Deduplicate maybeQuitOnLastWindowClosed handling

The functionality now lives in QGuiApplication, and is triggered
by QGuiApplication and QApplication after dispatching the close
event to the window.

The slight difference between how a Qt GUI and Qt Widget app
determines if a window should contribute to the close-on-quit
behavior has been abstracted into a QWindowPrivate helper.

The additional checks that were in place for skipping out of
the whole maybeQuitOnLastWindowClosed machinery have been kept.

Task-number: QTBUG-53286
Change-Id: I81bd474755f9adb3a2b082621e5ecaa1c4726808
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

4 files changed, 44 insertions, 42 deletions

diff --git a/src/gui/kernel/qguiapplication.cpp b/src/gui/kernel/qguiapplication.cpp
index 98b5ea03e6..294684584b 100644
--- a/src/gui/kernel/qguiapplication.cpp
+++ b/src/gui/kernel/qguiapplication.cpp
@@ -1918,6 +1918,8 @@ void QGuiApplicationPrivate::captureGlobalModifierState(QEvent *e)
 */
 bool QGuiApplication::notify(QObject *object, QEvent *event)
 {
+    Q_D(QGuiApplication);
+
     if (object->isWindowType()) {
         if (QGuiApplicationPrivate::sendQWindowEventToQPlatformWindow(static_cast<QWindow *>(object), event))
             return true; // Platform plugin ate the event
@@ -1925,7 +1927,12 @@ bool QGuiApplication::notify(QObject *object, QEvent *event)
 
     QGuiApplicationPrivate::captureGlobalModifierState(event);
 
-    return QCoreApplication::notify(object, event);
+    bool accepted = QCoreApplication::notify(object, event);
+
+    if (event->type() == QEvent::Close && object->isWindowType() && accepted)
+        d->maybeQuitOnLastWindowClosed(static_cast<QWindow*>(object));
+
+    return accepted;
 }
 
 /*! \reimp
@@ -3533,13 +3540,30 @@ void QGuiApplication::setQuitOnLastWindowClosed(bool quit)
     QCoreApplication::setQuitLockEnabled(quit);
 }
 
-
-
 bool QGuiApplication::quitOnLastWindowClosed()
 {
     return QCoreApplication::isQuitLockEnabled();
 }
 
+void QGuiApplicationPrivate::maybeQuitOnLastWindowClosed(QWindow *closedWindow)
+{
+    Q_ASSERT(closedWindow);
+
+    if (!qt_window_private(closedWindow)->shouldTriggerQuitOnClose())
+        return;
+
+    // Check if there are any remaining windows that should prevent us from quitting
+    for (auto *topLevelWindow : QGuiApplication::topLevelWindows()) {
+        auto *windowPrivate = qt_window_private(topLevelWindow);
+        if (windowPrivate->shouldCancelQuitOnClose())
+            return;
+    }
+
+    emitLastWindowClosed();
+
+    if (QGuiApplication::quitOnLastWindowClosed())
+        maybeQuit();
+}
 
 /*!
     \fn void QGuiApplication::lastWindowClosed()
diff --git a/src/gui/kernel/qguiapplication_p.h b/src/gui/kernel/qguiapplication_p.h
index 7b28c70993..3450c6e36b 100644
--- a/src/gui/kernel/qguiapplication_p.h
+++ b/src/gui/kernel/qguiapplication_p.h
@@ -109,6 +109,7 @@ public:
     void quit() override;
 
     bool shouldQuitInternal(const QWindowList &processedWindows);
+    void maybeQuitOnLastWindowClosed(QWindow *closedWindow);
 
     static void captureGlobalModifierState(QEvent *e);
     static Qt::KeyboardModifiers modifier_buttons;
diff --git a/src/gui/kernel/qwindow.cpp b/src/gui/kernel/qwindow.cpp
index e1733cbf46..cdb2534b2e 100644
--- a/src/gui/kernel/qwindow.cpp
+++ b/src/gui/kernel/qwindow.cpp
@@ -2268,6 +2268,18 @@ bool QWindow::close()
     return d->platformWindow->close();
 }
 
+bool QWindowPrivate::shouldTriggerQuitOnClose() const
+{
+    Q_Q(const QWindow);
+    return q->isTopLevel();
+}
+
+bool QWindowPrivate::shouldCancelQuitOnClose() const
+{
+    Q_Q(const QWindow);
+    return q->isVisible() && !q->transientParent() && q->type() != Qt::ToolTip;
+}
+
 /*!
     The expose event (\a ev) is sent by the window system when a window moves
     between the un-exposed and exposed states.
@@ -2444,17 +2456,8 @@ bool QWindow::event(QEvent *ev)
 
     case QEvent::Close:
         closeEvent(static_cast<QCloseEvent*>(ev));
-        if (ev->isAccepted()) {
-            Q_D(QWindow);
-            bool wasVisible = isVisible();
+        if (ev->isAccepted())
             destroy();
-            if (wasVisible) {
-                // FIXME: This check for visibility is a workaround for both QWidgetWindow
-                // and QWindow having logic to emit lastWindowClosed, and possibly quit the
-                // application. We should find a better way to handle this.
-                d->maybeQuitOnLastWindowClosed();
-            }
-        }
         break;
 
     case QEvent::Expose:
@@ -2806,34 +2809,6 @@ Q_GUI_EXPORT QWindowPrivate *qt_window_private(QWindow *window)
     return window->d_func();
 }
 
-void QWindowPrivate::maybeQuitOnLastWindowClosed()
-{
-    if (!QCoreApplication::instance())
-        return;
-
-    Q_Q(QWindow);
-    if (!q->isTopLevel())
-        return;
-
-    QWindowList list = QGuiApplication::topLevelWindows();
-    bool lastWindowClosed = true;
-    for (int i = 0; i < list.size(); ++i) {
-        QWindow *w = list.at(i);
-        if (!w->isVisible() || w->transientParent() || w->type() == Qt::ToolTip)
-            continue;
-        lastWindowClosed = false;
-        break;
-    }
-    if (lastWindowClosed) {
-        QGuiApplicationPrivate::emitLastWindowClosed();
-
-        if (QGuiApplication::quitOnLastWindowClosed()) {
-            QCoreApplicationPrivate *applicationPrivate = static_cast<QCoreApplicationPrivate*>(QObjectPrivate::get(QCoreApplication::instance()));
-            applicationPrivate->maybeQuit();
-        }
-    }
-}
-
 QWindow *QWindowPrivate::topLevelWindow(QWindow::AncestorMode mode) const
 {
     Q_Q(const QWindow);
diff --git a/src/gui/kernel/qwindow_p.h b/src/gui/kernel/qwindow_p.h
index fef8b4ca72..3eeafeff86 100644
--- a/src/gui/kernel/qwindow_p.h
+++ b/src/gui/kernel/qwindow_p.h
@@ -81,7 +81,6 @@ public:
 
     void init(QScreen *targetScreen = nullptr);
 
-    void maybeQuitOnLastWindowClosed();
 #ifndef QT_NO_CURSOR
     void setCursor(const QCursor *c = nullptr);
     bool applyCursor();
@@ -119,6 +118,9 @@ public:
 
     virtual void processSafeAreaMarginsChanged() {}
 
+    virtual bool shouldTriggerQuitOnClose() const;
+    virtual bool shouldCancelQuitOnClose() const;
+
     bool isPopup() const { return (windowFlags & Qt::WindowType_Mask) == Qt::Popup; }
     void setAutomaticPositionAndResizeEnabled(bool a)
     { positionAutomatic = resizeAutomatic = a; }