Dart

Overview

Dart artifacts are not built the same way in Fuchsia as they are on other platforms.

Instead of relying on pub to manage dependencies, sources of third-party packages we depend on are checked into the tree under //third_party/dart-pkg. This is to ensure we use consistent versions of our dependencies across multiple builds.

Likewise, no build output is placed in the source tree as everything goes under out/. That includes package_config.json files, which are generated as part of the build based on a target's dependency.

Exiting Dart programs

The Dart runner for Fuchsia does not monitor the FIDL channels opened by Dart programs and as a result does not end the program normally, but rather waits for the explicit call to fuchsia.exit() to indicate the program should be ended.

import 'package:fuchsia/fuchsia.dart' as fuchsia;

void main(List<String> args) {
  print('Hello Dart!');
  fuchsia.exit(23);
}

Targets

There are five gn targets for building Dart:

dart_library defines a library that can be used by other Dart targets;
dart_component defines a Fuchsia component based on a Dart library, that can be packaged using GN targets fuchsia_package or fuchsia_test_package;
dart_tool defines a Dart tool for the host;
flutter_component defines a Flutter component;
dart_test defines a group of test.

See the definitions of each of these targets for how to use them.

Package layout

We use a layout very similar to the standard layout.

my_package/
  |
  |-- pubspec.yaml           # Empty, used as a marker [mandatory]
  |-- BUILD.gn               # Contains all targets
  |-- analysis_options.yaml  # Analysis configuration [mandatory]
  |-- lib/                   # dart_library contents
  |-- bin/                   # dart_binary's (target) or dart_tool's (host)
  |-- test/                  # dart_test contents