GNU bug report logs - #77529
31.0.50; [Feature Request][VC] How can I get the current revision of the buffer opened by =vc-find-revision=?

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

From: jixiuf <jixiuf <at> qq.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 31.0.50; [Feature Request][VC] How can I get the current revision
 of the buffer opened by =vc-find-revision=?
Date: Fri, 04 Apr 2025 12:09:47 +0800

How can I retrieve the current revision when I'm in a buffer opened by
=vc-find-revision= ?

I'm attempting to write two commands: =vc-next-revision= and
=vc-prev-revision=, similar to =magit-blob-next= and
=magit-blob-previous=.

Currently, I obtain the revision from the buffer name (which might
support Git), but I don't consider this to be the best approach. Should
we add a local variable called =vc-revision=, similar to
=vc-parent-buffer=?

Alternatively, should Emacs implement =vc-next-revision= and
=vc-prev-revision= directly in =vc.el=?

----------------------------------

;;;###autoload
(defun vc-next-revision ()
  "Visit the next revision which modified the current file."
  (interactive)
  (let* ((buffname (buffer-name))
         (prev-buffer (current-buffer))
         (parent-buffer vc-parent-buffer)
         (fileset-arg (vc-deduce-fileset nil t))
         (backend (car fileset-arg))
         (filename (car (cadr fileset-arg)))
         rev next)
    (when parent-buffer
      ;; FIXME: support other bankend for find rev?
      (when (string-match "^\\([^~]+?\\)\\(?:\\.~\\([^~]+\\)~\\)?$" buffname)
        (setq rev (match-string 2 buffname)))
      (setq next (vc-call-backend backend 'next-revision
                                  filename rev))
      (kill-buffer prev-buffer)
      (if next
          (switch-to-buffer (vc-find-revision filename next))
        (find-file filename)
        (user-error "vc timemachine: You have reached the end of time")))))
;;;###autoload
(defun vct-prev-revision ()
  "Visit the prev revision which modified the current file."
  (interactive)
  (let* ((buffname (buffer-name))
         (cur-buffer (current-buffer))
         (parent-buffer vc-parent-buffer)
         (fileset-arg (vc-deduce-fileset nil t))
         (backend (car fileset-arg))
         (filename (car (cadr fileset-arg)))
         rev prev)
    ;; FIXME: support other bankend for find rev?
    (when (string-match "^\\([^~]+?\\)\\(?:\\.~\\([^~]+\\)~\\)?$" buffname)
      (setq rev (match-string 2 buffname)))
    (if rev
        (setq prev (vc-call-backend backend 'previous-revision
                                    filename rev))
      (setq prev (vc-short-revision filename)))
    (if prev
        (progn  (switch-to-buffer (vc-find-revision filename prev))
                (when parent-buffer (kill-buffer cur-buffer)))
      (user-error "vc timemachine: You have reached the beginning of time"))))

Message #8 received at 77529 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: jixiuf <jixiuf <at> qq.com>
Cc: 77529 <at> debbugs.gnu.org
Subject: Re: bug#77529: 31.0.50;
 [Feature Request][VC] How can I get the current revision of the
 buffer opened by =vc-find-revision=?
Date: Fri, 04 Apr 2025 14:02:50 +0300

> Date: Fri, 04 Apr 2025 12:09:47 +0800
> From:  jixiuf via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs <at> gnu.org>
> 
> How can I retrieve the current revision when I'm in a buffer opened by
> =vc-find-revision= ?
> 
> I'm attempting to write two commands: =vc-next-revision= and
> =vc-prev-revision=, similar to =magit-blob-next= and
> =magit-blob-previous=.

Emacs already has vc-git-next-revision, so if you need this only
for Git, the function is already there, you just need to wrap it with
a command.

As for vc-prev-revision, isn't that just SHA^, where SHA is the hash
of the revision used to call vc-prev-revision?

Message #11 received at 77529 <at> debbugs.gnu.org (full text, mbox):

From: jixiuf <jixiuf <at> qq.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 77529 <at> debbugs.gnu.org
Subject: Re: bug#77529: 31.0.50; [Feature Request][VC] How can I get the
 current revision of the buffer opened by =vc-find-revision=?
Date: Sat, 05 Apr 2025 15:41:28 +0800

Eli Zaretskii <eliz <at> gnu.org> writes:

>
> Emacs already has vc-git-next-revision, so if you need this only
> for Git, the function is already there, you just need to wrap it with
> a command.
>
> As for vc-prev-revision, isn't that just SHA^, where SHA is the hash
> of the revision used to call vc-prev-revision?

But how can I get the SHA of the current revision when I am in a buffer
opened by =vc-find-revision=?

Getting the SHA from the buffer name is not easy, as shown in the demo
below:

- 7f855b5297b..: Eli Zaretskii 2023-01-07 ; Fix description of etc/DOC  
- (origin/emacs-29)e9341119fe4..: Eli Zaretskii 2023-01-07 ; Fix documentation of etc/DOC  
- cae528457cb..: Eli Zaretskii 2023-01-01 ; Add 2023 to copyright years.  

(vc-git-previous-revision "doc/lispref/help.texi" "7f855b5297b")  
=> "remotes/origin/emacs-29"  

(vc-git-next-revision "doc/lispref/help.texi" "cae528457cb")  
=> "remotes/origin/emacs-29"  

(vc-find-revision "doc/lispref/help.texi" "remotes/origin/emacs-29")  
=> buffer-name: help.texi.~remotes_origin_emacs-29~  

As you can see, the SHA is "remotes_origin_emacs-29" (obtained from the
buffer name). I don’t know the true branch/tag name of
"remotes_origin_emacs-29"; it could be "remotes/origin/emacs-29" or
"remotes_origin_emacs-29."

Message #14 received at 77529 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: jixiuf <jixiuf <at> qq.com>
Cc: 77529 <at> debbugs.gnu.org
Subject: Re: bug#77529: 31.0.50; [Feature Request][VC] How can I get the
 current revision of the buffer opened by =vc-find-revision=?
Date: Sat, 05 Apr 2025 10:55:44 +0300

> From: jixiuf <jixiuf <at> qq.com>
> Cc: 77529 <at> debbugs.gnu.org
> Date: Sat, 05 Apr 2025 15:41:28 +0800
> 
> Eli Zaretskii <eliz <at> gnu.org> writes:
> 
> >
> > Emacs already has vc-git-next-revision, so if you need this only
> > for Git, the function is already there, you just need to wrap it with
> > a command.
> >
> > As for vc-prev-revision, isn't that just SHA^, where SHA is the hash
> > of the revision used to call vc-prev-revision?
> 
> But how can I get the SHA of the current revision when I am in a buffer
> opened by =vc-find-revision=?

That's the argument with which vc-find-revision was called, right?  So
the only change we might need is to record the revision in some
buffer-local variable, if we don't already do that (don't we show the
revision of the mode line?).

Message #17 received at 77529 <at> debbugs.gnu.org (full text, mbox):

From: jixiuf <jixiuf <at> qq.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 77529 <at> debbugs.gnu.org
Subject: Re: bug#77529: 31.0.50; [Feature Request][VC] How can I get the
 current revision of the buffer opened by =vc-find-revision=?
Date: Sat, 05 Apr 2025 17:53:25 +0800

[Message part 1 (text/plain, inline)]

Eli Zaretskii <eliz <at> gnu.org> writes:

>> But how can I get the SHA of the current revision when I am in a buffer
>> opened by =vc-find-revision=?
>
> That's the argument with which vc-find-revision was called, right?  So
> the only change we might need is to record the revision in some
> buffer-local variable, if we don't already do that (don't we show the
> revision of the mode line?).
Yes a buffer-local.

the 'revision' on the mode line is part of buffer name, not always a
revision.

(vc-find-revision "doc/lispref/help.texi" "remotes/origin/emacs-29"
'Git)

[20250405-174822.jpg (image/jpeg, inline)]

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