Description

A re-imagining of how we structure and describe builds for the flutter tool

Target build/system API

/// Assemble the assets used in the application into a build directory.
const Target copyAssets = Target(
  name: 'copy_assets',
  inputs: <Object>[
    '{PROJECT_DIR}/pubspec.yaml',
    listAssets, // <- parses pubspec file and outputs file paths.
  ],
  outputs: <Object>[
    '{BUILD_DIR}/flutter_assets/AssetManifest.json',
    '{BUILD_DIR}/flutter_assets/FontManifest.json',
    '{BUILD_DIR}/flutter_assets/LICENSE',
    listOutputAssets,
  ],
  dependencies: <Target>[],
  invocation: copyAssetsInvocation,
);

All files and directories are specified as file URIs relative to some "magic environment variable" defined below. This keeps us sane in the face of Windows. The {PROJECT_DIR}, {CACHE_DIR}, {BUILD_DIR} are automatically substituted variables that can be configured.

listAssets and listOutputAssets are top level or static functions which take a configuration object and return a list of files. These are used for dependency analysis when executing a target.

copyAssetsInvocation is a top level or static function which takes a configuration object. The tooling will verify that it produces the expected outputs. Placing all of the relevant configuration on single object (instead of providing some ambiently) makes it easier for the system to correctly invalidate and for authors and reviewers to identify whether the implementation is correct.

assemble command line API

The ability to inspect and execute targets is provided via a command line API. This is intended to be much lower level than the build APIs for integrating with external build systems. This is intended to initially replace the xcode_backend and desktop specific shell scripts with an API that can be directly embedded in the host build system.

Example: invoke a particular target

flutter assemble run -dbuildMode=debug  -dFlavor=cheese android_apk

Example: list the inputs for the macOS target

flutter assemble inputs macos_debug
> lib/main.dart
> pubspec.yaml
> assets/foo.png

Example: Direct integration into a makefile

$(FLUTTER_ROOT/bin/flutter assemble inputs linux_debug): flutter
flutter: $(FLUTTER_ROOT/bin/flutter assemble run linux_debug \ 
                --target-platform=linux-x64 \
                --build=mode=$(MODE) 

Related Issues

#27720
#28415
#16604

Tests

I added the following tests: Several

Checklist

Before you create this PR confirm that it meets all requirements listed below by checking the relevant checkboxes ([x]). This will ensure a smooth and quick review process.

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I signed the CLA.
• I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
• I updated/added relevant documentation (doc comments with ///).
• All existing and new tests are passing.
• The analyzer (flutter analyze --flutter-repo) does not report any problems on my PR.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Does your PR require Flutter developers to manually update their apps to accommodate your change?

• Yes, this is a breaking change (Please read Handling breaking changes). Replace this with a link to the e-mail where you asked for input on this proposed change.
• No, this is not a breaking change.