Generate a depfile for assets of a flutter_app. (#8961)

packages/flutter_tools/bin/fuchsia_builder.dart

@@ -25,13 +25,17 @@ const String _kOptionOutput = 'output-file';
 const String _kOptionHeader = 'header';
 const String _kOptionSnapshot = 'snapshot';
 const String _kOptionWorking = 'working-dir';
-const String _kOptionsManifest = 'manifest';
+const String _kOptionManifest = 'manifest';
+const String _kOptionDepFile = 'depfile';
+const String _kOptionBuildRoot = 'build-root';
 const List<String> _kRequiredOptions = const <String>[
   _kOptionPackages,
   _kOptionOutput,
   _kOptionHeader,
   _kOptionSnapshot,
   _kOptionWorking,
+  _kOptionDepFile,
+  _kOptionBuildRoot,
 ];
 
 Future<Null> main(List<String> args) async {
@@ -59,23 +63,36 @@ Future<Null> run(List<String> args) async {
     ..addOption(_kOptionSnapshot, help: 'The generated snapshot file')
     ..addOption(_kOptionWorking,
         help: 'The directory where to put temporary files')
-    ..addOption(_kOptionsManifest, help: 'The manifest file');
+    ..addOption(_kOptionManifest, help: 'The manifest file')
+    ..addOption(_kOptionDepFile, help: 'The generated depfile')
+    ..addOption(_kOptionBuildRoot, help: 'The build\'s root directory');
   final ArgResults argResults = parser.parse(args);
-  if (_kRequiredOptions.any((String option) => !argResults.options.contains(option))) {
+  if (_kRequiredOptions
+      .any((String option) => !argResults.options.contains(option))) {
     printError('Missing option! All options must be specified.');
     exit(1);
   }
   Cache.flutterRoot = platform.environment['FLUTTER_ROOT'];
   final String outputPath = argResults[_kOptionOutput];
   try {
-    await assemble(
+    final List<String> dependencies = await assemble(
       outputPath: outputPath,
       snapshotFile: fs.file(argResults[_kOptionSnapshot]),
       workingDirPath: argResults[_kOptionWorking],
       packagesPath: argResults[_kOptionPackages],
-      manifestPath: argResults[_kOptionsManifest] ?? defaultManifestPath,
+      manifestPath: argResults[_kOptionManifest] ?? defaultManifestPath,
       includeDefaultFonts: false,
     );
+    final String depFilePath = argResults[_kOptionDepFile];
+    final int depFileResult = _createDepfile(
+        depFilePath,
+        fs.path.relative(argResults[_kOptionOutput],
+            from: argResults[_kOptionBuildRoot]),
+        dependencies);
+    if (depFileResult != 0) {
+      printError('Error creating depfile $depFilePath: $depFileResult.');
+      exit(depFileResult);
+    }
   } on ToolExit catch (e) {
     printError(e.message);
     exit(e.exitCode);
@@ -87,6 +104,17 @@ Future<Null> run(List<String> args) async {
   exit(headerResult);
 }
 
+int _createDepfile(
+    String depFilePath, String target, List<String> dependencies) {
+  try {
+    final File depFile = fs.file(depFilePath);
+    depFile.writeAsStringSync('$target: ${dependencies.join(' ')}\n');
+    return 0;
+  } catch (_) {
+    return 1;
+  }
+}
+
 int _addHeader(String outputPath, String header) {
   try {
     final File outputFile = fs.file(outputPath);

packages/flutter_tools/lib/src/devfs.dart

@@ -42,6 +42,9 @@ abstract class DevFSContent {
   Stream<List<int>> contentsAsCompressedStream() {
     return contentsAsStream().transform(GZIP.encoder);
   }
+
+  /// Return the list of files this content depends on.
+  List<String> get fileDependencies => <String>[];
 }
 
 // File content to be copied to the device.
@@ -82,6 +85,9 @@ class DevFSFileContent extends DevFSContent {
     }
   }
 
+  @override
+  List<String> get fileDependencies => <String>[_getFile().path];
+
   @override
   bool get isModified {
     final FileStat _oldFileStat = _fileStat;

packages/flutter_tools/lib/src/flx.dart

@@ -107,10 +107,10 @@ Future<Null> build({
     packagesPath: packagesPath,
     includeRobotoFonts: includeRobotoFonts,
     reportLicensedPackages: reportLicensedPackages
-  );
+  ).then((_) => null);
 }
 
-Future<Null> assemble({
+Future<List<String>> assemble({
   String manifestPath,
   DevFSContent kernelContent,
   File snapshotFile,
@@ -145,6 +145,10 @@ Future<Null> assemble({
   // Add all entries from the asset bundle.
   zipBuilder.entries.addAll(assetBundle.entries);
 
+  final List<String> fileDependencies = assetBundle.entries.values
+      .expand((DevFSContent content) => content.fileDependencies)
+      .toList();
+
   if (kernelContent != null)
     zipBuilder.entries[_kKernelKey] = kernelContent;
   if (snapshotFile != null)
@@ -156,4 +160,6 @@ Future<Null> assemble({
   await zipBuilder.createZip(fs.file(outputPath), fs.directory(workingDirPath));
 
   printTrace('Built $outputPath.');
+
+  return fileDependencies;
 }