[misc-new-features 3/5] Add an option to sort tags automatically.

[James TD Smith <ahktenzero@mohorovi.cc>]

---
 lisp/ChangeLog |    3 +++
 lisp/org.el    |   17 ++++++++++++++++-
 2 files changed, 19 insertions(+), 1 deletions(-)

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 348ade3..9ce7a17 100755
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -11,6 +11,9 @@
 	SINCE_IA. These give the time since any active or inactive
 	timestamp in an entry.
 	(org-special-properties): Add SINCE, SINCE_IA.
+	(org-tags-sort-function): Add custom declaration for tags
+	sorting function.
+	(org-set-tags): Sort tags if org-tags-sort-function is set
 
 2009-07-08  Carsten Dominik  <carsten.dominik@gmail.com>
 
diff --git a/lisp/org.el b/lisp/org.el
index d08155a..854d09c 100644
--- a/lisp/org.el
+++ b/lisp/org.el
@@ -2337,6 +2337,15 @@ is better to limit inheritance to certain tags using the variables
 	  (const :tag "Yes, do list them" t)
 	  (const :tag "List them, indented with leading dots" indented)))
 
+(defcustom org-tags-sort-function nil
+  "When set, tags are sorted using this function as a comparator"
+  :group 'org-tags
+  :type '(choice
+	  (const :tag "No sorting" nil)
+	  (const :tag "Alphabetical" string<)
+	  (const :tag "Reverse alphabetical" string>)
+	  (function :tag "Custom function" nil)))
+
 (defvar org-tags-history nil
   "History of minibuffer reads for tags.")
 (defvar org-last-tags-completion-table nil
@@ -10840,11 +10849,17 @@ With prefix ARG, realign all tags in headings in the current buffer."
 	  ;; No boolean logic, just a list
 	  (setq tags (replace-match ":" t t tags))))
 
+      (if org-tags-sort-function
+	  (setq tags (mapconcat 'identity
+				(sort (org-split-string tags (org-re "[^[:alnum:]_@]+"))
+				      org-tags-sort-function) ":")))
+
       (if (string-match "\\`[\t ]*\\'" tags)
-          (setq tags "")
+	  (setq tags "")
 	(unless (string-match ":$" tags) (setq tags (concat tags ":")))
 	(unless (string-match "^:" tags) (setq tags (concat ":" tags))))
 
+
       ;; Insert new tags at the correct column
       (beginning-of-line 1)
       (cond
-- 
1.6.3.3