The method traversed QDockAreaLayoutInfo::item_list, to identify
dock widgets tabbed with the QDockWidget argument in a tab bar
It relied on bool QDockAreLayoutInfo::tabbed, which is set to true, when
a QMainWindowTabBar is to be added to a QDockAreaLayoutInfo. This flag
isn't cleared, when the second last dock widget is removed from the
tab bar. It can't be replaced by QMainWindowLayout::isDockWidgetTabbed,
because the flag also represents intermediate states, where e.g. a dock
widget is hovered over, prepares to become a floating tab and then rolls
back, because hovering doesn't result in a drop. In that case, tabbed
must become true, which the dock widget isn't actually tabbed.
Furthermore, the way to traverse item_list didn't find dock widgets
in a floating tab. In that case, tabifiedDockWidgets() wrongly returned
an empty list.
To fix both issues, refactor QMainWindow::tabifiedDockWidgets() to read
the list of dock widgets directly from the QMainWindowTabBar.
Add tests in tst_QDockWidget::floatingTabs() and
updateTabBarOnVisibilityChanged()
Fixes: QTBUG-122001
Pick-to: 6.7 6.6 6.5
Change-Id: Ia9eb3711be642101261f34ee447521cc6accc20c
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
cd2a3e970a