PlatformResolvedLocale localization message channel

lib/ui/hooks.dart

@@ -96,6 +96,22 @@ void _updateLocales(List<String> locales) {
   _invoke(window.onLocaleChanged, window._onLocaleChangedZone);
 }
 
+@pragma('vm:entry-point')
+// ignore: unused_element
+void _updatePlatformResolvedLocale(List<String> localeData) {
+  if (localeData.length != 4) {
+    return;
+  }
+  final String countryCode = localeData[1];
+  final String scriptCode = localeData[2];
+
+  window._platformResolvedLocale = Locale.fromSubtags(
+    languageCode: localeData[0],
+    countryCode: countryCode.isEmpty ? null : countryCode,
+    scriptCode: scriptCode.isEmpty ? null : scriptCode,
+  );
+}
+
 @pragma('vm:entry-point')
 // ignore: unused_element
 void _updateUserSettingsData(String jsonData) {

lib/ui/window.dart

@@ -792,6 +792,19 @@ class Window {
   List<Locale> get locales => _locales;
   List<Locale> _locales;
 
+  /// The locale that the platform's native locale resolution system resolves to.
+  ///
+  /// This value may differ between platforms and is meant to allow flutter locale
+  /// resoltion algorithms to into resolving consistently with other apps on the
+  /// device.
+  ///
+  /// This value may be used in a custom [localeListResolutionCallback] or used directly
+  /// in order to arrive at the most appropriate locale for the app.
+  ///
+  /// See [locales], which is the list of locales the user/device prefers.
+  Locale get platformResolvedLocale => _platformResolvedLocale;
+  Locale _platformResolvedLocale;
+
   /// A callback that is invoked whenever [locale] changes value.
   ///
   /// The framework invokes this callback in the same zone in which the

lib/ui/window/window.cc

@@ -227,6 +227,19 @@ void Window::UpdateLocales(const std::vector<std::string>& locales) {
       }));
 }
 
+void Window::UpdatePlatformResolvedLocale(
+    const std::vector<std::string>& locale) {
+  std::shared_ptr<tonic::DartState> dart_state = library_.dart_state().lock();
+  if (!dart_state)
+    return;
+  tonic::DartState::Scope scope(dart_state);
+  tonic::LogIfError(tonic::DartInvokeField(
+      library_.value(), "_updatePlatformResolvedLocale",
+      {
+          tonic::ToDart<std::vector<std::string>>(locale),
+      }));
+}
+
 void Window::UpdateUserSettingsData(const std::string& data) {
   std::shared_ptr<tonic::DartState> dart_state = library_.dart_state().lock();
   if (!dart_state)

lib/ui/window/window.h

@@ -77,6 +77,7 @@ class Window final {
   void DidCreateIsolate();
   void UpdateWindowMetrics(const ViewportMetrics& metrics);
   void UpdateLocales(const std::vector<std::string>& locales);
+  void UpdatePlatformResolvedLocale(const std::vector<std::string>& locale);
   void UpdateUserSettingsData(const std::string& data);
   void UpdateLifecycleState(const std::string& data);
   void UpdateSemanticsEnabled(bool enabled);

lib/web_ui/lib/src/ui/window.dart

@@ -699,6 +699,20 @@ abstract class Window {
   // TODO(flutter_web): Get the real locale from the browser.
   List<Locale> _locales = const [_enUS];
 
+  /// The locale that the platform's native locale resolution system resolves to.
+  ///
+  /// This value may differ between platforms and is meant to allow flutter locale
+  /// resoltion algorithms to into resolving consistently with other apps on the
+  /// device.
+  ///
+  /// This value may be used in a custom [localeListResolutionCallback] or used directly
+  /// in order to arrive at the most appropriate locale for the app.
+  ///
+  /// See [locales], which is the list of locales the user/device prefers.
+  Locale get platformResolvedLocale => _platformResolvedLocale;
+  // TODO(flutter_web): Compute the browser locale resolution and set it here.
+  Locale _platformResolvedLocale;
+
   /// A callback that is invoked whenever [locale] changes value.
   ///
   /// The framework invokes this callback in the same zone in which the

runtime/runtime_controller.cc

@@ -131,6 +131,8 @@ std::unique_ptr<RuntimeController> RuntimeController::Clone() const {
 bool RuntimeController::FlushRuntimeStateToIsolate() {
   return SetViewportMetrics(window_data_.viewport_metrics) &&
          SetLocales(window_data_.locale_data) &&
+         SetPlatformResolvedLocale(
+             window_data_.platform_resolved_locale_data) &&
          SetSemanticsEnabled(window_data_.semantics_enabled) &&
          SetAccessibilityFeatures(window_data_.accessibility_feature_flags_) &&
          SetUserSettingsData(window_data_.user_settings_data) &&
@@ -159,6 +161,18 @@ bool RuntimeController::SetLocales(
   return false;
 }
 
+bool RuntimeController::SetPlatformResolvedLocale(
+    const std::vector<std::string>& locale_data) {
+  window_data_.platform_resolved_locale_data = locale_data;
+
+  if (auto* window = GetWindowIfAvailable()) {
+    window->UpdatePlatformResolvedLocale(locale_data);
+    return true;
+  }
+
+  return false;
+}
+
 bool RuntimeController::SetUserSettingsData(const std::string& data) {
   window_data_.user_settings_data = data;
 

runtime/runtime_controller.h

@@ -154,12 +154,30 @@ class RuntimeController final : public WindowClient {
   /// @deprecated The persistent isolate data must be used for this purpose
   ///             instead.
   ///
-  /// @param[in]  locale_data  The locale data
+  /// @param[in]  locale_data  The locale data. This should consist of groups of
+  ///             4 strings, each group representing a single locale.
   ///
   /// @return     If the locale data was forwarded to the running isolate.
   ///
   bool SetLocales(const std::vector<std::string>& locale_data);
 
+  //----------------------------------------------------------------------------
+  /// @brief      Forward the specified locale data to the running isolate. If
+  ///             the isolate is not running, this data will be saved and
+  ///             flushed to the isolate when it starts running.
+  ///
+  ///
+  /// @deprecated The persistent isolate data must be used for this purpose
+  ///             instead.
+  ///
+  /// @param[in]  locale_data  The locale data. This should consist of avector
+  ///             of 4 strings, representing languageCode, contryCode,
+  ///             scriptCode, and variant of the locale.
+  ///
+  /// @return     If the locale data was forwarded to the running isolate.
+  ///
+  bool SetPlatformResolvedLocale(const std::vector<std::string>& locale_data);
+
   //----------------------------------------------------------------------------
   /// @brief      Forward the user settings data to the running isolate. If the
   ///             isolate is not running, this data will be saved and flushed to

runtime/window_data.h

@@ -36,6 +36,7 @@ struct WindowData {
   std::string script_code;
   std::string variant_code;
   std::vector<std::string> locale_data;
+  std::vector<std::string> platform_resolved_locale_data;
   std::string user_settings_data = "{}";
   std::string lifecycle_state;
   bool semantics_enabled = false;

shell/common/engine.cc

@@ -359,29 +359,50 @@ bool Engine::HandleLocalizationPlatformMessage(PlatformMessage* message) {
     return false;
   auto root = document.GetObject();
   auto method = root.FindMember("method");
-  if (method == root.MemberEnd() || method->value != "setLocale")
+  if (method == root.MemberEnd())
     return false;
+  const size_t strings_per_locale = 4;
+  if (method->value == "setLocale") {
+    // Decode and pass the list of locale data onwards to dart.
+    auto args = root.FindMember("args");
+    if (args == root.MemberEnd() || !args->value.IsArray())
+      return false;
 
-  auto args = root.FindMember("args");
-  if (args == root.MemberEnd() || !args->value.IsArray())
-    return false;
+    if (args->value.Size() % strings_per_locale != 0)
+      return false;
+    std::vector<std::string> locale_data;
+    for (size_t locale_index = 0; locale_index < args->value.Size();
+         locale_index += strings_per_locale) {
+      if (!args->value[locale_index].IsString() ||
+          !args->value[locale_index + 1].IsString())
+        return false;
+      locale_data.push_back(args->value[locale_index].GetString());
+      locale_data.push_back(args->value[locale_index + 1].GetString());
+      locale_data.push_back(args->value[locale_index + 2].GetString());
+      locale_data.push_back(args->value[locale_index + 3].GetString());
+    }
 
-  const size_t strings_per_locale = 4;
-  if (args->value.Size() % strings_per_locale != 0)
-    return false;
-  std::vector<std::string> locale_data;
-  for (size_t locale_index = 0; locale_index < args->value.Size();
-       locale_index += strings_per_locale) {
-    if (!args->value[locale_index].IsString() ||
-        !args->value[locale_index + 1].IsString())
+    return runtime_controller_->SetLocales(locale_data);
+  } else if (method->value == "setPlatformResolvedLocale") {
+    // Decode and pass the single locale data onwards to dart.
+    auto args = root.FindMember("args");
+    if (args == root.MemberEnd() || !args->value.IsArray())
+      return false;
+
+    if (args->value.Size() != strings_per_locale)
       return false;
-    locale_data.push_back(args->value[locale_index].GetString());
-    locale_data.push_back(args->value[locale_index + 1].GetString());
-    locale_data.push_back(args->value[locale_index + 2].GetString());
-    locale_data.push_back(args->value[locale_index + 3].GetString());
-  }
 
-  return runtime_controller_->SetLocales(locale_data);
+    std::vector<std::string> locale_data;
+    if (!args->value[0].IsString() || !args->value[1].IsString())
+      return false;
+    locale_data.push_back(args->value[0].GetString());
+    locale_data.push_back(args->value[1].GetString());
+    locale_data.push_back(args->value[2].GetString());
+    locale_data.push_back(args->value[3].GetString());
+
+    return runtime_controller_->SetPlatformResolvedLocale(locale_data);
+  }
+  return false;
 }
 
 void Engine::HandleSettingsPlatformMessage(PlatformMessage* message) {

shell/platform/android/io/flutter/embedding/android/FlutterView.java

@@ -40,6 +40,7 @@
 import io.flutter.plugin.platform.PlatformViewsController;
 import io.flutter.view.AccessibilityBridge;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Locale;
@@ -859,7 +860,22 @@ private void sendLocalesToFlutter(@NonNull Configuration config) {
     } else {
       locales.add(config.locale);
     }
-    flutterEngine.getLocalizationChannel().sendLocales(locales);
+
+    List<Locale.LanguageRange> languageRanges = new ArrayList<>();
+    Locale platformResolvedLocale = null;
+    if (Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.O) {
+      LocaleList localeList = config.getLocales();
+      int localeCount = localeList.size();
+      for (int index = 0; index < localeCount; ++index) {
+        Locale locale = localeList.get(index);
+        languageRanges.add(new Locale.LanguageRange(locale.toLanguageTag()));
+      }
+      // TODO(garyq) implement a real locale resolution.
+      platformResolvedLocale =
+          Locale.lookup(languageRanges, Arrays.asList(Locale.getAvailableLocales()));
+    }
+
+    flutterEngine.getLocalizationChannel().sendLocales(locales, platformResolvedLocale);
   }
 
   /**

shell/platform/android/io/flutter/embedding/engine/systemchannels/LocalizationChannel.java

@@ -26,8 +26,21 @@ public LocalizationChannel(@NonNull DartExecutor dartExecutor) {
   }
 
   /** Send the given {@code locales} to Dart. */
-  public void sendLocales(@NonNull List<Locale> locales) {
+  public void sendLocales(@NonNull List<Locale> locales, Locale platformResolvedLocale) {
     Log.v(TAG, "Sending Locales to Flutter.");
+    // Send platformResolvedLocale first as it may be used in the callback
+    // triggered by the user supported locales being updated/set.
+    if (platformResolvedLocale != null) {
+      List<String> platformResolvedLocaleData = new ArrayList<>();
+      platformResolvedLocaleData.add(platformResolvedLocale.getLanguage());
+      platformResolvedLocaleData.add(platformResolvedLocale.getCountry());
+      platformResolvedLocaleData.add(
+          Build.VERSION.SDK_INT >= 21 ? platformResolvedLocale.getScript() : "");
+      platformResolvedLocaleData.add(platformResolvedLocale.getVariant());
+      channel.invokeMethod("setPlatformResolvedLocale", platformResolvedLocaleData);
+    }
+
+    // Send the user's preferred locales.
     List<String> data = new ArrayList<>();
     for (Locale locale : locales) {
       Log.v(

shell/platform/android/io/flutter/view/FlutterView.java

@@ -60,6 +60,7 @@
 import io.flutter.plugin.platform.PlatformViewsController;
 import java.nio.ByteBuffer;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.List;
 import java.util.Locale;
 import java.util.concurrent.atomic.AtomicLong;
@@ -404,7 +405,22 @@ private void sendLocalesToDart(Configuration config) {
     } else {
       locales.add(config.locale);
     }
-    localizationChannel.sendLocales(locales);
+
+    List<Locale.LanguageRange> languageRanges = new ArrayList<>();
+    Locale platformResolvedLocale = null;
+    if (Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.O) {
+      LocaleList localeList = config.getLocales();
+      int localeCount = localeList.size();
+      for (int index = 0; index < localeCount; ++index) {
+        Locale locale = localeList.get(index);
+        languageRanges.add(new Locale.LanguageRange(locale.toLanguageTag()));
+      }
+      // TODO(garyq) implement a real locale resolution.
+      platformResolvedLocale =
+          Locale.lookup(languageRanges, Arrays.asList(Locale.getAvailableLocales()));
+    }
+
+    localizationChannel.sendLocales(locales, platformResolvedLocale);
   }
 
   @Override