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

From: Gregory Heytings <[email-masked]>
Date: Sat, 20 Aug 2022 17:14:35 +0000

>
> (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 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?