David Edmundson authored Sep 17, 2020 and Albert Astals Cid committed Sep 29, 2020

winId() creates a QPlaformWindow; i.e a native xcb_window or wl_surface.
This makes sense for a toplevel which will be a real window.

If someone (in this case localize) uses kmainwindow as a subwidget
inside an existing window the current code will create a subwindow for
this widget. It's a very weird window, as the window is never actually
mapped so all contents are drawn as part of the parent window. Leaving
us in a very corrupt state.

Doing this on XCB is wasteful but the side effects are unnoticed. On
QtWayland things explode in weird ways.

BUG: 424024