bug#59763: 29.0.60; Filling for c-ts-mode

[Yuan Fu]

IMO For c-ts-mode to be usable we need to have at least a basic filling
function. Below is the function I have in my init.el, could someone have
a look and see if it’s good? Alternatively we could copy out the comment
and fill it in a temp buffer with c-mode, but I didn’t have the time to try
it out and see how well it works.

(defun ts-c-fill-paragraph (&optional arg)
  (interactive)
  (let* ((node (treesit-node-at (point)))
         (start (treesit-node-start node))
         (end (treesit-node-end node))
         (pstart (save-excursion
                   (forward-paragraph -1)
                   (skip-syntax-forward "-")
                   (point)))
         (pend (save-excursion
                 (forward-paragraph 1)
                 (point))))
    (when (equal (treesit-node-type node) "comment")
      (fill-region (max start pstart) (min end pend)))
    t))

Yuan