Add conditional operator xor to subr.el

Suggested by Oleh Krehel and implemented by Basil Contovounesios in
the following thread:
https://lists.gnu.org/archive/html/emacs-devel/2019-07/msg00547.html

* lisp/array.el (xor): Move unused function from here...
* lisp/subr.el: ...to here, and improve.
* lisp/gnus/spam.el (spam-xor):
* lisp/play/5x5.el (5x5-xor):
* lisp/proced.el (proced-xor):
* lisp/progmodes/idlwave.el (idlwave-xor):
* lisp/vc/diff-mode.el (diff-xor): Define as obsolete aliases of,
and replace all uses with, xor.
* lisp/jsonrpc.el: Remove unused dependency on array.el.
* lisp/org/org.el (org-xor): Move from here...
* lisp/org/org-compat.el (org-xor): ...to here, as a compatibility
shim for xor.
* lisp/progmodes/idlw-shell.el (idlwave-shell-enable-all-bp):
* lisp/simple.el (exchange-point-and-mark):
* lisp/windmove.el (windmove-display-in-direction): Use xor.
* lisp/strokes.el (strokes-xor): Remove commented-out xor
implementation.

* doc/lispref/control.texi (Control Structures): Extend menu entry
for new combining condition.
(Combining Conditions):
* etc/NEWS (Lisp Changes): Document xor.

* test/lisp/subr-tests.el (subr-test-xor): New test.

1 files changed, 4 insertions, 7 deletions

diff --git a/lisp/proced.el b/lisp/proced.el
index db8bdb5ac80..24bc321f434 100644
--- a/lisp/proced.el
+++ b/lisp/proced.el
@@ -1194,10 +1194,7 @@ Return `equal' if T1 equals T2.  Return nil otherwise."
 
 ;;; Sorting
 
-(defsubst proced-xor (b1 b2)
-  "Return the logical exclusive or of args B1 and B2."
-  (and (or b1 b2)
-       (not (and b1 b2))))
+(define-obsolete-function-alias 'proced-xor 'xor "27.1")
 
 (defun proced-sort-p (p1 p2)
   "Predicate for sorting processes P1 and P2."
@@ -1208,8 +1205,8 @@ Return `equal' if T1 equals T2.  Return nil otherwise."
              (k2 (cdr (assq (car sorter) (cdr p2)))))
         ;; if the attributes are undefined, we should really abort sorting
         (if (and k1 k2)
-            (proced-xor (funcall (nth 1 sorter) k1 k2)
-                        (nth 2 sorter))))
+            (xor (funcall (nth 1 sorter) k1 k2)
+                 (nth 2 sorter))))
     (let ((sort-list proced-sort-internal) sorter predicate k1 k2)
       (catch 'done
         (while (setq sorter (pop sort-list))
@@ -1219,7 +1216,7 @@ Return `equal' if T1 equals T2.  Return nil otherwise."
                 (if (and k1 k2)
                     (funcall (nth 1 sorter) k1 k2)))
           (if (not (eq predicate 'equal))
-              (throw 'done (proced-xor predicate (nth 2 sorter)))))
+              (throw 'done (xor predicate (nth 2 sorter)))))
         (eq t predicate)))))
 
 (defun proced-sort (process-alist sorter descend)