Re: [hober0@gmail.com: Re: mode-line redisplay bug]

[storm@cua.dk (Kim F. Storm)]

Henrik Enberg <henrik.enberg@telia.com> writes:

>> From: Edward O'Connor <hober0@gmail.com>
>> Date: Fri, 12 Aug 2005 10:19:09 -0700
>> 
>> > Edward, can you please recheck if this problem happens with "emacs -Q"?
>> 
>> It still happens with emacs -q --no-site-file.
>
> FWIW, it happens for me too on GNU/Linux with emacs -q --no-site-file

It didn't happen when I just executed the code manually in *scratch*, but
it does happen for me if I save Edward's instructions in a file xx.el,
and run emacs like this:

      emacs -Q -D -l xx.el

---- xx.el:

;; Step 0: Launch an Emacs on some variety of window-system.

;; Step 1: Ensure that there's something in the mode-line that changes
;;         periodically.

(defvar frob " hello")

(add-to-list 'minor-mode-alist '(t frob))

(defun frob-it ()
  "Change `frob' to a random string, and force a mode-line update."
  (setq frob (concat " " (make-string (+ 2 (random 6))
				      (+ 97 (random 26)))))
  (force-mode-line-update t))

(run-with-timer 5 5 'frob-it)

;; Step 2: Ensure that there's a buffer with no mode-line.

(with-current-buffer (get-buffer "*scratch*")
  (setq header-line-format mode-line-format
	mode-line-format   nil))

;; Step 3: Make a key binding for switching between the buffer with no
;;         mode-line and a buffer with a mode-line which uses
;;         `switch-to-buffer'.

(global-set-key (kbd "C-c c")
		(lambda ()
		  (interactive)
		  (if (eq (current-buffer) (get-buffer "*Messages*"))
		      (switch-to-buffer (get-buffer "*scratch*"))
		    (switch-to-buffer (get-buffer "*Messages*")))))

;; Step 4: To observe the bug, switch to *scratch*, wait for the
;;         header-line to change, and hit C-c c. More often than not,
;;         the mode-line in *Messages* will be only partially
;;         displayed. (Try this several times, by repeated use of the
;;         C-c c key binding, if you don't observe the effect right
;;         away.) Typing C-l (unsurprisingly) fixes the display.

-- 
Kim F. Storm <storm@cua.dk> http://www.cua.dk