Subject: Re: bug#75609: Hideshow support for treesitter

From: Juri Linkov <[email-masked]>
Date: Thu, 23 Jan 2025 19:39:17 +0200

>> +(defun treesit-forward-comment (&optional count)
>> +  "Tree-sitter `forward-comment-function' implementation.
>> +
>> +COUNT is the same as in `forward-comment'."
>> +  (let ((res t) thing)
>> +    (while (> count 0)
>> +      (skip-syntax-forward " >")
>> +      (setq thing (treesit-thing-at (point) 'comment))
>> +      (if (and thing (eq (point) (treesit-node-start thing)))
>> +          (progn
>> +            (goto-char (min (1+ (treesit-node-end thing)) (point-max)))
>> +            (setq count (1- count)))
>> +        (setq count 0 res nil)))
>> +    (while (< count 0)
>> +      (skip-syntax-backward " >")
>> +      (setq thing (treesit-thing-at (max (1- (point)) (point-min)) 'comment))
>> +      (if (and thing (eq (point) (treesit-node-end thing)))
>> +          (progn
>> +            (goto-char (treesit-node-start thing))
>> +            (setq count (1+ count)))
>> +        (setq count 0 res nil)))
>> +    res))
>
> I'm curious: why do you have to use skip-syntax-forward/backward when
> tree-sitter already should know where a comment starts and ends?
> ideally, features that use tree-sitter should not need to consult any
> syntax tables set up by the major mode.  Or what am I missing?

tree-sitter has no information about whitespace, but whitespace is
essential part of the behavior according to the docstring of
'forward-comment':

  Stop scanning if we find something other than a comment or whitespace.
  If COUNT comments are found as expected, with nothing except whitespace
  between them, return t; otherwise return nil.

So treesit should be able to skip whitespace as well:

default implementation = skip whitespace + check syntax table
treesit implementation = skip whitespace + check syntax tree