New locale resolution algorithm to use full preferred locale list, include...

New locale resolution algorithm to use full preferred locale list, include scriptCode in Locale. (#23583)

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

@@ -90,6 +90,7 @@ class CupertinoApp extends StatefulWidget {
     this.color,
     this.locale,
     this.localizationsDelegates,
+    this.localeListResolutionCallback,
     this.localeResolutionCallback,
     this.supportedLocales = const <Locale>[Locale('en', 'US')],
     this.showPerformanceOverlay = false,
@@ -157,6 +158,11 @@ class CupertinoApp extends StatefulWidget {
   /// {@macro flutter.widgets.widgetsApp.localizationsDelegates}
   final Iterable<LocalizationsDelegate<dynamic>> localizationsDelegates;
 
+  /// {@macro flutter.widgets.widgetsApp.localeListResolutionCallback}
+  ///
+  /// This callback is passed along to the [WidgetsApp] built by this widget.
+  final LocaleListResolutionCallback localeListResolutionCallback;
+
   /// {@macro flutter.widgets.widgetsApp.localeResolutionCallback}
   ///
   /// This callback is passed along to the [WidgetsApp] built by this widget.
@@ -283,6 +289,7 @@ class _CupertinoAppState extends State<CupertinoApp> {
         locale: widget.locale,
         localizationsDelegates: _localizationsDelegates,
         localeResolutionCallback: widget.localeResolutionCallback,
+        localeListResolutionCallback: widget.localeListResolutionCallback,
         supportedLocales: widget.supportedLocales,
         showPerformanceOverlay: widget.showPerformanceOverlay,
         checkerboardRasterCacheImages: widget.checkerboardRasterCacheImages,

packages/flutter/lib/src/material/app.dart

@@ -98,6 +98,7 @@ class MaterialApp extends StatefulWidget {
     this.theme,
     this.locale,
     this.localizationsDelegates,
+    this.localeListResolutionCallback,
     this.localeResolutionCallback,
     this.supportedLocales = const <Locale>[Locale('en', 'US')],
     this.debugShowMaterialGrid = false,
@@ -264,6 +265,11 @@ class MaterialApp extends StatefulWidget {
   ///    <https://flutter.io/tutorials/internationalization/>.
   final Iterable<LocalizationsDelegate<dynamic>> localizationsDelegates;
 
+  /// {@macro flutter.widgets.widgetsApp.localeListResolutionCallback}
+  ///
+  /// This callback is passed along to the [WidgetsApp] built by this widget.
+  final LocaleListResolutionCallback localeListResolutionCallback;
+
   /// {@macro flutter.widgets.widgetsApp.localeResolutionCallback}
   ///
   /// This callback is passed along to the [WidgetsApp] built by this widget.
@@ -423,6 +429,7 @@ class _MaterialAppState extends State<MaterialApp> {
         locale: widget.locale,
         localizationsDelegates: _localizationsDelegates,
         localeResolutionCallback: widget.localeResolutionCallback,
+        localeListResolutionCallback: widget.localeListResolutionCallback,
         supportedLocales: widget.supportedLocales,
         showPerformanceOverlay: widget.showPerformanceOverlay,
         checkerboardRasterCacheImages: widget.checkerboardRasterCacheImages,

packages/flutter/lib/src/widgets/binding.dart

@@ -219,7 +219,7 @@ abstract class WidgetsBindingObserver {
   /// settings.
   ///
   /// This method exposes notifications from [Window.onLocaleChanged].
-  void didChangeLocale(Locale locale) { }
+  void didChangeLocales(List<Locale> locale) { }
 
   /// Called when the system puts the app in the background or returns
   /// the app to the foreground.
@@ -413,20 +413,20 @@ mixin WidgetsBinding on BindingBase, SchedulerBinding, GestureBinding, RendererB
   @protected
   @mustCallSuper
   void handleLocaleChanged() {
-    dispatchLocaleChanged(ui.window.locale);
+    dispatchLocalesChanged(ui.window.locales);
   }
 
   /// Notify all the observers that the locale has changed (using
-  /// [WidgetsBindingObserver.didChangeLocale]), giving them the
-  /// `locale` argument.
+  /// [WidgetsBindingObserver.didChangeLocales]), giving them the
+  /// `locales` argument.
   ///
   /// This is called by [handleLocaleChanged] when the [Window.onLocaleChanged]
   /// notification is received.
   @protected
   @mustCallSuper
-  void dispatchLocaleChanged(Locale locale) {
+  void dispatchLocalesChanged(List<Locale> locales) {
     for (WidgetsBindingObserver observer in _observers)
-      observer.didChangeLocale(locale);
+      observer.didChangeLocales(locales);
   }
 
   /// Notify all the observers that the active set of [AccessibilityFeatures]

packages/flutter_test/lib/src/binding.dart

@@ -225,13 +225,25 @@ abstract class TestWidgetsFlutterBinding extends BindingBase
     Duration additionalTime = const Duration(milliseconds: 250),
   });
 
-  /// Artificially calls dispatchLocaleChanged on the Widget binding,
+  /// Artificially calls dispatchLocalesChanged on the Widget binding,
   /// then flushes microtasks.
+  ///
+  /// Passes only one single Locale. Use [setLocales] to pass a full preferred
+  /// locales list.
   Future<void> setLocale(String languageCode, String countryCode) {
     return TestAsyncUtils.guard<void>(() async {
       assert(inTest);
-      final Locale locale = Locale(languageCode, countryCode);
-      dispatchLocaleChanged(locale);
+      final Locale locale = Locale(languageCode, countryCode == '' ? null : countryCode);
+      dispatchLocalesChanged(<Locale>[locale]);
+    });
+  }
+
+  /// Artificially calls dispatchLocalesChanged on the Widget binding,
+  /// then flushes microtasks.
+  Future<void> setLocales(List<Locale> locales) {
+    return TestAsyncUtils.guard<void>(() async {
+      assert(inTest);
+      dispatchLocalesChanged(locales);
     });
   }