How can I apply a hook to multiple Emacs modes at once?

Question

I was reading an article about well-formatted Git commits, and I was wondering how I could apply some of the rules to the Magit log mode.

It seems to use 3 major modes simultaneously: Magit, Log, Edit.

So how would I get just those modes, when used together, to hard-wrap at 72 characters automatically?

Answer 1

There can be only one major mode in Emacs buffer (unless you are using something like MMM or MuMaMo). In your case that one major mode is magit-log-edit-mode, whose name consists of three words ("Magit Log Edit"). You can just add to it whatever hook you like:

(defun my-turn-on-auto-fill ()
  (setq fill-column 72)
  (turn-on-auto-fill))

(add-hook 'magit-log-edit-mode-hook 'my-turn-on-auto-fill)