bug#68824: treesitter support for outline-minor-mode

[Yuan Fu <casouri@gmail.com>]

> On Feb 1, 2024, at 9:12 AM, Juri Linkov <juri@linkov.net> wrote:
> 
> Yuan, do you think it makes sense to add a new optional arg to
> 'treesit-search-forward' that will define the traversal order?
> 
> The problem is that to search the next outline heading in
> outline-minor-mode, there is a need to visit headings in
> the same order as they appear in the buffer
> where a parent is located before its children:
> 
> * Parent
> ** Child 1
> ** Child 2
> 
> Currently 'treesit-search-forward' returns "Child 1" before "Parent".
> 
> This means that 'treesit-search-forward' should return the
> topmost matched parent instead of starting to traverse children
> from the deepest leaf.
> 
> IOW, it's necessary to traverse nodes in this order:
> 
>                  o
>                  |
>                  о---------------------11
>                  |                     |
>         o--------S----------3          12
>         |        |          |
>    o--o-+--o  1--+--2    4--+-----7
>    |  |                  |        |
>    o  o                +-+-+   +--+--+
>                        |   |   |  |  |
>                        5   6   8  9  10
> 
> Please note there is no 11 or 12 at the parent of S node because
> it should traverse only the remaining siblings of the parent.
> This is because remaining parent siblings have treesit-node-start
> positions greater than treesit-node-start of S node.
> 
>> +(defun treesit-outline-search (&optional bound move backward looking-at)
>> +  (let* ((current (treesit-node-at (pos-bol)))
>> +         (current (or (treesit-parent-until current treesit-outline-predicate)
>> +                      current))
>> +         (node (treesit-search-forward
>> +                 current treesit-outline-predicate backward))

Instead of using treesit-search-forward, can you use treesit-beginning-of-thing or treesit--navigate-thing to do what you want? They handle the “child before parent” problem for you, and handles some other edge cases.

Yuan