Implement RawMenuAnchor (#158255)

This PR adds a `RawMenuAnchor()` widget to widgets.dart. The purpose of
this widget is to provide a menu primitive for the Material and
Cupertino libraries (and others) to build upon. Additionally, this PR
makes MenuController an inherited widget to simplify nested access to
the menu (e.g. if you want to launch a context menu from a deeply-nested
widget).

This PR:
* Centralizes core menu logic to a private class,` _RawMenuAnchor()`,
  * Provides the internals for interacting with menus:
    * TapRegion interop
    * DismissMenuAction handler
    * Close on scroll/resize
    * Focus traversal information, if applicable
* Subclasses override `_open`, `_close`, `_isOpen`, `_buildAnchor`, and
`_menuScopeNode`
* State is accessible by descendents via
`MenuController.maybeOf(context)._anchor`
* Adds 2 public constructors, backed by a `_RawMenuAnchor()` that
contains shared logic.
  * `RawMenuAnchor()`
    * Users build the overlay from scratch.
* Provides anchor/overlay position information and TapRegionGroupId to
builder
    * Does not provide FocusScope management.
  * `RawMenuAnchorGroup()`
    * A primitive for menus that do not have overlays (menu bars).
* This was previously called RawMenuAnchor.node(), but @dkwingsmt made a
good case for splitting out the constructor.

<s>Documentation examples have been added, and can be viewed at
https://menu-anchor.web.app/</s>

<s>https://github.com/user-attachments/assets/25d35f23-2aad-4d07-9172-5c3fd65d53cf</s>

@dkwingsmt

List which issues are fixed by this PR.
https://github.com/flutter/flutter/pull/143712

Some issues that need to be addressed:

Semantics:
<img width="1027" alt="image"
src="https://github.com/user-attachments/assets/d69661c9-8435-4d9c-b200-474968cb57eb">
I'm basing the menu semantics off of the comment
[here](https://github.com/flutter/engine/blob/ef3ca70db20230436b6defe5b4cdb0d242deea96/lib/web_ui/lib/src/engine/semantics/semantics.dart#L382),
but I'm unsure whether the route should be given a name. There is no
menubar/menu/menuitem role in Flutter, so I'm assuming the menu should
be composed of nested dialogs

<s>Unlike the menubar pattern from
[W3C](https://www.w3.org/WAI/ARIA/apg/patterns/menubar/examples/menubar-navigation/),
the RawMenuAnchor

- does not close on tab/shift-tab. I left this behavior out of the menu
so that users could customize tab behavior, but I'm not opinionated
either way
- does not open on ArrowUp/ArrowDown, because this could interfere with
user focus behavior in unconventional menu setups (e.g. a vertical
menu).
- does not automatically focus the first item in a menu overlay when
activated via enter/spacebar, but does focus the first item when
horizontal traversal opens a submenu. Automatically focusing the first
item whenever an overlay opens interferes with hover traversal, and I
couldn't think of a good way to only focus the first item when an
overlay is triggered via enter/spacebar.
- doesn't focus disabled items (I wasn't sure how to address this
without editing MenuItemButton)

While it is possible to nest menus -- for example, a dropdown anchor
within a full-app context menu area -- nested menus behave as a single
group. I was considering adding an additional parameter that separates
nested root menus from their parents, and am interested to hear your
feedback.</s>

*If you had to change anything in the [flutter/tests] repo, include a
link to the migration guide as per the [breaking change policy].*

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel
on [Discord].

<!-- Links -->
[Contributor Guide]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#overview
[Tree Hygiene]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md
[test-exempt]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#tests
[Flutter Style Guide]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md
[Features we expect every widget to implement]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md#features-we-expect-every-widget-to-implement
[CLA]: https://cla.developers.google.com/
[flutter/tests]: https://github.com/flutter/tests
[breaking change policy]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#handling-breaking-changes
[Discord]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Chat.md
[Data Driven Fixes]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Data-driven-Fixes.md

---------

Co-authored-by: Bruno Leroux <bruno.leroux@gmail.com>
Co-authored-by: chunhtai <47866232+chunhtai@users.noreply.github.com>
https://dart.googlesource.com/external/github.com/flutter/flutter/+/b29f8f7fb9b4a5ba8f0406bf7c1e3dfe944c3686
2 files changed
tree: 35a52eeff9021a5e05017a66367586e7fe623889
  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.