internationalization: fix select with incorrect message (#90096)

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

@@ -300,6 +300,11 @@ String _generateSelectMethod(Message message, String translationForMessage) {
         );
       }
     }
+  } else {
+    throw L10nException(
+      'Incorrect select message format for: ${message.resourceId}.\n'
+      'Check to see if the select message is in the proper ICU syntax format.'
+    );
   }
 
   final List<String> parameters = message.placeholders.map((Placeholder placeholder) {

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

@@ -1909,6 +1909,46 @@ import 'output-localization-file_en.dart' deferred as output-localization-file_e
           )),
         );
       });
+
+      testWithoutContext('should throw attempting to generate a select message with an incorrect message', () {
+        const String selectMessageWithoutPlaceholdersAttribute = '''
+{
+  "genderSelect": "{gender, select,}",
+  "@genderSelect": {
+    "placeholders": {
+      "gender": {}
+    }
+  }
+}''';
+
+        final Directory l10nDirectory = fs.currentDirectory.childDirectory('lib').childDirectory('l10n')
+          ..createSync(recursive: true);
+        l10nDirectory.childFile(defaultTemplateArbFileName)
+          .writeAsStringSync(selectMessageWithoutPlaceholdersAttribute);
+
+        expect(
+          () {
+            LocalizationsGenerator(
+              fileSystem: fs,
+              inputPathString: defaultL10nPathString,
+              outputPathString: defaultL10nPathString,
+              templateArbFileName: defaultTemplateArbFileName,
+              outputFileString: defaultOutputFileString,
+              classNameString: defaultClassNameString,
+            )
+              ..loadResources()
+              ..writeOutputFiles(BufferLogger.test());
+          },
+          throwsA(isA<L10nException>().having(
+            (L10nException e) => e.message,
+            'message',
+            allOf(
+              contains('Incorrect select message format for'),
+              contains('Check to see if the select message is in the proper ICU syntax format.'),
+            ),
+          )),
+        );
+      });
     });
 
     testWithoutContext('intl package import should be omitted in subclass files when no plurals are included', () {