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>

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()

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;

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);

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; }

src/widgets/kernel/qapplication.cpp

@@ -3342,6 +3342,10 @@ bool QApplication::notify(QObject *receiver, QEvent *e)
         break;
     }
 
+    // We don't call QGuiApplication::notify here, so we need to duplicate the logic
+    if (e->type() == QEvent::Close && receiver->isWindowType() && res)
+        d->maybeQuitOnLastWindowClosed(static_cast<QWindow *>(receiver));
+
     return res;
 }
 

src/widgets/kernel/qwidget.cpp

@@ -8399,8 +8399,6 @@ bool QWidgetPrivate::handleClose(CloseMode mode)
     QPointer<QWidget> that = q;
     QPointer<QWidget> parentWidget = (q->parentWidget() && !QObjectPrivate::get(q->parentWidget())->wasDeleted) ? q->parentWidget() : nullptr;
 
-    bool quitOnClose = q->testAttribute(Qt::WA_QuitOnClose);
-
     if (data.in_destructor)
         mode = CloseNoEvent;
 
@@ -8420,30 +8418,6 @@ bool QWidgetPrivate::handleClose(CloseMode mode)
     if (!that.isNull() && !q->isHidden())
         q->hide();
 
-    // Attempt to close the application only if this has WA_QuitOnClose set and a non-visible parent
-    quitOnClose = quitOnClose && (parentWidget.isNull() || !parentWidget->isVisible());
-
-    if (quitOnClose) {
-        /* if there is no non-withdrawn primary window left (except
-           the ones without QuitOnClose), we emit the lastWindowClosed
-           signal */
-        QWidgetList list = QApplication::topLevelWidgets();
-        bool lastWindowClosed = true;
-        for (int i = 0; i < list.size(); ++i) {
-            QWidget *w = list.at(i);
-            if (!w->isVisible() || w->parentWidget() || !w->testAttribute(Qt::WA_QuitOnClose))
-                continue;
-            lastWindowClosed = false;
-            break;
-        }
-        if (lastWindowClosed) {
-            QGuiApplicationPrivate::emitLastWindowClosed();
-            QCoreApplicationPrivate *applicationPrivate = static_cast<QCoreApplicationPrivate*>(QObjectPrivate::get(QCoreApplication::instance()));
-            applicationPrivate->maybeQuit();
-        }
-    }
-
-
     if (!that.isNull()) {
         data.is_closing = false;
         if (q->testAttribute(Qt::WA_DeleteOnClose)) {

src/widgets/kernel/qwidgetwindow.cpp

@@ -115,6 +115,9 @@ public:
         if (QWidget *widget = q->widget())
             QWidgetPrivate::get(widget)->updateContentsRect();
     }
+
+    bool shouldTriggerQuitOnClose() const override;
+    bool shouldCancelQuitOnClose() const override;
 };
 
 QRectF QWidgetWindowPrivate::closestAcceptableGeometry(const QRectF &rect) const
@@ -843,6 +846,37 @@ void QWidgetWindow::handleCloseEvent(QCloseEvent *event)
     event->setAccepted(accepted);
 }
 
+bool QWidgetWindowPrivate::shouldTriggerQuitOnClose() const
+{
+    Q_Q(const QWidgetWindow);
+    QWidget *widget = q->widget();
+
+    // Closing a window without WA_QuitOnClose should stop us from even
+    // looking at the other windows. Otherwise we might find that all the
+    // other windows miss WA_QuitOnClose as well, and end up quitting,
+    // but that's not what the user intended.
+    if (!widget->testAttribute(Qt::WA_QuitOnClose))
+        return false;
+
+    // Qt::Tool windows do not have WA_QuitOnClose set by default, which
+    // means that if you open a dialog from one, and the tool window is
+    // the only remaining window, then closing the dialog would result
+    // in quitting the application. To prevent this we check if the
+    // closed widget has a visible parent (the Qt:Tool window in this
+    // case), and if so bail out.
+    if (widget->parentWidget() && widget->parentWidget()->isVisible())
+        return false;
+
+    return true;
+}
+
+bool QWidgetWindowPrivate::shouldCancelQuitOnClose() const
+{
+    Q_Q(const QWidgetWindow);
+    QWidget *w = q->widget();
+    return w->isVisible() && !w->parentWidget() & w->testAttribute(Qt::WA_QuitOnClose);
+}
+
 #if QT_CONFIG(wheelevent)
 
 void QWidgetWindow::handleWheelEvent(QWheelEvent *event)