GNU bug report logs - #72721
31.0.50; Visual-wrap-prefix-mode breaks Magit log buffers

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From: Jim Porter <jporterbugs <at> gmail.com>
To: Gautier Ponsinet <gautier <at> gautierponsinet.xyz>, 72721 <at> debbugs.gnu.org
Cc: eliz <at> gnu.org
Subject: bug#72721: 31.0.50; Visual-wrap-prefix-mode breaks Magit log buffers
Date: Mon, 19 Aug 2024 17:46:18 -0700

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

On 8/19/2024 2:39 PM, Gautier Ponsinet wrote:
> Hello everyone,
> 
> The new visual-wrap-prefix-mode breaks the rendering of the Magit Log
> buffers.
> 
> In emacs -Q:
> * Install Magit and its dependencies and load Magit.
> * Go to a local repository (via M-x dired or M-x cd).
> * M-x global-visual-wrap-prefix-mode
> * M-x magit-log-current
> 
> Could someone please confirm/reproduce?

I can confirm this. I'm not quite sure of all the details, but it seem 
that this is due to a bad interaction between overlays and the 
'min-width' display spec. The end result was that we were calling 
'get-text-property' with a (large-ish) buffer position when the OBJECT 
arg was a string of length 1. That can happen in magit-log on the 
mostly-blank line where it's making the ASCII art just below a merge 
commit. (The leading whitespace makes 'visual-wrap-prefix-mode' do its 
thing.)

I'm not super familiar with how the display engine works, but I think we 
don't want to call 'display_min_width' when we're working with an 
overlay. See the attached patch.

Eli, I'm sure you understand this code much better than me. Does the 
above make sense? I can also try to improve the commentary in the code, 
but I'm just making some educated guesses as to what's happening here.

[0001-Fix-bad-interaction-between-min-width-display-spec-a.patch (text/plain, attachment)]

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