Re: treesitter local parser: huge slowdown and memory usage in a long file

[Eli Zaretskii]

> From: Yuan Fu <casouri@gmail.com>
> Date: Sun, 11 Feb 2024 20:16:11 -0800
> Cc: "Ergus via Emacs development discussions." <emacs-devel@gnu.org>,
>  Eli Zaretskii <eliz@gnu.org>
> 
> Thanks, the culprit is the call to treesit-update-ranges in 
> treesit--pre-redisplay, where we don’t pass it any specific range, so it 
> updates the range for the whole buffer. Eli, is there any way to get a rough 
> estimate the range that redisplay is refreshing? Do you think something like 
> this would work?
> 
>     (treesit-update-ranges
>      (max (point-min) (- (window-start) 1000)) ; BEG
>      (min (point-max) (+ (or (window-end) (+ (window-start) 4000)) 1000))) ; 
> END
> 
> I guess the window-start would be outdated in pre-redisplay-function...

The problem is that window-start is not guaranteed to be up-to-date
when pre-redisplay-function is called: the window-start is updated by
redisplay, and pre-redisplay-function is called before the update.
Moreover, pre-redisplay-function could be called either once or twice
in a redisplay cycle, and window-start is up-to-date only for the
second call.

The window-end point is basically never up-to-date during redisplay,
only at its very end.

So my suggestion would be to define the range from position of point,
using the window dimensions; see get_narrowed_width for ideas.  This
could lose if the buffer has a lot of invisible text, so I suggest to
check for invisible properties, and if they are present in the buffer,
punt and use the whole accessible portion of the buffer (I don't
expect PHP buffers, or any buffers in programming-language modes, to
have invisible text).