Ensure the flutter_gen project is correctly created as part of "flutter create" (#92975)

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

@@ -13,8 +13,11 @@ import '../android/gradle_utils.dart' as gradle;
 import '../base/common.dart';
 import '../base/file_system.dart';
 import '../base/utils.dart';
+import '../build_info.dart';
+import '../build_system/build_system.dart';
 import '../cache.dart';
 import '../convert.dart';
+import '../dart/generate_synthetic_packages.dart';
 import '../dart/pub.dart';
 import '../features.dart';
 import '../flutter_project_metadata.dart';
@@ -480,6 +483,27 @@ abstract class CreateBase extends FlutterCommand {
     }
 
     if (boolArg('pub')) {
+      final Environment environment = Environment(
+        artifacts: globals.artifacts,
+        logger: globals.logger,
+        cacheDir: globals.cache.getRoot(),
+        engineVersion: globals.flutterVersion.engineRevision,
+        fileSystem: globals.fs,
+        flutterRootDir: globals.fs.directory(Cache.flutterRoot),
+        outputDir: globals.fs.directory(getBuildDirectory()),
+        processManager: globals.processManager,
+        platform: globals.platform,
+        projectDir: project.directory,
+        generateDartPluginRegistry: true,
+      );
+
+      // Generate the l10n synthetic package that will be injected into the
+      // package_config in the call to pub.get() below.
+      await generateLocalizationsSyntheticPackage(
+        environment: environment,
+        buildSystem: globals.buildSystem,
+      );
+
       await pub.get(
         context: PubContext.create,
         directory: directory.path,

packages/flutter_tools/lib/src/localizations/gen_l10n.dart

@@ -1291,7 +1291,9 @@ class LocalizationsGenerator {
     // A pubspec.yaml file is required when using a synthetic package. If it does not
     // exist, create a blank one.
     if (useSyntheticPackage) {
-      final Directory syntheticPackageDirectory = _fs.directory(_defaultSyntheticPackagePath(_fs));
+      final Directory syntheticPackageDirectory = projectDirectory != null
+          ? projectDirectory!.childDirectory(_defaultSyntheticPackagePath(_fs))
+          : _fs.directory(_defaultSyntheticPackagePath(_fs));
       syntheticPackageDirectory.createSync(recursive: true);
       final File flutterGenPubspec = syntheticPackageDirectory.childFile('pubspec.yaml');
       if (!flutterGenPubspec.existsSync()) {

packages/flutter_tools/test/commands.shard/permeable/create_test.dart

@@ -147,6 +147,8 @@ void main() {
       projectDir,
       <String>['-t', 'skeleton', '-i', 'objc', '-a', 'java', '--implementation-tests'],
       <String>[
+        '.dart_tool/flutter_gen/pubspec.yaml',
+        '.dart_tool/flutter_gen/gen_l10n/app_localizations.dart',
         'analysis_options.yaml',
         'android/app/src/main/java/com/example/flutter_project/MainActivity.java',
         'android/app/src/main/java/io/flutter/plugins/GeneratedPluginRegistrant.java',