bug#68428: 29.1.90; info-xref-tests fails

[Eli Zaretskii <eliz@gnu.org>]

> From: Michael Albinus <michael.albinus@gmx.de>
> Cc: 68428@debbugs.gnu.org
> Date: Mon, 15 Jan 2024 12:59:03 +0100
> 
> Well, finally it is another bug. It is in function
> info-xref-subfile-p. This function tries to determine, whether a given
> file is an info subfile.
> 
> My emacs-29 branch is checked out in directory /home/albinus/src/emacs-29.
> So there is, for example, a call of
> 
> (info-xref-subfile-p "/home/albinus/src/emacs-29/info/auth.info")
> 
> The function tries to decompose the filename via the regexp
> "\\`\\(\\([^-]*-\\)*[^-]*\\)-[0-9]+\\(.*\\)\\'". This succeeds, and
> returns
> 
> (match-string 1 filename) => "/home/albinus/src/emacs"
> (match-string 3 filename) => "/info/auth.info"
> 
> This is wrong. string-match should return nil according to the
> intention. And the call of
> 
> (file-exists-p "/home/albinus/src/emacs/info/auth.info")
> 
> succeeds also, because my Emacs master branch is located in
> /home/albinus/src/emacs, and therefore
> "/home/albinus/src/emacs/info/auth.info" does exist.

Can you explain why you see the bug and I don't?  What exactly
triggers the bug, and why didn't we uncover it until now?

> The appended patch fixes this. Shall I install it in the emacs-29 or the
> master branch?

On master, please.  But first I'd like to understand the bug better.

Thanks.