Send MouseMove events without buttons if the press closed the popup

With nested popup widgets, pressing a mouse button on the lower
popup will close the active popup. MouseMove events that are generated
before the button is released again should not have that button
included, as it is likely to result in incorrect state handling in
the widget. This change removes all buttons from the MouseMove event,
which is the second best option.

This is mostly consistent with the behavior when closing a popup and
no other popup remains. The widget underneath will get MouseMove
events without the respective button included.

This change doesn't include a fix for the final release event, which
should ideally also not be delivered to the remaining popup, as it
never got a corresponding press event. Qt has already reset the states
in which it stores which widget received the press event at the time
the release is generated, such as qt_button_down and qt_popup_down.
So we can't separate a release grabbed by a newly opened popup (which
we want) from a release to the popup that became active after closing
(which we don't want).
However, widgets can more easily work around this issue, and the risk
of breaking things by changing the code further becomes too high.

Change-Id: I603bbdbc7e7355952d96ab77c5e2d2f1e6f94987
Fixes: QTBUG-82538
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
Reviewed-by: Gatis Paeglis <gatis.paeglis@qt.io>

1 files changed, 5 insertions, 3 deletions

diff --git a/src/widgets/kernel/qwidgetwindow.cpp b/src/widgets/kernel/qwidgetwindow.cpp
index 596343c52f..7b36699d5c 100644
--- a/src/widgets/kernel/qwidgetwindow.cpp
+++ b/src/widgets/kernel/qwidgetwindow.cpp
@@ -505,7 +505,7 @@ void QWidgetWindow::handleMouseEvent(QMouseEvent *event)
         QGuiApplicationPrivate::platformTheme()->themeHint(QPlatformTheme::ContextMenuOnMouseRelease).toBool() ?
         QEvent::MouseButtonRelease : QEvent::MouseButtonPress;
     if (QApplicationPrivate::inPopupMode()) {
-        QWidget *activePopupWidget = QApplication::activePopupWidget();
+        QPointer<QWidget> activePopupWidget = QApplication::activePopupWidget();
         QPoint mapped = event->pos();
         if (activePopupWidget != m_widget)
             mapped = activePopupWidget->mapFromGlobal(event->globalPos());
@@ -565,9 +565,11 @@ void QWidgetWindow::handleMouseEvent(QMouseEvent *event)
 #endif
             if ((event->type() != QEvent::MouseButtonPress)
                     || !(event->flags().testFlag(Qt::MouseEventCreatedDoubleClick))) {
-
+                // if the widget that was pressed is gone, then deliver move events without buttons
+                const auto buttons = event->type() == QEvent::MouseMove && qt_button_down == nullptr
+                                   ? Qt::NoButton : event->buttons();
                 QMouseEvent e(event->type(), widgetPos, event->windowPos(), event->screenPos(),
-                              event->button(), event->buttons(), event->modifiers(), event->source());
+                              event->button(), buttons, event->modifiers(), event->source());
                 e.setTimestamp(event->timestamp());
                 QApplicationPrivate::sendMouseEvent(receiver, &e, receiver, receiver->window(), &qt_button_down, qt_last_mouse_receiver);
                 qt_last_mouse_receiver = receiver;