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

From: Dmitry Gutov <[email-masked]>
Date: Thu, 28 Dec 2023 13:44:43 +0200

On 28/12/2023 10:07, Yuan Fu wrote:
> 
>> 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.

But then treesit major modes will be affected by user narrowing (e.g. if 
the user narrowed to inside the string, the buffer won't be highlighted 
as a string).