Re: bug-reference-prog-mode slows down CC Mode's scrolling by ~7%

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: acm@muc.de,  emacs-devel@gnu.org
> Date: Sat, 11 Sep 2021 13:04:31 -0400
> 
> >> and it will probably say nil.
> > That's sheer luck: it happens only when the invisible text between
> > headings is longer than jit-lock-chunk-size.
> 
> That was exactly the case I was talking about.
> That's why I wrote a few messages ago:
> 
>     Maybe a good way to see the waste is to measure the time for the
>     initial font-lock in an outline-mode buffer where the screen is
>     filled with single-line headers and everything else is hidden:
>     a whole chunk will be fontified for each line, so with a single
>     40-line screen you can expect to fontify 40 chunks (unless the
>     hidden text between lines is smaller than the chunk size, of
>     course).

That's okay, but the thing is we do fontify invisible text, and 1500
characters could be easily 40 lines, so the probability of more than
that to be hidden is not large, except in unusual cases like reading
Lisp in Outline mode with all the code hidden.