Native Style: rework style and focus window initializationHEADdev

QStyle is destroyed with the app singleton, but not re-created when a
new app is re-created. We change this to lazily initialize the style via
application static in QQuickStyleItem::style().

Furthermore the focus window is not re-connected to the new application
singleton, either. We lazily construct it and ensure that is cleaned up
when the application singleton is destroyed.

Pick-to: 6.10
Fixes: QTBUG-140220
Change-Id: I97281aaa91794a8a4e1c1fb3aa524dd54cf19709
Reviewed-by: Richard Moe Gustavsen <[email protected]>

5 files changed, 154 insertions, 115 deletions

diff --git a/src/quicknativestyle/CMakeLists.txt b/src/quicknativestyle/CMakeLists.txt
index f27553955b..e6b95579b3 100644
--- a/src/quicknativestyle/CMakeLists.txt
+++ b/src/quicknativestyle/CMakeLists.txt
@@ -72,7 +72,7 @@ qt_internal_add_qml_module(qtquickcontrols2nativestyleplugin
         qstyle/qquickcommonstyle.cpp qstyle/qquickcommonstyle.h qstyle/qquickcommonstyle_p.h
         qstyle/qquickcommonstylepixmaps_p.h
         qstyle/qquickdrawutil.cpp qstyle/qquickdrawutil.h
-        qstyle/qquicknativestyle.h
+        qstyle/qquicknativestyle.cpp qstyle/qquicknativestyle_p.h
         qstyle/qquickstyle.cpp qstyle/qquickstyle.h qstyle/qquickstyle_p.h
         qstyle/qquickstylehelper.cpp qstyle/qquickstylehelper_p.h
         qstyle/qquickstyleoption.cpp qstyle/qquickstyleoption.h
diff --git a/src/quicknativestyle/items/qquickstyleitem.h b/src/quicknativestyle/items/qquickstyleitem.h
index e4787ff269..42f131054a 100644
--- a/src/quicknativestyle/items/qquickstyleitem.h
+++ b/src/quicknativestyle/items/qquickstyleitem.h
@@ -11,7 +11,7 @@
 #include <QtQuick/private/qquickitem_p.h>
 #include <QtQuickTemplates2/private/qquickcontrol_p.h>
 
-#include "qquicknativestyle.h"
+#include "qquicknativestyle_p.h"
 #include "qquickstyle.h"
 #include "qquickstyleoption.h"
 
@@ -220,7 +220,7 @@ protected:
     void initStyleOptionBase(QStyleOption &styleOption) const;
 
     inline QSize contentSize() const { return QSize(qCeil(m_contentSize.width()), qCeil(m_contentSize.height())); }
-    inline static QStyle *style() { return QQuickNativeStyle::style(); }
+    inline static QStyle *style() { return QQC2::style(); }
 
     template <class T> inline const T* control() const {
 #ifdef QT_DEBUG
diff --git a/src/quicknativestyle/qstyle/qquicknativestyle.cpp b/src/quicknativestyle/qstyle/qquicknativestyle.cpp
new file mode 100644
index 0000000000..6c3ea9f2d0
--- /dev/null
+++ b/src/quicknativestyle/qstyle/qquicknativestyle.cpp
@@ -0,0 +1,117 @@
+// Copyright (C) 2025 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
+// Qt-Security score:significant reason:default
+
+#include "qquicknativestyle_p.h"
+
+#include <QtCore/qapplicationstatic.h>
+#include <QtCore/qloggingcategory.h>
+#include <QtCore/qthread.h>
+#include <QtGui/qguiapplication.h>
+#include <QtGui/qstylehints.h>
+
+#if defined(Q_OS_MACOS)
+#  include "qquickmacstyle_mac_p.h"
+#elif defined(Q_OS_WINDOWS)
+#  include "qquickwindowsxpstyle_p.h"
+#endif
+
+#include <memory>
+
+QT_BEGIN_NAMESPACE
+
+Q_STATIC_LOGGING_CATEGORY(lcNativeStylePlugin, "qt.quick.plugins.nativestyle");
+
+namespace QQC2 {
+
+namespace {
+
+// When we delete QStyle, it will free up its own internal resources. Especially
+// on macOS, this means releasing a lot of NSViews and NSCells from the QMacStyle
+// destructor. If we did this from ~QtQuickControls2NativeStylePlugin, it would
+// happen when the plugin was unloaded from a Q_DESTRUCTOR_FUNCTION in QLibrary,
+// which is very late in the tear-down process, and after qGuiApp has been set to
+// nullptr, NSApplication has stopped running, and perhaps also other static platform
+// variables (e.g in AppKit?) have been deleted. And to our best guess, this is also why
+// we see a crash in AppKit from the destructor in QMacStyle. So for this reason, we
+// delete QStyle from a post routine rather than from the destructor.
+//
+// Furthermore we need to ensure to recreate the QQuickFocusFrame when re-creating the qApplication
+
+struct StyleSingleton
+{
+    StyleSingleton();
+    ~StyleSingleton();
+    QStyle *style() { return m_style.get(); }
+
+private:
+    std::unique_ptr<QStyle> m_style;
+};
+
+Q_APPLICATION_STATIC(StyleSingleton, styleSingleton);
+
+StyleSingleton::StyleSingleton()
+{
+    qCDebug(lcNativeStylePlugin) << "Creating native style";
+
+    // Enable commonstyle as a reference style while
+    // the native styles are under development.
+    if (qEnvironmentVariable("QQC2_COMMONSTYLE") == u"true")
+        m_style = std::make_unique<QCommonStyle>();
+    else if (const QString envStyle = qEnvironmentVariable("QQC2_STYLE"); !envStyle.isNull()) {
+        if (envStyle == u"common")
+            m_style = std::make_unique<QCommonStyle>();
+#if defined(Q_OS_MACOS)
+        else if (envStyle == u"mac")
+            m_style.reset(QMacStyle::create());
+#endif
+#if defined(Q_OS_WINDOWS)
+        else if (envStyle == u"windows")
+            m_style = std::make_unique<QWindowsStyle>();
+        else if (envStyle == u"windowsxp")
+            m_style = std::make_unique<QWindowsXPStyle>();
+#endif
+    }
+
+    if (!m_style) {
+#if defined(Q_OS_MACOS)
+        m_style.reset(QMacStyle::create());
+#elif defined(Q_OS_WINDOWS)
+        m_style = std::make_unique<QWindowsXPStyle>();
+        if (QGuiApplication::styleHints()->colorScheme() == Qt::ColorScheme::Dark)
+            qobject_cast<QWindowsStyle *>(m_style.get())->refreshPalette();
+#endif
+    }
+
+    if (!m_style)
+        m_style = std::make_unique<QCommonStyle>();
+
+    // The native style plugin is neither the current style or fallback style
+    // during QQuickStylePlugin::registerTypes, so it's not given a chance to
+    // initialize or update the theme. But since it's used as an implementation
+    // detail of some of the other style plugins, it might need to know about
+    // theme changes.
+    Q_ASSERT(m_style->thread()->isMainThread());
+    QObject::connect(QGuiApplication::styleHints(), &QStyleHints::colorSchemeChanged, m_style.get(),
+                     [this] {
+        m_style->handleThemeChange();
+    });
+}
+
+StyleSingleton::~StyleSingleton()
+{
+    qCDebug(lcNativeStylePlugin) << "Destroying native style";
+
+    m_style.reset();
+}
+
+}; // namespace
+
+QStyle *style()
+{
+    return styleSingleton()->style();
+}
+
+} // namespace QQC2
+
+QT_END_NAMESPACE
diff --git a/src/quicknativestyle/qstyle/qquicknativestyle.h b/src/quicknativestyle/qstyle/qquicknativestyle_p.h
index 1ed40bef69..3f0a32fb6c 100644
--- a/src/quicknativestyle/qstyle/qquicknativestyle.h
+++ b/src/quicknativestyle/qstyle/qquicknativestyle_p.h
@@ -2,26 +2,29 @@
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
 // Qt-Security score:significant reason:default
 
+
 #ifndef QQUICKNATIVESTYLE_H
 #define QQUICKNATIVESTYLE_H
 
-#include "qquickstyle.h"
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API. It exists purely as an
+// implementation detail. This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+//
 
-#include <memory>
+
+#include "qquickstyle.h"
 
 QT_BEGIN_NAMESPACE
 
 namespace QQC2 {
 
-class QQuickNativeStyle
-{
-public:
-    static void setStyle(QStyle *style) { s_style.reset(style); }
-    static QStyle *style() { return s_style.get(); }
-
-private:
-    static inline std::unique_ptr<QStyle> s_style;
-};
+QStyle *style();
 
 } // namespace QQC2
 
diff --git a/src/quicknativestyle/qtquickcontrols2nativestyleplugin.cpp b/src/quicknativestyle/qtquickcontrols2nativestyleplugin.cpp
index 61443b475b..942f96e5f4 100644
--- a/src/quicknativestyle/qtquickcontrols2nativestyleplugin.cpp
+++ b/src/quicknativestyle/qtquickcontrols2nativestyleplugin.cpp
@@ -3,22 +3,13 @@
 // Qt-Security score:significant reason:default
 
 #include <QtQml/qqml.h>
+#include <QtQml/qqmlextensionplugin.h>
 #include <QtQuickControls2/private/qquickstyleplugin_p.h>
-#include <QtGui/qguiapplication.h>
-#include <QtGui/qpa/qplatformintegration.h>
-#include <QtGui/private/qguiapplication_p.h>
-#include <QtGui/qstylehints.h>
-#include <QtQuickTemplates2/private/qquicktheme_p.h>
-
-#include "qquicknativestyle.h"
-#include "qquickcommonstyle.h"
 
 #if defined(Q_OS_MACOS)
-#include "qquickmacfocusframe.h"
-#include "qquickmacstyle_mac_p.h"
+#  include "qquickmacfocusframe.h"
 #elif defined(Q_OS_WINDOWS)
-#include "qquickwindowsfocusframe.h"
-#include "qquickwindowsxpstyle_p.h"
+#  include "qquickwindowsfocusframe.h"
 #endif
 
 QT_BEGIN_NAMESPACE
@@ -26,7 +17,7 @@ QT_BEGIN_NAMESPACE
 extern void qml_register_types_QtQuick_NativeStyle();
 Q_GHS_KEEP_REFERENCE(qml_register_types_QtQuick_NativeStyle);
 
-using namespace QQC2;
+namespace QQC2 {
 
 class QtQuickControls2NativeStylePlugin : public QQuickStylePlugin
 {
@@ -35,31 +26,14 @@ class QtQuickControls2NativeStylePlugin : public QQuickStylePlugin
 
 public:
     QtQuickControls2NativeStylePlugin(QObject *parent = nullptr);
-    ~QtQuickControls2NativeStylePlugin() override;
+    ~QtQuickControls2NativeStylePlugin() override = default;
 
-    void initializeEngine(QQmlEngine *engine, const char *uri) override;
-    void initializeTheme(QQuickTheme *theme) override;
-    QString name() const override;
+    void initializeEngine(QQmlEngine *, const char * /*uri*/) override;
 
-#if defined(Q_OS_MACOS) || defined (Q_OS_WIN)
-    QScopedPointer<QQuickFocusFrame> m_focusFrame;
-#endif
+    void initializeTheme(QQuickTheme *) override { }
+    QString name() const override { return QStringLiteral("NativeStyle"); }
 };
 
-static void deleteQStyle()
-{
-    // When we delete QStyle, it will free up it's own internal resources. Especially
-    // on macOS, this means releasing a lot of NSViews and NSCells from the QMacStyle
-    // destructor. If we did this from ~QtQuickControls2NativeStylePlugin, it would
-    // happen when the plugin was unloaded from a Q_DESTRUCTOR_FUNCTION in QLibrary,
-    // which is very late in the tear-down process, and after qGuiApp has been set to
-    // nullptr, NSApplication has stopped running, and perhaps also other static platform
-    // variables (e.g in AppKit?) has been deleted. And to our best guess, this is also why
-    // we see a crash in AppKit from the destructor in QMacStyle. So for this reason, we
-    // delete QStyle from a post routine rather than from the destructor.
-    QQuickNativeStyle::setStyle(nullptr);
-}
-
 QtQuickControls2NativeStylePlugin::QtQuickControls2NativeStylePlugin(QObject *parent):
     QQuickStylePlugin(parent)
 {
@@ -67,82 +41,27 @@ QtQuickControls2NativeStylePlugin::QtQuickControls2NativeStylePlugin(QObject *pa
     Q_UNUSED(registration);
 }
 
-QtQuickControls2NativeStylePlugin::~QtQuickControls2NativeStylePlugin()
-{
-    if (!qGuiApp)
-        return;
-
-    // QGuiApplication is still running, so we need to remove the post
-    // routine to not be called after we have been unloaded.
-    qRemovePostRoutine(deleteQStyle);
-    QQuickNativeStyle::setStyle(nullptr);
-}
-
-QString QtQuickControls2NativeStylePlugin::name() const
-{
-    return QStringLiteral("NativeStyle");
-}
+static std::unique_ptr<QQuickFocusFrame> g_focusFrame;
 
-void QtQuickControls2NativeStylePlugin::initializeEngine(QQmlEngine *engine, const char *uri)
+void QtQuickControls2NativeStylePlugin::initializeEngine(QQmlEngine *, const char *)
 {
-    Q_UNUSED(engine);
-    Q_UNUSED(uri);
-    // Enable commonstyle as a reference style while
-    // the native styles are under development.
-    QStyle *style = nullptr;
-    if (qEnvironmentVariable("QQC2_COMMONSTYLE") == QStringLiteral("true")) {
-        style = new QCommonStyle;
-    } else {
-        const QString envStyle = qEnvironmentVariable("QQC2_STYLE");
-        if (!envStyle.isNull()) {
-            if (envStyle == QLatin1String("common"))
-                style = new QCommonStyle;
-#if defined(Q_OS_MACOS)
-            else if (envStyle == QLatin1String("mac"))
-                style = QMacStyle::create();
-#endif
-#if defined(Q_OS_WINDOWS)
-            else if (envStyle == QLatin1String("windows"))
-                style = new QWindowsStyle;
-            else if (envStyle == QLatin1String("windowsxp"))
-                style = new QWindowsXPStyle;
-#endif
-        }
-        if (!style) {
-#if defined(Q_OS_MACOS)
-            style = QMacStyle::create();
-#elif defined(Q_OS_WINDOWS)
-            style = new QWindowsXPStyle;
-            if (QGuiApplication::styleHints()->colorScheme() == Qt::ColorScheme::Dark)
-                qobject_cast<QWindowsStyle *>(style)->refreshPalette();
-#else
-            style = new QCommonStyle;
-#endif
-        }
-    }
+    if (g_focusFrame)
+        return;
 
 #if defined(Q_OS_MACOS)
-    m_focusFrame.reset(new QQuickMacFocusFrame());
+    g_focusFrame = std::make_unique<QQuickMacFocusFrame>();
 #elif defined(Q_OS_WIN)
-    m_focusFrame.reset(new QQuickWindowsFocusFrame());
+    g_focusFrame = std::make_unique<QQuickWindowsFocusFrame>();
 #endif
+    if (!g_focusFrame)
+        return;
 
-    // The native style plugin is neither the current style or fallback style
-    // during QQuickStylePlugin::registerTypes, so it's not given a chance to
-    // initialize or update the theme. But since it's used as an implementation
-    // detail of some of the other style plugins, it might need to know about
-    // theme changes.
-    Q_ASSERT(style->thread()->isMainThread());
-    connect(QGuiApplication::styleHints(), &QStyleHints::colorSchemeChanged,
-        style, [=]{ style->handleThemeChange(); });
-
-    qAddPostRoutine(deleteQStyle);
-    QQuickNativeStyle::setStyle(style);
+    qAddPostRoutine([] {
+        g_focusFrame.reset();
+    });
 }
 
-void QtQuickControls2NativeStylePlugin::initializeTheme(QQuickTheme * /*theme*/)
-{
-}
+} // namespace QQC2
 
 QT_END_NAMESPACE