The method calls show() on a dock widget group window, when the window
flags have changed. When all of its contained, tabbed dock widgets are
programmatically hidden or docked on the main window, an empty group
window is shown.
This patch implements bool hasVisibleDockWidgets(). It returns true, if
at least one of the group window's dockwidget children is not hidden.
It replaces show() by setVisible(), passing the return value of
hasVisibleChildren().
It adapts tst_QDockWidget::floatingTabs() to test the fix.
(Drive-by: remove dead code)
Fixes: QTBUG-115058
Pick-to: 6.6 6.5 6.2
Change-Id: Ifb8e2450e91a7c78decc06f592e160631ca2faf5
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>
e03bc88a80