bug#56682: Fix the long lines font locking related slowdowns

[Eli Zaretskii]

> Date: Thu, 04 Aug 2022 09:46:17 +0000
> From: Gregory Heytings <gregory@heytings.org>
> cc: dgutov@yandex.ru, gerd.moellmann@gmail.com, 56682@debbugs.gnu.org, 
>     monnier@iro.umontreal.ca
> 
> 
> >> I just pushed an improvement for Bidi.  I did not do so earlier because 
> >> I was trying to improve it further, but somehow I'm hitting a brick 
> >> wall here.  Could you please check, and tell me if what I already did 
> >> is okay?
> >
> > Hmm... which part(s) of the recent commit(s) on the branch are related 
> > to bidi?  I only see changes related to composed characters.  What did I 
> > miss?
> >
> 
> 82b602dc2f improves bidi in long lines, without indeed touching bidi.c.

The changes are related to compositions, not to bidi.  Displaying
Arabic (and maybe also other characters in that file) requires
character composition, but it has nothing in particular to do with
bidi per se.

Are you saying that if you replace the Arabic text there with some
other script that also requires composition processing (like one of
the Indic scripts, see lisp/language/indian.el), editing this file is
significantly faster?

Btw, I'm unable to edit that file on the branch, because
show-paren--default causes an assertion violation.  I'm pretty sure
that's due to the issues in narrow-to-region that were already fixed
on master.