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

[Dmitry Gutov]

On 30/12/2023 22:23, Yuan Fu wrote:
> > On Dec 30, 2023, at 8:21 AM, Denis Zubarev<dvzubarev@yandex.ru>  wrote:
> >
> > > I pushed a fix and now it shouldn’t crash anymore. However, I’m yet not sure 
> > > why at some point the buffer was widened. Is there any way to track who called 
> > > widen?
> >   Thank you, It doesn't crash anymore.
> >   > 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).
> >   I have performed a quite naive benchmark and haven't seen any significant 
> > slow down when inserting text in a narrowed buffer.
> Right, when you type, since the only thing that access the parser is font-lock, 
> which always widens the buffer, there’s no unnecessary reparse. If you invoke 
> some function that access the parser while the buffer is narrowed, that’ll 
> trigger a reparse, and the next time font-lock runs, it’ll widen and make the 
> parser reparse the full buffer again.

The difference might also only be noticeable with larger files: 
tree-sitter is pretty fast by itself, so an extra reparse might not make 
a difference unless it triggers a full re-fontification or application 
of text properties over a large span.