Detect when a key is rebound to another command

Question

First, some context:

I am in the process of debugging a strange interaction between smartparens and Org Speed Keys:

After editing an .org file for a while, specific speed keys for navigating the outline start to be treated as though they are modifying the buffer. For instance, if I press n on a heading after saving the file, the portion of the mode line that indicates whether the file has been modified or not changes from -- (unmodified) to ** (modified). No characters are inserted into the buffer though.

I tried to figure out what might be causing this problem by doing C-h k n right after opening the .org file and then again after the problematic behavior started. Turns out that initially, n is bound to org-self-insert-command, and gets rebound to sp--self-insert-command later on.

The problem is that I have no idea when the command bound to n changes. I also tried C-h l (view-lossage) a few times after the behavior changed but I couldn't detect any patterns that would give me a hint as to what might be triggering the change in behavior.

Question:

I think in order to solve this problem I need to pinpoint the exact command that is causing n to be rebound to sp--self-insert-command (if only to be able to automatically reset the binding).

So my question is: How can I detect when the command bound to n changes?

Answer 1

Use defadvice to intercept define-key and check for your desired key sequence.

(defadvice define-key (before define-key-check-n (keymap key def))
  (when (equal key "n")
    (message "`n' redefined")))

(You can change (message ...) to (debug) or something else that'll give you more information about where you are.)

Make the advice effective with

(ad-activate 'define-key)

To discard the advice, first disable it

(ad-disable-advice 'define-key 'before 'define-key-check-n)

and then "reconfigure" the function again

(ad-activate 'define-key)

Answer 2

You could do something like this:

(add-hook 'post-command-hook
          (lambda ()
            (when (not (eq (key-binding (kbd "n") t)
                           'org-self-insert-command))
              (message "Command %s rebound the key!" this-command)))
          nil t)

This will add the lambda function buffer-locally to be run after every command, so you can just kill the buffer to get rid of the behavior. If after a command (kbd "n") is not org-self-insert-command anymore, it will tell you which command did that.