This PR adds support invoking `link.dart` hooks.
Link hooks can add new assets. Link hooks can transform assets sent to link hook from build hooks.
This PR does not yet add support for getting tree-shake information in the link hooks. This is pending on defining the `resources.json` format (https://github.com/dart-lang/sdk/issues/55494).
Issue:
* https://github.com/flutter/flutter/issues/146263
## Implementation considerations
The build hooks could be run before Dart compilation and the link hooks after Dart compilation. (This is how it's done in Dart standalone.) However, due to the way the `Target`s are set up, this would require two targets and serializing and deserializing the `BuildResult` in between these. This would lead to more code but no benefits. Currently there is nothing that mandates running build hooks before Dart compilation.
## Testing
* The unit tests verify that the native_assets_builder `link` and `linkDryRun` would be invoked with help of the existing fake.
* The native assets integration test now also invokes an FFI call of a package that adds the asset during the link hook instead of the build hook.
* In order to keep coverage of the `flutter create --template=package_ffi`, `flutter create` is still run and the extra dependency is added and an extra ffi call is added. (Open to alternative suggestions.)
Fixes https://github.com/flutter/flutter/issues/141827
Reland: https://dart-review.googlesource.com/c/sdk/+/346960 has rolled into g3, so the imports should now resolve in g3 as well.
> [!CAUTION]
> _Do NOT merge if "Google Testing" bot didn't run!_
Rolls the packages from https://github.com/dart-lang/native in the native assets implementation.
Most notable we're refactoring `package:native_assets_cli` for `build.dart` use.
Therefore, all imports to that package for Flutter/Dart should be to the implementation internals that are no longer visible for `build.dart` writers. Hence all the import updates.
No behavior in Flutter apps should change.
This PR also updates the template to use the latests version of `package:native_assets_cli` which no longer exposes all the implementation details.
Rolls the packages from https://github.com/dart-lang/native in the native assets implementation.
Most notable we're refactoring `package:native_assets_cli` for `build.dart` use.
Therefore, all imports to that package for Flutter/Dart should be to the implementation internals that are no longer visible for `build.dart` writers. Hence all the import updates.
No behavior in Flutter apps should change.
This PR also updates the template to use the latests version of `package:native_assets_cli` which no longer exposes all the implementation details.
Pin the dependencies from dart-lang/native to a specific version during testing (rather than having them auto-upgrade during pub resolution). This will prevent tests using the template to start failing if a bad version is published to pub.
Closes: https://github.com/flutter/flutter/issues/137418
Also bumps dep in flutter_tools.
Support for FFI calls with `@Native external` functions through Native assets on Windows. This enables bundling native code without any build-system boilerplate code.
For more info see:
* https://github.com/flutter/flutter/issues/129757
### Implementation details for Windows.
Mainly follows the design of https://github.com/flutter/flutter/pull/134031.
Specifically for Windows in this PR is the logic for finding the compiler `cl.exe` and environment variables that contain the paths to the Windows headers `vcvars.bat` based on `vswhere.exe`.
Support for FFI calls with `@Native external` functions through Native assets on MacOS and iOS. This enables bundling native code without any build-system boilerplate code.
For more info see:
* https://github.com/flutter/flutter/issues/129757
### Implementation details for MacOS and iOS.
Dylibs are bundled by (1) making them fat binaries if multiple architectures are targeted, (2) code signing these, and (3) copying them to the frameworks folder. These steps are done manual rather than via CocoaPods. CocoaPods would have done the same steps, but (a) needs the dylibs to be there before the `xcodebuild` invocation (we could trick it, by having a minimal dylib in the place and replace it during the build process, that works), and (b) can't deal with having no dylibs to be bundled (we'd have to bundle a dummy dylib or include some dummy C code in the build file).
The dylibs are build as a new target inside flutter assemble, as that is the moment we know what build-mode and architecture to target.
The mapping from asset id to dylib-path is passed in to every kernel compilation path. The interesting case is hot-restart where the initial kernel file is compiled by the "inner" flutter assemble, while after hot restart the "outer" flutter run compiled kernel file is pushed to the device. Both kernel files need to contain the mapping. The "inner" flutter assemble gets its mapping from the NativeAssets target which builds the native assets. The "outer" flutter run get its mapping from a dry-run invocation. Since this hot restart can be used for multiple target devices (`flutter run -d all`) it contains the mapping for all known targets.
### Example vs template
The PR includes a new template that uses the new native assets in a package and has an app importing that. Separate discussion in: https://github.com/flutter/flutter/issues/131209.
### Tests
This PR adds new tests to cover the various use cases.
* dev/devicelab/bin/tasks/native_assets_ios.dart
* Runs an example app with native assets in all build modes, doing hot reload and hot restart in debug mode.
* dev/devicelab/bin/tasks/native_assets_ios_simulator.dart
* Runs an example app with native assets, doing hot reload and hot restart.
* packages/flutter_tools/test/integration.shard/native_assets_test.dart
* Runs (incl hot reload/hot restart), builds, builds frameworks for iOS, MacOS and flutter-tester.
* packages/flutter_tools/test/general.shard/build_system/targets/native_assets_test.dart
* Unit tests the new Target in the backend.
* packages/flutter_tools/test/general.shard/ios/native_assets_test.dart
* packages/flutter_tools/test/general.shard/macos/native_assets_test.dart
* Unit tests the native assets being packaged on a iOS/MacOS build.
It also extends various existing tests:
* dev/devicelab/bin/tasks/module_test_ios.dart
* Exercises the add2app scenario.
* packages/flutter_tools/test/general.shard/features_test.dart
* Unit test the new feature flag.
