bug#73404: 30.0.50; [forward/kill/etc]-sexp commands do not behave as expected in tree-sitter modes

[Juri Linkov <juri@linkov.net>]

While testing treesit-forward-sexp-list, I discovered that
thing-navigation functions are not restricted to named nodes.

I wonder if there a reason to find anonymous nodes as things?

The problem was found with the node "unless" in Ruby:

  unless cond
    a += 1
  else
    b -= 1
  end

Here the named node 'unless' has exactly the same name
as the anonymous node with the text "unless":

  (unless "unless" condition: (identifier)

Finding anonymous nodes breaks forward-sexp when point is on "unless":

  un-!-less cond
    a += 1
  else
    b -= 1
  end

because (treesit-thing-at (point) 'sexp t) finds

  #<treesit-node "unless" in 156-162>

instead of

  #<treesit-node unless in 156-203>

Also this breaks backward-sexp and backward-up-list
because treesit--thing-sibling finds
the anonymous node "unless" as a previous sibling
instead of the named node 'unless' as a parent.

Would the right solution be to check if the found thing
is a named node?  With something like:

diff --git a/lisp/treesit.el b/lisp/treesit.el
index 18200acf53f..9ad879ee40c 100644
--- a/lisp/treesit.el
+++ b/lisp/treesit.el
@@ -2711,6 +2774,7 @@ treesit--thing-sibling
                      (lambda (n) (>= (treesit-node-start n) pos))))
          (iter-pred (lambda (node)
                       (and (treesit-node-match-p node thing t)
+                           (treesit-node-check node 'named)
                            (funcall pos-pred node))))
          (sibling nil))
     (when cursor
@@ -2760,6 +2824,7 @@ treesit-thing-at
   (let* ((cursor (treesit-node-at pos))
          (iter-pred (lambda (node)
                       (and (treesit-node-match-p node thing t)
+                           (treesit-node-check node 'named)
                            (if strict
                                (< (treesit-node-start node) pos)
                              (<= (treesit-node-start node) pos))