Subject: Re: bug#31586: 27.0.50; `frame-title-format' doesn't save match data

From: Eli Zaretskii <[email-masked]>
Date: Fri, 25 May 2018 09:31:02 +0300

> From: Philipp <[email-masked]>
> Date: Thu, 24 May 2018 23:55:57 +0200
> 
> emacs -Q -eval "(setq frame-title-format '(\"\" (:eval (string-match \".\" \"a\"))))"
> 
> Then go to the first character in the scratch buffer (M-<), and run
> 
> M-% a RET b RET
> 
> The first time you attempt to replace something, Emacs will signal an
> error:
> 
> perform-replace: Args out of range: #<buffer *scratch*>, 0, 1

And this is an Emacs bug because...?  The :eval expression is yours,
so it's IMO your responsibility to protect it as needed.