bug#44180: 28.0.50; Emacs frames won't redisplay unless resized

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sun, 25 Oct 2020 17:26:18 +0100
> From: Sascha Sadeghian <sadeghian@acm.org>
> Cc: Eric Abrahamsen <eric@ericabrahamsen.net>, 44180@debbugs.gnu.org
> 
> Let’s say we start with an Emacs GTK window and an xterm window side by
> side, so that each has 50% of the total screen width ("split" mode in
> i3). If I switch to "tabbed" mode now and select the Emacs tab, the
> Emacs frame is unresponsive, and its contents are not redrawn any more.
> 
> This didn’t happen before 2c0cd90083.
> 
> Here is a quick demo with emacs -Q:
> 
>   https://webterm.io/bug-gnu-emacs/44180-working.webm
>   https://webterm.io/bug-gnu-emacs/44180-broken.webm
> 
> The bug can be reproduced with a single frame.
> 
> The confusing part is probably that for this frozen frame, keyboard
> input is still working, so buffers can be edited, while the edits are
> only visible in other, non-frozen frames (for example, a second
> emacsclient frame showing the same buffers). The GTK menu and toolbar
> are also not affected.

This is actually not confusing at all, it is entirely expected.

> Hope this helps!

I've just explained to Eric which information would be helpful to make
some progress here.  If you can help collecting that information, it
will be really appreciated.

Thanks.