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

From: Yuan Fu <[email-masked]>
Date: Sat, 23 Dec 2023 00:08:51 -0800

> On Dec 22, 2023, at 11:26 PM, Eli Zaretskii <[email-masked]> wrote:
> 
>> From: Denis Zubarev <[email-masked]>
>> Date: Sat, 23 Dec 2023 02:18:20 +0300
>> 
>> 1. emacs -Q
>> 2. M-x find-file /tmp/t.py
>> 3. paste there
>> start=1
>> def _init(self, param1, param2, param3=False):
>>    self._param1 = param2
>>    self._param2 = param2
>>    self._param3 = param3
>> 4. python-ts-mode
>> 5. select two last lines and M-x narrow-to-region
>> 6. answer all prompts
>> 7. Put cursor on the last self
>> 8. M-x eval-expression
>> (progn
>> (setq temp-node (treesit-node-at (point)))
>> (sit-for 2)
>> (garbage-collect)
>> (message "node %s" temp-node))
>> 9. Emacs crashes or prints node that contains garbage
> 
> Thanks.
> 
> Yuan, this also happens on the emacs-29 branch, so we should try
> fixing this crash ASAP.

Yeah. The node wants to print it’s type name (with ts_node_type), which access it’s parse tree, but the tree is already freed, that means the node is outdated and shouldn’t try to print it’s type name, but should rather print “outdated”.

But simply narrowing the buffer shouldn’t reparse the buffer and cause the parse tree to be freed. Anyway, let me see what’s going on.

Yuan