bug#81637: Regression: Tree-sitter font-lock drops highlighting in indirect buffers

On 2026-08-19 01:40, Yuan Fu wrote:
> 
> 
>> On Aug 17, 2026, at 3:59 AM, Eli Zaretskii <[email protected]> wrote:
>>
>>> Date: Sun, 16 Aug 2026 18:09:52 -0400
>>> From: James Cherti <[email protected]>
>>>
>>> There is a regression in tree-sitter where syntax
>>> highlighting is completely lost when creating an indirect
>>> buffer (via clone-indirect-buffer or C-x 4 c) from a base
>>> buffer running a tree-sitter major mode.
>>>
>>> This worked correctly in Emacs 29 but broke in the recent
>>> Emacs 31 and 32 changes.
>>>
>>> To reproduce:
>>>
>>> - Open a source file that uses a tree-sitter major mode.
>>> - Create an indirect buffer using
>>>    M-x clone-indirect-buffer (or 'C-x 4 c').
>>> - Observe that the syntax highlighting is entirely or
>>>    partially missing in the new indirect buffer.
>>
>> Thanks.  Yuan, could you please look into this?
> 
> Thanks for the CC. James, are you able to reproduce it with emacs -Q? Because I can’t reproduce it with either my personal Emacs session or emacs -Q. 🤔

Hello Yuan,

Yes, I can reproduce it with emacs -Q.

Please see the attached screenshot.

I used python-ts-mode in this example, but the bug also
occurs with other modes like yaml-ts-mode.

Here are the steps to reproduce the issue shown in the
screenshot:

- Open a Python file.
- Switch to python-ts-mode.
- Split the window to the right.
- Run M-x clone-indirect-buffer.
- Important: After cloning the file using
   clone-indirect-buffer, the initially displayed text is
   highlighted correctly. However, if you scroll down one to
   two pages, you will notice that the rest of the indirect
   buffer isn't highlighted.

> 
> Yuan
> 
> 

--
James Cherti
GitHub: https://github.com/jamescherti
Website: https://www.jamescherti.com/