[flutter_tools] reland: integrate l10n tool into hot reload/restart/build (#57510)

Reland: #56167

packages/flutter_tools/lib/src/base/command_help.dart

@@ -88,6 +88,12 @@ class CommandHelp {
     'Detach (terminate "flutter run" but leave application running).',
   );
 
+  CommandHelpOption _g;
+  CommandHelpOption get g => _g ??= _makeOption(
+    'g',
+    'Run source code generators.'
+  );
+
   CommandHelpOption _h;
   CommandHelpOption get h => _h ??= _makeOption(
     'h',

packages/flutter_tools/lib/src/build_runner/resident_web_runner.dart

@@ -487,6 +487,7 @@ class _ResidentWebRunner extends ResidentWebRunner {
     );
 
     if (debuggingOptions.buildInfo.isDebug) {
+      await runSourceGenerators();
       // Full restart is always false for web, since the extra recompile is wasteful.
       final UpdateFSReport report = await _updateDevFS(fullRestart: false);
       if (report.success) {

packages/flutter_tools/lib/src/build_system/build_system.dart

@@ -134,6 +134,12 @@ abstract class Target {
   /// A list of zero or more depfiles, located directly under {BUILD_DIR}.
   List<String> get depfiles => const <String>[];
 
+  /// Whether this target can be executed with the given [environment].
+  ///
+  /// Returning `true` will cause [build] to be skipped. This is equivalent
+  /// to a build that produces no outputs.
+  bool canSkip(Environment environment) => false;
+
   /// The action which performs this build step.
   Future<void> build(Environment environment);
 
@@ -773,18 +779,26 @@ class _BuildInstance {
         updateGraph();
         return succeeded;
       }
-      logger.printTrace('${node.target.name}: Starting due to ${node.invalidatedReasons}');
-      await node.target.build(environment);
-      logger.printTrace('${node.target.name}: Complete');
+      // Clear old inputs. These will be replaced with new inputs/outputs
+      // after the target is run. In the case of a runtime skip, each list
+      // must be empty to ensure the previous outputs are purged.
+      node.inputs.clear();
+      node.outputs.clear();
 
-      node.inputs
-        ..clear()
-        ..addAll(node.target.resolveInputs(environment).sources);
-      node.outputs
-        ..clear()
-        ..addAll(node.target.resolveOutputs(environment).sources);
+      // Check if we can skip via runtime dependencies.
+      final bool runtimeSkip = node.target.canSkip(environment);
+      if (runtimeSkip) {
+        logger.printTrace('Skipping target: ${node.target.name}');
+        skipped = true;
+      } else {
+        logger.printTrace('${node.target.name}: Starting due to ${node.invalidatedReasons}');
+        await node.target.build(environment);
+        logger.printTrace('${node.target.name}: Complete');
+        node.inputs.addAll(node.target.resolveInputs(environment).sources);
+        node.outputs.addAll(node.target.resolveOutputs(environment).sources);
+      }
 
-      // If we were missing the depfile, resolve  input files after executing the
+      // If we were missing the depfile, resolve input files after executing the
       // target so that all file hashes are up to date on the next run.
       if (node.missingDepfile) {
         await fileCache.diffFileList(node.inputs);

packages/flutter_tools/lib/src/build_system/targets/dart.dart

@@ -17,6 +17,7 @@ import '../depfile.dart';
 import '../exceptions.dart';
 import 'assets.dart';
 import 'icon_tree_shaker.dart';
+import 'localizations.dart';
 
 /// The define to pass a [BuildMode].
 const String kBuildMode = 'BuildMode';
@@ -183,7 +184,9 @@ class KernelSnapshot extends Target {
   ];
 
   @override
-  List<Target> get dependencies => <Target>[];
+  List<Target> get dependencies => const <Target>[
+    GenerateLocalizationsTarget(),
+  ];
 
   @override
   Future<void> build(Environment environment) async {

packages/flutter_tools/lib/src/build_system/targets/localizations.dart

@@ -0,0 +1,272 @@
+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:meta/meta.dart';
+import 'package:process/process.dart';
+import 'package:yaml/yaml.dart';
+
+import '../../artifacts.dart';
+import '../../base/file_system.dart';
+import '../../base/io.dart';
+import '../../base/logger.dart';
+import '../../convert.dart';
+import '../../globals.dart' as globals;
+import '../build_system.dart';
+import '../depfile.dart';
+
+const String _kDependenciesFileName = 'gen_l10n_inputs_and_outputs.json';
+
+/// Run the localizations generation script with the configuration [options].
+Future<void> generateLocalizations({
+  @required LocalizationOptions options,
+  @required String flutterRoot,
+  @required FileSystem fileSystem,
+  @required ProcessManager processManager,
+  @required Logger logger,
+  @required Directory projectDir,
+  @required String dartBinaryPath,
+  @required Directory dependenciesDir,
+}) async {
+  final String genL10nPath = fileSystem.path.join(
+    flutterRoot,
+    'dev',
+    'tools',
+    'localization',
+    'bin',
+    'gen_l10n.dart',
+  );
+  final ProcessResult result = await processManager.run(<String>[
+    dartBinaryPath,
+    genL10nPath,
+    '--gen-inputs-and-outputs-list=${dependenciesDir.path}',
+    if (options.arbDirectory != null)
+      '--arb-dir=${options.arbDirectory.toFilePath()}',
+    if (options.templateArbFile != null)
+      '--template-arb-file=${options.templateArbFile.toFilePath()}',
+    if (options.outputLocalizationsFile != null)
+      '--output-localization-file=${options.outputLocalizationsFile.toFilePath()}',
+    if (options.untranslatedMessagesFile != null)
+      '--untranslated-messages-file=${options.untranslatedMessagesFile.toFilePath()}',
+    if (options.outputClass != null)
+      '--output-class=${options.outputClass}',
+    if (options.headerFile != null)
+      '--header-file=${options.headerFile.toFilePath()}',
+    if (options.header != null)
+      '--header=${options.header}',
+    if (options.deferredLoading != null)
+      '--use-deferred-loading',
+    if (options.preferredSupportedLocales != null)
+      '--preferred-supported-locales=${options.preferredSupportedLocales}',
+  ]);
+  if (result.exitCode != 0) {
+    logger.printError(result.stdout + result.stderr as String);
+    throw Exception();
+  }
+}
+
+/// A build step that runs the generate localizations script from
+/// dev/tool/localizations.
+class GenerateLocalizationsTarget extends Target {
+  const GenerateLocalizationsTarget();
+
+  @override
+  List<Target> get dependencies => <Target>[];
+
+  @override
+  List<Source> get inputs => <Source>[
+    // This is added as a convenience for developing the tool.
+    const Source.pattern('{FLUTTER_ROOT}/packages/flutter_tools/lib/src/build_system/targets/localizations.dart'),
+    // TODO(jonahwilliams): once https://github.com/flutter/flutter/issues/56321 is
+    // complete, we should add the artifact as a dependency here. Since the tool runs
+    // this code from source, looking up each dependency will be cumbersome.
+  ];
+
+  @override
+  String get name => 'gen_localizations';
+
+  @override
+  List<Source> get outputs => <Source>[];
+
+  @override
+  List<String> get depfiles => <String>['gen_localizations.d'];
+
+  @override
+  bool canSkip(Environment environment) {
+    final File configFile = environment.projectDir.childFile('l10n.yaml');
+    return !configFile.existsSync();
+  }
+
+  @override
+  Future<void> build(Environment environment) async {
+    final File configFile = environment.projectDir.childFile('l10n.yaml');
+    assert(configFile.existsSync());
+
+    final LocalizationOptions options = parseLocalizationsOptions(
+      file: configFile,
+      logger: globals.logger,
+    );
+    final DepfileService depfileService = DepfileService(
+      logger: environment.logger,
+      fileSystem: environment.fileSystem,
+    );
+
+    await generateLocalizations(
+      fileSystem: environment.fileSystem,
+      flutterRoot: environment.flutterRootDir.path,
+      logger: environment.logger,
+      processManager: environment.processManager,
+      options: options,
+      projectDir: environment.projectDir,
+      dartBinaryPath: environment.artifacts
+        .getArtifactPath(Artifact.engineDartBinary),
+      dependenciesDir: environment.buildDir,
+    );
+    final Map<String, Object> dependencies = json
+      .decode(environment.buildDir.childFile(_kDependenciesFileName).readAsStringSync()) as Map<String, Object>;
+    final Depfile depfile = Depfile(
+      <File>[
+        configFile,
+        for (dynamic inputFile in dependencies['inputs'] as List<dynamic>)
+          environment.fileSystem.file(inputFile)
+      ],
+      <File>[
+        for (dynamic outputFile in dependencies['outputs'] as List<dynamic>)
+          environment.fileSystem.file(outputFile)
+      ]
+    );
+    depfileService.writeToFile(
+      depfile,
+      environment.buildDir.childFile('gen_localizations.d'),
+    );
+  }
+}
+
+/// Typed configuration from the localizations config file.
+class LocalizationOptions {
+  const LocalizationOptions({
+    this.arbDirectory,
+    this.templateArbFile,
+    this.outputLocalizationsFile,
+    this.untranslatedMessagesFile,
+    this.header,
+    this.outputClass,
+    this.preferredSupportedLocales,
+    this.headerFile,
+    this.deferredLoading,
+  });
+
+  /// The `--arb-dir` argument.
+  ///
+  /// The directory where all localization files should reside.
+  final Uri arbDirectory;
+
+  /// The `--template-arb-file` argument.
+  ///
+  /// This URI is relative to [arbDirectory].
+  final Uri templateArbFile;
+
+  /// The `--output-localization-file` argument.
+  ///
+  /// This URI is relative to [arbDirectory].
+  final Uri outputLocalizationsFile;
+
+  /// The `--untranslated-messages-file` argument.
+  ///
+  /// This URI is relative to [arbDirectory].
+  final Uri untranslatedMessagesFile;
+
+  /// The `--header` argument.
+  ///
+  /// The header to prepend to the generated Dart localizations
+  final String header;
+
+  /// The `--output-class` argument.
+  final String outputClass;
+
+  /// The `--preferred-supported-locales` argument.
+  final String preferredSupportedLocales;
+
+  /// The `--header-file` argument.
+  ///
+  /// A file containing the header to preprend to the generated
+  /// Dart localizations.
+  final Uri headerFile;
+
+  /// The `--use-deferred-loading` argument.
+  ///
+  /// Whether to generate the Dart localization file with locales imported
+  /// as deferred.
+  final bool deferredLoading;
+}
+
+/// Parse the localizations configuration options from [file].
+///
+/// Throws [Exception] if any of the contents are invalid. Returns a
+/// [LocalizationOptions] with all fields as `null` if the config file exists
+/// but is empty.
+LocalizationOptions parseLocalizationsOptions({
+  @required File file,
+  @required Logger logger,
+}) {
+  final String contents = file.readAsStringSync();
+  if (contents.trim().isEmpty) {
+    return const LocalizationOptions();
+  }
+  final YamlNode yamlNode = loadYamlNode(file.readAsStringSync());
+  if (yamlNode is! YamlMap) {
+    logger.printError('Expected ${file.path} to contain a map, instead was $yamlNode');
+    throw Exception();
+  }
+  final YamlMap yamlMap = yamlNode as YamlMap;
+  return LocalizationOptions(
+    arbDirectory: _tryReadUri(yamlMap, 'arb-dir', logger),
+    templateArbFile: _tryReadUri(yamlMap, 'template-arb-file', logger),
+    outputLocalizationsFile: _tryReadUri(yamlMap, 'output-localization-file', logger),
+    untranslatedMessagesFile: _tryReadUri(yamlMap, 'untranslated-messages-file', logger),
+    header: _tryReadString(yamlMap, 'header', logger),
+    outputClass: _tryReadString(yamlMap, 'output-class', logger),
+    preferredSupportedLocales: _tryReadString(yamlMap, 'preferred-supported-locales', logger),
+    headerFile: _tryReadUri(yamlMap, 'header-file', logger),
+    deferredLoading: _tryReadBool(yamlMap, 'use-deferred-loading', logger),
+  );
+}
+
+// Try to read a `bool` value or null from `yamlMap`, otherwise throw.
+bool _tryReadBool(YamlMap yamlMap, String key, Logger logger) {
+  final Object value = yamlMap[key];
+  if (value == null) {
+    return null;
+  }
+  if (value is! bool) {
+    logger.printError('Expected "$key" to have a bool value, instead was "$value"');
+    throw Exception();
+  }
+  return value as bool;
+}
+
+// Try to read a `String` value or null from `yamlMap`, otherwise throw.
+String _tryReadString(YamlMap yamlMap, String key, Logger logger) {
+  final Object value = yamlMap[key];
+  if (value == null) {
+    return null;
+  }
+  if (value is! String) {
+    logger.printError('Expected "$key" to have a String value, instead was "$value"');
+    throw Exception();
+  }
+  return value as String;
+}
+
+// Try to read a valid `Uri` or null from `yamlMap`, otherwise throw.
+Uri _tryReadUri(YamlMap yamlMap, String key, Logger logger) {
+  final String value = _tryReadString(yamlMap, key, logger);
+  if (value == null) {
+    return null;
+  }
+  final Uri uri = Uri.tryParse(value);
+  if (uri == null) {
+    logger.printError('"$value" must be a relative file URI');
+  }
+  return uri;
+}

packages/flutter_tools/lib/src/build_system/targets/web.dart

@@ -15,6 +15,7 @@ import '../build_system.dart';
 import '../depfile.dart';
 import 'assets.dart';
 import 'dart.dart';
+import 'localizations.dart';
 
 /// Whether web builds should call the platform initialization logic.
 const String kInitializePlatform = 'InitializePlatform';
@@ -132,7 +133,8 @@ class Dart2JSTarget extends Target {
 
   @override
   List<Target> get dependencies => const <Target>[
-    WebEntrypointTarget()
+    WebEntrypointTarget(),
+    GenerateLocalizationsTarget(),
   ];
 
   @override

packages/flutter_tools/lib/src/resident_runner.dart

@@ -4,10 +4,10 @@
 
 import 'dart:async';
 
-import 'package:vm_service/vm_service.dart' as vm_service;
 import 'package:devtools_server/devtools_server.dart' as devtools_server;
 import 'package:meta/meta.dart';
 import 'package:package_config/package_config.dart';
+import 'package:vm_service/vm_service.dart' as vm_service;
 
 import 'application_package.dart';
 import 'artifacts.dart';
@@ -21,7 +21,10 @@ import 'base/signals.dart';
 import 'base/terminal.dart';
 import 'base/utils.dart';
 import 'build_info.dart';
+import 'build_system/build_system.dart';
+import 'build_system/targets/localizations.dart';
 import 'bundle.dart';
+import 'cache.dart';
 import 'codegen.dart';
 import 'compile.dart';
 import 'convert.dart';
@@ -800,6 +803,40 @@ abstract class ResidentRunner {
     throw '${fullRestart ? 'Restart' : 'Reload'} is not supported in $mode mode';
   }
 
+
+  BuildResult _lastBuild;
+  Environment _environment;
+  Future<void> runSourceGenerators() async {
+    _environment ??= Environment(
+      artifacts: globals.artifacts,
+      logger: globals.logger,
+      cacheDir: globals.cache.getRoot(),
+      engineVersion: globals.flutterVersion.engineRevision,
+      fileSystem: globals.fs,
+      flutterRootDir: globals.fs.directory(Cache.flutterRoot),
+      outputDir: globals.fs.directory(getBuildDirectory()),
+      processManager: globals.processManager,
+      projectDir: globals.fs.currentDirectory,
+    );
+    globals.logger.printTrace('Starting incremental build...');
+    _lastBuild = await globals.buildSystem.buildIncremental(
+      const GenerateLocalizationsTarget(),
+      _environment,
+      _lastBuild,
+    );
+    if (!_lastBuild.success) {
+      for (final ExceptionMeasurement exceptionMeasurement in _lastBuild.exceptions.values) {
+        globals.logger.printError(
+          exceptionMeasurement.exception.toString(),
+          stackTrace: globals.logger.isVerbose
+            ? exceptionMeasurement.stackTrace
+            : null,
+        );
+      }
+    }
+    globals.logger.printTrace('complete');
+  }
+
   /// Toggle whether canvaskit is being used for rendering, returning the new
   /// state.
   ///
@@ -1200,6 +1237,7 @@ abstract class ResidentRunner {
         commandHelp.p.print();
         commandHelp.o.print();
         commandHelp.z.print();
+        commandHelp.g.print();
       } else {
         commandHelp.S.print();
         commandHelp.U.print();
@@ -1337,6 +1375,9 @@ class TerminalHandler {
       case 'D':
         await residentRunner.detach();
         return true;
+      case 'g':
+        await residentRunner.runSourceGenerators();
+        return true;
       case 'h':
       case 'H':
       case '?':

packages/flutter_tools/lib/src/run_hot.dart

@@ -7,8 +7,8 @@ import 'package:package_config/package_config.dart';
 import 'package:vm_service/vm_service.dart' as vm_service;
 import 'package:meta/meta.dart';
 import 'package:pool/pool.dart';
-import 'base/async_guard.dart';
 
+import 'base/async_guard.dart';
 import 'base/context.dart';
 import 'base/file_system.dart';
 import 'base/logger.dart';
@@ -365,6 +365,7 @@ class HotRunner extends ResidentRunner {
       // build, reducing overall initialization time. This is safe because the first
       // invocation of the frontend server produces a full dill file that the
       // subsequent invocation in devfs will not overwrite.
+      await runSourceGenerators();
       if (device.generator != null) {
         startupTasks.add(
           device.generator.recompile(
@@ -674,6 +675,10 @@ class HotRunner extends ResidentRunner {
       emulator = false;
     }
     final Stopwatch timer = Stopwatch()..start();
+
+    // Run source generation if needed.
+    await runSourceGenerators();
+
     if (fullRestart) {
       final OperationResult result = await _fullRestartHelper(
         targetPlatform: targetPlatform,
@@ -1190,7 +1195,7 @@ class ProjectFileInvalidator {
   static const String _pubCachePathWindows = 'Pub/Cache';
 
   // As of writing, Dart supports up to 32 asynchronous I/O threads per
-  // isolate.  We also want to avoid hitting platform limits on open file
+  // isolate. We also want to avoid hitting platform limits on open file
   // handles/descriptors.
   //
   // This value was chosen based on empirical tests scanning a set of
@@ -1223,7 +1228,6 @@ class ProjectFileInvalidator {
         if (_isNotInPubCache(uri)) uri,
     ];
     final List<Uri> invalidatedFiles = <Uri>[];
-
     if (asyncScanning) {
       final Pool pool = Pool(_kMaxPendingStats);
       final List<Future<void>> waitList = <Future<void>>[];

packages/flutter_tools/test/general.shard/base/command_help_test.dart

@@ -57,6 +57,7 @@ void _testMessageLength({
   expect(commandHelp.U.toString().length, lessThanOrEqualTo(expectedWidth));
   expect(commandHelp.a.toString().length, lessThanOrEqualTo(expectedWidth));
   expect(commandHelp.d.toString().length, lessThanOrEqualTo(expectedWidth));
+  expect(commandHelp.g.toString().length, lessThanOrEqualTo(expectedWidth));
   expect(commandHelp.h.toString().length, lessThanOrEqualTo(expectedWidth));
   expect(commandHelp.i.toString().length, lessThanOrEqualTo(expectedWidth));
   expect(commandHelp.k.toString().length, lessThanOrEqualTo(expectedWidth));
@@ -88,6 +89,7 @@ void main() {
         expect(commandHelp.U.toString(), startsWith('\x1B[1mU\x1B[22m'));
         expect(commandHelp.a.toString(), startsWith('\x1B[1ma\x1B[22m'));
         expect(commandHelp.d.toString(), startsWith('\x1B[1md\x1B[22m'));
+        expect(commandHelp.g.toString(), startsWith('\x1B[1mg\x1B[22m'));
         expect(commandHelp.h.toString(), startsWith('\x1B[1mh\x1B[22m'));
         expect(commandHelp.i.toString(), startsWith('\x1B[1mi\x1B[22m'));
         expect(commandHelp.o.toString(), startsWith('\x1B[1mo\x1B[22m'));
@@ -164,6 +166,7 @@ void main() {
         expect(commandHelp.U.toString(), equals('\x1B[1mU\x1B[22m Dump accessibility tree in inverse hit test order.            \x1B[1;30m(debugDumpSemantics)\x1B[39m'));
         expect(commandHelp.a.toString(), equals('\x1B[1ma\x1B[22m Toggle timeline events for all widget build methods.    \x1B[1;30m(debugProfileWidgetBuilds)\x1B[39m'));
         expect(commandHelp.d.toString(), equals('\x1B[1md\x1B[22m Detach (terminate "flutter run" but leave application running).'));
+        expect(commandHelp.g.toString(), equals('\x1B[1mg\x1B[22m Run source code generators.'));
         expect(commandHelp.h.toString(), equals('\x1B[1mh\x1B[22m Repeat this help message.'));
         expect(commandHelp.i.toString(), equals('\x1B[1mi\x1B[22m Toggle widget inspector.                  \x1B[1;30m(WidgetsApp.showWidgetInspectorOverride)\x1B[39m'));
         expect(commandHelp.o.toString(), equals('\x1B[1mo\x1B[22m Simulate different operating systems.                      \x1B[1;30m(defaultTargetPlatform)\x1B[39m'));
@@ -190,6 +193,7 @@ void main() {
         expect(commandHelp.U.toString(), equals('U Dump accessibility tree in inverse hit test order.            (debugDumpSemantics)'));
         expect(commandHelp.a.toString(), equals('a Toggle timeline events for all widget build methods.    (debugProfileWidgetBuilds)'));
         expect(commandHelp.d.toString(), equals('d Detach (terminate "flutter run" but leave application running).'));
+        expect(commandHelp.g.toString(), equals('g Run source code generators.'));
         expect(commandHelp.h.toString(), equals('h Repeat this help message.'));
         expect(commandHelp.i.toString(), equals('i Toggle widget inspector.                  (WidgetsApp.showWidgetInspectorOverride)'));
         expect(commandHelp.o.toString(), equals('o Simulate different operating systems.                      (defaultTargetPlatform)'));

packages/flutter_tools/test/general.shard/build_system/build_system_test.dart

@@ -581,6 +581,50 @@ void main() {
     expect(fileSystem.file('output/debug'), isNot(exists));
     expect(fileSystem.file('output/release'), exists);
   });
+
+  testWithoutContext('A target using canSkip can create a conditional output',  () async {
+    final BuildSystem buildSystem = setUpBuildSystem(fileSystem);
+    final File bar = environment.buildDir.childFile('bar');
+    final File foo = environment.buildDir.childFile('foo');
+
+    // The target will write a file `foo`, but only if `bar` already exists.
+    final TestTarget target = TestTarget(
+      (Environment environment) async {
+        foo.writeAsStringSync(bar.readAsStringSync());
+        environment.buildDir
+          .childFile('example.d')
+          .writeAsStringSync('${foo.path}: ${bar.path}');
+      },
+      (Environment environment) {
+        return !environment.buildDir.childFile('bar').existsSync();
+      }
+    )
+      ..depfiles = const <String>['example.d'];
+
+    // bar does not exist, there should be no inputs/outputs.
+    final BuildResult firstResult = await buildSystem.build(target, environment);
+
+    expect(foo, isNot(exists));
+    expect(firstResult.inputFiles, isEmpty);
+    expect(firstResult.outputFiles, isEmpty);
+
+    // bar is created, the target should be able to run.
+    bar.writeAsStringSync('content-1');
+    final BuildResult secondResult = await buildSystem.build(target, environment);
+
+    expect(foo, exists);
+    expect(secondResult.inputFiles.map((File file) => file.path), <String>[bar.path]);
+    expect(secondResult.outputFiles.map((File file) => file.path), <String>[foo.path]);
+
+    // bar is destroyed, foo is also deleted.
+    bar.deleteSync();
+    final BuildResult thirdResult = await buildSystem.build(target, environment);
+
+    expect(foo, isNot(exists));
+    expect(thirdResult.inputFiles, isEmpty);
+    expect(thirdResult.outputFiles, isEmpty);
+  });
+
 }
 
 BuildSystem setUpBuildSystem(FileSystem fileSystem) {
@@ -592,10 +636,20 @@ BuildSystem setUpBuildSystem(FileSystem fileSystem) {
 }
 
 class TestTarget extends Target {
-  TestTarget([this._build]);
+  TestTarget([this._build, this._canSkip]);
 
   final Future<void> Function(Environment environment) _build;
 
+  final bool Function(Environment environment) _canSkip;
+
+  @override
+  bool canSkip(Environment environment) {
+    if (_canSkip != null) {
+      return _canSkip(environment);
+    }
+    return super.canSkip(environment);
+  }
+
   @override
   Future<void> build(Environment environment) => _build(environment);
 

packages/flutter_tools/test/general.shard/build_system/targets/localizations_test.dart

@@ -0,0 +1,131 @@
+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:file/memory.dart';
+import 'package:flutter_tools/src/base/file_system.dart';
+import 'package:flutter_tools/src/base/logger.dart';
+import 'package:flutter_tools/src/build_system/build_system.dart';
+import 'package:flutter_tools/src/build_system/targets/localizations.dart';
+
+import '../../../src/common.dart';
+import '../../../src/context.dart';
+
+void main() {
+  // Verifies that values are correctly passed through the localizations
+  // target, but does not validate them beyond the serialized data type.
+  testWithoutContext('generateLocalizations forwards arguments correctly', () async {
+    final FileSystem fileSystem = MemoryFileSystem.test();
+    final Logger logger = BufferLogger.test();
+    final FakeProcessManager processManager = FakeProcessManager.list(<FakeCommand>[
+      const FakeCommand(
+        command: <String>[
+          'dart',
+          'dev/tools/localization/bin/gen_l10n.dart',
+          '--gen-inputs-and-outputs-list=/',
+          '--arb-dir=arb',
+          '--template-arb-file=example.arb',
+          '--output-localization-file=bar',
+          '--untranslated-messages-file=untranslated',
+          '--output-class=Foo',
+          '--header-file=header',
+          '--header=HEADER',
+          '--use-deferred-loading',
+          '--preferred-supported-locales=en_US'
+        ],
+      ),
+    ]);
+    final Directory arbDirectory = fileSystem.directory('arb')
+      ..createSync();
+    arbDirectory.childFile('foo.arb').createSync();
+    arbDirectory.childFile('bar.arb').createSync();
+
+    final LocalizationOptions options = LocalizationOptions(
+      header: 'HEADER',
+      headerFile: Uri.file('header'),
+      arbDirectory: Uri.file('arb'),
+      deferredLoading: true,
+      outputClass: 'Foo',
+      outputLocalizationsFile: Uri.file('bar'),
+      preferredSupportedLocales: 'en_US',
+      templateArbFile: Uri.file('example.arb'),
+      untranslatedMessagesFile: Uri.file('untranslated'),
+    );
+    await generateLocalizations(
+      options: options,
+      logger: logger,
+      fileSystem: fileSystem,
+      processManager: processManager,
+      projectDir: fileSystem.currentDirectory,
+      dartBinaryPath: 'dart',
+      flutterRoot: '',
+      dependenciesDir: fileSystem.currentDirectory,
+    );
+
+    expect(processManager.hasRemainingExpectations, false);
+  });
+
+  testWithoutContext('generateLocalizations is skipped if l10n.yaml does not exist.', () async {
+    final FileSystem fileSystem = MemoryFileSystem.test();
+    final Environment environment = Environment.test(
+      fileSystem.currentDirectory,
+      artifacts: null,
+      fileSystem: fileSystem,
+      logger: BufferLogger.test(),
+      processManager: FakeProcessManager.any(),
+    );
+
+    expect(const GenerateLocalizationsTarget().canSkip(environment), true);
+
+    environment.projectDir.childFile('l10n.yaml').createSync();
+
+    expect(const GenerateLocalizationsTarget().canSkip(environment), false);
+  });
+
+  testWithoutContext('parseLocalizationsOptions handles valid yaml configuration', () async {
+    final FileSystem fileSystem = MemoryFileSystem.test();
+    final File configFile = fileSystem.file('l10n.yaml')
+      ..writeAsStringSync('''
+arb-dir: arb
+template-arb-file: example.arb
+output-localization-file: bar
+untranslated-messages-file: untranslated
+output-class: Foo
+header-file: header
+header: HEADER
+use-deferred-loading: true
+preferred-supported-locales: en_US
+''');
+
+    final LocalizationOptions options = parseLocalizationsOptions(
+      file: configFile,
+      logger: BufferLogger.test(),
+    );
+
+    expect(options.arbDirectory, Uri.parse('arb'));
+    expect(options.templateArbFile, Uri.parse('example.arb'));
+    expect(options.outputLocalizationsFile, Uri.parse('bar'));
+    expect(options.untranslatedMessagesFile, Uri.parse('untranslated'));
+    expect(options.outputClass, 'Foo');
+    expect(options.headerFile, Uri.parse('header'));
+    expect(options.header, 'HEADER');
+    expect(options.deferredLoading, true);
+    expect(options.preferredSupportedLocales, 'en_US');
+  });
+
+  testWithoutContext('parseLocalizationsOptions throws exception on invalid yaml configuration', () async {
+    final FileSystem fileSystem = MemoryFileSystem.test();
+    final File configFile = fileSystem.file('l10n.yaml')
+      ..writeAsStringSync('''
+use-deferred-loading: string
+''');
+
+    expect(
+      () => parseLocalizationsOptions(
+        file: configFile,
+        logger: BufferLogger.test(),
+      ),
+      throwsA(isA<Exception>()),
+    );
+  });
+}

packages/flutter_tools/test/general.shard/resident_runner_test.dart

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 
+import 'package:flutter_tools/src/cache.dart';
 import 'package:vm_service/vm_service.dart' as vm_service;
 import 'package:file/memory.dart';
 import 'package:file_testing/file_testing.dart';
@@ -537,6 +538,61 @@ void main() {
     expect(cacheDill, isNot(exists));
   }));
 
+  test('ResidentRunner can run source generation', () => testbed.run(() async {
+    final FakeProcessManager processManager = globals.processManager as FakeProcessManager;
+    final Directory dependencies = globals.fs.directory(
+      globals.fs.path.join('build', '6ec2559087977927717927ede0a147f1'));
+    processManager.addCommand(FakeCommand(
+      command: <String>[
+        globals.artifacts.getArtifactPath(Artifact.engineDartBinary),
+        globals.fs.path.join(Cache.flutterRoot, 'dev', 'tools', 'localization', 'bin', 'gen_l10n.dart'),
+        '--gen-inputs-and-outputs-list=${dependencies.absolute.path}',
+      ],
+      onRun: () {
+        dependencies
+          .childFile('gen_l10n_inputs_and_outputs.json')
+          ..createSync()
+          ..writeAsStringSync('{"inputs":[],"outputs":[]}');
+      }
+    ));
+    globals.fs.file(globals.fs.path.join('lib', 'l10n', 'foo.arb'))
+      .createSync(recursive: true);
+    globals.fs.file('l10n.yaml').createSync();
+
+    await residentRunner.runSourceGenerators();
+
+    expect(testLogger.errorText, isEmpty);
+  }, overrides: <Type, Generator>{
+    ProcessManager: () => FakeProcessManager.list(<FakeCommand>[]),
+  }));
+
+  test('ResidentRunner can run source generation - generation fails', () => testbed.run(() async {
+    final FakeProcessManager processManager = globals.processManager as FakeProcessManager;
+    final Directory dependencies = globals.fs.directory(
+      globals.fs.path.join('build', '6ec2559087977927717927ede0a147f1'));
+    processManager.addCommand(FakeCommand(
+      command: <String>[
+        globals.artifacts.getArtifactPath(Artifact.engineDartBinary),
+        globals.fs.path.join(Cache.flutterRoot, 'dev', 'tools', 'localization', 'bin', 'gen_l10n.dart'),
+        '--gen-inputs-and-outputs-list=${dependencies.absolute.path}',
+      ],
+      exitCode: 1,
+      stderr: 'stderr'
+    ));
+    globals.fs.file(globals.fs.path.join('lib', 'l10n', 'foo.arb'))
+      .createSync(recursive: true);
+    globals.fs.file('l10n.yaml').createSync();
+
+    await residentRunner.runSourceGenerators();
+
+    expect(testLogger.errorText, allOf(
+      contains('stderr'), // Message from gen_l10n.dart
+      contains('Exception') // Message from build_system
+    ));
+  }, overrides: <Type, Generator>{
+    ProcessManager: () => FakeProcessManager.list(<FakeCommand>[]),
+  }));
+
   test('ResidentRunner printHelpDetails', () => testbed.run(() {
     fakeVmServiceHost = FakeVmServiceHost(requests: <VmServiceExpectation>[]);
     when(mockDevice.supportsHotRestart).thenReturn(true);
@@ -573,6 +629,7 @@ void main() {
           commandHelp.p,
           commandHelp.o,
           commandHelp.z,
+          commandHelp.g,
           commandHelp.M,
           commandHelp.v,
           commandHelp.P,

packages/flutter_tools/test/integration.shard/gen_l10n_test.dart

@@ -6,15 +6,14 @@ import 'dart:async';
 
 import 'package:file/file.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
-import 'package:flutter_tools/src/base/io.dart';
-import 'package:flutter_tools/src/globals.dart' as globals;
-import 'package:process/process.dart';
 
 import '../src/common.dart';
 import 'test_data/gen_l10n_project.dart';
 import 'test_driver.dart';
 import 'test_utils.dart';
 
+final GenL10nProject project = GenL10nProject();
+
 // Verify that the code generated by gen_l10n executes correctly.
 // It can fail if gen_l10n produces a lib/l10n/app_localizations.dart that:
 // - Does not analyze cleanly.
@@ -23,50 +22,23 @@ import 'test_utils.dart';
 // loaded workstation, so the test could time out on a heavily loaded bot.
 void main() {
   Directory tempDir;
-  final GenL10nProject _project = GenL10nProject();
-  FlutterRunTestDriver _flutter;
+  FlutterRunTestDriver flutter;
 
   setUp(() async {
     tempDir = createResolvedTempDirectorySync('gen_l10n_test.');
-    await _project.setUpIn(tempDir);
-    _flutter = FlutterRunTestDriver(tempDir);
   });
 
   tearDown(() async {
-    await _flutter.stop();
+    await flutter.stop();
     tryToDelete(tempDir);
   });
 
-  void runCommand(List<String> command) {
-    final ProcessResult result = const LocalProcessManager().runSync(
-      command,
-      workingDirectory: tempDir.path,
-      environment: <String, String>{ 'FLUTTER_ROOT': getFlutterRoot() },
-    );
-    if (result.exitCode != 0) {
-      throw Exception('FAILED [${result.exitCode}]: ${command.join(' ')}\n${result.stderr}\n${result.stdout}');
-    }
-  }
-
-  void setUpAndRunGenL10n({List<String> args}) {
-    // Get the intl packages before running gen_l10n.
-    final String flutterBin = globals.platform.isWindows ? 'flutter.bat' : 'flutter';
-    final String flutterPath = globals.fs.path.join(getFlutterRoot(), 'bin', flutterBin);
-    runCommand(<String>[flutterPath, 'pub', 'get']);
-
-    // Generate lib/l10n/app_localizations.dart
-    final String genL10nPath = globals.fs.path.join(getFlutterRoot(), 'dev', 'tools', 'localization', 'bin', 'gen_l10n.dart');
-    final String dartBin = globals.platform.isWindows ? 'dart.exe' : 'dart';
-    final String dartPath = globals.fs.path.join(getFlutterRoot(), 'bin', 'cache', 'dart-sdk', 'bin', dartBin);
-    runCommand(<String>[dartPath, genL10nPath, args?.join(' ')]);
-  }
-
   Future<StringBuffer> runApp() async {
     // Run the app defined in GenL10nProject.main and wait for it to
     // send '#l10n END' to its stdout.
     final Completer<void> l10nEnd = Completer<void>();
     final StringBuffer stdout = StringBuffer();
-    final StreamSubscription<String> subscription = _flutter.stdout.listen((String line) {
+    final StreamSubscription<String> subscription = flutter.stdout.listen((String line) {
       if (line.contains('#l10n')) {
         stdout.writeln(line.substring(line.indexOf('#l10n')));
       }
@@ -74,7 +46,7 @@ void main() {
         l10nEnd.complete();
       }
     });
-    await _flutter.run();
+    await flutter.run();
     await l10nEnd.future;
     await subscription.cancel();
     return stdout;
@@ -180,13 +152,15 @@ void main() {
   }
 
   test('generated l10n classes produce expected localized strings', () async {
-    setUpAndRunGenL10n();
+    await project.setUpIn(tempDir);
+    flutter = FlutterRunTestDriver(tempDir);
     final StringBuffer stdout = await runApp();
     expectOutput(stdout);
   });
 
   test('generated l10n classes produce expected localized strings with deferred loading', () async {
-    setUpAndRunGenL10n(args: <String>['--use-deferred-loading']);
+    await project.setUpIn(tempDir, useDeferredLoading: true);
+    flutter = FlutterRunTestDriver(tempDir);
     final StringBuffer stdout = await runApp();
     expectOutput(stdout);
   });

packages/flutter_tools/test/integration.shard/test_data/gen_l10n_project.dart

@@ -7,13 +7,16 @@ import 'dart:async';
 import 'package:file/file.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/globals.dart' as globals;
+import 'package:meta/meta.dart';
 
 import '../test_utils.dart';
 import 'project.dart';
 
 class GenL10nProject extends Project {
   @override
-  Future<void> setUpIn(Directory dir) {
+  Future<void> setUpIn(Directory dir, {
+    bool useDeferredLoading = false,
+  }) {
     this.dir = dir;
     writeFile(globals.fs.path.join(dir.path, 'lib', 'l10n', 'app_en.arb'), appEn);
     writeFile(globals.fs.path.join(dir.path, 'lib', 'l10n', 'app_en_CA.arb'), appEnCa);
@@ -24,6 +27,7 @@ class GenL10nProject extends Project {
     writeFile(globals.fs.path.join(dir.path, 'lib', 'l10n', 'app_zh_Hant.arb'), appZhHant);
     writeFile(globals.fs.path.join(dir.path, 'lib', 'l10n', 'app_zh_Hans.arb'), appZhHans);
     writeFile(globals.fs.path.join(dir.path, 'lib', 'l10n', 'app_zh_Hant_TW.arb'), appZhHantTw);
+    writeFile(globals.fs.path.join(dir.path, 'l10n.yaml'), l10nYaml(useDeferredLoading: useDeferredLoading));
     return super.setUpIn(dir);
   }
 
@@ -561,4 +565,15 @@ void main() {
   "helloWorld": "台灣繁體你好世界"
 }
 ''';
+
+  String l10nYaml({
+    @required bool useDeferredLoading,
+  }) {
+    if (useDeferredLoading) {
+      return r'''
+use-deferred-loading: false
+      ''';
+    }
+    return '';
+  }
 }