Send locale information in the Windows embedding (#20455)

Queries the system list of user-preferred languages, and sends it to the
engine just after starting it up.

Windows portion of https://github.com/flutter/flutter/issues/45152

ci/licenses_golden/licenses_flutter

@@ -1359,6 +1359,9 @@ FILE: ../../../flutter/shell/platform/windows/public/flutter_windows.h
 FILE: ../../../flutter/shell/platform/windows/string_conversion.cc
 FILE: ../../../flutter/shell/platform/windows/string_conversion.h
 FILE: ../../../flutter/shell/platform/windows/string_conversion_unittests.cc
+FILE: ../../../flutter/shell/platform/windows/system_utils.h
+FILE: ../../../flutter/shell/platform/windows/system_utils_unittests.cc
+FILE: ../../../flutter/shell/platform/windows/system_utils_win32.cc
 FILE: ../../../flutter/shell/platform/windows/text_input_plugin.cc
 FILE: ../../../flutter/shell/platform/windows/text_input_plugin.h
 FILE: ../../../flutter/shell/platform/windows/win32_dpi_utils.cc

shell/platform/windows/BUILD.gn

@@ -54,6 +54,8 @@ source_set("flutter_windows_source") {
     "keyboard_hook_handler.h",
     "string_conversion.cc",
     "string_conversion.h",
+    "system_utils.h",
+    "system_utils_win32.cc",
     "text_input_plugin.cc",
     "text_input_plugin.h",
     "win32_dpi_utils.cc",
@@ -118,6 +120,7 @@ executable("flutter_windows_unittests") {
 
   sources = [
     "string_conversion_unittests.cc",
+    "system_utils_unittests.cc",
     "testing/win32_flutter_window_test.cc",
     "testing/win32_flutter_window_test.h",
     "testing/win32_window_test.cc",

shell/platform/windows/flutter_windows_engine.cc

@@ -6,9 +6,12 @@
 
 #include <filesystem>
 #include <iostream>
+#include <sstream>
 
 #include "flutter/shell/platform/common/cpp/path_utils.h"
 #include "flutter/shell/platform/windows/flutter_windows_view.h"
+#include "flutter/shell/platform/windows/string_conversion.h"
+#include "flutter/shell/platform/windows/system_utils.h"
 
 namespace flutter {
 
@@ -69,6 +72,21 @@ static FlutterDesktopMessage ConvertToDesktopMessage(
   return message;
 }
 
+// Converts a LanguageInfo struct to a FlutterLocale struct. |info| must outlive
+// the returned value, since the returned FlutterLocale has pointers into it.
+FlutterLocale CovertToFlutterLocale(const LanguageInfo& info) {
+  FlutterLocale locale = {};
+  locale.struct_size = sizeof(FlutterLocale);
+  locale.language_code = info.language.c_str();
+  if (!info.region.empty()) {
+    locale.country_code = info.region.c_str();
+  }
+  if (!info.script.empty()) {
+    locale.script_code = info.script.c_str();
+  }
+  return locale;
+}
+
 }  // namespace
 
 FlutterWindowsEngine::FlutterWindowsEngine(const FlutterProjectBundle& project)
@@ -173,6 +191,8 @@ bool FlutterWindowsEngine::RunWithEntrypoint(const char* entrypoint) {
   }
 
   plugin_registrar_->messenger->engine = engine_;
+  SendSystemSettings();
+
   return true;
 }
 
@@ -213,4 +233,24 @@ void FlutterWindowsEngine::HandlePlatformMessage(
       message, [this] {}, [this] {});
 }
 
+void FlutterWindowsEngine::SendSystemSettings() {
+  std::vector<LanguageInfo> languages = GetPreferredLanguageInfo();
+  std::vector<FlutterLocale> flutter_locales;
+  flutter_locales.reserve(languages.size());
+  for (const auto& info : languages) {
+    flutter_locales.push_back(CovertToFlutterLocale(info));
+  }
+  // Convert the locale list to the locale pointer list that must be provided.
+  std::vector<const FlutterLocale*> flutter_locale_list;
+  flutter_locale_list.reserve(flutter_locales.size());
+  std::transform(
+      flutter_locales.begin(), flutter_locales.end(),
+      std::back_inserter(flutter_locale_list),
+      [](const auto& arg) -> const auto* { return &arg; });
+  FlutterEngineUpdateLocales(engine_, flutter_locale_list.data(),
+                             flutter_locale_list.size());
+
+  // TODO: Send 'flutter/settings' channel settings here as well.
+}
+
 }  // namespace flutter

shell/platform/windows/flutter_windows_engine.h

@@ -69,6 +69,12 @@ class FlutterWindowsEngine {
   void HandlePlatformMessage(const FlutterPlatformMessage*);
 
  private:
+  // Sends system settings (e.g., locale) to the engine.
+  //
+  // Should be called just after the engine is run, and after any relevant
+  // system changes.
+  void SendSystemSettings();
+
   // The handle to the embedder.h engine instance.
   FLUTTER_API_SYMBOL(FlutterEngine) engine_ = nullptr;
 

shell/platform/windows/system_utils.h

@@ -0,0 +1,36 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// This file contains utilities for system-level information/settings.
+
+#ifndef FLUTTER_SHELL_PLATFORM_WINDOWS_SYSTEM_UTILS_H_
+#define FLUTTER_SHELL_PLATFORM_WINDOWS_SYSTEM_UTILS_H_
+
+#include <string>
+#include <vector>
+
+namespace flutter {
+
+// Components of a system language/locale.
+struct LanguageInfo {
+  std::string language;
+  std::string region;
+  std::string script;
+};
+
+// Returns the list of user-preferred languages, in preference order,
+// parsed into LanguageInfo structures.
+std::vector<LanguageInfo> GetPreferredLanguageInfo();
+
+// Returns the list of user-preferred languages, in preference order.
+// The language names are as described at:
+// https://docs.microsoft.com/en-us/windows/win32/intl/language-names
+std::vector<std::wstring> GetPreferredLanguages();
+
+// Parses a Windows language name into its components.
+LanguageInfo ParseLanguageName(std::wstring language_name);
+
+}  // namespace flutter
+
+#endif  // FLUTTER_SHELL_PLATFORM_WINDOWS_SYSTEM_UTILS_H_

shell/platform/windows/system_utils_unittests.cc

@@ -0,0 +1,75 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <wchar.h>
+
+#include "flutter/shell/platform/windows/system_utils.h"
+#include "gtest/gtest.h"
+
+namespace flutter {
+namespace testing {
+
+TEST(SystemUtils, GetPreferredLanguageInfo) {
+  std::vector<LanguageInfo> languages = GetPreferredLanguageInfo();
+  // There should be at least one language.
+  ASSERT_GE(languages.size(), 1);
+  // The info should have a valid languge.
+  EXPECT_GE(languages[0].language.size(), 2);
+}
+
+TEST(SystemUtils, GetPreferredLanguages) {
+  std::vector<std::wstring> languages = GetPreferredLanguages();
+  // There should be at least one language.
+  ASSERT_GE(languages.size(), 1);
+  // The language should be non-empty.
+  EXPECT_FALSE(languages[0].empty());
+  // There should not be a trailing null from the parsing step.
+  EXPECT_EQ(languages[0].size(), wcslen(languages[0].c_str()));
+}
+
+TEST(SystemUtils, ParseLanguageNameGeneric) {
+  LanguageInfo info = ParseLanguageName(L"en");
+  EXPECT_EQ(info.language, "en");
+  EXPECT_TRUE(info.region.empty());
+  EXPECT_TRUE(info.script.empty());
+}
+
+TEST(SystemUtils, ParseLanguageNameWithRegion) {
+  LanguageInfo info = ParseLanguageName(L"hu-HU");
+  EXPECT_EQ(info.language, "hu");
+  EXPECT_EQ(info.region, "HU");
+  EXPECT_TRUE(info.script.empty());
+}
+
+TEST(SystemUtils, ParseLanguageNameWithScript) {
+  LanguageInfo info = ParseLanguageName(L"us-Latn");
+  EXPECT_EQ(info.language, "us");
+  EXPECT_TRUE(info.region.empty());
+  EXPECT_EQ(info.script, "Latn");
+}
+
+TEST(SystemUtils, ParseLanguageNameWithRegionAndScript) {
+  LanguageInfo info = ParseLanguageName(L"uz-Latn-UZ");
+  EXPECT_EQ(info.language, "uz");
+  EXPECT_EQ(info.region, "UZ");
+  EXPECT_EQ(info.script, "Latn");
+}
+
+TEST(SystemUtils, ParseLanguageNameWithSuplementalLanguage) {
+  LanguageInfo info = ParseLanguageName(L"en-US-x-fabricam");
+  EXPECT_EQ(info.language, "en");
+  EXPECT_EQ(info.region, "US");
+  EXPECT_TRUE(info.script.empty());
+}
+
+// Ensure that ISO 639-2/T codes are handled.
+TEST(SystemUtils, ParseLanguageNameWithThreeCharacterLanguage) {
+  LanguageInfo info = ParseLanguageName(L"ale-ZZ");
+  EXPECT_EQ(info.language, "ale");
+  EXPECT_EQ(info.region, "ZZ");
+  EXPECT_TRUE(info.script.empty());
+}
+
+}  // namespace testing
+}  // namespace flutter

shell/platform/windows/system_utils_win32.cc

@@ -0,0 +1,93 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "flutter/shell/platform/windows/system_utils.h"
+
+#include <Windows.h>
+
+#include <sstream>
+
+#include "flutter/shell/platform/windows/string_conversion.h"
+
+namespace flutter {
+
+std::vector<LanguageInfo> GetPreferredLanguageInfo() {
+  std::vector<std::wstring> languages = GetPreferredLanguages();
+  std::vector<LanguageInfo> language_info;
+  language_info.reserve(languages.size());
+
+  for (auto language : languages) {
+    language_info.push_back(ParseLanguageName(language));
+  }
+  return language_info;
+}
+
+std::vector<std::wstring> GetPreferredLanguages() {
+  std::vector<std::wstring> languages;
+  DWORD flags = MUI_LANGUAGE_NAME | MUI_UI_FALLBACK;
+
+  // Get buffer length.
+  ULONG count = 0;
+  ULONG buffer_size = 0;
+  if (!::GetThreadPreferredUILanguages(flags, &count, nullptr, &buffer_size)) {
+    return languages;
+  }
+
+  // Get the list of null-separated languages.
+  std::wstring buffer(buffer_size, '\0');
+  if (!::GetThreadPreferredUILanguages(flags, &count, buffer.data(),
+                                       &buffer_size)) {
+    return languages;
+  }
+
+  // Extract the individual languages from the buffer.
+  size_t start = 0;
+  while (true) {
+    // The buffer is terminated by an empty string (i.e., a double null).
+    if (buffer[start] == L'\0') {
+      break;
+    }
+    // Read the next null-terminated language.
+    std::wstring language(buffer.c_str() + start);
+    if (language.size() == 0) {
+      break;
+    }
+    languages.push_back(language);
+    // Skip past that language and its terminating null in the buffer.
+    start += language.size() + 1;
+  }
+  return languages;
+}
+
+LanguageInfo ParseLanguageName(std::wstring language_name) {
+  LanguageInfo info;
+
+  // Split by '-', discarding any suplemental language info (-x-foo).
+  std::vector<std::string> components;
+  std::istringstream stream(Utf8FromUtf16(language_name));
+  std::string component;
+  while (getline(stream, component, '-')) {
+    if (component == "x") {
+      break;
+    }
+    components.push_back(component);
+  }
+
+  // Determine which components are which.
+  info.language = components[0];
+  if (components.size() == 3) {
+    info.script = components[1];
+    info.region = components[2];
+  } else if (components.size() == 2) {
+    // A script code will always be four characters long.
+    if (components[1].size() == 4) {
+      info.script = components[1];
+    } else {
+      info.region = components[1];
+    }
+  }
+  return info;
+}
+
+}  // namespace flutter