[gen_l10n] keys can contain dollar sign (#114808)

* [gen_l10n] keys can contain dollar sign

Fixes #112250

* Update packages/flutter_tools/lib/src/localizations/gen_l10n.dart
Co-authored-by: Christopher Fujino <fujino@google.com>

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

@@ -838,15 +838,15 @@ class LocalizationsGenerator {
     if (name[0] == '_') {
       return false;
     }
-    // Dart getter and method name cannot contain non-alphanumeric symbols
-    if (name.contains(RegExp(r'[^a-zA-Z_\d]'))) {
+    // Dart identifiers can only use letters, numbers, underscores, and `$`
+    if (name.contains(RegExp(r'[^a-zA-Z_$\d]'))) {
       return false;
     }
-    // Dart method name must start with lower case character
+    // Dart getter and method name should start with lower case character
     if (name[0].contains(RegExp(r'[A-Z]'))) {
       return false;
     }
-    // Dart class name cannot start with a number
+    // Dart getter and method name cannot start with a number
     if (name[0].contains(RegExp(r'\d'))) {
       return false;
     }

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

@@ -2704,6 +2704,31 @@ import 'output-localization-file_en.dart' deferred as output-localization-file_e
           )),
         );
       });
+
+      testWithoutContext('can start with and contain a dollar sign', () {
+        const String dollarArbFile = r'''
+{
+  "$title$": "Stocks",
+  "@$title$": {
+    "description": "Title for the application"
+  }
+}''';
+        final Directory l10nDirectory = fs.currentDirectory.childDirectory('lib').childDirectory('l10n')
+          ..createSync(recursive: true);
+        l10nDirectory.childFile(defaultTemplateArbFileName)
+            .writeAsStringSync(dollarArbFile);
+
+        LocalizationsGenerator(
+          fileSystem: fs,
+          inputPathString: defaultL10nPathString,
+          templateArbFileName: defaultTemplateArbFileName,
+          outputFileString: defaultOutputFileString,
+          classNameString: defaultClassNameString,
+          logger: logger,
+        )
+          ..loadResources()
+          ..writeOutputFiles();
+      });
     });
 
     testWithoutContext('throws when the language code is not supported', () {