bug#67226: 30.0.50; Regression in previous-complete-history-element with empty input

[Eli Zaretskii <eliz@gnu.org>]

Stefan, any comments?

> Cc: Stefan Monnier <monnier@iro.umontreal.ca>, 67226@debbugs.gnu.org
> From: Juri Linkov <juri@linkov.net>
> Date: Thu, 16 Nov 2023 19:32:13 +0200
> 
> > When using previous-complete-history-element like:
> >
> > The behavior changed sometime recently, because
> >
> > When the input is empty it shows:
> >
> >  [No earlier matching history item]
> >
> > Previously it behaved like `previous-history-element` in that case.
> >
> > Is this intended due to some recent change or is it an issue?
> >
> > ```
> > Emacs -Q
> >
> > M-: (keymap-set minibuffer-local-map "<up>" #'previous-complete-history-element)
> >
> > M-x some-command1
> > M-x some-command2
> > M-x some-command3
> > M-x <up-arrow>
> > ```
> 
> The regression is on this line in `previous-matching-history-element`:
> 
>   (string-match (concat ".*\\(" regexp "\\)") match-string)
> 
> In GNU Emacs 29.1.90
> 
>   (string-match ".*\\(^\\)" "foo")
>   => 0
> 
> But in GNU Emacs 30.0.50
> 
>   (string-match ".*\\(^\\)" "foo")
>   => nil
> 
> Cc:ing Stefan.
> 
> 
> 
>