bug#66764: 29.1; Emacs scrolls for "(goto-char (point-max))" instead of jumping

[Eli Zaretskii]

Ping!  Gregory, could you please look into this?

> Cc: Gregory Heytings <gregory@heytings.org>, 66764@debbugs.gnu.org
> Date: Fri, 27 Oct 2023 09:50:33 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> 
> OK, I think I see the root cause of the problem: it's your
> font-lock-keywords setting, viz.:
> 
>  (font-lock-add-keywords nil '(((lambda (bound)) (1 'error prepend t))) t)
> 
> Without this setting, everything works as expected, and goto-char goes
> to the EOB almost instantaneously, even when scroll-conservatively is
> set to a large value.
> 
> AFAIU, the font-lock-keywords setting above causes the display engine
> to call this function every time it moves across some chunk of text,
> which slows down redisplay.  This shows with scroll-conservatively set
> to a large value because Emacs then attempts to find the minimum
> amount of scrolling the screen in order to bring point into the view.
> 
> It is a known fact that modes which use advanced font-lock settings
> should adapt to the long-line situation (when the function
> long-line-optimizations-p returns non-nil), so I think you should
> modify your font-lock settings to avoid this problem in that case.
> 
> CC'ing Gregory in case I missed something in this scenario.
> 
> 
> 
>