altering-key-bindings-from-minor-mode-keymaps.md

Removing/Altering Key Bindings from Minor Mode Keymaps

I wanted to bind C-a to beginning-of-visual-line when editing markdown files, which I did with the following:

First enable visual-line-mode when editing markdown files:

(add-hook 'gfm-mode-hook #'visual-line-mode)

And bind C-a to beginning-of-visual-line when in the visual line mode

(add-hook 'visual-line-mode
          (lambda ()
            (define-key visual-line-mode-map (kbd "C-a") 'beginning-of-visual-line)))

The problem was that C-a was already bound in prelude, to crux-move-beginning-of-line:

I knew how to unbind it, with something like

(add-hook 'gfm-mode-hook
          (lambda ()
            (define-key prelude-mode-map (kbd "C-a") nil)))

But it apparently always unbind it, since it's been removed from the keymap, as I still wanted to keep the C-a binding, I like it when editing other files, like Ruby for instance.

The solution was to do the following,

(defun my-gfm-mode-hook ()
  (let ((oldmap (cdr (assoc 'prelude-mode minor-mode-map-alist)))
        (newmap (make-sparse-keymap)))
    (set-keymap-parent newmap oldmap)
    (define-key newmap (kbd "C-a") nil)
    (make-local-variable 'minor-mode-overriding-map-alist)
    (push `(prelude-mode . ,newmap) minor-mode-overriding-map-alist))
  )

(add-hook 'gfm-mode-hook 'my-gfm-mode-hook)

Once again, thanks to Bozhidar Batsov!

Source: https://emacsredux.com/blog/2013/09/25/removing-key-bindings-from-minor-mode-keymaps/