bug#59630: 29.0.50; treesitter-buffer-root-node doesn't change when changing buffer restriction

[Yuan Fu]

> On Nov 27, 2022, at 4:49 AM, miha--- via Bug reports for GNU Emacs, the Swiss 
> army knife of text editors <bug-gnu-emacs@gnu.org> wrote:
> 
> Treesitter doesn't seem to change its parse tree when changing
> restriction. It gets it correct the first time when we query the root
> node, but then, after changing restriction, it doesn't seem to get
> updated.
> 
> The following is an M-x ielm session to demonstrate the problem
> 
>  ELISP> (set-buffer (get-buffer-create "test"))
>  ELISP> (insert "echo '123'")
>  ELISP> (narrow-to-region 1 4)
>  ELISP> (buffer-string)
>  "echo"
>  ELISP> (treesit-buffer-root-node 'bash)
>  #<treesit-node
>  (program)
>  in 1-4>  ;; This is expected
> 
>  ELISP> (widen)
>  ELISP> (treesit-buffer-root-node 'bash)
>  #<treesit-node
>  (program)
>  in 1-4>  ;; <---- This is not expected, the root node should span 1-9
> 
>  ELISP> (buffer-string)
>  "echo '123'"

Thanks. We didn’t edit the buffer after widening, so tree-sitter didn’t reparse 
and used the old tree, which sees the narrowed buffer. Eli, what would be a 
good and reliable way to know that narrowing has changed? I see 
current_buffer->clip_changed set to 1 in narrow-to-region and widen, but when 
are they set to 0?

Yuan