Why does this code fail to nullify all keybindings in a keymap?

Question

Long story short, there's a little library I like but I don't like any of the default keybindings. E.g. it's a global minor mode and binds a function to C-c C-s, but that shadows org-schedule in my org and org-agenda buffers.

I want to keep the little library but get rid of all the bindings in the little library keymap.

In an early attempt to do this, I tried the following (after confirming that little-library-mode-map is where the bindings live):

(with-eval-after-load "little-library-mode"
  (setq little-library-mode-map (make-sparse-keymap)))

The code "succeeds" (C-h v little-library-mode-map RET shows that it's just (keymap) now) but all the little library keybindings still "work" (C-c C-s still does the little library function, including in org and org-agenda buffers).

I've found another way to solve my issue, but I'm really curious why this approach fails. Emacs' keybindings still seem like black magic to me.

Answer 1

There are three important things in this story:

• the minor mode keymap
• its name
• the sparse keymap you create

Basically what you did is make the name point at the sparse keymap instead of the original, but it's too late: the minor mode uses the original.

Answer 2

At some point when activating little-library-mode the keymap stored in the variable little-library-mode-map gets added to minor-mode-map-alist:

(push (cons 'little-library-mode little-library-mode-map) minor-mode-map-alist)

Emacs uses this alist to lookup minor-mode bindings. When you bind the variable little-library-mode-map to a new value afterwards this has no effect on the keymap minor-mode-map-alist points to. As noted in the comment by @wasamasa one way to get rid of all bindings in this keymap is to mutate the keymap directly:

 (setcdr little-library-mode-map nil)

Another way is to reset the keymap before loading the library:

(setq little-library-mode-map (make-sparse-keymap))
(with-eval-after-load "little-library-mode" 
    ...more-setup-code)

If the minor-mode is well behaved, this will avoid instantiating its bindings, too.