = Frame.parseV8('    at eval (eval at <anonymous> '
+          '(https://example.com/stuff.dart.js:560:28))');
+      expect(frame.uri, equals(Uri.parse('https://example.com/stuff.dart.js')));
+      expect(frame.line, equals(560));
+      expect(frame.column, equals(28));
+      expect(frame.member, equals('eval'));
+    });
+
+    test('parses an IE10 eval stack frame correctly', () {
+      var frame = Frame.parseV8('    at eval (eval at Anonymous function '
+          '(https://example.com/stuff.dart.js:560:28))');
+      expect(frame.uri, equals(Uri.parse('https://example.com/stuff.dart.js')));
+      expect(frame.line, equals(560));
+      expect(frame.column, equals(28));
+      expect(frame.member, equals('eval'));
+    });
+
+    test('parses an eval stack frame with inner position info correctly', () {
+      var frame = Frame.parseV8('    at eval (eval at <anonymous> '
+          '(https://example.com/stuff.dart.js:560:28), <anonymous>:3:28)');
+      expect(frame.uri, equals(Uri.parse('https://example.com/stuff.dart.js')));
+      expect(frame.line, equals(560));
+      expect(frame.column, equals(28));
+      expect(frame.member, equals('eval'));
+    });
+
+    test('parses a nested eval stack frame correctly', () {
+      var frame = Frame.parseV8('    at eval (eval at <anonymous> '
+          '(eval at sub (https://example.com/stuff.dart.js:560:28)))');
+      expect(frame.uri, equals(Uri.parse('https://example.com/stuff.dart.js')));
+      expect(frame.line, equals(560));
+      expect(frame.column, equals(28));
+      expect(frame.member, equals('eval'));
+    });
+
+    test('converts "<anonymous>" to "<fn>"', () {
+      String? parsedMember(String member) =>
+          Frame.parseV8('    at $member (foo:0:0)').member;
+
+      expect(parsedMember('Foo.<anonymous>'), equals('Foo.<fn>'));
+      expect(
+          parsedMember('<anonymous>.<anonymous>.bar'), equals('<fn>.<fn>.bar'));
+    });
+
+    test('returns an UnparsedFrame for malformed frames', () {
+      expectIsUnparsed(Frame.parseV8, '');
+      expectIsUnparsed(Frame.parseV8, '    at');
+      expectIsUnparsed(Frame.parseV8, '    at Foo');
+      expectIsUnparsed(Frame.parseV8, '    at Foo (dart:async/future.dart)');
+      expectIsUnparsed(Frame.parseV8, '    at (dart:async/future.dart:10:15)');
+      expectIsUnparsed(Frame.parseV8, 'Foo (dart:async/future.dart:10:15)');
+      expectIsUnparsed(Frame.parseV8, '    at dart:async/future.dart');
+      expectIsUnparsed(Frame.parseV8, 'dart:async/future.dart:10:15');
+    });
+  });
+
+  group('.parseFirefox/.parseSafari', () {
+    test('parses a Firefox stack trace with anonymous function', () {
+      var trace = Trace.parse('''
+Foo._bar@https://example.com/stuff.js:18056:12
+anonymous/<@https://example.com/stuff.js line 693 > Function:3:40
+baz@https://pub.dev/buz.js:56355:55
+        ''');
+      expect(trace.frames[0].uri,
+          equals(Uri.parse('https://example.com/stuff.js')));
+      expect(trace.frames[0].line, equals(18056));
+      expect(trace.frames[0].column, equals(12));
+      expect(trace.frames[0].member, equals('Foo._bar'));
+      expect(trace.frames[1].uri,
+          equals(Uri.parse('https://example.com/stuff.js')));
+      expect(trace.frames[1].line, equals(693));
+      expect(trace.frames[1].column, isNull);
+      expect(trace.frames[1].member, equals('<fn>'));
+      expect(trace.frames[2].uri, equals(Uri.parse('https://pub.dev/buz.js')));
+      expect(trace.frames[2].line, equals(56355));
+      expect(trace.frames[2].column, equals(55));
+      expect(trace.frames[2].member, equals('baz'));
+    });
+
+    test('parses a Firefox stack trace with nested evals in anonymous function',
+        () {
+      var trace = Trace.parse('''
+        Foo._bar@https://example.com/stuff.js:18056:12
+        anonymous@file:///C:/example.html line 7 > eval line 1 > eval:1:1
+        anonymous@file:///C:/example.html line 45 > Function:1:1
+        ''');
+      expect(trace.frames[0].uri,
+          equals(Uri.parse('https://example.com/stuff.js')));
+      expect(trace.frames[0].line, equals(18056));
+      expect(trace.frames[0].column, equals(12));
+      expect(trace.frames[0].member, equals('Foo._bar'));
+      expect(trace.frames[1].uri, equals(Uri.parse('file:///C:/example.html')));
+      expect(trace.frames[1].line, equals(7));
+      expect(trace.frames[1].column, isNull);
+      expect(trace.frames[1].member, equals('<fn>'));
+      expect(trace.frames[2].uri, equals(Uri.parse('file:///C:/example.html')));
+      expect(trace.frames[2].line, equals(45));
+      expect(trace.frames[2].column, isNull);
+      expect(trace.frames[2].member, equals('<fn>'));
+    });
+
+    test('parses a simple stack frame correctly', () {
+      var frame = Frame.parseFirefox(
+          '.VW.call\$0@https://example.com/stuff.dart.js:560');
+      expect(frame.uri, equals(Uri.parse('https://example.com/stuff.dart.js')));
+      expect(frame.line, equals(560));
+      expect(frame.column, isNull);
+      expect(frame.member, equals('VW.call\$0'));
+    });
+
+    test('parses a stack frame with an absolute POSIX path correctly', () {
+      var frame = Frame.parseFirefox('.VW.call\$0@/path/to/stuff.dart.js:560');
+      expect(frame.uri, equals(Uri.parse('file:///path/to/stuff.dart.js')));
+      expect(frame.line, equals(560));
+      expect(frame.column, isNull);
+      expect(frame.member, equals('VW.call\$0'));
+    });
+
+    test('parses a stack frame with an absolute Windows path correctly', () {
+      var frame =
+          Frame.parseFirefox(r'.VW.call$0@C:\path\to\stuff.dart.js:560');
+      expect(frame.uri, equals(Uri.parse('file:///C:/path/to/stuff.dart.js')));
+      expect(frame.line, equals(560));
+      expect(frame.column, isNull);
+      expect(frame.member, equals('VW.call\$0'));
+    });
+
+    test('parses a stack frame with a Windows UNC path correctly', () {
+      var frame =
+          Frame.parseFirefox(r'.VW.call$0@\\mount\path\to\stuff.dart.js:560');
+      expect(
+          frame.uri, equals(Uri.parse('file://mount/path/to/stuff.dart.js')));
+      expect(frame.line, equals(560));
+      expect(frame.column, isNull);
+      expect(frame.member, equals('VW.call\$0'));
+    });
+
+    test('parses a stack frame with a relative POSIX path correctly', () {
+      var frame = Frame.parseFirefox('.VW.call\$0@path/to/stuff.dart.js:560');
+      expect(frame.uri, equals(Uri.parse('path/to/stuff.dart.js')));
+      expect(frame.line, equals(560));
+      expect(frame.column, isNull);
+      expect(frame.member, equals('VW.call\$0'));
+    });
+
+    test('parses a stack frame with a relative Windows path correctly', () {
+      var frame = Frame.parseFirefox(r'.VW.call$0@path\to\stuff.dart.js:560');
+      expect(frame.uri, equals(Uri.parse('path/to/stuff.dart.js')));
+      expect(frame.line, equals(560));
+      expect(frame.column, isNull);
+      expect(frame.member, equals('VW.call\$0'));
+    });
+
+    test('parses a simple anonymous stack frame correctly', () {
+      var frame = Frame.parseFirefox('@https://example.com/stuff.dart.js:560');
+      expect(frame.uri, equals(Uri.parse('https://example.com/stuff.dart.js')));
+      expect(frame.line, equals(560));
+      expect(frame.column, isNull);
+      expect(frame.member, equals('<fn>'));
+    });
+
+    test('parses a nested anonymous stack frame correctly', () {
+      var frame =
+          Frame.parseFirefox('.foo/<@https://example.com/stuff.dart.js:560');
+      expect(frame.uri, equals(Uri.parse('https://example.com/stuff.dart.js')));
+      expect(frame.line, equals(560));
+      expect(frame.column, isNull);
+      expect(frame.member, equals('foo.<fn>'));
+
+      frame = Frame.parseFirefox('.foo/@https://example.com/stuff.dart.js:560');
+      expect(frame.uri, equals(Uri.parse('https://example.com/stuff.dart.js')));
+      expect(frame.line, equals(560));
+      expect(frame.column, isNull);
+      expect(frame.member, equals('foo.<fn>'));
+    });
+
+    test('parses a named nested anonymous stack frame correctly', () {
+      var frame = Frame.parseFirefox(
+          '.foo/.name<@https://example.com/stuff.dart.js:560');
+      expect(frame.uri, equals(Uri.parse('https://example.com/stuff.dart.js')));
+      expect(frame.line, equals(560));
+      expect(frame.column, isNull);
+      expect(frame.member, equals('foo.<fn>'));
+
+      frame = Frame.parseFirefox(
+          '.foo/.name@https://example.com/stuff.dart.js:560');
+      expect(frame.uri, equals(Uri.parse('https://example.com/stuff.dart.js')));
+      expect(frame.line, equals(560));
+      expect(frame.column, isNull);
+      expect(frame.member, equals('foo.<fn>'));
+    });
+
+    test('parses a stack frame with parameters correctly', () {
+      var frame = Frame.parseFirefox(
+          '.foo(12, "@)()/<")@https://example.com/stuff.dart.js:560');
+      expect(frame.uri, equals(Uri.parse('https://example.com/stuff.dart.js')));
+      expect(frame.line, equals(560));
+      expect(frame.column, isNull);
+      expect(frame.member, equals('foo'));
+    });
+
+    test('parses a nested anonymous stack frame with parameters correctly', () {
+      var frame = Frame.parseFirefox(
+        '.foo(12, "@)()/<")/.fn<@https://example.com/stuff.dart.js:560',
+      );
+      expect(frame.uri, equals(Uri.parse('https://example.com/stuff.dart.js')));
+      expect(frame.line, equals(560));
+      expect(frame.column, isNull);
+      expect(frame.member, equals('foo.<fn>'));
+    });
+
+    test(
+        'parses a deeply-nested anonymous stack frame with parameters '
+        'correctly', () {
+      var frame = Frame.parseFirefox('.convertDartClosureToJS/\$function</<@'
+          'https://example.com/stuff.dart.js:560');
+      expect(frame.uri, equals(Uri.parse('https://example.com/stuff.dart.js')));
+      expect(frame.line, equals(560));
+      expect(frame.column, isNull);
+      expect(frame.member, equals('convertDartClosureToJS.<fn>.<fn>'));
+    });
+
+    test('returns an UnparsedFrame for malformed frames', () {
+      expectIsUnparsed(Frame.parseFirefox, '');
+      expectIsUnparsed(Frame.parseFirefox, '.foo');
+      expectIsUnparsed(Frame.parseFirefox, '.foo@dart:async/future.dart');
+      expectIsUnparsed(Frame.parseFirefox, '.foo(@dart:async/future.dart:10');
+      expectIsUnparsed(Frame.parseFirefox, '@dart:async/future.dart');
+    });
+
+    test('parses a simple stack frame correctly', () {
+      var frame =
+          Frame.parseFirefox('foo\$bar@https://dart.dev/foo/bar.dart:10:11');
+      expect(frame.uri, equals(Uri.parse('https://dart.dev/foo/bar.dart')));
+      expect(frame.line, equals(10));
+      expect(frame.column, equals(11));
+      expect(frame.member, equals('foo\$bar'));
+    });
+
+    test('parses an anonymous stack frame correctly', () {
+      var frame = Frame.parseFirefox('https://dart.dev/foo/bar.dart:10:11');
+      expect(frame.uri, equals(Uri.parse('https://dart.dev/foo/bar.dart')));
+      expect(frame.line, equals(10));
+      expect(frame.column, equals(11));
+      expect(frame.member, equals('<fn>'));
+    });
+
+    test('parses a stack frame with no line correctly', () {
+      var frame =
+          Frame.parseFirefox('foo\$bar@https://dart.dev/foo/bar.dart::11');
+      expect(frame.uri, equals(Uri.parse('https://dart.dev/foo/bar.dart')));
+      expect(frame.line, isNull);
+      expect(frame.column, equals(11));
+      expect(frame.member, equals('foo\$bar'));
+    });
+
+    test('parses a stack frame with no column correctly', () {
+      var frame =
+          Frame.parseFirefox('foo\$bar@https://dart.dev/foo/bar.dart:10:');
+      expect(frame.uri, equals(Uri.parse('https://dart.dev/foo/bar.dart')));
+      expect(frame.line, equals(10));
+      expect(frame.column, isNull);
+      expect(frame.member, equals('foo\$bar'));
+    });
+
+    test('parses a stack frame with no line or column correctly', () {
+      var frame =
+          Frame.parseFirefox('foo\$bar@https://dart.dev/foo/bar.dart:10:11');
+      expect(frame.uri, equals(Uri.parse('https://dart.dev/foo/bar.dart')));
+      expect(frame.line, equals(10));
+      expect(frame.column, equals(11));
+      expect(frame.member, equals('foo\$bar'));
+    });
+  });
+
+  group('.parseFriendly', () {
+    test('parses a simple stack frame correctly', () {
+      var frame = Frame.parseFriendly(
+          'https://dart.dev/foo/bar.dart 10:11  Foo.<fn>.bar');
+      expect(frame.uri, equals(Uri.parse('https://dart.dev/foo/bar.dart')));
+      expect(frame.line, equals(10));
+      expect(frame.column, equals(11));
+      expect(frame.member, equals('Foo.<fn>.bar'));
+    });
+
+    test('parses a stack frame with no line or column correctly', () {
+      var frame =
+          Frame.parseFriendly('https://dart.dev/foo/bar.dart  Foo.<fn>.bar');
+      expect(frame.uri, equals(Uri.parse('https://dart.dev/foo/bar.dart')));
+      expect(frame.line, isNull);
+      expect(frame.column, isNull);
+      expect(frame.member, equals('Foo.<fn>.bar'));
+    });
+
+    test('parses a stack frame with no column correctly', () {
+      var frame =
+          Frame.parseFriendly('https://dart.dev/foo/bar.dart 10  Foo.<fn>.bar');
+      expect(frame.uri, equals(Uri.parse('https://dart.dev/foo/bar.dart')));
+      expect(frame.line, equals(10));
+      expect(frame.column, isNull);
+      expect(frame.member, equals('Foo.<fn>.bar'));
+    });
+
+    test('parses a stack frame with a relative path correctly', () {
+      var frame = Frame.parseFriendly('foo/bar.dart 10:11    Foo.<fn>.bar');
+      expect(frame.uri,
+          equals(path.toUri(path.absolute(path.join('foo', 'bar.dart')))));
+      expect(frame.line, equals(10));
+      expect(frame.column, equals(11));
+      expect(frame.member, equals('Foo.<fn>.bar'));
+    });
+
+    test('returns an UnparsedFrame for malformed frames', () {
+      expectIsUnparsed(Frame.parseFriendly, '');
+      expectIsUnparsed(Frame.parseFriendly, 'foo/bar.dart');
+      expectIsUnparsed(Frame.parseFriendly, 'foo/bar.dart 10:11');
+    });
+
+    test('parses a data url stack frame with no line or column correctly', () {
+      var frame = Frame.parseFriendly('data:...  main');
+      expect(frame.uri.scheme, equals('data'));
+      expect(frame.line, isNull);
+      expect(frame.column, isNull);
+      expect(frame.member, equals('main'));
+    });
+
+    test('parses a data url stack frame correctly', () {
+      var frame = Frame.parseFriendly('data:... 10:11    main');
+      expect(frame.uri.scheme, equals('data'));
+      expect(frame.line, equals(10));
+      expect(frame.column, equals(11));
+      expect(frame.member, equals('main'));
+    });
+
+    test('parses a stack frame with spaces in the member name correctly', () {
+      var frame = Frame.parseFriendly(
+          'foo/bar.dart 10:11    (anonymous function).dart.fn');
+      expect(frame.uri,
+          equals(path.toUri(path.absolute(path.join('foo', 'bar.dart')))));
+      expect(frame.line, equals(10));
+      expect(frame.column, equals(11));
+      expect(frame.member, equals('(anonymous function).dart.fn'));
+    });
+
+    test(
+        'parses a stack frame with spaces in the member name and no line or '
+        'column correctly', () {
+      var frame = Frame.parseFriendly(
+          'https://dart.dev/foo/bar.dart  (anonymous function).dart.fn');
+      expect(frame.uri, equals(Uri.parse('https://dart.dev/foo/bar.dart')));
+      expect(frame.line, isNull);
+      expect(frame.column, isNull);
+      expect(frame.member, equals('(anonymous function).dart.fn'));
+    });
+  });
+
+  test('only considers dart URIs to be core', () {
+    bool isCore(String library) =>
+        Frame.parseVM('#0 Foo ($library:0:0)').isCore;
+
+    expect(isCore('dart:core'), isTrue);
+    expect(isCore('dart:async'), isTrue);
+    expect(isCore('dart:core/uri.dart'), isTrue);
+    expect(isCore('dart:async/future.dart'), isTrue);
+    expect(isCore('bart:core'), isFalse);
+    expect(isCore('sdart:core'), isFalse);
+    expect(isCore('darty:core'), isFalse);
+    expect(isCore('bart:core/uri.dart'), isFalse);
+  });
+
+  group('.library', () {
+    test('returns the URI string for non-file URIs', () {
+      expect(Frame.parseVM('#0 Foo (dart:async/future.dart:0:0)').library,
+          equals('dart:async/future.dart'));
+      expect(
+          Frame.parseVM('#0 Foo '
+                  '(https://dart.dev/stuff/thing.dart:0:0)')
+              .library,
+          equals('https://dart.dev/stuff/thing.dart'));
+    });
+
+    test('returns the relative path for file URIs', () {
+      expect(Frame.parseVM('#0 Foo (foo/bar.dart:0:0)').library,
+          equals(path.join('foo', 'bar.dart')));
+    });
+
+    test('truncates legacy data: URIs', () {
+      var frame = Frame.parseVM(
+          '#0 Foo (data:application/dart;charset=utf-8,blah:0:0)');
+      expect(frame.library, equals('data:...'));
+    });
+
+    test('truncates data: URIs', () {
+      var frame = Frame.parseVM(
+          '#0      main (<data:application/dart;charset=utf-8>:1:15)');
+      expect(frame.library, equals('data:...'));
+    });
+  });
+
+  group('.location', () {
+    test(
+        'returns the library and line/column numbers for non-core '
+        'libraries', () {
+      expect(
+          Frame.parseVM('#0 Foo '
+                  '(https://dart.dev/thing.dart:5:10)')
+              .location,
+          equals('https://dart.dev/thing.dart 5:10'));
+      expect(Frame.parseVM('#0 Foo (foo/bar.dart:1:2)').location,
+          equals('${path.join('foo', 'bar.dart')} 1:2'));
+    });
+  });
+
+  group('.package', () {
+    test('returns null for non-package URIs', () {
+      expect(
+          Frame.parseVM('#0 Foo (dart:async/future.dart:0:0)').package, isNull);
+      expect(
+          Frame.parseVM('#0 Foo '
+                  '(https://dart.dev/stuff/thing.dart:0:0)')
+              .package,
+          isNull);
+    });
+
+    test('returns the package name for package: URIs', () {
+      expect(Frame.parseVM('#0 Foo (package:foo/foo.dart:0:0)').package,
+          equals('foo'));
+      expect(Frame.parseVM('#0 Foo (package:foo/zap/bar.dart:0:0)').package,
+          equals('foo'));
+    });
+  });
+
+  group('.toString()', () {
+    test(
+        'returns the library and line/column numbers for non-core '
+        'libraries', () {
+      expect(
+          Frame.parseVM('#0 Foo (https://dart.dev/thing.dart:5:10)').toString(),
+          equals('https://dart.dev/thing.dart 5:10 in Foo'));
+    });
+
+    test('converts "<anonymous closure>" to "<fn>"', () {
+      expect(
+          Frame.parseVM('#0 Foo.<anonymous closure> '
+                  '(dart:core/uri.dart:5:10)')
+              .toString(),
+          equals('dart:core/uri.dart 5:10 in Foo.<fn>'));
+    });
+
+    test('prints a frame without a column correctly', () {
+      expect(Frame.parseVM('#0 Foo (dart:core/uri.dart:5)').toString(),
+          equals('dart:core/uri.dart 5 in Foo'));
+    });
+
+    test('prints relative paths as relative', () {
+      var relative = path.normalize('relative/path/to/foo.dart');
+      expect(Frame.parseFriendly('$relative 5:10  Foo').toString(),
+          equals('$relative 5:10 in Foo'));
+    });
+  });
+
+  test('parses a V8 Wasm frame with a name', () {
+    var frame = Frame.parseV8('    at Error._throwWithCurrentStackTrace '
+        '(wasm://wasm/0006d966:wasm-function[119]:0xbb13)');
+    expect(frame.uri, Uri.parse('wasm://wasm/0006d966'));
+    expect(frame.line, 1);
+    expect(frame.column, 0xbb13 + 1);
+    expect(frame.member, 'Error._throwWithCurrentStackTrace');
+  });
+
+  test('parses a V8 Wasm frame with a name with spaces', () {
+    var frame = Frame.parseV8('   at main tear-off trampoline '
+        '(wasm://wasm/0017fbea:wasm-function[863]:0x23cc8)');
+    expect(frame.uri, Uri.parse('wasm://wasm/0017fbea'));
+    expect(frame.line, 1);
+    expect(frame.column, 0x23cc8 + 1);
+    expect(frame.member, 'main tear-off trampoline');
+  });
+
+  test('parses a V8 Wasm frame with a name with colons and parens', () {
+    var frame = Frame.parseV8('   at a::b::c() '
+        '(https://a.b.com/x/y/z.wasm:wasm-function[66334]:0x12c28ad)');
+    expect(frame.uri, Uri.parse('https://a.b.com/x/y/z.wasm'));
+    expect(frame.line, 1);
+    expect(frame.column, 0x12c28ad + 1);
+    expect(frame.member, 'a::b::c()');
+  });
+
+  test('parses a V8 Wasm frame without a name', () {
+    var frame =
+        Frame.parseV8('    at wasm://wasm/0006d966:wasm-function[119]:0xbb13');
+    expect(frame.uri, Uri.parse('wasm://wasm/0006d966'));
+    expect(frame.line, 1);
+    expect(frame.column, 0xbb13 + 1);
+    expect(frame.member, '119');
+  });
+
+  test('parses a Firefox Wasm frame with a name', () {
+    var frame = Frame.parseFirefox(
+        'g@http://localhost:8080/test.wasm:wasm-function[796]:0x143b4');
+    expect(frame.uri, Uri.parse('http://localhost:8080/test.wasm'));
+    expect(frame.line, 1);
+    expect(frame.column, 0x143b4 + 1);
+    expect(frame.member, 'g');
+  });
+
+  test('parses a Firefox Wasm frame with a name with spaces', () {
+    var frame = Frame.parseFirefox(
+        'main tear-off trampoline@http://localhost:8080/test.wasm:wasm-function[794]:0x14387');
+    expect(frame.uri, Uri.parse('http://localhost:8080/test.wasm'));
+    expect(frame.line, 1);
+    expect(frame.column, 0x14387 + 1);
+    expect(frame.member, 'main tear-off trampoline');
+  });
+
+  test('parses a Firefox Wasm frame without a name', () {
+    var frame = Frame.parseFirefox(
+        '@http://localhost:8080/test.wasm:wasm-function[796]:0x143b4');
+    expect(frame.uri, Uri.parse('http://localhost:8080/test.wasm'));
+    expect(frame.line, 1);
+    expect(frame.column, 0x143b4 + 1);
+    expect(frame.member, '796');
+  });
+
+  test('parses a Safari Wasm frame with a name', () {
+    var frame = Frame.parseSafari('<?>.wasm-function[g]@[wasm code]');
+    expect(frame.uri, Uri.parse('wasm code'));
+    expect(frame.line, null);
+    expect(frame.column, null);
+    expect(frame.member, 'g');
+  });
+
+  test('parses a Safari Wasm frame with a name', () {
+    var frame = Frame.parseSafari(
+        '<?>.wasm-function[main tear-off trampoline]@[wasm code]');
+    expect(frame.uri, Uri.parse('wasm code'));
+    expect(frame.line, null);
+    expect(frame.column, null);
+    expect(frame.member, 'main tear-off trampoline');
+  });
+
+  test('parses a Safari Wasm frame without a name', () {
+    var frame = Frame.parseSafari('<?>.wasm-function[796]@[wasm code]');
+    expect(frame.uri, Uri.parse('wasm code'));
+    expect(frame.line, null);
+    expect(frame.column, null);
+    expect(frame.member, '796');
+  });
+}
+
+void expectIsUnparsed(Frame Function(String) constructor, String text) {
+  var frame = constructor(text);
+  expect(frame, isA<UnparsedFrame>());
+  expect(frame.toString(), equals(text));
+}

diff --git a/pkgs/stack_trace/test/trace_test.dart b/pkgs/stack_trace/test/trace_test.dart
new file mode 100644
index 0000000..e09de95
--- /dev/null
+++ b/pkgs/stack_trace/test/trace_test.dart

@@ -0,0 +1,615 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:path/path.dart' as path;
+import 'package:stack_trace/stack_trace.dart';
+import 'package:test/test.dart';
+
+void main() {
+  // This just shouldn't crash.
+  test('a native stack trace is parseable', Trace.current);
+
+  group('.parse', () {
+    test('.parse parses a V8 stack trace with eval statment correctly', () {
+      var trace = Trace.parse(r'''Error
+    at Object.eval (eval at Foo (main.dart.js:588), <anonymous>:3:47)''');
+      expect(trace.frames[0].uri, Uri.parse('main.dart.js'));
+      expect(trace.frames[0].member, equals('Object.eval'));
+      expect(trace.frames[0].line, equals(588));
+      expect(trace.frames[0].column, isNull);
+    });
+
+    test('.parse parses a VM stack trace correctly', () {
+      var trace = Trace.parse(
+        '#0      Foo._bar (file:///home/nweiz/code/stuff.dart:42:21)\n'
+        '#1      zip.<anonymous closure>.zap (dart:async/future.dart:0:2)\n'
+        '#2      zip.<anonymous closure>.zap (https://pub.dev/thing.dart:1:100)',
+      );
+
+      expect(trace.frames[0].uri,
+          equals(Uri.parse('file:///home/nweiz/code/stuff.dart')));
+      expect(trace.frames[1].uri, equals(Uri.parse('dart:async/future.dart')));
+      expect(
+          trace.frames[2].uri, equals(Uri.parse('https://pub.dev/thing.dart')));
+    });
+
+    test('parses a V8 stack trace correctly', () {
+      var trace = Trace.parse('Error\n'
+          '    at Foo._bar (https://example.com/stuff.js:42:21)\n'
+          '    at https://example.com/stuff.js:0:2\n'
+          '    at zip.<anonymous>.zap '
+          '(https://pub.dev/thing.js:1:100)');
+
+      expect(trace.frames[0].uri,
+          equals(Uri.parse('https://example.com/stuff.js')));
+      expect(trace.frames[1].uri,
+          equals(Uri.parse('https://example.com/stuff.js')));
+      expect(
+          trace.frames[2].uri, equals(Uri.parse('https://pub.dev/thing.js')));
+
+      trace = Trace.parse('Exception: foo\n'
+          '    at Foo._bar (https://example.com/stuff.js:42:21)\n'
+          '    at https://example.com/stuff.js:0:2\n'
+          '    at zip.<anonymous>.zap '
+          '(https://pub.dev/thing.js:1:100)');
+
+      expect(trace.frames[0].uri,
+          equals(Uri.parse('https://example.com/stuff.js')));
+      expect(trace.frames[1].uri,
+          equals(Uri.parse('https://example.com/stuff.js')));
+      expect(
+          trace.frames[2].uri, equals(Uri.parse('https://pub.dev/thing.js')));
+
+      trace = Trace.parse('Exception: foo\n'
+          '    bar\n'
+          '    at Foo._bar (https://example.com/stuff.js:42:21)\n'
+          '    at https://example.com/stuff.js:0:2\n'
+          '    at zip.<anonymous>.zap '
+          '(https://pub.dev/thing.js:1:100)');
+
+      expect(trace.frames[0].uri,
+          equals(Uri.parse('https://example.com/stuff.js')));
+      expect(trace.frames[1].uri,
+          equals(Uri.parse('https://example.com/stuff.js')));
+      expect(
+          trace.frames[2].uri, equals(Uri.parse('https://pub.dev/thing.js')));
+
+      trace = Trace.parse('Exception: foo\n'
+          '    bar\n'
+          '    at Foo._bar (https://example.com/stuff.js:42:21)\n'
+          '    at https://example.com/stuff.js:0:2\n'
+          '    at (anonymous function).zip.zap '
+          '(https://pub.dev/thing.js:1:100)');
+
+      expect(trace.frames[0].uri,
+          equals(Uri.parse('https://example.com/stuff.js')));
+      expect(trace.frames[1].uri,
+          equals(Uri.parse('https://example.com/stuff.js')));
+      expect(trace.frames[1].member, equals('<fn>'));
+      expect(
+          trace.frames[2].uri, equals(Uri.parse('https://pub.dev/thing.js')));
+      expect(trace.frames[2].member, equals('<fn>.zip.zap'));
+    });
+
+    // JavaScriptCore traces are just like V8, except that it doesn't have a
+    // header and it starts with a tab rather than spaces.
+    test('parses a JavaScriptCore stack trace correctly', () {
+      var trace =
+          Trace.parse('\tat Foo._bar (https://example.com/stuff.js:42:21)\n'
+              '\tat https://example.com/stuff.js:0:2\n'
+              '\tat zip.<anonymous>.zap '
+              '(https://pub.dev/thing.js:1:100)');
+
+      expect(trace.frames[0].uri,
+          equals(Uri.parse('https://example.com/stuff.js')));
+      expect(trace.frames[1].uri,
+          equals(Uri.parse('https://example.com/stuff.js')));
+      expect(
+          trace.frames[2].uri, equals(Uri.parse('https://pub.dev/thing.js')));
+
+      trace = Trace.parse('\tat Foo._bar (https://example.com/stuff.js:42:21)\n'
+          '\tat \n'
+          '\tat zip.<anonymous>.zap '
+          '(https://pub.dev/thing.js:1:100)');
+
+      expect(trace.frames[0].uri,
+          equals(Uri.parse('https://example.com/stuff.js')));
+      expect(
+          trace.frames[1].uri, equals(Uri.parse('https://pub.dev/thing.js')));
+    });
+
+    test('parses a Firefox/Safari stack trace correctly', () {
+      var trace = Trace.parse('Foo._bar@https://example.com/stuff.js:42\n'
+          'zip/<@https://example.com/stuff.js:0\n'
+          'zip.zap(12, "@)()/<")@https://pub.dev/thing.js:1');
+
+      expect(trace.frames[0].uri,
+          equals(Uri.parse('https://example.com/stuff.js')));
+      expect(trace.frames[1].uri,
+          equals(Uri.parse('https://example.com/stuff.js')));
+      expect(
+          trace.frames[2].uri, equals(Uri.parse('https://pub.dev/thing.js')));
+
+      trace = Trace.parse('zip/<@https://example.com/stuff.js:0\n'
+          'Foo._bar@https://example.com/stuff.js:42\n'
+          'zip.zap(12, "@)()/<")@https://pub.dev/thing.js:1');
+
+      expect(trace.frames[0].uri,
+          equals(Uri.parse('https://example.com/stuff.js')));
+      expect(trace.frames[1].uri,
+          equals(Uri.parse('https://example.com/stuff.js')));
+      expect(
+          trace.frames[2].uri, equals(Uri.parse('https://pub.dev/thing.js')));
+
+      trace = Trace.parse('zip.zap(12, "@)()/<")@https://pub.dev/thing.js:1\n'
+          'zip/<@https://example.com/stuff.js:0\n'
+          'Foo._bar@https://example.com/stuff.js:42');
+
+      expect(
+          trace.frames[0].uri, equals(Uri.parse('https://pub.dev/thing.js')));
+      expect(trace.frames[1].uri,
+          equals(Uri.parse('https://example.com/stuff.js')));
+      expect(trace.frames[2].uri,
+          equals(Uri.parse('https://example.com/stuff.js')));
+    });
+
+    test('parses a Firefox/Safari stack trace containing native code correctly',
+        () {
+      var trace = Trace.parse('Foo._bar@https://example.com/stuff.js:42\n'
+          'zip/<@https://example.com/stuff.js:0\n'
+          'zip.zap(12, "@)()/<")@https://pub.dev/thing.js:1\n'
+          '[native code]');
+
+      expect(trace.frames[0].uri,
+          equals(Uri.parse('https://example.com/stuff.js')));
+      expect(trace.frames[1].uri,
+          equals(Uri.parse('https://example.com/stuff.js')));
+      expect(
+          trace.frames[2].uri, equals(Uri.parse('https://pub.dev/thing.js')));
+      expect(trace.frames.length, equals(3));
+    });
+
+    test('parses a Firefox/Safari stack trace without a method name correctly',
+        () {
+      var trace = Trace.parse('https://example.com/stuff.js:42\n'
+          'zip/<@https://example.com/stuff.js:0\n'
+          'zip.zap(12, "@)()/<")@https://pub.dev/thing.js:1');
+
+      expect(trace.frames[0].uri,
+          equals(Uri.parse('https://example.com/stuff.js')));
+      expect(trace.frames[0].member, equals('<fn>'));
+      expect(trace.frames[1].uri,
+          equals(Uri.parse('https://example.com/stuff.js')));
+      expect(
+          trace.frames[2].uri, equals(Uri.parse('https://pub.dev/thing.js')));
+    });
+
+    test('parses a Firefox/Safari stack trace with an empty line correctly',
+        () {
+      var trace = Trace.parse('Foo._bar@https://example.com/stuff.js:42\n'
+          '\n'
+          'zip/<@https://example.com/stuff.js:0\n'
+          'zip.zap(12, "@)()/<")@https://pub.dev/thing.js:1');
+
+      expect(trace.frames[0].uri,
+          equals(Uri.parse('https://example.com/stuff.js')));
+      expect(trace.frames[1].uri,
+          equals(Uri.parse('https://example.com/stuff.js')));
+      expect(
+          trace.frames[2].uri, equals(Uri.parse('https://pub.dev/thing.js')));
+    });
+
+    test('parses a Firefox/Safari stack trace with a column number correctly',
+        () {
+      var trace = Trace.parse('Foo._bar@https://example.com/stuff.js:42:2\n'
+          'zip/<@https://example.com/stuff.js:0\n'
+          'zip.zap(12, "@)()/<")@https://pub.dev/thing.js:1');
+
+      expect(trace.frames[0].uri,
+          equals(Uri.parse('https://example.com/stuff.js')));
+      expect(trace.frames[0].line, equals(42));
+      expect(trace.frames[0].column, equals(2));
+      expect(trace.frames[1].uri,
+          equals(Uri.parse('https://example.com/stuff.js')));
+      expect(
+          trace.frames[2].uri, equals(Uri.parse('https://pub.dev/thing.js')));
+    });
+
+    test('parses a package:stack_trace stack trace correctly', () {
+      var trace =
+          Trace.parse('https://dart.dev/foo/bar.dart 10:11  Foo.<fn>.bar\n'
+              'https://dart.dev/foo/baz.dart        Foo.<fn>.bar');
+
+      expect(trace.frames[0].uri,
+          equals(Uri.parse('https://dart.dev/foo/bar.dart')));
+      expect(trace.frames[1].uri,
+          equals(Uri.parse('https://dart.dev/foo/baz.dart')));
+    });
+
+    test('parses a package:stack_trace stack chain correctly', () {
+      var trace =
+          Trace.parse('https://dart.dev/foo/bar.dart 10:11  Foo.<fn>.bar\n'
+              'https://dart.dev/foo/baz.dart        Foo.<fn>.bar\n'
+              '===== asynchronous gap ===========================\n'
+              'https://dart.dev/foo/bang.dart 10:11  Foo.<fn>.bar\n'
+              'https://dart.dev/foo/quux.dart        Foo.<fn>.bar');
+
+      expect(trace.frames[0].uri,
+          equals(Uri.parse('https://dart.dev/foo/bar.dart')));
+      expect(trace.frames[1].uri,
+          equals(Uri.parse('https://dart.dev/foo/baz.dart')));
+      expect(trace.frames[2].uri,
+          equals(Uri.parse('https://dart.dev/foo/bang.dart')));
+      expect(trace.frames[3].uri,
+          equals(Uri.parse('https://dart.dev/foo/quux.dart')));
+    });
+
+    test('parses a package:stack_trace stack chain with end gap correctly', () {
+      var trace = Trace.parse(
+        'https://dart.dev/foo/bar.dart 10:11  Foo.<fn>.bar\n'
+        'https://dart.dev/foo/baz.dart        Foo.<fn>.bar\n'
+        'https://dart.dev/foo/bang.dart 10:11  Foo.<fn>.bar\n'
+        'https://dart.dev/foo/quux.dart        Foo.<fn>.bar===== asynchronous gap ===========================\n',
+      );
+
+      expect(trace.frames.length, 4);
+      expect(trace.frames[0].uri,
+          equals(Uri.parse('https://dart.dev/foo/bar.dart')));
+      expect(trace.frames[1].uri,
+          equals(Uri.parse('https://dart.dev/foo/baz.dart')));
+      expect(trace.frames[2].uri,
+          equals(Uri.parse('https://dart.dev/foo/bang.dart')));
+      expect(trace.frames[3].uri,
+          equals(Uri.parse('https://dart.dev/foo/quux.dart')));
+    });
+
+    test('parses a real package:stack_trace stack trace correctly', () {
+      var traceString = Trace.current().toString();
+      expect(Trace.parse(traceString).toString(), equals(traceString));
+    });
+
+    test('parses an empty string correctly', () {
+      var trace = Trace.parse('');
+      expect(trace.frames, isEmpty);
+      expect(trace.toString(), equals(''));
+    });
+
+    test('parses trace with async gap correctly', () {
+      var trace = Trace.parse('#0      bop (file:///pull.dart:42:23)\n'
+          '<asynchronous suspension>\n'
+          '#1      twist (dart:the/future.dart:0:2)\n'
+          '#2      main (dart:my/file.dart:4:6)\n');
+
+      expect(trace.frames.length, 3);
+      expect(trace.frames[0].uri, equals(Uri.parse('file:///pull.dart')));
+      expect(trace.frames[1].uri, equals(Uri.parse('dart:the/future.dart')));
+      expect(trace.frames[2].uri, equals(Uri.parse('dart:my/file.dart')));
+    });
+
+    test('parses trace with async gap at end correctly', () {
+      var trace = Trace.parse('#0      bop (file:///pull.dart:42:23)\n'
+          '#1      twist (dart:the/future.dart:0:2)\n'
+          '<asynchronous suspension>\n');
+
+      expect(trace.frames.length, 2);
+      expect(trace.frames[0].uri, equals(Uri.parse('file:///pull.dart')));
+      expect(trace.frames[1].uri, equals(Uri.parse('dart:the/future.dart')));
+    });
+
+    test('parses a V8 stack frace with Wasm frames correctly', () {
+      var trace = Trace.parse(
+          '\tat Error._throwWithCurrentStackTrace (wasm://wasm/0006d892:wasm-function[119]:0xbaf8)\n'
+          '\tat main (wasm://wasm/0006d892:wasm-function[792]:0x14378)\n'
+          '\tat main tear-off trampoline (wasm://wasm/0006d892:wasm-function[794]:0x14387)\n'
+          '\tat _invokeMain (wasm://wasm/0006d892:wasm-function[70]:0xa56c)\n'
+          '\tat InstantiatedApp.invokeMain (/home/user/test.mjs:361:37)\n'
+          '\tat main (/home/user/run_wasm.js:416:21)\n'
+          '\tat async action (/home/user/run_wasm.js:353:38)\n'
+          '\tat async eventLoop (/home/user/run_wasm.js:329:9)');
+
+      expect(trace.frames.length, 8);
+
+      for (final frame in trace.frames) {
+        expect(frame is UnparsedFrame, false);
+      }
+
+      expect(trace.frames[0].uri, Uri.parse('wasm://wasm/0006d892'));
+      expect(trace.frames[0].line, 1);
+      expect(trace.frames[0].column, 0xbaf8 + 1);
+      expect(trace.frames[0].member, 'Error._throwWithCurrentStackTrace');
+
+      expect(trace.frames[4].uri, Uri.parse('file:///home/user/test.mjs'));
+      expect(trace.frames[4].line, 361);
+      expect(trace.frames[4].column, 37);
+      expect(trace.frames[4].member, 'InstantiatedApp.invokeMain');
+
+      expect(trace.frames[5].uri, Uri.parse('file:///home/user/run_wasm.js'));
+      expect(trace.frames[5].line, 416);
+      expect(trace.frames[5].column, 21);
+      expect(trace.frames[5].member, 'main');
+    });
+
+    test('parses Firefox stack frace with Wasm frames correctly', () {
+      var trace = Trace.parse(
+          'Error._throwWithCurrentStackTrace@http://localhost:8080/test.wasm:wasm-function[119]:0xbaf8\n'
+          'main@http://localhost:8080/test.wasm:wasm-function[792]:0x14378\n'
+          'main tear-off trampoline@http://localhost:8080/test.wasm:wasm-function[794]:0x14387\n'
+          '_invokeMain@http://localhost:8080/test.wasm:wasm-function[70]:0xa56c\n'
+          'invoke@http://localhost:8080/test.mjs:48:26');
+
+      expect(trace.frames.length, 5);
+
+      for (final frame in trace.frames) {
+        expect(frame is UnparsedFrame, false);
+      }
+
+      expect(trace.frames[0].uri, Uri.parse('http://localhost:8080/test.wasm'));
+      expect(trace.frames[0].line, 1);
+      expect(trace.frames[0].column, 0xbaf8 + 1);
+      expect(trace.frames[0].member, 'Error._throwWithCurrentStackTrace');
+
+      expect(trace.frames[4].uri, Uri.parse('http://localhost:8080/test.mjs'));
+      expect(trace.frames[4].line, 48);
+      expect(trace.frames[4].column, 26);
+      expect(trace.frames[4].member, 'invoke');
+    });
+
+    test('parses JSShell stack frace with Wasm frames correctly', () {
+      var trace = Trace.parse(
+          'Error._throwWithCurrentStackTrace@/home/user/test.mjs line 29 > WebAssembly.compile:wasm-function[119]:0xbaf8\n'
+          'main@/home/user/test.mjs line 29 > WebAssembly.compile:wasm-function[792]:0x14378\n'
+          'main tear-off trampoline@/home/user/test.mjs line 29 > WebAssembly.compile:wasm-function[794]:0x14387\n'
+          '_invokeMain@/home/user/test.mjs line 29 > WebAssembly.compile:wasm-function[70]:0xa56c\n'
+          'invokeMain@/home/user/test.mjs:361:37\n'
+          'main@/home/user/run_wasm.js:416:21\n'
+          'async*action@/home/user/run_wasm.js:353:44\n'
+          'eventLoop@/home/user/run_wasm.js:329:15\n'
+          'self.dartMainRunner@/home/user/run_wasm.js:354:14\n'
+          '@/home/user/run_wasm.js:419:15');
+
+      expect(trace.frames.length, 10);
+
+      for (final frame in trace.frames) {
+        expect(frame is UnparsedFrame, false);
+      }
+
+      expect(trace.frames[0].uri, Uri.parse('file:///home/user/test.mjs'));
+      expect(trace.frames[0].line, 1);
+      expect(trace.frames[0].column, 0xbaf8 + 1);
+      expect(trace.frames[0].member, 'Error._throwWithCurrentStackTrace');
+
+      expect(trace.frames[4].uri, Uri.parse('file:///home/user/test.mjs'));
+      expect(trace.frames[4].line, 361);
+      expect(trace.frames[4].column, 37);
+      expect(trace.frames[4].member, 'invokeMain');
+
+      expect(trace.frames[9].uri, Uri.parse('file:///home/user/run_wasm.js'));
+      expect(trace.frames[9].line, 419);
+      expect(trace.frames[9].column, 15);
+      expect(trace.frames[9].member, '<fn>');
+    });
+
+    test('parses Safari stack frace with Wasm frames correctly', () {
+      var trace = Trace.parse(
+          '<?>.wasm-function[Error._throwWithCurrentStackTrace]@[wasm code]\n'
+          '<?>.wasm-function[main]@[wasm code]\n'
+          '<?>.wasm-function[main tear-off trampoline]@[wasm code]\n'
+          '<?>.wasm-function[_invokeMain]@[wasm code]\n'
+          'invokeMain@/home/user/test.mjs:361:48\n'
+          '@/home/user/run_wasm.js:416:31');
+
+      expect(trace.frames.length, 6);
+
+      for (final frame in trace.frames) {
+        expect(frame is UnparsedFrame, false);
+      }
+
+      expect(trace.frames[0].uri, Uri.parse('wasm code'));
+      expect(trace.frames[0].line, null);
+      expect(trace.frames[0].column, null);
+      expect(trace.frames[0].member, 'Error._throwWithCurrentStackTrace');
+
+      expect(trace.frames[4].uri, Uri.parse('file:///home/user/test.mjs'));
+      expect(trace.frames[4].line, 361);
+      expect(trace.frames[4].column, 48);
+      expect(trace.frames[4].member, 'invokeMain');
+
+      expect(trace.frames[5].uri, Uri.parse('file:///home/user/run_wasm.js'));
+      expect(trace.frames[5].line, 416);
+      expect(trace.frames[5].column, 31);
+      expect(trace.frames[5].member, '<fn>');
+    });
+  });
+
+  test('.toString() nicely formats the stack trace', () {
+    var trace = Trace.parse('''
+#0      Foo._bar (foo/bar.dart:42:21)
+#1      zip.<anonymous closure>.zap (dart:async/future.dart:0:2)
+#2      zip.<anonymous closure>.zap (https://pub.dev/thing.dart:1:100)
+''');
+
+    expect(trace.toString(), equals('''
+${path.join('foo', 'bar.dart')} 42:21                Foo._bar
+dart:async/future.dart 0:2        zip.<fn>.zap
+https://pub.dev/thing.dart 1:100  zip.<fn>.zap
+'''));
+  });
+
+  test('.vmTrace returns a native-style trace', () {
+    var uri = path.toUri(path.absolute('foo'));
+    var trace = Trace([
+      Frame(uri, 10, 20, 'Foo.<fn>'),
+      Frame(Uri.parse('https://dart.dev/foo.dart'), null, null, 'bar'),
+      Frame(Uri.parse('dart:async'), 15, null, 'baz'),
+    ]);
+
+    expect(
+        trace.vmTrace.toString(),
+        equals('#1      Foo.<anonymous closure> ($uri:10:20)\n'
+            '#2      bar (https://dart.dev/foo.dart:0:0)\n'
+            '#3      baz (dart:async:15:0)\n'));
+  });
+
+  group('folding', () {
+    group('.terse', () {
+      test('folds core frames together bottom-up', () {
+        var trace = Trace.parse('''
+#1 top (dart:async/future.dart:0:2)
+#2 bottom (dart:core/uri.dart:1:100)
+#0 notCore (foo.dart:42:21)
+#3 top (dart:io:5:10)
+#4 bottom (dart:async-patch/future.dart:9:11)
+#5 alsoNotCore (bar.dart:10:20)
+''');
+
+        expect(trace.terse.toString(), equals('''
+dart:core       bottom
+foo.dart 42:21  notCore
+dart:async      bottom
+bar.dart 10:20  alsoNotCore
+'''));
+      });
+
+      test('folds empty async frames', () {
+        var trace = Trace.parse('''
+#0 top (dart:async/future.dart:0:2)
+#1 empty.<<anonymous closure>_async_body> (bar.dart)
+#2 bottom (dart:async-patch/future.dart:9:11)
+#3 notCore (foo.dart:42:21)
+''');
+
+        expect(trace.terse.toString(), equals('''
+dart:async      bottom
+foo.dart 42:21  notCore
+'''));
+      });
+
+      test('removes the bottom-most async frame', () {
+        var trace = Trace.parse('''
+#0 notCore (foo.dart:42:21)
+#1 top (dart:async/future.dart:0:2)
+#2 bottom (dart:core/uri.dart:1:100)
+#3 top (dart:io:5:10)
+#4 bottom (dart:async-patch/future.dart:9:11)
+''');
+
+        expect(trace.terse.toString(), equals('''
+foo.dart 42:21  notCore
+'''));
+      });
+
+      test("won't make a trace empty", () {
+        var trace = Trace.parse('''
+#1 top (dart:async/future.dart:0:2)
+#2 bottom (dart:core/uri.dart:1:100)
+''');
+
+        expect(trace.terse.toString(), equals('''
+dart:core  bottom
+'''));
+      });
+
+      test("won't panic on an empty trace", () {
+        expect(Trace.parse('').terse.toString(), equals(''));
+      });
+    });
+
+    group('.foldFrames', () {
+      test('folds frames together bottom-up', () {
+        var trace = Trace.parse('''
+#0 notFoo (foo.dart:42:21)
+#1 fooTop (bar.dart:0:2)
+#2 fooBottom (foo.dart:1:100)
+#3 alsoNotFoo (bar.dart:10:20)
+#4 fooTop (dart:io/socket.dart:5:10)
+#5 fooBottom (dart:async-patch/future.dart:9:11)
+''');
+
+        var folded =
+            trace.foldFrames((frame) => frame.member!.startsWith('foo'));
+        expect(folded.toString(), equals('''
+foo.dart 42:21                     notFoo
+foo.dart 1:100                     fooBottom
+bar.dart 10:20                     alsoNotFoo
+dart:async-patch/future.dart 9:11  fooBottom
+'''));
+      });
+
+      test('will never fold unparsed frames', () {
+        var trace = Trace.parse(r'''
+.g"cs$#:b";a#>sw{*{ul$"$xqwr`p
+%+j-?uppx<([j@#nu{{>*+$%x-={`{
+!e($b{nj)zs?cgr%!;bmw.+$j+pfj~
+''');
+
+        expect(trace.foldFrames((frame) => true).toString(), equals(r'''
+.g"cs$#:b";a#>sw{*{ul$"$xqwr`p
+%+j-?uppx<([j@#nu{{>*+$%x-={`{
+!e($b{nj)zs?cgr%!;bmw.+$j+pfj~
+'''));
+      });
+
+      group('with terse: true', () {
+        test('folds core frames as well', () {
+          var trace = Trace.parse('''
+#0 notFoo (foo.dart:42:21)
+#1 fooTop (bar.dart:0:2)
+#2 coreBottom (dart:async/future.dart:0:2)
+#3 alsoNotFoo (bar.dart:10:20)
+#4 fooTop (foo.dart:9:11)
+#5 coreBottom (dart:async-patch/future.dart:9:11)
+''');
+
+          var folded = trace.foldFrames(
+              (frame) => frame.member!.startsWith('foo'),
+              terse: true);
+          expect(folded.toString(), equals('''
+foo.dart 42:21  notFoo
+dart:async      coreBottom
+bar.dart 10:20  alsoNotFoo
+'''));
+        });
+
+        test('shortens folded frames', () {
+          var trace = Trace.parse('''
+#0 notFoo (foo.dart:42:21)
+#1 fooTop (bar.dart:0:2)
+#2 fooBottom (package:foo/bar.dart:0:2)
+#3 alsoNotFoo (bar.dart:10:20)
+#4 fooTop (foo.dart:9:11)
+#5 fooBottom (foo/bar.dart:9:11)
+#6 againNotFoo (bar.dart:20:20)
+''');
+
+          var folded = trace.foldFrames(
+              (frame) => frame.member!.startsWith('foo'),
+              terse: true);
+          expect(folded.toString(), equals('''
+foo.dart 42:21  notFoo
+package:foo     fooBottom
+bar.dart 10:20  alsoNotFoo
+foo             fooBottom
+bar.dart 20:20  againNotFoo
+'''));
+        });
+
+        test('removes the bottom-most folded frame', () {
+          var trace = Trace.parse('''
+#2 fooTop (package:foo/bar.dart:0:2)
+#3 notFoo (bar.dart:10:20)
+#5 fooBottom (foo/bar.dart:9:11)
+''');
+
+          var folded = trace.foldFrames(
+              (frame) => frame.member!.startsWith('foo'),
+              terse: true);
+          expect(folded.toString(), equals('''
+package:foo     fooTop
+bar.dart 10:20  notFoo
+'''));
+        });
+      });
+    });
+  });
+}

diff --git a/pkgs/stack_trace/test/utils.dart b/pkgs/stack_trace/test/utils.dart
new file mode 100644
index 0000000..98cb5ed
--- /dev/null
+++ b/pkgs/stack_trace/test/utils.dart

@@ -0,0 +1,14 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:stack_trace/stack_trace.dart';
+import 'package:test/test.dart';
+
+/// Returns a matcher that runs [matcher] against a [Frame]'s `member` field.
+Matcher frameMember(Object? matcher) =>
+    isA<Frame>().having((p0) => p0.member, 'member', matcher);
+
+/// Returns a matcher that runs [matcher] against a [Frame]'s `library` field.
+Matcher frameLibrary(Object? matcher) =>
+    isA<Frame>().having((p0) => p0.library, 'library', matcher);

diff --git a/pkgs/stack_trace/test/vm_test.dart b/pkgs/stack_trace/test/vm_test.dart
new file mode 100644
index 0000000..70ac014
--- /dev/null
+++ b/pkgs/stack_trace/test/vm_test.dart

@@ -0,0 +1,112 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// This file tests stack_trace's ability to parse live stack traces. It's a
+/// dual of dartium_test.dart, since method names can differ somewhat from
+/// platform to platform. No similar file exists for dart2js since the specific
+/// method names there are implementation details.
+@TestOn('vm')
+library;
+
+import 'package:path/path.dart' as path;
+import 'package:stack_trace/stack_trace.dart';
+import 'package:test/test.dart';
+
+// The name of this (trivial) function is verified as part of the test
+String getStackTraceString() => StackTrace.current.toString();
+
+// The name of this (trivial) function is verified as part of the test
+StackTrace getStackTraceObject() => StackTrace.current;
+
+Frame getCaller([int? level]) {
+  if (level == null) return Frame.caller();
+  return Frame.caller(level);
+}
+
+Frame nestedGetCaller(int level) => getCaller(level);
+
+Trace getCurrentTrace([int level = 0]) => Trace.current(level);
+
+Trace nestedGetCurrentTrace(int level) => getCurrentTrace(level);
+
+void main() {
+  group('Trace', () {
+    test('.parse parses a real stack trace correctly', () {
+      var string = getStackTraceString();
+      var trace = Trace.parse(string);
+      expect(path.url.basename(trace.frames.first.uri.path),
+          equals('vm_test.dart'));
+      expect(trace.frames.first.member, equals('getStackTraceString'));
+    });
+
+    test('converts from a native stack trace correctly', () {
+      var trace = Trace.from(getStackTraceObject());
+      expect(path.url.basename(trace.frames.first.uri.path),
+          equals('vm_test.dart'));
+      expect(trace.frames.first.member, equals('getStackTraceObject'));
+    });
+
+    test('.from handles a stack overflow trace correctly', () {
+      void overflow() => overflow();
+
+      late Trace? trace;
+      try {
+        overflow();
+      } catch (_, stackTrace) {
+        trace = Trace.from(stackTrace);
+      }
+
+      expect(trace!.frames.first.member, equals('main.<fn>.<fn>.overflow'));
+    });
+
+    group('.current()', () {
+      test('with no argument returns a trace starting at the current frame',
+          () {
+        var trace = Trace.current();
+        expect(trace.frames.first.member, equals('main.<fn>.<fn>.<fn>'));
+      });
+
+      test('at level 0 returns a trace starting at the current frame', () {
+        var trace = Trace.current();
+        expect(trace.frames.first.member, equals('main.<fn>.<fn>.<fn>'));
+      });
+
+      test('at level 1 returns a trace starting at the parent frame', () {
+        var trace = getCurrentTrace(1);
+        expect(trace.frames.first.member, equals('main.<fn>.<fn>.<fn>'));
+      });
+
+      test('at level 2 returns a trace starting at the grandparent frame', () {
+        var trace = nestedGetCurrentTrace(2);
+        expect(trace.frames.first.member, equals('main.<fn>.<fn>.<fn>'));
+      });
+
+      test('throws an ArgumentError for negative levels', () {
+        expect(() => Trace.current(-1), throwsArgumentError);
+      });
+    });
+  });
+
+  group('Frame.caller()', () {
+    test('with no argument returns the parent frame', () {
+      expect(getCaller().member, equals('main.<fn>.<fn>'));
+    });
+
+    test('at level 0 returns the current frame', () {
+      expect(getCaller(0).member, equals('getCaller'));
+    });
+
+    test('at level 1 returns the current frame', () {
+      expect(getCaller(1).member, equals('main.<fn>.<fn>'));
+    });
+
+    test('at level 2 returns the grandparent frame', () {
+      expect(nestedGetCaller(2).member, equals('main.<fn>.<fn>'));
+    });
+
+    test('throws an ArgumentError for negative levels', () {
+      expect(() => Frame.caller(-1), throwsArgumentError);
+    });
+  });
+}

diff --git a/pkgs/stream_channel/.gitignore b/pkgs/stream_channel/.gitignore
new file mode 100644
index 0000000..1447012
--- /dev/null
+++ b/pkgs/stream_channel/.gitignore

@@ -0,0 +1,10 @@
+.buildlog
+.dart_tool/
+.DS_Store
+.idea
+.pub/
+.settings/
+build/
+packages
+.packages
+pubspec.lock

diff --git a/pkgs/stream_channel/AUTHORS b/pkgs/stream_channel/AUTHORS
new file mode 100644
index 0000000..e8063a8
--- /dev/null
+++ b/pkgs/stream_channel/AUTHORS

@@ -0,0 +1,6 @@
+# Below is a list of people and organizations that have contributed
+# to the project. Names should be added to the list like so:
+#
+#   Name/Organization <email address>
+
+Google Inc.

diff --git a/pkgs/stream_channel/CHANGELOG.md b/pkgs/stream_channel/CHANGELOG.md
new file mode 100644
index 0000000..9dd3990
--- /dev/null
+++ b/pkgs/stream_channel/CHANGELOG.md

@@ -0,0 +1,162 @@
+## 2.1.4
+
+* Fix `StreamChannelMixin` so that it can be used as a mixin again.
+
+## 2.1.3
+
+* Require Dart 3.3
+* Move to `dart-lang/tools` monorepo.
+
+## 2.1.2
+
+* Require Dart 2.19
+* Add an example.
+* Fix a race condition in `IsolateChannel.connectReceive()` where the channel
+  could hang forever if its sink was closed before the connection was established.
+
+## 2.1.1
+
+* Require Dart 2.14
+* Populate the pubspec `repository` field.
+* Handle multichannel messages where the ID element is a `double` at runtime
+  instead of an `int`. When reading an array with `dart2wasm` numbers within the
+  array are parsed as `double`.
+
+## 2.1.0
+
+* Stable release for null safety.
+
+## 2.0.0
+
+**Breaking changes**
+
+* `IsolateChannel` requires a separate import
+  `package:stram_channel/isolate_channel.dart`.
+  `package:stream_channel/stream_channel.dart` will now not trigger any platform
+  concerns due to importing `dart:isolate`.
+* Remove `JsonDocumentTransformer` class. The `jsonDocument` top level is still
+  available.
+* Remove `StreamChannelTransformer.typed`. Use `.cast` on the transformed
+  channel instead.
+* Change `Future<dynamic>` returns to `Future<void>`.
+
+## 1.7.0
+
+* Make `IsolateChannel` available through
+  `package:stream_channel/isolate_channel.dart`. This will be the required
+  import in the next release.
+* Require `2.0.0` or newer SDK.
+* Internal style changes.
+
+## 1.6.8
+
+* Set max SDK version to `<3.0.0`, and adjust other dependencies.
+
+## 1.6.7+1
+
+* Fix Dart 2 runtime types in `IsolateChannel`.
+
+## 1.6.7
+
+* Update SDK version to 2.0.0-dev.17.0.
+* Add a type argument to `MultiChannel`.
+
+## 1.6.6
+
+* Fix a Dart 2 issue with inner stream transformation in `GuaranteeChannel`.
+
+* Fix a Dart 2 issue with `StreamChannelTransformer.fromCodec()`.
+
+## 1.6.5
+
+* Fix an issue with `JsonDocumentTransformer.bind` where it created an internal
+  stream channel which didn't get a properly inferred type for its `sink`.
+
+## 1.6.4
+
+* Fix a race condition in `MultiChannel` where messages from a remote virtual
+  channel could get dropped if the corresponding local channel wasn't registered
+  quickly enough.
+
+## 1.6.3
+
+* Use `pumpEventQueue()` from test.
+
+## 1.6.2
+
+* Declare support for `async` 2.0.0.
+
+## 1.6.1
+
+* Fix the type of `StreamChannel.transform()`. This previously inverted the
+  generic parameters, so it only really worked with transformers where both
+  generic types were identical.
+
+## 1.6.0
+
+* `Disconnector.disconnect()` now returns a future that completes when all the
+  inner `StreamSink.close()` futures have completed.
+
+## 1.5.0
+
+* Add `new StreamChannel.withCloseGuarantee()` to provide the specific guarantee
+  that closing the sink causes the stream to close before it emits any more
+  events. This is the only guarantee that isn't automatically preserved when
+  transforming a channel.
+
+* `StreamChannelTransformer`s provided by the `stream_channel` package now
+  properly provide the guarantee that closing the sink causes the stream to
+  close before it emits any more events
+
+## 1.4.0
+
+* Add `StreamChannel.cast()`, which soundly coerces the generic type of a
+  channel.
+
+* Add `StreamChannelTransformer.typed()`, which soundly coerces the generic type
+  of a transformer.
+
+## 1.3.2
+
+* Fix all strong-mode errors and warnings.
+
+## 1.3.1
+
+* Make `IsolateChannel` slightly more efficient.
+
+* Make `MultiChannel` follow the stream channel rules.
+
+## 1.3.0
+
+* Add `Disconnector`, a transformer that allows the caller to disconnect the
+  transformed channel.
+
+## 1.2.0
+
+* Add `new StreamChannel.withGuarantees()`, which creates a channel with extra
+  wrapping to ensure that it obeys the stream channel guarantees.
+
+* Add `StreamChannelController`, which can be used to create custom
+  `StreamChannel` objects.
+
+## 1.1.1
+
+* Fix the type annotation for `StreamChannel.transform()`'s parameter.
+
+## 1.1.0
+
+* Add `StreamChannel.transformStream()`, `StreamChannel.transformSink()`,
+  `StreamChannel.changeStream()`, and `StreamChannel.changeSink()` to support
+  changing only the stream or only the sink of a channel.
+
+* Be more explicit about `JsonDocumentTransformer`'s error-handling behavior.
+
+## 1.0.1
+
+* Fix `MultiChannel`'s constructor to take a `StreamChannel`. This is
+  technically a breaking change, but since 1.0.0 was only released an hour ago,
+  we're treating it as a bug fix.
+
+## 1.0.0
+
+* Initial version

diff --git a/pkgs/stream_channel/LICENSE b/pkgs/stream_channel/LICENSE
new file mode 100644
index 0000000..dbd2843
--- /dev/null
+++ b/pkgs/stream_channel/LICENSE

@@ -0,0 +1,27 @@
+Copyright 2015, the Dart project authors. 
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+    * Neither the name of Google LLC nor the names of its
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

diff --git a/pkgs/stream_channel/README.md b/pkgs/stream_channel/README.md
new file mode 100644
index 0000000..3677ccf
--- /dev/null
+++ b/pkgs/stream_channel/README.md

@@ -0,0 +1,20 @@
+[![Build Status](https://github.com/dart-lang/tools/actions/workflows/stream_channel.yaml/badge.svg)](https://github.com/dart-lang/tools/actions/workflows/stream_channel.yaml)
+[![pub package](https://img.shields.io/pub/v/stream_channel.svg)](https://pub.dev/packages/stream_channel)
+[![package publisher](https://img.shields.io/pub/publisher/stream_channel.svg)](https://pub.dev/packages/stream_channel/publisher)
+
+This package exposes the `StreamChannel` interface, which represents a two-way
+communication channel. Each `StreamChannel` exposes a `Stream` for receiving
+data and a `StreamSink` for sending it. 
+
+`StreamChannel` helps abstract communication logic away from the underlying
+protocol. For example, the [`test`][test] package re-uses its test suite
+communication protocol for both WebSocket connections to browser suites and
+Isolate connections to VM tests.
+
+[test]: https://pub.dev/packages/test
+
+This package also contains utilities for dealing with `StreamChannel`s and with
+two-way communications in general. For documentation of these utilities, see
+[the API docs][api].
+
+[api]: https://pub.dev/documentation/stream_channel/latest/

diff --git a/pkgs/stream_channel/analysis_options.yaml b/pkgs/stream_channel/analysis_options.yaml
new file mode 100644
index 0000000..44cda4d
--- /dev/null
+++ b/pkgs/stream_channel/analysis_options.yaml

@@ -0,0 +1,5 @@
+include: package:dart_flutter_team_lints/analysis_options.yaml
+
+analyzer:
+  language:
+    strict-casts: true

diff --git a/pkgs/stream_channel/example/example.dart b/pkgs/stream_channel/example/example.dart
new file mode 100644
index 0000000..b41d8d9
--- /dev/null
+++ b/pkgs/stream_channel/example/example.dart

@@ -0,0 +1,110 @@
+// Copyright (c) 2023, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+import 'dart:convert';
+import 'dart:io';
+import 'dart:isolate';
+
+import 'package:stream_channel/isolate_channel.dart';
+import 'package:stream_channel/stream_channel.dart';
+
+Future<void> main() async {
+  // A StreamChannel<T>, is in simplest terms, a wrapper around a Stream<T> and
+  // a StreamSink<T>. For example, you can create a channel that wraps standard
+  // IO:
+  var stdioChannel = StreamChannel(stdin, stdout);
+  stdioChannel.sink.add('Hello!\n'.codeUnits);
+
+  // Like a Stream<T> can be transformed with a StreamTransformer<T>, a
+  // StreamChannel<T> can be transformed with a StreamChannelTransformer<T>.
+  // For example, we can handle standard input as strings:
+  var stringChannel = stdioChannel
+      .transform(StreamChannelTransformer.fromCodec(utf8))
+      .transformStream(const LineSplitter());
+  stringChannel.sink.add('world!\n');
+
+  // You can implement StreamChannel<T> by extending StreamChannelMixin<T>, but
+  // it's much easier to use a StreamChannelController<T>. A controller has two
+  // StreamChannel<T> members: `local` and `foreign`. The creator of a
+  // controller should work with the `local` channel, while the recipient should
+  // work with the `foreign` channel, and usually will not have direct access to
+  // the underlying controller.
+  var ctrl = StreamChannelController<String>();
+  ctrl.local.stream.listen((event) {
+    // Do something useful here...
+  });
+
+  // You can also pipe events from one channel to another.
+  ctrl
+    ..foreign.pipe(stringChannel)
+    ..local.sink.add('Piped!\n');
+  await ctrl.local.sink.close();
+
+  // The StreamChannel<T> interface provides several guarantees, which can be
+  // found here:
+  // https://pub.dev/documentation/stream_channel/latest/stream_channel/StreamChannel-class.html
+  //
+  // By calling `StreamChannel<T>.withGuarantees()`, you can create a
+  // StreamChannel<T> that provides all guarantees.
+  var dummyCtrl0 = StreamChannelController<String>();
+  var guaranteedChannel = StreamChannel.withGuarantees(
+      dummyCtrl0.foreign.stream, dummyCtrl0.foreign.sink);
+
+  // To close a StreamChannel, use `sink.close()`.
+  await guaranteedChannel.sink.close();
+
+  // A MultiChannel<T> multiplexes multiple virtual channels across a single
+  // underlying transport layer. For example, an application listening over
+  // standard I/O can still support multiple clients if it has a mechanism to
+  // separate events from different clients.
+  //
+  // A MultiChannel<T> splits events into numbered channels, which are
+  // instances of VirtualChannel<T>.
+  var dummyCtrl1 = StreamChannelController<String>();
+  var multiChannel = MultiChannel<String>(dummyCtrl1.foreign);
+  var channel1 = multiChannel.virtualChannel();
+  await multiChannel.sink.close();
+
+  // The client/peer should also create its own MultiChannel<T>, connected to
+  // the underlying transport, use the corresponding ID's to handle events in
+  // their respective channels. It is up to you how to communicate channel ID's
+  // across different endpoints.
+  var dummyCtrl2 = StreamChannelController<String>();
+  var multiChannel2 = MultiChannel<String>(dummyCtrl2.foreign);
+  var channel2 = multiChannel2.virtualChannel(channel1.id);
+  await channel2.sink.close();
+  await multiChannel2.sink.close();
+
+  // Multiple instances of a Dart application can communicate easily across
+  // `SendPort`/`ReceivePort` pairs by means of the `IsolateChannel<T>` class.
+  // Typically, one endpoint will create a `ReceivePort`, and call the
+  // `IsolateChannel.connectReceive` constructor. The other endpoint will be
+  // given the corresponding `SendPort`, and then call
+  // `IsolateChannel.connectSend`.
+  var recv = ReceivePort();
+  var recvChannel = IsolateChannel<void>.connectReceive(recv);
+  var sendChannel = IsolateChannel<void>.connectSend(recv.sendPort);
+
+  // You must manually close `IsolateChannel<T>` sinks, however.
+  await recvChannel.sink.close();
+  await sendChannel.sink.close();
+
+  // You can use the `Disconnector` transformer to cause a channel to act as
+  // though the remote end of its transport had disconnected.
+  var disconnector = Disconnector<String>();
+  var disconnectable = stringChannel.transform(disconnector);
+  disconnectable.sink.add('Still connected!');
+  await disconnector.disconnect();
+
+  // Additionally:
+  //   * The `DelegatingStreamController<T>` class can be extended to build a
+  //     basis for wrapping other `StreamChannel<T>` objects.
+  //   * The `jsonDocument` transformer converts events to/from JSON, using
+  //     the `json` codec from `dart:convert`.
+  //   * `package:json_rpc_2` directly builds on top of
+  //     `package:stream_channel`, so any compatible transport can be used to
+  //      create interactive client/server or peer-to-peer applications (i.e.
+  //      language servers, microservices, etc.
+}

diff --git a/pkgs/stream_channel/lib/isolate_channel.dart b/pkgs/stream_channel/lib/isolate_channel.dart
new file mode 100644
index 0000000..5d9f6e1
--- /dev/null
+++ b/pkgs/stream_channel/lib/isolate_channel.dart

@@ -0,0 +1,5 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+export 'src/isolate_channel.dart' show IsolateChannel;

diff --git a/pkgs/stream_channel/lib/src/close_guarantee_channel.dart b/pkgs/stream_channel/lib/src/close_guarantee_channel.dart
new file mode 100644
index 0000000..13432d1
--- /dev/null
+++ b/pkgs/stream_channel/lib/src/close_guarantee_channel.dart

@@ -0,0 +1,91 @@
+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:async/async.dart';
+
+import '../stream_channel.dart';
+
+/// A [StreamChannel] that specifically enforces the stream channel guarantee
+/// that closing the sink causes the stream to close before it emits any more
+/// events
+///
+/// This is exposed via [StreamChannel.withCloseGuarantee].
+class CloseGuaranteeChannel<T> extends StreamChannelMixin<T> {
+  @override
+  Stream<T> get stream => _stream;
+  late final _CloseGuaranteeStream<T> _stream;
+
+  @override
+  StreamSink<T> get sink => _sink;
+  late final _CloseGuaranteeSink<T> _sink;
+
+  /// The subscription to the inner stream.
+  StreamSubscription<T>? _subscription;
+
+  /// Whether the sink has closed, causing the underlying channel to disconnect.
+  bool _disconnected = false;
+
+  CloseGuaranteeChannel(Stream<T> innerStream, StreamSink<T> innerSink) {
+    _sink = _CloseGuaranteeSink<T>(innerSink, this);
+    _stream = _CloseGuaranteeStream<T>(innerStream, this);
+  }
+}
+
+/// The stream for [CloseGuaranteeChannel].
+///
+/// This wraps the inner stream to save the subscription on the channel when
+/// [listen] is called.
+class _CloseGuaranteeStream<T> extends Stream<T> {
+  /// The inner stream this is delegating to.
+  final Stream<T> _inner;
+
+  /// The [CloseGuaranteeChannel] this belongs to.
+  final CloseGuaranteeChannel<T> _channel;
+
+  _CloseGuaranteeStream(this._inner, this._channel);
+
+  @override
+  StreamSubscription<T> listen(void Function(T)? onData,
+      {Function? onError, void Function()? onDone, bool? cancelOnError}) {
+    // If the channel is already disconnected, we shouldn't dispatch anything
+    // but a done event.
+    if (_channel._disconnected) {
+      onData = null;
+      onError = null;
+    }
+
+    var subscription = _inner.listen(onData,
+        onError: onError, onDone: onDone, cancelOnError: cancelOnError);
+    if (!_channel._disconnected) {
+      _channel._subscription = subscription;
+    }
+    return subscription;
+  }
+}
+
+/// The sink for [CloseGuaranteeChannel].
+///
+/// This wraps the inner sink to cancel the stream subscription when the sink is
+/// canceled.
+class _CloseGuaranteeSink<T> extends DelegatingStreamSink<T> {
+  /// The [CloseGuaranteeChannel] this belongs to.
+  final CloseGuaranteeChannel<T> _channel;
+
+  _CloseGuaranteeSink(super.inner, this._channel);
+
+  @override
+  Future<void> close() {
+    var done = super.close();
+    _channel._disconnected = true;
+    var subscription = _channel._subscription;
+    if (subscription != null) {
+      // Don't dispatch anything but a done event.
+      subscription.onData(null);
+      subscription.onError(null);
+    }
+    return done;
+  }
+}

diff --git a/pkgs/stream_channel/lib/src/delegating_stream_channel.dart b/pkgs/stream_channel/lib/src/delegating_stream_channel.dart
new file mode 100644
index 0000000..4484a59
--- /dev/null
+++ b/pkgs/stream_channel/lib/src/delegating_stream_channel.dart

@@ -0,0 +1,23 @@
+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import '../stream_channel.dart';
+
+/// A simple delegating wrapper around [StreamChannel].
+///
+/// Subclasses can override individual methods, or use this to expose only
+/// [StreamChannel] methods.
+class DelegatingStreamChannel<T> extends StreamChannelMixin<T> {
+  /// The inner channel to which methods are forwarded.
+  final StreamChannel<T> _inner;
+
+  @override
+  Stream<T> get stream => _inner.stream;
+  @override
+  StreamSink<T> get sink => _inner.sink;
+
+  DelegatingStreamChannel(this._inner);
+}

diff --git a/pkgs/stream_channel/lib/src/disconnector.dart b/pkgs/stream_channel/lib/src/disconnector.dart
new file mode 100644
index 0000000..3414e9c
--- /dev/null
+++ b/pkgs/stream_channel/lib/src/disconnector.dart

@@ -0,0 +1,153 @@
+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:async/async.dart';
+
+import '../stream_channel.dart';
+
+/// Allows the caller to force a channel to disconnect.
+///
+/// When [disconnect] is called, the channel (or channels) transformed by this
+/// transformer will act as though the remote end had disconnected—the stream
+/// will emit a done event, and the sink will ignore future inputs. The inner
+/// sink will also be closed to notify the remote end of the disconnection.
+///
+/// If a channel is transformed after the [disconnect] has been called, it will
+/// be disconnected immediately.
+class Disconnector<T> implements StreamChannelTransformer<T, T> {
+  /// Whether [disconnect] has been called.
+  bool get isDisconnected => _disconnectMemo.hasRun;
+
+  /// The sinks for transformed channels.
+  ///
+  /// Note that we assume that transformed channels provide the stream channel
+  /// guarantees. This allows us to only track sinks, because we know closing
+  /// the underlying sink will cause the stream to emit a done event.
+  final _sinks = <_DisconnectorSink<T>>[];
+
+  /// Disconnects all channels that have been transformed.
+  ///
+  /// Returns a future that completes when all inner sinks' [StreamSink.close]
+  /// futures have completed. Note that a [StreamController]'s sink won't close
+  /// until the corresponding stream has a listener.
+  Future<void> disconnect() => _disconnectMemo.runOnce(() {
+        var futures = _sinks.map((sink) => sink._disconnect()).toList();
+        _sinks.clear();
+        return Future.wait(futures, eagerError: true);
+      });
+  final _disconnectMemo = AsyncMemoizer<List<void>>();
+
+  @override
+  StreamChannel<T> bind(StreamChannel<T> channel) {
+    return channel.changeSink((innerSink) {
+      var sink = _DisconnectorSink<T>(innerSink);
+
+      if (isDisconnected) {
+        // Ignore errors here, because otherwise there would be no way for the
+        // user to handle them gracefully.
+        sink._disconnect().catchError((_) {});
+      } else {
+        _sinks.add(sink);
+      }
+
+      return sink;
+    });
+  }
+}
+
+/// A sink wrapper that can force a disconnection.
+class _DisconnectorSink<T> implements StreamSink<T> {
+  /// The inner sink.
+  final StreamSink<T> _inner;
+
+  @override
+  Future<void> get done => _inner.done;
+
+  /// Whether [Disconnector.disconnect] has been called.
+  var _isDisconnected = false;
+
+  /// Whether the user has called [close].
+  var _closed = false;
+
+  /// The subscription to the stream passed to [addStream], if a stream is
+  /// currently being added.
+  StreamSubscription<T>? _addStreamSubscription;
+
+  /// The completer for the future returned by [addStream], if a stream is
+  /// currently being added.
+  Completer? _addStreamCompleter;
+
+  /// Whether we're currently adding a stream with [addStream].
+  bool get _inAddStream => _addStreamSubscription != null;
+
+  _DisconnectorSink(this._inner);
+
+  @override
+  void add(T data) {
+    if (_closed) throw StateError('Cannot add event after closing.');
+    if (_inAddStream) {
+      throw StateError('Cannot add event while adding stream.');
+    }
+    if (_isDisconnected) return;
+
+    _inner.add(data);
+  }
+
+  @override
+  void addError(Object error, [StackTrace? stackTrace]) {
+    if (_closed) throw StateError('Cannot add event after closing.');
+    if (_inAddStream) {
+      throw StateError('Cannot add event while adding stream.');
+    }
+    if (_isDisconnected) return;
+
+    _inner.addError(error, stackTrace);
+  }
+
+  @override
+  Future<void> addStream(Stream<T> stream) {
+    if (_closed) throw StateError('Cannot add stream after closing.');
+    if (_inAddStream) {
+      throw StateError('Cannot add stream while adding stream.');
+    }
+    if (_isDisconnected) return Future.value();
+
+    _addStreamCompleter = Completer.sync();
+    _addStreamSubscription = stream.listen(_inner.add,
+        onError: _inner.addError, onDone: _addStreamCompleter!.complete);
+    return _addStreamCompleter!.future.then((_) {
+      _addStreamCompleter = null;
+      _addStreamSubscription = null;
+    });
+  }
+
+  @override
+  Future<void> close() {
+    if (_inAddStream) {
+      throw StateError('Cannot close sink while adding stream.');
+    }
+
+    _closed = true;
+    return _inner.close();
+  }
+
+  /// Disconnects this sink.
+  ///
+  /// This closes the underlying sink and stops forwarding events. It returns
+  /// the [StreamSink.close] future for the underlying sink.
+  Future<void> _disconnect() {
+    _isDisconnected = true;
+    var future = _inner.close();
+
+    if (_inAddStream) {
+      _addStreamCompleter!.complete(_addStreamSubscription!.cancel());
+      _addStreamCompleter = null;
+      _addStreamSubscription = null;
+    }
+
+    return future;
+  }
+}

diff --git a/pkgs/stream_channel/lib/src/guarantee_channel.dart b/pkgs/stream_channel/lib/src/guarantee_channel.dart
new file mode 100644
index 0000000..30ebe2e
--- /dev/null
+++ b/pkgs/stream_channel/lib/src/guarantee_channel.dart

@@ -0,0 +1,207 @@
+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:async/async.dart';
+
+import '../stream_channel.dart';
+
+/// A [StreamChannel] that enforces the stream channel guarantees.
+///
+/// This is exposed via [StreamChannel.withGuarantees].
+class GuaranteeChannel<T> extends StreamChannelMixin<T> {
+  @override
+  Stream<T> get stream => _streamController.stream;
+
+  @override
+  StreamSink<T> get sink => _sink;
+  late final _GuaranteeSink<T> _sink;
+
+  /// The controller for [stream].
+  ///
+  /// This intermediate controller allows us to continue listening for a done
+  /// event even after the user has canceled their subscription, and to send our
+  /// own done event when the sink is closed.
+  late final StreamController<T> _streamController;
+
+  /// The subscription to the inner stream.
+  StreamSubscription<T>? _subscription;
+
+  /// Whether the sink has closed, causing the underlying channel to disconnect.
+  bool _disconnected = false;
+
+  GuaranteeChannel(Stream<T> innerStream, StreamSink<T> innerSink,
+      {bool allowSinkErrors = true}) {
+    _sink = _GuaranteeSink<T>(innerSink, this, allowErrors: allowSinkErrors);
+
+    // Enforce the single-subscription guarantee by changing a broadcast stream
+    // to single-subscription.
+    if (innerStream.isBroadcast) {
+      innerStream =
+          innerStream.transform(SingleSubscriptionTransformer<T, T>());
+    }
+
+    _streamController = StreamController<T>(
+        onListen: () {
+          // If the sink has disconnected, we've already called
+          // [_streamController.close].
+          if (_disconnected) return;
+
+          _subscription = innerStream.listen(_streamController.add,
+              onError: _streamController.addError, onDone: () {
+            _sink._onStreamDisconnected();
+            _streamController.close();
+          });
+        },
+        sync: true);
+  }
+
+  /// Called by [_GuaranteeSink] when the user closes it.
+  ///
+  /// The sink closing indicates that the connection is closed, so the stream
+  /// should stop emitting events.
+  void _onSinkDisconnected() {
+    _disconnected = true;
+    var subscription = _subscription;
+    if (subscription != null) subscription.cancel();
+    _streamController.close();
+  }
+}
+
+/// The sink for [GuaranteeChannel].
+///
+/// This wraps the inner sink to ignore events and cancel any in-progress
+/// [addStream] calls when the underlying channel closes.
+class _GuaranteeSink<T> implements StreamSink<T> {
+  /// The inner sink being wrapped.
+  final StreamSink<T> _inner;
+
+  /// The [GuaranteeChannel] this belongs to.
+  final GuaranteeChannel<T> _channel;
+
+  @override
+  Future<void> get done => _doneCompleter.future;
+  final _doneCompleter = Completer<void>();
+
+  /// Whether connection is disconnected.
+  ///
+  /// This can happen because the stream has emitted a done event, or because
+  /// the user added an error when [_allowErrors] is `false`.
+  bool _disconnected = false;
+
+  /// Whether the user has called [close].
+  bool _closed = false;
+
+  /// The subscription to the stream passed to [addStream], if a stream is
+  /// currently being added.
+  StreamSubscription<T>? _addStreamSubscription;
+
+  /// The completer for the future returned by [addStream], if a stream is
+  /// currently being added.
+  Completer? _addStreamCompleter;
+
+  /// Whether we're currently adding a stream with [addStream].
+  bool get _inAddStream => _addStreamSubscription != null;
+
+  /// Whether errors are passed on to the underlying sink.
+  ///
+  /// If this is `false`, any error passed to the sink is piped to [done] and
+  /// the underlying sink is closed.
+  final bool _allowErrors;
+
+  _GuaranteeSink(this._inner, this._channel, {bool allowErrors = true})
+      : _allowErrors = allowErrors;
+
+  @override
+  void add(T data) {
+    if (_closed) throw StateError('Cannot add event after closing.');
+    if (_inAddStream) {
+      throw StateError('Cannot add event while adding stream.');
+    }
+    if (_disconnected) return;
+
+    _inner.add(data);
+  }
+
+  @override
+  void addError(Object error, [StackTrace? stackTrace]) {
+    if (_closed) throw StateError('Cannot add event after closing.');
+    if (_inAddStream) {
+      throw StateError('Cannot add event while adding stream.');
+    }
+    if (_disconnected) return;
+
+    _addError(error, stackTrace);
+  }
+
+  /// Like [addError], but doesn't check to ensure that an error can be added.
+  ///
+  /// This is called from [addStream], so it shouldn't fail if a stream is being
+  /// added.
+  void _addError(Object error, [StackTrace? stackTrace]) {
+    if (_allowErrors) {
+      _inner.addError(error, stackTrace);
+      return;
+    }
+
+    _doneCompleter.completeError(error, stackTrace);
+
+    // Treat an error like both the stream and sink disconnecting.
+    _onStreamDisconnected();
+    _channel._onSinkDisconnected();
+
+    // Ignore errors from the inner sink. We're already surfacing one error, and
+    // if the user handles it we don't want them to have another top-level.
+    _inner.close().catchError((_) {});
+  }
+
+  @override
+  Future<void> addStream(Stream<T> stream) {
+    if (_closed) throw StateError('Cannot add stream after closing.');
+    if (_inAddStream) {
+      throw StateError('Cannot add stream while adding stream.');
+    }
+    if (_disconnected) return Future.value();
+
+    _addStreamCompleter = Completer.sync();
+    _addStreamSubscription = stream.listen(_inner.add,
+        onError: _addError, onDone: _addStreamCompleter!.complete);
+    return _addStreamCompleter!.future.then((_) {
+      _addStreamCompleter = null;
+      _addStreamSubscription = null;
+    });
+  }
+
+  @override
+  Future<void> close() {
+    if (_inAddStream) {
+      throw StateError('Cannot close sink while adding stream.');
+    }
+
+    if (_closed) return done;
+    _closed = true;
+
+    if (!_disconnected) {
+      _channel._onSinkDisconnected();
+      _doneCompleter.complete(_inner.close());
+    }
+
+    return done;
+  }
+
+  /// Called by [GuaranteeChannel] when the stream emits a done event.
+  ///
+  /// The stream being done indicates that the connection is closed, so the
+  /// sink should stop forwarding events.
+  void _onStreamDisconnected() {
+    _disconnected = true;
+    if (!_doneCompleter.isCompleted) _doneCompleter.complete();
+
+    if (!_inAddStream) return;
+    _addStreamCompleter!.complete(_addStreamSubscription!.cancel());
+    _addStreamCompleter = null;
+    _addStreamSubscription = null;
+  }
+}

diff --git a/pkgs/stream_channel/lib/src/isolate_channel.dart b/pkgs/stream_channel/lib/src/isolate_channel.dart
new file mode 100644
index 0000000..15c68a4
--- /dev/null
+++ b/pkgs/stream_channel/lib/src/isolate_channel.dart

@@ -0,0 +1,115 @@
+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+import 'dart:isolate';
+
+import 'package:async/async.dart';
+
+import '../stream_channel.dart';
+
+/// A [StreamChannel] that communicates over a [ReceivePort]/[SendPort] pair,
+/// presumably with another isolate.
+///
+/// The remote endpoint doesn't necessarily need to be running an
+/// [IsolateChannel]. This can be used with any two ports, although the
+/// [StreamChannel] semantics mean that this class will treat them as being
+/// paired (for example, closing the [sink] will cause the [stream] to stop
+/// emitting events).
+///
+/// The underlying isolate ports have no notion of closing connections. This
+/// means that [stream] won't close unless [sink] is closed, and that closing
+/// [sink] won't cause the remote endpoint to close. Users should take care to
+/// ensure that they always close the [sink] of every [IsolateChannel] they use
+/// to avoid leaving dangling [ReceivePort]s.
+class IsolateChannel<T> extends StreamChannelMixin<T> {
+  @override
+  final Stream<T> stream;
+  @override
+  final StreamSink<T> sink;
+
+  /// Connects to a remote channel that was created with
+  /// [IsolateChannel.connectSend].
+  ///
+  /// These constructors establish a connection using only a single
+  /// [SendPort]/[ReceivePort] pair, as long as each side uses one of the
+  /// connect constructors.
+  ///
+  /// The connection protocol is guaranteed to remain compatible across versions
+  /// at least until the next major version release. If the protocol is
+  /// violated, the resulting channel will emit a single value on its stream and
+  /// then close.
+  factory IsolateChannel.connectReceive(ReceivePort receivePort) {
+    // We can't use a [StreamChannelCompleter] here because we need the return
+    // value to be an [IsolateChannel].
+    var isCompleted = false;
+    var streamCompleter = StreamCompleter<T>();
+    var sinkCompleter = StreamSinkCompleter<T>();
+
+    var channel = IsolateChannel<T>._(streamCompleter.stream, sinkCompleter.sink
+        .transform(StreamSinkTransformer.fromHandlers(handleDone: (sink) {
+      if (!isCompleted) {
+        receivePort.close();
+        streamCompleter.setSourceStream(const Stream.empty());
+        sinkCompleter.setDestinationSink(NullStreamSink<T>());
+      }
+      sink.close();
+    })));
+
+    // The first message across the ReceivePort should be a SendPort pointing to
+    // the remote end. If it's not, we'll make the stream emit an error
+    // complaining.
+    late StreamSubscription<dynamic> subscription;
+    subscription = receivePort.listen((message) {
+      isCompleted = true;
+      if (message is SendPort) {
+        var controller =
+            StreamChannelController<T>(allowForeignErrors: false, sync: true);
+        SubscriptionStream(subscription).cast<T>().pipe(controller.local.sink);
+        controller.local.stream
+            .listen((data) => message.send(data), onDone: receivePort.close);
+
+        streamCompleter.setSourceStream(controller.foreign.stream);
+        sinkCompleter.setDestinationSink(controller.foreign.sink);
+        return;
+      }
+
+      streamCompleter.setError(
+          StateError('Unexpected Isolate response "$message".'),
+          StackTrace.current);
+      sinkCompleter.setDestinationSink(NullStreamSink<T>());
+      subscription.cancel();
+    });
+
+    return channel;
+  }
+
+  /// Connects to a remote channel that was created with
+  /// [IsolateChannel.connectReceive].
+  ///
+  /// These constructors establish a connection using only a single
+  /// [SendPort]/[ReceivePort] pair, as long as each side uses one of the
+  /// connect constructors.
+  ///
+  /// The connection protocol is guaranteed to remain compatible across versions
+  /// at least until the next major version release.
+  factory IsolateChannel.connectSend(SendPort sendPort) {
+    var receivePort = ReceivePort();
+    sendPort.send(receivePort.sendPort);
+    return IsolateChannel(receivePort, sendPort);
+  }
+
+  /// Creates a stream channel that receives messages from [receivePort] and
+  /// sends them over [sendPort].
+  factory IsolateChannel(ReceivePort receivePort, SendPort sendPort) {
+    var controller =
+        StreamChannelController<T>(allowForeignErrors: false, sync: true);
+    receivePort.cast<T>().pipe(controller.local.sink);
+    controller.local.stream
+        .listen((data) => sendPort.send(data), onDone: receivePort.close);
+    return IsolateChannel._(controller.foreign.stream, controller.foreign.sink);
+  }
+
+  IsolateChannel._(this.stream, this.sink);
+}

diff --git a/pkgs/stream_channel/lib/src/json_document_transformer.dart b/pkgs/stream_channel/lib/src/json_document_transformer.dart
new file mode 100644
index 0000000..3feda43
--- /dev/null
+++ b/pkgs/stream_channel/lib/src/json_document_transformer.dart

@@ -0,0 +1,35 @@
+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:convert';
+
+import 'package:async/async.dart';
+
+import '../stream_channel.dart';
+
+/// A [StreamChannelTransformer] that transforms JSON documents—strings that
+/// contain individual objects encoded as JSON—into decoded Dart objects.
+///
+/// This decodes JSON that's emitted by the transformed channel's stream, and
+/// encodes objects so that JSON is passed to the transformed channel's sink.
+///
+/// If the transformed channel emits invalid JSON, this emits a
+/// [FormatException]. If an unencodable object is added to the sink, it
+/// synchronously throws a [JsonUnsupportedObjectError].
+final StreamChannelTransformer<Object?, String> jsonDocument =
+    const _JsonDocument();
+
+class _JsonDocument implements StreamChannelTransformer<Object?, String> {
+  const _JsonDocument();
+
+  @override
+  StreamChannel<Object?> bind(StreamChannel<String> channel) {
+    var stream = channel.stream.map(jsonDecode);
+    var sink = StreamSinkTransformer<Object, String>.fromHandlers(
+        handleData: (data, sink) {
+      sink.add(jsonEncode(data));
+    }).bind(channel.sink);
+    return StreamChannel.withCloseGuarantee(stream, sink);
+  }
+}

diff --git a/pkgs/stream_channel/lib/src/multi_channel.dart b/pkgs/stream_channel/lib/src/multi_channel.dart
new file mode 100644
index 0000000..4894239
--- /dev/null
+++ b/pkgs/stream_channel/lib/src/multi_channel.dart

@@ -0,0 +1,274 @@
+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:async/async.dart';
+
+import '../stream_channel.dart';
+
+/// A class that multiplexes multiple virtual channels across a single
+/// underlying transport layer.
+///
+/// This should be connected to another [MultiChannel] on the other end of the
+/// underlying channel. It starts with a single default virtual channel,
+/// accessible via [stream] and [sink]. Additional virtual channels can be
+/// created with [virtualChannel].
+///
+/// When a virtual channel is created by one endpoint, the other must connect to
+/// it before messages may be sent through it. The first endpoint passes its
+/// [VirtualChannel.id] to the second, which then creates a channel from that id
+/// also using [virtualChannel]. For example:
+///
+/// ```dart
+/// // First endpoint
+/// var virtual = multiChannel.virtualChannel();
+/// multiChannel.sink.add({
+///   "channel": virtual.id
+/// });
+///
+/// // Second endpoint
+/// multiChannel.stream.listen((message) {
+///   var virtual = multiChannel.virtualChannel(message["channel"]);
+///   // ...
+/// });
+/// ```
+///
+/// Sending errors across a [MultiChannel] is not supported. Any errors from the
+/// underlying stream will be reported only via the default
+/// [MultiChannel.stream].
+///
+/// Each virtual channel may be closed individually. When all of them are
+/// closed, the underlying [StreamSink] is closed automatically.
+abstract class MultiChannel<T> implements StreamChannel<T> {
+  /// The default input stream.
+  ///
+  /// This connects to the remote [sink].
+  @override
+  Stream<T> get stream;
+
+  /// The default output stream.
+  ///
+  /// This connects to the remote [stream]. If this is closed, the remote
+  /// [stream] will close, but other virtual channels will remain open and new
+  /// virtual channels may be opened.
+  @override
+  StreamSink<T> get sink;
+
+  /// Creates a new [MultiChannel] that sends and receives messages over
+  /// [inner].
+  ///
+  /// The inner channel must take JSON-like objects.
+  factory MultiChannel(StreamChannel<dynamic> inner) => _MultiChannel<T>(inner);
+
+  /// Creates a new virtual channel.
+  ///
+  /// If [id] is not passed, this creates a virtual channel from scratch. Before
+  /// it's used, its [VirtualChannel.id] must be sent to the remote endpoint
+  /// where [virtualChannel] should be called with that id.
+  ///
+  /// If [id] is passed, this creates a virtual channel corresponding to the
+  /// channel with that id on the remote channel.
+  ///
+  /// Throws an [ArgumentError] if a virtual channel already exists for [id].
+  /// Throws a [StateError] if the underlying channel is closed.
+  VirtualChannel<T> virtualChannel([int? id]);
+}
+
+/// The implementation of [MultiChannel].
+///
+/// This is private so that [VirtualChannel] can inherit from [MultiChannel]
+/// without having to implement all the private members.
+class _MultiChannel<T> extends StreamChannelMixin<T>
+    implements MultiChannel<T> {
+  /// The inner channel over which all communication is conducted.
+  ///
+  /// This will be `null` if the underlying communication channel is closed.
+  StreamChannel<dynamic>? _inner;
+
+  /// The subscription to [_inner].stream.
+  StreamSubscription<dynamic>? _innerStreamSubscription;
+
+  @override
+  Stream<T> get stream => _mainController.foreign.stream;
+  @override
+  StreamSink<T> get sink => _mainController.foreign.sink;
+
+  /// The controller for this channel.
+  final _mainController = StreamChannelController<T>(sync: true);
+
+  /// A map from input IDs to [StreamChannelController]s that should be used to
+  /// communicate over those channels.
+  final _controllers = <int, StreamChannelController<T>>{};
+
+  /// Input IDs of controllers in [_controllers] that we've received messages
+  /// for but that have not yet had a local [virtualChannel] created.
+  final _pendingIds = <int>{};
+
+  /// Input IDs of virtual channels that used to exist but have since been
+  /// closed.
+  final _closedIds = <int>{};
+
+  /// The next id to use for a local virtual channel.
+  ///
+  /// Ids are used to identify virtual channels. Each message is tagged with an
+  /// id; the receiving [MultiChannel] uses this id to look up which
+  /// [VirtualChannel] the message should be dispatched to.
+  ///
+  /// The id scheme for virtual channels is somewhat complicated. This is
+  /// necessary to ensure that there are no conflicts even when both endpoints
+  /// have virtual channels with the same id; since both endpoints can send and
+  /// receive messages across each virtual channel, a naïve scheme would make it
+  /// impossible to tell whether a message was from a channel that originated in
+  /// the remote endpoint or a reply on a channel that originated in the local
+  /// endpoint.
+  ///
+  /// The trick is that each endpoint only uses odd ids for its own channels.
+  /// When sending a message over a channel that was created by the remote
+  /// endpoint, the channel's id plus one is used. This way each [MultiChannel]
+  /// knows that if an incoming message has an odd id, it's coming from a
+  /// channel that was originally created remotely, but if it has an even id,
+  /// it's coming from a channel that was originally created locally.
+  var _nextId = 1;
+
+  _MultiChannel(StreamChannel<dynamic> inner) : _inner = inner {
+    // The default connection is a special case which has id 0 on both ends.
+    // This allows it to begin connected without having to send over an id.
+    _controllers[0] = _mainController;
+    _mainController.local.stream.listen(
+        (message) => _inner!.sink.add(<Object?>[0, message]),
+        onDone: () => _closeChannel(0, 0));
+
+    _innerStreamSubscription = _inner!.stream.cast<List>().listen((message) {
+      var id = (message[0] as num).toInt();
+
+      // If the channel was closed before an incoming message was processed,
+      // ignore that message.
+      if (_closedIds.contains(id)) return;
+
+      var controller = _controllers.putIfAbsent(id, () {
+        // If we receive a message for a controller that doesn't have a local
+        // counterpart yet, create a controller for it to buffer incoming
+        // messages for when a local connection is created.
+        _pendingIds.add(id);
+        return StreamChannelController(sync: true);
+      });
+
+      if (message.length > 1) {
+        controller.local.sink.add(message[1] as T);
+      } else {
+        // A message without data indicates that the channel has been closed. We
+        // can just close the sink here without doing any more cleanup, because
+        // the sink closing will cause the stream to emit a done event which
+        // will trigger more cleanup.
+        controller.local.sink.close();
+      }
+    },
+        onDone: _closeInnerChannel,
+        onError: _mainController.local.sink.addError);
+  }
+
+  @override
+  VirtualChannel<T> virtualChannel([int? id]) {
+    int inputId;
+    int outputId;
+    if (id != null) {
+      // Since the user is passing in an id, we're connected to a remote
+      // VirtualChannel. This means messages they send over this channel will
+      // have the original odd id, but our replies will have an even id.
+      inputId = id;
+      outputId = id + 1;
+    } else {
+      // Since we're generating an id, we originated this VirtualChannel. This
+      // means messages we send over this channel will have the original odd id,
+      // but the remote channel's replies will have an even id.
+      inputId = _nextId + 1;
+      outputId = _nextId;
+      _nextId += 2;
+    }
+
+    // If the inner channel has already closed, create new virtual channels in a
+    // closed state.
+    if (_inner == null) {
+      return VirtualChannel._(
+          this, inputId, const Stream.empty(), NullStreamSink());
+    }
+
+    late StreamChannelController<T> controller;
+    if (_pendingIds.remove(inputId)) {
+      // If we've already received messages for this channel, use the controller
+      // where those messages are buffered.
+      controller = _controllers[inputId]!;
+    } else if (_controllers.containsKey(inputId) ||
+        _closedIds.contains(inputId)) {
+      throw ArgumentError('A virtual channel with id $id already exists.');
+    } else {
+      controller = StreamChannelController(sync: true);
+      _controllers[inputId] = controller;
+    }
+
+    controller.local.stream.listen(
+        (message) => _inner!.sink.add(<Object?>[outputId, message]),
+        onDone: () => _closeChannel(inputId, outputId));
+    return VirtualChannel._(
+        this, outputId, controller.foreign.stream, controller.foreign.sink);
+  }
+
+  /// Closes the virtual channel for which incoming messages have [inputId] and
+  /// outgoing messages have [outputId].
+  void _closeChannel(int inputId, int outputId) {
+    _closedIds.add(inputId);
+    var controller = _controllers.remove(inputId)!;
+    controller.local.sink.close();
+
+    if (_inner == null) return;
+
+    // A message without data indicates that the virtual channel has been
+    // closed.
+    _inner!.sink.add([outputId]);
+    if (_controllers.isEmpty) _closeInnerChannel();
+  }
+
+  /// Closes the underlying communication channel.
+  void _closeInnerChannel() {
+    _inner!.sink.close();
+    _innerStreamSubscription!.cancel();
+    _inner = null;
+
+    // Convert this to a list because the close is dispatched synchronously, and
+    // that could conceivably remove a controller from [_controllers].
+    for (var controller in _controllers.values.toList(growable: false)) {
+      controller.local.sink.close();
+    }
+    _controllers.clear();
+  }
+}
+
+/// A virtual channel created by [MultiChannel].
+///
+/// This implements [MultiChannel] for convenience.
+/// [VirtualChannel.virtualChannel] is semantically identical to the parent's
+/// [MultiChannel.virtualChannel].
+class VirtualChannel<T> extends StreamChannelMixin<T>
+    implements MultiChannel<T> {
+  /// The [MultiChannel] that created this.
+  final MultiChannel<T> _parent;
+
+  /// The identifier for this channel.
+  ///
+  /// This can be sent across the [MultiChannel] to provide the remote endpoint
+  /// a means to connect to this channel. Nothing about this is guaranteed
+  /// except that it will be JSON-serializable.
+  final int id;
+
+  @override
+  final Stream<T> stream;
+  @override
+  final StreamSink<T> sink;
+
+  VirtualChannel._(this._parent, this.id, this.stream, this.sink);
+
+  @override
+  VirtualChannel<T> virtualChannel([int? id]) => _parent.virtualChannel(id);
+}

diff --git a/pkgs/stream_channel/lib/src/stream_channel_completer.dart b/pkgs/stream_channel/lib/src/stream_channel_completer.dart
new file mode 100644
index 0000000..9d007eb
--- /dev/null
+++ b/pkgs/stream_channel/lib/src/stream_channel_completer.dart

@@ -0,0 +1,74 @@
+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:async/async.dart';
+
+import '../stream_channel.dart';
+
+/// A [channel] where the source and destination are provided later.
+///
+/// The [channel] is a normal channel that can be listened to and that events
+/// can be added to immediately, but until [setChannel] is called it won't emit
+/// any events and all events added to it will be buffered.
+class StreamChannelCompleter<T> {
+  /// The completer for this channel's stream.
+  final _streamCompleter = StreamCompleter<T>();
+
+  /// The completer for this channel's sink.
+  final _sinkCompleter = StreamSinkCompleter<T>();
+
+  /// The channel for this completer.
+  StreamChannel<T> get channel => _channel;
+  late final StreamChannel<T> _channel;
+
+  /// Whether [setChannel] has been called.
+  bool _set = false;
+
+  /// Convert a `Future<StreamChannel>` to a `StreamChannel`.
+  ///
+  /// This creates a channel using a channel completer, and sets the source
+  /// channel to the result of the future when the future completes.
+  ///
+  /// If the future completes with an error, the returned channel's stream will
+  /// instead contain just that error. The sink will silently discard all
+  /// events.
+  static StreamChannel fromFuture(Future<StreamChannel> channelFuture) {
+    var completer = StreamChannelCompleter<void>();
+    channelFuture.then(completer.setChannel, onError: completer.setError);
+    return completer.channel;
+  }
+
+  StreamChannelCompleter() {
+    _channel = StreamChannel<T>(_streamCompleter.stream, _sinkCompleter.sink);
+  }
+
+  /// Set a channel as the source and destination for [channel].
+  ///
+  /// A channel may be set at most once.
+  ///
+  /// Either [setChannel] or [setError] may be called at most once. Trying to
+  /// call either of them again will fail.
+  void setChannel(StreamChannel<T> channel) {
+    if (_set) throw StateError('The channel has already been set.');
+    _set = true;
+
+    _streamCompleter.setSourceStream(channel.stream);
+    _sinkCompleter.setDestinationSink(channel.sink);
+  }
+
+  /// Indicates that there was an error connecting the channel.
+  ///
+  /// This makes the stream emit [error] and close. It makes the sink discard
+  /// all its events.
+  ///
+  /// Either [setChannel] or [setError] may be called at most once. Trying to
+  /// call either of them again will fail.
+  void setError(Object error, [StackTrace? stackTrace]) {
+    if (_set) throw StateError('The channel has already been set.');
+    _set = true;
+
+    _streamCompleter.setError(error, stackTrace);
+    _sinkCompleter.setDestinationSink(NullStreamSink());
+  }
+}

diff --git a/pkgs/stream_channel/lib/src/stream_channel_controller.dart b/pkgs/stream_channel/lib/src/stream_channel_controller.dart
new file mode 100644
index 0000000..25d5239
--- /dev/null
+++ b/pkgs/stream_channel/lib/src/stream_channel_controller.dart

@@ -0,0 +1,67 @@
+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// @docImport 'isolate_channel.dart';
+library;
+
+import 'dart:async';
+
+import '../stream_channel.dart';
+
+/// A controller for exposing a new [StreamChannel].
+///
+/// This exposes two connected [StreamChannel]s, [local] and [foreign]. The
+/// user's code should use [local] to emit and receive events. Then [foreign]
+/// can be returned for others to use. For example, here's a simplified version
+/// of the implementation of [IsolateChannel.new]:
+///
+/// ```dart
+/// StreamChannel isolateChannel(ReceivePort receivePort, SendPort sendPort) {
+///   var controller = new StreamChannelController(allowForeignErrors: false);
+///
+///   // Pipe all events from the receive port into the local sink...
+///   receivePort.pipe(controller.local.sink);
+///
+///   // ...and all events from the local stream into the send port.
+///   controller.local.stream.listen(sendPort.send, onDone: receivePort.close);
+///
+///   // Then return the foreign controller for your users to use.
+///   return controller.foreign;
+/// }
+/// ```
+class StreamChannelController<T> {
+  /// The local channel.
+  ///
+  /// This channel should be used directly by the creator of this
+  /// [StreamChannelController] to send and receive events.
+  StreamChannel<T> get local => _local;
+  late final StreamChannel<T> _local;
+
+  /// The foreign channel.
+  ///
+  /// This channel should be returned to external users so they can communicate
+  /// with [local].
+  StreamChannel<T> get foreign => _foreign;
+  late final StreamChannel<T> _foreign;
+
+  /// Creates a [StreamChannelController].
+  ///
+  /// If [sync] is true, events added to either channel's sink are synchronously
+  /// dispatched to the other channel's stream. This should only be done if the
+  /// source of those events is already asynchronous.
+  ///
+  /// If [allowForeignErrors] is `false`, errors are not allowed to be passed to
+  /// the foreign channel's sink. If any are, the connection will close and the
+  /// error will be forwarded to the foreign channel's [StreamSink.done] future.
+  /// This guarantees that the local stream will never emit errors.
+  StreamChannelController({bool allowForeignErrors = true, bool sync = false}) {
+    var localToForeignController = StreamController<T>(sync: sync);
+    var foreignToLocalController = StreamController<T>(sync: sync);
+    _local = StreamChannel<T>.withGuarantees(
+        foreignToLocalController.stream, localToForeignController.sink);
+    _foreign = StreamChannel<T>.withGuarantees(
+        localToForeignController.stream, foreignToLocalController.sink,
+        allowSinkErrors: allowForeignErrors);
+  }
+}

diff --git a/pkgs/stream_channel/lib/src/stream_channel_transformer.dart b/pkgs/stream_channel/lib/src/stream_channel_transformer.dart
new file mode 100644
index 0000000..cf62c76
--- /dev/null
+++ b/pkgs/stream_channel/lib/src/stream_channel_transformer.dart

@@ -0,0 +1,58 @@
+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+import 'dart:convert';
+
+import 'package:async/async.dart';
+
+import '../stream_channel.dart';
+
+/// A [StreamChannelTransformer] transforms the events being passed to and
+/// emitted by a [StreamChannel].
+///
+/// This works on the same principle as [StreamTransformer] and
+/// [StreamSinkTransformer]. Each transformer defines a [bind] method that takes
+/// in the original [StreamChannel] and returns the transformed version.
+///
+/// Transformers must be able to have [bind] called multiple times. If a
+/// subclass implements [bind] explicitly, it should be sure that the returned
+/// stream follows the second stream channel guarantee: closing the sink causes
+/// the stream to close before it emits any more events. This guarantee is
+/// invalidated when an asynchronous gap is added between the original stream's
+/// event dispatch and the returned stream's, for example by transforming it
+/// with a [StreamTransformer]. The guarantee can be easily preserved using
+/// [StreamChannel.withCloseGuarantee].
+class StreamChannelTransformer<S, T> {
+  /// The transformer to use on the channel's stream.
+  final StreamTransformer<T, S> _streamTransformer;
+
+  /// The transformer to use on the channel's sink.
+  final StreamSinkTransformer<S, T> _sinkTransformer;
+
+  /// Creates a [StreamChannelTransformer] from existing stream and sink
+  /// transformers.
+  const StreamChannelTransformer(
+      this._streamTransformer, this._sinkTransformer);
+
+  /// Creates a [StreamChannelTransformer] from a codec's encoder and decoder.
+  ///
+  /// All input to the inner channel's sink is encoded using [Codec.encoder],
+  /// and all output from its stream is decoded using [Codec.decoder].
+  StreamChannelTransformer.fromCodec(Codec<S, T> codec)
+      : this(codec.decoder,
+            StreamSinkTransformer.fromStreamTransformer(codec.encoder));
+
+  /// Transforms the events sent to and emitted by [channel].
+  ///
+  /// Creates a new channel. When events are passed to the returned channel's
+  /// sink, the transformer will transform them and pass the transformed
+  /// versions to `channel.sink`. When events are emitted from the
+  /// `channel.straem`, the transformer will transform them and pass the
+  /// transformed versions to the returned channel's stream.
+  StreamChannel<S> bind(StreamChannel<T> channel) =>
+      StreamChannel<S>.withCloseGuarantee(
+          channel.stream.transform(_streamTransformer),
+          _sinkTransformer.bind(channel.sink));
+}

diff --git a/pkgs/stream_channel/lib/stream_channel.dart b/pkgs/stream_channel/lib/stream_channel.dart
new file mode 100644
index 0000000..8e53096
--- /dev/null
+++ b/pkgs/stream_channel/lib/stream_channel.dart

@@ -0,0 +1,181 @@
+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:async/async.dart';
+
+import 'src/close_guarantee_channel.dart';
+import 'src/guarantee_channel.dart';
+import 'src/stream_channel_transformer.dart';
+
+export 'src/delegating_stream_channel.dart';
+export 'src/disconnector.dart';
+export 'src/json_document_transformer.dart';
+export 'src/multi_channel.dart';
+export 'src/stream_channel_completer.dart';
+export 'src/stream_channel_controller.dart';
+export 'src/stream_channel_transformer.dart';
+
+/// An abstract class representing a two-way communication channel.
+///
+/// Users should consider the [stream] emitting a "done" event to be the
+/// canonical indicator that the channel has closed. If they wish to close the
+/// channel, they should close the [sink]—canceling the stream subscription is
+/// not sufficient. Protocol errors may be emitted through the stream or through
+/// [sink].done, depending on their underlying cause. Note that the sink may
+/// silently drop events if the channel closes before [sink].close is called.
+///
+/// Implementations are strongly encouraged to mix in or extend
+/// [StreamChannelMixin] to get default implementations of the various instance
+/// methods. Adding new methods to this interface will not be considered a
+/// breaking change if implementations are also added to [StreamChannelMixin].
+///
+/// Implementations must provide the following guarantees:
+///
+/// * The stream is single-subscription, and must follow all the guarantees of
+///   single-subscription streams.
+///
+/// * Closing the sink causes the stream to close before it emits any more
+///   events.
+///
+/// * After the stream closes, the sink is automatically closed. If this
+///   happens, sink methods should silently drop their arguments until
+///   [sink].close is called.
+///
+/// * If the stream closes before it has a listener, the sink should silently
+///   drop events if possible.
+///
+/// * Canceling the stream's subscription has no effect on the sink. The channel
+///   must still be able to respond to the other endpoint closing the channel
+///   even after the subscription has been canceled.
+///
+/// * The sink *either* forwards errors to the other endpoint *or* closes as
+///   soon as an error is added and forwards that error to the [sink].done
+///   future.
+///
+/// These guarantees allow users to interact uniformly with all implementations,
+/// and ensure that either endpoint closing the stream produces consistent
+/// behavior.
+abstract class StreamChannel<T> {
+  /// The single-subscription stream that emits values from the other endpoint.
+  Stream<T> get stream;
+
+  /// The sink for sending values to the other endpoint.
+  StreamSink<T> get sink;
+
+  /// Creates a new [StreamChannel] that communicates over [stream] and [sink].
+  ///
+  /// Note that this stream/sink pair must provide the guarantees listed in the
+  /// [StreamChannel] documentation. If they don't do so natively,
+  /// [StreamChannel.withGuarantees] should be used instead.
+  factory StreamChannel(Stream<T> stream, StreamSink<T> sink) =>
+      _StreamChannel<T>(stream, sink);
+
+  /// Creates a new [StreamChannel] that communicates over [stream] and [sink].
+  ///
+  /// Unlike [StreamChannel.new], this enforces the guarantees listed in the
+  /// [StreamChannel] documentation. This makes it somewhat less efficient than
+  /// just wrapping a stream and a sink directly, so [StreamChannel.new] should
+  /// be used when the guarantees are provided natively.
+  ///
+  /// If [allowSinkErrors] is `false`, errors are not allowed to be passed to
+  /// [sink]. If any are, the connection will close and the error will be
+  /// forwarded to [sink].done.
+  factory StreamChannel.withGuarantees(Stream<T> stream, StreamSink<T> sink,
+          {bool allowSinkErrors = true}) =>
+      GuaranteeChannel(stream, sink, allowSinkErrors: allowSinkErrors);
+
+  /// Creates a new [StreamChannel] that communicates over [stream] and [sink].
+  ///
+  /// This specifically enforces the second guarantee: closing the sink causes
+  /// the stream to close before it emits any more events. This guarantee is
+  /// invalidated when an asynchronous gap is added between the original
+  /// stream's event dispatch and the returned stream's, for example by
+  /// transforming it with a [StreamTransformer]. This is a lighter-weight way
+  /// of preserving that guarantee in particular than
+  /// [StreamChannel.withGuarantees].
+  factory StreamChannel.withCloseGuarantee(
+          Stream<T> stream, StreamSink<T> sink) =>
+      CloseGuaranteeChannel(stream, sink);
+
+  /// Connects this to [other], so that any values emitted by either are sent
+  /// directly to the other.
+  void pipe(StreamChannel<T> other);
+
+  /// Transforms this using [transformer].
+  ///
+  /// This is identical to calling `transformer.bind(channel)`.
+  StreamChannel<S> transform<S>(StreamChannelTransformer<S, T> transformer);
+
+  /// Transforms only the [stream] component of this using [transformer].
+  StreamChannel<T> transformStream(StreamTransformer<T, T> transformer);
+
+  /// Transforms only the [sink] component of this using [transformer].
+  StreamChannel<T> transformSink(StreamSinkTransformer<T, T> transformer);
+
+  /// Returns a copy of this with [stream] replaced by [change]'s return
+  /// value.
+  StreamChannel<T> changeStream(Stream<T> Function(Stream<T>) change);
+
+  /// Returns a copy of this with [sink] replaced by [change]'s return
+  /// value.
+  StreamChannel<T> changeSink(StreamSink<T> Function(StreamSink<T>) change);
+
+  /// Returns a copy of this with the generic type coerced to [S].
+  ///
+  /// If any events emitted by [stream] aren't of type [S], they're converted
+  /// into [TypeError] events (`CastError` on some SDK versions). Similarly, if
+  /// any events are added to [sink] that aren't of type [S], a [TypeError] is
+  /// thrown.
+  StreamChannel<S> cast<S>();
+}
+
+/// An implementation of [StreamChannel] that simply takes a stream and a sink
+/// as parameters.
+///
+/// This is distinct from [StreamChannel] so that it can use
+/// [StreamChannelMixin].
+class _StreamChannel<T> extends StreamChannelMixin<T> {
+  @override
+  final Stream<T> stream;
+  @override
+  final StreamSink<T> sink;
+
+  _StreamChannel(this.stream, this.sink);
+}
+
+/// A mixin that implements the instance methods of [StreamChannel] in terms of
+/// [stream] and [sink].
+abstract mixin class StreamChannelMixin<T> implements StreamChannel<T> {
+  @override
+  void pipe(StreamChannel<T> other) {
+    stream.pipe(other.sink);
+    other.stream.pipe(sink);
+  }
+
+  @override
+  StreamChannel<S> transform<S>(StreamChannelTransformer<S, T> transformer) =>
+      transformer.bind(this);
+
+  @override
+  StreamChannel<T> transformStream(StreamTransformer<T, T> transformer) =>
+      changeStream(transformer.bind);
+
+  @override
+  StreamChannel<T> transformSink(StreamSinkTransformer<T, T> transformer) =>
+      changeSink(transformer.bind);
+
+  @override
+  StreamChannel<T> changeStream(Stream<T> Function(Stream<T>) change) =>
+      StreamChannel.withCloseGuarantee(change(stream), sink);
+
+  @override
+  StreamChannel<T> changeSink(StreamSink<T> Function(StreamSink<T>) change) =>
+      StreamChannel.withCloseGuarantee(stream, change(sink));
+
+  @override
+  StreamChannel<S> cast<S>() => StreamChannel(
+      stream.cast(), StreamController(sync: true)..stream.cast<T>().pipe(sink));
+}

diff --git a/pkgs/stream_channel/pubspec.yaml b/pkgs/stream_channel/pubspec.yaml
new file mode 100644
index 0000000..f050fca
--- /dev/null
+++ b/pkgs/stream_channel/pubspec.yaml

@@ -0,0 +1,16 @@
+name: stream_channel
+version: 2.1.4
+description: >-
+  An abstraction for two-way communication channels based on the Dart Stream
+  class.
+repository: https://github.com/dart-lang/tools/tree/main/pkgs/stream_channel
+
+environment:
+  sdk: ^3.3.0
+
+dependencies:
+  async: ^2.5.0
+
+dev_dependencies:
+  dart_flutter_team_lints: ^3.0.0
+  test: ^1.16.6

diff --git a/pkgs/stream_channel/test/disconnector_test.dart b/pkgs/stream_channel/test/disconnector_test.dart
new file mode 100644
index 0000000..bbba568
--- /dev/null
+++ b/pkgs/stream_channel/test/disconnector_test.dart

@@ -0,0 +1,152 @@
+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:async/async.dart';
+import 'package:stream_channel/stream_channel.dart';
+import 'package:test/test.dart';
+
+void main() {
+  late StreamController streamController;
+  late StreamController sinkController;
+  late Disconnector disconnector;
+  late StreamChannel channel;
+  setUp(() {
+    streamController = StreamController<void>();
+    sinkController = StreamController<void>();
+    disconnector = Disconnector();
+    channel = StreamChannel.withGuarantees(
+            streamController.stream, sinkController.sink)
+        .transform(disconnector);
+  });
+
+  group('before disconnection', () {
+    test('forwards events from the sink as normal', () {
+      channel.sink.add(1);
+      channel.sink.add(2);
+      channel.sink.add(3);
+      channel.sink.close();
+
+      expect(sinkController.stream.toList(), completion(equals([1, 2, 3])));
+    });
+
+    test('forwards events to the stream as normal', () {
+      streamController.add(1);
+      streamController.add(2);
+      streamController.add(3);
+      streamController.close();
+
+      expect(channel.stream.toList(), completion(equals([1, 2, 3])));
+    });
+
+    test("events can't be added when the sink is explicitly closed", () {
+      sinkController.stream.listen(null); // Work around sdk#19095.
+
+      expect(channel.sink.close(), completes);
+      expect(() => channel.sink.add(1), throwsStateError);
+      expect(() => channel.sink.addError('oh no'), throwsStateError);
+      expect(() => channel.sink.addStream(Stream.fromIterable([])),
+          throwsStateError);
+    });
+
+    test("events can't be added while a stream is being added", () {
+      var controller = StreamController<void>();
+      channel.sink.addStream(controller.stream);
+
+      expect(() => channel.sink.add(1), throwsStateError);
+      expect(() => channel.sink.addError('oh no'), throwsStateError);
+      expect(() => channel.sink.addStream(Stream.fromIterable([])),
+          throwsStateError);
+      expect(() => channel.sink.close(), throwsStateError);
+
+      controller.close();
+    });
+  });
+
+  test('cancels addStream when disconnected', () async {
+    var canceled = false;
+    var controller = StreamController<void>(onCancel: () {
+      canceled = true;
+    });
+    expect(channel.sink.addStream(controller.stream), completes);
+    unawaited(disconnector.disconnect());
+
+    await pumpEventQueue();
+    expect(canceled, isTrue);
+  });
+
+  test('disconnect() returns the close future from the inner sink', () async {
+    var streamController = StreamController<void>();
+    var sinkController = StreamController<void>();
+    var disconnector = Disconnector<void>();
+    var sink = _CloseCompleterSink(sinkController.sink);
+    StreamChannel.withGuarantees(streamController.stream, sink)
+        .transform(disconnector);
+
+    var disconnectFutureFired = false;
+    expect(
+        disconnector.disconnect().then((_) {
+          disconnectFutureFired = true;
+        }),
+        completes);
+
+    // Give the future time to fire early if it's going to.
+    await pumpEventQueue();
+    expect(disconnectFutureFired, isFalse);
+
+    // When the inner sink's close future completes, so should the
+    // disconnector's.
+    sink.completer.complete();
+    await pumpEventQueue();
+    expect(disconnectFutureFired, isTrue);
+  });
+
+  group('after disconnection', () {
+    setUp(() {
+      disconnector.disconnect();
+    });
+
+    test('closes the inner sink and ignores events to the outer sink', () {
+      channel.sink.add(1);
+      channel.sink.add(2);
+      channel.sink.add(3);
+      channel.sink.close();
+
+      expect(sinkController.stream.toList(), completion(isEmpty));
+    });
+
+    test('closes the stream', () {
+      expect(channel.stream.toList(), completion(isEmpty));
+    });
+
+    test('completes done', () {
+      sinkController.stream.listen(null); // Work around sdk#19095.
+      expect(channel.sink.done, completes);
+    });
+
+    test('still emits state errors after explicit close', () {
+      sinkController.stream.listen(null); // Work around sdk#19095.
+      expect(channel.sink.close(), completes);
+
+      expect(() => channel.sink.add(1), throwsStateError);
+      expect(() => channel.sink.addError('oh no'), throwsStateError);
+    });
+  });
+}
+
+/// A [StreamSink] wrapper that adds the ability to manually complete the Future
+/// returned by [close] using [completer].
+class _CloseCompleterSink extends DelegatingStreamSink {
+  /// The completer for the future returned by [close].
+  final completer = Completer<void>();
+
+  _CloseCompleterSink(super.inner);
+
+  @override
+  Future<void> close() {
+    super.close();
+    return completer.future;
+  }
+}

diff --git a/pkgs/stream_channel/test/isolate_channel_test.dart b/pkgs/stream_channel/test/isolate_channel_test.dart
new file mode 100644
index 0000000..3a8b42e
--- /dev/null
+++ b/pkgs/stream_channel/test/isolate_channel_test.dart

@@ -0,0 +1,174 @@
+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+@TestOn('vm')
+library;
+
+import 'dart:async';
+import 'dart:isolate';
+
+import 'package:stream_channel/isolate_channel.dart';
+import 'package:stream_channel/stream_channel.dart';
+import 'package:test/test.dart';
+
+void main() {
+  late ReceivePort receivePort;
+  late SendPort sendPort;
+  late StreamChannel channel;
+  setUp(() {
+    receivePort = ReceivePort();
+    var receivePortForSend = ReceivePort();
+    sendPort = receivePortForSend.sendPort;
+    channel = IsolateChannel(receivePortForSend, receivePort.sendPort);
+  });
+
+  tearDown(() {
+    receivePort.close();
+    channel.sink.close();
+  });
+
+  test('the channel can send messages', () {
+    channel.sink.add(1);
+    channel.sink.add(2);
+    channel.sink.add(3);
+
+    expect(receivePort.take(3).toList(), completion(equals([1, 2, 3])));
+  });
+
+  test('the channel can receive messages', () {
+    sendPort.send(1);
+    sendPort.send(2);
+    sendPort.send(3);
+
+    expect(channel.stream.take(3).toList(), completion(equals([1, 2, 3])));
+  });
+
+  test("events can't be added to an explicitly-closed sink", () {
+    expect(channel.sink.close(), completes);
+    expect(() => channel.sink.add(1), throwsStateError);
+    expect(() => channel.sink.addError('oh no'), throwsStateError);
+    expect(() => channel.sink.addStream(Stream.fromIterable([])),
+        throwsStateError);
+  });
+
+  test("events can't be added while a stream is being added", () {
+    var controller = StreamController<void>();
+    channel.sink.addStream(controller.stream);
+
+    expect(() => channel.sink.add(1), throwsStateError);
+    expect(() => channel.sink.addError('oh no'), throwsStateError);
+    expect(() => channel.sink.addStream(Stream.fromIterable([])),
+        throwsStateError);
+    expect(() => channel.sink.close(), throwsStateError);
+
+    controller.close();
+  });
+
+  group('stream channel rules', () {
+    test(
+        'closing the sink causes the stream to close before it emits any more '
+        'events', () {
+      sendPort.send(1);
+      sendPort.send(2);
+      sendPort.send(3);
+      sendPort.send(4);
+      sendPort.send(5);
+
+      channel.stream.listen(expectAsync1((message) {
+        expect(message, equals(1));
+        channel.sink.close();
+      }, count: 1));
+    });
+
+    test("cancelling the stream's subscription has no effect on the sink",
+        () async {
+      unawaited(channel.stream.listen(null).cancel());
+      await pumpEventQueue();
+
+      channel.sink.add(1);
+      channel.sink.add(2);
+      channel.sink.add(3);
+      expect(receivePort.take(3).toList(), completion(equals([1, 2, 3])));
+    });
+
+    test('the sink closes as soon as an error is added', () async {
+      channel.sink.addError('oh no');
+      channel.sink.add(1);
+      expect(channel.sink.done, throwsA('oh no'));
+
+      // Since the sink is closed, the stream should also be closed.
+      expect(channel.stream.isEmpty, completion(isTrue));
+
+      // The other end shouldn't receive the next event, since the sink was
+      // closed. Pump the event queue to give it a chance to.
+      receivePort.listen(expectAsync1((_) {}, count: 0));
+      await pumpEventQueue();
+    });
+
+    test('the sink closes as soon as an error is added via addStream',
+        () async {
+      var canceled = false;
+      var controller = StreamController<void>(onCancel: () {
+        canceled = true;
+      });
+
+      // This future shouldn't get the error, because it's sent to [Sink.done].
+      expect(channel.sink.addStream(controller.stream), completes);
+
+      controller.addError('oh no');
+      expect(channel.sink.done, throwsA('oh no'));
+      await pumpEventQueue();
+      expect(canceled, isTrue);
+
+      // Even though the sink is closed, this shouldn't throw an error because
+      // the user didn't explicitly close it.
+      channel.sink.add(1);
+    });
+  });
+
+  group('connect constructors', () {
+    late ReceivePort connectPort;
+    setUp(() {
+      connectPort = ReceivePort();
+    });
+
+    tearDown(() {
+      connectPort.close();
+    });
+
+    test('create a connected pair of channels', () async {
+      var channel1 = IsolateChannel<int>.connectReceive(connectPort);
+      var channel2 = IsolateChannel<int>.connectSend(connectPort.sendPort);
+
+      channel1.sink.add(1);
+      channel1.sink.add(2);
+      channel1.sink.add(3);
+      expect(await channel2.stream.take(3).toList(), equals([1, 2, 3]));
+
+      channel2.sink.add(4);
+      channel2.sink.add(5);
+      channel2.sink.add(6);
+      expect(await channel1.stream.take(3).toList(), equals([4, 5, 6]));
+
+      await channel2.sink.close();
+    });
+
+    test('the receiving channel produces an error if it gets the wrong message',
+        () {
+      var connectedChannel = IsolateChannel<int>.connectReceive(connectPort);
+      connectPort.sendPort.send('wrong value');
+
+      expect(connectedChannel.stream.toList(), throwsStateError);
+      expect(connectedChannel.sink.done, completes);
+    });
+
+    test('the receiving channel closes gracefully without a connection',
+        () async {
+      var connectedChannel = IsolateChannel<int>.connectReceive(connectPort);
+      await connectedChannel.sink.close();
+      await expectLater(connectedChannel.stream.toList(), completion(isEmpty));
+      await expectLater(connectedChannel.sink.done, completes);
+    });
+  });
+}

diff --git a/pkgs/stream_channel/test/json_document_transformer_test.dart b/pkgs/stream_channel/test/json_document_transformer_test.dart
new file mode 100644
index 0000000..290c4e2
--- /dev/null
+++ b/pkgs/stream_channel/test/json_document_transformer_test.dart

@@ -0,0 +1,46 @@
+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+import 'dart:convert';
+
+import 'package:stream_channel/stream_channel.dart';
+import 'package:test/test.dart';
+
+void main() {
+  late StreamController<String> streamController;
+  late StreamController<String> sinkController;
+  late StreamChannel<String> channel;
+  setUp(() {
+    streamController = StreamController<String>();
+    sinkController = StreamController<String>();
+    channel =
+        StreamChannel<String>(streamController.stream, sinkController.sink);
+  });
+
+  test('decodes JSON emitted by the channel', () {
+    var transformed = channel.transform(jsonDocument);
+    streamController.add('{"foo": "bar"}');
+    expect(transformed.stream.first, completion(equals({'foo': 'bar'})));
+  });
+
+  test('encodes objects added to the channel', () {
+    var transformed = channel.transform(jsonDocument);
+    transformed.sink.add({'foo': 'bar'});
+    expect(sinkController.stream.first,
+        completion(equals(jsonEncode({'foo': 'bar'}))));
+  });
+
+  test('emits a stream error when incoming JSON is malformed', () {
+    var transformed = channel.transform(jsonDocument);
+    streamController.add('{invalid');
+    expect(transformed.stream.first, throwsFormatException);
+  });
+
+  test('synchronously throws if an unencodable object is added', () {
+    var transformed = channel.transform(jsonDocument);
+    expect(() => transformed.sink.add(Object()),
+        throwsA(const TypeMatcher<JsonUnsupportedObjectError>()));
+  });
+}

diff --git a/pkgs/stream_channel/test/multi_channel_test.dart b/pkgs/stream_channel/test/multi_channel_test.dart
new file mode 100644
index 0000000..ee6f8d2
--- /dev/null
+++ b/pkgs/stream_channel/test/multi_channel_test.dart

@@ -0,0 +1,478 @@
+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:stream_channel/stream_channel.dart';
+import 'package:test/test.dart';
+
+void main() {
+  late StreamChannelController controller;
+  late MultiChannel channel1;
+  late MultiChannel channel2;
+  setUp(() {
+    controller = StreamChannelController();
+    channel1 = MultiChannel<int>(controller.local);
+    channel2 = MultiChannel<int>(controller.foreign);
+  });
+
+  group('the default virtual channel', () {
+    test('begins connected', () {
+      var first = true;
+      channel2.stream.listen(expectAsync1((message) {
+        if (first) {
+          expect(message, equals(1));
+          first = false;
+        } else {
+          expect(message, equals(2));
+        }
+      }, count: 2));
+
+      channel1.sink.add(1);
+      channel1.sink.add(2);
+    });
+
+    test('closes the remote virtual channel when it closes', () {
+      expect(channel2.stream.toList(), completion(isEmpty));
+      expect(channel2.sink.done, completes);
+
+      channel1.sink.close();
+    });
+
+    test('closes the local virtual channel when it closes', () {
+      expect(channel1.stream.toList(), completion(isEmpty));
+      expect(channel1.sink.done, completes);
+
+      channel1.sink.close();
+    });
+
+    test(
+        "doesn't closes the local virtual channel when the stream "
+        'subscription is canceled', () {
+      channel1.sink.done.then(expectAsync1((_) {}, count: 0));
+
+      channel1.stream.listen((_) {}).cancel();
+
+      // Ensure that there's enough time for the channel to close if it's going
+      // to.
+      return pumpEventQueue();
+    });
+
+    test(
+        'closes the underlying channel when it closes without any other '
+        'virtual channels', () {
+      expect(controller.local.sink.done, completes);
+      expect(controller.foreign.sink.done, completes);
+
+      channel1.sink.close();
+    });
+
+    test(
+        "doesn't close the underlying channel when it closes with other "
+        'virtual channels', () {
+      controller.local.sink.done.then(expectAsync1((_) {}, count: 0));
+      controller.foreign.sink.done.then(expectAsync1((_) {}, count: 0));
+
+      // Establish another virtual connection which should keep the underlying
+      // connection open.
+      channel2.virtualChannel(channel1.virtualChannel().id);
+      channel1.sink.close();
+
+      // Ensure that there's enough time for the underlying channel to complete
+      // if it's going to.
+      return pumpEventQueue();
+    });
+  });
+
+  group('a locally-created virtual channel', () {
+    late VirtualChannel virtual1;
+    late VirtualChannel virtual2;
+    setUp(() {
+      virtual1 = channel1.virtualChannel();
+      virtual2 = channel2.virtualChannel(virtual1.id);
+    });
+
+    test('sends messages only to the other virtual channel', () {
+      var first = true;
+      virtual2.stream.listen(expectAsync1((message) {
+        if (first) {
+          expect(message, equals(1));
+          first = false;
+        } else {
+          expect(message, equals(2));
+        }
+      }, count: 2));
+
+      // No other virtual channels should receive the message.
+      for (var i = 0; i < 10; i++) {
+        var virtual = channel2.virtualChannel(channel1.virtualChannel().id);
+        virtual.stream.listen(expectAsync1((_) {}, count: 0));
+      }
+      channel2.stream.listen(expectAsync1((_) {}, count: 0));
+
+      virtual1.sink.add(1);
+      virtual1.sink.add(2);
+    });
+
+    test('closes the remote virtual channel when it closes', () {
+      expect(virtual2.stream.toList(), completion(isEmpty));
+      expect(virtual2.sink.done, completes);
+
+      virtual1.sink.close();
+    });
+
+    test('closes the local virtual channel when it closes', () {
+      expect(virtual1.stream.toList(), completion(isEmpty));
+      expect(virtual1.sink.done, completes);
+
+      virtual1.sink.close();
+    });
+
+    test(
+        "doesn't closes the local virtual channel when the stream "
+        'subscription is canceled', () {
+      virtual1.sink.done.then(expectAsync1((_) {}, count: 0));
+      virtual1.stream.listen((_) {}).cancel();
+
+      // Ensure that there's enough time for the channel to close if it's going
+      // to.
+      return pumpEventQueue();
+    });
+
+    test(
+        'closes the underlying channel when it closes without any other '
+        'virtual channels', () async {
+      // First close the default channel so we can test the new channel as the
+      // last living virtual channel.
+      unawaited(channel1.sink.close());
+
+      await channel2.stream.toList();
+      expect(controller.local.sink.done, completes);
+      expect(controller.foreign.sink.done, completes);
+
+      unawaited(virtual1.sink.close());
+    });
+
+    test(
+        "doesn't close the underlying channel when it closes with other "
+        'virtual channels', () {
+      controller.local.sink.done.then(expectAsync1((_) {}, count: 0));
+      controller.foreign.sink.done.then(expectAsync1((_) {}, count: 0));
+
+      virtual1.sink.close();
+
+      // Ensure that there's enough time for the underlying channel to complete
+      // if it's going to.
+      return pumpEventQueue();
+    });
+
+    test("doesn't conflict with a remote virtual channel", () {
+      var virtual3 = channel2.virtualChannel();
+      var virtual4 = channel1.virtualChannel(virtual3.id);
+
+      // This is an implementation detail, but we assert it here to make sure
+      // we're properly testing two channels with the same id.
+      expect(virtual1.id, equals(virtual3.id));
+
+      virtual2.stream
+          .listen(expectAsync1((message) => expect(message, equals(1))));
+      virtual4.stream
+          .listen(expectAsync1((message) => expect(message, equals(2))));
+
+      virtual1.sink.add(1);
+      virtual3.sink.add(2);
+    });
+  });
+
+  group('a remotely-created virtual channel', () {
+    late VirtualChannel virtual1;
+    late VirtualChannel virtual2;
+    setUp(() {
+      virtual1 = channel1.virtualChannel();
+      virtual2 = channel2.virtualChannel(virtual1.id);
+    });
+
+    test('sends messages only to the other virtual channel', () {
+      var first = true;
+      virtual1.stream.listen(expectAsync1((message) {
+        if (first) {
+          expect(message, equals(1));
+          first = false;
+        } else {
+          expect(message, equals(2));
+        }
+      }, count: 2));
+
+      // No other virtual channels should receive the message.
+      for (var i = 0; i < 10; i++) {
+        var virtual = channel2.virtualChannel(channel1.virtualChannel().id);
+        virtual.stream.listen(expectAsync1((_) {}, count: 0));
+      }
+      channel1.stream.listen(expectAsync1((_) {}, count: 0));
+
+      virtual2.sink.add(1);
+      virtual2.sink.add(2);
+    });
+
+    test('closes the remote virtual channel when it closes', () {
+      expect(virtual1.stream.toList(), completion(isEmpty));
+      expect(virtual1.sink.done, completes);
+
+      virtual2.sink.close();
+    });
+
+    test('closes the local virtual channel when it closes', () {
+      expect(virtual2.stream.toList(), completion(isEmpty));
+      expect(virtual2.sink.done, completes);
+
+      virtual2.sink.close();
+    });
+
+    test(
+        "doesn't closes the local virtual channel when the stream "
+        'subscription is canceled', () {
+      virtual2.sink.done.then(expectAsync1((_) {}, count: 0));
+      virtual2.stream.listen((_) {}).cancel();
+
+      // Ensure that there's enough time for the channel to close if it's going
+      // to.
+      return pumpEventQueue();
+    });
+
+    test(
+        'closes the underlying channel when it closes without any other '
+        'virtual channels', () async {
+      // First close the default channel so we can test the new channel as the
+      // last living virtual channel.
+      unawaited(channel2.sink.close());
+
+      await channel1.stream.toList();
+      expect(controller.local.sink.done, completes);
+      expect(controller.foreign.sink.done, completes);
+
+      unawaited(virtual2.sink.close());
+    });
+
+    test(
+        "doesn't close the underlying channel when it closes with other "
+        'virtual channels', () {
+      controller.local.sink.done.then(expectAsync1((_) {}, count: 0));
+      controller.foreign.sink.done.then(expectAsync1((_) {}, count: 0));
+
+      virtual2.sink.close();
+
+      // Ensure that there's enough time for the underlying channel to complete
+      // if it's going to.
+      return pumpEventQueue();
+    });
+
+    test("doesn't allow another virtual channel with the same id", () {
+      expect(() => channel2.virtualChannel(virtual1.id), throwsArgumentError);
+    });
+
+    test('dispatches events received before the virtual channel is created',
+        () async {
+      virtual1 = channel1.virtualChannel();
+
+      virtual1.sink.add(1);
+      await pumpEventQueue();
+
+      virtual1.sink.add(2);
+      await pumpEventQueue();
+
+      expect(channel2.virtualChannel(virtual1.id).stream, emitsInOrder([1, 2]));
+    });
+
+    test(
+        'dispatches close events received before the virtual channel is '
+        'created', () async {
+      virtual1 = channel1.virtualChannel();
+
+      unawaited(virtual1.sink.close());
+      await pumpEventQueue();
+
+      expect(channel2.virtualChannel(virtual1.id).stream.toList(),
+          completion(isEmpty));
+    });
+  });
+
+  group('when the underlying stream', () {
+    late VirtualChannel virtual1;
+    late VirtualChannel virtual2;
+    setUp(() {
+      virtual1 = channel1.virtualChannel();
+      virtual2 = channel2.virtualChannel(virtual1.id);
+    });
+
+    test('closes, all virtual channels close', () {
+      expect(channel1.stream.toList(), completion(isEmpty));
+      expect(channel1.sink.done, completes);
+      expect(channel2.stream.toList(), completion(isEmpty));
+      expect(channel2.sink.done, completes);
+      expect(virtual1.stream.toList(), completion(isEmpty));
+      expect(virtual1.sink.done, completes);
+      expect(virtual2.stream.toList(), completion(isEmpty));
+      expect(virtual2.sink.done, completes);
+
+      controller.local.sink.close();
+    });
+
+    test('closes, more virtual channels are created closed', () async {
+      unawaited(channel2.sink.close());
+      unawaited(virtual2.sink.close());
+
+      // Wait for the existing channels to emit done events.
+      await channel1.stream.toList();
+      await virtual1.stream.toList();
+
+      var virtual = channel1.virtualChannel();
+      expect(virtual.stream.toList(), completion(isEmpty));
+      expect(virtual.sink.done, completes);
+
+      virtual = channel1.virtualChannel();
+      expect(virtual.stream.toList(), completion(isEmpty));
+      expect(virtual.sink.done, completes);
+    });
+
+    test('emits an error, the error is sent only to the default channel', () {
+      channel1.stream.listen(expectAsync1((_) {}, count: 0),
+          onError: expectAsync1((error) => expect(error, equals('oh no'))));
+      virtual1.stream.listen(expectAsync1((_) {}, count: 0),
+          onError: expectAsync1((_) {}, count: 0));
+
+      controller.foreign.sink.addError('oh no');
+    });
+  });
+
+  group('stream channel rules', () {
+    group('for the main stream:', () {
+      test(
+          'closing the sink causes the stream to close before it emits any '
+          'more events', () {
+        channel1.sink.add(1);
+        channel1.sink.add(2);
+        channel1.sink.add(3);
+
+        channel2.stream.listen(expectAsync1((message) {
+          expect(message, equals(1));
+          channel2.sink.close();
+        }, count: 1));
+      });
+
+      test('after the stream closes, the sink ignores events', () async {
+        unawaited(channel1.sink.close());
+
+        // Wait for the done event to be delivered.
+        await channel2.stream.toList();
+        channel2.sink.add(1);
+        channel2.sink.add(2);
+        channel2.sink.add(3);
+        unawaited(channel2.sink.close());
+
+        // None of our channel.sink additions should make it to the other
+        // endpoint.
+        channel1.stream.listen(expectAsync1((_) {}, count: 0));
+        await pumpEventQueue();
+      });
+
+      test("canceling the stream's subscription has no effect on the sink",
+          () async {
+        unawaited(channel1.stream.listen(null).cancel());
+        await pumpEventQueue();
+
+        channel1.sink.add(1);
+        channel1.sink.add(2);
+        channel1.sink.add(3);
+        unawaited(channel1.sink.close());
+        expect(channel2.stream.toList(), completion(equals([1, 2, 3])));
+      });
+
+      test("canceling the stream's subscription doesn't stop a done event",
+          () async {
+        unawaited(channel1.stream.listen(null).cancel());
+        await pumpEventQueue();
+
+        unawaited(channel2.sink.close());
+        await pumpEventQueue();
+
+        channel1.sink.add(1);
+        channel1.sink.add(2);
+        channel1.sink.add(3);
+        unawaited(channel1.sink.close());
+
+        // The sink should be ignoring events because the channel closed.
+        channel2.stream.listen(expectAsync1((_) {}, count: 0));
+        await pumpEventQueue();
+      });
+    });
+
+    group('for a virtual channel:', () {
+      late VirtualChannel virtual1;
+      late VirtualChannel virtual2;
+      setUp(() {
+        virtual1 = channel1.virtualChannel();
+        virtual2 = channel2.virtualChannel(virtual1.id);
+      });
+
+      test(
+          'closing the sink causes the stream to close before it emits any '
+          'more events', () {
+        virtual1.sink.add(1);
+        virtual1.sink.add(2);
+        virtual1.sink.add(3);
+
+        virtual2.stream.listen(expectAsync1((message) {
+          expect(message, equals(1));
+          virtual2.sink.close();
+        }, count: 1));
+      });
+
+      test('after the stream closes, the sink ignores events', () async {
+        unawaited(virtual1.sink.close());
+
+        // Wait for the done event to be delivered.
+        await virtual2.stream.toList();
+        virtual2.sink.add(1);
+        virtual2.sink.add(2);
+        virtual2.sink.add(3);
+        unawaited(virtual2.sink.close());
+
+        // None of our virtual.sink additions should make it to the other
+        // endpoint.
+        virtual1.stream.listen(expectAsync1((_) {}, count: 0));
+        await pumpEventQueue();
+      });
+
+      test("canceling the stream's subscription has no effect on the sink",
+          () async {
+        unawaited(virtual1.stream.listen(null).cancel());
+        await pumpEventQueue();
+
+        virtual1.sink.add(1);
+        virtual1.sink.add(2);
+        virtual1.sink.add(3);
+        unawaited(virtual1.sink.close());
+        expect(virtual2.stream.toList(), completion(equals([1, 2, 3])));
+      });
+
+      test("canceling the stream's subscription doesn't stop a done event",
+          () async {
+        unawaited(virtual1.stream.listen(null).cancel());
+        await pumpEventQueue();
+
+        unawaited(virtual2.sink.close());
+        await pumpEventQueue();
+
+        virtual1.sink.add(1);
+        virtual1.sink.add(2);
+        virtual1.sink.add(3);
+        unawaited(virtual1.sink.close());
+
+        // The sink should be ignoring events because the stream closed.
+        virtual2.stream.listen(expectAsync1((_) {}, count: 0));
+        await pumpEventQueue();
+      });
+    });
+  });
+}

diff --git a/pkgs/stream_channel/test/stream_channel_completer_test.dart b/pkgs/stream_channel/test/stream_channel_completer_test.dart
new file mode 100644
index 0000000..c6fddc0
--- /dev/null
+++ b/pkgs/stream_channel/test/stream_channel_completer_test.dart

@@ -0,0 +1,120 @@
+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:stream_channel/stream_channel.dart';
+import 'package:test/test.dart';
+
+void main() {
+  late StreamChannelCompleter completer;
+  late StreamController streamController;
+  late StreamController sinkController;
+  late StreamChannel innerChannel;
+  setUp(() {
+    completer = StreamChannelCompleter();
+    streamController = StreamController<void>();
+    sinkController = StreamController<void>();
+    innerChannel = StreamChannel(streamController.stream, sinkController.sink);
+  });
+
+  group('when a channel is set before accessing', () {
+    test('forwards events through the stream', () {
+      completer.setChannel(innerChannel);
+      expect(completer.channel.stream.toList(), completion(equals([1, 2, 3])));
+
+      streamController.add(1);
+      streamController.add(2);
+      streamController.add(3);
+      streamController.close();
+    });
+
+    test('forwards events through the sink', () {
+      completer.setChannel(innerChannel);
+      expect(sinkController.stream.toList(), completion(equals([1, 2, 3])));
+
+      completer.channel.sink.add(1);
+      completer.channel.sink.add(2);
+      completer.channel.sink.add(3);
+      completer.channel.sink.close();
+    });
+
+    test('forwards an error through the stream', () {
+      completer.setError('oh no');
+      expect(completer.channel.stream.first, throwsA('oh no'));
+    });
+
+    test('drops sink events', () {
+      completer.setError('oh no');
+      expect(completer.channel.sink.done, completes);
+      completer.channel.sink.add(1);
+      completer.channel.sink.addError('oh no');
+    });
+  });
+
+  group('when a channel is set after accessing', () {
+    test('forwards events through the stream', () async {
+      expect(completer.channel.stream.toList(), completion(equals([1, 2, 3])));
+      await pumpEventQueue();
+
+      completer.setChannel(innerChannel);
+      streamController.add(1);
+      streamController.add(2);
+      streamController.add(3);
+      unawaited(streamController.close());
+    });
+
+    test('forwards events through the sink', () async {
+      completer.channel.sink.add(1);
+      completer.channel.sink.add(2);
+      completer.channel.sink.add(3);
+      unawaited(completer.channel.sink.close());
+      await pumpEventQueue();
+
+      completer.setChannel(innerChannel);
+      expect(sinkController.stream.toList(), completion(equals([1, 2, 3])));
+    });
+
+    test('forwards an error through the stream', () async {
+      expect(completer.channel.stream.first, throwsA('oh no'));
+      await pumpEventQueue();
+
+      completer.setError('oh no');
+    });
+
+    test('drops sink events', () async {
+      expect(completer.channel.sink.done, completes);
+      completer.channel.sink.add(1);
+      completer.channel.sink.addError('oh no');
+      await pumpEventQueue();
+
+      completer.setError('oh no');
+    });
+  });
+
+  group('forFuture', () {
+    test('forwards a StreamChannel', () {
+      var channel =
+          StreamChannelCompleter.fromFuture(Future.value(innerChannel));
+      channel.sink.add(1);
+      channel.sink.close();
+      streamController.sink.add(2);
+      streamController.sink.close();
+
+      expect(sinkController.stream.toList(), completion(equals([1])));
+      expect(channel.stream.toList(), completion(equals([2])));
+    });
+
+    test('forwards an error', () {
+      var channel = StreamChannelCompleter.fromFuture(Future.error('oh no'));
+      expect(channel.stream.toList(), throwsA('oh no'));
+    });
+  });
+
+  test("doesn't allow the channel to be set multiple times", () {
+    completer.setChannel(innerChannel);
+    expect(() => completer.setChannel(innerChannel), throwsStateError);
+    expect(() => completer.setChannel(innerChannel), throwsStateError);
+  });
+}

diff --git a/pkgs/stream_channel/test/stream_channel_controller_test.dart b/pkgs/stream_channel/test/stream_channel_controller_test.dart
new file mode 100644
index 0000000..3d661e3
--- /dev/null
+++ b/pkgs/stream_channel/test/stream_channel_controller_test.dart

@@ -0,0 +1,104 @@
+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:stream_channel/stream_channel.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('asynchronously', () {
+    late StreamChannelController controller;
+    setUp(() {
+      controller = StreamChannelController();
+    });
+
+    test('forwards events from the local sink to the foreign stream', () {
+      controller.local.sink
+        ..add(1)
+        ..add(2)
+        ..add(3)
+        ..close();
+      expect(controller.foreign.stream.toList(), completion(equals([1, 2, 3])));
+    });
+
+    test('forwards events from the foreign sink to the local stream', () {
+      controller.foreign.sink
+        ..add(1)
+        ..add(2)
+        ..add(3)
+        ..close();
+      expect(controller.local.stream.toList(), completion(equals([1, 2, 3])));
+    });
+
+    test(
+        'with allowForeignErrors: false, shuts down the connection if an '
+        'error is added to the foreign channel', () {
+      controller = StreamChannelController(allowForeignErrors: false);
+
+      controller.foreign.sink.addError('oh no');
+      expect(controller.foreign.sink.done, throwsA('oh no'));
+      expect(controller.foreign.stream.toList(), completion(isEmpty));
+      expect(controller.local.sink.done, completes);
+      expect(controller.local.stream.toList(), completion(isEmpty));
+    });
+  });
+
+  group('synchronously', () {
+    late StreamChannelController controller;
+    setUp(() {
+      controller = StreamChannelController(sync: true);
+    });
+
+    test(
+        'synchronously forwards events from the local sink to the foreign '
+        'stream', () {
+      var receivedEvent = false;
+      var receivedError = false;
+      var receivedDone = false;
+      controller.foreign.stream.listen(expectAsync1((event) {
+        expect(event, equals(1));
+        receivedEvent = true;
+      }), onError: expectAsync1((error) {
+        expect(error, equals('oh no'));
+        receivedError = true;
+      }), onDone: expectAsync0(() {
+        receivedDone = true;
+      }));
+
+      controller.local.sink.add(1);
+      expect(receivedEvent, isTrue);
+
+      controller.local.sink.addError('oh no');
+      expect(receivedError, isTrue);
+
+      controller.local.sink.close();
+      expect(receivedDone, isTrue);
+    });
+
+    test(
+        'synchronously forwards events from the foreign sink to the local '
+        'stream', () {
+      var receivedEvent = false;
+      var receivedError = false;
+      var receivedDone = false;
+      controller.local.stream.listen(expectAsync1((event) {
+        expect(event, equals(1));
+        receivedEvent = true;
+      }), onError: expectAsync1((error) {
+        expect(error, equals('oh no'));
+        receivedError = true;
+      }), onDone: expectAsync0(() {
+        receivedDone = true;
+      }));
+
+      controller.foreign.sink.add(1);
+      expect(receivedEvent, isTrue);
+
+      controller.foreign.sink.addError('oh no');
+      expect(receivedError, isTrue);
+
+      controller.foreign.sink.close();
+      expect(receivedDone, isTrue);
+    });
+  });
+}

diff --git a/pkgs/stream_channel/test/stream_channel_test.dart b/pkgs/stream_channel/test/stream_channel_test.dart
new file mode 100644
index 0000000..166671d
--- /dev/null
+++ b/pkgs/stream_channel/test/stream_channel_test.dart

@@ -0,0 +1,180 @@
+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+import 'dart:convert';
+
+import 'package:async/async.dart';
+import 'package:stream_channel/stream_channel.dart';
+import 'package:test/test.dart';
+
+void main() {
+  test("pipe() pipes data from each channel's stream into the other's sink",
+      () {
+    var otherStreamController = StreamController<int>();
+    var otherSinkController = StreamController<int>();
+    var otherChannel =
+        StreamChannel(otherStreamController.stream, otherSinkController.sink);
+
+    var streamController = StreamController<int>();
+    var sinkController = StreamController<int>();
+    var channel = StreamChannel(streamController.stream, sinkController.sink);
+
+    channel.pipe(otherChannel);
+
+    streamController.add(1);
+    streamController.add(2);
+    streamController.add(3);
+    streamController.close();
+    expect(otherSinkController.stream.toList(), completion(equals([1, 2, 3])));
+
+    otherStreamController.add(4);
+    otherStreamController.add(5);
+    otherStreamController.add(6);
+    otherStreamController.close();
+    expect(sinkController.stream.toList(), completion(equals([4, 5, 6])));
+  });
+
+  test('transform() transforms the channel', () async {
+    var streamController = StreamController<List<int>>();
+    var sinkController = StreamController<List<int>>();
+    var channel = StreamChannel(streamController.stream, sinkController.sink);
+
+    var transformed = channel
+        .cast<List<int>>()
+        .transform(StreamChannelTransformer.fromCodec(utf8));
+
+    streamController.add([102, 111, 111, 98, 97, 114]);
+    unawaited(streamController.close());
+    expect(await transformed.stream.toList(), equals(['foobar']));
+
+    transformed.sink.add('fblthp');
+    unawaited(transformed.sink.close());
+    expect(
+        sinkController.stream.toList(),
+        completion(equals([
+          [102, 98, 108, 116, 104, 112]
+        ])));
+  });
+
+  test('transformStream() transforms only the stream', () async {
+    var streamController = StreamController<String>();
+    var sinkController = StreamController<String>();
+    var channel = StreamChannel(streamController.stream, sinkController.sink);
+
+    var transformed =
+        channel.cast<String>().transformStream(const LineSplitter());
+
+    streamController.add('hello world');
+    streamController.add(' what\nis');
+    streamController.add('\nup');
+    unawaited(streamController.close());
+    expect(await transformed.stream.toList(),
+        equals(['hello world what', 'is', 'up']));
+
+    transformed.sink.add('fbl\nthp');
+    unawaited(transformed.sink.close());
+    expect(sinkController.stream.toList(), completion(equals(['fbl\nthp'])));
+  });
+
+  test('transformSink() transforms only the sink', () async {
+    var streamController = StreamController<String>();
+    var sinkController = StreamController<String>();
+    var channel = StreamChannel(streamController.stream, sinkController.sink);
+
+    var transformed = channel.cast<String>().transformSink(
+        const StreamSinkTransformer.fromStreamTransformer(LineSplitter()));
+
+    streamController.add('fbl\nthp');
+    unawaited(streamController.close());
+    expect(await transformed.stream.toList(), equals(['fbl\nthp']));
+
+    transformed.sink.add('hello world');
+    transformed.sink.add(' what\nis');
+    transformed.sink.add('\nup');
+    unawaited(transformed.sink.close());
+    expect(sinkController.stream.toList(),
+        completion(equals(['hello world what', 'is', 'up'])));
+  });
+
+  test('changeStream() changes the stream', () {
+    var streamController = StreamController<int>();
+    var sinkController = StreamController<int>();
+    var channel = StreamChannel(streamController.stream, sinkController.sink);
+
+    var newController = StreamController<int>();
+    var changed = channel.changeStream((stream) {
+      expect(stream, equals(channel.stream));
+      return newController.stream;
+    });
+
+    newController.add(10);
+    newController.close();
+
+    streamController.add(20);
+    streamController.close();
+
+    expect(changed.stream.toList(), completion(equals([10])));
+  });
+
+  test('changeSink() changes the sink', () {
+    var streamController = StreamController<int>();
+    var sinkController = StreamController<int>();
+    var channel = StreamChannel(streamController.stream, sinkController.sink);
+
+    var newController = StreamController<int>();
+    var changed = channel.changeSink((sink) {
+      expect(sink, equals(channel.sink));
+      return newController.sink;
+    });
+
+    expect(newController.stream.toList(), completion(equals([10])));
+    streamController.stream.listen(expectAsync1((_) {}, count: 0));
+
+    changed.sink.add(10);
+    changed.sink.close();
+  });
+
+  group('StreamChannelMixin', () {
+    test('can be used as a mixin', () async {
+      var channel = StreamChannelMixinAsMixin<int>();
+      expect(channel.stream, emitsInOrder([1, 2, 3]));
+      channel.sink
+        ..add(1)
+        ..add(2)
+        ..add(3);
+      await channel.controller.close();
+    });
+
+    test('can be extended', () async {
+      var channel = StreamChannelMixinAsSuperclass<int>();
+      expect(channel.stream, emitsInOrder([1, 2, 3]));
+      channel.sink
+        ..add(1)
+        ..add(2)
+        ..add(3);
+      await channel.controller.close();
+    });
+  });
+}
+
+class StreamChannelMixinAsMixin<T> with StreamChannelMixin<T> {
+  final controller = StreamController<T>();
+
+  @override
+  StreamSink<T> get sink => controller.sink;
+
+  @override
+  Stream<T> get stream => controller.stream;
+}
+
+class StreamChannelMixinAsSuperclass<T> extends StreamChannelMixin<T> {
+  final controller = StreamController<T>();
+
+  @override
+  StreamSink<T> get sink => controller.sink;
+
+  @override
+  Stream<T> get stream => controller.stream;
+}

diff --git a/pkgs/stream_channel/test/with_close_guarantee_test.dart b/pkgs/stream_channel/test/with_close_guarantee_test.dart
new file mode 100644
index 0000000..9c0b729
--- /dev/null
+++ b/pkgs/stream_channel/test/with_close_guarantee_test.dart

@@ -0,0 +1,69 @@
+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:async/async.dart';
+import 'package:stream_channel/stream_channel.dart';
+import 'package:test/test.dart';
+
+final _delayTransformer = StreamTransformer.fromHandlers(
+    handleData: (data, sink) => Future.microtask(() => sink.add(data)),
+    handleDone: (sink) => Future.microtask(() => sink.close()));
+
+final _delaySinkTransformer =
+    StreamSinkTransformer.fromStreamTransformer(_delayTransformer);
+
+void main() {
+  late StreamChannelController controller;
+  late StreamChannel channel;
+  setUp(() {
+    controller = StreamChannelController();
+
+    // Add a bunch of layers of asynchronous dispatch between the channel and
+    // the underlying controllers.
+    var stream = controller.foreign.stream;
+    var sink = controller.foreign.sink;
+    for (var i = 0; i < 10; i++) {
+      stream = stream.transform(_delayTransformer);
+      sink = _delaySinkTransformer.bind(sink);
+    }
+
+    channel = StreamChannel.withCloseGuarantee(stream, sink);
+  });
+
+  test(
+      'closing the event sink causes the stream to close before it emits any '
+      'more events', () async {
+    controller.local.sink.add(1);
+    controller.local.sink.add(2);
+    controller.local.sink.add(3);
+
+    expect(
+        channel.stream
+            .listen(expectAsync1((event) {
+              if (event == 2) channel.sink.close();
+            }, count: 2))
+            .asFuture<void>(),
+        completes);
+
+    await pumpEventQueue();
+  });
+
+  test(
+      'closing the event sink before events are emitted causes the stream to '
+      'close immediately', () async {
+    unawaited(channel.sink.close());
+    channel.stream.listen(expectAsync1((_) {}, count: 0),
+        onError: expectAsync2((_, __) {}, count: 0),
+        onDone: expectAsync0(() {}));
+
+    controller.local.sink.add(1);
+    controller.local.sink.add(2);
+    controller.local.sink.add(3);
+    unawaited(controller.local.sink.close());
+
+    await pumpEventQueue();
+  });
+}

diff --git a/pkgs/stream_channel/test/with_guarantees_test.dart b/pkgs/stream_channel/test/with_guarantees_test.dart
new file mode 100644
index 0000000..f026079
--- /dev/null
+++ b/pkgs/stream_channel/test/with_guarantees_test.dart

@@ -0,0 +1,200 @@
+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:stream_channel/stream_channel.dart';
+import 'package:test/test.dart';
+
+void main() {
+  late StreamController streamController;
+  late StreamController sinkController;
+  late StreamChannel channel;
+  setUp(() {
+    streamController = StreamController<void>();
+    sinkController = StreamController<void>();
+    channel = StreamChannel.withGuarantees(
+        streamController.stream, sinkController.sink);
+  });
+
+  group('with a broadcast stream', () {
+    setUp(() {
+      streamController = StreamController.broadcast();
+      channel = StreamChannel.withGuarantees(
+          streamController.stream, sinkController.sink);
+    });
+
+    test('buffers events', () async {
+      streamController.add(1);
+      streamController.add(2);
+      streamController.add(3);
+      await pumpEventQueue();
+
+      expect(channel.stream.toList(), completion(equals([1, 2, 3])));
+      unawaited(streamController.close());
+    });
+
+    test('only allows a single subscription', () {
+      channel.stream.listen(null);
+      expect(() => channel.stream.listen(null), throwsStateError);
+    });
+  });
+
+  test(
+      'closing the event sink causes the stream to close before it emits any '
+      'more events', () {
+    streamController.add(1);
+    streamController.add(2);
+    streamController.add(3);
+
+    expect(
+        channel.stream
+            .listen(expectAsync1((event) {
+              if (event == 2) channel.sink.close();
+            }, count: 2))
+            .asFuture<void>(),
+        completes);
+  });
+
+  test('after the stream closes, the sink ignores events', () async {
+    unawaited(streamController.close());
+
+    // Wait for the done event to be delivered.
+    await channel.stream.toList();
+    channel.sink.add(1);
+    channel.sink.add(2);
+    channel.sink.add(3);
+    unawaited(channel.sink.close());
+
+    // None of our channel.sink additions should make it to the other endpoint.
+    sinkController.stream.listen(expectAsync1((_) {}, count: 0),
+        onDone: expectAsync0(() {}, count: 0));
+    await pumpEventQueue();
+  });
+
+  test("canceling the stream's subscription has no effect on the sink",
+      () async {
+    unawaited(channel.stream.listen(null).cancel());
+    await pumpEventQueue();
+
+    channel.sink.add(1);
+    channel.sink.add(2);
+    channel.sink.add(3);
+    unawaited(channel.sink.close());
+    expect(sinkController.stream.toList(), completion(equals([1, 2, 3])));
+  });
+
+  test("canceling the stream's subscription doesn't stop a done event",
+      () async {
+    unawaited(channel.stream.listen(null).cancel());
+    await pumpEventQueue();
+
+    unawaited(streamController.close());
+    await pumpEventQueue();
+
+    channel.sink.add(1);
+    channel.sink.add(2);
+    channel.sink.add(3);
+    unawaited(channel.sink.close());
+
+    // The sink should be ignoring events because the stream closed.
+    sinkController.stream.listen(expectAsync1((_) {}, count: 0),
+        onDone: expectAsync0(() {}, count: 0));
+    await pumpEventQueue();
+  });
+
+  test('forwards errors to the other endpoint', () {
+    channel.sink.addError('error');
+    expect(sinkController.stream.first, throwsA('error'));
+  });
+
+  test('Sink.done completes once the stream is done', () {
+    channel.stream.listen(null);
+    expect(channel.sink.done, completes);
+    streamController.close();
+  });
+
+  test("events can't be added to an explicitly-closed sink", () {
+    sinkController.stream.listen(null); // Work around sdk#19095.
+
+    expect(channel.sink.close(), completes);
+    expect(() => channel.sink.add(1), throwsStateError);
+    expect(() => channel.sink.addError('oh no'), throwsStateError);
+    expect(() => channel.sink.addStream(Stream.fromIterable([])),
+        throwsStateError);
+  });
+
+  test("events can't be added while a stream is being added", () {
+    var controller = StreamController<void>();
+    channel.sink.addStream(controller.stream);
+
+    expect(() => channel.sink.add(1), throwsStateError);
+    expect(() => channel.sink.addError('oh no'), throwsStateError);
+    expect(() => channel.sink.addStream(Stream.fromIterable([])),
+        throwsStateError);
+    expect(() => channel.sink.close(), throwsStateError);
+
+    controller.close();
+  });
+
+  group('with allowSinkErrors: false', () {
+    setUp(() {
+      streamController = StreamController<void>();
+      sinkController = StreamController<void>();
+      channel = StreamChannel.withGuarantees(
+          streamController.stream, sinkController.sink,
+          allowSinkErrors: false);
+    });
+
+    test('forwards errors to Sink.done but not the stream', () {
+      channel.sink.addError('oh no');
+      expect(channel.sink.done, throwsA('oh no'));
+      sinkController.stream
+          .listen(null, onError: expectAsync1((dynamic _) {}, count: 0));
+    });
+
+    test('adding an error causes the stream to emit a done event', () {
+      expect(channel.sink.done, throwsA('oh no'));
+
+      streamController.add(1);
+      streamController.add(2);
+      streamController.add(3);
+
+      expect(
+          channel.stream
+              .listen(expectAsync1((event) {
+                if (event == 2) channel.sink.addError('oh no');
+              }, count: 2))
+              .asFuture<void>(),
+          completes);
+    });
+
+    test('adding an error closes the inner sink', () {
+      channel.sink.addError('oh no');
+      expect(channel.sink.done, throwsA('oh no'));
+      expect(sinkController.stream.toList(), completion(isEmpty));
+    });
+
+    test(
+        'adding an error via via addStream causes the stream to emit a done '
+        'event', () async {
+      var canceled = false;
+      var controller = StreamController<void>(onCancel: () {
+        canceled = true;
+      });
+
+      // This future shouldn't get the error, because it's sent to [Sink.done].
+      expect(channel.sink.addStream(controller.stream), completes);
+
+      controller.addError('oh no');
+      expect(channel.sink.done, throwsA('oh no'));
+      await pumpEventQueue();
+      expect(canceled, isTrue);
+
+      // Even though the sink is closed, this shouldn't throw an error because
+      // the user didn't explicitly close it.
+      channel.sink.add(1);
+    });
+  });
+}

diff --git a/pkgs/stream_transform/.gitignore b/pkgs/stream_transform/.gitignore
new file mode 100644
index 0000000..bfffcc6
--- /dev/null
+++ b/pkgs/stream_transform/.gitignore

@@ -0,0 +1,6 @@
+.pub/
+.dart_tool/
+build/
+packages
+pubspec.lock
+.packages

diff --git a/pkgs/stream_transform/CHANGELOG.md b/pkgs/stream_transform/CHANGELOG.md
new file mode 100644
index 0000000..b09778b
--- /dev/null
+++ b/pkgs/stream_transform/CHANGELOG.md

@@ -0,0 +1,189 @@
+## 2.1.2-wip
+
+- Require Dart 3.4 or greater.
+
+## 2.1.1
+
+- Require Dart 3.1 or greater
+- Forward errors from the `trigger` future through to the result stream in
+  `takeUntil`. Previously an error would have not closed the stream, and instead
+  raised as an unhandled async error.
+- Move to `dart-lang/tools` monorepo.
+
+## 2.1.0
+
+- Add `whereNotNull`.
+
+## 2.0.1
+
+- Require Dart 2.14 or greater.
+- Wait for the future returned from `StreamSubscription.cancel()` before
+  listening to the subsequent stream in `switchLatest` and `switchMap`.
+
+## 2.0.0
+
+- Migrate to null safety.
+- Improve tests of `switchMap` and improve documentation with links and
+  clarification.
+- Add `trailing` argument to `throttle`.
+
+## 1.2.0
+
+-  Add support for emitting the "leading" event in `debounce`.
+
+## 1.1.1
+
+-   Fix a bug in `asyncMapSample`, `buffer`, `combineLatest`,
+    `combineLatestAll`, `merge`, and `mergeAll` which would cause an exception
+    when cancelling a subscription after using the transformer if the original
+    stream(s) returned `null` from cancelling their subscriptions.
+
+## 1.1.0
+
+-   Add `concurrentAsyncExpand` to interleave events emitted by multiple sub
+    streams created by a callback.
+
+## 1.0.0
+
+-   Remove the top level methods and retain the extensions only.
+
+## 0.0.20
+
+-   Add extension methods for most transformers. These should be used in place
+    of the current methods. All current implementations are deprecated and will
+    be removed in the next major version bump.
+    -   Migrating typical use: Instead of
+        `stream.transform(debounce(Duration(seconds: 1)))` use
+        `stream.debounce(Duration(seconds: 1))`.
+    -   To migrate a usage where a `StreamTransformer` instance is stored or
+        passed see "Getting a StreamTransformer instance" on the README.
+-   The `map` and `chainTransformers` utilities are no longer useful with the
+    new patterns so they are deprecated without a replacement. If you still have
+    a need for them they can be replicated with `StreamTransformer.fromBind`:
+
+    ```
+    // Replace `map(convert)`
+    StreamTransformer.fromBind((s) => s.map(convert));
+
+    // Replace `chainTransformers(first, second)`
+    StreamTransformer.fromBind((s) => s.transform(first).transform(second));
+    ```
+
+## 0.0.19
+
+- Add `asyncMapSample` transform.
+
+## 0.0.18
+
+- Internal cleanup. Passed "trigger" streams or futures now allow `<void>`
+  generic type rather than an implicit `dynamic>`
+
+## 0.0.17
+
+- Add concrete types to the `onError` callback in `tap`.
+
+## 0.0.16+1
+
+- Remove usage of Set literal which is not available before Dart 2.2.0
+
+## 0.0.16
+
+- Allow a `combine` callback to return a `FutureOr<T>` in `scan`. There are no
+  behavior changes for synchronous callbacks. **Potential breaking change** In
+  the unlikely situation where `scan` was used to produce a `Stream<Future>`
+  inference may now fail and require explicit generic type arguments.
+- Add `combineLatest`.
+- Add `combineLatestAll`.
+
+## 0.0.15
+
+- Add `whereType`.
+
+## 0.0.14+1
+
+- Allow using non-dev Dart 2 SDK.
+
+## 0.0.14
+
+- `asyncWhere` will now forward exceptions thrown by the callback through the
+  result Stream.
+- Added `concurrentAsyncMap`.
+
+## 0.0.13
+
+- `mergeAll` now accepts an `Iterable<Stream>` instead of only `List<Stream>`.
+
+## 0.0.12
+
+- Add `chainTransformers` and `map` for use cases where `StreamTransformer`
+  instances are stored as variables or passed to methods other than `transform`.
+
+## 0.0.11
+
+- Renamed `concat` as `followedBy` to match the naming of `Iterable.followedBy`.
+  `concat` is now deprecated.
+
+## 0.0.10
+
+- Updates to support Dart 2.0 core library changes (wave
+  2.2). See [issue 31847][sdk#31847] for details.
+
+  [sdk#31847]: https://github.com/dart-lang/sdk/issues/31847
+
+## 0.0.9
+
+- Add `asyncMapBuffer`.
+
+## 0.0.8
+
+- Add `takeUntil`.
+
+## 0.0.7
+
+- Bug Fix: Streams produced with `scan` and `switchMap` now correctly report
+  `isBroadcast`.
+- Add `startWith`, `startWithMany`, and `startWithStream`.
+
+## 0.0.6
+
+- Bug Fix: Some transformers did not correctly add data to all listeners on
+  broadcast streams. Fixed for `throttle`, `debounce`, `asyncWhere` and `audit`.
+- Bug Fix: Only call the `tap` data callback once per event rather than once per
+  listener.
+- Bug Fix: Allow canceling and re-listening to broadcast streams after a
+  `merge` transform.
+- Bug Fix: Broadcast streams which are buffered using a single-subscription
+  trigger can be canceled and re-listened.
+- Bug Fix: Buffer outputs one more value if there is a pending trigger before
+  the trigger closes.
+- Bug Fix: Single-subscription streams concatted after broadcast streams are
+  handled correctly.
+- Use sync `StreamControllers` for forwarding where possible.
+
+## 0.0.5
+
+- Bug Fix: Allow compiling switchLatest with Dart2Js.
+- Add `asyncWhere`: Like `where` but allows an asynchronous predicate.
+
+## 0.0.4
+- Add `scan`: fold which returns intermediate values
+- Add `throttle`: block events for a duration after emitting a value
+- Add `audit`: emits the last event received after a duration
+
+## 0.0.3
+
+- Add `tap`: React to values as they pass without being a subscriber on a stream
+- Add `switchMap` and `switchLatest`: Flatten a Stream of Streams into a Stream
+  which forwards values from the most recent Stream
+
+## 0.0.2
+
+- Add `concat`: Appends streams in series
+- Add `merge` and `mergeAll`: Interleaves streams
+
+## 0.0.1
+
+- Initial release with the following utilities:
+  - `buffer`: Collects events in a `List` until a `trigger` stream fires.
+  - `debounce`, `debounceBuffer`: Collect or drop events which occur closer in
+    time than a given duration.

diff --git a/pkgs/stream_transform/LICENSE b/pkgs/stream_transform/LICENSE
new file mode 100644
index 0000000..03af64a
--- /dev/null
+++ b/pkgs/stream_transform/LICENSE

@@ -0,0 +1,27 @@
+Copyright 2017, the Dart project authors. 
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+    * Neither the name of Google LLC nor the names of its
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

diff --git a/pkgs/stream_transform/README.md b/pkgs/stream_transform/README.md
new file mode 100644
index 0000000..e7049bd
--- /dev/null
+++ b/pkgs/stream_transform/README.md

@@ -0,0 +1,141 @@
+[![Build Status](https://github.com/dart-lang/tools/actions/workflows/stream_transform.yaml/badge.svg)](https://github.com/dart-lang/tools/actions/workflows/stream_transform.yaml)
+[![pub package](https://img.shields.io/pub/v/stream_transform.svg)](https://pub.dev/packages/stream_transform)
+[![package publisher](https://img.shields.io/pub/publisher/stream_transform.svg)](https://pub.dev/packages/stream_transform/publisher)
+
+Extension methods on `Stream` adding common transform operators.
+
+## Operators
+
+### asyncMapBuffer, asyncMapSample, concurrentAsyncMap
+
+Alternatives to `asyncMap`. `asyncMapBuffer` prevents the callback from
+overlapping execution and collects events while it is executing.
+`asyncMapSample` prevents overlapping execution and discards events while it is
+executing. `concurrentAsyncMap` allows overlap and removes ordering guarantees
+for higher throughput.
+
+Like `asyncMap` but events are buffered in a List until previous events have
+been processed rather than being called for each element individually.
+
+### asyncWhere
+
+Like `where` but allows an asynchronous predicate.
+
+### audit
+
+Waits for a period of time after receiving a value and then only emits the most
+recent value.
+
+### buffer
+
+Collects values from a source stream until a `trigger` stream fires and the
+collected values are emitted.
+
+### combineLatest, combineLatestAll
+
+Combine the most recent event from multiple streams through a callback or into a
+list.
+
+### debounce, debounceBuffer
+
+Prevents a source stream from emitting too frequently by dropping or collecting
+values that occur within a given duration.
+
+### followedBy
+
+Appends the values of a stream after another stream finishes.
+
+### merge, mergeAll, concurrentAsyncExpand
+
+Interleaves events from multiple streams into a single stream.
+
+### scan
+
+Scan is like fold, but instead of producing a single value it yields each
+intermediate accumulation.
+
+### startWith, startWithMany, startWithStream
+
+Prepend a value, an iterable, or a stream to the beginning of another stream.
+
+### switchMap, switchLatest
+
+Flatten a Stream of Streams into a Stream which forwards values from the most
+recent Stream
+
+### takeUntil
+
+Let values through until a Future fires.
+
+### tap
+
+Taps into a single-subscriber stream to react to values as they pass, without
+being a real subscriber.
+
+### throttle
+
+Blocks events for a duration after an event is successfully emitted.
+
+### whereType
+
+Like `Iterable.whereType` for a stream.
+
+## Comparison to Rx Operators
+
+The semantics and naming in this package have some overlap, and some conflict,
+with the [ReactiveX](https://reactivex.io/) suite of libraries. Some of the
+conflict is intentional - Dart `Stream` predates `Observable` and coherence with
+the Dart ecosystem semantics and naming is a strictly higher priority than
+consistency with ReactiveX.
+
+Rx Operator Category      | variation                                              | `stream_transform`
+------------------------- | ------------------------------------------------------ | ------------------
+[`sample`][rx_sample]     | `sample/throttleLast(Duration)`                        | `sample(Stream.periodic(Duration), longPoll: false)`
+&#x200B;                  | `throttleFirst(Duration)`                              | [`throttle`][throttle]
+&#x200B;                  | `sample(Observable)`                                   | `sample(trigger, longPoll: false)`
+[`debounce`][rx_debounce] | `debounce/throttleWithTimeout(Duration)`               | [`debounce`][debounce]
+&#x200B;                  | `debounce(Observable)`                                 | No equivalent
+[`buffer`][rx_buffer]     | `buffer(boundary)`, `bufferWithTime`,`bufferWithCount` | No equivalent
+&#x200B;                  | `buffer(boundaryClosingSelector)`                      | `buffer(trigger, longPoll: false)`
+RxJs extensions           | [`audit(callback)`][rxjs_audit]                        | No equivalent
+&#x200B;                  | [`auditTime(Duration)`][rxjs_auditTime]                | [`audit`][audit]
+&#x200B;                  | [`exhaustMap`][rxjs_exhaustMap]                        | No equivalent
+&#x200B;                  | [`throttleTime(trailing: true)`][rxjs_throttleTime]    | `throttle(trailing: true)`
+&#x200B;                  | `throttleTime(leading: false, trailing: true)`         | No equivalent
+No equivalent?            |                                                        | [`asyncMapBuffer`][asyncMapBuffer]
+&#x200B;                  |                                                        | [`asyncMapSample`][asyncMapSample]
+&#x200B;                  |                                                        | [`buffer`][buffer]
+&#x200B;                  |                                                        | [`sample`][sample]
+&#x200B;                  |                                                        | [`debounceBuffer`][debounceBuffer]
+&#x200B;                  |                                                        | `debounce(leading: true, trailing: false)`
+&#x200B;                  |                                                        | `debounce(leading: true, trailing: true)`
+
+[rx_sample]:https://reactivex.io/documentation/operators/sample.html
+[rx_debounce]:https://reactivex.io/documentation/operators/debounce.html
+[rx_buffer]:https://reactivex.io/documentation/operators/buffer.html
+[rxjs_audit]:https://rxjs.dev/api/operators/audit
+[rxjs_auditTime]:https://rxjs.dev/api/operators/auditTime
+[rxjs_throttleTime]:https://rxjs.dev/api/operators/throttleTime
+[rxjs_exhaustMap]:https://rxjs.dev/api/operators/exhaustMap
+[asyncMapBuffer]:https://pub.dev/documentation/stream_transform/latest/stream_transform/AsyncMap/asyncMapBuffer.html
+[asyncMapSample]:https://pub.dev/documentation/stream_transform/latest/stream_transform/AsyncMap/asyncMapSample.html
+[audit]:https://pub.dev/documentation/stream_transform/latest/stream_transform/RateLimit/audit.html
+[buffer]:https://pub.dev/documentation/stream_transform/latest/stream_transform/RateLimit/buffer.html
+[sample]:https://pub.dev/documentation/stream_transform/latest/stream_transform/RateLimit/sample.html
+[debounceBuffer]:https://pub.dev/documentation/stream_transform/latest/stream_transform/RateLimit/debounceBuffer.html
+[debounce]:https://pub.dev/documentation/stream_transform/latest/stream_transform/RateLimit/debounce.html
+[throttle]:https://pub.dev/documentation/stream_transform/latest/stream_transform/RateLimit/throttle.html
+
+## Getting a `StreamTransformer` instance
+
+It may be useful to pass an instance of `StreamTransformer` so that it can be
+used with `stream.transform` calls rather than reference the specific operator
+in place. Any operator on `Stream` that returns a `Stream` can be modeled as a
+`StreamTransformer` using the [`fromBind` constructor][fromBind].
+
+```dart
+final debounce = StreamTransformer.fromBind(
+    (s) => s.debounce(const Duration(milliseconds: 100)));
+```
+
+[fromBind]: https://api.dart.dev/stable/dart-async/StreamTransformer/StreamTransformer.fromBind.html

diff --git a/pkgs/stream_transform/analysis_options.yaml b/pkgs/stream_transform/analysis_options.yaml
new file mode 100644
index 0000000..05f1af1
--- /dev/null
+++ b/pkgs/stream_transform/analysis_options.yaml

@@ -0,0 +1,16 @@
+include: package:dart_flutter_team_lints/analysis_options.yaml
+
+analyzer:
+  language:
+    strict-casts: true
+    strict-raw-types: true
+
+linter:
+  rules:
+    - avoid_bool_literals_in_conditional_expressions
+    - avoid_classes_with_only_static_members
+    - avoid_returning_this
+    - avoid_unused_constructor_parameters
+    - cascade_invocations
+    - join_return_with_assignment
+    - no_adjacent_strings_in_list

diff --git a/pkgs/stream_transform/example/index.html b/pkgs/stream_transform/example/index.html
new file mode 100644
index 0000000..aecdc09
--- /dev/null
+++ b/pkgs/stream_transform/example/index.html

@@ -0,0 +1,11 @@
+<html>
+  <head>
+    <script defer src="main.dart.js" type="application/javascript"></script>
+  </head>
+  <body>
+    <input id="first_input"><br>
+    <input id="second_input"><br>
+    <p id="output">
+    </p>
+  </body>
+</html>

diff --git a/pkgs/stream_transform/example/main.dart b/pkgs/stream_transform/example/main.dart
new file mode 100644
index 0000000..8224393
--- /dev/null
+++ b/pkgs/stream_transform/example/main.dart

@@ -0,0 +1,25 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:stream_transform/stream_transform.dart';
+import 'package:web/web.dart';
+
+void main() {
+  var firstInput = document.querySelector('#first_input') as HTMLInputElement;
+  var secondInput = document.querySelector('#second_input') as HTMLInputElement;
+  var output = document.querySelector('#output')!;
+
+  _inputValues(firstInput)
+      .combineLatest(_inputValues(secondInput),
+          (first, second) => 'First: $first, Second: $second')
+      .tap((v) {
+    print('Saw: $v');
+  }).forEach((v) {
+    output.text = v;
+  });
+}
+
+Stream<String?> _inputValues(HTMLInputElement element) => element.onKeyUp
+    .debounce(const Duration(milliseconds: 100))
+    .map((_) => element.value);

diff --git a/pkgs/stream_transform/lib/src/aggregate_sample.dart b/pkgs/stream_transform/lib/src/aggregate_sample.dart
new file mode 100644
index 0000000..f2ff8ed
--- /dev/null
+++ b/pkgs/stream_transform/lib/src/aggregate_sample.dart

@@ -0,0 +1,146 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'common_callbacks.dart';
+
+extension AggregateSample<T> on Stream<T> {
+  /// Computes a value based on sequences of events, then emits that value when
+  /// [trigger] emits an event.
+  ///
+  /// Every time this stream emits an event, an intermediate value is created
+  /// by combining the new event with the previous intermediate value, or with
+  /// `null` if there is no previous value, using the [aggregate] function.
+  ///
+  /// When [trigger] emits value, the returned stream emits the current
+  /// intermediate value and clears it.
+  ///
+  /// If [longPoll] is `false`, if there is no intermediate value when [trigger]
+  /// emits an event, the [onEmpty] function is called with a [Sink] which can
+  /// add events to the returned stream.
+  ///
+  /// If [longPoll] is `true`, and there is no intermediate value when [trigger]
+  /// emits one or more events, then the *next* event from this stream is
+  /// immediately put through [aggregate] and emitted on the returned stream.
+  /// Subsequent events on [trigger] while there have been no events on this
+  /// stream are ignored.
+  /// In that case, [onEmpty] is never used.
+  ///
+  /// The result stream will close as soon as there is a guarantee it will not
+  /// emit any more events. There will not be any more events emitted if:
+  /// - [trigger] is closed and there is no waiting long poll.
+  /// - Or, the source stream is closed and there are no buffered events.
+  ///
+  /// If the source stream is a broadcast stream, the result will be as well.
+  /// Errors from the source stream or the trigger are immediately forwarded to
+  /// the output.
+  Stream<S> aggregateSample<S>(
+      {required Stream<void> trigger,
+      required S Function(T, S?) aggregate,
+      required bool longPoll,
+      required void Function(Sink<S>) onEmpty}) {
+    var controller = isBroadcast
+        ? StreamController<S>.broadcast(sync: true)
+        : StreamController<S>(sync: true);
+
+    S? currentResults;
+    var hasCurrentResults = false;
+    var activeLongPoll = false;
+    var isTriggerDone = false;
+    var isValueDone = false;
+    StreamSubscription<T>? valueSub;
+    StreamSubscription<void>? triggerSub;
+
+    void emit(S results) {
+      currentResults = null;
+      hasCurrentResults = false;
+      controller.add(results);
+    }
+
+    void onValue(T value) {
+      currentResults = aggregate(value, currentResults);
+      hasCurrentResults = true;
+      if (!longPoll) return;
+
+      if (activeLongPoll) {
+        activeLongPoll = false;
+        emit(currentResults as S);
+      }
+
+      if (isTriggerDone) {
+        valueSub!.cancel();
+        controller.close();
+      }
+    }
+
+    void onValuesDone() {
+      isValueDone = true;
+      if (!hasCurrentResults) {
+        triggerSub?.cancel();
+        controller.close();
+      }
+    }
+
+    void onTrigger(_) {
+      if (hasCurrentResults) {
+        emit(currentResults as S);
+      } else if (longPoll) {
+        activeLongPoll = true;
+      } else {
+        onEmpty(controller);
+      }
+
+      if (isValueDone) {
+        triggerSub!.cancel();
+        controller.close();
+      }
+    }
+
+    void onTriggerDone() {
+      isTriggerDone = true;
+      if (!activeLongPoll) {
+        valueSub?.cancel();
+        controller.close();
+      }
+    }
+
+    controller.onListen = () {
+      assert(valueSub == null);
+      valueSub =
+          listen(onValue, onError: controller.addError, onDone: onValuesDone);
+      final priorTriggerSub = triggerSub;
+      if (priorTriggerSub != null) {
+        if (priorTriggerSub.isPaused) priorTriggerSub.resume();
+      } else {
+        triggerSub = trigger.listen(onTrigger,
+            onError: controller.addError, onDone: onTriggerDone);
+      }
+      if (!isBroadcast) {
+        controller
+          ..onPause = () {
+            valueSub?.pause();
+            triggerSub?.pause();
+          }
+          ..onResume = () {
+            valueSub?.resume();
+            triggerSub?.resume();
+          };
+      }
+      controller.onCancel = () {
+        var cancels = <Future<void>>[if (!isValueDone) valueSub!.cancel()];
+        valueSub = null;
+        if (trigger.isBroadcast || !isBroadcast) {
+          if (!isTriggerDone) cancels.add(triggerSub!.cancel());
+          triggerSub = null;
+        } else {
+          triggerSub!.pause();
+        }
+        if (cancels.isEmpty) return null;
+        return cancels.wait.then(ignoreArgument);
+      };
+    };
+    return controller.stream;
+  }
+}

diff --git a/pkgs/stream_transform/lib/src/async_expand.dart b/pkgs/stream_transform/lib/src/async_expand.dart
new file mode 100644
index 0000000..28d2f40
--- /dev/null
+++ b/pkgs/stream_transform/lib/src/async_expand.dart

@@ -0,0 +1,89 @@
+// Copyright (c) 2022, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'common_callbacks.dart';
+import 'switch.dart';
+
+/// Alternatives to [asyncExpand].
+///
+/// The built in [asyncExpand] will not overlap the inner streams and every
+/// event will be sent to the callback individually.
+///
+/// - [concurrentAsyncExpand] allow overlap and merges inner streams without
+///   ordering guarantees.
+extension AsyncExpand<T> on Stream<T> {
+  /// Like [asyncExpand] but the [convert] callback may be called for an element
+  /// before the [Stream] emitted by the previous element has closed.
+  ///
+  /// Events on the result stream will be emitted in the order they are emitted
+  /// by the sub streams, which may not match the order of this stream.
+  ///
+  /// Errors from [convert], the source stream, or any of the sub streams are
+  /// forwarded to the result stream.
+  ///
+  /// The result stream will not close until the source stream closes and all
+  /// sub streams have closed.
+  ///
+  /// If the source stream is a broadcast stream, the result will be as well,
+  /// regardless of the types of streams created by [convert]. In this case,
+  /// some care should be taken:
+  /// -  If [convert] returns a single subscription stream it may be listened to
+  /// and never canceled.
+  /// -  For any period of time where there are no listeners on the result
+  /// stream, any sub streams from previously emitted events will be ignored,
+  /// regardless of whether they emit further events after a listener is added
+  /// back.
+  ///
+  /// See also:
+  /// - [switchMap], which cancels subscriptions to the previous sub stream
+  /// instead of concurrently emitting events from all sub streams.
+  Stream<S> concurrentAsyncExpand<S>(Stream<S> Function(T) convert) {
+    final controller = isBroadcast
+        ? StreamController<S>.broadcast(sync: true)
+        : StreamController<S>(sync: true);
+
+    controller.onListen = () {
+      final subscriptions = <StreamSubscription<dynamic>>[];
+      final outerSubscription = map(convert).listen((inner) {
+        if (isBroadcast && !inner.isBroadcast) {
+          inner = inner.asBroadcastStream();
+        }
+        final subscription =
+            inner.listen(controller.add, onError: controller.addError);
+        subscription.onDone(() {
+          subscriptions.remove(subscription);
+          if (subscriptions.isEmpty) controller.close();
+        });
+        subscriptions.add(subscription);
+      }, onError: controller.addError);
+      outerSubscription.onDone(() {
+        subscriptions.remove(outerSubscription);
+        if (subscriptions.isEmpty) controller.close();
+      });
+      subscriptions.add(outerSubscription);
+      if (!isBroadcast) {
+        controller
+          ..onPause = () {
+            for (final subscription in subscriptions) {
+              subscription.pause();
+            }
+          }
+          ..onResume = () {
+            for (final subscription in subscriptions) {
+              subscription.resume();
+            }
+          };
+      }
+      controller.onCancel = () {
+        if (subscriptions.isEmpty) return null;
+        return [for (var s in subscriptions) s.cancel()]
+            .wait
+            .then(ignoreArgument);
+      };
+    };
+    return controller.stream;
+  }
+}

diff --git a/pkgs/stream_transform/lib/src/async_map.dart b/pkgs/stream_transform/lib/src/async_map.dart
new file mode 100644
index 0000000..094df9c
--- /dev/null
+++ b/pkgs/stream_transform/lib/src/async_map.dart

@@ -0,0 +1,136 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'aggregate_sample.dart';
+import 'common_callbacks.dart';
+import 'from_handlers.dart';
+import 'rate_limit.dart';
+
+/// Alternatives to [asyncMap].
+///
+/// The built in [asyncMap] will not overlap execution of the passed callback,
+/// and every event will be sent to the callback individually.
+///
+/// - [asyncMapBuffer] prevents the callback from overlapping execution and
+///   collects events while it is executing to process in batches.
+/// - [asyncMapSample] prevents overlapping execution and discards events while
+///   it is executing.
+/// - [concurrentAsyncMap] allows overlap and removes ordering guarantees.
+extension AsyncMap<T> on Stream<T> {
+  /// Like [asyncMap] but events are buffered until previous events have been
+  /// processed by [convert].
+  ///
+  /// If this stream is a broadcast stream the result will be as well.
+  /// When used with a broadcast stream behavior also differs from [asyncMap] in
+  /// that the [convert] function is only called once per event, rather than
+  /// once per listener per event.
+  ///
+  /// The first event from this stream is always passed to [convert] as a
+  /// list with a single element.
+  /// After that, events are buffered until the previous Future returned from
+  /// [convert] has completed.
+  ///
+  /// Errors from this stream are forwarded directly to the result stream.
+  /// Errors during the conversion are also forwarded to the result stream and
+  /// are considered completing work so the next values are let through.
+  ///
+  /// The result stream will not close until this stream closes and all pending
+  /// conversions have finished.
+  Stream<S> asyncMapBuffer<S>(Future<S> Function(List<T>) convert) {
+    var workFinished = StreamController<void>()
+      // Let the first event through.
+      ..add(null);
+    return buffer(workFinished.stream)._asyncMapThen(convert, workFinished.add);
+  }
+
+  /// Like [asyncMap] but events are discarded while work is happening in
+  /// [convert].
+  ///
+  /// If this stream is a broadcast stream the result will be as well.
+  /// When used with a broadcast stream behavior also differs from [asyncMap] in
+  /// that the [convert] function is only called once per event, rather than
+  /// once per listener per event.
+  ///
+  /// If no work is happening when an event is emitted it will be immediately
+  /// passed to [convert]. If there is ongoing work when an event is emitted it
+  /// will be held until the work is finished. New events emitted will replace a
+  /// pending event.
+  ///
+  /// Errors from this stream are forwarded directly to the result stream.
+  /// Errors during the conversion are also forwarded to the result stream and
+  /// are considered completing work so the next values are let through.
+  ///
+  /// The result stream will not close until this stream closes and all pending
+  /// conversions have finished.
+  Stream<S> asyncMapSample<S>(Future<S> Function(T) convert) {
+    var workFinished = StreamController<void>()
+      // Let the first event through.
+      ..add(null);
+    return aggregateSample(
+            trigger: workFinished.stream,
+            aggregate: _dropPrevious,
+            longPoll: true,
+            onEmpty: ignoreArgument)
+        ._asyncMapThen(convert, workFinished.add);
+  }
+
+  /// Like [asyncMap] but the [convert] callback may be called for an element
+  /// before processing for the previous element is finished.
+  ///
+  /// Events on the result stream will be emitted in the order that [convert]
+  /// completed which may not match the order of this stream.
+  ///
+  /// If this stream is a broadcast stream the result will be as well.
+  /// When used with a broadcast stream behavior also differs from [asyncMap] in
+  /// that the [convert] function is only called once per event, rather than
+  /// once per listener per event. The [convert] callback won't be called for
+  /// events while a broadcast stream has no listener.
+  ///
+  /// Errors from [convert] or this stream are forwarded directly to the
+  /// result stream.
+  ///
+  /// The result stream will not close until this stream closes and all pending
+  /// conversions have finished.
+  Stream<S> concurrentAsyncMap<S>(FutureOr<S> Function(T) convert) {
+    var valuesWaiting = 0;
+    var sourceDone = false;
+    return transformByHandlers(onData: (element, sink) {
+      valuesWaiting++;
+      () async {
+        try {
+          sink.add(await convert(element));
+        } catch (e, st) {
+          sink.addError(e, st);
+        }
+        valuesWaiting--;
+        if (valuesWaiting <= 0 && sourceDone) sink.close();
+      }();
+    }, onDone: (sink) {
+      sourceDone = true;
+      if (valuesWaiting <= 0) sink.close();
+    });
+  }
+
+  /// Like [Stream.asyncMap] but the [convert] is only called once per event,
+  /// rather than once per listener, and [then] is called after completing the
+  /// work.
+  Stream<S> _asyncMapThen<S>(
+      Future<S> Function(T) convert, void Function(void) then) {
+    Future<void>? pendingEvent;
+    return transformByHandlers(onData: (event, sink) {
+      pendingEvent =
+          convert(event).then(sink.add).catchError(sink.addError).then(then);
+    }, onDone: (sink) {
+      if (pendingEvent != null) {
+        pendingEvent!.then((_) => sink.close());
+      } else {
+        sink.close();
+      }
+    });
+  }
+}
+
+T _dropPrevious<T>(T event, _) => event;

diff --git a/pkgs/stream_transform/lib/src/combine_latest.dart b/pkgs/stream_transform/lib/src/combine_latest.dart
new file mode 100644
index 0000000..f02a19e
--- /dev/null
+++ b/pkgs/stream_transform/lib/src/combine_latest.dart

@@ -0,0 +1,240 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'common_callbacks.dart';
+
+/// Utilities to combine events from multiple streams through a callback or into
+/// a list.
+extension CombineLatest<T> on Stream<T> {
+  /// Combines the latest values from this stream with the latest values from
+  /// [other] using [combine].
+  ///
+  /// No event will be emitted until both the source stream and [other] have
+  /// each emitted at least one event. If either the source stream or [other]
+  /// emit multiple events before the other emits the first event, all but the
+  /// last value will be discarded. Once both streams have emitted at least
+  /// once, the result stream will emit any time either input stream emits.
+  ///
+  /// The result stream will not close until both the source stream and [other]
+  /// have closed.
+  ///
+  /// For example:
+  ///
+  ///     source.combineLatest(other, (a, b) => a + b);
+  ///
+  ///     source: --1--2--------4--|
+  ///     other:  -------3--|
+  ///     result: -------5------7--|
+  ///
+  /// Errors thrown by [combine], along with any errors on the source stream or
+  /// [other], are forwarded to the result stream.
+  ///
+  /// If the source stream is a broadcast stream, the result stream will be as
+  /// well, regardless of [other]'s type. If a single subscription stream is
+  /// combined with a broadcast stream it may never be canceled.
+  Stream<S> combineLatest<T2, S>(
+      Stream<T2> other, FutureOr<S> Function(T, T2) combine) {
+    final controller = isBroadcast
+        ? StreamController<S>.broadcast(sync: true)
+        : StreamController<S>(sync: true);
+
+    other =
+        (isBroadcast && !other.isBroadcast) ? other.asBroadcastStream() : other;
+
+    StreamSubscription<T>? sourceSubscription;
+    StreamSubscription<T2>? otherSubscription;
+
+    var sourceDone = false;
+    var otherDone = false;
+
+    late T latestSource;
+    late T2 latestOther;
+
+    var sourceStarted = false;
+    var otherStarted = false;
+
+    void emitCombined() {
+      if (!sourceStarted || !otherStarted) return;
+      FutureOr<S> result;
+      try {
+        result = combine(latestSource, latestOther);
+      } catch (e, s) {
+        controller.addError(e, s);
+        return;
+      }
+      if (result is Future<S>) {
+        sourceSubscription!.pause();
+        otherSubscription!.pause();
+        result
+            .then(controller.add, onError: controller.addError)
+            .whenComplete(() {
+          sourceSubscription!.resume();
+          otherSubscription!.resume();
+        });
+      } else {
+        controller.add(result);
+      }
+    }
+
+    controller.onListen = () {
+      assert(sourceSubscription == null);
+      sourceSubscription = listen(
+          (s) {
+            sourceStarted = true;
+            latestSource = s;
+            emitCombined();
+          },
+          onError: controller.addError,
+          onDone: () {
+            sourceDone = true;
+            if (otherDone) {
+              controller.close();
+            } else if (!sourceStarted) {
+              // Nothing can ever be emitted
+              otherSubscription!.cancel();
+              controller.close();
+            }
+          });
+      otherSubscription = other.listen(
+          (o) {
+            otherStarted = true;
+            latestOther = o;
+            emitCombined();
+          },
+          onError: controller.addError,
+          onDone: () {
+            otherDone = true;
+            if (sourceDone) {
+              controller.close();
+            } else if (!otherStarted) {
+              // Nothing can ever be emitted
+              sourceSubscription!.cancel();
+              controller.close();
+            }
+          });
+      if (!isBroadcast) {
+        controller
+          ..onPause = () {
+            sourceSubscription!.pause();
+            otherSubscription!.pause();
+          }
+          ..onResume = () {
+            sourceSubscription!.resume();
+            otherSubscription!.resume();
+          };
+      }
+      controller.onCancel = () {
+        var cancels = [
+          sourceSubscription!.cancel(),
+          otherSubscription!.cancel()
+        ];
+        sourceSubscription = null;
+        otherSubscription = null;
+        return cancels.wait.then(ignoreArgument);
+      };
+    };
+    return controller.stream;
+  }
+
+  /// Combine the latest value emitted from the source stream with the latest
+  /// values emitted from [others].
+  ///
+  /// [combineLatestAll] subscribes to the source stream and [others] and when
+  /// any one of the streams emits, the result stream will emit a [List<T>] of
+  /// the latest values emitted from all streams.
+  ///
+  /// No event will be emitted until all source streams emit at least once. If a
+  /// source stream emits multiple values before another starts emitting, all
+  /// but the last value will be discarded. Once all source streams have emitted
+  /// at least once, the result stream will emit any time any source stream
+  /// emits.
+  ///
+  /// The result stream will not close until all source streams have closed.
+  /// When a source stream closes, the result stream will continue to emit the
+  /// last value from the closed stream when the other source streams emit until
+  /// the result stream has closed. If a source stream closes without emitting
+  /// any value, the result stream will close as well.
+  ///
+  /// For example:
+  ///
+  ///     final combined = first
+  ///         .combineLatestAll([second, third])
+  ///         .map((data) => data.join());
+  ///
+  ///     first:    a----b------------------c--------d---|
+  ///     second:   --1---------2-----------------|
+  ///     third:    -------&----------%---|
+  ///     combined: -------b1&--b2&---b2%---c2%------d2%-|
+  ///
+  /// Errors thrown by any source stream will be forwarded to the result stream.
+  ///
+  /// If the source stream is a broadcast stream, the result stream will be as
+  /// well, regardless of the types of [others]. If a single subscription stream
+  /// is combined with a broadcast source stream, it may never be canceled.
+  Stream<List<T>> combineLatestAll(Iterable<Stream<T>> others) {
+    final controller = isBroadcast
+        ? StreamController<List<T>>.broadcast(sync: true)
+        : StreamController<List<T>>(sync: true);
+
+    final allStreams = [
+      this,
+      for (final other in others)
+        !isBroadcast || other.isBroadcast ? other : other.asBroadcastStream(),
+    ];
+
+    controller.onListen = () {
+      final subscriptions = <StreamSubscription<T>>[];
+
+      final latestData = List<T?>.filled(allStreams.length, null);
+      final hasEmitted = <int>{};
+      void handleData(int index, T data) {
+        latestData[index] = data;
+        hasEmitted.add(index);
+        if (hasEmitted.length == allStreams.length) {
+          controller.add(List.from(latestData));
+        }
+      }
+
+      var streamId = 0;
+      for (final stream in allStreams) {
+        final index = streamId;
+
+        final subscription = stream.listen((data) => handleData(index, data),
+            onError: controller.addError);
+        subscription.onDone(() {
+          assert(subscriptions.contains(subscription));
+          subscriptions.remove(subscription);
+          if (subscriptions.isEmpty || !hasEmitted.contains(index)) {
+            controller.close();
+          }
+        });
+        subscriptions.add(subscription);
+
+        streamId++;
+      }
+      if (!isBroadcast) {
+        controller
+          ..onPause = () {
+            for (final subscription in subscriptions) {
+              subscription.pause();
+            }
+          }
+          ..onResume = () {
+            for (final subscription in subscriptions) {
+              subscription.resume();
+            }
+          };
+      }
+      controller.onCancel = () {
+        if (subscriptions.isEmpty) return null;
+        return [for (var s in subscriptions) s.cancel()]
+            .wait
+            .then(ignoreArgument);
+      };
+    };
+    return controller.stream;
+  }
+}

diff --git a/pkgs/stream_transform/lib/src/common_callbacks.dart b/pkgs/stream_transform/lib/src/common_callbacks.dart
new file mode 100644
index 0000000..e211cf9
--- /dev/null
+++ b/pkgs/stream_transform/lib/src/common_callbacks.dart

@@ -0,0 +1,5 @@
+// Copyright (c) 2024, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+void ignoreArgument(Object? _) {}

diff --git a/pkgs/stream_transform/lib/src/concatenate.dart b/pkgs/stream_transform/lib/src/concatenate.dart
new file mode 100644
index 0000000..0330dd7
--- /dev/null
+++ b/pkgs/stream_transform/lib/src/concatenate.dart

@@ -0,0 +1,112 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+/// Utilities to append or prepend to a stream.
+extension Concatenate<T> on Stream<T> {
+  /// Emits all values and errors from [next] following all values and errors
+  /// from this stream.
+  ///
+  /// If this stream never finishes, the [next] stream will never get a
+  /// listener.
+  ///
+  /// If this stream is a broadcast stream, the result will be as well.
+  /// If a single-subscription follows a broadcast stream it may be listened
+  /// to and never canceled since there may be broadcast listeners added later.
+  ///
+  /// If a broadcast stream follows any other stream it will miss any events or
+  /// errors which occur before this stream is done.
+  /// If a broadcast stream follows a single-subscription stream, pausing the
+  /// stream while it is listening to the second stream will cause events to be
+  /// dropped rather than buffered.
+  Stream<T> followedBy(Stream<T> next) {
+    var controller = isBroadcast
+        ? StreamController<T>.broadcast(sync: true)
+        : StreamController<T>(sync: true);
+
+    next = isBroadcast && !next.isBroadcast ? next.asBroadcastStream() : next;
+
+    StreamSubscription<T>? subscription;
+    var currentStream = this;
+    var thisDone = false;
+    var secondDone = false;
+
+    late void Function() currentDoneHandler;
+
+    void listen() {
+      subscription = currentStream.listen(controller.add,
+          onError: controller.addError, onDone: () => currentDoneHandler());
+    }
+
+    void onSecondDone() {
+      secondDone = true;
+      controller.close();
+    }
+
+    void onThisDone() {
+      thisDone = true;
+      currentStream = next;
+      currentDoneHandler = onSecondDone;
+      listen();
+    }
+
+    currentDoneHandler = onThisDone;
+
+    controller.onListen = () {
+      assert(subscription == null);
+      listen();
+      if (!isBroadcast) {
+        controller
+          ..onPause = () {
+            if (!thisDone || !next.isBroadcast) return subscription!.pause();
+            subscription!.cancel();
+            subscription = null;
+          }
+          ..onResume = () {
+            if (!thisDone || !next.isBroadcast) return subscription!.resume();
+            listen();
+          };
+      }
+      controller.onCancel = () {
+        if (secondDone) return null;
+        var toCancel = subscription!;
+        subscription = null;
+        return toCancel.cancel();
+      };
+    };
+    return controller.stream;
+  }
+
+  /// Emits [initial] before any values or errors from the this stream.
+  ///
+  /// If this stream is a broadcast stream the result will be as well.
+  /// If this stream is a broadcast stream, the returned stream will only
+  /// contain events of this stream that are emitted after the [initial] value
+  /// has been emitted on the returned stream.
+  Stream<T> startWith(T initial) =>
+      startWithStream(Future.value(initial).asStream());
+
+  /// Emits all values in [initial] before any values or errors from this
+  /// stream.
+  ///
+  /// If this stream is a broadcast stream the result will be as well.
+  /// If this stream is a broadcast stream it will miss any events which
+  /// occur before the initial values are all emitted.
+  Stream<T> startWithMany(Iterable<T> initial) =>
+      startWithStream(Stream.fromIterable(initial));
+
+  /// Emits all values and errors in [initial] before any values or errors from
+  /// this stream.
+  ///
+  /// If this stream is a broadcast stream the result will be as well.
+  /// If this stream is a broadcast stream it will miss any events which occur
+  /// before [initial] closes.
+  Stream<T> startWithStream(Stream<T> initial) {
+    if (isBroadcast && !initial.isBroadcast) {
+      initial = initial.asBroadcastStream();
+    }
+    return initial.followedBy(this);
+  }
+}

diff --git a/pkgs/stream_transform/lib/src/from_handlers.dart b/pkgs/stream_transform/lib/src/from_handlers.dart
new file mode 100644
index 0000000..1146a13
--- /dev/null
+++ b/pkgs/stream_transform/lib/src/from_handlers.dart

@@ -0,0 +1,58 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+extension TransformByHandlers<S> on Stream<S> {
+  /// Transform a stream by callbacks.
+  ///
+  /// This is similar to `transform(StreamTransformer.fromHandler(...))` except
+  /// that the handlers are called once per event rather than called for the
+  /// same event for each listener on a broadcast stream.
+  Stream<T> transformByHandlers<T>(
+      {required void Function(S, EventSink<T>) onData,
+      void Function(Object, StackTrace, EventSink<T>)? onError,
+      void Function(EventSink<T>)? onDone}) {
+    final handleError = onError ?? _defaultHandleError;
+    final handleDone = onDone ?? _defaultHandleDone;
+
+    var controller = isBroadcast
+        ? StreamController<T>.broadcast(sync: true)
+        : StreamController<T>(sync: true);
+
+    StreamSubscription<S>? subscription;
+    controller.onListen = () {
+      assert(subscription == null);
+      var valuesDone = false;
+      subscription = listen((value) => onData(value, controller),
+          onError: (Object error, StackTrace stackTrace) {
+        handleError(error, stackTrace, controller);
+      }, onDone: () {
+        valuesDone = true;
+        handleDone(controller);
+      });
+      if (!isBroadcast) {
+        controller
+          ..onPause = subscription!.pause
+          ..onResume = subscription!.resume;
+      }
+      controller.onCancel = () {
+        var toCancel = subscription;
+        subscription = null;
+        if (!valuesDone) return toCancel!.cancel();
+        return null;
+      };
+    };
+    return controller.stream;
+  }
+
+  static void _defaultHandleError<T>(
+      Object error, StackTrace stackTrace, EventSink<T> sink) {
+    sink.addError(error, stackTrace);
+  }
+
+  static void _defaultHandleDone<T>(EventSink<T> sink) {
+    sink.close();
+  }
+}

diff --git a/pkgs/stream_transform/lib/src/merge.dart b/pkgs/stream_transform/lib/src/merge.dart
new file mode 100644
index 0000000..3bfe06c
--- /dev/null
+++ b/pkgs/stream_transform/lib/src/merge.dart

@@ -0,0 +1,102 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'common_callbacks.dart';
+
+/// Utilities to interleave events from multiple streams.
+extension Merge<T> on Stream<T> {
+  /// Merges values and errors from this stream and [other] in any order as they
+  /// arrive.
+  ///
+  /// The result stream will not close until both this stream and [other] have
+  /// closed.
+  ///
+  /// For example:
+  ///
+  ///     final result = source.merge(other);
+  ///
+  ///     source:  1--2-----3--|
+  ///     other:   ------4-------5--|
+  ///     result:  1--2--4--3----5--|
+  ///
+  /// If this stream is a broadcast stream, the result stream will be as
+  /// well, regardless of [other]'s type. If a single subscription stream is
+  /// merged into a broadcast stream it may never be canceled since there may be
+  /// broadcast listeners added later.
+  ///
+  /// If a broadcast stream is merged into a single-subscription stream any
+  /// events emitted by [other] before the result stream has a subscriber will
+  /// be discarded.
+  Stream<T> merge(Stream<T> other) => mergeAll([other]);
+
+  /// Merges values and errors from this stream and any stream in [others] in
+  /// any order as they arrive.
+  ///
+  /// The result stream will not close until this stream and all streams
+  /// in [others] have closed.
+  ///
+  /// For example:
+  ///
+  ///     final result = first.mergeAll([second, third]);
+  ///
+  ///     first:   1--2--------3--|
+  ///     second:  ---------4-------5--|
+  ///     third:   ------6---------------7--|
+  ///     result:  1--2--6--4--3----5----7--|
+  ///
+  /// If this stream is a broadcast stream, the result stream will be as
+  /// well, regardless the types of streams in [others]. If a single
+  /// subscription stream is merged into a broadcast stream it may never be
+  /// canceled since there may be broadcast listeners added later.
+  ///
+  /// If a broadcast stream is merged into a single-subscription stream any
+  /// events emitted by that stream before the result stream has a subscriber
+  /// will be discarded.
+  Stream<T> mergeAll(Iterable<Stream<T>> others) {
+    final controller = isBroadcast
+        ? StreamController<T>.broadcast(sync: true)
+        : StreamController<T>(sync: true);
+
+    final allStreams = [
+      this,
+      for (final other in others)
+        !isBroadcast || other.isBroadcast ? other : other.asBroadcastStream(),
+    ];
+
+    controller.onListen = () {
+      final subscriptions = <StreamSubscription<T>>[];
+      for (final stream in allStreams) {
+        final subscription =
+            stream.listen(controller.add, onError: controller.addError);
+        subscription.onDone(() {
+          subscriptions.remove(subscription);
+          if (subscriptions.isEmpty) controller.close();
+        });
+        subscriptions.add(subscription);
+      }
+      if (!isBroadcast) {
+        controller
+          ..onPause = () {
+            for (final subscription in subscriptions) {
+              subscription.pause();
+            }
+          }
+          ..onResume = () {
+            for (final subscription in subscriptions) {
+              subscription.resume();
+            }
+          };
+      }
+      controller.onCancel = () {
+        if (subscriptions.isEmpty) return null;
+        return [for (var s in subscriptions) s.cancel()]
+            .wait
+            .then(ignoreArgument);
+      };
+    };
+    return controller.stream;
+  }
+}

diff --git a/pkgs/stream_transform/lib/src/rate_limit.dart b/pkgs/stream_transform/lib/src/rate_limit.dart
new file mode 100644
index 0000000..299c230
--- /dev/null
+++ b/pkgs/stream_transform/lib/src/rate_limit.dart

@@ -0,0 +1,356 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'aggregate_sample.dart';
+import 'common_callbacks.dart';
+import 'from_handlers.dart';
+
+/// Utilities to rate limit events.
+///
+/// - [debounce] - emit the the _first_ or _last_ event of a series of closely
+///   spaced events.
+/// - [debounceBuffer] - emit _all_ events at the _end_ of a series of closely
+///   spaced events.
+/// - [throttle] - emit the _first_ event at the _beginning_ of the period.
+/// - [audit] - emit the _last_ event at the _end_ of the period.
+/// - [buffer] - emit _all_ events on a _trigger_.
+extension RateLimit<T> on Stream<T> {
+  /// Suppresses events with less inter-event spacing than [duration].
+  ///
+  /// Events which are emitted with less than [duration] elapsed between them
+  /// are considered to be part of the same "series". If [leading] is `true`,
+  /// the first event of this series is emitted immediately. If [trailing] is
+  /// `true` the last event of this series is emitted with a delay of at least
+  /// [duration]. By default only trailing events are emitted, both arguments
+  /// must be specified with `leading: true, trailing: false` to emit only
+  /// leading events.
+  ///
+  /// If this stream is a broadcast stream, the result will be as well.
+  /// Errors are forwarded immediately.
+  ///
+  /// If there is a trailing event waiting during the debounce period when the
+  /// source stream closes the returned stream will wait to emit it following
+  /// the debounce period before closing. If there is no pending debounced event
+  /// when this stream closes the returned stream will close immediately.
+  ///
+  /// For example:
+  ///
+  ///     source.debounce(Duration(seconds: 1));
+  ///
+  ///     source: 1-2-3---4---5-6-|
+  ///     result: ------3---4-----6|
+  ///
+  ///     source.debounce(Duration(seconds: 1), leading: true, trailing: false);
+  ///
+  ///     source: 1-2-3---4---5-6-|
+  ///     result: 1-------4---5---|
+  ///
+  ///     source.debounce(Duration(seconds: 1), leading: true);
+  ///
+  ///     source: 1-2-3---4---5-6-|
+  ///     result: 1-----3-4---5---6|
+  ///
+  /// To collect values emitted during the debounce period see [debounceBuffer].
+  Stream<T> debounce(Duration duration,
+          {bool leading = false, bool trailing = true}) =>
+      _debounceAggregate(duration, _dropPrevious,
+          leading: leading, trailing: trailing);
+
+  /// Buffers values until this stream does not emit for [duration] then emits
+  /// the collected values.
+  ///
+  /// Values will always be delayed by at least [duration], and values which
+  /// come within this time will be aggregated into the same list.
+  ///
+  /// If this stream is a broadcast stream, the result will be as well.
+  /// Errors are forwarded immediately.
+  ///
+  /// If there are events waiting during the debounce period when this stream
+  /// closes the returned stream will wait to emit them following the debounce
+  /// period before closing. If there are no pending debounced events when this
+  /// stream closes the returned stream will close immediately.
+  ///
+  /// To keep only the most recent event during the debounce period see
+  /// [debounce].
+  Stream<List<T>> debounceBuffer(Duration duration) =>
+      _debounceAggregate(duration, _collect, leading: false, trailing: true);
+
+  /// Reduces the rate that events are emitted to at most once per [duration].
+  ///
+  /// No events will ever be emitted within [duration] of another event on the
+  /// result stream.
+  /// If this stream is a broadcast stream, the result will be as well.
+  /// Errors are forwarded immediately.
+  ///
+  /// If [trailing] is `false`, source events emitted during the [duration]
+  /// period following a result event are discarded.
+  /// The result stream will not emit an event until this stream emits an event
+  /// following the throttled period.
+  /// If this stream is consistently emitting events with less than
+  /// [duration] between events, the time between events on the result stream
+  /// may still be more than [duration].
+  /// The result stream will close immediately when this stream closes.
+  ///
+  /// If [trailing] is `true`, the latest source event emitted during the
+  /// [duration] period following an result event is held and emitted following
+  /// the period.
+  /// If this stream is consistently emitting events with less than [duration]
+  /// between events, the time between events on the result stream will be
+  /// [duration].
+  /// If this stream closes the result stream will wait to emit a pending event
+  /// before closing.
+  ///
+  /// For example:
+  ///
+  ///     source.throttle(Duration(seconds: 6));
+  ///
+  ///     source: 1-2-3---4-5-6---7-8-|
+  ///     result: 1-------4-------7---|
+  ///
+  ///     source.throttle(Duration(seconds: 6), trailing: true);
+  ///
+  ///     source: 1-2-3---4-5----6--|
+  ///     result: 1-----3-----5-----6|
+  ///
+  ///     source.throttle(Duration(seconds: 6), trailing: true);
+  ///
+  ///     source: 1-2-----------3|
+  ///     result: 1-----2-------3|
+  ///
+  /// See also:
+  /// - [audit], which emits the most recent event at the end of the period.
+  /// Compared to `audit`, `throttle` will not introduce delay to forwarded
+  /// elements, except for the [trailing] events.
+  /// - [debounce], which uses inter-event spacing instead of a fixed period
+  /// from the first event in a window. Compared to `debouce`, `throttle` cannot
+  /// be starved by having events emitted continuously within [duration].
+  Stream<T> throttle(Duration duration, {bool trailing = false}) =>
+      trailing ? _throttleTrailing(duration) : _throttle(duration);
+
+  Stream<T> _throttle(Duration duration) {
+    Timer? timer;
+
+    return transformByHandlers(onData: (data, sink) {
+      if (timer == null) {
+        sink.add(data);
+        timer = Timer(duration, () {
+          timer = null;
+        });
+      }
+    });
+  }
+
+  Stream<T> _throttleTrailing(Duration duration) {
+    Timer? timer;
+    T? pending;
+    var hasPending = false;
+    var isDone = false;
+
+    return transformByHandlers(onData: (data, sink) {
+      void onTimer() {
+        if (hasPending) {
+          sink.add(pending as T);
+          if (isDone) {
+            sink.close();
+          } else {
+            timer = Timer(duration, onTimer);
+            hasPending = false;
+            pending = null;
+          }
+        } else {
+          timer = null;
+        }
+      }
+
+      if (timer == null) {
+        sink.add(data);
+        timer = Timer(duration, onTimer);
+      } else {
+        hasPending = true;
+        pending = data;
+      }
+    }, onDone: (sink) {
+      isDone = true;
+      if (hasPending) return; // Will be closed by timer.
+      sink.close();
+      timer?.cancel();
+      timer = null;
+    });
+  }
+
+  /// Audit a single event from each [duration] length period where there are
+  /// events on this stream.
+  ///
+  /// No events will ever be emitted within [duration] of another event on the
+  /// result stream.
+  /// If this stream is a broadcast stream, the result will be as well.
+  /// Errors are forwarded immediately.
+  ///
+  /// The first event will begin the audit period. At the end of the audit
+  /// period the most recent event is emitted, and the next event restarts the
+  /// audit period.
+  ///
+  /// If the event that started the period is the one that is emitted it will be
+  /// delayed by [duration]. If a later event comes in within the period it's
+  /// delay will be shorter by the difference in arrival times.
+  ///
+  /// If there is no pending event when this stream closes the output
+  /// stream will close immediately. If there is a pending event the output
+  /// stream will wait to emit it before closing.
+  ///
+  /// For example:
+  ///
+  ///     source.audit(Duration(seconds: 5));
+  ///
+  ///     source: a------b--c----d--|
+  ///     output: -----a------c--------d|
+  ///
+  /// See also:
+  /// - [throttle], which emits the _first_ event during the window, instead of
+  /// the last event in the window. Compared to `throttle`, `audit` will
+  /// introduce delay to forwarded events.
+  /// - [debounce], which only emits after the stream has not emitted for some
+  /// period. Compared to `debouce`, `audit` cannot be starved by having events
+  /// emitted continuously within [duration].
+  Stream<T> audit(Duration duration) {
+    Timer? timer;
+    var shouldClose = false;
+    T recentData;
+
+    return transformByHandlers(onData: (data, sink) {
+      recentData = data;
+      timer ??= Timer(duration, () {
+        sink.add(recentData);
+        timer = null;
+        if (shouldClose) {
+          sink.close();
+        }
+      });
+    }, onDone: (sink) {
+      if (timer != null) {
+        shouldClose = true;
+      } else {
+        sink.close();
+      }
+    });
+  }
+
+  /// Buffers the values emitted on this stream and emits them when [trigger]
+  /// emits an event.
+  ///
+  /// If [longPoll] is `false`, if there are no buffered values when [trigger]
+  /// emits an empty list is immediately emitted.
+  ///
+  /// If [longPoll] is `true`, and there are no buffered values when [trigger]
+  /// emits one or more events, then the *next* value from this stream is
+  /// immediately emitted on the returned stream as a single element list.
+  /// Subsequent events on [trigger] while there have been no events on this
+  /// stream are ignored.
+  ///
+  /// The result stream will close as soon as there is a guarantee it will not
+  /// emit any more events. There will not be any more events emitted if:
+  /// - [trigger] is closed and there is no waiting long poll.
+  /// - Or, this stream is closed and previously buffered events have been
+  /// delivered.
+  ///
+  /// If this stream is a broadcast stream, the result will be as well.
+  /// Errors from this stream or the trigger are immediately forwarded to the
+  /// output.
+  ///
+  /// See also:
+  /// - [sample] which use a [trigger] stream in the same way, but keeps only
+  /// the most recent source event.
+  Stream<List<T>> buffer(Stream<void> trigger, {bool longPoll = true}) =>
+      aggregateSample(
+          trigger: trigger,
+          aggregate: _collect,
+          longPoll: longPoll,
+          onEmpty: _empty);
+
+  /// Emits the most recent new value from this stream when [trigger] emits an
+  /// event.
+  ///
+  /// If [longPoll] is `false`, then an event on [trigger] when there is no
+  /// pending source event will be ignored.
+  /// If [longPoll] is `true` (the default), then an event on [trigger] when
+  /// there is no pending source event will cause the next source event
+  /// to immediately flow to the result stream.
+  ///
+  /// If [longPoll] is `false`, if there is no pending source event when
+  /// [trigger] emits, then the trigger event will be ignored.
+  ///
+  /// If [longPoll] is `true`, and there are no buffered values when [trigger]
+  /// emits one or more events, then the *next* value from this stream is
+  /// immediately emitted on the returned stream as a single element list.
+  /// Subsequent events on [trigger] while there have been no events on this
+  /// stream are ignored.
+  ///
+  /// The result stream will close as soon as there is a guarantee it will not
+  /// emit any more events. There will not be any more events emitted if:
+  /// - [trigger] is closed and there is no waiting long poll.
+  /// - Or, this source stream is closed and any pending source event has been
+  /// delivered.
+  ///
+  /// If this source stream is a broadcast stream, the result will be as well.
+  /// Errors from this source stream or the trigger are immediately forwarded to
+  /// the output.
+  ///
+  /// See also:
+  /// - [buffer] which use [trigger] stream in the same way, but keeps a list of
+  /// pending source events.
+  Stream<T> sample(Stream<void> trigger, {bool longPoll = true}) =>
+      aggregateSample(
+          trigger: trigger,
+          aggregate: _dropPrevious,
+          longPoll: longPoll,
+          onEmpty: ignoreArgument);
+
+  /// Aggregates values until this source stream does not emit for [duration],
+  /// then emits the aggregated values.
+  Stream<S> _debounceAggregate<S>(
+      Duration duration, S Function(T element, S? soFar) collect,
+      {required bool leading, required bool trailing}) {
+    Timer? timer;
+    S? soFar;
+    var hasPending = false;
+    var shouldClose = false;
+    var emittedLatestAsLeading = false;
+
+    return transformByHandlers(onData: (value, sink) {
+      void emit() {
+        sink.add(soFar as S);
+        soFar = null;
+        hasPending = false;
+      }
+
+      timer?.cancel();
+      soFar = collect(value, soFar);
+      hasPending = true;
+      if (timer == null && leading) {
+        emittedLatestAsLeading = true;
+        emit();
+      } else {
+        emittedLatestAsLeading = false;
+      }
+      timer = Timer(duration, () {
+        if (trailing && !emittedLatestAsLeading) emit();
+        if (shouldClose) sink.close();
+        timer = null;
+      });
+    }, onDone: (EventSink<S> sink) {
+      if (hasPending && trailing) {
+        shouldClose = true;
+      } else {
+        timer?.cancel();
+        sink.close();
+      }
+    });
+  }
+}
+
+T _dropPrevious<T>(T element, _) => element;
+List<T> _collect<T>(T event, List<T>? soFar) => (soFar ?? <T>[])..add(event);
+void _empty<T>(Sink<List<T>> sink) => sink.add([]);

diff --git a/pkgs/stream_transform/lib/src/scan.dart b/pkgs/stream_transform/lib/src/scan.dart
new file mode 100644
index 0000000..acd3c76
--- /dev/null
+++ b/pkgs/stream_transform/lib/src/scan.dart

@@ -0,0 +1,31 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+/// A utility similar to [fold] which emits intermediate accumulations.
+extension Scan<T> on Stream<T> {
+  /// Emits a sequence of the accumulated values from repeatedly applying
+  /// [combine].
+  ///
+  /// Like [fold], but instead of producing a single value it yields each
+  /// intermediate result.
+  ///
+  /// If [combine] returns a future it will not be called again for subsequent
+  /// events from the source until it completes, therefore [combine] is always
+  /// called for elements in order, and the result stream always maintains the
+  /// same order as this stream.
+  Stream<S> scan<S>(
+      S initialValue, FutureOr<S> Function(S soFar, T element) combine) {
+    var accumulated = initialValue;
+    return asyncMap((value) {
+      var result = combine(accumulated, value);
+      if (result is Future<S>) {
+        return result.then((r) => accumulated = r);
+      } else {
+        return accumulated = result;
+      }
+    });
+  }
+}

diff --git a/pkgs/stream_transform/lib/src/switch.dart b/pkgs/stream_transform/lib/src/switch.dart
new file mode 100644
index 0000000..546036e
--- /dev/null
+++ b/pkgs/stream_transform/lib/src/switch.dart

@@ -0,0 +1,135 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'async_expand.dart';
+import 'common_callbacks.dart';
+
+/// A utility to take events from the most recent sub stream returned by a
+/// callback.
+extension Switch<T> on Stream<T> {
+  /// Maps events to a Stream and emits values from the most recently created
+  /// Stream.
+  ///
+  /// When the source emits a value it will be converted to a [Stream] using
+  /// [convert] and the output will switch to emitting events from that result.
+  /// Like [asyncExpand] but the [Stream] emitted by a previous element
+  /// will be ignored as soon as the source stream emits a new event.
+  ///
+  /// This means that the source stream is not paused until a sub stream
+  /// returned from the [convert] callback is done. Instead, the subscription
+  /// to the sub stream is canceled as soon as the source stream emits a new
+  /// event.
+  ///
+  /// Errors from [convert], the source stream, or any of the sub streams are
+  /// forwarded to the result stream.
+  ///
+  /// The result stream will not close until the source stream closes and
+  /// the current sub stream have closed.
+  ///
+  /// If the source stream is a broadcast stream, the result will be as well,
+  /// regardless of the types of streams created by [convert]. In this case,
+  /// some care should be taken:
+  ///
+  ///  * If [convert] returns a single subscription stream it may be listened to
+  /// and never canceled.
+  ///
+  /// See also:
+  /// - [concurrentAsyncExpand], which emits events from all sub streams
+  ///   concurrently instead of cancelling subscriptions to previous subs
+  ///   streams.
+  Stream<S> switchMap<S>(Stream<S> Function(T) convert) {
+    return map(convert).switchLatest();
+  }
+}
+
+/// A utility to take events from the most recent sub stream.
+extension SwitchLatest<T> on Stream<Stream<T>> {
+  /// Emits values from the most recently emitted Stream.
+  ///
+  /// When the source emits a stream, the output will switch to emitting events
+  /// from that stream.
+  ///
+  /// Whether the source stream is a single-subscription stream or a
+  /// broadcast stream, the result stream will be the same kind of stream,
+  /// regardless of the types of streams emitted.
+  Stream<T> switchLatest() {
+    var controller = isBroadcast
+        ? StreamController<T>.broadcast(sync: true)
+        : StreamController<T>(sync: true);
+
+    controller.onListen = () {
+      StreamSubscription<T>? innerSubscription;
+      var outerStreamDone = false;
+
+      void listenToInnerStream(Stream<T> innerStream) {
+        assert(innerSubscription == null);
+        var subscription = innerStream
+            .listen(controller.add, onError: controller.addError, onDone: () {
+          innerSubscription = null;
+          if (outerStreamDone) controller.close();
+        });
+        // If a pause happens during an innerSubscription.cancel,
+        // we still listen to the next stream when the cancel is done.
+        // Then we immediately pause it again here.
+        if (controller.isPaused) subscription.pause();
+        innerSubscription = subscription;
+      }
+
+      var addError = controller.addError;
+      final outerSubscription = listen(null, onError: addError, onDone: () {
+        outerStreamDone = true;
+        if (innerSubscription == null) controller.close();
+      });
+      outerSubscription.onData((innerStream) async {
+        var currentSubscription = innerSubscription;
+        if (currentSubscription == null) {
+          listenToInnerStream(innerStream);
+          return;
+        }
+        innerSubscription = null;
+        outerSubscription.pause();
+        try {
+          await currentSubscription.cancel();
+        } catch (error, stack) {
+          controller.addError(error, stack);
+        } finally {
+          if (!isBroadcast && !controller.hasListener) {
+            // Result single-subscription stream subscription was cancelled
+            // while waiting for previous innerStream cancel.
+            //
+            // Ensure that the last received stream is also listened to and
+            // cancelled, then do nothing further.
+            innerStream.listen(null).cancel().ignore();
+          } else {
+            outerSubscription.resume();
+            listenToInnerStream(innerStream);
+          }
+        }
+      });
+      if (!isBroadcast) {
+        controller
+          ..onPause = () {
+            innerSubscription?.pause();
+            outerSubscription.pause();
+          }
+          ..onResume = () {
+            innerSubscription?.resume();
+            outerSubscription.resume();
+          };
+      }
+      controller.onCancel = () {
+        var sub = innerSubscription;
+        var cancels = [
+          if (!outerStreamDone) outerSubscription.cancel(),
+          if (sub != null) sub.cancel(),
+        ];
+        if (cancels.isEmpty) return null;
+        return cancels.wait.then(ignoreArgument);
+      };
+    };
+    return controller.stream;
+  }
+}

diff --git a/pkgs/stream_transform/lib/src/take_until.dart b/pkgs/stream_transform/lib/src/take_until.dart
new file mode 100644
index 0000000..e6deaa1
--- /dev/null
+++ b/pkgs/stream_transform/lib/src/take_until.dart

@@ -0,0 +1,64 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+/// A utility to end a stream based on an external trigger.
+extension TakeUntil<T> on Stream<T> {
+  /// Takes values from this stream which are emitted before [trigger]
+  /// completes.
+  ///
+  /// Completing [trigger] differs from canceling a subscription in that values
+  /// which are emitted before the trigger, but have further asynchronous delays
+  /// in transformations following the takeUtil, will still go through.
+  /// Cancelling a subscription immediately stops values.
+  ///
+  /// If [trigger] completes as an error, the error will be forwarded through
+  /// the result stream before the result stream closes.
+  ///
+  /// If [trigger] completes as a value or as an error after this stream has
+  /// already ended, the completion will be ignored.
+  Stream<T> takeUntil(Future<void> trigger) {
+    var controller = isBroadcast
+        ? StreamController<T>.broadcast(sync: true)
+        : StreamController<T>(sync: true);
+
+    StreamSubscription<T>? subscription;
+    var isDone = false;
+    trigger.then((_) {
+      if (isDone) return;
+      isDone = true;
+      subscription?.cancel();
+      controller.close();
+    }, onError: (Object error, StackTrace stackTrace) {
+      if (isDone) return;
+      isDone = true;
+      controller
+        ..addError(error, stackTrace)
+        ..close();
+    });
+
+    controller.onListen = () {
+      if (isDone) return;
+      subscription =
+          listen(controller.add, onError: controller.addError, onDone: () {
+        if (isDone) return;
+        isDone = true;
+        controller.close();
+      });
+      if (!isBroadcast) {
+        controller
+          ..onPause = subscription!.pause
+          ..onResume = subscription!.resume;
+      }
+      controller.onCancel = () {
+        if (isDone) return null;
+        var toCancel = subscription!;
+        subscription = null;
+        return toCancel.cancel();
+      };
+    };
+    return controller.stream;
+  }
+}

diff --git a/pkgs/stream_transform/lib/src/tap.dart b/pkgs/stream_transform/lib/src/tap.dart
new file mode 100644
index 0000000..4b16ab5
--- /dev/null
+++ b/pkgs/stream_transform/lib/src/tap.dart

@@ -0,0 +1,44 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+import 'from_handlers.dart';
+
+/// A utility to chain extra behavior on a stream.
+extension Tap<T> on Stream<T> {
+  /// Taps into this stream to allow additional handling on a single-subscriber
+  /// stream without first wrapping as a broadcast stream.
+  ///
+  /// The [onValue] callback will be called with every value from this stream
+  /// before it is forwarded to listeners on the resulting stream.
+  /// May be null if only [onError] or [onDone] callbacks are needed.
+  ///
+  /// The [onError] callback will be called with every error from this stream
+  /// before it is forwarded to listeners on the resulting stream.
+  ///
+  /// The [onDone] callback will be called after this stream closes and before
+  /// the resulting stream is closed.
+  ///
+  /// Errors from any of the callbacks are caught and ignored.
+  ///
+  /// The callbacks may not be called until the tapped stream has a listener,
+  /// and may not be called after the listener has canceled the subscription.
+  Stream<T> tap(void Function(T)? onValue,
+          {void Function(Object, StackTrace)? onError,
+          void Function()? onDone}) =>
+      transformByHandlers(onData: (value, sink) {
+        try {
+          onValue?.call(value);
+        } catch (_) {/*Ignore*/}
+        sink.add(value);
+      }, onError: (error, stackTrace, sink) {
+        try {
+          onError?.call(error, stackTrace);
+        } catch (_) {/*Ignore*/}
+        sink.addError(error, stackTrace);
+      }, onDone: (sink) {
+        try {
+          onDone?.call();
+        } catch (_) {/*Ignore*/}
+        sink.close();
+      });
+}

diff --git a/pkgs/stream_transform/lib/src/where.dart b/pkgs/stream_transform/lib/src/where.dart
new file mode 100644
index 0000000..76aa28a
--- /dev/null
+++ b/pkgs/stream_transform/lib/src/where.dart

@@ -0,0 +1,71 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'from_handlers.dart';
+
+/// Utilities to filter events.
+extension Where<T> on Stream<T> {
+  /// Discards events from this stream that are not of type [S].
+  ///
+  /// If the source stream is a broadcast stream the result will be as well.
+  ///
+  /// Errors from the source stream are forwarded directly to the result stream.
+  ///
+  /// [S] should be a subtype of the stream's generic type, otherwise nothing of
+  /// type [S] could possibly be emitted, however there is no static or runtime
+  /// checking that this is the case.
+  Stream<S> whereType<S>() => transformByHandlers(onData: (event, sink) {
+        if (event is S) sink.add(event);
+      });
+
+  /// Discards events from this stream based on an asynchronous [test] callback.
+  ///
+  /// Like [where] but allows the [test] to return a [Future].
+  ///
+  /// Events on the result stream will be emitted in the order that [test]
+  /// completes which may not match the order of this stream.
+  ///
+  /// If the source stream is a broadcast stream the result will be as well.
+  /// When used with a broadcast stream behavior also differs from [where] in
+  /// that the [test] function is only called once per event, rather than once
+  /// per listener per event.
+  ///
+  /// Errors from the source stream are forwarded directly to the result stream.
+  /// Errors from [test] are also forwarded to the result stream.
+  ///
+  /// The result stream will not close until the source stream closes and all
+  /// pending [test] calls have finished.
+  Stream<T> asyncWhere(FutureOr<bool> Function(T) test) {
+    var valuesWaiting = 0;
+    var sourceDone = false;
+    return transformByHandlers(onData: (element, sink) {
+      valuesWaiting++;
+      () async {
+        try {
+          if (await test(element)) sink.add(element);
+        } catch (e, st) {
+          sink.addError(e, st);
+        }
+        valuesWaiting--;
+        if (valuesWaiting <= 0 && sourceDone) sink.close();
+      }();
+    }, onDone: (sink) {
+      sourceDone = true;
+      if (valuesWaiting <= 0) sink.close();
+    });
+  }
+}
+
+extension WhereNotNull<T extends Object> on Stream<T?> {
+  /// Discards `null` events from this stream.
+  ///
+  /// If the source stream is a broadcast stream the result will be as well.
+  ///
+  /// Errors from the source stream are forwarded directly to the result stream.
+  Stream<T> whereNotNull() => transformByHandlers(onData: (event, sink) {
+        if (event != null) sink.add(event);
+      });
+}

diff --git a/pkgs/stream_transform/lib/stream_transform.dart b/pkgs/stream_transform/lib/stream_transform.dart
new file mode 100644
index 0000000..edf4df9
--- /dev/null
+++ b/pkgs/stream_transform/lib/stream_transform.dart

@@ -0,0 +1,15 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+export 'src/async_expand.dart';
+export 'src/async_map.dart';
+export 'src/combine_latest.dart';
+export 'src/concatenate.dart';
+export 'src/merge.dart';
+export 'src/rate_limit.dart';
+export 'src/scan.dart';
+export 'src/switch.dart';
+export 'src/take_until.dart';
+export 'src/tap.dart';
+export 'src/where.dart';

diff --git a/pkgs/stream_transform/pubspec.yaml b/pkgs/stream_transform/pubspec.yaml
new file mode 100644
index 0000000..91840b7
--- /dev/null
+++ b/pkgs/stream_transform/pubspec.yaml

@@ -0,0 +1,14 @@
+name: stream_transform
+version: 2.1.2-wip
+description: A collection of utilities to transform and manipulate streams.
+repository: https://github.com/dart-lang/tools/tree/main/pkgs/stream_transform
+
+environment:
+  sdk: ^3.4.0
+
+dev_dependencies:
+  async: ^2.5.0
+  dart_flutter_team_lints: ^3.0.0
+  fake_async: ^1.3.0
+  test: ^1.16.0
+  web: ^1.1.0

diff --git a/pkgs/stream_transform/test/async_expand_test.dart b/pkgs/stream_transform/test/async_expand_test.dart
new file mode 100644
index 0000000..8d84300
--- /dev/null
+++ b/pkgs/stream_transform/test/async_expand_test.dart

@@ -0,0 +1,195 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:stream_transform/stream_transform.dart';
+import 'package:test/test.dart';
+
+import 'utils.dart';
+
+void main() {
+  test('forwards errors from the convert callback', () async {
+    var errors = <String>[];
+    var source = Stream.fromIterable([1, 2, 3]);
+    source.concurrentAsyncExpand<void>((i) {
+      // ignore: only_throw_errors
+      throw 'Error: $i';
+    }).listen((_) {}, onError: errors.add);
+    await Future<void>(() {});
+    expect(errors, ['Error: 1', 'Error: 2', 'Error: 3']);
+  });
+
+  for (var outerType in streamTypes) {
+    for (var innerType in streamTypes) {
+      group('concurrentAsyncExpand $outerType to $innerType', () {
+        late StreamController<int> outerController;
+        late bool outerCanceled;
+        late List<StreamController<String>> innerControllers;
+        late List<bool> innerCanceled;
+        late List<String> emittedValues;
+        late bool isDone;
+        late List<String> errors;
+        late Stream<String> transformed;
+        late StreamSubscription<String> subscription;
+
+        setUp(() {
+          outerController = createController(outerType)
+            ..onCancel = () {
+              outerCanceled = true;
+            };
+          outerCanceled = false;
+          innerControllers = [];
+          innerCanceled = [];
+          emittedValues = [];
+          errors = [];
+          isDone = false;
+          transformed = outerController.stream.concurrentAsyncExpand((i) {
+            var index = innerControllers.length;
+            innerCanceled.add(false);
+            innerControllers.add(createController<String>(innerType)
+              ..onCancel = () {
+                innerCanceled[index] = true;
+              });
+            return innerControllers.last.stream;
+          });
+          subscription = transformed
+              .listen(emittedValues.add, onError: errors.add, onDone: () {
+            isDone = true;
+          });
+        });
+
+        test('interleaves events from sub streams', () async {
+          outerController
+            ..add(1)
+            ..add(2);
+          await Future<void>(() {});
+          expect(emittedValues, isEmpty);
+          expect(innerControllers, hasLength(2));
+          innerControllers[0].add('First');
+          innerControllers[1].add('Second');
+          innerControllers[0].add('First again');
+          await Future<void>(() {});
+          expect(emittedValues, ['First', 'Second', 'First again']);
+        });
+
+        test('forwards errors from outer stream', () async {
+          outerController.addError('Error');
+          await Future<void>(() {});
+          expect(errors, ['Error']);
+        });
+
+        test('forwards errors from inner streams', () async {
+          outerController
+            ..add(1)
+            ..add(2);
+          await Future<void>(() {});
+          innerControllers[0].addError('Error 1');
+          innerControllers[1].addError('Error 2');
+          await Future<void>(() {});
+          expect(errors, ['Error 1', 'Error 2']);
+        });
+
+        test('can continue handling events after an error in outer stream',
+            () async {
+          outerController
+            ..addError('Error')
+            ..add(1);
+          await Future<void>(() {});
+          innerControllers[0].add('First');
+          await Future<void>(() {});
+          expect(emittedValues, ['First']);
+          expect(errors, ['Error']);
+        });
+
+        test('cancels outer subscription if output canceled', () async {
+          await subscription.cancel();
+          expect(outerCanceled, true);
+        });
+
+        if (outerType != 'broadcast' || innerType != 'single subscription') {
+          // A single subscription inner stream in a broadcast outer stream is
+          // not canceled.
+          test('cancels inner subscriptions if output canceled', () async {
+            outerController
+              ..add(1)
+              ..add(2);
+            await Future<void>(() {});
+            await subscription.cancel();
+            expect(innerCanceled, [true, true]);
+          });
+        }
+
+        test('stays open if any inner stream is still open', () async {
+          outerController.add(1);
+          await outerController.close();
+          await Future<void>(() {});
+          expect(isDone, false);
+        });
+
+        test('stays open if outer stream is still open', () async {
+          outerController.add(1);
+          await Future<void>(() {});
+          await innerControllers[0].close();
+          await Future<void>(() {});
+          expect(isDone, false);
+        });
+
+        test('closes after all inner streams and outer stream close', () async {
+          outerController.add(1);
+          await Future<void>(() {});
+          await innerControllers[0].close();
+          await outerController.close();
+          await Future<void>(() {});
+          expect(isDone, true);
+        });
+
+        if (outerType == 'broadcast') {
+          test('multiple listerns all get values', () async {
+            var otherValues = <String>[];
+            transformed.listen(otherValues.add);
+            outerController.add(1);
+            await Future<void>(() {});
+            innerControllers[0].add('First');
+            await Future<void>(() {});
+            expect(emittedValues, ['First']);
+            expect(otherValues, ['First']);
+          });
+
+          test('multiple listeners get closed', () async {
+            var otherDone = false;
+            transformed.listen(null, onDone: () => otherDone = true);
+            outerController.add(1);
+            await Future<void>(() {});
+            await innerControllers[0].close();
+            await outerController.close();
+            await Future<void>(() {});
+            expect(isDone, true);
+            expect(otherDone, true);
+          });
+
+          test('can cancel and relisten', () async {
+            outerController
+              ..add(1)
+              ..add(2);
+            await Future(() {});
+            innerControllers[0].add('First');
+            innerControllers[1].add('Second');
+            await Future(() {});
+            await subscription.cancel();
+            innerControllers[0].add('Ignored');
+            await Future(() {});
+            subscription = transformed.listen(emittedValues.add);
+            innerControllers[0].add('Also ignored');
+            outerController.add(3);
+            await Future(() {});
+            innerControllers[2].add('More');
+            await Future(() {});
+            expect(emittedValues, ['First', 'Second', 'More']);
+          });
+        }
+      });
+    }
+  }
+}

diff --git a/pkgs/stream_transform/test/async_map_buffer_test.dart b/pkgs/stream_transform/test/async_map_buffer_test.dart
new file mode 100644
index 0000000..2386217
--- /dev/null
+++ b/pkgs/stream_transform/test/async_map_buffer_test.dart

@@ -0,0 +1,204 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:stream_transform/stream_transform.dart';
+import 'package:test/test.dart';
+
+import 'utils.dart';
+
+void main() {
+  late StreamController<int> values;
+  late List<String> emittedValues;
+  late bool valuesCanceled;
+  late bool isDone;
+  late List<String> errors;
+  late Stream<String> transformed;
+  late StreamSubscription<String> subscription;
+
+  Completer<String>? finishWork;
+  List<int>? workArgument;
+
+  /// Represents the async `convert` function and asserts that is is only called
+  /// after the previous iteration has completed.
+  Future<String> work(List<int> values) {
+    expect(finishWork, isNull,
+        reason: 'See $values befor previous work is complete');
+    workArgument = values;
+    finishWork = Completer()
+      ..future.then((_) {
+        workArgument = null;
+        finishWork = null;
+      }).catchError((_) {
+        workArgument = null;
+        finishWork = null;
+      });
+    return finishWork!.future;
+  }
+
+  for (var streamType in streamTypes) {
+    group('asyncMapBuffer for stream type: [$streamType]', () {
+      setUp(() {
+        valuesCanceled = false;
+        values = createController(streamType)
+          ..onCancel = () {
+            valuesCanceled = true;
+          };
+        emittedValues = [];
+        errors = [];
+        isDone = false;
+        finishWork = null;
+        workArgument = null;
+        transformed = values.stream.asyncMapBuffer(work);
+        subscription = transformed
+            .listen(emittedValues.add, onError: errors.add, onDone: () {
+          isDone = true;
+        });
+      });
+
+      test('does not emit before work finishes', () async {
+        values.add(1);
+        await Future(() {});
+        expect(emittedValues, isEmpty);
+        expect(workArgument, [1]);
+        finishWork!.complete('result');
+        await Future(() {});
+        expect(emittedValues, ['result']);
+      });
+
+      test('buffers values while work is ongoing', () async {
+        values.add(1);
+        await Future(() {});
+        values
+          ..add(2)
+          ..add(3);
+        await Future(() {});
+        finishWork!.complete('');
+        await Future(() {});
+        expect(workArgument, [2, 3]);
+      });
+
+      test('forwards errors without waiting for work', () async {
+        values.add(1);
+        await Future(() {});
+        values.addError('error');
+        await Future(() {});
+        expect(errors, ['error']);
+      });
+
+      test('forwards errors which occur during the work', () async {
+        values.add(1);
+        await Future(() {});
+        finishWork!.completeError('error');
+        await Future(() {});
+        expect(errors, ['error']);
+      });
+
+      test('can continue handling events after an error', () async {
+        values.add(1);
+        await Future(() {});
+        finishWork!.completeError('error');
+        values.add(2);
+        await Future(() {});
+        expect(workArgument, [2]);
+        finishWork!.completeError('another');
+        await Future(() {});
+        expect(errors, ['error', 'another']);
+      });
+
+      test('does not start next work early due to an error in values',
+          () async {
+        values.add(1);
+        await Future(() {});
+        values
+          ..addError('error')
+          ..add(2);
+        await Future(() {});
+        expect(errors, ['error']);
+        // [work] will assert that the second iteration is not called because
+        // the first has not completed.
+      });
+
+      test('cancels value subscription when output canceled', () async {
+        expect(valuesCanceled, false);
+        await subscription.cancel();
+        expect(valuesCanceled, true);
+      });
+
+      test('closes when values end if no work is pending', () async {
+        expect(isDone, false);
+        await values.close();
+        await Future(() {});
+        expect(isDone, true);
+      });
+
+      test('waits for pending work when values close', () async {
+        values.add(1);
+        await Future(() {});
+        expect(isDone, false);
+        values.add(2);
+        await values.close();
+        expect(isDone, false);
+        finishWork!.complete('');
+        await Future(() {});
+        // Still a pending value
+        expect(isDone, false);
+        finishWork!.complete('');
+        await Future(() {});
+        expect(isDone, true);
+      });
+
+      test('forwards errors from values', () async {
+        values.addError('error');
+        await Future(() {});
+        expect(errors, ['error']);
+      });
+
+      if (streamType == 'broadcast') {
+        test('multiple listeners all get values', () async {
+          var otherValues = <String>[];
+          transformed.listen(otherValues.add);
+          values.add(1);
+          await Future(() {});
+          finishWork!.complete('result');
+          await Future(() {});
+          expect(emittedValues, ['result']);
+          expect(otherValues, ['result']);
+        });
+
+        test('multiple listeners get done when values end', () async {
+          var otherDone = false;
+          transformed.listen(null, onDone: () => otherDone = true);
+          values.add(1);
+          await Future(() {});
+          await values.close();
+          expect(isDone, false);
+          expect(otherDone, false);
+          finishWork!.complete('');
+          await Future(() {});
+          expect(isDone, true);
+          expect(otherDone, true);
+        });
+
+        test('can cancel and relisten', () async {
+          values.add(1);
+          await Future(() {});
+          finishWork!.complete('first');
+          await Future(() {});
+          await subscription.cancel();
+          values.add(2);
+          await Future(() {});
+          subscription = transformed.listen(emittedValues.add);
+          values.add(3);
+          await Future(() {});
+          expect(workArgument, [3]);
+          finishWork!.complete('second');
+          await Future(() {});
+          expect(emittedValues, ['first', 'second']);
+        });
+      }
+    });
+  }
+}

diff --git a/pkgs/stream_transform/test/async_map_sample_test.dart b/pkgs/stream_transform/test/async_map_sample_test.dart
new file mode 100644
index 0000000..62b1b92
--- /dev/null
+++ b/pkgs/stream_transform/test/async_map_sample_test.dart

@@ -0,0 +1,209 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:stream_transform/stream_transform.dart';
+import 'package:test/test.dart';
+
+import 'utils.dart';
+
+void main() {
+  late StreamController<int> values;
+  late List<String> emittedValues;
+  late bool valuesCanceled;
+  late bool isDone;
+  late List<String> errors;
+  late Stream<String> transformed;
+  late StreamSubscription<String> subscription;
+
+  Completer<String>? finishWork;
+  int? workArgument;
+
+  /// Represents the async `convert` function and asserts that is is only called
+  /// after the previous iteration has completed.
+  Future<String> work(int value) {
+    expect(finishWork, isNull,
+        reason: 'See $values befor previous work is complete');
+    workArgument = value;
+    finishWork = Completer()
+      ..future.then((_) {
+        workArgument = null;
+        finishWork = null;
+      }).catchError((_) {
+        workArgument = null;
+        finishWork = null;
+      });
+    return finishWork!.future;
+  }
+
+  for (var streamType in streamTypes) {
+    group('asyncMapSample for stream type: [$streamType]', () {
+      setUp(() {
+        valuesCanceled = false;
+        values = createController(streamType)
+          ..onCancel = () {
+            valuesCanceled = true;
+          };
+        emittedValues = [];
+        errors = [];
+        isDone = false;
+        finishWork = null;
+        workArgument = null;
+        transformed = values.stream.asyncMapSample(work);
+        subscription = transformed
+            .listen(emittedValues.add, onError: errors.add, onDone: () {
+          isDone = true;
+        });
+      });
+
+      test('does not emit before work finishes', () async {
+        values.add(1);
+        await Future(() {});
+        expect(emittedValues, isEmpty);
+        expect(workArgument, 1);
+        finishWork!.complete('result');
+        await Future(() {});
+        expect(emittedValues, ['result']);
+      });
+
+      test('buffers values while work is ongoing', () async {
+        values.add(1);
+        await Future(() {});
+        values
+          ..add(2)
+          ..add(3);
+        await Future(() {});
+        finishWork!.complete('');
+        await Future(() {});
+        expect(workArgument, 3);
+      });
+
+      test('forwards errors without waiting for work', () async {
+        values.add(1);
+        await Future(() {});
+        values.addError('error');
+        await Future(() {});
+        expect(errors, ['error']);
+      });
+
+      test('forwards errors which occur during the work', () async {
+        values.add(1);
+        await Future(() {});
+        finishWork!.completeError('error');
+        await Future(() {});
+        expect(errors, ['error']);
+      });
+
+      test('can continue handling events after an error', () async {
+        values.add(1);
+        await Future(() {});
+        finishWork!.completeError('error');
+        values.add(2);
+        await Future(() {});
+        expect(workArgument, 2);
+        finishWork!.completeError('another');
+        await Future(() {});
+        expect(errors, ['error', 'another']);
+      });
+
+      test('does not start next work early due to an error in values',
+          () async {
+        values.add(1);
+        await Future(() {});
+        values
+          ..addError('error')
+          ..add(2);
+        await Future(() {});
+        expect(errors, ['error']);
+        // [work] will assert that the second iteration is not called because
+        // the first has not completed.
+      });
+
+      test('cancels value subscription when output canceled', () async {
+        expect(valuesCanceled, false);
+        await subscription.cancel();
+        expect(valuesCanceled, true);
+      });
+
+      test('closes when values end if no work is pending', () async {
+        expect(isDone, false);
+        await values.close();
+        await Future(() {});
+        expect(isDone, true);
+      });
+
+      test('waits for pending work when values close', () async {
+        values.add(1);
+        await Future(() {});
+        expect(isDone, false);
+        values.add(2);
+        await values.close();
+        expect(isDone, false);
+        finishWork!.complete('');
+        await Future(() {});
+        // Still a pending value
+        expect(isDone, false);
+        finishWork!.complete('');
+        await Future(() {});
+        expect(isDone, true);
+      });
+
+      test('forwards errors from values', () async {
+        values.addError('error');
+        await Future(() {});
+        expect(errors, ['error']);
+      });
+
+      if (streamType == 'broadcast') {
+        test('multiple listeners all get values', () async {
+          var otherValues = <String>[];
+          transformed.listen(otherValues.add);
+          values.add(1);
+          await Future(() {});
+          finishWork!.complete('result');
+          await Future(() {});
+          expect(emittedValues, ['result']);
+          expect(otherValues, ['result']);
+        });
+
+        test('multiple listeners get done when values end', () async {
+          var otherDone = false;
+          transformed.listen(null, onDone: () => otherDone = true);
+          values.add(1);
+          await Future(() {});
+          await values.close();
+          expect(isDone, false);
+          expect(otherDone, false);
+          finishWork!.complete('');
+          await Future(() {});
+          expect(isDone, true);
+          expect(otherDone, true);
+        });
+
+        test('can cancel and relisten', () async {
+          values.add(1);
+          await Future(() {});
+          finishWork!.complete('first');
+          await Future(() {});
+          await subscription.cancel();
+          values.add(2);
+          await Future(() {});
+          subscription = transformed.listen(emittedValues.add);
+          values.add(3);
+          await Future(() {});
+          expect(workArgument, 3);
+          finishWork!.complete('second');
+          await Future(() {});
+          expect(emittedValues, ['first', 'second']);
+        });
+      }
+    });
+  }
+
+  test('allows nulls', () async {
+    var stream = Stream<int?>.value(null);
+    await stream.asyncMapSample(expectAsync1((_) async {})).drain<void>();
+  });
+}

diff --git a/pkgs/stream_transform/test/async_where_test.dart b/pkgs/stream_transform/test/async_where_test.dart
new file mode 100644
index 0000000..6ea4e76
--- /dev/null
+++ b/pkgs/stream_transform/test/async_where_test.dart

@@ -0,0 +1,90 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+import 'dart:async';
+
+import 'package:stream_transform/stream_transform.dart';
+import 'package:test/test.dart';
+
+void main() {
+  test('forwards only events that pass the predicate', () async {
+    var values = Stream.fromIterable([1, 2, 3, 4]);
+    var filtered = values.asyncWhere((e) async => e > 2);
+    expect(await filtered.toList(), [3, 4]);
+  });
+
+  test('allows predicates that go through event loop', () async {
+    var values = Stream.fromIterable([1, 2, 3, 4]);
+    var filtered = values.asyncWhere((e) async {
+      await Future(() {});
+      return e > 2;
+    });
+    expect(await filtered.toList(), [3, 4]);
+  });
+
+  test('allows synchronous predicate', () async {
+    var values = Stream.fromIterable([1, 2, 3, 4]);
+    var filtered = values.asyncWhere((e) => e > 2);
+    expect(await filtered.toList(), [3, 4]);
+  });
+
+  test('can result in empty stream', () async {
+    var values = Stream.fromIterable([1, 2, 3, 4]);
+    var filtered = values.asyncWhere((e) => e > 4);
+    expect(await filtered.isEmpty, true);
+  });
+
+  test('forwards values to multiple listeners', () async {
+    var values = StreamController<int>.broadcast();
+    var filtered = values.stream.asyncWhere((e) async => e > 2);
+    var firstValues = <int>[];
+    var secondValues = <int>[];
+    filtered
+      ..listen(firstValues.add)
+      ..listen(secondValues.add);
+    values
+      ..add(1)
+      ..add(2)
+      ..add(3)
+      ..add(4);
+    await Future(() {});
+    expect(firstValues, [3, 4]);
+    expect(secondValues, [3, 4]);
+  });
+
+  test('closes streams with multiple listeners', () async {
+    var values = StreamController<int>.broadcast();
+    var predicate = Completer<bool>();
+    var filtered = values.stream.asyncWhere((_) => predicate.future);
+    var firstDone = false;
+    var secondDone = false;
+    filtered
+      ..listen(null, onDone: () => firstDone = true)
+      ..listen(null, onDone: () => secondDone = true);
+    values.add(1);
+    await values.close();
+    expect(firstDone, false);
+    expect(secondDone, false);
+
+    predicate.complete(true);
+    await Future(() {});
+    expect(firstDone, true);
+    expect(secondDone, true);
+  });
+
+  test('forwards errors emitted by the test callback', () async {
+    var errors = <Object>[];
+    var emitted = <Object>[];
+    var values = Stream.fromIterable([1, 2, 3, 4]);
+    var filtered = values.asyncWhere((e) async {
+      await Future(() {});
+      if (e.isEven) throw Exception('$e');
+      return true;
+    });
+    var done = Completer<Object?>();
+    filtered.listen(emitted.add, onError: errors.add, onDone: done.complete);
+    await done.future;
+    expect(emitted, [1, 3]);
+    expect(errors.map((e) => '$e'), ['Exception: 2', 'Exception: 4']);
+  });
+}

diff --git a/pkgs/stream_transform/test/audit_test.dart b/pkgs/stream_transform/test/audit_test.dart
new file mode 100644
index 0000000..28537db
--- /dev/null
+++ b/pkgs/stream_transform/test/audit_test.dart

@@ -0,0 +1,140 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:fake_async/fake_async.dart';
+import 'package:stream_transform/stream_transform.dart';
+import 'package:test/test.dart';
+
+import 'utils.dart';
+
+void main() {
+  for (var streamType in streamTypes) {
+    group('Stream type [$streamType]', () {
+      late StreamController<int> values;
+      late List<int> emittedValues;
+      late bool valuesCanceled;
+      late bool isDone;
+      late List<String> errors;
+      late Stream<int> transformed;
+      late StreamSubscription<int> subscription;
+
+      group('audit', () {
+        setUp(() {
+          valuesCanceled = false;
+          values = createController(streamType)
+            ..onCancel = () {
+              valuesCanceled = true;
+            };
+          emittedValues = [];
+          errors = [];
+          isDone = false;
+          transformed = values.stream.audit(const Duration(milliseconds: 6));
+        });
+
+        void listen() {
+          subscription = transformed
+              .listen(emittedValues.add, onError: errors.add, onDone: () {
+            isDone = true;
+          });
+        }
+
+        test('cancels values', () async {
+          listen();
+          await subscription.cancel();
+          expect(valuesCanceled, true);
+        });
+
+        test('swallows values that come faster than duration', () {
+          fakeAsync((async) {
+            listen();
+            values
+              ..add(1)
+              ..add(2)
+              ..close();
+            async.elapse(const Duration(milliseconds: 6));
+            expect(emittedValues, [2]);
+          });
+        });
+
+        test('outputs multiple values spaced further than duration', () {
+          fakeAsync((async) {
+            listen();
+            values.add(1);
+            async.elapse(const Duration(milliseconds: 6));
+            values.add(2);
+            async.elapse(const Duration(milliseconds: 6));
+            expect(emittedValues, [1, 2]);
+          });
+        });
+
+        test('waits for pending value to close', () {
+          fakeAsync((async) {
+            listen();
+            values
+              ..add(1)
+              ..close();
+            expect(isDone, false);
+            async.elapse(const Duration(milliseconds: 6));
+            expect(isDone, true);
+          });
+        });
+
+        test('closes output if there are no pending values', () {
+          fakeAsync((async) {
+            listen();
+            values.add(1);
+            async.elapse(const Duration(milliseconds: 6));
+            values
+              ..add(2)
+              ..close();
+            expect(isDone, false);
+            expect(emittedValues, [1]);
+            async.elapse(const Duration(milliseconds: 6));
+            expect(isDone, true);
+            expect(emittedValues, [1, 2]);
+          });
+        });
+
+        test('does not starve output if many values come closer than duration',
+            () {
+          fakeAsync((async) {
+            listen();
+            values.add(1);
+            async.elapse(const Duration(milliseconds: 3));
+            values.add(2);
+            async.elapse(const Duration(milliseconds: 3));
+            values.add(3);
+            async.elapse(const Duration(milliseconds: 6));
+            expect(emittedValues, [2, 3]);
+          });
+        });
+
+        if (streamType == 'broadcast') {
+          test('multiple listeners all get the values', () {
+            fakeAsync((async) {
+              listen();
+              values.add(1);
+              async.elapse(const Duration(milliseconds: 3));
+              values.add(2);
+              var otherValues = <int>[];
+              transformed.listen(otherValues.add);
+              values.add(3);
+              async.elapse(const Duration(milliseconds: 3));
+              values.add(4);
+              async.elapse(const Duration(milliseconds: 3));
+              values
+                ..add(5)
+                ..close();
+              async.elapse(const Duration(milliseconds: 6));
+              expect(emittedValues, [3, 5]);
+              expect(otherValues, [3, 5]);
+            });
+          });
+        }
+      });
+    });
+  }
+}

diff --git a/pkgs/stream_transform/test/buffer_test.dart b/pkgs/stream_transform/test/buffer_test.dart
new file mode 100644
index 0000000..830f555
--- /dev/null
+++ b/pkgs/stream_transform/test/buffer_test.dart

@@ -0,0 +1,305 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+import 'dart:async';
+
+import 'package:stream_transform/stream_transform.dart';
+import 'package:test/test.dart';
+
+import 'utils.dart';
+
+void main() {
+  late StreamController<void> trigger;
+  late StreamController<int> values;
+  late List<List<int>> emittedValues;
+  late bool valuesCanceled;
+  late bool triggerCanceled;
+  late bool triggerPaused;
+  late bool isDone;
+  late List<String> errors;
+  late Stream<List<int>> transformed;
+  late StreamSubscription<List<int>> subscription;
+
+  void setUpForStreamTypes(String triggerType, String valuesType,
+      {required bool longPoll}) {
+    valuesCanceled = false;
+    triggerCanceled = false;
+    triggerPaused = false;
+    trigger = createController(triggerType)
+      ..onCancel = () {
+        triggerCanceled = true;
+      };
+    if (triggerType == 'single subscription') {
+      trigger.onPause = () {
+        triggerPaused = true;
+      };
+    }
+    values = createController(valuesType)
+      ..onCancel = () {
+        valuesCanceled = true;
+      };
+    emittedValues = [];
+    errors = [];
+    isDone = false;
+    transformed = values.stream.buffer(trigger.stream, longPoll: longPoll);
+    subscription =
+        transformed.listen(emittedValues.add, onError: errors.add, onDone: () {
+      isDone = true;
+    });
+  }
+
+  for (var triggerType in streamTypes) {
+    for (var valuesType in streamTypes) {
+      group('Trigger type: [$triggerType], Values type: [$valuesType]', () {
+        group('general behavior', () {
+          setUp(() {
+            setUpForStreamTypes(triggerType, valuesType, longPoll: true);
+          });
+
+          test('does not emit before `trigger`', () async {
+            values.add(1);
+            await Future(() {});
+            expect(emittedValues, isEmpty);
+            trigger.add(null);
+            await Future(() {});
+            expect(emittedValues, [
+              [1]
+            ]);
+          });
+
+          test('groups values between trigger', () async {
+            values
+              ..add(1)
+              ..add(2);
+            await Future(() {});
+            trigger.add(null);
+            values
+              ..add(3)
+              ..add(4);
+            await Future(() {});
+            trigger.add(null);
+            await Future(() {});
+            expect(emittedValues, [
+              [1, 2],
+              [3, 4]
+            ]);
+          });
+
+          test('cancels value subscription when output canceled', () async {
+            expect(valuesCanceled, false);
+            await subscription.cancel();
+            expect(valuesCanceled, true);
+          });
+
+          test('closes when trigger ends', () async {
+            expect(isDone, false);
+            await trigger.close();
+            await Future(() {});
+            expect(isDone, true);
+          });
+
+          test('closes after outputting final values when source closes',
+              () async {
+            expect(isDone, false);
+            values.add(1);
+            await values.close();
+            expect(isDone, false);
+            trigger.add(null);
+            await Future(() {});
+            expect(emittedValues, [
+              [1]
+            ]);
+            expect(isDone, true);
+          });
+
+          test('closes when source closes and there are no buffered', () async {
+            expect(isDone, false);
+            await values.close();
+            await Future(() {});
+            expect(isDone, true);
+          });
+
+          test('forwards errors from trigger', () async {
+            trigger.addError('error');
+            await Future(() {});
+            expect(errors, ['error']);
+          });
+
+          test('forwards errors from values', () async {
+            values.addError('error');
+            await Future(() {});
+            expect(errors, ['error']);
+          });
+        });
+
+        group('long polling', () {
+          setUp(() {
+            setUpForStreamTypes(triggerType, valuesType, longPoll: true);
+          });
+
+          test('emits immediately if trigger emits before a value', () async {
+            trigger.add(null);
+            await Future(() {});
+            expect(emittedValues, isEmpty);
+            values.add(1);
+            await Future(() {});
+            expect(emittedValues, [
+              [1]
+            ]);
+          });
+
+          test('two triggers in a row - emit buffere then emit next value',
+              () async {
+            values
+              ..add(1)
+              ..add(2);
+            await Future(() {});
+            trigger
+              ..add(null)
+              ..add(null);
+            await Future(() {});
+            values.add(3);
+            await Future(() {});
+            expect(emittedValues, [
+              [1, 2],
+              [3]
+            ]);
+          });
+
+          test('pre-emptive trigger then trigger after values', () async {
+            trigger.add(null);
+            await Future(() {});
+            values
+              ..add(1)
+              ..add(2);
+            await Future(() {});
+            trigger.add(null);
+            await Future(() {});
+            expect(emittedValues, [
+              [1],
+              [2]
+            ]);
+          });
+
+          test('multiple pre-emptive triggers, only emits first value',
+              () async {
+            trigger
+              ..add(null)
+              ..add(null);
+            await Future(() {});
+            values
+              ..add(1)
+              ..add(2);
+            await Future(() {});
+            expect(emittedValues, [
+              [1]
+            ]);
+          });
+
+          test('closes if there is no waiting long poll when source closes',
+              () async {
+            expect(isDone, false);
+            values.add(1);
+            trigger.add(null);
+            await values.close();
+            await Future(() {});
+            expect(isDone, true);
+          });
+
+          test('waits to emit if there waiting long poll when trigger closes',
+              () async {
+            trigger.add(null);
+            await trigger.close();
+            expect(isDone, false);
+            values.add(1);
+            await Future(() {});
+            expect(emittedValues, [
+              [1]
+            ]);
+            expect(isDone, true);
+          });
+        });
+
+        group('immediate polling', () {
+          setUp(() {
+            setUpForStreamTypes(triggerType, valuesType, longPoll: false);
+          });
+
+          test('emits empty list before values', () async {
+            trigger.add(null);
+            await Future(() {});
+            expect(emittedValues, [<int>[]]);
+          });
+
+          test('emits empty list after emitting values', () async {
+            values
+              ..add(1)
+              ..add(2);
+            await Future(() {});
+            trigger
+              ..add(null)
+              ..add(null);
+            await Future(() {});
+            expect(emittedValues, [
+              [1, 2],
+              <int>[]
+            ]);
+          });
+        });
+      });
+    }
+  }
+
+  test('always cancels trigger if values is singlesubscription', () async {
+    setUpForStreamTypes('broadcast', 'single subscription', longPoll: true);
+    expect(triggerCanceled, false);
+    await subscription.cancel();
+    expect(triggerCanceled, true);
+
+    setUpForStreamTypes('single subscription', 'single subscription',
+        longPoll: true);
+    expect(triggerCanceled, false);
+    await subscription.cancel();
+    expect(triggerCanceled, true);
+  });
+
+  test('cancels trigger if trigger is broadcast', () async {
+    setUpForStreamTypes('broadcast', 'broadcast', longPoll: true);
+    expect(triggerCanceled, false);
+    await subscription.cancel();
+    expect(triggerCanceled, true);
+  });
+
+  test('pauses single subscription trigger for broadcast values', () async {
+    setUpForStreamTypes('single subscription', 'broadcast', longPoll: true);
+    expect(triggerCanceled, false);
+    expect(triggerPaused, false);
+    await subscription.cancel();
+    expect(triggerCanceled, false);
+    expect(triggerPaused, true);
+  });
+
+  for (var triggerType in streamTypes) {
+    test('cancel and relisten with [$triggerType] trigger', () async {
+      setUpForStreamTypes(triggerType, 'broadcast', longPoll: true);
+      values.add(1);
+      trigger.add(null);
+      await Future(() {});
+      expect(emittedValues, [
+        [1]
+      ]);
+      await subscription.cancel();
+      values.add(2);
+      trigger.add(null);
+      await Future(() {});
+      subscription = transformed.listen(emittedValues.add);
+      values.add(3);
+      trigger.add(null);
+      await Future(() {});
+      expect(emittedValues, [
+        [1],
+        [3]
+      ]);
+    });
+  }
+}

diff --git a/pkgs/stream_transform/test/combine_latest_all_test.dart b/pkgs/stream_transform/test/combine_latest_all_test.dart
new file mode 100644
index 0000000..f4b719c
--- /dev/null
+++ b/pkgs/stream_transform/test/combine_latest_all_test.dart

@@ -0,0 +1,166 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:stream_transform/stream_transform.dart';
+import 'package:test/test.dart';
+
+Future<void> tick() => Future(() {});
+
+void main() {
+  group('combineLatestAll', () {
+    test('emits latest values', () async {
+      final first = StreamController<String>();
+      final second = StreamController<String>();
+      final third = StreamController<String>();
+      final combined = first.stream.combineLatestAll(
+          [second.stream, third.stream]).map((data) => data.join());
+
+      // first:    a----b------------------c--------d---|
+      // second:   --1---------2-----------------|
+      // third:    -------&----------%---|
+      // combined: -------b1&--b2&---b2%---c2%------d2%-|
+
+      expect(combined,
+          emitsInOrder(['b1&', 'b2&', 'b2%', 'c2%', 'd2%', emitsDone]));
+
+      first.add('a');
+      await tick();
+      second.add('1');
+      await tick();
+      first.add('b');
+      await tick();
+      third.add('&');
+      await tick();
+      second.add('2');
+      await tick();
+      third.add('%');
+      await tick();
+      await third.close();
+      await tick();
+      first.add('c');
+      await tick();
+      await second.close();
+      await tick();
+      first.add('d');
+      await tick();
+      await first.close();
+    });
+
+    test('ends if a Stream closes without ever emitting a value', () async {
+      final first = StreamController<String>();
+      final second = StreamController<String>();
+      final combined = first.stream.combineLatestAll([second.stream]);
+
+      // first:    -a------b-------|
+      // second:   -----|
+      // combined: -----|
+
+      expect(combined, emits(emitsDone));
+
+      first.add('a');
+      await tick();
+      await second.close();
+      await tick();
+      first.add('b');
+    });
+
+    test('forwards errors', () async {
+      final first = StreamController<String>();
+      final second = StreamController<String>();
+      final combined = first.stream
+          .combineLatestAll([second.stream]).map((data) => data.join());
+
+      // first:    -a---------|
+      // second:   ----1---#
+      // combined: ----a1--#
+
+      expect(combined, emitsThrough(emitsError('doh')));
+
+      first.add('a');
+      await tick();
+      second.add('1');
+      await tick();
+      second.addError('doh');
+    });
+
+    test('ends after both streams have ended', () async {
+      final first = StreamController<String>();
+      final second = StreamController<String>();
+
+      var done = false;
+      first.stream.combineLatestAll([second.stream]).listen(null,
+          onDone: () => done = true);
+
+      // first:    -a---|
+      // second:   --------1--|
+      // combined: --------a1-|
+
+      first.add('a');
+      await tick();
+      await first.close();
+      await tick();
+
+      expect(done, isFalse);
+
+      second.add('1');
+      await tick();
+      await second.close();
+      await tick();
+
+      expect(done, isTrue);
+    });
+
+    group('broadcast source', () {
+      test('can cancel and relisten to broadcast stream', () async {
+        final first = StreamController<String>.broadcast();
+        final second = StreamController<String>.broadcast();
+        final combined = first.stream
+            .combineLatestAll([second.stream]).map((data) => data.join());
+
+        // first:    a------b----------------c------d----e---|
+        // second:   --1---------2---3---4------5-|
+        // combined: --a1---b1---b2--b3--b4-----c5--d5---e5--|
+        // sub1:     ^-----------------!
+        // sub2:     ----------------------^-----------------|
+
+        expect(combined.take(4), emitsInOrder(['a1', 'b1', 'b2', 'b3']));
+
+        first.add('a');
+        await tick();
+        second.add('1');
+        await tick();
+        first.add('b');
+        await tick();
+        second.add('2');
+        await tick();
+        second.add('3');
+        await tick();
+
+        // First subscription is canceled here by .take(4)
+        expect(first.hasListener, isFalse);
+        expect(second.hasListener, isFalse);
+
+        // This emit is thrown away because there are no subscribers
+        second.add('4');
+        await tick();
+
+        expect(combined, emitsInOrder(['c5', 'd5', 'e5', emitsDone]));
+
+        first.add('c');
+        await tick();
+        second.add('5');
+        await tick();
+        await second.close();
+        await tick();
+        first.add('d');
+        await tick();
+        first.add('e');
+        await tick();
+        await first.close();
+      });
+    });
+  });
+}

diff --git a/pkgs/stream_transform/test/combine_latest_test.dart b/pkgs/stream_transform/test/combine_latest_test.dart
new file mode 100644
index 0000000..1985c75
--- /dev/null
+++ b/pkgs/stream_transform/test/combine_latest_test.dart

@@ -0,0 +1,179 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:stream_transform/stream_transform.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('combineLatest', () {
+    test('flows through combine callback', () async {
+      var source = StreamController<int>();
+      var other = StreamController<int>();
+      int sum(int a, int b) => a + b;
+
+      var results = <int>[];
+      unawaited(
+          source.stream.combineLatest(other.stream, sum).forEach(results.add));
+
+      source.add(1);
+      await Future(() {});
+      expect(results, isEmpty);
+
+      other.add(2);
+      await Future(() {});
+      expect(results, [3]);
+
+      source.add(3);
+      await Future(() {});
+      expect(results, [3, 5]);
+
+      source.add(4);
+      await Future(() {});
+      expect(results, [3, 5, 6]);
+
+      other.add(5);
+      await Future(() {});
+      expect(results, [3, 5, 6, 9]);
+    });
+
+    test('can combine different typed streams', () async {
+      var source = StreamController<String>();
+      var other = StreamController<int>();
+      String times(String a, int b) => a * b;
+
+      var results = <String>[];
+      unawaited(source.stream
+          .combineLatest(other.stream, times)
+          .forEach(results.add));
+
+      source
+        ..add('a')
+        ..add('b');
+      await Future(() {});
+      expect(results, isEmpty);
+
+      other.add(2);
+      await Future(() {});
+      expect(results, ['bb']);
+
+      other.add(3);
+      await Future(() {});
+      expect(results, ['bb', 'bbb']);
+
+      source.add('c');
+      await Future(() {});
+      expect(results, ['bb', 'bbb', 'ccc']);
+    });
+
+    test('ends after both streams have ended', () async {
+      var source = StreamController<int>();
+      var other = StreamController<int>();
+      int sum(int a, int b) => a + b;
+
+      var done = false;
+      source.stream
+          .combineLatest(other.stream, sum)
+          .listen(null, onDone: () => done = true);
+
+      source.add(1);
+
+      await source.close();
+      await Future(() {});
+      expect(done, false);
+
+      await other.close();
+      await Future(() {});
+      expect(done, true);
+    });
+
+    test('ends if source stream closes without ever emitting a value',
+        () async {
+      var source = const Stream<int>.empty();
+      var other = StreamController<int>();
+
+      int sum(int a, int b) => a + b;
+
+      var done = false;
+      source
+          .combineLatest(other.stream, sum)
+          .listen(null, onDone: () => done = true);
+
+      await Future(() {});
+      // Nothing can ever be emitted on the result, may as well close.
+      expect(done, true);
+    });
+
+    test('ends if other stream closes without ever emitting a value', () async {
+      var source = StreamController<int>();
+      var other = const Stream<int>.empty();
+
+      int sum(int a, int b) => a + b;
+
+      var done = false;
+      source.stream
+          .combineLatest(other, sum)
+          .listen(null, onDone: () => done = true);
+
+      await Future(() {});
+      // Nothing can ever be emitted on the result, may as well close.
+      expect(done, true);
+    });
+
+    test('forwards errors', () async {
+      var source = StreamController<int>();
+      var other = StreamController<int>();
+      int sum(int a, int b) => throw _NumberedException(3);
+
+      var errors = <Object>[];
+      source.stream
+          .combineLatest(other.stream, sum)
+          .listen(null, onError: errors.add);
+
+      source.addError(_NumberedException(1));
+      other.addError(_NumberedException(2));
+
+      source.add(1);
+      other.add(2);
+
+      await Future(() {});
+
+      expect(errors, [_isException(1), _isException(2), _isException(3)]);
+    });
+
+    group('broadcast source', () {
+      test('can cancel and relisten to broadcast stream', () async {
+        var source = StreamController<int>.broadcast();
+        var other = StreamController<int>();
+        int combine(int a, int b) => a + b;
+
+        var emittedValues = <int>[];
+        var transformed = source.stream.combineLatest(other.stream, combine);
+
+        var subscription = transformed.listen(emittedValues.add);
+
+        source.add(1);
+        other.add(2);
+        await Future(() {});
+        expect(emittedValues, [3]);
+
+        await subscription.cancel();
+
+        subscription = transformed.listen(emittedValues.add);
+        source.add(3);
+        await Future(() {});
+        expect(emittedValues, [3, 5]);
+      });
+    });
+  });
+}
+
+class _NumberedException implements Exception {
+  final int id;
+  _NumberedException(this.id);
+}
+
+Matcher _isException(int id) =>
+    const TypeMatcher<_NumberedException>().having((n) => n.id, 'id', id);

diff --git a/pkgs/stream_transform/test/concurrent_async_map_test.dart b/pkgs/stream_transform/test/concurrent_async_map_test.dart
new file mode 100644
index 0000000..1807f9f
--- /dev/null
+++ b/pkgs/stream_transform/test/concurrent_async_map_test.dart

@@ -0,0 +1,157 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:stream_transform/stream_transform.dart';
+import 'package:test/test.dart';
+
+import 'utils.dart';
+
+void main() {
+  late StreamController<int> controller;
+  late List<String> emittedValues;
+  late bool valuesCanceled;
+  late bool isDone;
+  late List<String> errors;
+  late Stream<String> transformed;
+  late StreamSubscription<String> subscription;
+
+  late List<Completer<String>> finishWork;
+  late List<dynamic> values;
+
+  Future<String> convert(int value) {
+    values.add(value);
+    var completer = Completer<String>();
+    finishWork.add(completer);
+    return completer.future;
+  }
+
+  for (var streamType in streamTypes) {
+    group('concurrentAsyncMap for stream type: [$streamType]', () {
+      setUp(() {
+        valuesCanceled = false;
+        controller = createController(streamType)
+          ..onCancel = () {
+            valuesCanceled = true;
+          };
+        emittedValues = [];
+        errors = [];
+        isDone = false;
+        finishWork = [];
+        values = [];
+        transformed = controller.stream.concurrentAsyncMap(convert);
+        subscription = transformed
+            .listen(emittedValues.add, onError: errors.add, onDone: () {
+          isDone = true;
+        });
+      });
+
+      test('does not emit before convert finishes', () async {
+        controller.add(1);
+        await Future(() {});
+        expect(emittedValues, isEmpty);
+        expect(values, [1]);
+        finishWork.first.complete('result');
+        await Future(() {});
+        expect(emittedValues, ['result']);
+      });
+
+      test('allows calls to convert before the last one finished', () async {
+        controller
+          ..add(1)
+          ..add(2)
+          ..add(3);
+        await Future(() {});
+        expect(values, [1, 2, 3]);
+      });
+
+      test('forwards errors directly without waiting for previous convert',
+          () async {
+        controller.add(1);
+        await Future(() {});
+        controller.addError('error');
+        await Future(() {});
+        expect(errors, ['error']);
+      });
+
+      test('forwards errors which occur during the convert', () async {
+        controller.add(1);
+        await Future(() {});
+        finishWork.first.completeError('error');
+        await Future(() {});
+        expect(errors, ['error']);
+      });
+
+      test('can continue handling events after an error', () async {
+        controller.add(1);
+        await Future(() {});
+        finishWork[0].completeError('error');
+        controller.add(2);
+        await Future(() {});
+        expect(values, [1, 2]);
+        finishWork[1].completeError('another');
+        await Future(() {});
+        expect(errors, ['error', 'another']);
+      });
+
+      test('cancels value subscription when output canceled', () async {
+        expect(valuesCanceled, false);
+        await subscription.cancel();
+        expect(valuesCanceled, true);
+      });
+
+      test('closes when values end if no conversion is pending', () async {
+        expect(isDone, false);
+        await controller.close();
+        await Future(() {});
+        expect(isDone, true);
+      });
+
+      if (streamType == 'broadcast') {
+        test('multiple listeners all get values', () async {
+          var otherValues = <String>[];
+          transformed.listen(otherValues.add);
+          controller.add(1);
+          await Future(() {});
+          finishWork.first.complete('result');
+          await Future(() {});
+          expect(emittedValues, ['result']);
+          expect(otherValues, ['result']);
+        });
+
+        test('multiple listeners get done when values end', () async {
+          var otherDone = false;
+          transformed.listen(null, onDone: () => otherDone = true);
+          controller.add(1);
+          await Future(() {});
+          await controller.close();
+          expect(isDone, false);
+          expect(otherDone, false);
+          finishWork.first.complete('');
+          await Future(() {});
+          expect(isDone, true);
+          expect(otherDone, true);
+        });
+
+        test('can cancel and relisten', () async {
+          controller.add(1);
+          await Future(() {});
+          finishWork.first.complete('first');
+          await Future(() {});
+          await subscription.cancel();
+          controller.add(2);
+          await Future(() {});
+          subscription = transformed.listen(emittedValues.add);
+          controller.add(3);
+          await Future(() {});
+          expect(values, [1, 3]);
+          finishWork[1].complete('second');
+          await Future(() {});
+          expect(emittedValues, ['first', 'second']);
+        });
+      }
+    });
+  }
+}

diff --git a/pkgs/stream_transform/test/debounce_test.dart b/pkgs/stream_transform/test/debounce_test.dart
new file mode 100644
index 0000000..19de055
--- /dev/null
+++ b/pkgs/stream_transform/test/debounce_test.dart

@@ -0,0 +1,310 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:fake_async/fake_async.dart';
+import 'package:stream_transform/stream_transform.dart';
+import 'package:test/test.dart';
+
+import 'utils.dart';
+
+void main() {
+  for (var streamType in streamTypes) {
+    group('Stream type [$streamType]', () {
+      group('debounce - trailing', () {
+        late StreamController<int> values;
+        late List<int> emittedValues;
+        late bool valuesCanceled;
+        late bool isDone;
+        late List<String> errors;
+        late StreamSubscription<int> subscription;
+        late Stream<int> transformed;
+
+        setUp(() async {
+          valuesCanceled = false;
+          values = createController(streamType)
+            ..onCancel = () {
+              valuesCanceled = true;
+            };
+          emittedValues = [];
+          errors = [];
+          isDone = false;
+          transformed = values.stream.debounce(const Duration(milliseconds: 5));
+        });
+
+        void listen() {
+          subscription = transformed
+              .listen(emittedValues.add, onError: errors.add, onDone: () {
+            isDone = true;
+          });
+        }
+
+        test('cancels values', () async {
+          listen();
+          await subscription.cancel();
+          expect(valuesCanceled, true);
+        });
+
+        test('swallows values that come faster than duration', () {
+          fakeAsync((async) {
+            listen();
+            values
+              ..add(1)
+              ..add(2)
+              ..close();
+            async.elapse(const Duration(milliseconds: 6));
+            expect(emittedValues, [2]);
+          });
+        });
+
+        test('outputs multiple values spaced further than duration', () {
+          fakeAsync((async) {
+            listen();
+            values.add(1);
+            async.elapse(const Duration(milliseconds: 6));
+            values.add(2);
+            async.elapse(const Duration(milliseconds: 6));
+            expect(emittedValues, [1, 2]);
+          });
+        });
+
+        test('waits for pending value to close', () {
+          fakeAsync((async) {
+            listen();
+            values.add(1);
+            async.elapse(const Duration(milliseconds: 6));
+            values.close();
+            async.flushMicrotasks();
+            expect(isDone, true);
+          });
+        });
+
+        test('closes output if there are no pending values', () {
+          fakeAsync((async) {
+            listen();
+            values.add(1);
+            async.elapse(const Duration(milliseconds: 6));
+            values
+              ..add(2)
+              ..close();
+            async.flushMicrotasks();
+            expect(isDone, false);
+            async.elapse(const Duration(milliseconds: 6));
+            expect(isDone, true);
+          });
+        });
+
+        if (streamType == 'broadcast') {
+          test('multiple listeners all get values', () {
+            fakeAsync((async) {
+              listen();
+              var otherValues = <int>[];
+              transformed.listen(otherValues.add);
+              values
+                ..add(1)
+                ..add(2);
+              async.elapse(const Duration(milliseconds: 6));
+              expect(emittedValues, [2]);
+              expect(otherValues, [2]);
+            });
+          });
+        }
+      });
+
+      group('debounce - leading', () {
+        late StreamController<int> values;
+        late List<int> emittedValues;
+        late Stream<int> transformed;
+        late bool isDone;
+
+        setUp(() async {
+          values = createController(streamType);
+          emittedValues = [];
+          isDone = false;
+          transformed = values.stream.debounce(const Duration(milliseconds: 5),
+              leading: true, trailing: false);
+        });
+
+        void listen() {
+          transformed.listen(emittedValues.add, onDone: () {
+            isDone = true;
+          });
+        }
+
+        test('swallows values that come faster than duration', () async {
+          listen();
+          values
+            ..add(1)
+            ..add(2);
+          await values.close();
+          expect(emittedValues, [1]);
+        });
+
+        test('outputs multiple values spaced further than duration', () {
+          fakeAsync((async) {
+            listen();
+            values.add(1);
+            async.elapse(const Duration(milliseconds: 6));
+            values.add(2);
+            async.elapse(const Duration(milliseconds: 6));
+            expect(emittedValues, [1, 2]);
+          });
+        });
+
+        if (streamType == 'broadcast') {
+          test('multiple listeners all get values', () {
+            fakeAsync((async) {
+              listen();
+              var otherValues = <int>[];
+              transformed.listen(otherValues.add);
+              values
+                ..add(1)
+                ..add(2);
+              async.elapse(const Duration(milliseconds: 6));
+              expect(emittedValues, [1]);
+              expect(otherValues, [1]);
+            });
+          });
+        }
+
+        test('closes output immediately if not waiting for trailing value',
+            () async {
+          listen();
+          values.add(1);
+          await values.close();
+          expect(isDone, true);
+        });
+      });
+
+      group('debounce - leading and trailing', () {
+        late StreamController<int> values;
+        late List<int> emittedValues;
+        late Stream<int> transformed;
+
+        setUp(() async {
+          values = createController(streamType);
+          emittedValues = [];
+          transformed = values.stream.debounce(const Duration(milliseconds: 5),
+              leading: true, trailing: true);
+        });
+        void listen() {
+          transformed.listen(emittedValues.add);
+        }
+
+        test('swallows values that come faster than duration', () {
+          fakeAsync((async) {
+            listen();
+            values
+              ..add(1)
+              ..add(2)
+              ..add(3)
+              ..close();
+            async.elapse(const Duration(milliseconds: 6));
+            expect(emittedValues, [1, 3]);
+          });
+        });
+
+        test('outputs multiple values spaced further than duration', () {
+          fakeAsync((async) {
+            listen();
+            values.add(1);
+            async.elapse(const Duration(milliseconds: 6));
+            values.add(2);
+            async.elapse(const Duration(milliseconds: 6));
+            expect(emittedValues, [1, 2]);
+          });
+        });
+
+        if (streamType == 'broadcast') {
+          test('multiple listeners all get values', () {
+            fakeAsync((async) {
+              listen();
+              var otherValues = <int>[];
+              transformed.listen(otherValues.add);
+              values
+                ..add(1)
+                ..add(2);
+              async.elapse(const Duration(milliseconds: 6));
+              expect(emittedValues, [1, 2]);
+              expect(otherValues, [1, 2]);
+            });
+          });
+        }
+      });
+
+      group('debounceBuffer', () {
+        late StreamController<int> values;
+        late List<List<int>> emittedValues;
+        late List<String> errors;
+        late Stream<List<int>> transformed;
+
+        setUp(() async {
+          values = createController(streamType);
+          emittedValues = [];
+          errors = [];
+          transformed =
+              values.stream.debounceBuffer(const Duration(milliseconds: 5));
+        });
+        void listen() {
+          transformed.listen(emittedValues.add, onError: errors.add);
+        }
+
+        test('Emits all values as a list', () {
+          fakeAsync((async) {
+            listen();
+            values
+              ..add(1)
+              ..add(2)
+              ..close();
+            async.elapse(const Duration(milliseconds: 6));
+            expect(emittedValues, [
+              [1, 2]
+            ]);
+          });
+        });
+
+        test('separate lists for multiple values spaced further than duration',
+            () {
+          fakeAsync((async) {
+            listen();
+            values.add(1);
+            async.elapse(const Duration(milliseconds: 6));
+            values.add(2);
+            async.elapse(const Duration(milliseconds: 6));
+            expect(emittedValues, [
+              [1],
+              [2]
+            ]);
+          });
+        });
+
+        if (streamType == 'broadcast') {
+          test('multiple listeners all get values', () {
+            fakeAsync((async) {
+              listen();
+              var otherValues = <List<int>>[];
+              transformed.listen(otherValues.add);
+              values
+                ..add(1)
+                ..add(2);
+              async.elapse(const Duration(milliseconds: 6));
+              expect(emittedValues, [
+                [1, 2]
+              ]);
+              expect(otherValues, [
+                [1, 2]
+              ]);
+            });
+          });
+        }
+      });
+    });
+  }
+  test('allows nulls', () async {
+    final values = Stream<int?>.fromIterable([null]);
+    final transformed = values.debounce(const Duration(milliseconds: 1));
+    expect(await transformed.toList(), [null]);
+  });
+}

diff --git a/pkgs/stream_transform/test/followd_by_test.dart b/pkgs/stream_transform/test/followd_by_test.dart
new file mode 100644
index 0000000..d600d13
--- /dev/null
+++ b/pkgs/stream_transform/test/followd_by_test.dart

@@ -0,0 +1,159 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+import 'dart:async';
+
+import 'package:stream_transform/stream_transform.dart';
+import 'package:test/test.dart';
+
+import 'utils.dart';
+
+void main() {
+  for (var firstType in streamTypes) {
+    for (var secondType in streamTypes) {
+      group('followedBy [$firstType] with [$secondType]', () {
+        late StreamController<int> first;
+        late StreamController<int> second;
+
+        late List<int> emittedValues;
+        late bool firstCanceled;
+        late bool secondCanceled;
+        late bool secondListened;
+        late bool isDone;
+        late List<String> errors;
+        late Stream<int> transformed;
+        late StreamSubscription<int> subscription;
+
+        setUp(() async {
+          firstCanceled = false;
+          secondCanceled = false;
+          secondListened = false;
+          first = createController(firstType)
+            ..onCancel = () {
+              firstCanceled = true;
+            };
+          second = createController(secondType)
+            ..onCancel = () {
+              secondCanceled = true;
+            }
+            ..onListen = () {
+              secondListened = true;
+            };
+          emittedValues = [];
+          errors = [];
+          isDone = false;
+          transformed = first.stream.followedBy(second.stream);
+          subscription = transformed
+              .listen(emittedValues.add, onError: errors.add, onDone: () {
+            isDone = true;
+          });
+        });
+
+        test('adds all values from both streams', () async {
+          first
+            ..add(1)
+            ..add(2);
+          await first.close();
+          await Future(() {});
+          second
+            ..add(3)
+            ..add(4);
+          await Future(() {});
+          expect(emittedValues, [1, 2, 3, 4]);
+        });
+
+        test('Does not listen to second stream before first stream finishes',
+            () async {
+          expect(secondListened, false);
+          await first.close();
+          expect(secondListened, true);
+        });
+
+        test('closes stream after both inputs close', () async {
+          await first.close();
+          await second.close();
+          expect(isDone, true);
+        });
+
+        test('cancels any type of first stream on cancel', () async {
+          await subscription.cancel();
+          expect(firstCanceled, true);
+        });
+
+        if (firstType == 'single subscription') {
+          test(
+              'cancels any type of second stream on cancel if first is '
+              'broadcast', () async {
+            await first.close();
+            await subscription.cancel();
+            expect(secondCanceled, true);
+          });
+
+          if (secondType == 'broadcast') {
+            test('can pause and resume during second stream - dropping values',
+                () async {
+              await first.close();
+              subscription.pause();
+              second.add(1);
+              await Future(() {});
+              subscription.resume();
+              second.add(2);
+              await Future(() {});
+              expect(emittedValues, [2]);
+            });
+          } else {
+            test('can pause and resume during second stream - buffering values',
+                () async {
+              await first.close();
+              subscription.pause();
+              second.add(1);
+              await Future(() {});
+              subscription.resume();
+              second.add(2);
+              await Future(() {});
+              expect(emittedValues, [1, 2]);
+            });
+          }
+        }
+
+        if (firstType == 'broadcast') {
+          test('can cancel and relisten during first stream', () async {
+            await subscription.cancel();
+            first.add(1);
+            subscription = transformed.listen(emittedValues.add);
+            first.add(2);
+            await Future(() {});
+            expect(emittedValues, [2]);
+          });
+
+          test('can cancel and relisten during second stream', () async {
+            await first.close();
+            await subscription.cancel();
+            second.add(2);
+            await Future(() {});
+            subscription = transformed.listen(emittedValues.add);
+            second.add(3);
+            await Future(() {});
+            expect(emittedValues, [3]);
+          });
+
+          test('forwards values to multiple listeners', () async {
+            var otherValues = <int>[];
+            transformed.listen(otherValues.add);
+            first.add(1);
+            await first.close();
+            second.add(2);
+            await Future(() {});
+            var thirdValues = <int>[];
+            transformed.listen(thirdValues.add);
+            second.add(3);
+            await Future(() {});
+            expect(emittedValues, [1, 2, 3]);
+            expect(otherValues, [1, 2, 3]);
+            expect(thirdValues, [3]);
+          });
+        }
+      });
+    }
+  }
+}

diff --git a/pkgs/stream_transform/test/from_handlers_test.dart b/pkgs/stream_transform/test/from_handlers_test.dart
new file mode 100644
index 0000000..694199c
--- /dev/null
+++ b/pkgs/stream_transform/test/from_handlers_test.dart

@@ -0,0 +1,183 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:stream_transform/src/from_handlers.dart';
+import 'package:test/test.dart';
+
+void main() {
+  late StreamController<int> values;
+  late List<int> emittedValues;
+  late bool valuesCanceled;
+  late bool isDone;
+  late List<String> errors;
+  late Stream<int> transformed;
+  late StreamSubscription<int> subscription;
+
+  void setUpForController(StreamController<int> controller,
+      Stream<int> Function(Stream<int>) transform) {
+    valuesCanceled = false;
+    values = controller
+      ..onCancel = () {
+        valuesCanceled = true;
+      };
+    emittedValues = [];
+    errors = [];
+    isDone = false;
+    transformed = transform(values.stream);
+    subscription =
+        transformed.listen(emittedValues.add, onError: errors.add, onDone: () {
+      isDone = true;
+    });
+  }
+
+  group('default from_handlers', () {
+    group('Single subscription stream', () {
+      setUp(() {
+        setUpForController(StreamController(),
+            (s) => s.transformByHandlers(onData: (e, sink) => sink.add(e)));
+      });
+
+      test('has correct stream type', () {
+        expect(transformed.isBroadcast, false);
+      });
+
+      test('forwards values', () async {
+        values
+          ..add(1)
+          ..add(2);
+        await Future(() {});
+        expect(emittedValues, [1, 2]);
+      });
+
+      test('forwards errors', () async {
+        values.addError('error');
+        await Future(() {});
+        expect(errors, ['error']);
+      });
+
+      test('forwards done', () async {
+        await values.close();
+        expect(isDone, true);
+      });
+
+      test('forwards cancel', () async {
+        await subscription.cancel();
+        expect(valuesCanceled, true);
+      });
+    });
+
+    group('broadcast stream with muliple listeners', () {
+      late List<int> emittedValues2;
+      late List<String> errors2;
+      late bool isDone2;
+      late StreamSubscription<int> subscription2;
+
+      setUp(() {
+        setUpForController(StreamController.broadcast(),
+            (s) => s.transformByHandlers(onData: (e, sink) => sink.add(e)));
+        emittedValues2 = [];
+        errors2 = [];
+        isDone2 = false;
+        subscription2 = transformed
+            .listen(emittedValues2.add, onError: errors2.add, onDone: () {
+          isDone2 = true;
+        });
+      });
+
+      test('has correct stream type', () {
+        expect(transformed.isBroadcast, true);
+      });
+
+      test('forwards values', () async {
+        values
+          ..add(1)
+          ..add(2);
+        await Future(() {});
+        expect(emittedValues, [1, 2]);
+        expect(emittedValues2, [1, 2]);
+      });
+
+      test('forwards errors', () async {
+        values.addError('error');
+        await Future(() {});
+        expect(errors, ['error']);
+        expect(errors2, ['error']);
+      });
+
+      test('forwards done', () async {
+        await values.close();
+        expect(isDone, true);
+        expect(isDone2, true);
+      });
+
+      test('forwards cancel', () async {
+        await subscription.cancel();
+        expect(valuesCanceled, false);
+        await subscription2.cancel();
+        expect(valuesCanceled, true);
+      });
+    });
+  });
+
+  group('custom handlers', () {
+    group('single subscription', () {
+      setUp(() async {
+        setUpForController(
+            StreamController(),
+            (s) => s.transformByHandlers(onData: (value, sink) {
+                  sink.add(value + 1);
+                }));
+      });
+      test('uses transform from handleData', () async {
+        values
+          ..add(1)
+          ..add(2);
+        await Future(() {});
+        expect(emittedValues, [2, 3]);
+      });
+    });
+
+    group('broadcast stream with multiple listeners', () {
+      late int dataCallCount;
+      late int doneCallCount;
+      late int errorCallCount;
+
+      setUp(() async {
+        dataCallCount = 0;
+        doneCallCount = 0;
+        errorCallCount = 0;
+        setUpForController(
+            StreamController.broadcast(),
+            (s) => s.transformByHandlers(onData: (value, sink) {
+                  dataCallCount++;
+                }, onError: (error, stackTrace, sink) {
+                  errorCallCount++;
+                  sink.addError(error, stackTrace);
+                }, onDone: (sink) {
+                  doneCallCount++;
+                }));
+        transformed.listen((_) {}, onError: (_, __) {});
+      });
+
+      test('handles data once', () async {
+        values.add(1);
+        await Future(() {});
+        expect(dataCallCount, 1);
+      });
+
+      test('handles done once', () async {
+        await values.close();
+        expect(doneCallCount, 1);
+      });
+
+      test('handles errors once', () async {
+        values.addError('error');
+        await Future(() {});
+        expect(errorCallCount, 1);
+      });
+    });
+  });
+}

diff --git a/pkgs/stream_transform/test/merge_test.dart b/pkgs/stream_transform/test/merge_test.dart
new file mode 100644
index 0000000..ecbf97f
--- /dev/null
+++ b/pkgs/stream_transform/test/merge_test.dart

@@ -0,0 +1,140 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:stream_transform/stream_transform.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('merge', () {
+    test('includes all values', () async {
+      var first = Stream.fromIterable([1, 2, 3]);
+      var second = Stream.fromIterable([4, 5, 6]);
+      var allValues = await first.merge(second).toList();
+      expect(allValues, containsAllInOrder([1, 2, 3]));
+      expect(allValues, containsAllInOrder([4, 5, 6]));
+      expect(allValues, hasLength(6));
+    });
+
+    test('cancels both sources', () async {
+      var firstCanceled = false;
+      var first = StreamController<int>()
+        ..onCancel = () {
+          firstCanceled = true;
+        };
+      var secondCanceled = false;
+      var second = StreamController<int>()
+        ..onCancel = () {
+          secondCanceled = true;
+        };
+      var subscription = first.stream.merge(second.stream).listen((_) {});
+      await subscription.cancel();
+      expect(firstCanceled, true);
+      expect(secondCanceled, true);
+    });
+
+    test('completes when both sources complete', () async {
+      var first = StreamController<int>();
+      var second = StreamController<int>();
+      var isDone = false;
+      first.stream.merge(second.stream).listen((_) {}, onDone: () {
+        isDone = true;
+      });
+      await first.close();
+      expect(isDone, false);
+      await second.close();
+      expect(isDone, true);
+    });
+
+    test('can cancel and relisten to broadcast stream', () async {
+      var first = StreamController<int>.broadcast();
+      var second = StreamController<int>();
+      var emittedValues = <int>[];
+      var transformed = first.stream.merge(second.stream);
+      var subscription = transformed.listen(emittedValues.add);
+      first.add(1);
+      second.add(2);
+      await Future(() {});
+      expect(emittedValues, contains(1));
+      expect(emittedValues, contains(2));
+      await subscription.cancel();
+      emittedValues = [];
+      subscription = transformed.listen(emittedValues.add);
+      first.add(3);
+      second.add(4);
+      await Future(() {});
+      expect(emittedValues, contains(3));
+      expect(emittedValues, contains(4));
+    });
+  });
+
+  group('mergeAll', () {
+    test('includes all values', () async {
+      var first = Stream.fromIterable([1, 2, 3]);
+      var second = Stream.fromIterable([4, 5, 6]);
+      var third = Stream.fromIterable([7, 8, 9]);
+      var allValues = await first.mergeAll([second, third]).toList();
+      expect(allValues, containsAllInOrder([1, 2, 3]));
+      expect(allValues, containsAllInOrder([4, 5, 6]));
+      expect(allValues, containsAllInOrder([7, 8, 9]));
+      expect(allValues, hasLength(9));
+    });
+
+    test('handles mix of broadcast and single-subscription', () async {
+      var firstCanceled = false;
+      var first = StreamController<int>.broadcast()
+        ..onCancel = () {
+          firstCanceled = true;
+        };
+      var secondBroadcastCanceled = false;
+      var secondBroadcast = StreamController<int>.broadcast()
+        ..onCancel = () {
+          secondBroadcastCanceled = true;
+        };
+      var secondSingleCanceled = false;
+      var secondSingle = StreamController<int>()
+        ..onCancel = () {
+          secondSingleCanceled = true;
+        };
+
+      var merged =
+          first.stream.mergeAll([secondBroadcast.stream, secondSingle.stream]);
+
+      var firstListenerValues = <int>[];
+      var secondListenerValues = <int>[];
+
+      var firstSubscription = merged.listen(firstListenerValues.add);
+      var secondSubscription = merged.listen(secondListenerValues.add);
+
+      first.add(1);
+      secondBroadcast.add(2);
+      secondSingle.add(3);
+
+      await Future(() {});
+      await firstSubscription.cancel();
+
+      expect(firstCanceled, false);
+      expect(secondBroadcastCanceled, false);
+      expect(secondSingleCanceled, false);
+
+      first.add(4);
+      secondBroadcast.add(5);
+      secondSingle.add(6);
+
+      await Future(() {});
+      await secondSubscription.cancel();
+
+      await Future(() {});
+      expect(firstCanceled, true);
+      expect(secondBroadcastCanceled, true);
+      expect(secondSingleCanceled, false,
+          reason: 'Single subscription streams merged into broadcast streams '
+              'are not canceled');
+
+      expect(firstListenerValues, [1, 2, 3]);
+      expect(secondListenerValues, [1, 2, 3, 4, 5, 6]);
+    });
+  });
+}

diff --git a/pkgs/stream_transform/test/sample_test.dart b/pkgs/stream_transform/test/sample_test.dart
new file mode 100644
index 0000000..66ca09d
--- /dev/null
+++ b/pkgs/stream_transform/test/sample_test.dart

@@ -0,0 +1,291 @@
+// Copyright (c) 2022, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:stream_transform/stream_transform.dart';
+import 'package:test/test.dart';
+
+import 'utils.dart';
+
+void main() {
+  late StreamController<void> trigger;
+  late StreamController<int> values;
+  late List<int> emittedValues;
+  late bool valuesCanceled;
+  late bool triggerCanceled;
+  late bool triggerPaused;
+  late bool isDone;
+  late List<String> errors;
+  late Stream<int> transformed;
+  late StreamSubscription<int> subscription;
+
+  void setUpForStreamTypes(String triggerType, String valuesType,
+      {required bool longPoll}) {
+    valuesCanceled = false;
+    triggerCanceled = false;
+    triggerPaused = false;
+    trigger = createController(triggerType)
+      ..onCancel = () {
+        triggerCanceled = true;
+      };
+    if (triggerType == 'single subscription') {
+      trigger.onPause = () {
+        triggerPaused = true;
+      };
+    }
+    values = createController(valuesType)
+      ..onCancel = () {
+        valuesCanceled = true;
+      };
+    emittedValues = [];
+    errors = [];
+    isDone = false;
+    transformed = values.stream.sample(trigger.stream, longPoll: longPoll);
+    subscription =
+        transformed.listen(emittedValues.add, onError: errors.add, onDone: () {
+      isDone = true;
+    });
+  }
+
+  for (var triggerType in streamTypes) {
+    for (var valuesType in streamTypes) {
+      group('Trigger type: [$triggerType], Values type: [$valuesType]', () {
+        group('general behavior', () {
+          setUp(() {
+            setUpForStreamTypes(triggerType, valuesType, longPoll: true);
+          });
+
+          test('does not emit before `trigger`', () async {
+            values.add(1);
+            await Future(() {});
+            expect(emittedValues, isEmpty);
+            trigger.add(null);
+            await Future(() {});
+            expect(emittedValues, [1]);
+          });
+
+          test('keeps most recent event between triggers', () async {
+            values
+              ..add(1)
+              ..add(2);
+            await Future(() {});
+            trigger.add(null);
+            values
+              ..add(3)
+              ..add(4);
+            await Future(() {});
+            trigger.add(null);
+            await Future(() {});
+            expect(emittedValues, [2, 4]);
+          });
+
+          test('cancels value subscription when output canceled', () async {
+            expect(valuesCanceled, false);
+            await subscription.cancel();
+            expect(valuesCanceled, true);
+          });
+
+          test('closes when trigger ends', () async {
+            expect(isDone, false);
+            await trigger.close();
+            await Future(() {});
+            expect(isDone, true);
+          });
+
+          test('closes after outputting final values when source closes',
+              () async {
+            expect(isDone, false);
+            values.add(1);
+            await values.close();
+            expect(isDone, false);
+            trigger.add(null);
+            await Future(() {});
+            expect(emittedValues, [1]);
+            expect(isDone, true);
+          });
+
+          test('closes when source closes and there is no pending', () async {
+            expect(isDone, false);
+            await values.close();
+            await Future(() {});
+            expect(isDone, true);
+          });
+
+          test('forwards errors from trigger', () async {
+            trigger.addError('error');
+            await Future(() {});
+            expect(errors, ['error']);
+          });
+
+          test('forwards errors from values', () async {
+            values.addError('error');
+            await Future(() {});
+            expect(errors, ['error']);
+          });
+        });
+
+        group('long polling', () {
+          setUp(() {
+            setUpForStreamTypes(triggerType, valuesType, longPoll: true);
+          });
+
+          test('emits immediately if trigger emits before a value', () async {
+            trigger.add(null);
+            await Future(() {});
+            expect(emittedValues, isEmpty);
+            values.add(1);
+            await Future(() {});
+            expect(emittedValues, [1]);
+          });
+
+          test('two triggers in a row - emit buffere then emit next value',
+              () async {
+            values
+              ..add(1)
+              ..add(2);
+            await Future(() {});
+            trigger
+              ..add(null)
+              ..add(null);
+            await Future(() {});
+            values.add(3);
+            await Future(() {});
+            expect(emittedValues, [2, 3]);
+          });
+
+          test('pre-emptive trigger then trigger after values', () async {
+            trigger.add(null);
+            await Future(() {});
+            values
+              ..add(1)
+              ..add(2);
+            await Future(() {});
+            trigger.add(null);
+            await Future(() {});
+            expect(emittedValues, [1, 2]);
+          });
+
+          test('multiple pre-emptive triggers, only emits first value',
+              () async {
+            trigger
+              ..add(null)
+              ..add(null);
+            await Future(() {});
+            values
+              ..add(1)
+              ..add(2);
+            await Future(() {});
+            expect(emittedValues, [1]);
+          });
+
+          test('closes if there is no waiting long poll when source closes',
+              () async {
+            expect(isDone, false);
+            values.add(1);
+            trigger.add(null);
+            await values.close();
+            await Future(() {});
+            expect(isDone, true);
+          });
+
+          test('waits to emit if there waiting long poll when trigger closes',
+              () async {
+            trigger.add(null);
+            await trigger.close();
+            expect(isDone, false);
+            values.add(1);
+            await Future(() {});
+            expect(emittedValues, [1]);
+            expect(isDone, true);
+          });
+        });
+
+        group('immediate polling', () {
+          setUp(() {
+            setUpForStreamTypes(triggerType, valuesType, longPoll: false);
+          });
+
+          test('ignores trigger before values', () async {
+            trigger.add(null);
+            await Future(() {});
+            values
+              ..add(1)
+              ..add(2);
+            await Future(() {});
+            trigger.add(null);
+            await Future(() {});
+            expect(emittedValues, [2]);
+          });
+
+          test('ignores trigger if no pending values', () async {
+            values
+              ..add(1)
+              ..add(2);
+            await Future(() {});
+            trigger
+              ..add(null)
+              ..add(null);
+            await Future(() {});
+            values
+              ..add(3)
+              ..add(4);
+            await Future(() {});
+            trigger.add(null);
+            await Future(() {});
+            expect(emittedValues, [2, 4]);
+          });
+        });
+      });
+    }
+  }
+
+  test('always cancels trigger if values is singlesubscription', () async {
+    setUpForStreamTypes('broadcast', 'single subscription', longPoll: true);
+    expect(triggerCanceled, false);
+    await subscription.cancel();
+    expect(triggerCanceled, true);
+
+    setUpForStreamTypes('single subscription', 'single subscription',
+        longPoll: true);
+    expect(triggerCanceled, false);
+    await subscription.cancel();
+    expect(triggerCanceled, true);
+  });
+
+  test('cancels trigger if trigger is broadcast', () async {
+    setUpForStreamTypes('broadcast', 'broadcast', longPoll: true);
+    expect(triggerCanceled, false);
+    await subscription.cancel();
+    expect(triggerCanceled, true);
+  });
+
+  test('pauses single subscription trigger for broadcast values', () async {
+    setUpForStreamTypes('single subscription', 'broadcast', longPoll: true);
+    expect(triggerCanceled, false);
+    expect(triggerPaused, false);
+    await subscription.cancel();
+    expect(triggerCanceled, false);
+    expect(triggerPaused, true);
+  });
+
+  for (var triggerType in streamTypes) {
+    test('cancel and relisten with [$triggerType] trigger', () async {
+      setUpForStreamTypes(triggerType, 'broadcast', longPoll: true);
+      values.add(1);
+      trigger.add(null);
+      await Future(() {});
+      expect(emittedValues, [1]);
+      await subscription.cancel();
+      values.add(2);
+      trigger.add(null);
+      await Future(() {});
+      subscription = transformed.listen(emittedValues.add);
+      values.add(3);
+      trigger.add(null);
+      await Future(() {});
+      expect(emittedValues, [1, 3]);
+    });
+  }
+}

diff --git a/pkgs/stream_transform/test/scan_test.dart b/pkgs/stream_transform/test/scan_test.dart
new file mode 100644
index 0000000..3c749e7
--- /dev/null
+++ b/pkgs/stream_transform/test/scan_test.dart

@@ -0,0 +1,109 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:stream_transform/stream_transform.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('Scan', () {
+    test('produces intermediate values', () async {
+      var source = Stream.fromIterable([1, 2, 3, 4]);
+      int sum(int x, int y) => x + y;
+      var result = await source.scan(0, sum).toList();
+
+      expect(result, [1, 3, 6, 10]);
+    });
+
+    test('can create a broadcast stream', () {
+      var source = StreamController<int>.broadcast();
+
+      var transformed = source.stream.scan(null, (_, __) {});
+
+      expect(transformed.isBroadcast, true);
+    });
+
+    test('forwards errors from source', () async {
+      var source = StreamController<int>();
+
+      int sum(int x, int y) => x + y;
+
+      var errors = <Object>[];
+
+      source.stream.scan(0, sum).listen(null, onError: errors.add);
+
+      source.addError(StateError('fail'));
+      await Future(() {});
+
+      expect(errors, [isStateError]);
+    });
+
+    group('with async combine', () {
+      test('returns a Stream of non-futures', () async {
+        var source = Stream.fromIterable([1, 2, 3, 4]);
+        Future<int> sum(int x, int y) async => x + y;
+        var result = await source.scan(0, sum).toList();
+
+        expect(result, [1, 3, 6, 10]);
+      });
+
+      test('can return a Stream of futures when specified', () async {
+        var source = Stream.fromIterable([1, 2]);
+        Future<int> sum(Future<int> x, int y) async => (await x) + y;
+        var result =
+            await source.scan<Future<int>>(Future.value(0), sum).toList();
+
+        expect(result, [
+          const TypeMatcher<Future<void>>(),
+          const TypeMatcher<Future<void>>()
+        ]);
+        expect(await result.wait, [1, 3]);
+      });
+
+      test('does not call for subsequent values while waiting', () async {
+        var source = StreamController<int>();
+
+        var calledWith = <int>[];
+        var block = Completer<void>();
+        Future<int> combine(int x, int y) async {
+          calledWith.add(y);
+          await block.future;
+          return x + y;
+        }
+
+        var results = <int>[];
+
+        unawaited(source.stream.scan(0, combine).forEach(results.add));
+
+        source
+          ..add(1)
+          ..add(2);
+        await Future(() {});
+        expect(calledWith, [1]);
+        expect(results, isEmpty);
+
+        block.complete();
+        await Future(() {});
+        expect(calledWith, [1, 2]);
+        expect(results, [1, 3]);
+      });
+
+      test('forwards async errors', () async {
+        var source = StreamController<int>();
+
+        Future<int> combine(int x, int y) async => throw StateError('fail');
+
+        var errors = <Object>[];
+
+        source.stream.scan(0, combine).listen(null, onError: errors.add);
+
+        source.add(1);
+        await Future(() {});
+
+        expect(errors, [isStateError]);
+      });
+    });
+  });
+}

diff --git a/pkgs/stream_transform/test/start_with_test.dart b/pkgs/stream_transform/test/start_with_test.dart
new file mode 100644
index 0000000..35f0330
--- /dev/null
+++ b/pkgs/stream_transform/test/start_with_test.dart

@@ -0,0 +1,167 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:stream_transform/stream_transform.dart';
+import 'package:test/test.dart';
+
+import 'utils.dart';
+
+void main() {
+  late StreamController<int> values;
+  late Stream<int> transformed;
+  late StreamSubscription<int> subscription;
+
+  late List<int> emittedValues;
+  late bool isDone;
+
+  void setupForStreamType(
+      String streamType, Stream<int> Function(Stream<int>) transform) {
+    emittedValues = [];
+    isDone = false;
+    values = createController(streamType);
+    transformed = transform(values.stream);
+    subscription =
+        transformed.listen(emittedValues.add, onDone: () => isDone = true);
+  }
+
+  for (var streamType in streamTypes) {
+    group('startWith then [$streamType]', () {
+      setUp(() => setupForStreamType(streamType, (s) => s.startWith(1)));
+
+      test('outputs all values', () async {
+        values
+          ..add(2)
+          ..add(3);
+        await Future(() {});
+        expect(emittedValues, [1, 2, 3]);
+      });
+
+      test('outputs initial when followed by empty stream', () async {
+        await values.close();
+        expect(emittedValues, [1]);
+      });
+
+      test('closes with values', () async {
+        expect(isDone, false);
+        await values.close();
+        expect(isDone, true);
+      });
+
+      if (streamType == 'broadcast') {
+        test('can cancel and relisten', () async {
+          values.add(2);
+          await Future(() {});
+          await subscription.cancel();
+          subscription = transformed.listen(emittedValues.add);
+          values.add(3);
+          await Future(() {});
+          await Future(() {});
+          expect(emittedValues, [1, 2, 3]);
+        });
+      }
+    });
+
+    group('startWithMany then [$streamType]', () {
+      setUp(() async {
+        setupForStreamType(streamType, (s) => s.startWithMany([1, 2]));
+        // Ensure all initial values go through
+        await Future(() {});
+      });
+
+      test('outputs all values', () async {
+        values
+          ..add(3)
+          ..add(4);
+        await Future(() {});
+        expect(emittedValues, [1, 2, 3, 4]);
+      });
+
+      test('outputs initial when followed by empty stream', () async {
+        await values.close();
+        expect(emittedValues, [1, 2]);
+      });
+
+      test('closes with values', () async {
+        expect(isDone, false);
+        await values.close();
+        expect(isDone, true);
+      });
+
+      if (streamType == 'broadcast') {
+        test('can cancel and relisten', () async {
+          values.add(3);
+          await Future(() {});
+          await subscription.cancel();
+          subscription = transformed.listen(emittedValues.add);
+          values.add(4);
+          await Future(() {});
+          expect(emittedValues, [1, 2, 3, 4]);
+        });
+      }
+    });
+
+    for (var startingStreamType in streamTypes) {
+      group('startWithStream [$startingStreamType] then [$streamType]', () {
+        late StreamController<int> starting;
+        setUp(() async {
+          starting = createController(startingStreamType);
+          setupForStreamType(
+              streamType, (s) => s.startWithStream(starting.stream));
+        });
+
+        test('outputs all values', () async {
+          starting
+            ..add(1)
+            ..add(2);
+          await starting.close();
+          values
+            ..add(3)
+            ..add(4);
+          await Future(() {});
+          expect(emittedValues, [1, 2, 3, 4]);
+        });
+
+        test('closes with values', () async {
+          expect(isDone, false);
+          await starting.close();
+          expect(isDone, false);
+          await values.close();
+          expect(isDone, true);
+        });
+
+        if (streamType == 'broadcast') {
+          test('can cancel and relisten during starting', () async {
+            starting.add(1);
+            await Future(() {});
+            await subscription.cancel();
+            subscription = transformed.listen(emittedValues.add);
+            starting.add(2);
+            await starting.close();
+            values
+              ..add(3)
+              ..add(4);
+            await Future(() {});
+            expect(emittedValues, [1, 2, 3, 4]);
+          });
+
+          test('can cancel and relisten during values', () async {
+            starting
+              ..add(1)
+              ..add(2);
+            await starting.close();
+            values.add(3);
+            await Future(() {});
+            await subscription.cancel();
+            subscription = transformed.listen(emittedValues.add);
+            values.add(4);
+            await Future(() {});
+            expect(emittedValues, [1, 2, 3, 4]);
+          });
+        }
+      });
+    }
+  }
+}

diff --git a/pkgs/stream_transform/test/switch_test.dart b/pkgs/stream_transform/test/switch_test.dart
new file mode 100644
index 0000000..9e70c08
--- /dev/null
+++ b/pkgs/stream_transform/test/switch_test.dart

@@ -0,0 +1,229 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:stream_transform/stream_transform.dart';
+import 'package:test/test.dart';
+
+import 'utils.dart';
+
+void main() {
+  for (var outerType in streamTypes) {
+    for (var innerType in streamTypes) {
+      group('Outer type: [$outerType], Inner type: [$innerType]', () {
+        late StreamController<int> first;
+        late StreamController<int> second;
+        late StreamController<int> third;
+        late StreamController<Stream<int>> outer;
+
+        late List<int> emittedValues;
+        late bool firstCanceled;
+        late bool outerCanceled;
+        late bool isDone;
+        late List<String> errors;
+        late StreamSubscription<int> subscription;
+
+        setUp(() async {
+          firstCanceled = false;
+          outerCanceled = false;
+          outer = createController(outerType)
+            ..onCancel = () {
+              outerCanceled = true;
+            };
+          first = createController(innerType)
+            ..onCancel = () {
+              firstCanceled = true;
+            };
+          second = createController(innerType);
+          third = createController(innerType);
+          emittedValues = [];
+          errors = [];
+          isDone = false;
+          subscription = outer.stream
+              .switchLatest()
+              .listen(emittedValues.add, onError: errors.add, onDone: () {
+            isDone = true;
+          });
+        });
+
+        test('forwards events', () async {
+          outer.add(first.stream);
+          await Future(() {});
+          first
+            ..add(1)
+            ..add(2);
+          await Future(() {});
+
+          outer.add(second.stream);
+          await Future(() {});
+          second
+            ..add(3)
+            ..add(4);
+          await Future(() {});
+
+          expect(emittedValues, [1, 2, 3, 4]);
+        });
+
+        test('forwards errors from outer Stream', () async {
+          outer.addError('error');
+          await Future(() {});
+          expect(errors, ['error']);
+        });
+
+        test('forwards errors from inner Stream', () async {
+          outer.add(first.stream);
+          await Future(() {});
+          first.addError('error');
+          await Future(() {});
+          expect(errors, ['error']);
+        });
+
+        test('closes when final stream is done', () async {
+          outer.add(first.stream);
+          await Future(() {});
+
+          outer.add(second.stream);
+          await Future(() {});
+
+          await outer.close();
+          expect(isDone, false);
+
+          await second.close();
+          expect(isDone, true);
+        });
+
+        test(
+            'closes when outer stream closes if latest inner stream already '
+            'closed', () async {
+          outer.add(first.stream);
+          await Future(() {});
+          await first.close();
+          expect(isDone, false);
+
+          await outer.close();
+          expect(isDone, true);
+        });
+
+        test('cancels listeners on previous streams', () async {
+          outer.add(first.stream);
+          await Future(() {});
+
+          outer.add(second.stream);
+          await Future(() {});
+          expect(firstCanceled, true);
+        });
+
+        if (innerType != 'broadcast') {
+          test('waits for cancel before listening to subsequent stream',
+              () async {
+            var cancelWork = Completer<void>();
+            first.onCancel = () => cancelWork.future;
+            outer.add(first.stream);
+            await Future(() {});
+
+            var cancelDone = false;
+            second.onListen = expectAsync0(() {
+              expect(cancelDone, true);
+            });
+            outer.add(second.stream);
+            await Future(() {});
+            cancelWork.complete();
+            cancelDone = true;
+          });
+
+          test('all streams are listened to, even while cancelling', () async {
+            var cancelWork = Completer<void>();
+            first.onCancel = () => cancelWork.future;
+            outer.add(first.stream);
+            await Future(() {});
+
+            var cancelDone = false;
+            second.onListen = expectAsync0(() {
+              expect(cancelDone, true);
+            });
+            third.onListen = expectAsync0(() {
+              expect(cancelDone, true);
+            });
+            outer
+              ..add(second.stream)
+              ..add(third.stream);
+            await Future(() {});
+            cancelWork.complete();
+            cancelDone = true;
+          });
+        }
+
+        if (outerType != 'broadcast' && innerType != 'broadcast') {
+          test('pausing while cancelling an inner stream is respected',
+              () async {
+            var cancelWork = Completer<void>();
+            first.onCancel = () => cancelWork.future;
+            outer.add(first.stream);
+            await Future(() {});
+
+            var cancelDone = false;
+            second.onListen = expectAsync0(() {
+              expect(cancelDone, true);
+            });
+            outer.add(second.stream);
+            await Future(() {});
+            subscription.pause();
+            cancelWork.complete();
+            cancelDone = true;
+            await Future(() {});
+            expect(second.isPaused, true);
+            subscription.resume();
+          });
+        }
+
+        test('cancels listener on current and outer stream on cancel',
+            () async {
+          outer.add(first.stream);
+          await Future(() {});
+          await subscription.cancel();
+
+          await Future(() {});
+          expect(outerCanceled, true);
+          expect(firstCanceled, true);
+        });
+      });
+    }
+  }
+
+  group('switchMap', () {
+    test('uses map function', () async {
+      var outer = StreamController<List<int>>();
+
+      var values = <int>[];
+      outer.stream.switchMap(Stream.fromIterable).listen(values.add);
+
+      outer.add([1, 2, 3]);
+      await Future(() {});
+      outer.add([4, 5, 6]);
+      await Future(() {});
+      expect(values, [1, 2, 3, 4, 5, 6]);
+    });
+
+    test('can create a broadcast stream', () async {
+      var outer = StreamController<int>.broadcast();
+
+      var transformed =
+          outer.stream.switchMap((_) => const Stream<int>.empty());
+
+      expect(transformed.isBroadcast, true);
+    });
+
+    test('forwards errors from the convert callback', () async {
+      var errors = <String>[];
+      var source = Stream.fromIterable([1, 2, 3]);
+      source.switchMap<int>((i) {
+        // ignore: only_throw_errors
+        throw 'Error: $i';
+      }).listen((_) {}, onError: errors.add);
+      await Future<void>(() {});
+      expect(errors, ['Error: 1', 'Error: 2', 'Error: 3']);
+    });
+  });
+}

diff --git a/pkgs/stream_transform/test/take_until_test.dart b/pkgs/stream_transform/test/take_until_test.dart
new file mode 100644
index 0000000..982b3da
--- /dev/null
+++ b/pkgs/stream_transform/test/take_until_test.dart

@@ -0,0 +1,135 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:stream_transform/stream_transform.dart';
+import 'package:test/test.dart';
+
+import 'utils.dart';
+
+void main() {
+  for (var streamType in streamTypes) {
+    group('takeUntil on Stream type [$streamType]', () {
+      late StreamController<int> values;
+      late List<int> emittedValues;
+      late bool valuesCanceled;
+      late bool isDone;
+      late List<String> errors;
+      late Stream<int> transformed;
+      late StreamSubscription<int> subscription;
+      late Completer<void> closeTrigger;
+
+      setUp(() {
+        valuesCanceled = false;
+        values = createController(streamType)
+          ..onCancel = () {
+            valuesCanceled = true;
+          };
+        emittedValues = [];
+        errors = [];
+        isDone = false;
+        closeTrigger = Completer();
+        transformed = values.stream.takeUntil(closeTrigger.future);
+        subscription = transformed
+            .listen(emittedValues.add, onError: errors.add, onDone: () {
+          isDone = true;
+        });
+      });
+
+      test('forwards cancellation', () async {
+        await subscription.cancel();
+        expect(valuesCanceled, true);
+      });
+
+      test('lets values through before trigger', () async {
+        values
+          ..add(1)
+          ..add(2);
+        await Future(() {});
+        expect(emittedValues, [1, 2]);
+      });
+
+      test('forwards errors', () async {
+        values.addError('error');
+        await Future(() {});
+        expect(errors, ['error']);
+      });
+
+      test('sends done if original strem ends', () async {
+        await values.close();
+        expect(isDone, true);
+      });
+
+      test('sends done when trigger fires', () async {
+        closeTrigger.complete();
+        await Future(() {});
+        expect(isDone, true);
+      });
+
+      test('forwards errors from the close trigger', () async {
+        closeTrigger.completeError('sad');
+        await Future(() {});
+        expect(errors, ['sad']);
+        expect(isDone, true);
+      });
+
+      test('ignores errors from the close trigger after stream closed',
+          () async {
+        await values.close();
+        closeTrigger.completeError('sad');
+        await Future(() {});
+        expect(errors, <Object>[]);
+      });
+
+      test('cancels value subscription when trigger fires', () async {
+        closeTrigger.complete();
+        await Future(() {});
+        expect(valuesCanceled, true);
+      });
+
+      if (streamType == 'broadcast') {
+        test('multiple listeners all get values', () async {
+          var otherValues = <Object>[];
+          transformed.listen(otherValues.add);
+          values
+            ..add(1)
+            ..add(2);
+          await Future(() {});
+          expect(emittedValues, [1, 2]);
+          expect(otherValues, [1, 2]);
+        });
+
+        test('multiple listeners get done when trigger fires', () async {
+          var otherDone = false;
+          transformed.listen(null, onDone: () => otherDone = true);
+          closeTrigger.complete();
+          await Future(() {});
+          expect(otherDone, true);
+          expect(isDone, true);
+        });
+
+        test('multiple listeners get done when values end', () async {
+          var otherDone = false;
+          transformed.listen(null, onDone: () => otherDone = true);
+          await values.close();
+          expect(otherDone, true);
+          expect(isDone, true);
+        });
+
+        test('can cancel and relisten before trigger fires', () async {
+          values.add(1);
+          await Future(() {});
+          await subscription.cancel();
+          values.add(2);
+          await Future(() {});
+          subscription = transformed.listen(emittedValues.add);
+          values.add(3);
+          await Future(() {});
+          expect(emittedValues, [1, 3]);
+        });
+      }
+    });
+  }
+}

diff --git a/pkgs/stream_transform/test/tap_test.dart b/pkgs/stream_transform/test/tap_test.dart
new file mode 100644
index 0000000..f2b4346
--- /dev/null
+++ b/pkgs/stream_transform/test/tap_test.dart

@@ -0,0 +1,116 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:stream_transform/stream_transform.dart';
+import 'package:test/test.dart';
+
+void main() {
+  test('calls function for values', () async {
+    var valuesSeen = <int>[];
+    var stream = Stream.fromIterable([1, 2, 3]);
+    await stream.tap(valuesSeen.add).last;
+    expect(valuesSeen, [1, 2, 3]);
+  });
+
+  test('forwards values', () async {
+    var stream = Stream.fromIterable([1, 2, 3]);
+    var values = await stream.tap((_) {}).toList();
+    expect(values, [1, 2, 3]);
+  });
+
+  test('calls function for errors', () async {
+    dynamic error;
+    var source = StreamController<int>();
+    source.stream.tap((_) {}, onError: (e, st) {
+      error = e;
+    }).listen((_) {}, onError: (_) {});
+    source.addError('error');
+    await Future(() {});
+    expect(error, 'error');
+  });
+
+  test('forwards errors', () async {
+    dynamic error;
+    var source = StreamController<int>();
+    source.stream.tap((_) {}, onError: (e, st) {}).listen((_) {},
+        onError: (Object e) {
+      error = e;
+    });
+    source.addError('error');
+    await Future(() {});
+    expect(error, 'error');
+  });
+
+  test('calls function on done', () async {
+    var doneCalled = false;
+    var source = StreamController<int>();
+    source.stream.tap((_) {}, onDone: () {
+      doneCalled = true;
+    }).listen((_) {});
+    await source.close();
+    expect(doneCalled, true);
+  });
+
+  test('forwards only once with multiple listeners on a broadcast stream',
+      () async {
+    var dataCallCount = 0;
+    var source = StreamController<int>.broadcast();
+    source.stream.tap((_) {
+      dataCallCount++;
+    })
+      ..listen((_) {})
+      ..listen((_) {});
+    source.add(1);
+    await Future(() {});
+    expect(dataCallCount, 1);
+  });
+
+  test(
+      'forwards errors only once with multiple listeners on a broadcast stream',
+      () async {
+    var errorCallCount = 0;
+    var source = StreamController<int>.broadcast();
+    source.stream.tap((_) {}, onError: (_, __) {
+      errorCallCount++;
+    })
+      ..listen((_) {}, onError: (_, __) {})
+      ..listen((_) {}, onError: (_, __) {});
+    source.addError('error');
+    await Future(() {});
+    expect(errorCallCount, 1);
+  });
+
+  test('calls onDone only once with multiple listeners on a broadcast stream',
+      () async {
+    var doneCallCount = 0;
+    var source = StreamController<int>.broadcast();
+    source.stream.tap((_) {}, onDone: () {
+      doneCallCount++;
+    })
+      ..listen((_) {})
+      ..listen((_) {});
+    await source.close();
+    expect(doneCallCount, 1);
+  });
+
+  test('forwards values to multiple listeners', () async {
+    var source = StreamController<int>.broadcast();
+    var emittedValues1 = <int>[];
+    var emittedValues2 = <int>[];
+    source.stream.tap((_) {})
+      ..listen(emittedValues1.add)
+      ..listen(emittedValues2.add);
+    source.add(1);
+    await Future(() {});
+    expect(emittedValues1, [1]);
+    expect(emittedValues2, [1]);
+  });
+
+  test('allows null callback', () async {
+    var stream = Stream.fromIterable([1, 2, 3]);
+    await stream.tap(null).last;
+  });
+}

diff --git a/pkgs/stream_transform/test/throttle_test.dart b/pkgs/stream_transform/test/throttle_test.dart
new file mode 100644
index 0000000..07f607a
--- /dev/null
+++ b/pkgs/stream_transform/test/throttle_test.dart

@@ -0,0 +1,193 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:fake_async/fake_async.dart';
+import 'package:stream_transform/stream_transform.dart';
+import 'package:test/test.dart';
+
+import 'utils.dart';
+
+void main() {
+  for (var streamType in streamTypes) {
+    group('Stream type [$streamType]', () {
+      late StreamController<int> values;
+      late List<int> emittedValues;
+      late bool valuesCanceled;
+      late bool isDone;
+      late Stream<int> transformed;
+      late StreamSubscription<int> subscription;
+
+      group('throttle - trailing: false', () {
+        setUp(() async {
+          valuesCanceled = false;
+          values = createController(streamType)
+            ..onCancel = () {
+              valuesCanceled = true;
+            };
+          emittedValues = [];
+          isDone = false;
+          transformed = values.stream.throttle(const Duration(milliseconds: 5));
+        });
+
+        void listen() {
+          subscription = transformed.listen(emittedValues.add, onDone: () {
+            isDone = true;
+          });
+        }
+
+        test('cancels values', () async {
+          listen();
+          await subscription.cancel();
+          expect(valuesCanceled, true);
+        });
+
+        test('swallows values that come faster than duration', () {
+          fakeAsync((async) {
+            listen();
+            values
+              ..add(1)
+              ..add(2)
+              ..close();
+            async.elapse(const Duration(milliseconds: 6));
+            expect(emittedValues, [1]);
+          });
+        });
+
+        test('outputs multiple values spaced further than duration', () {
+          fakeAsync((async) {
+            listen();
+            values.add(1);
+            async.elapse(const Duration(milliseconds: 6));
+            values.add(2);
+            async.elapse(const Duration(milliseconds: 6));
+            expect(emittedValues, [1, 2]);
+            async.elapse(const Duration(milliseconds: 6));
+          });
+        });
+
+        test('closes output immediately', () {
+          fakeAsync((async) {
+            listen();
+            values.add(1);
+            async.elapse(const Duration(milliseconds: 6));
+            values
+              ..add(2)
+              ..close();
+            async.flushMicrotasks();
+            expect(isDone, true);
+          });
+        });
+
+        if (streamType == 'broadcast') {
+          test('multiple listeners all get values', () {
+            fakeAsync((async) {
+              listen();
+              var otherValues = <int>[];
+              transformed.listen(otherValues.add);
+              values.add(1);
+              async.flushMicrotasks();
+              expect(emittedValues, [1]);
+              expect(otherValues, [1]);
+            });
+          });
+        }
+      });
+
+      group('throttle - trailing: true', () {
+        setUp(() async {
+          valuesCanceled = false;
+          values = createController(streamType)
+            ..onCancel = () {
+              valuesCanceled = true;
+            };
+          emittedValues = [];
+          isDone = false;
+          transformed = values.stream
+              .throttle(const Duration(milliseconds: 5), trailing: true);
+        });
+        void listen() {
+          subscription = transformed.listen(emittedValues.add, onDone: () {
+            isDone = true;
+          });
+        }
+
+        test('emits both first and last in a period', () {
+          fakeAsync((async) {
+            listen();
+            values
+              ..add(1)
+              ..add(2)
+              ..close();
+            async.elapse(const Duration(milliseconds: 6));
+            expect(emittedValues, [1, 2]);
+          });
+        });
+
+        test('swallows values that are not the latest in a period', () {
+          fakeAsync((async) {
+            listen();
+            values
+              ..add(1)
+              ..add(2)
+              ..add(3)
+              ..close();
+            async.elapse(const Duration(milliseconds: 6));
+            expect(emittedValues, [1, 3]);
+          });
+        });
+
+        test('waits to output the last value even if the stream closes',
+            () async {
+          fakeAsync((async) {
+            listen();
+            values
+              ..add(1)
+              ..add(2)
+              ..close();
+            async.flushMicrotasks();
+            expect(isDone, false);
+            expect(emittedValues, [1],
+                reason: 'Should not be emitted until after duration');
+            async.elapse(const Duration(milliseconds: 6));
+            expect(emittedValues, [1, 2]);
+            expect(isDone, true);
+            async.elapse(const Duration(milliseconds: 6));
+          });
+        });
+
+        test('closes immediately if there is no pending value', () {
+          fakeAsync((async) {
+            listen();
+            values
+              ..add(1)
+              ..close();
+            async.flushMicrotasks();
+            expect(isDone, true);
+          });
+        });
+
+        if (streamType == 'broadcast') {
+          test('multiple listeners all get values', () {
+            fakeAsync((async) {
+              listen();
+              var otherValues = <int>[];
+              transformed.listen(otherValues.add);
+              values
+                ..add(1)
+                ..add(2);
+              async.flushMicrotasks();
+              expect(emittedValues, [1]);
+              expect(otherValues, [1]);
+              async.elapse(const Duration(milliseconds: 6));
+              expect(emittedValues, [1, 2]);
+              expect(otherValues, [1, 2]);
+            });
+          });
+        }
+      });
+    });
+  }
+}

diff --git a/pkgs/stream_transform/test/utils.dart b/pkgs/stream_transform/test/utils.dart
new file mode 100644
index 0000000..42d9613
--- /dev/null
+++ b/pkgs/stream_transform/test/utils.dart

@@ -0,0 +1,19 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+StreamController<T> createController<T>(String streamType) {
+  switch (streamType) {
+    case 'single subscription':
+      return StreamController<T>();
+    case 'broadcast':
+      return StreamController<T>.broadcast();
+    default:
+      throw ArgumentError.value(
+          streamType, 'streamType', 'Must be one of $streamTypes');
+  }
+}
+
+const streamTypes = ['single subscription', 'broadcast'];

diff --git a/pkgs/stream_transform/test/where_not_null_test.dart b/pkgs/stream_transform/test/where_not_null_test.dart
new file mode 100644
index 0000000..c9af794
--- /dev/null
+++ b/pkgs/stream_transform/test/where_not_null_test.dart

@@ -0,0 +1,56 @@
+// Copyright (c) 2022, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:stream_transform/stream_transform.dart';
+import 'package:test/test.dart';
+
+void main() {
+  test('forwards only events that match the type', () async {
+    var values = Stream.fromIterable([null, 'a', null, 'b']);
+    var filtered = values.whereNotNull();
+    expect(await filtered.toList(), ['a', 'b']);
+  });
+
+  test('can result in empty stream', () async {
+    var values = Stream<Object?>.fromIterable([null, null]);
+    var filtered = values.whereNotNull();
+    expect(await filtered.isEmpty, true);
+  });
+
+  test('forwards values to multiple listeners', () async {
+    var values = StreamController<Object?>.broadcast();
+    var filtered = values.stream.whereNotNull();
+    var firstValues = <Object>[];
+    var secondValues = <Object>[];
+    filtered
+      ..listen(firstValues.add)
+      ..listen(secondValues.add);
+    values
+      ..add(null)
+      ..add('a')
+      ..add(null)
+      ..add('b');
+    await Future(() {});
+    expect(firstValues, ['a', 'b']);
+    expect(secondValues, ['a', 'b']);
+  });
+
+  test('closes streams with multiple listeners', () async {
+    var values = StreamController<Object?>.broadcast();
+    var filtered = values.stream.whereNotNull();
+    var firstDone = false;
+    var secondDone = false;
+    filtered
+      ..listen(null, onDone: () => firstDone = true)
+      ..listen(null, onDone: () => secondDone = true);
+    values
+      ..add(null)
+      ..add('a');
+    await values.close();
+    expect(firstDone, true);
+    expect(secondDone, true);
+  });
+}

diff --git a/pkgs/stream_transform/test/where_type_test.dart b/pkgs/stream_transform/test/where_type_test.dart
new file mode 100644
index 0000000..4cbea37
--- /dev/null
+++ b/pkgs/stream_transform/test/where_type_test.dart

@@ -0,0 +1,56 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:stream_transform/stream_transform.dart';
+import 'package:test/test.dart';
+
+void main() {
+  test('forwards only events that match the type', () async {
+    var values = Stream.fromIterable([1, 'a', 2, 'b']);
+    var filtered = values.whereType<String>();
+    expect(await filtered.toList(), ['a', 'b']);
+  });
+
+  test('can result in empty stream', () async {
+    var values = Stream.fromIterable([1, 2, 3, 4]);
+    var filtered = values.whereType<String>();
+    expect(await filtered.isEmpty, true);
+  });
+
+  test('forwards values to multiple listeners', () async {
+    var values = StreamController<Object>.broadcast();
+    var filtered = values.stream.whereType<String>();
+    var firstValues = <Object>[];
+    var secondValues = <Object>[];
+    filtered
+      ..listen(firstValues.add)
+      ..listen(secondValues.add);
+    values
+      ..add(1)
+      ..add('a')
+      ..add(2)
+      ..add('b');
+    await Future(() {});
+    expect(firstValues, ['a', 'b']);
+    expect(secondValues, ['a', 'b']);
+  });
+
+  test('closes streams with multiple listeners', () async {
+    var values = StreamController<Object>.broadcast();
+    var filtered = values.stream.whereType<String>();
+    var firstDone = false;
+    var secondDone = false;
+    filtered
+      ..listen(null, onDone: () => firstDone = true)
+      ..listen(null, onDone: () => secondDone = true);
+    values
+      ..add(1)
+      ..add('a');
+    await values.close();
+    expect(firstDone, true);
+    expect(secondDone, true);
+  });
+}

diff --git a/pkgs/string_scanner/.github/dependabot.yml b/pkgs/string_scanner/.github/dependabot.yml
new file mode 100644
index 0000000..a19a66a
--- /dev/null
+++ b/pkgs/string_scanner/.github/dependabot.yml

@@ -0,0 +1,16 @@
+# Set update schedule for GitHub Actions
+# See https://docs.github.com/en/free-pro-team@latest/github/administering-a-repository/keeping-your-actions-up-to-date-with-dependabot
+
+version: 2
+updates:
+
+- package-ecosystem: github-actions
+  directory: /
+  schedule:
+    interval: monthly
+  labels:
+    - autosubmit
+  groups:
+    github-actions:
+      patterns:
+        - "*"

diff --git a/pkgs/string_scanner/.github/workflows/publish.yaml b/pkgs/string_scanner/.github/workflows/publish.yaml
new file mode 100644
index 0000000..27157a0
--- /dev/null
+++ b/pkgs/string_scanner/.github/workflows/publish.yaml

@@ -0,0 +1,17 @@
+# A CI configuration to auto-publish pub packages.
+
+name: Publish
+
+on:
+  pull_request:
+    branches: [ master ]
+  push:
+    tags: [ 'v[0-9]+.[0-9]+.[0-9]+' ]
+
+jobs:
+  publish:
+    if: ${{ github.repository_owner == 'dart-lang' }}
+    uses: dart-lang/ecosystem/.github/workflows/publish.yaml@main
+    permissions:
+      id-token: write # Required for authentication using OIDC
+      pull-requests: write # Required for writing the pull request note

diff --git a/pkgs/string_scanner/.github/workflows/test-package.yml b/pkgs/string_scanner/.github/workflows/test-package.yml
new file mode 100644
index 0000000..c60f710
--- /dev/null
+++ b/pkgs/string_scanner/.github/workflows/test-package.yml

@@ -0,0 +1,64 @@
+name: Dart CI
+
+on:
+  # Run on PRs and pushes to the default branch.
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+  schedule:
+    - cron: "0 0 * * 0"
+
+env:
+  PUB_ENVIRONMENT: bot.github
+
+jobs:
+  # Check code formatting and static analysis on a single OS (linux)
+  # against Dart dev.
+  analyze:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        sdk: [dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Check formatting
+        run: dart format --output=none --set-exit-if-changed .
+        if: always() && steps.install.outcome == 'success'
+      - name: Analyze code
+        run: dart analyze --fatal-infos
+        if: always() && steps.install.outcome == 'success'
+
+  # Run tests on a matrix consisting of two dimensions:
+  # 1. OS: ubuntu-latest, (macos-latest, windows-latest)
+  # 2. release channel: dev
+  test:
+    needs: analyze
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        # Add macos-latest and/or windows-latest if relevant for this package.
+        os: [ubuntu-latest]
+        sdk: [3.1, dev]
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: dart-lang/setup-dart@e630b99d28a3b71860378cafdc2a067c71107f94
+        with:
+          sdk: ${{ matrix.sdk }}
+      - id: install
+        name: Install dependencies
+        run: dart pub get
+      - name: Run VM tests
+        run: dart test --platform vm
+        if: always() && steps.install.outcome == 'success'
+      - name: Run Chrome tests
+        run: dart test --platform chrome
+        if: always() && steps.install.outcome == 'success'

diff --git a/pkgs/string_scanner/.gitignore b/pkgs/string_scanner/.gitignore
new file mode 100644
index 0000000..fb97bde
--- /dev/null
+++ b/pkgs/string_scanner/.gitignore

@@ -0,0 +1,5 @@
+# Don’t commit the following directories created by pub.
+.dart_tool/
+.pub/
+.packages
+pubspec.lock

diff --git a/pkgs/string_scanner/CHANGELOG.md b/pkgs/string_scanner/CHANGELOG.md
new file mode 100644
index 0000000..082e9f2
--- /dev/null
+++ b/pkgs/string_scanner/CHANGELOG.md

@@ -0,0 +1,175 @@
+## 1.4.1
+
+* Move to `dart-lang/tools` monorepo.
+
+## 1.4.0
+
+* Fix `LineScanner`'s handling of `\r\n`'s to preventing errors scanning
+  zero-length matches when between CR and LF. CR is treated as a new line only
+  if not immediately followed by a LF.
+* Fix `LineScanner`'s updating of `column` when setting `position` if the
+  current position is not `0`.
+
+## 1.3.0
+
+* Require Dart 3.1.0
+
+* Add a `SpanScanner.spanFromPosition()` method which takes raw code units
+  rather than `SpanScanner.spanFrom()`'s `LineScannerState`s.
+
+## 1.2.0
+
+* Require Dart 2.18.0
+
+* Add better support for reading code points in the Unicode supplementary plane:
+
+  * Added `StringScanner.readCodePoint()`, which consumes an entire Unicode code
+    point even if it's represented by two UTF-16 code units.
+
+  * Added `StringScanner.peekCodePoint()`, which returns an entire Unicode code
+    point even if it's represented by two UTF-16 code units.
+
+  * `StringScanner.scanChar()` and `StringScanner.expectChar()` will now
+    properly consume two UTF-16 code units if they're passed Unicode code points
+    in the supplementary plane.
+
+## 1.1.1
+
+* Populate the pubspec `repository` field.
+* Switch to `package:lints`.
+* Remove a dependency on `package:charcode`.
+
+## 1.1.0
+
+* Stable release for null safety.
+
+## 1.1.0-nullsafety.3
+
+* Update SDK constraints to `>=2.12.0-0 <3.0.0` based on beta release
+  guidelines.
+
+## 1.1.0-nullsafety.2
+
+* Allow prerelease versions of the 2.12 sdk.
+
+## 1.1.0-nullsafety.1
+
+- Allow 2.10 stable and 2.11.0 dev SDK versions.
+
+## 1.1.0-nullsafety
+
+- Migrate to null safety.
+
+## 1.0.5
+
+- Added an example.
+
+- Update Dart SDK constraint to `>=2.0.0 <3.0.0`.
+
+## 1.0.4
+
+* Add @alwaysThrows annotation to error method.
+
+## 1.0.3
+
+* Set max SDK version to `<3.0.0`, and adjust other dependencies.
+
+## 1.0.2
+
+* `SpanScanner` no longer crashes when creating a span that contains a UTF-16
+  surrogate pair.
+
+## 1.0.1
+
+* Fix the error text emitted by `StringScanner.expectChar()`.
+
+## 1.0.0
+
+* **Breaking change**: `StringScanner.error()`'s `length` argument now defaults
+  to `0` rather than `1` when no match data is available.
+
+* **Breaking change**: `StringScanner.lastMatch` and related methods are now
+  reset when the scanner's position changes without producing a new match.
+
+**Note**: While the changes in `1.0.0` are user-visible, they're unlikely to
+actually break any code in practice. Unless you know that your package is
+incompatible with 0.1.x, consider using 0.1.5 as your lower bound rather
+than 1.0.0. For example, `string_scanner: ">=0.1.5 <2.0.0"`.
+
+## 0.1.5
+
+* Add `new SpanScanner.within()`, which scans within a existing `FileSpan`.
+
+* Add `StringScanner.scanChar()` and `StringScanner.expectChar()`.
+
+## 0.1.4+1
+
+* Remove the dependency on `path`, since we don't actually import it.
+
+## 0.1.4
+
+* Add `new SpanScanner.eager()` for creating a `SpanScanner` that eagerly
+  computes its current line and column numbers.
+
+## 0.1.3+2
+
+* Fix `LineScanner`'s handling of carriage returns to match that of
+  `SpanScanner`.
+
+## 0.1.3+1
+
+* Fixed the homepage URL.
+
+## 0.1.3
+
+* Add an optional `endState` argument to `SpanScanner.spanFrom`.
+
+## 0.1.2
+
+* Add `StringScanner.substring`, which returns a substring of the source string.
+
+## 0.1.1
+
+* Declare `SpanScanner`'s exposed `SourceSpan`s and `SourceLocation`s to be
+  `FileSpan`s and `FileLocation`s. They always were underneath, but callers may
+  now rely on it.
+
+* Add `SpanScanner.location`, which returns the scanner's current
+  `SourceLocation`.
+
+## 0.1.0
+
+* Switch from `source_maps`' `Span` class to `source_span`'s `SourceSpan` class.
+
+* `new StringScanner()`'s `sourceUrl` parameter is now named to make it clear
+  that it can be safely `null`.
+
+* `new StringScannerException()` takes different arguments in a different order
+  to match `SpanFormatException`.
+
+* `StringScannerException.string` has been renamed to
+  `StringScannerException.source` to match the `FormatException` interface.
+
+## 0.0.3
+
+* Make `StringScannerException` inherit from source_map's `SpanFormatException`.
+
+## 0.0.2
+
+* `new StringScanner()` now takes an optional `sourceUrl` argument that provides
+  the URL of the source file. This is used for error reporting.
+
+* Add `StringScanner.readChar()` and `StringScanner.peekChar()` methods for
+  doing character-by-character scanning.
+
+* Scanners now throw `StringScannerException`s which provide more detailed
+  access to information about the errors that were thrown and can provide
+  terminal-colored messages.
+
+* Add a `LineScanner` subclass of `StringScanner` that automatically tracks line
+  and column information of the text being scanned.
+
+* Add a `SpanScanner` subclass of `LineScanner` that exposes matched ranges as
+  [source map][] `Span` objects.
+
+[source_map]: https://pub.dev/packages/source_maps

diff --git a/pkgs/string_scanner/LICENSE b/pkgs/string_scanner/LICENSE
new file mode 100644
index 0000000..000cd7b
--- /dev/null
+++ b/pkgs/string_scanner/LICENSE

@@ -0,0 +1,27 @@
+Copyright 2014, the Dart project authors. 
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+    * Neither the name of Google LLC nor the names of its
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

diff --git a/pkgs/string_scanner/README.md b/pkgs/string_scanner/README.md
new file mode 100644
index 0000000..e06e325
--- /dev/null
+++ b/pkgs/string_scanner/README.md

@@ -0,0 +1,41 @@
+[![Dart CI](https://github.com/dart-lang/string_scanner/actions/workflows/test-package.yml/badge.svg)](https://github.com/dart-lang/string_scanner/actions/workflows/test-package.yml)
+[![pub package](https://img.shields.io/pub/v/string_scanner.svg)](https://pub.dev/packages/string_scanner)
+[![package publisher](https://img.shields.io/pub/publisher/string_scanner.svg)](https://pub.dev/packages/string_scanner/publisher)
+
+This package exposes a `StringScanner` type that makes it easy to parse a string
+using a series of `Pattern`s. For example:
+
+```dart
+import 'dart:math' as math;
+
+import 'package:string_scanner/string_scanner.dart';
+
+num parseNumber(String source) {
+  // Scan a number ("1", "1.5", "-3").
+  final scanner = StringScanner(source);
+
+  // [Scanner.scan] tries to consume a [Pattern] and returns whether or not it
+  // succeeded. It will move the scan pointer past the end of the pattern.
+  final negative = scanner.scan('-');
+
+  // [Scanner.expect] consumes a [Pattern] and throws a [FormatError] if it
+  // fails. Like [Scanner.scan], it will move the scan pointer forward.
+  scanner.expect(RegExp(r'\d+'));
+
+  // [Scanner.lastMatch] holds the [MatchData] for the most recent call to
+  // [Scanner.scan], [Scanner.expect], or [Scanner.matches].
+  var number = num.parse(scanner.lastMatch![0]!);
+
+  if (scanner.scan('.')) {
+    scanner.expect(RegExp(r'\d+'));
+    final decimal = scanner.lastMatch![0]!;
+    number += int.parse(decimal) / math.pow(10, decimal.length);
+  }
+
+  // [Scanner.expectDone] will throw a [FormatError] if there's any input that
+  // hasn't yet been consumed.
+  scanner.expectDone();
+
+  return (negative ? -1 : 1) * number;
+}
+```

diff --git a/pkgs/string_scanner/analysis_options.yaml b/pkgs/string_scanner/analysis_options.yaml
new file mode 100644
index 0000000..59f763a
--- /dev/null
+++ b/pkgs/string_scanner/analysis_options.yaml

@@ -0,0 +1,32 @@
+# https://dart.dev/guides/language/analysis-options
+include: package:dart_flutter_team_lints/analysis_options.yaml
+
+analyzer:
+  language:
+    strict-casts: true
+    strict-inference: true
+    strict-raw-types: true
+
+linter:
+  rules:
+    - avoid_bool_literals_in_conditional_expressions
+    - avoid_classes_with_only_static_members
+    - avoid_private_typedef_functions
+    - avoid_redundant_argument_values
+    - avoid_returning_this
+    - avoid_unused_constructor_parameters
+    - avoid_void_async
+    - cancel_subscriptions
+    - join_return_with_assignment
+    - literal_only_boolean_expressions
+    - missing_whitespace_between_adjacent_strings
+    - no_adjacent_strings_in_list
+    - no_runtimeType_toString
+    - prefer_const_declarations
+    - prefer_expression_function_bodies
+    - prefer_final_locals
+    - unnecessary_await_in_return
+    - unnecessary_raw_strings
+    - use_if_null_to_convert_nulls_to_bools
+    - use_raw_strings
+    - use_string_buffers

diff --git a/pkgs/string_scanner/example/example.dart b/pkgs/string_scanner/example/example.dart
new file mode 100644
index 0000000..ec9dd76
--- /dev/null
+++ b/pkgs/string_scanner/example/example.dart

@@ -0,0 +1,40 @@
+// Copyright (c) 2019, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:math' as math;
+
+import 'package:string_scanner/string_scanner.dart';
+
+void main(List<String> args) {
+  print(parseNumber(args.single));
+}
+
+num parseNumber(String source) {
+  // Scan a number ("1", "1.5", "-3").
+  final scanner = StringScanner(source);
+
+  // [Scanner.scan] tries to consume a [Pattern] and returns whether or not it
+  // succeeded. It will move the scan pointer past the end of the pattern.
+  final negative = scanner.scan('-');
+
+  // [Scanner.expect] consumes a [Pattern] and throws a [FormatError] if it
+  // fails. Like [Scanner.scan], it will move the scan pointer forward.
+  scanner.expect(RegExp(r'\d+'));
+
+  // [Scanner.lastMatch] holds the [MatchData] for the most recent call to
+  // [Scanner.scan], [Scanner.expect], or [Scanner.matches].
+  var number = num.parse(scanner.lastMatch![0]!);
+
+  if (scanner.scan('.')) {
+    scanner.expect(RegExp(r'\d+'));
+    final decimal = scanner.lastMatch![0]!;
+    number += int.parse(decimal) / math.pow(10, decimal.length);
+  }
+
+  // [Scanner.expectDone] will throw a [FormatError] if there's any input that
+  // hasn't yet been consumed.
+  scanner.expectDone();
+
+  return (negative ? -1 : 1) * number;
+}

diff --git a/pkgs/string_scanner/lib/src/charcode.dart b/pkgs/string_scanner/lib/src/charcode.dart
new file mode 100644
index 0000000..d157749
--- /dev/null
+++ b/pkgs/string_scanner/lib/src/charcode.dart

@@ -0,0 +1,24 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Character '\'.
+const int $backslash = 0x5C;
+
+/// "Carriage return" control character.
+const int $cr = 0x0D;
+
+/// Character '"'.
+const int $doubleQuote = 0x22;
+
+/// Character 'f'.
+const int $f = 0x66;
+
+/// "Line feed" control character.
+const int $lf = 0x0A;
+
+/// Space character.
+const int $space = 0x20;
+
+/// Character 'x'.
+const int $x = 0x78;

diff --git a/pkgs/string_scanner/lib/src/eager_span_scanner.dart b/pkgs/string_scanner/lib/src/eager_span_scanner.dart
new file mode 100644
index 0000000..1ccc746
--- /dev/null
+++ b/pkgs/string_scanner/lib/src/eager_span_scanner.dart

@@ -0,0 +1,133 @@
+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'charcode.dart';
+import 'line_scanner.dart';
+import 'span_scanner.dart';
+import 'utils.dart';
+
+// TODO(nweiz): Currently this duplicates code in line_scanner.dart. Once
+// sdk#23770 is fully complete, we should move the shared code into a mixin.
+
+/// A regular expression matching newlines across platforms.
+final _newlineRegExp = RegExp(r'\r\n?|\n');
+
+/// A [SpanScanner] that tracks the line and column eagerly, like [LineScanner].
+class EagerSpanScanner extends SpanScanner {
+  @override
+  int get line => _line;
+  int _line = 0;
+
+  @override
+  int get column => _column;
+  int _column = 0;
+
+  @override
+  LineScannerState get state =>
+      _EagerSpanScannerState(this, position, line, column);
+
+  bool get _betweenCRLF => peekChar(-1) == $cr && peekChar() == $lf;
+
+  @override
+  set state(LineScannerState state) {
+    if (state is! _EagerSpanScannerState || !identical(state._scanner, this)) {
+      throw ArgumentError('The given LineScannerState was not returned by '
+          'this LineScanner.');
+    }
+
+    super.position = state.position;
+    _line = state.line;
+    _column = state.column;
+  }
+
+  @override
+  set position(int newPosition) {
+    final oldPosition = position;
+    super.position = newPosition;
+
+    if (newPosition > oldPosition) {
+      final newlines = _newlinesIn(string.substring(oldPosition, newPosition));
+      _line += newlines.length;
+      if (newlines.isEmpty) {
+        _column += newPosition - oldPosition;
+      } else {
+        _column = newPosition - newlines.last.end;
+      }
+    } else {
+      final newlines = _newlinesIn(string.substring(newPosition, oldPosition));
+      if (_betweenCRLF) newlines.removeLast();
+
+      _line -= newlines.length;
+      if (newlines.isEmpty) {
+        _column -= oldPosition - newPosition;
+      } else {
+        _column =
+            newPosition - string.lastIndexOf(_newlineRegExp, newPosition) - 1;
+      }
+    }
+  }
+
+  EagerSpanScanner(super.string, {super.sourceUrl, super.position});
+
+  @override
+  bool scanChar(int character) {
+    if (!super.scanChar(character)) return false;
+    _adjustLineAndColumn(character);
+    return true;
+  }
+
+  @override
+  int readChar() {
+    final character = super.readChar();
+    _adjustLineAndColumn(character);
+    return character;
+  }
+
+  /// Adjusts [_line] and [_column] after having consumed [character].
+  void _adjustLineAndColumn(int character) {
+    if (character == $lf || (character == $cr && peekChar() != $lf)) {
+      _line += 1;
+      _column = 0;
+    } else {
+      _column += inSupplementaryPlane(character) ? 2 : 1;
+    }
+  }
+
+  @override
+  bool scan(Pattern pattern) {
+    if (!super.scan(pattern)) return false;
+    final firstMatch = lastMatch![0]!;
+
+    final newlines = _newlinesIn(firstMatch);
+    _line += newlines.length;
+    if (newlines.isEmpty) {
+      _column += firstMatch.length;
+    } else {
+      _column = firstMatch.length - newlines.last.end;
+    }
+
+    return true;
+  }
+
+  /// Returns a list of [Match]es describing all the newlines in [text], which
+  /// is assumed to end at [position].
+  List<Match> _newlinesIn(String text) {
+    final newlines = _newlineRegExp.allMatches(text).toList();
+    if (_betweenCRLF) newlines.removeLast();
+    return newlines;
+  }
+}
+
+/// A class representing the state of an [EagerSpanScanner].
+class _EagerSpanScannerState implements LineScannerState {
+  final EagerSpanScanner _scanner;
+  @override
+  final int position;
+  @override
+  final int line;
+  @override
+  final int column;
+
+  _EagerSpanScannerState(this._scanner, this.position, this.line, this.column);
+}

diff --git a/pkgs/string_scanner/lib/src/exception.dart b/pkgs/string_scanner/lib/src/exception.dart
new file mode 100644
index 0000000..57af541
--- /dev/null
+++ b/pkgs/string_scanner/lib/src/exception.dart

@@ -0,0 +1,21 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:source_span/source_span.dart';
+
+import 'string_scanner.dart';
+
+/// An exception thrown by a [StringScanner] that failed to parse a string.
+class StringScannerException extends SourceSpanFormatException {
+  @override
+  String get source => super.source as String;
+
+  /// The URL of the source file being parsed.
+  ///
+  /// This may be `null`, indicating that the source URL is unknown.
+  Uri? get sourceUrl => span?.sourceUrl;
+
+  StringScannerException(
+      super.message, SourceSpan super.span, String super.source);
+}

diff --git a/pkgs/string_scanner/lib/src/line_scanner.dart b/pkgs/string_scanner/lib/src/line_scanner.dart
new file mode 100644
index 0000000..b18d610
--- /dev/null
+++ b/pkgs/string_scanner/lib/src/line_scanner.dart

@@ -0,0 +1,183 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'charcode.dart';
+import 'string_scanner.dart';
+import 'utils.dart';
+
+// Note that much of this code is duplicated in eager_span_scanner.dart.
+
+/// A regular expression matching newlines. A newline is either a `\n`, a `\r\n`
+/// or a `\r` that is not immediately followed by a `\n`.
+final _newlineRegExp = RegExp(r'\n|\r\n|\r(?!\n)');
+
+/// A subclass of [StringScanner] that tracks line and column information.
+class LineScanner extends StringScanner {
+  /// The scanner's current (zero-based) line number.
+  int get line => _line;
+  int _line = 0;
+
+  /// The scanner's current (zero-based) column number.
+  int get column => _column;
+  int _column = 0;
+
+  /// The scanner's state, including line and column information.
+  ///
+  /// This can be used to efficiently save and restore the state of the scanner
+  /// when backtracking. A given [LineScannerState] is only valid for the
+  /// [LineScanner] that created it.
+  ///
+  /// This does not include the scanner's match information.
+  LineScannerState get state =>
+      LineScannerState._(this, position, line, column);
+
+  /// Whether the current position is between a CR character and an LF
+  /// charactet.
+  bool get _betweenCRLF => peekChar(-1) == $cr && peekChar() == $lf;
+
+  set state(LineScannerState state) {
+    if (!identical(state._scanner, this)) {
+      throw ArgumentError('The given LineScannerState was not returned by '
+          'this LineScanner.');
+    }
+
+    super.position = state.position;
+    _line = state.line;
+    _column = state.column;
+  }
+
+  @override
+  set position(int newPosition) {
+    if (newPosition == position) {
+      return;
+    }
+
+    final oldPosition = position;
+    super.position = newPosition;
+
+    if (newPosition == 0) {
+      _line = 0;
+      _column = 0;
+    } else if (newPosition > oldPosition) {
+      final newlines = _newlinesIn(string.substring(oldPosition, newPosition),
+          endPosition: newPosition);
+      _line += newlines.length;
+      if (newlines.isEmpty) {
+        _column += newPosition - oldPosition;
+      } else {
+        // The regex got a substring, so we need to account for where it started
+        // in the string.
+        final offsetOfLastNewline = oldPosition + newlines.last.end;
+        _column = newPosition - offsetOfLastNewline;
+      }
+    } else if (newPosition < oldPosition) {
+      final newlines = _newlinesIn(string.substring(newPosition, oldPosition),
+          endPosition: oldPosition);
+
+      _line -= newlines.length;
+      if (newlines.isEmpty) {
+        _column -= oldPosition - newPosition;
+      } else {
+        // To compute the new column, we need to locate the last newline before
+        // the new position. When searching, we must exclude the CR if we're
+        // between a CRLF because it's not considered a newline.
+        final crOffset = _betweenCRLF ? -1 : 0;
+        // Additionally, if we use newPosition as the end of the search and the
+        // character at that position itself (the next character) is a newline
+        // we should not use it, so also offset to account for that.
+        const currentCharOffset = -1;
+        final lastNewline = string.lastIndexOf(
+            _newlineRegExp, newPosition + currentCharOffset + crOffset);
+
+        // Now we need to know the offset after the newline. This is the index
+        // above plus the length of the newline (eg. if we found `\r\n`) we need
+        // to add two. However if no newline was found, that index is 0.
+        final offsetAfterLastNewline = lastNewline == -1
+            ? 0
+            : string[lastNewline] == '\r' && string[lastNewline + 1] == '\n'
+                ? lastNewline + 2
+                : lastNewline + 1;
+
+        _column = newPosition - offsetAfterLastNewline;
+      }
+    }
+  }
+
+  LineScanner(super.string, {super.sourceUrl, super.position});
+
+  @override
+  bool scanChar(int character) {
+    if (!super.scanChar(character)) return false;
+    _adjustLineAndColumn(character);
+    return true;
+  }
+
+  @override
+  int readChar() {
+    final character = super.readChar();
+    _adjustLineAndColumn(character);
+    return character;
+  }
+
+  /// Adjusts [_line] and [_column] after having consumed [character].
+  void _adjustLineAndColumn(int character) {
+    if (character == $lf || (character == $cr && peekChar() != $lf)) {
+      _line += 1;
+      _column = 0;
+    } else {
+      _column += inSupplementaryPlane(character) ? 2 : 1;
+    }
+  }
+
+  @override
+  bool scan(Pattern pattern) {
+    if (!super.scan(pattern)) return false;
+
+    final newlines = _newlinesIn(lastMatch![0]!, endPosition: position);
+    _line += newlines.length;
+    if (newlines.isEmpty) {
+      _column += lastMatch![0]!.length;
+    } else {
+      _column = lastMatch![0]!.length - newlines.last.end;
+    }
+
+    return true;
+  }
+
+  /// Returns a list of [Match]es describing all the newlines in [text], which
+  /// ends at [endPosition].
+  ///
+  /// If [text] ends with `\r`, it will only be treated as a newline if the next
+  /// character at [position] is not a `\n`.
+  List<Match> _newlinesIn(String text, {required int endPosition}) {
+    final newlines = _newlineRegExp.allMatches(text).toList();
+    // If the last character is a `\r` it will have been treated as a newline,
+    // but this is only valid if the next character is not a `\n`.
+    if (endPosition < string.length &&
+        text.endsWith('\r') &&
+        string[endPosition] == '\n') {
+      // newlines should never be empty here, because if `text` ends with `\r`
+      // it would have matched `\r(?!\n)` in the newline regex.
+      newlines.removeLast();
+    }
+    return newlines;
+  }
+}
+
+/// A class representing the state of a [LineScanner].
+class LineScannerState {
+  /// The [LineScanner] that created this.
+  final LineScanner _scanner;
+
+  /// The position of the scanner in this state.
+  final int position;
+
+  /// The zero-based line number of the scanner in this state.
+  final int line;
+
+  /// The zero-based column number of the scanner in this state.
+  final int column;
+
+  LineScannerState._(this._scanner, this.position, this.line, this.column);
+}

diff --git a/pkgs/string_scanner/lib/src/relative_span_scanner.dart b/pkgs/string_scanner/lib/src/relative_span_scanner.dart
new file mode 100644
index 0000000..cd9af0e
--- /dev/null
+++ b/pkgs/string_scanner/lib/src/relative_span_scanner.dart

@@ -0,0 +1,132 @@
+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:source_span/source_span.dart';
+
+import 'exception.dart';
+import 'line_scanner.dart';
+import 'span_scanner.dart';
+import 'string_scanner.dart';
+import 'utils.dart';
+
+/// A [SpanScanner] that scans within an existing [FileSpan].
+///
+/// This re-implements chunks of [SpanScanner] rather than using a dummy span or
+/// inheritance because scanning is often a performance-critical operation, so
+/// it's important to avoid adding extra overhead when relative scanning isn't
+/// needed.
+class RelativeSpanScanner extends StringScanner implements SpanScanner {
+  /// The source of the scanner.
+  ///
+  /// This caches line break information and is used to generate [SourceSpan]s.
+  final SourceFile _sourceFile;
+
+  /// The start location of the span within which this scanner is scanning.
+  ///
+  /// This is used to convert between span-relative and file-relative fields.
+  final FileLocation _startLocation;
+
+  @override
+  int get line =>
+      _sourceFile.getLine(_startLocation.offset + position) -
+      _startLocation.line;
+
+  @override
+  int get column {
+    final line = _sourceFile.getLine(_startLocation.offset + position);
+    final column =
+        _sourceFile.getColumn(_startLocation.offset + position, line: line);
+    return line == _startLocation.line
+        ? column - _startLocation.column
+        : column;
+  }
+
+  @override
+  LineScannerState get state => _SpanScannerState(this, position);
+
+  @override
+  set state(LineScannerState state) {
+    if (state is! _SpanScannerState || !identical(state._scanner, this)) {
+      throw ArgumentError('The given LineScannerState was not returned by '
+          'this LineScanner.');
+    }
+
+    position = state.position;
+  }
+
+  @override
+  FileSpan? get lastSpan => _lastSpan;
+  FileSpan? _lastSpan;
+
+  @override
+  FileLocation get location =>
+      _sourceFile.location(_startLocation.offset + position);
+
+  @override
+  FileSpan get emptySpan => location.pointSpan();
+
+  RelativeSpanScanner(FileSpan span)
+      : _sourceFile = span.file,
+        _startLocation = span.start,
+        super(span.text, sourceUrl: span.sourceUrl);
+
+  @override
+  FileSpan spanFrom(LineScannerState startState, [LineScannerState? endState]) {
+    final endPosition = endState == null ? position : endState.position;
+    return _sourceFile.span(_startLocation.offset + startState.position,
+        _startLocation.offset + endPosition);
+  }
+
+  @override
+  FileSpan spanFromPosition(int startPosition, [int? endPosition]) {
+    RangeError.checkValidRange(
+        startPosition,
+        endPosition,
+        _sourceFile.length - _startLocation.offset,
+        'startPosition',
+        'endPosition');
+    return _sourceFile.span(_startLocation.offset + startPosition,
+        _startLocation.offset + (endPosition ?? position));
+  }
+
+  @override
+  bool matches(Pattern pattern) {
+    if (!super.matches(pattern)) {
+      _lastSpan = null;
+      return false;
+    }
+
+    _lastSpan = _sourceFile.span(_startLocation.offset + position,
+        _startLocation.offset + lastMatch!.end);
+    return true;
+  }
+
+  @override
+  Never error(String message, {Match? match, int? position, int? length}) {
+    validateErrorArgs(string, match, position, length);
+
+    if (match == null && position == null && length == null) match = lastMatch;
+    position ??= match == null ? this.position : match.start;
+    length ??= match == null ? 1 : match.end - match.start;
+
+    final span = _sourceFile.span(_startLocation.offset + position,
+        _startLocation.offset + position + length);
+    throw StringScannerException(message, span, string);
+  }
+}
+
+/// A class representing the state of a [SpanScanner].
+class _SpanScannerState implements LineScannerState {
+  /// The [SpanScanner] that created this.
+  final RelativeSpanScanner _scanner;
+
+  @override
+  final int position;
+  @override
+  int get line => _scanner._sourceFile.getLine(position);
+  @override
+  int get column => _scanner._sourceFile.getColumn(position);
+
+  _SpanScannerState(this._scanner, this.position);
+}

diff --git a/pkgs/string_scanner/lib/src/span_scanner.dart b/pkgs/string_scanner/lib/src/span_scanner.dart
new file mode 100644
index 0000000..509cf60
--- /dev/null
+++ b/pkgs/string_scanner/lib/src/span_scanner.dart

@@ -0,0 +1,142 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:source_span/source_span.dart';
+
+import 'eager_span_scanner.dart';
+import 'exception.dart';
+import 'line_scanner.dart';
+import 'relative_span_scanner.dart';
+import 'string_scanner.dart';
+import 'utils.dart';
+
+/// A subclass of [LineScanner] that exposes matched ranges as source map
+/// [FileSpan]s.
+class SpanScanner extends StringScanner implements LineScanner {
+  /// The source of the scanner.
+  ///
+  /// This caches line break information and is used to generate [FileSpan]s.
+  final SourceFile _sourceFile;
+
+  @override
+  int get line => _sourceFile.getLine(position);
+  @override
+  int get column => _sourceFile.getColumn(position);
+
+  @override
+  LineScannerState get state => _SpanScannerState(this, position);
+
+  @override
+  set state(LineScannerState state) {
+    if (state is! _SpanScannerState || !identical(state._scanner, this)) {
+      throw ArgumentError('The given LineScannerState was not returned by '
+          'this LineScanner.');
+    }
+
+    position = state.position;
+  }
+
+  /// The [FileSpan] for [lastMatch].
+  ///
+  /// This is the span for the entire match. There's no way to get spans for
+  /// subgroups since [Match] exposes no information about their positions.
+  FileSpan? get lastSpan {
+    if (lastMatch == null) _lastSpan = null;
+    return _lastSpan;
+  }
+
+  FileSpan? _lastSpan;
+
+  /// The current location of the scanner.
+  FileLocation get location => _sourceFile.location(position);
+
+  /// Returns an empty span at the current location.
+  FileSpan get emptySpan => location.pointSpan();
+
+  /// Creates a new [SpanScanner] that starts scanning from [position].
+  ///
+  /// [sourceUrl] is used as [SourceLocation.sourceUrl] for the returned
+  /// [FileSpan]s as well as for error reporting. It can be a [String], a
+  /// [Uri], or `null`.
+  SpanScanner(super.string, {super.sourceUrl, super.position})
+      : _sourceFile = SourceFile.fromString(string, url: sourceUrl);
+
+  /// Creates a new [SpanScanner] that eagerly computes line and column numbers.
+  ///
+  /// In general [SpanScanner.new] will be more efficient, since it avoids extra
+  /// computation on every scan. However, eager scanning can be useful for
+  /// situations where the normal course of parsing frequently involves
+  /// accessing the current line and column numbers.
+  ///
+  /// Note that *only* the `line` and `column` fields on the `SpanScanner`
+  /// itself and its `LineScannerState` are eagerly computed. To limit their
+  /// memory footprint, returned spans and locations will still lazily compute
+  /// their line and column numbers.
+  factory SpanScanner.eager(String string, {sourceUrl, int? position}) =
+      EagerSpanScanner;
+
+  /// Creates a new [SpanScanner] that scans within [span].
+  ///
+  /// This scans through [span]`.text, but emits new spans from [span]`.file` in
+  /// their appropriate relative positions. The [string] field contains only
+  /// [span]`.text`, and [position], [line], and [column] are all relative to
+  /// the span.
+  factory SpanScanner.within(FileSpan span) = RelativeSpanScanner;
+
+  /// Creates a [FileSpan] representing the source range between [startState]
+  /// and the current position.
+  FileSpan spanFrom(LineScannerState startState, [LineScannerState? endState]) {
+    final endPosition = endState == null ? position : endState.position;
+    return _sourceFile.span(startState.position, endPosition);
+  }
+
+  /// Creates a [FileSpan] representing the source range between [startPosition]
+  /// and [endPosition], or the current position if [endPosition] is null.
+  ///
+  /// Each position should be a code unit offset into the string being scanned,
+  /// with the same conventions as [StringScanner.position].
+  ///
+  /// Throws a [RangeError] if [startPosition] or [endPosition] aren't within
+  /// this source file.
+  FileSpan spanFromPosition(int startPosition, [int? endPosition]) =>
+      _sourceFile.span(startPosition, endPosition ?? position);
+
+  @override
+  bool matches(Pattern pattern) {
+    if (!super.matches(pattern)) {
+      _lastSpan = null;
+      return false;
+    }
+
+    _lastSpan = _sourceFile.span(position, lastMatch!.end);
+    return true;
+  }
+
+  @override
+  Never error(String message, {Match? match, int? position, int? length}) {
+    validateErrorArgs(string, match, position, length);
+
+    if (match == null && position == null && length == null) match = lastMatch;
+    position ??= match == null ? this.position : match.start;
+    length ??= match == null ? 0 : match.end - match.start;
+
+    final span = _sourceFile.span(position, position + length);
+    throw StringScannerException(message, span, string);
+  }
+}
+
+/// A class representing the state of a [SpanScanner].
+class _SpanScannerState implements LineScannerState {
+  /// The [SpanScanner] that created this.
+  final SpanScanner _scanner;
+
+  @override
+  final int position;
+  @override
+  int get line => _scanner._sourceFile.getLine(position);
+  @override
+  int get column => _scanner._sourceFile.getColumn(position);
+
+  _SpanScannerState(this._scanner, this.position);
+}

diff --git a/pkgs/string_scanner/lib/src/string_scanner.dart b/pkgs/string_scanner/lib/src/string_scanner.dart
new file mode 100644
index 0000000..1466944
--- /dev/null
+++ b/pkgs/string_scanner/lib/src/string_scanner.dart

@@ -0,0 +1,272 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:source_span/source_span.dart';
+
+import 'charcode.dart';
+import 'exception.dart';
+import 'utils.dart';
+
+/// A class that scans through a string using [Pattern]s.
+class StringScanner {
+  /// The URL of the source of the string being scanned.
+  ///
+  /// This is used for error reporting. It may be `null`, indicating that the
+  /// source URL is unknown or unavailable.
+  final Uri? sourceUrl;
+
+  /// The string being scanned through.
+  final String string;
+
+  /// The current position of the scanner in the string, in characters.
+  int get position => _position;
+  set position(int position) {
+    if (position.isNegative || position > string.length) {
+      throw ArgumentError('Invalid position $position');
+    }
+
+    _position = position;
+    _lastMatch = null;
+  }
+
+  int _position = 0;
+
+  /// The data about the previous match made by the scanner.
+  ///
+  /// If the last match failed, this will be `null`.
+  Match? get lastMatch {
+    // Lazily unset [_lastMatch] so that we avoid extra assignments in
+    // character-by-character methods that are used in core loops.
+    if (_position != _lastMatchPosition) _lastMatch = null;
+    return _lastMatch;
+  }
+
+  Match? _lastMatch;
+  int? _lastMatchPosition;
+
+  /// The portion of the string that hasn't yet been scanned.
+  String get rest => string.substring(position);
+
+  /// Whether the scanner has completely consumed [string].
+  bool get isDone => position == string.length;
+
+  /// Creates a new [StringScanner] that starts scanning from [position].
+  ///
+  /// [position] defaults to 0, the beginning of the string. [sourceUrl] is the
+  /// URL of the source of the string being scanned, if available. It can be
+  /// a [String], a [Uri], or `null`.
+  StringScanner(this.string, {Object? sourceUrl, int? position})
+      : sourceUrl = sourceUrl == null
+            ? null
+            : sourceUrl is String
+                ? Uri.parse(sourceUrl)
+                : sourceUrl as Uri {
+    if (position != null) this.position = position;
+  }
+
+  /// Consumes a single character and returns its character code.
+  ///
+  /// This throws a [FormatException] if the string has been fully consumed. It
+  /// doesn't affect [lastMatch].
+  int readChar() {
+    if (isDone) _fail('more input');
+    return string.codeUnitAt(_position++);
+  }
+
+  /// Returns the character code of the character [offset] away from [position].
+  ///
+  /// [offset] defaults to zero, and may be negative to inspect already-consumed
+  /// characters.
+  ///
+  /// This returns `null` if [offset] points outside the string. It doesn't
+  /// affect [lastMatch].
+  int? peekChar([int? offset]) {
+    offset ??= 0;
+    final index = position + offset;
+    if (index < 0 || index >= string.length) return null;
+    return string.codeUnitAt(index);
+  }
+
+  /// If the next character in the string is [character], consumes it.
+  ///
+  /// If [character] is a Unicode code point in a supplementary plane, this will
+  /// consume two code units. Dart's string representation is UTF-16, which
+  /// represents supplementary-plane code units as two code units.
+  ///
+  /// Returns whether or not [character] was consumed.
+  bool scanChar(int character) {
+    if (inSupplementaryPlane(character)) {
+      if (_position + 1 >= string.length ||
+          string.codeUnitAt(_position) != highSurrogate(character) ||
+          string.codeUnitAt(_position + 1) != lowSurrogate(character)) {
+        return false;
+      } else {
+        _position += 2;
+        return true;
+      }
+    } else {
+      if (isDone) return false;
+      if (string.codeUnitAt(_position) != character) return false;
+      _position++;
+      return true;
+    }
+  }
+
+  /// If the next character in the string is [character], consumes it.
+  ///
+  /// If [character] is a Unicode code point in a supplementary plane, this will
+  /// consume two code units. Dart's string representation is UTF-16, which
+  /// represents supplementary-plane code units as two code units.
+  ///
+  /// If [character] could not be consumed, throws a [FormatException]
+  /// describing the position of the failure. [name] is used in this error as
+  /// the expected name of the character being matched; if it's `null`, the
+  /// character itself is used instead.
+  void expectChar(int character, {String? name}) {
+    if (scanChar(character)) return;
+
+    if (name == null) {
+      if (character == $backslash) {
+        name = r'"\"';
+      } else if (character == $doubleQuote) {
+        name = r'"\""';
+      } else {
+        name = '"${String.fromCharCode(character)}"';
+      }
+    }
+
+    _fail(name);
+  }
+
+  /// Consumes a single Unicode code unit and returns it.
+  ///
+  /// This works like [readChar], except that it automatically handles UTF-16
+  /// surrogate pairs. Specifically, if the next two code units form a surrogate
+  /// pair, consumes them both and returns the corresponding Unicode code point.
+  ///
+  /// If next two characters are not a surrogate pair, the next code unit is
+  /// returned as-is, even if it's an unpaired surrogate.
+  int readCodePoint() {
+    final first = readChar();
+    if (!isHighSurrogate(first)) return first;
+
+    final next = peekChar();
+    if (next == null || !isLowSurrogate(next)) return first;
+
+    readChar();
+    return decodeSurrogatePair(first, next);
+  }
+
+  /// Returns the Unicode code point immediately after [position].
+  ///
+  /// This works like [peekChar], except that it automatically handles UTF-16
+  /// surrogate pairs. Specifically, if the next two code units form a surrogate
+  /// pair, returns the corresponding Unicode code point.
+  ///
+  /// If next two characters are not a surrogate pair, the next code unit is
+  /// returned as-is, even if it's an unpaired surrogate.
+  int? peekCodePoint() {
+    final first = peekChar();
+    if (first == null || !isHighSurrogate(first)) return first;
+
+    final next = peekChar(1);
+    if (next == null || !isLowSurrogate(next)) return first;
+
+    return decodeSurrogatePair(first, next);
+  }
+
+  /// If [pattern] matches at the current position of the string, scans forward
+  /// until the end of the match.
+  ///
+  /// Returns whether or not [pattern] matched.
+  bool scan(Pattern pattern) {
+    final success = matches(pattern);
+    if (success) {
+      _position = _lastMatch!.end;
+      _lastMatchPosition = _position;
+    }
+    return success;
+  }
+
+  /// If [pattern] matches at the current position of the string, scans forward
+  /// until the end of the match.
+  ///
+  /// If [pattern] did not match, throws a [FormatException] describing the
+  /// position of the failure. [name] is used in this error as the expected name
+  /// of the pattern being matched; if it's `null`, the pattern itself is used
+  /// instead.
+  void expect(Pattern pattern, {String? name}) {
+    if (scan(pattern)) return;
+
+    if (name == null) {
+      if (pattern is RegExp) {
+        final source = pattern.pattern;
+        name = '/$source/';
+      } else {
+        name =
+            pattern.toString().replaceAll(r'\', r'\\').replaceAll('"', r'\"');
+        name = '"$name"';
+      }
+    }
+    _fail(name);
+  }
+
+  /// If the string has not been fully consumed, this throws a
+  /// [FormatException].
+  void expectDone() {
+    if (isDone) return;
+    _fail('no more input');
+  }
+
+  /// Returns whether or not [pattern] matches at the current position of the
+  /// string.
+  ///
+  /// This doesn't move the scan pointer forward.
+  bool matches(Pattern pattern) {
+    _lastMatch = pattern.matchAsPrefix(string, position);
+    _lastMatchPosition = _position;
+    return _lastMatch != null;
+  }
+
+  /// Returns the substring of [string] between [start] and [end].
+  ///
+  /// Unlike [String.substring], [end] defaults to [position] rather than the
+  /// end of the string.
+  String substring(int start, [int? end]) {
+    end ??= position;
+    return string.substring(start, end);
+  }
+
+  /// Throws a [FormatException] with [message] as well as a detailed
+  /// description of the location of the error in the string.
+  ///
+  /// [match] is the match information for the span of the string with which the
+  /// error is associated. This should be a match returned by this scanner's
+  /// [lastMatch] property. By default, the error is associated with the last
+  /// match.
+  ///
+  /// If [position] and/or [length] are passed, they are used as the error span
+  /// instead. If only [length] is passed, [position] defaults to the current
+  /// position; if only [position] is passed, [length] defaults to 0.
+  ///
+  /// It's an error to pass [match] at the same time as [position] or [length].
+  Never error(String message, {Match? match, int? position, int? length}) {
+    validateErrorArgs(string, match, position, length);
+
+    if (match == null && position == null && length == null) match = lastMatch;
+    position ??= match == null ? this.position : match.start;
+    length ??= match == null ? 0 : match.end - match.start;
+
+    final sourceFile = SourceFile.fromString(string, url: sourceUrl);
+    final span = sourceFile.span(position, position + length);
+    throw StringScannerException(message, span, string);
+  }
+
+  // TODO(nweiz): Make this handle long lines more gracefully.
+  /// Throws a [FormatException] describing that [name] is expected at the
+  /// current position in the string.
+  Never _fail(String name) {
+    error('expected $name.', position: position, length: 0);
+  }
+}

diff --git a/pkgs/string_scanner/lib/src/utils.dart b/pkgs/string_scanner/lib/src/utils.dart
new file mode 100644
index 0000000..39891a1
--- /dev/null
+++ b/pkgs/string_scanner/lib/src/utils.dart

@@ -0,0 +1,95 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'string_scanner.dart';
+
+/// Validates the arguments passed to [StringScanner.error].
+void validateErrorArgs(
+    String string, Match? match, int? position, int? length) {
+  if (match != null && (position != null || length != null)) {
+    throw ArgumentError("Can't pass both match and position/length.");
+  }
+
+  if (position != null) {
+    if (position < 0) {
+      throw RangeError('position must be greater than or equal to 0.');
+    } else if (position > string.length) {
+      throw RangeError('position must be less than or equal to the '
+          'string length.');
+    }
+  }
+
+  if (length != null && length < 0) {
+    throw RangeError('length must be greater than or equal to 0.');
+  }
+
+  if (position != null && length != null && position + length > string.length) {
+    throw RangeError('position plus length must not go beyond the end of '
+        'the string.');
+  }
+}
+
+// See https://en.wikipedia.org/wiki/UTF-16#Code_points_from_U+010000_to_U+10FFFF
+// for documentation on how UTF-16 encoding works and definitions of various
+// related terms.
+
+/// The inclusive lower bound of Unicode's supplementary plane.
+const _supplementaryPlaneLowerBound = 0x10000;
+
+/// The inclusive upper bound of Unicode's supplementary plane.
+const _supplementaryPlaneUpperBound = 0x10FFFF;
+
+/// The inclusive lower bound of the UTF-16 high surrogate block.
+const _highSurrogateLowerBound = 0xD800;
+
+/// The inclusive lower bound of the UTF-16 low surrogate block.
+const _lowSurrogateLowerBound = 0xDC00;
+
+/// The number of low bits in each code unit of a surrogate pair that goes into
+/// determining which code point it encodes.
+const _surrogateBits = 10;
+
+/// A bit mask that covers the lower [_surrogateBits] of a code point, which can
+/// be used to extract the value of a surrogate or the low surrogate value of a
+/// code unit.
+const _surrogateValueMask = (1 << _surrogateBits) - 1;
+
+/// Returns whether [codePoint] is in the Unicode supplementary plane, and thus
+/// must be represented as a surrogate pair in UTF-16.
+bool inSupplementaryPlane(int codePoint) =>
+    codePoint >= _supplementaryPlaneLowerBound &&
+    codePoint <= _supplementaryPlaneUpperBound;
+
+/// Returns whether [codeUnit] is a UTF-16 high surrogate.
+bool isHighSurrogate(int codeUnit) =>
+    (codeUnit & ~_surrogateValueMask) == _highSurrogateLowerBound;
+
+/// Returns whether [codeUnit] is a UTF-16 low surrogate.
+bool isLowSurrogate(int codeUnit) =>
+    (codeUnit >> _surrogateBits) == (_lowSurrogateLowerBound >> _surrogateBits);
+
+/// Returns the high surrogate needed to encode the supplementary-plane
+/// [codePoint].
+int highSurrogate(int codePoint) {
+  assert(inSupplementaryPlane(codePoint));
+  return ((codePoint - _supplementaryPlaneLowerBound) >> _surrogateBits) +
+      _highSurrogateLowerBound;
+}
+
+/// Returns the low surrogate needed to encode the supplementary-plane
+/// [codePoint].
+int lowSurrogate(int codePoint) {
+  assert(inSupplementaryPlane(codePoint));
+  return ((codePoint - _supplementaryPlaneLowerBound) & _surrogateValueMask) +
+      _lowSurrogateLowerBound;
+}
+
+/// Converts a UTF-16 surrogate pair into the Unicode code unit it represents.
+int decodeSurrogatePair(int highSurrogate, int lowSurrogate) {
+  assert(isHighSurrogate(highSurrogate));
+  assert(isLowSurrogate(lowSurrogate));
+  return _supplementaryPlaneLowerBound +
+      (((highSurrogate & _surrogateValueMask) << _surrogateBits) |
+          (lowSurrogate & _surrogateValueMask));
+}

diff --git a/pkgs/string_scanner/lib/string_scanner.dart b/pkgs/string_scanner/lib/string_scanner.dart
new file mode 100644
index 0000000..e641ae7
--- /dev/null
+++ b/pkgs/string_scanner/lib/string_scanner.dart

@@ -0,0 +1,11 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// A library for parsing strings using a sequence of patterns.
+library;
+
+export 'src/exception.dart';
+export 'src/line_scanner.dart';
+export 'src/span_scanner.dart';
+export 'src/string_scanner.dart';

diff --git a/pkgs/string_scanner/pubspec.yaml b/pkgs/string_scanner/pubspec.yaml
new file mode 100644
index 0000000..9b259cf
--- /dev/null
+++ b/pkgs/string_scanner/pubspec.yaml

@@ -0,0 +1,14 @@
+name: string_scanner
+version: 1.4.1
+description: A class for parsing strings using a sequence of patterns.
+repository: https://github.com/dart-lang/tools/tree/main/pkgs/string_scanner
+
+environment:
+  sdk: ^3.1.0
+
+dependencies:
+  source_span: ^1.8.0
+
+dev_dependencies:
+  dart_flutter_team_lints: ^3.0.0
+  test: ^1.16.6

diff --git a/pkgs/string_scanner/test/error_test.dart b/pkgs/string_scanner/test/error_test.dart
new file mode 100644
index 0000000..1f98c32
--- /dev/null
+++ b/pkgs/string_scanner/test/error_test.dart

@@ -0,0 +1,143 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:string_scanner/string_scanner.dart';
+import 'package:test/test.dart';
+
+import 'utils.dart';
+
+void main() {
+  test('defaults to the last match', () {
+    final scanner = StringScanner('foo bar baz');
+    scanner.expect('foo ');
+    scanner.expect('bar');
+    expect(() => scanner.error('oh no!'), throwsStringScannerException('bar'));
+  });
+
+  group('with match', () {
+    test('supports an earlier match', () {
+      final scanner = StringScanner('foo bar baz');
+      scanner.expect('foo ');
+      final match = scanner.lastMatch;
+      scanner.expect('bar');
+      expect(() => scanner.error('oh no!', match: match),
+          throwsStringScannerException('foo '));
+    });
+
+    test('supports a match on a previous line', () {
+      final scanner = StringScanner('foo bar baz\ndo re mi\nearth fire water');
+      scanner.expect('foo bar baz\ndo ');
+      scanner.expect('re');
+      final match = scanner.lastMatch;
+      scanner.expect(' mi\nearth ');
+      expect(() => scanner.error('oh no!', match: match),
+          throwsStringScannerException('re'));
+    });
+
+    test('supports a multiline match', () {
+      final scanner = StringScanner('foo bar baz\ndo re mi\nearth fire water');
+      scanner.expect('foo bar ');
+      scanner.expect('baz\ndo');
+      final match = scanner.lastMatch;
+      scanner.expect(' re mi');
+      expect(() => scanner.error('oh no!', match: match),
+          throwsStringScannerException('baz\ndo'));
+    });
+
+    test('supports a match after position', () {
+      final scanner = StringScanner('foo bar baz');
+      scanner.expect('foo ');
+      scanner.expect('bar');
+      final match = scanner.lastMatch;
+      scanner.position = 0;
+      expect(() => scanner.error('oh no!', match: match),
+          throwsStringScannerException('bar'));
+    });
+  });
+
+  group('with position and/or length', () {
+    test('defaults to length 0', () {
+      final scanner = StringScanner('foo bar baz');
+      scanner.expect('foo ');
+      expect(() => scanner.error('oh no!', position: 1),
+          throwsStringScannerException(''));
+    });
+
+    test('defaults to the current position', () {
+      final scanner = StringScanner('foo bar baz');
+      scanner.expect('foo ');
+      expect(() => scanner.error('oh no!', length: 3),
+          throwsStringScannerException('bar'));
+    });
+
+    test('supports an earlier position', () {
+      final scanner = StringScanner('foo bar baz');
+      scanner.expect('foo ');
+      expect(() => scanner.error('oh no!', position: 1, length: 2),
+          throwsStringScannerException('oo'));
+    });
+
+    test('supports a position on a previous line', () {
+      final scanner = StringScanner('foo bar baz\ndo re mi\nearth fire water');
+      scanner.expect('foo bar baz\ndo re mi\nearth');
+      expect(() => scanner.error('oh no!', position: 15, length: 2),
+          throwsStringScannerException('re'));
+    });
+
+    test('supports a multiline length', () {
+      final scanner = StringScanner('foo bar baz\ndo re mi\nearth fire water');
+      scanner.expect('foo bar baz\ndo re mi\nearth');
+      expect(() => scanner.error('oh no!', position: 8, length: 8),
+          throwsStringScannerException('baz\ndo r'));
+    });
+
+    test('supports a position after the current one', () {
+      final scanner = StringScanner('foo bar baz');
+      expect(() => scanner.error('oh no!', position: 4, length: 3),
+          throwsStringScannerException('bar'));
+    });
+
+    test('supports a length of zero', () {
+      final scanner = StringScanner('foo bar baz');
+      expect(() => scanner.error('oh no!', position: 4, length: 0),
+          throwsStringScannerException(''));
+    });
+  });
+
+  group('argument errors', () {
+    late StringScanner scanner;
+    setUp(() {
+      scanner = StringScanner('foo bar baz');
+      scanner.scan('foo');
+    });
+
+    test('if match is passed with position', () {
+      expect(
+          () => scanner.error('oh no!', match: scanner.lastMatch, position: 1),
+          throwsArgumentError);
+    });
+
+    test('if match is passed with length', () {
+      expect(() => scanner.error('oh no!', match: scanner.lastMatch, length: 1),
+          throwsArgumentError);
+    });
+
+    test('if position is negative', () {
+      expect(() => scanner.error('oh no!', position: -1), throwsArgumentError);
+    });
+
+    test('if position is outside the string', () {
+      expect(() => scanner.error('oh no!', position: 100), throwsArgumentError);
+    });
+
+    test('if position + length is outside the string', () {
+      expect(() => scanner.error('oh no!', position: 7, length: 7),
+          throwsArgumentError);
+    });
+
+    test('if length is negative', () {
+      expect(() => scanner.error('oh no!', length: -1), throwsArgumentError);
+    });
+  });
+}

diff --git a/pkgs/string_scanner/test/line_scanner_test.dart b/pkgs/string_scanner/test/line_scanner_test.dart
new file mode 100644
index 0000000..1af5c36
--- /dev/null
+++ b/pkgs/string_scanner/test/line_scanner_test.dart

@@ -0,0 +1,465 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:string_scanner/src/charcode.dart';
+import 'package:string_scanner/string_scanner.dart';
+import 'package:test/test.dart';
+
+void main() {
+  late LineScanner scanner;
+  setUp(() {
+    scanner = LineScanner('foo\nbar\r\nbaz');
+  });
+
+  test('begins with line and column 0', () {
+    expect(scanner.line, equals(0));
+    expect(scanner.column, equals(0));
+  });
+
+  group('scan()', () {
+    test('consuming no newlines increases the column but not the line', () {
+      scanner.expect('foo');
+      expect(scanner.line, equals(0));
+      expect(scanner.column, equals(3));
+    });
+
+    test('consuming a LF resets the column and increases the line', () {
+      scanner.expect('foo\nba');
+      expect(scanner.line, equals(1));
+      expect(scanner.column, equals(2));
+    });
+
+    test('consuming multiple LFs resets the column and increases the line', () {
+      scanner.expect('foo\nbar\r\nb');
+      expect(scanner.line, equals(2));
+      expect(scanner.column, equals(1));
+    });
+
+    test('consuming a CR LF increases the line only after the LF', () {
+      scanner.expect('foo\nbar\r');
+      expect(scanner.line, equals(1));
+      expect(scanner.column, equals(4));
+
+      scanner.expect('\nb');
+      expect(scanner.line, equals(2));
+      expect(scanner.column, equals(1));
+    });
+
+    test('consuming a CR not followed by LF increases the line', () {
+      scanner = LineScanner('foo\nbar\rbaz');
+      scanner.expect('foo\nbar\r');
+      expect(scanner.line, equals(2));
+      expect(scanner.column, equals(0));
+
+      scanner.expect('b');
+      expect(scanner.line, equals(2));
+      expect(scanner.column, equals(1));
+    });
+
+    test('consuming a CR at the end increases the line', () {
+      scanner = LineScanner('foo\nbar\r');
+      scanner.expect('foo\nbar\r');
+      expect(scanner.line, equals(2));
+      expect(scanner.column, equals(0));
+      expect(scanner.isDone, isTrue);
+    });
+
+    test('consuming a mix of CR, LF, CR+LF increases the line', () {
+      scanner = LineScanner('0\n1\r2\r\n3');
+      scanner.expect('0\n1\r2\r\n3');
+      expect(scanner.line, equals(3));
+      expect(scanner.column, equals(1));
+    });
+
+    test('scanning a zero length match between CR LF does not fail', () {
+      scanner.expect('foo\nbar\r');
+      expect(scanner.line, equals(1));
+      expect(scanner.column, equals(4));
+      scanner.expect(RegExp('(?!x)'));
+      expect(scanner.line, equals(1));
+      expect(scanner.column, equals(4));
+    });
+  });
+
+  group('readChar()', () {
+    test('on a non-newline character increases the column but not the line',
+        () {
+      scanner.readChar();
+      expect(scanner.line, equals(0));
+      expect(scanner.column, equals(1));
+    });
+
+    test('consuming a LF resets the column and increases the line', () {
+      scanner.expect('foo');
+      expect(scanner.line, equals(0));
+      expect(scanner.column, equals(3));
+
+      scanner.readChar();
+      expect(scanner.line, equals(1));
+      expect(scanner.column, equals(0));
+    });
+
+    test('consuming a CR LF increases the line only after the LF', () {
+      scanner = LineScanner('foo\r\nbar');
+      scanner.expect('foo');
+      expect(scanner.line, equals(0));
+      expect(scanner.column, equals(3));
+
+      scanner.readChar();
+      expect(scanner.line, equals(0));
+      expect(scanner.column, equals(4));
+
+      scanner.readChar();
+      expect(scanner.line, equals(1));
+      expect(scanner.column, equals(0));
+    });
+
+    test('consuming a CR not followed by a LF increases the line', () {
+      scanner = LineScanner('foo\nbar\rbaz');
+      scanner.expect('foo\nbar');
+      expect(scanner.line, equals(1));
+      expect(scanner.column, equals(3));
+
+      scanner.readChar();
+      expect(scanner.line, equals(2));
+      expect(scanner.column, equals(0));
+    });
+
+    test('consuming a CR at the end increases the line', () {
+      scanner = LineScanner('foo\nbar\r');
+      scanner.expect('foo\nbar');
+      expect(scanner.line, equals(1));
+      expect(scanner.column, equals(3));
+
+      scanner.readChar();
+      expect(scanner.line, equals(2));
+      expect(scanner.column, equals(0));
+    });
+
+    test('consuming a mix of CR, LF, CR+LF increases the line', () {
+      scanner = LineScanner('0\n1\r2\r\n3');
+      for (var i = 0; i < scanner.string.length; i++) {
+        scanner.readChar();
+      }
+
+      expect(scanner.line, equals(3));
+      expect(scanner.column, equals(1));
+    });
+  });
+
+  group('readCodePoint()', () {
+    test('on a non-newline character increases the column but not the line',
+        () {
+      scanner.readCodePoint();
+      expect(scanner.line, equals(0));
+      expect(scanner.column, equals(1));
+    });
+
+    test('consuming a newline resets the column and increases the line', () {
+      scanner.expect('foo');
+      expect(scanner.line, equals(0));
+      expect(scanner.column, equals(3));
+
+      scanner.readCodePoint();
+      expect(scanner.line, equals(1));
+      expect(scanner.column, equals(0));
+    });
+
+    test("consuming halfway through a CR LF doesn't count as a line", () {
+      scanner.expect('foo\nbar');
+      expect(scanner.line, equals(1));
+      expect(scanner.column, equals(3));
+
+      scanner.readCodePoint();
+      expect(scanner.line, equals(1));
+      expect(scanner.column, equals(4));
+
+      scanner.readCodePoint();
+      expect(scanner.line, equals(2));
+      expect(scanner.column, equals(0));
+    });
+  });
+
+  group('scanChar()', () {
+    test('on a non-newline character increases the column but not the line',
+        () {
+      scanner.scanChar($f);
+      expect(scanner.line, equals(0));
+      expect(scanner.column, equals(1));
+    });
+
+    test('consuming a LF resets the column and increases the line', () {
+      scanner.expect('foo');
+      expect(scanner.line, equals(0));
+      expect(scanner.column, equals(3));
+
+      scanner.scanChar($lf);
+      expect(scanner.line, equals(1));
+      expect(scanner.column, equals(0));
+    });
+
+    test('consuming a CR LF increases the line only after the LF', () {
+      scanner.expect('foo\nbar');
+      expect(scanner.line, equals(1));
+      expect(scanner.column, equals(3));
+
+      scanner.scanChar($cr);
+      expect(scanner.line, equals(1));
+      expect(scanner.column, equals(4));
+
+      scanner.scanChar($lf);
+      expect(scanner.line, equals(2));
+      expect(scanner.column, equals(0));
+    });
+
+    test('consuming a CR not followed by LF increases the line', () {
+      scanner = LineScanner('foo\rbar');
+      scanner.expect('foo');
+      expect(scanner.line, equals(0));
+      expect(scanner.column, equals(3));
+
+      scanner.scanChar($cr);
+      expect(scanner.line, equals(1));
+      expect(scanner.column, equals(0));
+    });
+
+    test('consuming a CR at the end increases the line', () {
+      scanner = LineScanner('foo\r');
+      scanner.expect('foo');
+      expect(scanner.line, equals(0));
+      expect(scanner.column, equals(3));
+
+      scanner.scanChar($cr);
+      expect(scanner.line, equals(1));
+      expect(scanner.column, equals(0));
+    });
+
+    test('consuming a mix of CR, LF, CR+LF increases the line', () {
+      scanner = LineScanner('0\n1\r2\r\n3');
+      for (var i = 0; i < scanner.string.length; i++) {
+        scanner.scanChar(scanner.string[i].codeUnits.single);
+      }
+
+      expect(scanner.line, equals(3));
+      expect(scanner.column, equals(1));
+    });
+  });
+
+  group('before a surrogate pair', () {
+    final codePoint = '\uD83D\uDC6D'.runes.first;
+    const highSurrogate = 0xD83D;
+
+    late LineScanner scanner;
+    setUp(() {
+      scanner = LineScanner('foo: \uD83D\uDC6D');
+      expect(scanner.scan('foo: '), isTrue);
+    });
+
+    test('readChar returns the high surrogate and moves into the pair', () {
+      expect(scanner.readChar(), equals(highSurrogate));
+      expect(scanner.line, equals(0));
+      expect(scanner.column, equals(6));
+      expect(scanner.position, equals(6));
+    });
+
+    test('readCodePoint returns the code unit and moves past the pair', () {
+      expect(scanner.readCodePoint(), equals(codePoint));
+      expect(scanner.line, equals(0));
+      expect(scanner.column, equals(7));
+      expect(scanner.position, equals(7));
+    });
+
+    test('scanChar with the high surrogate moves into the pair', () {
+      expect(scanner.scanChar(highSurrogate), isTrue);
+      expect(scanner.line, equals(0));
+      expect(scanner.column, equals(6));
+      expect(scanner.position, equals(6));
+    });
+
+    test('scanChar with the code point moves past the pair', () {
+      expect(scanner.scanChar(codePoint), isTrue);
+      expect(scanner.line, equals(0));
+      expect(scanner.column, equals(7));
+      expect(scanner.position, equals(7));
+    });
+
+    test('expectChar with the high surrogate moves into the pair', () {
+      scanner.expectChar(highSurrogate);
+      expect(scanner.line, equals(0));
+      expect(scanner.column, equals(6));
+      expect(scanner.position, equals(6));
+    });
+
+    test('expectChar with the code point moves past the pair', () {
+      scanner.expectChar(codePoint);
+      expect(scanner.line, equals(0));
+      expect(scanner.column, equals(7));
+      expect(scanner.position, equals(7));
+    });
+  });
+
+  group('position=', () {
+    test('forward through LFs sets the line and column', () {
+      scanner = LineScanner('foo\nbar\nbaz');
+      scanner.position = 9; // "foo\nbar\nb"
+      expect(scanner.line, equals(2));
+      expect(scanner.column, equals(1));
+    });
+
+    test('forward from non-zero character through LFs sets the line and column',
+        () {
+      scanner = LineScanner('foo\nbar\nbaz');
+      scanner.expect('fo');
+      scanner.position = 9; // "foo\nbar\nb"
+      expect(scanner.line, equals(2));
+      expect(scanner.column, equals(1));
+    });
+
+    test('forward through CR LFs sets the line and column', () {
+      scanner = LineScanner('foo\r\nbar\r\nbaz');
+      scanner.position = 11; // "foo\r\nbar\r\nb"
+      expect(scanner.line, equals(2));
+      expect(scanner.column, equals(1));
+    });
+
+    test('forward through CR not followed by LFs sets the line and column', () {
+      scanner = LineScanner('foo\rbar\rbaz');
+      scanner.position = 9; // "foo\rbar\rb"
+      expect(scanner.line, equals(2));
+      expect(scanner.column, equals(1));
+    });
+
+    test('forward through CR at end sets the line and column', () {
+      scanner = LineScanner('foo\rbar\r');
+      scanner.position = 8; // "foo\rbar\r"
+      expect(scanner.line, equals(2));
+      expect(scanner.column, equals(0));
+    });
+
+    test('forward through a mix of CR, LF, CR+LF sets the line and column', () {
+      scanner = LineScanner('0\n1\r2\r\n3');
+      scanner.position = scanner.string.length;
+
+      expect(scanner.line, equals(3));
+      expect(scanner.column, equals(1));
+    });
+
+    test('forward through no newlines sets the column', () {
+      scanner.position = 2; // "fo"
+      expect(scanner.line, equals(0));
+      expect(scanner.column, equals(2));
+    });
+
+    test('backward through LFs sets the line and column', () {
+      scanner = LineScanner('foo\nbar\nbaz');
+      scanner.expect('foo\nbar\nbaz');
+      scanner.position = 2; // "fo"
+      expect(scanner.line, equals(0));
+      expect(scanner.column, equals(2));
+    });
+
+    test('backward through CR LFs sets the line and column', () {
+      scanner = LineScanner('foo\r\nbar\r\nbaz');
+      scanner.expect('foo\r\nbar\r\nbaz');
+      scanner.position = 2; // "fo"
+      expect(scanner.line, equals(0));
+      expect(scanner.column, equals(2));
+    });
+
+    test('backward through CR not followed by LFs sets the line and column',
+        () {
+      scanner = LineScanner('foo\rbar\rbaz');
+      scanner.expect('foo\rbar\rbaz');
+      scanner.position = 2; // "fo"
+      expect(scanner.line, equals(0));
+      expect(scanner.column, equals(2));
+    });
+
+    test('backward through CR at end sets the line and column', () {
+      scanner = LineScanner('foo\rbar\r');
+      scanner.expect('foo\rbar\r');
+      scanner.position = 2; // "fo"
+      expect(scanner.line, equals(0));
+      expect(scanner.column, equals(2));
+    });
+
+    test('backward through a mix of CR, LF, CR+LF sets the line and column',
+        () {
+      scanner = LineScanner('0\n1\r2\r\n3');
+      scanner.expect(scanner.string);
+
+      scanner.position = 1;
+      expect(scanner.line, equals(0));
+      expect(scanner.column, equals(1));
+    });
+
+    test('backward through no newlines sets the column', () {
+      scanner.expect('foo\nbar\r\nbaz');
+      scanner.position = 10; // "foo\nbar\r\nb"
+      expect(scanner.line, equals(2));
+      expect(scanner.column, equals(1));
+    });
+
+    test("forward halfway through a CR LF doesn't count as a line", () {
+      scanner.position = 8; // "foo\nbar\r"
+      expect(scanner.line, equals(1));
+      expect(scanner.column, equals(4));
+    });
+
+    test('forward from halfway through a CR LF counts as a line', () {
+      scanner.expect('foo\nbar\r');
+      scanner.position = 11; // "foo\nbar\r\nba"
+      expect(scanner.line, equals(2));
+      expect(scanner.column, equals(2));
+    });
+
+    test('backward to between CR LF', () {
+      scanner.expect('foo\nbar\r\nbaz');
+      scanner.position = 8; // "foo\nbar\r"
+      expect(scanner.line, equals(1));
+      expect(scanner.column, equals(4));
+    });
+
+    test('backward from between CR LF', () {
+      scanner.expect('foo\nbar\r');
+      expect(scanner.line, equals(1));
+      expect(scanner.column, equals(4));
+      scanner.position = 5; // "foo\nb"
+      expect(scanner.line, equals(1));
+      expect(scanner.column, equals(1));
+    });
+
+    test('backward to after CR LF', () {
+      scanner.expect('foo\nbar\r\nbaz');
+      scanner.position = 9; // "foo\nbar\r\n"
+      expect(scanner.line, equals(2));
+      expect(scanner.column, equals(0));
+    });
+
+    test('backward to before CR LF', () {
+      scanner.expect('foo\nbar\r\nbaz');
+      scanner.position = 7; // "foo\nbar"
+      expect(scanner.line, equals(1));
+      expect(scanner.column, equals(3));
+    });
+  });
+
+  test('state= restores the line, column, and position', () {
+    scanner.expect('foo\nb');
+    final state = scanner.state;
+
+    scanner.scan('ar\nba');
+    scanner.state = state;
+    expect(scanner.rest, equals('ar\r\nbaz'));
+    expect(scanner.line, equals(1));
+    expect(scanner.column, equals(1));
+  });
+
+  test('state= rejects a foreign state', () {
+    scanner.scan('foo\nb');
+
+    expect(() => LineScanner(scanner.string).state = scanner.state,
+        throwsArgumentError);
+  });
+}

diff --git a/pkgs/string_scanner/test/span_scanner_test.dart b/pkgs/string_scanner/test/span_scanner_test.dart
new file mode 100644
index 0000000..93d9c47
--- /dev/null
+++ b/pkgs/string_scanner/test/span_scanner_test.dart

@@ -0,0 +1,238 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:source_span/source_span.dart';
+import 'package:string_scanner/string_scanner.dart';
+import 'package:test/test.dart';
+
+import 'utils.dart';
+
+void main() {
+  testForImplementation(
+      'lazy',
+      ([String? string]) =>
+          SpanScanner(string ?? 'foo\nbar\nbaz', sourceUrl: 'source'));
+
+  testForImplementation(
+      'eager',
+      ([String? string]) =>
+          SpanScanner.eager(string ?? 'foo\nbar\nbaz', sourceUrl: 'source'));
+
+  group('within', () {
+    const text = 'first\nbefore: foo\nbar\nbaz :after\nlast';
+    final startOffset = text.indexOf('foo');
+
+    late SpanScanner scanner;
+    setUp(() {
+      final file = SourceFile.fromString(text, url: 'source');
+      scanner =
+          SpanScanner.within(file.span(startOffset, text.indexOf(' :after')));
+    });
+
+    test('string only includes the span text', () {
+      expect(scanner.string, equals('foo\nbar\nbaz'));
+    });
+
+    test('line and column are span-relative', () {
+      expect(scanner.line, equals(0));
+      expect(scanner.column, equals(0));
+
+      scanner.scan('foo');
+      expect(scanner.line, equals(0));
+      expect(scanner.column, equals(3));
+
+      scanner.scan('\n');
+      expect(scanner.line, equals(1));
+      expect(scanner.column, equals(0));
+    });
+
+    test('tracks the span for the last match', () {
+      scanner.scan('fo');
+      scanner.scan('o\nba');
+
+      final span = scanner.lastSpan!;
+      expect(span.start.offset, equals(startOffset + 2));
+      expect(span.start.line, equals(1));
+      expect(span.start.column, equals(10));
+      expect(span.start.sourceUrl, equals(Uri.parse('source')));
+
+      expect(span.end.offset, equals(startOffset + 6));
+      expect(span.end.line, equals(2));
+      expect(span.end.column, equals(2));
+      expect(span.start.sourceUrl, equals(Uri.parse('source')));
+
+      expect(span.text, equals('o\nba'));
+    });
+
+    test('.spanFrom() returns a span from a previous state', () {
+      scanner.scan('fo');
+      final state = scanner.state;
+      scanner.scan('o\nba');
+      scanner.scan('r\nba');
+
+      final span = scanner.spanFrom(state);
+      expect(span.text, equals('o\nbar\nba'));
+    });
+
+    test('.spanFromPosition() returns a span from a previous state', () {
+      scanner.scan('fo');
+      final start = scanner.position;
+      scanner.scan('o\nba');
+      scanner.scan('r\nba');
+
+      final span = scanner.spanFromPosition(start + 2, start + 5);
+      expect(span.text, equals('bar'));
+    });
+
+    test('.emptySpan returns an empty span at the current location', () {
+      scanner.scan('foo\nba');
+
+      final span = scanner.emptySpan;
+      expect(span.start.offset, equals(startOffset + 6));
+      expect(span.start.line, equals(2));
+      expect(span.start.column, equals(2));
+      expect(span.start.sourceUrl, equals(Uri.parse('source')));
+
+      expect(span.end.offset, equals(startOffset + 6));
+      expect(span.end.line, equals(2));
+      expect(span.end.column, equals(2));
+      expect(span.start.sourceUrl, equals(Uri.parse('source')));
+
+      expect(span.text, equals(''));
+    });
+
+    test('.error() uses an absolute span', () {
+      scanner.expect('foo');
+      expect(
+          () => scanner.error('oh no!'), throwsStringScannerException('foo'));
+    });
+
+    test('.isDone returns true at the end of the span', () {
+      scanner.expect('foo\nbar\nbaz');
+      expect(scanner.isDone, isTrue);
+    });
+  });
+}
+
+void testForImplementation(
+    String name, SpanScanner Function([String string]) create) {
+  group('for a $name scanner', () {
+    late SpanScanner scanner;
+    setUp(() => scanner = create());
+
+    test('tracks the span for the last match', () {
+      scanner.scan('fo');
+      scanner.scan('o\nba');
+
+      final span = scanner.lastSpan!;
+      expect(span.start.offset, equals(2));
+      expect(span.start.line, equals(0));
+      expect(span.start.column, equals(2));
+      expect(span.start.sourceUrl, equals(Uri.parse('source')));
+
+      expect(span.end.offset, equals(6));
+      expect(span.end.line, equals(1));
+      expect(span.end.column, equals(2));
+      expect(span.start.sourceUrl, equals(Uri.parse('source')));
+
+      expect(span.text, equals('o\nba'));
+    });
+
+    test('.spanFrom() returns a span from a previous state', () {
+      scanner.scan('fo');
+      final state = scanner.state;
+      scanner.scan('o\nba');
+      scanner.scan('r\nba');
+
+      final span = scanner.spanFrom(state);
+      expect(span.text, equals('o\nbar\nba'));
+    });
+
+    test('.spanFromPosition() returns a span from a previous state', () {
+      scanner.scan('fo');
+      final start = scanner.position;
+      scanner.scan('o\nba');
+      scanner.scan('r\nba');
+
+      final span = scanner.spanFromPosition(start + 2, start + 5);
+      expect(span.text, equals('bar'));
+    });
+
+    test('.emptySpan returns an empty span at the current location', () {
+      scanner.scan('foo\nba');
+
+      final span = scanner.emptySpan;
+      expect(span.start.offset, equals(6));
+      expect(span.start.line, equals(1));
+      expect(span.start.column, equals(2));
+      expect(span.start.sourceUrl, equals(Uri.parse('source')));
+
+      expect(span.end.offset, equals(6));
+      expect(span.end.line, equals(1));
+      expect(span.end.column, equals(2));
+      expect(span.start.sourceUrl, equals(Uri.parse('source')));
+
+      expect(span.text, equals(''));
+    });
+
+    group('before a surrogate pair', () {
+      final codePoint = '\uD83D\uDC6D'.runes.first;
+      const highSurrogate = 0xD83D;
+
+      late SpanScanner scanner;
+      setUp(() {
+        scanner = create('foo: \uD83D\uDC6D bar');
+        expect(scanner.scan('foo: '), isTrue);
+      });
+
+      test('readChar returns the high surrogate and moves into the pair', () {
+        expect(scanner.readChar(), equals(highSurrogate));
+        expect(scanner.line, equals(0));
+        expect(scanner.column, equals(6));
+        expect(scanner.position, equals(6));
+      });
+
+      test('readCodePoint returns the code unit and moves past the pair', () {
+        expect(scanner.readCodePoint(), equals(codePoint));
+        expect(scanner.line, equals(0));
+        expect(scanner.column, equals(7));
+        expect(scanner.position, equals(7));
+      });
+
+      test('scanChar with the high surrogate moves into the pair', () {
+        expect(scanner.scanChar(highSurrogate), isTrue);
+        expect(scanner.line, equals(0));
+        expect(scanner.column, equals(6));
+        expect(scanner.position, equals(6));
+      });
+
+      test('scanChar with the code point moves past the pair', () {
+        expect(scanner.scanChar(codePoint), isTrue);
+        expect(scanner.line, equals(0));
+        expect(scanner.column, equals(7));
+        expect(scanner.position, equals(7));
+      });
+
+      test('expectChar with the high surrogate moves into the pair', () {
+        scanner.expectChar(highSurrogate);
+        expect(scanner.line, equals(0));
+        expect(scanner.column, equals(6));
+        expect(scanner.position, equals(6));
+      });
+
+      test('expectChar with the code point moves past the pair', () {
+        scanner.expectChar(codePoint);
+        expect(scanner.line, equals(0));
+        expect(scanner.column, equals(7));
+        expect(scanner.position, equals(7));
+      });
+
+      test('spanFrom covers the surrogate pair', () {
+        final state = scanner.state;
+        scanner.scan('\uD83D\uDC6D b');
+        expect(scanner.spanFrom(state).text, equals('\uD83D\uDC6D b'));
+      });
+    });
+  });
+}

diff --git a/pkgs/string_scanner/test/string_scanner_test.dart b/pkgs/string_scanner/test/string_scanner_test.dart
new file mode 100644
index 0000000..36a737e
--- /dev/null
+++ b/pkgs/string_scanner/test/string_scanner_test.dart

@@ -0,0 +1,564 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:string_scanner/src/charcode.dart';
+import 'package:string_scanner/string_scanner.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('with an empty string', () {
+    late StringScanner scanner;
+    setUp(() {
+      scanner = StringScanner('');
+    });
+
+    test('is done', () {
+      expect(scanner.isDone, isTrue);
+      expect(scanner.expectDone, isNot(throwsFormatException));
+    });
+
+    test('rest is empty', () {
+      expect(scanner.rest, isEmpty);
+    });
+
+    test('lastMatch is null', () {
+      expect(scanner.lastMatch, isNull);
+    });
+
+    test('position is zero', () {
+      expect(scanner.position, equals(0));
+    });
+
+    test("readChar fails and doesn't change the state", () {
+      expect(scanner.readChar, throwsFormatException);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(0));
+    });
+
+    test("readCodePoint fails and doesn't change the state", () {
+      expect(scanner.readCodePoint, throwsFormatException);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(0));
+    });
+
+    test("peekChar returns null and doesn't change the state", () {
+      expect(scanner.peekChar(), isNull);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(0));
+    });
+
+    test("peekCodePoint returns null and doesn't change the state", () {
+      expect(scanner.peekCodePoint(), isNull);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(0));
+    });
+
+    test("scanChar returns false and doesn't change the state", () {
+      expect(scanner.scanChar($f), isFalse);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(0));
+    });
+
+    test("expectChar fails and doesn't change the state", () {
+      expect(() => scanner.expectChar($f), throwsFormatException);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(0));
+    });
+
+    test("scan returns false and doesn't change the state", () {
+      expect(scanner.scan(RegExp('.')), isFalse);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(0));
+    });
+
+    test("expect throws a FormatException and doesn't change the state", () {
+      expect(() => scanner.expect(RegExp('.')), throwsFormatException);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(0));
+    });
+
+    test("matches returns false and doesn't change the state", () {
+      expect(scanner.matches(RegExp('.')), isFalse);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(0));
+    });
+
+    test('substring returns the empty string', () {
+      expect(scanner.substring(0), isEmpty);
+    });
+
+    test('setting position to 1 throws an ArgumentError', () {
+      expect(() {
+        scanner.position = 1;
+      }, throwsArgumentError);
+    });
+
+    test('setting position to -1 throws an ArgumentError', () {
+      expect(() {
+        scanner.position = -1;
+      }, throwsArgumentError);
+    });
+  });
+
+  group('at the beginning of a string', () {
+    late StringScanner scanner;
+    setUp(() {
+      scanner = StringScanner('foo bar');
+    });
+
+    test('is not done', () {
+      expect(scanner.isDone, isFalse);
+      expect(scanner.expectDone, throwsFormatException);
+    });
+
+    test('rest is the whole string', () {
+      expect(scanner.rest, equals('foo bar'));
+    });
+
+    test('lastMatch is null', () {
+      expect(scanner.lastMatch, isNull);
+    });
+
+    test('position is zero', () {
+      expect(scanner.position, equals(0));
+    });
+
+    test('readChar returns the first character and moves forward', () {
+      expect(scanner.readChar(), equals(0x66));
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(1));
+    });
+
+    test('readCodePoint returns the first character and moves forward', () {
+      expect(scanner.readCodePoint(), equals(0x66));
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(1));
+    });
+
+    test('peekChar returns the first character', () {
+      expect(scanner.peekChar(), equals(0x66));
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(0));
+    });
+
+    test('peekChar with an argument returns the nth character', () {
+      expect(scanner.peekChar(4), equals(0x62));
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(0));
+    });
+
+    test('peekCodePoint returns the first character', () {
+      expect(scanner.peekCodePoint(), equals(0x66));
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(0));
+    });
+
+    test('a matching scanChar returns true moves forward', () {
+      expect(scanner.scanChar($f), isTrue);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(1));
+    });
+
+    test('a non-matching scanChar returns false and does nothing', () {
+      expect(scanner.scanChar($x), isFalse);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(0));
+    });
+
+    test('a matching expectChar moves forward', () {
+      scanner.expectChar($f);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(1));
+    });
+
+    test('a non-matching expectChar fails', () {
+      expect(() => scanner.expectChar($x), throwsFormatException);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(0));
+    });
+
+    test('a matching scan returns true and changes the state', () {
+      expect(scanner.scan(RegExp('f(..)')), isTrue);
+      expect(scanner.lastMatch![1], equals('oo'));
+      expect(scanner.position, equals(3));
+      expect(scanner.rest, equals(' bar'));
+    });
+
+    test('a non-matching scan returns false and sets lastMatch to null', () {
+      expect(scanner.matches(RegExp('f(..)')), isTrue);
+      expect(scanner.lastMatch, isNotNull);
+
+      expect(scanner.scan(RegExp('b(..)')), isFalse);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(0));
+      expect(scanner.rest, equals('foo bar'));
+    });
+
+    test('a matching expect changes the state', () {
+      scanner.expect(RegExp('f(..)'));
+      expect(scanner.lastMatch![1], equals('oo'));
+      expect(scanner.position, equals(3));
+      expect(scanner.rest, equals(' bar'));
+    });
+
+    test(
+        'a non-matching expect throws a FormatException and sets lastMatch to '
+        'null', () {
+      expect(scanner.matches(RegExp('f(..)')), isTrue);
+      expect(scanner.lastMatch, isNotNull);
+
+      expect(() => scanner.expect(RegExp('b(..)')), throwsFormatException);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(0));
+      expect(scanner.rest, equals('foo bar'));
+    });
+
+    test('a matching matches returns true and only changes lastMatch', () {
+      expect(scanner.matches(RegExp('f(..)')), isTrue);
+      expect(scanner.lastMatch![1], equals('oo'));
+      expect(scanner.position, equals(0));
+      expect(scanner.rest, equals('foo bar'));
+    });
+
+    test("a non-matching matches returns false and doesn't change the state",
+        () {
+      expect(scanner.matches(RegExp('b(..)')), isFalse);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(0));
+      expect(scanner.rest, equals('foo bar'));
+    });
+
+    test('substring from the beginning returns the empty string', () {
+      expect(scanner.substring(0), isEmpty);
+    });
+
+    test('substring with a custom end returns the substring', () {
+      expect(scanner.substring(0, 3), equals('foo'));
+    });
+
+    test('substring with the string length returns the whole string', () {
+      expect(scanner.substring(0, 7), equals('foo bar'));
+    });
+
+    test('setting position to 1 moves the cursor forward', () {
+      scanner.position = 1;
+      expect(scanner.position, equals(1));
+      expect(scanner.rest, equals('oo bar'));
+
+      expect(scanner.scan(RegExp('oo.')), isTrue);
+      expect(scanner.lastMatch![0], equals('oo '));
+      expect(scanner.position, equals(4));
+      expect(scanner.rest, equals('bar'));
+    });
+
+    test('setting position beyond the string throws an ArgumentError', () {
+      expect(() {
+        scanner.position = 8;
+      }, throwsArgumentError);
+    });
+
+    test('setting position to -1 throws an ArgumentError', () {
+      expect(() {
+        scanner.position = -1;
+      }, throwsArgumentError);
+    });
+
+    test('scan accepts any Pattern', () {
+      expect(scanner.scan('foo'), isTrue);
+      expect(scanner.lastMatch![0], equals('foo'));
+      expect(scanner.position, equals(3));
+      expect(scanner.rest, equals(' bar'));
+    });
+
+    test('scans multiple times', () {
+      expect(scanner.scan(RegExp('f(..)')), isTrue);
+      expect(scanner.lastMatch![1], equals('oo'));
+      expect(scanner.position, equals(3));
+      expect(scanner.rest, equals(' bar'));
+
+      expect(scanner.scan(RegExp(' b(..)')), isTrue);
+      expect(scanner.lastMatch![1], equals('ar'));
+      expect(scanner.position, equals(7));
+      expect(scanner.rest, equals(''));
+      expect(scanner.isDone, isTrue);
+      expect(scanner.expectDone, isNot(throwsFormatException));
+    });
+  });
+
+  group('after a scan', () {
+    late StringScanner scanner;
+    setUp(() {
+      scanner = StringScanner('foo bar');
+      expect(scanner.scan('foo'), isTrue);
+    });
+
+    test('readChar returns the first character and unsets the last match', () {
+      expect(scanner.readChar(), equals($space));
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(4));
+    });
+
+    test('readCodePoint returns the first character and unsets the last match',
+        () {
+      expect(scanner.readCodePoint(), equals($space));
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(4));
+    });
+
+    test('a matching scanChar returns true and unsets the last match', () {
+      expect(scanner.scanChar($space), isTrue);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(4));
+    });
+
+    test('a matching expectChar returns true and unsets the last match', () {
+      scanner.expectChar($space);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(4));
+    });
+  });
+
+  group('at the end of a string', () {
+    late StringScanner scanner;
+    setUp(() {
+      scanner = StringScanner('foo bar');
+      expect(scanner.scan('foo bar'), isTrue);
+    });
+
+    test('is done', () {
+      expect(scanner.isDone, isTrue);
+      expect(scanner.expectDone, isNot(throwsFormatException));
+    });
+
+    test('rest is empty', () {
+      expect(scanner.rest, isEmpty);
+    });
+
+    test('position is zero', () {
+      expect(scanner.position, equals(7));
+    });
+
+    test("readChar fails and doesn't change the state", () {
+      expect(scanner.readChar, throwsFormatException);
+      expect(scanner.lastMatch, isNotNull);
+      expect(scanner.position, equals(7));
+    });
+
+    test("readCodePoint fails and doesn't change the state", () {
+      expect(scanner.readCodePoint, throwsFormatException);
+      expect(scanner.lastMatch, isNotNull);
+      expect(scanner.position, equals(7));
+    });
+
+    test("peekChar returns null and doesn't change the state", () {
+      expect(scanner.peekChar(), isNull);
+      expect(scanner.lastMatch, isNotNull);
+      expect(scanner.position, equals(7));
+    });
+
+    test("peekCodePoint returns null and doesn't change the state", () {
+      expect(scanner.peekCodePoint(), isNull);
+      expect(scanner.lastMatch, isNotNull);
+      expect(scanner.position, equals(7));
+    });
+
+    test("scanChar returns false and doesn't change the state", () {
+      expect(scanner.scanChar($f), isFalse);
+      expect(scanner.lastMatch, isNotNull);
+      expect(scanner.position, equals(7));
+    });
+
+    test("expectChar fails and doesn't change the state", () {
+      expect(() => scanner.expectChar($f), throwsFormatException);
+      expect(scanner.lastMatch, isNotNull);
+      expect(scanner.position, equals(7));
+    });
+
+    test('scan returns false and sets lastMatch to null', () {
+      expect(scanner.scan(RegExp('.')), isFalse);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(7));
+    });
+
+    test('expect throws a FormatException and sets lastMatch to null', () {
+      expect(() => scanner.expect(RegExp('.')), throwsFormatException);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(7));
+    });
+
+    test('matches returns false sets lastMatch to null', () {
+      expect(scanner.matches(RegExp('.')), isFalse);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(7));
+    });
+
+    test('substring from the beginning returns the whole string', () {
+      expect(scanner.substring(0), equals('foo bar'));
+    });
+
+    test('substring with a custom start returns a substring from there', () {
+      expect(scanner.substring(4), equals('bar'));
+    });
+
+    test('substring with a custom start and end returns that substring', () {
+      expect(scanner.substring(3, 5), equals(' b'));
+    });
+
+    test('setting position to 1 moves the cursor backward', () {
+      scanner.position = 1;
+      expect(scanner.position, equals(1));
+      expect(scanner.rest, equals('oo bar'));
+
+      expect(scanner.scan(RegExp('oo.')), isTrue);
+      expect(scanner.lastMatch![0], equals('oo '));
+      expect(scanner.position, equals(4));
+      expect(scanner.rest, equals('bar'));
+    });
+
+    test('setting and resetting position clears lastMatch', () {
+      final oldPosition = scanner.position;
+      scanner.position = 1;
+      scanner.position = oldPosition;
+      expect(scanner.lastMatch, isNull);
+    });
+
+    test('setting position beyond the string throws an ArgumentError', () {
+      expect(() {
+        scanner.position = 8;
+      }, throwsArgumentError);
+    });
+
+    test('setting position to -1 throws an ArgumentError', () {
+      expect(() {
+        scanner.position = -1;
+      }, throwsArgumentError);
+    });
+  });
+
+  group('before a surrogate pair', () {
+    final codePoint = '\uD83D\uDC6D'.runes.first;
+    const highSurrogate = 0xD83D;
+
+    late StringScanner scanner;
+    setUp(() {
+      scanner = StringScanner('foo: \uD83D\uDC6D');
+      expect(scanner.scan('foo: '), isTrue);
+    });
+
+    test('readChar returns the high surrogate and moves into the pair', () {
+      expect(scanner.readChar(), equals(highSurrogate));
+      expect(scanner.position, equals(6));
+    });
+
+    test('readCodePoint returns the code unit and moves past the pair', () {
+      expect(scanner.readCodePoint(), equals(codePoint));
+      expect(scanner.position, equals(7));
+    });
+
+    test('peekChar returns the high surrogate', () {
+      expect(scanner.peekChar(), equals(highSurrogate));
+      expect(scanner.position, equals(5));
+    });
+
+    test('peekCodePoint returns the code unit', () {
+      expect(scanner.peekCodePoint(), equals(codePoint));
+      expect(scanner.position, equals(5));
+    });
+
+    test('scanChar with the high surrogate moves into the pair', () {
+      expect(scanner.scanChar(highSurrogate), isTrue);
+      expect(scanner.position, equals(6));
+    });
+
+    test('scanChar with the code point moves past the pair', () {
+      expect(scanner.scanChar(codePoint), isTrue);
+      expect(scanner.position, equals(7));
+    });
+
+    test('expectChar with the high surrogate moves into the pair', () {
+      scanner.expectChar(highSurrogate);
+      expect(scanner.position, equals(6));
+    });
+
+    test('expectChar with the code point moves past the pair', () {
+      scanner.expectChar(codePoint);
+      expect(scanner.position, equals(7));
+    });
+  });
+
+  group('before an invalid surrogate pair', () {
+    // This surrogate pair is invalid because U+E000 is just outside the range
+    // of low surrogates. If it were interpreted as a surrogate pair anyway, the
+    // value would be U+110000, which is outside of the Unicode gamut.
+    const codePoint = 0x110000;
+    const highSurrogate = 0xD800;
+
+    late StringScanner scanner;
+    setUp(() {
+      scanner = StringScanner('foo: \uD800\uE000');
+      expect(scanner.scan('foo: '), isTrue);
+    });
+
+    test('readChar returns the high surrogate and moves into the pair', () {
+      expect(scanner.readChar(), equals(highSurrogate));
+      expect(scanner.position, equals(6));
+    });
+
+    test('readCodePoint returns the high surrogate and moves past the pair',
+        () {
+      expect(scanner.readCodePoint(), equals(highSurrogate));
+      expect(scanner.position, equals(6));
+    });
+
+    test('peekChar returns the high surrogate', () {
+      expect(scanner.peekChar(), equals(highSurrogate));
+      expect(scanner.position, equals(5));
+    });
+
+    test('peekCodePoint returns the high surrogate', () {
+      expect(scanner.peekCodePoint(), equals(highSurrogate));
+      expect(scanner.position, equals(5));
+    });
+
+    test('scanChar with the high surrogate moves into the pair', () {
+      expect(scanner.scanChar(highSurrogate), isTrue);
+      expect(scanner.position, equals(6));
+    });
+
+    test('scanChar with the fake code point returns false', () {
+      expect(scanner.scanChar(codePoint), isFalse);
+      expect(scanner.position, equals(5));
+    });
+
+    test('expectChar with the high surrogate moves into the pair', () {
+      scanner.expectChar(highSurrogate);
+      expect(scanner.position, equals(6));
+    });
+
+    test('expectChar with the fake code point fails', () {
+      expect(() => scanner.expectChar(codePoint), throwsRangeError);
+    });
+  });
+
+  group('a scanner constructed with a custom position', () {
+    test('starts scanning from that position', () {
+      final scanner = StringScanner('foo bar', position: 1);
+      expect(scanner.position, equals(1));
+      expect(scanner.rest, equals('oo bar'));
+
+      expect(scanner.scan(RegExp('oo.')), isTrue);
+      expect(scanner.lastMatch![0], equals('oo '));
+      expect(scanner.position, equals(4));
+      expect(scanner.rest, equals('bar'));
+    });
+
+    test('throws an ArgumentError if the position is -1', () {
+      expect(() => StringScanner('foo bar', position: -1), throwsArgumentError);
+    });
+
+    test('throws an ArgumentError if the position is beyond the string', () {
+      expect(() => StringScanner('foo bar', position: 8), throwsArgumentError);
+    });
+  });
+}

diff --git a/pkgs/string_scanner/test/utils.dart b/pkgs/string_scanner/test/utils.dart
new file mode 100644
index 0000000..ca03c06
--- /dev/null
+++ b/pkgs/string_scanner/test/utils.dart

@@ -0,0 +1,12 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:string_scanner/string_scanner.dart';
+import 'package:test/test.dart';
+
+/// Returns a matcher that asserts that a closure throws a
+/// [StringScannerException] with the given [text].
+Matcher throwsStringScannerException(String text) =>
+    throwsA(const TypeMatcher<StringScannerException>()
+        .having((e) => e.span!.text, 'span.text', text));

diff --git a/pkgs/term_glyph/.gitignore b/pkgs/term_glyph/.gitignore
new file mode 100644
index 0000000..01d42c0
--- /dev/null
+++ b/pkgs/term_glyph/.gitignore

@@ -0,0 +1,4 @@
+.dart_tool/
+.pub/
+.packages
+pubspec.lock

diff --git a/pkgs/term_glyph/AUTHORS b/pkgs/term_glyph/AUTHORS
new file mode 100644
index 0000000..e8063a8
--- /dev/null
+++ b/pkgs/term_glyph/AUTHORS

@@ -0,0 +1,6 @@
+# Below is a list of people and organizations that have contributed
+# to the project. Names should be added to the list like so:
+#
+#   Name/Organization <email address>
+
+Google Inc.

diff --git a/pkgs/term_glyph/CHANGELOG.md b/pkgs/term_glyph/CHANGELOG.md
new file mode 100644
index 0000000..bf8eb79
--- /dev/null
+++ b/pkgs/term_glyph/CHANGELOG.md

@@ -0,0 +1,33 @@
+## 1.2.3-wip
+
+## 1.2.2
+
+* Require Dart 3.1
+* Move to `dart-lang/tools` monorepo.
+
+## 1.2.1
+
+* Migrate to `package:lints`.
+* Populate the pubspec `repository` field.
+
+## 1.2.0
+
+* Stable release for null safety.
+* Update SDK constraints to `>=2.12.0-0 <3.0.0` based on beta release
+  guidelines.
+
+## 1.1.0
+
+* Add a `GlyphSet` class that can be used to easily choose which set of glyphs
+  to use for a particular chunk of code.
+
+* Add `asciiGlyphs`, `unicodeGlyphs`, and `glyphs` getters that provide access
+  to `GlyphSet`s.
+
+## 1.0.1
+
+* Set max SDK version to `<3.0.0`.
+
+## 1.0.0
+
+* Initial version.

diff --git a/pkgs/term_glyph/LICENSE b/pkgs/term_glyph/LICENSE
new file mode 100644
index 0000000..03af64a
--- /dev/null
+++ b/pkgs/term_glyph/LICENSE

@@ -0,0 +1,27 @@
+Copyright 2017, the Dart project authors. 
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+    * Neither the name of Google LLC nor the names of its
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

diff --git a/pkgs/term_glyph/README.md b/pkgs/term_glyph/README.md
new file mode 100644
index 0000000..75039aa
--- /dev/null
+++ b/pkgs/term_glyph/README.md

@@ -0,0 +1,47 @@
+[![Build Status](https://github.com/dart-lang/tools/actions/workflows/term_glyph.yaml/badge.svg)](https://github.com/dart-lang/tools/actions/workflows/term_glyph.yaml)
+[![pub package](https://img.shields.io/pub/v/term_glyph.svg)](https://pub.dev/packages/term_glyph)
+[![package publisher](https://img.shields.io/pub/publisher/term_glyph.svg)](https://pub.dev/packages/term_glyph/publisher)
+
+This library contains getters for useful Unicode glyphs as well as plain ASCII
+alternatives. It's intended to be used in command-line applications that may run
+in places where Unicode isn't well-supported and libraries that may be used by
+those applications.
+
+We recommend that you import this library with the prefix "glyph". For example:
+
+```dart
+import 'package:term_glyph/term_glyph.dart' as glyph;
+
+/// Formats [items] into a bulleted list, with one item per line.
+String bulletedList(List<String> items) =>
+    items.map((item) => "${glyph.bullet} $item").join("\n");
+```
+
+## ASCII Mode
+
+Some shells are unable to display Unicode characters, so this package is able to
+transparently switch its glyphs to ASCII alternatives by setting [the `ascii`
+attribute][ascii]. When this attribute is `true`, all glyphs use ASCII
+characters instead. It currently defaults to `false`, although in the future it
+may default to `true` for applications running on the Dart VM on Windows. For
+example:
+
+[ascii]: https://pub.dev/documentation/term_glyph/latest/term_glyph/ascii.html
+
+```dart
+import 'dart:io';
+
+import 'package:term_glyph/term_glyph.dart' as glyph;
+
+void main() {
+  glyph.ascii = Platform.isWindows;
+
+  // Prints "Unicode => ASCII" on Windows, "Unicode ━▶ ASCII" everywhere else.
+  print("Unicode ${glyph.rightArrow} ASCII");
+}
+```
+
+All ASCII glyphs are guaranteed to be the same number of characters as the
+corresponding Unicode glyphs, so that they line up properly when printed on a
+terminal. The specific ASCII text for a given Unicode glyph may change over
+time; this is not considered a breaking change.

diff --git a/pkgs/term_glyph/analysis_options.yaml b/pkgs/term_glyph/analysis_options.yaml
new file mode 100644
index 0000000..6d74ee9
--- /dev/null
+++ b/pkgs/term_glyph/analysis_options.yaml

@@ -0,0 +1,32 @@
+# https://dart.dev/guides/language/analysis-options
+include: package:dart_flutter_team_lints/analysis_options.yaml
+
+analyzer:
+  language:
+    strict-casts: true
+    strict-inference: true
+    strict-raw-types: true
+
+linter:
+  rules:
+    - avoid_bool_literals_in_conditional_expressions
+    - avoid_classes_with_only_static_members
+    - avoid_private_typedef_functions
+    - avoid_redundant_argument_values
+    - avoid_returning_this
+    - avoid_unused_constructor_parameters
+    - avoid_void_async
+    - cancel_subscriptions
+    - join_return_with_assignment
+    - literal_only_boolean_expressions
+    - missing_whitespace_between_adjacent_strings
+    - no_adjacent_strings_in_list
+    - no_runtimeType_toString
+    - prefer_const_declarations
+    - prefer_expression_function_bodies
+    - prefer_final_locals
+    - unnecessary_await_in_return
+    - unnecessary_breaks
+    - use_if_null_to_convert_nulls_to_bools
+    - use_raw_strings
+    - use_string_buffers

diff --git a/pkgs/term_glyph/data.csv b/pkgs/term_glyph/data.csv
new file mode 100644
index 0000000..92a72f7
--- /dev/null
+++ b/pkgs/term_glyph/data.csv

@@ -0,0 +1,85 @@
+# Miscellaneous
+bullet,•,*,A bullet point.
+
+# Arrows
+leftArrow,←,<,"A left-pointing arrow.
+
+Note that the Unicode arrow glyphs may overlap with adjacent characters in some
+terminal fonts, and should generally be surrounding by spaces."
+rightArrow,→,>,"A right-pointing arrow.
+
+Note that the Unicode arrow glyphs may overlap with adjacent characters in some
+terminal fonts, and should generally be surrounding by spaces."
+upArrow,↑,^,An upwards-pointing arrow.
+downArrow,↓,v,A downwards-pointing arrow.
+longLeftArrow,◀━,<=,A two-character left-pointing arrow.
+longRightArrow,━▶,=>,A two-character right-pointing arrow.
+
+# Box drawing characters
+
+## Normal
+horizontalLine,─,-,A horizontal line that can be used to draw a box.
+verticalLine,│,|,A vertical line that can be used to draw a box.
+topLeftCorner,┌,",",The upper left-hand corner of a box.
+topRightCorner,┐,",",The upper right-hand corner of a box.
+bottomLeftCorner,└,',The lower left-hand corner of a box.
+bottomRightCorner,┘,',The lower right-hand corner of a box.
+cross,┼,+,An intersection of vertical and horizontal box lines.
+teeUp,┴,+,A horizontal box line with a vertical line going up from the middle.
+teeDown,┬,+,A horizontal box line with a vertical line going down from the middle.
+teeLeft,┤,+,A vertical box line with a horizontal line going left from the middle.
+teeRight,├,+,A vertical box line with a horizontal line going right from the middle.
+upEnd,╵,',The top half of a vertical box line.
+downEnd,╷,",",The bottom half of a vertical box line.
+leftEnd,╴,-,The left half of a horizontal box line.
+rightEnd,╶,-,The right half of a horizontal box line.
+
+## Bold
+horizontalLineBold,━,=,A bold horizontal line that can be used to draw a box.
+verticalLineBold,┃,|,A bold vertical line that can be used to draw a box.
+topLeftCornerBold,┏,",",The bold upper left-hand corner of a box.
+topRightCornerBold,┓,",",The bold upper right-hand corner of a box.
+bottomLeftCornerBold,┗,',The bold lower left-hand corner of a box.
+bottomRightCornerBold,┛,',The bold lower right-hand corner of a box.
+crossBold,╋,+,An intersection of bold vertical and horizontal box lines.
+teeUpBold,┻,+,A bold horizontal box line with a vertical line going up from the middle.
+teeDownBold,┳,+,A bold horizontal box line with a vertical line going down from the middle.
+teeLeftBold,┫,+,A bold vertical box line with a horizontal line going left from the middle.
+teeRightBold,┣,+,A bold vertical box line with a horizontal line going right from the middle.
+upEndBold,╹,',The top half of a bold vertical box line.
+downEndBold,╻,",",The bottom half of a bold vertical box line.
+leftEndBold,╸,-,The left half of a bold horizontal box line.
+rightEndBold,╺,-,The right half of a bold horizontal box line.
+
+## Double
+horizontalLineDouble,═,=,A double horizontal line that can be used to draw a box.
+verticalLineDouble,║,|,A double vertical line that can be used to draw a box.
+topLeftCornerDouble,╔,",",The double upper left-hand corner of a box.
+topRightCornerDouble,╗,",",The double upper right-hand corner of a box.
+bottomLeftCornerDouble,╚,"""",The double lower left-hand corner of a box.
+bottomRightCornerDouble,╝,"""",The double lower right-hand corner of a box.
+crossDouble,╬,+,An intersection of double vertical and horizontal box lines.
+teeUpDouble,╩,+,A double horizontal box line with a vertical line going up from the middle.
+teeDownDouble,╦,+,A double horizontal box line with a vertical line going down from the middle.
+teeLeftDouble,╣,+,A double vertical box line with a horizontal line going left from the middle.
+teeRightDouble,╠,+,A double vertical box line with a horizontal line going right from the middle.
+
+## Dashed
+
+### Double
+horizontalLineDoubleDash,╌,-,A dashed horizontal line that can be used to draw a box.
+horizontalLineDoubleDashBold,╍,-,A bold dashed horizontal line that can be used to draw a box.
+verticalLineDoubleDash,╎,|,A dashed vertical line that can be used to draw a box.
+verticalLineDoubleDashBold,╏,|,A bold dashed vertical line that can be used to draw a box.
+
+### Triple
+horizontalLineTripleDash,┄,-,A dashed horizontal line that can be used to draw a box.
+horizontalLineTripleDashBold,┅,-,A bold dashed horizontal line that can be used to draw a box.
+verticalLineTripleDash,┆,|,A dashed vertical line that can be used to draw a box.
+verticalLineTripleDashBold,┇,|,A bold dashed vertical line that can be used to draw a box.
+
+### Quadruple
+horizontalLineQuadrupleDash,┈,-,A dashed horizontal line that can be used to draw a box.
+horizontalLineQuadrupleDashBold,┉,-,A bold dashed horizontal line that can be used to draw a box.
+verticalLineQuadrupleDash,┊,|,A dashed vertical line that can be used to draw a box.
+verticalLineQuadrupleDashBold,┋,|,A bold dashed vertical line that can be used to draw a box.

diff --git a/pkgs/term_glyph/lib/src/generated/ascii_glyph_set.dart b/pkgs/term_glyph/lib/src/generated/ascii_glyph_set.dart
new file mode 100644
index 0000000..08534a0
--- /dev/null
+++ b/pkgs/term_glyph/lib/src/generated/ascii_glyph_set.dart

@@ -0,0 +1,139 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Don't modify this file by hand! It's generated by tool/generate.dart.
+
+// ignore_for_file: lines_longer_than_80_chars
+
+import 'glyph_set.dart';
+
+/// A [GlyphSet] that includes only ASCII glyphs.
+class AsciiGlyphSet implements GlyphSet {
+  const AsciiGlyphSet();
+
+  /// Returns [glyph] if `this` supports Unicode glyphs and [alternative]
+  /// otherwise.
+  @override
+  String glyphOrAscii(String glyph, String alternative) => alternative;
+  @override
+  String get bullet => '*';
+  @override
+  String get leftArrow => '<';
+  @override
+  String get rightArrow => '>';
+  @override
+  String get upArrow => '^';
+  @override
+  String get downArrow => 'v';
+  @override
+  String get longLeftArrow => '<=';
+  @override
+  String get longRightArrow => '=>';
+  @override
+  String get horizontalLine => '-';
+  @override
+  String get verticalLine => '|';
+  @override
+  String get topLeftCorner => ',';
+  @override
+  String get topRightCorner => ',';
+  @override
+  String get bottomLeftCorner => "'";
+  @override
+  String get bottomRightCorner => "'";
+  @override
+  String get cross => '+';
+  @override
+  String get teeUp => '+';
+  @override
+  String get teeDown => '+';
+  @override
+  String get teeLeft => '+';
+  @override
+  String get teeRight => '+';
+  @override
+  String get upEnd => "'";
+  @override
+  String get downEnd => ',';
+  @override
+  String get leftEnd => '-';
+  @override
+  String get rightEnd => '-';
+  @override
+  String get horizontalLineBold => '=';
+  @override
+  String get verticalLineBold => '|';
+  @override
+  String get topLeftCornerBold => ',';
+  @override
+  String get topRightCornerBold => ',';
+  @override
+  String get bottomLeftCornerBold => "'";
+  @override
+  String get bottomRightCornerBold => "'";
+  @override
+  String get crossBold => '+';
+  @override
+  String get teeUpBold => '+';
+  @override
+  String get teeDownBold => '+';
+  @override
+  String get teeLeftBold => '+';
+  @override
+  String get teeRightBold => '+';
+  @override
+  String get upEndBold => "'";
+  @override
+  String get downEndBold => ',';
+  @override
+  String get leftEndBold => '-';
+  @override
+  String get rightEndBold => '-';
+  @override
+  String get horizontalLineDouble => '=';
+  @override
+  String get verticalLineDouble => '|';
+  @override
+  String get topLeftCornerDouble => ',';
+  @override
+  String get topRightCornerDouble => ',';
+  @override
+  String get bottomLeftCornerDouble => '"';
+  @override
+  String get bottomRightCornerDouble => '"';
+  @override
+  String get crossDouble => '+';
+  @override
+  String get teeUpDouble => '+';
+  @override
+  String get teeDownDouble => '+';
+  @override
+  String get teeLeftDouble => '+';
+  @override
+  String get teeRightDouble => '+';
+  @override
+  String get horizontalLineDoubleDash => '-';
+  @override
+  String get horizontalLineDoubleDashBold => '-';
+  @override
+  String get verticalLineDoubleDash => '|';
+  @override
+  String get verticalLineDoubleDashBold => '|';
+  @override
+  String get horizontalLineTripleDash => '-';
+  @override
+  String get horizontalLineTripleDashBold => '-';
+  @override
+  String get verticalLineTripleDash => '|';
+  @override
+  String get verticalLineTripleDashBold => '|';
+  @override
+  String get horizontalLineQuadrupleDash => '-';
+  @override
+  String get horizontalLineQuadrupleDashBold => '-';
+  @override
+  String get verticalLineQuadrupleDash => '|';
+  @override
+  String get verticalLineQuadrupleDashBold => '|';
+}

diff --git a/pkgs/term_glyph/lib/src/generated/glyph_set.dart b/pkgs/term_glyph/lib/src/generated/glyph_set.dart
new file mode 100644
index 0000000..c8cc4a9
--- /dev/null
+++ b/pkgs/term_glyph/lib/src/generated/glyph_set.dart

@@ -0,0 +1,222 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Don't modify this file by hand! It's generated by tool/generate.dart.
+
+// ignore_for_file: lines_longer_than_80_chars
+
+/// A class that provides access to every configurable glyph.
+///
+/// This is provided as a class so that individual chunks of code can choose
+/// between `ascii` and `unicode` glyphs. For example:
+///
+/// ```dart
+/// import 'package:term_glyph/term_glyph.dart' as glyph;
+///
+/// /// Adds a vertical line to the left of [text].
+/// ///
+/// /// If [unicode] is `true`, this uses Unicode for the line. If it's
+/// /// `false`, this uses plain ASCII characters. If it's `null`, it
+/// /// defaults to [glyph.ascii].
+/// void addVerticalLine(String text, {bool unicode}) {
+///   var glyphs =
+///       (unicode ?? !glyph.ascii) ? glyph.unicodeGlyphs : glyph.asciiGlyphs;
+///
+///   return text
+///       .split('\n')
+///       .map((line) => '${glyphs.verticalLine} $line')
+///       .join('\n');
+/// }
+/// ```
+abstract class GlyphSet {
+  /// Returns [glyph] if `this` supports Unicode glyphs and [alternative]
+  /// otherwise.
+  String glyphOrAscii(String glyph, String alternative);
+
+  /// A bullet point.
+  String get bullet;
+
+  /// A left-pointing arrow.
+  ///
+  /// Note that the Unicode arrow glyphs may overlap with adjacent characters in some
+  /// terminal fonts, and should generally be surrounding by spaces.
+  String get leftArrow;
+
+  /// A right-pointing arrow.
+  ///
+  /// Note that the Unicode arrow glyphs may overlap with adjacent characters in some
+  /// terminal fonts, and should generally be surrounding by spaces.
+  String get rightArrow;
+
+  /// An upwards-pointing arrow.
+  String get upArrow;
+
+  /// A downwards-pointing arrow.
+  String get downArrow;
+
+  /// A two-character left-pointing arrow.
+  String get longLeftArrow;
+
+  /// A two-character right-pointing arrow.
+  String get longRightArrow;
+
+  /// A horizontal line that can be used to draw a box.
+  String get horizontalLine;
+
+  /// A vertical line that can be used to draw a box.
+  String get verticalLine;
+
+  /// The upper left-hand corner of a box.
+  String get topLeftCorner;
+
+  /// The upper right-hand corner of a box.
+  String get topRightCorner;
+
+  /// The lower left-hand corner of a box.
+  String get bottomLeftCorner;
+
+  /// The lower right-hand corner of a box.
+  String get bottomRightCorner;
+
+  /// An intersection of vertical and horizontal box lines.
+  String get cross;
+
+  /// A horizontal box line with a vertical line going up from the middle.
+  String get teeUp;
+
+  /// A horizontal box line with a vertical line going down from the middle.
+  String get teeDown;
+
+  /// A vertical box line with a horizontal line going left from the middle.
+  String get teeLeft;
+
+  /// A vertical box line with a horizontal line going right from the middle.
+  String get teeRight;
+
+  /// The top half of a vertical box line.
+  String get upEnd;
+
+  /// The bottom half of a vertical box line.
+  String get downEnd;
+
+  /// The left half of a horizontal box line.
+  String get leftEnd;
+
+  /// The right half of a horizontal box line.
+  String get rightEnd;
+
+  /// A bold horizontal line that can be used to draw a box.
+  String get horizontalLineBold;
+
+  /// A bold vertical line that can be used to draw a box.
+  String get verticalLineBold;
+
+  /// The bold upper left-hand corner of a box.
+  String get topLeftCornerBold;
+
+  /// The bold upper right-hand corner of a box.
+  String get topRightCornerBold;
+
+  /// The bold lower left-hand corner of a box.
+  String get bottomLeftCornerBold;
+
+  /// The bold lower right-hand corner of a box.
+  String get bottomRightCornerBold;
+
+  /// An intersection of bold vertical and horizontal box lines.
+  String get crossBold;
+
+  /// A bold horizontal box line with a vertical line going up from the middle.
+  String get teeUpBold;
+
+  /// A bold horizontal box line with a vertical line going down from the middle.
+  String get teeDownBold;
+
+  /// A bold vertical box line with a horizontal line going left from the middle.
+  String get teeLeftBold;
+
+  /// A bold vertical box line with a horizontal line going right from the middle.
+  String get teeRightBold;
+
+  /// The top half of a bold vertical box line.
+  String get upEndBold;
+
+  /// The bottom half of a bold vertical box line.
+  String get downEndBold;
+
+  /// The left half of a bold horizontal box line.
+  String get leftEndBold;
+
+  /// The right half of a bold horizontal box line.
+  String get rightEndBold;
+
+  /// A double horizontal line that can be used to draw a box.
+  String get horizontalLineDouble;
+
+  /// A double vertical line that can be used to draw a box.
+  String get verticalLineDouble;
+
+  /// The double upper left-hand corner of a box.
+  String get topLeftCornerDouble;
+
+  /// The double upper right-hand corner of a box.
+  String get topRightCornerDouble;
+
+  /// The double lower left-hand corner of a box.
+  String get bottomLeftCornerDouble;
+
+  /// The double lower right-hand corner of a box.
+  String get bottomRightCornerDouble;
+
+  /// An intersection of double vertical and horizontal box lines.
+  String get crossDouble;
+
+  /// A double horizontal box line with a vertical line going up from the middle.
+  String get teeUpDouble;
+
+  /// A double horizontal box line with a vertical line going down from the middle.
+  String get teeDownDouble;
+
+  /// A double vertical box line with a horizontal line going left from the middle.
+  String get teeLeftDouble;
+
+  /// A double vertical box line with a horizontal line going right from the middle.
+  String get teeRightDouble;
+
+  /// A dashed horizontal line that can be used to draw a box.
+  String get horizontalLineDoubleDash;
+
+  /// A bold dashed horizontal line that can be used to draw a box.
+  String get horizontalLineDoubleDashBold;
+
+  /// A dashed vertical line that can be used to draw a box.
+  String get verticalLineDoubleDash;
+
+  /// A bold dashed vertical line that can be used to draw a box.
+  String get verticalLineDoubleDashBold;
+
+  /// A dashed horizontal line that can be used to draw a box.
+  String get horizontalLineTripleDash;
+
+  /// A bold dashed horizontal line that can be used to draw a box.
+  String get horizontalLineTripleDashBold;
+
+  /// A dashed vertical line that can be used to draw a box.
+  String get verticalLineTripleDash;
+
+  /// A bold dashed vertical line that can be used to draw a box.
+  String get verticalLineTripleDashBold;
+
+  /// A dashed horizontal line that can be used to draw a box.
+  String get horizontalLineQuadrupleDash;
+
+  /// A bold dashed horizontal line that can be used to draw a box.
+  String get horizontalLineQuadrupleDashBold;
+
+  /// A dashed vertical line that can be used to draw a box.
+  String get verticalLineQuadrupleDash;
+
+  /// A bold dashed vertical line that can be used to draw a box.
+  String get verticalLineQuadrupleDashBold;
+}

diff --git a/pkgs/term_glyph/lib/src/generated/top_level.dart b/pkgs/term_glyph/lib/src/generated/top_level.dart
new file mode 100644
index 0000000..848ef6d
--- /dev/null
+++ b/pkgs/term_glyph/lib/src/generated/top_level.dart

@@ -0,0 +1,382 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Don't modify this file by hand! It's generated by tool/generate.dart.
+
+// ignore_for_file: lines_longer_than_80_chars
+
+import '../../term_glyph.dart' as glyph;
+
+/// A bullet point.
+///
+/// If [glyph.ascii] is `false`, this is "•". If it's `true`, this is
+/// "*" instead.
+String get bullet => glyph.glyphs.bullet;
+
+/// A left-pointing arrow.
+///
+/// Note that the Unicode arrow glyphs may overlap with adjacent characters in some
+/// terminal fonts, and should generally be surrounding by spaces.
+///
+/// If [glyph.ascii] is `false`, this is "←". If it's `true`, this is
+/// "<" instead.
+String get leftArrow => glyph.glyphs.leftArrow;
+
+/// A right-pointing arrow.
+///
+/// Note that the Unicode arrow glyphs may overlap with adjacent characters in some
+/// terminal fonts, and should generally be surrounding by spaces.
+///
+/// If [glyph.ascii] is `false`, this is "→". If it's `true`, this is
+/// ">" instead.
+String get rightArrow => glyph.glyphs.rightArrow;
+
+/// An upwards-pointing arrow.
+///
+/// If [glyph.ascii] is `false`, this is "↑". If it's `true`, this is
+/// "^" instead.
+String get upArrow => glyph.glyphs.upArrow;
+
+/// A downwards-pointing arrow.
+///
+/// If [glyph.ascii] is `false`, this is "↓". If it's `true`, this is
+/// "v" instead.
+String get downArrow => glyph.glyphs.downArrow;
+
+/// A two-character left-pointing arrow.
+///
+/// If [glyph.ascii] is `false`, this is "◀━". If it's `true`, this is
+/// "<=" instead.
+String get longLeftArrow => glyph.glyphs.longLeftArrow;
+
+/// A two-character right-pointing arrow.
+///
+/// If [glyph.ascii] is `false`, this is "━▶". If it's `true`, this is
+/// "=>" instead.
+String get longRightArrow => glyph.glyphs.longRightArrow;
+
+/// A horizontal line that can be used to draw a box.
+///
+/// If [glyph.ascii] is `false`, this is "─". If it's `true`, this is
+/// "-" instead.
+String get horizontalLine => glyph.glyphs.horizontalLine;
+
+/// A vertical line that can be used to draw a box.
+///
+/// If [glyph.ascii] is `false`, this is "│". If it's `true`, this is
+/// "|" instead.
+String get verticalLine => glyph.glyphs.verticalLine;
+
+/// The upper left-hand corner of a box.
+///
+/// If [glyph.ascii] is `false`, this is "┌". If it's `true`, this is
+/// "," instead.
+String get topLeftCorner => glyph.glyphs.topLeftCorner;
+
+/// The upper right-hand corner of a box.
+///
+/// If [glyph.ascii] is `false`, this is "┐". If it's `true`, this is
+/// "," instead.
+String get topRightCorner => glyph.glyphs.topRightCorner;
+
+/// The lower left-hand corner of a box.
+///
+/// If [glyph.ascii] is `false`, this is "└". If it's `true`, this is
+/// "'" instead.
+String get bottomLeftCorner => glyph.glyphs.bottomLeftCorner;
+
+/// The lower right-hand corner of a box.
+///
+/// If [glyph.ascii] is `false`, this is "┘". If it's `true`, this is
+/// "'" instead.
+String get bottomRightCorner => glyph.glyphs.bottomRightCorner;
+
+/// An intersection of vertical and horizontal box lines.
+///
+/// If [glyph.ascii] is `false`, this is "┼". If it's `true`, this is
+/// "+" instead.
+String get cross => glyph.glyphs.cross;
+
+/// A horizontal box line with a vertical line going up from the middle.
+///
+/// If [glyph.ascii] is `false`, this is "┴". If it's `true`, this is
+/// "+" instead.
+String get teeUp => glyph.glyphs.teeUp;
+
+/// A horizontal box line with a vertical line going down from the middle.
+///
+/// If [glyph.ascii] is `false`, this is "┬". If it's `true`, this is
+/// "+" instead.
+String get teeDown => glyph.glyphs.teeDown;
+
+/// A vertical box line with a horizontal line going left from the middle.
+///
+/// If [glyph.ascii] is `false`, this is "┤". If it's `true`, this is
+/// "+" instead.
+String get teeLeft => glyph.glyphs.teeLeft;
+
+/// A vertical box line with a horizontal line going right from the middle.
+///
+/// If [glyph.ascii] is `false`, this is "├". If it's `true`, this is
+/// "+" instead.
+String get teeRight => glyph.glyphs.teeRight;
+
+/// The top half of a vertical box line.
+///
+/// If [glyph.ascii] is `false`, this is "╵". If it's `true`, this is
+/// "'" instead.
+String get upEnd => glyph.glyphs.upEnd;
+
+/// The bottom half of a vertical box line.
+///
+/// If [glyph.ascii] is `false`, this is "╷". If it's `true`, this is
+/// "," instead.
+String get downEnd => glyph.glyphs.downEnd;
+
+/// The left half of a horizontal box line.
+///
+/// If [glyph.ascii] is `false`, this is "╴". If it's `true`, this is
+/// "-" instead.
+String get leftEnd => glyph.glyphs.leftEnd;
+
+/// The right half of a horizontal box line.
+///
+/// If [glyph.ascii] is `false`, this is "╶". If it's `true`, this is
+/// "-" instead.
+String get rightEnd => glyph.glyphs.rightEnd;
+
+/// A bold horizontal line that can be used to draw a box.
+///
+/// If [glyph.ascii] is `false`, this is "━". If it's `true`, this is
+/// "=" instead.
+String get horizontalLineBold => glyph.glyphs.horizontalLineBold;
+
+/// A bold vertical line that can be used to draw a box.
+///
+/// If [glyph.ascii] is `false`, this is "┃". If it's `true`, this is
+/// "|" instead.
+String get verticalLineBold => glyph.glyphs.verticalLineBold;
+
+/// The bold upper left-hand corner of a box.
+///
+/// If [glyph.ascii] is `false`, this is "┏". If it's `true`, this is
+/// "," instead.
+String get topLeftCornerBold => glyph.glyphs.topLeftCornerBold;
+
+/// The bold upper right-hand corner of a box.
+///
+/// If [glyph.ascii] is `false`, this is "┓". If it's `true`, this is
+/// "," instead.
+String get topRightCornerBold => glyph.glyphs.topRightCornerBold;
+
+/// The bold lower left-hand corner of a box.
+///
+/// If [glyph.ascii] is `false`, this is "┗". If it's `true`, this is
+/// "'" instead.
+String get bottomLeftCornerBold => glyph.glyphs.bottomLeftCornerBold;
+
+/// The bold lower right-hand corner of a box.
+///
+/// If [glyph.ascii] is `false`, this is "┛". If it's `true`, this is
+/// "'" instead.
+String get bottomRightCornerBold => glyph.glyphs.bottomRightCornerBold;
+
+/// An intersection of bold vertical and horizontal box lines.
+///
+/// If [glyph.ascii] is `false`, this is "╋". If it's `true`, this is
+/// "+" instead.
+String get crossBold => glyph.glyphs.crossBold;
+
+/// A bold horizontal box line with a vertical line going up from the middle.
+///
+/// If [glyph.ascii] is `false`, this is "┻". If it's `true`, this is
+/// "+" instead.
+String get teeUpBold => glyph.glyphs.teeUpBold;
+
+/// A bold horizontal box line with a vertical line going down from the middle.
+///
+/// If [glyph.ascii] is `false`, this is "┳". If it's `true`, this is
+/// "+" instead.
+String get teeDownBold => glyph.glyphs.teeDownBold;
+
+/// A bold vertical box line with a horizontal line going left from the middle.
+///
+/// If [glyph.ascii] is `false`, this is "┫". If it's `true`, this is
+/// "+" instead.
+String get teeLeftBold => glyph.glyphs.teeLeftBold;
+
+/// A bold vertical box line with a horizontal line going right from the middle.
+///
+/// If [glyph.ascii] is `false`, this is "┣". If it's `true`, this is
+/// "+" instead.
+String get teeRightBold => glyph.glyphs.teeRightBold;
+
+/// The top half of a bold vertical box line.
+///
+/// If [glyph.ascii] is `false`, this is "╹". If it's `true`, this is
+/// "'" instead.
+String get upEndBold => glyph.glyphs.upEndBold;
+
+/// The bottom half of a bold vertical box line.
+///
+/// If [glyph.ascii] is `false`, this is "╻". If it's `true`, this is
+/// "," instead.
+String get downEndBold => glyph.glyphs.downEndBold;
+
+/// The left half of a bold horizontal box line.
+///
+/// If [glyph.ascii] is `false`, this is "╸". If it's `true`, this is
+/// "-" instead.
+String get leftEndBold => glyph.glyphs.leftEndBold;
+
+/// The right half of a bold horizontal box line.
+///
+/// If [glyph.ascii] is `false`, this is "╺". If it's `true`, this is
+/// "-" instead.
+String get rightEndBold => glyph.glyphs.rightEndBold;
+
+/// A double horizontal line that can be used to draw a box.
+///
+/// If [glyph.ascii] is `false`, this is "═". If it's `true`, this is
+/// "=" instead.
+String get horizontalLineDouble => glyph.glyphs.horizontalLineDouble;
+
+/// A double vertical line that can be used to draw a box.
+///
+/// If [glyph.ascii] is `false`, this is "║". If it's `true`, this is
+/// "|" instead.
+String get verticalLineDouble => glyph.glyphs.verticalLineDouble;
+
+/// The double upper left-hand corner of a box.
+///
+/// If [glyph.ascii] is `false`, this is "╔". If it's `true`, this is
+/// "," instead.
+String get topLeftCornerDouble => glyph.glyphs.topLeftCornerDouble;
+
+/// The double upper right-hand corner of a box.
+///
+/// If [glyph.ascii] is `false`, this is "╗". If it's `true`, this is
+/// "," instead.
+String get topRightCornerDouble => glyph.glyphs.topRightCornerDouble;
+
+/// The double lower left-hand corner of a box.
+///
+/// If [glyph.ascii] is `false`, this is "╚". If it's `true`, this is
+/// """ instead.
+String get bottomLeftCornerDouble => glyph.glyphs.bottomLeftCornerDouble;
+
+/// The double lower right-hand corner of a box.
+///
+/// If [glyph.ascii] is `false`, this is "╝". If it's `true`, this is
+/// """ instead.
+String get bottomRightCornerDouble => glyph.glyphs.bottomRightCornerDouble;
+
+/// An intersection of double vertical and horizontal box lines.
+///
+/// If [glyph.ascii] is `false`, this is "╬". If it's `true`, this is
+/// "+" instead.
+String get crossDouble => glyph.glyphs.crossDouble;
+
+/// A double horizontal box line with a vertical line going up from the middle.
+///
+/// If [glyph.ascii] is `false`, this is "╩". If it's `true`, this is
+/// "+" instead.
+String get teeUpDouble => glyph.glyphs.teeUpDouble;
+
+/// A double horizontal box line with a vertical line going down from the middle.
+///
+/// If [glyph.ascii] is `false`, this is "╦". If it's `true`, this is
+/// "+" instead.
+String get teeDownDouble => glyph.glyphs.teeDownDouble;
+
+/// A double vertical box line with a horizontal line going left from the middle.
+///
+/// If [glyph.ascii] is `false`, this is "╣". If it's `true`, this is
+/// "+" instead.
+String get teeLeftDouble => glyph.glyphs.teeLeftDouble;
+
+/// A double vertical box line with a horizontal line going right from the middle.
+///
+/// If [glyph.ascii] is `false`, this is "╠". If it's `true`, this is
+/// "+" instead.
+String get teeRightDouble => glyph.glyphs.teeRightDouble;
+
+/// A dashed horizontal line that can be used to draw a box.
+///
+/// If [glyph.ascii] is `false`, this is "╌". If it's `true`, this is
+/// "-" instead.
+String get horizontalLineDoubleDash => glyph.glyphs.horizontalLineDoubleDash;
+
+/// A bold dashed horizontal line that can be used to draw a box.
+///
+/// If [glyph.ascii] is `false`, this is "╍". If it's `true`, this is
+/// "-" instead.
+String get horizontalLineDoubleDashBold =>
+    glyph.glyphs.horizontalLineDoubleDashBold;
+
+/// A dashed vertical line that can be used to draw a box.
+///
+/// If [glyph.ascii] is `false`, this is "╎". If it's `true`, this is
+/// "|" instead.
+String get verticalLineDoubleDash => glyph.glyphs.verticalLineDoubleDash;
+
+/// A bold dashed vertical line that can be used to draw a box.
+///
+/// If [glyph.ascii] is `false`, this is "╏". If it's `true`, this is
+/// "|" instead.
+String get verticalLineDoubleDashBold =>
+    glyph.glyphs.verticalLineDoubleDashBold;
+
+/// A dashed horizontal line that can be used to draw a box.
+///
+/// If [glyph.ascii] is `false`, this is "┄". If it's `true`, this is
+/// "-" instead.
+String get horizontalLineTripleDash => glyph.glyphs.horizontalLineTripleDash;
+
+/// A bold dashed horizontal line that can be used to draw a box.
+///
+/// If [glyph.ascii] is `false`, this is "┅". If it's `true`, this is
+/// "-" instead.
+String get horizontalLineTripleDashBold =>
+    glyph.glyphs.horizontalLineTripleDashBold;
+
+/// A dashed vertical line that can be used to draw a box.
+///
+/// If [glyph.ascii] is `false`, this is "┆". If it's `true`, this is
+/// "|" instead.
+String get verticalLineTripleDash => glyph.glyphs.verticalLineTripleDash;
+
+/// A bold dashed vertical line that can be used to draw a box.
+///
+/// If [glyph.ascii] is `false`, this is "┇". If it's `true`, this is
+/// "|" instead.
+String get verticalLineTripleDashBold =>
+    glyph.glyphs.verticalLineTripleDashBold;
+
+/// A dashed horizontal line that can be used to draw a box.
+///
+/// If [glyph.ascii] is `false`, this is "┈". If it's `true`, this is
+/// "-" instead.
+String get horizontalLineQuadrupleDash =>
+    glyph.glyphs.horizontalLineQuadrupleDash;
+
+/// A bold dashed horizontal line that can be used to draw a box.
+///
+/// If [glyph.ascii] is `false`, this is "┉". If it's `true`, this is
+/// "-" instead.
+String get horizontalLineQuadrupleDashBold =>
+    glyph.glyphs.horizontalLineQuadrupleDashBold;
+
+/// A dashed vertical line that can be used to draw a box.
+///
+/// If [glyph.ascii] is `false`, this is "┊". If it's `true`, this is
+/// "|" instead.
+String get verticalLineQuadrupleDash => glyph.glyphs.verticalLineQuadrupleDash;
+
+/// A bold dashed vertical line that can be used to draw a box.
+///
+/// If [glyph.ascii] is `false`, this is "┋". If it's `true`, this is
+/// "|" instead.
+String get verticalLineQuadrupleDashBold =>
+    glyph.glyphs.verticalLineQuadrupleDashBold;

diff --git a/pkgs/term_glyph/lib/src/generated/unicode_glyph_set.dart b/pkgs/term_glyph/lib/src/generated/unicode_glyph_set.dart
new file mode 100644
index 0000000..7264e6d
--- /dev/null
+++ b/pkgs/term_glyph/lib/src/generated/unicode_glyph_set.dart

@@ -0,0 +1,139 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Don't modify this file by hand! It's generated by tool/generate.dart.
+
+// ignore_for_file: lines_longer_than_80_chars
+
+import 'glyph_set.dart';
+
+/// A [GlyphSet] that includes only Unicode glyphs.
+class UnicodeGlyphSet implements GlyphSet {
+  const UnicodeGlyphSet();
+
+  /// Returns [glyph] if `this` supports Unicode glyphs and [alternative]
+  /// otherwise.
+  @override
+  String glyphOrAscii(String glyph, String alternative) => glyph;
+  @override
+  String get bullet => '•';
+  @override
+  String get leftArrow => '←';
+  @override
+  String get rightArrow => '→';
+  @override
+  String get upArrow => '↑';
+  @override
+  String get downArrow => '↓';
+  @override
+  String get longLeftArrow => '◀━';
+  @override
+  String get longRightArrow => '━▶';
+  @override
+  String get horizontalLine => '─';
+  @override
+  String get verticalLine => '│';
+  @override
+  String get topLeftCorner => '┌';
+  @override
+  String get topRightCorner => '┐';
+  @override
+  String get bottomLeftCorner => '└';
+  @override
+  String get bottomRightCorner => '┘';
+  @override
+  String get cross => '┼';
+  @override
+  String get teeUp => '┴';
+  @override
+  String get teeDown => '┬';
+  @override
+  String get teeLeft => '┤';
+  @override
+  String get teeRight => '├';
+  @override
+  String get upEnd => '╵';
+  @override
+  String get downEnd => '╷';
+  @override
+  String get leftEnd => '╴';
+  @override
+  String get rightEnd => '╶';
+  @override
+  String get horizontalLineBold => '━';
+  @override
+  String get verticalLineBold => '┃';
+  @override
+  String get topLeftCornerBold => '┏';
+  @override
+  String get topRightCornerBold => '┓';
+  @override
+  String get bottomLeftCornerBold => '┗';
+  @override
+  String get bottomRightCornerBold => '┛';
+  @override
+  String get crossBold => '╋';
+  @override
+  String get teeUpBold => '┻';
+  @override
+  String get teeDownBold => '┳';
+  @override
+  String get teeLeftBold => '┫';
+  @override
+  String get teeRightBold => '┣';
+  @override
+  String get upEndBold => '╹';
+  @override
+  String get downEndBold => '╻';
+  @override
+  String get leftEndBold => '╸';
+  @override
+  String get rightEndBold => '╺';
+  @override
+  String get horizontalLineDouble => '═';
+  @override
+  String get verticalLineDouble => '║';
+  @override
+  String get topLeftCornerDouble => '╔';
+  @override
+  String get topRightCornerDouble => '╗';
+  @override
+  String get bottomLeftCornerDouble => '╚';
+  @override
+  String get bottomRightCornerDouble => '╝';
+  @override
+  String get crossDouble => '╬';
+  @override
+  String get teeUpDouble => '╩';
+  @override
+  String get teeDownDouble => '╦';
+  @override
+  String get teeLeftDouble => '╣';
+  @override
+  String get teeRightDouble => '╠';
+  @override
+  String get horizontalLineDoubleDash => '╌';
+  @override
+  String get horizontalLineDoubleDashBold => '╍';
+  @override
+  String get verticalLineDoubleDash => '╎';
+  @override
+  String get verticalLineDoubleDashBold => '╏';
+  @override
+  String get horizontalLineTripleDash => '┄';
+  @override
+  String get horizontalLineTripleDashBold => '┅';
+  @override
+  String get verticalLineTripleDash => '┆';
+  @override
+  String get verticalLineTripleDashBold => '┇';
+  @override
+  String get horizontalLineQuadrupleDash => '┈';
+  @override
+  String get horizontalLineQuadrupleDashBold => '┉';
+  @override
+  String get verticalLineQuadrupleDash => '┊';
+  @override
+  String get verticalLineQuadrupleDashBold => '┋';
+}

diff --git a/pkgs/term_glyph/lib/term_glyph.dart b/pkgs/term_glyph/lib/term_glyph.dart
new file mode 100644
index 0000000..9f2b422
--- /dev/null
+++ b/pkgs/term_glyph/lib/term_glyph.dart

@@ -0,0 +1,37 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'src/generated/ascii_glyph_set.dart';
+import 'src/generated/glyph_set.dart';
+import 'src/generated/unicode_glyph_set.dart';
+
+export 'src/generated/glyph_set.dart';
+export 'src/generated/top_level.dart';
+
+/// A [GlyphSet] that always returns ASCII glyphs.
+const GlyphSet asciiGlyphs = AsciiGlyphSet();
+
+/// A [GlyphSet] that always returns Unicode glyphs.
+const GlyphSet unicodeGlyphs = UnicodeGlyphSet();
+
+/// Returns [asciiGlyphs] if [ascii] is `true` or [unicodeGlyphs] otherwise.
+///
+/// Returns [unicodeGlyphs] by default.
+GlyphSet get glyphs => _glyphs;
+GlyphSet _glyphs = unicodeGlyphs;
+
+/// Whether the glyph getters return plain ASCII, as opposed to Unicode
+/// characters or sequences.
+///
+/// Defaults to `false`.
+bool get ascii => glyphs == asciiGlyphs;
+
+set ascii(bool value) {
+  _glyphs = value ? asciiGlyphs : unicodeGlyphs;
+}
+
+/// Returns [glyph] if Unicode glyph are allowed, and [alternative] if they
+/// aren't.
+String glyphOrAscii(String glyph, String alternative) =>
+    glyphs.glyphOrAscii(glyph, alternative);

diff --git a/pkgs/term_glyph/pubspec.yaml b/pkgs/term_glyph/pubspec.yaml
new file mode 100644
index 0000000..bac16f1
--- /dev/null
+++ b/pkgs/term_glyph/pubspec.yaml

@@ -0,0 +1,12 @@
+name: term_glyph
+version: 1.2.3-wip
+description: Useful Unicode glyphs and ASCII substitutes.
+repository: https://github.com/dart-lang/tools/tree/main/pkgs/term_glyph
+
+environment:
+  sdk: ^3.1.0
+
+dev_dependencies:
+  csv: ^6.0.0
+  dart_flutter_team_lints: ^3.0.0
+  test: ^1.16.6

diff --git a/pkgs/term_glyph/test/symbol_test.dart b/pkgs/term_glyph/test/symbol_test.dart
new file mode 100644
index 0000000..b3b4d09
--- /dev/null
+++ b/pkgs/term_glyph/test/symbol_test.dart

@@ -0,0 +1,60 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:term_glyph/term_glyph.dart' as glyph;
+import 'package:test/test.dart';
+
+void main() {
+  group('with ascii = false', () {
+    setUpAll(() {
+      glyph.ascii = false;
+    });
+
+    test('glyph getters return Unicode versions', () {
+      expect(glyph.topLeftCorner, equals('┌'));
+      expect(glyph.teeUpBold, equals('┻'));
+      expect(glyph.longLeftArrow, equals('◀━'));
+    });
+
+    test('glyphOrAscii returns the first argument', () {
+      expect(glyph.glyphOrAscii('A', 'B'), equals('A'));
+    });
+
+    test('glyphs returns unicodeGlyphs', () {
+      expect(glyph.glyphs, equals(glyph.unicodeGlyphs));
+    });
+
+    test('asciiGlyphs still returns ASCII characters', () {
+      expect(glyph.asciiGlyphs.topLeftCorner, equals(','));
+      expect(glyph.asciiGlyphs.teeUpBold, equals('+'));
+      expect(glyph.asciiGlyphs.longLeftArrow, equals('<='));
+    });
+  });
+
+  group('with ascii = true', () {
+    setUpAll(() {
+      glyph.ascii = true;
+    });
+
+    test('glyphs return ASCII versions', () {
+      expect(glyph.topLeftCorner, equals(','));
+      expect(glyph.teeUpBold, equals('+'));
+      expect(glyph.longLeftArrow, equals('<='));
+    });
+
+    test('glyphOrAscii returns the second argument', () {
+      expect(glyph.glyphOrAscii('A', 'B'), equals('B'));
+    });
+
+    test('glyphs returns asciiGlyphs', () {
+      expect(glyph.glyphs, equals(glyph.asciiGlyphs));
+    });
+
+    test('unicodeGlyphs still returns Unicode characters', () {
+      expect(glyph.unicodeGlyphs.topLeftCorner, equals('┌'));
+      expect(glyph.unicodeGlyphs.teeUpBold, equals('┻'));
+      expect(glyph.unicodeGlyphs.longLeftArrow, equals('◀━'));
+    });
+  });
+}

diff --git a/pkgs/term_glyph/tool/generate.dart b/pkgs/term_glyph/tool/generate.dart
new file mode 100644
index 0000000..b96b7bd
--- /dev/null
+++ b/pkgs/term_glyph/tool/generate.dart

@@ -0,0 +1,156 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:io';
+
+import 'package:csv/csv.dart';
+
+void main() {
+  final csv = CsvCodec(eol: '\n');
+  final data = csv.decoder.convert(File('data.csv').readAsStringSync());
+
+  // Remove comments and empty lines.
+  data.removeWhere((row) => row.length < 3);
+
+  Directory(_generatedDir).createSync(recursive: true);
+
+  _writeGlyphSetInterface(data);
+  _writeGlyphSet(data, ascii: false);
+  _writeGlyphSet(data, ascii: true);
+  _writeTopLevel(data);
+
+  final result = Process.runSync(Platform.resolvedExecutable, [
+    'format',
+    _generatedDir,
+  ]);
+  print(result.stderr);
+  exit(result.exitCode);
+}
+
+const _generatedDir = 'lib/src/generated';
+
+/// Writes `lib/src/generated/glyph_set.dart`.
+void _writeGlyphSetInterface(List<List<dynamic>> data) {
+  final file =
+      File('$_generatedDir/glyph_set.dart').openSync(mode: FileMode.write);
+  file.writeStringSync(_header);
+  file.writeStringSync(r'''
+
+    /// A class that provides access to every configurable glyph.
+    ///
+    /// This is provided as a class so that individual chunks of code can choose
+    /// between `ascii` and `unicode` glyphs. For example:
+    ///
+    /// ```dart
+    /// import 'package:term_glyph/term_glyph.dart' as glyph;
+    ///
+    /// /// Adds a vertical line to the left of [text].
+    /// ///
+    /// /// If [unicode] is `true`, this uses Unicode for the line. If it's
+    /// /// `false`, this uses plain ASCII characters. If it's `null`, it
+    /// /// defaults to [glyph.ascii].
+    /// void addVerticalLine(String text, {bool unicode}) {
+    ///   var glyphs =
+    ///       (unicode ?? !glyph.ascii) ? glyph.unicodeGlyphs : glyph.asciiGlyphs;
+    ///
+    ///   return text
+    ///       .split('\n')
+    ///       .map((line) => '${glyphs.verticalLine} $line')
+    ///       .join('\n');
+    /// }
+    /// ```
+    abstract class GlyphSet {
+      /// Returns [glyph] if `this` supports Unicode glyphs and [alternative]
+      /// otherwise.
+      String glyphOrAscii(String glyph, String alternative);
+  ''');
+
+  for (var glyph in data) {
+    for (var line in (glyph[3] as String).split('\n')) {
+      file.writeStringSync('/// $line\n');
+    }
+
+    file.writeStringSync('String get ${glyph[0]};');
+  }
+
+  file.writeStringSync('}');
+  file.closeSync();
+}
+
+/// Writes `lib/src/generated/${prefix.toLowerCase()}_glyph_set.dart`.
+///
+/// If [ascii] is `true`, this writes the ASCII glyph set. Otherwise it writes
+/// the Unicode glyph set.
+void _writeGlyphSet(List<List<dynamic>> data, {required bool ascii}) {
+  final file =
+      File('$_generatedDir/${ascii ? "ascii" : "unicode"}_glyph_set.dart')
+          .openSync(mode: FileMode.write);
+
+  final className = '${ascii ? "Ascii" : "Unicode"}GlyphSet';
+  file.writeStringSync('''
+    $_header
+
+
+    import 'glyph_set.dart';
+
+    /// A [GlyphSet] that includes only ${ascii ? "ASCII" : "Unicode"} glyphs.
+    class $className implements GlyphSet {
+      const $className();
+      /// Returns [glyph] if `this` supports Unicode glyphs and [alternative]
+      /// otherwise.
+      @override
+      String glyphOrAscii(String glyph, String alternative) =>
+          ${ascii ? "alternative" : "glyph"};
+  ''');
+
+  final index = ascii ? 2 : 1;
+  for (var glyph in data) {
+    file.writeStringSync('''
+      @override
+      String get ${glyph[0]} => ${_quote(glyph[index] as String)};
+    ''');
+  }
+
+  file.writeStringSync('}');
+  file.closeSync();
+}
+
+/// Writes `lib/src/generated/top_level.dart`.
+void _writeTopLevel(List<List<dynamic>> data) {
+  final file =
+      File('$_generatedDir/top_level.dart').openSync(mode: FileMode.write);
+
+  file.writeStringSync('''
+    $_header
+
+    import '../../term_glyph.dart' as glyph;
+  ''');
+
+  for (var glyph in data) {
+    for (var line in (glyph[3] as String).split('\n')) {
+      file.writeStringSync('/// $line\n');
+    }
+
+    file.writeStringSync('''
+      ///
+      /// If [glyph.ascii] is `false`, this is "${glyph[1]}". If it's `true`, this is
+      /// "${glyph[2]}" instead.
+      String get ${glyph[0]} => glyph.glyphs.${glyph[0]};
+    ''');
+  }
+
+  file.closeSync();
+}
+
+String _quote(String input) => input.contains("'") ? '"$input"' : "'$input'";
+
+const _header = '''
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Don't modify this file by hand! It's generated by tool/generate.dart.
+
+// ignore_for_file: lines_longer_than_80_chars
+''';

diff --git a/pkgs/test_reflective_loader/.gitignore b/pkgs/test_reflective_loader/.gitignore
new file mode 100644
index 0000000..2a2c261
--- /dev/null
+++ b/pkgs/test_reflective_loader/.gitignore

@@ -0,0 +1,11 @@
+.buildlog
+.DS_Store
+.idea
+.dart_tool/
+.pub/
+.project
+.settings/
+build/
+packages
+.packages
+pubspec.lock

diff --git a/pkgs/test_reflective_loader/AUTHORS b/pkgs/test_reflective_loader/AUTHORS
new file mode 100644
index 0000000..e8063a8
--- /dev/null
+++ b/pkgs/test_reflective_loader/AUTHORS

@@ -0,0 +1,6 @@
+# Below is a list of people and organizations that have contributed
+# to the project. Names should be added to the list like so:
+#
+#   Name/Organization <email address>
+
+Google Inc.

diff --git a/pkgs/test_reflective_loader/CHANGELOG.md b/pkgs/test_reflective_loader/CHANGELOG.md
new file mode 100644
index 0000000..803eb0e
--- /dev/null
+++ b/pkgs/test_reflective_loader/CHANGELOG.md

@@ -0,0 +1,72 @@
+## 0.2.3
+
+- Require Dart `^3.1.0`.
+- Move to `dart-lang/tools` monorepo.
+
+## 0.2.2
+
+- Update to package:lints 2.0.0 and move it to a dev dependency.
+
+## 0.2.1
+
+- Use package:lints for analysis.
+- Populate the pubspec `repository` field.
+
+## 0.2.0
+
+- Stable null safety release.
+
+## 0.2.0-nullsafety.0
+
+- Migrate to the null safety language feature.
+
+## 0.1.9
+
+- Add `@SkippedTest` annotation and `skip_test` prefix.
+
+## 0.1.8
+
+- Update `FailingTest` to add named parameters `issue` and `reason`.
+
+## 0.1.7
+
+- Update documentation comments.
+- Remove `@MirrorsUsed` annotation on `dart:mirrors`.
+
+## 0.1.6
+
+- Make `FailingTest` public, with the URI of the issue that causes
+  the test to break.
+
+## 0.1.5
+
+- Set max SDK version to `<3.0.0`, and adjust other dependencies.
+
+## 0.1.3
+
+- Fix `@failingTest` to fail when the test passes.
+
+## 0.1.2
+
+- Update the pubspec `dependencies` section to include `package:test`
+
+## 0.1.1
+
+- For `@failingTest` tests, properly handle when the test fails by throwing an
+  exception in a timer task
+- Analyze this package in strong mode
+
+## 0.1.0
+
+- Switched from 'package:unittest' to 'package:test'.
+- Since 'package:test' does not define 'solo_test', in order to keep this
+  functionality, `defineReflectiveSuite` must be used to wrap all
+  `defineReflectiveTests` invocations.
+
+## 0.0.4
+
+- Added @failingTest, @assertFailingTest and @soloTest annotations.
+
+## 0.0.1
+
+- Initial version

diff --git a/pkgs/test_reflective_loader/LICENSE b/pkgs/test_reflective_loader/LICENSE
new file mode 100644
index 0000000..633672a
--- /dev/null
+++ b/pkgs/test_reflective_loader/LICENSE

@@ -0,0 +1,27 @@
+Copyright 2015, the Dart project authors.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+    * Neither the name of Google LLC nor the names of its
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

diff --git a/pkgs/test_reflective_loader/README.md b/pkgs/test_reflective_loader/README.md
new file mode 100644
index 0000000..9b5a83d
--- /dev/null
+++ b/pkgs/test_reflective_loader/README.md

@@ -0,0 +1,28 @@
+[![Build Status](https://github.com/dart-lang/tools/actions/workflows/test_reflective_loader.yaml/badge.svg)](https://github.com/dart-lang/tools/actions/workflows/test_reflective_loader.yaml)
+[![pub package](https://img.shields.io/pub/v/test_reflective_loader.svg)](https://pub.dev/packages/test_reflective_loader)
+[![package publisher](https://img.shields.io/pub/publisher/test_reflective_loader.svg)](https://pub.dev/packages/test_reflective_loader/publisher)
+
+Support for discovering tests and test suites using reflection.
+
+This package follows the xUnit style where each class is a test suite, and each
+method with the name prefix `test_` is a single test.
+
+Methods with names starting with `test_` are run using the `test()` function with
+the corresponding name. If the class defines methods `setUp()` or `tearDown()`,
+they are executed before / after each test correspondingly, even if the test fails.
+
+Methods with names starting with `solo_test_` are run using the `solo_test()` function.
+
+Methods with names starting with `fail_` are expected to fail.
+
+Methods with names starting with `solo_fail_` are run using the `solo_test()` function
+and expected to fail.
+
+Method returning `Future` class instances are asynchronous, so `tearDown()` is
+executed after the returned `Future` completes.
+
+## Features and bugs
+
+Please file feature requests and bugs at the [issue tracker][tracker].
+
+[tracker]: https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Atest_reflective_loader

diff --git a/pkgs/test_reflective_loader/analysis_options.yaml b/pkgs/test_reflective_loader/analysis_options.yaml
new file mode 100644
index 0000000..ea61158
--- /dev/null
+++ b/pkgs/test_reflective_loader/analysis_options.yaml

@@ -0,0 +1,5 @@
+include: package:dart_flutter_team_lints/analysis_options.yaml
+
+linter:
+  rules:
+    - public_member_api_docs

diff --git a/pkgs/test_reflective_loader/lib/test_reflective_loader.dart b/pkgs/test_reflective_loader/lib/test_reflective_loader.dart
new file mode 100644
index 0000000..cb69bf3
--- /dev/null
+++ b/pkgs/test_reflective_loader/lib/test_reflective_loader.dart

@@ -0,0 +1,354 @@
+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+import 'dart:mirrors';
+
+import 'package:test/test.dart' as test_package;
+
+/// A marker annotation used to annotate test methods which are expected to fail
+/// when asserts are enabled.
+const Object assertFailingTest = _AssertFailingTest();
+
+/// A marker annotation used to annotate test methods which are expected to
+/// fail.
+const Object failingTest = FailingTest();
+
+/// A marker annotation used to instruct dart2js to keep reflection information
+/// for the annotated classes.
+const Object reflectiveTest = _ReflectiveTest();
+
+/// A marker annotation used to annotate test methods that should be skipped.
+const Object skippedTest = SkippedTest();
+
+/// A marker annotation used to annotate "solo" groups and tests.
+const Object soloTest = _SoloTest();
+
+final List<_Group> _currentGroups = <_Group>[];
+int _currentSuiteLevel = 0;
+String _currentSuiteName = '';
+
+/// Is `true` the application is running in the checked mode.
+final bool _isCheckedMode = () {
+  try {
+    assert(false);
+    return false;
+  } catch (_) {
+    return true;
+  }
+}();
+
+/// Run the [define] function parameter that calls [defineReflectiveTests] to
+/// add normal and "solo" tests, and also calls [defineReflectiveSuite] to
+/// create embedded suites.  If the current suite is the top-level one, perform
+/// check for "solo" groups and tests, and run all or only "solo" items.
+void defineReflectiveSuite(void Function() define, {String name = ''}) {
+  var groupName = _currentSuiteName;
+  _currentSuiteLevel++;
+  try {
+    _currentSuiteName = _combineNames(_currentSuiteName, name);
+    define();
+  } finally {
+    _currentSuiteName = groupName;
+    _currentSuiteLevel--;
+  }
+  _addTestsIfTopLevelSuite();
+}
+
+/// Runs test methods existing in the given [type].
+///
+/// If there is a "solo" test method in the top-level suite, only "solo" methods
+/// are run.
+///
+/// If there is a "solo" test type, only its test methods are run.
+///
+/// Otherwise all tests methods of all test types are run.
+///
+/// Each method is run with a new instance of [type].
+/// So, [type] should have a default constructor.
+///
+/// If [type] declares method `setUp`, it methods will be invoked before any
+/// test method invocation.
+///
+/// If [type] declares method `tearDown`, it will be invoked after any test
+/// method invocation. If method returns [Future] to test some asynchronous
+/// behavior, then `tearDown` will be invoked in `Future.complete`.
+void defineReflectiveTests(Type type) {
+  var classMirror = reflectClass(type);
+  if (!classMirror.metadata.any((InstanceMirror annotation) =>
+      annotation.type.reflectedType == _ReflectiveTest)) {
+    var name = MirrorSystem.getName(classMirror.qualifiedName);
+    throw Exception('Class $name must have annotation "@reflectiveTest" '
+        'in order to be run by runReflectiveTests.');
+  }
+
+  _Group group;
+  {
+    var isSolo = _hasAnnotationInstance(classMirror, soloTest);
+    var className = MirrorSystem.getName(classMirror.simpleName);
+    group = _Group(isSolo, _combineNames(_currentSuiteName, className));
+    _currentGroups.add(group);
+  }
+
+  classMirror.instanceMembers
+      .forEach((Symbol symbol, MethodMirror memberMirror) {
+    // we need only methods
+    if (!memberMirror.isRegularMethod) {
+      return;
+    }
+    // prepare information about the method
+    var memberName = MirrorSystem.getName(symbol);
+    var isSolo = memberName.startsWith('solo_') ||
+        _hasAnnotationInstance(memberMirror, soloTest);
+    // test_
+    if (memberName.startsWith('test_')) {
+      if (_hasSkippedTestAnnotation(memberMirror)) {
+        group.addSkippedTest(memberName);
+      } else {
+        group.addTest(isSolo, memberName, memberMirror, () {
+          if (_hasFailingTestAnnotation(memberMirror) ||
+              _isCheckedMode && _hasAssertFailingTestAnnotation(memberMirror)) {
+            return _runFailingTest(classMirror, symbol);
+          } else {
+            return _runTest(classMirror, symbol);
+          }
+        });
+      }
+      return;
+    }
+    // solo_test_
+    if (memberName.startsWith('solo_test_')) {
+      group.addTest(true, memberName, memberMirror, () {
+        return _runTest(classMirror, symbol);
+      });
+    }
+    // fail_test_
+    if (memberName.startsWith('fail_')) {
+      group.addTest(isSolo, memberName, memberMirror, () {
+        return _runFailingTest(classMirror, symbol);
+      });
+    }
+    // solo_fail_test_
+    if (memberName.startsWith('solo_fail_')) {
+      group.addTest(true, memberName, memberMirror, () {
+        return _runFailingTest(classMirror, symbol);
+      });
+    }
+    // skip_test_
+    if (memberName.startsWith('skip_test_')) {
+      group.addSkippedTest(memberName);
+    }
+  });
+
+  // Support for the case of missing enclosing [defineReflectiveSuite].
+  _addTestsIfTopLevelSuite();
+}
+
+/// If the current suite is the top-level one, add tests to the `test` package.
+void _addTestsIfTopLevelSuite() {
+  if (_currentSuiteLevel == 0) {
+    void runTests({required bool allGroups, required bool allTests}) {
+      for (var group in _currentGroups) {
+        if (allGroups || group.isSolo) {
+          for (var test in group.tests) {
+            if (allTests || test.isSolo) {
+              test_package.test(test.name, test.function,
+                  timeout: test.timeout, skip: test.isSkipped);
+            }
+          }
+        }
+      }
+    }
+
+    if (_currentGroups.any((g) => g.hasSoloTest)) {
+      runTests(allGroups: true, allTests: false);
+    } else if (_currentGroups.any((g) => g.isSolo)) {
+      runTests(allGroups: false, allTests: true);
+    } else {
+      runTests(allGroups: true, allTests: true);
+    }
+    _currentGroups.clear();
+  }
+}
+
+/// Return the combination of the [base] and [addition] names.
+/// If any other two is `null`, then the other one is returned.
+String _combineNames(String base, String addition) {
+  if (base.isEmpty) {
+    return addition;
+  } else if (addition.isEmpty) {
+    return base;
+  } else {
+    return '$base | $addition';
+  }
+}
+
+Object? _getAnnotationInstance(DeclarationMirror declaration, Type type) {
+  for (var annotation in declaration.metadata) {
+    if ((annotation.reflectee as Object).runtimeType == type) {
+      return annotation.reflectee;
+    }
+  }
+  return null;
+}
+
+bool _hasAnnotationInstance(DeclarationMirror declaration, Object instance) =>
+    declaration.metadata.any((InstanceMirror annotation) =>
+        identical(annotation.reflectee, instance));
+
+bool _hasAssertFailingTestAnnotation(MethodMirror method) =>
+    _hasAnnotationInstance(method, assertFailingTest);
+
+bool _hasFailingTestAnnotation(MethodMirror method) =>
+    _hasAnnotationInstance(method, failingTest);
+
+bool _hasSkippedTestAnnotation(MethodMirror method) =>
+    _hasAnnotationInstance(method, skippedTest);
+
+Future<Object?> _invokeSymbolIfExists(
+    InstanceMirror instanceMirror, Symbol symbol) {
+  Object? invocationResult;
+  InstanceMirror? closure;
+  try {
+    closure = instanceMirror.getField(symbol);
+    // ignore: avoid_catching_errors
+  } on NoSuchMethodError {
+    // ignore
+  }
+
+  if (closure is ClosureMirror) {
+    invocationResult = closure.apply([]).reflectee;
+  }
+  return Future.value(invocationResult);
+}
+
+/// Run a test that is expected to fail, and confirm that it fails.
+///
+/// This properly handles the following cases:
+/// - The test fails by throwing an exception
+/// - The test returns a future which completes with an error.
+/// - An exception is thrown to the zone handler from a timer task.
+Future<Object?>? _runFailingTest(ClassMirror classMirror, Symbol symbol) {
+  var passed = false;
+  return runZonedGuarded(() {
+    // ignore: void_checks
+    return Future.sync(() => _runTest(classMirror, symbol)).then<void>((_) {
+      passed = true;
+      test_package.fail('Test passed - expected to fail.');
+    }).catchError((Object e) {
+      // if passed, and we call fail(), rethrow this exception
+      if (passed) {
+        // ignore: only_throw_errors
+        throw e;
+      }
+      // otherwise, an exception is not a failure for _runFailingTest
+    });
+  }, (e, st) {
+    // if passed, and we call fail(), rethrow this exception
+    if (passed) {
+      // ignore: only_throw_errors
+      throw e;
+    }
+    // otherwise, an exception is not a failure for _runFailingTest
+  });
+}
+
+Future<void> _runTest(ClassMirror classMirror, Symbol symbol) async {
+  var instanceMirror = classMirror.newInstance(const Symbol(''), []);
+  try {
+    await _invokeSymbolIfExists(instanceMirror, #setUp);
+    await instanceMirror.invoke(symbol, []).reflectee;
+  } finally {
+    await _invokeSymbolIfExists(instanceMirror, #tearDown);
+  }
+}
+
+typedef _TestFunction = dynamic Function();
+
+/// A marker annotation used to annotate test methods which are expected to
+/// fail.
+class FailingTest {
+  /// Initialize this annotation with the given arguments.
+  ///
+  /// [issue] is a full URI describing the failure and used for tracking.
+  /// [reason] is a free form textual description.
+  const FailingTest({String? issue, String? reason});
+}
+
+/// A marker annotation used to annotate test methods which are skipped.
+class SkippedTest {
+  /// Initialize this annotation with the given arguments.
+  ///
+  /// [issue] is a full URI describing the failure and used for tracking.
+  /// [reason] is a free form textual description.
+  const SkippedTest({String? issue, String? reason});
+}
+
+/// A marker annotation used to annotate test methods with additional timeout
+/// information.
+class TestTimeout {
+  final test_package.Timeout _timeout;
+
+  /// Initialize this annotation with the given timeout.
+  const TestTimeout(test_package.Timeout timeout) : _timeout = timeout;
+}
+
+/// A marker annotation used to annotate test methods which are expected to fail
+/// when asserts are enabled.
+class _AssertFailingTest {
+  const _AssertFailingTest();
+}
+
+/// Information about a type based test group.
+class _Group {
+  final bool isSolo;
+  final String name;
+  final List<_Test> tests = <_Test>[];
+
+  _Group(this.isSolo, this.name);
+
+  bool get hasSoloTest => tests.any((test) => test.isSolo);
+
+  void addSkippedTest(String name) {
+    var fullName = _combineNames(this.name, name);
+    tests.add(_Test.skipped(isSolo, fullName));
+  }
+
+  void addTest(bool isSolo, String name, MethodMirror memberMirror,
+      _TestFunction function) {
+    var fullName = _combineNames(this.name, name);
+    var timeout =
+        _getAnnotationInstance(memberMirror, TestTimeout) as TestTimeout?;
+    tests.add(_Test(isSolo, fullName, function, timeout?._timeout));
+  }
+}
+
+/// A marker annotation used to instruct dart2js to keep reflection information
+/// for the annotated classes.
+class _ReflectiveTest {
+  const _ReflectiveTest();
+}
+
+/// A marker annotation used to annotate "solo" groups and tests.
+class _SoloTest {
+  const _SoloTest();
+}
+
+/// Information about a test.
+class _Test {
+  final bool isSolo;
+  final String name;
+  final _TestFunction function;
+  final test_package.Timeout? timeout;
+
+  final bool isSkipped;
+
+  _Test(this.isSolo, this.name, this.function, this.timeout)
+      : isSkipped = false;
+
+  _Test.skipped(this.isSolo, this.name)
+      : isSkipped = true,
+        function = (() {}),
+        timeout = null;
+}

diff --git a/pkgs/test_reflective_loader/pubspec.yaml b/pkgs/test_reflective_loader/pubspec.yaml
new file mode 100644
index 0000000..569933f
--- /dev/null
+++ b/pkgs/test_reflective_loader/pubspec.yaml

@@ -0,0 +1,13 @@
+name: test_reflective_loader
+version: 0.2.3
+description: Support for discovering tests and test suites using reflection.
+repository: https://github.com/dart-lang/tools/tree/main/pkgs/test_reflective_loader
+
+environment:
+  sdk: ^3.1.0
+
+dependencies:
+  test: ^1.16.0
+
+dev_dependencies:
+  dart_flutter_team_lints: ^3.0.0

diff --git a/pkgs/test_reflective_loader/test/test_reflective_loader_test.dart b/pkgs/test_reflective_loader/test/test_reflective_loader_test.dart
new file mode 100644
index 0000000..fad98a5
--- /dev/null
+++ b/pkgs/test_reflective_loader/test/test_reflective_loader_test.dart

@@ -0,0 +1,48 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// ignore_for_file: non_constant_identifier_names
+
+import 'dart:async';
+
+import 'package:test/test.dart';
+import 'package:test_reflective_loader/test_reflective_loader.dart';
+
+void main() {
+  defineReflectiveSuite(() {
+    defineReflectiveTests(TestReflectiveLoaderTest);
+  });
+}
+
+@reflectiveTest
+class TestReflectiveLoaderTest {
+  void test_passes() {
+    expect(true, true);
+  }
+
+  @failingTest
+  void test_fails() {
+    expect(false, true);
+  }
+
+  @failingTest
+  void test_fails_throws_sync() {
+    throw StateError('foo');
+  }
+
+  @failingTest
+  Future test_fails_throws_async() {
+    return Future.error('foo');
+  }
+
+  @skippedTest
+  void test_fails_but_skipped() {
+    throw StateError('foo');
+  }
+
+  @skippedTest
+  void test_times_out_but_skipped() {
+    while (true) {}
+  }
+}

diff --git a/pkgs/timing/.gitignore b/pkgs/timing/.gitignore
new file mode 100644
index 0000000..1ddf798
--- /dev/null
+++ b/pkgs/timing/.gitignore

@@ -0,0 +1,7 @@
+.packages
+/build/
+pubspec.lock
+
+# Files generated by dart tools
+.dart_tool
+doc/

diff --git a/pkgs/timing/CHANGELOG.md b/pkgs/timing/CHANGELOG.md
new file mode 100644
index 0000000..8cdb8ea
--- /dev/null
+++ b/pkgs/timing/CHANGELOG.md

@@ -0,0 +1,34 @@
+## 1.0.2
+
+- Require Dart `3.4`.
+- Move to `dart-lang/tools` monorepo.
+
+## 1.0.1
+
+- Require Dart `2.14`.
+
+## 1.0.0
+
+- Enable null safety.
+- Require Dart `2.12`.
+
+## 0.1.1+3
+
+- Allow `package:json_annotation` `'>=1.0.0 <5.0.0'`.
+
+## 0.1.1+2
+
+- Support the latest version of `package:json_annotation`.
+- Require Dart 2.2 or later.
+
+## 0.1.1+1
+
+- Support the latest version of `package:json_annotation`.
+
+## 0.1.1
+
+- Add JSON serialization
+
+## 0.1.0
+
+- Initial release

diff --git a/pkgs/timing/LICENSE b/pkgs/timing/LICENSE
new file mode 100644
index 0000000..9972f6e
--- /dev/null
+++ b/pkgs/timing/LICENSE

@@ -0,0 +1,27 @@
+Copyright 2018, the Dart project authors. 
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+    * Neither the name of Google LLC nor the names of its
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

diff --git a/pkgs/timing/README.md b/pkgs/timing/README.md
new file mode 100644
index 0000000..9dab7cc
--- /dev/null
+++ b/pkgs/timing/README.md

@@ -0,0 +1,30 @@
+[![Build Status](https://github.com/dart-lang/tools/actions/workflows/timing.yaml/badge.svg)](https://github.com/dart-lang/tools/actions/workflows/timing.yaml)
+[![pub package](https://img.shields.io/pub/v/timing.svg)](https://pub.dev/packages/timing)
+[![package publisher](https://img.shields.io/pub/publisher/timing.svg)](https://pub.dev/packages/timing/publisher)
+
+Timing is a simple package for tracking performance of both async and sync actions
+
+## Usage
+
+```dart
+var tracker = AsyncTimeTracker();
+await tracker.track(() async {
+  // some async code here
+});
+
+// Use results
+print('${tracker.duration} ${tracker.innerDuration} ${tracker.slices}');
+```
+
+## Building
+
+Use the following command to re-generate `lib/src/timing.g.dart` file:
+
+```bash
+dart pub run build_runner build
+```
+
+## Publishing automation
+
+For information about our publishing automation and release process, see
+https://github.com/dart-lang/ecosystem/wiki/Publishing-automation.

diff --git a/pkgs/timing/analysis_options.yaml b/pkgs/timing/analysis_options.yaml
new file mode 100644
index 0000000..396236d
--- /dev/null
+++ b/pkgs/timing/analysis_options.yaml

@@ -0,0 +1,2 @@
+# https://dart.dev/tools/analysis#the-analysis-options-file
+include: package:dart_flutter_team_lints/analysis_options.yaml

diff --git a/pkgs/timing/lib/src/clock.dart b/pkgs/timing/lib/src/clock.dart
new file mode 100644
index 0000000..6a9d295
--- /dev/null
+++ b/pkgs/timing/lib/src/clock.dart

@@ -0,0 +1,20 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+/// A function that returns the current [DateTime].
+typedef _Clock = DateTime Function();
+DateTime _defaultClock() => DateTime.now();
+
+const _zoneKey = #timing_Clock;
+
+/// Returns the current [DateTime].
+///
+/// May be overridden for tests using [scopeClock].
+DateTime now() => (Zone.current[_zoneKey] as _Clock? ?? _defaultClock)();
+
+/// Runs [f], with [clock] scoped whenever [now] is called.
+T scopeClock<T>(DateTime Function() clock, T Function() f) =>
+    runZoned(f, zoneValues: {_zoneKey: clock});

diff --git a/pkgs/timing/lib/src/timing.dart b/pkgs/timing/lib/src/timing.dart
new file mode 100644
index 0000000..049ba81
--- /dev/null
+++ b/pkgs/timing/lib/src/timing.dart

@@ -0,0 +1,338 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:json_annotation/json_annotation.dart';
+
+import 'clock.dart';
+
+part 'timing.g.dart';
+
+/// The timings of an operation, including its [startTime], [stopTime], and
+/// [duration].
+@JsonSerializable()
+class TimeSlice {
+  /// The total duration of this operation, equivalent to taking the difference
+  /// between [stopTime] and [startTime].
+  Duration get duration => stopTime.difference(startTime);
+
+  final DateTime startTime;
+
+  final DateTime stopTime;
+
+  TimeSlice(this.startTime, this.stopTime);
+
+  factory TimeSlice.fromJson(Map<String, dynamic> json) =>
+      _$TimeSliceFromJson(json);
+
+  Map<String, dynamic> toJson() => _$TimeSliceToJson(this);
+
+  @override
+  String toString() => '($startTime + $duration)';
+}
+
+/// The timings of an async operation, consist of several sync [slices] and
+/// includes total [startTime], [stopTime], and [duration].
+@JsonSerializable()
+class TimeSliceGroup implements TimeSlice {
+  final List<TimeSlice> slices;
+
+  @override
+  DateTime get startTime => slices.first.startTime;
+
+  @override
+  DateTime get stopTime => slices.last.stopTime;
+
+  /// The total duration of this operation, equivalent to taking the difference
+  /// between [stopTime] and [startTime].
+  @override
+  Duration get duration => stopTime.difference(startTime);
+
+  /// Sum of [duration]s of all [slices].
+  ///
+  /// If some of slices implements [TimeSliceGroup] [innerDuration] will be used
+  /// to compute sum.
+  Duration get innerDuration => slices.fold(
+      Duration.zero,
+      (duration, slice) =>
+          duration +
+          (slice is TimeSliceGroup ? slice.innerDuration : slice.duration));
+
+  TimeSliceGroup(this.slices);
+
+  /// Constructs TimeSliceGroup from JSON representation
+  factory TimeSliceGroup.fromJson(Map<String, dynamic> json) =>
+      _$TimeSliceGroupFromJson(json);
+
+  @override
+  Map<String, dynamic> toJson() => _$TimeSliceGroupToJson(this);
+
+  @override
+  String toString() => slices.toString();
+}
+
+abstract class TimeTracker implements TimeSlice {
+  /// Whether tracking is active.
+  ///
+  /// Tracking is only active after `isStarted` and before `isFinished`.
+  bool get isTracking;
+
+  /// Whether tracking is finished.
+  ///
+  /// Tracker can't be used as [TimeSlice] before it is finished
+  bool get isFinished;
+
+  /// Whether tracking was started.
+  ///
+  /// Equivalent of `isTracking || isFinished`
+  bool get isStarted;
+
+  T track<T>(T Function() action);
+}
+
+/// Tracks only sync actions
+class SyncTimeTracker implements TimeTracker {
+  /// When this operation started, call [_start] to set this.
+  @override
+  DateTime get startTime => _startTime!;
+  DateTime? _startTime;
+
+  /// When this operation stopped, call [_stop] to set this.
+  @override
+  DateTime get stopTime => _stopTime!;
+  DateTime? _stopTime;
+
+  /// Start tracking this operation, must only be called once, before [_stop].
+  void _start() {
+    assert(_startTime == null && _stopTime == null);
+    _startTime = now();
+  }
+
+  /// Stop tracking this operation, must only be called once, after [_start].
+  void _stop() {
+    assert(_startTime != null && _stopTime == null);
+    _stopTime = now();
+  }
+
+  /// Splits tracker into two slices.
+  ///
+  /// Returns new [TimeSlice] started on [startTime] and ended now. Modifies
+  /// [startTime] of tracker to current time point
+  ///
+  /// Don't change state of tracker. Can be called only while [isTracking], and
+  /// tracker will sill be tracking after call.
+  TimeSlice _split() {
+    if (!isTracking) {
+      throw StateError('Can be only called while tracking');
+    }
+    final splitPoint = now();
+    final prevSlice = TimeSlice(_startTime!, splitPoint);
+    _startTime = splitPoint;
+    return prevSlice;
+  }
+
+  @override
+  T track<T>(T Function() action) {
+    if (isStarted) {
+      throw StateError('Can not be tracked twice');
+    }
+    _start();
+    try {
+      return action();
+    } finally {
+      _stop();
+    }
+  }
+
+  @override
+  bool get isStarted => _startTime != null;
+
+  @override
+  bool get isTracking => _startTime != null && _stopTime == null;
+
+  @override
+  bool get isFinished => _startTime != null && _stopTime != null;
+
+  @override
+  Duration get duration => _stopTime!.difference(_startTime!);
+
+  /// Converts to JSON representation
+  ///
+  /// Can't be used before [isFinished]
+  @override
+  Map<String, dynamic> toJson() => _$TimeSliceToJson(this);
+}
+
+/// Async actions returning [Future] will be tracked as single sync time span
+/// from the beginning of execution till completion of future
+class SimpleAsyncTimeTracker extends SyncTimeTracker {
+  @override
+  T track<T>(T Function() action) {
+    if (isStarted) {
+      throw StateError('Can not be tracked twice');
+    }
+    T result;
+    _start();
+    try {
+      result = action();
+    } catch (_) {
+      _stop();
+      rethrow;
+    }
+    if (result is Future) {
+      return result.whenComplete(_stop) as T;
+    } else {
+      _stop();
+      return result;
+    }
+  }
+}
+
+/// No-op implementation of [SyncTimeTracker] that does nothing.
+class NoOpTimeTracker implements TimeTracker {
+  static final sharedInstance = NoOpTimeTracker();
+
+  @override
+  Duration get duration =>
+      throw UnsupportedError('Unsupported in no-op implementation');
+
+  @override
+  DateTime get startTime =>
+      throw UnsupportedError('Unsupported in no-op implementation');
+
+  @override
+  DateTime get stopTime =>
+      throw UnsupportedError('Unsupported in no-op implementation');
+
+  @override
+  bool get isStarted =>
+      throw UnsupportedError('Unsupported in no-op implementation');
+
+  @override
+  bool get isTracking =>
+      throw UnsupportedError('Unsupported in no-op implementation');
+
+  @override
+  bool get isFinished =>
+      throw UnsupportedError('Unsupported in no-op implementation');
+
+  @override
+  T track<T>(T Function() action) => action();
+
+  @override
+  Map<String, dynamic> toJson() =>
+      throw UnsupportedError('Unsupported in no-op implementation');
+}
+
+/// Track all async execution as disjoint time [slices] in ascending order.
+///
+/// Can [track] both async and sync actions.
+/// Can exclude time of tested trackers.
+///
+/// If tracked action spawns some dangled async executions behavior is't
+/// defined. Tracked might or might not track time of such executions
+class AsyncTimeTracker extends TimeSliceGroup implements TimeTracker {
+  final bool trackNested;
+
+  static const _zoneKey = #timing_AsyncTimeTracker;
+
+  AsyncTimeTracker({this.trackNested = true}) : super([]);
+
+  T _trackSyncSlice<T>(ZoneDelegate parent, Zone zone, T Function() action) {
+    // Ignore dangling runs after tracker completes
+    if (isFinished) {
+      return action();
+    }
+
+    final isNestedRun = slices.isNotEmpty &&
+        slices.last is SyncTimeTracker &&
+        (slices.last as SyncTimeTracker).isTracking;
+    final isExcludedNestedTrack = !trackNested && zone[_zoneKey] != this;
+
+    // Exclude nested sync tracks
+    if (isNestedRun && isExcludedNestedTrack) {
+      final timer = slices.last as SyncTimeTracker;
+      // Split already tracked time into new slice.
+      // Replace tracker in slices.last with splitted slice, to indicate for
+      // recursive calls that we not tracking.
+      slices.last = parent.run(zone, timer._split);
+      try {
+        return action();
+      } finally {
+        // Split tracker again and discard slice from nested tracker
+        parent.run(zone, timer._split);
+        // Add tracker back to list of slices and continue tracking
+        slices.add(timer);
+      }
+    }
+
+    // Exclude nested async tracks
+    if (isExcludedNestedTrack) {
+      return action();
+    }
+
+    // Split time slices in nested sync runs
+    if (isNestedRun) {
+      return action();
+    }
+
+    final timer = SyncTimeTracker();
+    slices.add(timer);
+
+    // Pass to parent zone, in case of overwritten clock
+    return parent.runUnary(zone, timer.track, action);
+  }
+
+  static final asyncTimeTrackerZoneSpecification = ZoneSpecification(
+    run: <R>(Zone self, ZoneDelegate parent, Zone zone, R Function() f) {
+      final tracker = self[_zoneKey] as AsyncTimeTracker;
+      return tracker._trackSyncSlice(parent, zone, () => parent.run(zone, f));
+    },
+    runUnary: <R, T>(Zone self, ZoneDelegate parent, Zone zone, R Function(T) f,
+        T arg) {
+      final tracker = self[_zoneKey] as AsyncTimeTracker;
+      return tracker._trackSyncSlice(
+          parent, zone, () => parent.runUnary(zone, f, arg));
+    },
+    runBinary: <R, T1, T2>(Zone self, ZoneDelegate parent, Zone zone,
+        R Function(T1, T2) f, T1 arg1, T2 arg2) {
+      final tracker = self[_zoneKey] as AsyncTimeTracker;
+      return tracker._trackSyncSlice(
+          parent, zone, () => parent.runBinary(zone, f, arg1, arg2));
+    },
+  );
+
+  @override
+  T track<T>(T Function() action) {
+    if (isStarted) {
+      throw StateError('Can not be tracked twice');
+    }
+    _tracking = true;
+    final result = runZoned(action,
+        zoneSpecification: asyncTimeTrackerZoneSpecification,
+        zoneValues: {_zoneKey: this});
+    if (result is Future) {
+      return result
+          // Break possible sync processing of future completion, so slice
+          // trackers can be finished
+          .whenComplete(Future.value)
+          .whenComplete(() => _tracking = false) as T;
+    } else {
+      _tracking = false;
+      return result;
+    }
+  }
+
+  bool? _tracking;
+
+  @override
+  bool get isStarted => _tracking != null;
+
+  @override
+  bool get isFinished => _tracking == false;
+
+  @override
+  bool get isTracking => _tracking == true;
+}

diff --git a/pkgs/timing/lib/src/timing.g.dart b/pkgs/timing/lib/src/timing.g.dart
new file mode 100644
index 0000000..679c082
--- /dev/null
+++ b/pkgs/timing/lib/src/timing.g.dart

@@ -0,0 +1,29 @@
+// GENERATED CODE - DO NOT MODIFY BY HAND
+
+part of 'timing.dart';
+
+// **************************************************************************
+// JsonSerializableGenerator
+// **************************************************************************
+
+TimeSlice _$TimeSliceFromJson(Map<String, dynamic> json) => TimeSlice(
+      DateTime.parse(json['startTime'] as String),
+      DateTime.parse(json['stopTime'] as String),
+    );
+
+Map<String, dynamic> _$TimeSliceToJson(TimeSlice instance) => <String, dynamic>{
+      'startTime': instance.startTime.toIso8601String(),
+      'stopTime': instance.stopTime.toIso8601String(),
+    };
+
+TimeSliceGroup _$TimeSliceGroupFromJson(Map<String, dynamic> json) =>
+    TimeSliceGroup(
+      (json['slices'] as List<dynamic>)
+          .map((e) => TimeSlice.fromJson(e as Map<String, dynamic>))
+          .toList(),
+    );
+
+Map<String, dynamic> _$TimeSliceGroupToJson(TimeSliceGroup instance) =>
+    <String, dynamic>{
+      'slices': instance.slices,
+    };

diff --git a/pkgs/timing/lib/timing.dart b/pkgs/timing/lib/timing.dart
new file mode 100644
index 0000000..5cb16d4
--- /dev/null
+++ b/pkgs/timing/lib/timing.dart

@@ -0,0 +1,13 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+export 'src/timing.dart'
+    show
+        AsyncTimeTracker,
+        NoOpTimeTracker,
+        SimpleAsyncTimeTracker,
+        SyncTimeTracker,
+        TimeSlice,
+        TimeSliceGroup,
+        TimeTracker;

diff --git a/pkgs/timing/pubspec.yaml b/pkgs/timing/pubspec.yaml
new file mode 100644
index 0000000..891a8af
--- /dev/null
+++ b/pkgs/timing/pubspec.yaml

@@ -0,0 +1,18 @@
+name: timing
+version: 1.0.2
+description: >-
+  A simple package for tracking the performance of synchronous and asynchronous
+  actions.
+repository: https://github.com/dart-lang/tools/tree/main/pkgs/timing
+
+environment:
+  sdk: ^3.4.0
+
+dependencies:
+  json_annotation: ^4.9.0
+
+dev_dependencies:
+  build_runner: ^2.0.6
+  dart_flutter_team_lints: ^3.0.0
+  json_serializable: ^6.0.0
+  test: ^1.17.10

diff --git a/pkgs/timing/test/timing_test.dart b/pkgs/timing/test/timing_test.dart
new file mode 100644
index 0000000..b5836d9
--- /dev/null
+++ b/pkgs/timing/test/timing_test.dart

@@ -0,0 +1,416 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// ignore_for_file: only_throw_errors, inference_failure_on_instance_creation
+
+import 'dart:async';
+
+import 'package:test/test.dart';
+import 'package:timing/src/clock.dart';
+import 'package:timing/src/timing.dart';
+
+void _noop() {}
+
+void main() {
+  late DateTime time;
+  final startTime = DateTime(2017);
+  DateTime fakeClock() => time;
+
+  late TimeTracker tracker;
+  late TimeTracker nestedTracker;
+
+  T scopedTrack<T>(T Function() f) =>
+      scopeClock(fakeClock, () => tracker.track(f));
+
+  setUp(() {
+    time = startTime;
+  });
+
+  void canHandleSync([void Function() additionalExpects = _noop]) {
+    test('Can track sync code', () {
+      expect(tracker.isStarted, false);
+      expect(tracker.isTracking, false);
+      expect(tracker.isFinished, false);
+      scopedTrack(() {
+        expect(tracker.isStarted, true);
+        expect(tracker.isTracking, true);
+        expect(tracker.isFinished, false);
+        time = time.add(const Duration(seconds: 5));
+      });
+      expect(tracker.isStarted, true);
+      expect(tracker.isTracking, false);
+      expect(tracker.isFinished, true);
+      expect(tracker.startTime, startTime);
+      expect(tracker.stopTime, time);
+      expect(tracker.duration, const Duration(seconds: 5));
+      additionalExpects();
+    });
+
+    test('Can track handled sync exceptions', () async {
+      scopedTrack(() {
+        try {
+          time = time.add(const Duration(seconds: 4));
+          throw 'error';
+        } on String {
+          time = time.add(const Duration(seconds: 1));
+        }
+      });
+      expect(tracker.isFinished, true);
+      expect(tracker.startTime, startTime);
+      expect(tracker.stopTime, time);
+      expect(tracker.duration, const Duration(seconds: 5));
+      additionalExpects();
+    });
+
+    test('Can track in case of unhandled sync exceptions', () async {
+      expect(
+          () => scopedTrack(() {
+                time = time.add(const Duration(seconds: 5));
+                throw 'error';
+              }),
+          throwsA(const TypeMatcher<String>()));
+      expect(tracker.startTime, startTime);
+      expect(tracker.stopTime, time);
+      expect(tracker.duration, const Duration(seconds: 5));
+      additionalExpects();
+    });
+
+    test('Can be nested sync', () {
+      scopedTrack(() {
+        time = time.add(const Duration(seconds: 1));
+        nestedTracker.track(() {
+          time = time.add(const Duration(seconds: 2));
+        });
+        time = time.add(const Duration(seconds: 4));
+      });
+      expect(tracker.isFinished, true);
+      expect(tracker.startTime, startTime);
+      expect(tracker.stopTime, time);
+      expect(tracker.duration, const Duration(seconds: 7));
+      expect(nestedTracker.startTime.isAfter(startTime), true);
+      expect(nestedTracker.stopTime.isBefore(time), true);
+      expect(nestedTracker.duration, const Duration(seconds: 2));
+      additionalExpects();
+    });
+  }
+
+  void canHandleAsync([void Function() additionalExpects = _noop]) {
+    test('Can track async code', () async {
+      expect(tracker.isStarted, false);
+      expect(tracker.isTracking, false);
+      expect(tracker.isFinished, false);
+      await scopedTrack(() => Future(() {
+            expect(tracker.isStarted, true);
+            expect(tracker.isTracking, true);
+            expect(tracker.isFinished, false);
+            time = time.add(const Duration(seconds: 5));
+          }));
+      expect(tracker.isStarted, true);
+      expect(tracker.isTracking, false);
+      expect(tracker.isFinished, true);
+      expect(tracker.startTime, startTime);
+      expect(tracker.stopTime, time);
+      expect(tracker.duration, const Duration(seconds: 5));
+      additionalExpects();
+    });
+
+    test('Can track handled async exceptions', () async {
+      await scopedTrack(() {
+        time = time.add(const Duration(seconds: 1));
+        return Future(() {
+          time = time.add(const Duration(seconds: 2));
+          throw 'error';
+        }).then((_) {
+          time = time.add(const Duration(seconds: 4));
+        }).catchError((error, stack) {
+          time = time.add(const Duration(seconds: 8));
+        });
+      });
+      expect(tracker.isFinished, true);
+      expect(tracker.startTime, startTime);
+      expect(tracker.stopTime, time);
+      expect(tracker.duration, const Duration(seconds: 11));
+      additionalExpects();
+    });
+
+    test('Can track in case of unhandled async exceptions', () async {
+      final future = scopedTrack(() {
+        time = time.add(const Duration(seconds: 1));
+        return Future(() {
+          time = time.add(const Duration(seconds: 2));
+          throw 'error';
+        }).then((_) {
+          time = time.add(const Duration(seconds: 4));
+        });
+      });
+      await expectLater(future, throwsA(const TypeMatcher<String>()));
+      expect(tracker.isFinished, true);
+      expect(tracker.startTime, startTime);
+      expect(tracker.stopTime, time);
+      expect(tracker.duration, const Duration(seconds: 3));
+      additionalExpects();
+    });
+
+    test('Can be nested async', () async {
+      await scopedTrack(() async {
+        time = time.add(const Duration(milliseconds: 1));
+        await Future.value();
+        time = time.add(const Duration(milliseconds: 2));
+        await nestedTracker.track(() async {
+          time = time.add(const Duration(milliseconds: 4));
+          await Future.value();
+          time = time.add(const Duration(milliseconds: 8));
+          await Future.value();
+          time = time.add(const Duration(milliseconds: 16));
+        });
+        time = time.add(const Duration(milliseconds: 32));
+        await Future.value();
+        time = time.add(const Duration(milliseconds: 64));
+      });
+      expect(tracker.isFinished, true);
+      expect(tracker.startTime, startTime);
+      expect(tracker.stopTime, time);
+      expect(tracker.duration, const Duration(milliseconds: 127));
+      expect(nestedTracker.startTime.isAfter(startTime), true);
+      expect(nestedTracker.stopTime.isBefore(time), true);
+      expect(nestedTracker.duration, const Duration(milliseconds: 28));
+      additionalExpects();
+    });
+  }
+
+  group('SyncTimeTracker', () {
+    setUp(() {
+      tracker = SyncTimeTracker();
+      nestedTracker = SyncTimeTracker();
+    });
+
+    canHandleSync();
+
+    test('Can not track async code', () async {
+      await scopedTrack(() => Future(() {
+            time = time.add(const Duration(seconds: 5));
+          }));
+      expect(tracker.isFinished, true);
+      expect(tracker.startTime, startTime);
+      expect(tracker.stopTime, startTime);
+      expect(tracker.duration, const Duration(seconds: 0));
+    });
+  });
+
+  group('AsyncTimeTracker.simple', () {
+    setUp(() {
+      tracker = SimpleAsyncTimeTracker();
+      nestedTracker = SimpleAsyncTimeTracker();
+    });
+
+    canHandleSync();
+
+    canHandleAsync();
+
+    test('Can not distinguish own async code', () async {
+      final future = scopedTrack(() => Future(() {
+            time = time.add(const Duration(seconds: 5));
+          }));
+      time = time.add(const Duration(seconds: 10));
+      await future;
+      expect(tracker.isFinished, true);
+      expect(tracker.startTime, startTime);
+      expect(tracker.stopTime, time);
+      expect(tracker.duration, const Duration(seconds: 15));
+    });
+  });
+
+  group('AsyncTimeTracker', () {
+    late AsyncTimeTracker asyncTracker;
+    late AsyncTimeTracker nestedAsyncTracker;
+    setUp(() {
+      tracker = asyncTracker = AsyncTimeTracker();
+      nestedTracker = nestedAsyncTracker = AsyncTimeTracker();
+    });
+
+    canHandleSync(() {
+      expect(asyncTracker.innerDuration, asyncTracker.duration);
+      expect(asyncTracker.slices.length, 1);
+    });
+
+    canHandleAsync(() {
+      expect(asyncTracker.innerDuration, asyncTracker.duration);
+      expect(asyncTracker.slices.length, greaterThan(1));
+    });
+
+    test('Can track complex async innerDuration', () async {
+      final completer = Completer();
+      final future = scopedTrack(() async {
+        time = time.add(const Duration(seconds: 1)); // Tracked sync
+        await Future.value();
+        time = time.add(const Duration(seconds: 2)); // Tracked async
+        await completer.future;
+        time = time.add(const Duration(seconds: 4)); // Tracked async, delayed
+      }).then((_) {
+        time = time.add(const Duration(seconds: 8)); // Async, after tracking
+      });
+      time = time.add(const Duration(seconds: 16)); // Sync, between slices
+
+      await Future(() {
+        // Async, between slices
+        time = time.add(const Duration(seconds: 32));
+        completer.complete();
+      });
+      await future;
+      expect(asyncTracker.isFinished, true);
+      expect(asyncTracker.startTime, startTime);
+      expect(asyncTracker.stopTime.isBefore(time), true);
+      expect(asyncTracker.duration, const Duration(seconds: 55));
+      expect(asyncTracker.innerDuration, const Duration(seconds: 7));
+      expect(asyncTracker.slices.length, greaterThan(1));
+    });
+
+    test('Can exclude nested sync', () {
+      tracker = asyncTracker = AsyncTimeTracker(trackNested: false);
+      scopedTrack(() {
+        time = time.add(const Duration(seconds: 1));
+        nestedAsyncTracker.track(() {
+          time = time.add(const Duration(seconds: 2));
+        });
+        time = time.add(const Duration(seconds: 4));
+      });
+      expect(asyncTracker.isFinished, true);
+      expect(asyncTracker.startTime, startTime);
+      expect(asyncTracker.stopTime, time);
+      expect(asyncTracker.duration, const Duration(seconds: 7));
+      expect(asyncTracker.innerDuration, const Duration(seconds: 5));
+      expect(asyncTracker.slices.length, greaterThan(1));
+      expect(nestedAsyncTracker.startTime.isAfter(startTime), true);
+      expect(nestedAsyncTracker.stopTime.isBefore(time), true);
+      expect(nestedAsyncTracker.duration, const Duration(seconds: 2));
+      expect(nestedAsyncTracker.innerDuration, const Duration(seconds: 2));
+      expect(nestedAsyncTracker.slices.length, 1);
+    });
+
+    test('Can exclude complex nested sync', () {
+      tracker = asyncTracker = AsyncTimeTracker(trackNested: false);
+      nestedAsyncTracker = AsyncTimeTracker(trackNested: false);
+      final nestedAsyncTracker2 = AsyncTimeTracker(trackNested: false);
+      scopedTrack(() {
+        time = time.add(const Duration(seconds: 1));
+        nestedAsyncTracker.track(() {
+          time = time.add(const Duration(seconds: 2));
+          nestedAsyncTracker2.track(() {
+            time = time.add(const Duration(seconds: 4));
+          });
+          time = time.add(const Duration(seconds: 8));
+        });
+        time = time.add(const Duration(seconds: 16));
+      });
+      expect(asyncTracker.isFinished, true);
+      expect(asyncTracker.startTime, startTime);
+      expect(asyncTracker.stopTime, time);
+      expect(asyncTracker.duration, const Duration(seconds: 31));
+      expect(asyncTracker.innerDuration, const Duration(seconds: 17));
+      expect(asyncTracker.slices.length, greaterThan(1));
+      expect(nestedAsyncTracker.startTime.isAfter(startTime), true);
+      expect(nestedAsyncTracker.stopTime.isBefore(time), true);
+      expect(nestedAsyncTracker.duration, const Duration(seconds: 14));
+      expect(nestedAsyncTracker.innerDuration, const Duration(seconds: 10));
+      expect(nestedAsyncTracker.slices.length, greaterThan(1));
+      expect(nestedAsyncTracker2.startTime.isAfter(startTime), true);
+      expect(nestedAsyncTracker2.stopTime.isBefore(time), true);
+      expect(nestedAsyncTracker2.duration, const Duration(seconds: 4));
+      expect(nestedAsyncTracker2.innerDuration, const Duration(seconds: 4));
+      expect(nestedAsyncTracker2.slices.length, 1);
+    });
+
+    test(
+        'Can track all on grand-parent level and '
+        'exclude grand-childrens from parent', () {
+      tracker = asyncTracker = AsyncTimeTracker(trackNested: true);
+      nestedAsyncTracker = AsyncTimeTracker(trackNested: false);
+      final nestedAsyncTracker2 = AsyncTimeTracker();
+      scopedTrack(() {
+        time = time.add(const Duration(seconds: 1));
+        nestedAsyncTracker.track(() {
+          time = time.add(const Duration(seconds: 2));
+          nestedAsyncTracker2.track(() {
+            time = time.add(const Duration(seconds: 4));
+          });
+          time = time.add(const Duration(seconds: 8));
+        });
+        time = time.add(const Duration(seconds: 16));
+      });
+      expect(asyncTracker.isFinished, true);
+      expect(asyncTracker.startTime, startTime);
+      expect(asyncTracker.stopTime, time);
+      expect(asyncTracker.duration, const Duration(seconds: 31));
+      expect(asyncTracker.innerDuration, const Duration(seconds: 31));
+      expect(asyncTracker.slices.length, 1);
+      expect(nestedAsyncTracker.startTime.isAfter(startTime), true);
+      expect(nestedAsyncTracker.stopTime.isBefore(time), true);
+      expect(nestedAsyncTracker.duration, const Duration(seconds: 14));
+      expect(nestedAsyncTracker.innerDuration, const Duration(seconds: 10));
+      expect(nestedAsyncTracker.slices.length, greaterThan(1));
+      expect(nestedAsyncTracker2.startTime.isAfter(startTime), true);
+      expect(nestedAsyncTracker2.stopTime.isBefore(time), true);
+      expect(nestedAsyncTracker2.duration, const Duration(seconds: 4));
+      expect(nestedAsyncTracker2.innerDuration, const Duration(seconds: 4));
+      expect(nestedAsyncTracker2.slices.length, 1);
+    });
+
+    test('Can exclude nested async', () async {
+      tracker = asyncTracker = AsyncTimeTracker(trackNested: false);
+      await scopedTrack(() async {
+        time = time.add(const Duration(seconds: 1));
+        await nestedAsyncTracker.track(() async {
+          time = time.add(const Duration(seconds: 2));
+          await Future.value();
+          time = time.add(const Duration(seconds: 4));
+          await Future.value();
+          time = time.add(const Duration(seconds: 8));
+        });
+        time = time.add(const Duration(seconds: 16));
+      });
+      expect(asyncTracker.isFinished, true);
+      expect(asyncTracker.startTime, startTime);
+      expect(asyncTracker.stopTime, time);
+      expect(asyncTracker.duration, const Duration(seconds: 31));
+      expect(asyncTracker.innerDuration, const Duration(seconds: 17));
+      expect(asyncTracker.slices.length, greaterThan(1));
+      expect(nestedAsyncTracker.startTime.isAfter(startTime), true);
+      expect(nestedAsyncTracker.stopTime.isBefore(time), true);
+      expect(nestedAsyncTracker.duration, const Duration(seconds: 14));
+      expect(nestedAsyncTracker.innerDuration, const Duration(seconds: 14));
+      expect(nestedAsyncTracker.slices.length, greaterThan(1));
+    });
+
+    test('Can handle callbacks in excluded nested async', () async {
+      tracker = asyncTracker = AsyncTimeTracker(trackNested: false);
+      await scopedTrack(() async {
+        time = time.add(const Duration(seconds: 1));
+        final completer = Completer();
+        final future = completer.future.then((_) {
+          time = time.add(const Duration(seconds: 2));
+        });
+        await nestedAsyncTracker.track(() async {
+          time = time.add(const Duration(seconds: 4));
+          await Future.value();
+          time = time.add(const Duration(seconds: 8));
+          completer.complete();
+          await future;
+          time = time.add(const Duration(seconds: 16));
+        });
+        time = time.add(const Duration(seconds: 32));
+      });
+      expect(asyncTracker.isFinished, true);
+      expect(asyncTracker.startTime, startTime);
+      expect(asyncTracker.stopTime, time);
+      expect(asyncTracker.duration, const Duration(seconds: 63));
+      expect(asyncTracker.innerDuration, const Duration(seconds: 35));
+      expect(asyncTracker.slices.length, greaterThan(1));
+      expect(nestedAsyncTracker.startTime.isAfter(startTime), true);
+      expect(nestedAsyncTracker.stopTime.isBefore(time), true);
+      expect(nestedAsyncTracker.duration, const Duration(seconds: 30));
+      expect(nestedAsyncTracker.innerDuration, const Duration(seconds: 28));
+      expect(nestedAsyncTracker.slices.length, greaterThan(1));
+    });
+  });
+}

diff --git a/pkgs/watcher/.gitignore b/pkgs/watcher/.gitignore
new file mode 100644
index 0000000..ac98e87
--- /dev/null
+++ b/pkgs/watcher/.gitignore

@@ -0,0 +1,4 @@
+# Don’t commit the following directories created by pub.
+.dart_tool
+.packages
+pubspec.lock

diff --git a/pkgs/watcher/.test_config b/pkgs/watcher/.test_config
new file mode 100644
index 0000000..531426a
--- /dev/null
+++ b/pkgs/watcher/.test_config

@@ -0,0 +1,5 @@
+{
+  "test_package": {
+    "platforms": ["vm"]
+  }
+}
\ No newline at end of file

diff --git a/pkgs/watcher/CHANGELOG.md b/pkgs/watcher/CHANGELOG.md
new file mode 100644
index 0000000..ef3a7e2
--- /dev/null
+++ b/pkgs/watcher/CHANGELOG.md

@@ -0,0 +1,130 @@
+## 1.1.1
+
+- Ensure `PollingFileWatcher.ready` completes for files that do not exist.
+- Require Dart SDK `^3.1.0`
+- Move to `dart-lang/tools` monorepo.
+
+## 1.1.0
+
+- Require Dart SDK >= 3.0.0
+- Remove usage of redundant ConstructableFileSystemEvent classes.
+
+## 1.0.3-dev
+
+- Require Dart SDK >= 2.19
+
+## 1.0.2
+
+- Require Dart SDK >= 2.14
+- Ensure `DirectoryWatcher.ready` completes even when errors occur that close the watcher.
+- Add markdown badges to the readme.
+
+## 1.0.1
+
+* Drop package:pedantic and use package:lints instead.
+
+## 1.0.0
+
+* Require Dart SDK >= 2.12
+* Add the ability to create custom Watcher types for specific file paths.
+
+## 0.9.7+15
+
+* Fix a bug on Mac where modifying a directory with a path exactly matching a
+  prefix of a modified file would suppress change events for that file.
+
+## 0.9.7+14
+
+* Prepare for breaking change in SDK where modified times for not found files
+  becomes meaningless instead of null.
+
+## 0.9.7+13
+
+* Catch & forward `FileSystemException` from unexpectedly closed file watchers
+  on windows; the watcher will also be automatically restarted when this occurs.
+
+## 0.9.7+12
+
+* Catch `FileSystemException` during `existsSync()` on Windows.
+* Internal cleanup.
+
+## 0.9.7+11
+
+* Fix an analysis hint.
+
+## 0.9.7+10
+
+* Set max SDK version to `<3.0.0`, and adjust other dependencies.
+
+## 0.9.7+9
+
+* Internal changes only.
+
+## 0.9.7+8
+
+* Fix Dart 2.0 type issues on Mac and Windows.
+
+## 0.9.7+7
+
+* Updates to support Dart 2.0 core library changes (wave 2.2).
+  See [issue 31847][sdk#31847] for details.
+
+  [sdk#31847]: https://github.com/dart-lang/sdk/issues/31847
+
+
+## 0.9.7+6
+
+* Internal changes only, namely removing dep on scheduled test.
+
+## 0.9.7+5
+
+* Fix an analysis warning.
+
+## 0.9.7+4
+
+* Declare support for `async` 2.0.0.
+
+## 0.9.7+3
+
+* Fix a crashing bug on Linux.
+
+## 0.9.7+2
+
+* Narrow the constraint on `async` to reflect the APIs this package is actually
+  using.
+
+## 0.9.7+1
+
+* Fix all strong-mode warnings.
+
+## 0.9.7
+
+* Fix a bug in `FileWatcher` where events could be added after watchers were
+  closed.
+
+## 0.9.6
+
+* Add a `Watcher` interface that encompasses watching both files and
+  directories.
+
+* Add `FileWatcher` and `PollingFileWatcher` classes for watching changes to
+  individual files.
+
+* Deprecate `DirectoryWatcher.directory`. Use `DirectoryWatcher.path` instead.
+
+## 0.9.5
+
+* Fix bugs where events could be added after watchers were closed.
+
+## 0.9.4
+
+* Treat add events for known files as modifications instead of discarding them
+  on Mac OS.
+
+## 0.9.3
+
+* Improved support for Windows via `WindowsDirectoryWatcher`.
+
+* Simplified `PollingDirectoryWatcher`.
+
+* Fixed bugs in `MacOSDirectoryWatcher`

diff --git a/pkgs/watcher/LICENSE b/pkgs/watcher/LICENSE
new file mode 100644
index 0000000..000cd7b
--- /dev/null
+++ b/pkgs/watcher/LICENSE

@@ -0,0 +1,27 @@
+Copyright 2014, the Dart project authors. 
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+    * Neither the name of Google LLC nor the names of its
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

diff --git a/pkgs/watcher/README.md b/pkgs/watcher/README.md
new file mode 100644
index 0000000..83a0324
--- /dev/null
+++ b/pkgs/watcher/README.md

@@ -0,0 +1,10 @@
+[![Build Status](https://github.com/dart-lang/tools/actions/workflows/watcher.yaml/badge.svg)](https://github.com/dart-lang/tools/actions/workflows/watcher.yaml)
+[![pub package](https://img.shields.io/pub/v/watcher.svg)](https://pub.dev/packages/watcher)
+[![package publisher](https://img.shields.io/pub/publisher/watcher.svg)](https://pub.dev/packages/watcher/publisher)
+
+A file system watcher.
+
+## What's this?
+
+`package:watcher` monitors changes to contents of directories and sends
+notifications when files have been added, removed, or modified.

diff --git a/pkgs/watcher/analysis_options.yaml b/pkgs/watcher/analysis_options.yaml
new file mode 100644
index 0000000..d978f81
--- /dev/null
+++ b/pkgs/watcher/analysis_options.yaml

@@ -0,0 +1 @@
+include: package:dart_flutter_team_lints/analysis_options.yaml

diff --git a/pkgs/watcher/benchmark/path_set.dart b/pkgs/watcher/benchmark/path_set.dart
new file mode 100644
index 0000000..e7929d8
--- /dev/null
+++ b/pkgs/watcher/benchmark/path_set.dart

@@ -0,0 +1,158 @@
+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Benchmarks for the PathSet class.
+library;
+
+import 'dart:io';
+import 'dart:math' as math;
+
+import 'package:benchmark_harness/benchmark_harness.dart';
+import 'package:path/path.dart' as p;
+import 'package:watcher/src/path_set.dart';
+
+final String root = Platform.isWindows ? r'C:\root' : '/root';
+
+/// Base class for benchmarks on [PathSet].
+abstract class PathSetBenchmark extends BenchmarkBase {
+  PathSetBenchmark(String method) : super('PathSet.$method');
+
+  final PathSet pathSet = PathSet(root);
+
+  /// Use a fixed [math.Random] with a constant seed to ensure the tests are
+  /// deterministic.
+  final math.Random random = math.Random(1234);
+
+  /// Walks over a virtual directory [depth] levels deep invoking [callback]
+  /// for each "file".
+  ///
+  /// Each virtual directory contains ten entries: either subdirectories or
+  /// files.
+  void walkTree(int depth, void Function(String) callback) {
+    void recurse(String path, int remainingDepth) {
+      for (var i = 0; i < 10; i++) {
+        var padded = i.toString().padLeft(2, '0');
+        if (remainingDepth == 0) {
+          callback(p.join(path, 'file_$padded.txt'));
+        } else {
+          var subdir = p.join(path, 'subdirectory_$padded');
+          recurse(subdir, remainingDepth - 1);
+        }
+      }
+    }
+
+    recurse(root, depth);
+  }
+}
+
+class AddBenchmark extends PathSetBenchmark {
+  AddBenchmark() : super('add()');
+
+  final List<String> paths = [];
+
+  @override
+  void setup() {
+    // Make a bunch of paths in about the same order we expect to get them from
+    // Directory.list().
+    walkTree(3, paths.add);
+  }
+
+  @override
+  void run() {
+    for (var path in paths) {
+      pathSet.add(path);
+    }
+  }
+}
+
+class ContainsBenchmark extends PathSetBenchmark {
+  ContainsBenchmark() : super('contains()');
+
+  final List<String> paths = [];
+
+  @override
+  void setup() {
+    // Add a bunch of paths to the set.
+    walkTree(3, (path) {
+      pathSet.add(path);
+      paths.add(path);
+    });
+
+    // Add some non-existent paths to test the false case.
+    for (var i = 0; i < 100; i++) {
+      paths.addAll([
+        '/nope',
+        '/root/nope',
+        '/root/subdirectory_04/nope',
+        '/root/subdirectory_04/subdirectory_04/nope',
+        '/root/subdirectory_04/subdirectory_04/subdirectory_04/nope',
+        '/root/subdirectory_04/subdirectory_04/subdirectory_04/nope/file_04.txt',
+      ]);
+    }
+  }
+
+  @override
+  void run() {
+    var contained = 0;
+    for (var path in paths) {
+      if (pathSet.contains(path)) contained++;
+    }
+
+    if (contained != 10000) throw StateError('Wrong result: $contained');
+  }
+}
+
+class PathsBenchmark extends PathSetBenchmark {
+  PathsBenchmark() : super('toSet()');
+
+  @override
+  void setup() {
+    walkTree(3, pathSet.add);
+  }
+
+  @override
+  void run() {
+    var count = 0;
+    for (var _ in pathSet.paths) {
+      count++;
+    }
+
+    if (count != 10000) throw StateError('Wrong result: $count');
+  }
+}
+
+class RemoveBenchmark extends PathSetBenchmark {
+  RemoveBenchmark() : super('remove()');
+
+  final List<String> paths = [];
+
+  @override
+  void setup() {
+    // Make a bunch of paths. Do this here so that we don't spend benchmarked
+    // time synthesizing paths.
+    walkTree(3, (path) {
+      pathSet.add(path);
+      paths.add(path);
+    });
+
+    // Shuffle the paths so that we delete them in a random order that
+    // hopefully mimics real-world file system usage. Do the shuffling here so
+    // that we don't spend benchmarked time shuffling.
+    paths.shuffle(random);
+  }
+
+  @override
+  void run() {
+    for (var path in paths) {
+      pathSet.remove(path);
+    }
+  }
+}
+
+void main() {
+  AddBenchmark().report();
+  ContainsBenchmark().report();
+  PathsBenchmark().report();
+  RemoveBenchmark().report();
+}

diff --git a/pkgs/watcher/example/watch.dart b/pkgs/watcher/example/watch.dart
new file mode 100644
index 0000000..37931d3
--- /dev/null
+++ b/pkgs/watcher/example/watch.dart

@@ -0,0 +1,19 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Watches the given directory and prints each modification to it.
+library;
+
+import 'package:path/path.dart' as p;
+import 'package:watcher/watcher.dart';
+
+void main(List<String> arguments) {
+  if (arguments.length != 1) {
+    print('Usage: watch <directory path>');
+    return;
+  }
+
+  var watcher = DirectoryWatcher(p.absolute(arguments[0]));
+  watcher.events.listen(print);
+}

diff --git a/pkgs/watcher/lib/src/async_queue.dart b/pkgs/watcher/lib/src/async_queue.dart
new file mode 100644
index 0000000..f6c76a9
--- /dev/null
+++ b/pkgs/watcher/lib/src/async_queue.dart

@@ -0,0 +1,70 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:collection';
+
+typedef ItemProcessor<T> = Future<void> Function(T item);
+
+/// A queue of items that are sequentially, asynchronously processed.
+///
+/// Unlike [Stream.map] or [Stream.forEach], the callback used to process each
+/// item returns a [Future], and it will not advance to the next item until the
+/// current item is finished processing.
+///
+/// Items can be added at any point in time and processing will be started as
+/// needed. When all items are processed, it stops processing until more items
+/// are added.
+class AsyncQueue<T> {
+  final _items = Queue<T>();
+
+  /// Whether or not the queue is currently waiting on a processing future to
+  /// complete.
+  bool _isProcessing = false;
+
+  /// The callback to invoke on each queued item.
+  ///
+  /// The next item in the queue will not be processed until the [Future]
+  /// returned by this completes.
+  final ItemProcessor<T> _processor;
+
+  /// The handler for errors thrown during processing.
+  ///
+  /// Used to avoid top-leveling asynchronous errors.
+  final void Function(Object, StackTrace) _errorHandler;
+
+  AsyncQueue(this._processor,
+      {required void Function(Object, StackTrace) onError})
+      : _errorHandler = onError;
+
+  /// Enqueues [item] to be processed and starts asynchronously processing it
+  /// if a process isn't already running.
+  void add(T item) {
+    _items.add(item);
+
+    // Start up the asynchronous processing if not already running.
+    if (_isProcessing) return;
+    _isProcessing = true;
+
+    _processNextItem().catchError(_errorHandler);
+  }
+
+  /// Removes all remaining items to be processed.
+  void clear() {
+    _items.clear();
+  }
+
+  /// Pulls the next item off [_items] and processes it.
+  ///
+  /// When complete, recursively calls itself to continue processing unless
+  /// the process was cancelled.
+  Future<void> _processNextItem() async {
+    var item = _items.removeFirst();
+    await _processor(item);
+    if (_items.isNotEmpty) return _processNextItem();
+
+    // We have drained the queue, stop processing and wait until something
+    // has been enqueued.
+    _isProcessing = false;
+  }
+}

diff --git a/pkgs/watcher/lib/src/custom_watcher_factory.dart b/pkgs/watcher/lib/src/custom_watcher_factory.dart
new file mode 100644
index 0000000..fc4e3fb
--- /dev/null
+++ b/pkgs/watcher/lib/src/custom_watcher_factory.dart

@@ -0,0 +1,88 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import '../watcher.dart';
+
+/// A factory to produce custom watchers for specific file paths.
+class _CustomWatcherFactory {
+  final String id;
+  final DirectoryWatcher? Function(String path, {Duration? pollingDelay})
+      createDirectoryWatcher;
+  final FileWatcher? Function(String path, {Duration? pollingDelay})
+      createFileWatcher;
+
+  _CustomWatcherFactory(
+      this.id, this.createDirectoryWatcher, this.createFileWatcher);
+}
+
+/// Registers a custom watcher.
+///
+/// Each custom watcher must have a unique [id] and the same watcher may not be
+/// registered more than once.
+/// [createDirectoryWatcher] and [createFileWatcher] should return watchers for
+/// the file paths they are able to handle. If the custom watcher is not able to
+/// handle the path it should return null.
+/// The paths handled by each custom watch may not overlap, at most one custom
+/// matcher may return a non-null watcher for a given path.
+///
+/// When a file or directory watcher is created the path is checked against each
+/// registered custom watcher, and if exactly one custom watcher is available it
+/// will be used instead of the default.
+void registerCustomWatcher(
+  String id,
+  DirectoryWatcher? Function(String path, {Duration? pollingDelay})?
+      createDirectoryWatcher,
+  FileWatcher? Function(String path, {Duration? pollingDelay})?
+      createFileWatcher,
+) {
+  if (_customWatcherFactories.containsKey(id)) {
+    throw ArgumentError('A custom watcher with id `$id` '
+        'has already been registered');
+  }
+  _customWatcherFactories[id] = _CustomWatcherFactory(
+      id,
+      createDirectoryWatcher ?? (_, {pollingDelay}) => null,
+      createFileWatcher ?? (_, {pollingDelay}) => null);
+}
+
+/// Tries to create a custom [DirectoryWatcher] and returns it.
+///
+/// Returns `null` if no custom watcher was applicable and throws a [StateError]
+/// if more than one was.
+DirectoryWatcher? createCustomDirectoryWatcher(String path,
+    {Duration? pollingDelay}) {
+  DirectoryWatcher? customWatcher;
+  String? customFactoryId;
+  for (var watcherFactory in _customWatcherFactories.values) {
+    if (customWatcher != null) {
+      throw StateError('Two `CustomWatcherFactory`s applicable: '
+          '`$customFactoryId` and `${watcherFactory.id}` for `$path`');
+    }
+    customWatcher =
+        watcherFactory.createDirectoryWatcher(path, pollingDelay: pollingDelay);
+    customFactoryId = watcherFactory.id;
+  }
+  return customWatcher;
+}
+
+/// Tries to create a custom [FileWatcher] and returns it.
+///
+/// Returns `null` if no custom watcher was applicable and throws a [StateError]
+/// if more than one was.
+FileWatcher? createCustomFileWatcher(String path, {Duration? pollingDelay}) {
+  FileWatcher? customWatcher;
+  String? customFactoryId;
+  for (var watcherFactory in _customWatcherFactories.values) {
+    if (customWatcher != null) {
+      throw StateError('Two `CustomWatcherFactory`s applicable: '
+          '`$customFactoryId` and `${watcherFactory.id}` for `$path`');
+    }
+    customWatcher =
+        watcherFactory.createFileWatcher(path, pollingDelay: pollingDelay);
+    customFactoryId = watcherFactory.id;
+  }
+  return customWatcher;
+}
+
+final _customWatcherFactories = <String, _CustomWatcherFactory>{};

diff --git a/pkgs/watcher/lib/src/directory_watcher.dart b/pkgs/watcher/lib/src/directory_watcher.dart
new file mode 100644
index 0000000..158b86b
--- /dev/null
+++ b/pkgs/watcher/lib/src/directory_watcher.dart

@@ -0,0 +1,41 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:io';
+
+import '../watcher.dart';
+import 'custom_watcher_factory.dart';
+import 'directory_watcher/linux.dart';
+import 'directory_watcher/mac_os.dart';
+import 'directory_watcher/windows.dart';
+
+/// Watches the contents of a directory and emits [WatchEvent]s when something
+/// in the directory has changed.
+abstract class DirectoryWatcher implements Watcher {
+  /// The directory whose contents are being monitored.
+  @Deprecated('Expires in 1.0.0. Use DirectoryWatcher.path instead.')
+  String get directory;
+
+  /// Creates a new [DirectoryWatcher] monitoring [directory].
+  ///
+  /// If a native directory watcher is available for this platform, this will
+  /// use it. Otherwise, it will fall back to a [PollingDirectoryWatcher].
+  ///
+  /// If [pollingDelay] is passed, it specifies the amount of time the watcher
+  /// will pause between successive polls of the directory contents. Making this
+  /// shorter will give more immediate feedback at the expense of doing more IO
+  /// and higher CPU usage. Defaults to one second. Ignored for non-polling
+  /// watchers.
+  factory DirectoryWatcher(String directory, {Duration? pollingDelay}) {
+    if (FileSystemEntity.isWatchSupported) {
+      var customWatcher =
+          createCustomDirectoryWatcher(directory, pollingDelay: pollingDelay);
+      if (customWatcher != null) return customWatcher;
+      if (Platform.isLinux) return LinuxDirectoryWatcher(directory);
+      if (Platform.isMacOS) return MacOSDirectoryWatcher(directory);
+      if (Platform.isWindows) return WindowsDirectoryWatcher(directory);
+    }
+    return PollingDirectoryWatcher(directory, pollingDelay: pollingDelay);
+  }
+}

diff --git a/pkgs/watcher/lib/src/directory_watcher/linux.dart b/pkgs/watcher/lib/src/directory_watcher/linux.dart
new file mode 100644
index 0000000..cb1d077
--- /dev/null
+++ b/pkgs/watcher/lib/src/directory_watcher/linux.dart

@@ -0,0 +1,294 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+import 'dart:io';
+
+import 'package:async/async.dart';
+
+import '../directory_watcher.dart';
+import '../path_set.dart';
+import '../resubscribable.dart';
+import '../utils.dart';
+import '../watch_event.dart';
+
+/// Uses the inotify subsystem to watch for filesystem events.
+///
+/// Inotify doesn't suport recursively watching subdirectories, nor does
+/// [Directory.watch] polyfill that functionality. This class polyfills it
+/// instead.
+///
+/// This class also compensates for the non-inotify-specific issues of
+/// [Directory.watch] producing multiple events for a single logical action
+/// (issue 14372) and providing insufficient information about move events
+/// (issue 14424).
+class LinuxDirectoryWatcher extends ResubscribableWatcher
+    implements DirectoryWatcher {
+  @override
+  String get directory => path;
+
+  LinuxDirectoryWatcher(String directory)
+      : super(directory, () => _LinuxDirectoryWatcher(directory));
+}
+
+class _LinuxDirectoryWatcher
+    implements DirectoryWatcher, ManuallyClosedWatcher {
+  @override
+  String get directory => _files.root;
+  @override
+  String get path => _files.root;
+
+  @override
+  Stream<WatchEvent> get events => _eventsController.stream;
+  final _eventsController = StreamController<WatchEvent>.broadcast();
+
+  @override
+  bool get isReady => _readyCompleter.isCompleted;
+
+  @override
+  Future<void> get ready => _readyCompleter.future;
+  final _readyCompleter = Completer<void>();
+
+  /// A stream group for the [Directory.watch] events of [path] and all its
+  /// subdirectories.
+  final _nativeEvents = StreamGroup<FileSystemEvent>();
+
+  /// All known files recursively within [path].
+  final PathSet _files;
+
+  /// [Directory.watch] streams for [path]'s subdirectories, indexed by name.
+  ///
+  /// A stream is in this map if and only if it's also in [_nativeEvents].
+  final _subdirStreams = <String, Stream<FileSystemEvent>>{};
+
+  /// A set of all subscriptions that this watcher subscribes to.
+  ///
+  /// These are gathered together so that they may all be canceled when the
+  /// watcher is closed.
+  final _subscriptions = <StreamSubscription>{};
+
+  _LinuxDirectoryWatcher(String path) : _files = PathSet(path) {
+    _nativeEvents.add(Directory(path)
+        .watch()
+        .transform(StreamTransformer.fromHandlers(handleDone: (sink) {
+      // Handle the done event here rather than in the call to [_listen] because
+      // [innerStream] won't close until we close the [StreamGroup]. However, if
+      // we close the [StreamGroup] here, we run the risk of new-directory
+      // events being fired after the group is closed, since batching delays
+      // those events. See b/30768513.
+      _onDone();
+    })));
+
+    // Batch the inotify changes together so that we can dedup events.
+    var innerStream = _nativeEvents.stream.batchEvents();
+    _listen(innerStream, _onBatch,
+        onError: (Object error, StackTrace stackTrace) {
+      // Guarantee that ready always completes.
+      if (!isReady) {
+        _readyCompleter.complete();
+      }
+      _eventsController.addError(error, stackTrace);
+    });
+
+    _listen(
+      Directory(path).list(recursive: true),
+      (FileSystemEntity entity) {
+        if (entity is Directory) {
+          _watchSubdir(entity.path);
+        } else {
+          _files.add(entity.path);
+        }
+      },
+      onError: _emitError,
+      onDone: () {
+        if (!isReady) {
+          _readyCompleter.complete();
+        }
+      },
+      cancelOnError: true,
+    );
+  }
+
+  @override
+  void close() {
+    for (var subscription in _subscriptions) {
+      subscription.cancel();
+    }
+
+    _subscriptions.clear();
+    _subdirStreams.clear();
+    _files.clear();
+    _nativeEvents.close();
+    _eventsController.close();
+  }
+
+  /// Watch a subdirectory of [directory] for changes.
+  void _watchSubdir(String path) {
+    // TODO(nweiz): Right now it's possible for the watcher to emit an event for
+    // a file before the directory list is complete. This could lead to the user
+    // seeing a MODIFY or REMOVE event for a file before they see an ADD event,
+    // which is bad. We should handle that.
+    //
+    // One possibility is to provide a general means (e.g.
+    // `DirectoryWatcher.eventsAndExistingFiles`) to tell a watcher to emit
+    // events for all the files that already exist. This would be useful for
+    // top-level clients such as barback as well, and could be implemented with
+    // a wrapper similar to how listening/canceling works now.
+
+    // TODO(nweiz): Catch any errors here that indicate that the directory in
+    // question doesn't exist and silently stop watching it instead of
+    // propagating the errors.
+    var stream = Directory(path).watch();
+    _subdirStreams[path] = stream;
+    _nativeEvents.add(stream);
+  }
+
+  /// The callback that's run when a batch of changes comes in.
+  void _onBatch(List<FileSystemEvent> batch) {
+    var files = <String>{};
+    var dirs = <String>{};
+    var changed = <String>{};
+
+    // inotify event batches are ordered by occurrence, so we treat them as a
+    // log of what happened to a file. We only emit events based on the
+    // difference between the state before the batch and the state after it, not
+    // the intermediate state.
+    for (var event in batch) {
+      // If the watched directory is deleted or moved, we'll get a deletion
+      // event for it. Ignore it; we handle closing [this] when the underlying
+      // stream is closed.
+      if (event.path == path) continue;
+
+      changed.add(event.path);
+
+      if (event is FileSystemMoveEvent) {
+        files.remove(event.path);
+        dirs.remove(event.path);
+
+        var destination = event.destination;
+        if (destination == null) continue;
+
+        changed.add(destination);
+        if (event.isDirectory) {
+          files.remove(destination);
+          dirs.add(destination);
+        } else {
+          files.add(destination);
+          dirs.remove(destination);
+        }
+      } else if (event is FileSystemDeleteEvent) {
+        files.remove(event.path);
+        dirs.remove(event.path);
+      } else if (event.isDirectory) {
+        files.remove(event.path);
+        dirs.add(event.path);
+      } else {
+        files.add(event.path);
+        dirs.remove(event.path);
+      }
+    }
+
+    _applyChanges(files, dirs, changed);
+  }
+
+  /// Applies the net changes computed for a batch.
+  ///
+  /// The [files] and [dirs] sets contain the files and directories that now
+  /// exist, respectively. The [changed] set contains all files and directories
+  /// that have changed (including being removed), and so is a superset of
+  /// [files] and [dirs].
+  void _applyChanges(Set<String> files, Set<String> dirs, Set<String> changed) {
+    for (var path in changed) {
+      var stream = _subdirStreams.remove(path);
+      if (stream != null) _nativeEvents.add(stream);
+
+      // Unless [path] was a file and still is, emit REMOVE events for it or its
+      // contents,
+      if (files.contains(path) && _files.contains(path)) continue;
+      for (var file in _files.remove(path)) {
+        _emitEvent(ChangeType.REMOVE, file);
+      }
+    }
+
+    for (var file in files) {
+      if (_files.contains(file)) {
+        _emitEvent(ChangeType.MODIFY, file);
+      } else {
+        _emitEvent(ChangeType.ADD, file);
+        _files.add(file);
+      }
+    }
+
+    for (var dir in dirs) {
+      _watchSubdir(dir);
+      _addSubdir(dir);
+    }
+  }
+
+  /// Emits [ChangeType.ADD] events for the recursive contents of [path].
+  void _addSubdir(String path) {
+    _listen(Directory(path).list(recursive: true), (FileSystemEntity entity) {
+      if (entity is Directory) {
+        _watchSubdir(entity.path);
+      } else {
+        _files.add(entity.path);
+        _emitEvent(ChangeType.ADD, entity.path);
+      }
+    }, onError: (Object error, StackTrace stackTrace) {
+      // Ignore an exception caused by the dir not existing. It's fine if it
+      // was added and then quickly removed.
+      if (error is FileSystemException) return;
+
+      _emitError(error, stackTrace);
+    }, cancelOnError: true);
+  }
+
+  /// Handles the underlying event stream closing, indicating that the directory
+  /// being watched was removed.
+  void _onDone() {
+    // Most of the time when a directory is removed, its contents will get
+    // individual REMOVE events before the watch stream is closed -- in that
+    // case, [_files] will be empty here. However, if the directory's removal is
+    // caused by a MOVE, we need to manually emit events.
+    if (isReady) {
+      for (var file in _files.paths) {
+        _emitEvent(ChangeType.REMOVE, file);
+      }
+    }
+
+    close();
+  }
+
+  /// Emits a [WatchEvent] with [type] and [path] if this watcher is in a state
+  /// to emit events.
+  void _emitEvent(ChangeType type, String path) {
+    if (!isReady) return;
+    if (_eventsController.isClosed) return;
+    _eventsController.add(WatchEvent(type, path));
+  }
+
+  /// Emit an error, then close the watcher.
+  void _emitError(Object error, StackTrace stackTrace) {
+    // Guarantee that ready always completes.
+    if (!isReady) {
+      _readyCompleter.complete();
+    }
+    _eventsController.addError(error, stackTrace);
+    close();
+  }
+
+  /// Like [Stream.listen], but automatically adds the subscription to
+  /// [_subscriptions] so that it can be canceled when [close] is called.
+  void _listen<T>(Stream<T> stream, void Function(T) onData,
+      {Function? onError,
+      void Function()? onDone,
+      bool cancelOnError = false}) {
+    late StreamSubscription<T> subscription;
+    subscription = stream.listen(onData, onError: onError, onDone: () {
+      _subscriptions.remove(subscription);
+      onDone?.call();
+    }, cancelOnError: cancelOnError);
+    _subscriptions.add(subscription);
+  }
+}

diff --git a/pkgs/watcher/lib/src/directory_watcher/mac_os.dart b/pkgs/watcher/lib/src/directory_watcher/mac_os.dart
new file mode 100644
index 0000000..b461383
--- /dev/null
+++ b/pkgs/watcher/lib/src/directory_watcher/mac_os.dart

@@ -0,0 +1,410 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+import 'dart:io';
+
+import 'package:path/path.dart' as p;
+
+import '../directory_watcher.dart';
+import '../path_set.dart';
+import '../resubscribable.dart';
+import '../utils.dart';
+import '../watch_event.dart';
+
+/// Uses the FSEvents subsystem to watch for filesystem events.
+///
+/// FSEvents has two main idiosyncrasies that this class works around. First, it
+/// will occasionally report events that occurred before the filesystem watch
+/// was initiated. Second, if multiple events happen to the same file in close
+/// succession, it won't report them in the order they occurred. See issue
+/// 14373.
+///
+/// This also works around issues 16003 and 14849 in the implementation of
+/// [Directory.watch].
+class MacOSDirectoryWatcher extends ResubscribableWatcher
+    implements DirectoryWatcher {
+  @override
+  String get directory => path;
+
+  MacOSDirectoryWatcher(String directory)
+      : super(directory, () => _MacOSDirectoryWatcher(directory));
+}
+
+class _MacOSDirectoryWatcher
+    implements DirectoryWatcher, ManuallyClosedWatcher {
+  @override
+  String get directory => path;
+  @override
+  final String path;
+
+  @override
+  Stream<WatchEvent> get events => _eventsController.stream;
+  final _eventsController = StreamController<WatchEvent>.broadcast();
+
+  @override
+  bool get isReady => _readyCompleter.isCompleted;
+
+  @override
+  Future<void> get ready => _readyCompleter.future;
+  final _readyCompleter = Completer<void>();
+
+  /// The set of files that are known to exist recursively within the watched
+  /// directory.
+  ///
+  /// The state of files on the filesystem is compared against this to determine
+  /// the real change that occurred when working around issue 14373. This is
+  /// also used to emit REMOVE events when subdirectories are moved out of the
+  /// watched directory.
+  final PathSet _files;
+
+  /// The subscription to the stream returned by [Directory.watch].
+  ///
+  /// This is separate from [_listSubscriptions] because this stream
+  /// occasionally needs to be resubscribed in order to work around issue 14849.
+  StreamSubscription<List<FileSystemEvent>>? _watchSubscription;
+
+  /// The subscription to the [Directory.list] call for the initial listing of
+  /// the directory to determine its initial state.
+  StreamSubscription<FileSystemEntity>? _initialListSubscription;
+
+  /// The subscriptions to [Directory.list] calls for listing the contents of a
+  /// subdirectory that was moved into the watched directory.
+  final _listSubscriptions = <StreamSubscription<FileSystemEntity>>{};
+
+  /// The timer for tracking how long we wait for an initial batch of bogus
+  /// events (see issue 14373).
+  late Timer _bogusEventTimer;
+
+  _MacOSDirectoryWatcher(this.path) : _files = PathSet(path) {
+    _startWatch();
+
+    // Before we're ready to emit events, wait for [_listDir] to complete and
+    // for enough time to elapse that if bogus events (issue 14373) would be
+    // emitted, they will be.
+    //
+    // If we do receive a batch of events, [_onBatch] will ensure that these
+    // futures don't fire and that the directory is re-listed.
+    Future.wait([_listDir(), _waitForBogusEvents()]).then((_) {
+      if (!isReady) {
+        _readyCompleter.complete();
+      }
+    });
+  }
+
+  @override
+  void close() {
+    _watchSubscription?.cancel();
+    _initialListSubscription?.cancel();
+    _watchSubscription = null;
+    _initialListSubscription = null;
+
+    for (var subscription in _listSubscriptions) {
+      subscription.cancel();
+    }
+    _listSubscriptions.clear();
+
+    _eventsController.close();
+  }
+
+  /// The callback that's run when [Directory.watch] emits a batch of events.
+  void _onBatch(List<FileSystemEvent> batch) {
+    // If we get a batch of events before we're ready to begin emitting events,
+    // it's probable that it's a batch of pre-watcher events (see issue 14373).
+    // Ignore those events and re-list the directory.
+    if (!isReady) {
+      // Cancel the timer because bogus events only occur in the first batch, so
+      // we can fire [ready] as soon as we're done listing the directory.
+      _bogusEventTimer.cancel();
+      _listDir().then((_) {
+        if (!isReady) {
+          _readyCompleter.complete();
+        }
+      });
+      return;
+    }
+
+    _sortEvents(batch).forEach((path, eventSet) {
+      var canonicalEvent = _canonicalEvent(eventSet);
+      var events = canonicalEvent == null
+          ? _eventsBasedOnFileSystem(path)
+          : [canonicalEvent];
+
+      for (var event in events) {
+        if (event is FileSystemCreateEvent) {
+          if (!event.isDirectory) {
+            // If we already know about the file, treat it like a modification.
+            // This can happen if a file is copied on top of an existing one.
+            // We'll see an ADD event for the latter file when from the user's
+            // perspective, the file's contents just changed.
+            var type =
+                _files.contains(path) ? ChangeType.MODIFY : ChangeType.ADD;
+
+            _emitEvent(type, path);
+            _files.add(path);
+            continue;
+          }
+
+          if (_files.containsDir(path)) continue;
+
+          var stream = Directory(path).list(recursive: true);
+          var subscription = stream.listen((entity) {
+            if (entity is Directory) return;
+            if (_files.contains(path)) return;
+
+            _emitEvent(ChangeType.ADD, entity.path);
+            _files.add(entity.path);
+          }, cancelOnError: true);
+          subscription.onDone(() {
+            _listSubscriptions.remove(subscription);
+          });
+          subscription.onError(_emitError);
+          _listSubscriptions.add(subscription);
+        } else if (event is FileSystemModifyEvent) {
+          assert(!event.isDirectory);
+          _emitEvent(ChangeType.MODIFY, path);
+        } else {
+          assert(event is FileSystemDeleteEvent);
+          for (var removedPath in _files.remove(path)) {
+            _emitEvent(ChangeType.REMOVE, removedPath);
+          }
+        }
+      }
+    });
+  }
+
+  /// Sort all the events in a batch into sets based on their path.
+  ///
+  /// A single input event may result in multiple events in the returned map;
+  /// for example, a MOVE event becomes a DELETE event for the source and a
+  /// CREATE event for the destination.
+  ///
+  /// The returned events won't contain any [FileSystemMoveEvent]s, nor will it
+  /// contain any events relating to [path].
+  Map<String, Set<FileSystemEvent>> _sortEvents(List<FileSystemEvent> batch) {
+    var eventsForPaths = <String, Set<FileSystemEvent>>{};
+
+    // FSEvents can report past events, including events on the root directory
+    // such as it being created. We want to ignore these. If the directory is
+    // really deleted, that's handled by [_onDone].
+    batch = batch.where((event) => event.path != path).toList();
+
+    // Events within directories that already have events are superfluous; the
+    // directory's full contents will be examined anyway, so we ignore such
+    // events. Emitting them could cause useless or out-of-order events.
+    var directories = unionAll(batch.map((event) {
+      if (!event.isDirectory) return <String>{};
+      if (event is FileSystemMoveEvent) {
+        var destination = event.destination;
+        if (destination != null) {
+          return {event.path, destination};
+        }
+      }
+      return {event.path};
+    }));
+
+    bool isInModifiedDirectory(String path) =>
+        directories.any((dir) => path != dir && p.isWithin(dir, path));
+
+    void addEvent(String path, FileSystemEvent event) {
+      if (isInModifiedDirectory(path)) return;
+      eventsForPaths.putIfAbsent(path, () => <FileSystemEvent>{}).add(event);
+    }
+
+    for (var event in batch) {
+      // The Mac OS watcher doesn't emit move events. See issue 14806.
+      assert(event is! FileSystemMoveEvent);
+      addEvent(event.path, event);
+    }
+
+    return eventsForPaths;
+  }
+
+  /// Returns the canonical event from a batch of events on the same path, if
+  /// one exists.
+  ///
+  /// If [batch] doesn't contain any contradictory events (e.g. DELETE and
+  /// CREATE, or events with different values for `isDirectory`), this returns a
+  /// single event that describes what happened to the path in question.
+  ///
+  /// If [batch] does contain contradictory events, this returns `null` to
+  /// indicate that the state of the path on the filesystem should be checked to
+  /// determine what occurred.
+  FileSystemEvent? _canonicalEvent(Set<FileSystemEvent> batch) {
+    // An empty batch indicates that we've learned earlier that the batch is
+    // contradictory (e.g. because of a move).
+    if (batch.isEmpty) return null;
+
+    var type = batch.first.type;
+    var isDir = batch.first.isDirectory;
+    var hadModifyEvent = false;
+
+    for (var event in batch.skip(1)) {
+      // If one event reports that the file is a directory and another event
+      // doesn't, that's a contradiction.
+      if (isDir != event.isDirectory) return null;
+
+      // Modify events don't contradict either CREATE or REMOVE events. We can
+      // safely assume the file was modified after a CREATE or before the
+      // REMOVE; otherwise there will also be a REMOVE or CREATE event
+      // (respectively) that will be contradictory.
+      if (event is FileSystemModifyEvent) {
+        hadModifyEvent = true;
+        continue;
+      }
+      assert(event is FileSystemCreateEvent || event is FileSystemDeleteEvent);
+
+      // If we previously thought this was a MODIFY, we now consider it to be a
+      // CREATE or REMOVE event. This is safe for the same reason as above.
+      if (type == FileSystemEvent.modify) {
+        type = event.type;
+        continue;
+      }
+
+      // A CREATE event contradicts a REMOVE event and vice versa.
+      assert(type == FileSystemEvent.create || type == FileSystemEvent.delete);
+      if (type != event.type) return null;
+    }
+
+    // If we got a CREATE event for a file we already knew about, that comes
+    // from FSEvents reporting an add that happened prior to the watch
+    // beginning. If we also received a MODIFY event, we want to report that,
+    // but not the CREATE.
+    if (type == FileSystemEvent.create &&
+        hadModifyEvent &&
+        _files.contains(batch.first.path)) {
+      type = FileSystemEvent.modify;
+    }
+
+    switch (type) {
+      case FileSystemEvent.create:
+        // Issue 16003 means that a CREATE event for a directory can indicate
+        // that the directory was moved and then re-created.
+        // [_eventsBasedOnFileSystem] will handle this correctly by producing a
+        // DELETE event followed by a CREATE event if the directory exists.
+        if (isDir) return null;
+        return FileSystemCreateEvent(batch.first.path, false);
+      case FileSystemEvent.delete:
+        return FileSystemDeleteEvent(batch.first.path, isDir);
+      case FileSystemEvent.modify:
+        return FileSystemModifyEvent(batch.first.path, isDir, false);
+      default:
+        throw StateError('unreachable');
+    }
+  }
+
+  /// Returns one or more events that describe the change between the last known
+  /// state of [path] and its current state on the filesystem.
+  ///
+  /// This returns a list whose order should be reflected in the events emitted
+  /// to the user, unlike the batched events from [Directory.watch]. The
+  /// returned list may be empty, indicating that no changes occurred to [path]
+  /// (probably indicating that it was created and then immediately deleted).
+  List<FileSystemEvent> _eventsBasedOnFileSystem(String path) {
+    var fileExisted = _files.contains(path);
+    var dirExisted = _files.containsDir(path);
+    var fileExists = File(path).existsSync();
+    var dirExists = Directory(path).existsSync();
+
+    var events = <FileSystemEvent>[];
+    if (fileExisted) {
+      if (fileExists) {
+        events.add(FileSystemModifyEvent(path, false, false));
+      } else {
+        events.add(FileSystemDeleteEvent(path, false));
+      }
+    } else if (dirExisted) {
+      if (dirExists) {
+        // If we got contradictory events for a directory that used to exist and
+        // still exists, we need to rescan the whole thing in case it was
+        // replaced with a different directory.
+        events.add(FileSystemDeleteEvent(path, true));
+        events.add(FileSystemCreateEvent(path, true));
+      } else {
+        events.add(FileSystemDeleteEvent(path, true));
+      }
+    }
+
+    if (!fileExisted && fileExists) {
+      events.add(FileSystemCreateEvent(path, false));
+    } else if (!dirExisted && dirExists) {
+      events.add(FileSystemCreateEvent(path, true));
+    }
+
+    return events;
+  }
+
+  /// The callback that's run when the [Directory.watch] stream is closed.
+  void _onDone() {
+    _watchSubscription = null;
+
+    // If the directory still exists and we're still expecting bogus events,
+    // this is probably issue 14849 rather than a real close event. We should
+    // just restart the watcher.
+    if (!isReady && Directory(path).existsSync()) {
+      _startWatch();
+      return;
+    }
+
+    // FSEvents can fail to report the contents of the directory being removed
+    // when the directory itself is removed, so we need to manually mark the
+    // files as removed.
+    for (var file in _files.paths) {
+      _emitEvent(ChangeType.REMOVE, file);
+    }
+    _files.clear();
+    close();
+  }
+
+  /// Start or restart the underlying [Directory.watch] stream.
+  void _startWatch() {
+    // Batch the FSEvent changes together so that we can dedup events.
+    var innerStream = Directory(path).watch(recursive: true).batchEvents();
+    _watchSubscription = innerStream.listen(_onBatch,
+        onError: _eventsController.addError, onDone: _onDone);
+  }
+
+  /// Starts or restarts listing the watched directory to get an initial picture
+  /// of its state.
+  Future<void> _listDir() {
+    assert(!isReady);
+    _initialListSubscription?.cancel();
+
+    _files.clear();
+    var completer = Completer<void>();
+    var stream = Directory(path).list(recursive: true);
+    _initialListSubscription = stream.listen((entity) {
+      if (entity is! Directory) _files.add(entity.path);
+    }, onError: _emitError, onDone: completer.complete, cancelOnError: true);
+    return completer.future;
+  }
+
+  /// Wait 200ms for a batch of bogus events (issue 14373) to come in.
+  ///
+  /// 200ms is short in terms of human interaction, but longer than any Mac OS
+  /// watcher tests take on the bots, so it should be safe to assume that any
+  /// bogus events will be signaled in that time frame.
+  Future<void> _waitForBogusEvents() {
+    var completer = Completer<void>();
+    _bogusEventTimer =
+        Timer(const Duration(milliseconds: 200), completer.complete);
+    return completer.future;
+  }
+
+  /// Emit an event with the given [type] and [path].
+  void _emitEvent(ChangeType type, String path) {
+    if (!isReady) return;
+    _eventsController.add(WatchEvent(type, path));
+  }
+
+  /// Emit an error, then close the watcher.
+  void _emitError(Object error, StackTrace stackTrace) {
+    // Guarantee that ready always completes.
+    if (!isReady) {
+      _readyCompleter.complete();
+    }
+    _eventsController.addError(error, stackTrace);
+    close();
+  }
+}

diff --git a/pkgs/watcher/lib/src/directory_watcher/polling.dart b/pkgs/watcher/lib/src/directory_watcher/polling.dart
new file mode 100644
index 0000000..207679b
--- /dev/null
+++ b/pkgs/watcher/lib/src/directory_watcher/polling.dart

@@ -0,0 +1,191 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+import 'dart:io';
+
+import '../async_queue.dart';
+import '../directory_watcher.dart';
+import '../resubscribable.dart';
+import '../stat.dart';
+import '../utils.dart';
+import '../watch_event.dart';
+
+/// Periodically polls a directory for changes.
+class PollingDirectoryWatcher extends ResubscribableWatcher
+    implements DirectoryWatcher {
+  @override
+  String get directory => path;
+
+  /// Creates a new polling watcher monitoring [directory].
+  ///
+  /// If [pollingDelay] is passed, it specifies the amount of time the watcher
+  /// will pause between successive polls of the directory contents. Making this
+  /// shorter will give more immediate feedback at the expense of doing more IO
+  /// and higher CPU usage. Defaults to one second.
+  PollingDirectoryWatcher(String directory, {Duration? pollingDelay})
+      : super(directory, () {
+          return _PollingDirectoryWatcher(
+              directory, pollingDelay ?? const Duration(seconds: 1));
+        });
+}
+
+class _PollingDirectoryWatcher
+    implements DirectoryWatcher, ManuallyClosedWatcher {
+  @override
+  String get directory => path;
+  @override
+  final String path;
+
+  @override
+  Stream<WatchEvent> get events => _events.stream;
+  final _events = StreamController<WatchEvent>.broadcast();
+
+  @override
+  bool get isReady => _readyCompleter.isCompleted;
+
+  @override
+  Future<void> get ready => _readyCompleter.future;
+  final _readyCompleter = Completer<void>();
+
+  /// The amount of time the watcher pauses between successive polls of the
+  /// directory contents.
+  final Duration _pollingDelay;
+
+  /// The previous modification times of the files in the directory.
+  ///
+  /// Used to tell which files have been modified.
+  final _lastModifieds = <String, DateTime?>{};
+
+  /// The subscription used while [directory] is being listed.
+  ///
+  /// Will be `null` if a list is not currently happening.
+  StreamSubscription<FileSystemEntity>? _listSubscription;
+
+  /// The queue of files waiting to be processed to see if they have been
+  /// modified.
+  ///
+  /// Processing a file is asynchronous, as is listing the directory, so the
+  /// queue exists to let each of those proceed at their own rate. The lister
+  /// will enqueue files as quickly as it can. Meanwhile, files are dequeued
+  /// and processed sequentially.
+  late final AsyncQueue<String?> _filesToProcess =
+      AsyncQueue<String?>(_processFile, onError: (error, stackTrace) {
+    if (!_events.isClosed) _events.addError(error, stackTrace);
+  });
+
+  /// The set of files that have been seen in the current directory listing.
+  ///
+  /// Used to tell which files have been removed: files that are in
+  /// [_lastModifieds] but not in here when a poll completes have been removed.
+  final _polledFiles = <String>{};
+
+  _PollingDirectoryWatcher(this.path, this._pollingDelay) {
+    _poll();
+  }
+
+  @override
+  void close() {
+    _events.close();
+
+    // If we're in the middle of listing the directory, stop.
+    _listSubscription?.cancel();
+
+    // Don't process any remaining files.
+    _filesToProcess.clear();
+    _polledFiles.clear();
+    _lastModifieds.clear();
+  }
+
+  /// Scans the contents of the directory once to see which files have been
+  /// added, removed, and modified.
+  void _poll() {
+    _filesToProcess.clear();
+    _polledFiles.clear();
+
+    void endListing() {
+      assert(!_events.isClosed);
+      _listSubscription = null;
+
+      // Null tells the queue consumer that we're done listing.
+      _filesToProcess.add(null);
+    }
+
+    var stream = Directory(path).list(recursive: true);
+    _listSubscription = stream.listen((entity) {
+      assert(!_events.isClosed);
+
+      if (entity is! File) return;
+      _filesToProcess.add(entity.path);
+    }, onError: (Object error, StackTrace stackTrace) {
+      // Guarantee that ready always completes.
+      if (!isReady) {
+        _readyCompleter.complete();
+      }
+      if (!isDirectoryNotFoundException(error)) {
+        // It's some unknown error. Pipe it over to the event stream so the
+        // user can see it.
+        _events.addError(error, stackTrace);
+      }
+
+      // When an error occurs, we end the listing normally, which has the
+      // desired effect of marking all files that were in the directory as
+      // being removed.
+      endListing();
+    }, onDone: endListing, cancelOnError: true);
+  }
+
+  /// Processes [file] to determine if it has been modified since the last
+  /// time it was scanned.
+  Future<void> _processFile(String? file) async {
+    // `null` is the sentinel which means the directory listing is complete.
+    if (file == null) {
+      await _completePoll();
+      return;
+    }
+
+    final modified = await modificationTime(file);
+
+    if (_events.isClosed) return;
+
+    var lastModified = _lastModifieds[file];
+
+    // If its modification time hasn't changed, assume the file is unchanged.
+    if (lastModified != null && lastModified == modified) {
+      // The file is still here.
+      _polledFiles.add(file);
+      return;
+    }
+
+    if (_events.isClosed) return;
+
+    _lastModifieds[file] = modified;
+    _polledFiles.add(file);
+
+    // Only notify if we're ready to emit events.
+    if (!isReady) return;
+
+    var type = lastModified == null ? ChangeType.ADD : ChangeType.MODIFY;
+    _events.add(WatchEvent(type, file));
+  }
+
+  /// After the directory listing is complete, this determines which files were
+  /// removed and then restarts the next poll.
+  Future<void> _completePoll() async {
+    // Any files that were not seen in the last poll but that we have a
+    // status for must have been removed.
+    var removedFiles = _lastModifieds.keys.toSet().difference(_polledFiles);
+    for (var removed in removedFiles) {
+      if (isReady) _events.add(WatchEvent(ChangeType.REMOVE, removed));
+      _lastModifieds.remove(removed);
+    }
+
+    if (!isReady) _readyCompleter.complete();
+
+    // Wait and then poll again.
+    await Future<void>.delayed(_pollingDelay);
+    if (_events.isClosed) return;
+    _poll();
+  }
+}

diff --git a/pkgs/watcher/lib/src/directory_watcher/windows.dart b/pkgs/watcher/lib/src/directory_watcher/windows.dart
new file mode 100644
index 0000000..d1c98be
--- /dev/null
+++ b/pkgs/watcher/lib/src/directory_watcher/windows.dart

@@ -0,0 +1,437 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+// TODO(rnystrom): Merge with mac_os version.
+
+import 'dart:async';
+import 'dart:collection';
+import 'dart:io';
+
+import 'package:path/path.dart' as p;
+
+import '../directory_watcher.dart';
+import '../path_set.dart';
+import '../resubscribable.dart';
+import '../utils.dart';
+import '../watch_event.dart';
+
+class WindowsDirectoryWatcher extends ResubscribableWatcher
+    implements DirectoryWatcher {
+  @override
+  String get directory => path;
+
+  WindowsDirectoryWatcher(String directory)
+      : super(directory, () => _WindowsDirectoryWatcher(directory));
+}
+
+class _EventBatcher {
+  static const Duration _batchDelay = Duration(milliseconds: 100);
+  final List<FileSystemEvent> events = [];
+  Timer? timer;
+
+  void addEvent(FileSystemEvent event, void Function() callback) {
+    events.add(event);
+    timer?.cancel();
+    timer = Timer(_batchDelay, callback);
+  }
+
+  void cancelTimer() {
+    timer?.cancel();
+  }
+}
+
+class _WindowsDirectoryWatcher
+    implements DirectoryWatcher, ManuallyClosedWatcher {
+  @override
+  String get directory => path;
+  @override
+  final String path;
+
+  @override
+  Stream<WatchEvent> get events => _eventsController.stream;
+  final _eventsController = StreamController<WatchEvent>.broadcast();
+
+  @override
+  bool get isReady => _readyCompleter.isCompleted;
+
+  @override
+  Future<void> get ready => _readyCompleter.future;
+  final _readyCompleter = Completer<void>();
+
+  final Map<String, _EventBatcher> _eventBatchers =
+      HashMap<String, _EventBatcher>();
+
+  /// The set of files that are known to exist recursively within the watched
+  /// directory.
+  ///
+  /// The state of files on the filesystem is compared against this to determine
+  /// the real change that occurred. This is also used to emit REMOVE events
+  /// when subdirectories are moved out of the watched directory.
+  final PathSet _files;
+
+  /// The subscription to the stream returned by [Directory.watch].
+  StreamSubscription<FileSystemEvent>? _watchSubscription;
+
+  /// The subscription to the stream returned by [Directory.watch] of the
+  /// parent directory to [directory]. This is needed to detect changes to
+  /// [directory], as they are not included on Windows.
+  StreamSubscription<FileSystemEvent>? _parentWatchSubscription;
+
+  /// The subscription to the [Directory.list] call for the initial listing of
+  /// the directory to determine its initial state.
+  StreamSubscription<FileSystemEntity>? _initialListSubscription;
+
+  /// The subscriptions to the [Directory.list] calls for listing the contents
+  /// of subdirectories that were moved into the watched directory.
+  final Set<StreamSubscription<FileSystemEntity>> _listSubscriptions =
+      HashSet<StreamSubscription<FileSystemEntity>>();
+
+  _WindowsDirectoryWatcher(this.path) : _files = PathSet(path) {
+    // Before we're ready to emit events, wait for [_listDir] to complete.
+    _listDir().then((_) {
+      _startWatch();
+      _startParentWatcher();
+      if (!isReady) {
+        _readyCompleter.complete();
+      }
+    });
+  }
+
+  @override
+  void close() {
+    _watchSubscription?.cancel();
+    _parentWatchSubscription?.cancel();
+    _initialListSubscription?.cancel();
+    for (var sub in _listSubscriptions) {
+      sub.cancel();
+    }
+    _listSubscriptions.clear();
+    for (var batcher in _eventBatchers.values) {
+      batcher.cancelTimer();
+    }
+    _eventBatchers.clear();
+    _watchSubscription = null;
+    _parentWatchSubscription = null;
+    _initialListSubscription = null;
+    _eventsController.close();
+  }
+
+  /// On Windows, if [directory] is deleted, we will not receive any event.
+  ///
+  /// Instead, we add a watcher on the parent folder (if any), that can notify
+  /// us about [path]. This also includes events such as moves.
+  void _startParentWatcher() {
+    var absoluteDir = p.absolute(path);
+    var parent = p.dirname(absoluteDir);
+    // Check if [path] is already the root directory.
+    if (FileSystemEntity.identicalSync(parent, path)) return;
+    var parentStream = Directory(parent).watch(recursive: false);
+    _parentWatchSubscription = parentStream.listen((event) {
+      // Only look at events for 'directory'.
+      if (p.basename(event.path) != p.basename(absoluteDir)) return;
+      // Test if the directory is removed. FileSystemEntity.typeSync will
+      // return NOT_FOUND if it's unable to decide upon the type, including
+      // access denied issues, which may happen when the directory is deleted.
+      // FileSystemMoveEvent and FileSystemDeleteEvent events will always mean
+      // the directory is now gone.
+      if (event is FileSystemMoveEvent ||
+          event is FileSystemDeleteEvent ||
+          (FileSystemEntity.typeSync(path) == FileSystemEntityType.notFound)) {
+        for (var path in _files.paths) {
+          _emitEvent(ChangeType.REMOVE, path);
+        }
+        _files.clear();
+        close();
+      }
+    }, onError: (error) {
+      // Ignore errors, simply close the stream. The user listens on
+      // [directory], and while it can fail to listen on the parent, we may
+      // still be able to listen on the path requested.
+      _parentWatchSubscription?.cancel();
+      _parentWatchSubscription = null;
+    });
+  }
+
+  void _onEvent(FileSystemEvent event) {
+    assert(isReady);
+    final batcher = _eventBatchers.putIfAbsent(event.path, _EventBatcher.new);
+    batcher.addEvent(event, () {
+      _eventBatchers.remove(event.path);
+      _onBatch(batcher.events);
+    });
+  }
+
+  /// The callback that's run when [Directory.watch] emits a batch of events.
+  void _onBatch(List<FileSystemEvent> batch) {
+    _sortEvents(batch).forEach((path, eventSet) {
+      var canonicalEvent = _canonicalEvent(eventSet);
+      var events = canonicalEvent == null
+          ? _eventsBasedOnFileSystem(path)
+          : [canonicalEvent];
+
+      for (var event in events) {
+        if (event is FileSystemCreateEvent) {
+          if (!event.isDirectory) {
+            if (_files.contains(path)) continue;
+
+            _emitEvent(ChangeType.ADD, path);
+            _files.add(path);
+            continue;
+          }
+
+          if (_files.containsDir(path)) continue;
+
+          var stream = Directory(path).list(recursive: true);
+          var subscription = stream.listen((entity) {
+            if (entity is Directory) return;
+            if (_files.contains(path)) return;
+
+            _emitEvent(ChangeType.ADD, entity.path);
+            _files.add(entity.path);
+          }, cancelOnError: true);
+          subscription.onDone(() {
+            _listSubscriptions.remove(subscription);
+          });
+          subscription.onError((Object e, StackTrace stackTrace) {
+            _listSubscriptions.remove(subscription);
+            _emitError(e, stackTrace);
+          });
+          _listSubscriptions.add(subscription);
+        } else if (event is FileSystemModifyEvent) {
+          if (!event.isDirectory) {
+            _emitEvent(ChangeType.MODIFY, path);
+          }
+        } else {
+          assert(event is FileSystemDeleteEvent);
+          for (var removedPath in _files.remove(path)) {
+            _emitEvent(ChangeType.REMOVE, removedPath);
+          }
+        }
+      }
+    });
+  }
+
+  /// Sort all the events in a batch into sets based on their path.
+  ///
+  /// A single input event may result in multiple events in the returned map;
+  /// for example, a MOVE event becomes a DELETE event for the source and a
+  /// CREATE event for the destination.
+  ///
+  /// The returned events won't contain any [FileSystemMoveEvent]s, nor will it
+  /// contain any events relating to [path].
+  Map<String, Set<FileSystemEvent>> _sortEvents(List<FileSystemEvent> batch) {
+    var eventsForPaths = <String, Set<FileSystemEvent>>{};
+
+    // Events within directories that already have events are superfluous; the
+    // directory's full contents will be examined anyway, so we ignore such
+    // events. Emitting them could cause useless or out-of-order events.
+    var directories = unionAll(batch.map((event) {
+      if (!event.isDirectory) return <String>{};
+      if (event is FileSystemMoveEvent) {
+        var destination = event.destination;
+        if (destination != null) {
+          return {event.path, destination};
+        }
+      }
+      return {event.path};
+    }));
+
+    bool isInModifiedDirectory(String path) =>
+        directories.any((dir) => path != dir && p.isWithin(dir, path));
+
+    void addEvent(String path, FileSystemEvent event) {
+      if (isInModifiedDirectory(path)) return;
+      eventsForPaths.putIfAbsent(path, () => <FileSystemEvent>{}).add(event);
+    }
+
+    for (var event in batch) {
+      if (event is FileSystemMoveEvent) {
+        var destination = event.destination;
+        if (destination != null) {
+          addEvent(destination, event);
+        }
+      }
+      addEvent(event.path, event);
+    }
+
+    return eventsForPaths;
+  }
+
+  /// Returns the canonical event from a batch of events on the same path, if
+  /// one exists.
+  ///
+  /// If [batch] doesn't contain any contradictory events (e.g. DELETE and
+  /// CREATE, or events with different values for `isDirectory`), this returns a
+  /// single event that describes what happened to the path in question.
+  ///
+  /// If [batch] does contain contradictory events, this returns `null` to
+  /// indicate that the state of the path on the filesystem should be checked to
+  /// determine what occurred.
+  FileSystemEvent? _canonicalEvent(Set<FileSystemEvent> batch) {
+    // An empty batch indicates that we've learned earlier that the batch is
+    // contradictory (e.g. because of a move).
+    if (batch.isEmpty) return null;
+
+    var type = batch.first.type;
+    var isDir = batch.first.isDirectory;
+
+    for (var event in batch.skip(1)) {
+      // If one event reports that the file is a directory and another event
+      // doesn't, that's a contradiction.
+      if (isDir != event.isDirectory) return null;
+
+      // Modify events don't contradict either CREATE or REMOVE events. We can
+      // safely assume the file was modified after a CREATE or before the
+      // REMOVE; otherwise there will also be a REMOVE or CREATE event
+      // (respectively) that will be contradictory.
+      if (event is FileSystemModifyEvent) continue;
+      assert(event is FileSystemCreateEvent ||
+          event is FileSystemDeleteEvent ||
+          event is FileSystemMoveEvent);
+
+      // If we previously thought this was a MODIFY, we now consider it to be a
+      // CREATE or REMOVE event. This is safe for the same reason as above.
+      if (type == FileSystemEvent.modify) {
+        type = event.type;
+        continue;
+      }
+
+      // A CREATE event contradicts a REMOVE event and vice versa.
+      assert(type == FileSystemEvent.create ||
+          type == FileSystemEvent.delete ||
+          type == FileSystemEvent.move);
+      if (type != event.type) return null;
+    }
+
+    switch (type) {
+      case FileSystemEvent.create:
+        return FileSystemCreateEvent(batch.first.path, isDir);
+      case FileSystemEvent.delete:
+        return FileSystemDeleteEvent(batch.first.path, isDir);
+      case FileSystemEvent.modify:
+        return FileSystemModifyEvent(batch.first.path, isDir, false);
+      case FileSystemEvent.move:
+        return null;
+      default:
+        throw StateError('unreachable');
+    }
+  }
+
+  /// Returns zero or more events that describe the change between the last
+  /// known state of [path] and its current state on the filesystem.
+  ///
+  /// This returns a list whose order should be reflected in the events emitted
+  /// to the user, unlike the batched events from [Directory.watch]. The
+  /// returned list may be empty, indicating that no changes occurred to [path]
+  /// (probably indicating that it was created and then immediately deleted).
+  List<FileSystemEvent> _eventsBasedOnFileSystem(String path) {
+    var fileExisted = _files.contains(path);
+    var dirExisted = _files.containsDir(path);
+
+    bool fileExists;
+    bool dirExists;
+    try {
+      fileExists = File(path).existsSync();
+      dirExists = Directory(path).existsSync();
+    } on FileSystemException {
+      return const <FileSystemEvent>[];
+    }
+
+    var events = <FileSystemEvent>[];
+    if (fileExisted) {
+      if (fileExists) {
+        events.add(FileSystemModifyEvent(path, false, false));
+      } else {
+        events.add(FileSystemDeleteEvent(path, false));
+      }
+    } else if (dirExisted) {
+      if (dirExists) {
+        // If we got contradictory events for a directory that used to exist and
+        // still exists, we need to rescan the whole thing in case it was
+        // replaced with a different directory.
+        events.add(FileSystemDeleteEvent(path, true));
+        events.add(FileSystemCreateEvent(path, true));
+      } else {
+        events.add(FileSystemDeleteEvent(path, true));
+      }
+    }
+
+    if (!fileExisted && fileExists) {
+      events.add(FileSystemCreateEvent(path, false));
+    } else if (!dirExisted && dirExists) {
+      events.add(FileSystemCreateEvent(path, true));
+    }
+
+    return events;
+  }
+
+  /// The callback that's run when the [Directory.watch] stream is closed.
+  /// Note that this is unlikely to happen on Windows, unless the system itself
+  /// closes the handle.
+  void _onDone() {
+    _watchSubscription = null;
+
+    // Emit remove events for any remaining files.
+    for (var file in _files.paths) {
+      _emitEvent(ChangeType.REMOVE, file);
+    }
+    _files.clear();
+    close();
+  }
+
+  /// Start or restart the underlying [Directory.watch] stream.
+  void _startWatch() {
+    // Note: "watcher closed" exceptions do not get sent over the stream
+    // returned by watch, and must be caught via a zone handler.
+    runZonedGuarded(() {
+      var innerStream = Directory(path).watch(recursive: true);
+      _watchSubscription = innerStream.listen(_onEvent,
+          onError: _eventsController.addError, onDone: _onDone);
+    }, (error, stackTrace) {
+      if (error is FileSystemException &&
+          error.message.startsWith('Directory watcher closed unexpectedly')) {
+        _watchSubscription?.cancel();
+        _eventsController.addError(error, stackTrace);
+        _startWatch();
+      } else {
+        // ignore: only_throw_errors
+        throw error;
+      }
+    });
+  }
+
+  /// Starts or restarts listing the watched directory to get an initial picture
+  /// of its state.
+  Future<void> _listDir() {
+    assert(!isReady);
+    _initialListSubscription?.cancel();
+
+    _files.clear();
+    var completer = Completer<void>();
+    var stream = Directory(path).list(recursive: true);
+    void handleEntity(FileSystemEntity entity) {
+      if (entity is! Directory) _files.add(entity.path);
+    }
+
+    _initialListSubscription = stream.listen(handleEntity,
+        onError: _emitError, onDone: completer.complete, cancelOnError: true);
+    return completer.future;
+  }
+
+  /// Emit an event with the given [type] and [path].
+  void _emitEvent(ChangeType type, String path) {
+    if (!isReady) return;
+
+    _eventsController.add(WatchEvent(type, path));
+  }
+
+  /// Emit an error, then close the watcher.
+  void _emitError(Object error, StackTrace stackTrace) {
+    // Guarantee that ready always completes.
+    if (!isReady) {
+      _readyCompleter.complete();
+    }
+    _eventsController.addError(error, stackTrace);
+    close();
+  }
+}

diff --git a/pkgs/watcher/lib/src/file_watcher.dart b/pkgs/watcher/lib/src/file_watcher.dart
new file mode 100644
index 0000000..143aa31
--- /dev/null
+++ b/pkgs/watcher/lib/src/file_watcher.dart

@@ -0,0 +1,44 @@
+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:io';
+
+import '../watcher.dart';
+import 'custom_watcher_factory.dart';
+import 'file_watcher/native.dart';
+
+/// Watches a file and emits [WatchEvent]s when the file has changed.
+///
+/// Note that since each watcher only watches a single file, it will only emit
+/// [ChangeType.MODIFY] events, except when the file is deleted at which point
+/// it will emit a single [ChangeType.REMOVE] event and then close the stream.
+///
+/// If the file is deleted and quickly replaced (when a new file is moved in its
+/// place, for example) this will emit a [ChangeType.MODIFY] event.
+abstract class FileWatcher implements Watcher {
+  /// Creates a new [FileWatcher] monitoring [file].
+  ///
+  /// If a native file watcher is available for this platform, this will use it.
+  /// Otherwise, it will fall back to a [PollingFileWatcher]. Notably, native
+  /// file watching is *not* supported on Windows.
+  ///
+  /// If [pollingDelay] is passed, it specifies the amount of time the watcher
+  /// will pause between successive polls of the directory contents. Making this
+  /// shorter will give more immediate feedback at the expense of doing more IO
+  /// and higher CPU usage. Defaults to one second. Ignored for non-polling
+  /// watchers.
+  factory FileWatcher(String file, {Duration? pollingDelay}) {
+    var customWatcher =
+        createCustomFileWatcher(file, pollingDelay: pollingDelay);
+    if (customWatcher != null) return customWatcher;
+
+    // [File.watch] doesn't work on Windows, but
+    // [FileSystemEntity.isWatchSupported] is still true because directory
+    // watching does work.
+    if (FileSystemEntity.isWatchSupported && !Platform.isWindows) {
+      return NativeFileWatcher(file);
+    }
+    return PollingFileWatcher(file, pollingDelay: pollingDelay);
+  }
+}

diff --git a/pkgs/watcher/lib/src/file_watcher/native.dart b/pkgs/watcher/lib/src/file_watcher/native.dart
new file mode 100644
index 0000000..502aa10
--- /dev/null
+++ b/pkgs/watcher/lib/src/file_watcher/native.dart

@@ -0,0 +1,90 @@
+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+import 'dart:io';
+
+import '../file_watcher.dart';
+import '../resubscribable.dart';
+import '../utils.dart';
+import '../watch_event.dart';
+
+/// Uses the native file system notifications to watch for filesystem events.
+///
+/// Single-file notifications are much simpler than those for multiple files, so
+/// this doesn't need to be split out into multiple OS-specific classes.
+class NativeFileWatcher extends ResubscribableWatcher implements FileWatcher {
+  NativeFileWatcher(String path) : super(path, () => _NativeFileWatcher(path));
+}
+
+class _NativeFileWatcher implements FileWatcher, ManuallyClosedWatcher {
+  @override
+  final String path;
+
+  @override
+  Stream<WatchEvent> get events => _eventsController.stream;
+  final _eventsController = StreamController<WatchEvent>.broadcast();
+
+  @override
+  bool get isReady => _readyCompleter.isCompleted;
+
+  @override
+  Future<void> get ready => _readyCompleter.future;
+  final _readyCompleter = Completer<void>();
+
+  StreamSubscription<List<FileSystemEvent>>? _subscription;
+
+  _NativeFileWatcher(this.path) {
+    _listen();
+
+    // We don't need to do any initial set-up, so we're ready immediately after
+    // being listened to.
+    _readyCompleter.complete();
+  }
+
+  void _listen() {
+    // Batch the events together so that we can dedup them.
+    _subscription = File(path)
+        .watch()
+        .batchEvents()
+        .listen(_onBatch, onError: _eventsController.addError, onDone: _onDone);
+  }
+
+  void _onBatch(List<FileSystemEvent> batch) {
+    if (batch.any((event) => event.type == FileSystemEvent.delete)) {
+      // If the file is deleted, the underlying stream will close. We handle
+      // emitting our own REMOVE event in [_onDone].
+      return;
+    }
+
+    _eventsController.add(WatchEvent(ChangeType.MODIFY, path));
+  }
+
+  void _onDone() async {
+    var fileExists = await File(path).exists();
+
+    // Check for this after checking whether the file exists because it's
+    // possible that [close] was called between [File.exists] being called and
+    // it completing.
+    if (_eventsController.isClosed) return;
+
+    if (fileExists) {
+      // If the file exists now, it was probably removed and quickly replaced;
+      // this can happen for example when another file is moved on top of it.
+      // Re-subscribe and report a modify event.
+      _eventsController.add(WatchEvent(ChangeType.MODIFY, path));
+      _listen();
+    } else {
+      _eventsController.add(WatchEvent(ChangeType.REMOVE, path));
+      close();
+    }
+  }
+
+  @override
+  void close() {
+    _subscription?.cancel();
+    _subscription = null;
+    _eventsController.close();
+  }
+}

diff --git a/pkgs/watcher/lib/src/file_watcher/polling.dart b/pkgs/watcher/lib/src/file_watcher/polling.dart
new file mode 100644
index 0000000..15ff9ab
--- /dev/null
+++ b/pkgs/watcher/lib/src/file_watcher/polling.dart

@@ -0,0 +1,106 @@
+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+import 'dart:io';
+
+import '../file_watcher.dart';
+import '../resubscribable.dart';
+import '../stat.dart';
+import '../watch_event.dart';
+
+/// Periodically polls a file for changes.
+class PollingFileWatcher extends ResubscribableWatcher implements FileWatcher {
+  PollingFileWatcher(String path, {Duration? pollingDelay})
+      : super(path, () {
+          return _PollingFileWatcher(
+              path, pollingDelay ?? const Duration(seconds: 1));
+        });
+}
+
+class _PollingFileWatcher implements FileWatcher, ManuallyClosedWatcher {
+  @override
+  final String path;
+
+  @override
+  Stream<WatchEvent> get events => _eventsController.stream;
+  final _eventsController = StreamController<WatchEvent>.broadcast();
+
+  @override
+  bool get isReady => _readyCompleter.isCompleted;
+
+  @override
+  Future<void> get ready => _readyCompleter.future;
+  final _readyCompleter = Completer<void>();
+
+  /// The timer that controls polling.
+  late final Timer _timer;
+
+  /// The previous modification time of the file.
+  ///
+  /// `null` indicates the file does not (or did not on the last poll) exist.
+  DateTime? _lastModified;
+
+  _PollingFileWatcher(this.path, Duration pollingDelay) {
+    _timer = Timer.periodic(pollingDelay, (_) => _poll());
+    _poll();
+  }
+
+  /// Checks the mtime of the file and whether it's been removed.
+  Future<void> _poll() async {
+    // We don't mark the file as removed if this is the first poll. Instead,
+    // below we forward the dart:io error that comes from trying to read the
+    // mtime below.
+    var pathExists = await File(path).exists();
+    if (_eventsController.isClosed) return;
+
+    if (_lastModified != null && !pathExists) {
+      _flagReady();
+      _eventsController.add(WatchEvent(ChangeType.REMOVE, path));
+      unawaited(close());
+      return;
+    }
+
+    DateTime? modified;
+    try {
+      modified = await modificationTime(path);
+    } on FileSystemException catch (error, stackTrace) {
+      if (!_eventsController.isClosed) {
+        _flagReady();
+        _eventsController.addError(error, stackTrace);
+        await close();
+      }
+    }
+    if (_eventsController.isClosed) {
+      _flagReady();
+      return;
+    }
+
+    if (!isReady) {
+      // If this is the first poll, don't emit an event, just set the last mtime
+      // and complete the completer.
+      _lastModified = modified;
+      _flagReady();
+      return;
+    }
+
+    if (_lastModified == modified) return;
+
+    _lastModified = modified;
+    _eventsController.add(WatchEvent(ChangeType.MODIFY, path));
+  }
+
+  /// Flags this watcher as ready if it has not already been done.
+  void _flagReady() {
+    if (!isReady) {
+      _readyCompleter.complete();
+    }
+  }
+
+  @override
+  Future<void> close() async {
+    _timer.cancel();
+    await _eventsController.close();
+  }
+}

diff --git a/pkgs/watcher/lib/src/path_set.dart b/pkgs/watcher/lib/src/path_set.dart
new file mode 100644
index 0000000..4f41cf9
--- /dev/null
+++ b/pkgs/watcher/lib/src/path_set.dart

@@ -0,0 +1,190 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:collection';
+
+import 'package:path/path.dart' as p;
+
+/// A set of paths, organized into a directory hierarchy.
+///
+/// When a path is [add]ed, it creates an implicit directory structure above
+/// that path. Directories can be inspected using [containsDir] and removed
+/// using [remove]. If they're removed, their contents are removed as well.
+///
+/// The paths in the set are normalized so that they all begin with [root].
+class PathSet {
+  /// The root path, which all paths in the set must be under.
+  final String root;
+
+  /// The path set's directory hierarchy.
+  ///
+  /// Each entry represents a directory or file. It may be a file or directory
+  /// that was explicitly added, or a parent directory that was implicitly
+  /// added in order to add a child.
+  final _Entry _entries = _Entry();
+
+  PathSet(this.root);
+
+  /// Adds [path] to the set.
+  void add(String path) {
+    path = _normalize(path);
+
+    var parts = p.split(path);
+    var entry = _entries;
+    for (var part in parts) {
+      entry = entry.contents.putIfAbsent(part, _Entry.new);
+    }
+
+    entry.isExplicit = true;
+  }
+
+  /// Removes [path] and any paths beneath it from the set and returns the
+  /// removed paths.
+  ///
+  /// Even if [path] itself isn't in the set, if it's a directory containing
+  /// paths that are in the set those paths will be removed and returned.
+  ///
+  /// If neither [path] nor any paths beneath it are in the set, returns an
+  /// empty set.
+  Set<String> remove(String path) {
+    path = _normalize(path);
+    var parts = Queue.of(p.split(path));
+
+    // Remove the children of [dir], as well as [dir] itself if necessary.
+    //
+    // [partialPath] is the path to [dir], and a prefix of [path]; the remaining
+    // components of [path] are in [parts].
+    Set<String> recurse(_Entry dir, String partialPath) {
+      if (parts.length > 1) {
+        // If there's more than one component left in [path], recurse down to
+        // the next level.
+        var part = parts.removeFirst();
+        var entry = dir.contents[part];
+        if (entry == null || entry.contents.isEmpty) return <String>{};
+
+        partialPath = p.join(partialPath, part);
+        var paths = recurse(entry, partialPath);
+        // After removing this entry's children, if it has no more children and
+        // it's not in the set in its own right, remove it as well.
+        if (entry.contents.isEmpty && !entry.isExplicit) {
+          dir.contents.remove(part);
+        }
+        return paths;
+      }
+
+      // If there's only one component left in [path], we should remove it.
+      var entry = dir.contents.remove(parts.first);
+      if (entry == null) return <String>{};
+
+      if (entry.contents.isEmpty) {
+        return {p.join(root, path)};
+      }
+
+      var set = _explicitPathsWithin(entry, path);
+      if (entry.isExplicit) {
+        set.add(p.join(root, path));
+      }
+
+      return set;
+    }
+
+    return recurse(_entries, root);
+  }
+
+  /// Recursively lists all of the explicit paths within [dir].
+  ///
+  /// [dirPath] should be the path to [dir].
+  Set<String> _explicitPathsWithin(_Entry dir, String dirPath) {
+    var paths = <String>{};
+    void recurse(_Entry dir, String path) {
+      dir.contents.forEach((name, entry) {
+        var entryPath = p.join(path, name);
+        if (entry.isExplicit) paths.add(p.join(root, entryPath));
+
+        recurse(entry, entryPath);
+      });
+    }
+
+    recurse(dir, dirPath);
+    return paths;
+  }
+
+  /// Returns whether this set contains [path].
+  ///
+  /// This only returns true for paths explicitly added to this set.
+  /// Implicitly-added directories can be inspected using [containsDir].
+  bool contains(String path) {
+    path = _normalize(path);
+    var entry = _entries;
+
+    for (var part in p.split(path)) {
+      var child = entry.contents[part];
+      if (child == null) return false;
+      entry = child;
+    }
+
+    return entry.isExplicit;
+  }
+
+  /// Returns whether this set contains paths beneath [path].
+  bool containsDir(String path) {
+    path = _normalize(path);
+    var entry = _entries;
+
+    for (var part in p.split(path)) {
+      var child = entry.contents[part];
+      if (child == null) return false;
+      entry = child;
+    }
+
+    return entry.contents.isNotEmpty;
+  }
+
+  /// All of the paths explicitly added to this set.
+  List<String> get paths {
+    var result = <String>[];
+
+    void recurse(_Entry dir, String path) {
+      for (var mapEntry in dir.contents.entries) {
+        var entry = mapEntry.value;
+        var entryPath = p.join(path, mapEntry.key);
+        if (entry.isExplicit) result.add(entryPath);
+        recurse(entry, entryPath);
+      }
+    }
+
+    recurse(_entries, root);
+    return result;
+  }
+
+  /// Removes all paths from this set.
+  void clear() {
+    _entries.contents.clear();
+  }
+
+  /// Returns a normalized version of [path].
+  ///
+  /// This removes any extra ".." or "."s and ensure that the returned path
+  /// begins with [root]. It's an error if [path] isn't within [root].
+  String _normalize(String path) {
+    assert(p.isWithin(root, path));
+
+    return p.relative(p.normalize(path), from: root);
+  }
+}
+
+/// A virtual file system entity tracked by the [PathSet].
+///
+/// It may have child entries in [contents], which implies it's a directory.
+class _Entry {
+  /// The child entries contained in this directory.
+  final Map<String, _Entry> contents = {};
+
+  /// If this entry was explicitly added as a leaf file system entity, this
+  /// will be true.
+  ///
+  /// Otherwise, it represents a parent directory that was implicitly added
+  /// when added some child of it.
+  bool isExplicit = false;
+}

diff --git a/pkgs/watcher/lib/src/resubscribable.dart b/pkgs/watcher/lib/src/resubscribable.dart
new file mode 100644
index 0000000..b99e9d7
--- /dev/null
+++ b/pkgs/watcher/lib/src/resubscribable.dart

@@ -0,0 +1,79 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import '../watcher.dart';
+
+/// A wrapper for [ManuallyClosedWatcher] that encapsulates support for closing
+/// the watcher when it has no subscribers and re-opening it when it's
+/// re-subscribed.
+///
+/// It's simpler to implement watchers without worrying about this behavior.
+/// This class wraps a watcher class which can be written with the simplifying
+/// assumption that it can continue emitting events until an explicit `close`
+/// method is called, at which point it will cease emitting events entirely. The
+/// [ManuallyClosedWatcher] interface is used for these watchers.
+///
+/// This would be more cleanly implemented as a function that takes a class and
+/// emits a new class, but Dart doesn't support that sort of thing. Instead it
+/// takes a factory function that produces instances of the inner class.
+abstract class ResubscribableWatcher implements Watcher {
+  /// The factory function that produces instances of the inner class.
+  final ManuallyClosedWatcher Function() _factory;
+
+  @override
+  final String path;
+
+  @override
+  Stream<WatchEvent> get events => _eventsController.stream;
+  late StreamController<WatchEvent> _eventsController;
+
+  @override
+  bool get isReady => _readyCompleter.isCompleted;
+
+  @override
+  Future<void> get ready => _readyCompleter.future;
+  var _readyCompleter = Completer<void>();
+
+  /// Creates a new [ResubscribableWatcher] wrapping the watchers
+  /// emitted by [_factory].
+  ResubscribableWatcher(this.path, this._factory) {
+    late ManuallyClosedWatcher watcher;
+    late StreamSubscription<WatchEvent> subscription;
+
+    _eventsController = StreamController<WatchEvent>.broadcast(
+        onListen: () async {
+          watcher = _factory();
+          subscription = watcher.events.listen(_eventsController.add,
+              onError: _eventsController.addError,
+              onDone: _eventsController.close);
+
+          // It's important that we complete the value of [_readyCompleter] at
+          // the time [onListen] is called, as opposed to the value when
+          // [watcher.ready] fires. A new completer may be created by that time.
+          await watcher.ready;
+          _readyCompleter.complete();
+        },
+        onCancel: () {
+          // Cancel the subscription before closing the watcher so that the
+          // watcher's `onDone` event doesn't close [events].
+          subscription.cancel();
+          watcher.close();
+          _readyCompleter = Completer();
+        },
+        sync: true);
+  }
+}
+
+/// An interface for watchers with an explicit, manual [close] method.
+///
+/// See [ResubscribableWatcher].
+abstract class ManuallyClosedWatcher implements Watcher {
+  /// Closes the watcher.
+  ///
+  /// Subclasses should close their [events] stream and release any internal
+  /// resources.
+  void close();
+}

diff --git a/pkgs/watcher/lib/src/stat.dart b/pkgs/watcher/lib/src/stat.dart
new file mode 100644
index 0000000..fe0f155
--- /dev/null
+++ b/pkgs/watcher/lib/src/stat.dart

@@ -0,0 +1,34 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:io';
+
+/// A function that takes a file path and returns the last modified time for
+/// the file at that path.
+typedef MockTimeCallback = DateTime? Function(String path);
+
+MockTimeCallback? _mockTimeCallback;
+
+/// Overrides the default behavior for accessing a file's modification time
+/// with [callback].
+///
+/// The OS file modification time has pretty rough granularity (like a few
+/// seconds) which can make for slow tests that rely on modtime. This lets you
+/// replace it with something you control.
+void mockGetModificationTime(MockTimeCallback callback) {
+  _mockTimeCallback = callback;
+}
+
+/// Gets the modification time for the file at [path].
+/// Completes with `null` if the file does not exist.
+Future<DateTime?> modificationTime(String path) async {
+  var mockTimeCallback = _mockTimeCallback;
+  if (mockTimeCallback != null) {
+    return mockTimeCallback(path);
+  }
+
+  final stat = await FileStat.stat(path);
+  if (stat.type == FileSystemEntityType.notFound) return null;
+  return stat.modified;
+}

diff --git a/pkgs/watcher/lib/src/utils.dart b/pkgs/watcher/lib/src/utils.dart
new file mode 100644
index 0000000..c2e71b3
--- /dev/null
+++ b/pkgs/watcher/lib/src/utils.dart

@@ -0,0 +1,52 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+import 'dart:collection';
+import 'dart:io';
+
+/// Returns `true` if [error] is a [FileSystemException] for a missing
+/// directory.
+bool isDirectoryNotFoundException(Object error) {
+  if (error is! FileSystemException) return false;
+
+  // See dartbug.com/12461 and tests/standalone/io/directory_error_test.dart.
+  var notFoundCode = Platform.operatingSystem == 'windows' ? 3 : 2;
+  return error.osError?.errorCode == notFoundCode;
+}
+
+/// Returns the union of all elements in each set in [sets].
+Set<T> unionAll<T>(Iterable<Set<T>> sets) =>
+    sets.fold(<T>{}, (union, set) => union.union(set));
+
+extension BatchEvents<T> on Stream<T> {
+  /// Batches all events that are sent at the same time.
+  ///
+  /// When multiple events are synchronously added to a stream controller, the
+  /// [StreamController] implementation uses [scheduleMicrotask] to schedule the
+  /// asynchronous firing of each event. In order to recreate the synchronous
+  /// batches, this collates all the events that are received in "nearby"
+  /// microtasks.
+  Stream<List<T>> batchEvents() {
+    var batch = Queue<T>();
+    return StreamTransformer<T, List<T>>.fromHandlers(
+        handleData: (event, sink) {
+      batch.add(event);
+
+      // [Timer.run] schedules an event that runs after any microtasks that have
+      // been scheduled.
+      Timer.run(() {
+        if (batch.isEmpty) return;
+        sink.add(batch.toList());
+        batch.clear();
+      });
+    }, handleDone: (sink) {
+      if (batch.isNotEmpty) {
+        sink.add(batch.toList());
+        batch.clear();
+      }
+      sink.close();
+    }).bind(this);
+  }
+}

diff --git a/pkgs/watcher/lib/src/watch_event.dart b/pkgs/watcher/lib/src/watch_event.dart
new file mode 100644
index 0000000..b65afc2
--- /dev/null
+++ b/pkgs/watcher/lib/src/watch_event.dart

@@ -0,0 +1,38 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// An event describing a single change to the file system.
+class WatchEvent {
+  /// The manner in which the file at [path] has changed.
+  final ChangeType type;
+
+  /// The path of the file that changed.
+  final String path;
+
+  WatchEvent(this.type, this.path);
+
+  @override
+  String toString() => '$type $path';
+}
+
+/// Enum for what kind of change has happened to a file.
+class ChangeType {
+  /// A new file has been added.
+  // ignore: constant_identifier_names
+  static const ADD = ChangeType('add');
+
+  /// A file has been removed.
+  // ignore: constant_identifier_names
+  static const REMOVE = ChangeType('remove');
+
+  /// The contents of a file have changed.
+  // ignore: constant_identifier_names
+  static const MODIFY = ChangeType('modify');
+
+  final String _name;
+  const ChangeType(this._name);
+
+  @override
+  String toString() => _name;
+}

diff --git a/pkgs/watcher/lib/watcher.dart b/pkgs/watcher/lib/watcher.dart
new file mode 100644
index 0000000..12a5369
--- /dev/null
+++ b/pkgs/watcher/lib/watcher.dart

@@ -0,0 +1,70 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:io';
+
+import 'src/directory_watcher.dart';
+import 'src/file_watcher.dart';
+import 'src/watch_event.dart';
+
+export 'src/custom_watcher_factory.dart' show registerCustomWatcher;
+export 'src/directory_watcher.dart';
+export 'src/directory_watcher/polling.dart';
+export 'src/file_watcher.dart';
+export 'src/file_watcher/polling.dart';
+export 'src/watch_event.dart';
+
+abstract class Watcher {
+  /// The path to the file or directory whose contents are being monitored.
+  String get path;
+
+  /// The broadcast [Stream] of events that have occurred to the watched file or
+  /// files in the watched directory.
+  ///
+  /// Changes will only be monitored while this stream has subscribers. Any
+  /// changes that occur during periods when there are no subscribers will not
+  /// be reported the next time a subscriber is added.
+  Stream<WatchEvent> get events;
+
+  /// Whether the watcher is initialized and watching for changes.
+  ///
+  /// This is true if and only if [ready] is complete.
+  bool get isReady;
+
+  /// A [Future] that completes when the watcher is initialized and watching for
+  /// changes.
+  ///
+  /// If the watcher is not currently monitoring the file or directory (because
+  /// there are no subscribers to [events]), this returns a future that isn't
+  /// complete yet. It will complete when a subscriber starts listening and the
+  /// watcher finishes any initialization work it needs to do.
+  ///
+  /// If the watcher is already monitoring, this returns an already complete
+  /// future.
+  ///
+  /// This future always completes successfully as errors are provided through
+  /// the [events] stream.
+  Future get ready;
+
+  /// Creates a new [DirectoryWatcher] or [FileWatcher] monitoring [path],
+  /// depending on whether it's a file or directory.
+  ///
+  /// If a native watcher is available for this platform, this will use it.
+  /// Otherwise, it will fall back to a polling watcher. Notably, watching
+  /// individual files is not natively supported on Windows, although watching
+  /// directories is.
+  ///
+  /// If [pollingDelay] is passed, it specifies the amount of time the watcher
+  /// will pause between successive polls of the contents of [path]. Making this
+  /// shorter will give more immediate feedback at the expense of doing more IO
+  /// and higher CPU usage. Defaults to one second. Ignored for non-polling
+  /// watchers.
+  factory Watcher(String path, {Duration? pollingDelay}) {
+    if (File(path).existsSync()) {
+      return FileWatcher(path, pollingDelay: pollingDelay);
+    } else {
+      return DirectoryWatcher(path, pollingDelay: pollingDelay);
+    }
+  }
+}

diff --git a/pkgs/watcher/pubspec.yaml b/pkgs/watcher/pubspec.yaml
new file mode 100644
index 0000000..7781bd4
--- /dev/null
+++ b/pkgs/watcher/pubspec.yaml

@@ -0,0 +1,19 @@
+name: watcher
+version: 1.1.1
+description: >-
+  A file system watcher. It monitors changes to contents of directories and
+  sends notifications when files have been added, removed, or modified.
+repository: https://github.com/dart-lang/tools/tree/main/pkgs/watcher
+
+environment:
+  sdk: ^3.1.0
+
+dependencies:
+  async: ^2.5.0
+  path: ^1.8.0
+
+dev_dependencies:
+  benchmark_harness: ^2.0.0
+  dart_flutter_team_lints: ^3.0.0
+  test: ^1.16.6
+  test_descriptor: ^2.0.0

diff --git a/pkgs/watcher/test/custom_watcher_factory_test.dart b/pkgs/watcher/test/custom_watcher_factory_test.dart
new file mode 100644
index 0000000..e9d65bb
--- /dev/null
+++ b/pkgs/watcher/test/custom_watcher_factory_test.dart

@@ -0,0 +1,142 @@
+import 'dart:async';
+
+import 'package:test/test.dart';
+import 'package:watcher/watcher.dart';
+
+void main() {
+  late _MemFs memFs;
+  final memFsFactoryId = 'MemFs';
+  final noOpFactoryId = 'NoOp';
+
+  setUpAll(() {
+    memFs = _MemFs();
+    var memFsWatcherFactory = _MemFsWatcherFactory(memFs);
+    var noOpWatcherFactory = _NoOpWatcherFactory();
+    registerCustomWatcher(
+        noOpFactoryId,
+        noOpWatcherFactory.createDirectoryWatcher,
+        noOpWatcherFactory.createFileWatcher);
+    registerCustomWatcher(
+        memFsFactoryId,
+        memFsWatcherFactory.createDirectoryWatcher,
+        memFsWatcherFactory.createFileWatcher);
+  });
+
+  test('notifies for files', () async {
+    var watcher = FileWatcher('file.txt');
+
+    var completer = Completer<WatchEvent>();
+    watcher.events.listen((event) => completer.complete(event));
+    await watcher.ready;
+    memFs.add('file.txt');
+    var event = await completer.future;
+
+    expect(event.type, ChangeType.ADD);
+    expect(event.path, 'file.txt');
+  });
+
+  test('notifies for directories', () async {
+    var watcher = DirectoryWatcher('dir');
+
+    var completer = Completer<WatchEvent>();
+    watcher.events.listen((event) => completer.complete(event));
+    await watcher.ready;
+    memFs.add('dir');
+    var event = await completer.future;
+
+    expect(event.type, ChangeType.ADD);
+    expect(event.path, 'dir');
+  });
+
+  test('registering twice throws', () async {
+    expect(
+      () => registerCustomWatcher(
+          memFsFactoryId,
+          (_, {pollingDelay}) => throw UnimplementedError(),
+          (_, {pollingDelay}) => throw UnimplementedError()),
+      throwsA(isA<ArgumentError>()),
+    );
+  });
+
+  test('finding two applicable factories throws', () async {
+    // Note that _MemFsWatcherFactory always returns a watcher, so having two
+    // will always produce a conflict.
+    var watcherFactory = _MemFsWatcherFactory(memFs);
+    registerCustomWatcher('Different id', watcherFactory.createDirectoryWatcher,
+        watcherFactory.createFileWatcher);
+    expect(() => FileWatcher('file.txt'), throwsA(isA<StateError>()));
+    expect(() => DirectoryWatcher('dir'), throwsA(isA<StateError>()));
+  });
+}
+
+class _MemFs {
+  final _streams = <String, Set<StreamController<WatchEvent>>>{};
+
+  StreamController<WatchEvent> watchStream(String path) {
+    var controller = StreamController<WatchEvent>();
+    _streams
+        .putIfAbsent(path, () => <StreamController<WatchEvent>>{})
+        .add(controller);
+    return controller;
+  }
+
+  void add(String path) {
+    var controllers = _streams[path];
+    if (controllers != null) {
+      for (var controller in controllers) {
+        controller.add(WatchEvent(ChangeType.ADD, path));
+      }
+    }
+  }
+
+  void remove(String path) {
+    var controllers = _streams[path];
+    if (controllers != null) {
+      for (var controller in controllers) {
+        controller.add(WatchEvent(ChangeType.REMOVE, path));
+      }
+    }
+  }
+}
+
+class _MemFsWatcher implements FileWatcher, DirectoryWatcher, Watcher {
+  final String _path;
+  final StreamController<WatchEvent> _controller;
+
+  _MemFsWatcher(this._path, this._controller);
+
+  @override
+  String get path => _path;
+
+  @override
+  String get directory => throw UnsupportedError('directory is not supported');
+
+  @override
+  Stream<WatchEvent> get events => _controller.stream;
+
+  @override
+  bool get isReady => true;
+
+  @override
+  Future<void> get ready async {}
+}
+
+class _MemFsWatcherFactory {
+  final _MemFs _memFs;
+  _MemFsWatcherFactory(this._memFs);
+
+  DirectoryWatcher? createDirectoryWatcher(String path,
+          {Duration? pollingDelay}) =>
+      _MemFsWatcher(path, _memFs.watchStream(path));
+
+  FileWatcher? createFileWatcher(String path, {Duration? pollingDelay}) =>
+      _MemFsWatcher(path, _memFs.watchStream(path));
+}
+
+class _NoOpWatcherFactory {
+  DirectoryWatcher? createDirectoryWatcher(String path,
+          {Duration? pollingDelay}) =>
+      null;
+
+  FileWatcher? createFileWatcher(String path, {Duration? pollingDelay}) => null;
+}

diff --git a/pkgs/watcher/test/directory_watcher/linux_test.dart b/pkgs/watcher/test/directory_watcher/linux_test.dart
new file mode 100644
index 0000000..a10a72c
--- /dev/null
+++ b/pkgs/watcher/test/directory_watcher/linux_test.dart

@@ -0,0 +1,44 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+@TestOn('linux')
+library;
+
+import 'package:test/test.dart';
+import 'package:watcher/src/directory_watcher/linux.dart';
+import 'package:watcher/watcher.dart';
+
+import '../utils.dart';
+import 'shared.dart';
+
+void main() {
+  watcherFactory = LinuxDirectoryWatcher.new;
+
+  sharedTests();
+
+  test('DirectoryWatcher creates a LinuxDirectoryWatcher on Linux', () {
+    expect(DirectoryWatcher('.'), const TypeMatcher<LinuxDirectoryWatcher>());
+  });
+
+  test('emits events for many nested files moved out then immediately back in',
+      () async {
+    withPermutations(
+        (i, j, k) => writeFile('dir/sub/sub-$i/sub-$j/file-$k.txt'));
+    await startWatcher(path: 'dir');
+
+    renameDir('dir/sub', 'sub');
+    renameDir('sub', 'dir/sub');
+
+    await allowEither(() {
+      inAnyOrder(withPermutations(
+          (i, j, k) => isRemoveEvent('dir/sub/sub-$i/sub-$j/file-$k.txt')));
+
+      inAnyOrder(withPermutations(
+          (i, j, k) => isAddEvent('dir/sub/sub-$i/sub-$j/file-$k.txt')));
+    }, () {
+      inAnyOrder(withPermutations(
+          (i, j, k) => isModifyEvent('dir/sub/sub-$i/sub-$j/file-$k.txt')));
+    });
+  });
+}

diff --git a/pkgs/watcher/test/directory_watcher/mac_os_test.dart b/pkgs/watcher/test/directory_watcher/mac_os_test.dart
new file mode 100644
index 0000000..3376626
--- /dev/null
+++ b/pkgs/watcher/test/directory_watcher/mac_os_test.dart

@@ -0,0 +1,69 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+@TestOn('mac-os')
+library;
+
+import 'package:test/test.dart';
+import 'package:watcher/src/directory_watcher/mac_os.dart';
+import 'package:watcher/watcher.dart';
+
+import '../utils.dart';
+import 'shared.dart';
+
+void main() {
+  watcherFactory = MacOSDirectoryWatcher.new;
+
+  sharedTests();
+
+  test('DirectoryWatcher creates a MacOSDirectoryWatcher on Mac OS', () {
+    expect(DirectoryWatcher('.'), const TypeMatcher<MacOSDirectoryWatcher>());
+  });
+
+  test(
+      'does not notify about the watched directory being deleted and '
+      'recreated immediately before watching', () async {
+    createDir('dir');
+    writeFile('dir/old.txt');
+    deleteDir('dir');
+    createDir('dir');
+
+    await startWatcher(path: 'dir');
+    writeFile('dir/newer.txt');
+    await expectAddEvent('dir/newer.txt');
+  });
+
+  test('emits events for many nested files moved out then immediately back in',
+      () async {
+    withPermutations(
+        (i, j, k) => writeFile('dir/sub/sub-$i/sub-$j/file-$k.txt'));
+
+    await startWatcher(path: 'dir');
+
+    renameDir('dir/sub', 'sub');
+    renameDir('sub', 'dir/sub');
+
+    await allowEither(() {
+      inAnyOrder(withPermutations(
+          (i, j, k) => isRemoveEvent('dir/sub/sub-$i/sub-$j/file-$k.txt')));
+
+      inAnyOrder(withPermutations(
+          (i, j, k) => isAddEvent('dir/sub/sub-$i/sub-$j/file-$k.txt')));
+    }, () {
+      inAnyOrder(withPermutations(
+          (i, j, k) => isModifyEvent('dir/sub/sub-$i/sub-$j/file-$k.txt')));
+    });
+  });
+  test('does not suppress files with the same prefix as a directory', () async {
+    // Regression test for https://github.com/dart-lang/watcher/issues/83
+    writeFile('some_name.txt');
+
+    await startWatcher();
+
+    writeFile('some_name/some_name.txt');
+    deleteFile('some_name.txt');
+
+    await expectRemoveEvent('some_name.txt');
+  });
+}

diff --git a/pkgs/watcher/test/directory_watcher/polling_test.dart b/pkgs/watcher/test/directory_watcher/polling_test.dart
new file mode 100644
index 0000000..f4ec8f4
--- /dev/null
+++ b/pkgs/watcher/test/directory_watcher/polling_test.dart

@@ -0,0 +1,26 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:test/test.dart';
+import 'package:watcher/watcher.dart';
+
+import '../utils.dart';
+import 'shared.dart';
+
+void main() {
+  // Use a short delay to make the tests run quickly.
+  watcherFactory = (dir) => PollingDirectoryWatcher(dir,
+      pollingDelay: const Duration(milliseconds: 100));
+
+  sharedTests();
+
+  test('does not notify if the modification time did not change', () async {
+    writeFile('a.txt', contents: 'before');
+    writeFile('b.txt', contents: 'before');
+    await startWatcher();
+    writeFile('a.txt', contents: 'after', updateModified: false);
+    writeFile('b.txt', contents: 'after');
+    await expectModifyEvent('b.txt');
+  });
+}

diff --git a/pkgs/watcher/test/directory_watcher/shared.dart b/pkgs/watcher/test/directory_watcher/shared.dart
new file mode 100644
index 0000000..1ebc78d
--- /dev/null
+++ b/pkgs/watcher/test/directory_watcher/shared.dart

@@ -0,0 +1,344 @@
+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:test/test.dart';
+import 'package:watcher/src/utils.dart';
+
+import '../utils.dart';
+
+void sharedTests() {
+  test('does not notify for files that already exist when started', () async {
+    // Make some pre-existing files.
+    writeFile('a.txt');
+    writeFile('b.txt');
+
+    await startWatcher();
+
+    // Change one after the watcher is running.
+    writeFile('b.txt', contents: 'modified');
+
+    // We should get a modify event for the changed file, but no add events
+    // for them before this.
+    await expectModifyEvent('b.txt');
+  });
+
+  test('notifies when a file is added', () async {
+    await startWatcher();
+    writeFile('file.txt');
+    await expectAddEvent('file.txt');
+  });
+
+  test('notifies when a file is modified', () async {
+    writeFile('file.txt');
+    await startWatcher();
+    writeFile('file.txt', contents: 'modified');
+    await expectModifyEvent('file.txt');
+  });
+
+  test('notifies when a file is removed', () async {
+    writeFile('file.txt');
+    await startWatcher();
+    deleteFile('file.txt');
+    await expectRemoveEvent('file.txt');
+  });
+
+  test('notifies when a file is modified multiple times', () async {
+    writeFile('file.txt');
+    await startWatcher();
+    writeFile('file.txt', contents: 'modified');
+    await expectModifyEvent('file.txt');
+    writeFile('file.txt', contents: 'modified again');
+    await expectModifyEvent('file.txt');
+  });
+
+  test('notifies even if the file contents are unchanged', () async {
+    writeFile('a.txt', contents: 'same');
+    writeFile('b.txt', contents: 'before');
+    await startWatcher();
+
+    writeFile('a.txt', contents: 'same');
+    writeFile('b.txt', contents: 'after');
+    await inAnyOrder([isModifyEvent('a.txt'), isModifyEvent('b.txt')]);
+  });
+
+  test('when the watched directory is deleted, removes all files', () async {
+    writeFile('dir/a.txt');
+    writeFile('dir/b.txt');
+
+    await startWatcher(path: 'dir');
+
+    deleteDir('dir');
+    await inAnyOrder([isRemoveEvent('dir/a.txt'), isRemoveEvent('dir/b.txt')]);
+  });
+
+  test('when the watched directory is moved, removes all files', () async {
+    writeFile('dir/a.txt');
+    writeFile('dir/b.txt');
+
+    await startWatcher(path: 'dir');
+
+    renameDir('dir', 'moved_dir');
+    createDir('dir');
+    await inAnyOrder([isRemoveEvent('dir/a.txt'), isRemoveEvent('dir/b.txt')]);
+  });
+
+  // Regression test for b/30768513.
+  test(
+      "doesn't crash when the directory is moved immediately after a subdir "
+      'is added', () async {
+    writeFile('dir/a.txt');
+    writeFile('dir/b.txt');
+
+    await startWatcher(path: 'dir');
+
+    createDir('dir/subdir');
+    renameDir('dir', 'moved_dir');
+    createDir('dir');
+    await inAnyOrder([isRemoveEvent('dir/a.txt'), isRemoveEvent('dir/b.txt')]);
+  });
+
+  group('moves', () {
+    test('notifies when a file is moved within the watched directory',
+        () async {
+      writeFile('old.txt');
+      await startWatcher();
+      renameFile('old.txt', 'new.txt');
+
+      await inAnyOrder([isAddEvent('new.txt'), isRemoveEvent('old.txt')]);
+    });
+
+    test('notifies when a file is moved from outside the watched directory',
+        () async {
+      writeFile('old.txt');
+      createDir('dir');
+      await startWatcher(path: 'dir');
+
+      renameFile('old.txt', 'dir/new.txt');
+      await expectAddEvent('dir/new.txt');
+    });
+
+    test('notifies when a file is moved outside the watched directory',
+        () async {
+      writeFile('dir/old.txt');
+      await startWatcher(path: 'dir');
+
+      renameFile('dir/old.txt', 'new.txt');
+      await expectRemoveEvent('dir/old.txt');
+    });
+
+    test('notifies when a file is moved onto an existing one', () async {
+      writeFile('from.txt');
+      writeFile('to.txt');
+      await startWatcher();
+
+      renameFile('from.txt', 'to.txt');
+      await inAnyOrder([isRemoveEvent('from.txt'), isModifyEvent('to.txt')]);
+    }, onPlatform: {
+      'windows': const Skip('https://github.com/dart-lang/watcher/issues/125')
+    });
+  });
+
+  // Most of the time, when multiple filesystem actions happen in sequence,
+  // they'll be batched together and the watcher will see them all at once.
+  // These tests verify that the watcher normalizes and combine these events
+  // properly. However, very occasionally the events will be reported in
+  // separate batches, and the watcher will report them as though they occurred
+  // far apart in time, so each of these tests has a "backup case" to allow for
+  // that as well.
+  group('clustered changes', () {
+    test("doesn't notify when a file is created and then immediately removed",
+        () async {
+      writeFile('test.txt');
+      await startWatcher();
+      writeFile('file.txt');
+      deleteFile('file.txt');
+
+      // Backup case.
+      startClosingEventStream();
+      await allowEvents(() {
+        expectAddEvent('file.txt');
+        expectRemoveEvent('file.txt');
+      });
+    });
+
+    test(
+        'reports a modification when a file is deleted and then immediately '
+        'recreated', () async {
+      writeFile('file.txt');
+      await startWatcher();
+
+      deleteFile('file.txt');
+      writeFile('file.txt', contents: 're-created');
+
+      await allowEither(() {
+        expectModifyEvent('file.txt');
+      }, () {
+        // Backup case.
+        expectRemoveEvent('file.txt');
+        expectAddEvent('file.txt');
+      });
+    });
+
+    test(
+        'reports a modification when a file is moved and then immediately '
+        'recreated', () async {
+      writeFile('old.txt');
+      await startWatcher();
+
+      renameFile('old.txt', 'new.txt');
+      writeFile('old.txt', contents: 're-created');
+
+      await allowEither(() {
+        inAnyOrder([isModifyEvent('old.txt'), isAddEvent('new.txt')]);
+      }, () {
+        // Backup case.
+        expectRemoveEvent('old.txt');
+        expectAddEvent('new.txt');
+        expectAddEvent('old.txt');
+      });
+    });
+
+    test(
+        'reports a removal when a file is modified and then immediately '
+        'removed', () async {
+      writeFile('file.txt');
+      await startWatcher();
+
+      writeFile('file.txt', contents: 'modified');
+      deleteFile('file.txt');
+
+      // Backup case.
+      await allowModifyEvent('file.txt');
+
+      await expectRemoveEvent('file.txt');
+    });
+
+    test('reports an add when a file is added and then immediately modified',
+        () async {
+      await startWatcher();
+
+      writeFile('file.txt');
+      writeFile('file.txt', contents: 'modified');
+
+      await expectAddEvent('file.txt');
+
+      // Backup case.
+      startClosingEventStream();
+      await allowModifyEvent('file.txt');
+    });
+  });
+
+  group('subdirectories', () {
+    test('watches files in subdirectories', () async {
+      await startWatcher();
+      writeFile('a/b/c/d/file.txt');
+      await expectAddEvent('a/b/c/d/file.txt');
+    });
+
+    test(
+        'notifies when a subdirectory is moved within the watched directory '
+        'and then its contents are modified', () async {
+      writeFile('old/file.txt');
+      await startWatcher();
+
+      renameDir('old', 'new');
+      await inAnyOrder(
+          [isRemoveEvent('old/file.txt'), isAddEvent('new/file.txt')]);
+
+      writeFile('new/file.txt', contents: 'modified');
+      await expectModifyEvent('new/file.txt');
+    });
+
+    test('notifies when a file is replaced by a subdirectory', () async {
+      writeFile('new');
+      writeFile('old/file.txt');
+      await startWatcher();
+
+      deleteFile('new');
+      renameDir('old', 'new');
+      await inAnyOrder([
+        isRemoveEvent('new'),
+        isRemoveEvent('old/file.txt'),
+        isAddEvent('new/file.txt')
+      ]);
+    });
+
+    test('notifies when a subdirectory is replaced by a file', () async {
+      writeFile('old');
+      writeFile('new/file.txt');
+      await startWatcher();
+
+      renameDir('new', 'newer');
+      renameFile('old', 'new');
+      await inAnyOrder([
+        isRemoveEvent('new/file.txt'),
+        isAddEvent('newer/file.txt'),
+        isRemoveEvent('old'),
+        isAddEvent('new')
+      ]);
+    }, onPlatform: {
+      'windows': const Skip('https://github.com/dart-lang/watcher/issues/21')
+    });
+
+    test('emits events for many nested files added at once', () async {
+      withPermutations((i, j, k) => writeFile('sub/sub-$i/sub-$j/file-$k.txt'));
+
+      createDir('dir');
+      await startWatcher(path: 'dir');
+      renameDir('sub', 'dir/sub');
+
+      await inAnyOrder(withPermutations(
+          (i, j, k) => isAddEvent('dir/sub/sub-$i/sub-$j/file-$k.txt')));
+    });
+
+    test('emits events for many nested files removed at once', () async {
+      withPermutations(
+          (i, j, k) => writeFile('dir/sub/sub-$i/sub-$j/file-$k.txt'));
+
+      createDir('dir');
+      await startWatcher(path: 'dir');
+
+      // Rename the directory rather than deleting it because native watchers
+      // report a rename as a single DELETE event for the directory, whereas
+      // they report recursive deletion with DELETE events for every file in the
+      // directory.
+      renameDir('dir/sub', 'sub');
+
+      await inAnyOrder(withPermutations(
+          (i, j, k) => isRemoveEvent('dir/sub/sub-$i/sub-$j/file-$k.txt')));
+    });
+
+    test('emits events for many nested files moved at once', () async {
+      withPermutations(
+          (i, j, k) => writeFile('dir/old/sub-$i/sub-$j/file-$k.txt'));
+
+      createDir('dir');
+      await startWatcher(path: 'dir');
+      renameDir('dir/old', 'dir/new');
+
+      await inAnyOrder(unionAll(withPermutations((i, j, k) {
+        return {
+          isRemoveEvent('dir/old/sub-$i/sub-$j/file-$k.txt'),
+          isAddEvent('dir/new/sub-$i/sub-$j/file-$k.txt')
+        };
+      })));
+    });
+
+    test(
+        'emits events for many files added at once in a subdirectory with the '
+        'same name as a removed file', () async {
+      writeFile('dir/sub');
+      withPermutations((i, j, k) => writeFile('old/sub-$i/sub-$j/file-$k.txt'));
+      await startWatcher(path: 'dir');
+
+      deleteFile('dir/sub');
+      renameDir('old', 'dir/sub');
+
+      var events = withPermutations(
+          (i, j, k) => isAddEvent('dir/sub/sub-$i/sub-$j/file-$k.txt'));
+      events.add(isRemoveEvent('dir/sub'));
+      await inAnyOrder(events);
+    });
+  });
+}

diff --git a/pkgs/watcher/test/directory_watcher/windows_test.dart b/pkgs/watcher/test/directory_watcher/windows_test.dart
new file mode 100644
index 0000000..499e7fb
--- /dev/null
+++ b/pkgs/watcher/test/directory_watcher/windows_test.dart

@@ -0,0 +1,23 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+@TestOn('windows')
+library;
+
+import 'package:test/test.dart';
+import 'package:watcher/src/directory_watcher/windows.dart';
+import 'package:watcher/watcher.dart';
+
+import '../utils.dart';
+import 'shared.dart';
+
+void main() {
+  watcherFactory = WindowsDirectoryWatcher.new;
+
+  group('Shared Tests:', sharedTests);
+
+  test('DirectoryWatcher creates a WindowsDirectoryWatcher on Windows', () {
+    expect(DirectoryWatcher('.'), const TypeMatcher<WindowsDirectoryWatcher>());
+  });
+}

diff --git a/pkgs/watcher/test/file_watcher/native_test.dart b/pkgs/watcher/test/file_watcher/native_test.dart
new file mode 100644
index 0000000..0d4ad63
--- /dev/null
+++ b/pkgs/watcher/test/file_watcher/native_test.dart

@@ -0,0 +1,22 @@
+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+@TestOn('linux || mac-os')
+library;
+
+import 'package:test/test.dart';
+import 'package:watcher/src/file_watcher/native.dart';
+
+import '../utils.dart';
+import 'shared.dart';
+
+void main() {
+  watcherFactory = NativeFileWatcher.new;
+
+  setUp(() {
+    writeFile('file.txt');
+  });
+
+  sharedTests();
+}

diff --git a/pkgs/watcher/test/file_watcher/polling_test.dart b/pkgs/watcher/test/file_watcher/polling_test.dart
new file mode 100644
index 0000000..861fcb2
--- /dev/null
+++ b/pkgs/watcher/test/file_watcher/polling_test.dart

@@ -0,0 +1,20 @@
+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:test/test.dart';
+import 'package:watcher/watcher.dart';
+
+import '../utils.dart';
+import 'shared.dart';
+
+void main() {
+  watcherFactory = (file) =>
+      PollingFileWatcher(file, pollingDelay: const Duration(milliseconds: 100));
+
+  setUp(() {
+    writeFile('file.txt');
+  });
+
+  sharedTests();
+}

diff --git a/pkgs/watcher/test/file_watcher/shared.dart b/pkgs/watcher/test/file_watcher/shared.dart
new file mode 100644
index 0000000..081b92e
--- /dev/null
+++ b/pkgs/watcher/test/file_watcher/shared.dart

@@ -0,0 +1,73 @@
+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:test/test.dart';
+
+import '../utils.dart';
+
+void sharedTests() {
+  test("doesn't notify if the file isn't modified", () async {
+    await startWatcher(path: 'file.txt');
+    await pumpEventQueue();
+    deleteFile('file.txt');
+    await expectRemoveEvent('file.txt');
+  });
+
+  test('notifies when a file is modified', () async {
+    await startWatcher(path: 'file.txt');
+    writeFile('file.txt', contents: 'modified');
+    await expectModifyEvent('file.txt');
+  });
+
+  test('notifies when a file is removed', () async {
+    await startWatcher(path: 'file.txt');
+    deleteFile('file.txt');
+    await expectRemoveEvent('file.txt');
+  });
+
+  test('notifies when a file is modified multiple times', () async {
+    await startWatcher(path: 'file.txt');
+    writeFile('file.txt', contents: 'modified');
+    await expectModifyEvent('file.txt');
+    writeFile('file.txt', contents: 'modified again');
+    await expectModifyEvent('file.txt');
+  });
+
+  test('notifies even if the file contents are unchanged', () async {
+    await startWatcher(path: 'file.txt');
+    writeFile('file.txt');
+    await expectModifyEvent('file.txt');
+  });
+
+  test('emits a remove event when the watched file is moved away', () async {
+    await startWatcher(path: 'file.txt');
+    renameFile('file.txt', 'new.txt');
+    await expectRemoveEvent('file.txt');
+  });
+
+  test(
+      'emits a modify event when another file is moved on top of the watched '
+      'file', () async {
+    writeFile('old.txt');
+    await startWatcher(path: 'file.txt');
+    renameFile('old.txt', 'file.txt');
+    await expectModifyEvent('file.txt');
+  });
+
+  // Regression test for a race condition.
+  test('closes the watcher immediately after deleting the file', () async {
+    writeFile('old.txt');
+    var watcher = createWatcher(path: 'file.txt');
+    var sub = watcher.events.listen(null);
+
+    deleteFile('file.txt');
+    await Future<void>.delayed(const Duration(milliseconds: 10));
+    await sub.cancel();
+  });
+
+  test('ready completes even if file does not exist', () async {
+    // startWatcher awaits 'ready'
+    await startWatcher(path: 'foo/bar/baz');
+  });
+}

diff --git a/pkgs/watcher/test/no_subscription/linux_test.dart b/pkgs/watcher/test/no_subscription/linux_test.dart
new file mode 100644
index 0000000..aac0810
--- /dev/null
+++ b/pkgs/watcher/test/no_subscription/linux_test.dart

@@ -0,0 +1,18 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+@TestOn('linux')
+library;
+
+import 'package:test/test.dart';
+import 'package:watcher/src/directory_watcher/linux.dart';
+
+import '../utils.dart';
+import 'shared.dart';
+
+void main() {
+  watcherFactory = LinuxDirectoryWatcher.new;
+
+  sharedTests();
+}

diff --git a/pkgs/watcher/test/no_subscription/mac_os_test.dart b/pkgs/watcher/test/no_subscription/mac_os_test.dart
new file mode 100644
index 0000000..55a8308
--- /dev/null
+++ b/pkgs/watcher/test/no_subscription/mac_os_test.dart

@@ -0,0 +1,18 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+@TestOn('mac-os')
+library;
+
+import 'package:test/test.dart';
+import 'package:watcher/src/directory_watcher/mac_os.dart';
+
+import '../utils.dart';
+import 'shared.dart';
+
+void main() {
+  watcherFactory = MacOSDirectoryWatcher.new;
+
+  sharedTests();
+}

diff --git a/pkgs/watcher/test/no_subscription/polling_test.dart b/pkgs/watcher/test/no_subscription/polling_test.dart
new file mode 100644
index 0000000..bfd2958
--- /dev/null
+++ b/pkgs/watcher/test/no_subscription/polling_test.dart

@@ -0,0 +1,14 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:watcher/watcher.dart';
+
+import '../utils.dart';
+import 'shared.dart';
+
+void main() {
+  watcherFactory = PollingDirectoryWatcher.new;
+
+  sharedTests();
+}

diff --git a/pkgs/watcher/test/no_subscription/shared.dart b/pkgs/watcher/test/no_subscription/shared.dart
new file mode 100644
index 0000000..e7a6144
--- /dev/null
+++ b/pkgs/watcher/test/no_subscription/shared.dart

@@ -0,0 +1,54 @@
+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:async/async.dart';
+import 'package:test/test.dart';
+import 'package:watcher/watcher.dart';
+
+import '../utils.dart';
+
+void sharedTests() {
+  test('does not notify for changes when there are no subscribers', () async {
+    // Note that this test doesn't rely as heavily on the test functions in
+    // utils.dart because it needs to be very explicit about when the event
+    // stream is and is not subscribed.
+    var watcher = createWatcher();
+    var queue = StreamQueue(watcher.events);
+    unawaited(queue.hasNext);
+
+    var future =
+        expectLater(queue, emits(isWatchEvent(ChangeType.ADD, 'file.txt')));
+    expect(queue, neverEmits(anything));
+
+    await watcher.ready;
+
+    writeFile('file.txt');
+
+    await future;
+
+    // Unsubscribe.
+    await queue.cancel(immediate: true);
+
+    // Now write a file while we aren't listening.
+    writeFile('unwatched.txt');
+
+    queue = StreamQueue(watcher.events);
+    future =
+        expectLater(queue, emits(isWatchEvent(ChangeType.ADD, 'added.txt')));
+    expect(queue, neverEmits(isWatchEvent(ChangeType.ADD, 'unwatched.txt')));
+
+    // Wait until the watcher is ready to dispatch events again.
+    await watcher.ready;
+
+    // And add a third file.
+    writeFile('added.txt');
+
+    // Wait until we get an event for the third file.
+    await future;
+
+    await queue.cancel(immediate: true);
+  });
+}

diff --git a/pkgs/watcher/test/no_subscription/windows_test.dart b/pkgs/watcher/test/no_subscription/windows_test.dart
new file mode 100644
index 0000000..9f9e5a9
--- /dev/null
+++ b/pkgs/watcher/test/no_subscription/windows_test.dart

@@ -0,0 +1,18 @@
+// Copyright (c) 2022, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+@TestOn('windows')
+library;
+
+import 'package:test/test.dart';
+import 'package:watcher/src/directory_watcher/windows.dart';
+
+import '../utils.dart';
+import 'shared.dart';
+
+void main() {
+  watcherFactory = WindowsDirectoryWatcher.new;
+
+  sharedTests();
+}

diff --git a/pkgs/watcher/test/path_set_test.dart b/pkgs/watcher/test/path_set_test.dart
new file mode 100644
index 0000000..61ab2cd
--- /dev/null
+++ b/pkgs/watcher/test/path_set_test.dart

@@ -0,0 +1,228 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:path/path.dart' as p;
+import 'package:test/test.dart';
+import 'package:watcher/src/path_set.dart';
+
+Matcher containsPath(String path) => predicate(
+    (paths) => paths is PathSet && paths.contains(path),
+    'set contains "$path"');
+
+Matcher containsDir(String path) => predicate(
+    (paths) => paths is PathSet && paths.containsDir(path),
+    'set contains directory "$path"');
+
+void main() {
+  late PathSet paths;
+  setUp(() => paths = PathSet('root'));
+
+  group('adding a path', () {
+    test('stores the path in the set', () {
+      paths.add('root/path/to/file');
+      expect(paths, containsPath('root/path/to/file'));
+    });
+
+    test("that's a subdir of another path keeps both in the set", () {
+      paths.add('root/path');
+      paths.add('root/path/to/file');
+      expect(paths, containsPath('root/path'));
+      expect(paths, containsPath('root/path/to/file'));
+    });
+
+    test("that's not normalized normalizes the path before storing it", () {
+      paths.add('root/../root/path/to/../to/././file');
+      expect(paths, containsPath('root/path/to/file'));
+    });
+
+    test("that's absolute normalizes the path before storing it", () {
+      paths.add(p.absolute('root/path/to/file'));
+      expect(paths, containsPath('root/path/to/file'));
+    });
+  });
+
+  group('removing a path', () {
+    test("that's in the set removes and returns that path", () {
+      paths.add('root/path/to/file');
+      expect(paths.remove('root/path/to/file'),
+          unorderedEquals([p.normalize('root/path/to/file')]));
+      expect(paths, isNot(containsPath('root/path/to/file')));
+    });
+
+    test("that's not in the set returns an empty set", () {
+      paths.add('root/path/to/file');
+      expect(paths.remove('root/path/to/nothing'), isEmpty);
+    });
+
+    test("that's a directory removes and returns all files beneath it", () {
+      paths.add('root/outside');
+      paths.add('root/path/to/one');
+      paths.add('root/path/to/two');
+      paths.add('root/path/to/sub/three');
+
+      expect(
+          paths.remove('root/path'),
+          unorderedEquals([
+            'root/path/to/one',
+            'root/path/to/two',
+            'root/path/to/sub/three'
+          ].map(p.normalize)));
+
+      expect(paths, containsPath('root/outside'));
+      expect(paths, isNot(containsPath('root/path/to/one')));
+      expect(paths, isNot(containsPath('root/path/to/two')));
+      expect(paths, isNot(containsPath('root/path/to/sub/three')));
+    });
+
+    test(
+        "that's a directory in the set removes and returns it and all files "
+        'beneath it', () {
+      paths.add('root/path');
+      paths.add('root/path/to/one');
+      paths.add('root/path/to/two');
+      paths.add('root/path/to/sub/three');
+
+      expect(
+          paths.remove('root/path'),
+          unorderedEquals([
+            'root/path',
+            'root/path/to/one',
+            'root/path/to/two',
+            'root/path/to/sub/three'
+          ].map(p.normalize)));
+
+      expect(paths, isNot(containsPath('root/path')));
+      expect(paths, isNot(containsPath('root/path/to/one')));
+      expect(paths, isNot(containsPath('root/path/to/two')));
+      expect(paths, isNot(containsPath('root/path/to/sub/three')));
+    });
+
+    test("that's not normalized removes and returns the normalized path", () {
+      paths.add('root/path/to/file');
+      expect(paths.remove('root/../root/path/to/../to/./file'),
+          unorderedEquals([p.normalize('root/path/to/file')]));
+    });
+
+    test("that's absolute removes and returns the normalized path", () {
+      paths.add('root/path/to/file');
+      expect(paths.remove(p.absolute('root/path/to/file')),
+          unorderedEquals([p.normalize('root/path/to/file')]));
+    });
+  });
+
+  group('containsPath()', () {
+    test('returns false for a non-existent path', () {
+      paths.add('root/path/to/file');
+      expect(paths, isNot(containsPath('root/path/to/nothing')));
+    });
+
+    test("returns false for a directory that wasn't added explicitly", () {
+      paths.add('root/path/to/file');
+      expect(paths, isNot(containsPath('root/path')));
+    });
+
+    test('returns true for a directory that was added explicitly', () {
+      paths.add('root/path');
+      paths.add('root/path/to/file');
+      expect(paths, containsPath('root/path'));
+    });
+
+    test('with a non-normalized path normalizes the path before looking it up',
+        () {
+      paths.add('root/path/to/file');
+      expect(paths, containsPath('root/../root/path/to/../to/././file'));
+    });
+
+    test('with an absolute path normalizes the path before looking it up', () {
+      paths.add('root/path/to/file');
+      expect(paths, containsPath(p.absolute('root/path/to/file')));
+    });
+  });
+
+  group('containsDir()', () {
+    test('returns true for a directory that was added implicitly', () {
+      paths.add('root/path/to/file');
+      expect(paths, containsDir('root/path'));
+      expect(paths, containsDir('root/path/to'));
+    });
+
+    test('returns true for a directory that was added explicitly', () {
+      paths.add('root/path');
+      paths.add('root/path/to/file');
+      expect(paths, containsDir('root/path'));
+    });
+
+    test("returns false for a directory that wasn't added", () {
+      expect(paths, isNot(containsDir('root/nothing')));
+    });
+
+    test('returns false for a non-directory path that was added', () {
+      paths.add('root/path/to/file');
+      expect(paths, isNot(containsDir('root/path/to/file')));
+    });
+
+    test(
+        'returns false for a directory that was added implicitly and then '
+        'removed implicitly', () {
+      paths.add('root/path/to/file');
+      paths.remove('root/path/to/file');
+      expect(paths, isNot(containsDir('root/path')));
+    });
+
+    test(
+        'returns false for a directory that was added explicitly whose '
+        'children were then removed', () {
+      paths.add('root/path');
+      paths.add('root/path/to/file');
+      paths.remove('root/path/to/file');
+      expect(paths, isNot(containsDir('root/path')));
+    });
+
+    test('with a non-normalized path normalizes the path before looking it up',
+        () {
+      paths.add('root/path/to/file');
+      expect(paths, containsDir('root/../root/path/to/../to/.'));
+    });
+
+    test('with an absolute path normalizes the path before looking it up', () {
+      paths.add('root/path/to/file');
+      expect(paths, containsDir(p.absolute('root/path')));
+    });
+  });
+
+  group('paths', () {
+    test('returns paths added to the set', () {
+      paths.add('root/path');
+      paths.add('root/path/to/one');
+      paths.add('root/path/to/two');
+
+      expect(
+          paths.paths,
+          unorderedEquals([
+            'root/path',
+            'root/path/to/one',
+            'root/path/to/two',
+          ].map(p.normalize)));
+    });
+
+    test("doesn't return paths removed from the set", () {
+      paths.add('root/path/to/one');
+      paths.add('root/path/to/two');
+      paths.remove('root/path/to/two');
+
+      expect(paths.paths, unorderedEquals([p.normalize('root/path/to/one')]));
+    });
+  });
+
+  group('clear', () {
+    test('removes all paths from the set', () {
+      paths.add('root/path');
+      paths.add('root/path/to/one');
+      paths.add('root/path/to/two');
+
+      paths.clear();
+      expect(paths.paths, isEmpty);
+    });
+  });
+}

diff --git a/pkgs/watcher/test/ready/linux_test.dart b/pkgs/watcher/test/ready/linux_test.dart
new file mode 100644
index 0000000..aac0810
--- /dev/null
+++ b/pkgs/watcher/test/ready/linux_test.dart

@@ -0,0 +1,18 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+@TestOn('linux')
+library;
+
+import 'package:test/test.dart';
+import 'package:watcher/src/directory_watcher/linux.dart';
+
+import '../utils.dart';
+import 'shared.dart';
+
+void main() {
+  watcherFactory = LinuxDirectoryWatcher.new;
+
+  sharedTests();
+}

diff --git a/pkgs/watcher/test/ready/mac_os_test.dart b/pkgs/watcher/test/ready/mac_os_test.dart
new file mode 100644
index 0000000..55a8308
--- /dev/null
+++ b/pkgs/watcher/test/ready/mac_os_test.dart

@@ -0,0 +1,18 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+@TestOn('mac-os')
+library;
+
+import 'package:test/test.dart';
+import 'package:watcher/src/directory_watcher/mac_os.dart';
+
+import '../utils.dart';
+import 'shared.dart';
+
+void main() {
+  watcherFactory = MacOSDirectoryWatcher.new;
+
+  sharedTests();
+}

diff --git a/pkgs/watcher/test/ready/polling_test.dart b/pkgs/watcher/test/ready/polling_test.dart
new file mode 100644
index 0000000..bfd2958
--- /dev/null
+++ b/pkgs/watcher/test/ready/polling_test.dart

@@ -0,0 +1,14 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:watcher/watcher.dart';
+
+import '../utils.dart';
+import 'shared.dart';
+
+void main() {
+  watcherFactory = PollingDirectoryWatcher.new;
+
+  sharedTests();
+}

diff --git a/pkgs/watcher/test/ready/shared.dart b/pkgs/watcher/test/ready/shared.dart
new file mode 100644
index 0000000..ab2c3e1
--- /dev/null
+++ b/pkgs/watcher/test/ready/shared.dart

@@ -0,0 +1,84 @@
+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:test/test.dart';
+
+import '../utils.dart';
+
+void sharedTests() {
+  test('ready does not complete until after subscription', () async {
+    var watcher = createWatcher();
+
+    var ready = false;
+    unawaited(watcher.ready.then((_) {
+      ready = true;
+    }));
+    await pumpEventQueue();
+
+    expect(ready, isFalse);
+
+    // Subscribe to the events.
+    var subscription = watcher.events.listen((event) {});
+
+    await watcher.ready;
+
+    // Should eventually be ready.
+    expect(watcher.isReady, isTrue);
+
+    await subscription.cancel();
+  });
+
+  test('ready completes immediately when already ready', () async {
+    var watcher = createWatcher();
+
+    // Subscribe to the events.
+    var subscription = watcher.events.listen((event) {});
+
+    // Allow watcher to become ready
+    await watcher.ready;
+
+    // Ensure ready completes immediately
+    expect(
+      watcher.ready.timeout(
+        const Duration(milliseconds: 0),
+        onTimeout: () => throw StateError('Does not complete immediately'),
+      ),
+      completes,
+    );
+
+    await subscription.cancel();
+  });
+
+  test('ready returns a future that does not complete after unsubscribing',
+      () async {
+    var watcher = createWatcher();
+
+    // Subscribe to the events.
+    var subscription = watcher.events.listen((event) {});
+
+    // Wait until ready.
+    await watcher.ready;
+
+    // Now unsubscribe.
+    await subscription.cancel();
+
+    // Should be back to not ready.
+    expect(watcher.ready, doesNotComplete);
+  });
+
+  test('ready completes even if directory does not exist', () async {
+    var watcher = createWatcher(path: 'does/not/exist');
+
+    // Subscribe to the events (else ready will never fire).
+    var subscription = watcher.events.listen((event) {}, onError: (error) {});
+
+    // Expect ready still completes.
+    await watcher.ready;
+
+    // Now unsubscribe.
+    await subscription.cancel();
+  });
+}

diff --git a/pkgs/watcher/test/ready/windows_test.dart b/pkgs/watcher/test/ready/windows_test.dart
new file mode 100644
index 0000000..9f9e5a9
--- /dev/null
+++ b/pkgs/watcher/test/ready/windows_test.dart

@@ -0,0 +1,18 @@
+// Copyright (c) 2022, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+@TestOn('windows')
+library;
+
+import 'package:test/test.dart';
+import 'package:watcher/src/directory_watcher/windows.dart';
+
+import '../utils.dart';
+import 'shared.dart';
+
+void main() {
+  watcherFactory = WindowsDirectoryWatcher.new;
+
+  sharedTests();
+}

diff --git a/pkgs/watcher/test/utils.dart b/pkgs/watcher/test/utils.dart
new file mode 100644
index 0000000..7867b9f
--- /dev/null
+++ b/pkgs/watcher/test/utils.dart

@@ -0,0 +1,288 @@
+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+import 'dart:io';
+
+import 'package:async/async.dart';
+import 'package:path/path.dart' as p;
+import 'package:test/test.dart';
+import 'package:test_descriptor/test_descriptor.dart' as d;
+import 'package:watcher/src/stat.dart';
+import 'package:watcher/watcher.dart';
+
+typedef WatcherFactory = Watcher Function(String directory);
+
+/// Sets the function used to create the watcher.
+set watcherFactory(WatcherFactory factory) {
+  _watcherFactory = factory;
+}
+
+/// The mock modification times (in milliseconds since epoch) for each file.
+///
+/// The actual file system has pretty coarse granularity for file modification
+/// times. This means using the real file system requires us to put delays in
+/// the tests to ensure we wait long enough between operations for the mod time
+/// to be different.
+///
+/// Instead, we'll just mock that out. Each time a file is written, we manually
+/// increment the mod time for that file instantly.
+final _mockFileModificationTimes = <String, int>{};
+
+late WatcherFactory _watcherFactory;
+
+/// Creates a new [Watcher] that watches a temporary file or directory.
+///
+/// If [path] is provided, watches a subdirectory in the sandbox with that name.
+Watcher createWatcher({String? path}) {
+  if (path == null) {
+    path = d.sandbox;
+  } else {
+    path = p.join(d.sandbox, path);
+  }
+
+  return _watcherFactory(path);
+}
+
+/// The stream of events from the watcher started with [startWatcher].
+late StreamQueue<WatchEvent> _watcherEvents;
+
+/// Whether the event stream has been closed.
+///
+/// If this is not done by a test (by calling [startClosingEventStream]) it will
+/// be done automatically via [addTearDown] in [startWatcher].
+var _hasClosedStream = true;
+
+/// Creates a new [Watcher] that watches a temporary file or directory and
+/// starts monitoring it for events.
+///
+/// If [path] is provided, watches a path in the sandbox with that name.
+Future<void> startWatcher({String? path}) async {
+  mockGetModificationTime((path) {
+    final normalized = p.normalize(p.relative(path, from: d.sandbox));
+
+    // Make sure we got a path in the sandbox.
+    assert(p.isRelative(normalized) && !normalized.startsWith('..'),
+        'Path is not in the sandbox: $path not in ${d.sandbox}');
+
+    var mtime = _mockFileModificationTimes[normalized];
+    return mtime != null ? DateTime.fromMillisecondsSinceEpoch(mtime) : null;
+  });
+
+  // We want to wait until we're ready *after* we subscribe to the watcher's
+  // events.
+  var watcher = createWatcher(path: path);
+  _watcherEvents = StreamQueue(watcher.events);
+  // Forces a subscription to the underlying stream.
+  unawaited(_watcherEvents.hasNext);
+
+  _hasClosedStream = false;
+  addTearDown(startClosingEventStream);
+
+  await watcher.ready;
+}
+
+/// Schedule closing the watcher stream after the event queue has been pumped.
+///
+/// This is necessary when events are allowed to occur, but don't have to occur,
+/// at the end of a test. Otherwise, if they don't occur, the test will wait
+/// indefinitely because they might in the future and because the watcher is
+/// normally only closed after the test completes.
+void startClosingEventStream() async {
+  if (_hasClosedStream) return;
+  _hasClosedStream = true;
+  await pumpEventQueue();
+  await _watcherEvents.cancel(immediate: true);
+}
+
+/// A list of [StreamMatcher]s that have been collected using
+/// [_collectStreamMatcher].
+List<StreamMatcher>? _collectedStreamMatchers;
+
+/// Collects all stream matchers that are registered within [block] into a
+/// single stream matcher.
+///
+/// The returned matcher will match each of the collected matchers in order.
+StreamMatcher _collectStreamMatcher(void Function() block) {
+  var oldStreamMatchers = _collectedStreamMatchers;
+  var collectedStreamMatchers = _collectedStreamMatchers = <StreamMatcher>[];
+  try {
+    block();
+    return emitsInOrder(collectedStreamMatchers);
+  } finally {
+    _collectedStreamMatchers = oldStreamMatchers;
+  }
+}
+
+/// Either add [streamMatcher] as an expectation to [_watcherEvents], or collect
+/// it with [_collectStreamMatcher].
+///
+/// [streamMatcher] can be a [StreamMatcher], a [Matcher], or a value.
+Future _expectOrCollect(Matcher streamMatcher) {
+  var collectedStreamMatchers = _collectedStreamMatchers;
+  if (collectedStreamMatchers != null) {
+    collectedStreamMatchers.add(emits(streamMatcher));
+    return Future.sync(() {});
+  } else {
+    return expectLater(_watcherEvents, emits(streamMatcher));
+  }
+}
+
+/// Expects that [matchers] will match emitted events in any order.
+///
+/// [matchers] may be [Matcher]s or values, but not [StreamMatcher]s.
+Future inAnyOrder(Iterable matchers) {
+  matchers = matchers.toSet();
+  return _expectOrCollect(emitsInAnyOrder(matchers));
+}
+
+/// Expects that the expectations established in either [block1] or [block2]
+/// will match the emitted events.
+///
+/// If both blocks match, the one that consumed more events will be used.
+Future allowEither(void Function() block1, void Function() block2) =>
+    _expectOrCollect(emitsAnyOf(
+        [_collectStreamMatcher(block1), _collectStreamMatcher(block2)]));
+
+/// Allows the expectations established in [block] to match the emitted events.
+///
+/// If the expectations in [block] don't match, no error will be raised and no
+/// events will be consumed. If this is used at the end of a test,
+/// [startClosingEventStream] should be called before it.
+Future allowEvents(void Function() block) =>
+    _expectOrCollect(mayEmit(_collectStreamMatcher(block)));
+
+/// Returns a StreamMatcher that matches a [WatchEvent] with the given [type]
+/// and [path].
+Matcher isWatchEvent(ChangeType type, String path) {
+  return predicate((e) {
+    return e is WatchEvent &&
+        e.type == type &&
+        e.path == p.join(d.sandbox, p.normalize(path));
+  }, 'is $type $path');
+}
+
+/// Returns a [Matcher] that matches a [WatchEvent] for an add event for [path].
+Matcher isAddEvent(String path) => isWatchEvent(ChangeType.ADD, path);
+
+/// Returns a [Matcher] that matches a [WatchEvent] for a modification event for
+/// [path].
+Matcher isModifyEvent(String path) => isWatchEvent(ChangeType.MODIFY, path);
+
+/// Returns a [Matcher] that matches a [WatchEvent] for a removal event for
+/// [path].
+Matcher isRemoveEvent(String path) => isWatchEvent(ChangeType.REMOVE, path);
+
+/// Expects that the next event emitted will be for an add event for [path].
+Future expectAddEvent(String path) =>
+    _expectOrCollect(isWatchEvent(ChangeType.ADD, path));
+
+/// Expects that the next event emitted will be for a modification event for
+/// [path].
+Future expectModifyEvent(String path) =>
+    _expectOrCollect(isWatchEvent(ChangeType.MODIFY, path));
+
+/// Expects that the next event emitted will be for a removal event for [path].
+Future expectRemoveEvent(String path) =>
+    _expectOrCollect(isWatchEvent(ChangeType.REMOVE, path));
+
+/// Consumes a modification event for [path] if one is emitted at this point in
+/// the schedule, but doesn't throw an error if it isn't.
+///
+/// If this is used at the end of a test, [startClosingEventStream] should be
+/// called before it.
+Future allowModifyEvent(String path) =>
+    _expectOrCollect(mayEmit(isWatchEvent(ChangeType.MODIFY, path)));
+
+/// Track a fake timestamp to be used when writing files. This always increases
+/// so that files that are deleted and re-created do not have their timestamp
+/// set back to a previously used value.
+int _nextTimestamp = 1;
+
+/// Schedules writing a file in the sandbox at [path] with [contents].
+///
+/// If [contents] is omitted, creates an empty file. If [updateModified] is
+/// `false`, the mock file modification time is not changed.
+void writeFile(String path, {String? contents, bool? updateModified}) {
+  contents ??= '';
+  updateModified ??= true;
+
+  var fullPath = p.join(d.sandbox, path);
+
+  // Create any needed subdirectories.
+  var dir = Directory(p.dirname(fullPath));
+  if (!dir.existsSync()) {
+    dir.createSync(recursive: true);
+  }
+
+  File(fullPath).writeAsStringSync(contents);
+
+  if (updateModified) {
+    path = p.normalize(path);
+
+    _mockFileModificationTimes[path] = _nextTimestamp++;
+  }
+}
+
+/// Schedules deleting a file in the sandbox at [path].
+void deleteFile(String path) {
+  File(p.join(d.sandbox, path)).deleteSync();
+
+  _mockFileModificationTimes.remove(path);
+}
+
+/// Schedules renaming a file in the sandbox from [from] to [to].
+void renameFile(String from, String to) {
+  File(p.join(d.sandbox, from)).renameSync(p.join(d.sandbox, to));
+
+  // Make sure we always use the same separator on Windows.
+  to = p.normalize(to);
+
+  _mockFileModificationTimes.update(to, (value) => value + 1,
+      ifAbsent: () => 1);
+}
+
+/// Schedules creating a directory in the sandbox at [path].
+void createDir(String path) {
+  Directory(p.join(d.sandbox, path)).createSync();
+}
+
+/// Schedules renaming a directory in the sandbox from [from] to [to].
+void renameDir(String from, String to) {
+  Directory(p.join(d.sandbox, from)).renameSync(p.join(d.sandbox, to));
+
+  // Migrate timestamps for any files in this folder.
+  final knownFilePaths = _mockFileModificationTimes.keys.toList();
+  for (final filePath in knownFilePaths) {
+    if (p.isWithin(from, filePath)) {
+      _mockFileModificationTimes[filePath.replaceAll(from, to)] =
+          _mockFileModificationTimes[filePath]!;
+      _mockFileModificationTimes.remove(filePath);
+    }
+  }
+}
+
+/// Schedules deleting a directory in the sandbox at [path].
+void deleteDir(String path) {
+  Directory(p.join(d.sandbox, path)).deleteSync(recursive: true);
+}
+
+/// Runs [callback] with every permutation of non-negative numbers for each
+/// argument less than [limit].
+///
+/// Returns a set of all values returns by [callback].
+///
+/// [limit] defaults to 3.
+Set<S> withPermutations<S>(S Function(int, int, int) callback, {int? limit}) {
+  limit ??= 3;
+  var results = <S>{};
+  for (var i = 0; i < limit; i++) {
+    for (var j = 0; j < limit; j++) {
+      for (var k = 0; k < limit; k++) {
+        results.add(callback(i, j, k));
+      }
+    }
+  }
+  return results;
+}

diff --git a/pkgs/yaml/.gitignore b/pkgs/yaml/.gitignore
new file mode 100644
index 0000000..ab3cb76
--- /dev/null
+++ b/pkgs/yaml/.gitignore

@@ -0,0 +1,16 @@
+# Don’t commit the following directories created by pub.
+.buildlog
+.dart_tool/
+.pub/
+build/
+packages
+.packages
+
+# Or the files created by dart2js.
+*.dart.js
+*.js_
+*.js.deps
+*.js.map
+
+# Include when developing application packages.
+pubspec.lock

diff --git a/pkgs/yaml/CHANGELOG.md b/pkgs/yaml/CHANGELOG.md
new file mode 100644
index 0000000..3f9d3fd
--- /dev/null
+++ b/pkgs/yaml/CHANGELOG.md

@@ -0,0 +1,199 @@
+## 3.1.3
+
+* Require Dart 3.4
+* Fix UTF-16 surrogate pair handling in plain scaler.
+* Move to `dart-lang/tools` monorepo.
+
+## 3.1.2
+
+* Require Dart 2.19
+* Added `topics` in `pubspec.yaml`.
+
+## 3.1.1
+
+* Switch to using package:lints.
+* Populate the pubspec `repository` field.
+
+## 3.1.0
+
+* `loadYaml` and related functions now accept a `recover` flag instructing the parser
+  to attempt to recover from parse errors and may return invalid or synthetic nodes.
+  When recovering, an `ErrorListener` can also be supplied to listen for errors that
+  are recovered from.
+* Drop dependency on `package:charcode`.
+
+## 3.0.0
+
+* Stable null safety release.
+
+## 3.0.0-nullsafety.0
+
+* Updated to support 2.12.0 and null safety.
+* Allow `YamlNode`s to be wrapped with an optional `style` parameter.
+* **BREAKING** The `sourceUrl` named argument is statically typed as `Uri`
+  instead of allowing `String` or `Uri`.
+
+## 2.2.1
+
+* Update min Dart SDK to `2.4.0`.
+* Fixed span for null nodes in block lists.
+
+## 2.2.0
+
+* POSSIBLY BREAKING CHANGE: Make `YamlMap` preserve parsed key order.
+  This is breaking because some programs may rely on the
+  `HashMap` sort order.
+
+## 2.1.16
+
+* Fixed deprecated API usage in README.
+* Fixed lints that affect package score.
+
+## 2.1.15
+
+* Set max SDK version to `<3.0.0`, and adjust other dependencies.
+
+## 2.1.14
+
+* Remove use of deprecated features.
+* Updated SDK version to 2.0.0-dev.17.0
+
+## 2.1.13
+
+* Stop using comment-based generic syntax.
+
+## 2.1.12
+
+* Properly refuse mappings with duplicate keys.
+
+## 2.1.11
+
+* Fix an infinite loop when parsing some invalid documents.
+
+## 2.1.10
+
+* Support `string_scanner` 1.0.0.
+
+## 2.1.9
+
+* Fix all strong-mode warnings.
+
+## 2.1.8
+
+* Remove the dependency on `path`, since we don't actually import it.
+
+## 2.1.7
+
+* Fix more strong mode warnings.
+
+## 2.1.6
+
+* Fix two analysis issues with DDC's strong mode.
+
+## 2.1.5
+
+* Fix a bug with 2.1.4 where source span information was being discarded for
+  scalar values.
+
+## 2.1.4
+
+* Substantially improve performance.
+
+## 2.1.3
+
+* Add a hint that a colon might be missing when a mapping value is found in the
+  wrong context.
+
+## 2.1.2
+
+* Fix a crashing bug when parsing block scalars.
+
+## 2.1.1
+
+* Properly scope `SourceSpan`s for scalar values surrounded by whitespace.
+
+## 2.1.0
+
+* Rewrite the parser for a 10x speed improvement.
+
+* Support anchors and aliases (`&foo` and `*foo`).
+
+* Support explicit tags (e.g. `!!str`). Note that user-defined tags are still
+  not fully supported.
+
+* `%YAML` and `%TAG` directives are now parsed, although again user-defined tags
+  are not fully supported.
+
+* `YamlScalar`, `YamlList`, and `YamlMap` now expose the styles in which they
+  were written (for example plain vs folded, block vs flow).
+
+* A `yamlWarningCallback` field is exposed. This field can be used to customize
+  how YAML warnings are displayed.
+
+## 2.0.1+1
+
+* Fix an import in a test.
+
+* Widen the version constraint on the `collection` package.
+
+## 2.0.1
+
+* Fix a few lingering references to the old `Span` class in documentation and
+  tests.
+
+## 2.0.0
+
+* Switch from `source_maps`' `Span` class to `source_span`'s `SourceSpan` class.
+
+* For consistency with `source_span` and `string_scanner`, all `sourceName`
+  parameters have been renamed to `sourceUrl`. They now accept Urls as well as
+  Strings.
+
+## 1.1.1
+
+* Fix broken type arguments that caused breakage on dart2js.
+
+* Fix an analyzer warning in `yaml_node_wrapper.dart`.
+
+## 1.1.0
+
+* Add new publicly-accessible constructors for `YamlNode` subclasses. These
+  constructors make it possible to use the same API to access non-YAML data as
+  YAML data.
+
+* Make `YamlException` inherit from source_map's `SpanFormatException`. This
+  improves the error formatting and allows callers access to source range
+  information.
+
+## 1.0.0+1
+
+* Fix a variable name typo.
+
+## 1.0.0
+
+* **Backwards incompatibility**: The data structures returned by `loadYaml` and
+  `loadYamlStream` are now immutable.
+
+* **Backwards incompatibility**: The interface of the `YamlMap` class has
+  changed substantially in numerous ways. External users may no longer construct
+  their own instances.
+
+* Maps and lists returned by `loadYaml` and `loadYamlStream` now contain
+  information about their source locations.
+
+* A new `loadYamlNode` function returns the source location of top-level scalars
+  as well.
+
+## 0.10.0
+
+* Improve error messages when a file fails to parse.
+
+## 0.9.0+2
+
+* Ensure that maps are order-independent when used as map keys.
+
+## 0.9.0+1
+
+* The `YamlMap` class is deprecated. In a future version, maps returned by
+  `loadYaml` and `loadYamlStream` will be Dart `HashMap`s with a custom equality
+  operation.

diff --git a/pkgs/yaml/LICENSE b/pkgs/yaml/LICENSE
new file mode 100644
index 0000000..e7589cb
--- /dev/null
+++ b/pkgs/yaml/LICENSE

@@ -0,0 +1,20 @@
+Copyright (c) 2014, the Dart project authors.
+Copyright (c) 2006, Kirill Simonov.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of
+this software and associated documentation files (the "Software"), to deal in
+the Software without restriction, including without limitation the rights to
+use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
+of the Software, and to permit persons to whom the Software is furnished to do
+so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

diff --git a/pkgs/yaml/README.md b/pkgs/yaml/README.md
new file mode 100644
index 0000000..ba56893
--- /dev/null
+++ b/pkgs/yaml/README.md

@@ -0,0 +1,33 @@
+[![Build Status](https://github.com/dart-lang/tools/actions/workflows/yaml.yaml/badge.svg)](https://github.com/dart-lang/tools/actions/workflows/yaml.yaml)
+[![pub package](https://img.shields.io/pub/v/yaml.svg)](https://pub.dev/packages/yaml)
+[![package publisher](https://img.shields.io/pub/publisher/yaml.svg)](https://pub.dev/packages/yaml/publisher)
+
+
+A parser for [YAML](https://yaml.org/).
+
+## Usage
+
+Use `loadYaml` to load a single document, or `loadYamlStream` to load a
+stream of documents. For example:
+
+```dart
+import 'package:yaml/yaml.dart';
+
+main() {
+  var doc = loadYaml("YAML: YAML Ain't Markup Language");
+  print(doc['YAML']);
+}
+```
+
+This library currently doesn't support dumping to YAML. You should use
+`json.encode` from `dart:convert` instead:
+
+```dart
+import 'dart:convert';
+import 'package:yaml/yaml.dart';
+
+main() {
+  var doc = loadYaml("YAML: YAML Ain't Markup Language");
+  print(json.encode(doc));
+}
+```

diff --git a/pkgs/yaml/analysis_options.yaml b/pkgs/yaml/analysis_options.yaml
new file mode 100644
index 0000000..46e45f0
--- /dev/null
+++ b/pkgs/yaml/analysis_options.yaml

@@ -0,0 +1,18 @@
+include: package:dart_flutter_team_lints/analysis_options.yaml
+
+analyzer:
+  language:
+    strict-casts: true
+
+linter:
+  rules:
+    - avoid_private_typedef_functions
+    - avoid_redundant_argument_values
+    - avoid_unused_constructor_parameters
+    - cancel_subscriptions
+    - join_return_with_assignment
+    - missing_whitespace_between_adjacent_strings
+    - no_runtimeType_toString
+    - prefer_const_declarations
+    - prefer_expression_function_bodies
+    - use_string_buffers

diff --git a/pkgs/yaml/benchmark/benchmark.dart b/pkgs/yaml/benchmark/benchmark.dart
new file mode 100644
index 0000000..afc3c97
--- /dev/null
+++ b/pkgs/yaml/benchmark/benchmark.dart

@@ -0,0 +1,65 @@
+// Copyright (c) 2015, the Dart project authors.
+// Copyright (c) 2006, Kirill Simonov.
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'dart:convert';
+import 'dart:io';
+
+import 'package:path/path.dart' as p;
+import 'package:yaml/yaml.dart';
+
+const numTrials = 100;
+const runsPerTrial = 1000;
+
+final source = _loadFile('input.yaml');
+final expected = _loadFile('output.json');
+
+void main(List<String> args) {
+  var best = double.infinity;
+
+  // Run the benchmark several times. This ensures the VM is warmed up and lets
+  // us see how much variance there is.
+  for (var i = 0; i <= numTrials; i++) {
+    var start = DateTime.now();
+
+    // For a single benchmark, convert the source multiple times.
+    Object? result;
+    for (var j = 0; j < runsPerTrial; j++) {
+      result = loadYaml(source);
+    }
+
+    var elapsed =
+        DateTime.now().difference(start).inMilliseconds / runsPerTrial;
+
+    // Keep track of the best run so far.
+    if (elapsed >= best) continue;
+    best = elapsed;
+
+    // Sanity check to make sure the output is what we expect and to make sure
+    // the VM doesn't optimize "dead" code away.
+    if (jsonEncode(result) != expected) {
+      print('Incorrect output:\n${jsonEncode(result)}');
+      exit(1);
+    }
+
+    // Don't print the first run. It's always terrible since the VM hasn't
+    // warmed up yet.
+    if (i == 0) continue;
+    _printResult("Run ${'#$i'.padLeft(3, '')}", elapsed);
+  }
+
+  _printResult('Best   ', best);
+}
+
+String _loadFile(String name) {
+  var path = p.join(p.dirname(p.fromUri(Platform.script)), name);
+  return File(path).readAsStringSync();
+}
+
+void _printResult(String label, double time) {
+  print('$label: ${time.toStringAsFixed(3).padLeft(4, '0')}ms '
+      "${'=' * ((time * 100).toInt())}");
+}

diff --git a/pkgs/yaml/benchmark/input.yaml b/pkgs/yaml/benchmark/input.yaml
new file mode 100644
index 0000000..89bf9dc
--- /dev/null
+++ b/pkgs/yaml/benchmark/input.yaml

@@ -0,0 +1,48 @@
+verb: RecommendCafes
+recipe:
+  - verb: List
+    outputs: ["Cafe[]"]
+  - verb: Fetch
+    inputs: ["Cafe[]"]
+    outputs: ["CafeWithMenu[]"]
+  - verb: Flatten
+    inputs: ["CafeWithMenu[]"]
+    outputs: ["DishOffering[]"]
+  - verb: Score
+    inputs: ["DishOffering[]"]
+    outputs: ["DishOffering[]/Scored"]
+  - verb: Display
+    inputs: ["DishOffering[]/Scored"]
+tags:
+  booleans: [ true, false ]
+  dates:
+  - canonical: 2001-12-15T02:59:43.1Z
+  - iso8601: 2001-12-14t21:59:43.10-05:00
+  - spaced: 2001-12-14 21:59:43.10 -5
+  - date: 2002-12-14
+  numbers:
+  - int: 12345
+  - negative: -345
+  - floating-point: 345.678
+  - hexidecimal: 0x123abc
+  - exponential: 12.3015e+02
+  - octal: 0o14
+  strings:
+  - unicode: "Sosa did fine.\u263A"
+  - control: "\b1998\t1999\t2000\n"
+  - hex esc: "\x0d\x0a is \r\n"
+  - single: '"Howdy!" he cried.'
+  - quoted: ' # Not a ''comment''.'
+  - tie-fighter: '|\-*-/|'
+  - plain:
+      This unquoted scalar
+      spans many lines.
+
+  - quoted: "So does this
+      quoted scalar.\n"
+  - accomplishment: >
+      Mark set a major league
+      home run record in 1998.
+  - stats: |
+      65 Home Runs
+      0.278 Batting Average

diff --git a/pkgs/yaml/benchmark/output.json b/pkgs/yaml/benchmark/output.json
new file mode 100644
index 0000000..9e6cb84
--- /dev/null
+++ b/pkgs/yaml/benchmark/output.json

@@ -0,0 +1 @@
+{"verb":"RecommendCafes","recipe":[{"verb":"List","outputs":["Cafe[]"]},{"verb":"Fetch","inputs":["Cafe[]"],"outputs":["CafeWithMenu[]"]},{"verb":"Flatten","inputs":["CafeWithMenu[]"],"outputs":["DishOffering[]"]},{"verb":"Score","inputs":["DishOffering[]"],"outputs":["DishOffering[]/Scored"]},{"verb":"Display","inputs":["DishOffering[]/Scored"]}],"tags":{"booleans":[true,false],"dates":[{"canonical":"2001-12-15T02:59:43.1Z"},{"iso8601":"2001-12-14t21:59:43.10-05:00"},{"spaced":"2001-12-14 21:59:43.10 -5"},{"date":"2002-12-14"}],"numbers":[{"int":12345},{"negative":-345},{"floating-point":345.678},{"hexidecimal":1194684},{"exponential":1230.15},{"octal":12}],"strings":[{"unicode":"Sosa did fine.☺"},{"control":"\b1998\t1999\t2000\n"},{"hex esc":"\r\n is \r\n"},{"single":"\"Howdy!\" he cried."},{"quoted":" # Not a 'comment'."},{"tie-fighter":"|\\-*-/|"},{"plain":"This unquoted scalar spans many lines."},{"quoted":"So does this quoted scalar.\n"},{"accomplishment":"Mark set a major league home run record in 1998.\n"},{"stats":"65 Home Runs\n0.278 Batting Average\n"}]}}
\ No newline at end of file

diff --git a/pkgs/yaml/example/example.dart b/pkgs/yaml/example/example.dart
new file mode 100644
index 0000000..bb283a3
--- /dev/null
+++ b/pkgs/yaml/example/example.dart

@@ -0,0 +1,13 @@
+// Copyright (c) 2020, the Dart project authors.
+// Copyright (c) 2006, Kirill Simonov.
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'package:yaml/yaml.dart';
+
+void main() {
+  var doc = loadYaml("YAML: YAML Ain't Markup Language") as Map;
+  print(doc['YAML']);
+}

diff --git a/pkgs/yaml/lib/src/charcodes.dart b/pkgs/yaml/lib/src/charcodes.dart
new file mode 100644
index 0000000..602d597
--- /dev/null
+++ b/pkgs/yaml/lib/src/charcodes.dart

@@ -0,0 +1,48 @@
+// Copyright (c) 2021, the Dart project authors.
+// Copyright (c) 2006, Kirill Simonov.
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+/// Character `+`.
+const int $plus = 0x2b;
+
+/// Character `-`.
+const int $minus = 0x2d;
+
+/// Character `.`.
+const int $dot = 0x2e;
+
+/// Character `0`.
+const int $0 = 0x30;
+
+/// Character `9`.
+const int $9 = 0x39;
+
+/// Character `F`.
+const int $F = 0x46;
+
+/// Character `N`.
+const int $N = 0x4e;
+
+/// Character `T`.
+const int $T = 0x54;
+
+/// Character `f`.
+const int $f = 0x66;
+
+/// Character `n`.
+const int $n = 0x6e;
+
+/// Character `o`.
+const int $o = 0x6f;
+
+/// Character `t`.
+const int $t = 0x74;
+
+/// Character `x`.
+const int $x = 0x78;
+
+/// Character `~`.
+const int $tilde = 0x7e;

diff --git a/pkgs/yaml/lib/src/equality.dart b/pkgs/yaml/lib/src/equality.dart
new file mode 100644
index 0000000..c833dc6
--- /dev/null
+++ b/pkgs/yaml/lib/src/equality.dart

@@ -0,0 +1,128 @@
+// Copyright (c) 2014, the Dart project authors.
+// Copyright (c) 2006, Kirill Simonov.
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'dart:collection';
+
+import 'package:collection/collection.dart';
+
+import 'yaml_node.dart';
+
+/// Returns a [Map] that compares its keys based on [deepEquals].
+Map<K, V> deepEqualsMap<K, V>() =>
+    LinkedHashMap(equals: deepEquals, hashCode: deepHashCode);
+
+/// Returns whether two objects are structurally equivalent.
+///
+/// This considers `NaN` values to be equivalent, handles self-referential
+/// structures, and considers [YamlScalar]s to be equal to their values.
+bool deepEquals(Object? obj1, Object? obj2) => _DeepEquals().equals(obj1, obj2);
+
+/// A class that provides access to the list of parent objects used for loop
+/// detection.
+class _DeepEquals {
+  final _parents1 = <Object?>[];
+  final _parents2 = <Object?>[];
+
+  /// Returns whether [obj1] and [obj2] are structurally equivalent.
+  bool equals(Object? obj1, Object? obj2) {
+    if (obj1 is YamlScalar) obj1 = obj1.value;
+    if (obj2 is YamlScalar) obj2 = obj2.value;
+
+    // _parents1 and _parents2 are guaranteed to be the same size.
+    for (var i = 0; i < _parents1.length; i++) {
+      var loop1 = identical(obj1, _parents1[i]);
+      var loop2 = identical(obj2, _parents2[i]);
+      // If both structures loop in the same place, they're equal at that point
+      // in the structure. If one loops and the other doesn't, they're not
+      // equal.
+      if (loop1 && loop2) return true;
+      if (loop1 || loop2) return false;
+    }
+
+    _parents1.add(obj1);
+    _parents2.add(obj2);
+    try {
+      if (obj1 is List && obj2 is List) {
+        return _listEquals(obj1, obj2);
+      } else if (obj1 is Map && obj2 is Map) {
+        return _mapEquals(obj1, obj2);
+      } else if (obj1 is num && obj2 is num) {
+        return _numEquals(obj1, obj2);
+      } else {
+        return obj1 == obj2;
+      }
+    } finally {
+      _parents1.removeLast();
+      _parents2.removeLast();
+    }
+  }
+
+  /// Returns whether [list1] and [list2] are structurally equal.
+  bool _listEquals(List list1, List list2) {
+    if (list1.length != list2.length) return false;
+
+    for (var i = 0; i < list1.length; i++) {
+      if (!equals(list1[i], list2[i])) return false;
+    }
+
+    return true;
+  }
+
+  /// Returns whether [map1] and [map2] are structurally equal.
+  bool _mapEquals(Map map1, Map map2) {
+    if (map1.length != map2.length) return false;
+
+    for (var key in map1.keys) {
+      if (!map2.containsKey(key)) return false;
+      if (!equals(map1[key], map2[key])) return false;
+    }
+
+    return true;
+  }
+
+  /// Returns whether two numbers are equivalent.
+  ///
+  /// This differs from `n1 == n2` in that it considers `NaN` to be equal to
+  /// itself.
+  bool _numEquals(num n1, num n2) {
+    if (n1.isNaN && n2.isNaN) return true;
+    return n1 == n2;
+  }
+}
+
+/// Returns a hash code for [obj] such that structurally equivalent objects
+/// will have the same hash code.
+///
+/// This supports deep equality for maps and lists, including those with
+/// self-referential structures, and returns the same hash code for
+/// [YamlScalar]s and their values.
+int deepHashCode(Object? obj) {
+  var parents = <Object?>[];
+
+  int deepHashCodeInner(Object? value) {
+    if (parents.any((parent) => identical(parent, value))) return -1;
+
+    parents.add(value);
+    try {
+      if (value is Map) {
+        var equality = const UnorderedIterableEquality<Object?>();
+        return equality.hash(value.keys.map(deepHashCodeInner)) ^
+            equality.hash(value.values.map(deepHashCodeInner));
+      } else if (value is Iterable) {
+        return const IterableEquality<Object?>().hash(value.map(deepHashCode));
+      } else if (value is YamlScalar) {
+        return (value.value as Object?).hashCode;
+      } else {
+        return value.hashCode;
+      }
+    } finally {
+      parents.removeLast();
+    }
+  }
+
+  return deepHashCodeInner(obj);
+}

diff --git a/pkgs/yaml/lib/src/error_listener.dart b/pkgs/yaml/lib/src/error_listener.dart
new file mode 100644
index 0000000..0498d68
--- /dev/null
+++ b/pkgs/yaml/lib/src/error_listener.dart

@@ -0,0 +1,22 @@
+// Copyright (c) 2021, the Dart project authors.
+// Copyright (c) 2006, Kirill Simonov.
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'yaml_exception.dart';
+
+/// A listener that is notified of [YamlException]s during scanning/parsing.
+abstract class ErrorListener {
+  /// This method is invoked when an [error] has been found in the YAML.
+  void onError(YamlException error);
+}
+
+/// An [ErrorListener] that collects all errors into [errors].
+class ErrorCollector extends ErrorListener {
+  final List<YamlException> errors = [];
+
+  @override
+  void onError(YamlException error) => errors.add(error);
+}

diff --git a/pkgs/yaml/lib/src/event.dart b/pkgs/yaml/lib/src/event.dart
new file mode 100644
index 0000000..1476311
--- /dev/null
+++ b/pkgs/yaml/lib/src/event.dart

@@ -0,0 +1,171 @@
+// Copyright (c) 2014, the Dart project authors.
+// Copyright (c) 2006, Kirill Simonov.
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'package:source_span/source_span.dart';
+
+import 'parser.dart';
+import 'style.dart';
+import 'yaml_document.dart';
+
+/// An event emitted by a [Parser].
+class Event {
+  final EventType type;
+  final FileSpan span;
+
+  Event(this.type, this.span);
+
+  @override
+  String toString() => type.toString();
+}
+
+/// An event indicating the beginning of a YAML document.
+class DocumentStartEvent implements Event {
+  @override
+  EventType get type => EventType.documentStart;
+  @override
+  final FileSpan span;
+
+  /// The document's `%YAML` directive, or `null` if there was none.
+  final VersionDirective? versionDirective;
+
+  /// The document's `%TAG` directives, if any.
+  final List<TagDirective> tagDirectives;
+
+  /// Whether the document started implicitly (that is, without an explicit
+  /// `===` sequence).
+  final bool isImplicit;
+
+  DocumentStartEvent(this.span,
+      {this.versionDirective,
+      List<TagDirective>? tagDirectives,
+      this.isImplicit = true})
+      : tagDirectives = tagDirectives ?? [];
+
+  @override
+  String toString() => 'DOCUMENT_START';
+}
+
+/// An event indicating the end of a YAML document.
+class DocumentEndEvent implements Event {
+  @override
+  EventType get type => EventType.documentEnd;
+  @override
+  final FileSpan span;
+
+  /// Whether the document ended implicitly (that is, without an explicit
+  /// `...` sequence).
+  final bool isImplicit;
+
+  DocumentEndEvent(this.span, {this.isImplicit = true});
+
+  @override
+  String toString() => 'DOCUMENT_END';
+}
+
+/// An event indicating that an alias was referenced.
+class AliasEvent implements Event {
+  @override
+  EventType get type => EventType.alias;
+  @override
+  final FileSpan span;
+
+  /// The alias name.
+  final String name;
+
+  AliasEvent(this.span, this.name);
+
+  @override
+  String toString() => 'ALIAS $name';
+}
+
+/// An event that can have associated anchor and tag properties.
+abstract class _ValueEvent implements Event {
+  /// The name of the value's anchor, or `null` if it wasn't anchored.
+  String? get anchor;
+
+  /// The text of the value's tag, or `null` if it wasn't tagged.
+  String? get tag;
+
+  @override
+  String toString() {
+    var buffer = StringBuffer('$type');
+    if (anchor != null) buffer.write(' &$anchor');
+    if (tag != null) buffer.write(' $tag');
+    return buffer.toString();
+  }
+}
+
+/// An event indicating a single scalar value.
+class ScalarEvent extends _ValueEvent {
+  @override
+  EventType get type => EventType.scalar;
+  @override
+  final FileSpan span;
+  @override
+  final String? anchor;
+  @override
+  final String? tag;
+
+  /// The contents of the scalar.
+  final String value;
+
+  /// The style of the scalar in the original source.
+  final ScalarStyle style;
+
+  ScalarEvent(this.span, this.value, this.style, {this.anchor, this.tag});
+
+  @override
+  String toString() => '${super.toString()} "$value"';
+}
+
+/// An event indicating the beginning of a sequence.
+class SequenceStartEvent extends _ValueEvent {
+  @override
+  EventType get type => EventType.sequenceStart;
+  @override
+  final FileSpan span;
+  @override
+  final String? anchor;
+  @override
+  final String? tag;
+
+  /// The style of the collection in the original source.
+  final CollectionStyle style;
+
+  SequenceStartEvent(this.span, this.style, {this.anchor, this.tag});
+}
+
+/// An event indicating the beginning of a mapping.
+class MappingStartEvent extends _ValueEvent {
+  @override
+  EventType get type => EventType.mappingStart;
+  @override
+  final FileSpan span;
+  @override
+  final String? anchor;
+  @override
+  final String? tag;
+
+  /// The style of the collection in the original source.
+  final CollectionStyle style;
+
+  MappingStartEvent(this.span, this.style, {this.anchor, this.tag});
+}
+
+/// The types of [Event] objects.
+enum EventType {
+  streamStart,
+  streamEnd,
+  documentStart,
+  documentEnd,
+  alias,
+  scalar,
+  sequenceStart,
+  sequenceEnd,
+  mappingStart,
+  mappingEnd
+}

diff --git a/pkgs/yaml/lib/src/loader.dart b/pkgs/yaml/lib/src/loader.dart
new file mode 100644
index 0000000..7cdf45a
--- /dev/null
+++ b/pkgs/yaml/lib/src/loader.dart

@@ -0,0 +1,343 @@
+// Copyright (c) 2014, the Dart project authors.
+// Copyright (c) 2006, Kirill Simonov.
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'package:source_span/source_span.dart';
+
+import 'charcodes.dart';
+import 'equality.dart';
+import 'error_listener.dart';
+import 'event.dart';
+import 'parser.dart';
+import 'yaml_document.dart';
+import 'yaml_exception.dart';
+import 'yaml_node.dart';
+
+/// A loader that reads [Event]s emitted by a [Parser] and emits
+/// [YamlDocument]s.
+///
+/// This is based on the libyaml loader, available at
+/// https://github.com/yaml/libyaml/blob/master/src/loader.c. The license for
+/// that is available in ../../libyaml-license.txt.
+class Loader {
+  /// The underlying [Parser] that generates [Event]s.
+  final Parser _parser;
+
+  /// Aliases by the alias name.
+  final _aliases = <String, YamlNode>{};
+
+  /// The span of the entire stream emitted so far.
+  FileSpan get span => _span;
+  FileSpan _span;
+
+  /// Creates a loader that loads [source].
+  factory Loader(String source,
+      {Uri? sourceUrl, bool recover = false, ErrorListener? errorListener}) {
+    var parser = Parser(source,
+        sourceUrl: sourceUrl, recover: recover, errorListener: errorListener);
+    var event = parser.parse();
+    assert(event.type == EventType.streamStart);
+    return Loader._(parser, event.span);
+  }
+
+  Loader._(this._parser, this._span);
+
+  /// Loads the next document from the stream.
+  ///
+  /// If there are no more documents, returns `null`.
+  YamlDocument? load() {
+    if (_parser.isDone) return null;
+
+    var event = _parser.parse();
+    if (event.type == EventType.streamEnd) {
+      _span = _span.expand(event.span);
+      return null;
+    }
+
+    var document = _loadDocument(event as DocumentStartEvent);
+    _span = _span.expand(document.span as FileSpan);
+    _aliases.clear();
+    return document;
+  }
+
+  /// Composes a document object.
+  YamlDocument _loadDocument(DocumentStartEvent firstEvent) {
+    var contents = _loadNode(_parser.parse());
+
+    var lastEvent = _parser.parse() as DocumentEndEvent;
+    assert(lastEvent.type == EventType.documentEnd);
+
+    return YamlDocument.internal(
+        contents,
+        firstEvent.span.expand(lastEvent.span),
+        firstEvent.versionDirective,
+        firstEvent.tagDirectives,
+        startImplicit: firstEvent.isImplicit,
+        endImplicit: lastEvent.isImplicit);
+  }
+
+  /// Composes a node.
+  YamlNode _loadNode(Event firstEvent) => switch (firstEvent.type) {
+        EventType.alias => _loadAlias(firstEvent as AliasEvent),
+        EventType.scalar => _loadScalar(firstEvent as ScalarEvent),
+        EventType.sequenceStart =>
+          _loadSequence(firstEvent as SequenceStartEvent),
+        EventType.mappingStart => _loadMapping(firstEvent as MappingStartEvent),
+        _ => throw StateError('Unreachable')
+      };
+
+  /// Registers an anchor.
+  void _registerAnchor(String? anchor, YamlNode node) {
+    if (anchor == null) return;
+
+    // libyaml throws an error for duplicate anchors, but example 7.1 makes it
+    // clear that they should be overridden:
+    // http://yaml.org/spec/1.2/spec.html#id2786448.
+
+    _aliases[anchor] = node;
+  }
+
+  /// Composes a node corresponding to an alias.
+  YamlNode _loadAlias(AliasEvent event) {
+    var alias = _aliases[event.name];
+    if (alias != null) return alias;
+
+    throw YamlException('Undefined alias.', event.span);
+  }
+
+  /// Composes a scalar node.
+  YamlNode _loadScalar(ScalarEvent scalar) {
+    YamlNode node;
+    if (scalar.tag == '!') {
+      node = YamlScalar.internal(scalar.value, scalar);
+    } else if (scalar.tag != null) {
+      node = _parseByTag(scalar);
+    } else {
+      node = _parseScalar(scalar);
+    }
+
+    _registerAnchor(scalar.anchor, node);
+    return node;
+  }
+
+  /// Composes a sequence node.
+  YamlNode _loadSequence(SequenceStartEvent firstEvent) {
+    if (firstEvent.tag != '!' &&
+        firstEvent.tag != null &&
+        firstEvent.tag != 'tag:yaml.org,2002:seq') {
+      throw YamlException('Invalid tag for sequence.', firstEvent.span);
+    }
+
+    var children = <YamlNode>[];
+    var node = YamlList.internal(children, firstEvent.span, firstEvent.style);
+    _registerAnchor(firstEvent.anchor, node);
+
+    var event = _parser.parse();
+    while (event.type != EventType.sequenceEnd) {
+      children.add(_loadNode(event));
+      event = _parser.parse();
+    }
+
+    setSpan(node, firstEvent.span.expand(event.span));
+    return node;
+  }
+
+  /// Composes a mapping node.
+  YamlNode _loadMapping(MappingStartEvent firstEvent) {
+    if (firstEvent.tag != '!' &&
+        firstEvent.tag != null &&
+        firstEvent.tag != 'tag:yaml.org,2002:map') {
+      throw YamlException('Invalid tag for mapping.', firstEvent.span);
+    }
+
+    var children = deepEqualsMap<dynamic, YamlNode>();
+    var node = YamlMap.internal(children, firstEvent.span, firstEvent.style);
+    _registerAnchor(firstEvent.anchor, node);
+
+    var event = _parser.parse();
+    while (event.type != EventType.mappingEnd) {
+      var key = _loadNode(event);
+      var value = _loadNode(_parser.parse());
+      if (children.containsKey(key)) {
+        throw YamlException('Duplicate mapping key.', key.span);
+      }
+
+      children[key] = value;
+      event = _parser.parse();
+    }
+
+    setSpan(node, firstEvent.span.expand(event.span));
+    return node;
+  }
+
+  /// Parses a scalar according to its tag name.
+  YamlScalar _parseByTag(ScalarEvent scalar) {
+    switch (scalar.tag) {
+      case 'tag:yaml.org,2002:null':
+        var result = _parseNull(scalar);
+        if (result != null) return result;
+        throw YamlException('Invalid null scalar.', scalar.span);
+      case 'tag:yaml.org,2002:bool':
+        var result = _parseBool(scalar);
+        if (result != null) return result;
+        throw YamlException('Invalid bool scalar.', scalar.span);
+      case 'tag:yaml.org,2002:int':
+        var result = _parseNumber(scalar, allowFloat: false);
+        if (result != null) return result;
+        throw YamlException('Invalid int scalar.', scalar.span);
+      case 'tag:yaml.org,2002:float':
+        var result = _parseNumber(scalar, allowInt: false);
+        if (result != null) return result;
+        throw YamlException('Invalid float scalar.', scalar.span);
+      case 'tag:yaml.org,2002:str':
+        return YamlScalar.internal(scalar.value, scalar);
+      default:
+        throw YamlException('Undefined tag: ${scalar.tag}.', scalar.span);
+    }
+  }
+
+  /// Parses [scalar], which may be one of several types.
+  YamlScalar _parseScalar(ScalarEvent scalar) =>
+      _tryParseScalar(scalar) ?? YamlScalar.internal(scalar.value, scalar);
+
+  /// Tries to parse [scalar].
+  ///
+  /// If parsing fails, this returns `null`, indicating that the scalar should
+  /// be parsed as a string.
+  YamlScalar? _tryParseScalar(ScalarEvent scalar) {
+    // Quickly check for the empty string, which means null.
+    var length = scalar.value.length;
+    if (length == 0) return YamlScalar.internal(null, scalar);
+
+    // Dispatch on the first character.
+    var firstChar = scalar.value.codeUnitAt(0);
+    return switch (firstChar) {
+      $dot || $plus || $minus => _parseNumber(scalar),
+      $n || $N => length == 4 ? _parseNull(scalar) : null,
+      $t || $T => length == 4 ? _parseBool(scalar) : null,
+      $f || $F => length == 5 ? _parseBool(scalar) : null,
+      $tilde => length == 1 ? YamlScalar.internal(null, scalar) : null,
+      _ => (firstChar >= $0 && firstChar <= $9) ? _parseNumber(scalar) : null
+    };
+  }
+
+  /// Parse a null scalar.
+  ///
+  /// Returns a Dart `null` if parsing fails.
+  YamlScalar? _parseNull(ScalarEvent scalar) => switch (scalar.value) {
+        '' ||
+        'null' ||
+        'Null' ||
+        'NULL' ||
+        '~' =>
+          YamlScalar.internal(null, scalar),
+        _ => null
+      };
+
+  /// Parse a boolean scalar.
+  ///
+  /// Returns `null` if parsing fails.
+  YamlScalar? _parseBool(ScalarEvent scalar) => switch (scalar.value) {
+        'true' || 'True' || 'TRUE' => YamlScalar.internal(true, scalar),
+        'false' || 'False' || 'FALSE' => YamlScalar.internal(false, scalar),
+        _ => null
+      };
+
+  /// Parses a numeric scalar.
+  ///
+  /// Returns `null` if parsing fails.
+  YamlScalar? _parseNumber(ScalarEvent scalar,
+      {bool allowInt = true, bool allowFloat = true}) {
+    var value = _parseNumberValue(scalar.value,
+        allowInt: allowInt, allowFloat: allowFloat);
+    return value == null ? null : YamlScalar.internal(value, scalar);
+  }
+
+  /// Parses the value of a number.
+  ///
+  /// Returns the number if it's parsed successfully, or `null` if it's not.
+  num? _parseNumberValue(String contents,
+      {bool allowInt = true, bool allowFloat = true}) {
+    assert(allowInt || allowFloat);
+
+    var firstChar = contents.codeUnitAt(0);
+    var length = contents.length;
+
+    // Quick check for single digit integers.
+    if (allowInt && length == 1) {
+      var value = firstChar - $0;
+      return value >= 0 && value <= 9 ? value : null;
+    }
+
+    var secondChar = contents.codeUnitAt(1);
+
+    // Hexadecimal or octal integers.
+    if (allowInt && firstChar == $0) {
+      // int.tryParse supports 0x natively.
+      if (secondChar == $x) return int.tryParse(contents);
+
+      if (secondChar == $o) {
+        var afterRadix = contents.substring(2);
+        return int.tryParse(afterRadix, radix: 8);
+      }
+    }
+
+    // Int or float starting with a digit or a +/- sign.
+    if ((firstChar >= $0 && firstChar <= $9) ||
+        ((firstChar == $plus || firstChar == $minus) &&
+            secondChar >= $0 &&
+            secondChar <= $9)) {
+      // Try to parse an int or, failing that, a double.
+      num? result;
+      if (allowInt) {
+        // Pass "radix: 10" explicitly to ensure that "-0x10", which is valid
+        // Dart but invalid YAML, doesn't get parsed.
+        result = int.tryParse(contents, radix: 10);
+      }
+
+      if (allowFloat) result ??= double.tryParse(contents);
+      return result;
+    }
+
+    if (!allowFloat) return null;
+
+    // Now the only possibility is to parse a float starting with a dot or a
+    // sign and a dot, or the signed/unsigned infinity values and not-a-numbers.
+    if ((firstChar == $dot && secondChar >= $0 && secondChar <= $9) ||
+        (firstChar == $minus || firstChar == $plus) && secondChar == $dot) {
+      // Starting with a . and a number or a sign followed by a dot.
+      if (length == 5) {
+        switch (contents) {
+          case '+.inf':
+          case '+.Inf':
+          case '+.INF':
+            return double.infinity;
+          case '-.inf':
+          case '-.Inf':
+          case '-.INF':
+            return -double.infinity;
+        }
+      }
+
+      return double.tryParse(contents);
+    }
+
+    if (length == 4 && firstChar == $dot) {
+      switch (contents) {
+        case '.inf':
+        case '.Inf':
+        case '.INF':
+          return double.infinity;
+        case '.nan':
+        case '.NaN':
+        case '.NAN':
+          return double.nan;
+      }
+    }
+
+    return null;
+  }
+}

diff --git a/pkgs/yaml/lib/src/null_span.dart b/pkgs/yaml/lib/src/null_span.dart
new file mode 100644
index 0000000..49e1a1c
--- /dev/null
+++ b/pkgs/yaml/lib/src/null_span.dart

@@ -0,0 +1,26 @@
+// Copyright (c) 2014, the Dart project authors.
+// Copyright (c) 2006, Kirill Simonov.
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'package:source_span/source_span.dart';
+
+import 'yaml_node.dart';
+
+/// A [SourceSpan] with no location information.
+///
+/// This is used with [YamlMap.wrap] and [YamlList.wrap] to provide means of
+/// accessing a non-YAML map that behaves transparently like a map parsed from
+/// YAML.
+class NullSpan extends SourceSpanMixin {
+  @override
+  final SourceLocation start;
+  @override
+  SourceLocation get end => start;
+  @override
+  final text = '';
+
+  NullSpan(Object? sourceUrl) : start = SourceLocation(0, sourceUrl: sourceUrl);
+}

diff --git a/pkgs/yaml/lib/src/parser.dart b/pkgs/yaml/lib/src/parser.dart
new file mode 100644
index 0000000..e924e40
--- /dev/null
+++ b/pkgs/yaml/lib/src/parser.dart

@@ -0,0 +1,805 @@
+// Copyright (c) 2014, the Dart project authors.
+// Copyright (c) 2006, Kirill Simonov.
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+// ignore_for_file: constant_identifier_names
+
+import 'package:source_span/source_span.dart';
+import 'package:string_scanner/string_scanner.dart';
+
+import 'error_listener.dart';
+import 'event.dart';
+import 'scanner.dart';
+import 'style.dart';
+import 'token.dart';
+import 'utils.dart';
+import 'yaml_document.dart';
+import 'yaml_exception.dart';
+
+/// A parser that reads [Token]s emitted by a [Scanner] and emits [Event]s.
+///
+/// This is based on the libyaml parser, available at
+/// https://github.com/yaml/libyaml/blob/master/src/parser.c. The license for
+/// that is available in ../../libyaml-license.txt.
+class Parser {
+  /// The underlying [Scanner] that generates [Token]s.
+  final Scanner _scanner;
+
+  /// The stack of parse states for nested contexts.
+  final _states = <_State>[];
+
+  /// The current parse state.
+  var _state = _State.STREAM_START;
+
+  /// The custom tag directives, by tag handle.
+  final _tagDirectives = <String, TagDirective>{};
+
+  /// Whether the parser has finished parsing.
+  bool get isDone => _state == _State.END;
+
+  /// Creates a parser that parses [source].
+  ///
+  /// If [recover] is true, will attempt to recover from parse errors and may
+  /// return invalid or synthetic nodes. If [errorListener] is also supplied,
+  /// its onError method will be called for each error recovered from. It is not
+  /// valid to provide [errorListener] if [recover] is false.
+  Parser(String source,
+      {Uri? sourceUrl, bool recover = false, ErrorListener? errorListener})
+      : assert(recover || errorListener == null),
+        _scanner = Scanner(source,
+            sourceUrl: sourceUrl,
+            recover: recover,
+            errorListener: errorListener);
+
+  /// Consumes and returns the next event.
+  Event parse() {
+    try {
+      if (isDone) throw StateError('No more events.');
+      var event = _stateMachine();
+      return event;
+    } on StringScannerException catch (error) {
+      throw YamlException(error.message, error.span);
+    }
+  }
+
+  /// Dispatches parsing based on the current state.
+  Event _stateMachine() {
+    switch (_state) {
+      case _State.STREAM_START:
+        return _parseStreamStart();
+      case _State.DOCUMENT_START:
+        return _parseDocumentStart();
+      case _State.DOCUMENT_CONTENT:
+        return _parseDocumentContent();
+      case _State.DOCUMENT_END:
+        return _parseDocumentEnd();
+      case _State.BLOCK_NODE:
+        return _parseNode(block: true);
+      case _State.BLOCK_NODE_OR_INDENTLESS_SEQUENCE:
+        return _parseNode(block: true, indentlessSequence: true);
+      case _State.FLOW_NODE:
+        return _parseNode();
+      case _State.BLOCK_SEQUENCE_FIRST_ENTRY:
+        // Scan past the `BLOCK-SEQUENCE-FIRST-ENTRY` token to the
+        // `BLOCK-SEQUENCE-ENTRY` token.
+        _scanner.scan();
+        return _parseBlockSequenceEntry();
+      case _State.BLOCK_SEQUENCE_ENTRY:
+        return _parseBlockSequenceEntry();
+      case _State.INDENTLESS_SEQUENCE_ENTRY:
+        return _parseIndentlessSequenceEntry();
+      case _State.BLOCK_MAPPING_FIRST_KEY:
+        // Scan past the `BLOCK-MAPPING-FIRST-KEY` token to the
+        // `BLOCK-MAPPING-KEY` token.
+        _scanner.scan();
+        return _parseBlockMappingKey();
+      case _State.BLOCK_MAPPING_KEY:
+        return _parseBlockMappingKey();
+      case _State.BLOCK_MAPPING_VALUE:
+        return _parseBlockMappingValue();
+      case _State.FLOW_SEQUENCE_FIRST_ENTRY:
+        return _parseFlowSequenceEntry(first: true);
+      case _State.FLOW_SEQUENCE_ENTRY:
+        return _parseFlowSequenceEntry();
+      case _State.FLOW_SEQUENCE_ENTRY_MAPPING_KEY:
+        return _parseFlowSequenceEntryMappingKey();
+      case _State.FLOW_SEQUENCE_ENTRY_MAPPING_VALUE:
+        return _parseFlowSequenceEntryMappingValue();
+      case _State.FLOW_SEQUENCE_ENTRY_MAPPING_END:
+        return _parseFlowSequenceEntryMappingEnd();
+      case _State.FLOW_MAPPING_FIRST_KEY:
+        return _parseFlowMappingKey(first: true);
+      case _State.FLOW_MAPPING_KEY:
+        return _parseFlowMappingKey();
+      case _State.FLOW_MAPPING_VALUE:
+        return _parseFlowMappingValue();
+      case _State.FLOW_MAPPING_EMPTY_VALUE:
+        return _parseFlowMappingValue(empty: true);
+      default:
+        throw StateError('Unreachable');
+    }
+  }
+
+  /// Parses the production:
+  ///
+  ///     stream ::=
+  ///       STREAM-START implicit_document? explicit_document* STREAM-END
+  ///       ************
+  Event _parseStreamStart() {
+    var token = _scanner.scan();
+    assert(token.type == TokenType.streamStart);
+
+    _state = _State.DOCUMENT_START;
+    return Event(EventType.streamStart, token.span);
+  }
+
+  /// Parses the productions:
+  ///
+  ///     implicit_document    ::= block_node DOCUMENT-END*
+  ///                              *
+  ///     explicit_document    ::=
+  ///       DIRECTIVE* DOCUMENT-START block_node? DOCUMENT-END*
+  ///       *************************
+  Event _parseDocumentStart() {
+    var token = _scanner.peek()!;
+
+    // libyaml requires any document beyond the first in the stream to have an
+    // explicit document start indicator, but the spec allows it to be omitted
+    // as long as there was an end indicator.
+
+    // Parse extra document end indicators.
+    while (token.type == TokenType.documentEnd) {
+      token = _scanner.advance()!;
+    }
+
+    if (token.type != TokenType.versionDirective &&
+        token.type != TokenType.tagDirective &&
+        token.type != TokenType.documentStart &&
+        token.type != TokenType.streamEnd) {
+      // Parse an implicit document.
+      _processDirectives();
+      _states.add(_State.DOCUMENT_END);
+      _state = _State.BLOCK_NODE;
+      return DocumentStartEvent(token.span.start.pointSpan());
+    }
+
+    if (token.type == TokenType.streamEnd) {
+      _state = _State.END;
+      _scanner.scan();
+      return Event(EventType.streamEnd, token.span);
+    }
+
+    // Parse an explicit document.
+    var start = token.span;
+    var (versionDirective, tagDirectives) = _processDirectives();
+    token = _scanner.peek()!;
+    if (token.type != TokenType.documentStart) {
+      throw YamlException('Expected document start.', token.span);
+    }
+
+    _states.add(_State.DOCUMENT_END);
+    _state = _State.DOCUMENT_CONTENT;
+    _scanner.scan();
+    return DocumentStartEvent(start.expand(token.span),
+        versionDirective: versionDirective,
+        tagDirectives: tagDirectives,
+        isImplicit: false);
+  }
+
+  /// Parses the productions:
+  ///
+  ///     explicit_document    ::=
+  ///       DIRECTIVE* DOCUMENT-START block_node? DOCUMENT-END*
+  ///                                 ***********
+  Event _parseDocumentContent() {
+    var token = _scanner.peek()!;
+
+    switch (token.type) {
+      case TokenType.versionDirective:
+      case TokenType.tagDirective:
+      case TokenType.documentStart:
+      case TokenType.documentEnd:
+      case TokenType.streamEnd:
+        _state = _states.removeLast();
+        return _processEmptyScalar(token.span.start);
+      default:
+        return _parseNode(block: true);
+    }
+  }
+
+  /// Parses the productions:
+  ///
+  ///     implicit_document    ::= block_node DOCUMENT-END*
+  ///                                         *************
+  ///     explicit_document    ::=
+  ///       DIRECTIVE* DOCUMENT-START block_node? DOCUMENT-END*
+  ///                                             *************
+  Event _parseDocumentEnd() {
+    _tagDirectives.clear();
+    _state = _State.DOCUMENT_START;
+
+    var token = _scanner.peek()!;
+    if (token.type == TokenType.documentEnd) {
+      _scanner.scan();
+      return DocumentEndEvent(token.span, isImplicit: false);
+    } else {
+      return DocumentEndEvent(token.span.start.pointSpan());
+    }
+  }
+
+  /// Parses the productions:
+  ///
+  ///     block_node_or_indentless_sequence    ::=
+  ///       ALIAS
+  ///       *****
+  ///       | properties (block_content | indentless_block_sequence)?
+  ///         **********  *
+  ///       | block_content | indentless_block_sequence
+  ///         *
+  ///     block_node           ::= ALIAS
+  ///                              *****
+  ///                              | properties block_content?
+  ///                                ********** *
+  ///                              | block_content
+  ///                                *
+  ///     flow_node            ::= ALIAS
+  ///                              *****
+  ///                              | properties flow_content?
+  ///                                ********** *
+  ///                              | flow_content
+  ///                                *
+  ///     properties           ::= TAG ANCHOR? | ANCHOR TAG?
+  ///                              *************************
+  ///     block_content        ::= block_collection | flow_collection | SCALAR
+  ///                                                                   ******
+  ///     flow_content         ::= flow_collection | SCALAR
+  ///                                                ******
+  Event _parseNode({bool block = false, bool indentlessSequence = false}) {
+    var token = _scanner.peek()!;
+
+    if (token is AliasToken) {
+      _scanner.scan();
+      _state = _states.removeLast();
+      return AliasEvent(token.span, token.name);
+    }
+
+    String? anchor;
+    TagToken? tagToken;
+    var span = token.span.start.pointSpan();
+    Token parseAnchor(AnchorToken token) {
+      anchor = token.name;
+      span = span.expand(token.span);
+      return _scanner.advance()!;
+    }
+
+    Token parseTag(TagToken token) {
+      tagToken = token;
+      span = span.expand(token.span);
+      return _scanner.advance()!;
+    }
+
+    if (token is AnchorToken) {
+      token = parseAnchor(token);
+      if (token is TagToken) token = parseTag(token);
+    } else if (token is TagToken) {
+      token = parseTag(token);
+      if (token is AnchorToken) token = parseAnchor(token);
+    }
+
+    String? tag;
+    if (tagToken != null) {
+      if (tagToken!.handle == null) {
+        tag = tagToken!.suffix;
+      } else {
+        var tagDirective = _tagDirectives[tagToken!.handle];
+        if (tagDirective == null) {
+          throw YamlException('Undefined tag handle.', tagToken!.span);
+        }
+
+        tag = tagDirective.prefix + (tagToken?.suffix ?? '');
+      }
+    }
+
+    if (indentlessSequence && token.type == TokenType.blockEntry) {
+      _state = _State.INDENTLESS_SEQUENCE_ENTRY;
+      return SequenceStartEvent(span.expand(token.span), CollectionStyle.BLOCK,
+          anchor: anchor, tag: tag);
+    }
+
+    if (token is ScalarToken) {
+      // All non-plain scalars have the "!" tag by default.
+      if (tag == null && token.style != ScalarStyle.PLAIN) tag = '!';
+
+      _state = _states.removeLast();
+      _scanner.scan();
+      return ScalarEvent(span.expand(token.span), token.value, token.style,
+          anchor: anchor, tag: tag);
+    }
+
+    if (token.type == TokenType.flowSequenceStart) {
+      _state = _State.FLOW_SEQUENCE_FIRST_ENTRY;
+      return SequenceStartEvent(span.expand(token.span), CollectionStyle.FLOW,
+          anchor: anchor, tag: tag);
+    }
+
+    if (token.type == TokenType.flowMappingStart) {
+      _state = _State.FLOW_MAPPING_FIRST_KEY;
+      return MappingStartEvent(span.expand(token.span), CollectionStyle.FLOW,
+          anchor: anchor, tag: tag);
+    }
+
+    if (block && token.type == TokenType.blockSequenceStart) {
+      _state = _State.BLOCK_SEQUENCE_FIRST_ENTRY;
+      return SequenceStartEvent(span.expand(token.span), CollectionStyle.BLOCK,
+          anchor: anchor, tag: tag);
+    }
+
+    if (block && token.type == TokenType.blockMappingStart) {
+      _state = _State.BLOCK_MAPPING_FIRST_KEY;
+      return MappingStartEvent(span.expand(token.span), CollectionStyle.BLOCK,
+          anchor: anchor, tag: tag);
+    }
+
+    if (anchor != null || tag != null) {
+      _state = _states.removeLast();
+      return ScalarEvent(span, '', ScalarStyle.PLAIN, anchor: anchor, tag: tag);
+    }
+
+    throw YamlException('Expected node content.', span);
+  }
+
+  /// Parses the productions:
+  ///
+  ///     block_sequence ::=
+  ///       BLOCK-SEQUENCE-START (BLOCK-ENTRY block_node?)* BLOCK-END
+  ///       ********************  *********** *             *********
+  Event _parseBlockSequenceEntry() {
+    var token = _scanner.peek()!;
+
+    if (token.type == TokenType.blockEntry) {
+      var start = token.span.start;
+      token = _scanner.advance()!;
+
+      if (token.type == TokenType.blockEntry ||
+          token.type == TokenType.blockEnd) {
+        _state = _State.BLOCK_SEQUENCE_ENTRY;
+        return _processEmptyScalar(start);
+      } else {
+        _states.add(_State.BLOCK_SEQUENCE_ENTRY);
+        return _parseNode(block: true);
+      }
+    }
+
+    if (token.type == TokenType.blockEnd) {
+      _scanner.scan();
+      _state = _states.removeLast();
+      return Event(EventType.sequenceEnd, token.span);
+    }
+
+    throw YamlException("While parsing a block collection, expected '-'.",
+        token.span.start.pointSpan());
+  }
+
+  /// Parses the productions:
+  ///
+  ///     indentless_sequence  ::= (BLOCK-ENTRY block_node?)+
+  ///                               *********** *
+  Event _parseIndentlessSequenceEntry() {
+    var token = _scanner.peek()!;
+
+    if (token.type != TokenType.blockEntry) {
+      _state = _states.removeLast();
+      return Event(EventType.sequenceEnd, token.span.start.pointSpan());
+    }
+
+    var start = token.span.start;
+    token = _scanner.advance()!;
+
+    if (token.type == TokenType.blockEntry ||
+        token.type == TokenType.key ||
+        token.type == TokenType.value ||
+        token.type == TokenType.blockEnd) {
+      _state = _State.INDENTLESS_SEQUENCE_ENTRY;
+      return _processEmptyScalar(start);
+    } else {
+      _states.add(_State.INDENTLESS_SEQUENCE_ENTRY);
+      return _parseNode(block: true);
+    }
+  }
+
+  /// Parses the productions:
+  ///
+  ///     block_mapping        ::= BLOCK-MAPPING_START
+  ///                              *******************
+  ///                              ((KEY block_node_or_indentless_sequence?)?
+  ///                                *** *
+  ///                              (VALUE block_node_or_indentless_sequence?)?)*
+  ///
+  ///                              BLOCK-END
+  ///                              *********
+  Event _parseBlockMappingKey() {
+    var token = _scanner.peek()!;
+    if (token.type == TokenType.key) {
+      var start = token.span.start;
+      token = _scanner.advance()!;
+
+      if (token.type == TokenType.key ||
+          token.type == TokenType.value ||
+          token.type == TokenType.blockEnd) {
+        _state = _State.BLOCK_MAPPING_VALUE;
+        return _processEmptyScalar(start);
+      } else {
+        _states.add(_State.BLOCK_MAPPING_VALUE);
+        return _parseNode(block: true, indentlessSequence: true);
+      }
+    }
+
+    // libyaml doesn't allow empty keys without an explicit key indicator, but
+    // the spec does. See example 8.18:
+    // http://yaml.org/spec/1.2/spec.html#id2798896.
+    if (token.type == TokenType.value) {
+      _state = _State.BLOCK_MAPPING_VALUE;
+      return _processEmptyScalar(token.span.start);
+    }
+
+    if (token.type == TokenType.blockEnd) {
+      _scanner.scan();
+      _state = _states.removeLast();
+      return Event(EventType.mappingEnd, token.span);
+    }
+
+    throw YamlException('Expected a key while parsing a block mapping.',
+        token.span.start.pointSpan());
+  }
+
+  /// Parses the productions:
+  ///
+  ///     block_mapping        ::= BLOCK-MAPPING_START
+  ///
+  ///                              ((KEY block_node_or_indentless_sequence?)?
+  ///
+  ///                              (VALUE block_node_or_indentless_sequence?)?)*
+  ///                               ***** *
+  ///                              BLOCK-END
+  ///
+  Event _parseBlockMappingValue() {
+    var token = _scanner.peek()!;
+
+    if (token.type != TokenType.value) {
+      _state = _State.BLOCK_MAPPING_KEY;
+      return _processEmptyScalar(token.span.start);
+    }
+
+    var start = token.span.start;
+    token = _scanner.advance()!;
+    if (token.type == TokenType.key ||
+        token.type == TokenType.value ||
+        token.type == TokenType.blockEnd) {
+      _state = _State.BLOCK_MAPPING_KEY;
+      return _processEmptyScalar(start);
+    } else {
+      _states.add(_State.BLOCK_MAPPING_KEY);
+      return _parseNode(block: true, indentlessSequence: true);
+    }
+  }
+
+  /// Parses the productions:
+  ///
+  ///     flow_sequence        ::= FLOW-SEQUENCE-START
+  ///                              *******************
+  ///                              (flow_sequence_entry FLOW-ENTRY)*
+  ///                               *                   **********
+  ///                              flow_sequence_entry?
+  ///                              *
+  ///                              FLOW-SEQUENCE-END
+  ///                              *****************
+  ///     flow_sequence_entry  ::=
+  ///       flow_node | KEY flow_node? (VALUE flow_node?)?
+  ///       *
+  Event _parseFlowSequenceEntry({bool first = false}) {
+    if (first) _scanner.scan();
+    var token = _scanner.peek()!;
+
+    if (token.type != TokenType.flowSequenceEnd) {
+      if (!first) {
+        if (token.type != TokenType.flowEntry) {
+          throw YamlException(
+              "While parsing a flow sequence, expected ',' or ']'.",
+              token.span.start.pointSpan());
+        }
+
+        token = _scanner.advance()!;
+      }
+
+      if (token.type == TokenType.key) {
+        _state = _State.FLOW_SEQUENCE_ENTRY_MAPPING_KEY;
+        _scanner.scan();
+        return MappingStartEvent(token.span, CollectionStyle.FLOW);
+      } else if (token.type != TokenType.flowSequenceEnd) {
+        _states.add(_State.FLOW_SEQUENCE_ENTRY);
+        return _parseNode();
+      }
+    }
+
+    _scanner.scan();
+    _state = _states.removeLast();
+    return Event(EventType.sequenceEnd, token.span);
+  }
+
+  /// Parses the productions:
+  ///
+  ///     flow_sequence_entry  ::=
+  ///       flow_node | KEY flow_node? (VALUE flow_node?)?
+  ///                   *** *
+  Event _parseFlowSequenceEntryMappingKey() {
+    var token = _scanner.peek()!;
+
+    if (token.type == TokenType.value ||
+        token.type == TokenType.flowEntry ||
+        token.type == TokenType.flowSequenceEnd) {
+      // libyaml consumes the token here, but that seems like a bug, since it
+      // always causes [_parseFlowSequenceEntryMappingValue] to emit an empty
+      // scalar.
+
+      var start = token.span.start;
+      _state = _State.FLOW_SEQUENCE_ENTRY_MAPPING_VALUE;
+      return _processEmptyScalar(start);
+    } else {
+      _states.add(_State.FLOW_SEQUENCE_ENTRY_MAPPING_VALUE);
+      return _parseNode();
+    }
+  }
+
+  /// Parses the productions:
+  ///
+  ///     flow_sequence_entry  ::=
+  ///       flow_node | KEY flow_node? (VALUE flow_node?)?
+  ///                                   ***** *
+  Event _parseFlowSequenceEntryMappingValue() {
+    var token = _scanner.peek()!;
+
+    if (token.type == TokenType.value) {
+      token = _scanner.advance()!;
+      if (token.type != TokenType.flowEntry &&
+          token.type != TokenType.flowSequenceEnd) {
+        _states.add(_State.FLOW_SEQUENCE_ENTRY_MAPPING_END);
+        return _parseNode();
+      }
+    }
+
+    _state = _State.FLOW_SEQUENCE_ENTRY_MAPPING_END;
+    return _processEmptyScalar(token.span.start);
+  }
+
+  /// Parses the productions:
+  ///
+  ///     flow_sequence_entry  ::=
+  ///       flow_node | KEY flow_node? (VALUE flow_node?)?
+  ///                                                   *
+  Event _parseFlowSequenceEntryMappingEnd() {
+    _state = _State.FLOW_SEQUENCE_ENTRY;
+    return Event(EventType.mappingEnd, _scanner.peek()!.span.start.pointSpan());
+  }
+
+  /// Parses the productions:
+  ///
+  ///     flow_mapping         ::= FLOW-MAPPING-START
+  ///                              ******************
+  ///                              (flow_mapping_entry FLOW-ENTRY)*
+  ///                               *                  **********
+  ///                              flow_mapping_entry?
+  ///                              ******************
+  ///                              FLOW-MAPPING-END
+  ///                              ****************
+  ///     flow_mapping_entry   ::=
+  ///       flow_node | KEY flow_node? (VALUE flow_node?)?
+  ///       *           *** *
+  Event _parseFlowMappingKey({bool first = false}) {
+    if (first) _scanner.scan();
+    var token = _scanner.peek()!;
+
+    if (token.type != TokenType.flowMappingEnd) {
+      if (!first) {
+        if (token.type != TokenType.flowEntry) {
+          throw YamlException(
+              "While parsing a flow mapping, expected ',' or '}'.",
+              token.span.start.pointSpan());
+        }
+
+        token = _scanner.advance()!;
+      }
+
+      if (token.type == TokenType.key) {
+        token = _scanner.advance()!;
+        if (token.type != TokenType.value &&
+            token.type != TokenType.flowEntry &&
+            token.type != TokenType.flowMappingEnd) {
+          _states.add(_State.FLOW_MAPPING_VALUE);
+          return _parseNode();
+        } else {
+          _state = _State.FLOW_MAPPING_VALUE;
+          return _processEmptyScalar(token.span.start);
+        }
+      } else if (token.type != TokenType.flowMappingEnd) {
+        _states.add(_State.FLOW_MAPPING_EMPTY_VALUE);
+        return _parseNode();
+      }
+    }
+
+    _scanner.scan();
+    _state = _states.removeLast();
+    return Event(EventType.mappingEnd, token.span);
+  }
+
+  /// Parses the productions:
+  ///
+  ///     flow_mapping_entry   ::=
+  ///       flow_node | KEY flow_node? (VALUE flow_node?)?
+  ///                *                  ***** *
+  Event _parseFlowMappingValue({bool empty = false}) {
+    var token = _scanner.peek()!;
+
+    if (empty) {
+      _state = _State.FLOW_MAPPING_KEY;
+      return _processEmptyScalar(token.span.start);
+    }
+
+    if (token.type == TokenType.value) {
+      token = _scanner.advance()!;
+      if (token.type != TokenType.flowEntry &&
+          token.type != TokenType.flowMappingEnd) {
+        _states.add(_State.FLOW_MAPPING_KEY);
+        return _parseNode();
+      }
+    }
+
+    _state = _State.FLOW_MAPPING_KEY;
+    return _processEmptyScalar(token.span.start);
+  }
+
+  /// Generate an empty scalar event.
+  Event _processEmptyScalar(SourceLocation location) =>
+      ScalarEvent(location.pointSpan() as FileSpan, '', ScalarStyle.PLAIN);
+
+  /// Parses directives.
+  (VersionDirective?, List<TagDirective>) _processDirectives() {
+    var token = _scanner.peek()!;
+
+    VersionDirective? versionDirective;
+    var tagDirectives = <TagDirective>[];
+    while (token.type == TokenType.versionDirective ||
+        token.type == TokenType.tagDirective) {
+      if (token is VersionDirectiveToken) {
+        if (versionDirective != null) {
+          throw YamlException('Duplicate %YAML directive.', token.span);
+        }
+
+        if (token.major != 1 || token.minor == 0) {
+          throw YamlException(
+              'Incompatible YAML document. This parser only supports YAML 1.1 '
+              'and 1.2.',
+              token.span);
+        } else if (token.minor > 2) {
+          // TODO(nweiz): Print to stderr when issue 6943 is fixed and dart:io
+          // is available.
+          warn('Warning: this parser only supports YAML 1.1 and 1.2.',
+              token.span);
+        }
+
+        versionDirective = VersionDirective(token.major, token.minor);
+      } else if (token is TagDirectiveToken) {
+        var tagDirective = TagDirective(token.handle, token.prefix);
+        _appendTagDirective(tagDirective, token.span);
+        tagDirectives.add(tagDirective);
+      }
+
+      token = _scanner.advance()!;
+    }
+
+    _appendTagDirective(TagDirective('!', '!'), token.span.start.pointSpan(),
+        allowDuplicates: true);
+    _appendTagDirective(
+        TagDirective('!!', 'tag:yaml.org,2002:'), token.span.start.pointSpan(),
+        allowDuplicates: true);
+
+    return (versionDirective, tagDirectives);
+  }
+
+  /// Adds a tag directive to the directives stack.
+  void _appendTagDirective(TagDirective newDirective, FileSpan span,
+      {bool allowDuplicates = false}) {
+    if (_tagDirectives.containsKey(newDirective.handle)) {
+      if (allowDuplicates) return;
+      throw YamlException('Duplicate %TAG directive.', span);
+    }
+
+    _tagDirectives[newDirective.handle] = newDirective;
+  }
+}
+
+/// The possible states for the parser.
+class _State {
+  /// Expect [TokenType.streamStart].
+  static const STREAM_START = _State('STREAM_START');
+
+  /// Expect [TokenType.documentStart].
+  static const DOCUMENT_START = _State('DOCUMENT_START');
+
+  /// Expect the content of a document.
+  static const DOCUMENT_CONTENT = _State('DOCUMENT_CONTENT');
+
+  /// Expect [TokenType.documentEnd].
+  static const DOCUMENT_END = _State('DOCUMENT_END');
+
+  /// Expect a block node.
+  static const BLOCK_NODE = _State('BLOCK_NODE');
+
+  /// Expect a block node or indentless sequence.
+  static const BLOCK_NODE_OR_INDENTLESS_SEQUENCE =
+      _State('BLOCK_NODE_OR_INDENTLESS_SEQUENCE');
+
+  /// Expect a flow node.
+  static const FLOW_NODE = _State('FLOW_NODE');
+
+  /// Expect the first entry of a block sequence.
+  static const BLOCK_SEQUENCE_FIRST_ENTRY =
+      _State('BLOCK_SEQUENCE_FIRST_ENTRY');
+
+  /// Expect an entry of a block sequence.
+  static const BLOCK_SEQUENCE_ENTRY = _State('BLOCK_SEQUENCE_ENTRY');
+
+  /// Expect an entry of an indentless sequence.
+  static const INDENTLESS_SEQUENCE_ENTRY = _State('INDENTLESS_SEQUENCE_ENTRY');
+
+  /// Expect the first key of a block mapping.
+  static const BLOCK_MAPPING_FIRST_KEY = _State('BLOCK_MAPPING_FIRST_KEY');
+
+  /// Expect a block mapping key.
+  static const BLOCK_MAPPING_KEY = _State('BLOCK_MAPPING_KEY');
+
+  /// Expect a block mapping value.
+  static const BLOCK_MAPPING_VALUE = _State('BLOCK_MAPPING_VALUE');
+
+  /// Expect the first entry of a flow sequence.
+  static const FLOW_SEQUENCE_FIRST_ENTRY = _State('FLOW_SEQUENCE_FIRST_ENTRY');
+
+  /// Expect an entry of a flow sequence.
+  static const FLOW_SEQUENCE_ENTRY = _State('FLOW_SEQUENCE_ENTRY');
+
+  /// Expect a key of an ordered mapping.
+  static const FLOW_SEQUENCE_ENTRY_MAPPING_KEY =
+      _State('FLOW_SEQUENCE_ENTRY_MAPPING_KEY');
+
+  /// Expect a value of an ordered mapping.
+  static const FLOW_SEQUENCE_ENTRY_MAPPING_VALUE =
+      _State('FLOW_SEQUENCE_ENTRY_MAPPING_VALUE');
+
+  /// Expect the and of an ordered mapping entry.
+  static const FLOW_SEQUENCE_ENTRY_MAPPING_END =
+      _State('FLOW_SEQUENCE_ENTRY_MAPPING_END');
+
+  /// Expect the first key of a flow mapping.
+  static const FLOW_MAPPING_FIRST_KEY = _State('FLOW_MAPPING_FIRST_KEY');
+
+  /// Expect a key of a flow mapping.
+  static const FLOW_MAPPING_KEY = _State('FLOW_MAPPING_KEY');
+
+  /// Expect a value of a flow mapping.
+  static const FLOW_MAPPING_VALUE = _State('FLOW_MAPPING_VALUE');
+
+  /// Expect an empty value of a flow mapping.
+  static const FLOW_MAPPING_EMPTY_VALUE = _State('FLOW_MAPPING_EMPTY_VALUE');
+
+  /// Expect nothing.
+  static const END = _State('END');
+
+  final String name;
+
+  const _State(this.name);
+
+  @override
+  String toString() => name;
+}

diff --git a/pkgs/yaml/lib/src/scanner.dart b/pkgs/yaml/lib/src/scanner.dart
new file mode 100644
index 0000000..1cfd3af
--- /dev/null
+++ b/pkgs/yaml/lib/src/scanner.dart

@@ -0,0 +1,1695 @@
+// Copyright (c) 2014, the Dart project authors.
+// Copyright (c) 2006, Kirill Simonov.
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+// ignore_for_file: constant_identifier_names
+
+import 'package:collection/collection.dart';
+import 'package:source_span/source_span.dart';
+import 'package:string_scanner/string_scanner.dart';
+
+import 'error_listener.dart';
+import 'style.dart';
+import 'token.dart';
+import 'utils.dart';
+import 'yaml_exception.dart';
+
+/// A scanner that reads a string of Unicode characters and emits [Token]s.
+///
+/// This is based on the libyaml scanner, available at
+/// https://github.com/yaml/libyaml/blob/master/src/scanner.c. The license for
+/// that is available in ../../libyaml-license.txt.
+class Scanner {
+  static const TAB = 0x9;
+  static const LF = 0xA;
+  static const CR = 0xD;
+  static const SP = 0x20;
+  static const DOLLAR = 0x24;
+  static const LEFT_PAREN = 0x28;
+  static const RIGHT_PAREN = 0x29;
+  static const PLUS = 0x2B;
+  static const COMMA = 0x2C;
+  static const HYPHEN = 0x2D;
+  static const PERIOD = 0x2E;
+  static const QUESTION = 0x3F;
+  static const COLON = 0x3A;
+  static const SEMICOLON = 0x3B;
+  static const EQUALS = 0x3D;
+  static const LEFT_SQUARE = 0x5B;
+  static const RIGHT_SQUARE = 0x5D;
+  static const LEFT_CURLY = 0x7B;
+  static const RIGHT_CURLY = 0x7D;
+  static const HASH = 0x23;
+  static const AMPERSAND = 0x26;
+  static const ASTERISK = 0x2A;
+  static const EXCLAMATION = 0x21;
+  static const VERTICAL_BAR = 0x7C;
+  static const LEFT_ANGLE = 0x3C;
+  static const RIGHT_ANGLE = 0x3E;
+  static const SINGLE_QUOTE = 0x27;
+  static const DOUBLE_QUOTE = 0x22;
+  static const PERCENT = 0x25;
+  static const AT = 0x40;
+  static const GRAVE_ACCENT = 0x60;
+  static const TILDE = 0x7E;
+
+  static const NULL = 0x0;
+  static const BELL = 0x7;
+  static const BACKSPACE = 0x8;
+  static const VERTICAL_TAB = 0xB;
+  static const FORM_FEED = 0xC;
+  static const ESCAPE = 0x1B;
+  static const SLASH = 0x2F;
+  static const BACKSLASH = 0x5C;
+  static const UNDERSCORE = 0x5F;
+  static const NEL = 0x85;
+  static const NBSP = 0xA0;
+  static const LINE_SEPARATOR = 0x2028;
+  static const PARAGRAPH_SEPARATOR = 0x2029;
+  static const BOM = 0xFEFF;
+
+  static const NUMBER_0 = 0x30;
+  static const NUMBER_9 = 0x39;
+
+  static const LETTER_A = 0x61;
+  static const LETTER_B = 0x62;
+  static const LETTER_E = 0x65;
+  static const LETTER_F = 0x66;
+  static const LETTER_N = 0x6E;
+  static const LETTER_R = 0x72;
+  static const LETTER_T = 0x74;
+  static const LETTER_U = 0x75;
+  static const LETTER_V = 0x76;
+  static const LETTER_X = 0x78;
+  static const LETTER_Z = 0x7A;
+
+  static const LETTER_CAP_A = 0x41;
+  static const LETTER_CAP_F = 0x46;
+  static const LETTER_CAP_L = 0x4C;
+  static const LETTER_CAP_N = 0x4E;
+  static const LETTER_CAP_P = 0x50;
+  static const LETTER_CAP_U = 0x55;
+  static const LETTER_CAP_X = 0x58;
+  static const LETTER_CAP_Z = 0x5A;
+
+  /// Whether this scanner should attempt to recover when parsing invalid YAML.
+  final bool _recover;
+
+  /// A listener to report YAML errors to.
+  final ErrorListener? _errorListener;
+
+  /// The underlying [SpanScanner] used to read characters from the source text.
+  ///
+  /// This is also used to track line and column information and to generate
+  /// [SourceSpan]s.
+  final SpanScanner _scanner;
+
+  /// Whether this scanner has produced a [TokenType.streamStart] token
+  /// indicating the beginning of the YAML stream.
+  var _streamStartProduced = false;
+
+  /// Whether this scanner has produced a [TokenType.streamEnd] token
+  /// indicating the end of the YAML stream.
+  var _streamEndProduced = false;
+
+  /// The queue of tokens yet to be emitted.
+  ///
+  /// These are queued up in advance so that [TokenType.key] tokens can be
+  /// inserted once the scanner determines that a series of tokens represents a
+  /// mapping key.
+  final _tokens = QueueList<Token>();
+
+  /// The number of tokens that have been emitted.
+  ///
+  /// This doesn't count tokens in [_tokens].
+  var _tokensParsed = 0;
+
+  /// Whether the next token in [_tokens] is ready to be returned.
+  ///
+  /// It might not be ready if there may still be a [TokenType.key] inserted
+  /// before it.
+  var _tokenAvailable = false;
+
+  /// The stack of indent levels for the current nested block contexts.
+  ///
+  /// The YAML spec specifies that the initial indentation level is -1 spaces.
+  final _indents = <int>[-1];
+
+  /// Whether a simple key is allowed in this context.
+  ///
+  /// A simple key refers to any mapping key that doesn't have an explicit "?".
+  var _simpleKeyAllowed = true;
+
+  /// The stack of potential simple keys for each level of flow nesting.
+  ///
+  /// Entries in this list may be `null`, indicating that there is no valid
+  /// simple key for the associated level of nesting.
+  ///
+  /// When a ":" is parsed and there's a simple key available, a [TokenType.key]
+  /// token is inserted in [_tokens] before that key's token. This allows the
+  /// parser to tell that the key is intended to be a mapping key.
+  final _simpleKeys = <_SimpleKey?>[null];
+
+  /// The current indentation level.
+  int get _indent => _indents.last;
+
+  /// Whether the scanner's currently positioned in a block-level structure (as
+  /// opposed to flow-level).
+  bool get _inBlockContext => _simpleKeys.length == 1;
+
+  /// Whether the current character is a line break or the end of the source.
+  bool get _isBreakOrEnd => _scanner.isDone || _isBreak;
+
+  /// Whether the current character is a line break.
+  bool get _isBreak => _isBreakAt(0);
+
+  /// Whether the current character is whitespace or the end of the source.
+  bool get _isBlankOrEnd => _isBlankOrEndAt(0);
+
+  /// Whether the current character is whitespace.
+  bool get _isBlank => _isBlankAt(0);
+
+  /// Whether the current character is a valid tag name character.
+  ///
+  /// See http://yaml.org/spec/1.2/spec.html#ns-tag-name.
+  bool get _isTagChar {
+    var char = _scanner.peekChar();
+    if (char == null) return false;
+    switch (char) {
+      case HYPHEN:
+      case SEMICOLON:
+      case SLASH:
+      case COLON:
+      case AT:
+      case AMPERSAND:
+      case EQUALS:
+      case PLUS:
+      case DOLLAR:
+      case PERIOD:
+      case TILDE:
+      case QUESTION:
+      case ASTERISK:
+      case SINGLE_QUOTE:
+      case LEFT_PAREN:
+      case RIGHT_PAREN:
+      case PERCENT:
+        return true;
+      default:
+        return (char >= NUMBER_0 && char <= NUMBER_9) ||
+            (char >= LETTER_A && char <= LETTER_Z) ||
+            (char >= LETTER_CAP_A && char <= LETTER_CAP_Z);
+    }
+  }
+
+  /// Whether the current character is a valid anchor name character.
+  ///
+  /// See http://yaml.org/spec/1.2/spec.html#ns-anchor-name.
+  bool get _isAnchorChar {
+    if (!_isNonSpace) return false;
+
+    switch (_scanner.peekChar()) {
+      case COMMA:
+      case LEFT_SQUARE:
+      case RIGHT_SQUARE:
+      case LEFT_CURLY:
+      case RIGHT_CURLY:
+        return false;
+      default:
+        return true;
+    }
+  }
+
+  /// Whether the character at the current position is a decimal digit.
+  bool get _isDigit {
+    var char = _scanner.peekChar();
+    return char != null && (char >= NUMBER_0 && char <= NUMBER_9);
+  }
+
+  /// Whether the character at the current position is a hexidecimal
+  /// digit.
+  bool get _isHex {
+    var char = _scanner.peekChar();
+    if (char == null) return false;
+    return (char >= NUMBER_0 && char <= NUMBER_9) ||
+        (char >= LETTER_A && char <= LETTER_F) ||
+        (char >= LETTER_CAP_A && char <= LETTER_CAP_F);
+  }
+
+  /// Whether the character at the current position is a plain character.
+  ///
+  /// See http://yaml.org/spec/1.2/spec.html#ns-plain-char(c).
+  bool get _isPlainChar => _isPlainCharAt(0);
+
+  /// Whether the character at the current position is a printable character
+  /// other than a line break or byte-order mark.
+  ///
+  /// See http://yaml.org/spec/1.2/spec.html#nb-char.
+  bool get _isNonBreak {
+    var char = _scanner.peekChar();
+    return switch (char) {
+      null => false,
+      LF || CR || BOM => false,
+      TAB || NEL => true,
+      _ => _isStandardCharacterAt(0),
+    };
+  }
+
+  /// Whether the character at the current position is a printable character
+  /// other than whitespace.
+  ///
+  /// See http://yaml.org/spec/1.2/spec.html#nb-char.
+  bool get _isNonSpace {
+    var char = _scanner.peekChar();
+    return switch (char) {
+      null => false,
+      LF || CR || BOM || SP => false,
+      NEL => true,
+      _ => _isStandardCharacterAt(0),
+    };
+  }
+
+  /// Returns Whether or not the current character begins a documentation
+  /// indicator.
+  ///
+  /// If so, this sets the scanner's last match to that indicator.
+  bool get _isDocumentIndicator =>
+      _scanner.column == 0 &&
+      _isBlankOrEndAt(3) &&
+      (_scanner.matches('---') || _scanner.matches('...'));
+
+  /// Creates a scanner that scans [source].
+  Scanner(String source,
+      {Uri? sourceUrl, bool recover = false, ErrorListener? errorListener})
+      : _recover = recover,
+        _errorListener = errorListener,
+        _scanner = SpanScanner.eager(source, sourceUrl: sourceUrl);
+
+  /// Consumes and returns the next token.
+  Token scan() {
+    if (_streamEndProduced) throw StateError('Out of tokens.');
+    if (!_tokenAvailable) _fetchMoreTokens();
+
+    var token = _tokens.removeFirst();
+    _tokenAvailable = false;
+    _tokensParsed++;
+    _streamEndProduced = token.type == TokenType.streamEnd;
+    return token;
+  }
+
+  /// Consumes the next token and returns the one after that.
+  Token? advance() {
+    scan();
+    return peek();
+  }
+
+  /// Returns the next token without consuming it.
+  Token? peek() {
+    if (_streamEndProduced) return null;
+    if (!_tokenAvailable) _fetchMoreTokens();
+    return _tokens.first;
+  }
+
+  /// Ensures that [_tokens] contains at least one token which can be returned.
+  void _fetchMoreTokens() {
+    while (true) {
+      if (_tokens.isNotEmpty) {
+        _staleSimpleKeys();
+
+        // If there are no more tokens to fetch, break.
+        if (_tokens.last.type == TokenType.streamEnd) break;
+
+        // If the current token could be a simple key, we need to scan more
+        // tokens until we determine whether it is or not. Otherwise we might
+        // not emit the `KEY` token before we emit the value of the key.
+        if (!_simpleKeys
+            .any((key) => key != null && key.tokenNumber == _tokensParsed)) {
+          break;
+        }
+      }
+
+      _fetchNextToken();
+    }
+    _tokenAvailable = true;
+  }
+
+  /// The dispatcher for token fetchers.
+  void _fetchNextToken() {
+    if (!_streamStartProduced) {
+      _fetchStreamStart();
+      return;
+    }
+
+    _scanToNextToken();
+    _staleSimpleKeys();
+    _unrollIndent(_scanner.column);
+
+    if (_scanner.isDone) {
+      _fetchStreamEnd();
+      return;
+    }
+
+    if (_scanner.column == 0) {
+      if (_scanner.peekChar() == PERCENT) {
+        _fetchDirective();
+        return;
+      }
+
+      if (_isBlankOrEndAt(3)) {
+        if (_scanner.matches('---')) {
+          _fetchDocumentIndicator(TokenType.documentStart);
+          return;
+        }
+
+        if (_scanner.matches('...')) {
+          _fetchDocumentIndicator(TokenType.documentEnd);
+          return;
+        }
+      }
+    }
+
+    switch (_scanner.peekChar()) {
+      case LEFT_SQUARE:
+        _fetchFlowCollectionStart(TokenType.flowSequenceStart);
+        return;
+      case LEFT_CURLY:
+        _fetchFlowCollectionStart(TokenType.flowMappingStart);
+        return;
+      case RIGHT_SQUARE:
+        _fetchFlowCollectionEnd(TokenType.flowSequenceEnd);
+        return;
+      case RIGHT_CURLY:
+        _fetchFlowCollectionEnd(TokenType.flowMappingEnd);
+        return;
+      case COMMA:
+        _fetchFlowEntry();
+        return;
+      case ASTERISK:
+        _fetchAnchor(anchor: false);
+        return;
+      case AMPERSAND:
+        _fetchAnchor();
+        return;
+      case EXCLAMATION:
+        _fetchTag();
+        return;
+      case SINGLE_QUOTE:
+        _fetchFlowScalar(singleQuote: true);
+        return;
+      case DOUBLE_QUOTE:
+        _fetchFlowScalar();
+        return;
+      case VERTICAL_BAR:
+        if (!_inBlockContext) _invalidScalarCharacter();
+        _fetchBlockScalar(literal: true);
+        return;
+      case RIGHT_ANGLE:
+        if (!_inBlockContext) _invalidScalarCharacter();
+        _fetchBlockScalar();
+        return;
+      case PERCENT:
+      case AT:
+      case GRAVE_ACCENT:
+        _invalidScalarCharacter();
+        return;
+
+      // These characters may sometimes begin plain scalars.
+      case HYPHEN:
+        if (_isPlainCharAt(1)) {
+          _fetchPlainScalar();
+        } else {
+          _fetchBlockEntry();
+        }
+        return;
+      case QUESTION:
+        if (_isPlainCharAt(1)) {
+          _fetchPlainScalar();
+        } else {
+          _fetchKey();
+        }
+        return;
+      case COLON:
+        if (!_inBlockContext && _tokens.isNotEmpty) {
+          // If a colon follows a "JSON-like" value (an explicit map or list, or
+          // a quoted string) it isn't required to have whitespace after it
+          // since it unambiguously describes a map.
+          var token = _tokens.last;
+          if (token.type == TokenType.flowSequenceEnd ||
+              token.type == TokenType.flowMappingEnd ||
+              (token.type == TokenType.scalar &&
+                  (token as ScalarToken).style.isQuoted)) {
+            _fetchValue();
+            return;
+          }
+        }
+
+        if (_isPlainCharAt(1)) {
+          _fetchPlainScalar();
+        } else {
+          _fetchValue();
+        }
+        return;
+      default:
+        if (!_isNonBreak) _invalidScalarCharacter();
+
+        _fetchPlainScalar();
+        return;
+    }
+  }
+
+  /// Throws an error about a disallowed character.
+  void _invalidScalarCharacter() =>
+      _scanner.error('Unexpected character.', length: 1);
+
+  /// Checks the list of potential simple keys and remove the positions that
+  /// cannot contain simple keys anymore.
+  void _staleSimpleKeys() {
+    for (var i = 0; i < _simpleKeys.length; i++) {
+      var key = _simpleKeys[i];
+      if (key == null) continue;
+
+      // libyaml requires that all simple keys be a single line and no longer
+      // than 1024 characters. However, in section 7.4.2 of the spec
+      // (http://yaml.org/spec/1.2/spec.html#id2790832), these restrictions are
+      // only applied when the curly braces are omitted. It's difficult to
+      // retain enough context to know which keys need to have the restriction
+      // placed on them, so for now we go the other direction and allow
+      // everything but multiline simple keys in a block context.
+      if (!_inBlockContext) continue;
+
+      if (key.line == _scanner.line) continue;
+
+      if (key.required) {
+        _reportError(YamlException("Expected ':'.", _scanner.emptySpan));
+        _tokens.insert(key.tokenNumber - _tokensParsed,
+            Token(TokenType.key, key.location.pointSpan() as FileSpan));
+      }
+
+      _simpleKeys[i] = null;
+    }
+  }
+
+  /// Checks if a simple key may start at the current position and saves it if
+  /// so.
+  void _saveSimpleKey() {
+    // A simple key is required at the current position if the scanner is in the
+    // block context and the current column coincides with the indentation
+    // level.
+    var required = _inBlockContext && _indent == _scanner.column;
+
+    // A simple key is required only when it is the first token in the current
+    // line. Therefore it is always allowed. But we add a check anyway.
+    assert(_simpleKeyAllowed || !required);
+
+    if (!_simpleKeyAllowed) return;
+
+    // If the current position may start a simple key, save it.
+    _removeSimpleKey();
+    _simpleKeys[_simpleKeys.length - 1] = _SimpleKey(
+        _tokensParsed + _tokens.length,
+        _scanner.line,
+        _scanner.column,
+        _scanner.location,
+        required: required);
+  }
+
+  /// Removes a potential simple key at the current flow level.
+  void _removeSimpleKey() {
+    var key = _simpleKeys.last;
+    if (key != null && key.required) {
+      throw YamlException("Could not find expected ':' for simple key.",
+          key.location.pointSpan());
+    }
+
+    _simpleKeys[_simpleKeys.length - 1] = null;
+  }
+
+  /// Increases the flow level and resizes the simple key list.
+  void _increaseFlowLevel() {
+    _simpleKeys.add(null);
+  }
+
+  /// Decreases the flow level.
+  void _decreaseFlowLevel() {
+    if (_inBlockContext) return;
+    _simpleKeys.removeLast();
+  }
+
+  /// Pushes the current indentation level to the stack and sets the new level
+  /// if [column] is greater than [_indent].
+  ///
+  /// If it is, appends or inserts the specified token into [_tokens]. If
+  /// [tokenNumber] is provided, the corresponding token will be replaced;
+  /// otherwise, the token will be added at the end.
+  void _rollIndent(int column, TokenType type, SourceLocation location,
+      {int? tokenNumber}) {
+    if (!_inBlockContext) return;
+    if (_indent != -1 && _indent >= column) return;
+
+    // Push the current indentation level to the stack and set the new
+    // indentation level.
+    _indents.add(column);
+
+    // Create a token and insert it into the queue.
+    var token = Token(type, location.pointSpan() as FileSpan);
+    if (tokenNumber == null) {
+      _tokens.add(token);
+    } else {
+      _tokens.insert(tokenNumber - _tokensParsed, token);
+    }
+  }
+
+  /// Pops indentation levels from [_indents] until the current level becomes
+  /// less than or equal to [column].
+  ///
+  /// For each indentation level, appends a [TokenType.blockEnd] token.
+  void _unrollIndent(int column) {
+    if (!_inBlockContext) return;
+
+    while (_indent > column) {
+      _tokens.add(Token(TokenType.blockEnd, _scanner.emptySpan));
+      _indents.removeLast();
+    }
+  }
+
+  /// Pops indentation levels from [_indents] until the current level resets to
+  /// -1.
+  ///
+  /// For each indentation level, appends a [TokenType.blockEnd] token.
+  void _resetIndent() => _unrollIndent(-1);
+
+  /// Produces a [TokenType.streamStart] token.
+  void _fetchStreamStart() {
+    // Much of libyaml's initialization logic here is done in variable
+    // initializers instead.
+    _streamStartProduced = true;
+    _tokens.add(Token(TokenType.streamStart, _scanner.emptySpan));
+  }
+
+  /// Produces a [TokenType.streamEnd] token.
+  void _fetchStreamEnd() {
+    _resetIndent();
+    _removeSimpleKey();
+    _simpleKeyAllowed = false;
+    _tokens.add(Token(TokenType.streamEnd, _scanner.emptySpan));
+  }
+
+  /// Produces a [TokenType.versionDirective] or [TokenType.tagDirective]
+  /// token.
+  void _fetchDirective() {
+    _resetIndent();
+    _removeSimpleKey();
+    _simpleKeyAllowed = false;
+    var directive = _scanDirective();
+    if (directive != null) _tokens.add(directive);
+  }
+
+  /// Produces a [TokenType.documentStart] or [TokenType.documentEnd] token.
+  void _fetchDocumentIndicator(TokenType type) {
+    _resetIndent();
+    _removeSimpleKey();
+    _simpleKeyAllowed = false;
+
+    // Consume the indicator token.
+    var start = _scanner.state;
+    _scanner.readCodePoint();
+    _scanner.readCodePoint();
+    _scanner.readCodePoint();
+
+    _tokens.add(Token(type, _scanner.spanFrom(start)));
+  }
+
+  /// Produces a [TokenType.flowSequenceStart] or
+  /// [TokenType.flowMappingStart] token.
+  void _fetchFlowCollectionStart(TokenType type) {
+    _saveSimpleKey();
+    _increaseFlowLevel();
+    _simpleKeyAllowed = true;
+    _addCharToken(type);
+  }
+
+  /// Produces a [TokenType.flowSequenceEnd] or [TokenType.flowMappingEnd]
+  /// token.
+  void _fetchFlowCollectionEnd(TokenType type) {
+    _removeSimpleKey();
+    _decreaseFlowLevel();
+    _simpleKeyAllowed = false;
+    _addCharToken(type);
+  }
+
+  /// Produces a [TokenType.flowEntry] token.
+  void _fetchFlowEntry() {
+    _removeSimpleKey();
+    _simpleKeyAllowed = true;
+    _addCharToken(TokenType.flowEntry);
+  }
+
+  /// Produces a [TokenType.blockEntry] token.
+  void _fetchBlockEntry() {
+    if (_inBlockContext) {
+      if (!_simpleKeyAllowed) {
+        throw YamlException(
+            'Block sequence entries are not allowed here.', _scanner.emptySpan);
+      }
+
+      _rollIndent(
+          _scanner.column, TokenType.blockSequenceStart, _scanner.location);
+    } else {
+      // It is an error for the '-' indicator to occur in the flow context, but
+      // we let the Parser detect and report it because it's able to point to
+      // the context.
+    }
+
+    _removeSimpleKey();
+    _simpleKeyAllowed = true;
+    _addCharToken(TokenType.blockEntry);
+  }
+
+  /// Produces the [TokenType.key] token.
+  void _fetchKey() {
+    if (_inBlockContext) {
+      if (!_simpleKeyAllowed) {
+        throw YamlException(
+            'Mapping keys are not allowed here.', _scanner.emptySpan);
+      }
+
+      _rollIndent(
+          _scanner.column, TokenType.blockMappingStart, _scanner.location);
+    }
+
+    // Simple keys are allowed after `?` in a block context.
+    _simpleKeyAllowed = _inBlockContext;
+    _addCharToken(TokenType.key);
+  }
+
+  /// Produces the [TokenType.value] token.
+  void _fetchValue() {
+    var simpleKey = _simpleKeys.last;
+    if (simpleKey != null) {
+      // Add a [TokenType.KEY] directive before the first token of the simple
+      // key so the parser knows that it's part of a key/value pair.
+      _tokens.insert(simpleKey.tokenNumber - _tokensParsed,
+          Token(TokenType.key, simpleKey.location.pointSpan() as FileSpan));
+
+      // In the block context, we may need to add the
+      // [TokenType.BLOCK_MAPPING_START] token.
+      _rollIndent(
+          simpleKey.column, TokenType.blockMappingStart, simpleKey.location,
+          tokenNumber: simpleKey.tokenNumber);
+
+      // Remove the simple key.
+      _simpleKeys[_simpleKeys.length - 1] = null;
+
+      // A simple key cannot follow another simple key.
+      _simpleKeyAllowed = false;
+    } else if (_inBlockContext) {
+      if (!_simpleKeyAllowed) {
+        throw YamlException(
+            'Mapping values are not allowed here. Did you miss a colon '
+            'earlier?',
+            _scanner.emptySpan);
+      }
+
+      // If we're here, we've found the ':' indicator following a complex key.
+
+      _rollIndent(
+          _scanner.column, TokenType.blockMappingStart, _scanner.location);
+      _simpleKeyAllowed = true;
+    } else if (_simpleKeyAllowed) {
+      // If we're here, we've found the ':' indicator with an empty key. This
+      // behavior differs from libyaml, which disallows empty implicit keys.
+      _simpleKeyAllowed = false;
+      _addCharToken(TokenType.key);
+    }
+
+    _addCharToken(TokenType.value);
+  }
+
+  /// Adds a token with [type] to [_tokens].
+  ///
+  /// The span of the new token is the current character.
+  void _addCharToken(TokenType type) {
+    var start = _scanner.state;
+    _scanner.readCodePoint();
+    _tokens.add(Token(type, _scanner.spanFrom(start)));
+  }
+
+  /// Produces a [TokenType.alias] or [TokenType.anchor] token.
+  void _fetchAnchor({bool anchor = true}) {
+    _saveSimpleKey();
+    _simpleKeyAllowed = false;
+    _tokens.add(_scanAnchor(anchor: anchor));
+  }
+
+  /// Produces a [TokenType.tag] token.
+  void _fetchTag() {
+    _saveSimpleKey();
+    _simpleKeyAllowed = false;
+    _tokens.add(_scanTag());
+  }
+
+  /// Produces a [TokenType.scalar] token with style [ScalarStyle.LITERAL] or
+  /// [ScalarStyle.FOLDED].
+  void _fetchBlockScalar({bool literal = false}) {
+    _removeSimpleKey();
+    _simpleKeyAllowed = true;
+    _tokens.add(_scanBlockScalar(literal: literal));
+  }
+
+  /// Produces a [TokenType.scalar] token with style [ScalarStyle.SINGLE_QUOTED]
+  /// or [ScalarStyle.DOUBLE_QUOTED].
+  void _fetchFlowScalar({bool singleQuote = false}) {
+    _saveSimpleKey();
+    _simpleKeyAllowed = false;
+    _tokens.add(_scanFlowScalar(singleQuote: singleQuote));
+  }
+
+  /// Produces a [TokenType.scalar] token with style [ScalarStyle.PLAIN].
+  void _fetchPlainScalar() {
+    _saveSimpleKey();
+    _simpleKeyAllowed = false;
+    _tokens.add(_scanPlainScalar());
+  }
+
+  /// Eats whitespace and comments until the next token is found.
+  void _scanToNextToken() {
+    var afterLineBreak = false;
+    while (true) {
+      // Allow the BOM to start a line.
+      if (_scanner.column == 0) _scanner.scan('\uFEFF');
+
+      // Eat whitespace.
+      //
+      // libyaml disallows tabs after "-", "?", or ":", but the spec allows
+      // them. See section 6.2: http://yaml.org/spec/1.2/spec.html#id2778241.
+      while (_scanner.peekChar() == SP ||
+          ((!_inBlockContext || !afterLineBreak) &&
+              _scanner.peekChar() == TAB)) {
+        _scanner.readChar();
+      }
+
+      if (_scanner.peekChar() == TAB) {
+        _scanner.error('Tab characters are not allowed as indentation.',
+            length: 1);
+      }
+
+      // Eat a comment until a line break.
+      _skipComment();
+
+      // If we're at a line break, eat it.
+      if (_isBreak) {
+        _skipLine();
+
+        // In the block context, a new line may start a simple key.
+        if (_inBlockContext) _simpleKeyAllowed = true;
+        afterLineBreak = true;
+      } else {
+        // Otherwise we've found a token.
+        break;
+      }
+    }
+  }
+
+  /// Scans a [TokenType.versionDirective] or [TokenType.tagDirective] token.
+  ///
+  ///     %YAML    1.2    # a comment \n
+  ///     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+  ///     %TAG    !yaml!  tag:yaml.org,2002:  \n
+  ///     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+  Token? _scanDirective() {
+    var start = _scanner.state;
+
+    // Eat '%'.
+    _scanner.readChar();
+
+    Token token;
+    var name = _scanDirectiveName();
+    if (name == 'YAML') {
+      token = _scanVersionDirectiveValue(start);
+    } else if (name == 'TAG') {
+      token = _scanTagDirectiveValue(start);
+    } else {
+      warn('Warning: unknown directive.', _scanner.spanFrom(start));
+
+      // libyaml doesn't support unknown directives, but the spec says to ignore
+      // them and warn: http://yaml.org/spec/1.2/spec.html#id2781147.
+      while (!_isBreakOrEnd) {
+        _scanner.readCodePoint();
+      }
+
+      return null;
+    }
+
+    // Eat the rest of the line, including any comments.
+    _skipBlanks();
+    _skipComment();
+
+    if (!_isBreakOrEnd) {
+      throw YamlException('Expected comment or line break after directive.',
+          _scanner.spanFrom(start));
+    }
+
+    _skipLine();
+    return token;
+  }
+
+  /// Scans a directive name.
+  ///
+  ///      %YAML   1.2     # a comment \n
+  ///       ^^^^
+  ///      %TAG    !yaml!  tag:yaml.org,2002:  \n
+  ///       ^^^
+  String _scanDirectiveName() {
+    // libyaml only allows word characters in directive names, but the spec
+    // disagrees: http://yaml.org/spec/1.2/spec.html#ns-directive-name.
+    var start = _scanner.position;
+    while (_isNonSpace) {
+      _scanner.readCodePoint();
+    }
+
+    var name = _scanner.substring(start);
+    if (name.isEmpty) {
+      throw YamlException('Expected directive name.', _scanner.emptySpan);
+    } else if (!_isBlankOrEnd) {
+      throw YamlException(
+          'Unexpected character in directive name.', _scanner.emptySpan);
+    }
+
+    return name;
+  }
+
+  /// Scans the value of a version directive.
+  ///
+  ///      %YAML   1.2     # a comment \n
+  ///           ^^^^^^
+  Token _scanVersionDirectiveValue(LineScannerState start) {
+    _skipBlanks();
+
+    var major = _scanVersionDirectiveNumber();
+    _scanner.expect('.');
+    var minor = _scanVersionDirectiveNumber();
+
+    return VersionDirectiveToken(_scanner.spanFrom(start), major, minor);
+  }
+
+  /// Scans the version number of a version directive.
+  ///
+  ///      %YAML   1.2     # a comment \n
+  ///              ^
+  ///      %YAML   1.2     # a comment \n
+  ///                ^
+  int _scanVersionDirectiveNumber() {
+    var start = _scanner.position;
+    while (_isDigit) {
+      _scanner.readChar();
+    }
+
+    var number = _scanner.substring(start);
+    if (number.isEmpty) {
+      throw YamlException('Expected version number.', _scanner.emptySpan);
+    }
+
+    return int.parse(number);
+  }
+
+  /// Scans the value of a tag directive.
+  ///
+  ///      %TAG    !yaml!  tag:yaml.org,2002:  \n
+  ///          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+  Token _scanTagDirectiveValue(LineScannerState start) {
+    _skipBlanks();
+
+    var handle = _scanTagHandle(directive: true);
+    if (!_isBlank) {
+      throw YamlException('Expected whitespace.', _scanner.emptySpan);
+    }
+
+    _skipBlanks();
+
+    var prefix = _scanTagUri();
+    if (!_isBlankOrEnd) {
+      throw YamlException('Expected whitespace.', _scanner.emptySpan);
+    }
+
+    return TagDirectiveToken(_scanner.spanFrom(start), handle, prefix);
+  }
+
+  /// Scans a [TokenType.anchor] token.
+  Token _scanAnchor({bool anchor = true}) {
+    var start = _scanner.state;
+
+    // Eat the indicator character.
+    _scanner.readCodePoint();
+
+    // libyaml only allows word characters in anchor names, but the spec
+    // disagrees: http://yaml.org/spec/1.2/spec.html#ns-anchor-char.
+    var startPosition = _scanner.position;
+    while (_isAnchorChar) {
+      _scanner.readCodePoint();
+    }
+    var name = _scanner.substring(startPosition);
+
+    var next = _scanner.peekChar();
+    if (name.isEmpty ||
+        (!_isBlankOrEnd &&
+            next != QUESTION &&
+            next != COLON &&
+            next != COMMA &&
+            next != RIGHT_SQUARE &&
+            next != RIGHT_CURLY &&
+            next != PERCENT &&
+            next != AT &&
+            next != GRAVE_ACCENT)) {
+      throw YamlException(
+          'Expected alphanumeric character.', _scanner.emptySpan);
+    }
+
+    if (anchor) {
+      return AnchorToken(_scanner.spanFrom(start), name);
+    } else {
+      return AliasToken(_scanner.spanFrom(start), name);
+    }
+  }
+
+  /// Scans a [TokenType.tag] token.
+  Token _scanTag() {
+    String? handle;
+    String suffix;
+    var start = _scanner.state;
+
+    // Check if the tag is in the canonical form.
+    if (_scanner.peekChar(1) == LEFT_ANGLE) {
+      // Eat '!<'.
+      _scanner.readChar();
+      _scanner.readChar();
+
+      handle = '';
+      suffix = _scanTagUri();
+
+      _scanner.expect('>');
+    } else {
+      // The tag has either the '!suffix' or the '!handle!suffix' form.
+
+      // First, try to scan a handle.
+      handle = _scanTagHandle();
+
+      if (handle.length > 1 && handle.startsWith('!') && handle.endsWith('!')) {
+        suffix = _scanTagUri(flowSeparators: false);
+      } else {
+        suffix = _scanTagUri(head: handle, flowSeparators: false);
+
+        // There was no explicit handle.
+        if (suffix.isEmpty) {
+          // This is the special '!' tag.
+          handle = null;
+          suffix = '!';
+        } else {
+          handle = '!';
+        }
+      }
+    }
+
+    // libyaml insists on whitespace after a tag, but example 7.2 indicates
+    // that it's not required: http://yaml.org/spec/1.2/spec.html#id2786720.
+
+    return TagToken(_scanner.spanFrom(start), handle, suffix);
+  }
+
+  /// Scans a tag handle.
+  String _scanTagHandle({bool directive = false}) {
+    _scanner.expect('!');
+
+    var buffer = StringBuffer('!');
+
+    // libyaml only allows word characters in tags, but the spec disagrees:
+    // http://yaml.org/spec/1.2/spec.html#ns-tag-char.
+    var start = _scanner.position;
+    while (_isTagChar) {
+      _scanner.readChar();
+    }
+    buffer.write(_scanner.substring(start));
+
+    if (_scanner.peekChar() == EXCLAMATION) {
+      buffer.writeCharCode(_scanner.readCodePoint());
+    } else {
+      // It's either the '!' tag or not really a tag handle. If it's a %TAG
+      // directive, it's an error. If it's a tag token, it must be part of a
+      // URI.
+      if (directive && buffer.toString() != '!') _scanner.expect('!');
+    }
+
+    return buffer.toString();
+  }
+
+  /// Scans a tag URI.
+  ///
+  /// [head] is the initial portion of the tag that's already been scanned.
+  /// [flowSeparators] indicates whether the tag URI can contain flow
+  /// separators.
+  String _scanTagUri({String? head, bool flowSeparators = true}) {
+    var length = head == null ? 0 : head.length;
+    var buffer = StringBuffer();
+
+    // Copy the head if needed.
+    //
+    // Note that we don't copy the leading '!' character.
+    if (length > 1) buffer.write(head!.substring(1));
+
+    // The set of characters that may appear in URI is as follows:
+    //
+    //      '0'-'9', 'A'-'Z', 'a'-'z', '_', '-', ';', '/', '?', ':', '@', '&',
+    //      '=', '+', '$', ',', '.', '!', '~', '*', '\'', '(', ')', '[', ']',
+    //      '%'.
+    //
+    // In a shorthand tag annotation, the flow separators ',', '[', and ']' are
+    // disallowed.
+    var start = _scanner.position;
+    var char = _scanner.peekChar();
+    while (_isTagChar ||
+        (flowSeparators &&
+            (char == COMMA || char == LEFT_SQUARE || char == RIGHT_SQUARE))) {
+      _scanner.readChar();
+      char = _scanner.peekChar();
+    }
+
+    // libyaml manually decodes the URL, but we don't have to do that.
+    return Uri.decodeFull(_scanner.substring(start));
+  }
+
+  /// Scans a block scalar.
+  Token _scanBlockScalar({bool literal = false}) {
+    var start = _scanner.state;
+
+    // Eat the indicator '|' or '>'.
+    _scanner.readCodePoint();
+
+    // Check for a chomping indicator.
+    var chomping = _Chomping.clip;
+    var increment = 0;
+    var char = _scanner.peekChar();
+    if (char == PLUS || char == HYPHEN) {
+      chomping = char == PLUS ? _Chomping.keep : _Chomping.strip;
+      _scanner.readCodePoint();
+
+      // Check for an indentation indicator.
+      if (_isDigit) {
+        // Check that the indentation is greater than 0.
+        if (_scanner.peekChar() == NUMBER_0) {
+          throw YamlException('0 may not be used as an indentation indicator.',
+              _scanner.spanFrom(start));
+        }
+
+        increment = _scanner.readCodePoint() - NUMBER_0;
+      }
+    } else if (_isDigit) {
+      // Do the same as above, but in the opposite order.
+      if (_scanner.peekChar() == NUMBER_0) {
+        throw YamlException('0 may not be used as an indentation indicator.',
+            _scanner.spanFrom(start));
+      }
+
+      increment = _scanner.readCodePoint() - NUMBER_0;
+
+      char = _scanner.peekChar();
+      if (char == PLUS || char == HYPHEN) {
+        chomping = char == PLUS ? _Chomping.keep : _Chomping.strip;
+        _scanner.readCodePoint();
+      }
+    }
+
+    // Eat whitespace and comments to the end of the line.
+    _skipBlanks();
+    _skipComment();
+
+    // Check if we're at the end of the line.
+    if (!_isBreakOrEnd) {
+      throw YamlException(
+          'Expected comment or line break.', _scanner.emptySpan);
+    }
+
+    _skipLine();
+
+    // If the block scalar has an explicit indentation indicator, add that to
+    // the current indentation to get the indentation level for the scalar's
+    // contents.
+    var indent = 0;
+    if (increment != 0) {
+      indent = _indent >= 0 ? _indent + increment : increment;
+    }
+
+    // Scan the leading line breaks to determine the indentation level if
+    // needed.
+    var pair = _scanBlockScalarBreaks(indent);
+    indent = pair.indent;
+    var trailingBreaks = pair.trailingBreaks;
+
+    // Scan the block scalar contents.
+    var buffer = StringBuffer();
+    var leadingBreak = '';
+    var leadingBlank = false;
+    var trailingBlank = false;
+    var end = _scanner.state;
+    while (_scanner.column == indent && !_scanner.isDone) {
+      // Check for a document indicator. libyaml doesn't do this, but the spec
+      // mandates it. See example 9.5:
+      // http://yaml.org/spec/1.2/spec.html#id2801606.
+      if (_isDocumentIndicator) break;
+
+      // We are at the beginning of a non-empty line.
+
+      // Is there trailing whitespace?
+      trailingBlank = _isBlank;
+
+      // Check if we need to fold the leading line break.
+      if (!literal &&
+          leadingBreak.isNotEmpty &&
+          !leadingBlank &&
+          !trailingBlank) {
+        // Do we need to join the lines with a space?
+        if (trailingBreaks.isEmpty) buffer.writeCharCode(SP);
+      } else {
+        buffer.write(leadingBreak);
+      }
+      leadingBreak = '';
+
+      // Append the remaining line breaks.
+      buffer.write(trailingBreaks);
+
+      // Is there leading whitespace?
+      leadingBlank = _isBlank;
+
+      var startPosition = _scanner.position;
+      while (!_isBreakOrEnd) {
+        _scanner.readCodePoint();
+      }
+      buffer.write(_scanner.substring(startPosition));
+      end = _scanner.state;
+
+      // libyaml always reads a line here, but this breaks on block scalars at
+      // the end of the document that end without newlines. See example 8.1:
+      // http://yaml.org/spec/1.2/spec.html#id2793888.
+      if (!_scanner.isDone) leadingBreak = _readLine();
+
+      // Eat the following indentation and spaces.
+      var pair = _scanBlockScalarBreaks(indent);
+      indent = pair.indent;
+      trailingBreaks = pair.trailingBreaks;
+    }
+
+    // Chomp the tail.
+    if (chomping != _Chomping.strip) buffer.write(leadingBreak);
+    if (chomping == _Chomping.keep) buffer.write(trailingBreaks);
+
+    return ScalarToken(_scanner.spanFrom(start, end), buffer.toString(),
+        literal ? ScalarStyle.LITERAL : ScalarStyle.FOLDED);
+  }
+
+  /// Scans indentation spaces and line breaks for a block scalar.
+  ///
+  /// Determines the intendation level if needed. Returns the new indentation
+  /// level and the text of the line breaks.
+  ({int indent, String trailingBreaks}) _scanBlockScalarBreaks(int indent) {
+    var maxIndent = 0;
+    var breaks = StringBuffer();
+
+    while (true) {
+      while ((indent == 0 || _scanner.column < indent) &&
+          _scanner.peekChar() == SP) {
+        _scanner.readChar();
+      }
+
+      if (_scanner.column > maxIndent) maxIndent = _scanner.column;
+
+      // libyaml throws an error here if a tab character is detected, but the
+      // spec treats tabs like any other non-space character. See example 8.2:
+      // http://yaml.org/spec/1.2/spec.html#id2794311.
+
+      if (!_isBreak) break;
+      breaks.write(_readLine());
+    }
+
+    if (indent == 0) {
+      indent = maxIndent;
+      if (indent < _indent + 1) indent = _indent + 1;
+
+      // libyaml forces indent to be at least 1 here, but that doesn't seem to
+      // be supported by the spec.
+    }
+
+    return (indent: indent, trailingBreaks: breaks.toString());
+  }
+
+  // Scans a quoted scalar.
+  Token _scanFlowScalar({bool singleQuote = false}) {
+    var start = _scanner.state;
+    var buffer = StringBuffer();
+
+    // Eat the left quote.
+    _scanner.readChar();
+
+    while (true) {
+      // Check that there are no document indicators at the beginning of the
+      // line.
+      if (_isDocumentIndicator) {
+        _scanner.error('Unexpected document indicator.');
+      }
+
+      if (_scanner.isDone) {
+        throw YamlException('Unexpected end of file.', _scanner.emptySpan);
+      }
+
+      var leadingBlanks = false;
+      while (!_isBlankOrEnd) {
+        var char = _scanner.peekChar();
+        if (singleQuote &&
+            char == SINGLE_QUOTE &&
+            _scanner.peekChar(1) == SINGLE_QUOTE) {
+          // An escaped single quote.
+          _scanner.readChar();
+          _scanner.readChar();
+          buffer.writeCharCode(SINGLE_QUOTE);
+        } else if (char == (singleQuote ? SINGLE_QUOTE : DOUBLE_QUOTE)) {
+          // The closing quote.
+          break;
+        } else if (!singleQuote && char == BACKSLASH && _isBreakAt(1)) {
+          // An escaped newline.
+          _scanner.readChar();
+          _skipLine();
+          leadingBlanks = true;
+          break;
+        } else if (!singleQuote && char == BACKSLASH) {
+          var escapeStart = _scanner.state;
+
+          // An escape sequence.
+          int? codeLength;
+          switch (_scanner.peekChar(1)) {
+            case NUMBER_0:
+              buffer.writeCharCode(NULL);
+              break;
+            case LETTER_A:
+              buffer.writeCharCode(BELL);
+              break;
+            case LETTER_B:
+              buffer.writeCharCode(BACKSPACE);
+              break;
+            case LETTER_T:
+            case TAB:
+              buffer.writeCharCode(TAB);
+              break;
+            case LETTER_N:
+              buffer.writeCharCode(LF);
+              break;
+            case LETTER_V:
+              buffer.writeCharCode(VERTICAL_TAB);
+              break;
+            case LETTER_F:
+              buffer.writeCharCode(FORM_FEED);
+              break;
+            case LETTER_R:
+              buffer.writeCharCode(CR);
+              break;
+            case LETTER_E:
+              buffer.writeCharCode(ESCAPE);
+              break;
+            case SP:
+            case DOUBLE_QUOTE:
+            case SLASH:
+            case BACKSLASH:
+              // libyaml doesn't support an escaped forward slash, but it was
+              // added in YAML 1.2. See section 5.7:
+              // http://yaml.org/spec/1.2/spec.html#id2776092
+              buffer.writeCharCode(_scanner.peekChar(1)!);
+              break;
+            case LETTER_CAP_N:
+              buffer.writeCharCode(NEL);
+              break;
+            case UNDERSCORE:
+              buffer.writeCharCode(NBSP);
+              break;
+            case LETTER_CAP_L:
+              buffer.writeCharCode(LINE_SEPARATOR);
+              break;
+            case LETTER_CAP_P:
+              buffer.writeCharCode(PARAGRAPH_SEPARATOR);
+              break;
+            case LETTER_X:
+              codeLength = 2;
+              break;
+            case LETTER_U:
+              codeLength = 4;
+              break;
+            case LETTER_CAP_U:
+              codeLength = 8;
+              break;
+            default:
+              throw YamlException(
+                  'Unknown escape character.', _scanner.spanFrom(escapeStart));
+          }
+
+          _scanner.readChar();
+          _scanner.readChar();
+
+          if (codeLength != null) {
+            var value = 0;
+            for (var i = 0; i < codeLength; i++) {
+              if (!_isHex) {
+                _scanner.readChar();
+                throw YamlException(
+                    'Expected $codeLength-digit hexidecimal number.',
+                    _scanner.spanFrom(escapeStart));
+              }
+
+              value = (value << 4) + _asHex(_scanner.readChar());
+            }
+
+            // Check the value and write the character.
+            if ((value >= 0xD800 && value <= 0xDFFF) || value > 0x10FFFF) {
+              throw YamlException('Invalid Unicode character escape code.',
+                  _scanner.spanFrom(escapeStart));
+            }
+
+            buffer.writeCharCode(value);
+          }
+        } else {
+          buffer.writeCharCode(_scanner.readCodePoint());
+        }
+      }
+
+      // Check if we're at the end of a scalar.
+      if (_scanner.peekChar() == (singleQuote ? SINGLE_QUOTE : DOUBLE_QUOTE)) {
+        break;
+      }
+
+      var whitespace = StringBuffer();
+      var leadingBreak = '';
+      var trailingBreaks = StringBuffer();
+      while (_isBlank || _isBreak) {
+        if (_isBlank) {
+          // Consume a space or a tab.
+          if (!leadingBlanks) {
+            whitespace.writeCharCode(_scanner.readChar());
+          } else {
+            _scanner.readChar();
+          }
+        } else {
+          // Check if it's a first line break.
+          if (!leadingBlanks) {
+            whitespace.clear();
+            leadingBreak = _readLine();
+            leadingBlanks = true;
+          } else {
+            trailingBreaks.write(_readLine());
+          }
+        }
+      }
+
+      // Join the whitespace or fold line breaks.
+      if (leadingBlanks) {
+        if (leadingBreak.isNotEmpty && trailingBreaks.isEmpty) {
+          buffer.writeCharCode(SP);
+        } else {
+          buffer.write(trailingBreaks);
+        }
+      } else {
+        buffer.write(whitespace);
+        whitespace.clear();
+      }
+    }
+
+    // Eat the right quote.
+    _scanner.readChar();
+
+    return ScalarToken(_scanner.spanFrom(start), buffer.toString(),
+        singleQuote ? ScalarStyle.SINGLE_QUOTED : ScalarStyle.DOUBLE_QUOTED);
+  }
+
+  /// Scans a plain scalar.
+  Token _scanPlainScalar() {
+    var start = _scanner.state;
+    var end = _scanner.state;
+    var buffer = StringBuffer();
+    var leadingBreak = '';
+    var trailingBreaks = '';
+    var whitespace = StringBuffer();
+    var indent = _indent + 1;
+
+    while (true) {
+      // Check for a document indicator.
+      if (_isDocumentIndicator) break;
+
+      // Check for a comment.
+      if (_scanner.peekChar() == HASH) break;
+
+      if (_isPlainChar) {
+        // Join the whitespace or fold line breaks.
+        if (leadingBreak.isNotEmpty) {
+          if (trailingBreaks.isEmpty) {
+            buffer.writeCharCode(SP);
+          } else {
+            buffer.write(trailingBreaks);
+          }
+          leadingBreak = '';
+          trailingBreaks = '';
+        } else {
+          buffer.write(whitespace);
+          whitespace.clear();
+        }
+      }
+
+      // libyaml's notion of valid identifiers differs substantially from YAML
+      // 1.2's. We use [_isPlainChar] instead of libyaml's character here.
+      var startPosition = _scanner.position;
+      while (_isPlainChar) {
+        _scanner.readCodePoint();
+      }
+      buffer.write(_scanner.substring(startPosition));
+      end = _scanner.state;
+
+      // Is it the end?
+      if (!_isBlank && !_isBreak) break;
+
+      while (_isBlank || _isBreak) {
+        if (_isBlank) {
+          // Check for a tab character messing up the intendation.
+          if (leadingBreak.isNotEmpty &&
+              _scanner.column < indent &&
+              _scanner.peekChar() == TAB) {
+            _scanner.error('Expected a space but found a tab.', length: 1);
+          }
+
+          if (leadingBreak.isEmpty) {
+            whitespace.writeCharCode(_scanner.readChar());
+          } else {
+            _scanner.readChar();
+          }
+        } else {
+          // Check if it's a first line break.
+          if (leadingBreak.isEmpty) {
+            leadingBreak = _readLine();
+            whitespace.clear();
+          } else {
+            trailingBreaks = _readLine();
+          }
+        }
+      }
+
+      // Check the indentation level.
+      if (_inBlockContext && _scanner.column < indent) break;
+    }
+
+    // Allow a simple key after a plain scalar with leading blanks.
+    if (leadingBreak.isNotEmpty) _simpleKeyAllowed = true;
+
+    return ScalarToken(
+        _scanner.spanFrom(start, end), buffer.toString(), ScalarStyle.PLAIN);
+  }
+
+  /// Moves past the current line break, if there is one.
+  void _skipLine() {
+    var char = _scanner.peekChar();
+    if (char != CR && char != LF) return;
+    _scanner.readChar();
+    if (char == CR && _scanner.peekChar() == LF) _scanner.readChar();
+  }
+
+  // Moves past the current line break and returns a newline.
+  String _readLine() {
+    var char = _scanner.peekChar();
+
+    // libyaml supports NEL, PS, and LS characters as line separators, but this
+    // is explicitly forbidden in section 5.4 of the YAML spec.
+    if (char != CR && char != LF) {
+      throw YamlException('Expected newline.', _scanner.emptySpan);
+    }
+
+    _scanner.readChar();
+    // CR LF | CR | LF -> LF
+    if (char == CR && _scanner.peekChar() == LF) _scanner.readChar();
+    return '\n';
+  }
+
+  // Returns whether the character at [offset] is whitespace.
+  bool _isBlankAt(int offset) {
+    var char = _scanner.peekChar(offset);
+    return char == SP || char == TAB;
+  }
+
+  // Returns whether the character at [offset] is a line break.
+  bool _isBreakAt(int offset) {
+    // Libyaml considers NEL, LS, and PS to be line breaks as well, but that's
+    // contrary to the spec.
+    var char = _scanner.peekChar(offset);
+    return char == CR || char == LF;
+  }
+
+  // Returns whether the character at [offset] is whitespace or past the end of
+  // the source.
+  bool _isBlankOrEndAt(int offset) {
+    var char = _scanner.peekChar(offset);
+    return char == null ||
+        char == SP ||
+        char == TAB ||
+        char == CR ||
+        char == LF;
+  }
+
+  /// Returns whether the character at [offset] is a plain character.
+  ///
+  /// See http://yaml.org/spec/1.2/spec.html#ns-plain-char(c).
+  bool _isPlainCharAt(int offset) {
+    switch (_scanner.peekChar(offset)) {
+      case COLON:
+        return _isPlainSafeAt(offset + 1);
+      case HASH:
+        var previous = _scanner.peekChar(offset - 1);
+        return previous != SP && previous != TAB;
+      default:
+        return _isPlainSafeAt(offset);
+    }
+  }
+
+  /// Returns whether the character at [offset] is a plain-safe character.
+  ///
+  /// See http://yaml.org/spec/1.2/spec.html#ns-plain-safe(c).
+  bool _isPlainSafeAt(int offset) {
+    var char = _scanner.peekChar(offset);
+    return switch (char) {
+      null => false,
+      COMMA ||
+      LEFT_SQUARE ||
+      RIGHT_SQUARE ||
+      LEFT_CURLY ||
+      RIGHT_CURLY =>
+        // These characters are delimiters in a flow context and thus are only
+        // safe in a block context.
+        _inBlockContext,
+      SP || TAB || LF || CR || BOM => false,
+      NEL => true,
+      _ => _isStandardCharacterAt(offset)
+    };
+  }
+
+  bool _isStandardCharacterAt(int offset) {
+    var first = _scanner.peekChar(offset);
+    if (first == null) return false;
+
+    if (isHighSurrogate(first)) {
+      var next = _scanner.peekChar(offset + 1);
+      // A surrogate pair encodes code points from U+010000 to U+10FFFF, so it
+      // must be a standard character.
+      return next != null && isLowSurrogate(next);
+    }
+
+    return _isStandardCharacter(first);
+  }
+
+  bool _isStandardCharacter(int char) =>
+      (char >= 0x0020 && char <= 0x007E) ||
+      (char >= 0x00A0 && char <= 0xD7FF) ||
+      (char >= 0xE000 && char <= 0xFFFD);
+
+  /// Returns the hexidecimal value of [char].
+  int _asHex(int char) {
+    if (char <= NUMBER_9) return char - NUMBER_0;
+    if (char <= LETTER_CAP_F) return 10 + char - LETTER_CAP_A;
+    return 10 + char - LETTER_A;
+  }
+
+  /// Moves the scanner past any blank characters.
+  void _skipBlanks() {
+    while (_isBlank) {
+      _scanner.readChar();
+    }
+  }
+
+  /// Moves the scanner past a comment, if one starts at the current position.
+  void _skipComment() {
+    if (_scanner.peekChar() != HASH) return;
+    while (!_isBreakOrEnd) {
+      _scanner.readChar();
+    }
+  }
+
+  /// Reports a [YamlException] to [_errorListener] if [_recover] is true,
+  /// otherwise throws the exception.
+  void _reportError(YamlException exception) {
+    if (!_recover) {
+      throw exception;
+    }
+    _errorListener?.onError(exception);
+  }
+}
+
+/// A record of the location of a potential simple key.
+class _SimpleKey {
+  /// The index of the token that begins the simple key.
+  ///
+  /// This is the index relative to all tokens emitted, rather than relative to
+  /// [location].
+  final int tokenNumber;
+
+  /// The source location of the beginning of the simple key.
+  ///
+  /// This is used for error reporting and for determining when a simple key is
+  /// no longer on the current line.
+  final SourceLocation location;
+
+  /// The line on which the key appears.
+  ///
+  /// We could get this from [location], but that requires a binary search
+  /// whereas this is O(1).
+  final int line;
+
+  /// The column on which the key appears.
+  ///
+  /// We could get this from [location], but that requires a binary search
+  /// whereas this is O(1).
+  final int column;
+
+  /// Whether this key must exist for the document to be scanned.
+  final bool required;
+
+  _SimpleKey(
+    this.tokenNumber,
+    this.line,
+    this.column,
+    this.location, {
+    required this.required,
+  });
+}
+
+/// The ways to handle trailing whitespace for a block scalar.
+///
+/// See http://yaml.org/spec/1.2/spec.html#id2794534.
+enum _Chomping {
+  /// All trailing whitespace is discarded.
+  strip,
+
+  /// A single trailing newline is retained.
+  clip,
+
+  /// All trailing whitespace is preserved.
+  keep
+}

diff --git a/pkgs/yaml/lib/src/style.dart b/pkgs/yaml/lib/src/style.dart
new file mode 100644
index 0000000..96c3b94
--- /dev/null
+++ b/pkgs/yaml/lib/src/style.dart

@@ -0,0 +1,79 @@
+// Copyright (c) 2014, the Dart project authors.
+// Copyright (c) 2006, Kirill Simonov.
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+// ignore_for_file: constant_identifier_names
+
+import 'yaml_node.dart';
+
+/// An enum of source scalar styles.
+class ScalarStyle {
+  /// No source style was specified.
+  ///
+  /// This usually indicates a scalar constructed with [YamlScalar.wrap].
+  static const ANY = ScalarStyle._('ANY');
+
+  /// The plain scalar style, unquoted and without a prefix.
+  ///
+  /// See http://yaml.org/spec/1.2/spec.html#style/flow/plain.
+  static const PLAIN = ScalarStyle._('PLAIN');
+
+  /// The literal scalar style, with a `|` prefix.
+  ///
+  /// See http://yaml.org/spec/1.2/spec.html#id2795688.
+  static const LITERAL = ScalarStyle._('LITERAL');
+
+  /// The folded scalar style, with a `>` prefix.
+  ///
+  /// See http://yaml.org/spec/1.2/spec.html#id2796251.
+  static const FOLDED = ScalarStyle._('FOLDED');
+
+  /// The single-quoted scalar style.
+  ///
+  /// See http://yaml.org/spec/1.2/spec.html#style/flow/single-quoted.
+  static const SINGLE_QUOTED = ScalarStyle._('SINGLE_QUOTED');
+
+  /// The double-quoted scalar style.
+  ///
+  /// See http://yaml.org/spec/1.2/spec.html#style/flow/double-quoted.
+  static const DOUBLE_QUOTED = ScalarStyle._('DOUBLE_QUOTED');
+
+  final String name;
+
+  /// Whether this is a quoted style ([SINGLE_QUOTED] or [DOUBLE_QUOTED]).
+  bool get isQuoted => this == SINGLE_QUOTED || this == DOUBLE_QUOTED;
+
+  const ScalarStyle._(this.name);
+
+  @override
+  String toString() => name;
+}
+
+/// An enum of collection styles.
+class CollectionStyle {
+  /// No source style was specified.
+  ///
+  /// This usually indicates a collection constructed with [YamlList.wrap] or
+  /// [YamlMap.wrap].
+  static const ANY = CollectionStyle._('ANY');
+
+  /// The indentation-based block style.
+  ///
+  /// See http://yaml.org/spec/1.2/spec.html#id2797293.
+  static const BLOCK = CollectionStyle._('BLOCK');
+
+  /// The delimiter-based block style.
+  ///
+  /// See http://yaml.org/spec/1.2/spec.html#id2790088.
+  static const FLOW = CollectionStyle._('FLOW');
+
+  final String name;
+
+  const CollectionStyle._(this.name);
+
+  @override
+  String toString() => name;
+}

diff --git a/pkgs/yaml/lib/src/token.dart b/pkgs/yaml/lib/src/token.dart
new file mode 100644
index 0000000..7d5d6bc
--- /dev/null
+++ b/pkgs/yaml/lib/src/token.dart

@@ -0,0 +1,158 @@
+// Copyright (c) 2014, the Dart project authors.
+// Copyright (c) 2006, Kirill Simonov.
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'package:source_span/source_span.dart';
+
+import 'scanner.dart';
+import 'style.dart';
+
+/// A token emitted by a [Scanner].
+class Token {
+  final TokenType type;
+  final FileSpan span;
+
+  Token(this.type, this.span);
+
+  @override
+  String toString() => type.toString();
+}
+
+/// A token representing a `%YAML` directive.
+class VersionDirectiveToken implements Token {
+  @override
+  TokenType get type => TokenType.versionDirective;
+  @override
+  final FileSpan span;
+
+  /// The declared major version of the document.
+  final int major;
+
+  /// The declared minor version of the document.
+  final int minor;
+
+  VersionDirectiveToken(this.span, this.major, this.minor);
+
+  @override
+  String toString() => 'VERSION_DIRECTIVE $major.$minor';
+}
+
+/// A token representing a `%TAG` directive.
+class TagDirectiveToken implements Token {
+  @override
+  TokenType get type => TokenType.tagDirective;
+  @override
+  final FileSpan span;
+
+  /// The tag handle used in the document.
+  final String handle;
+
+  /// The tag prefix that the handle maps to.
+  final String prefix;
+
+  TagDirectiveToken(this.span, this.handle, this.prefix);
+
+  @override
+  String toString() => 'TAG_DIRECTIVE $handle $prefix';
+}
+
+/// A token representing an anchor (`&foo`).
+class AnchorToken implements Token {
+  @override
+  TokenType get type => TokenType.anchor;
+  @override
+  final FileSpan span;
+
+  final String name;
+
+  AnchorToken(this.span, this.name);
+
+  @override
+  String toString() => 'ANCHOR $name';
+}
+
+/// A token representing an alias (`*foo`).
+class AliasToken implements Token {
+  @override
+  TokenType get type => TokenType.alias;
+  @override
+  final FileSpan span;
+
+  final String name;
+
+  AliasToken(this.span, this.name);
+
+  @override
+  String toString() => 'ALIAS $name';
+}
+
+/// A token representing a tag (`!foo`).
+class TagToken implements Token {
+  @override
+  TokenType get type => TokenType.tag;
+  @override
+  final FileSpan span;
+
+  /// The tag handle for named tags.
+  final String? handle;
+
+  /// The tag suffix.
+  final String suffix;
+
+  TagToken(this.span, this.handle, this.suffix);
+
+  @override
+  String toString() => 'TAG $handle $suffix';
+}
+
+/// A scalar value.
+class ScalarToken implements Token {
+  @override
+  TokenType get type => TokenType.scalar;
+  @override
+  final FileSpan span;
+
+  /// The unparsed contents of the value..
+  final String value;
+
+  /// The style of the scalar in the original source.
+  final ScalarStyle style;
+
+  ScalarToken(this.span, this.value, this.style);
+
+  @override
+  String toString() => 'SCALAR $style "$value"';
+}
+
+/// The types of [Token] objects.
+enum TokenType {
+  streamStart,
+  streamEnd,
+
+  versionDirective,
+  tagDirective,
+  documentStart,
+  documentEnd,
+
+  blockSequenceStart,
+  blockMappingStart,
+  blockEnd,
+
+  flowSequenceStart,
+  flowSequenceEnd,
+  flowMappingStart,
+  flowMappingEnd,
+
+  blockEntry,
+  flowEntry,
+  key,
+  value,
+
+  alias,
+  anchor,
+  tag,
+  scalar
+}

diff --git a/pkgs/yaml/lib/src/utils.dart b/pkgs/yaml/lib/src/utils.dart
new file mode 100644
index 0000000..0dc132f
--- /dev/null
+++ b/pkgs/yaml/lib/src/utils.dart

@@ -0,0 +1,40 @@
+// Copyright (c) 2013, the Dart project authors.
+// Copyright (c) 2006, Kirill Simonov.
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'package:source_span/source_span.dart';
+
+/// Print a warning.
+///
+/// If [span] is passed, associates the warning with that span.
+void warn(String message, [SourceSpan? span]) =>
+    yamlWarningCallback(message, span);
+
+/// A callback for emitting a warning.
+///
+/// [message] is the text of the warning. If [span] is passed, it's the portion
+/// of the document that the warning is associated with and should be included
+/// in the printed warning.
+typedef YamlWarningCallback = void Function(String message, [SourceSpan? span]);
+
+/// A callback for emitting a warning.
+///
+/// In a very few cases, the YAML spec indicates that an implementation should
+/// emit a warning. To do so, it calls this callback. The default implementation
+/// prints a message using [print].
+// ignore: prefer_function_declarations_over_variables
+YamlWarningCallback yamlWarningCallback = (message, [SourceSpan? span]) {
+  // TODO(nweiz): Print to stderr with color when issue 6943 is fixed and
+  // dart:io is available.
+  if (span != null) message = span.message(message);
+  print(message);
+};
+
+/// Whether [codeUnit] is a UTF-16 high surrogate.
+bool isHighSurrogate(int codeUnit) => codeUnit >>> 10 == 0x36;
+
+/// Whether [codeUnit] is a UTF-16 low surrogate.
+bool isLowSurrogate(int codeUnit) => codeUnit >>> 10 == 0x37;

diff --git a/pkgs/yaml/lib/src/yaml_document.dart b/pkgs/yaml/lib/src/yaml_document.dart
new file mode 100644
index 0000000..da6aa1e
--- /dev/null
+++ b/pkgs/yaml/lib/src/yaml_document.dart

@@ -0,0 +1,71 @@
+// Copyright (c) 2014, the Dart project authors.
+// Copyright (c) 2006, Kirill Simonov.
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'dart:collection';
+
+import 'package:source_span/source_span.dart';
+
+import 'yaml_node.dart';
+
+/// A YAML document, complete with metadata.
+class YamlDocument {
+  /// The contents of the document.
+  final YamlNode contents;
+
+  /// The span covering the entire document.
+  final SourceSpan span;
+
+  /// The version directive for the document, if any.
+  final VersionDirective? versionDirective;
+
+  /// The tag directives for the document.
+  final List<TagDirective> tagDirectives;
+
+  /// Whether the beginning of the document was implicit (versus explicit via
+  /// `===`).
+  final bool startImplicit;
+
+  /// Whether the end of the document was implicit (versus explicit via `...`).
+  final bool endImplicit;
+
+  /// Users of the library should not use this constructor.
+  YamlDocument.internal(this.contents, this.span, this.versionDirective,
+      List<TagDirective> tagDirectives,
+      {this.startImplicit = false, this.endImplicit = false})
+      : tagDirectives = UnmodifiableListView(tagDirectives);
+
+  @override
+  String toString() => contents.toString();
+}
+
+/// A directive indicating which version of YAML a document was written to.
+class VersionDirective {
+  /// The major version number.
+  final int major;
+
+  /// The minor version number.
+  final int minor;
+
+  VersionDirective(this.major, this.minor);
+
+  @override
+  String toString() => '%YAML $major.$minor';
+}
+
+/// A directive describing a custom tag handle.
+class TagDirective {
+  /// The handle for use in the document.
+  final String handle;
+
+  /// The prefix that the handle maps to.
+  final String prefix;
+
+  TagDirective(this.handle, this.prefix);
+
+  @override
+  String toString() => '%TAG $handle $prefix';
+}

diff --git a/pkgs/yaml/lib/src/yaml_exception.dart b/pkgs/yaml/lib/src/yaml_exception.dart
new file mode 100644
index 0000000..7aa5389
--- /dev/null
+++ b/pkgs/yaml/lib/src/yaml_exception.dart

@@ -0,0 +1,13 @@
+// Copyright (c) 2013, the Dart project authors.
+// Copyright (c) 2006, Kirill Simonov.
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'package:source_span/source_span.dart';
+
+/// An error thrown by the YAML processor.
+class YamlException extends SourceSpanFormatException {
+  YamlException(super.message, super.span);
+}

diff --git a/pkgs/yaml/lib/src/yaml_node.dart b/pkgs/yaml/lib/src/yaml_node.dart
new file mode 100644
index 0000000..bd17b6c
--- /dev/null
+++ b/pkgs/yaml/lib/src/yaml_node.dart

@@ -0,0 +1,191 @@
+// Copyright (c) 2012, the Dart project authors.
+// Copyright (c) 2006, Kirill Simonov.
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'dart:collection' as collection;
+
+import 'package:collection/collection.dart';
+import 'package:source_span/source_span.dart';
+
+import 'event.dart';
+import 'null_span.dart';
+import 'style.dart';
+import 'yaml_node_wrapper.dart';
+
+/// An interface for parsed nodes from a YAML source tree.
+///
+/// [YamlMap]s and [YamlList]s implement this interface in addition to the
+/// normal [Map] and [List] interfaces, so any maps and lists will be
+/// [YamlNode]s regardless of how they're accessed.
+///
+/// Scalars values like strings and numbers, on the other hand, don't have this
+/// interface by default. Instead, they can be accessed as [YamlScalar]s via
+/// [YamlMap.nodes] or [YamlList.nodes].
+abstract class YamlNode {
+  /// The source span for this node.
+  ///
+  /// [SourceSpan.message] can be used to produce a human-friendly message about
+  /// this node.
+  SourceSpan get span => _span;
+  SourceSpan _span;
+
+  YamlNode._(this._span);
+
+  /// The inner value of this node.
+  ///
+  /// For [YamlScalar]s, this will return the wrapped value. For [YamlMap] and
+  /// [YamlList], it will return `this`, since they already implement [Map] and
+  /// [List], respectively.
+  dynamic get value;
+}
+
+/// A read-only [Map] parsed from YAML.
+class YamlMap extends YamlNode with collection.MapMixin, UnmodifiableMapMixin {
+  /// A view of `this` where the keys and values are guaranteed to be
+  /// [YamlNode]s.
+  ///
+  /// The key type is `dynamic` to allow values to be accessed using
+  /// non-[YamlNode] keys, but [Map.keys] and [Map.forEach] will always expose
+  /// them as [YamlNode]s. For example, for `{"foo": [1, 2, 3]}` [nodes] will be
+  /// a map from a [YamlScalar] to a [YamlList], but since the key type is
+  /// `dynamic` `map.nodes["foo"]` will still work.
+  final Map<dynamic, YamlNode> nodes;
+
+  /// The style used for the map in the original document.
+  final CollectionStyle style;
+
+  @override
+  Map get value => this;
+
+  @override
+  Iterable get keys => nodes.keys.map((node) => (node as YamlNode).value);
+
+  /// Creates an empty YamlMap.
+  ///
+  /// This map's [span] won't have useful location information. However, it will
+  /// have a reasonable implementation of [SourceSpan.message]. If [sourceUrl]
+  /// is passed, it's used as the [SourceSpan.sourceUrl].
+  ///
+  /// [sourceUrl] may be either a [String], a [Uri], or `null`.
+  factory YamlMap({Object? sourceUrl}) => YamlMapWrapper(const {}, sourceUrl);
+
+  /// Wraps a Dart map so that it can be accessed (recursively) like a
+  /// [YamlMap].
+  ///
+  /// Any [SourceSpan]s returned by this map or its children will be dummies
+  /// without useful location information. However, they will have a reasonable
+  /// implementation of [SourceSpan.message]. If [sourceUrl] is
+  /// passed, it's used as the [SourceSpan.sourceUrl].
+  ///
+  /// [sourceUrl] may be either a [String], a [Uri], or `null`.
+  factory YamlMap.wrap(Map dartMap,
+          {Object? sourceUrl, CollectionStyle style = CollectionStyle.ANY}) =>
+      YamlMapWrapper(dartMap, sourceUrl, style: style);
+
+  /// Users of the library should not use this constructor.
+  YamlMap.internal(Map<dynamic, YamlNode> nodes, super.span, this.style)
+      : nodes = UnmodifiableMapView<dynamic, YamlNode>(nodes),
+        super._();
+
+  @override
+  dynamic operator [](Object? key) => nodes[key]?.value;
+}
+
+// TODO(nweiz): Use UnmodifiableListMixin when issue 18970 is fixed.
+/// A read-only [List] parsed from YAML.
+class YamlList extends YamlNode with collection.ListMixin {
+  final List<YamlNode> nodes;
+
+  /// The style used for the list in the original document.
+  final CollectionStyle style;
+
+  @override
+  List get value => this;
+
+  @override
+  int get length => nodes.length;
+
+  @override
+  set length(int index) {
+    throw UnsupportedError('Cannot modify an unmodifiable List');
+  }
+
+  /// Creates an empty YamlList.
+  ///
+  /// This list's [span] won't have useful location information. However, it
+  /// will have a reasonable implementation of [SourceSpan.message]. If
+  /// [sourceUrl] is passed, it's used as the [SourceSpan.sourceUrl].
+  ///
+  /// [sourceUrl] may be either a [String], a [Uri], or `null`.
+  factory YamlList({Object? sourceUrl}) => YamlListWrapper(const [], sourceUrl);
+
+  /// Wraps a Dart list so that it can be accessed (recursively) like a
+  /// [YamlList].
+  ///
+  /// Any [SourceSpan]s returned by this list or its children will be dummies
+  /// without useful location information. However, they will have a reasonable
+  /// implementation of [SourceSpan.message]. If [sourceUrl] is
+  /// passed, it's used as the [SourceSpan.sourceUrl].
+  ///
+  /// [sourceUrl] may be either a [String], a [Uri], or `null`.
+  factory YamlList.wrap(List dartList,
+          {Object? sourceUrl, CollectionStyle style = CollectionStyle.ANY}) =>
+      YamlListWrapper(dartList, sourceUrl, style: style);
+
+  /// Users of the library should not use this constructor.
+  YamlList.internal(List<YamlNode> nodes, super.span, this.style)
+      : nodes = UnmodifiableListView<YamlNode>(nodes),
+        super._();
+
+  @override
+  dynamic operator [](int index) => nodes[index].value;
+
+  @override
+  void operator []=(int index, Object? value) {
+    throw UnsupportedError('Cannot modify an unmodifiable List');
+  }
+}
+
+/// A wrapped scalar value parsed from YAML.
+class YamlScalar extends YamlNode {
+  @override
+  final dynamic value;
+
+  /// The style used for the scalar in the original document.
+  final ScalarStyle style;
+
+  /// Wraps a Dart value in a [YamlScalar].
+  ///
+  /// This scalar's [span] won't have useful location information. However, it
+  /// will have a reasonable implementation of [SourceSpan.message]. If
+  /// [sourceUrl] is passed, it's used as the [SourceSpan.sourceUrl].
+  ///
+  /// [sourceUrl] may be either a [String], a [Uri], or `null`.
+  YamlScalar.wrap(this.value, {Object? sourceUrl, this.style = ScalarStyle.ANY})
+      : super._(NullSpan(sourceUrl)) {
+    ArgumentError.checkNotNull(style, 'style');
+  }
+
+  /// Users of the library should not use this constructor.
+  YamlScalar.internal(this.value, ScalarEvent scalar)
+      : style = scalar.style,
+        super._(scalar.span);
+
+  /// Users of the library should not use this constructor.
+  YamlScalar.internalWithSpan(this.value, SourceSpan span)
+      : style = ScalarStyle.ANY,
+        super._(span);
+
+  @override
+  String toString() => value.toString();
+}
+
+/// Sets the source span of a [YamlNode].
+///
+/// This method is not exposed publicly.
+void setSpan(YamlNode node, SourceSpan span) {
+  node._span = span;
+}

diff --git a/pkgs/yaml/lib/src/yaml_node_wrapper.dart b/pkgs/yaml/lib/src/yaml_node_wrapper.dart
new file mode 100644
index 0000000..5250844
--- /dev/null
+++ b/pkgs/yaml/lib/src/yaml_node_wrapper.dart

@@ -0,0 +1,189 @@
+// Copyright (c) 2014, the Dart project authors.
+// Copyright (c) 2006, Kirill Simonov.
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'dart:collection';
+
+import 'package:collection/collection.dart' as pkg_collection;
+import 'package:source_span/source_span.dart';
+
+import 'null_span.dart';
+import 'style.dart';
+import 'yaml_node.dart';
+
+/// A wrapper that makes a normal Dart map behave like a [YamlMap].
+class YamlMapWrapper extends MapBase
+    with pkg_collection.UnmodifiableMapMixin
+    implements YamlMap {
+  @override
+  final CollectionStyle style;
+
+  final Map _dartMap;
+
+  @override
+  final SourceSpan span;
+
+  @override
+  final Map<dynamic, YamlNode> nodes;
+
+  @override
+  Map get value => this;
+
+  @override
+  Iterable get keys => _dartMap.keys;
+
+  YamlMapWrapper(Map dartMap, Object? sourceUrl,
+      {CollectionStyle style = CollectionStyle.ANY})
+      : this._(dartMap, NullSpan(sourceUrl), style: style);
+
+  YamlMapWrapper._(Map dartMap, this.span, {this.style = CollectionStyle.ANY})
+      : _dartMap = dartMap,
+        nodes = _YamlMapNodes(dartMap, span) {
+    ArgumentError.checkNotNull(style, 'style');
+  }
+
+  @override
+  dynamic operator [](Object? key) {
+    var value = _dartMap[key];
+    if (value is Map) return YamlMapWrapper._(value, span);
+    if (value is List) return YamlListWrapper._(value, span);
+    return value;
+  }
+
+  @override
+  int get hashCode => _dartMap.hashCode;
+
+  @override
+  bool operator ==(Object other) =>
+      other is YamlMapWrapper && other._dartMap == _dartMap;
+}
+
+/// The implementation of [YamlMapWrapper.nodes] as a wrapper around the Dart
+/// map.
+class _YamlMapNodes extends MapBase<dynamic, YamlNode>
+    with pkg_collection.UnmodifiableMapMixin<dynamic, YamlNode> {
+  final Map _dartMap;
+
+  final SourceSpan _span;
+
+  @override
+  Iterable get keys =>
+      _dartMap.keys.map((key) => YamlScalar.internalWithSpan(key, _span));
+
+  _YamlMapNodes(this._dartMap, this._span);
+
+  @override
+  YamlNode? operator [](Object? key) {
+    // Use "as" here because key being assigned to invalidates type propagation.
+    if (key is YamlScalar) key = key.value;
+    if (!_dartMap.containsKey(key)) return null;
+    return _nodeForValue(_dartMap[key], _span);
+  }
+
+  @override
+  int get hashCode => _dartMap.hashCode;
+
+  @override
+  bool operator ==(Object other) =>
+      other is _YamlMapNodes && other._dartMap == _dartMap;
+}
+
+// TODO(nweiz): Use UnmodifiableListMixin when issue 18970 is fixed.
+/// A wrapper that makes a normal Dart list behave like a [YamlList].
+class YamlListWrapper extends ListBase implements YamlList {
+  @override
+  final CollectionStyle style;
+
+  final List _dartList;
+
+  @override
+  final SourceSpan span;
+
+  @override
+  final List<YamlNode> nodes;
+
+  @override
+  List get value => this;
+
+  @override
+  int get length => _dartList.length;
+
+  @override
+  set length(int index) {
+    throw UnsupportedError('Cannot modify an unmodifiable List.');
+  }
+
+  YamlListWrapper(List dartList, Object? sourceUrl,
+      {CollectionStyle style = CollectionStyle.ANY})
+      : this._(dartList, NullSpan(sourceUrl), style: style);
+
+  YamlListWrapper._(List dartList, this.span,
+      {this.style = CollectionStyle.ANY})
+      : _dartList = dartList,
+        nodes = _YamlListNodes(dartList, span) {
+    ArgumentError.checkNotNull(style, 'style');
+  }
+
+  @override
+  dynamic operator [](int index) {
+    var value = _dartList[index];
+    if (value is Map) return YamlMapWrapper._(value, span);
+    if (value is List) return YamlListWrapper._(value, span);
+    return value;
+  }
+
+  @override
+  void operator []=(int index, Object? value) {
+    throw UnsupportedError('Cannot modify an unmodifiable List.');
+  }
+
+  @override
+  int get hashCode => _dartList.hashCode;
+
+  @override
+  bool operator ==(Object other) =>
+      other is YamlListWrapper && other._dartList == _dartList;
+}
+
+// TODO(nweiz): Use UnmodifiableListMixin when issue 18970 is fixed.
+/// The implementation of [YamlListWrapper.nodes] as a wrapper around the Dart
+/// list.
+class _YamlListNodes extends ListBase<YamlNode> {
+  final List _dartList;
+
+  final SourceSpan _span;
+
+  @override
+  int get length => _dartList.length;
+
+  @override
+  set length(int index) {
+    throw UnsupportedError('Cannot modify an unmodifiable List.');
+  }
+
+  _YamlListNodes(this._dartList, this._span);
+
+  @override
+  YamlNode operator [](int index) => _nodeForValue(_dartList[index], _span);
+
+  @override
+  void operator []=(int index, Object? value) {
+    throw UnsupportedError('Cannot modify an unmodifiable List.');
+  }
+
+  @override
+  int get hashCode => _dartList.hashCode;
+
+  @override
+  bool operator ==(Object other) =>
+      other is _YamlListNodes && other._dartList == _dartList;
+}
+
+YamlNode _nodeForValue(Object? value, SourceSpan span) {
+  if (value is Map) return YamlMapWrapper._(value, span);
+  if (value is List) return YamlListWrapper._(value, span);
+  return YamlScalar.internalWithSpan(value, span);
+}

diff --git a/pkgs/yaml/lib/yaml.dart b/pkgs/yaml/lib/yaml.dart
new file mode 100644
index 0000000..26cc9b8
--- /dev/null
+++ b/pkgs/yaml/lib/yaml.dart

@@ -0,0 +1,126 @@
+// Copyright (c) 2012, the Dart project authors.
+// Copyright (c) 2006, Kirill Simonov.
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'src/error_listener.dart';
+import 'src/loader.dart';
+import 'src/style.dart';
+import 'src/yaml_document.dart';
+import 'src/yaml_exception.dart';
+import 'src/yaml_node.dart';
+
+export 'src/style.dart';
+export 'src/utils.dart' show YamlWarningCallback, yamlWarningCallback;
+export 'src/yaml_document.dart';
+export 'src/yaml_exception.dart';
+export 'src/yaml_node.dart' hide setSpan;
+
+/// Loads a single document from a YAML string.
+///
+/// If the string contains more than one document, this throws a
+/// [YamlException]. In future releases, this will become an [ArgumentError].
+///
+/// The return value is mostly normal Dart objects. However, since YAML mappings
+/// support some key types that the default Dart map implementation doesn't
+/// (NaN, lists, and maps), all maps in the returned document are [YamlMap]s.
+/// These have a few small behavioral differences from the default Map
+/// implementation; for details, see the [YamlMap] class.
+///
+/// If [sourceUrl] is passed, it's used as the URL from which the YAML
+/// originated for error reporting.
+///
+/// If [recover] is true, will attempt to recover from parse errors and may
+/// return invalid or synthetic nodes. If [errorListener] is also supplied, its
+/// onError method will be called for each error recovered from. It is not valid
+/// to provide [errorListener] if [recover] is false.
+dynamic loadYaml(String yaml,
+        {Uri? sourceUrl, bool recover = false, ErrorListener? errorListener}) =>
+    loadYamlNode(yaml,
+            sourceUrl: sourceUrl,
+            recover: recover,
+            errorListener: errorListener)
+        .value;
+
+/// Loads a single document from a YAML string as a [YamlNode].
+///
+/// This is just like [loadYaml], except that where [loadYaml] would return a
+/// normal Dart value this returns a [YamlNode] instead. This allows the caller
+/// to be confident that the return value will always be a [YamlNode].
+YamlNode loadYamlNode(String yaml,
+        {Uri? sourceUrl, bool recover = false, ErrorListener? errorListener}) =>
+    loadYamlDocument(yaml,
+            sourceUrl: sourceUrl,
+            recover: recover,
+            errorListener: errorListener)
+        .contents;
+
+/// Loads a single document from a YAML string as a [YamlDocument].
+///
+/// This is just like [loadYaml], except that where [loadYaml] would return a
+/// normal Dart value this returns a [YamlDocument] instead. This allows the
+/// caller to access document metadata.
+YamlDocument loadYamlDocument(String yaml,
+    {Uri? sourceUrl, bool recover = false, ErrorListener? errorListener}) {
+  var loader = Loader(yaml,
+      sourceUrl: sourceUrl, recover: recover, errorListener: errorListener);
+  var document = loader.load();
+  if (document == null) {
+    return YamlDocument.internal(YamlScalar.internalWithSpan(null, loader.span),
+        loader.span, null, const []);
+  }
+
+  var nextDocument = loader.load();
+  if (nextDocument != null) {
+    throw YamlException('Only expected one document.', nextDocument.span);
+  }
+
+  return document;
+}
+
+/// Loads a stream of documents from a YAML string.
+///
+/// The return value is mostly normal Dart objects. However, since YAML mappings
+/// support some key types that the default Dart map implementation doesn't
+/// (NaN, lists, and maps), all maps in the returned document are [YamlMap]s.
+/// These have a few small behavioral differences from the default Map
+/// implementation; for details, see the [YamlMap] class.
+///
+/// If [sourceUrl] is passed, it's used as the URL from which the YAML
+/// originated for error reporting.
+YamlList loadYamlStream(String yaml, {Uri? sourceUrl}) {
+  var loader = Loader(yaml, sourceUrl: sourceUrl);
+
+  var documents = <YamlDocument>[];
+  var document = loader.load();
+  while (document != null) {
+    documents.add(document);
+    document = loader.load();
+  }
+
+  // TODO(jmesserly): the type on the `document` parameter is a workaround for:
+  // https://github.com/dart-lang/dev_compiler/issues/203
+  return YamlList.internal(
+      documents.map((YamlDocument document) => document.contents).toList(),
+      loader.span,
+      CollectionStyle.ANY);
+}
+
+/// Loads a stream of documents from a YAML string.
+///
+/// This is like [loadYamlStream], except that it returns [YamlDocument]s with
+/// metadata wrapping the document contents.
+List<YamlDocument> loadYamlDocuments(String yaml, {Uri? sourceUrl}) {
+  var loader = Loader(yaml, sourceUrl: sourceUrl);
+
+  var documents = <YamlDocument>[];
+  var document = loader.load();
+  while (document != null) {
+    documents.add(document);
+    document = loader.load();
+  }
+
+  return documents;
+}

diff --git a/pkgs/yaml/pubspec.yaml b/pkgs/yaml/pubspec.yaml
new file mode 100644
index 0000000..fb37436
--- /dev/null
+++ b/pkgs/yaml/pubspec.yaml

@@ -0,0 +1,21 @@
+name: yaml
+version: 3.1.3
+description: A parser for YAML, a human-friendly data serialization standard
+repository: https://github.com/dart-lang/tools/tree/main/pkgs/yaml
+
+topics:
+ - yaml
+ - config-format
+
+environment:
+  sdk: ^3.4.0
+
+dependencies:
+  collection: ^1.15.0
+  source_span: ^1.8.0
+  string_scanner: ^1.2.0
+
+dev_dependencies:
+  dart_flutter_team_lints: ^3.0.0
+  path: ^1.8.0
+  test: ^1.16.6

diff --git a/pkgs/yaml/test/span_test.dart b/pkgs/yaml/test/span_test.dart
new file mode 100644
index 0000000..03b7f9c
--- /dev/null
+++ b/pkgs/yaml/test/span_test.dart

@@ -0,0 +1,173 @@
+// Copyright (c) 2019, the Dart project authors.
+// Copyright (c) 2006, Kirill Simonov.
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'dart:convert';
+
+import 'package:source_span/source_span.dart';
+import 'package:test/test.dart';
+import 'package:yaml/yaml.dart';
+
+void _expectSpan(SourceSpan source, String expected) {
+  final result = source.message('message');
+  printOnFailure("r'''\n$result'''");
+
+  expect(result, expected);
+}
+
+void main() {
+  late YamlMap yaml;
+
+  setUpAll(() {
+    yaml = loadYaml(const JsonEncoder.withIndent(' ').convert({
+      'num': 42,
+      'nested': {
+        'null': null,
+        'num': 42,
+      },
+      'null': null,
+    })) as YamlMap;
+  });
+
+  test('first root key', () {
+    _expectSpan(
+      yaml.nodes['num']!.span,
+      r'''
+line 2, column 9: message
+  ╷
+2 │  "num": 42,
+  │         ^^
+  ╵''',
+    );
+  });
+
+  test('first root key', () {
+    _expectSpan(
+      yaml.nodes['null']!.span,
+      r'''
+line 7, column 10: message
+  ╷
+7 │  "null": null
+  │          ^^^^
+  ╵''',
+    );
+  });
+
+  group('nested', () {
+    late YamlMap nestedMap;
+
+    setUpAll(() {
+      nestedMap = yaml.nodes['nested'] as YamlMap;
+    });
+
+    test('first root key', () {
+      _expectSpan(
+        nestedMap.nodes['null']!.span,
+        r'''
+line 4, column 11: message
+  ╷
+4 │   "null": null,
+  │           ^^^^
+  ╵''',
+      );
+    });
+
+    test('first root key', () {
+      _expectSpan(
+        nestedMap.nodes['num']!.span,
+        r'''
+line 5, column 10: message
+  ╷
+5 │     "num": 42
+  │ ┌──────────^
+6 │ │  },
+  │ └─^
+  ╵''',
+      );
+    });
+  });
+
+  group('block', () {
+    late YamlList list, nestedList;
+
+    setUpAll(() {
+      const yamlStr = '''
+- foo
+- 
+  - one
+  - 
+  - three
+  - 
+  - five
+  -
+- 
+  a : b
+  c : d
+- bar
+''';
+
+      list = loadYaml(yamlStr) as YamlList;
+      nestedList = list.nodes[1] as YamlList;
+    });
+
+    test('root nodes span', () {
+      _expectSpan(list.nodes[0].span, r'''
+line 1, column 3: message
+  ╷
+1 │ - foo
+  │   ^^^
+  ╵''');
+
+      _expectSpan(list.nodes[1].span, r'''
+line 3, column 3: message
+  ╷
+3 │ ┌   - one
+4 │ │   - 
+5 │ │   - three
+6 │ │   - 
+7 │ │   - five
+8 │ └   -
+  ╵''');
+
+      _expectSpan(list.nodes[2].span, r'''
+line 10, column 3: message
+   ╷
+10 │ ┌   a : b
+11 │ └   c : d
+   ╵''');
+
+      _expectSpan(list.nodes[3].span, r'''
+line 12, column 3: message
+   ╷
+12 │ - bar
+   │   ^^^
+   ╵''');
+    });
+
+    test('null nodes span', () {
+      _expectSpan(nestedList.nodes[1].span, r'''
+line 4, column 3: message
+  ╷
+4 │   - 
+  │   ^
+  ╵''');
+
+      _expectSpan(nestedList.nodes[3].span, r'''
+line 6, column 3: message
+  ╷
+6 │   - 
+  │   ^
+  ╵''');
+
+      _expectSpan(nestedList.nodes[5].span, r'''
+line 8, column 3: message
+  ╷
+8 │   -
+  │   ^
+  ╵''');
+    });
+  });
+}

diff --git a/pkgs/yaml/test/utils.dart b/pkgs/yaml/test/utils.dart
new file mode 100644
index 0000000..372440a
--- /dev/null
+++ b/pkgs/yaml/test/utils.dart

@@ -0,0 +1,95 @@
+// Copyright (c) 2014, the Dart project authors.
+// Copyright (c) 2006, Kirill Simonov.
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'package:test/test.dart';
+import 'package:yaml/src/equality.dart' as equality;
+import 'package:yaml/yaml.dart';
+
+/// A matcher that validates that a closure or Future throws a [YamlException].
+final Matcher throwsYamlException = throwsA(isA<YamlException>());
+
+/// Returns a matcher that asserts that the value equals [expected].
+///
+/// This handles recursive loops and considers `NaN` to equal itself.
+Matcher deepEquals(Object? expected) => predicate(
+    (actual) => equality.deepEquals(actual, expected), 'equals $expected');
+
+/// Constructs a new yaml.YamlMap, optionally from a normal Map.
+Map deepEqualsMap([Map? from]) {
+  var map = equality.deepEqualsMap<Object?, Object?>();
+  if (from != null) map.addAll(from);
+  return map;
+}
+
+/// Asserts that an error has the given message and starts at the given line/col.
+void expectErrorAtLineCol(
+    YamlException error, String message, int line, int col) {
+  expect(error.message, equals(message));
+  expect(error.span!.start.line, equals(line));
+  expect(error.span!.start.column, equals(col));
+}
+
+/// Asserts that a string containing a single YAML document produces a given
+/// value when loaded.
+void expectYamlLoads(Object? expected, String source) {
+  var actual = loadYaml(cleanUpLiteral(source));
+  expect(actual, deepEquals(expected));
+}
+
+/// Asserts that a string containing a stream of YAML documents produces a given
+/// list of values when loaded.
+void expectYamlStreamLoads(List expected, String source) {
+  var actual = loadYamlStream(cleanUpLiteral(source));
+  expect(actual, deepEquals(expected));
+}
+
+/// Asserts that a string containing a single YAML document throws a
+/// [YamlException].
+void expectYamlFails(String source) {
+  expect(() => loadYaml(cleanUpLiteral(source)), throwsYamlException);
+}
+
+/// Removes eight spaces of leading indentation from a multiline string.
+///
+/// Note that this is very sensitive to how the literals are styled. They should
+/// be:
+///     '''
+///     Text starts on own line. Lines up with subsequent lines.
+///     Lines are indented exactly 8 characters from the left margin.
+///     Close is on the same line.'''
+///
+/// This does nothing if text is only a single line.
+String cleanUpLiteral(String text) {
+  var lines = text.split('\n');
+  if (lines.length <= 1) return text;
+
+  for (var j = 0; j < lines.length; j++) {
+    if (lines[j].length > 8) {
+      lines[j] = lines[j].substring(8, lines[j].length);
+    } else {
+      lines[j] = '';
+    }
+  }
+
+  return lines.join('\n');
+}
+
+/// Indents each line of [text] so that, when passed to [cleanUpLiteral], it
+/// will produce output identical to [text].
+///
+/// This is useful for literals that need to include newlines but can't be
+/// conveniently represented as multi-line strings.
+String indentLiteral(String text) {
+  var lines = text.split('\n');
+  if (lines.length <= 1) return text;
+
+  for (var i = 0; i < lines.length; i++) {
+    lines[i] = '        ${lines[i]}';
+  }
+
+  return lines.join('\n');
+}

diff --git a/pkgs/yaml/test/yaml_node_wrapper_test.dart b/pkgs/yaml/test/yaml_node_wrapper_test.dart
new file mode 100644
index 0000000..637b778
--- /dev/null
+++ b/pkgs/yaml/test/yaml_node_wrapper_test.dart

@@ -0,0 +1,235 @@
+// Copyright (c) 2012, the Dart project authors.
+// Copyright (c) 2006, Kirill Simonov.
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+// ignore_for_file: avoid_dynamic_calls
+
+import 'package:source_span/source_span.dart';
+import 'package:test/test.dart';
+import 'package:yaml/yaml.dart';
+
+void main() {
+  test('YamlMap() with no sourceUrl', () {
+    var map = YamlMap();
+    expect(map, isEmpty);
+    expect(map.nodes, isEmpty);
+    expect(map.span, isNullSpan(isNull));
+  });
+
+  test('YamlMap() with a sourceUrl', () {
+    var map = YamlMap(sourceUrl: 'source');
+    expect(map.span, isNullSpan(Uri.parse('source')));
+  });
+
+  test('YamlList() with no sourceUrl', () {
+    var list = YamlList();
+    expect(list, isEmpty);
+    expect(list.nodes, isEmpty);
+    expect(list.span, isNullSpan(isNull));
+  });
+
+  test('YamlList() with a sourceUrl', () {
+    var list = YamlList(sourceUrl: 'source');
+    expect(list.span, isNullSpan(Uri.parse('source')));
+  });
+
+  test('YamlMap.wrap() with no sourceUrl', () {
+    var map = YamlMap.wrap({
+      'list': [1, 2, 3],
+      'map': {
+        'foo': 'bar',
+        'nested': [4, 5, 6]
+      },
+      'scalar': 'value'
+    });
+
+    expect(
+        map,
+        equals({
+          'list': [1, 2, 3],
+          'map': {
+            'foo': 'bar',
+            'nested': [4, 5, 6]
+          },
+          'scalar': 'value'
+        }));
+
+    expect(map.span, isNullSpan(isNull));
+    expect(map['list'], isA<YamlList>());
+    expect(map['list'].nodes[0], isA<YamlScalar>());
+    expect(map['list'].span, isNullSpan(isNull));
+    expect(map['map'], isA<YamlMap>());
+    expect(map['map'].nodes['foo'], isA<YamlScalar>());
+    expect(map['map']['nested'], isA<YamlList>());
+    expect(map['map'].span, isNullSpan(isNull));
+    expect(map.nodes['scalar'], isA<YamlScalar>());
+    expect(map.nodes['scalar']!.value, 'value');
+    expect(map.nodes['scalar']!.span, isNullSpan(isNull));
+    expect(map['scalar'], 'value');
+    expect(map.keys, unorderedEquals(['list', 'map', 'scalar']));
+    expect(map.nodes.keys, everyElement(isA<YamlScalar>()));
+    expect(map.nodes[YamlScalar.wrap('list')], equals([1, 2, 3]));
+    expect(map.style, equals(CollectionStyle.ANY));
+    expect((map.nodes['list'] as YamlList).style, equals(CollectionStyle.ANY));
+    expect((map.nodes['map'] as YamlMap).style, equals(CollectionStyle.ANY));
+    expect((map['map'].nodes['nested'] as YamlList).style,
+        equals(CollectionStyle.ANY));
+  });
+
+  test('YamlMap.wrap() with a sourceUrl', () {
+    var map = YamlMap.wrap({
+      'list': [1, 2, 3],
+      'map': {
+        'foo': 'bar',
+        'nested': [4, 5, 6]
+      },
+      'scalar': 'value'
+    }, sourceUrl: 'source');
+
+    var source = Uri.parse('source');
+    expect(map.span, isNullSpan(source));
+    expect(map['list'].span, isNullSpan(source));
+    expect(map['map'].span, isNullSpan(source));
+    expect(map.nodes['scalar']!.span, isNullSpan(source));
+  });
+
+  test('YamlMap.wrap() with a sourceUrl and style', () {
+    var map = YamlMap.wrap({
+      'list': [1, 2, 3],
+      'map': {
+        'foo': 'bar',
+        'nested': [4, 5, 6]
+      },
+      'scalar': 'value'
+    }, sourceUrl: 'source', style: CollectionStyle.BLOCK);
+
+    expect(map.style, equals(CollectionStyle.BLOCK));
+    expect((map.nodes['list'] as YamlList).style, equals(CollectionStyle.ANY));
+    expect((map.nodes['map'] as YamlMap).style, equals(CollectionStyle.ANY));
+    expect((map['map'].nodes['nested'] as YamlList).style,
+        equals(CollectionStyle.ANY));
+  });
+
+  test('YamlList.wrap() with no sourceUrl', () {
+    var list = YamlList.wrap([
+      [1, 2, 3],
+      {
+        'foo': 'bar',
+        'nested': [4, 5, 6]
+      },
+      'value'
+    ]);
+
+    expect(
+        list,
+        equals([
+          [1, 2, 3],
+          {
+            'foo': 'bar',
+            'nested': [4, 5, 6]
+          },
+          'value'
+        ]));
+
+    expect(list.span, isNullSpan(isNull));
+    expect(list[0], isA<YamlList>());
+    expect(list[0].nodes[0], isA<YamlScalar>());
+    expect(list[0].span, isNullSpan(isNull));
+    expect(list[1], isA<YamlMap>());
+    expect(list[1].nodes['foo'], isA<YamlScalar>());
+    expect(list[1]['nested'], isA<YamlList>());
+    expect(list[1].span, isNullSpan(isNull));
+    expect(list.nodes[2], isA<YamlScalar>());
+    expect(list.nodes[2].value, 'value');
+    expect(list.nodes[2].span, isNullSpan(isNull));
+    expect(list[2], 'value');
+    expect(list.style, equals(CollectionStyle.ANY));
+    expect((list[0] as YamlList).style, equals(CollectionStyle.ANY));
+    expect((list[1] as YamlMap).style, equals(CollectionStyle.ANY));
+    expect((list[1]['nested'] as YamlList).style, equals(CollectionStyle.ANY));
+  });
+
+  test('YamlList.wrap() with a sourceUrl', () {
+    var list = YamlList.wrap([
+      [1, 2, 3],
+      {
+        'foo': 'bar',
+        'nested': [4, 5, 6]
+      },
+      'value'
+    ], sourceUrl: 'source');
+
+    var source = Uri.parse('source');
+    expect(list.span, isNullSpan(source));
+    expect(list[0].span, isNullSpan(source));
+    expect(list[1].span, isNullSpan(source));
+    expect(list.nodes[2].span, isNullSpan(source));
+  });
+
+  test('YamlList.wrap() with a sourceUrl and style', () {
+    var list = YamlList.wrap([
+      [1, 2, 3],
+      {
+        'foo': 'bar',
+        'nested': [4, 5, 6]
+      },
+      'value'
+    ], sourceUrl: 'source', style: CollectionStyle.FLOW);
+
+    expect(list.style, equals(CollectionStyle.FLOW));
+    expect((list[0] as YamlList).style, equals(CollectionStyle.ANY));
+    expect((list[1] as YamlMap).style, equals(CollectionStyle.ANY));
+    expect((list[1]['nested'] as YamlList).style, equals(CollectionStyle.ANY));
+  });
+
+  test('re-wrapped objects equal one another', () {
+    var list = YamlList.wrap([
+      [1, 2, 3],
+      {'foo': 'bar'}
+    ]);
+
+    expect(list[0] == list[0], isTrue);
+    expect(list[0].nodes == list[0].nodes, isTrue);
+    expect(list[0] == YamlList.wrap([1, 2, 3]), isFalse);
+    expect(list[1] == list[1], isTrue);
+    expect(list[1].nodes == list[1].nodes, isTrue);
+    expect(list[1] == YamlMap.wrap({'foo': 'bar'}), isFalse);
+  });
+
+  test('YamlScalar.wrap() with no sourceUrl', () {
+    var scalar = YamlScalar.wrap('foo');
+
+    expect(scalar.span, isNullSpan(isNull));
+    expect(scalar.value, 'foo');
+    expect(scalar.style, equals(ScalarStyle.ANY));
+  });
+
+  test('YamlScalar.wrap() with sourceUrl', () {
+    var scalar = YamlScalar.wrap('foo', sourceUrl: 'source');
+
+    var source = Uri.parse('source');
+    expect(scalar.span, isNullSpan(source));
+  });
+
+  test('YamlScalar.wrap() with sourceUrl and style', () {
+    var scalar = YamlScalar.wrap('foo',
+        sourceUrl: 'source', style: ScalarStyle.DOUBLE_QUOTED);
+
+    expect(scalar.style, equals(ScalarStyle.DOUBLE_QUOTED));
+  });
+}
+
+Matcher isNullSpan(Object sourceUrl) => predicate((SourceSpan span) {
+      expect(span, isA<SourceSpan>());
+      expect(span.length, equals(0));
+      expect(span.text, isEmpty);
+      expect(span.start, equals(span.end));
+      expect(span.start.offset, equals(0));
+      expect(span.start.line, equals(0));
+      expect(span.start.column, equals(0));
+      expect(span.sourceUrl, sourceUrl);
+      return true;
+    });

diff --git a/pkgs/yaml/test/yaml_test.dart b/pkgs/yaml/test/yaml_test.dart
new file mode 100644
index 0000000..3b5b77d
--- /dev/null
+++ b/pkgs/yaml/test/yaml_test.dart

@@ -0,0 +1,1921 @@
+// Copyright (c) 2012, the Dart project authors.
+// Copyright (c) 2006, Kirill Simonov.
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+// ignore_for_file: avoid_dynamic_calls
+
+import 'package:test/test.dart';
+import 'package:yaml/src/error_listener.dart';
+import 'package:yaml/yaml.dart';
+
+import 'utils.dart';
+
+void main() {
+  var infinity = double.parse('Infinity');
+  var nan = double.parse('NaN');
+
+  group('has a friendly error message for', () {
+    var tabError = predicate((e) =>
+        e.toString().contains('Tab characters are not allowed as indentation'));
+
+    test('using a tab as indentation', () {
+      expect(() => loadYaml('foo:\n\tbar'), throwsA(tabError));
+    });
+
+    test('using a tab not as indentation', () {
+      expect(() => loadYaml('''
+          "foo
+          \tbar"
+          error'''), throwsA(isNot(tabError)));
+    });
+  });
+
+  group('refuses', () {
+    // Regression test for #19.
+    test('invalid contents', () {
+      expectYamlFails('{');
+    });
+
+    test('duplicate mapping keys', () {
+      expectYamlFails('{a: 1, a: 2}');
+    });
+
+    group('documents that declare version', () {
+      test('1.0', () {
+        expectYamlFails('''
+         %YAML 1.0
+         --- text
+         ''');
+      });
+
+      test('1.3', () {
+        expectYamlFails('''
+           %YAML 1.3
+           --- text
+           ''');
+      });
+
+      test('2.0', () {
+        expectYamlFails('''
+           %YAML 2.0
+           --- text
+           ''');
+      });
+    });
+  });
+
+  group('recovers', () {
+    var collector = ErrorCollector();
+    setUp(() {
+      collector = ErrorCollector();
+    });
+
+    test('from incomplete leading keys', () {
+      final yaml = cleanUpLiteral(r'''
+        dependencies:
+          zero
+          one: any
+          ''');
+      var result = loadYaml(yaml, recover: true, errorListener: collector);
+      expect(
+          result,
+          deepEquals({
+            'dependencies': {
+              'zero': null,
+              'one': 'any',
+            }
+          }));
+      expect(collector.errors.length, equals(1));
+      // These errors are reported at the start of the next token (after the
+      // whitespace/newlines).
+      expectErrorAtLineCol(collector.errors[0], "Expected ':'.", 2, 2);
+      // Skipped because this case is not currently handled. If it's the first
+      // package without the colon, because the value is indented from the line
+      // above, the whole `zero\n     one` is treated as a scalar value.
+    }, skip: true);
+    test('from incomplete keys', () {
+      final yaml = cleanUpLiteral(r'''
+        dependencies:
+          one: any
+          two
+          three:
+          four
+          five:
+            1.2.3
+          six: 5.4.3
+          ''');
+      var result = loadYaml(yaml, recover: true, errorListener: collector);
+      expect(
+          result,
+          deepEquals({
+            'dependencies': {
+              'one': 'any',
+              'two': null,
+              'three': null,
+              'four': null,
+              'five': '1.2.3',
+              'six': '5.4.3',
+            }
+          }));
+
+      expect(collector.errors.length, equals(2));
+      // These errors are reported at the start of the next token (after the
+      // whitespace/newlines).
+      expectErrorAtLineCol(collector.errors[0], "Expected ':'.", 3, 2);
+      expectErrorAtLineCol(collector.errors[1], "Expected ':'.", 5, 2);
+    });
+    test('from incomplete trailing keys', () {
+      final yaml = cleanUpLiteral(r'''
+        dependencies:
+          six: 5.4.3
+          seven
+          ''');
+      var result = loadYaml(yaml, recover: true);
+      expect(
+          result,
+          deepEquals({
+            'dependencies': {
+              'six': '5.4.3',
+              'seven': null,
+            }
+          }));
+    });
+  });
+
+  test('includes source span information', () {
+    var yaml = loadYamlNode(r'''
+- foo:
+    bar
+- 123
+''') as YamlList;
+
+    expect(yaml.span.start.line, equals(0));
+    expect(yaml.span.start.column, equals(0));
+    expect(yaml.span.end.line, equals(3));
+    expect(yaml.span.end.column, equals(0));
+
+    var map = yaml.nodes.first as YamlMap;
+    expect(map.span.start.line, equals(0));
+    expect(map.span.start.column, equals(2));
+    expect(map.span.end.line, equals(2));
+    expect(map.span.end.column, equals(0));
+
+    var key = map.nodes.keys.first;
+    expect(key.span.start.line, equals(0));
+    expect(key.span.start.column, equals(2));
+    expect(key.span.end.line, equals(0));
+    expect(key.span.end.column, equals(5));
+
+    var value = map.nodes.values.first;
+    expect(value.span.start.line, equals(1));
+    expect(value.span.start.column, equals(4));
+    expect(value.span.end.line, equals(1));
+    expect(value.span.end.column, equals(7));
+
+    var scalar = yaml.nodes.last;
+    expect(scalar.span.start.line, equals(2));
+    expect(scalar.span.start.column, equals(2));
+    expect(scalar.span.end.line, equals(2));
+    expect(scalar.span.end.column, equals(5));
+  });
+
+  // The following tests are all taken directly from the YAML spec
+  // (http://www.yaml.org/spec/1.2/spec.html). Most of them are code examples
+  // that are directly included in the spec, but additional tests are derived
+  // from the prose.
+
+  // A few examples from the spec are deliberately excluded, because they test
+  // features that this implementation doesn't intend to support (character
+  // encoding detection and user-defined tags). More tests are commented out,
+  // because they're intended to be supported but not yet implemented.
+
+  // Chapter 2 is just a preview of various Yaml documents. It's probably not
+  // necessary to test its examples, but it would be nice to test everything in
+  // the spec.
+  group('2.1: Collections', () {
+    test('[Example 2.1]', () {
+      expectYamlLoads(['Mark McGwire', 'Sammy Sosa', 'Ken Griffey'], '''
+        - Mark McGwire
+        - Sammy Sosa
+        - Ken Griffey''');
+    });
+
+    test('[Example 2.2]', () {
+      expectYamlLoads({'hr': 65, 'avg': 0.278, 'rbi': 147}, '''
+        hr:  65    # Home runs
+        avg: 0.278 # Batting average
+        rbi: 147   # Runs Batted In''');
+    });
+
+    test('[Example 2.3]', () {
+      expectYamlLoads({
+        'american': ['Boston Red Sox', 'Detroit Tigers', 'New York Yankees'],
+        'national': ['New York Mets', 'Chicago Cubs', 'Atlanta Braves'],
+      }, '''
+        american:
+          - Boston Red Sox
+          - Detroit Tigers
+          - New York Yankees
+        national:
+          - New York Mets
+          - Chicago Cubs
+          - Atlanta Braves''');
+    });
+
+    test('[Example 2.4]', () {
+      expectYamlLoads([
+        {'name': 'Mark McGwire', 'hr': 65, 'avg': 0.278},
+        {'name': 'Sammy Sosa', 'hr': 63, 'avg': 0.288},
+      ], '''
+        -
+          name: Mark McGwire
+          hr:   65
+          avg:  0.278
+        -
+          name: Sammy Sosa
+          hr:   63
+          avg:  0.288''');
+    });
+
+    test('[Example 2.5]', () {
+      expectYamlLoads([
+        ['name', 'hr', 'avg'],
+        ['Mark McGwire', 65, 0.278],
+        ['Sammy Sosa', 63, 0.288]
+      ], '''
+        - [name        , hr, avg  ]
+        - [Mark McGwire, 65, 0.278]
+        - [Sammy Sosa  , 63, 0.288]''');
+    });
+
+    test('[Example 2.6]', () {
+      expectYamlLoads({
+        'Mark McGwire': {'hr': 65, 'avg': 0.278},
+        'Sammy Sosa': {'hr': 63, 'avg': 0.288}
+      }, '''
+        Mark McGwire: {hr: 65, avg: 0.278}
+        Sammy Sosa: {
+            hr: 63,
+            avg: 0.288
+          }''');
+    });
+  });
+
+  group('2.2: Structures', () {
+    test('[Example 2.7]', () {
+      expectYamlStreamLoads([
+        ['Mark McGwire', 'Sammy Sosa', 'Ken Griffey'],
+        ['Chicago Cubs', 'St Louis Cardinals']
+      ], '''
+        # Ranking of 1998 home runs
+        ---
+        - Mark McGwire
+        - Sammy Sosa
+        - Ken Griffey
+
+        # Team ranking
+        ---
+        - Chicago Cubs
+        - St Louis Cardinals''');
+    });
+
+    test('[Example 2.8]', () {
+      expectYamlStreamLoads([
+        {'time': '20:03:20', 'player': 'Sammy Sosa', 'action': 'strike (miss)'},
+        {'time': '20:03:47', 'player': 'Sammy Sosa', 'action': 'grand slam'},
+      ], '''
+        ---
+        time: 20:03:20
+        player: Sammy Sosa
+        action: strike (miss)
+        ...
+        ---
+        time: 20:03:47
+        player: Sammy Sosa
+        action: grand slam
+        ...''');
+    });
+
+    test('[Example 2.9]', () {
+      expectYamlLoads({
+        'hr': ['Mark McGwire', 'Sammy Sosa'],
+        'rbi': ['Sammy Sosa', 'Ken Griffey']
+      }, '''
+        ---
+        hr: # 1998 hr ranking
+          - Mark McGwire
+          - Sammy Sosa
+        rbi:
+          # 1998 rbi ranking
+          - Sammy Sosa
+          - Ken Griffey''');
+    });
+
+    test('[Example 2.10]', () {
+      expectYamlLoads({
+        'hr': ['Mark McGwire', 'Sammy Sosa'],
+        'rbi': ['Sammy Sosa', 'Ken Griffey']
+      }, '''
+        ---
+        hr:
+          - Mark McGwire
+          # Following node labeled SS
+          - &SS Sammy Sosa
+        rbi:
+          - *SS # Subsequent occurrence
+          - Ken Griffey''');
+    });
+
+    test('[Example 2.11]', () {
+      var doc = deepEqualsMap();
+      doc[['Detroit Tigers', 'Chicago cubs']] = ['2001-07-23'];
+      doc[['New York Yankees', 'Atlanta Braves']] = [
+        '2001-07-02',
+        '2001-08-12',
+        '2001-08-14'
+      ];
+      expectYamlLoads(doc, '''
+        ? - Detroit Tigers
+          - Chicago cubs
+        :
+          - 2001-07-23
+
+        ? [ New York Yankees,
+            Atlanta Braves ]
+        : [ 2001-07-02, 2001-08-12,
+            2001-08-14 ]''');
+    });
+
+    test('[Example 2.12]', () {
+      expectYamlLoads([
+        {'item': 'Super Hoop', 'quantity': 1},
+        {'item': 'Basketball', 'quantity': 4},
+        {'item': 'Big Shoes', 'quantity': 1},
+      ], '''
+        ---
+        # Products purchased
+        - item    : Super Hoop
+          quantity: 1
+        - item    : Basketball
+          quantity: 4
+        - item    : Big Shoes
+          quantity: 1''');
+    });
+  });
+
+  group('2.3: Scalars', () {
+    test('[Example 2.13]', () {
+      expectYamlLoads(cleanUpLiteral('''
+        \\//||\\/||
+        // ||  ||__'''), '''
+        # ASCII Art
+        --- |
+          \\//||\\/||
+          // ||  ||__''');
+    });
+
+    test('[Example 2.14]', () {
+      expectYamlLoads("Mark McGwire's year was crippled by a knee injury.", '''
+        --- >
+          Mark McGwire's
+          year was crippled
+          by a knee injury.''');
+    });
+
+    test('[Example 2.15]', () {
+      expectYamlLoads(cleanUpLiteral('''
+        Sammy Sosa completed another fine season with great stats.
+
+          63 Home Runs
+          0.288 Batting Average
+
+        What a year!'''), '''
+        >
+         Sammy Sosa completed another
+         fine season with great stats.
+
+           63 Home Runs
+           0.288 Batting Average
+
+         What a year!''');
+    });
+
+    test('[Example 2.16]', () {
+      expectYamlLoads({
+        'name': 'Mark McGwire',
+        'accomplishment': 'Mark set a major league home run record in 1998.\n',
+        'stats': '65 Home Runs\n0.278 Batting Average'
+      }, '''
+        name: Mark McGwire
+        accomplishment: >
+          Mark set a major league
+          home run record in 1998.
+        stats: |
+          65 Home Runs
+          0.278 Batting Average''');
+    });
+
+    test('[Example 2.17]', () {
+      expectYamlLoads({
+        'unicode': 'Sosa did fine.\u263A \u{1F680}',
+        'control': '\b1998\t1999\t2000\n',
+        'hex esc': '\r\n is \r\n',
+        'single': '"Howdy!" he cried.',
+        'quoted': " # Not a 'comment'.",
+        'tie-fighter': '|\\-*-/|',
+        'surrogate-pair': 'I \u{D83D}\u{DE03}  ️Dart!',
+        'key-\u{D83D}\u{DD11}': 'Look\u{D83D}\u{DE03}\u{D83C}\u{DF89}surprise!',
+      }, """
+        unicode: "Sosa did fine.\\u263A \\U0001F680"
+        control: "\\b1998\\t1999\\t2000\\n"
+        hex esc: "\\x0d\\x0a is \\r\\n"
+
+        single: '"Howdy!" he cried.'
+        quoted: ' # Not a ''comment''.'
+        tie-fighter: '|\\-*-/|'
+        
+        surrogate-pair: I \u{D83D}\u{DE03}  ️Dart!
+        key-\u{D83D}\u{DD11}: Look\u{D83D}\u{DE03}\u{D83C}\u{DF89}surprise!""");
+    });
+
+    test('[Example 2.18]', () {
+      expectYamlLoads({
+        'plain': 'This unquoted scalar spans many lines.',
+        'quoted': 'So does this quoted scalar.\n'
+      }, '''
+        plain:
+          This unquoted scalar
+          spans many lines.
+
+        quoted: "So does this
+          quoted scalar.\\n"''');
+    });
+  });
+
+  group('2.4: Tags', () {
+    test('[Example 2.19]', () {
+      expectYamlLoads({
+        'canonical': 12345,
+        'decimal': 12345,
+        'octal': 12,
+        'hexadecimal': 12
+      }, '''
+        canonical: 12345
+        decimal: +12345
+        octal: 0o14
+        hexadecimal: 0xC''');
+    });
+
+    test('[Example 2.20]', () {
+      expectYamlLoads({
+        'canonical': 1230.15,
+        'exponential': 1230.15,
+        'fixed': 1230.15,
+        'negative infinity': -infinity,
+        'not a number': nan
+      }, '''
+        canonical: 1.23015e+3
+        exponential: 12.3015e+02
+        fixed: 1230.15
+        negative infinity: -.inf
+        not a number: .NaN''');
+    });
+
+    test('[Example 2.21]', () {
+      var doc = deepEqualsMap({
+        'booleans': [true, false],
+        'string': '012345'
+      });
+      doc[null] = null;
+      expectYamlLoads(doc, """
+        null:
+        booleans: [ true, false ]
+        string: '012345'""");
+    });
+
+    // Examples 2.22 through 2.26 test custom tag URIs, which this
+    // implementation currently doesn't plan to support.
+  });
+
+  group('2.5 Full Length Example', () {
+    // Example 2.27 tests custom tag URIs, which this implementation currently
+    // doesn't plan to support.
+
+    test('[Example 2.28]', () {
+      expectYamlStreamLoads([
+        {
+          'Time': '2001-11-23 15:01:42 -5',
+          'User': 'ed',
+          'Warning': 'This is an error message for the log file'
+        },
+        {
+          'Time': '2001-11-23 15:02:31 -5',
+          'User': 'ed',
+          'Warning': 'A slightly different error message.'
+        },
+        {
+          'DateTime': '2001-11-23 15:03:17 -5',
+          'User': 'ed',
+          'Fatal': 'Unknown variable "bar"',
+          'Stack': [
+            {
+              'file': 'TopClass.py',
+              'line': 23,
+              'code': 'x = MoreObject("345\\n")\n'
+            },
+            {'file': 'MoreClass.py', 'line': 58, 'code': 'foo = bar'}
+          ]
+        }
+      ], '''
+        ---
+        Time: 2001-11-23 15:01:42 -5
+        User: ed
+        Warning:
+          This is an error message
+          for the log file
+        ---
+        Time: 2001-11-23 15:02:31 -5
+        User: ed
+        Warning:
+          A slightly different error
+          message.
+        ---
+        DateTime: 2001-11-23 15:03:17 -5
+        User: ed
+        Fatal:
+          Unknown variable "bar"
+        Stack:
+          - file: TopClass.py
+            line: 23
+            code: |
+              x = MoreObject("345\\n")
+          - file: MoreClass.py
+            line: 58
+            code: |-
+              foo = bar''');
+    });
+  });
+
+  // Chapter 3 just talks about the structure of loading and dumping Yaml.
+  // Chapter 4 explains conventions used in the spec.
+
+  // Chapter 5: Characters
+  group('5.1: Character Set', () {
+    void expectAllowsCharacter(int charCode) {
+      var char = String.fromCharCodes([charCode]);
+      expectYamlLoads('The character "$char" is allowed',
+          'The character "$char" is allowed');
+    }
+
+    void expectAllowsQuotedCharacter(int charCode) {
+      var char = String.fromCharCodes([charCode]);
+      expectYamlLoads("The character '$char' is allowed",
+          '"The character \'$char\' is allowed"');
+    }
+
+    void expectDisallowsCharacter(int charCode) {
+      var char = String.fromCharCodes([charCode]);
+      expectYamlFails('The character "$char" is disallowed');
+    }
+
+    test("doesn't include C0 control characters", () {
+      expectDisallowsCharacter(0x0);
+      expectDisallowsCharacter(0x8);
+      expectDisallowsCharacter(0x1F);
+    });
+
+    test('includes TAB', () => expectAllowsCharacter(0x9));
+    test("doesn't include DEL", () => expectDisallowsCharacter(0x7F));
+
+    test("doesn't include C1 control characters", () {
+      expectDisallowsCharacter(0x80);
+      expectDisallowsCharacter(0x8A);
+      expectDisallowsCharacter(0x9F);
+    });
+
+    test('includes NEL', () => expectAllowsCharacter(0x85));
+
+    group('within quoted strings', () {
+      test('includes DEL', () => expectAllowsQuotedCharacter(0x7F));
+      test('includes C1 control characters', () {
+        expectAllowsQuotedCharacter(0x80);
+        expectAllowsQuotedCharacter(0x8A);
+        expectAllowsQuotedCharacter(0x9F);
+      });
+    });
+  });
+
+  // Skipping section 5.2 (Character Encodings), since at the moment the module
+  // assumes that the client code is providing it with a string of the proper
+  // encoding.
+
+  group('5.3: Indicator Characters', () {
+    test('[Example 5.3]', () {
+      expectYamlLoads({
+        'sequence': ['one', 'two'],
+        'mapping': {'sky': 'blue', 'sea': 'green'}
+      }, '''
+        sequence:
+        - one
+        - two
+        mapping:
+          ? sky
+          : blue
+          sea : green''');
+    });
+
+    test('[Example 5.4]', () {
+      expectYamlLoads({
+        'sequence': ['one', 'two'],
+        'mapping': {'sky': 'blue', 'sea': 'green'}
+      }, '''
+        sequence: [ one, two, ]
+        mapping: { sky: blue, sea: green }''');
+    });
+
+    test('[Example 5.5]', () => expectYamlLoads(null, '# Comment only.'));
+
+    // Skipping 5.6 because it uses an undefined tag.
+
+    test('[Example 5.7]', () {
+      expectYamlLoads({'literal': 'some\ntext\n', 'folded': 'some text\n'}, '''
+        literal: |
+          some
+          text
+        folded: >
+          some
+          text
+        ''');
+    });
+
+    test('[Example 5.8]', () {
+      expectYamlLoads({'single': 'text', 'double': 'text'}, '''
+        single: 'text'
+        double: "text"
+        ''');
+    });
+
+    test('[Example 5.9]', () {
+      expectYamlLoads('text', '''
+        %YAML 1.2
+        --- text''');
+    });
+
+    test('[Example 5.10]', () {
+      expectYamlFails('commercial-at: @text');
+      expectYamlFails('commercial-at: `text');
+    });
+  });
+
+  group('5.4: Line Break Characters', () {
+    group('include', () {
+      test('\\n', () => expectYamlLoads([1, 2], indentLiteral('- 1\n- 2')));
+      test('\\r', () => expectYamlLoads([1, 2], '- 1\r- 2'));
+    });
+
+    group('do not include', () {
+      test('form feed', () => expectYamlFails('- 1\x0C- 2'));
+      test('NEL', () => expectYamlLoads(['1\x85- 2'], '- 1\x85- 2'));
+      test('0x2028', () => expectYamlLoads(['1\u2028- 2'], '- 1\u2028- 2'));
+      test('0x2029', () => expectYamlLoads(['1\u2029- 2'], '- 1\u2029- 2'));
+    });
+
+    group('in a scalar context must be normalized', () {
+      test(
+          'from \\r to \\n',
+          () => expectYamlLoads(
+              ['foo\nbar'], indentLiteral('- |\n  foo\r  bar')));
+      test(
+          'from \\r\\n to \\n',
+          () => expectYamlLoads(
+              ['foo\nbar'], indentLiteral('- |\n  foo\r\n  bar')));
+    });
+
+    test('[Example 5.11]', () {
+      expectYamlLoads(cleanUpLiteral('''
+        Line break (no glyph)
+        Line break (glyphed)'''), '''
+        |
+          Line break (no glyph)
+          Line break (glyphed)''');
+    });
+  });
+
+  group('5.5: White Space Characters', () {
+    test('[Example 5.12]', () {
+      expectYamlLoads({
+        'quoted': 'Quoted \t',
+        'block': 'void main() {\n\tprintf("Hello, world!\\n");\n}\n'
+      }, '''
+        # Tabs and spaces
+        quoted: "Quoted \t"
+        block:\t|
+          void main() {
+          \tprintf("Hello, world!\\n");
+          }
+        ''');
+    });
+  });
+
+  group('5.7: Escaped Characters', () {
+    test('[Example 5.13]', () {
+      expectYamlLoads(
+          'Fun with \x5C '
+              '\x22 \x07 \x08 \x1B \x0C '
+              '\x0A \x0D \x09 \x0B \x00 '
+              '\x20 \xA0 \x85 \u2028 \u2029 '
+              'A A A',
+          '''
+        "Fun with \\\\
+        \\" \\a \\b \\e \\f \\
+        \\n \\r \\t \\v \\0 \\
+        \\  \\_ \\N \\L \\P \\
+        \\x41 \\u0041 \\U00000041"''');
+    });
+
+    test('[Example 5.14]', () {
+      expectYamlFails('Bad escape: "\\c"');
+      expectYamlFails('Bad escape: "\\xq-"');
+    });
+  });
+
+  // Chapter 6: Basic Structures
+  group('6.1: Indentation Spaces', () {
+    test('may not include TAB characters', () {
+      expectYamlFails('''
+        -
+        \t- foo
+        \t- bar''');
+    });
+
+    test('must be the same for all sibling nodes', () {
+      expectYamlFails('''
+        -
+          - foo
+         - bar''');
+    });
+
+    test('may be different for the children of sibling nodes', () {
+      expectYamlLoads([
+        ['foo'],
+        ['bar']
+      ], '''
+        -
+          - foo
+        -
+         - bar''');
+    });
+
+    test('[Example 6.1]', () {
+      expectYamlLoads({
+        'Not indented': {
+          'By one space': 'By four\n  spaces\n',
+          'Flow style': ['By two', 'Also by two', 'Still by two']
+        }
+      }, '''
+          # Leading comment line spaces are
+           # neither content nor indentation.
+            
+        Not indented:
+         By one space: |
+            By four
+              spaces
+         Flow style: [    # Leading spaces
+           By two,        # in flow style
+          Also by two,    # are neither
+          \tStill by two   # content nor
+            ]             # indentation.''');
+    });
+
+    test('[Example 6.2]', () {
+      expectYamlLoads({
+        'a': [
+          'b',
+          ['c', 'd']
+        ]
+      }, '''
+        ? a
+        : -\tb
+          -  -\tc
+             - d''');
+    });
+  });
+
+  group('6.2: Separation Spaces', () {
+    test('[Example 6.3]', () {
+      expectYamlLoads([
+        {'foo': 'bar'},
+        ['baz', 'baz']
+      ], '''
+        - foo:\t bar
+        - - baz
+          -\tbaz''');
+    });
+  });
+
+  group('6.3: Line Prefixes', () {
+    test('[Example 6.4]', () {
+      expectYamlLoads({
+        'plain': 'text lines',
+        'quoted': 'text lines',
+        'block': 'text\n \tlines\n'
+      }, '''
+        plain: text
+          lines
+        quoted: "text
+          \tlines"
+        block: |
+          text
+           \tlines
+        ''');
+    });
+  });
+
+  group('6.4: Empty Lines', () {
+    test('[Example 6.5]', () {
+      expectYamlLoads({
+        'Folding': 'Empty line\nas a line feed',
+        'Chomping': 'Clipped empty lines\n',
+      }, '''
+        Folding:
+          "Empty line
+           \t
+          as a line feed"
+        Chomping: |
+          Clipped empty lines
+         ''');
+    });
+  });
+
+  group('6.5: Line Folding', () {
+    test('[Example 6.6]', () {
+      expectYamlLoads('trimmed\n\n\nas space', '''
+        >-
+          trimmed
+          
+         
+
+          as
+          space
+        ''');
+    });
+
+    test('[Example 6.7]', () {
+      expectYamlLoads('foo \n\n\t bar\n\nbaz\n', '''
+        >
+          foo 
+         
+          \t bar
+
+          baz
+        ''');
+    });
+
+    test('[Example 6.8]', () {
+      expectYamlLoads(' foo\nbar\nbaz ', '''
+        "
+          foo 
+         
+          \t bar
+
+          baz
+        "''');
+    });
+  });
+
+  group('6.6: Comments', () {
+    test('must be separated from other tokens by white space characters', () {
+      expectYamlLoads('foo#bar', 'foo#bar');
+      expectYamlLoads('foo:#bar', 'foo:#bar');
+      expectYamlLoads('-#bar', '-#bar');
+    });
+
+    test('[Example 6.9]', () {
+      expectYamlLoads({'key': 'value'}, '''
+        key:    # Comment
+          value''');
+    });
+
+    group('outside of scalar content', () {
+      test('may appear on a line of their own', () {
+        expectYamlLoads([1, 2], '''
+        - 1
+        # Comment
+        - 2''');
+      });
+
+      test('are independent of indentation level', () {
+        expectYamlLoads([
+          [1, 2]
+        ], '''
+        -
+          - 1
+         # Comment
+          - 2''');
+      });
+
+      test('include lines containing only white space characters', () {
+        expectYamlLoads([1, 2], '''
+        - 1
+          \t  
+        - 2''');
+      });
+    });
+
+    group('within scalar content', () {
+      test('may not appear on a line of their own', () {
+        expectYamlLoads(['foo\n# not comment\nbar\n'], '''
+        - |
+          foo
+          # not comment
+          bar
+        ''');
+      });
+
+      test("don't include lines containing only white space characters", () {
+        expectYamlLoads(['foo\n  \t   \nbar\n'], '''
+        - |
+          foo
+            \t   
+          bar
+        ''');
+      });
+    });
+
+    test('[Example 6.10]', () {
+      expectYamlLoads(null, '''
+          # Comment
+           
+        ''');
+    });
+
+    test('[Example 6.11]', () {
+      expectYamlLoads({'key': 'value'}, '''
+        key:    # Comment
+                # lines
+          value
+        ''');
+    });
+
+    group('ending a block scalar header', () {
+      test('may not be followed by additional comment lines', () {
+        expectYamlLoads(['# not comment\nfoo\n'], '''
+        - | # comment
+            # not comment
+            foo
+        ''');
+      });
+    });
+  });
+
+  group('6.7: Separation Lines', () {
+    test('may not be used within implicit keys', () {
+      expectYamlFails('''
+        [1,
+         2]: 3''');
+    });
+
+    test('[Example 6.12]', () {
+      var doc = deepEqualsMap();
+      doc[{'first': 'Sammy', 'last': 'Sosa'}] = {'hr': 65, 'avg': 0.278};
+      expectYamlLoads(doc, '''
+        { first: Sammy, last: Sosa }:
+        # Statistics:
+          hr:  # Home runs
+             65
+          avg: # Average
+           0.278''');
+    });
+  });
+
+  group('6.8: Directives', () {
+    // TODO(nweiz): assert that this produces a warning
+    test('[Example 6.13]', () {
+      expectYamlLoads('foo', '''
+        %FOO  bar baz # Should be ignored
+                      # with a warning.
+        --- "foo"''');
+    });
+
+    // TODO(nweiz): assert that this produces a warning.
+    test('[Example 6.14]', () {
+      expectYamlLoads('foo', '''
+        %YAML 1.3 # Attempt parsing
+                   # with a warning
+        ---
+        "foo"''');
+    });
+
+    test('[Example 6.15]', () {
+      expectYamlFails('''
+        %YAML 1.2
+        %YAML 1.1
+        foo''');
+    });
+
+    test('[Example 6.16]', () {
+      expectYamlLoads('foo', '''
+        %TAG !yaml! tag:yaml.org,2002:
+        ---
+        !yaml!str "foo"''');
+    });
+
+    test('[Example 6.17]', () {
+      expectYamlFails('''
+        %TAG ! !foo
+        %TAG ! !foo
+        bar''');
+    });
+
+    // Examples 6.18 through 6.22 test custom tag URIs, which this
+    // implementation currently doesn't plan to support.
+  });
+
+  group('6.9: Node Properties', () {
+    test('may be specified in any order', () {
+      expectYamlLoads(['foo', 'bar'], '''
+        - !!str &a1 foo
+        - &a2 !!str bar''');
+    });
+
+    test('[Example 6.23]', () {
+      expectYamlLoads({'foo': 'bar', 'baz': 'foo'}, '''
+        !!str &a1 "foo":
+          !!str bar
+        &a2 baz : *a1''');
+    });
+
+    // Example 6.24 tests custom tag URIs, which this implementation currently
+    // doesn't plan to support.
+
+    test('[Example 6.25]', () {
+      expectYamlFails('- !<!> foo');
+      expectYamlFails('- !<\$:?> foo');
+    });
+
+    // Examples 6.26 and 6.27 test custom tag URIs, which this implementation
+    // currently doesn't plan to support.
+
+    test('[Example 6.28]', () {
+      expectYamlLoads(['12', 12, '12'], '''
+        # Assuming conventional resolution:
+        - "12"
+        - 12
+        - ! 12''');
+    });
+
+    test('[Example 6.29]', () {
+      expectYamlLoads(
+          {'First occurrence': 'Value', 'Second occurrence': 'Value'}, '''
+        First occurrence: &anchor Value
+        Second occurrence: *anchor''');
+    });
+  });
+
+  // Chapter 7: Flow Styles
+  group('7.1: Alias Nodes', () {
+    test("must not use an anchor that doesn't previously occur", () {
+      expectYamlFails('''
+        - *anchor
+        - &anchor foo''');
+    });
+
+    test("don't have to exist for a given anchor node", () {
+      expectYamlLoads(['foo'], '- &anchor foo');
+    });
+
+    group('must not specify', () {
+      test('tag properties', () => expectYamlFails('''
+        - &anchor foo
+        - !str *anchor'''));
+
+      test('anchor properties', () => expectYamlFails('''
+        - &anchor foo
+        - &anchor2 *anchor'''));
+
+      test('content', () => expectYamlFails('''
+        - &anchor foo
+        - *anchor bar'''));
+    });
+
+    test('must preserve structural equality', () {
+      var doc = loadYaml(cleanUpLiteral('''
+        anchor: &anchor [a, b, c]
+        alias: *anchor'''));
+      var anchorList = doc['anchor'];
+      var aliasList = doc['alias'];
+      expect(anchorList, same(aliasList));
+
+      doc = loadYaml(cleanUpLiteral('''
+        ? &anchor [a, b, c]
+        : ? *anchor
+          : bar'''));
+      anchorList = doc.keys.first;
+      aliasList = doc[['a', 'b', 'c']].keys.first;
+      expect(anchorList, same(aliasList));
+    });
+
+    test('[Example 7.1]', () {
+      expectYamlLoads({
+        'First occurrence': 'Foo',
+        'Second occurrence': 'Foo',
+        'Override anchor': 'Bar',
+        'Reuse anchor': 'Bar',
+      }, '''
+        First occurrence: &anchor Foo
+        Second occurrence: *anchor
+        Override anchor: &anchor Bar
+        Reuse anchor: *anchor''');
+    });
+  });
+
+  group('7.2: Empty Nodes', () {
+    test('[Example 7.2]', () {
+      expectYamlLoads({'foo': '', '': 'bar'}, '''
+        {
+          foo : !!str,
+          !!str : bar,
+        }''');
+    });
+
+    test('[Example 7.3]', () {
+      var doc = deepEqualsMap({'foo': null});
+      doc[null] = 'bar';
+      expectYamlLoads(doc, '''
+        {
+          ? foo :,
+          : bar,
+        }''');
+    });
+  });
+
+  group('7.3: Flow Scalar Styles', () {
+    test('[Example 7.4]', () {
+      expectYamlLoads({
+        'implicit block key': [
+          {'implicit flow key': 'value'}
+        ]
+      }, '''
+        "implicit block key" : [
+          "implicit flow key" : value,
+         ]''');
+    });
+
+    test('[Example 7.5]', () {
+      expectYamlLoads(
+          'folded to a space,\nto a line feed, or \t \tnon-content', '''
+        "folded 
+        to a space,\t
+         
+        to a line feed, or \t\\
+         \\ \tnon-content"''');
+    });
+
+    test('[Example 7.6]', () {
+      expectYamlLoads(' 1st non-empty\n2nd non-empty 3rd non-empty ', '''
+        " 1st non-empty
+
+         2nd non-empty 
+        \t3rd non-empty "''');
+    });
+
+    test('[Example 7.7]', () {
+      expectYamlLoads("here's to \"quotes\"", "'here''s to \"quotes\"'");
+    });
+
+    test('[Example 7.8]', () {
+      expectYamlLoads({
+        'implicit block key': [
+          {'implicit flow key': 'value'}
+        ]
+      }, """
+        'implicit block key' : [
+          'implicit flow key' : value,
+         ]""");
+    });
+
+    test('[Example 7.9]', () {
+      expectYamlLoads(' 1st non-empty\n2nd non-empty 3rd non-empty ', """
+        ' 1st non-empty
+
+         2nd non-empty 
+        \t3rd non-empty '""");
+    });
+
+    test('[Example 7.10]', () {
+      expectYamlLoads([
+        '::vector',
+        ': - ()',
+        'Up, up, and away!',
+        -123,
+        'http://example.com/foo#bar',
+        [
+          '::vector',
+          ': - ()',
+          'Up, up, and away!',
+          -123,
+          'http://example.com/foo#bar'
+        ]
+      ], '''
+        # Outside flow collection:
+        - ::vector
+        - ": - ()"
+        - Up, up, and away!
+        - -123
+        - http://example.com/foo#bar
+        # Inside flow collection:
+        - [ ::vector,
+          ": - ()",
+          "Up, up, and away!",
+          -123,
+          http://example.com/foo#bar ]''');
+    });
+
+    test('[Example 7.11]', () {
+      expectYamlLoads({
+        'implicit block key': [
+          {'implicit flow key': 'value'}
+        ]
+      }, '''
+        implicit block key : [
+          implicit flow key : value,
+         ]''');
+    });
+
+    test('[Example 7.12]', () {
+      expectYamlLoads('1st non-empty\n2nd non-empty 3rd non-empty', '''
+        1st non-empty
+
+         2nd non-empty 
+        \t3rd non-empty''');
+    });
+  });
+
+  group('7.4: Flow Collection Styles', () {
+    test('[Example 7.13]', () {
+      expectYamlLoads([
+        ['one', 'two'],
+        ['three', 'four']
+      ], '''
+        - [ one, two, ]
+        - [three ,four]''');
+    });
+
+    test('[Example 7.14]', () {
+      expectYamlLoads([
+        'double quoted',
+        'single quoted',
+        'plain text',
+        ['nested'],
+        {'single': 'pair'}
+      ], """
+        [
+        "double
+         quoted", 'single
+                   quoted',
+        plain
+         text, [ nested ],
+        single: pair,
+        ]""");
+    });
+
+    test('[Example 7.15]', () {
+      expectYamlLoads([
+        {'one': 'two', 'three': 'four'},
+        {'five': 'six', 'seven': 'eight'},
+      ], '''
+        - { one : two , three: four , }
+        - {five: six,seven : eight}''');
+    });
+
+    test('[Example 7.16]', () {
+      var doc = deepEqualsMap({'explicit': 'entry', 'implicit': 'entry'});
+      doc[null] = null;
+      expectYamlLoads(doc, '''
+        {
+        ? explicit: entry,
+        implicit: entry,
+        ?
+        }''');
+    });
+
+    test('[Example 7.17]', () {
+      var doc = deepEqualsMap({
+        'unquoted': 'separate',
+        'http://foo.com': null,
+        'omitted value': null
+      });
+      doc[null] = 'omitted key';
+      expectYamlLoads(doc, '''
+        {
+        unquoted : "separate",
+        http://foo.com,
+        omitted value:,
+        : omitted key,
+        }''');
+    });
+
+    test('[Example 7.18]', () {
+      expectYamlLoads(
+          {'adjacent': 'value', 'readable': 'value', 'empty': null}, '''
+        {
+        "adjacent":value,
+        "readable": value,
+        "empty":
+        }''');
+    });
+
+    test('[Example 7.19]', () {
+      expectYamlLoads([
+        {'foo': 'bar'}
+      ], '''
+        [
+        foo: bar
+        ]''');
+    });
+
+    test('[Example 7.20]', () {
+      expectYamlLoads([
+        {'foo bar': 'baz'}
+      ], '''
+        [
+        ? foo
+         bar : baz
+        ]''');
+    });
+
+    test('[Example 7.21]', () {
+      var el1 = deepEqualsMap();
+      el1[null] = 'empty key entry';
+
+      var el2 = deepEqualsMap();
+      el2[{'JSON': 'like'}] = 'adjacent';
+
+      expectYamlLoads([
+        [
+          {'YAML': 'separate'}
+        ],
+        [el1],
+        [el2]
+      ], '''
+        - [ YAML : separate ]
+        - [ : empty key entry ]
+        - [ {JSON: like}:adjacent ]''');
+    });
+
+    // TODO(nweiz): enable this when we throw an error for long or multiline
+    // keys.
+    // test('[Example 7.22]', () {
+    //   expectYamlFails(
+    //     """
+    //     [ foo
+    //      bar: invalid ]""");
+    //
+    //   var dotList = new List.filled(1024, ' ');
+    //   var dots = dotList.join();
+    //   expectYamlFails('[ "foo...$dots...bar": invalid ]');
+    // });
+  });
+
+  group('7.5: Flow Nodes', () {
+    test('[Example 7.23]', () {
+      expectYamlLoads([
+        ['a', 'b'],
+        {'a': 'b'},
+        'a',
+        'b',
+        'c'
+      ], '''
+        - [ a, b ]
+        - { a: b }
+        - 'a'
+        - 'b'
+        - c''');
+    });
+
+    test('[Example 7.24]', () {
+      expectYamlLoads(['a', 'b', 'c', 'c', ''], '''
+        - !!str "a"
+        - 'b'
+        - &anchor "c"
+        - *anchor
+        - !!str''');
+    });
+  });
+
+  // Chapter 8: Block Styles
+  group('8.1: Block Scalar Styles', () {
+    test('[Example 8.1]', () {
+      expectYamlLoads(['literal\n', ' folded\n', 'keep\n\n', ' strip'], '''
+        - | # Empty header
+         literal
+        - >1 # Indentation indicator
+          folded
+        - |+ # Chomping indicator
+         keep
+
+        - >1- # Both indicators
+          strip''');
+    });
+
+    test('[Example 8.2]', () {
+      // Note: in the spec, the fourth element in this array is listed as
+      // "\t detected\n", not "\t\ndetected\n". However, I'm reasonably
+      // confident that "\t\ndetected\n" is correct when parsed according to the
+      // rest of the spec.
+      expectYamlLoads(
+          ['detected\n', '\n\n# detected\n', ' explicit\n', '\t\ndetected\n'],
+          '''
+        - |
+         detected
+        - >
+
+
+          # detected
+        - |1
+          explicit
+        - >
+         \t
+         detected
+        ''');
+    });
+
+    test('[Example 8.3]', () {
+      expectYamlFails('''
+        - |
+          
+         text''');
+
+      expectYamlFails('''
+        - >
+          text
+         text''');
+
+      expectYamlFails('''
+        - |2
+         text''');
+    });
+
+    test('[Example 8.4]', () {
+      expectYamlLoads({'strip': 'text', 'clip': 'text\n', 'keep': 'text\n'}, '''
+        strip: |-
+          text
+        clip: |
+          text
+        keep: |+
+          text
+        ''');
+    });
+
+    test('[Example 8.5]', () {
+      // This example in the spec only includes a single newline in the "keep"
+      // value, but as far as I can tell that's not how it's supposed to be
+      // parsed according to the rest of the spec.
+      expectYamlLoads(
+          {'strip': '# text', 'clip': '# text\n', 'keep': '# text\n\n'}, '''
+         # Strip
+          # Comments:
+        strip: |-
+          # text
+          
+         # Clip
+          # comments:
+
+        clip: |
+          # text
+         
+         # Keep
+          # comments:
+
+        keep: |+
+          # text
+
+         # Trail
+          # comments.
+        ''');
+    });
+
+    test('[Example 8.6]', () {
+      expectYamlLoads({'strip': '', 'clip': '', 'keep': '\n'}, '''
+        strip: >-
+
+        clip: >
+
+        keep: |+
+
+        ''');
+    });
+
+    test('[Example 8.7]', () {
+      expectYamlLoads('literal\n\ttext\n', '''
+        |
+         literal
+         \ttext
+        ''');
+    });
+
+    test('[Example 8.8]', () {
+      expectYamlLoads('\n\nliteral\n \n\ntext\n', '''
+        |
+         
+          
+          literal
+           
+          
+          text
+
+         # Comment''');
+    });
+
+    test('[Example 8.9]', () {
+      expectYamlLoads('folded text\n', '''
+        >
+         folded
+         text
+        ''');
+    });
+
+    test('[Example 8.10]', () {
+      expectYamlLoads(cleanUpLiteral('''
+
+        folded line
+        next line
+          * bullet
+
+          * list
+          * lines
+
+        last line
+        '''), '''
+        >
+
+         folded
+         line
+
+         next
+         line
+           * bullet
+
+           * list
+           * lines
+
+         last
+         line
+
+        # Comment''');
+    });
+
+    // Examples 8.11 through 8.13 are duplicates of 8.10.
+  });
+
+  group('8.2: Block Collection Styles', () {
+    test('[Example 8.14]', () {
+      expectYamlLoads({
+        'block sequence': [
+          'one',
+          {'two': 'three'}
+        ]
+      }, '''
+        block sequence:
+          - one
+          - two : three''');
+    });
+
+    test('[Example 8.15]', () {
+      expectYamlLoads([
+        null,
+        'block node\n',
+        ['one', 'two'],
+        {'one': 'two'}
+      ], '''
+        - # Empty
+        - |
+         block node
+        - - one # Compact
+          - two # sequence
+        - one: two # Compact mapping''');
+    });
+
+    test('[Example 8.16]', () {
+      expectYamlLoads({
+        'block mapping': {'key': 'value'}
+      }, '''
+        block mapping:
+         key: value''');
+    });
+
+    test('[Example 8.17]', () {
+      expectYamlLoads({
+        'explicit key': null,
+        'block key\n': ['one', 'two']
+      }, '''
+        ? explicit key # Empty value
+        ? |
+          block key
+        : - one # Explicit compact
+          - two # block value''');
+    });
+
+    test('[Example 8.18]', () {
+      var doc = deepEqualsMap({
+        'plain key': 'in-line value',
+        'quoted key': ['entry']
+      });
+      doc[null] = null;
+      expectYamlLoads(doc, '''
+        plain key: in-line value
+        : # Both empty
+        "quoted key":
+        - entry''');
+    });
+
+    test('[Example 8.19]', () {
+      var el = deepEqualsMap();
+      el[{'earth': 'blue'}] = {'moon': 'white'};
+      expectYamlLoads([
+        {'sun': 'yellow'},
+        el
+      ], '''
+        - sun: yellow
+        - ? earth: blue
+          : moon: white''');
+    });
+
+    test('[Example 8.20]', () {
+      expectYamlLoads([
+        'flow in block',
+        'Block scalar\n',
+        {'foo': 'bar'}
+      ], '''
+        -
+          "flow in block"
+        - >
+         Block scalar
+        - !!map # Block collection
+          foo : bar''');
+    });
+
+    test('[Example 8.21]', () {
+      // The spec doesn't include a newline after "value" in the parsed map, but
+      // the block scalar is clipped so it should be retained.
+      expectYamlLoads({'literal': 'value\n', 'folded': 'value'}, '''
+        literal: |2
+          value
+        folded:
+           !!str
+          >1
+         value''');
+    });
+
+    test('[Example 8.22]', () {
+      expectYamlLoads({
+        'sequence': [
+          'entry',
+          ['nested']
+        ],
+        'mapping': {'foo': 'bar'}
+      }, '''
+        sequence: !!seq
+        - entry
+        - !!seq
+         - nested
+        mapping: !!map
+         foo: bar''');
+    });
+  });
+
+  // Chapter 9: YAML Character Stream
+  group('9.1: Documents', () {
+    // Example 9.1 tests the use of a BOM, which this implementation currently
+    // doesn't plan to support.
+
+    test('[Example 9.2]', () {
+      expectYamlLoads('Document', '''
+        %YAML 1.2
+        ---
+        Document
+        ... # Suffix''');
+    });
+
+    test('[Example 9.3]', () {
+      // The spec example indicates that the comment after "%!PS-Adobe-2.0"
+      // should be stripped, which would imply that that line is not part of the
+      // literal defined by the "|". The rest of the spec is ambiguous on this
+      // point; the allowable indentation for non-indented literal content is
+      // not clearly explained. However, if both the "|" and the text were
+      // indented the same amount, the text would be part of the literal, which
+      // implies that the spec's parse of this document is incorrect.
+      expectYamlStreamLoads(
+          ['Bare document', '%!PS-Adobe-2.0 # Not the first line\n'], '''
+        Bare
+        document
+        ...
+        # No document
+        ...
+        |
+        %!PS-Adobe-2.0 # Not the first line
+        ''');
+    });
+
+    test('[Example 9.4]', () {
+      expectYamlStreamLoads([
+        {'matches %': 20},
+        null
+      ], '''
+        ---
+        { matches
+        % : 20 }
+        ...
+        ---
+        # Empty
+        ...''');
+    });
+
+    test('[Example 9.5]', () {
+      // The spec doesn't have a space between the second
+      // "YAML" and "1.2", but this seems to be a typo.
+      expectYamlStreamLoads(['%!PS-Adobe-2.0\n', null], '''
+        %YAML 1.2
+        --- |
+        %!PS-Adobe-2.0
+        ...
+        %YAML 1.2
+        ---
+        # Empty
+        ...''');
+    });
+
+    test('[Example 9.6]', () {
+      expectYamlStreamLoads([
+        'Document',
+        null,
+        {'matches %': 20}
+      ], '''
+        Document
+        ---
+        # Empty
+        ...
+        %YAML 1.2
+        ---
+        matches %: 20''');
+    });
+  });
+
+  // Chapter 10: Recommended Schemas
+  group('10.1: Failsafe Schema', () {
+    test('[Example 10.1]', () {
+      expectYamlLoads({
+        'Block style': {
+          'Clark': 'Evans',
+          'Ingy': 'döt Net',
+          'Oren': 'Ben-Kiki'
+        },
+        'Flow style': {'Clark': 'Evans', 'Ingy': 'döt Net', 'Oren': 'Ben-Kiki'}
+      }, '''
+        Block style: !!map
+          Clark : Evans
+          Ingy  : döt Net
+          Oren  : Ben-Kiki
+
+        Flow style: !!map { Clark: Evans, Ingy: döt Net, Oren: Ben-Kiki }''');
+    });
+
+    test('[Example 10.2]', () {
+      expectYamlLoads({
+        'Block style': ['Clark Evans', 'Ingy döt Net', 'Oren Ben-Kiki'],
+        'Flow style': ['Clark Evans', 'Ingy döt Net', 'Oren Ben-Kiki']
+      }, '''
+        Block style: !!seq
+        - Clark Evans
+        - Ingy döt Net
+        - Oren Ben-Kiki
+
+        Flow style: !!seq [ Clark Evans, Ingy döt Net, Oren Ben-Kiki ]''');
+    });
+
+    test('[Example 10.3]', () {
+      expectYamlLoads({
+        'Block style': 'String: just a theory.',
+        'Flow style': 'String: just a theory.'
+      }, '''
+        Block style: !!str |-
+          String: just a theory.
+
+        Flow style: !!str "String: just a theory."''');
+    });
+  });
+
+  group('10.2: JSON Schema', () {
+    test('[Example 10.4]', () {
+      var doc = deepEqualsMap({'key with null value': null});
+      doc[null] = 'value for null key';
+      expectYamlStreamLoads([doc], '''
+        !!null null: value for null key
+        key with null value: !!null null''');
+    });
+
+    test('[Example 10.5]', () {
+      expectYamlStreamLoads([
+        {'YAML is a superset of JSON': true, 'Pluto is a planet': false}
+      ], '''
+        YAML is a superset of JSON: !!bool true
+        Pluto is a planet: !!bool false''');
+    });
+
+    test('[Example 10.6]', () {
+      expectYamlStreamLoads([
+        {'negative': -12, 'zero': 0, 'positive': 34}
+      ], '''
+        negative: !!int -12
+        zero: !!int 0
+        positive: !!int 34''');
+    });
+
+    test('[Example 10.7]', () {
+      expectYamlStreamLoads([
+        {
+          'negative': -1,
+          'zero': 0,
+          'positive': 23000,
+          'infinity': infinity,
+          'not a number': nan
+        }
+      ], '''
+        negative: !!float -1
+        zero: !!float 0
+        positive: !!float 2.3e4
+        infinity: !!float .inf
+        not a number: !!float .nan''');
+    }, skip: 'Fails for single digit float');
+
+    test('[Example 10.8]', () {
+      expectYamlStreamLoads([
+        {
+          'A null': null,
+          'Booleans': [true, false],
+          'Integers': [0, -0, 3, -19],
+          'Floats': [0, 0, 12000, -200000],
+          // Despite being invalid in the JSON schema, these values are valid in
+          // the core schema which this implementation supports.
+          'Invalid': [true, null, 7, 0x3A, 12.3]
+        }
+      ], '''
+        A null: null
+        Booleans: [ true, false ]
+        Integers: [ 0, -0, 3, -19 ]
+        Floats: [ 0., -0.0, 12e03, -2E+05 ]
+        Invalid: [ True, Null, 0o7, 0x3A, +12.3 ]''');
+    });
+  });
+
+  group('10.3: Core Schema', () {
+    test('[Example 10.9]', () {
+      expectYamlLoads({
+        'A null': null,
+        'Also a null': null,
+        'Not a null': '',
+        'Booleans': [true, true, false, false],
+        'Integers': [0, 7, 0x3A, -19],
+        'Floats': [0, 0, 0.5, 12000, -200000],
+        'Also floats': [infinity, -infinity, infinity, nan]
+      }, '''
+        A null: null
+        Also a null: # Empty
+        Not a null: ""
+        Booleans: [ true, True, false, FALSE ]
+        Integers: [ 0, 0o7, 0x3A, -19 ]
+        Floats: [ 0., -0.0, .5, +12e03, -2E+05 ]
+        Also floats: [ .inf, -.Inf, +.INF, .NAN ]''');
+    });
+  });
+
+  test('preserves key order', () {
+    const keys = ['a', 'b', 'c', 'd', 'e', 'f'];
+    var sanityCheckCount = 0;
+    for (var permutation in _generatePermutations(keys)) {
+      final yaml = permutation.map((key) => '$key: value').join('\n');
+      expect(loadYaml(yaml).keys.toList(), permutation);
+      sanityCheckCount++;
+    }
+    final expectedPermutationCount =
+        List.generate(keys.length, (i) => i + 1).reduce((n, i) => n * i);
+    expect(sanityCheckCount, expectedPermutationCount);
+  });
+}
+
+Iterable<List<String>> _generatePermutations(List<String> keys) sync* {
+  if (keys.length <= 1) {
+    yield keys;
+    return;
+  }
+  for (var i = 0; i < keys.length; i++) {
+    final first = keys[i];
+    final rest = <String>[...keys.sublist(0, i), ...keys.sublist(i + 1)];
+    for (var subPermutation in _generatePermutations(rest)) {
+      yield <String>[first, ...subPermutation];
+    }
+  }
+}

diff --git a/pkgs/yaml_edit/.gitignore b/pkgs/yaml_edit/.gitignore
new file mode 100644
index 0000000..7886c3d
--- /dev/null
+++ b/pkgs/yaml_edit/.gitignore

@@ -0,0 +1,3 @@
+/.dart_tool/
+/.packages
+/pubspec.lock

diff --git a/pkgs/yaml_edit/CHANGELOG.md b/pkgs/yaml_edit/CHANGELOG.md
new file mode 100644
index 0000000..9342e9f
--- /dev/null
+++ b/pkgs/yaml_edit/CHANGELOG.md

@@ -0,0 +1,95 @@
+## 2.2.2
+
+- Suppress warnings previously printed to `stdout` when parsing YAML internally.
+- Fix error thrown when inserting duplicate keys to different maps in the same
+  list.
+  ([#69](https://github.com/dart-lang/yaml_edit/issues/69))
+
+- Fix error thrown when inserting in nested list using `spliceList` method
+  ([#83](https://github.com/dart-lang/yaml_edit/issues/83))
+
+- Fix error thrown when string has spaces when applying `ScalarStyle.FOLDED`.
+  ([#41](https://github.com/dart-lang/yaml_edit/issues/41)). Resolves
+  ([[#86](https://github.com/dart-lang/yaml_edit/issues/86)]).
+
+- Require Dart 3.1
+
+- Move to `dart-lang/tools` monorepo.
+
+## 2.2.1
+
+- Require Dart 3.0
+- Fix removal of last key in blockmap when key has no value
+  ([#55](https://github.com/dart-lang/yaml_edit/issues/55)).
+
+## 2.2.0
+
+- Fix inconsistent line endings when inserting maps into a document using `\r\n`.
+  ([#65](https://github.com/dart-lang/yaml_edit/issues/65))
+
+- `AliasError` is changed to `AliasException` and exposed in the public API.
+
+  All node-mutating methods on `YamlEditor`, i.e. `update()`, `appendToList()`,
+  `prependToList()`, `insertIntoList()`, `spliceList()`, `remove()` will now
+  throw an exception instead of an error when encountering an alias on the path
+  to modify.
+
+  This allows catching and handling when this is happening.
+
+## 2.1.1
+
+- Require Dart 2.19
+
+## 2.1.0
+
+- **Breaking** `wrapAsYamlNode(value, collectionStyle, scalarStyle)` will apply
+  `collectionStyle` and `scalarStyle` recursively when wrapping a children of
+  `Map` and `List`.
+  While this may change the style of the YAML documents written by applications
+  that rely on the old behavior, such YAML documents should still be valid.
+  Hence, we hope it is reasonable to make this change in a minor release.
+- Fix for cases that can't be encoded correctly with
+  `scalarStyle: ScalarStyle.SINGLE_QUOTED`.
+- Fix YamlEditor `appendToList` and `insertIntoList` functions inserts new item into next yaml item
+  rather than at end of list.
+  ([#23](https://github.com/dart-lang/yaml_edit/issues/23))
+
+## 2.0.3
+
+- Updated the value of the pubspec `repository` field.
+
+## 2.0.2
+
+- Fix trailing whitespace after adding new key with block-value to map
+  ([#15](https://github.com/dart-lang/yaml_edit/issues/15)).
+- Updated `repository` and other meta-data in `pubspec.yaml`.
+
+## 2.0.1
+
+- License changed to BSD, as this package is now maintained by the Dart team.
+- Fixed minor lints.
+
+## 2.0.0
+
+- Migrated to null-safety.
+- API will no-longer return `null` in-place of a `YamlNode`, instead a
+  `YamlNode` with `YamlNode.value == null` should be used. These are easily
+  created with `wrapAsYamlNode(null)`.
+
+## 1.0.3
+
+- Fixed bug in adding an empty map as a map value.
+
+## 1.0.2
+
+- Throws an error if the final YAML after edit is not parsable.
+- Fixed bug in adding to empty map values, when it is followed by other content.
+
+## 1.0.1
+
+- Updated behavior surrounding list and map removal.
+- Fixed bug in dealing with empty values.
+
+## 1.0.0
+
+- Initial release.

diff --git a/pkgs/yaml_edit/LICENSE b/pkgs/yaml_edit/LICENSE
new file mode 100644
index 0000000..413ed83
--- /dev/null
+++ b/pkgs/yaml_edit/LICENSE

@@ -0,0 +1,26 @@
+Copyright 2020, the Dart project authors.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+    * Neither the name of Google LLC nor the names of its
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

diff --git a/pkgs/yaml_edit/README.md b/pkgs/yaml_edit/README.md
new file mode 100644
index 0000000..f10560b
--- /dev/null
+++ b/pkgs/yaml_edit/README.md

@@ -0,0 +1,61 @@
+[![Dart CI](https://github.com/dart-lang/yaml_edit/actions/workflows/test-package.yml/badge.svg)](https://github.com/dart-lang/yaml_edit/actions/workflows/test-package.yml)
+[![pub package](https://img.shields.io/pub/v/yaml_edit.svg)](https://pub.dev/packages/yaml_edit)
+[![package publisher](https://img.shields.io/pub/publisher/yaml_edit.svg)](https://pub.dev/packages/yaml_edit/publisher)
+[![Coverage Status](https://coveralls.io/repos/github/dart-lang/yaml_edit/badge.svg)](https://coveralls.io/github/dart-lang/yaml_edit)
+
+A library for [YAML](https://yaml.org) manipulation while preserving comments.
+
+## Usage
+
+A simple usage example:
+
+```dart
+import 'package:yaml_edit/yaml_edit.dart';
+
+void main() {
+  final yamlEditor = YamlEditor('{YAML: YAML}');
+  yamlEditor.update(['YAML'], "YAML Ain't Markup Language");
+  print(yamlEditor);
+  // Expected output:
+  // {YAML: YAML Ain't Markup Language}
+}
+```
+
+### Example: Converting JSON to YAML (block formatted)
+
+```dart
+void main() {
+  final jsonString = r'''
+{
+  "key": "value",
+  "list": [
+    "first",
+    "second",
+    "last entry in the list"
+  ],
+  "map": {
+    "multiline": "this is a fairly long string with\nline breaks..."
+  }
+}
+''';
+  final jsonValue = json.decode(jsonString);
+
+  // Convert jsonValue to YAML
+  final yamlEditor = YamlEditor('');
+  yamlEditor.update([], jsonValue);
+  print(yamlEditor.toString());
+}
+```
+
+## Testing
+
+Testing is done in two strategies: Unit testing (`/test/editor_test.dart`) and
+Golden testing (`/test/golden_test.dart`). More information on Golden testing
+and the input/output format can be found at `/test/testdata/README.md`.
+
+These tests are automatically run with `pub run test`.
+
+## Limitations
+
+1. Users are not allowed to define tags in the modifications.
+2. Map keys will always be added in the flow style.

diff --git a/pkgs/yaml_edit/analysis_options.yaml b/pkgs/yaml_edit/analysis_options.yaml
new file mode 100644
index 0000000..937e7fe
--- /dev/null
+++ b/pkgs/yaml_edit/analysis_options.yaml

@@ -0,0 +1,8 @@
+include: package:dart_flutter_team_lints/analysis_options.yaml
+
+analyzer:
+  errors:
+    inference_failure_on_collection_literal: ignore
+    inference_failure_on_function_invocation: ignore
+    inference_failure_on_function_return_type: ignore
+    inference_failure_on_instance_creation: ignore

diff --git a/pkgs/yaml_edit/example/example.dart b/pkgs/yaml_edit/example/example.dart
new file mode 100644
index 0000000..d49c39b
--- /dev/null
+++ b/pkgs/yaml_edit/example/example.dart

@@ -0,0 +1,12 @@
+import 'package:yaml_edit/yaml_edit.dart';
+
+void main() {
+  final doc = YamlEditor('''
+- 0 # comment 0
+- 1 # comment 1
+- 2 # comment 2
+''');
+  doc.remove([1]);
+
+  print(doc);
+}

diff --git a/pkgs/yaml_edit/example/json2yaml.dart b/pkgs/yaml_edit/example/json2yaml.dart
new file mode 100644
index 0000000..d6204d3
--- /dev/null
+++ b/pkgs/yaml_edit/example/json2yaml.dart

@@ -0,0 +1,28 @@
+// Copyright (c) 2023, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:convert' show json;
+
+import 'package:yaml_edit/yaml_edit.dart';
+
+void main() {
+  final jsonString = r'''
+{
+  "key": "value",
+  "list": [
+    "first",
+    "second",
+    "last entry in the list"
+  ],
+  "map": {
+    "multiline": "this is a fairly long string with\nline breaks..."
+  }
+}
+''';
+  final jsonValue = json.decode(jsonString);
+
+  final yamlEditor = YamlEditor('');
+  yamlEditor.update([], jsonValue);
+  print(yamlEditor.toString());
+}

diff --git a/pkgs/yaml_edit/lib/src/editor.dart b/pkgs/yaml_edit/lib/src/editor.dart
new file mode 100644
index 0000000..54775cc
--- /dev/null
+++ b/pkgs/yaml_edit/lib/src/editor.dart

@@ -0,0 +1,634 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:meta/meta.dart';
+import 'package:source_span/source_span.dart';
+import 'package:yaml/yaml.dart';
+
+import 'equality.dart';
+import 'errors.dart';
+import 'list_mutations.dart';
+import 'map_mutations.dart';
+import 'source_edit.dart';
+import 'strings.dart';
+import 'utils.dart';
+import 'wrap.dart';
+
+/// An interface for modifying [YAML][1] documents while preserving comments
+/// and whitespaces.
+///
+/// YAML parsing is supported by `package:yaml`, and modifications are performed
+/// as string operations. An error will be thrown if internal assertions fail -
+/// such a situation should be extremely rare, and should only occur with
+/// degenerate formatting.
+///
+/// Most modification methods require the user to pass in an `Iterable<Object>`
+/// path that holds the keys/indices to navigate to the element.
+///
+/// **Example:**
+/// ```yaml
+/// a: 1
+/// b: 2
+/// c:
+///   - 3
+///   - 4
+///   - {e: 5, f: [6, 7]}
+/// ```
+///
+/// To get to `7`, our path will be `['c', 2, 'f', 1]`. The path for the base
+/// object is the empty array `[]`. All modification methods will throw a
+/// [ArgumentError] if the path provided is invalid. Note also that that the
+/// order of elements in the path is important, and it should be arranged in
+/// order of calling, with the first element being the first key or index to be
+/// called.
+///
+/// In most modification methods, users are required to pass in a value to be
+/// used for updating the YAML tree. This value is only allowed to either be a
+/// valid scalar that is recognizable by YAML (i.e. `bool`, `String`, `List`,
+/// `Map`, `num`, `null`) or a [YamlNode]. Should the user want to specify
+/// the style to be applied to the value passed in, the user may wrap the value
+/// using [wrapAsYamlNode] while passing in the appropriate `scalarStyle` or
+/// `collectionStyle`. While we try to respect the style that is passed in,
+/// there will be instances where the formatting will not result in valid YAML,
+/// and as such we will fallback to a default formatting while preserving the
+/// content.
+///
+/// To dump the YAML after all the modifications have been completed, simply
+/// call [toString()].
+///
+/// [1]: https://yaml.org/
+@sealed
+class YamlEditor {
+  final List<SourceEdit> _edits = [];
+
+  /// List of [SourceEdit]s that have been applied to [_yaml] since the creation
+  /// of this instance, in chronological order. Intended to be compatible with
+  /// `package:analysis_server`.
+  ///
+  /// The [SourceEdit] objects can be serialized to JSON using the `toJSON`
+  /// function, deserialized using [SourceEdit.fromJson], and applied to a
+  /// string using the `apply` function. Multiple [SourceEdit]s can be applied
+  /// to a string using [SourceEdit.applyAll].
+  ///
+  /// For more information, refer to the [SourceEdit] class.
+  List<SourceEdit> get edits => [..._edits];
+
+  /// Current YAML string.
+  String _yaml;
+
+  /// Root node of YAML AST.
+  YamlNode _contents;
+
+  /// Stores the list of nodes in [_contents] that are connected by aliases.
+  ///
+  /// When a node is anchored with an alias and subsequently referenced,
+  /// the full content of the anchored node is thought to be copied in the
+  /// following references.
+  ///
+  /// **Example:**
+  /// ```dart
+  /// a: &SS Sammy Sosa
+  /// b: *SS
+  /// ```
+  ///
+  /// is equivalent to
+  ///
+  /// ```dart
+  /// a: Sammy Sosa
+  /// b: Sammy Sosa
+  /// ```
+  ///
+  /// As such, aliased nodes have to be treated with special caution when
+  /// any modification is taking place.
+  ///
+  /// See 7.1 Alias Nodes: https://yaml.org/spec/1.2/spec.html#id2786196
+  Set<YamlNode> _aliases = {};
+
+  /// Returns the current YAML string.
+  @override
+  String toString() => _yaml;
+
+  factory YamlEditor(String yaml) => YamlEditor._(yaml);
+
+  YamlEditor._(this._yaml) : _contents = loadYamlNode(_yaml) {
+    _initialize();
+  }
+
+  /// Traverses the YAML tree formed to detect alias nodes.
+  void _initialize() {
+    _aliases = {};
+
+    /// Performs a DFS on [_contents] to detect alias nodes.
+    final visited = <YamlNode>{};
+    void collectAliases(YamlNode node) {
+      if (visited.add(node)) {
+        if (node is YamlMap) {
+          node.nodes.forEach((key, value) {
+            collectAliases(key as YamlNode);
+            collectAliases(value);
+          });
+        } else if (node is YamlList) {
+          node.nodes.forEach(collectAliases);
+        }
+      } else {
+        _aliases.add(node);
+      }
+    }
+
+    collectAliases(_contents);
+  }
+
+  /// Parses the document to return [YamlNode] currently present at [path].
+  ///
+  /// If no [YamlNode]s exist at [path], the result of invoking the [orElse]
+  /// function is returned.
+  ///
+  /// If [orElse] is omitted, it defaults to throwing a [ArgumentError].
+  ///
+  /// To get a default value when [path] does not point to a value in the
+  /// [YamlNode]-tree, simply pass `orElse: () => ...`.
+  ///
+  /// **Example:** (using orElse)
+  /// ```dart
+  /// final myYamlEditor('{"key": "value"}');
+  /// final node = myYamlEditor.valueAt(
+  ///   ['invalid', 'path'],
+  ///   orElse: () => wrapAsYamlNode(null),
+  /// );
+  /// print(node.value); // null
+  /// ```
+  ///
+  /// **Example:** (common usage)
+  /// ```dart
+  ///   final doc = YamlEditor('''
+  /// a: 1
+  /// b:
+  ///   d: 4
+  ///   e: [5, 6, 7]
+  /// c: 3
+  /// ''');
+  /// print(doc.parseAt(['b', 'e', 2])); // 7
+  /// ```
+  /// The value returned by [parseAt] is invalidated when the documented is
+  /// mutated, as illustrated below:
+  ///
+  /// **Example:** (old [parseAt] value is invalidated)
+  /// ```dart
+  /// final doc = YamlEditor("YAML: YAML Ain't Markup Language");
+  /// final node = doc.parseAt(['YAML']);
+  ///
+  /// print(node.value); // Expected output: "YAML Ain't Markup Language"
+  ///
+  /// doc.update(['YAML'], 'YAML');
+  ///
+  /// final newNode = doc.parseAt(['YAML']);
+  ///
+  /// // Note that the value does not change
+  /// print(newNode.value); // "YAML"
+  /// print(node.value); // "YAML Ain't Markup Language"
+  /// ```
+  YamlNode parseAt(Iterable<Object?> path, {YamlNode Function()? orElse}) {
+    return _traverse(path, orElse: orElse);
+  }
+
+  /// Sets [value] in the [path].
+  ///
+  /// There is a subtle difference between [update] and [remove] followed by
+  /// an [insertIntoList], because [update] preserves comments at the same
+  /// level.
+  ///
+  /// Throws a [ArgumentError] if [path] is invalid.
+  ///
+  /// Throws an [AliasException] if a node on [path] is an alias or anchor.
+  ///
+  /// **Example:** (using [update])
+  /// ```dart
+  /// final doc = YamlEditor('''
+  ///   - 0
+  ///   - 1 # comment
+  ///   - 2
+  /// ''');
+  /// doc.update([1], 'test');
+  /// ```
+  ///
+  /// **Expected Output:**
+  /// ```yaml
+  ///   - 0
+  ///   - test # comment
+  ///   - 2
+  /// ```
+  ///
+  /// **Example:** (using [remove] and [insertIntoList])
+  /// ```dart
+  /// final doc2 = YamlEditor('''
+  ///   - 0
+  ///   - 1 # comment
+  ///   - 2
+  /// ''');
+  /// doc2.remove([1]);
+  /// doc2.insertIntoList([], 1, 'test');
+  /// ```
+  ///
+  /// **Expected Output:**
+  /// ```yaml
+  ///   - 0
+  ///   - test
+  ///   - 2
+  /// ```
+  void update(Iterable<Object?> path, Object? value) {
+    final valueNode = wrapAsYamlNode(value);
+
+    if (path.isEmpty) {
+      final start = _contents.span.start.offset;
+      final end = getContentSensitiveEnd(_contents);
+      final lineEnding = getLineEnding(_yaml);
+      final edit = SourceEdit(
+          start, end - start, yamlEncodeBlock(valueNode, 0, lineEnding));
+
+      return _performEdit(edit, path, valueNode);
+    }
+
+    final pathAsList = path.toList();
+    final collectionPath = pathAsList.take(path.length - 1);
+    final keyOrIndex = pathAsList.last;
+    final parentNode = _traverse(collectionPath, checkAlias: true);
+
+    if (parentNode is YamlList) {
+      if (keyOrIndex is! int) {
+        throw PathError(path, path, parentNode);
+      }
+      final expected = wrapAsYamlNode(
+        [...parentNode.nodes]..[keyOrIndex] = valueNode,
+      );
+
+      return _performEdit(updateInList(this, parentNode, keyOrIndex, valueNode),
+          collectionPath, expected);
+    }
+
+    if (parentNode is YamlMap) {
+      final expectedMap =
+          updatedYamlMap(parentNode, (nodes) => nodes[keyOrIndex] = valueNode);
+      return _performEdit(updateInMap(this, parentNode, keyOrIndex, valueNode),
+          collectionPath, expectedMap);
+    }
+
+    throw PathError.unexpected(
+        path, 'Scalar $parentNode does not have key $keyOrIndex');
+  }
+
+  /// Appends [value] to the list at [path].
+  ///
+  /// Throws a [ArgumentError] if the element at the given path is not a
+  /// [YamlList] or if the path is invalid.
+  ///
+  /// Throws an [AliasException] if a node on [path] is an alias or anchor.
+  ///
+  /// **Example:**
+  /// ```dart
+  /// final doc = YamlEditor('[0, 1]');
+  /// doc.appendToList([], 2); // [0, 1, 2]
+  /// ```
+  void appendToList(Iterable<Object?> path, Object? value) {
+    final yamlList = _traverseToList(path);
+
+    insertIntoList(path, yamlList.length, value);
+  }
+
+  /// Prepends [value] to the list at [path].
+  ///
+  /// Throws a [ArgumentError] if the element at the given path is not a
+  /// [YamlList] or if the path is invalid.
+  ///
+  /// Throws an [AliasException] if a node on [path] is an alias or anchor.
+  ///
+  /// **Example:**
+  /// ```dart
+  /// final doc = YamlEditor('[1, 2]');
+  /// doc.prependToList([], 0); // [0, 1, 2]
+  /// ```
+  void prependToList(Iterable<Object?> path, Object? value) {
+    insertIntoList(path, 0, value);
+  }
+
+  /// Inserts [value] into the list at [path].
+  ///
+  /// [index] must be non-negative and no greater than the list's length.
+  ///
+  /// Throws a [ArgumentError] if the element at the given path is not a
+  /// [YamlList] or if the path is invalid.
+  ///
+  /// Throws an [AliasException] if a node on [path] is an alias or anchor.
+  ///
+  /// **Example:**
+  /// ```dart
+  /// final doc = YamlEditor('[0, 2]');
+  /// doc.insertIntoList([], 1, 1); // [0, 1, 2]
+  /// ```
+  void insertIntoList(Iterable<Object?> path, int index, Object? value) {
+    final valueNode = wrapAsYamlNode(value);
+
+    final list = _traverseToList(path, checkAlias: true);
+    RangeError.checkValueInInterval(index, 0, list.length);
+
+    final edit = insertInList(this, list, index, valueNode);
+    final expected = wrapAsYamlNode(
+      [...list.nodes]..insert(index, valueNode),
+    );
+
+    _performEdit(edit, path, expected);
+  }
+
+  /// Changes the contents of the list at [path] by removing [deleteCount]
+  /// items at [index], and inserting [values] in-place. Returns the elements
+  /// that are deleted.
+  ///
+  /// [index] and [deleteCount] must be non-negative and [index] + [deleteCount]
+  /// must be no greater than the list's length.
+  ///
+  /// Throws a [ArgumentError] if the element at the given path is not a
+  /// [YamlList] or if the path is invalid.
+  ///
+  /// Throws an [AliasException] if a node on [path] is an alias or anchor.
+  ///
+  /// **Example:**
+  /// ```dart
+  /// final doc = YamlEditor('[Jan, March, April, June]');
+  /// doc.spliceList([], 1, 0, ['Feb']); // [Jan, Feb, March, April, June]
+  /// doc.spliceList([], 4, 1, ['May']); // [Jan, Feb, March, April, May]
+  /// ```
+  Iterable<YamlNode> spliceList(Iterable<Object?> path, int index,
+      int deleteCount, Iterable<Object?> values) {
+    final list = _traverseToList(path, checkAlias: true);
+
+    RangeError.checkValueInInterval(index, 0, list.length);
+    RangeError.checkValueInInterval(index + deleteCount, 0, list.length);
+
+    final nodesToRemove = list.nodes.getRange(index, index + deleteCount);
+
+    // Perform addition of elements before removal to avoid scenarios where
+    // a block list gets emptied out to {} to avoid changing collection styles
+    // where possible.
+
+    // Reverse [values] and insert them.
+    final reversedValues = values.toList().reversed;
+    for (final value in reversedValues) {
+      insertIntoList(path, index, value);
+    }
+
+    for (var i = 0; i < deleteCount; i++) {
+      remove([...path, index + values.length]);
+    }
+
+    return nodesToRemove;
+  }
+
+  /// Removes the node at [path]. Comments "belonging" to the node will be
+  /// removed while surrounding comments will be left untouched.
+  ///
+  /// Throws an [ArgumentError] if [path] is invalid.
+  ///
+  /// Throws an [AliasException] if a node on [path] is an alias or anchor.
+  ///
+  /// **Example:**
+  /// ```dart
+  /// final doc = YamlEditor('''
+  /// - 0 # comment 0
+  /// # comment A
+  /// - 1 # comment 1
+  /// # comment B
+  /// - 2 # comment 2
+  /// ''');
+  /// doc.remove([1]);
+  /// ```
+  ///
+  /// **Expected Result:**
+  /// ```dart
+  /// '''
+  /// - 0 # comment 0
+  /// # comment A
+  /// # comment B
+  /// - 2 # comment 2
+  /// '''
+  /// ```
+  YamlNode remove(Iterable<Object?> path) {
+    late SourceEdit edit;
+    late YamlNode expectedNode;
+    final nodeToRemove = _traverse(path, checkAlias: true);
+
+    if (path.isEmpty) {
+      edit = SourceEdit(0, _yaml.length, '');
+      expectedNode = wrapAsYamlNode(null);
+
+      /// Parsing an empty YAML document returns YamlScalar with value `null`.
+      _performEdit(edit, path, expectedNode);
+      return nodeToRemove;
+    }
+
+    final pathAsList = path.toList();
+    final collectionPath = pathAsList.take(path.length - 1);
+    final keyOrIndex = pathAsList.last;
+    final parentNode = _traverse(collectionPath);
+
+    if (parentNode is YamlList) {
+      edit = removeInList(this, parentNode, keyOrIndex as int);
+      expectedNode = wrapAsYamlNode(
+        [...parentNode.nodes]..removeAt(keyOrIndex),
+      );
+    } else if (parentNode is YamlMap) {
+      edit = removeInMap(this, parentNode, keyOrIndex);
+
+      expectedNode =
+          updatedYamlMap(parentNode, (nodes) => nodes.remove(keyOrIndex));
+    }
+
+    _performEdit(edit, collectionPath, expectedNode);
+
+    return nodeToRemove;
+  }
+
+  /// Traverses down [path] to return the [YamlNode] at [path] if successful.
+  ///
+  /// If no [YamlNode]s exist at [path], the result of invoking the [orElse]
+  /// function is returned.
+  ///
+  /// If [orElse] is omitted, it defaults to throwing a [PathError].
+  ///
+  /// If [checkAlias] is `true`, throw [AliasException] if an aliased node is
+  /// encountered.
+  YamlNode _traverse(Iterable<Object?> path,
+      {bool checkAlias = false, YamlNode Function()? orElse}) {
+    if (path.isEmpty) return _contents;
+
+    var currentNode = _contents;
+    final pathList = path.toList();
+
+    for (var i = 0; i < pathList.length; i++) {
+      final keyOrIndex = pathList[i];
+
+      if (checkAlias && _aliases.contains(currentNode)) {
+        throw AliasException(path, currentNode);
+      }
+
+      if (currentNode is YamlList) {
+        final list = currentNode;
+        if (!isValidIndex(keyOrIndex, list.length)) {
+          return _pathErrorOrElse(path, path.take(i + 1), list, orElse);
+        }
+
+        currentNode = list.nodes[keyOrIndex as int];
+      } else if (currentNode is YamlMap) {
+        final map = currentNode;
+
+        if (!containsKey(map, keyOrIndex)) {
+          return _pathErrorOrElse(path, path.take(i + 1), map, orElse);
+        }
+        final keyNode = getKeyNode(map, keyOrIndex);
+
+        if (checkAlias) {
+          if (_aliases.contains(keyNode)) throw AliasException(path, keyNode);
+        }
+
+        currentNode = map.nodes[keyNode]!;
+      } else {
+        return _pathErrorOrElse(path, path.take(i + 1), currentNode, orElse);
+      }
+    }
+
+    if (checkAlias) _assertNoChildAlias(path, currentNode);
+
+    return currentNode;
+  }
+
+  /// Throws a [PathError] if [orElse] is not provided, returns the result
+  /// of invoking the [orElse] function otherwise.
+  YamlNode _pathErrorOrElse(Iterable<Object?> path, Iterable<Object?> subPath,
+      YamlNode parent, YamlNode Function()? orElse) {
+    if (orElse == null) throw PathError(path, subPath, parent);
+    return orElse();
+  }
+
+  /// Asserts that [node] and none its children are aliases
+  void _assertNoChildAlias(Iterable<Object?> path, [YamlNode? node]) {
+    if (node == null) return _assertNoChildAlias(path, _traverse(path));
+    if (_aliases.contains(node)) throw AliasException(path, node);
+
+    if (node is YamlScalar) return;
+
+    if (node is YamlList) {
+      for (var i = 0; i < node.length; i++) {
+        final updatedPath = [...path, i];
+        _assertNoChildAlias(updatedPath, node.nodes[i]);
+      }
+    }
+
+    if (node is YamlMap) {
+      final keyList = node.keys.toList();
+      for (var i = 0; i < node.length; i++) {
+        final updatedPath = [...path, keyList[i]];
+        if (_aliases.contains(keyList[i])) {
+          throw AliasException(path, keyList[i] as YamlNode);
+        }
+        _assertNoChildAlias(updatedPath, node.nodes[keyList[i]]);
+      }
+    }
+  }
+
+  /// Traverses down the provided [path] to return the [YamlList] at [path].
+  ///
+  /// Convenience function to ensure that a [YamlList] is returned.
+  ///
+  /// Throws [ArgumentError] if the element at the given path is not a
+  /// [YamlList] or if the path is invalid. If [checkAlias] is `true`, and an
+  /// aliased node is encountered along [path], an [AliasException] will be
+  /// thrown.
+  YamlList _traverseToList(Iterable<Object?> path, {bool checkAlias = false}) {
+    final possibleList = _traverse(path, checkAlias: checkAlias);
+
+    if (possibleList is YamlList) {
+      return possibleList;
+    } else {
+      throw PathError.unexpected(
+          path, 'Path $path does not point to a YamlList!');
+    }
+  }
+
+  /// Utility method to replace the substring of [_yaml] according to [edit].
+  ///
+  /// When [_yaml] is modified with this method, the resulting string is parsed
+  /// and reloaded and traversed down [path] to ensure that the reloaded YAML
+  /// tree is equal to our expectations by deep equality of values. Throws an
+  /// [AssertionError] if the two trees do not match.
+  void _performEdit(
+      SourceEdit edit, Iterable<Object?> path, YamlNode expectedNode) {
+    final expectedTree = _deepModify(_contents, path, [], expectedNode);
+    final initialYaml = _yaml;
+    _yaml = edit.apply(_yaml);
+
+    try {
+      _initialize();
+    } on YamlException {
+      throw createAssertionError(
+          'Failed to produce valid YAML after modification.',
+          initialYaml,
+          _yaml);
+    }
+
+    final actualTree = withYamlWarningCallback(() => loadYamlNode(_yaml));
+    if (!deepEquals(actualTree, expectedTree)) {
+      throw createAssertionError(
+          'Modification did not result in expected result.',
+          initialYaml,
+          _yaml);
+    }
+
+    _contents = actualTree;
+    _edits.add(edit);
+  }
+
+  /// Utility method to produce an updated YAML tree equivalent to converting
+  /// the [YamlNode] at [path] to be [expectedNode]. [subPath] holds the portion
+  /// of [path] that has been traversed thus far.
+  ///
+  /// Throws a [PathError] if path is invalid.
+  ///
+  /// When called, it creates a new [YamlNode] of the same type as [tree], and
+  /// copies its children over, except for the child that is on the path. Doing
+  /// so allows us to "update" the immutable [YamlNode] without having to clone
+  /// the whole tree.
+  ///
+  /// [SourceSpan]s in this new tree are not guaranteed to be accurate.
+  YamlNode _deepModify(YamlNode tree, Iterable<Object?> path,
+      Iterable<Object?> subPath, YamlNode expectedNode) {
+    RangeError.checkValueInInterval(subPath.length, 0, path.length);
+
+    if (path.length == subPath.length) return expectedNode;
+
+    final keyOrIndex = path.elementAt(subPath.length);
+
+    if (tree is YamlList) {
+      if (!isValidIndex(keyOrIndex, tree.length)) {
+        throw PathError(path, subPath, tree);
+      }
+
+      return wrapAsYamlNode([...tree.nodes]..[keyOrIndex as int] = _deepModify(
+          tree.nodes[keyOrIndex],
+          path,
+          path.take(subPath.length + 1),
+          expectedNode));
+    }
+
+    if (tree is YamlMap) {
+      return updatedYamlMap(
+          tree,
+          (nodes) => nodes[keyOrIndex] = _deepModify(
+              nodes[keyOrIndex] as YamlNode,
+              path,
+              path.take(subPath.length + 1),
+              expectedNode));
+    }
+
+    /// Should not ever reach here.
+    throw PathError(path, subPath, tree);
+  }
+}

diff --git a/pkgs/yaml_edit/lib/src/equality.dart b/pkgs/yaml_edit/lib/src/equality.dart
new file mode 100644
index 0000000..0c6a952
--- /dev/null
+++ b/pkgs/yaml_edit/lib/src/equality.dart

@@ -0,0 +1,116 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:collection';
+
+import 'package:collection/collection.dart';
+import 'package:yaml/yaml.dart';
+
+/// Creates a map that uses our custom [deepEquals] and [deepHashCode] functions
+/// to determine equality.
+Map<K, V> deepEqualsMap<K, V>() =>
+    LinkedHashMap(equals: deepEquals, hashCode: deepHashCode);
+
+/// Compares two [Object]s for deep equality. This implementation differs from
+/// `package:yaml`'s deep equality notation by allowing for comparison of
+/// non-scalar map keys.
+bool deepEquals(dynamic obj1, dynamic obj2) {
+  if (obj1 is YamlNode) obj1 = obj1.value;
+  if (obj2 is YamlNode) obj2 = obj2.value;
+
+  if (obj1 is Map && obj2 is Map) {
+    return mapDeepEquals(obj1, obj2);
+  }
+
+  if (obj1 is List && obj2 is List) {
+    return listDeepEquals(obj1, obj2);
+  }
+
+  return obj1 == obj2;
+}
+
+/// Compares two [List]s for deep equality.
+bool listDeepEquals(List list1, List list2) {
+  if (list1.length != list2.length) return false;
+
+  if (list1 is YamlList) list1 = list1.nodes;
+  if (list2 is YamlList) list2 = list2.nodes;
+
+  for (var i = 0; i < list1.length; i++) {
+    if (!deepEquals(list1[i], list2[i])) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+/// Compares two [Map]s for deep equality. Differs from `package:yaml`'s deep
+/// equality notation by allowing for comparison of non-scalar map keys.
+bool mapDeepEquals(Map map1, Map map2) {
+  if (map1.length != map2.length) return false;
+
+  if (map1 is YamlList) map1 = (map1 as YamlMap).nodes;
+  if (map2 is YamlList) map2 = (map2 as YamlMap).nodes;
+
+  return map1.keys.every((key) {
+    if (!containsKey(map2, key)) return false;
+
+    /// Because two keys may be equal by deep equality but using one key on the
+    /// other map might not get a hit since they may not be both using our
+    /// [deepEqualsMap].
+    final key2 = getKey(map2, key);
+
+    if (!deepEquals(map1[key], map2[key2])) {
+      return false;
+    }
+
+    return true;
+  });
+}
+
+/// Returns a hashcode for [value] such that structures that are equal by
+/// [deepEquals] will have the same hash code.
+int deepHashCode(Object? value) {
+  if (value is Map) {
+    const equality = UnorderedIterableEquality();
+    return equality.hash(value.keys.map(deepHashCode)) ^
+        equality.hash(value.values.map(deepHashCode));
+  } else if (value is Iterable) {
+    return const IterableEquality().hash(value.map(deepHashCode));
+  } else if (value is YamlScalar) {
+    return (value.value as Object?).hashCode;
+  }
+
+  return value.hashCode;
+}
+
+/// Returns the [YamlNode] corresponding to the provided [key].
+YamlNode getKeyNode(YamlMap map, Object? key) {
+  return map.nodes.keys.firstWhere((node) => deepEquals(node, key)) as YamlNode;
+}
+
+/// Returns the [YamlNode] after the [YamlNode] corresponding to the provided
+/// [key].
+YamlNode? getNextKeyNode(YamlMap map, Object? key) {
+  final keyIterator = map.nodes.keys.iterator;
+  while (keyIterator.moveNext()) {
+    if (deepEquals(keyIterator.current, key) && keyIterator.moveNext()) {
+      return keyIterator.current as YamlNode?;
+    }
+  }
+
+  return null;
+}
+
+/// Returns the key in [map] that is equal to the provided [key] by the notion
+/// of deep equality.
+Object? getKey(Map map, Object? key) {
+  return map.keys.firstWhere((k) => deepEquals(k, key));
+}
+
+/// Checks if [map] has any keys equal to the provided [key] by deep equality.
+bool containsKey(Map map, Object? key) {
+  return map.keys.where((node) => deepEquals(node, key)).isNotEmpty;
+}

diff --git a/pkgs/yaml_edit/lib/src/errors.dart b/pkgs/yaml_edit/lib/src/errors.dart
new file mode 100644
index 0000000..0e60dd8
--- /dev/null
+++ b/pkgs/yaml_edit/lib/src/errors.dart

@@ -0,0 +1,99 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:meta/meta.dart';
+import 'package:yaml/yaml.dart';
+
+/// Error thrown when a function is passed an invalid path.
+@sealed
+class PathError extends ArgumentError {
+  /// The full path that caused the error
+  final Iterable<Object?> path;
+
+  /// The subpath that caused the error
+  final Iterable<Object?> subPath;
+
+  /// The last element of [path] that could be traversed.
+  YamlNode? parent;
+
+  PathError(this.path, this.subPath, this.parent, [String? message])
+      : super.value(subPath, 'path', message);
+
+  PathError.unexpected(this.path, String message)
+      : subPath = path,
+        super(message);
+
+  @override
+  String toString() {
+    if (message == null) {
+      var errorMessage = 'Failed to traverse to subpath $subPath!';
+
+      if (subPath.isNotEmpty) {
+        errorMessage +=
+            ' Parent $parent does not contain key or index ${subPath.last}';
+      }
+
+      return 'Invalid path: $path. $errorMessage.';
+    }
+
+    return 'Invalid path: $path. $message';
+  }
+}
+
+/// Exception thrown when the path contains an alias along the way.
+///
+/// When a path contains an aliased node, the behavior becomes less well-defined
+/// because we cannot be certain if the user wishes for the change to propagate
+/// throughout all the other aliased nodes, or if the user wishes for only that
+/// particular node to be modified. As such, [AliasException] reflects the
+/// detection that our change will impact an alias, and we do not intend on
+/// supporting such changes for the foreseeable future.
+@sealed
+class AliasException extends FormatException {
+  /// The path that caused the error
+  final Iterable<Object?> path;
+
+  /// The anchor node of the alias
+  final YamlNode anchor;
+
+  AliasException(this.path, this.anchor)
+      : super('Encountered an alias node along $path! '
+            'Alias nodes are nodes that refer to a previously serialized '
+            'nodes, and are denoted by either the "*" or the "&" indicators in '
+            'the original YAML. As the resulting behavior of mutations on '
+            'these nodes is not well-defined, the operation will not be '
+            'supported by this library.\n\n'
+            '${anchor.span.message('The alias was first defined here.')}');
+}
+
+/// Error thrown when an assertion about the YAML fails. Extends
+/// [AssertionError] to override the [toString] method for pretty printing.
+class _YamlAssertionError extends AssertionError {
+  _YamlAssertionError(super.message);
+
+  @override
+  String toString() {
+    if (message != null) {
+      return 'Assertion failed: $message';
+    }
+    return 'Assertion failed';
+  }
+}
+
+/// Throws an [AssertionError] with the given [message], and format
+/// [oldYaml] and [newYaml] for information.
+Error createAssertionError(String message, String oldYaml, String newYaml) {
+  return _YamlAssertionError('''
+(package:yaml_edit) $message
+
+# YAML before edit:
+> ${oldYaml.replaceAll('\n', '\n> ')}
+
+# YAML after edit:
+> ${newYaml.replaceAll('\n', '\n> ')}
+
+Please file an issue at:
+https://github.com/dart-lang/yaml_edit/issues/new?labels=bug
+''');
+}

diff --git a/pkgs/yaml_edit/lib/src/list_mutations.dart b/pkgs/yaml_edit/lib/src/list_mutations.dart
new file mode 100644
index 0000000..17da6dd
--- /dev/null
+++ b/pkgs/yaml_edit/lib/src/list_mutations.dart

@@ -0,0 +1,403 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:yaml/yaml.dart';
+
+import 'editor.dart';
+import 'source_edit.dart';
+import 'strings.dart';
+import 'utils.dart';
+import 'wrap.dart';
+
+/// Returns a [SourceEdit] describing the change to be made on [yamlEdit] to
+/// achieve the effect of setting the element at [index] to [newValue] when
+/// re-parsed.
+SourceEdit updateInList(
+    YamlEditor yamlEdit, YamlList list, int index, YamlNode newValue) {
+  RangeError.checkValueInInterval(index, 0, list.length - 1);
+
+  final currValue = list.nodes[index];
+  var offset = currValue.span.start.offset;
+  final yaml = yamlEdit.toString();
+  String valueString;
+
+  /// We do not use [_formatNewBlock] since we want to only replace the contents
+  /// of this node while preserving comments/whitespace, while [_formatNewBlock]
+  /// produces a string representation of a new node.
+  if (list.style == CollectionStyle.BLOCK) {
+    final listIndentation = getListIndentation(yaml, list);
+    final indentation = listIndentation + getIndentation(yamlEdit);
+    final lineEnding = getLineEnding(yaml);
+    valueString =
+        yamlEncodeBlock(wrapAsYamlNode(newValue), indentation, lineEnding);
+
+    /// We prefer the compact nested notation for collections.
+    ///
+    /// By virtue of [yamlEncodeBlockString], collections automatically
+    /// have the necessary line endings.
+    if ((newValue is List && (newValue as List).isNotEmpty) ||
+        (newValue is Map && (newValue as Map).isNotEmpty)) {
+      valueString = valueString.substring(indentation);
+    } else if (currValue.collectionStyle == CollectionStyle.BLOCK) {
+      valueString += lineEnding;
+    }
+
+    var end = getContentSensitiveEnd(currValue);
+    if (end <= offset) {
+      offset++;
+      end = offset;
+      valueString = ' $valueString';
+    }
+
+    return SourceEdit(offset, end - offset, valueString);
+  } else {
+    valueString = yamlEncodeFlow(newValue);
+    return SourceEdit(offset, currValue.span.length, valueString);
+  }
+}
+
+/// Returns a [SourceEdit] describing the change to be made on [yamlEdit] to
+/// achieve the effect of appending [item] to the list.
+SourceEdit appendIntoList(YamlEditor yamlEdit, YamlList list, YamlNode item) {
+  if (list.style == CollectionStyle.FLOW) {
+    return _appendToFlowList(yamlEdit, list, item);
+  } else {
+    return _appendToBlockList(yamlEdit, list, item);
+  }
+}
+
+/// Returns a [SourceEdit] describing the change to be made on [yamlEdit] to
+/// achieve the effect of inserting [item] to the list at [index].
+SourceEdit insertInList(
+    YamlEditor yamlEdit, YamlList list, int index, YamlNode item) {
+  RangeError.checkValueInInterval(index, 0, list.length);
+
+  /// We call the append method if the user wants to append it to the end of the
+  /// list because appending requires different techniques.
+  if (index == list.length) {
+    return appendIntoList(yamlEdit, list, item);
+  } else {
+    if (list.style == CollectionStyle.FLOW) {
+      return _insertInFlowList(yamlEdit, list, index, item);
+    } else {
+      return _insertInBlockList(yamlEdit, list, index, item);
+    }
+  }
+}
+
+/// Returns a [SourceEdit] describing the change to be made on [yamlEdit] to
+/// achieve the effect of removing the element at [index] when re-parsed.
+SourceEdit removeInList(YamlEditor yamlEdit, YamlList list, int index) {
+  final nodeToRemove = list.nodes[index];
+
+  if (list.style == CollectionStyle.FLOW) {
+    return _removeFromFlowList(yamlEdit, list, nodeToRemove, index);
+  } else {
+    return _removeFromBlockList(yamlEdit, list, nodeToRemove, index);
+  }
+}
+
+/// Returns a [SourceEdit] describing the change to be made on [yamlEdit] to
+/// achieve the effect of addition [item] into [list], noting that this is a
+/// flow list.
+SourceEdit _appendToFlowList(
+    YamlEditor yamlEdit, YamlList list, YamlNode item) {
+  final valueString = _formatNewFlow(list, item, true);
+  return SourceEdit(list.span.end.offset - 1, 0, valueString);
+}
+
+/// Returns a [SourceEdit] describing the change to be made on [yamlEdit] to
+/// achieve the effect of addition [item] into [list], noting that this is a
+/// block list.
+SourceEdit _appendToBlockList(
+    YamlEditor yamlEdit, YamlList list, YamlNode item) {
+  var (indentSize, valueToIndent) = _formatNewBlock(yamlEdit, list, item);
+  var formattedValue = '${' ' * indentSize}$valueToIndent';
+
+  final yaml = yamlEdit.toString();
+  var offset = list.span.end.offset;
+
+  // Adjusts offset to after the trailing newline of the last entry, if it
+  // exists
+  if (list.isNotEmpty) {
+    final lastValueSpanEnd = list.nodes.last.span.end.offset;
+    final nextNewLineIndex = yaml.indexOf('\n', lastValueSpanEnd - 1);
+    if (nextNewLineIndex == -1) {
+      formattedValue = getLineEnding(yaml) + formattedValue;
+    } else {
+      offset = nextNewLineIndex + 1;
+    }
+  }
+
+  return SourceEdit(offset, 0, formattedValue);
+}
+
+/// Formats [item] into a new node for block lists.
+(int indentSize, String valueStringToIndent) _formatNewBlock(
+    YamlEditor yamlEdit, YamlList list, YamlNode item) {
+  final yaml = yamlEdit.toString();
+  final listIndentation = getListIndentation(yaml, list);
+  final newIndentation = listIndentation + getIndentation(yamlEdit);
+  final lineEnding = getLineEnding(yaml);
+
+  var valueString = yamlEncodeBlock(item, newIndentation, lineEnding);
+  if (isCollection(item) && !isFlowYamlCollectionNode(item) && !isEmpty(item)) {
+    valueString = valueString.substring(newIndentation);
+  }
+
+  return (listIndentation, '- $valueString$lineEnding');
+}
+
+/// Formats [item] into a new node for flow lists.
+String _formatNewFlow(YamlList list, YamlNode item, [bool isLast = false]) {
+  var valueString = yamlEncodeFlow(item);
+  if (list.isNotEmpty) {
+    if (isLast) {
+      valueString = ', $valueString';
+    } else {
+      valueString += ', ';
+    }
+  }
+
+  return valueString;
+}
+
+/// Returns a [SourceEdit] describing the change to be made on [yamlEdit] to
+/// achieve the effect of inserting [item] into [list] at [index], noting that
+/// this is a block list.
+///
+/// [index] should be non-negative and less than or equal to `list.length`.
+SourceEdit _insertInBlockList(
+    YamlEditor yamlEdit, YamlList list, int index, YamlNode item) {
+  RangeError.checkValueInInterval(index, 0, list.length);
+
+  if (index == list.length) return _appendToBlockList(yamlEdit, list, item);
+
+  var (indentSize, formattedValue) = _formatNewBlock(yamlEdit, list, item);
+
+  final currNode = list.nodes[index];
+  final currNodeStart = currNode.span.start.offset;
+  final yaml = yamlEdit.toString();
+
+  final currSequenceOffset = yaml.lastIndexOf('-', currNodeStart - 1);
+
+  final (isNested, offset) = _isNestedInBlockList(currSequenceOffset, yaml);
+
+  /// We have to get rid of the left indentation applied by default
+  if (isNested && index == 0) {
+    /// The [insertionIndex] will be equal to the start of
+    /// [currentSequenceOffset] of the element we are inserting before in most
+    /// cases.
+    ///
+    /// Example:
+    ///
+    ///   - - value
+    ///     ^ Inserting before this and we get rid of indent
+    ///
+    /// If not, we need to account for the space between them that is not an
+    /// indent.
+    ///
+    /// Example:
+    ///
+    ///   -   - value
+    ///       ^ Inserting before this and we get rid of indent. But also account
+    ///         for space in between
+    final leftPad = currSequenceOffset - offset;
+    final padding = ' ' * leftPad;
+
+    final indent = ' ' * (indentSize - leftPad);
+
+    // Give the indent to the first element
+    formattedValue = '$padding${formattedValue.trimLeft()}$indent';
+  } else {
+    final indent = ' ' * indentSize; // Calculate indent normally
+    formattedValue = '$indent$formattedValue';
+  }
+
+  return SourceEdit(offset, 0, formattedValue);
+}
+
+/// Determines if the list containing an element is nested within another list.
+/// The [currentSequenceOffset] indicates the index of the element's `-` and
+/// [yaml] represents the entire yaml document.
+///
+/// ```yaml
+/// # Returns true
+/// - - value
+///
+/// # Returns true
+/// -       - value
+///
+/// # Returns false
+/// key:
+///   - value
+///
+/// # Returns false. Even though nested, a "\n" precedes the previous "-"
+/// -
+///   - value
+/// ```
+(bool isNested, int offset) _isNestedInBlockList(
+    int currentSequenceOffset, String yaml) {
+  final startIndex = currentSequenceOffset - 1;
+
+  /// Indicates the element we are inserting before is at index `0` of the list
+  /// at the root of the yaml
+  ///
+  /// Example:
+  ///
+  /// - foo
+  /// ^ Inserting before this
+  if (startIndex < 0) return (false, 0);
+
+  final newLineStart = yaml.lastIndexOf('\n', startIndex);
+  final seqStart = yaml.lastIndexOf('-', startIndex);
+
+  /// Indicates that a `\n` is closer to the last `-`. Meaning this list is not
+  /// nested.
+  ///
+  /// Example:
+  ///
+  ///   key:
+  ///     - value
+  ///     ^ Inserting before this and we need to keep the indent.
+  ///
+  /// Also this list may be nested but the nested list starts its indent after
+  /// a new line.
+  ///
+  /// Example:
+  ///
+  ///   -
+  ///     - value
+  ///     ^ Inserting before this and we need to keep the indent.
+  if (newLineStart >= seqStart) {
+    return (false, newLineStart + 1);
+  }
+
+  return (true, seqStart + 2); // Inclusive of space
+}
+
+/// Returns a [SourceEdit] describing the change to be made on [yamlEdit] to
+/// achieve the effect of inserting [item] into [list] at [index], noting that
+/// this is a flow list.
+///
+/// [index] should be non-negative and less than or equal to `list.length`.
+SourceEdit _insertInFlowList(
+    YamlEditor yamlEdit, YamlList list, int index, YamlNode item) {
+  RangeError.checkValueInInterval(index, 0, list.length);
+
+  if (index == list.length) return _appendToFlowList(yamlEdit, list, item);
+
+  final formattedValue = _formatNewFlow(list, item);
+
+  final yaml = yamlEdit.toString();
+  final currNode = list.nodes[index];
+  final currNodeStart = currNode.span.start.offset;
+  var start = yaml.lastIndexOf(RegExp(r',|\['), currNodeStart - 1) + 1;
+  if (yaml[start] == ' ') start++;
+
+  return SourceEdit(start, 0, formattedValue);
+}
+
+/// Returns a [SourceEdit] describing the change to be made on [yamlEdit] to
+/// achieve the effect of removing [nodeToRemove] from [list], noting that this
+/// is a block list.
+///
+/// [index] should be non-negative and less than or equal to `list.length`.
+SourceEdit _removeFromBlockList(
+    YamlEditor yamlEdit, YamlList list, YamlNode nodeToRemove, int index) {
+  RangeError.checkValueInInterval(index, 0, list.length - 1);
+
+  var end = getContentSensitiveEnd(nodeToRemove);
+
+  /// If we are removing the last element in a block list, convert it into a
+  /// flow empty list.
+  if (list.length == 1) {
+    final start = list.span.start.offset;
+
+    return SourceEdit(start, end - start, '[]');
+  }
+
+  final yaml = yamlEdit.toString();
+  final span = nodeToRemove.span;
+
+  /// Adjust the end to clear the new line after the end too.
+  ///
+  /// We do this because we suspect that our users will want the inline
+  /// comments to disappear too.
+  final nextNewLine = yaml.indexOf('\n', end);
+  if (nextNewLine != -1) {
+    end = nextNewLine + 1;
+  }
+
+  /// If the value is empty
+  if (span.length == 0) {
+    var start = span.start.offset;
+    return SourceEdit(start, end - start, '');
+  }
+
+  /// -1 accounts for the fact that the content can start with a dash
+  var start = yaml.lastIndexOf('-', span.start.offset - 1);
+
+  /// Check if there is a `-` before the node
+  if (start > 0) {
+    final lastHyphen = yaml.lastIndexOf('-', start - 1);
+    final lastNewLine = yaml.lastIndexOf('\n', start - 1);
+    if (lastHyphen > lastNewLine) {
+      start = lastHyphen + 2;
+
+      /// If there is a `-` before the node, we need to check if we have
+      /// to update the indentation of the next node.
+      if (index < list.length - 1) {
+        /// Since [end] is currently set to the next new line after the current
+        /// node, check if we see a possible comment first, or a hyphen first.
+        /// Note that no actual content can appear here.
+        ///
+        /// We check this way because the start of a span in a block list is
+        /// the start of its value, and checking from the back leaves us
+        /// easily confused if there are comments that have dashes in them.
+        final nextHash = yaml.indexOf('#', end);
+        final nextHyphen = yaml.indexOf('-', end);
+        final nextNewLine = yaml.indexOf('\n', end);
+
+        /// If [end] is on the same line as the hyphen of the next node
+        if ((nextHash == -1 || nextHyphen < nextHash) &&
+            nextHyphen < nextNewLine) {
+          end = nextHyphen;
+        }
+      }
+    } else if (lastNewLine > lastHyphen) {
+      start = lastNewLine + 1;
+    }
+  }
+
+  return SourceEdit(start, end - start, '');
+}
+
+/// Returns a [SourceEdit] describing the change to be made on [yamlEdit] to
+/// achieve the effect of removing [nodeToRemove] from [list], noting that this
+/// is a flow list.
+///
+/// [index] should be non-negative and less than or equal to `list.length`.
+SourceEdit _removeFromFlowList(
+    YamlEditor yamlEdit, YamlList list, YamlNode nodeToRemove, int index) {
+  RangeError.checkValueInInterval(index, 0, list.length - 1);
+
+  final span = nodeToRemove.span;
+  final yaml = yamlEdit.toString();
+  var start = span.start.offset;
+  var end = span.end.offset;
+
+  if (index == 0) {
+    start = yaml.lastIndexOf('[', start - 1) + 1;
+    if (index == list.length - 1) {
+      end = yaml.indexOf(']', end);
+    } else {
+      end = yaml.indexOf(',', end) + 1;
+    }
+  } else {
+    start = yaml.lastIndexOf(',', start - 1);
+  }
+
+  return SourceEdit(start, end - start, '');
+}

diff --git a/pkgs/yaml_edit/lib/src/map_mutations.dart b/pkgs/yaml_edit/lib/src/map_mutations.dart
new file mode 100644
index 0000000..46e8c79
--- /dev/null
+++ b/pkgs/yaml_edit/lib/src/map_mutations.dart

@@ -0,0 +1,257 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:yaml/yaml.dart';
+
+import 'editor.dart';
+import 'equality.dart';
+import 'source_edit.dart';
+import 'strings.dart';
+import 'utils.dart';
+import 'wrap.dart';
+
+/// Performs the string operation on [yamlEdit] to achieve the effect of setting
+/// the element at [key] to [newValue] when re-parsed.
+SourceEdit updateInMap(
+    YamlEditor yamlEdit, YamlMap map, Object? key, YamlNode newValue) {
+  if (!containsKey(map, key)) {
+    final keyNode = wrapAsYamlNode(key);
+
+    if (map.style == CollectionStyle.FLOW) {
+      return _addToFlowMap(yamlEdit, map, keyNode, newValue);
+    } else {
+      return _addToBlockMap(yamlEdit, map, keyNode, newValue);
+    }
+  } else {
+    if (map.style == CollectionStyle.FLOW) {
+      return _replaceInFlowMap(yamlEdit, map, key, newValue);
+    } else {
+      return _replaceInBlockMap(yamlEdit, map, key, newValue);
+    }
+  }
+}
+
+/// Performs the string operation on [yamlEdit] to achieve the effect of
+/// removing the element at [key] when re-parsed.
+SourceEdit removeInMap(YamlEditor yamlEdit, YamlMap map, Object? key) {
+  assert(containsKey(map, key));
+  final keyNode = getKeyNode(map, key);
+  final valueNode = map.nodes[keyNode]!;
+
+  if (map.style == CollectionStyle.FLOW) {
+    return _removeFromFlowMap(yamlEdit, map, keyNode, valueNode);
+  } else {
+    return _removeFromBlockMap(yamlEdit, map, keyNode, valueNode);
+  }
+}
+
+/// Performs the string operation on [yamlEdit] to achieve the effect of adding
+/// the [key]:[newValue] pair when reparsed, bearing in mind that this is a
+/// block map.
+SourceEdit _addToBlockMap(
+    YamlEditor yamlEdit, YamlMap map, Object key, YamlNode newValue) {
+  final yaml = yamlEdit.toString();
+  final newIndentation =
+      getMapIndentation(yaml, map) + getIndentation(yamlEdit);
+  final keyString = yamlEncodeFlow(wrapAsYamlNode(key));
+  final lineEnding = getLineEnding(yaml);
+
+  var formattedValue = ' ' * getMapIndentation(yaml, map);
+  var offset = map.span.end.offset;
+
+  final insertionIndex = getMapInsertionIndex(map, keyString);
+
+  if (map.isNotEmpty) {
+    /// Adjusts offset to after the trailing newline of the last entry, if it
+    /// exists
+    if (insertionIndex == map.length) {
+      final lastValueSpanEnd = getContentSensitiveEnd(map.nodes.values.last);
+      final nextNewLineIndex = yaml.indexOf('\n', lastValueSpanEnd);
+
+      if (nextNewLineIndex != -1) {
+        offset = nextNewLineIndex + 1;
+      } else {
+        formattedValue = lineEnding + formattedValue;
+      }
+    } else {
+      final keyAtIndex = map.nodes.keys.toList()[insertionIndex] as YamlNode;
+      final keySpanStart = keyAtIndex.span.start.offset;
+      final prevNewLineIndex = yaml.lastIndexOf('\n', keySpanStart);
+
+      offset = prevNewLineIndex + 1;
+    }
+  }
+
+  var valueString = yamlEncodeBlock(newValue, newIndentation, lineEnding);
+  if (isCollection(newValue) &&
+      !isFlowYamlCollectionNode(newValue) &&
+      !isEmpty(newValue)) {
+    formattedValue += '$keyString:$lineEnding$valueString$lineEnding';
+  } else {
+    formattedValue += '$keyString: $valueString$lineEnding';
+  }
+
+  return SourceEdit(offset, 0, formattedValue);
+}
+
+/// Performs the string operation on [yamlEdit] to achieve the effect of adding
+/// the [keyNode]:[newValue] pair when reparsed, bearing in mind that this is a
+/// flow map.
+SourceEdit _addToFlowMap(
+    YamlEditor yamlEdit, YamlMap map, YamlNode keyNode, YamlNode newValue) {
+  final keyString = yamlEncodeFlow(keyNode);
+  final valueString = yamlEncodeFlow(newValue);
+
+  // The -1 accounts for the closing bracket.
+  if (map.isEmpty) {
+    return SourceEdit(map.span.end.offset - 1, 0, '$keyString: $valueString');
+  }
+
+  final insertionIndex = getMapInsertionIndex(map, keyString);
+
+  if (insertionIndex == map.length) {
+    return SourceEdit(map.span.end.offset - 1, 0, ', $keyString: $valueString');
+  }
+
+  final insertionOffset =
+      (map.nodes.keys.toList()[insertionIndex] as YamlNode).span.start.offset;
+
+  return SourceEdit(insertionOffset, 0, '$keyString: $valueString, ');
+}
+
+/// Performs the string operation on [yamlEdit] to achieve the effect of
+/// replacing the value at [key] with [newValue] when reparsed, bearing in mind
+/// that this is a block map.
+SourceEdit _replaceInBlockMap(
+    YamlEditor yamlEdit, YamlMap map, Object? key, YamlNode newValue) {
+  final yaml = yamlEdit.toString();
+  final lineEnding = getLineEnding(yaml);
+  final newIndentation =
+      getMapIndentation(yaml, map) + getIndentation(yamlEdit);
+
+  final keyNode = getKeyNode(map, key);
+  var valueAsString =
+      yamlEncodeBlock(wrapAsYamlNode(newValue), newIndentation, lineEnding);
+  if (isCollection(newValue) &&
+      !isFlowYamlCollectionNode(newValue) &&
+      !isEmpty(newValue)) {
+    valueAsString = lineEnding + valueAsString;
+  }
+
+  if (!valueAsString.startsWith(lineEnding)) {
+    // prepend whitespace to ensure there is space after colon.
+    valueAsString = ' $valueAsString';
+  }
+
+  /// +1 accounts for the colon
+  // TODO: What if here is a whitespace following the key, before the colon?
+  final start = keyNode.span.end.offset + 1;
+  var end = getContentSensitiveEnd(map.nodes[key]!);
+
+  /// `package:yaml` parses empty nodes in a way where the start/end of the
+  /// empty value node is the end of the key node, so we have to adjust for
+  /// this.
+  if (end < start) end = start;
+
+  return SourceEdit(start, end - start, valueAsString);
+}
+
+/// Performs the string operation on [yamlEdit] to achieve the effect of
+/// replacing the value at [key] with [newValue] when reparsed, bearing in mind
+/// that this is a flow map.
+SourceEdit _replaceInFlowMap(
+    YamlEditor yamlEdit, YamlMap map, Object? key, YamlNode newValue) {
+  final valueSpan = map.nodes[key]!.span;
+  final valueString = yamlEncodeFlow(newValue);
+
+  return SourceEdit(valueSpan.start.offset, valueSpan.length, valueString);
+}
+
+/// Performs the string operation on [yamlEdit] to achieve the effect of
+/// removing the [keyNode] from the map, bearing in mind that this is a block
+/// map.
+SourceEdit _removeFromBlockMap(
+    YamlEditor yamlEdit, YamlMap map, YamlNode keyNode, YamlNode valueNode) {
+  final keySpan = keyNode.span;
+  var end = getContentSensitiveEnd(valueNode);
+  final yaml = yamlEdit.toString();
+  final lineEnding = getLineEnding(yaml);
+
+  if (map.length == 1) {
+    final start = map.span.start.offset;
+    final nextNewLine = yaml.indexOf(lineEnding, end);
+    if (nextNewLine != -1) {
+      // Remove everything up to the next newline, this strips comments that
+      // follows on the same line as the value we're removing.
+      // It also ensures we consume colon when [valueNode.value] is `null`
+      // because there is no value (e.g. `key: \n`). Because [valueNode.span] in
+      // such cases point to the colon `:`.
+      end = nextNewLine;
+    } else {
+      // Remove everything until the end of the document, if there is no newline
+      end = yaml.length;
+    }
+    return SourceEdit(start, end - start, '{}');
+  }
+
+  var start = keySpan.start.offset;
+
+  /// Adjust the end to clear the new line after the end too.
+  ///
+  /// We do this because we suspect that our users will want the inline
+  /// comments to disappear too.
+  final nextNewLine = yaml.indexOf(lineEnding, end);
+  if (nextNewLine != -1) {
+    end = nextNewLine + lineEnding.length;
+  } else {
+    // Remove everything until the end of the document, if there is no newline
+    end = yaml.length;
+  }
+
+  final nextNode = getNextKeyNode(map, keyNode);
+
+  if (start > 0) {
+    final lastHyphen = yaml.lastIndexOf('-', start - 1);
+    final lastNewLine = yaml.lastIndexOf(lineEnding, start - 1);
+    if (lastHyphen > lastNewLine) {
+      start = lastHyphen + 2;
+
+      /// If there is a `-` before the node, and the end is on the same line
+      /// as the next node, we need to add the necessary offset to the end to
+      /// make sure the next node has the correct indentation.
+      if (nextNode != null &&
+          nextNode.span.start.offset - end <= nextNode.span.start.column) {
+        end += nextNode.span.start.column;
+      }
+    } else if (lastNewLine > lastHyphen) {
+      start = lastNewLine + lineEnding.length;
+    }
+  }
+
+  return SourceEdit(start, end - start, '');
+}
+
+/// Performs the string operation on [yamlEdit] to achieve the effect of
+/// removing the [keyNode] from the map, bearing in mind that this is a flow
+/// map.
+SourceEdit _removeFromFlowMap(
+    YamlEditor yamlEdit, YamlMap map, YamlNode keyNode, YamlNode valueNode) {
+  var start = keyNode.span.start.offset;
+  var end = valueNode.span.end.offset;
+  final yaml = yamlEdit.toString();
+
+  if (deepEquals(keyNode, map.keys.first)) {
+    start = yaml.lastIndexOf('{', start - 1) + 1;
+
+    if (deepEquals(keyNode, map.keys.last)) {
+      end = yaml.indexOf('}', end);
+    } else {
+      end = yaml.indexOf(',', end) + 1;
+    }
+  } else {
+    start = yaml.lastIndexOf(',', start - 1);
+  }
+
+  return SourceEdit(start, end - start, '');
+}

diff --git a/pkgs/yaml_edit/lib/src/source_edit.dart b/pkgs/yaml_edit/lib/src/source_edit.dart
new file mode 100644
index 0000000..d177a19
--- /dev/null
+++ b/pkgs/yaml_edit/lib/src/source_edit.dart

@@ -0,0 +1,133 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:meta/meta.dart';
+
+/// A class representing a change on a [String], intended to be compatible with
+/// `package:analysis_server`'s [SourceEdit].
+///
+/// For example, changing a string from
+/// ```
+/// foo: foobar
+/// ```
+/// to
+/// ```
+/// foo: barbar
+/// ```
+/// will be represented by
+/// `SourceEdit(offset: 4, length: 3, replacement: 'bar')`
+@sealed
+class SourceEdit {
+  /// The offset from the start of the string where the modification begins.
+  final int offset;
+
+  /// The length of the substring to be replaced.
+  final int length;
+
+  /// The replacement string to be used.
+  final String replacement;
+
+  /// Creates a new [SourceEdit] instance. [offset], [length] and [replacement]
+  /// must be non-null, and [offset] and [length] must be non-negative.
+  factory SourceEdit(int offset, int length, String replacement) =>
+      SourceEdit._(offset, length, replacement);
+
+  SourceEdit._(this.offset, this.length, this.replacement) {
+    RangeError.checkNotNegative(offset);
+    RangeError.checkNotNegative(length);
+  }
+
+  @override
+  bool operator ==(Object other) {
+    if (other is SourceEdit) {
+      return offset == other.offset &&
+          length == other.length &&
+          replacement == other.replacement;
+    }
+
+    return false;
+  }
+
+  @override
+  int get hashCode => offset.hashCode ^ length.hashCode ^ replacement.hashCode;
+
+  /// Constructs a SourceEdit from JSON.
+  ///
+  /// **Example:**
+  /// ```dart
+  /// final edit = {
+  ///   'offset': 1,
+  ///   'length': 2,
+  ///   'replacement': 'replacement string'
+  /// };
+  ///
+  /// final sourceEdit = SourceEdit.fromJson(edit);
+  /// ```
+  factory SourceEdit.fromJson(Map<String, dynamic> json) {
+    final offset = json['offset'];
+    final length = json['length'];
+    final replacement = json['replacement'];
+
+    if (offset is int && length is int && replacement is String) {
+      return SourceEdit(offset, length, replacement);
+    }
+
+    throw const FormatException('Invalid JSON passed to SourceEdit');
+  }
+
+  /// Encodes this object as JSON-compatible structure.
+  ///
+  /// **Example:**
+  /// ```dart
+  /// import 'dart:convert' show jsonEncode;
+  ///
+  /// final edit = SourceEdit(offset, length, 'replacement string');
+  /// final jsonString = jsonEncode(edit.toJson());
+  /// print(jsonString);
+  /// ```
+  Map<String, dynamic> toJson() {
+    return {'offset': offset, 'length': length, 'replacement': replacement};
+  }
+
+  @override
+  String toString() => 'SourceEdit($offset, $length, "$replacement")';
+
+  /// Applies a series of [SourceEdit]s to an original string, and return the
+  /// final output.
+  ///
+  /// [edits] should be in order i.e. the first [SourceEdit] in [edits] should
+  /// be the first edit applied to [original].
+  ///
+  /// **Example:**
+  /// ```dart
+  /// const original = 'YAML: YAML';
+  /// final sourceEdits = [
+  ///        SourceEdit(6, 4, "YAML Ain't Markup Language"),
+  ///        SourceEdit(6, 4, "YAML Ain't Markup Language"),
+  ///        SourceEdit(0, 4, "YAML Ain't Markup Language")
+  ///      ];
+  /// final result = SourceEdit.applyAll(original, sourceEdits);
+  /// ```
+  /// **Expected result:**
+  /// ```dart
+  /// "YAML Ain't Markup Language: YAML Ain't Markup Language Ain't Markup
+  /// Language"
+  /// ```
+  static String applyAll(String original, Iterable<SourceEdit> edits) {
+    return edits.fold(original, (current, edit) => edit.apply(current));
+  }
+
+  /// Applies one [SourceEdit]s to an original string, and return the final
+  /// output.
+  ///
+  /// **Example:**
+  /// ```dart
+  /// final edit = SourceEdit(4, 3, 'bar');
+  /// final originalString = 'foo: foobar';
+  /// print(edit.apply(originalString)); // 'foo: barbar'
+  /// ```
+  String apply(String original) {
+    return original.replaceRange(offset, offset + length, replacement);
+  }
+}

diff --git a/pkgs/yaml_edit/lib/src/strings.dart b/pkgs/yaml_edit/lib/src/strings.dart
new file mode 100644
index 0000000..1b85641
--- /dev/null
+++ b/pkgs/yaml_edit/lib/src/strings.dart

@@ -0,0 +1,366 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:collection/collection.dart';
+import 'package:yaml/yaml.dart';
+
+import 'utils.dart';
+
+/// Given [value], tries to format it into a plain string recognizable by YAML.
+///
+/// Not all values can be formatted into a plain string. If the string contains
+/// an escape sequence, it can only be detected when in a double-quoted
+/// sequence. Plain strings may also be misinterpreted by the YAML parser (e.g.
+/// ' null').
+///
+/// Returns `null` if [value] cannot be encoded as a plain string.
+String? _tryYamlEncodePlain(String value) {
+  /// If it contains a dangerous character we want to wrap the result with
+  /// double quotes because the double quoted style allows for arbitrary
+  /// strings with "\" escape sequences.
+  ///
+  /// See 7.3.1 Double-Quoted Style
+  /// https://yaml.org/spec/1.2/spec.html#id2787109
+  return isDangerousString(value) ? null : value;
+}
+
+/// Checks if [string] has unprintable characters according to
+/// [unprintableCharCodes].
+bool _hasUnprintableCharacters(String string) {
+  final codeUnits = string.codeUnits;
+
+  for (final key in unprintableCharCodes.keys) {
+    if (codeUnits.contains(key)) return true;
+  }
+
+  return false;
+}
+
+/// Generates a YAML-safe double-quoted string based on [string], escaping the
+/// list of characters as defined by the YAML 1.2 spec.
+///
+/// See 5.7 Escaped Characters https://yaml.org/spec/1.2/spec.html#id2776092
+String _yamlEncodeDoubleQuoted(String string) {
+  final buffer = StringBuffer();
+  for (final codeUnit in string.codeUnits) {
+    if (doubleQuoteEscapeChars[codeUnit] != null) {
+      buffer.write(doubleQuoteEscapeChars[codeUnit]);
+    } else {
+      buffer.writeCharCode(codeUnit);
+    }
+  }
+
+  return '"$buffer"';
+}
+
+/// Encodes [string] as YAML single quoted string.
+///
+/// Returns `null`, if the [string] can't be encoded as single-quoted string.
+/// This might happen if it contains line-breaks or [_hasUnprintableCharacters].
+///
+/// See: https://yaml.org/spec/1.2.2/#732-single-quoted-style
+String? _tryYamlEncodeSingleQuoted(String string) {
+  // If [string] contains a newline we'll use double quoted strings instead.
+  // Single quoted strings can represent newlines, but then we have to use an
+  // empty line (replace \n with \n\n). But since leading spaces following
+  // line breaks are ignored, we can't represent "\n ".
+  // Thus, if the string contains `\n` and we're asked to do single quoted,
+  // we'll fallback to a double quoted string.
+  if (_hasUnprintableCharacters(string) || string.contains('\n')) return null;
+
+  final result = string.replaceAll('\'', '\'\'');
+  return '\'$result\'';
+}
+
+/// Attempts to encode a [string] as a _YAML folded string_ and apply the
+/// appropriate _chomping indicator_.
+///
+/// Returns `null`, if the [string] cannot be encoded as a _YAML folded
+/// string_.
+///
+/// **Examples** of folded strings.
+/// ```yaml
+/// # With the "strip" chomping indicator
+/// key: >-
+///   my folded
+///   string
+///
+/// # With the "keep" chomping indicator
+/// key: >+
+///   my folded
+///   string
+/// ```
+///
+/// See: https://yaml.org/spec/1.2.2/#813-folded-style
+String? _tryYamlEncodeFolded(String string, int indentSize, String lineEnding) {
+  // A string that starts with space or newline followed by space can't be
+  // encoded in folded mode.
+  if (string.isEmpty || string.trim().length != string.length) return null;
+
+  if (_hasUnprintableCharacters(string)) return null;
+
+  // TODO: Are there other strings we can't encode in folded mode?
+
+  final indent = ' ' * indentSize;
+
+  /// Remove trailing `\n` & white-space to ease string folding
+  var trimmed = string.trimRight();
+  final stripped = string.substring(trimmed.length);
+
+  final trimmedSplit =
+      trimmed.replaceAll('\n', lineEnding + indent).split(lineEnding);
+
+  /// Try folding to match specification:
+  /// * https://yaml.org/spec/1.2.2/#65-line-folding
+  trimmed = trimmedSplit.reduceIndexed((index, previous, current) {
+    var updated = current;
+
+    /// If initially empty, this line holds only `\n` or white-space. This
+    /// tells us we don't need to apply an additional `\n`.
+    ///
+    /// See https://yaml.org/spec/1.2.2/#64-empty-lines
+    ///
+    /// If this line is not empty, we need to apply an additional `\n` if and
+    /// only if:
+    ///   1. The preceding line was non-empty too
+    ///   2. If the current line doesn't begin with white-space
+    ///
+    /// Such that we apply `\n` for `foo\nbar` but not `foo\n bar`.
+    if (current.trim().isNotEmpty &&
+        trimmedSplit[index - 1].trim().isNotEmpty &&
+        !current.replaceFirst(indent, '').startsWith(' ')) {
+      updated = lineEnding + updated;
+    }
+
+    /// Apply a `\n` by default.
+    return previous + lineEnding + updated;
+  });
+
+  return '>-\n'
+      '$indent$trimmed'
+      '${stripped.replaceAll('\n', lineEnding + indent)}';
+}
+
+/// Attempts to encode a [string] as a _YAML literal string_ and apply the
+/// appropriate _chomping indicator_.
+///
+/// Returns `null`, if the [string] cannot be encoded as a _YAML literal
+/// string_.
+///
+/// **Examples** of literal strings.
+/// ```yaml
+/// # With the "strip" chomping indicator
+/// key: |-
+///   my literal
+///   string
+///
+/// # Without chomping indicator
+/// key: |
+///   my literal
+///   string
+/// ```
+///
+/// See: https://yaml.org/spec/1.2.2/#812-literal-style
+String? _tryYamlEncodeLiteral(
+    String string, int indentSize, String lineEnding) {
+  if (string.isEmpty || string.trim().length != string.length) return null;
+
+  // A string that starts with space or newline followed by space can't be
+  // encoded in literal mode.
+  if (_hasUnprintableCharacters(string)) return null;
+
+  // TODO: Are there other strings we can't encode in literal mode?
+
+  final indent = ' ' * indentSize;
+
+  /// Simplest block style.
+  /// * https://yaml.org/spec/1.2.2/#812-literal-style
+  return '|-\n$indent${string.replaceAll('\n', lineEnding + indent)}';
+}
+
+/// Encodes a flow [YamlScalar] based on the provided [YamlScalar.style].
+///
+/// Falls back to [ScalarStyle.DOUBLE_QUOTED] if the [yamlScalar] cannot be
+/// encoded with the [YamlScalar.style] or with [ScalarStyle.PLAIN] when the
+/// [yamlScalar] is not a [String].
+String _yamlEncodeFlowScalar(YamlScalar yamlScalar) {
+  final YamlScalar(:value, :style) = yamlScalar;
+
+  if (value is! String) {
+    return value.toString();
+  }
+
+  switch (style) {
+    /// Only encode as double-quoted if it's a string.
+    case ScalarStyle.DOUBLE_QUOTED:
+      return _yamlEncodeDoubleQuoted(value);
+
+    case ScalarStyle.SINGLE_QUOTED:
+      return _tryYamlEncodeSingleQuoted(value) ??
+          _yamlEncodeDoubleQuoted(value);
+
+    /// Cast into [String] if [null] as this condition only returns [null]
+    /// for a [String] that can't be encoded.
+    default:
+      return _tryYamlEncodePlain(value) ?? _yamlEncodeDoubleQuoted(value);
+  }
+}
+
+/// Encodes a block [YamlScalar] based on the provided [YamlScalar.style].
+///
+/// Falls back to [ScalarStyle.DOUBLE_QUOTED] if the [yamlScalar] cannot be
+/// encoded with the [YamlScalar.style] provided.
+String _yamlEncodeBlockScalar(
+  YamlScalar yamlScalar,
+  int indentation,
+  String lineEnding,
+) {
+  final YamlScalar(:value, :style) = yamlScalar;
+  assertValidScalar(value);
+
+  if (value is! String) {
+    return value.toString();
+  }
+
+  switch (style) {
+    /// Prefer 'plain', fallback to "double quoted"
+    case ScalarStyle.PLAIN:
+      return _tryYamlEncodePlain(value) ?? _yamlEncodeDoubleQuoted(value);
+
+    // Prefer 'single quoted', fallback to "double quoted"
+    case ScalarStyle.SINGLE_QUOTED:
+      return _tryYamlEncodeSingleQuoted(value) ??
+          _yamlEncodeDoubleQuoted(value);
+
+    /// Prefer folded string, fallback to "double quoted"
+    case ScalarStyle.FOLDED:
+      return _tryYamlEncodeFolded(value, indentation, lineEnding) ??
+          _yamlEncodeDoubleQuoted(value);
+
+    /// Prefer literal string, fallback to "double quoted"
+    case ScalarStyle.LITERAL:
+      return _tryYamlEncodeLiteral(value, indentation, lineEnding) ??
+          _yamlEncodeDoubleQuoted(value);
+
+    /// Prefer plain, fallback to "double quoted"
+    default:
+      return _tryYamlEncodePlain(value) ?? _yamlEncodeDoubleQuoted(value);
+  }
+}
+
+/// Returns [value] with the necessary formatting applied in a flow context.
+///
+/// If [value] is a [YamlNode], we try to respect its [YamlScalar.style]
+/// parameter where possible. Certain cases make this impossible (e.g. a plain
+/// string scalar that starts with '>', a child having a block style
+/// parameters), in which case we will produce [value] with default styling
+/// options.
+String yamlEncodeFlow(YamlNode value) {
+  if (value is YamlList) {
+    final list = value.nodes;
+
+    final safeValues = list.map(yamlEncodeFlow);
+    return '[${safeValues.join(', ')}]';
+  } else if (value is YamlMap) {
+    final safeEntries = value.nodes.entries.map((entry) {
+      final safeKey = yamlEncodeFlow(entry.key as YamlNode);
+      final safeValue = yamlEncodeFlow(entry.value);
+      return '$safeKey: $safeValue';
+    });
+
+    return '{${safeEntries.join(', ')}}';
+  }
+
+  return _yamlEncodeFlowScalar(value as YamlScalar);
+}
+
+/// Returns [value] with the necessary formatting applied in a block context.
+String yamlEncodeBlock(
+  YamlNode value,
+  int indentation,
+  String lineEnding,
+) {
+  const additionalIndentation = 2;
+
+  if (!isBlockNode(value)) return yamlEncodeFlow(value);
+
+  final newIndentation = indentation + additionalIndentation;
+
+  if (value is YamlList) {
+    if (value.isEmpty) return '${' ' * indentation}[]';
+
+    Iterable<String> safeValues;
+
+    final children = value.nodes;
+
+    safeValues = children.map((child) {
+      var valueString = yamlEncodeBlock(child, newIndentation, lineEnding);
+      if (isCollection(child) && !isFlowYamlCollectionNode(child)) {
+        valueString = valueString.substring(newIndentation);
+      }
+
+      return '${' ' * indentation}- $valueString';
+    });
+
+    return safeValues.join(lineEnding);
+  } else if (value is YamlMap) {
+    if (value.isEmpty) return '${' ' * indentation}{}';
+
+    return value.nodes.entries.map((entry) {
+      final MapEntry(:key, :value) = entry;
+
+      final safeKey = yamlEncodeFlow(key as YamlNode);
+      final formattedKey = ' ' * indentation + safeKey;
+
+      final formattedValue = yamlEncodeBlock(
+        value,
+        newIndentation,
+        lineEnding,
+      );
+
+      /// Empty collections are always encoded in flow-style, so new-line must
+      /// be avoided
+      if (isCollection(value) && !isEmpty(value)) {
+        return '$formattedKey:$lineEnding$formattedValue';
+      }
+
+      return '$formattedKey: $formattedValue';
+    }).join(lineEnding);
+  }
+
+  return _yamlEncodeBlockScalar(
+    value as YamlScalar,
+    newIndentation,
+    lineEnding,
+  );
+}
+
+/// List of unprintable characters.
+///
+/// See 5.7 Escape Characters https://yaml.org/spec/1.2/spec.html#id2776092
+final Map<int, String> unprintableCharCodes = {
+  0: '\\0', //  Escaped ASCII null (#x0) character.
+  7: '\\a', //  Escaped ASCII bell (#x7) character.
+  8: '\\b', //  Escaped ASCII backspace (#x8) character.
+  11: '\\v', // 	Escaped ASCII vertical tab (#xB) character.
+  12: '\\f', //  Escaped ASCII form feed (#xC) character.
+  13: '\\r', //  Escaped ASCII carriage return (#xD) character. Line Break.
+  27: '\\e', //  Escaped ASCII escape (#x1B) character.
+  133: '\\N', //  Escaped Unicode next line (#x85) character.
+  160: '\\_', //  Escaped Unicode non-breaking space (#xA0) character.
+  8232: '\\L', //  Escaped Unicode line separator (#x2028) character.
+  8233: '\\P', //  Escaped Unicode paragraph separator (#x2029) character.
+};
+
+/// List of escape characters.
+///
+/// See 5.7 Escape Characters https://yaml.org/spec/1.2/spec.html#id2776092
+final Map<int, String> doubleQuoteEscapeChars = {
+  ...unprintableCharCodes,
+  9: '\\t', //  Escaped ASCII horizontal tab (#x9) character. Printable
+  10: '\\n', //  Escaped ASCII line feed (#xA) character. Line Break.
+  34: '\\"', //  Escaped ASCII double quote (#x22).
+  47: '\\/', //  Escaped ASCII slash (#x2F), for JSON compatibility.
+  92: '\\\\', //  Escaped ASCII back slash (#x5C).
+};

diff --git a/pkgs/yaml_edit/lib/src/utils.dart b/pkgs/yaml_edit/lib/src/utils.dart
new file mode 100644
index 0000000..ef85526
--- /dev/null
+++ b/pkgs/yaml_edit/lib/src/utils.dart

@@ -0,0 +1,291 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:source_span/source_span.dart';
+import 'package:yaml/yaml.dart';
+
+import 'editor.dart';
+import 'wrap.dart';
+
+/// Invoke [fn] while setting [yamlWarningCallback] to [warn], and restore
+/// [YamlWarningCallback] after [fn] returns.
+///
+/// Defaults to a [warn] function that ignores all warnings.
+T withYamlWarningCallback<T>(
+  T Function() fn, {
+  YamlWarningCallback warn = _ignoreWarning,
+}) {
+  final original = yamlWarningCallback;
+  try {
+    yamlWarningCallback = warn;
+    return fn();
+  } finally {
+    yamlWarningCallback = original;
+  }
+}
+
+void _ignoreWarning(String warning, [SourceSpan? span]) {/* ignore warning */}
+
+/// Determines if [string] is dangerous by checking if parsing the plain string
+/// can return a result different from [string].
+///
+/// This function is also capable of detecting if non-printable characters are
+/// in [string].
+bool isDangerousString(String string) {
+  try {
+    final node = withYamlWarningCallback(() => loadYamlNode(string));
+    if (node.value != string) {
+      return true;
+    }
+
+    // [string] should also not contain the `[`, `]`, `,`, `{` and `}` indicator
+    // characters.
+    return string.contains(RegExp(r'\{|\[|\]|\}|,'));
+  } catch (e) {
+    /// This catch statement catches [ArgumentError] in `loadYamlNode` when
+    /// a string can be interpreted as a URI tag, but catches for other
+    /// [YamlException]s
+    return true;
+  }
+}
+
+/// Asserts that [value] is a valid scalar according to YAML.
+///
+/// A valid scalar is a number, String, boolean, or null.
+void assertValidScalar(Object? value) {
+  if (value is num || value is String || value is bool || value == null) {
+    return;
+  }
+
+  throw ArgumentError.value(value, 'value', 'Not a valid scalar type!');
+}
+
+/// Checks if [node] is a [YamlNode] with block styling.
+///
+/// [ScalarStyle.ANY] and [CollectionStyle.ANY] are considered to be block
+/// styling by default for maximum flexibility.
+bool isBlockNode(YamlNode node) {
+  if (node is YamlScalar) {
+    if (node.style == ScalarStyle.LITERAL ||
+        node.style == ScalarStyle.FOLDED ||
+        node.style == ScalarStyle.ANY) {
+      return true;
+    }
+  }
+
+  if (node is YamlList &&
+      (node.style == CollectionStyle.BLOCK ||
+          node.style == CollectionStyle.ANY)) {
+    return true;
+  }
+  if (node is YamlMap &&
+      (node.style == CollectionStyle.BLOCK ||
+          node.style == CollectionStyle.ANY)) {
+    return true;
+  }
+
+  return false;
+}
+
+/// Returns the content sensitive ending offset of [yamlNode] (i.e. where the
+/// last meaningful content happens)
+int getContentSensitiveEnd(YamlNode yamlNode) {
+  if (yamlNode is YamlList) {
+    if (yamlNode.style == CollectionStyle.FLOW) {
+      return yamlNode.span.end.offset;
+    } else {
+      return getContentSensitiveEnd(yamlNode.nodes.last);
+    }
+  } else if (yamlNode is YamlMap) {
+    if (yamlNode.style == CollectionStyle.FLOW) {
+      return yamlNode.span.end.offset;
+    } else {
+      return getContentSensitiveEnd(yamlNode.nodes.values.last);
+    }
+  }
+
+  return yamlNode.span.end.offset;
+}
+
+/// Checks if the item is a Map or a List
+bool isCollection(Object item) => item is Map || item is List;
+
+/// Checks if [index] is [int], >=0, < [length]
+bool isValidIndex(Object? index, int length) {
+  return index is int && index >= 0 && index < length;
+}
+
+/// Checks if the item is empty, if it is a List or a Map.
+///
+/// Returns `false` if [item] is not a List or Map.
+bool isEmpty(Object item) {
+  if (item is Map) return item.isEmpty;
+  if (item is List) return item.isEmpty;
+
+  return false;
+}
+
+/// Creates a [SourceSpan] from [sourceUrl] with no meaningful location
+/// information.
+///
+/// Mainly used with [wrapAsYamlNode] to allow for a reasonable
+/// implementation of [SourceSpan.message].
+SourceSpan shellSpan(Object? sourceUrl) {
+  final shellSourceLocation = SourceLocation(0, sourceUrl: sourceUrl);
+  return SourceSpanBase(shellSourceLocation, shellSourceLocation, '');
+}
+
+/// Returns if [value] is a [YamlList] or [YamlMap] with [CollectionStyle.FLOW].
+bool isFlowYamlCollectionNode(Object value) =>
+    value is YamlNode && value.collectionStyle == CollectionStyle.FLOW;
+
+/// Determines the index where [newKey] will be inserted if the keys in [map]
+/// are in alphabetical order when converted to strings.
+///
+/// Returns the length of [map] if the keys in [map] are not in alphabetical
+/// order.
+int getMapInsertionIndex(YamlMap map, Object newKey) {
+  final keys = map.nodes.keys.map((k) => k.toString()).toList();
+
+  // We can't deduce ordering if list is empty, so then we just we just append
+  if (keys.length <= 1) {
+    return map.length;
+  }
+
+  for (var i = 1; i < keys.length; i++) {
+    if (keys[i].compareTo(keys[i - 1]) < 0) {
+      return map.length;
+    }
+  }
+
+  final insertionIndex =
+      keys.indexWhere((key) => key.compareTo(newKey as String) > 0);
+
+  if (insertionIndex != -1) return insertionIndex;
+
+  return map.length;
+}
+
+/// Returns the detected indentation step used in [editor], or defaults to a
+/// value of `2` if no indentation step can be detected.
+///
+/// Indentation step is determined by the difference in indentation of the
+/// first block-styled yaml collection in the second level as compared to the
+/// top-level elements. In the case where there are multiple possible
+/// candidates, we choose the candidate closest to the start of [editor].
+int getIndentation(YamlEditor editor) {
+  final node = editor.parseAt([]);
+  Iterable<YamlNode>? children;
+  var indentation = 2;
+
+  if (node is YamlMap && node.style == CollectionStyle.BLOCK) {
+    children = node.nodes.values;
+  } else if (node is YamlList && node.style == CollectionStyle.BLOCK) {
+    children = node.nodes;
+  }
+
+  if (children != null) {
+    for (final child in children) {
+      var indent = 0;
+      if (child is YamlList) {
+        indent = getListIndentation(editor.toString(), child);
+      } else if (child is YamlMap) {
+        indent = getMapIndentation(editor.toString(), child);
+      }
+
+      if (indent != 0) indentation = indent;
+    }
+  }
+  return indentation;
+}
+
+/// Gets the indentation level of [list]. This is 0 if it is a flow list,
+/// but returns the number of spaces before the hyphen of elements for
+/// block lists.
+///
+/// Throws [UnsupportedError] if an empty block map is passed in.
+int getListIndentation(String yaml, YamlList list) {
+  if (list.style == CollectionStyle.FLOW) return 0;
+
+  /// An empty block map doesn't really exist.
+  if (list.isEmpty) {
+    throw UnsupportedError('Unable to get indentation for empty block list');
+  }
+
+  final lastSpanOffset = list.nodes.last.span.start.offset;
+  final lastHyphen = yaml.lastIndexOf('-', lastSpanOffset - 1);
+
+  if (lastHyphen == 0) return lastHyphen;
+
+  // Look for '\n' that's before hyphen
+  final lastNewLine = yaml.lastIndexOf('\n', lastHyphen - 1);
+
+  return lastHyphen - lastNewLine - 1;
+}
+
+/// Gets the indentation level of [map]. This is 0 if it is a flow map,
+/// but returns the number of spaces before the keys for block maps.
+int getMapIndentation(String yaml, YamlMap map) {
+  if (map.style == CollectionStyle.FLOW) return 0;
+
+  /// An empty block map doesn't really exist.
+  if (map.isEmpty) {
+    throw UnsupportedError('Unable to get indentation for empty block map');
+  }
+
+  /// Use the number of spaces between the last key and the newline as
+  /// indentation.
+  final lastKey = map.nodes.keys.last as YamlNode;
+  final lastSpanOffset = lastKey.span.start.offset;
+  final lastNewLine = yaml.lastIndexOf('\n', lastSpanOffset);
+  final lastQuestionMark = yaml.lastIndexOf('?', lastSpanOffset);
+
+  if (lastQuestionMark == -1) {
+    if (lastNewLine == -1) return lastSpanOffset;
+    return lastSpanOffset - lastNewLine - 1;
+  }
+
+  /// If there is a question mark, it might be a complex key. Check if it
+  /// is on the same line as the key node to verify.
+  if (lastNewLine == -1) return lastQuestionMark;
+  if (lastQuestionMark > lastNewLine) {
+    return lastQuestionMark - lastNewLine - 1;
+  }
+
+  return lastSpanOffset - lastNewLine - 1;
+}
+
+/// Returns the detected line ending used in [yaml], more specifically, whether
+/// [yaml] appears to use Windows `\r\n` or Unix `\n` line endings.
+///
+/// The heuristic used is to count all `\n` in the text and if strictly more
+/// than half of them are preceded by `\r` we report that windows line endings
+/// are used.
+String getLineEnding(String yaml) {
+  var index = -1;
+  var unixNewlines = 0;
+  var windowsNewlines = 0;
+  while ((index = yaml.indexOf('\n', index + 1)) != -1) {
+    if (index != 0 && yaml[index - 1] == '\r') {
+      windowsNewlines++;
+    } else {
+      unixNewlines++;
+    }
+  }
+
+  return windowsNewlines > unixNewlines ? '\r\n' : '\n';
+}
+
+extension YamlNodeExtension on YamlNode {
+  /// Returns the [CollectionStyle] of `this` if `this` is [YamlMap] or
+  /// [YamlList].
+  ///
+  /// Otherwise, returns `null`.
+  CollectionStyle? get collectionStyle {
+    final me = this;
+    if (me is YamlMap) return me.style;
+    if (me is YamlList) return me.style;
+    return null;
+  }
+}

diff --git a/pkgs/yaml_edit/lib/src/wrap.dart b/pkgs/yaml_edit/lib/src/wrap.dart
new file mode 100644
index 0000000..73f7751
--- /dev/null
+++ b/pkgs/yaml_edit/lib/src/wrap.dart

@@ -0,0 +1,216 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:collection' as collection;
+
+import 'package:collection/collection.dart';
+import 'package:source_span/source_span.dart';
+import 'package:yaml/yaml.dart';
+
+import 'equality.dart';
+import 'utils.dart';
+
+/// Returns a new [YamlMap] constructed by applying [update] onto the nodes of
+/// this [YamlMap].
+YamlMap updatedYamlMap(YamlMap map, Function(Map) update) {
+  final dummyMap = deepEqualsMap();
+  dummyMap.addAll(map.nodes);
+
+  update(dummyMap);
+
+  return wrapAsYamlNode(dummyMap) as YamlMap;
+}
+
+/// Wraps [value] into a [YamlNode].
+///
+/// [Map]s, [List]s and Scalars will be wrapped as [YamlMap]s, [YamlList]s,
+/// and [YamlScalar]s respectively. If [collectionStyle]/[scalarStyle] is
+/// defined, and [value] is a collection or scalar, the wrapped [YamlNode] will
+/// have the respective style, otherwise it defaults to the ANY style.
+///
+/// If [value] is a [Map] or [List], then [wrapAsYamlNode] will be called
+/// recursively on all children, and [collectionStyle]/[scalarStyle] will be
+/// applied to any children that are not instances of [YamlNode].
+///
+/// If a [YamlNode] is passed in, no further wrapping will be done, and the
+/// [collectionStyle]/[scalarStyle] will not be applied.
+YamlNode wrapAsYamlNode(
+  Object? value, {
+  CollectionStyle collectionStyle = CollectionStyle.ANY,
+  ScalarStyle scalarStyle = ScalarStyle.ANY,
+}) {
+  if (value is YamlScalar) {
+    assertValidScalar(value.value);
+    return value;
+  } else if (value is YamlList) {
+    for (final item in value.nodes) {
+      wrapAsYamlNode(item);
+    }
+
+    return value;
+  } else if (value is YamlMap) {
+    /// Both [entry.key] and [entry.values] are guaranteed to be [YamlNode]s,
+    /// so running this will just assert that they are valid scalars.
+    for (final entry in value.nodes.entries) {
+      wrapAsYamlNode(entry.key);
+      wrapAsYamlNode(entry.value);
+    }
+
+    return value;
+  } else if (value is Map) {
+    return YamlMapWrap(
+      value,
+      collectionStyle: collectionStyle,
+      scalarStyle: scalarStyle,
+    );
+  } else if (value is List) {
+    return YamlListWrap(
+      value,
+      collectionStyle: collectionStyle,
+      scalarStyle: scalarStyle,
+    );
+  } else {
+    assertValidScalar(value);
+
+    return YamlScalarWrap(value, style: scalarStyle);
+  }
+}
+
+/// Internal class that allows us to define a constructor on [YamlScalar]
+/// which takes in [style] as an argument.
+class YamlScalarWrap implements YamlScalar {
+  /// The [ScalarStyle] to be used for the scalar.
+  @override
+  final ScalarStyle style;
+
+  @override
+  final SourceSpan span;
+
+  @override
+  final dynamic value;
+
+  YamlScalarWrap(this.value, {this.style = ScalarStyle.ANY, Object? sourceUrl})
+      : span = shellSpan(sourceUrl);
+
+  @override
+  String toString() => value.toString();
+}
+
+/// Internal class that allows us to define a constructor on [YamlMap]
+/// which takes in [style] as an argument.
+class YamlMapWrap
+    with collection.MapMixin, UnmodifiableMapMixin
+    implements YamlMap {
+  /// The [CollectionStyle] to be used for the map.
+  @override
+  final CollectionStyle style;
+
+  @override
+  final Map<dynamic, YamlNode> nodes;
+
+  @override
+  final SourceSpan span;
+
+  factory YamlMapWrap(
+    Map dartMap, {
+    CollectionStyle collectionStyle = CollectionStyle.ANY,
+    ScalarStyle scalarStyle = ScalarStyle.ANY,
+    Object? sourceUrl,
+  }) {
+    final wrappedMap = deepEqualsMap<dynamic, YamlNode>();
+
+    for (final entry in dartMap.entries) {
+      final wrappedKey = wrapAsYamlNode(
+        entry.key,
+        collectionStyle: collectionStyle,
+        scalarStyle: scalarStyle,
+      );
+      final wrappedValue = wrapAsYamlNode(
+        entry.value,
+        collectionStyle: collectionStyle,
+        scalarStyle: scalarStyle,
+      );
+      wrappedMap[wrappedKey] = wrappedValue;
+    }
+
+    return YamlMapWrap._(
+      wrappedMap,
+      style: collectionStyle,
+      sourceUrl: sourceUrl,
+    );
+  }
+
+  YamlMapWrap._(
+    this.nodes, {
+    CollectionStyle style = CollectionStyle.ANY,
+    Object? sourceUrl,
+  })  : span = shellSpan(sourceUrl),
+        style = nodes.isEmpty ? CollectionStyle.FLOW : style;
+
+  @override
+  dynamic operator [](Object? key) => nodes[key]?.value;
+
+  @override
+  Iterable get keys => nodes.keys.map((node) => (node as YamlNode).value);
+
+  @override
+  Map get value => this;
+}
+
+/// Internal class that allows us to define a constructor on [YamlList]
+/// which takes in [style] as an argument.
+class YamlListWrap with collection.ListMixin implements YamlList {
+  /// The [CollectionStyle] to be used for the list.
+  @override
+  final CollectionStyle style;
+
+  @override
+  final List<YamlNode> nodes;
+
+  @override
+  final SourceSpan span;
+
+  @override
+  int get length => nodes.length;
+
+  @override
+  set length(int index) {
+    throw UnsupportedError('Cannot modify an unmodifiable List');
+  }
+
+  factory YamlListWrap(
+    List dartList, {
+    CollectionStyle collectionStyle = CollectionStyle.ANY,
+    ScalarStyle scalarStyle = ScalarStyle.ANY,
+    Object? sourceUrl,
+  }) {
+    return YamlListWrap._(
+      dartList
+          .map((v) => wrapAsYamlNode(
+                v,
+                collectionStyle: collectionStyle,
+                scalarStyle: scalarStyle,
+              ))
+          .toList(),
+      style: collectionStyle,
+      sourceUrl: sourceUrl,
+    );
+  }
+
+  YamlListWrap._(this.nodes,
+      {CollectionStyle style = CollectionStyle.ANY, Object? sourceUrl})
+      : span = shellSpan(sourceUrl),
+        style = nodes.isEmpty ? CollectionStyle.FLOW : style;
+
+  @override
+  dynamic operator [](int index) => nodes[index].value;
+
+  @override
+  void operator []=(int index, Object? value) {
+    throw UnsupportedError('Cannot modify an unmodifiable List');
+  }
+
+  @override
+  List get value => this;
+}

diff --git a/pkgs/yaml_edit/lib/yaml_edit.dart b/pkgs/yaml_edit/lib/yaml_edit.dart
new file mode 100644
index 0000000..49558b2
--- /dev/null
+++ b/pkgs/yaml_edit/lib/yaml_edit.dart

@@ -0,0 +1,28 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// YAML parsing is supported by `package:yaml`, and each time a change is
+/// made, the resulting YAML AST is compared against our expected output
+/// with deep equality to ensure that the output conforms to our expectations.
+///
+/// **Example**
+/// ```dart
+/// import 'package:yaml_edit/yaml_edit.dart';
+///
+/// void main() {
+///   final yamlEditor = YamlEditor('{YAML: YAML}');
+///   yamlEditor.update(['YAML'], "YAML Ain't Markup Language");
+///   print(yamlEditor);
+///   // Expected Output:
+///   // {YAML: YAML Ain't Markup Language}
+/// }
+/// ```
+///
+/// [1]: https://yaml.org/
+library;
+
+export 'src/editor.dart';
+export 'src/errors.dart' show AliasException;
+export 'src/source_edit.dart';
+export 'src/wrap.dart' show wrapAsYamlNode;

diff --git a/pkgs/yaml_edit/pubspec.yaml b/pkgs/yaml_edit/pubspec.yaml
new file mode 100644
index 0000000..8127a12
--- /dev/null
+++ b/pkgs/yaml_edit/pubspec.yaml

@@ -0,0 +1,25 @@
+name: yaml_edit
+version: 2.2.2
+description: >-
+  A library for YAML manipulation with comment and whitespace preservation.
+repository: https://github.com/dart-lang/tools/tree/main/pkgs/yaml_edit
+
+issue_tracker: https://github.com/dart-lang/yaml_edit/issues
+
+topics:
+ - yaml
+
+environment:
+  sdk: ^3.1.0
+
+dependencies:
+  collection: ^1.15.0
+  meta: ^1.7.0
+  source_span: ^1.8.1
+  yaml: ^3.1.0
+
+dev_dependencies:
+  coverage: any # we only need format_coverage, don't care what version
+  dart_flutter_team_lints: ^3.0.0
+  path: ^1.8.0
+  test: ^1.17.12

diff --git a/pkgs/yaml_edit/test/alias_test.dart b/pkgs/yaml_edit/test/alias_test.dart
new file mode 100644
index 0000000..acc0df7
--- /dev/null
+++ b/pkgs/yaml_edit/test/alias_test.dart

@@ -0,0 +1,139 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:test/test.dart';
+import 'package:yaml_edit/yaml_edit.dart';
+
+import 'test_utils.dart';
+
+/// This test suite is a temporary measure until we are able to better handle
+/// aliases.
+void main() {
+  group('list ', () {
+    test('removing an alias anchor results in AliasError', () {
+      final doc = YamlEditor('''
+- &SS Sammy Sosa
+- *SS
+''');
+      expect(() => doc.remove([0]), throwsAliasException);
+    });
+
+    test('removing an alias reference results in AliasError', () {
+      final doc = YamlEditor('''
+- &SS Sammy Sosa
+- *SS
+''');
+
+      expect(() => doc.remove([1]), throwsAliasException);
+    });
+
+    test('it is okay to remove a non-alias node', () {
+      final doc = YamlEditor('''
+- &SS Sammy Sosa
+- *SS
+- Sammy Sosa
+''');
+
+      doc.remove([2]);
+      expect(doc.toString(), equals('''
+- &SS Sammy Sosa
+- *SS
+'''));
+    });
+  });
+
+  group('map', () {
+    test('removing an alias anchor value results in AliasError', () {
+      final doc = YamlEditor('''
+a: &SS Sammy Sosa
+b: *SS
+''');
+
+      expect(() => doc.remove(['a']), throwsAliasException);
+    });
+
+    test('removing an alias reference value results in AliasError', () {
+      final doc = YamlEditor('''
+a: &SS Sammy Sosa
+b: *SS
+''');
+
+      expect(() => doc.remove(['b']), throwsAliasException);
+    });
+
+    test('removing an alias anchor key results in AliasError', () {
+      final doc = YamlEditor('''
+&SS Sammy Sosa: a
+b: *SS
+''');
+
+      expect(() => doc.remove(['Sammy Sosa']), throwsAliasException);
+    });
+
+    test('removing an alias reference key results in AliasError', () {
+      final doc = YamlEditor('''
+a: &SS Sammy Sosa
+*SS : b
+''');
+
+      expect(() => doc.remove(['Sammy Sosa']), throwsAliasException);
+    });
+
+    test('it is okay to remove a non-alias node', () {
+      final doc = YamlEditor('''
+a: &SS Sammy Sosa
+b: *SS
+c: Sammy Sosa
+''');
+
+      doc.remove(['c']);
+      expect(doc.toString(), equals('''
+a: &SS Sammy Sosa
+b: *SS
+'''));
+    });
+  });
+
+  group('nested alias', () {
+    test('nested list alias anchors are detected too', () {
+      final doc = YamlEditor('''
+- 
+  - &SS Sammy Sosa
+- *SS
+''');
+
+      expect(() => doc.remove([0]), throwsAliasException);
+    });
+
+    test('nested list alias references are detected too', () {
+      final doc = YamlEditor('''
+- &SS Sammy Sosa
+- 
+  - *SS
+''');
+
+      expect(() => doc.remove([1]), throwsAliasException);
+    });
+
+    test('removing nested map alias anchor results in AliasError', () {
+      final doc = YamlEditor('''
+a:
+  c: &SS Sammy Sosa
+b: *SS
+''');
+
+      expect(() => doc.remove(['a']), throwsAliasException);
+    });
+
+    test('removing nested map alias reference results in AliasError', () {
+      final doc = YamlEditor('''
+a: &SS Sammy Sosa
+b:
+  c: *SS
+''');
+
+      expect(() => doc.remove(['b']), throwsAliasException);
+    });
+  });
+}

diff --git a/pkgs/yaml_edit/test/append_test.dart b/pkgs/yaml_edit/test/append_test.dart
new file mode 100644
index 0000000..cb705ed
--- /dev/null
+++ b/pkgs/yaml_edit/test/append_test.dart

@@ -0,0 +1,269 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:test/test.dart';
+import 'package:yaml_edit/yaml_edit.dart';
+
+import 'test_utils.dart';
+
+void main() {
+  group('throws PathError', () {
+    test('if it is a map', () {
+      final doc = YamlEditor('a:1');
+      expect(() => doc.appendToList([], 4), throwsPathError);
+    });
+
+    test('if it is a scalar', () {
+      final doc = YamlEditor('1');
+      expect(() => doc.appendToList([], 4), throwsPathError);
+    });
+  });
+
+  group('block list', () {
+    test('(1)', () {
+      final doc = YamlEditor('''
+- 0
+- 1
+- 2
+- 3
+''');
+      doc.appendToList([], 4);
+      expect(doc.toString(), equals('''
+- 0
+- 1
+- 2
+- 3
+- 4
+'''));
+      expectYamlBuilderValue(doc, [0, 1, 2, 3, 4]);
+    });
+
+    test('null path', () {
+      final doc = YamlEditor('''
+~:
+  - 0
+  - 1
+  - 2
+  - 3
+''');
+      doc.appendToList([null], 4);
+      expect(doc.toString(), equals('''
+~:
+  - 0
+  - 1
+  - 2
+  - 3
+  - 4
+'''));
+      expectYamlBuilderValue(doc, {
+        null: [0, 1, 2, 3, 4]
+      });
+    });
+
+    test('element to simple block list ', () {
+      final doc = YamlEditor('''
+- 0
+- 1
+- 2
+- 3
+''');
+      doc.appendToList([], [4, 5, 6]);
+      expect(doc.toString(), equals('''
+- 0
+- 1
+- 2
+- 3
+- - 4
+  - 5
+  - 6
+'''));
+      expectYamlBuilderValue(doc, [
+        0,
+        1,
+        2,
+        3,
+        [4, 5, 6]
+      ]);
+    });
+
+    test('nested', () {
+      final doc = YamlEditor('''
+- 0
+- - 1
+  - 2
+''');
+      doc.appendToList([1], 3);
+      expect(doc.toString(), equals('''
+- 0
+- - 1
+  - 2
+  - 3
+'''));
+      expectYamlBuilderValue(doc, [
+        0,
+        [1, 2, 3]
+      ]);
+    });
+
+    test('block list element to nested block list ', () {
+      final doc = YamlEditor('''
+- 0
+- - 1
+  - 2
+''');
+      doc.appendToList([1], [3, 4, 5]);
+
+      expect(doc.toString(), equals('''
+- 0
+- - 1
+  - 2
+  - - 3
+    - 4
+    - 5
+'''));
+      expectYamlBuilderValue(doc, [
+        0,
+        [
+          1,
+          2,
+          [3, 4, 5]
+        ]
+      ]);
+    });
+
+    test('nested', () {
+      final yamlEditor = YamlEditor('''
+a:
+  1:
+    - null
+  2: null
+''');
+      yamlEditor.appendToList(['a', 1], false);
+
+      expect(yamlEditor.toString(), equals('''
+a:
+  1:
+    - null
+    - false
+  2: null
+'''));
+    });
+
+    test('block append (1)', () {
+      final yamlEditor = YamlEditor('''
+# comment
+- z:
+    x: 1
+    y: 2
+- z:
+    x: 3
+    y: 4
+''');
+      yamlEditor.appendToList([], {
+        'z': {'x': 5, 'y': 6}
+      });
+
+      expect(yamlEditor.toString(), equals('''
+# comment
+- z:
+    x: 1
+    y: 2
+- z:
+    x: 3
+    y: 4
+- z:
+    x: 5
+    y: 6
+'''));
+    });
+
+    test('block append (2)', () {
+      final yamlEditor = YamlEditor('''
+# comment
+a:
+  - z:
+      x: 1
+      y: 2
+  - z:
+      x: 3
+      y: 4
+b:
+  - w:
+      m: 2
+      n: 4
+''');
+      yamlEditor.appendToList([
+        'a'
+      ], {
+        'z': {'x': 5, 'y': 6}
+      });
+
+      expect(yamlEditor.toString(), equals('''
+# comment
+a:
+  - z:
+      x: 1
+      y: 2
+  - z:
+      x: 3
+      y: 4
+  - z:
+      x: 5
+      y: 6
+b:
+  - w:
+      m: 2
+      n: 4
+'''));
+    });
+
+    test('block append nested and with comments', () {
+      final yamlEditor = YamlEditor('''
+a:
+  b:
+    - c:
+        d: 1
+    - c:
+        d: 2
+# comment
+  e:
+    - g:
+        e: 1
+        f: 2 
+# comment
+''');
+      expect(
+          () => yamlEditor.appendToList([
+                'a',
+                'e'
+              ], {
+                'g': {'e': 3, 'f': 4}
+              }),
+          returnsNormally);
+    });
+  });
+
+  group('flow list', () {
+    test('(1)', () {
+      final doc = YamlEditor('[0, 1, 2]');
+      doc.appendToList([], 3);
+      expect(doc.toString(), equals('[0, 1, 2, 3]'));
+      expectYamlBuilderValue(doc, [0, 1, 2, 3]);
+    });
+
+    test('null value', () {
+      final doc = YamlEditor('[0, 1, 2]');
+      doc.appendToList([], null);
+      expect(doc.toString(), equals('[0, 1, 2, null]'));
+      expectYamlBuilderValue(doc, [0, 1, 2, null]);
+    });
+
+    test('empty ', () {
+      final doc = YamlEditor('[]');
+      doc.appendToList([], 0);
+      expect(doc.toString(), equals('[0]'));
+      expectYamlBuilderValue(doc, [0]);
+    });
+  });
+}

diff --git a/pkgs/yaml_edit/test/editor_test.dart b/pkgs/yaml_edit/test/editor_test.dart
new file mode 100644
index 0000000..b0a0081
--- /dev/null
+++ b/pkgs/yaml_edit/test/editor_test.dart

@@ -0,0 +1,56 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:test/test.dart';
+import 'package:yaml_edit/yaml_edit.dart';
+
+void main() {
+  group('YamlEditor records edits', () {
+    test('returns empty list at start', () {
+      final yamlEditor = YamlEditor('YAML: YAML');
+
+      expect(yamlEditor.edits, []);
+    });
+
+    test('after one change', () {
+      final yamlEditor = YamlEditor('YAML: YAML');
+      yamlEditor.update(['YAML'], "YAML Ain't Markup Language");
+
+      expect(
+          yamlEditor.edits, [SourceEdit(5, 5, " YAML Ain't Markup Language")]);
+    });
+
+    test('after multiple changes', () {
+      final yamlEditor = YamlEditor('YAML: YAML');
+      yamlEditor.update(['YAML'], "YAML Ain't Markup Language");
+      yamlEditor.update(['XML'], 'Extensible Markup Language');
+      yamlEditor.remove(['YAML']);
+
+      expect(yamlEditor.edits, [
+        SourceEdit(5, 5, " YAML Ain't Markup Language"),
+        SourceEdit(32, 0, '\nXML: Extensible Markup Language\n'),
+        SourceEdit(0, 33, '')
+      ]);
+    });
+
+    test('that do not automatically update with internal list', () {
+      final yamlEditor = YamlEditor('YAML: YAML');
+      yamlEditor.update(['YAML'], "YAML Ain't Markup Language");
+
+      final firstEdits = yamlEditor.edits;
+
+      expect(firstEdits, [SourceEdit(5, 5, " YAML Ain't Markup Language")]);
+
+      yamlEditor.update(['XML'], 'Extensible Markup Language');
+      yamlEditor.remove(['YAML']);
+
+      expect(firstEdits, [SourceEdit(5, 5, " YAML Ain't Markup Language")]);
+      expect(yamlEditor.edits, [
+        SourceEdit(5, 5, " YAML Ain't Markup Language"),
+        SourceEdit(32, 0, '\nXML: Extensible Markup Language\n'),
+        SourceEdit(0, 33, '')
+      ]);
+    });
+  });
+}

diff --git a/pkgs/yaml_edit/test/golden_test.dart b/pkgs/yaml_edit/test/golden_test.dart
new file mode 100644
index 0000000..1dd6ff3
--- /dev/null
+++ b/pkgs/yaml_edit/test/golden_test.dart

@@ -0,0 +1,40 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+@TestOn('vm')
+library;
+
+import 'dart:io';
+import 'dart:isolate';
+
+import 'package:test/test.dart';
+
+import 'test_case.dart';
+
+/// This script performs snapshot testing of the inputs in the testing directory
+/// against golden files if they exist, and creates the golden files otherwise.
+///
+/// Input directory should be in `test/test_cases`, while the golden files should
+/// be in `test/test_cases_golden`.
+///
+/// For more information on the expected input and output, refer to the README
+/// in the testdata folder
+Future<void> main() async {
+  final packageUri = await Isolate.resolvePackageUri(
+      Uri.parse('package:yaml_edit/yaml_edit.dart'));
+
+  final testdataUri = packageUri!.resolve('../test/testdata/');
+  final inputDirectory = Directory.fromUri(testdataUri.resolve('input/'));
+  final goldDirectoryUri = testdataUri.resolve('output/');
+
+  if (!inputDirectory.existsSync()) {
+    throw FileSystemException(
+        'Testing Directory does not exist!', inputDirectory.path);
+  }
+
+  final testCases =
+      await TestCases.getTestCases(inputDirectory.uri, goldDirectoryUri);
+
+  testCases.test();
+}

diff --git a/pkgs/yaml_edit/test/insert_test.dart b/pkgs/yaml_edit/test/insert_test.dart
new file mode 100644
index 0000000..8c0e3b2
--- /dev/null
+++ b/pkgs/yaml_edit/test/insert_test.dart

@@ -0,0 +1,207 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:test/test.dart';
+import 'package:yaml_edit/yaml_edit.dart';
+
+import 'test_utils.dart';
+
+void main() {
+  group('throws PathError', () {
+    test('if it is a map', () {
+      final doc = YamlEditor('a:1');
+      expect(() => doc.insertIntoList([], 0, 4), throwsPathError);
+    });
+
+    test('if it is a scalar', () {
+      final doc = YamlEditor('1');
+      expect(() => doc.insertIntoList([], 0, 4), throwsPathError);
+    });
+  });
+
+  test('throws RangeError if index is out of range', () {
+    final doc = YamlEditor('[1, 2]');
+    expect(() => doc.insertIntoList([], -1, 0), throwsRangeError);
+    expect(() => doc.insertIntoList([], 3, 0), throwsRangeError);
+  });
+
+  group('block list', () {
+    test('(1)', () {
+      final doc = YamlEditor('''
+- 1
+- 2''');
+      doc.insertIntoList([], 0, 0);
+      expect(doc.toString(), equals('''
+- 0
+- 1
+- 2'''));
+      expectYamlBuilderValue(doc, [0, 1, 2]);
+    });
+
+    test('(2)', () {
+      final doc = YamlEditor('''
+- 1
+- 2''');
+      doc.insertIntoList([], 1, 3);
+      expect(doc.toString(), equals('''
+- 1
+- 3
+- 2'''));
+      expectYamlBuilderValue(doc, [1, 3, 2]);
+    });
+
+    test('(3)', () {
+      final doc = YamlEditor('''
+- 1
+- 2
+''');
+      doc.insertIntoList([], 2, 3);
+      expect(doc.toString(), equals('''
+- 1
+- 2
+- 3
+'''));
+      expectYamlBuilderValue(doc, [1, 2, 3]);
+    });
+
+    test('(4)', () {
+      final doc = YamlEditor('''
+- 1
+- 3
+''');
+      doc.insertIntoList([], 1, [4, 5, 6]);
+      expect(doc.toString(), equals('''
+- 1
+- - 4
+  - 5
+  - 6
+- 3
+'''));
+      expectYamlBuilderValue(doc, [
+        1,
+        [4, 5, 6],
+        3
+      ]);
+    });
+
+    test(' with comments', () {
+      final doc = YamlEditor('''
+- 0 # comment a
+- 2 # comment b
+''');
+      doc.insertIntoList([], 1, 1);
+      expect(doc.toString(), equals('''
+- 0 # comment a
+- 1
+- 2 # comment b
+'''));
+      expectYamlBuilderValue(doc, [0, 1, 2]);
+    });
+
+    for (var i = 0; i < 3; i++) {
+      test('block insert(1) at $i', () {
+        final yamlEditor = YamlEditor('''
+# comment
+- z:
+    x: 1
+    y: 2
+- z:
+    x: 3
+    y: 4
+''');
+        expect(
+            () => yamlEditor.insertIntoList(
+                [],
+                i,
+                {
+                  'z': {'x': 5, 'y': 6}
+                }),
+            returnsNormally);
+      });
+    }
+
+    for (var i = 0; i < 3; i++) {
+      test('block insert(2) at $i', () {
+        final yamlEditor = YamlEditor('''
+a:
+  - z:
+      x: 1
+      y: 2
+  - z:
+      x: 3
+      y: 4
+b:
+  - w:
+      m: 2
+      n: 4
+''');
+        expect(
+            () => yamlEditor.insertIntoList(
+                ['a'],
+                i,
+                {
+                  'z': {'x': 5, 'y': 6}
+                }),
+            returnsNormally);
+      });
+    }
+
+    for (var i = 0; i < 2; i++) {
+      test('block insert nested and with comments at $i', () {
+        final yamlEditor = YamlEditor('''
+a:
+  b:
+    - c:
+        d: 1
+    - c:
+        d: 2
+# comment
+  e:
+    - g:
+        e: 1
+        f: 2 
+# comment
+''');
+        expect(
+            () => yamlEditor.insertIntoList(
+                ['a', 'b'],
+                i,
+                {
+                  'g': {'e': 3, 'f': 4}
+                }),
+            returnsNormally);
+      });
+    }
+  });
+
+  group('flow list', () {
+    test('(1)', () {
+      final doc = YamlEditor('[1, 2]');
+      doc.insertIntoList([], 0, 0);
+      expect(doc.toString(), equals('[0, 1, 2]'));
+      expectYamlBuilderValue(doc, [0, 1, 2]);
+    });
+
+    test('(2)', () {
+      final doc = YamlEditor('[1, 2]');
+      doc.insertIntoList([], 1, 3);
+      expect(doc.toString(), equals('[1, 3, 2]'));
+      expectYamlBuilderValue(doc, [1, 3, 2]);
+    });
+
+    test('(3)', () {
+      final doc = YamlEditor('[1, 2]');
+      doc.insertIntoList([], 2, 3);
+      expect(doc.toString(), equals('[1, 2, 3]'));
+      expectYamlBuilderValue(doc, [1, 2, 3]);
+    });
+
+    test('(4)', () {
+      final doc = YamlEditor('["[],", "[],"]');
+      doc.insertIntoList([], 1, 'test');
+      expect(doc.toString(), equals('["[],", test, "[],"]'));
+      expectYamlBuilderValue(doc, ['[],', 'test', '[],']);
+    });
+  });
+}

diff --git a/pkgs/yaml_edit/test/naughty_test.dart b/pkgs/yaml_edit/test/naughty_test.dart
new file mode 100644
index 0000000..533a535
--- /dev/null
+++ b/pkgs/yaml_edit/test/naughty_test.dart

@@ -0,0 +1,30 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:test/test.dart';
+import 'package:yaml_edit/yaml_edit.dart';
+
+import 'problem_strings.dart';
+
+void main() {
+  for (final string in problemStrings) {
+    test('expect string $string', () {
+      final doc = YamlEditor('');
+
+      /// Using [runZoned] to hide `package:yaml`'s warnings.
+      /// Test failures and errors will still be shown.
+      runZoned(() {
+        expect(() => doc.update([], string), returnsNormally);
+        final value = doc.parseAt([]).value;
+        expect(value, isA<String>());
+        expect(value, equals(string));
+      },
+          zoneSpecification: ZoneSpecification(
+              print: (Zone self, ZoneDelegate parent, Zone zone,
+                  String message) {}));
+    });
+  }
+}

diff --git a/pkgs/yaml_edit/test/parse_test.dart b/pkgs/yaml_edit/test/parse_test.dart
new file mode 100644
index 0000000..382307c
--- /dev/null
+++ b/pkgs/yaml_edit/test/parse_test.dart

@@ -0,0 +1,156 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:test/test.dart';
+import 'package:yaml/yaml.dart';
+import 'package:yaml_edit/yaml_edit.dart';
+
+import 'test_utils.dart';
+
+void main() {
+  group('throws', () {
+    test('PathError if key does not exist', () {
+      final doc = YamlEditor('{a: 4}');
+      final path = ['b'];
+
+      expect(() => doc.parseAt(path), throwsPathError);
+    });
+
+    test('PathError if path tries to go deeper into a scalar', () {
+      final doc = YamlEditor('{a: 4}');
+      final path = ['a', 'b'];
+
+      expect(() => doc.parseAt(path), throwsPathError);
+    });
+
+    test('PathError if index is out of bounds', () {
+      final doc = YamlEditor('[0,1]');
+      final path = [2];
+
+      expect(() => doc.parseAt(path), throwsPathError);
+    });
+
+    test('PathError if index is not an integer', () {
+      final doc = YamlEditor('[0,1]');
+      final path = ['2'];
+
+      expect(() => doc.parseAt(path), throwsPathError);
+    });
+  });
+
+  group('orElse provides a default value', () {
+    test('simple example with null node return ', () {
+      final doc = YamlEditor('{a: {d: 4}, c: ~}');
+      final result = doc.parseAt(['b'], orElse: () => wrapAsYamlNode(null));
+
+      expect(result.value, equals(null));
+    });
+
+    test('simple example with map return', () {
+      final doc = YamlEditor('{a: {d: 4}, c: ~}');
+      final result =
+          doc.parseAt(['b'], orElse: () => wrapAsYamlNode({'a': 42}));
+
+      expect(result, isA<YamlMap>());
+      expect(result.value, equals({'a': 42}));
+    });
+
+    test('simple example with scalar return', () {
+      final doc = YamlEditor('{a: {d: 4}, c: ~}');
+      final result = doc.parseAt(['b'], orElse: () => wrapAsYamlNode(42));
+
+      expect(result, isA<YamlScalar>());
+      expect(result.value, equals(42));
+    });
+
+    test('simple example with list return', () {
+      final doc = YamlEditor('{a: {d: 4}, c: ~}');
+      final result = doc.parseAt(['b'], orElse: () => wrapAsYamlNode([42]));
+
+      expect(result, isA<YamlList>());
+      expect(result.value, equals([42]));
+    });
+  });
+
+  group('returns a YamlNode', () {
+    test('with the correct type', () {
+      final doc = YamlEditor("YAML: YAML Ain't Markup Language");
+      final expectedYamlScalar = doc.parseAt(['YAML']);
+
+      expect(expectedYamlScalar, isA<YamlScalar>());
+    });
+
+    test('with the correct value', () {
+      final doc = YamlEditor("YAML: YAML Ain't Markup Language");
+
+      expect(doc.parseAt(['YAML']).value, "YAML Ain't Markup Language");
+    });
+
+    test('with the correct value in nested collection', () {
+      final doc = YamlEditor('''
+a: 1
+b:
+  d: 4
+  e: [5, 6, 7]
+c: 3
+''');
+
+      expect(doc.parseAt(['b', 'e', 2]).value, 7);
+    });
+
+    test('with a null value in nested collection', () {
+      final doc = YamlEditor('''
+key1:
+  key2: null
+''');
+
+      expect(doc.parseAt(['key1', 'key2']).value, null);
+    });
+
+    test('with the correct type (2)', () {
+      final doc = YamlEditor("YAML: YAML Ain't Markup Language");
+      final expectedYamlMap = doc.parseAt([]);
+
+      expect(expectedYamlMap is YamlMap, equals(true));
+    });
+
+    test('that is immutable', () {
+      final doc = YamlEditor("YAML: YAML Ain't Markup Language");
+      final expectedYamlMap = doc.parseAt([]);
+
+      expect(() => (expectedYamlMap as YamlMap)['YAML'] = 'test',
+          throwsUnsupportedError);
+    });
+
+    test('that has immutable children', () {
+      final doc = YamlEditor("YAML: ['Y', 'A', 'M', 'L']");
+      final expectedYamlMap = doc.parseAt([]);
+
+      expect(() => ((expectedYamlMap as YamlMap)['YAML'] as List)[0] = 'X',
+          throwsUnsupportedError);
+    });
+  });
+
+  test('works with map keys', () {
+    final doc = YamlEditor('{a: {{[1, 2]: 3}: 4}}');
+    expect(
+        doc.parseAt([
+          'a',
+          {
+            [1, 2]: 3
+          }
+        ]).value,
+        equals(4));
+  });
+
+  test('works with null in path', () {
+    final doc = YamlEditor('{a: { ~: 4}}');
+    expect(doc.parseAt(['a', null]).value, equals(4));
+  });
+
+  test('works with null value', () {
+    final doc = YamlEditor('{a: null}');
+    expect(doc.parseAt(['a']).value, equals(null));
+  });
+}

diff --git a/pkgs/yaml_edit/test/prepend_test.dart b/pkgs/yaml_edit/test/prepend_test.dart
new file mode 100644
index 0000000..3112653
--- /dev/null
+++ b/pkgs/yaml_edit/test/prepend_test.dart

@@ -0,0 +1,169 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:test/test.dart';
+import 'package:yaml/yaml.dart';
+import 'package:yaml_edit/yaml_edit.dart';
+
+import 'test_utils.dart';
+
+void main() {
+  group('throws PathError', () {
+    test('if it is a map', () {
+      final doc = YamlEditor('a:1');
+      expect(() => doc.prependToList([], 4), throwsPathError);
+    });
+
+    test('if it is a scalar', () {
+      final doc = YamlEditor('1');
+      expect(() => doc.prependToList([], 4), throwsPathError);
+    });
+  });
+
+  group('flow list', () {
+    test('(1)', () {
+      final doc = YamlEditor('[1, 2]');
+      doc.prependToList([], 0);
+      expect(doc.toString(), equals('[0, 1, 2]'));
+      expectYamlBuilderValue(doc, [0, 1, 2]);
+    });
+
+    test('null value', () {
+      final doc = YamlEditor('[1, 2]');
+      doc.prependToList([], null);
+      expect(doc.toString(), equals('[null, 1, 2]'));
+      expectYamlBuilderValue(doc, [null, 1, 2]);
+    });
+
+    test('with spaces (1)', () {
+      final doc = YamlEditor('[ 1 , 2 ]');
+      doc.prependToList([], 0);
+      expect(doc.toString(), equals('[ 0, 1 , 2 ]'));
+      expectYamlBuilderValue(doc, [0, 1, 2]);
+    });
+  });
+
+  group('block list', () {
+    test('(1)', () {
+      final doc = YamlEditor('''
+- 1
+- 2''');
+      doc.prependToList([], 0);
+      expect(doc.toString(), equals('''
+- 0
+- 1
+- 2'''));
+      expectYamlBuilderValue(doc, [0, 1, 2]);
+    });
+
+    /// Regression testing for no trailing spaces.
+    test('(2)', () {
+      final doc = YamlEditor('''- 1
+- 2''');
+      doc.prependToList([], 0);
+      expect(doc.toString(), equals('''- 0
+- 1
+- 2'''));
+      expectYamlBuilderValue(doc, [0, 1, 2]);
+    });
+
+    test('(3)', () {
+      final doc = YamlEditor('''
+- 1
+- 2
+''');
+      doc.prependToList([], [4, 5, 6]);
+      expect(doc.toString(), equals('''
+- - 4
+  - 5
+  - 6
+- 1
+- 2
+'''));
+      expectYamlBuilderValue(doc, [
+        [4, 5, 6],
+        1,
+        2
+      ]);
+    });
+
+    test('(4)', () {
+      final doc = YamlEditor('''
+a:
+ - b
+ - - c
+   - d
+''');
+      doc.prependToList(
+          ['a'], wrapAsYamlNode({1: 2}, collectionStyle: CollectionStyle.FLOW));
+
+      expect(doc.toString(), equals('''
+a:
+ - {1: 2}
+ - b
+ - - c
+   - d
+'''));
+      expectYamlBuilderValue(doc, {
+        'a': [
+          {1: 2},
+          'b',
+          ['c', 'd']
+        ]
+      });
+    });
+
+    test('with comments ', () {
+      final doc = YamlEditor('''
+# comments
+- 1 # comments
+- 2
+''');
+      doc.prependToList([], 0);
+      expect(doc.toString(), equals('''
+# comments
+- 0
+- 1 # comments
+- 2
+'''));
+      expectYamlBuilderValue(doc, [0, 1, 2]);
+    });
+
+    test('nested in map', () {
+      final doc = YamlEditor('''
+a:
+  - 1
+  - 2
+''');
+      doc.prependToList(['a'], 0);
+      expect(doc.toString(), equals('''
+a:
+  - 0
+  - 1
+  - 2
+'''));
+      expectYamlBuilderValue(doc, {
+        'a': [0, 1, 2]
+      });
+    });
+
+    test('nested in map with comments ', () {
+      final doc = YamlEditor('''
+a: # comments
+  - 1 # comments
+  - 2
+''');
+      doc.prependToList(['a'], 0);
+      expect(doc.toString(), equals('''
+a: # comments
+  - 0
+  - 1 # comments
+  - 2
+'''));
+      expectYamlBuilderValue(doc, {
+        'a': [0, 1, 2]
+      });
+    });
+  });
+}

diff --git a/pkgs/yaml_edit/test/preservation_test.dart b/pkgs/yaml_edit/test/preservation_test.dart
new file mode 100644
index 0000000..a763296
--- /dev/null
+++ b/pkgs/yaml_edit/test/preservation_test.dart

@@ -0,0 +1,61 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:test/test.dart';
+
+import 'test_utils.dart';
+
+void main() {
+  group('preserves original yaml: ', () {
+    test('number', expectLoadPreservesYAML('2'));
+    test('number with leading and trailing lines', expectLoadPreservesYAML('''
+      
+      2
+      
+      '''));
+    test('octal numbers', expectLoadPreservesYAML('0o14'));
+    test('negative numbers', expectLoadPreservesYAML('-345'));
+    test('hexadecimal numbers', expectLoadPreservesYAML('0x123abc'));
+    test('floating point numbers', expectLoadPreservesYAML('345.678'));
+    test('exponential numbers', expectLoadPreservesYAML('12.3015e+02'));
+    test('string', expectLoadPreservesYAML('a string'));
+    test('string with control characters',
+        expectLoadPreservesYAML('a string \\n'));
+    test('string with control characters',
+        expectLoadPreservesYAML('a string \n\r'));
+    test('string with hex escapes',
+        expectLoadPreservesYAML('\\x0d\\x0a is \\r\\n'));
+    test('flow map', expectLoadPreservesYAML('{a: 2}'));
+    test('flow list', expectLoadPreservesYAML('[1, 2]'));
+    test('flow list with different types of elements',
+        expectLoadPreservesYAML('[1, a]'));
+    test('flow list with weird spaces',
+        expectLoadPreservesYAML('[ 1 ,      2]'));
+    test('multiline string', expectLoadPreservesYAML('''
+      Mark set a major league
+      home run record in 1998.'''));
+    test('tilde', expectLoadPreservesYAML('~'));
+    test('false', expectLoadPreservesYAML('false'));
+
+    test('block map', expectLoadPreservesYAML('''a:
+    b: 1
+    '''));
+    test('block list', expectLoadPreservesYAML('''a:
+    - 1
+    '''));
+    test('complicated example', () {
+      expectLoadPreservesYAML('''verb: RecommendCafes
+map:
+  a:
+    b: 1
+recipe:
+  - verb: Score
+    outputs: ["DishOffering[]/Scored", "Suggestions"]
+    name: Hotpot
+  - verb: Rate
+    inputs: Dish
+    ''');
+    });
+  });
+}

diff --git a/pkgs/yaml_edit/test/problem_strings.dart b/pkgs/yaml_edit/test/problem_strings.dart
new file mode 100644
index 0000000..527a9e0
--- /dev/null
+++ b/pkgs/yaml_edit/test/problem_strings.dart

@@ -0,0 +1,91 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// ignore_for_file: lines_longer_than_80_chars
+
+const problemStrings = [
+  '[]',
+  '{}',
+  '',
+  ',',
+  '~',
+  'undefined',
+  'undef',
+  'null',
+  'NULL',
+  '(null)',
+  'nil',
+  'NIL',
+  'true',
+  'false',
+  'True',
+  'False',
+  'TRUE',
+  'FALSE',
+  'None',
+  '\\',
+  '\\\\',
+  '0',
+  '1',
+  '\$1.00',
+  '1/2',
+  '1E2',
+  '-\$1.00',
+  '-1/2',
+  '-1E+02',
+  '1/0',
+  '0/0',
+  '-0',
+  '+0.0',
+  '0..0',
+  '.',
+  '0.0.0',
+  '0,00',
+  ',',
+  '0.0/0',
+  '1.0/0.0',
+  '0.0/0.0',
+  '--1',
+  '-',
+  '-.',
+  '-,',
+  '999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999',
+  'NaN',
+  'Infinity',
+  '-Infinity',
+  'INF',
+  '1#INF',
+  '0x0',
+  '0xffffffffffffffff',
+  "1'000.00",
+  '1,000,000.00',
+  '1.000,00',
+  "1'000,00",
+  '1.000.000,00',
+  ",./;'[]\\-=",
+  '<>?:"{}|_+',
+  '!@#\$%^&*()`~',
+  '\u0001\u0002\u0003\u0004\u0005\u0006\u0007\b\u000e\u000f\u0010\u0011\u0012\u0013\u0014\u0015\u0016\u0017\u0018\u0019\u001a\u001b\u001c\u001d\u001e\u001f',
+  '\t\u000b\f                  　',
+  'ด้้้้้็็็็็้้้้้็็็็็้้้้้้้้็็็็็้้้้้็็็็็้้้้้้้้็็็็็้้้้้็็็็็้้้้้้้้็็็็็้้้้้็็็็ ด้้้้้็็็็็้้้้้็็็็็้้้้้้้้็็็็็้้้้้็็็็็้้้้้้้้็็็็็้้้้้็็็็็้้้้้้้้็็็็็้้้้้็็็็ ด้้้้้็็็็็้้้้้็็็็็้้้้้้้้็็็็็้้้้้็็็็็้้้้้้้้็็็็็้้้้้็็็็็้้้้้้้้็็็็็้้้้้็็็็',
+  "'",
+  '"',
+  "''",
+  '\'"',
+  "'\"'",
+  '社會科學院語學研究所',
+  'Ⱥ',
+  'ヽ༼ຈل͜ຈ༽ﾉ ヽ༼ຈل͜ຈ༽ﾉ',
+  '❤️ 💔 💌 💕 💞 💓 💗 💖 💘 💝 💟 💜 💛 💚 💙',
+  '𝕋𝕙𝕖 𝕢𝕦𝕚𝕔𝕜 𝕓𝕣𝕠𝕨𝕟 𝕗𝕠𝕩 𝕛𝕦𝕞𝕡𝕤 𝕠𝕧𝕖𝕣 𝕥𝕙𝕖 𝕝𝕒𝕫𝕪 𝕕𝕠𝕘',
+  ' ',
+  '%',
+  '%d',
+  '%s%s%s%s%s',
+  '{0}',
+  '%*.*s',
+  '%@',
+  '%n',
+  'The quic\b\b\b\b\b\bk brown fo\u0007\u0007\u0007\u0007\u0007\u0007\u0007\u0007\u0007\u0007\u0007x... [Beeeep]',
+];

diff --git a/pkgs/yaml_edit/test/random_test.dart b/pkgs/yaml_edit/test/random_test.dart
new file mode 100644
index 0000000..85cea4a
--- /dev/null
+++ b/pkgs/yaml_edit/test/random_test.dart

@@ -0,0 +1,311 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:math' show Random;
+
+import 'package:test/test.dart';
+import 'package:yaml/yaml.dart';
+import 'package:yaml_edit/yaml_edit.dart';
+
+import 'problem_strings.dart';
+import 'test_utils.dart';
+
+/// Performs naive fuzzing on an initial YAML file based on an initial seed.
+///
+/// Starting with a template YAML, we randomly generate modifications and their
+/// inputs (boolean, null, strings, or numbers) to modify the YAML and assert
+/// that the change produced was expected.
+void main() {
+  final generator = _Generator(maxDepth: 5);
+
+  const roundsOfTesting = 40;
+  const modificationsPerRound = 1000;
+
+  for (var i = 0; i < roundsOfTesting; i++) {
+    test(
+      'testing with randomly generated modifications: test $i',
+      () {
+        final editor = YamlEditor('''
+name: yaml_edit
+description: A library for YAML manipulation with comment and whitespace preservation.
+version: 0.0.1-dev
+
+environment:
+  sdk: ">=2.4.0 <3.0.0"
+
+dependencies:
+  meta: ^1.1.8
+  quiver_hashcode: ^2.0.0
+
+dev_dependencies:
+  pedantic: ^1.9.0
+  test: ^1.14.4
+''');
+
+        for (var j = 0; j < modificationsPerRound; j++) {
+          expect(
+            () => generator.performNextModification(editor, i),
+            returnsNormally,
+          );
+        }
+      },
+    );
+  }
+}
+
+/// Generates the random variables we need for fuzzing.
+class _Generator {
+  final Random r;
+
+  /// 2^32
+  static const int maxInt = 4294967296;
+
+  /// Maximum depth of random YAML collection generated.
+  final int maxDepth;
+
+  // ignore: unused_element
+  _Generator({int seed = 0, required this.maxDepth}) : r = Random(seed);
+
+  int nextInt([int max = maxInt]) => r.nextInt(max);
+
+  double nextDouble() => r.nextDouble();
+
+  bool nextBool() => r.nextBool();
+
+  /// Generates a new string by individually generating characters and
+  /// appending them to a buffer. Currently only generates strings from
+  /// ascii 32 - 127.
+  String nextString() {
+    if (nextBool()) {
+      return problemStrings[nextInt(problemStrings.length)];
+    }
+
+    final length = nextInt(100);
+    final buffer = StringBuffer();
+
+    for (var i = 0; i < length; i++) {
+      final charCode = nextInt(95) + 32;
+      buffer.writeCharCode(charCode);
+    }
+
+    return buffer.toString();
+  }
+
+  /// Generates a new scalar recognizable by YAML.
+  Object? nextScalar() {
+    final typeIndex = nextInt(5);
+
+    switch (typeIndex) {
+      case 0:
+        return nextBool();
+      case 1:
+        return nextDouble();
+      case 2:
+        return nextInt();
+      case 3:
+        return null;
+      default:
+        return nextString();
+    }
+  }
+
+  YamlScalar nextYamlScalar() {
+    return wrapAsYamlNode(nextScalar(), scalarStyle: nextScalarStyle())
+        as YamlScalar;
+  }
+
+  /// Generates the next [YamlList], with the current [depth].
+  YamlList nextYamlList(int depth) {
+    final length = nextInt(9);
+    final list = [];
+
+    for (var i = 0; i < length; i++) {
+      list.add(nextYamlNode(depth + 1));
+    }
+
+    return wrapAsYamlNode(list, collectionStyle: nextCollectionStyle())
+        as YamlList;
+  }
+
+  /// Generates the next [YamlList], with the current [depth].
+  YamlMap nextYamlMap(int depth) {
+    final length = nextInt(9);
+    final nodes = {};
+
+    for (var i = 0; i < length; i++) {
+      nodes[nextYamlNode(depth + 1)] = nextYamlScalar();
+    }
+
+    return wrapAsYamlNode(nodes, collectionStyle: nextCollectionStyle())
+        as YamlMap;
+  }
+
+  /// Returns a [YamlNode], with it being a [YamlScalar] 80% of the time, a
+  /// [YamlList] 10% of the time, and a [YamlMap] 10% of the time.
+  ///
+  /// If [depth] is greater than [maxDepth], we instantly return a [YamlScalar]
+  /// to prevent the parent from growing any further, to improve our speeds.
+  YamlNode nextYamlNode([int depth = 0]) {
+    if (depth >= maxDepth) {
+      return nextYamlScalar();
+    }
+
+    final roll = nextInt(10);
+
+    if (roll < 8) {
+      return nextYamlScalar();
+    } else if (roll == 8) {
+      return nextYamlList(depth);
+    } else {
+      return nextYamlMap(depth);
+    }
+  }
+
+  /// Performs a random modification
+  void performNextModification(YamlEditor editor, int count) {
+    final path = findPath(editor);
+    final node = editor.parseAt(path);
+    final initialString = editor.toString();
+    final args = [];
+    var method = YamlModificationMethod.remove;
+
+    try {
+      if (node is YamlScalar) {
+        editor.remove(path);
+        return;
+      }
+
+      if (node is YamlList) {
+        final methodIndex = nextInt(YamlModificationMethod.values.length);
+        method = YamlModificationMethod.values[methodIndex];
+
+        switch (method) {
+          case YamlModificationMethod.remove:
+            editor.remove(path);
+            break;
+          case YamlModificationMethod.update:
+            if (node.isEmpty) break;
+            final index = nextInt(node.length);
+            args.add(nextYamlNode());
+            path.add(index);
+            editor.update(path, args[0]);
+            break;
+          case YamlModificationMethod.appendTo:
+            args.add(nextYamlNode());
+            editor.appendToList(path, args[0]);
+            break;
+          case YamlModificationMethod.prependTo:
+            args.add(nextYamlNode());
+            editor.prependToList(path, args[0]);
+            break;
+          case YamlModificationMethod.insert:
+            args.add(nextInt(node.length + 1));
+            args.add(nextYamlNode());
+            editor.insertIntoList(path, args[0] as int, args[1]);
+            break;
+          case YamlModificationMethod.splice:
+            args.add(nextInt(node.length + 1));
+            args.add(nextInt(node.length + 1 - (args[0] as int)));
+            args.add(nextYamlList(0));
+            editor.spliceList(
+                path, args[0] as int, args[1] as int, args[2] as List);
+            break;
+        }
+        return;
+      }
+
+      if (node is YamlMap) {
+        final replace = nextBool();
+        method = YamlModificationMethod.update;
+
+        if (replace && node.isNotEmpty) {
+          final keyList = node.keys.toList();
+          path.add(keyList[nextInt(keyList.length)]);
+        } else {
+          path.add(nextScalar());
+        }
+        final value = nextYamlNode();
+        args.add(value);
+        editor.update(path, value);
+        return;
+      }
+    } catch (error, stacktrace) {
+      /// TODO: Fix once reproducible. Identify pattern.
+      if (count == 20) return;
+
+      print('''
+Failed to call $method on:
+$initialString
+with the following arguments:
+$args
+and path:
+$path
+
+Error Details:
+$error
+
+$stacktrace
+''');
+      rethrow;
+    }
+
+    throw AssertionError('Got invalid node');
+  }
+
+  /// Obtains a random path by traversing [editor].
+  ///
+  /// At every node, we return the path to the node if the node has no children.
+  /// Otherwise, we return at a 50% chance, or traverse to one random child.
+  List<Object?> findPath(YamlEditor editor) {
+    final path = <Object?>[];
+
+    // 50% chance of stopping at the collection
+    while (nextBool()) {
+      final node = editor.parseAt(path);
+
+      if (node is YamlList && node.isNotEmpty) {
+        path.add(nextInt(node.length));
+      } else if (node is YamlMap && node.isNotEmpty) {
+        final keyList = node.keys.toList();
+        path.add(keyList[nextInt(keyList.length)]);
+      } else {
+        break;
+      }
+    }
+
+    return path;
+  }
+
+  ScalarStyle nextScalarStyle() {
+    final seed = nextInt(6);
+
+    switch (seed) {
+      case 0:
+        return ScalarStyle.DOUBLE_QUOTED;
+      case 1:
+        return ScalarStyle.FOLDED;
+      case 2:
+        return ScalarStyle.LITERAL;
+      case 3:
+        return ScalarStyle.PLAIN;
+      case 4:
+        return ScalarStyle.SINGLE_QUOTED;
+      default:
+        return ScalarStyle.ANY;
+    }
+  }
+
+  CollectionStyle nextCollectionStyle() {
+    final seed = nextInt(3);
+
+    switch (seed) {
+      case 0:
+        return CollectionStyle.BLOCK;
+      case 1:
+        return CollectionStyle.FLOW;
+      default:
+        return CollectionStyle.ANY;
+    }
+  }
+}

diff --git a/pkgs/yaml_edit/test/remove_test.dart b/pkgs/yaml_edit/test/remove_test.dart
new file mode 100644
index 0000000..4742b56
--- /dev/null
+++ b/pkgs/yaml_edit/test/remove_test.dart

@@ -0,0 +1,603 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:test/test.dart';
+import 'package:yaml_edit/yaml_edit.dart';
+
+import 'test_utils.dart';
+
+void main() {
+  group('throws', () {
+    test('PathError if collectionPath points to a scalar', () {
+      final doc = YamlEditor('''
+a: 1
+b: 2
+c: 3
+''');
+
+      expect(() => doc.remove(['a', 0]), throwsPathError);
+    });
+
+    test('PathError if collectionPath is invalid', () {
+      final doc = YamlEditor('''
+a: 1
+b: 2
+c: 3
+''');
+
+      expect(() => doc.remove(['d']), throwsPathError);
+    });
+
+    test('PathError if collectionPath is invalid in nested path', () {
+      final doc = YamlEditor('''
+a:
+  b: 'foo'
+''');
+
+      expect(() => doc.remove(['d']), throwsPathError);
+    });
+
+    test('PathError if collectionPath is invalid - list', () {
+      final doc = YamlEditor('''
+[1, 2, 3]
+''');
+
+      expect(() => doc.remove([4]), throwsPathError);
+    });
+
+    test('PathError in list if using a non-integer as index', () {
+      final doc = YamlEditor("{ a: ['b', 'c'] }");
+      expect(() => doc.remove(['a', 'b']), throwsPathError);
+    });
+
+    test('PathError if path is invalid', () {
+      final doc = YamlEditor("{ a: ['b', 'c'] }");
+      expect(() => doc.remove(['a', 0, '1']), throwsPathError);
+    });
+  });
+
+  group('returns', () {
+    test('returns the removed node when successful', () {
+      final doc = YamlEditor('{ a: { b: foo } }');
+      final node = doc.remove(['a', 'b']);
+      expect(node.value, equals('foo'));
+    });
+
+    test('returns null-value node when doc is empty and path is empty', () {
+      final doc = YamlEditor('');
+      final node = doc.remove([]);
+      expect(node.value, equals(null));
+    });
+  });
+
+  test('empty path should clear string', () {
+    final doc = YamlEditor('''
+a: 1
+b: 2
+c: [3, 4]
+''');
+    doc.remove([]);
+    expect(doc.toString(), equals(''));
+  });
+
+  group('block map', () {
+    test('(1)', () {
+      final doc = YamlEditor('''
+a: 1
+b: 2
+c: 3
+''');
+      doc.remove(['b']);
+      expect(doc.toString(), equals('''
+a: 1
+c: 3
+'''));
+    });
+
+    test('empty value', () {
+      final doc = YamlEditor('''
+a: 1
+b:
+c: 3
+''');
+      doc.remove(['b']);
+      expect(doc.toString(), equals('''
+a: 1
+c: 3
+'''));
+    });
+
+    test('empty value (2)', () {
+      final doc = YamlEditor('''
+- a: 1
+  b:
+  c: 3
+''');
+      doc.remove([0, 'b']);
+      expect(doc.toString(), equals('''
+- a: 1
+  c: 3
+'''));
+    });
+
+    test('empty value (3)', () {
+      final doc = YamlEditor('''
+- a: 1
+  b:
+
+  c: 3
+''');
+      doc.remove([0, 'b']);
+      expect(doc.toString(), equals('''
+- a: 1
+
+  c: 3
+'''));
+    });
+
+    test('preserves comments', () {
+      final doc = YamlEditor('''
+a: 1 # preserved 1
+# preserved 2
+b: 2
+# preserved 3
+c: 3 # preserved 4
+''');
+      doc.remove(['b']);
+      expect(doc.toString(), equals('''
+a: 1 # preserved 1
+# preserved 2
+# preserved 3
+c: 3 # preserved 4
+'''));
+    });
+
+    test('final element in map', () {
+      final doc = YamlEditor('''
+a: 1
+b: 2
+''');
+      doc.remove(['b']);
+      expect(doc.toString(), equals('''
+a: 1
+'''));
+    });
+
+    test('final element in nested map', () {
+      final doc = YamlEditor('''
+a:
+  aa: 11
+  bb: 22
+b: 2
+''');
+      doc.remove(['a', 'bb']);
+      expect(doc.toString(), equals('''
+a:
+  aa: 11
+b: 2
+'''));
+    });
+
+    test('last element should return flow empty map', () {
+      final doc = YamlEditor('''
+a: 1
+''');
+      doc.remove(['a']);
+      expect(doc.toString(), equals('''
+{}
+'''));
+    });
+
+    test('last element should return flow empty map (2)', () {
+      final doc = YamlEditor('''
+- a: 1
+- b: 2
+''');
+      doc.remove([0, 'a']);
+      expect(doc.toString(), equals('''
+- {}
+- b: 2
+'''));
+    });
+
+    test('nested', () {
+      final doc = YamlEditor('''
+a: 1
+b:
+  d: 4
+  e: 5
+c: 3
+''');
+      doc.remove(['b', 'd']);
+      expect(doc.toString(), equals('''
+a: 1
+b:
+  e: 5
+c: 3
+'''));
+    });
+
+    test('issue #55 reopend', () {
+      final doc = YamlEditor('''name: sample
+version: 0.1.0
+environment:
+  sdk: ^3.0.0
+dependencies:
+  retry: ^3.1.2
+dev_dependencies:
+  retry:''');
+      doc.remove(['dev_dependencies']);
+    });
+
+    test('issue #55 reopend, variant 2', () {
+      final doc = YamlEditor('''name: sample
+version: 0.1.0
+environment:
+  sdk: ^3.0.0
+dependencies:
+  retry: ^3.1.2
+dev_dependencies:
+  retry:''');
+      doc.remove(['dev_dependencies', 'retry']);
+    });
+  });
+
+  group('flow map', () {
+    test('(1)', () {
+      final doc = YamlEditor('{a: 1, b: 2, c: 3}');
+      doc.remove(['b']);
+      expect(doc.toString(), equals('{a: 1, c: 3}'));
+    });
+
+    test('(2) ', () {
+      final doc = YamlEditor('{a: 1}');
+      doc.remove(['a'
commit	d785fbb4c08f368f312f02744f2e3b63009630d9	[log] [tgz]
author	Moritz <mosum@google.com>	Mon Jan 13 09:24:45 2025 +0100
committer	GitHub <noreply@github.com>	Mon Jan 13 09:24:45 2025 +0100
tree	b2ce928425d3be58faceed72700081ed0c22023d
parent	54b89986ce979324476b5c0ff4b6c0231d7c7c55 [diff]
parent	a8abbfb306f035bfc80ecb337a46cd3c9513f28c [diff]