Propagate application termination requests through QPA

Instead of having each platform plugin deal with application termination
in their own weird ways, we now have a QPA API to signal that the system
requested the application to terminate.

On the QGuiApplication side this results in a Quit event being sent to
the application, which triggers the default behavior of closing all app
windows, and then finally calling QCoreApplication::quit().

The quit event replaces the misuse of a close event being sent to the
application. Close events are documented as being sent to windows.

The close events that are sent to individual windows as part of the
quit process can be ignored. This will skip the final quit() of
the application, and also inform the platform that the quit was
not accepted, in case that should be propagated further.

In the future the logic for closing windows should be unified
between the various approaches in closeAllWindows, shouldQuit,
and friends.

Change-Id: I0ed7f1c0d3f0bf1a755e1dd4066e1575fc3a28e1
Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>

1 files changed, 8 insertions, 11 deletions

diff --git a/src/widgets/kernel/qapplication.cpp b/src/widgets/kernel/qapplication.cpp
index 3223781b63..dfa1bc23b1 100644
--- a/src/widgets/kernel/qapplication.cpp
+++ b/src/widgets/kernel/qapplication.cpp
@@ -1866,22 +1866,19 @@ void QApplication::aboutQt()
 bool QApplication::event(QEvent *e)
 {
     Q_D(QApplication);
-    if(e->type() == QEvent::Close) {
-        QCloseEvent *ce = static_cast<QCloseEvent*>(e);
-        ce->accept();
+    if (e->type() == QEvent::Quit) {
         closeAllWindows();
-
-        const QWidgetList list = topLevelWidgets();
-        for (auto *w : list) {
+        for (auto *w : topLevelWidgets()) {
             if (w->isVisible() && !(w->windowType() == Qt::Desktop) && !(w->windowType() == Qt::Popup) &&
                  (!(w->windowType() == Qt::Dialog) || !w->parentWidget())) {
-                ce->ignore();
-                break;
+                e->ignore();
+                return true;
             }
         }
-        if (ce->isAccepted()) {
-            return true;
-        }
+        // Explicitly call QCoreApplication instead of QGuiApplication so that
+        // we don't let QGuiApplication close any windows we skipped earlier in
+        // closeAllWindows(). FIXME: Unify all this close magic through closeAllWindows.
+        return QCoreApplication::event(e);
 #ifndef Q_OS_WIN
     } else if (e->type() == QEvent::LocaleChange) {
         // on Windows the event propagation is taken care by the