GNU bug report logs - #58578
29.0.50; Font lock randomly breaks in some buffers and gets worse over time

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Stefan Kangas <stefankangas <at> gmail.com>
Subject: bug#58578: closed (Re: bug#58578: 29.0.50; Font lock randomly
 breaks in some buffers and gets worse over time)
Date: Sun, 10 Sep 2023 23:54:01 +0000

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Your bug report

#58578: 29.0.50; Font lock randomly breaks in some buffers and gets worse over time

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 58578 <at> debbugs.gnu.org.

-- 
58578: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=58578
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Stefan Kangas <stefankangas <at> gmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 58578-done <at> debbugs.gnu.org
Subject: Re: bug#58578: 29.0.50; Font lock randomly breaks in some buffers and
 gets worse over time
Date: Sun, 10 Sep 2023 16:53:11 -0700

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

> Maybe.  Or maybe this is specific to notmuch-message-mode.
>
> I would suggest to focus on more popular modes.

This heisenbug has not manifested itself in a while, so I'm closing this
bug.  I will reopen if it pops up again.

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From: Stefan Kangas <stefankangas <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 29.0.50; Font lock randomly breaks in some buffers and gets worse
 over time
Date: Mon, 17 Oct 2022 04:40:50 +0000

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I'm seeing broken font lock in long running sessions, seemingly at
random.  After it goes on for a while, font lock breaks down completely
in some buffers, and it seemingly gets worse over time.  In some cases,
the only remedy has been to restart Emacs.

This has been going on for a couple of weeks at least, and I thought I
was doing something wrong, so I haven't reported it.  I also haven't
seriously tried to reproduce it in "emacs -Q", so I've only seen using
my own init file.  (I haven't made any changes in that configuration
recently that would obviously relate to font-locking.)

I've failed at my attempts to understand it, so I hope that someone can
help me with ideas on how to debug this.  What makes this a bit
discouraging to debug is that it usually only shows up after more than a
day of use (sometimes several days, AFAIR), and it's unbearable to work
in "emacs -Q" for that long.  I also have no idea where to even begin
looking.

I have seen it in more than one major mode, both built-in and
third-party modes (from the top of my head, I've seen it in `c-mode' and
`org-mode' too).

Here is a screenshot from `notmuch-message-mode', based on
`message-mode':

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[font-lock-bug.png (image/png, attachment)]

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