bug#67977: 30.0.50; tree-sitter: Emacs crashes when accessing treesit-nodes in a narrowed buffer

[Eli Zaretskii]

> From: Yuan Fu <casouri@gmail.com>
> Date: Tue, 26 Dec 2023 20:15:24 -0800
> Cc: Denis Zubarev <dvzubarev@yandex.ru>,
>  67977@debbugs.gnu.org
> 
> > Btw, I hope that these calls to 'widen' don't require unnecessary
> > reparsing by tree-sitter, do they?
> 
> Yes, but only because we called treesit-node-at while the buffer is narrowed, 
> which triggers a reparse. Font-lock and jit-lock themselves always access the 
> parser with widened buffer so they don’t trigger reparse on their own. 
> 
> So it seems working in a narrowed buffer would trigger a lot of 
> back-and-fortch reparse. I wonder if it’s worth optimizing for (eg, use two 
> parsers behind the scenes, one for widened buffer and one for narrowed 
> buffer).

Could font-lock-dont-widen help, perhaps?