org-list: Modify M-RET on a description tag

* lisp/org-list.el (org-list-insert-item): On a description tag,
  insert item before current one.  However, past the colons, insert it
  after.
* testing/lisp/test-org-list.el (test-org-list/insert-item): Add
  tests.

Reported-by: Leo Ufimtsev <lufimtse@redhat.com>
<http://permalink.gmane.org/gmane.emacs.orgmode/96330>

lisp/org-list.el

@@ -1273,12 +1273,16 @@ This function modifies STRUCT."
 	   (beforep
 	    (progn
 	      (looking-at org-list-full-item-re)
-	      ;; Do not count tag in a non-descriptive list.
-	      (<= pos (if (and (match-beginning 4)
-			       (save-match-data
-				 (string-match "[.)]" (match-string 1))))
-			  (match-beginning 4)
-			(match-end 0)))))
+	      (<= pos
+		  (cond
+		   ((not (match-beginning 4)) (match-end 0))
+		   ;; Ignore tag in a non-descriptive list.
+		   ((save-match-data (string-match "[.)]" (match-string 1)))
+		    (match-beginning 4))
+		   (t (save-excursion
+			(goto-char (match-end 4))
+			(skip-chars-forward " \t")
+			(point)))))))
 	   (split-line-p (org-get-alist-option org-M-RET-may-split-line 'item))
 	   (blank-nb (org-list-separating-blank-lines-number
 		      pos struct prevs))

testing/lisp/test-org-list.el

@@ -711,7 +711,45 @@
        (goto-char (point-max))
        (org-insert-item)
        (forward-line -1)
-       (looking-at "$")))))
+       (looking-at "$"))))
+  ;; When called before or on the bullet, insert new item before
+  ;; current one.
+  (should
+   (equal "- \n- item"
+	  (org-test-with-temp-text "- item"
+	    (org-insert-item)
+	    (buffer-string))))
+  (should
+   (equal "- \n- item"
+	  (org-test-with-temp-text "- <point>item"
+	    (org-insert-item)
+	    (buffer-string))))
+  ;; When called on tag in a descriptive list, insert new item before
+  ;; current one too.
+  (should
+   (equal "-  :: \n- tag :: item"
+	  (org-test-with-temp-text "- tag <point>:: item"
+	    (org-insert-item)
+	    (buffer-string))))
+  (should
+   (equal "-  :: \n- tag :: item"
+	  (org-test-with-temp-text "- ta<point>g :: item"
+	    (org-insert-item)
+	    (buffer-string))))
+  ;; Further, it splits the line or add a blank new item after it,
+  ;; according to `org-M-RET-may-split-line'.
+  (should
+   (equal "- it\n- em"
+	  (org-test-with-temp-text "- it<point>em"
+	    (let ((org-M-RET-may-split-line  '((default . t))))
+	      (org-insert-item))
+	    (buffer-string))))
+  (should
+   (equal "- item\n- "
+	  (org-test-with-temp-text "- it<point>em"
+	    (let ((org-M-RET-may-split-line  '((default . nil))))
+	      (org-insert-item))
+	    (buffer-string)))))
 
 (ert-deftest test-org-list/repair ()
   "Test `org-list-repair' specifications."