Make gen-l10n error handling independent of logger state (#119644)

* init

* lint

* lint again

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

@@ -579,6 +579,10 @@ class LocalizationsGenerator {
   // Whether we want to use escaping for ICU messages.
   bool useEscaping = false;
 
+  /// Whether any errors were caught. This is set after encountering any errors
+  /// from calling [_generateMethod].
+  bool hadErrors = false;
+
   /// The list of all arb path strings in [inputDirectory].
   List<String> get arbPathStrings {
     return _allBundles.bundles.map((AppResourceBundle bundle) => bundle.file.path).toList();
@@ -1238,6 +1242,7 @@ The plural cases must be one of "=0", "=1", "=2", "zero", "one", "two", "few", "
                 .replaceAll('@(none)\n', '');
     } on L10nParserException catch (error) {
       logger.printError(error.toString());
+      hadErrors = true;
       return '';
     }
   }
@@ -1247,7 +1252,7 @@ The plural cases must be one of "=0", "=1", "=2", "zero", "one", "two", "few", "
     final String generatedLocalizationsFile = _generateCode();
 
     // If there were any syntax errors, don't write to files.
-    if (logger.hadErrorOutput) {
+    if (hadErrors) {
       throw L10nException('Found syntax errors.');
     }
 

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

@@ -785,6 +785,28 @@ void main() {
   });
 
   group('generateLocalizations', () {
+    // Regression test for https://github.com/flutter/flutter/issues/119593
+    testWithoutContext('other logs from flutter_tools does not affect gen-l10n', () async {
+      _standardFlutterDirectoryL10nSetup(fs);
+
+      final Logger logger = BufferLogger.test();
+      logger.printError('An error output from a different tool in flutter_tools');
+
+      // Should run without error.
+      generateLocalizations(
+        fileSystem: fs,
+        options: LocalizationOptions(
+          arbDirectory: Uri.directory(defaultL10nPathString),
+          outputDirectory: Uri.directory(defaultL10nPathString, windows: false),
+          templateArbFile: Uri.file(defaultTemplateArbFileName, windows: false),
+          useSyntheticPackage: false,
+        ),
+        logger: logger,
+        projectDir: fs.currentDirectory,
+        dependenciesDir: fs.currentDirectory,
+      );
+    });
+
     testWithoutContext('forwards arguments correctly', () async {
       _standardFlutterDirectoryL10nSetup(fs);
       final LocalizationOptions options = LocalizationOptions(