bug#74448: 30.0.92; c-ts-mode outlines only work with GNU or emacs style

[Filippo Argiolas <filippo.argiolas@gmail.com>]

Hi, I've been playing with the new treesitter based outline minor mode
and c-ts-mode.

It seems that `outline-hide-subtree' is only working properly when code
is formatted with either GNU or emacs style.

To test try it with a function where the function declarator is preceded on the
same line by either type or storage class and type. It will fold the
function heading instead of the function body.

Problem seems `c-ts-mode--outline-predicate' only checks for
function_declarator nodes at the beginning of line (like in GNU coding
style) but other coding style will start the function line with either
storage class (e.g. static) or type.

Something like this seems to work a little better:

(defun c-ts-mode--outline-predicate (node)
  "Match outlines on lines with function names."
  (or (and (or (equal (treesit-node-type node) "function_declarator")
               (equal (treesit-node-type node) "storage_class_specifier")
               (equal (treesit-node-type node) "primitive_type")
               (equal (treesit-node-type node) "type_identifier"))
           (equal (treesit-node-type (treesit-node-parent node))
                  "function_definition"))
      ;; DEFUNs in Emacs sources.
      (and c-ts-mode-emacs-sources-support
           (c-ts-mode--emacs-defun-p node))))

But it kind of breaks GNU style by adding two outlines per function
definition. Also it seems a bit ugly to enumerate all the node types by
hand, there probably is a nicer way to detect a line with a
function_declarator not at bol.

Any better idea?

Thanks,
Filippo