GNU bug report logs - #33697
26.1; file-truename messes with match data

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: kevin.legouguec <at> gmail.com (Kévin Le Gouguec)
To: bug-gnu-emacs <at> gnu.org
Subject: 26.1; file-truename messes with match data
Date: Mon, 10 Dec 2018 22:02:09 +0100

Hi,

I set frame-title-format so that it displays the basename of the current
project's root folder for the active buffer.  However, my $HOME is under
version control; I do not want this particular "project" to show up in
the frame's title.

Here is the code that I use:

    (require 'subr-x)

    (defun my/project-name ()
      (when-let* ((project (project-current))
                  (root (car (project-roots project))))
        (when (not (file-equal-p root "~"))
          (file-name-nondirectory (string-trim-right root "/")))))

    (setq frame-title-format
          '(:eval
            (let ((project (my/project-name)))
              (concat (when project (format "[%s] " project)) "%b"))))

After adding the above to my .emacs, I started experiencing weird
failures with query-replace.  I managed to reproduce this with emacs -Q:

- evaluate the above
- move to the beginning of *scratch*
- M-% a RET b RET
⇒ perform-replace: Args out of range: #<buffer *scratch*>, 0, 2
  (point has moved after the first match)

I dug a bit and file-equal-p calls file-truename, whose first (cond …)
ends up calling string-match.  Although I did not delve much longer and
could be wrong, I imagine that query-replace finds the first match,
moves point to it, leaves the minibuffer; this causes frame-title-format
to be evaluated; file-equal-p calls file-truename, the global match data
is updated, then perform-replace gets confused about what to do.

Wrapping the (cond …) with (save-match-data …) solves the issue for me
(as does wrapping my/project-name).  I do not know if this is the
preferred way to address this; I do not even know if this is a "bug" (as
in, nobody said file-equal-p does *not* modify match data).


Thank you for your time.



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Message #8 received at 33697 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: kevin.legouguec <at> gmail.com (Kévin Le Gouguec)
Cc: 33697 <at> debbugs.gnu.org
Subject: Re: bug#33697: 26.1; file-truename messes with match data
Date: Tue, 11 Dec 2018 06:55:33 +0200

merge 33697 31586
thanks

> From: kevin.legouguec <at> gmail.com (Kévin Le Gouguec)
> Date: Mon, 10 Dec 2018 22:02:09 +0100
> 
> I set frame-title-format so that it displays the basename of the current
> project's root folder for the active buffer.  However, my $HOME is under
> version control; I do not want this particular "project" to show up in
> the frame's title.
> 
> Here is the code that I use:
> 
>     (require 'subr-x)
> 
>     (defun my/project-name ()
>       (when-let* ((project (project-current))
>                   (root (car (project-roots project))))
>         (when (not (file-equal-p root "~"))
>           (file-name-nondirectory (string-trim-right root "/")))))
> 
>     (setq frame-title-format
>           '(:eval
>             (let ((project (my/project-name)))
>               (concat (when project (format "[%s] " project)) "%b"))))
> 
> After adding the above to my .emacs, I started experiencing weird
> failures with query-replace.  I managed to reproduce this with emacs -Q:
> 
> - evaluate the above
> - move to the beginning of *scratch*
> - M-% a RET b RET
> ⇒ perform-replace: Args out of range: #<buffer *scratch*>, 0, 2
>   (point has moved after the first match)

This is bug#31586, please see the discussions there.

Message #15 received at 33697 <at> debbugs.gnu.org (full text, mbox):

From: Kévin Le Gouguec <kevin.legouguec <at> gmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 33697 <at> debbugs.gnu.org
Subject: Re: bug#33697: 26.1; file-truename messes with match data
Date: Tue, 11 Dec 2018 20:59:44 +0100

My bad, I assumed this would be a no-brainer and did not bother to
search the bug database.  I will be more diligent next time.

I would argue that this is different, since my code does not explicitly
call string-match; however bug#31586 seems to consider the bigger
picture, so I guess it makes more sense to focus on that one.

Thank you for pointing me towards this discussion!

Message #18 received at 33697 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Philipp <p.stephani2 <at> gmail.com>
Cc: 33697 <at> debbugs.gnu.org, 31586 <at> debbugs.gnu.org
Subject: Re: bug#33697: 26.1; file-truename messes with match data
Date: Fri, 06 May 2022 19:29:54 +0200

Philipp <p.stephani2 <at> gmail.com> writes:

> 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
>
> Backtrace:
>
> Debugger entered--Lisp error: (args-out-of-range #<buffer *scratch*> 0 1)
>   buffer-substring-no-properties(0 1)

(I'm going through old bug reports that unfortunately weren't resolved
at the time.)

I can reproduce this in Emacs 26.1, but not in Emacs 28.1, so I guess
this has been fixed in the years since it was reported, and I'm closing
this bug report.  If you're still seeing the problem in recent Emacs
versions, please respond to the debbugs address and we'll reopen.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

Message #23 received at 33697 <at> debbugs.gnu.org (full text, mbox):

From: Juri Linkov <juri <at> linkov.net>
To: Lars Ingebrigtsen <larsi <at> gnus.org>
Cc: Philipp <p.stephani2 <at> gmail.com>, 33697 <at> debbugs.gnu.org,
 31586 <at> debbugs.gnu.org
Subject: Re: bug#33697: 26.1; file-truename messes with match data
Date: Fri, 06 May 2022 20:49:19 +0300

>> 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
>>
>> Backtrace:
>>
>> Debugger entered--Lisp error: (args-out-of-range #<buffer *scratch*> 0 1)
>>   buffer-substring-no-properties(0 1)
>
> (I'm going through old bug reports that unfortunately weren't resolved
> at the time.)
>
> I can reproduce this in Emacs 26.1, but not in Emacs 28.1, so I guess
> this has been fixed in the years since it was reported, and I'm closing
> this bug report.  If you're still seeing the problem in recent Emacs
> versions, please respond to the debbugs address and we'll reopen.

This was fixed in bug#36328.

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