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

From: Yuan Fu <[email-masked]>
Date: Thu, 28 Dec 2023 00:07:51 -0800

> On Dec 27, 2023, at 4:57 AM, Eli Zaretskii <[email-masked]> wrote:
> 
>> From: Yuan Fu <[email-masked]>
>> Date: Tue, 26 Dec 2023 20:15:24 -0800
>> Cc: Denis Zubarev <[email-masked]>,
>> [email-masked]
>> 
>>> 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?

Yes. If font-lock doesn’t widen, then there wouldn’t be back-and-forth reparses. 

Yuan