bug#30874: 27.0.50; Emacs crashes

[Eli Zaretskii]

> From: Jan Synacek <jsynacek@redhat.com>
> Date: Tue, 20 Mar 2018 13:12:53 +0100
> Cc: 30874@debbugs.gnu.org
> 
> > Please show a C-level backtrace from the crash.
> 
> Since the reproducer is so trivial, I didn't consider it important,

It is always important.  I couldn't reproduce this on my system.

> but there you go (just basic backtrace, the full one is hilariously
> huge):

Thanks.  Sounds like a duplicate of bug#30045.

Can you run this in X synchronous mode, so that we see which operation
triggers the original X error?  etc/DEBUG tells how to do that under
"If you encounter X protocol errors".