bug#34690: 26.1; Emacs gets stuck when replacing text

[Eli Zaretskii <eliz@gnu.org>]

> Date: Tue, 2 Apr 2019 23:43:13 -0300
> From: Daniel Hernández <daniel@degu.cl>
> Cc: 34690@debbugs.gnu.org
> 
> > > (custom-set-faces
> > >  ;; custom-set-faces was added by Custom.
> > >  ;; If you edit it by hand, you could mess it up, so be careful.
> > >  ;; Your init file should contain only one such instance.
> > >  ;; If there is more than one, they won't work right.
> > >  '(default ((t (:family "Inconsolata" :foundry "unknown" :slant
> > >  normal :weight normal :height 128 :width normal)))))
> > 
> > Does (setq query-replace-from-to-separator " -> ") avoid the problem
> > (as suggested in Bug#30291)?
> 
> Yes, this solve the issue in the computer where I detected the issue. I
> have another computer where that code is not needed, because there is
> no problem with the inconsolata font.

It would be good to discover where Emacs loops with the problematic
font, so we could at least try to present some meaningful error
message, if not avoid this entirely.  It would help if someone who can
reproduce the problem used the technique in etc/DEBUG for finding the
place in the code where we loop.

Thanks.