Inserting a link after typing “[[” in Org

Many personal wiki systems use “[[” to insert internal links. Often times when a user types “[[”, an autocomplete prompt will be shown.

Org-roam also implements this with a completion-at-point backend, but personally I prefer autocompletion with Ivy over Company. I find Ivy easier to navigate when there is a large number of candidates.

I have a custom k/insert-link command, which functionally serves the same purpose as org-roam-insert. I will use that command to insert links, but the latter can also be used.

My requirements

I still want to be able to type “[” on its own without having to use quoted-insert.
I also don't want to use a timeout to detect if we're typing “[” or “[[”. This rules out key-chord.
It'd be nice if this can be generalized to other keys.

Details

How do we detect which key is pressed?

There is a last-command-event variable which turns out to contain what we want.

We can try to probe what its value usually is by defining a command like this:

(defun k/test-last-command-event ()
  (interactive)
  (message "%s" last-command-event))

(general-def
  :keymaps 'text-mode-map
  :states 'insert
  "a" #'k/test-last-command-event
  "b" #'k/test-last-command-event)

Then test it out:

Type “a” → Notice 97 (the character code for “a”) in the echo area
Type “b” → Notice 98 (the character code for “b”) in the echo area
Type “a” then “b” → Notice the second time still wrote 98 to the echo area, confirming that we don't see events from the previous command.

After testing this can be done to undo the binding:

(general-unbind
  :keymaps 'text-mode-map
  :states 'insert
  "a" "b")

How do we detect if we're truly typing “[[” at once?

We can check last-command and see if it's our command. If it isn't, we simply fall back to inserting the character.

(cond
 ((and (eq last-command #'k/insert-link/double-key) ; this line
       (eq (char-before) last-command-event))
  (delete-char -1)
  (call-interactively #'k/insert-link))
 (t (insert (string last-command-event))))

The full command

(defun k/insert-link/double-key ()
  "Insert a link after calling this command twice with the same key.

For example, to insert a link after typing \"[[\":

  (general-def :keymaps 'org-mode-map :states 'insert
    \"[\" #'k/insert-link/double-key)"
  (interactive)
  (cond
   ((and (eq last-command #'k/insert-link/double-key)
         (eq (char-before) last-command-event))
    (delete-char -1)
    (call-interactively #'k/insert-link))
   (t (insert (string last-command-event)))))

And I can bind it to a key like this:

(general-def
  :keymaps 'org-mode-map
  :states 'insert
  "[" #'k/insert-link/double-key)

Now if I type “[[” in Org mode in insert state, I'll be prompted with a list of notes to insert.