[gen_l10n] Improve status message when untranslated messages are still present (#72944)

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

@@ -66,7 +66,7 @@ void generateLocalizations({
         untranslatedMessagesFile: options?.untranslatedMessagesFile?.toFilePath(),
       )
       ..loadResources()
-      ..writeOutputFiles(logger);
+      ..writeOutputFiles(logger, isFromYaml: true);
   } on L10nException catch (e) {
     logger.printError(e.message);
     throw Exception();

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

@@ -1033,7 +1033,7 @@ class LocalizationsGenerator {
       .replaceAll('@(delegateClass)', delegateClass);
   }
 
-  void writeOutputFiles(Logger logger) {
+  void writeOutputFiles(Logger logger, { bool isFromYaml = false }) {
     // First, generate the string contents of all necessary files.
     _generateCode();
 
@@ -1077,10 +1077,25 @@ class LocalizationsGenerator {
       _unimplementedMessages.forEach((LocaleInfo locale, List<String> messages) {
         logger.printStatus('"$locale": ${messages.length} untranslated message(s).');
       });
+      if (isFromYaml) {
+        logger.printStatus(
+          'To see a detailed report, use the untranslated-messages-file \n'
+          'option in the l10n.yaml file:\n'
+          'untranslated-messages-file: desiredFileName.txt\n'
+          '<other option>: <other selection> \n\n'
+        );
+      } else {
+        logger.printStatus(
+          'To see a detailed report, use the --untranslated-messages-file \n'
+          'option in the flutter gen-l10n tool:\n'
+          'flutter gen-l10n --untranslated-messages-file=desiredFileName.txt\n'
+          '<other options> \n\n'
+        );
+      }
+
       logger.printStatus(
-        'To see a detailed report, use the --untranslated-messages-file \n'
-        'option in the tool to generate a JSON format file containing \n'
-        'all messages that need to be translated.'
+        'This will generate a JSON format file containing all messages that \n'
+        'need to be translated.'
       );
     }
 

packages/flutter_tools/test/general.shard/build_system/targets/localizations_test.dart

@@ -70,7 +70,7 @@ void main() {
       ),
     ).called(1);
     verify(mockLocalizationsGenerator.loadResources()).called(1);
-    verify(mockLocalizationsGenerator.writeOutputFiles(logger)).called(1);
+    verify(mockLocalizationsGenerator.writeOutputFiles(logger, isFromYaml: true)).called(1);
   });
 
   testUsingContext('generateLocalizations throws exception on missing flutter: generate: true flag', () async {

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

@@ -548,7 +548,8 @@ void main() {
   });
 
   test(
-    'untranslated messages suggestion is printed when translation is missing',
+    'untranslated messages suggestion is printed when translation is missing: '
+    'command line message',
     () {
       final BufferLogger testLogger = BufferLogger.test();
       fs.currentDirectory.childDirectory('lib').childDirectory('l10n')
@@ -566,6 +567,7 @@ void main() {
             templateArbFileName: defaultTemplateArbFileName,
             outputFileString: defaultOutputFileString,
             classNameString: defaultClassNameString,
+            useSyntheticPackage: false,
           )
           ..loadResources()
           ..writeOutputFiles(testLogger);
@@ -573,7 +575,51 @@ void main() {
         fail('Generating output should not fail: \n${e.message}');
       }
 
-      expect(testLogger.statusText, contains('To see a detailed report, use the --untranslated-messages-file'));
+      expect(
+        testLogger.statusText,
+        contains('To see a detailed report, use the --untranslated-messages-file'),
+      );
+      expect(
+        testLogger.statusText,
+        contains('flutter gen-l10n --untranslated-messages-file=desiredFileName.txt'),
+      );
+    },
+  );
+
+  test(
+    'untranslated messages suggestion is printed when translation is missing: '
+    'l10n.yaml message',
+    () {
+      final BufferLogger testLogger = BufferLogger.test();
+      fs.currentDirectory.childDirectory('lib').childDirectory('l10n')
+        ..createSync(recursive: true)
+        ..childFile(defaultTemplateArbFileName).writeAsStringSync(twoMessageArbFileString)
+        ..childFile(esArbFileName).writeAsStringSync(singleEsMessageArbFileString);
+
+      LocalizationsGenerator generator;
+      try {
+        generator = LocalizationsGenerator(fs);
+        generator
+          ..initialize(
+            inputPathString: defaultL10nPathString,
+            templateArbFileName: defaultTemplateArbFileName,
+            outputFileString: defaultOutputFileString,
+            classNameString: defaultClassNameString,
+          )
+          ..loadResources()
+          ..writeOutputFiles(testLogger, isFromYaml: true);
+      } on L10nException catch (e) {
+        fail('Generating output should not fail: \n${e.message}');
+      }
+
+      expect(
+        testLogger.statusText,
+        contains('To see a detailed report, use the untranslated-messages-file'),
+      );
+      expect(
+        testLogger.statusText,
+        contains('untranslated-messages-file: desiredFileName.txt'),
+      );
     },
   );