🐛 Treat empty ARB content as empty map when decoding (#131242)

Fixes #128932.

packages/flutter_tools/lib/src/localizations/gen_l10n_types.dart

@@ -566,13 +566,18 @@ class Message {
   }
 }
 
-// Represents the contents of one ARB file.
+/// Represents the contents of one ARB file.
 class AppResourceBundle {
+  /// Assuming that the caller has verified that the file exists and is readable.
   factory AppResourceBundle(File file) {
-    // Assuming that the caller has verified that the file exists and is readable.
-    Map<String, Object?> resources;
+    final Map<String, Object?> resources;
     try {
-      resources = json.decode(file.readAsStringSync()) as Map<String, Object?>;
+      final String content = file.readAsStringSync().trim();
+      if (content.isEmpty) {
+        resources = <String, Object?>{};
+      } else {
+        resources = json.decode(content) as Map<String, Object?>;
+      }
     } on FormatException catch (e) {
       throw L10nException(
         'The arb file ${file.path} has the following formatting issue: \n'
@@ -657,20 +662,26 @@ class AppResourceBundleCollection {
     final RegExp filenameRE = RegExp(r'(\w+)\.arb$');
     final Map<LocaleInfo, AppResourceBundle> localeToBundle = <LocaleInfo, AppResourceBundle>{};
     final Map<String, List<LocaleInfo>> languageToLocales = <String, List<LocaleInfo>>{};
-    final List<File> files = directory.listSync().whereType<File>().toList()..sort(sortFilesByPath);
+    // We require the list of files to be sorted so that
+    // "languageToLocales[bundle.locale.languageCode]" is not null
+    // by the time we handle locales with country codes.
+    final List<File> files = directory
+      .listSync()
+      .whereType<File>()
+      .where((File e) => filenameRE.hasMatch(e.path))
+      .toList()
+      ..sort(sortFilesByPath);
     for (final File file in files) {
-      if (filenameRE.hasMatch(file.path)) {
-        final AppResourceBundle bundle = AppResourceBundle(file);
-        if (localeToBundle[bundle.locale] != null) {
-          throw L10nException(
-            "Multiple arb files with the same '${bundle.locale}' locale detected. \n"
-            'Ensure that there is exactly one arb file for each locale.'
-          );
-        }
-        localeToBundle[bundle.locale] = bundle;
-        languageToLocales[bundle.locale.languageCode] ??= <LocaleInfo>[];
-        languageToLocales[bundle.locale.languageCode]!.add(bundle.locale);
+      final AppResourceBundle bundle = AppResourceBundle(file);
+      if (localeToBundle[bundle.locale] != null) {
+        throw L10nException(
+          "Multiple arb files with the same '${bundle.locale}' locale detected. \n"
+          'Ensure that there is exactly one arb file for each locale.'
+        );
       }
+      localeToBundle[bundle.locale] = bundle;
+      languageToLocales[bundle.locale.languageCode] ??= <LocaleInfo>[];
+      languageToLocales[bundle.locale.languageCode]!.add(bundle.locale);
     }
 
     languageToLocales.forEach((String language, List<LocaleInfo> listOfCorrespondingLocales) {

packages/flutter_tools/test/commands.shard/hermetic/generate_localizations_test.dart

@@ -10,6 +10,7 @@ import 'package:flutter_tools/src/build_system/build_system.dart';
 import 'package:flutter_tools/src/build_system/targets/localizations.dart';
 import 'package:flutter_tools/src/cache.dart';
 import 'package:flutter_tools/src/commands/generate_localizations.dart';
+import 'package:flutter_tools/src/localizations/gen_l10n_types.dart';
 
 import '../../integration.shard/test_data/basic_project.dart';
 import '../../src/common.dart';
@@ -501,4 +502,33 @@ format: true
       throwsToolExit(message: 'Unexpected positional argument "false".')
     );
   });
+
+  group(AppResourceBundle, () {
+    testWithoutContext("can be parsed without FormatException when it's content is empty", () {
+      final File arbFile = fileSystem.file(fileSystem.path.join('lib', 'l10n', 'app_en.arb'))
+        ..createSync(recursive: true);
+      expect(AppResourceBundle(arbFile), isA<AppResourceBundle>());
+    });
+
+    testUsingContext("would not fail the gen-l10n command when it's content is empty", () async {
+      fileSystem.file(fileSystem.path.join('lib', 'l10n', 'app_en.arb')).createSync(recursive: true);
+      final File pubspecFile = fileSystem.file('pubspec.yaml')..createSync();
+      pubspecFile.writeAsStringSync(BasicProjectWithFlutterGen().pubspec);
+      final GenerateLocalizationsCommand command = GenerateLocalizationsCommand(
+        fileSystem: fileSystem,
+        logger: logger,
+        artifacts: artifacts,
+        processManager: processManager,
+      );
+      await createTestCommandRunner(command).run(<String>['gen-l10n']);
+
+      final Directory outputDirectory = fileSystem.directory(fileSystem.path.join('.dart_tool', 'flutter_gen', 'gen_l10n'));
+      expect(outputDirectory.existsSync(), true);
+      expect(outputDirectory.childFile('app_localizations_en.dart').existsSync(), true);
+      expect(outputDirectory.childFile('app_localizations.dart').existsSync(), true);
+    }, overrides: <Type, Generator>{
+      FileSystem: () => fileSystem,
+      ProcessManager: () => FakeProcessManager.any(),
+    });
+  });
 }