435da40cc0
Instead of aggregating a QMutableSinglePointEvent by value, which
depends on the QEvent copy assignment operator, and casting it to a
QMouseEvent that it isn't, introduce QEventStorage which is a bit like
std::optional, but, by each event subclass befriending it, can store
event copies by-value, unlike clone(), which is restricted to the
heap. We could have befriended std::optional<QMouseEvent>, too, but by
adding our own type in _p.h, we can better control which code uses
this dangerous construct.
Added a guard to avoid clobbering lastMouseEvent with a copy of itself
in storeMouseEvent(). Before, we'd self-assign to lastMouseEvent,
which didn't invalidate the reference. Now, a store() is the
equivalent of a dtor + copy constructor, so we need to be a bit more
careful.
Fixes UBSan reports when running tst_qgraphicsview:
qgraphicsview/qgraphicsview.cpp:612:27: runtime error: downcast of address 0x61a000035e90 which does not point to an object of type 'QMouseEvent'
0x61a000035e90: note: object is of type 'QMutableSinglePointEvent'
00 00 00 00 30 47 ef 8b 99 7f 00 00 02 00 00 00 00 00 00 e0 d0 91 00 00 20 60 00 00 00 00 00 00
^~~~~~~~~~~~~~~~~~~~~~~
vptr for 'QMutableSinglePointEvent'
#0 0x7f99a27c7a47 in QGraphicsViewPrivate::replayLastMouseEvent() qgraphicsview.cpp:612
qgraphicsview.cpp:653:39: runtime error: member call on address 0x61a0000fe290 which does not point to an object of type 'QMouseEvent'
0x61a0000fe290: note: object is of type 'QMutableSinglePointEvent'
00 00 00 00 30 47 ef 8b 99 7f 00 00 05 00 00 00 00 00 00 e0 d0 91 00 00 20 60 00 00 00 00 00 00
^~~~~~~~~~~~~~~~~~~~~~~
vptr for 'QMutableSinglePointEvent'
#0 0x7f99a27c3609 in QGraphicsViewPrivate::mouseMoveEventHandler(QMouseEvent*) qgraphicsview.cpp:653
#1 0x7f99a27c7832 in QGraphicsViewPrivate::replayLastMouseEvent() qgraphicsview.cpp:612
qgraphicsview.cpp:654:37: runtime error: member call on address 0x61a0000fe290 which does not point to an object of type 'QMouseEvent'
0x61a0000fe290: note: object is of type 'QMutableSinglePointEvent'
00 00 00 00 30 47 ef 8b 99 7f 00 00 05 00 00 00 00 00 00 e0 d0 91 00 00 20 60 00 00 00 00 00 00
^~~~~~~~~~~~~~~~~~~~~~~
vptr for 'QMutableSinglePointEvent'
#0 0x7f99a27c358b in QGraphicsViewPrivate::mouseMoveEventHandler(QMouseEvent*) qgraphicsview.cpp:654
#1 0x7f99a27c7832 in QGraphicsViewPrivate::replayLastMouseEvent() qgraphicsview.cpp:612
Task-number: QTBUG-99563
Change-Id: Ib642d416b8aef98c7fd8b1fa164ec2449189992a
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>
(cherry picked from commit dd264cc9c00e09eb995f1c6f9b1fd651f1d4b2f4)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>