bug#54051: 29.0.50; latest master build with lucid crashes

[Eli Zaretskii <eliz@gnu.org>]

> Date: Fri, 18 Feb 2022 11:29:40 +0800
> From: merrick--- via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> 
> I can reliably reproduce this issue on my desktop running i3 on X11.
> 
> 1. run emacs with "emacs -Q"
> 2. M-x server-start
> 3. opens a terminal emulator and make it full screen (which covers the
> emacs frame)
> 4. run "emacsclient -c"
> 5. emacs crashes
> 
> Unfortunately I can't get backtrace from `./src/emacs -q -xrm
> 'Emacs.synchronous: true' since it hangs forever after doing the above
> steps.

The file etc/DEBUG in the Emacs source tree has some advice how to get
control to debugger in the "Getting control to the debugger" section.
It also has advice for how to investigate hangs in the "If the symptom
of the bug is that Emacs fails to respond" section.  Please try some
of that and see what information you can collect.

We need a backtrace from a 'Emacs.synchronous: true' session because
without that parameter X errors are not reported immediately when a
faulty X request is sent, but can be delayed by any number of Xlib
calls.  So the backtrace you produce without 'Emacs.synchronous true'
is not useful, since it doesn't show us what was the offending Xlib
call made by Emacs; instead, it shows some unrelated call.

Bottom line: the crucial information we need to investigate this bug
is which Xlib call in Emacs causes the crash in your case.

Thanks.