[flutter_tools] disable source maps by default for release builds, enable for run and with command line arg (#67331)

Disables source map production by default for build web. For web builds performed as a part of flutter run --release, enable the source maps, or allow force enabling with --source-maps command line flag.

fixes #67328

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

@@ -39,6 +39,9 @@ const String kCspMode = 'cspMode';
 /// The caching strategy to use for service worker generation.
 const String kServiceWorkerStrategy = 'ServiceWorkerStratgey';
 
+/// Whether the dart2js build should output source maps.
+const String kSourceMapsEnabled = 'SourceMaps';
+
 /// The caching strategy for the generated service worker.
 enum ServiceWorkerStrategy {
   /// Download the app shell eagerly and all other assets lazily.
@@ -194,6 +197,7 @@ class Dart2JSTarget extends Target {
   @override
   Future<void> build(Environment environment) async {
     final BuildMode buildMode = getBuildModeForName(environment.defines[kBuildMode]);
+    final bool sourceMapsEnabled = environment.defines[kSourceMapsEnabled] == 'true';
 
     final List<String> sharedCommandOptions = <String>[
       globals.artifacts.getArtifactPath(Artifact.engineDartBinary),
@@ -207,6 +211,8 @@ class Dart2JSTarget extends Target {
         '-Ddart.vm.product=true',
       for (final String dartDefine in decodeDartDefines(environment.defines, kDartDefines))
         '-D$dartDefine',
+      if (!sourceMapsEnabled)
+        '--no-source-maps',
     ];
 
     // Run the dart2js compilation in two stages, so that icon tree shaking can
@@ -227,7 +233,7 @@ class Dart2JSTarget extends Target {
     final File outputJSFile = environment.buildDir.childFile('main.dart.js');
     final bool csp = environment.defines[kCspMode] == 'true';
 
-    final ProcessResult javaScriptResult = await globals.processManager.run(<String>[
+    final ProcessResult javaScriptResult = await environment.processManager.run(<String>[
       ...sharedCommandOptions,
       if (dart2jsOptimization != null) '-$dart2jsOptimization' else '-O4',
       if (buildMode == BuildMode.profile) '--no-minify',

packages/flutter_tools/lib/src/commands/build_web.dart

@@ -37,6 +37,13 @@ class BuildWebCommand extends BuildSubCommand {
       help: 'Disable dynamic generation of code in the generated output. '
         'This is necessary to satisfy CSP restrictions (see http://www.w3.org/TR/CSP/).'
     );
+    argParser.addFlag(
+      'source-maps',
+      defaultsTo: false,
+      help: 'Whether to generate a sourcemap file. These can be used by browsers '
+      'To view and debug the original source code of a compiled and minified Dart '
+      'application. Defaults to false (no sourcemaps produced).'
+    );
     argParser.addOption('pwa-strategy',
       defaultsTo: kOfflineFirst,
       help:
@@ -88,6 +95,7 @@ class BuildWebCommand extends BuildSubCommand {
       boolArg('web-initialize-platform'),
       boolArg('csp'),
       stringArg('pwa-strategy'),
+      boolArg('source-maps')
     );
     return FlutterCommandResult.success();
   }

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

@@ -531,6 +531,7 @@ class _ResidentWebRunner extends ResidentWebRunner {
             debuggingOptions.initializePlatform,
             false,
             kNoneWorker,
+            true,
           );
         }
         await device.device.startApp(
@@ -601,6 +602,7 @@ class _ResidentWebRunner extends ResidentWebRunner {
           debuggingOptions.initializePlatform,
           false,
           kNoneWorker,
+          true,
         );
       } on ToolExit {
         return OperationResult(1, 'Failed to recompile application.');

packages/flutter_tools/lib/src/web/compile.dart

@@ -29,19 +29,25 @@ Future<void> buildWeb(
   bool initializePlatform,
   bool csp,
   String serviceWorkerStrategy,
+  bool sourceMaps,
 ) async {
   if (!flutterProject.web.existsSync()) {
     throwToolExit('Missing index.html.');
   }
   final bool hasWebPlugins = (await findPlugins(flutterProject))
     .any((Plugin p) => p.platforms.containsKey(WebPlugin.kConfigKey));
+  final Directory outputDirectory = globals.fs.directory(getWebBuildDirectory());
+  if (outputDirectory.existsSync()) {
+    outputDirectory.deleteSync(recursive: true);
+    outputDirectory.createSync(recursive: true);
+  }
   await injectPlugins(flutterProject, checkProjects: true);
   final Status status = globals.logger.startProgress('Compiling $target for the Web...', timeout: null);
   final Stopwatch sw = Stopwatch()..start();
   try {
     final BuildResult result = await globals.buildSystem.build(const WebServiceWorker(), Environment(
       projectDir: globals.fs.currentDirectory,
-      outputDir: globals.fs.directory(getWebBuildDirectory()),
+      outputDir: outputDirectory,
       buildDir: flutterProject.directory
         .childDirectory('.dart_tool')
         .childDirectory('flutter_build'),
@@ -53,6 +59,7 @@ Future<void> buildWeb(
         kDartDefines: encodeDartDefines(buildInfo.dartDefines),
         kCspMode: csp.toString(),
         kIconTreeShakerFlag: buildInfo.treeShakeIcons.toString(),
+        kSourceMapsEnabled: sourceMaps.toString(),
         if (serviceWorkerStrategy != null)
          kServiceWorkerStrategy: serviceWorkerStrategy,
         if (buildInfo.extraFrontEndOptions?.isNotEmpty ?? false)

packages/flutter_tools/test/commands.shard/hermetic/build_web_test.dart

@@ -57,6 +57,7 @@ void main() {
       false,
       false,
       null,
+      true,
     ), throwsToolExit());
   }, overrides: <Type, Generator>{
     Platform: () => fakePlatform,

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

@@ -305,6 +305,7 @@ void main() {
       command: <String>[
         ...kDart2jsLinuxArgs,
         '-Ddart.vm.profile=true',
+        '--no-source-maps',
         '-o',
         environment.buildDir.childFile('app.dill').absolute.path,
         '--packages=.packages',
@@ -316,6 +317,7 @@ void main() {
       command: <String>[
         ...kDart2jsLinuxArgs,
         '-Ddart.vm.profile=true',
+        '--no-source-maps',
         '-O4',
         '--no-minify',
         '--csp',
@@ -339,6 +341,7 @@ void main() {
         ...kDart2jsLinuxArgs,
         '--enable-experiment=non-nullable',
         '-Ddart.vm.profile=true',
+        '--no-source-maps',
         '-o',
         environment.buildDir.childFile('app.dill').absolute.path,
         '--packages=.packages',
@@ -351,6 +354,7 @@ void main() {
         ...kDart2jsLinuxArgs,
         '--enable-experiment=non-nullable',
         '-Ddart.vm.profile=true',
+        '--no-source-maps',
         '-O4',
         '--no-minify',
         '-o',
@@ -370,6 +374,7 @@ void main() {
       command: <String>[
         ...kDart2jsLinuxArgs,
         '-Ddart.vm.profile=true',
+        '--no-source-maps',
         '-o',
         environment.buildDir.childFile('app.dill').absolute.path,
         '--packages=.packages',
@@ -381,6 +386,7 @@ void main() {
       command: <String>[
         ...kDart2jsLinuxArgs,
         '-Ddart.vm.profile=true',
+        '--no-source-maps',
         '-O4',
         '--no-minify',
         '-o',
@@ -400,6 +406,7 @@ void main() {
       command: <String>[
         ...kDart2jsLinuxArgs,
         '-Ddart.vm.product=true',
+        '--no-source-maps',
         '-o',
         environment.buildDir.childFile('app.dill').absolute.path,
         '--packages=.packages',
@@ -411,6 +418,7 @@ void main() {
       command: <String>[
         ...kDart2jsLinuxArgs,
         '-Ddart.vm.product=true',
+        '--no-source-maps',
         '-O4',
         '-o',
         environment.buildDir.childFile('main.dart.js').absolute.path,
@@ -430,6 +438,7 @@ void main() {
       command: <String>[
         ...kDart2jsLinuxArgs,
         '-Ddart.vm.product=true',
+        '--no-source-maps',
         '-o',
         environment.buildDir.childFile('app.dill').absolute.path,
         '--packages=.packages',
@@ -441,6 +450,7 @@ void main() {
       command: <String>[
         ...kDart2jsLinuxArgs,
         '-Ddart.vm.product=true',
+        '--no-source-maps',
         '-O3',
         '-o',
         environment.buildDir.childFile('main.dart.js').absolute.path,
@@ -481,6 +491,7 @@ void main() {
         '-Ddart.vm.product=true',
         '-DFOO=bar',
         '-DBAZ=qux',
+        '--no-source-maps',
         '-o',
         environment.buildDir.childFile('app.dill').absolute.path,
         '--packages=.packages',
@@ -494,6 +505,7 @@ void main() {
         '-Ddart.vm.product=true',
         '-DFOO=bar',
         '-DBAZ=qux',
+        '--no-source-maps',
         '-O4',
         '-o',
         environment.buildDir.childFile('main.dart.js').absolute.path,
@@ -506,6 +518,37 @@ void main() {
     ProcessManager: () => processManager,
   }));
 
+  test('Dart2JSTarget can enable source maps', () => testbed.run(() async {
+    environment.defines[kBuildMode] = 'release';
+    environment.defines[kSourceMapsEnabled] = 'true';
+    processManager.addCommand(FakeCommand(
+      command: <String>[
+        ...kDart2jsLinuxArgs,
+        '-Ddart.vm.product=true',
+        '-o',
+        environment.buildDir.childFile('app.dill').absolute.path,
+        '--packages=.packages',
+       '--cfe-only',
+        environment.buildDir.childFile('main.dart').absolute.path,
+      ]
+    ));
+    processManager.addCommand(FakeCommand(
+      command: <String>[
+        ...kDart2jsLinuxArgs,
+        '-Ddart.vm.product=true',
+        '-O4',
+        '-o',
+        environment.buildDir.childFile('main.dart.js').absolute.path,
+        environment.buildDir.childFile('app.dill').absolute.path,
+      ]
+    ));
+
+    await const Dart2JSTarget().build(environment);
+  }, overrides: <Type, Generator>{
+    ProcessManager: () => processManager,
+  }));
+
+
   test('Dart2JSTarget calls dart2js with Dart defines in profile mode', () => testbed.run(() async {
     environment.defines[kBuildMode] = 'profile';
     environment.defines[kDartDefines] = 'FOO=bar,BAZ=qux';
@@ -515,6 +558,7 @@ void main() {
         '-Ddart.vm.profile=true',
         '-DFOO=bar',
         '-DBAZ=qux',
+        '--no-source-maps',
         '-o',
         environment.buildDir.childFile('app.dill').absolute.path,
         '--packages=.packages',
@@ -528,6 +572,7 @@ void main() {
         '-Ddart.vm.profile=true',
         '-DFOO=bar',
         '-DBAZ=qux',
+        '--no-source-maps',
         '-O4',
         '--no-minify',
         '-o',