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

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

Juri Linkov <juri@linkov.net> writes:

>> 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?
>
> Could you please send a few of short examples of each style.
> This would help to make a better decision.
> And later these examples could be added to tests.

You should be able to see it with this example

int bar(void) {
  return 1;
}

static int
foo (int bar) {
  return 2;
}

int main(void) {
  return 3;
}

If you go to the third function and call `outline-hide-subtree' it
replaces the function name with an ellipsis.

Now if you call `outline-show-all' and try to collapse the second
function (GNU style) it will show

foo (int bar) {...

which looks correct to me.

If you show all again and collapse the first one it will do nothing and
say "Before the first heading". This while still showing the outline
icon in the margin.

At the moment I am experimenting with this solution (DEFUN part omitted
for brevity) but it's probably missing some edge case I am not aware of:

(defun c-ts-mode--outline-predicate (node)
  "Match outlines on lines with function names."
  (when-let* ((decl (treesit-node-child-by-field-name
                     (treesit-node-parent node) "declarator"))
              (node-pos (treesit-node-start node))
              (decl-pos (treesit-node-start decl))
              (eol (save-excursion (goto-char node-pos) (line-end-position))))
    (and (equal (treesit-node-type decl) "function_declarator")
         (<= node-pos decl-pos)
         (< decl-pos eol))))

Idea is to match a function declarator in the same line as `node' no
matter what node is at bol.

Ciao,
Filippo