Warn, don't crash during nested delivery of mouse or touch presses

If during delivery of a mouse press, user code calls qApp->sendEvent()
with another mouse press, then when delivery of the nested event is
finished, we call QQuickPointerMouseEvent::reset(nullptr).  Then when
delivery of the original mouse press resumes, crashes are possible
because most of the code assumes that QQuickPointerEvent::m_event is
not null during delivery.

Change-Id: Id65b1f2f64351e40d03bcd4f4d16693d616729da
Fixes: QTBUG-70898
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

1 files changed, 8 insertions, 0 deletions

diff --git a/src/quick/items/qquickwindow.cpp b/src/quick/items/qquickwindow.cpp
index 1c44afc594..53c0231f87 100644
--- a/src/quick/items/qquickwindow.cpp
+++ b/src/quick/items/qquickwindow.cpp
@@ -2508,6 +2508,10 @@ bool QQuickWindowPrivate::deliverPressOrReleaseEvent(QQuickPointerEvent *event,
     }
 
     for (QQuickItem *item : targetItems) {
+        if (!event->m_event) {
+            qWarning("event went missing during delivery! (nested sendEvent() is not allowed)");
+            break;
+        }
         if (!handlersOnly && sendFilteredPointerEvent(event, item)) {
             if (event->isAccepted()) {
                 for (int i = 0; i < event->pointCount(); ++i)
@@ -2521,6 +2525,10 @@ bool QQuickWindowPrivate::deliverPressOrReleaseEvent(QQuickPointerEvent *event,
         // nor to any item which already had a chance to filter.
         if (skipDelivery.contains(item))
             continue;
+        if (!event->m_event) {
+            qWarning("event went missing during delivery! (nested sendEvent() is not allowed)");
+            break;
+        }
         deliverMatchingPointsToItem(item, event, handlersOnly);
         if (event->allPointsAccepted())
             handlersOnly = true;