GCC, with ubsan and optimization enabled, issues -Warray-bounds for
the cast from &polygonItem to QGraphicsTextItem*, because the latter
is-a QObject and the former is not, so the cast has to adjust the
pointer value to correct for the fact that QGraphicsItem is not the
first base class of QGraphicsTextItem:
qgraphicsitem.h:973:56: warning: array subscript -1 is outside array bounds of ‘QGraphicsPolygonItem [1]’ [-Warray-bounds]
973 | || (item && int(Item::Type) == item->type()) ? static_cast<T>(item) : nullptr;
| ^~~~~~~~~~~~~~~~~~~~
tst_qgraphicsitem.cpp:3193:26: note: while referencing ‘polygonItem’
Check the implementation is correct in this respect by not just
checking for nullptr or non-nullptr, but checking that the result
matches what dynamic_cast produces.
We can assume dynamic_cast works on QGraphicsItems because QPA is
using dynamic_cast, so both QtGui and QtWidgets need to have been
compiled with RTTI enabled.
This doesn't eliminate the GCC warning, but confirms that it is a
False Positive.
Pick-to: 6.9 6.8 6.5
Change-Id: Ifc262cb6e715e8e68c180855adc2467960da89a1
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
101427957b