Changing the value of window.hide_decoration makes qutebrowser stop handling bindings

[emanuele6]

Version info: https://paste.the-compiler.org/view/45600897

qutebrowser v2.5.2
Git commit: 
Backend: QtWebEngine 5.15.10, based on Chromium 87.0.4280.144
Qt: 5.15.5 (compiled 5.15.4)

Does the bug happen if you start with --temp-basedir?:
Yes.

Description
qutebrowser goes into a buggy state in which bindings stop being handled until the window gets refocused (similar to #7234) when the value of window.hide_decoration changes.

How to reproduce
Unlike #7234, I was able to reproduce this bug in window managers other than bspwm (I tested it on bspwm and mwm) so I think it is likely reproducible with any window manager.

Steps:

• run :set window.hide_decoration true (or :set window.hide_decoration false)
• see that bindings stop being handled until you focus another window and refocus qutebrowser.

Video of the bug being reproduced under mwm

qutebug.mp4

[toofar]

I can reproduce with awesome on X11. There's nothing in the debug logs I could see. Possibly it's a Qt issue, possibly it's us doing things in a less than ordeal order, possibly we could work around it by raising again or something.
Anyway I'm putting the low priority label on it because it's the first (?) time it's came up and there is an easily available workaround.

[rien333]

I think I once implemented the code, but since I don't really use the functionality anymore nor have much time for programming, it's been more or less sitting there rotting (see also #4067). IIRC Qt changed something that once worked.

If I have time left over my summer break (should be in a month or so) I might finally look into it, but don't count on it.

possibly we could work around it by raising again or something

Sounds hacky, but I'm not totally against it. I should really look into the documentation, but I think hiding window decorations is actually meant for auxiliary rather than main windows, and if so, we could consider this whole setting a big hack.

[emanuele6]

One easy (but maybe "lazy") solution could be to make window.hide_decoration require a restart (like colors.webpage.darkmode.enabled for example).