Fix gen_date_localizations script and regenerate (#124547)

Internal bug: b/256596915

Turns out we need to regenerate date localizations in order for the
`intl` package to be setup properly within Flutter. This PR fixes the
script (since it assumes the use of the old `.packages` way of handling
packages), and regenerates the `generated_date_localizations.dart` file.

dev/tools/localization/bin/gen_date_localizations.dart

@@ -46,32 +46,39 @@ Future<void> main(List<String> rawArgs) async {
 
   final bool writeToFile = parseArgs(rawArgs).writeToFile;
 
-  final File dotPackagesFile = File(path.join('packages', 'flutter_localizations', '.packages'));
-  final bool dotPackagesExists = dotPackagesFile.existsSync();
+  final File packageConfigFile = File(path.join('packages', 'flutter_localizations', '.dart_tool', 'package_config.json'));
+  final bool packageConfigExists = packageConfigFile.existsSync();
 
-  if (!dotPackagesExists) {
+  if (!packageConfigExists) {
     exitWithError(
-      'File not found: ${dotPackagesFile.path}. $_kCommandName must be run '
+      'File not found: ${packageConfigFile.path}. $_kCommandName must be run '
       'after a successful "flutter update-packages".'
     );
   }
 
-  final String pathToIntl = dotPackagesFile
-    .readAsStringSync()
-    .split('\n')
-    .firstWhere(
-      (String line) => line.startsWith('intl:'),
-      orElse: () {
-        exitWithError('intl dependency not found in ${dotPackagesFile.path}');
-        return ''; // unreachable
-      },
-    )
-    .split(':')
-    .last;
+  final List<Object?> packages = (
+    json.decode(packageConfigFile.readAsStringSync()) as Map<String, Object?>
+  )['packages']! as List<Object?>;
 
-  final Directory dateSymbolsDirectory = Directory(path.join(pathToIntl, 'src', 'data', 'dates', 'symbols'));
+  String? pathToIntl;
+  for (final Object? package in packages) {
+    final Map<String, Object?> packageAsMap = package! as Map<String, Object?>;
+    if (packageAsMap['name'] == 'intl') {
+      pathToIntl = Uri.parse(packageAsMap['rootUri']! as String).toFilePath();
+      break;
+    }
+  }
+
+  if (pathToIntl == null) {
+    exitWithError(
+      'Could not find "intl" package. $_kCommandName must be run '
+      'after a successful "flutter update-packages".'
+    );
+  }
+
+  final Directory dateSymbolsDirectory = Directory(path.join(pathToIntl!, 'lib', 'src', 'data', 'dates', 'symbols'));
   final Map<String, File> symbolFiles = _listIntlData(dateSymbolsDirectory);
-  final Directory datePatternsDirectory = Directory(path.join(pathToIntl, 'src', 'data', 'dates', 'patterns'));
+  final Directory datePatternsDirectory = Directory(path.join(pathToIntl, 'lib', 'src', 'data', 'dates', 'patterns'));
   final Map<String, File> patternFiles = _listIntlData(datePatternsDirectory);
   final StringBuffer buffer = StringBuffer();
   final Set<String> supportedLocales = _supportedLocales();

packages/flutter_localizations/test/material/date_picker_test.dart

@@ -31,7 +31,7 @@ void main() {
       // Tests a different first day of week.
       const Locale('ru', 'RU'): <String, dynamic>{
         'textDirection': TextDirection.ltr,
-        'expectedDaysOfWeek': <String>['пн', 'вт', 'ср', 'чт', 'пт', 'сб', 'вс'],
+        'expectedDaysOfWeek': <String>['В', 'П', 'В', 'С', 'Ч', 'П', 'С',],
         'expectedDaysOfMonth': List<String>.generate(30, (int i) => '${i + 1}'),
         'expectedMonthYearHeader': 'сентябрь 2017 г.',
       },

packages/flutter_localizations/test/material/date_time_test.dart

@@ -193,6 +193,22 @@ void main() {
 
     expect(dateFormat.locale, 'en_US');
   });
+
+  testWidgets('cy is initialized correctly by Flutter when DateFormat is used', (WidgetTester tester) async {
+    late DateFormat dateFormat;
+
+    await tester.pumpWidget(MaterialApp(
+      locale: const Locale('cy'),
+      localizationsDelegates: GlobalMaterialLocalizations.delegates,
+      home: Builder(builder: (BuildContext context) {
+        dateFormat = DateFormat.yMMMd('cy');
+        return Container();
+      }),
+    ));
+
+    expect(dateFormat.locale, 'cy');
+    expect(dateFormat.format(DateTime(2023, 4, 10, 2, 32)), equals('10 Ebr 2023'));
+  });
 }
 
 enum DateType { year, medium, full, monthYear }

packages/flutter_localizations/test/material/translations_test.dart

@@ -176,7 +176,7 @@ void main() {
     expect(localizations.formatFullDate(DateTime(2015, 7, 23)), 'Thursday, 23 July 2015');
 
     localizations = await GlobalMaterialLocalizations.delegate.load(const Locale('es'));
-    expect(localizations.formatMediumDate(DateTime(2015, 7, 23)), 'jue., 23 jul.');
+    expect(localizations.formatMediumDate(DateTime(2015, 7, 23)), 'jue, 23 jul');
     expect(localizations.formatFullDate(DateTime(2015, 7, 23)), 'jueves, 23 de julio de 2015');
 
     localizations = await GlobalMaterialLocalizations.delegate.load(const Locale('de'));