Enable asset transformation for `flutter run -d <browser>` and `flutter test` (#144734)

Partial implementation of https://github.com/flutter/flutter/issues/143348.

The title says it all. Feel free to experiment with the feature using this project: https://github.com/andrewkolos/asset_transformers_test.

packages/flutter_tools/lib/src/bundle_builder.dart

@@ -14,6 +14,7 @@ import 'base/logger.dart';
 import 'build_info.dart';
 import 'build_system/build_system.dart';
 import 'build_system/depfile.dart';
+import 'build_system/tools/asset_transformer.dart';
 import 'build_system/tools/scene_importer.dart';
 import 'build_system/tools/shader_compiler.dart';
 import 'bundle.dart';
@@ -145,6 +146,7 @@ Future<void> writeBundle(
   required FileSystem fileSystem,
   required Artifacts artifacts,
   required Logger logger,
+  required Directory projectDir,
 }) async {
   if (bundleDir.existsSync()) {
     try {
@@ -172,6 +174,12 @@ Future<void> writeBundle(
     artifacts: artifacts,
   );
 
+  final AssetTransformer assetTransformer = AssetTransformer(
+    processManager: processManager,
+    fileSystem: fileSystem,
+    dartBinaryPath: artifacts.getArtifactPath(Artifact.engineDartBinary),
+  );
+
   // Limit number of open files to avoid running out of file descriptors.
   final Pool pool = Pool(64);
   await Future.wait<void>(
@@ -190,8 +198,20 @@ Future<void> writeBundle(
           final File input = devFSContent.file as File;
           bool doCopy = true;
           switch (entry.value.kind) {
-            case AssetKind.regular:
+          case AssetKind.regular:
+            if (entry.value.transformers.isEmpty) {
               break;
+            }
+            final AssetTransformationFailure? failure = await assetTransformer.transformAsset(
+              asset: input,
+              outputPath: file.path,
+              workingDirectory: projectDir.path,
+              transformerEntries: entry.value.transformers,
+            );
+            doCopy = false;
+            if (failure != null) {
+              throwToolExit(failure.message);
+            }
             case AssetKind.font:
               break;
             case AssetKind.shader:

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

@@ -675,6 +675,7 @@ class TestCommand extends FlutterCommand with DeviceBasedDevelopmentArtifacts {
         fileSystem: globals.fs,
         artifacts: globals.artifacts!,
         logger: globals.logger,
+        projectDir: globals.fs.currentDirectory,
       );
     }
   }

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

@@ -946,6 +946,7 @@ class WebDevFS implements DevFS {
           fileSystem: globals.fs,
           artifacts: globals.artifacts!,
           logger: globals.logger,
+          projectDir: rootDirectory,
         );
       }
     }

packages/flutter_tools/test/general.shard/asset_bundle_test.dart

@@ -543,6 +543,7 @@ flutter:
       fileSystem: globals.fs,
       artifacts: globals.artifacts!,
       logger: testLogger,
+      projectDir: globals.fs.currentDirectory
     );
 
     expect(testLogger.warningText, contains('Expected Error Text'));
@@ -668,6 +669,7 @@ flutter:
         fileSystem: globals.fs,
         artifacts: globals.artifacts!,
         logger: testLogger,
+        projectDir: globals.fs.currentDirectory,
       );
 
     }, overrides: <Type, Generator>{
@@ -719,6 +721,7 @@ flutter:
         fileSystem: globals.fs,
         artifacts: globals.artifacts!,
         logger: testLogger,
+        projectDir: globals.fs.currentDirectory,
       );
 
     }, overrides: <Type, Generator>{
@@ -805,6 +808,7 @@ flutter:
         fileSystem: globals.fs,
         artifacts: globals.artifacts!,
         logger: testLogger,
+        projectDir: globals.fs.currentDirectory,
       );
       expect((globals.processManager as FakeProcessManager).hasRemainingExpectations, false);
     }, overrides: <Type, Generator>{

packages/flutter_tools/test/general.shard/bundle_builder_test.dart

@@ -2,15 +2,26 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:typed_data';
+
+import 'package:args/args.dart';
 import 'package:file/memory.dart';
+import 'package:file_testing/file_testing.dart';
+import 'package:flutter_tools/src/artifacts.dart';
+import 'package:flutter_tools/src/asset.dart';
 import 'package:flutter_tools/src/base/config.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
+import 'package:flutter_tools/src/base/logger.dart';
 import 'package:flutter_tools/src/build_info.dart';
 import 'package:flutter_tools/src/build_system/build_system.dart';
-import 'package:flutter_tools/src/bundle.dart';
+import 'package:flutter_tools/src/bundle.dart' hide defaultManifestPath;
 import 'package:flutter_tools/src/bundle_builder.dart';
+import 'package:flutter_tools/src/devfs.dart';
+import 'package:flutter_tools/src/device.dart';
+import 'package:flutter_tools/src/flutter_manifest.dart';
 import 'package:flutter_tools/src/globals.dart' as globals;
 import 'package:flutter_tools/src/project.dart';
+import 'package:test/fake.dart';
 
 import '../src/common.dart';
 import '../src/context.dart';
@@ -46,6 +57,75 @@ void main() {
     ProcessManager: () => FakeProcessManager.any(),
   });
 
+  testWithoutContext('writeBundle applies transformations to any assets that have them defined', () async {
+    final MemoryFileSystem fileSystem = MemoryFileSystem.test();
+    final File asset = fileSystem.file('my-asset.txt')
+      ..createSync()
+      ..writeAsBytesSync(<int>[1, 2, 3]);
+    final Artifacts artifacts = Artifacts.test();
+
+    final FakeProcessManager processManager = FakeProcessManager.list(
+        <FakeCommand>[
+          FakeCommand(
+            command: <Pattern>[
+              artifacts.getArtifactPath(Artifact.engineDartBinary),
+              'run',
+              'increment',
+              '--input=/.tmp_rand0/my-asset.txt-transformOutput0.txt',
+              '--output=/.tmp_rand0/my-asset.txt-transformOutput1.txt'
+            ],
+            onRun: (List<String> command) {
+              final ArgResults argParseResults = (ArgParser()
+                  ..addOption('input', mandatory: true)
+                  ..addOption('output', mandatory: true))
+                .parse(command);
+
+              final File inputFile = fileSystem.file(argParseResults['input']);
+              final File outputFile = fileSystem.file(argParseResults['output']);
+
+              expect(inputFile, exists);
+              outputFile
+                ..createSync()
+                ..writeAsBytesSync(
+                  Uint8List.fromList(
+                    inputFile.readAsBytesSync().map((int b) => b + 1).toList(),
+                  ),
+                );
+            },
+          ),
+        ],
+      );
+
+    final FakeAssetBundle bundle = FakeAssetBundle()
+      ..entries['my-asset.txt'] = AssetBundleEntry(
+        DevFSFileContent(asset),
+        kind: AssetKind.regular,
+        transformers: const <AssetTransformerEntry>[
+          AssetTransformerEntry(package: 'increment', args: <String>[]),
+        ],
+      );
+
+    final Directory bundleDir = fileSystem.directory(
+      getAssetBuildDirectory(Config.test(), fileSystem),
+    );
+
+    await writeBundle(
+      bundleDir,
+      bundle.entries,
+      targetPlatform: TargetPlatform.tester,
+      impellerStatus: ImpellerStatus.platformDefault,
+      processManager: processManager,
+      fileSystem: fileSystem,
+      artifacts: artifacts,
+      logger: BufferLogger.test(),
+      projectDir: fileSystem.currentDirectory,
+    );
+
+    final File outputAssetFile = fileSystem.file('build/flutter_assets/my-asset.txt');
+    expect(outputAssetFile, exists);
+    expect(outputAssetFile.readAsBytesSync(), orderedEquals(<int>[2, 3, 4]));
+  });
+
   testUsingContext('Handles build system failure', () {
     expect(
       () => BundleBuilder().build(
@@ -157,3 +237,8 @@ void main() {
     ), 'build/95b595cca01caa5f0ca0a690339dd7f6.cache.dill.track.dill');
   });
 }
+
+class FakeAssetBundle extends Fake implements AssetBundle {
+  @override
+  final Map<String, AssetBundleEntry> entries = <String, AssetBundleEntry>{};
+}