Split Snapshotter into AOT and Script classes (#17159)

There's very little code-sharing between the two, and what little there
is is concentrated in the GenSnapshotClass and the fingerprint
reading/writing utility methods.

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

@@ -166,9 +166,9 @@ Future<Set<String>> readDepfile(String depfilePath) async {
 ///     suitable for loading with `mmap`.
 ///   * Assembly AOT snapshot: architecture-specific ahead-of-time compile to
 ///     assembly suitable for compilation as a static or dynamic library.
-class Snapshotter {
+class ScriptSnapshotter {
   /// Builds an architecture-independent snapshot of the specified script.
-  Future<int> buildScriptSnapshot({
+  Future<int> build({
     @required String mainPath,
     @required String snapshotPath,
     @required String depfilePath,
@@ -206,51 +206,11 @@ class Snapshotter {
     await _writeFingerprint(snapshotType, outputPaths, depfilePath, mainPath, fingerprintPath);
     return exitCode;
   }
+}
 
-  /// Compiles a Dart file to kernel.
-  ///
-  /// Returns the output kernel file path, or null on failure.
-  Future<String> compileKernel({
-    @required TargetPlatform platform,
-    @required BuildMode buildMode,
-    @required String mainPath,
-    @required String outputPath,
-    List<String> extraFrontEndOptions: const <String>[],
-  }) async {
-    final Directory outputDir = fs.directory(outputPath);
-    outputDir.createSync(recursive: true);
-
-    printTrace('Compiling Dart to kernel: $mainPath');
-    final List<String> entryPointsJsonFiles = <String>[
-      artifacts.getArtifactPath(Artifact.entryPointsJson, platform, buildMode),
-      artifacts.getArtifactPath(Artifact.entryPointsExtraJson, platform, buildMode),
-    ];
-
-    if ((extraFrontEndOptions != null) && extraFrontEndOptions.isNotEmpty)
-      printTrace('Extra front-end options: $extraFrontEndOptions');
-
-    final String depfilePath = fs.path.join(outputPath, 'kernel_compile.d');
-    final CompilerOutput compilerOutput = await kernelCompiler.compile(
-      sdkRoot: artifacts.getArtifactPath(Artifact.flutterPatchedSdkPath),
-      mainPath: mainPath,
-      outputFilePath: fs.path.join(outputPath, 'app.dill'),
-      depFilePath: depfilePath,
-      extraFrontEndOptions: extraFrontEndOptions,
-      linkPlatformKernelIn: true,
-      aot: true,
-      entryPointsJsonFiles: entryPointsJsonFiles,
-      trackWidgetCreation: false,
-    );
-
-    // Write path to frontend_server, since things need to be re-generated when that changes.
-    final String frontendPath = artifacts.getArtifactPath(Artifact.frontendServerSnapshotForEngineDartSdk);
-    await fs.directory(outputPath).childFile('frontend_server.d').writeAsString('frontend_server.d: $frontendPath\n');
-
-    return compilerOutput?.outputFilename;
-  }
-
+class AOTSnapshotter {
   /// Builds an architecture-specific ahead-of-time compiled snapshot of the specified script.
-  Future<int> buildAotSnapshot({
+  Future<int> build({
     @required TargetPlatform platform,
     @required BuildMode buildMode,
     @required String mainPath,
@@ -415,6 +375,48 @@ class Snapshotter {
     return 0;
   }
 
+  /// Compiles a Dart file to kernel.
+  ///
+  /// Returns the output kernel file path, or null on failure.
+  Future<String> compileKernel({
+    @required TargetPlatform platform,
+    @required BuildMode buildMode,
+    @required String mainPath,
+    @required String outputPath,
+    List<String> extraFrontEndOptions: const <String>[],
+  }) async {
+    final Directory outputDir = fs.directory(outputPath);
+    outputDir.createSync(recursive: true);
+
+    printTrace('Compiling Dart to kernel: $mainPath');
+    final List<String> entryPointsJsonFiles = <String>[
+      artifacts.getArtifactPath(Artifact.entryPointsJson, platform, buildMode),
+      artifacts.getArtifactPath(Artifact.entryPointsExtraJson, platform, buildMode),
+    ];
+
+    if ((extraFrontEndOptions != null) && extraFrontEndOptions.isNotEmpty)
+      printTrace('Extra front-end options: $extraFrontEndOptions');
+
+    final String depfilePath = fs.path.join(outputPath, 'kernel_compile.d');
+    final CompilerOutput compilerOutput = await kernelCompiler.compile(
+      sdkRoot: artifacts.getArtifactPath(Artifact.flutterPatchedSdkPath),
+      mainPath: mainPath,
+      outputFilePath: fs.path.join(outputPath, 'app.dill'),
+      depFilePath: depfilePath,
+      extraFrontEndOptions: extraFrontEndOptions,
+      linkPlatformKernelIn: true,
+      aot: true,
+      entryPointsJsonFiles: entryPointsJsonFiles,
+      trackWidgetCreation: false,
+    );
+
+    // Write path to frontend_server, since things need to be re-generated when that changes.
+    final String frontendPath = artifacts.getArtifactPath(Artifact.frontendServerSnapshotForEngineDartSdk);
+    await fs.directory(outputPath).childFile('frontend_server.d').writeAsString('frontend_server.d: $frontendPath\n');
+
+    return compilerOutput?.outputFilename;
+  }
+
   bool _isValidAotPlatform(TargetPlatform platform, BuildMode buildMode) {
     if (platform == TargetPlatform.ios && buildMode == BuildMode.debug)
       return false;
@@ -428,8 +430,9 @@ class Snapshotter {
   String _getPackagePath(PackageMap packageMap, String package) {
     return fs.path.dirname(fs.path.fromUri(packageMap.map[package]));
   }
+}
 
-  Future<bool> _isBuildRequired(SnapshotType type, Set<String> outputPaths, String depfilePath, String mainPath, String fingerprintPath) async {
+Future<bool> _isBuildRequired(SnapshotType type, Set<String> outputPaths, String depfilePath, String mainPath, String fingerprintPath) async {
   final File fingerprintFile = fs.file(fingerprintPath);
   final List<String> requiredFiles = <String>[fingerprintPath, depfilePath]..addAll(outputPaths);
   if (!requiredFiles.every(fs.isFileSync))
@@ -447,9 +450,9 @@ class Snapshotter {
     printTrace('Rebuilding snapshot due to fingerprint check error: $e');
   }
   return true;
-  }
+}
 
-  Future<Null> _writeFingerprint(SnapshotType type, Set<String> outputPaths, String depfilePath, String mainPath, String fingerprintPath) async {
+Future<Null> _writeFingerprint(SnapshotType type, Set<String> outputPaths, String depfilePath, String mainPath, String fingerprintPath) async {
   try {
     final Set<String> inputFilePaths = await readDepfile(depfilePath)
       ..add(mainPath)
@@ -460,9 +463,9 @@ class Snapshotter {
     // Log exception and continue, this step is a performance improvement only.
     printStatus('Error during snapshot fingerprinting: $e\n$s');
   }
-  }
+}
 
-  static Fingerprint createFingerprint(SnapshotType type, String mainPath, Iterable<String> inputFilePaths) {
+Fingerprint createFingerprint(SnapshotType type, String mainPath, Iterable<String> inputFilePaths) {
   final Map<String, String> properties = <String, String>{
     'buildMode': type.mode.toString(),
     'targetPlatform': type.platform?.toString() ?? '',
@@ -472,5 +475,4 @@ class Snapshotter {
     ..add(artifacts.getArtifactPath(Artifact.vmSnapshotData))
     ..add(artifacts.getArtifactPath(Artifact.isolateSnapshotData));
   return new Fingerprint.fromBuildInputs(properties, pathsWithSnapshotData);
-  }
 }

packages/flutter_tools/lib/src/bundle.dart

@@ -56,8 +56,7 @@ Future<void> build({
 
     // In a precompiled snapshot, the instruction buffer contains script
     // content equivalents
-    final Snapshotter snapshotter = new Snapshotter();
-    final int result = await snapshotter.buildScriptSnapshot(
+    final int result = await new ScriptSnapshotter().build(
       mainPath: mainPath,
       snapshotPath: snapshotPath,
       depfilePath: depfilePath,

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

@@ -72,7 +72,7 @@ class BuildAotCommand extends BuildSubCommand {
     try {
       final bool previewDart2 = argResults['preview-dart-2'];
       String mainPath = findMainDartFile(targetFile);
-      final Snapshotter snapshotter = new Snapshotter();
+      final AOTSnapshotter snapshotter = new AOTSnapshotter();
 
       // Compile to kernel, if Dart 2.
       if (previewDart2) {
@@ -90,7 +90,7 @@ class BuildAotCommand extends BuildSubCommand {
       }
 
       // Build AOT snapshot.
-      final int snapshotExitCode = await snapshotter.buildAotSnapshot(
+      final int snapshotExitCode = await snapshotter.build(
         platform: platform,
         buildMode: buildMode,
         mainPath: mainPath,

packages/flutter_tools/test/base/build_test.dart

@@ -335,7 +335,7 @@ void main() {
     _FakeGenSnapshot genSnapshot;
     MemoryFileSystem fs;
     MockFlutterVersion mockVersion;
-    Snapshotter snapshotter;
+    ScriptSnapshotter snapshotter;
     MockArtifacts mockArtifacts;
 
     setUp(() {
@@ -349,7 +349,7 @@ void main() {
       };
       mockVersion = new MockFlutterVersion();
       when(mockVersion.frameworkRevision).thenReturn(kVersion);
-      snapshotter = new Snapshotter();
+      snapshotter = new ScriptSnapshotter();
       mockArtifacts = new MockArtifacts();
       when(mockArtifacts.getArtifactPath(Artifact.isolateSnapshotData)).thenReturn(kIsolateSnapshotData);
       when(mockArtifacts.getArtifactPath(Artifact.vmSnapshotData)).thenReturn(kVmSnapshotData);
@@ -395,7 +395,7 @@ void main() {
       await fs.file('main.dart').writeAsString('void main() {}');
       await fs.file('output.snapshot').create();
       await fs.file('output.snapshot.d').writeAsString('snapshot : main.dart');
-      await snapshotter.buildScriptSnapshot(
+      await snapshotter.build(
         mainPath: 'main.dart',
         snapshotPath: 'output.snapshot',
         depfilePath: 'output.snapshot.d',
@@ -429,7 +429,7 @@ void main() {
         'main.dart': '27f5ebf0f8c559b2af9419d190299a5e',
         'output.snapshot': 'deadbeef000b204e9800998ecaaaaa',
       });
-      await snapshotter.buildScriptSnapshot(
+      await snapshotter.build(
         mainPath: 'main.dart',
         snapshotPath: 'output.snapshot',
         depfilePath: 'output.snapshot.d',
@@ -450,7 +450,7 @@ void main() {
         'main.dart': '27f5ebf0f8c559b2af9419d190299a5e',
         'output.snapshot': 'd41d8cd98f00b204e9800998ecf8427e',
       });
-      await snapshotter.buildScriptSnapshot(
+      await snapshotter.build(
         mainPath: 'main.dart',
         snapshotPath: 'output.snapshot',
         depfilePath: 'output.snapshot.d',
@@ -479,7 +479,7 @@ void main() {
         'output.snapshot.d': 'output.snapshot : main.dart other.dart',
       };
 
-      await snapshotter.buildScriptSnapshot(
+      await snapshotter.build(
         mainPath: 'other.dart',
         snapshotPath: 'output.snapshot',
         depfilePath: 'output.snapshot.d',
@@ -505,7 +505,7 @@ void main() {
         'main.dart': '27f5ebf0f8c559b2af9419d190299a5e',
         'output.snapshot': 'd41d8cd98f00b204e9800998ecf8427e',
       });
-      await snapshotter.buildScriptSnapshot(
+      await snapshotter.build(
         mainPath: 'main.dart',
         snapshotPath: 'output.snapshot',
         depfilePath: 'output.snapshot.d',
@@ -529,7 +529,7 @@ void main() {
         kIsolateSnapshotData,
       ];
       testUsingContext('creates fingerprint with target platform', () {
-        final Fingerprint fingerprint = Snapshotter.createFingerprint(
+        final Fingerprint fingerprint = createFingerprint(
           new SnapshotType(TargetPlatform.android_x64, BuildMode.release),
           'a.dart',
           <String>[],
@@ -541,7 +541,7 @@ void main() {
         }, artifactPaths));
       }, overrides: contextOverrides);
       testUsingContext('creates fingerprint without target platform', () {
-        final Fingerprint fingerprint = Snapshotter.createFingerprint(
+        final Fingerprint fingerprint = createFingerprint(
           new SnapshotType(null, BuildMode.release),
           'a.dart',
           <String>[],
@@ -555,7 +555,7 @@ void main() {
       testUsingContext('creates fingerprint with file checksums', () async {
         await fs.file('a.dart').create();
         await fs.file('b.dart').create();
-        final Fingerprint fingerprint = Snapshotter.createFingerprint(
+        final Fingerprint fingerprint = createFingerprint(
           new SnapshotType(TargetPlatform.android_x64, BuildMode.release),
           'a.dart',
           <String>['a.dart', 'b.dart'],
@@ -582,7 +582,7 @@ void main() {
 
     _FakeGenSnapshot genSnapshot;
     MemoryFileSystem fs;
-    Snapshotter snapshotter;
+    AOTSnapshotter snapshotter;
     MockArtifacts mockArtifacts;
     MockXcode mockXcode;
 
@@ -603,7 +603,7 @@ void main() {
       fs.file(fs.path.join(skyEnginePath, 'sdk_ext', 'vmservice_io.dart')).createSync();
 
       genSnapshot = new _FakeGenSnapshot();
-      snapshotter = new Snapshotter();
+      snapshotter = new AOTSnapshotter();
       mockArtifacts = new MockArtifacts();
       mockXcode = new MockXcode();
       for (BuildMode mode in BuildMode.values) {
@@ -624,7 +624,7 @@ void main() {
 
     testUsingContext('iOS debug AOT snapshot is invalid', () async {
       final String outputPath = fs.path.join('build', 'foo');
-      expect(await snapshotter.buildAotSnapshot(
+      expect(await snapshotter.build(
         platform: TargetPlatform.ios,
         buildMode: BuildMode.debug,
         mainPath: 'main.dill',
@@ -646,7 +646,7 @@ void main() {
         fs.path.join(outputPath, 'snapshot.d'): '',
       };
 
-      final int genSnapshotExitCode = await snapshotter.buildAotSnapshot(
+      final int genSnapshotExitCode = await snapshotter.build(
         platform: TargetPlatform.ios,
         buildMode: BuildMode.profile,
         mainPath: 'main.dill',
@@ -690,7 +690,7 @@ void main() {
         fs.path.join(outputPath, 'snapshot.d'): '',
       };
 
-      final int genSnapshotExitCode = await snapshotter.buildAotSnapshot(
+      final int genSnapshotExitCode = await snapshotter.build(
         platform: TargetPlatform.ios,
         buildMode: BuildMode.release,
         mainPath: 'main.dill',