Be more helpful when l10n generation fails (#83134)

packages/flutter_tools/lib/src/dart/generate_synthetic_packages.dart

@@ -9,6 +9,7 @@ import 'package:yaml/yaml.dart';
 
 import '../base/common.dart';
 import '../base/file_system.dart';
+import '../base/utils.dart';
 import '../build_system/build_system.dart';
 import '../build_system/targets/localizations.dart';
 
@@ -62,7 +63,14 @@ Future<void> generateLocalizationsSyntheticPackage({
     environment,
   );
 
-  if (result == null || result.hasException) {
-    throwToolExit('Generating synthetic localizations package has failed.');
+  if (result == null) {
+    throwToolExit('Generating synthetic localizations package failed: result is null.');
+  }
+  if (result.hasException) {
+    throwToolExit(
+      'Generating synthetic localizations package failed with ${result.exceptions.length} ${pluralize('error', result.exceptions.length)}:'
+      '\n\n'
+      '${result.exceptions.values.map<Object>((ExceptionMeasurement e) => e.exception).join('\n\n')}',
+    );
   }
 }

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

@@ -45,7 +45,7 @@ void main() {
     );
     final Completer<void> completer = Completer<void>();
     final BuildResult exception = BuildResult(success: false, exceptions: <String, ExceptionMeasurement>{
-      'hello': ExceptionMeasurement('hello', 'bar', null),
+      'hello': ExceptionMeasurement('hello', const FormatException('illegal character in input string'), null),
     });
     final TestBuildSystem buildSystem = TestBuildSystem.all(exception, (Target target, Environment environment) {
       expect(target, const GenerateLocalizationsTarget());
@@ -58,7 +58,11 @@ void main() {
         environment: environment,
         buildSystem: buildSystem,
       ),
-      throwsToolExit(message: 'Generating synthetic localizations package has failed.'),
+      throwsToolExit(message:
+        'Generating synthetic localizations package failed with 1 error:'
+        '\n\n'
+        'FormatException: illegal character in input string',
+      ),
     );
     await completer.future;
   });
@@ -90,7 +94,7 @@ void main() {
     );
     final Completer<void> completer = Completer<void>();
     final BuildResult exception = BuildResult(success: false, exceptions: <String, ExceptionMeasurement>{
-      'hello': ExceptionMeasurement('hello', 'bar', null),
+      'hello': ExceptionMeasurement('hello', const FormatException('illegal character in input string'), null),
     });
     final TestBuildSystem buildSystem = TestBuildSystem.all(exception, (Target target, Environment environment) {
       expect(target, const GenerateLocalizationsTarget());
@@ -103,7 +107,11 @@ void main() {
         environment: environment,
         buildSystem: buildSystem,
       ),
-      throwsToolExit(message: 'Generating synthetic localizations package has failed.'),
+      throwsToolExit(message:
+        'Generating synthetic localizations package failed with 1 error:'
+        '\n\n'
+        'FormatException: illegal character in input string',
+      ),
     );
     await completer.future;
   });
@@ -133,7 +141,7 @@ void main() {
     );
     final Completer<void> completer = Completer<void>();
     final BuildResult exception = BuildResult(success: false, exceptions: <String, ExceptionMeasurement>{
-      'hello': ExceptionMeasurement('hello', 'bar', null),
+      'hello': ExceptionMeasurement('hello', const FormatException('illegal character in input string'), null),
     });
     final TestBuildSystem buildSystem = TestBuildSystem.all(exception, (Target target, Environment environment) {
       expect(target, const GenerateLocalizationsTarget());
@@ -146,7 +154,11 @@ void main() {
         environment: environment,
         buildSystem: buildSystem,
       ),
-      throwsToolExit(message: 'Generating synthetic localizations package has failed.'),
+      throwsToolExit(message:
+        'Generating synthetic localizations package failed with 1 error:'
+        '\n\n'
+        'FormatException: illegal character in input string',
+      ),
     );
     await completer.future;
   });