ensure we can disable --track-widget-creation in debug mode (#43016)

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

@@ -31,6 +31,9 @@ const String kTargetFile = 'TargetFile';
 /// The define to control whether the AOT snapshot is built with bitcode.
 const String kBitcodeFlag = 'EnableBitcode';
 
+/// Whether to enable or disable track widget creation.
+const String kTrackWidgetCreation = 'TrackWidgetCreation';
+
 /// The define to control what iOS architectures are built for.
 ///
 /// This is expected to be a comma-separated list of architectures. If not
@@ -208,12 +211,14 @@ class KernelSnapshot extends Target {
     final String targetFile = environment.defines[kTargetFile] ?? fs.path.join('lib', 'main.dart');
     final String packagesPath = environment.projectDir.childFile('.packages').path;
     final String targetFileAbsolute = fs.file(targetFile).absolute.path;
+    // everything besides 'false' is considered to be enabled.
+    final bool trackWidgetCreation = environment.defines[kTrackWidgetCreation] != 'false';
 
     final CompilerOutput output = await compiler.compile(
       sdkRoot: artifacts.getArtifactPath(Artifact.flutterPatchedSdkPath, mode: buildMode),
       aot: buildMode != BuildMode.debug,
       buildMode: buildMode,
-      trackWidgetCreation: buildMode == BuildMode.debug,
+      trackWidgetCreation: trackWidgetCreation && buildMode == BuildMode.debug,
       targetModel: TargetModel.flutter,
       outputFilePath: environment.buildDir.childFile('app.dill').path,
       packagesPath: packagesPath,

packages/flutter_tools/lib/src/bundle.dart

@@ -80,6 +80,7 @@ class BundleBuilder {
       outputDir: assetDirPath,
       depfilePath: depfilePath,
       precompiled: precompiledSnapshot,
+      trackWidgetCreation: trackWidgetCreation,
     );
     // Work around for flutter_tester placing kernel artifacts in odd places.
     if (applicationKernelFilePath != null) {
@@ -103,6 +104,7 @@ Future<void> buildWithAssemble({
   @required String outputDir,
   @required String depfilePath,
   @required bool precompiled,
+  bool trackWidgetCreation,
 }) async {
   // If the precompiled flag was not passed, force us into debug mode.
   buildMode = precompiled ? buildMode : BuildMode.debug;
@@ -114,6 +116,7 @@ Future<void> buildWithAssemble({
       kTargetFile: mainPath,
       kBuildMode: getNameForBuildMode(buildMode),
       kTargetPlatform: getNameForTargetPlatform(targetPlatform),
+      kTrackWidgetCreation: trackWidgetCreation?.toString(),
     },
   );
   final Target target = buildMode == BuildMode.debug

packages/flutter_tools/test/commands.shard/permeable/build_bundle_test.dart

@@ -6,6 +6,8 @@ import 'package:args/command_runner.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/common.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
+import 'package:flutter_tools/src/build_system/build_system.dart';
+import 'package:flutter_tools/src/build_system/targets/dart.dart';
 import 'package:flutter_tools/src/bundle.dart';
 import 'package:flutter_tools/src/cache.dart';
 import 'package:flutter_tools/src/commands/build_bundle.dart';
@@ -202,6 +204,37 @@ void main() {
     ProcessManager: () => FakeProcessManager(<FakeCommand>[]),
     FeatureFlags: () => TestFeatureFlags(isMacOSEnabled: true),
   });
+
+  testUsingContext('passes track widget creation through', () async {
+    fs.file('lib/main.dart').createSync(recursive: true);
+    fs.file('pubspec.yaml').createSync();
+    fs.file('.packages').createSync();
+    final CommandRunner<void> runner = createTestCommandRunner(BuildBundleCommand());
+    when(buildSystem.build(any, any)).thenAnswer((Invocation invocation) async {
+      final Environment environment = invocation.positionalArguments[1];
+      expect(environment.defines, <String, String>{
+        kTargetFile: fs.path.join('lib', 'main.dart'),
+        kBuildMode: 'debug',
+        kTargetPlatform: 'android-arm',
+        kTrackWidgetCreation: 'true',
+      });
+
+      return BuildResult(success: true);
+    });
+
+    await runner.run(<String>[
+      'bundle',
+      '--no-pub',
+      '--debug',
+      '--target-platform=android-arm',
+      '--track-widget-creation'
+    ]);
+  }, overrides: <Type, Generator>{
+    FileSystem: () => MemoryFileSystem(),
+    BuildSystem: () => MockBuildSystem(),
+    ProcessManager: () => FakeProcessManager(<FakeCommand>[]),
+  });
 }
 
 class MockBundleBuilder extends Mock implements BundleBuilder {}
+class MockBuildSystem extends Mock implements BuildSystem {}

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

@@ -168,6 +168,30 @@ flutter_tools:lib/''');
     KernelCompilerFactory: () => MockKernelCompilerFactory(),
   }));
 
+  test('kernel_snapshot can disable track-widget-creation on debug builds', () => testbed.run(() async {
+    final MockKernelCompiler mockKernelCompiler = MockKernelCompiler();
+    when(kernelCompilerFactory.create(any)).thenAnswer((Invocation _) async {
+      return mockKernelCompiler;
+    });
+    when(mockKernelCompiler.compile(
+      sdkRoot: anyNamed('sdkRoot'),
+      aot: anyNamed('aot'),
+      buildMode: anyNamed('buildMode'),
+      trackWidgetCreation: false,
+      targetModel: anyNamed('targetModel'),
+      outputFilePath: anyNamed('outputFilePath'),
+      depFilePath: anyNamed('depFilePath'),
+      packagesPath: anyNamed('packagesPath'),
+      mainPath: anyNamed('mainPath'),
+    )).thenAnswer((Invocation _) async {
+      return const CompilerOutput('example', 0, <Uri>[]);
+    });
+
+    await const KernelSnapshot().build(androidEnvironment..defines[kTrackWidgetCreation] = 'false');
+  }, overrides: <Type, Generator>{
+    KernelCompilerFactory: () => MockKernelCompilerFactory(),
+  }));
+
   test('kernel_snapshot does use track widget creation on debug builds', () => testbed.run(() async {
     final MockKernelCompiler mockKernelCompiler = MockKernelCompiler();
     when(kernelCompilerFactory.create(any)).thenAnswer((Invocation _) async {