org-clone-subtree-with-time-shift: Accept 0 clones

* lisp/org.el (org-clone-subtree-with-time-shift): Allow argument
  specifying number of clones to be 0.

* testing/lisp/test-org.el (test-org/clone-with-time-shift): Add
  tests.

This makes it possible to clone a subtree with a repeating timestamp
so that the repeater is removed from the original subtree and a single
shifted, repeating clone is created.  If the original subtree does not
have a repeating timestamp, no clones will be made.

etc/ORG-NEWS

@@ -392,6 +392,10 @@ of tables and lists of listings can be inserted in the document with
 *** Countdown timer support hh:mm:ss format
 In addition to setting countdown timers in minutes, they can also be
 set using the hh:mm:ss format.
+*** Extend ~org-clone-subtree-with-time-shift~
+~org-clone-subtree-with-time-shift~ now accepts 0 as an argument for
+the number of clones, which removes the repeater from the original
+subtree and creates one shifted, repeating clone.
 ** Miscellaneous
 *** Strip all meta data from ITEM special property
 ITEM special property does not contain TODO, priority or tags anymore.

lisp/org.el

@@ -8739,7 +8739,12 @@ the following will happen:
 - the start days in the repeater in the original entry will be shifted
   to past the last clone.
 In this way you can spell out a number of instances of a repeating task,
-and still retain the repeater to cover future instances of the task."
+and still retain the repeater to cover future instances of the task.
+
+As described above, N+1 clones are produced when the original
+subtree has a repeater.  Setting N to 0, then, can be used to
+remove the repeater from a subtree and create a shifted clone
+with the original repeater."
   (interactive "nNumber of clones to produce: ")
   (let ((shift
 	 (or shift
@@ -8757,8 +8762,8 @@ and still retain the repeater to cover future instances of the task."
 	(org-clock-re (format "^[ \t]*%s.*$" org-clock-string))
 	beg end template task idprop
 	shift-n shift-what doshift nmin nmax)
-    (if (not (and (integerp n) (> n 0)))
+    (unless (wholenump n)
-	(user-error "Invalid number of replications %s" n))
+      (user-error "Invalid number of replications %s" n))
     (if (and (setq doshift (and (stringp shift) (string-match "\\S-" shift)))
 	     (not (string-match "\\`[ \t]*\\+?\\([0-9]+\\)\\([hdwmy]\\)[ \t]*\\'"
 				shift)))

testing/lisp/test-org.el

@@ -1067,6 +1067,52 @@
      (org-insert-todo-heading-respect-content)
      (and (eobp) (org-at-heading-p)))))
 
+(ert-deftest test-org/clone-with-time-shift ()
+  "Test `org-clone-subtree-with-time-shift'."
+  ;; Clone non-repeating once.
+  (should
+   (equal "\
+* H1\n<2015-06-21>
+* H1\n<2015-06-23>
+"
+	  (org-test-with-temp-text "* H1\n<2015-06-21 Sun>"
+	    (org-clone-subtree-with-time-shift 1 "+2d")
+	    (replace-regexp-in-string
+	     "\\( [.A-Za-z]+\\)\\( \\+[0-9][hdmwy]\\)?>" "" (buffer-string)
+	     nil nil 1))))
+  ;; Clone repeating once.
+  (should
+   (equal "\
+* H1\n<2015-06-21>
+* H1\n<2015-06-23>
+* H1\n<2015-06-25 +1w>
+"
+	  (org-test-with-temp-text "* H1\n<2015-06-21 Sun +1w>"
+	    (org-clone-subtree-with-time-shift 1 "+2d")
+	    (replace-regexp-in-string
+	     "\\( [.A-Za-z]+\\)\\( \\+[0-9][hdmwy]\\)?>" "" (buffer-string)
+	     nil nil 1))))
+  ;; Clone non-repeating zero times.
+  (should
+   (equal "\
+* H1\n<2015-06-21>
+"
+	  (org-test-with-temp-text "* H1\n<2015-06-21 Sun>"
+	    (org-clone-subtree-with-time-shift 0 "+2d")
+	    (replace-regexp-in-string
+	     "\\( [.A-Za-z]+\\)\\( \\+[0-9][hdmwy]\\)?>" "" (buffer-string)
+	     nil nil 1))))
+  ;; Clone repeating "zero" times.
+  (should
+   (equal "\
+* H1\n<2015-06-21>
+* H1\n<2015-06-23 +1w>
+"
+	  (org-test-with-temp-text "* H1\n<2015-06-21 Sun +1w>"
+	    (org-clone-subtree-with-time-shift 0 "+2d")
+	    (replace-regexp-in-string
+	     "\\( [.A-Za-z]+\\)\\( \\+[0-9][hdmwy]\\)?>" "" (buffer-string)
+	     nil nil 1)))))
 
 
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