auto-fill inside comments does not work

[CSRaghunandan]

I've set (setq comment-auto-fill-only-comments t) and I've noticed that when structured-haskell-mode is enabled, comments aren't getting auto-filled by default. I'd have to manually select a long comment and execute fill-region.

[emmanueldenloye]

Hey CSRaghunandan, give this piece of code a whirl. (I might add it to pull request). It is not quite what you want, but advise fill-paragraph (or hindent-reformat-decl-or-fill if it replaces it) to use this function with defadvice.

(defun shm-fill-comment ()
"Fill the comment(s)."
(cond ((shm-in-comment)
(fill-paragraph))
((when-let ((beg (save-excursion
(comment-beginning))))
(string= "-- " (buffer-substring-no-properties beg (point))))
(let* ((start (save-excursion (comment-beginning)))
(commentStart (save-excursion
(goto-char start)
(let ((back start))
(while back
(goto-char (- back 1))
(setq back (comment-beginning))))
(point)))
(commentEnd (save-excursion
(goto-char start)
(while (comment-forward))
(point))))
(fill-region commentStart commentEnd)))))

[CSRaghunandan]

@emmanueldenloye can you tell me how I can test this function out? I tried adding advice to hindent-reformat-decl-or-fill and fill-paragraph but could not get the desired feature.
What I want is auto-fill-mode to behave like it does with other modes when comment-auto-fill-only-comments set to t. What it does is, when I type a word and it exceeds the fill-column value, a new comment is created on the next line automatically.

PS. I can also press return and the comment will get auto filled to multiple lines as necessary. No need press M-q.