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>

3 files changed, 38 insertions, 26 deletions

diff --git a/src/widgets/kernel/qapplication.cpp b/src/widgets/kernel/qapplication.cpp
index 9069b9005d..74868077b3 100644
--- a/src/widgets/kernel/qapplication.cpp
+++ b/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;
 }
 
diff --git a/src/widgets/kernel/qwidget.cpp b/src/widgets/kernel/qwidget.cpp
index dcd3d1f1d9..a92454547a 100644
--- a/src/widgets/kernel/qwidget.cpp
+++ b/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-        /* if there is no non-withdrawn primary window left (except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)) {
diff --git a/src/widgets/kernel/qwidgetwindow.cpp b/src/widgets/kernel/qwidgetwindow.cpp
index 80e9b1ab5c..0d73e55719 100644
--- a/src/widgets/kernel/qwidgetwindow.cpp
+++ b/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)