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

[Dmitry Gutov]

On 14.08.2022 20:54, Gregory Heytings wrote:
> > > If the conclusion is, after some reasonable effort, that there is no 
> > > way to make syntax-ppss significantly faster in one way or another in 
> > > such cases, and that there is no way to make font locking reasonably 
> > > accurate even when it doesn't have access to the whole buffer, it 
> > > might make sense to provide user options to fine-tune the behavior.  
> > > But we are not there yet.
> >
> > Both conclusions lead to removing the applications of narrowing from 
> > handle_fontified_prop.
>
> I have seen no effort whatsoever to make syntax-ppss significantly 
> faster in one way or another.

syntax-ppss is limited in its performance by parse-partial-sexp.

Could you take a look at it? Seems like more of your area of expertise.