GNU bug report logs - #42300
Visual bug in diff-mode

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

From: Gregory Heytings <ghe <at> sdf.org>
To: bug-gnu-emacs <at> gnu.org
Subject: Visual bug in diff-mode
Date: Thu, 9 Jul 2020 21:23:36 +0200 (CEST)

Diff-mode was updated in Emacs 27, and it is now possible to use the 
fringe to indicate whether the lines were added, deleted, or are common. 
The face is omitted in the display property in the case common lines, 
which leads to the bug described below.

Steps to reproduce:

1. start emacs -Q
2. (setq diff-font-lock-prettify t)
3. to make the bug clearly visible: (set-face-attribute 'fringe nil :background "red" :foreground "yellow")
4. open a diff file (with "common" lines, that is, lines starting with a space)
5. observe that the fringe in front of the common lines is red
6. press C-x C-+, the fringe in front of the common lines is now white
7. press -, the fringe in front of the common lines is now red again

Fix:

--- diff-mode.el.orig	2020-06-29 17:39:26.000000000 +0000
+++ diff-mode.el	2020-07-09 18:44:08.000000000 +0000
@@ -2518,7 +2518,7 @@
                                '((?+ . (left-fringe diff-fringe-add diff-indicator-added))
                                  (?- . (left-fringe diff-fringe-del diff-indicator-removed))
                                  (?! . (left-fringe diff-fringe-rep diff-indicator-changed))
-                                 (?\s . (left-fringe diff-fringe-nul))))))
+                                 (?\s . (left-fringe diff-fringe-nul fringe))))))
           (put-text-property (match-beginning 0) (match-end 0) 'display spec))))
     ;; Mimicks the output of Magit's diff.
     ;; FIXME: This has only been tested with Git's diff output.

Message #14 received at 42300 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Kangas <stefan <at> marxist.se>
To: Gregory Heytings <ghe <at> sdf.org>
Cc: 42300 <at> debbugs.gnu.org
Subject: Re: bug#42300: Visual bug in diff-mode
Date: Thu, 13 Aug 2020 09:23:52 -0700

tags 42300 + confirmed
found 42300 28.0.50
thanks

Gregory Heytings <ghe <at> sdf.org> writes:

> Diff-mode was updated in Emacs 27, and it is now possible to use the fringe to
> indicate whether the lines were added, deleted, or are common. The face is
> omitted in the display property in the case common lines, which leads to the bug
> described below.
>
> Steps to reproduce:
>
> 1. start emacs -Q
> 2. (setq diff-font-lock-prettify t)
> 3. to make the bug clearly visible: (set-face-attribute 'fringe nil :background "red" :foreground "yellow")
> 4. open a diff file (with "common" lines, that is, lines starting with a space)
> 5. observe that the fringe in front of the common lines is red
> 6. press C-x C-+, the fringe in front of the common lines is now white
> 7. press -, the fringe in front of the common lines is now red again

I can reproduce this on current master, and verify that the below change
fixes it.

I'm not that familiar with diff-mode.ela nor font-locking so it's better
that someone else takes a look and installs the fix.

> --- diff-mode.el.orig	2020-06-29 17:39:26.000000000 +0000
> +++ diff-mode.el	2020-07-09 18:44:08.000000000 +0000
> @@ -2518,7 +2518,7 @@
>                                 '((?+ . (left-fringe diff-fringe-add diff-indicator-added))
>                                   (?- . (left-fringe diff-fringe-del diff-indicator-removed))
>                                   (?! . (left-fringe diff-fringe-rep diff-indicator-changed))
> -                                 (?\s . (left-fringe diff-fringe-nul))))))
> +                                 (?\s . (left-fringe diff-fringe-nul fringe))))))
>            (put-text-property (match-beginning 0) (match-end 0) 'display spec))))
>      ;; Mimicks the output of Magit's diff.
>      ;; FIXME: This has only been tested with Git's diff output.

Best regards,
Stefan Kangas

Message #17 received at 42300 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Stefan Kangas <stefan <at> marxist.se>
Cc: Gregory Heytings <ghe <at> sdf.org>, 42300 <at> debbugs.gnu.org
Subject: Re: bug#42300: Visual bug in diff-mode
Date: Fri, 14 Aug 2020 17:33:49 +0200

Stefan Kangas <stefan <at> marxist.se> writes:

> I can reproduce this on current master, and verify that the below change
> fixes it.
>
> I'm not that familiar with diff-mode.ela nor font-locking so it's better
> that someone else takes a look and installs the fix.

I'm not very familiar with that, either, but it seems "obviously
correct", if I understand that code correctly.  So I went ahead and
pushed it to Emacs 28.

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

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