GNU bug report logs - #57804
An infinite loop in a `fontify-region' function causes Emacs to hang indefinitely

Previous Next

Full log

View this message in rfc822 format

From: Eli Zaretskii <eliz <at> gnu.org>
To: Po Lu <luangruo <at> yahoo.com>
Cc: larsi <at> gnus.org, 57804 <at> debbugs.gnu.org, pogonyshev <at> gmail.com
Subject: bug#57804: An infinite loop in a `fontify-region' function causes Emacs to hang indefinitely
Date: Thu, 15 Sep 2022 09:27:14 +0300

> From: Po Lu <luangruo <at> yahoo.com>
> Cc: Eli Zaretskii <eliz <at> gnu.org>,  57804 <at> debbugs.gnu.org,  Paul Pogonyshev
>  <pogonyshev <at> gmail.com>
> Date: Thu, 15 Sep 2022 13:20:51 +0800
> 
> Lars Ingebrigtsen <larsi <at> gnus.org> writes:
> 
> > Eli Zaretskii <eliz <at> gnu.org> writes:
> >
> >> This case is exactly one of those which I think we shouldn't try to
> >> fix, because it's the case of "buggy Lisp program", a.k.a. "don't do
> >> that".  There's no reason for any useful Lisp program to have an
> >> infloop like this:
> >>
> >>>   (while t
> >>>     "whoopsie")
> >
> > You've never accidentally put an infloop into a font locking function?
> > Then you've been very lucky.
> >
> > We should definitely fix this is we can.
> 
> Why isn't jit-lock-debug-mode an option?

It definitely is, for the particular use case of debugging font-lock.

So is running font-lock-fontify-buffer by hand.

So is attaching a debugger when such an infloop is bumped into
accidentally without expecting it.

There's also the recently-added backtrace-on-redisplay-error feature,
which could help with diagnosing such problems, perhaps combined with
debug-on-entry or somesuch.

IOW, I think we have already several useful tools available for the
particular problem of debugging loops in font-lock, if we want to
interpret this bug report in that narrow interpretation.

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.