Emacs auto-minor-mode based on extension

Question

I found this question somewhat on the topic, but is there a way [in emacs] to set a minor mode (or a list thereof) based on extension? For example, it\'s pretty easy to

Answer 1

This code seems to give what you want:

(defvar auto-minor-mode-alist ()
  "Alist of filename patterns vs correpsonding minor mode functions, see `auto-mode-alist'
All elements of this alist are checked, meaning you can enable multiple minor modes for the same regexp.")

(defun enable-minor-mode-based-on-extension ()
  "Check file name against `auto-minor-mode-alist' to enable minor modes
the checking happens for all pairs in auto-minor-mode-alist"
  (when buffer-file-name
    (let ((name (file-name-sans-versions buffer-file-name))
          (remote-id (file-remote-p buffer-file-name))
          (case-fold-search auto-mode-case-fold)
          (alist auto-minor-mode-alist))
      ;; Remove remote file name identification.
      (when (and (stringp remote-id)
                 (string-match-p (regexp-quote remote-id) name))
        (setq name (substring name (match-end 0))))
      (while (and alist (caar alist) (cdar alist))
        (if (string-match-p (caar alist) name)
            (funcall (cdar alist) 1))
        (setq alist (cdr alist))))))

(add-hook 'find-file-hook #'enable-minor-mode-based-on-extension)

Note: the comparison is done with string-match-p which follows the case-fold-search settings during comparison.

Answer 2

The answer by Trey Jackson seems to be a very robust and extensible solution, but I was looking for something simpler. The following code will enable the fictional hmmm-mode when editing .hmmm files:

(add-hook 'find-file-hook
          (lambda ()
            (when (string= (file-name-extension buffer-file-name) "hmmm")
              (hmmm-mode +1))))