GNU bug report logs - #31764
26.1; Point in VC change log is not centered as documented

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

From: Carlos Pita <carlosjosepita <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 26.1; Point in VC change log is not centered as documented
Date: Fri, 08 Jun 2018 16:23:40 -0300

The documentation states [1]:

  Point is centered at the revision of the file currently being
  visited. With a prefix argument, the command prompts for the revision to
  center on, and the maximum number of revisions to display.

But I get a log which is sorted from most recent to oldest revision with
the point positioned at the end. This is not only different from the
documented behavior but also very inconvenient since the initial
revision is probably the least interesting one.

I'm testing this in a simple git repository with a few revisions of
one file.

[1] https://www.gnu.org/software/emacs/draft/manual/html_node/emacs/VC-Change-Log.html#VC-Change-Log

---


In GNU Emacs 26.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.22.30)
 of 2018-05-29 built on juergen
Windowing system distributor 'The X.Org Foundation', version 11.0.11906000
System Description:	Manjaro Linux

Recent messages:
previous-line: Beginning of buffer [19 times]
Checking out /tmp/repo/x.txt.~c952114056dcaf2a9f3819efca2bcb6d7a9e216f~...done
C-c C-c is undefined
Mark set
Press C-c C-c when you are done editing.
Enter a change comment.  Type C-c C-c when done
Checking in /tmp/repo/x.txt...done
Mark set
Quit [3 times]
funcall-interactively: End of buffer

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Message #8 received at 31764 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Carlos Pita <carlosjosepita <at> gmail.com>
Cc: 31764 <at> debbugs.gnu.org
Subject: Re: bug#31764: 26.1;
 Point in VC change log is not centered as documented
Date: Fri, 08 Jun 2018 22:38:47 +0300

> From: Carlos Pita <carlosjosepita <at> gmail.com>
> Date: Fri, 08 Jun 2018 16:23:40 -0300
> 
> The documentation states [1]:
> 
>   Point is centered at the revision of the file currently being
>   visited. With a prefix argument, the command prompts for the revision to
>   center on, and the maximum number of revisions to display.
> 
> But I get a log which is sorted from most recent to oldest revision with
> the point positioned at the end. This is not only different from the
> documented behavior but also very inconvenient since the initial
> revision is probably the least interesting one.

I cannot reproduce this.  I get the documented behavior.

Do you see that in "emacs -Q"?

Message #11 received at 31764 <at> debbugs.gnu.org (full text, mbox):

From: Carlos Pita <carlosjosepita <at> gmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 31764 <at> debbugs.gnu.org
Subject: Re: bug#31764: 26.1;
 Point in VC change log is not centered as documented
Date: Fri, 8 Jun 2018 16:57:33 -0300

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

Sure. Consider this example:

/tmp:: mkdir test-repo
/tmp:: cd test-repo/
/tmp/test-repo:: git init
Initialized empty Git repository in /tmp/test-repo/.git/
/tmp/test-repo:: echo 1 > test-file
/tmp/test-repo:: git add test-file
/tmp/test-repo:: git commit -am rev1
/tmp/test-repo:master: echo 2 > test-file
/tmp/test-repo:master: git commit -am rev2
/tmp/test-repo:master: echo 3 > test-file
/tmp/test-repo:master: git commit -am rev3
/tmp/test-repo:master: echo 4 > test-file
/tmp/test-repo:master: git commit -am rev4

Now I run `emacs -Q test-file` and type C-x v l and get the window
shown in the attached screenshot.

[Screenshot from 2018-06-08 16-56-37.png (image/png, attachment)]

Message #14 received at 31764 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Carlos Pita <carlosjosepita <at> gmail.com>
Cc: 31764 <at> debbugs.gnu.org
Subject: Re: bug#31764: 26.1;
 Point in VC change log is not centered as documented
Date: Fri, 08 Jun 2018 23:12:29 +0300

> From: Carlos Pita <carlosjosepita <at> gmail.com>
> Date: Fri, 8 Jun 2018 16:57:33 -0300
> Cc: 31764 <at> debbugs.gnu.org
> 
> Sure. Consider this example:
> 
> /tmp:: mkdir test-repo
> /tmp:: cd test-repo/
> /tmp/test-repo:: git init
> Initialized empty Git repository in /tmp/test-repo/.git/
> /tmp/test-repo:: echo 1 > test-file
> /tmp/test-repo:: git add test-file
> /tmp/test-repo:: git commit -am rev1
> /tmp/test-repo:master: echo 2 > test-file
> /tmp/test-repo:master: git commit -am rev2
> /tmp/test-repo:master: echo 3 > test-file
> /tmp/test-repo:master: git commit -am rev3
> /tmp/test-repo:master: echo 4 > test-file
> /tmp/test-repo:master: git commit -am rev4
> 
> Now I run `emacs -Q test-file` and type C-x v l and get the window
> shown in the attached screenshot.

Strange.  I just did all of these steps, and I still get the
documented behavior.

What version of Git do you have?  (Not that I can explain how that
could matter.)

Message #17 received at 31764 <at> debbugs.gnu.org (full text, mbox):

From: Carlos Pita <carlosjosepita <at> gmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 31764 <at> debbugs.gnu.org
Subject: Re: bug#31764: 26.1;
 Point in VC change log is not centered as documented
Date: Fri, 8 Jun 2018 17:15:10 -0300

/tmp/test-repo:master: git --version

git version 2.17.1

/tmp/test-repo:master: cat ~/.gitconfig

[user]
    name = memeplex
    email = carlosjosepita <at> gmail.com
[credential]
    helper = cache --timeout=3600
[pager]
    status = true

I'm going to debug this later and see what I find out.

Message #20 received at 31764 <at> debbugs.gnu.org (full text, mbox):

From: Carlos Pita <carlosjosepita <at> gmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 31764 <at> debbugs.gnu.org
Subject: Re: bug#31764: 26.1;
 Point in VC change log is not centered as documented
Date: Fri, 8 Jun 2018 18:28:55 -0300

AFAICS what I'm observing is consistent with the docstrings of
vc-print-log and vc-print-log-internal:

vc-print-log
    It is bound to C-x v l
    ...
    If WORKING-REVISION is non-nil, leave point at that revision.
    ...
    When called interactively with a prefix argument, prompt for
    WORKING-REVISION and LIMIT.

vc-print-log-internal
   ...
   Leave point at WORKING-REVISION, if it is non-nil.

So without a prefix I'm indeed passing a nil working-revision argument
(I checked this with edebug).

Now, when I pass a prefix argument it asks me for a revision (default
is the last one) but it's again unable to set the point at that
revision. The default revision is shown as "last revision" and its
value is nil (so despite the ambiguity in the docstrings, no prefix
arg invocation should go to "last revision" too).

In the call to vc-log-internal-common goto-location-func is nil. This
is the next to last argument which is passed by vc-print-log-internal
with value:

       ;; When it's nil, point really shouldn't move (bug#15322).
       (when working-revision
         (lambda (bk)
           (vc-call-backend bk 'show-log-entry working-revision)))

So it's no surprise the point is not being moved around at all. But
the comment is not right: nil is "last revision". Now, #15322 is a
very old bug so maybe the representation of the "last revision"
changed since then?

Message #23 received at 31764 <at> debbugs.gnu.org (full text, mbox):

From: Carlos Pita <carlosjosepita <at> gmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 31764 <at> debbugs.gnu.org
Subject: Re: bug#31764: 26.1;
 Point in VC change log is not centered as documented
Date: Fri, 8 Jun 2018 18:47:40 -0300

One could say that the right fix there is to bind C-x v l to a call
that explicitly pass the revision for the current file. But then it's
also necessary to modify the default value for the prefix case, since
it's reading the default as nil.
I'm curious about how is this working for you. Maybe it was fixed
since 26.1 release.

Message #26 received at 31764 <at> debbugs.gnu.org (full text, mbox):

From: Carlos Pita <carlosjosepita <at> gmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 31764 <at> debbugs.gnu.org
Subject: Re: bug#31764: 26.1;
 Point in VC change log is not centered as documented
Date: Fri, 8 Jun 2018 19:10:38 -0300

As a workaround I installed this advice:

(advice-add 'vc-print-log
        :filter-args (lambda (args)
               (cons (or (car args)
                     (vc-working-revision (buffer-file-name)))
                 (cdr args))))

The default that it sets feels like the right fix (so that nil could
mean "don't move") to me but I'm not sure.

Message #29 received at 31764 <at> debbugs.gnu.org (full text, mbox):

From: Noam Postavsky <npostavs <at> gmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: Carlos Pita <carlosjosepita <at> gmail.com>, 31764 <at> debbugs.gnu.org
Subject: Re: bug#31764: 26.1;
 Point in VC change log is not centered as documented
Date: Fri, 08 Jun 2018 20:29:42 -0400

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

>> From: Carlos Pita <carlosjosepita <at> gmail.com>
>> Date: Fri, 8 Jun 2018 16:57:33 -0300
>> Cc: 31764 <at> debbugs.gnu.org

>> Now I run `emacs -Q test-file` and type C-x v l and get the window
>> shown in the attached screenshot.
>
> Strange.  I just did all of these steps, and I still get the
> documented behavior.
>
> What version of Git do you have?  (Not that I can explain how that
> could matter.)

I can reproduce this on GNU/Linux, but not on Windows (both tested with
latest emacs-26).

Message #32 received at 31764 <at> debbugs.gnu.org (full text, mbox):

From: Carlos Pita <carlosjosepita <at> gmail.com>
To: Noam Postavsky <npostavs <at> gmail.com>
Cc: Eli Zaretskii <eliz <at> gnu.org>, 31764 <at> debbugs.gnu.org
Subject: Re: bug#31764: 26.1;
 Point in VC change log is not centered as documented
Date: Fri, 8 Jun 2018 21:57:37 -0300

I can confirm that the same happens with the latest from master.

Message #35 received at 31764 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Noam Postavsky <npostavs <at> gmail.com>
Cc: carlosjosepita <at> gmail.com, 31764 <at> debbugs.gnu.org
Subject: Re: bug#31764: 26.1;
 Point in VC change log is not centered as documented
Date: Sat, 09 Jun 2018 09:46:42 +0300

> From: Noam Postavsky <npostavs <at> gmail.com>
> Cc: Carlos Pita <carlosjosepita <at> gmail.com>,  31764 <at> debbugs.gnu.org
> Date: Fri, 08 Jun 2018 20:29:42 -0400
> 
> Eli Zaretskii <eliz <at> gnu.org> writes:
> 
> >> From: Carlos Pita <carlosjosepita <at> gmail.com>
> >> Date: Fri, 8 Jun 2018 16:57:33 -0300
> >> Cc: 31764 <at> debbugs.gnu.org
> 
> >> Now I run `emacs -Q test-file` and type C-x v l and get the window
> >> shown in the attached screenshot.
> >
> > Strange.  I just did all of these steps, and I still get the
> > documented behavior.
> >
> > What version of Git do you have?  (Not that I can explain how that
> > could matter.)
> 
> I can reproduce this on GNU/Linux, but not on Windows (both tested with
> latest emacs-26).

Isn't that strange?  The code involved isn't platform specific.

On a hunch, I suggest to set switch-to-buffer-preserve-window-point to
nil, and see if that makes the problem disappear.  If it does, then
the difference between platforms is that one of them changes buffers
in a different sequence.

Message #38 received at 31764 <at> debbugs.gnu.org (full text, mbox):

From: Carlos Pita <carlosjosepita <at> gmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 31764 <at> debbugs.gnu.org, Noam Postavsky <npostavs <at> gmail.com>
Subject: Re: bug#31764: 26.1;
 Point in VC change log is not centered as documented
Date: Sat, 9 Jun 2018 11:18:10 -0300

Sadly it doesn't improve matters, Eli.

Below I'm repeating the conclusions of my debugging session in a more
orderly fashion:

1) `C-x v l` is bound to vc-print-log

2) vc-print-log takes an optional working-revision argument. When
called with a prefix argument, working-revision is prompted for.

3) In both cases (prompted or not) the default value for this argument is nil.

4) vc-print-log calls (vc-print-log-internal backend files
working-revision nil limit)

5) Then vc-print-log-internal calls vc-log-internal-common.

6) This last function takes a goto-location-func argument that the
caller is passing as the result of:

       ;; When it's nil, point really shouldn't move (bug#15322).
       (when working-revision
         (lambda (bk)
           (vc-call-backend bk 'show-log-entry working-revision)))

that is, nil by default.

7) vc-log-internal-common only moves the point when goto-location-func
is not nil:

       (when goto-location-func
         (funcall goto-location-func backend)
         (setq vc-sentinel-movepoint (point)))


So I'm really failing to see how this could work at all.

Besides, there is the point that this advice, that changes the nil
default for the working version of the current buffer, makes it work
as documented:

(advice-add 'vc-print-log
        :filter-args (lambda (args)
               (cons (or (car args)
                     (and (buffer-file-name)
                      (vc-working-revision (buffer-file-name))))
                 (cdr args))))

Message #41 received at 31764 <at> debbugs.gnu.org (full text, mbox):

From: Noam Postavsky <npostavs <at> gmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: carlosjosepita <at> gmail.com, 31764 <at> debbugs.gnu.org
Subject: Re: bug#31764: 26.1;
 Point in VC change log is not centered as documented
Date: Mon, 11 Jun 2018 20:10:17 -0400

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

tags 31764 + patch
quit

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

>> I can reproduce this on GNU/Linux, but not on Windows (both tested with
>> latest emacs-26).
>
> Isn't that strange?  The code involved isn't platform specific.

Looks like a matter of timing, if I add a (sit-for 1) to beginning of
vc-exec-after (or use edebug), then I can reproduce on Windows too.
Adding a save-excursion seems to fix it.

[v1-0001-Keep-vc-print-log-from-putting-point-at-buffer-en.patch (text/x-diff, inline)]

From 895d29eb6b010093245a67d7f05808d765195b7a Mon Sep 17 00:00:00 2001
From: Noam Postavsky <npostavs <at> gmail.com>
Date: Mon, 11 Jun 2018 20:00:54 -0400
Subject: [PATCH v1] Keep vc-print-log from putting point at buffer end
 (Bug#31764)

* lisp/vc/vc.el (vc-print-log-internal): Use `save-excursion' around
`vc-print-log-setup-buttons'.
---
 lisp/vc/vc.el | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/lisp/vc/vc.el b/lisp/vc/vc.el
index 93e9c25cbf..41a76e0007 100644
--- a/lisp/vc/vc.el
+++ b/lisp/vc/vc.el
@@ -2256,8 +2256,9 @@ vc-print-log-internal
 	 (vc-call-backend bk 'print-log files-arg buf shortlog
                           (when is-start-revision working-revision) limit))
        (lambda (_bk _files-arg ret)
-	 (vc-print-log-setup-buttons working-revision
-				     is-start-revision limit ret))
+         (save-excursion
+           (vc-print-log-setup-buttons working-revision
+                                       is-start-revision limit ret)))
        ;; When it's nil, point really shouldn't move (bug#15322).
        (when working-revision
          (lambda (bk)
-- 
2.11.0

Message #46 received at 31764 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Noam Postavsky <npostavs <at> gmail.com>
Cc: carlosjosepita <at> gmail.com, 31764 <at> debbugs.gnu.org
Subject: Re: bug#31764: 26.1;
 Point in VC change log is not centered as documented
Date: Tue, 12 Jun 2018 05:32:50 +0300

> From: Noam Postavsky <npostavs <at> gmail.com>
> Cc: carlosjosepita <at> gmail.com,  31764 <at> debbugs.gnu.org
> Date: Mon, 11 Jun 2018 20:10:17 -0400
> 
> Looks like a matter of timing, if I add a (sit-for 1) to beginning of
> vc-exec-after (or use edebug), then I can reproduce on Windows too.
> Adding a save-excursion seems to fix it.

Then please push to the emacs-26 branch, and thanks.

Message #49 received at 31764 <at> debbugs.gnu.org (full text, mbox):

From: Noam Postavsky <npostavs <at> gmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: carlosjosepita <at> gmail.com, 31764 <at> debbugs.gnu.org
Subject: Re: bug#31764: 26.1;
 Point in VC change log is not centered as documented
Date: Thu, 14 Jun 2018 19:20:37 -0400

tags 31764 fixed
close 31764 26.2
quit

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

>> Adding a save-excursion seems to fix it.

> Then please push to the emacs-26 branch, and thanks.

Done.

[1: fcd66d059c]: 2018-06-14 19:17:20 -0400
  Keep vc-print-log from putting point at buffer end (Bug#31764)
  https://git.savannah.gnu.org/cgit/emacs.git/commit/?id=fcd66d059cffbcfff8325304c2c100b64d28ae29

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