Use correct locale for CupertinoDatePicker weekday (#151494)

#120052 introduces the `showDayOfWeek` flag to `CupertinoDatePicker` for mode `CupertinoDatePickerMode.date`, but the default `en` locale from `DefaultCupertinoLocalizations` is always used for the day of the week:

5103d75743/packages/flutter_localizations/lib/src/cupertino_localizations.dart (L116-L119)

This PR introduces a new `intl.DateFormat` `weekdayFormat` to replace the default with the abbreviated weekday for any supported locales.

| Before | After | 
| --- | --- |
|  <img width="379" alt="Screenshot 2024-07-09 at 5 08 43 PM" src="https://github.com/flutter/flutter/assets/77553258/d6899c6b-bd0a-4484-a6a8-3ef1512aeae1">  |  <img width="379" alt="Screenshot 2024-07-09 at 5 08 11 PM" src="https://github.com/flutter/flutter/assets/77553258/f320c634-80d1-4f3b-adfd-ed85a9dfc3f6"> |

Fixes #141875

dev/tools/localization/gen_cupertino_localizations.dart

@@ -41,6 +41,7 @@ String generateCupertinoConstructor(LocaleInfo locale) {
     super.localeName = '$localeName',
     required super.fullYearFormat,
     required super.dayFormat,
+    required super.weekdayFormat,
     required super.mediumDateFormat,
     required super.singleDigitHourFormat,
     required super.singleDigitMinuteFormat,
@@ -57,6 +58,7 @@ GlobalCupertinoLocalizations? getCupertinoTranslation(
   Locale locale,
   intl.DateFormat fullYearFormat,
   intl.DateFormat dayFormat,
+  intl.DateFormat weekdayFormat,
   intl.DateFormat mediumDateFormat,
   intl.DateFormat singleDigitHourFormat,
   intl.DateFormat singleDigitMinuteFormat,
@@ -66,7 +68,7 @@ GlobalCupertinoLocalizations? getCupertinoTranslation(
 ) {''';
 
 const String cupertinoFactoryArguments =
-    'fullYearFormat: fullYearFormat, dayFormat: dayFormat, mediumDateFormat: mediumDateFormat, singleDigitHourFormat: singleDigitHourFormat, singleDigitMinuteFormat: singleDigitMinuteFormat, doubleDigitMinuteFormat: doubleDigitMinuteFormat, singleDigitSecondFormat: singleDigitSecondFormat, decimalFormat: decimalFormat';
+    'fullYearFormat: fullYearFormat, dayFormat: dayFormat, weekdayFormat: weekdayFormat, mediumDateFormat: mediumDateFormat, singleDigitHourFormat: singleDigitHourFormat, singleDigitMinuteFormat: singleDigitMinuteFormat, doubleDigitMinuteFormat: doubleDigitMinuteFormat, singleDigitSecondFormat: singleDigitSecondFormat, decimalFormat: decimalFormat';
 
 const String cupertinoSupportedLanguagesConstant = 'kCupertinoSupportedLanguages';
 

packages/flutter/lib/src/cupertino/localizations.dart

@@ -343,7 +343,7 @@ class DefaultCupertinoLocalizations implements CupertinoLocalizations {
   const DefaultCupertinoLocalizations();
 
   /// Short version of days of week.
-  static const List<String> shortWeekdays = <String>[
+  static const List<String> _shortWeekdays = <String>[
     'Mon',
     'Tue',
     'Wed',
@@ -397,7 +397,7 @@ class DefaultCupertinoLocalizations implements CupertinoLocalizations {
   @override
   String datePickerDayOfMonth(int dayIndex, [int? weekDay]) {
     if (weekDay != null) {
-      return ' ${shortWeekdays[weekDay - DateTime.monday]} $dayIndex ';
+      return ' ${_shortWeekdays[weekDay - DateTime.monday]} $dayIndex ';
     }
 
     return dayIndex.toString();
@@ -422,7 +422,7 @@ class DefaultCupertinoLocalizations implements CupertinoLocalizations {
 
   @override
   String datePickerMediumDate(DateTime date) {
-    return '${shortWeekdays[date.weekday - DateTime.monday]} '
+    return '${_shortWeekdays[date.weekday - DateTime.monday]} '
       '${_shortMonths[date.month - DateTime.january]} '
       '${date.day.toString().padRight(2)}';
   }

packages/flutter_localizations/lib/src/cupertino_localizations.dart

@@ -61,6 +61,7 @@ abstract class GlobalCupertinoLocalizations implements CupertinoLocalizations {
     required String localeName,
     required intl.DateFormat fullYearFormat,
     required intl.DateFormat dayFormat,
+    required intl.DateFormat weekdayFormat,
     required intl.DateFormat mediumDateFormat,
     required intl.DateFormat singleDigitHourFormat,
     required intl.DateFormat singleDigitMinuteFormat,
@@ -70,6 +71,7 @@ abstract class GlobalCupertinoLocalizations implements CupertinoLocalizations {
   }) : _localeName = localeName,
        _fullYearFormat = fullYearFormat,
        _dayFormat = dayFormat,
+       _weekdayFormat = weekdayFormat,
        _mediumDateFormat = mediumDateFormat,
        _singleDigitHourFormat = singleDigitHourFormat,
        _singleDigitMinuteFormat = singleDigitMinuteFormat,
@@ -80,6 +82,7 @@ abstract class GlobalCupertinoLocalizations implements CupertinoLocalizations {
   final String _localeName;
   final intl.DateFormat _fullYearFormat;
   final intl.DateFormat _dayFormat;
+  final intl.DateFormat _weekdayFormat;
   final intl.DateFormat _mediumDateFormat;
   final intl.DateFormat _singleDigitHourFormat;
   final intl.DateFormat _singleDigitMinuteFormat;
@@ -114,11 +117,10 @@ abstract class GlobalCupertinoLocalizations implements CupertinoLocalizations {
 
   @override
   String datePickerDayOfMonth(int dayIndex, [int? weekDay]) {
-     if (weekDay != null) {
+    return weekDay != null
-      return ' ${DefaultCupertinoLocalizations.shortWeekdays[weekDay - DateTime.monday]} $dayIndex ';
+      ? '${_weekdayFormat.format(DateTime.utc(1, 1, weekDay))} ${_dayFormat.format(DateTime.utc(1, 1, dayIndex))}'
-    }
+      // Year and month doesn't matter since we just want to day formatted.
-    // Year and month doesn't matter since we just want to day formatted.
+      : _dayFormat.format(DateTime.utc(0, 0, dayIndex));
-    return _dayFormat.format(DateTime.utc(0, 0, dayIndex));
   }
 
   @override
@@ -486,6 +488,7 @@ class _GlobalCupertinoLocalizationsDelegate extends LocalizationsDelegate<Cupert
 
       late intl.DateFormat fullYearFormat;
       late intl.DateFormat dayFormat;
+      late intl.DateFormat weekdayFormat;
       late intl.DateFormat mediumDateFormat;
       // We don't want any additional decoration here. The am/pm is handled in
       // the date picker. We just want an hour number localized.
@@ -498,6 +501,7 @@ class _GlobalCupertinoLocalizationsDelegate extends LocalizationsDelegate<Cupert
       void loadFormats(String? locale) {
         fullYearFormat = intl.DateFormat.y(locale);
         dayFormat = intl.DateFormat.d(locale);
+        weekdayFormat = intl.DateFormat.E(locale);
         mediumDateFormat = intl.DateFormat.MMMEd(locale);
         // TODO(xster): fix when https://github.com/dart-lang/intl/issues/207 is resolved.
         singleDigitHourFormat = intl.DateFormat('HH', locale);
@@ -519,6 +523,7 @@ class _GlobalCupertinoLocalizationsDelegate extends LocalizationsDelegate<Cupert
         locale,
         fullYearFormat,
         dayFormat,
+        weekdayFormat,
         mediumDateFormat,
         singleDigitHourFormat,
         singleDigitMinuteFormat,

packages/flutter_localizations/test/cupertino/translations_test.dart

@@ -239,6 +239,15 @@ void main() {
     expect(localizations, isA<CupertinoLocalizationZh>());
     expect(localizations.lookUpButtonLabel, '查询');
   });
+
+  testWidgets('localizations.datePickerDayOfMonth uses the current locale for weekdays', (WidgetTester tester) async {
+    const Locale locale = Locale('zh');
+    expect(GlobalCupertinoLocalizations.delegate.isSupported(locale), isTrue);
+    final CupertinoLocalizations localizations = await GlobalCupertinoLocalizations.delegate.load(locale);
+    expect(localizations, isA<CupertinoLocalizationZh>());
+    expect(localizations.datePickerDayOfMonth(1), '1日');
+    expect(localizations.datePickerDayOfMonth(1, 2), '周二 1日');
+  });
 }
 
 class _FakeEditableText extends EditableText {