Re: How the long-lines "optimisation" breaks font locking.

[Eli Zaretskii]

> Date: Fri, 5 Aug 2022 16:04:08 +0300
> Cc: larsi@gnus.org, emacs-devel@gnu.org, gregory@heytings.org
> From: Dmitry Gutov <dgutov@yandex.ru>
> 
> On 05.08.2022 14:20, Eli Zaretskii wrote:
> > Thanks.  Any improvements in font-lock of any major mode is welcome.
> > If/when enough of them get their act together, we might revisit the
> > default value of long-line-threshold, as I already said many times.
> 
> As I said, changing long-line-threshold's default is not the solution 
> because this variable also determines when the fixes for the other 
> redisplay logic come into play.
> 
> And those cause sluggishness more extensively and much earlier than 
> font-lock becomes a problem.

That's incorrect, or at least inaccurate: part of slow redisplay is
due to the fact that we fontify as part of displaying or as part of
layout calculations.