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

[Yuan Fu]

Yuan Fu <casouri@gmail.com> writes:

> Eli Zaretskii <eliz@gnu.org> writes:
>
>>> From: Yuan Fu <casouri@gmail.com>
>>> Date: Sun, 27 Nov 2022 14:40:41 -0800
>>> Cc: 59630@debbugs.gnu.org,
>>>  Eli Zaretskii <eliz@gnu.org>
>>> 
>>> >  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?
>>
>> Not sure what exactly are you after.  If you want to catch the moment when
>> we change the buffer restriction, you will have to add something to
>> Fnarrow_to_region and Fwiden.  However, why does tree-sitter need to know
>> about changes in the narrowing, unless it is asked to update something or
>> produce a tree?  I thought we decided to update this stuff lazily, only when
>> actually needed?  Being sensitive to these changes would require you to have
>> some logic, because a buffer can be narrowed and widened several times in a
>> sequence without any consequences for tree-sitter, and asking the parser to
>> update itself will just burn CPU cycles.  So if this is really needed, let's
>> discuss for which purposes and under what conditions.
>>
>> I actually don't think why we should be worried by the above scenario; can
>> you explain?
>>
>
> We still parse lazily, and narrow/widen wouldn’t affect the parse tree,
> until user requests for a node when the restriction is different from
> last time we parsed the buffer.  Basically:
>
> request-node <-- last time we parsed
> narrow
> widen
> narrow
> widen
> request-node <-- no need to reparse (1)
>
> request-node <-- last time we parsed
> edits-buffer
> request-node <-- need to reparse (2)
>
> request-node <-- last time we parsed
> narrow
> request-node <-- need to reparse (3)
>
> Right now in case (3) we don’t reparse the buffer. I have a reasonable
> fix in f794263da20.

Closing since I believe this is fixed.

Yuan