GNU bug report logs - #77465
29.4; VC annotate does not display tabs properly

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

From: Tom Tromey <tromey <at> adacore.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 29.4; VC annotate does not display tabs properly
Date: Wed, 02 Apr 2025 10:30:57 -0600

Some projects I work on use tab characters for indentation.
I used 'C-x v =' to annotate a file from one of these projects.

In this case, because the VC-provided margin text is not a multiple of 8
characters, the tabs are rendered improperly, making the program text
look strange.

As an example, open emacs/src/alloc.c and C-x v =

Then search for the tab character in code (with comments the weirdness
isn't as pronounced).

Here's an example from emacs where I've turned the tabs into spaces so
you can see the effect:

b88e9cded7ae (Paul Eggert             2016-01-26  226)   else
b88e9cded7ae (Paul Eggert             2016-01-26  227)     {
b88e9cded7ae (Paul Eggert             2016-01-26  228)       if (!malloc_using_checking)
b88e9cded7ae (Paul Eggert             2016-01-26  229)  {
b88e9cded7ae (Paul Eggert             2016-01-26  230)    /* Work around a bug in glibc's malloc.  MALLOC_CHECK_ must be


One simple fix would be to ensure that the margin text is always a
multiple of 8.  However, a more sophisticated approach may be possible
as well.



In GNU Emacs 29.4 (build 1, x86_64-redhat-linux-gnu, GTK+ Version
 3.24.43, cairo version 1.18.2) of 2025-03-13 built on
 0cbb79ebeb714371b64bef3269323882
System Description: Fedora Linux 41 (Workstation Edition)

Configured using:
 'configure --build=x86_64-redhat-linux-gnu
 --host=x86_64-redhat-linux-gnu --program-prefix=
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Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GSETTINGS HARFBUZZ JPEG JSON
LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 MODULES NATIVE_COMP NOTIFY INOTIFY
PDUMPER PGTK PNG RSVG SECCOMP SOUND SQLITE3 THREADS TIFF
TOOLKIT_SCROLL_BARS TREE_SITTER WEBP XIM GTK3 ZLIB

Important settings:
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Annotate

Minor modes in effect:
  shell-dirtrack-mode: t
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  erc-services-mode: t
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Load-path shadows:
/home/tromey/.emacs.d/elpa/ggtags-0.9.0/ggtags hides /home/tromey/.emacs.d/elpa/ggtags-0.8.13/ggtags
/home/tromey/.emacs.d/elpa/ggtags-0.9.0/ggtags-pkg hides /home/tromey/.emacs.d/elpa/ggtags-0.8.13/ggtags-pkg
/home/tromey/.emacs.d/elpa/ggtags-0.9.0/ggtags-autoloads hides /home/tromey/.emacs.d/elpa/ggtags-0.8.13/ggtags-autoloads

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Message #8 received at 77465 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Tom Tromey <tromey <at> adacore.com>
Cc: 77465 <at> debbugs.gnu.org
Subject: Re: bug#77465: 29.4; VC annotate does not display tabs properly
Date: Thu, 03 Apr 2025 10:47:17 +0300

> Date: Wed, 02 Apr 2025 10:30:57 -0600
> From:  Tom Tromey via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs <at> gnu.org>
> 
> 
> Some projects I work on use tab characters for indentation.

Emacs uses TABs mixed with SPCes as a matter of policy.

> I used 'C-x v =' to annotate a file from one of these projects.
> 
> In this case, because the VC-provided margin text is not a multiple of 8
> characters, the tabs are rendered improperly, making the program text
> look strange.
> 
> As an example, open emacs/src/alloc.c and C-x v =
> 
> Then search for the tab character in code (with comments the weirdness
> isn't as pronounced).
> 
> Here's an example from emacs where I've turned the tabs into spaces so
> you can see the effect:
> 
> b88e9cded7ae (Paul Eggert             2016-01-26  226)   else
> b88e9cded7ae (Paul Eggert             2016-01-26  227)     {
> b88e9cded7ae (Paul Eggert             2016-01-26  228)       if (!malloc_using_checking)
> b88e9cded7ae (Paul Eggert             2016-01-26  229)  {
> b88e9cded7ae (Paul Eggert             2016-01-26  230)    /* Work around a bug in glibc's malloc.  MALLOC_CHECK_ must be

AFAICT, "git annotate" produces the same effect when invoked from the
shell prompt.  I'm not sure we should try to be "holier than the Pope"
here.

> One simple fix would be to ensure that the margin text is always a
> multiple of 8.

I don't think this is practical, since Git doesn't guarantee the
prefix of a line to be of a fixed width.  Here's a typical example:

47099d6f7       (Richard M. Stallman    1993-06-06 21:16:51 +0000       27)
4588ec205       (Jim Blandy     1991-07-03 12:10:07 +0000       28)
a08795204       (Richard M. Stallman    1995-11-12 05:20:12 +0000       29)
fd2e066a8       (Geoff Voelker  1995-11-07 07:14:59 +0000       30)
fd2e066a8       (Geoff Voelker  1995-11-07 07:14:59 +0000       31)
e5560ff7d       (Andreas Schwab 2012-06-16 14:24:15 +0200       32)
d43721a22       (Andrew Innes   2000-08-22 22:14:00 +0000       33)
502b9b644       (Jim Blandy     1992-07-13 19:54:34 +0000       34)
428a555ec       (Károly Lőrentey        2004-01-05 05:54:35 +0000       35)
4588ec205       (Jim Blandy     1991-07-03 12:10:07 +0000       36)
4588ec205       (Jim Blandy     1991-07-03 12:10:07 +0000       37)
4588ec205       (Jim Blandy     1991-07-03 12:10:07 +0000       38)
97cf50e75       (Richard M. Stallman    1996-04-23 20:32:58 +0000       39)
58b2bb63f       (Richard M. Stallman    1995-08-21 21:56:40 +0000       40)

> However, a more sophisticated approach may be possible as well.

The only idea I have is to replace each tab with a suitable number of
spaces, but that would probably make this command much slower, since
the buffer created by "C-x v =" is typically very large.

Any other ideas?

Message #11 received at 77465 <at> debbugs.gnu.org (full text, mbox):

From: Tom Tromey <tromey <at> adacore.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 77465 <at> debbugs.gnu.org, Tom Tromey <tromey <at> adacore.com>
Subject: Re: bug#77465: 29.4; VC annotate does not display tabs properly
Date: Thu, 03 Apr 2025 08:56:12 -0600

>> b88e9cded7ae (Paul Eggert             2016-01-26  230)    /* Work around a bug in glibc's malloc.  MALLOC_CHECK_ must be

Eli> AFAICT, "git annotate" produces the same effect when invoked from the
Eli> shell prompt.  I'm not sure we should try to be "holier than the Pope"
Eli> here.

I see it as being along the line of font-locking the annotation buffer
by age -- it's a display feature to help make the output more readable.
That is, git may do the wrong thing but Emacs doesn't have to.

>> One simple fix would be to ensure that the margin text is always a
>> multiple of 8.

Eli> I don't think this is practical, since Git doesn't guarantee the
Eli> prefix of a line to be of a fixed width.

I didn't realize that.

>> However, a more sophisticated approach may be possible as well.

Eli> The only idea I have is to replace each tab with a suitable number of
Eli> spaces, but that would probably make this command much slower, since
Eli> the buffer created by "C-x v =" is typically very large.

Eli> Any other ideas?

It's been a long time since I dug into this kind of thing but I was
wondering if there is some kind of display and/or text property feature
that would help.

Maybe putting a :align-to on the space following the ")" would help.

Note that, at least in the repositories I use, annotation display is
already slow enough (presumably due to extensive history in git) that
another minor slowdown to find the correct width would not really be
noticeable.

Tom

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