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

[Dmitry Gutov]

On 04.08.2022 04:41, Gregory Heytings wrote:
> > We cannot perform every basic operation in fixed time for any 
> > arbitrarily sized file. There are limits of what we can possibly do.
>
> Apparently the limits are lower than what you think.  Provided that we 
> accept some compromises, such as mis-fontification, which is also what 
> syntax-wholeline-max does, and against which you didn't protest.

syntax-wholelines-max indeed can potentially cause problems too, but in 
a much narrow range of situations (and only with major modes which have 
non-trivial syntax-propertize-function).

In any case, I would be happy to investigate further improvements in 
Lisp which would be implemented in the same area of code that 
syntax-wholelines-max lives in.

> > I'd really like it if we could scope this discussion to solving that 
> > particular problem. Not the speed of operations in large files in 
> > general.
>
> I don't understand what you mean.  Which "particular problem"?  The 
> point of this discussion is of course the speed of operations in large 
> files in general.

The particular problem is long lines. It not the same as "large files in 
general".

> If you take that out of the picture, everything is of 
> course possible. I'm not even sure what remains in fact, Emacs is an 
> editor, not a displayer.

The well-known problem we have had for a while is that Emacs screeches 
to a halt even on medium-sized buffers as soon as it encounters a long line.