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

[Dmitry Gutov]

On 15.08.2022 23:53, Gregory Heytings wrote:
> > I said those words just as I was working on improving font-lock's 
> > performance in JSON files. An effort which doesn't make sense if you 
> > narrow around font-lock anyway.
> >
> > Also note that until now it has been impossible to improve redisplay 
> > of big files by working on font-lock (other bottlenecks were much more 
> > significant).
>
> Wrong.  The (much more common) case of big files _without_ long lines, 
> in which the same font locking slowdowns already exist, has AFAICS not 
> been a sufficient incentive to improve font locking.

Okay, you're right about that.

There have been many more complaints about being unable to edit a file 
with a 5000+ line comfortably, than about editing 100+ MB files.