wasm: Add QLocale backend

This is a simple backend based on navigator.languages,
which gives us a prioritized list of languages in the
form '["en-US", "zh-CN", "ja-JP"]'.

Use this to implement QSystemLocale::query() for UILanguages
and QSystemLocale::fallbackLocale().

Register an event handler for the native QWindow:languagechange
event in the QSystemLocale constructor. This event handler
stays active for the lifetime of the QSystemLocale object.

Task-number: QTBUG-116613
Change-Id: Ibd176748377e891b63a3f1d57605af0c2a49edb3
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>

src/corelib/CMakeLists.txt

@@ -797,7 +797,7 @@ qt_internal_extend_target(Core CONDITION APPLE
         text/qlocale_mac.mm
 )
 
-qt_internal_extend_target(Core CONDITION UNIX AND NOT APPLE
+qt_internal_extend_target(Core CONDITION UNIX AND NOT APPLE AND NOT WASM
     SOURCES
         text/qlocale_unix.cpp
 )
@@ -807,6 +807,11 @@ qt_internal_extend_target(Core CONDITION WIN32
         text/qlocale_win.cpp
 )
 
+qt_internal_extend_target(Core CONDITION WASM
+    SOURCES
+        text/qlocale_wasm.cpp
+)
+
 # On MS-Win, clang has two flavors, one of which immitates MSVC (so claims to be it)
 qt_internal_extend_target(Core CONDITION MSVC
     LIBRARIES

src/corelib/text/qlocale.cpp

@@ -720,6 +720,17 @@ QSystemLocale::QSystemLocale() : next(_systemLocale)
     _systemLocale = this;
 
     systemLocaleData.m_language_id = 0;
+
+#ifdef Q_OS_WASM
+    onLanguageChanged = std::make_unique<qstdweb::EventCallback>(
+        emscripten::val::global("window"), "languagechange", [](emscripten::val) {
+            systemLocaleData.m_language_id = 0;
+            QEvent languageChangeEvent(QEvent::LanguageChange);
+            QCoreApplication::sendEvent(qApp, &languageChangeEvent);
+            QEvent localeChangeEvent(QEvent::LocaleChange);
+            QCoreApplication::sendEvent(qApp, &localeChangeEvent);
+    });
+#endif
 }
 
 /*!

src/corelib/text/qlocale_p.h

@@ -25,6 +25,9 @@
 #include <QtCore/qstring.h>
 #include <QtCore/qvariant.h>
 #include <QtCore/qvarlengtharray.h>
+#ifdef Q_OS_WASM
+#include <private/qstdweb_p.h>
+#endif
 
 #include <limits>
 #include <cmath>
@@ -103,6 +106,10 @@ struct QLocaleData;
 class Q_CORE_EXPORT QSystemLocale
 {
     QSystemLocale *next = nullptr; // Maintains a stack.
+#ifdef Q_OS_WASM
+    std::unique_ptr<qstdweb::EventCallback> onLanguageChanged;
+#endif
+
 public:
     QSystemLocale();
     virtual ~QSystemLocale();

src/corelib/text/qlocale_wasm.cpp

@@ -0,0 +1,54 @@
+// Copyright (C) 2023 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
+
+#include "qlocale_p.h"
+
+#include <emscripten/val.h>
+
+#include <string>
+#include <vector>
+
+QT_BEGIN_NAMESPACE
+
+#ifndef QT_NO_SYSTEMLOCALE
+
+namespace {
+
+QStringList navigatorLanguages()
+{
+    using emscripten::val;
+    const val navigator = val::global("navigator");
+    const auto languages = emscripten::vecFromJSArray<std::string>(navigator["languages"]);
+    QStringList qtLanguages;
+    for (const std::string& language : languages)
+        qtLanguages.append(QString::fromStdString(language));
+    return qtLanguages;
+}
+
+}
+
+QVariant QSystemLocale::query(QueryType query, QVariant in) const
+{
+    Q_UNUSED(in);
+
+    switch (query) {
+    case QSystemLocale::UILanguages:
+        return QVariant(navigatorLanguages());
+    default:
+    break;
+    }
+
+    return QVariant();
+}
+
+QLocale QSystemLocale::fallbackLocale() const
+{
+    const QStringList languages = navigatorLanguages();
+    if (languages.isEmpty())
+        return QLocale(u"en-US");
+    return QLocale(languages[0]);
+}
+
+#endif // QT_NO_SYSTEMLOCALE
+
+QT_END_NAMESPACE