QApplication tries to close all windows on quit using closeAllWindows,
but closeAllWindows skips some windows, in particular any widget with
WA_DontShowOnScreen set.
QApplication then tries to verify that all windows have been closed,
and that logic should skip the same kind of windows as closeAllWindows
does.
We include WA_DontShowOnScreen so that widgets that are proxied via
QGraphicProxyWidget will not prevent the application from quitting.
There's still some divergence between closeAllWindows and the logic
in QApplication::event's quit handling, but aligning that requires
more work than this particular fix, and should probably also be
based on using the return value of tryCloseAllWindows() directly.
Change-Id: I2555eeee0cb04b8e736109fed57f37150efd1964
Fixes: QTBUG-81107
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>
5af73cd9db