bug#57207: 29.0.50; Fontification is slow after e7b5912b23 (Improvements to long lines handling)

[Eli Zaretskii]

> Date: Sat, 20 Aug 2022 17:14:35 +0000
> From: Gregory Heytings <gregory@heytings.org>
> cc: Eli Zaretskii <eliz@gnu.org>, 57207@debbugs.gnu.org, yantar92@gmail.com
> 
> > (progn
> >  (pop-to-buffer "foo.txt")
> >  (flyspell-mode)
> >  (insert (propertize (make-string 20000 ?x) 'display "foo")
> >       "\n\n"))
> >
> > Then type "d".  [Narrow] is shown in the mode line.
> >
> 
> I can reproduce that, too.  The "Narrow" indication disappears with the 
> next redisplay cycle, so it seems to be a not-too-grave issue (but a bug 
> nonetheless).

It doesn't disappear if you keep typing fast enough, or lean on a key.

> It could probably be solved by moving the calculation of "BUF_BEGV (b) > 
> BUF_BEG (b) || BUF_ZV (b) < BUF_Z (b)" from decode_mode_spec to 
> mark_window_display_accurate_1, which would set a one-bit field in struct 
> buffer.
> 
> WDYT?

That's too late, I think?  How do we ensure after that the update of
the mode-line (in case the hook really wants to change the
restriction)?