bug#71681: 29.3.50; tree-sitter crash

[Juri Linkov <juri@linkov.net>]

>> Evaluating this expression causes a crash:
>>
>> (progn
>>  (find-file (expand-file-name "src/treesit.c" installation-directory))
>>  (c-ts-mode)
>>  (font-lock-ensure 63209 63387))
>>
>> in latest master, but not in latest emacs-29 (only in 5-months old emacs-29).
>>
>> If this is not reproducible, I could provide more details.
>>
>> libtree-sitter is at the latest version.
>
> Hmm, I can’t reproduce with latest master and libtree-sitter. Maybe you can send me the exact commits that you used?
>
> Here’s mine:
>
> Emacs: 72f2b01e318
> Tree-sitter: 6ec478c1

Probably reproducibility depends on the content of the src/treesit.c file.
Then the most reliable way to reproduce it is this:

0. emacs -Q
1. eval: (add-to-list 'major-mode-remap-alist '(c-mode . c-ts-mode))
2. C-x v L
3. in the *vc-change-log* buffer move point to the commit 20af58d3a13
4. type D
5. crash caused by diff-font-lock-syntax fontification that uses treesit

The numbers in (font-lock-ensure 63209 63387) above were extracted
from diff hunk boundaries that might be different when the file was edited.