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

[Eli Zaretskii]

> Date: Tue, 16 Aug 2022 17:00:18 +0300
> Cc: 56682@debbugs.gnu.org, gregory@heytings.org, monnier@iro.umontreal.ca
> From: Dmitry Gutov <dgutov@yandex.ru>
> 
> >> It's a buffer without long lines. Simply a large file.
> > 
> > ??? Are we talking about long-line.xml, or are we talking about
> > some other file?  We did nothing to change the behavior in large files
> > without long lines.
> 
> I'm talking about a 20 MB file I created manually with some simple 
> contents. Just no long lines.

That's a different problem, one we didn't try to fix yet.

> > If you are saying that 'recenter' takes too long in some file, and
> > therefore delays M-> for too long, it is probably a separate issue, so
> > please report that as a separate bug, preferably with the file that
> > causes it.
> 
> It seems pertinent to me since ultimately the decision to narrow in 
> handle_fontified_prop is driven by the idea that font-lock in large 
> files ends up being a problem anyway. And here we have a large file 
> where this doesn't help.

Because it's a different problem, with likely a different solution.

> But I can file it separately, of course.

Yes, please.