[ddc] Fixes for DDC async lowering.

--- Super fix ---
When the arguments to a call contain an async gap (an await in this case), the new lowering will save the receiver to a temp variable so it can be accessed on re-entry to the function body. This is skipped for literals as the literal does not need to be stored in a variable, it can simply be used as-is.

However, the DDC JS AST did not treat "this" or "super" as literals so we ended up with invalid JS like "let temp = super; // do await; temp.foo(...);". In this case "let temp = super;" is invalid, "super" cannot be used as a bare expression.

--- Function scope change ---
The original approach of using TemporaryIds for all the hoisted variables had a large flaw in that it didn't account for scopes captured by closures within async code. Hoisted variables were lifted out of their attached scope and so closures captured the single hoisted declaration and all modified the same variable. See async_scope_capture_test.dart for an example of this breaking.

To fix this we need to box any captured variables into a JS object. We then wrap any closures in an IIFE and pass the correct scope objects in as arguments to "capture" them. This is similar to dart2js's approach of boxing variables for closures. The approach is a little less fine-grained though and we simply box every variable. This makes the logic simpler and provides a better debug experience as users will just be able to look at the available "asyncScope" variables and see all the declarations in the original source code.

--- Add async callback ---
After further study, none of the other backends add implicit calls to 'async_helper.asyncStart' or 'async_helper.asyncEnd'. All the tests (with the exception of the hot_restart_timer_test updated below) are all set up to call asyncStart if they need it. As such we can simply remove and calls in the runtime/sdk to 'addAsyncCallback' (which is then calling 'async_helper.asyncStart'). Ditto with their remove/end counterparts.

Change-Id: Iac9a3774cc43fc2270e3bb2e992893358042e604
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/376020
Reviewed-by: Nicholas Shahan <nshahan@google.com>
Reviewed-by: Mark Zhou <markzipan@google.com>
Reviewed-by: Bob Nystrom <rnystrom@google.com>

https://dart.googlesource.com/sdk/+/90162cc1f616ec22fc6751fba478cda9d59d4e35
2 files changed
tree: 1bf88858d183c2685159e76f8bc8aa0a66761cd3
  1. ci/
  2. tools/
  3. .gitignore
  4. commits.json
  5. DEPS
  6. OWNERS
  7. README.md
README.md

Monorepo

A gclient solution for checking out Dart and Flutter source trees

Monorepo is:

  • Optimized for Tip-of-Tree testing: The Monorepo DEPS used to check out Dart and Flutter dependencies comes from the Flutter engine DEPS with updated dependencies from Dart.

Checking out Monorepo

With depot_tools installed and on your path, create a directory for your monorepo checkout and run these commands to create a gclient solution in that directory:

mkdir monorepo
cd monorepo
gclient config --unmanaged https://dart.googlesource.com/monorepo
gclient sync -D

This gives you a checkout in the monorepo directory that contains:

monorepo/
  DEPS - the DEPS used for this gclient checkout
  commits.json - the pinned commits for Dart, flutter/engine,
                 and flutter/flutter
  tools/ - scripts used to create monorepo DEPS
engine/src/ - the flutter/buildroot repo
    flutter/ - the flutter/engine repo
    out/ - the build directory, where Flutter engine builds are created
    third_party/ - Flutter dependencies checked out by DEPS
      dart/ - the Dart SDK checkout.
        third_party - Dart dependencies, also used by Flutter
flutter/ - the flutter/flutter repo

Building Flutter engine

Flutter's instructions for building the engine are at Compiling the engine

They can be followed closely, with a few changes:

  • Googlers working on Dart do not need to switch to Fuchsia's Goma RBE, except for Windows. The GOMA_DIR enviroment variable can just point to the .cipd_bin directory in a depot_tools installation, and just goma_ctl ensure_start is sufficient.
  • The --no-prebuilt-dart-sdk option has to be added to every gn command, so that the build is set up to build and use a local Dart SDK.
  • The --full-dart-sdk option must be added to gn for the host build target if you will be building web or desktop apps.

Example build commands that work on linux:

MONOREPO_PATH=$PWD
if [[ ! $PATH =~ (^|:)$MONOREPO_PATH/flutter/bin(:|$) ]]; then
  PATH=$MONOREPO_PATH/flutter/bin:$PATH
fi

export GOMA_DIR=$(dirname $(command -v gclient))/.cipd_bin
goma_ctl ensure_start

pushd engine/src
flutter/tools/gn --goma --no-prebuilt-dart-sdk --unoptimized --full-dart-sdk
autoninja -C out/host_debug_unopt
popd

Building Flutter apps

The Flutter commands used to build and run apps will use the locally built Flutter engine and Dart SDK, instead of the one downloaded by the Flutter tool, if the --local-engine option is provided.

For example, to build and run the Flutter spinning square sample on the web platform,

MONOREPO_PATH=$PWD
cd flutter/examples/layers
flutter --local-engine=host_debug_unopt \
  -d chrome run widgets/spinning_square.dart
cd $MONOREPO_PATH

To build for desktop, specify the desktop platform device in flutter run as -d macos or -d linux or -d windows. You may also need to run the command

flutter create --platforms=windows,macos,linux

on existing apps, such as sample apps. New apps created with flutter create already include these support files. Details of desktop support are at Desktop Support for Flutter

Testing

Tests in the Flutter source tree can be run with the flutter test command, run in the directory of a package containing tests. For example:

MONOREPO_PATH=$PWD
cd flutter/packages/flutter
flutter test --local-engine=host_debug_unopt
cd $MONOREPO_PATH

Troubleshooting

Please file an issue or email the dart-engprod team with any problems with or questions about using monorepo.

We will update this documentation to address them.

  • flutter commands may download the engine and Dart SDK files for the configured channel, even though they will be using the local engine and its SDK.

Windows

  • On Windows, gclient sync needs to be run in an administrator session, because some installed dependencies create symlinks.