bug#4081: Overlay keymap and timers

[Mihai Bazon]

Hi folks,

I identified a possible bug, just wondering if there's a known
workaround.  Please CC me in any reply as I'm not subscribed to the
list.

Short description
=================

    When creating overlays in a function called by run-with-timer,
    their keymap becomes available only *after* some key has been
    pressed.

Sample code
===========

    (setq counter 0)
    (setq my-keymap (make-sparse-keymap))
    (define-key my-keymap (kbd "M-n") 
      (lambda()
        (interactive)
        (message "Got it %s!" (setq counter (+ counter 1)))))
    
    (defun my-highlight ()
      (interactive)
      (save-excursion
        (beginning-of-buffer)
        (while (search-forward-regexp "\\<overlay\\>" nil t)
          (let ((overlay (make-overlay (- (point) 7) (point))))
            (overlay-put overlay 'face 'highlight)
            (overlay-put overlay 'evaporate t)
            ;; using 'local-map doesn't make any difference
            (overlay-put overlay 'keymap my-keymap)
            (overlay-put overlay 'my-property t)))))
    
    (defun my-highlight-with-timer ()
      (interactive)
      (run-with-timer 0.5 nil 'my-highlight))
    
    (defun my-highlight-clear ()
      (interactive)
      (remove-overlays (point-min) (point-max) 'my-property t))

Eval this code, then type "overlay" in some buffer and move the caret
somewhere in the middle of the word.

* Case 1.  M-x my-highlight.  The word gets colored.  If you press M-n,
  it will display "Got it 1!" in the minibuffer -- works as expected.

Now clear it with M-x my-highlight-clear.

* Case 2.  M-x my-highlight-with-timer.  After half a second, the word
  gets colored.  If we immediately press M-n now, we get "M-n is 
  undefined". However, pressing M-n a second time works.

Clear it again with my-highlight-clear.

* Case 3.  M-x my-highlight-with-timer, then press some key such as C-f
  (make sure the cursor doesn't leave the overlay).  Then pressing M-n
  works as expected.

My guess is that the keymap becomes active the moment a key is released
(?) (or in some post-command-hook?) and the cursor is within the
overlay.  So if set without a timer, it gets a chance to be activated
straight away, but with a timer there isn't any key release to trigger
it so it becomes active only after some key has been pressed.

Not sure if this is a bug, but it's sure annoying and I've no idea how
to work around it.  Any help is appreciated.

Cheers,
-Mihai