CP: Throw error when plural case had undefined behavior (flutter#116622) (flutter#119384)

* Throw error when plural case had undefined behavior (flutter#116622)

* init

* add comment

* make error more actionable

* improve test

* increase debugging for find_commit.dart

---------

Co-authored-by: Tae Hyung Kim <[email protected]>
Co-authored-by: Xilai Zhang <[email protected]>

Author: 3 people

dev/tools/bin/find_commit.dart

@@ -10,7 +10,7 @@
 
 import 'dart:io';
 
-const bool debugLogging = false;
+const bool debugLogging = true;
 
 void log(String message) {
   if (debugLogging) {
@@ -84,7 +84,7 @@ String findCommit({
 String git(String workingDirectory, List<String> arguments) {
   final ProcessResult result = Process.runSync('git', arguments, workingDirectory: workingDirectory);
   if (result.exitCode != 0 || '${result.stderr}'.isNotEmpty) {
-    throw ProcessException('git', arguments, '${result.stdout}${result.stderr}', result.exitCode);
+    throw ProcessException('git', arguments, 'working directory: "$workingDirectory"\n${result.stdout}\n${result.stderr}', result.exitCode);
   }
   return '${result.stdout}';
 }

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

@@ -1163,7 +1163,20 @@ class LocalizationsGenerator {
             }
             if (!pluralLogicArgs.containsKey(pluralCases[pluralCase])) {
               final String pluralPartExpression = generateVariables(pluralMessage);
-              pluralLogicArgs[pluralCases[pluralCase]!] = '      ${pluralCases[pluralCase]}: $pluralPartExpression,';
+              final String? transformedPluralCase = pluralCases[pluralCase];
+              // A valid plural case is one of "=0", "=1", "=2", "zero", "one", "two", "few", "many", or "other".
+              if (transformedPluralCase == null) {
+                throw L10nParserException(
+                  '''
+The plural cases must be one of "=0", "=1", "=2", "zero", "one", "two", "few", "many", or "other.
+    $pluralCase is not a valid plural case.''',
+                  _inputFileNames[locale]!,
+                  message.resourceId,
+                  translationForMessage,
+                  pluralPart.positionInMessage,
+                );
+              }
+              pluralLogicArgs[transformedPluralCase] = '      ${pluralCases[pluralCase]}: $pluralPartExpression,';
             } else if (!suppressWarnings) {
               logger.printWarning('''
 [${_inputFileNames[locale]}:${message.resourceId}] ICU Syntax Warning: The plural part specified below is overridden by a later plural part.

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

@@ -1957,6 +1957,39 @@ import 'output-localization-file_en.dart' deferred as output-localization-file_e
                    ^'''));
       });
 
+      testWithoutContext('undefined plural cases throws syntax error', () {
+         const String pluralMessageWithUndefinedParts = '''
+{
+  "count": "{count,plural, =0{None} =1{One} =2{Two} =3{Undefined Behavior!} other{Hmm...}}"
+}''';
+        final Directory l10nDirectory = fs.currentDirectory.childDirectory('lib').childDirectory('l10n')
+          ..createSync(recursive: true);
+        l10nDirectory.childFile(defaultTemplateArbFileName)
+          .writeAsStringSync(pluralMessageWithUndefinedParts);
+        try {
+          LocalizationsGenerator(
+            fileSystem: fs,
+            inputPathString: defaultL10nPathString,
+            outputPathString: defaultL10nPathString,
+            templateArbFileName: defaultTemplateArbFileName,
+            outputFileString: defaultOutputFileString,
+            classNameString: defaultClassNameString,
+            logger: logger,
+          )
+            ..loadResources()
+            ..writeOutputFiles();
+          fail('expected L10nException');
+        } on L10nException catch (error) {
+          expect(error.message, contains('Found syntax errors.'));
+          expect(logger.hadErrorOutput, isTrue);
+          expect(logger.errorText, contains('''
+[app_en.arb:count] The plural cases must be one of "=0", "=1", "=2", "zero", "one", "two", "few", "many", or "other.
+    3 is not a valid plural case.
+    {count,plural, =0{None} =1{One} =2{Two} =3{Undefined Behavior!} other{Hmm...}}
+                                            ^'''));
+        }
+      });
+
       testWithoutContext('should automatically infer plural placeholders that are not explicitly defined', () {
         const String pluralMessageWithoutPlaceholdersAttribute = '''
 {