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

[Dmitry Gutov]

On 15.08.2022 23:29, Gregory Heytings wrote:

> > If you wanted the development to take this route, it would have really 
> > made more sense to hold off on applying the narrowing to 
> > fontification-functions, keeping font-lock slow-ish in large files. 
> > That would have encouraged direct work on speeding it up.
>
> That's your opinion.  What I think would have most likely happened is 
> what you yourself said: these are large files, it's unavoidable that 
> font locking takes somes time (these are not your exact words, I hope 
> they express what you said faithfully).

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).

> > But anyway. Suppose we have some more success with syntax-ppss. Two 
> > options:
>
> There are many other options besides the two options you listed.

Perhaps. I don't think anybody's mentioned them here, though.