Only save clock stuff if it has been loaded as well

Kai Tetzlaff writes:

> i noticed that when using the org-mode clock persistence, the
> stored clock data gets deleted when i start emacs and exit again
> without turning on org-mode in between.
>
> When looking at org-clock-persistence-insinuate it looks like
> org-clock load will only run after org-mode gets started whereas
> org-clock-save will always be called when exiting emacs:
>
> (defun org-clock-persistence-insinuate ()
>  "Set up hooks for clock persistence"
>  (add-hook 'org-mode-hook 'org-clock-load)
>  (add-hook 'kill-emacs-hook 'org-clock-save))
>
> Not running org-mode-hook (i.e. not starting org-mode) thus does
> not load clock data but org-clock-save overwrites any prviously
> saved data when exiting emacs.
>
> An easy fix for that would be to just add org-clock-load to e.g.
> emacs-startup-hook. But this will only work if the code in
> org-clock-load does not depend on any org-mode initialization
> code (or would require loading org-mode).
>
> So org-clock-save should probably check if org-clock-load has
> been running during the current emacs session (or if clock
> persistence was just enabled) and only then save clock data when
> exiting emacs. I tried to add this to the code in org-clock-save:

lisp/ChangeLog

@@ -1,3 +1,10 @@
+2009-10-25  Carsten Dominik  <carsten.dominik@gmail.com>
+
+	* org-clock.el (org-clock-has-been-used): New variable.
+	(org-clock-in): Set `org-clock-has-been-used'.
+	(org-clock-save): Save only if clock data has been used or created
+	during this session.
+
 2009-10-24  Carsten Dominik  <carsten.dominik@gmail.com>
 
 	* org-clock.el (org-clock-persist): New value, to store only the

lisp/org-clock.el

@@ -233,6 +233,8 @@ to add an effort property.")
   "Hook run when cancelling the current clock.")
 (defvar org-clock-goto-hook nil
   "Hook run when selecting the currently clocked-in entry.")
+(defvar org-clock-has-been-used nil
+  "Has the clock been used during the current Emacs session?")
 
 ;;; The clock for measuring work time.
 
@@ -937,6 +939,7 @@ the clocking selection, associated with the letter `d'."
 	    (move-marker org-clock-hd-marker
 			 (save-excursion (org-back-to-heading t) (point))
 			 (buffer-base-buffer))
+	    (setq org-clock-has-been-used t)
 	    (or global-mode-string (setq global-mode-string '("")))
 	    (or (memq 'org-mode-line-string global-mode-string)
 		(setq global-mode-string
@@ -1824,7 +1827,10 @@ This function is made for clock tables."
   "Persist various clock-related data to disk.
 The details of what will be saved are regulated by the variable
 `org-clock-persist'."
-  (when org-clock-persist
+  (when (and org-clock-persist
+             (or org-clock-loaded
+		 org-clock-has-been-used
+		 (not (file-exists-p org-clock-persist-file))))
     (let (b)
       (with-current-buffer (find-file (expand-file-name org-clock-persist-file))
 	(progn