How to turn on emacs auto-fill-mode only for code comments?

Question

I have tried

(set (make-local-variable 'comment-auto-fill-only-comments) t)

and also

(auto-fill-mode 0)

Though amazingly, neither of those work after emacs is restarted.

Toggling it works fine with M-x auto-fill-mode.

UPDATE

Using a combination of (thanks Rémi):

(auto-fill-mode 1)
(setq comment-auto-fill-only-comments t)

It works perfectly within programming files, where there are comments. However, in text mode, it auto-fills everywhere.

How can I turn off auto-fill-mode completely when inside text documents?

Emacs has detailed online documentation. It might be helpful to use describe-function, describe-variable to find out how you could use a function, a variable. — jfs
try describe-variable, it may show you that comment-auto-fill-only-comments is not what you think it is. If that's the case, then possibly there's a hook running after you set the value, that stomps on your value. — Cheeso

Rémi Rémi · Accepted Answer · 2010-12-18T11:59:25

If you want Emacs to auto-fill comments you must not make comment-auto-fill-only-comments a local variable:

(setq comment-auto-fill-only-comments t)

If you want it only in some mode but not all you have to add it to the correct hook:

(add-hook 'ruby-mode-hook 
          (lambda () ((set (make-local-variable 'comment-auto-fill-only-comments) t)))

UPDATE answer

To remove auto-fill from text mode, you have to use hook:

(add-hook 'text-mode-hook 
          (lambda () (auto-fill-mode -1)))

Note that this will change also the auto-fill state in mode deriving off text-mode (latex-mode is one examples, there are a lot of other such mode)