Fix Dart plugin registrant interaction with 'flutter test' (#90288)

Building an application for a desktop platform that transitively included any Dart-based plugins (such as path_provider) broke `flutter test`, because its compilation was overriding the provided main (in this case, the test main) with `generated_main.dart` if it was present. This PR:
- Changes the `flutter test` compilation path to update `generated_main.dart`, so that the tests will work, and will include any registered Dart plugins.
- Makes using `generated_main.dart` during recompile opt-in, to try to reduce the chance of a similar bug happening with other codepaths in the future.

Fixes https://github.com/flutter/flutter/issues/88794

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

@@ -33,27 +33,23 @@ class DartPluginRegistrantTarget extends Target {
   @override
   Future<void> build(Environment environment) async {
     assert(environment.generateDartPluginRegistry);
-    final File packagesFile = environment.projectDir
+    final FlutterProject project = _project
-        .childDirectory('.dart_tool')
+      ?? FlutterProject.fromDirectory(environment.projectDir);
-        .childFile('package_config.json');
     final PackageConfig packageConfig = await loadPackageConfigWithLogging(
-      packagesFile,
+      project.packageConfigFile,
       logger: environment.logger,
     );
-    final String targetFile = environment.defines[kTargetFile] ??
+    final String targetFilePath = environment.defines[kTargetFile] ??
         environment.fileSystem.path.join('lib', 'main.dart');
-    final File mainFile = environment.fileSystem.file(targetFile);
+    final File mainFile = environment.fileSystem.file(targetFilePath);
     final Uri mainFileUri = mainFile.absolute.uri;
-    final String mainUri = packageConfig.toPackageUri(mainFileUri)?.toString() ?? mainFileUri.toString();
+    final String mainFileUriString = packageConfig.toPackageUri(mainFileUri)?.toString()
-    final File newMainDart = environment.projectDir
+      ?? mainFileUri.toString();
-        .childDirectory('.dart_tool')
+
-        .childDirectory('flutter_build')
-        .childFile('generated_main.dart');
     await generateMainDartWithPluginRegistrant(
-      _project ?? FlutterProject.fromDirectory(environment.projectDir),
+      project,
       packageConfig,
-      mainUri,
+      mainFileUriString,
-      newMainDart,
       mainFile,
       throwOnPluginPubspecError: false,
     );

packages/flutter_tools/lib/src/compile.dart

@@ -462,6 +462,10 @@ abstract class ResidentCompiler {
   /// point that is used for recompilation.
   /// Binary file name is returned if compilation was successful, otherwise
   /// null is returned.
+  ///
+  /// If [checkDartPluginRegistry] is true, it is the caller's responsibility
+  /// to ensure that the generated registrant file has been updated such that
+  /// it is wrapping [mainUri].
   Future<CompilerOutput?> recompile(
     Uri mainUri,
     List<Uri>? invalidatedFiles, {
@@ -470,6 +474,7 @@ abstract class ResidentCompiler {
     required String projectRootPath,
     required FileSystem fs,
     bool suppressErrors = false,
+    bool checkDartPluginRegistry = false,
   });
 
   Future<CompilerOutput?> compileExpression(
@@ -610,6 +615,7 @@ class DefaultResidentCompiler implements ResidentCompiler {
     required String outputPath,
     required PackageConfig packageConfig,
     bool suppressErrors = false,
+    bool checkDartPluginRegistry = false,
     String? projectRootPath,
     FileSystem? fs,
   }) async {
@@ -618,7 +624,7 @@ class DefaultResidentCompiler implements ResidentCompiler {
       _controller.stream.listen(_handleCompilationRequest);
     }
     // `generated_main.dart` contains the Dart plugin registry.
-    if (projectRootPath != null && fs != null) {
+    if (checkDartPluginRegistry && projectRootPath != null && fs != null) {
       final File generatedMainDart = fs.file(
         fs.path.join(
           projectRootPath,

packages/flutter_tools/lib/src/devfs.dart

@@ -613,6 +613,7 @@ class DevFS {
       fs: _fileSystem,
       projectRootPath: projectRootPath,
       packageConfig: packageConfig,
+      checkDartPluginRegistry: true, // The entry point is assumed not to have changed.
     ).then((CompilerOutput result) {
       compileTimer.stop();
       return result;

packages/flutter_tools/lib/src/flutter_plugins.dart

@@ -1233,7 +1233,6 @@ Future<void> generateMainDartWithPluginRegistrant(
   FlutterProject rootProject,
   PackageConfig packageConfig,
   String currentMainUri,
-  File newMainDart,
   File mainFile, {
   bool throwOnPluginPubspecError = false,
 }) async {
@@ -1254,6 +1253,7 @@ Future<void> generateMainDartWithPluginRegistrant(
     MacOSPlugin.kConfigKey: <Object?>[],
     WindowsPlugin.kConfigKey: <Object?>[],
   };
+  final File newMainDart = rootProject.dartPluginRegistrant;
   if (resolutions.isEmpty) {
     try {
       if (newMainDart.existsSync()) {

packages/flutter_tools/lib/src/project.dart

@@ -219,6 +219,11 @@ class FlutterProject {
     .childDirectory('generated')
     .childDirectory(manifest.appName);
 
+  /// The generated Dart plugin registrant for non-web platforms.
+  File get dartPluginRegistrant => dartTool
+    .childDirectory('flutter_build')
+    .childFile('generated_main.dart');
+
   /// The example sub-project of this project.
   FlutterProject get example => FlutterProject(
     _exampleDirectory(directory),

packages/flutter_tools/lib/src/run_hot.dart

@@ -381,6 +381,7 @@ class HotRunner extends ResidentRunner {
             // the native build step. If there is a Dart compilation error, it
             // should only be displayed once.
             suppressErrors: applicationBinary == null,
+            checkDartPluginRegistry: true,
             outputPath: dillOutputPath ??
               getDefaultApplicationKernelPath(
                 trackWidgetCreation: debuggingOptions.buildInfo.trackWidgetCreation,

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

@@ -13,6 +13,7 @@ import '../base/file_system.dart';
 import '../build_info.dart';
 import '../bundle.dart';
 import '../compile.dart';
+import '../flutter_plugins.dart';
 import '../globals_null_migrated.dart' as globals;
 import '../project.dart';
 
@@ -143,12 +144,29 @@ class TestCompiler {
         compiler = await createCompiler();
         firstCompile = true;
       }
+
+      final List<Uri> invalidatedRegistrantFiles = <Uri>[];
+      if (flutterProject != null) {
+        // Update the generated registrant to use the test target's main.
+        final String mainUriString = buildInfo.packageConfig.toPackageUri(request.mainUri)?.toString()
+          ?? request.mainUri.toString();
+        await generateMainDartWithPluginRegistrant(
+          flutterProject,
+          buildInfo.packageConfig,
+          mainUriString,
+          globals.fs.file(request.mainUri),
+          throwOnPluginPubspecError: false,
+        );
+        invalidatedRegistrantFiles.add(flutterProject.dartPluginRegistrant.absolute.uri);
+      }
+
       final CompilerOutput compilerOutput = await compiler.recompile(
         request.mainUri,
-        <Uri>[request.mainUri],
+        <Uri>[request.mainUri, ...invalidatedRegistrantFiles],
         outputPath: outputDill.path,
         packageConfig: buildInfo.packageConfig,
         projectRootPath: flutterProject?.directory?.absolute?.path,
+        checkDartPluginRegistry: true,
         fs: globals.fs,
       );
       final String outputPath = compilerOutput?.outputFilename;

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

@@ -33,7 +33,8 @@ void main() {
         ..manifest = flutterManifest
         ..directory = directory
         ..flutterPluginsFile = directory.childFile('.flutter-plugins')
-        ..flutterPluginsDependenciesFile = directory.childFile('.flutter-plugins-dependencies');
+        ..flutterPluginsDependenciesFile = directory.childFile('.flutter-plugins-dependencies')
+        ..dartPluginRegistrant = directory.childFile('generated_main.dart');
       flutterProject.directory.childFile('.packages').createSync(recursive: true);
     });
 
@@ -610,7 +611,6 @@ void main() {
 void main() {
 }
 ''');
-        final File generatedMainFile = flutterProject.directory.childFile('generated_main.dart');
         final PackageConfig packageConfig = await loadPackageConfigWithLogging(
           flutterProject.directory.childDirectory('.dart_tool').childFile('package_config.json'),
           logger: globals.logger,
@@ -620,11 +620,10 @@ void main() {
           flutterProject,
           packageConfig,
           'package:app/main.dart',
-          generatedMainFile,
           mainFile,
           throwOnPluginPubspecError: true,
         );
-        expect(generatedMainFile.readAsStringSync(),
+        expect(flutterProject.dartPluginRegistrant.readAsStringSync(),
           '//\n'
           '// Generated file. Do not edit.\n'
           '// This file is generated from template in file `flutter_tools/lib/src/flutter_plugins.dart`.\n'
@@ -730,7 +729,6 @@ void main() {
         libDir.createSync(recursive: true);
 
         final File mainFile = libDir.childFile('main.dart')..writeAsStringSync('');
-        final File generatedMainFile = flutterProject.directory.childFile('generated_main.dart');
         final PackageConfig packageConfig = await loadPackageConfigWithLogging(
           flutterProject.directory.childDirectory('.dart_tool').childFile('package_config.json'),
           logger: globals.logger,
@@ -741,7 +739,6 @@ void main() {
             flutterProject,
             packageConfig,
             'package:app/main.dart',
-            generatedMainFile,
             mainFile,
             throwOnPluginPubspecError: true,
           ), throwsToolExit(message:
@@ -773,7 +770,6 @@ void main() {
         libDir.createSync(recursive: true);
 
         final File mainFile = libDir.childFile('main.dart')..writeAsStringSync('');
-        final File generatedMainFile = flutterProject.directory.childFile('generated_main.dart');
         final PackageConfig packageConfig = await loadPackageConfigWithLogging(
           flutterProject.directory.childDirectory('.dart_tool').childFile('package_config.json'),
           logger: globals.logger,
@@ -784,7 +780,6 @@ void main() {
             flutterProject,
             packageConfig,
             'package:app/main.dart',
-            generatedMainFile,
             mainFile,
             throwOnPluginPubspecError: true,
           ), throwsToolExit(message:
@@ -834,7 +829,6 @@ void main() {
         libDir.createSync(recursive: true);
 
         final File mainFile = libDir.childFile('main.dart')..writeAsStringSync('');
-        final File generatedMainFile = flutterProject.directory.childFile('generated_main.dart');
         final PackageConfig packageConfig = await loadPackageConfigWithLogging(
           flutterProject.directory.childDirectory('.dart_tool').childFile('package_config.json'),
           logger: globals.logger,
@@ -844,11 +838,10 @@ void main() {
           flutterProject,
           packageConfig,
           'package:app/main.dart',
-          generatedMainFile,
           mainFile,
           throwOnPluginPubspecError: true,
         );
-        expect(generatedMainFile.existsSync(), isFalse);
+        expect(flutterProject.dartPluginRegistrant.existsSync(), isFalse);
       }, overrides: <Type, Generator>{
         FileSystem: () => fs,
         ProcessManager: () => FakeProcessManager.any(),
@@ -876,7 +869,6 @@ void main() {
         libDir.createSync(recursive: true);
 
         final File mainFile = libDir.childFile('main.dart')..writeAsStringSync('');
-        final File generatedMainFile = flutterProject.directory.childFile('generated_main.dart');
         final PackageConfig packageConfig = await loadPackageConfigWithLogging(
           flutterProject.directory.childDirectory('.dart_tool').childFile('package_config.json'),
           logger: globals.logger,
@@ -886,11 +878,10 @@ void main() {
           flutterProject,
           packageConfig,
           'package:app/main.dart',
-          generatedMainFile,
           mainFile,
           throwOnPluginPubspecError: true,
         );
-        expect(generatedMainFile.existsSync(), isTrue);
+        expect(flutterProject.dartPluginRegistrant.existsSync(), isTrue);
 
         // No plugins.
         createFakeDartPlugins(
@@ -903,11 +894,10 @@ void main() {
           flutterProject,
           packageConfig,
           'package:app/main.dart',
-          generatedMainFile,
           mainFile,
           throwOnPluginPubspecError: true,
         );
-        expect(generatedMainFile.existsSync(), isFalse);
+        expect(flutterProject.dartPluginRegistrant.existsSync(), isFalse);
       }, overrides: <Type, Generator>{
         FileSystem: () => fs,
         ProcessManager: () => FakeProcessManager.any(),
@@ -962,6 +952,9 @@ class FakeFlutterProject extends Fake implements FlutterProject {
   @override
   File flutterPluginsDependenciesFile;
 
+  @override
+  File dartPluginRegistrant;
+
   @override
   IosProject ios;
 

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

@@ -476,7 +476,7 @@ class FakeResidentCompiler extends Fake implements ResidentCompiler {
   Future<CompilerOutput> Function(Uri mainUri, List<Uri> invalidatedFiles) onRecompile;
 
   @override
-  Future<CompilerOutput> recompile(Uri mainUri, List<Uri> invalidatedFiles, {String outputPath, PackageConfig packageConfig, String projectRootPath, FileSystem fs, bool suppressErrors = false}) {
+  Future<CompilerOutput> recompile(Uri mainUri, List<Uri> invalidatedFiles, {String outputPath, PackageConfig packageConfig, String projectRootPath, FileSystem fs, bool suppressErrors = false, bool checkDartPluginRegistry = false}) {
     return onRecompile?.call(mainUri, invalidatedFiles)
       ?? Future<CompilerOutput>.value(const CompilerOutput('', 1, <Uri>[]));
   }

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

@@ -2191,6 +2191,7 @@ class FakeResidentCompiler extends Fake implements ResidentCompiler {
     @required String projectRootPath,
     @required FileSystem fs,
     bool suppressErrors = false,
+    bool checkDartPluginRegistry = false,
   }) async {
     didSuppressErrors = suppressErrors;
     return nextOutput ?? const CompilerOutput('foo.dill', 0, <Uri>[]);

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

@@ -1115,6 +1115,7 @@ class FakeResidentCompiler extends Fake implements ResidentCompiler {
     @required String projectRootPath,
     @required FileSystem fs,
     bool suppressErrors = false,
+    bool checkDartPluginRegistry = false,
   }) async {
     return const CompilerOutput('foo.dill', 0, <Uri>[]);
   }

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

@@ -5,6 +5,7 @@
 // @dart = 2.8
 
 import 'package:file/memory.dart';
+import 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/logger.dart';
 import 'package:flutter_tools/src/base/platform.dart';
@@ -40,6 +41,7 @@ void main() {
     fileSystem = MemoryFileSystem.test();
     fileSystem.file('pubspec.yaml').createSync();
     fileSystem.file('test/foo.dart').createSync(recursive: true);
+    fileSystem.file('.packages').createSync();
     residentCompiler = FakeResidentCompiler(fileSystem);
   });
 
@@ -113,6 +115,57 @@ void main() {
     ProcessManager: () => FakeProcessManager.any(),
     Logger: () => BufferLogger.test(),
   });
+
+  testUsingContext('TestCompiler updates generated_main.dart', () async {
+    final Directory fakeDartPlugin = fileSystem.directory('a_plugin');
+      fileSystem.file('pubspec.yaml').writeAsStringSync('''
+name: foo
+dependencies:
+  flutter:
+    sdk: flutter
+  a_plugin: 1.0.0
+''');
+      fileSystem.file('.packages').writeAsStringSync('a_plugin:/a_plugin/lib/');
+      fakeDartPlugin.childFile('pubspec.yaml')
+          ..createSync(recursive: true)
+          ..writeAsStringSync('''
+name: a_plugin
+flutter:
+  plugin:
+    implements: a
+    platforms:
+      linux:
+        dartPluginClass: APlugin
+environment:
+  sdk: ">=2.14.0 <3.0.0"
+  flutter: ">=2.5.0"
+''');
+
+    residentCompiler.compilerOutput = const CompilerOutput('abc.dill', 0, <Uri>[]);
+    final FakeTestCompiler testCompiler = FakeTestCompiler(
+      debugBuild,
+      FlutterProject.fromDirectoryTest(fileSystem.currentDirectory),
+      residentCompiler,
+    );
+
+    await testCompiler.compile(Uri.parse('test/foo.dart'));
+
+    final File generatedMain = fileSystem
+      .directory('.dart_tool')
+      .childDirectory('flutter_build')
+      .childFile('generated_main.dart');
+
+    expect(generatedMain, exists);
+    expect(
+      generatedMain.readAsLinesSync(),
+      contains("import 'test/foo.dart' as entrypoint;")
+    );
+  }, overrides: <Type, Generator>{
+    FileSystem: () => fileSystem,
+    Platform: () => linuxPlatform,
+    ProcessManager: () => FakeProcessManager.any(),
+    Logger: () => BufferLogger.test(),
+  });
 }
 
 /// Override the creation of the Resident Compiler to simplify testing.
@@ -150,6 +203,7 @@ class FakeResidentCompiler extends Fake implements ResidentCompiler {
     String projectRootPath,
     FileSystem fs,
     bool suppressErrors = false,
+    bool checkDartPluginRegistry = false,
   }) async {
     if (compilerOutput != null) {
       fileSystem.file(compilerOutput.outputFilename).createSync(recursive: true);

packages/flutter_tools/test/general.shard/web/devfs_web_test.dart

@@ -1077,6 +1077,7 @@ class FakeResidentCompiler extends Fake implements ResidentCompiler {
     String projectRootPath,
     FileSystem fs,
     bool suppressErrors = false,
+    bool checkDartPluginRegistry = false,
   }) async {
     return output;
   }