Use depfile with dart2wasm to determine when to rebuild. (#122817)

Use depfile with dart2wasm to determine when to rebuild.

Author: eyebrowsoffire

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

@@ -295,6 +295,7 @@ class Dart2WasmTarget extends Dart2WebTarget {
     final BuildMode buildMode = getBuildModeForName(buildModeEnvironment);
     final Artifacts artifacts = globals.artifacts!;
     final File outputWasmFile = environment.buildDir.childFile('main.dart.wasm');
+    final File depFile = environment.buildDir.childFile('dart2wasm.d');
     final String dartSdkPath = artifacts.getArtifactPath(Artifact.engineDartSdkPath, platform: TargetPlatform.web_javascript);
     final String dartSdkRoot = environment.fileSystem.directory(dartSdkPath).parent.path;
 
@@ -319,10 +320,12 @@ class Dart2WasmTarget extends Dart2WebTarget {
       dartSdkRoot,
       '--libraries-spec',
       artifacts.getHostArtifact(HostArtifact.flutterWebLibrariesJson).path,
+      '--depfile=${depFile.path}',
 
       environment.buildDir.childFile('main.dart').path, // dartfile
       outputWasmFile.path,
     ];
+    globals.printTrace('compiling dart code to wasm with command "${compilationArgs.join(' ')}"');
     final ProcessResult compileResult = await globals.processManager.run(compilationArgs);
     if (compileResult.exitCode != 0) {
       throw Exception(_collectOutput(compileResult));
@@ -335,6 +338,11 @@ class Dart2WasmTarget extends Dart2WebTarget {
   @override
   String get name => 'dart2wasm';
 
+  @override
+  List<String> get depfiles => const <String>[
+    'dart2wasm.d',
+  ];
+
   @override
   List<Source> get outputs => const <Source>[
     Source.pattern('{OUTPUT_DIR}/main.dart.wasm'),

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

@@ -778,6 +778,8 @@ void main() {
     environment.defines[kBuildMode] = 'profile';
     environment.defines[kDartDefines] = encodeDartDefines(<String>['FOO=bar', 'BAZ=qux']);
 
+    final File depFile = environment.buildDir.childFile('dart2wasm.d');
+
     processManager.addCommand(FakeCommand(
       command: <String>[
         'bin/cache/dart-sdk/bin/dartaotruntime',
@@ -796,6 +798,7 @@ void main() {
         'bin/cache',
         '--libraries-spec',
         'bin/cache/flutter_web_sdk/libraries.json',
+        '--depfile=${depFile.absolute.path}',
 
         environment.buildDir.childFile('main.dart').absolute.path,
         environment.buildDir.childFile('main.dart.wasm').absolute.path,