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

[Dmitry Gutov]

On 31.07.2022 13:50, Gregory Heytings wrote:
> > > BTW, my tests show that syntax-ppss can be rather slow, when the file 
> > > is large enough (say 1 GB).
> >
> > No doubt.  But it's no slower with long lines than with short lines.
>
> Yes, I wasn't clear enough, I should have written "when the file is 
> large enough (say 1 GB), even without long lines".

What kind of scenario are you thinking of that would exhibit this 
slowness in a 1 GB file?

If we're talking about syntax-ppss only, regular editing operations 
(typing and deleting code) limited to, say, one screen should trigger 
only a rescan of a limited area inside such buffer.

Both when the editing happens near the beginning or near the end of the 
buffer. Or in the middle -- no difference.