Re: How to automatically write *Messages" buffer to a file?

[Joe Corneli <jcorneli@math.utexas.edu>]

   > From: Pascal Bourguignon <spam@mouse-potato.com>
   > Date: 24 Nov 2004 15:06:38 +0100
   > 
   > Brad Collins <brad@chenla.org> writes:
   > 
   > > Is there is a simple way of getting Emacs to automatically append
   > > messages in the message buffer to a file so messages work as a log file?
   > > 
   > > I've been looking around and it seems this should be dead easy but I
   > > can't figure it out?
   > 
   > The best I can figure is that the simple way to do it would be to
   > modify the C source of emacs.  message is a buit-in function.

   How about an after-change function that'd do this only for the
   *Messages* buffer?

If you want a faithful account of what is actually in the *Messages*
buffer, that would definitely be better than defadvising `message' --
because a significant amount of stuff that is written to the
*Messages* buffer is not put there by `message'.

   > I know of no way from emacs lisp to append a line to a file.

   ??? What's wrong with append-to-file?

Something fairly minor... namely that it adds text to the *Messages*
buffer (not through the `message' mechanism), so one has to delicately
advise it to shut up (for use in this application).

Here is a little code that *does not work as desired* but I think it
is pretty close.  I'd be happy if someone could point out the bug(s).


(defvar messaging-on t
  "Control whether or not messages will be printed.
By default, they are.")

(defadvice write-region (around no-wrote-file activate)
  "Turn off the printout associated with writing files.
This is necessary to add as a supplement to `nomessage' because
the \"Wrote file\" or \"Added to file\" message is not printed
through the `message' mechanism.  The observed effect of this
piece of advice is that neither `save-buffer' nor `write-file'
will print anything out when they run."
  (if messaging-on
      ad-do-it
    (set-buffer-modified-p nil)
    (ad-set-arg 4 t)
    (ad-set-arg 6 nil)
    ad-do-it))

(defun turn-on-logging-advice ()
  (ad-enable-advice 'write-region 'around 'no-wrote-file)
  (ad-activate 'write-region))

(defun turn-off-logging-advice ()
  (ad-disable-advice 'write-region 'around 'no-wrote-file)
  (ad-activate 'write-region))

(turn-off-logging-advice)

;;

(defun setup-logging ()
  (interactive)
  (message "begin logging")
  (set-buffer "*Messages*")
  (make-variable-buffer-local 'after-change-functions)
  ;; be less destructive if you care
  (setq after-change-functions
         '(log-message))
  (turn-on-logging-advice))

(defun stop-logging ()
  (interactive)
  (message "stop logging")
  ;; see prev comment
  (setq after-change-functions nil)
  (turn-off-logging-advice))

(defun log-message (beg end range)
  (let ((messaging-on nil))
    (append-to-file beg end "~/LOG")))

(defun test-message ()
  (interactive)
  (message "hi"))