1 files changed, 19 insertions, 11 deletions

diff --git a/lisp/subr.el b/lisp/subr.el
index ee6c468d711..956fcef64f4 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -1123,28 +1123,36 @@ The return value is the new value of LIST-VAR."
                                 (< oa ob)
                               oa)))))))
 
-(defun add-to-history (history-var newelt &optional maxelt)
+(defun add-to-history (history-var newelt &optional maxelt keep-all)
   "Add NEWELT to the history list stored in the variable HISTORY-VAR.
 Return the new history list.
 If MAXELT is non-nil, it specifies the maximum length of the history.
 Otherwise, the maximum history length is the value of the `history-length'
 property on symbol HISTORY-VAR, if set, or the value of the `history-length'
 variable.
-Remove duplicates of NEWELT unless `history-delete-duplicates' is nil."
+Remove duplicates of NEWELT if `history-delete-duplicates' is non-nil.
+If optional fourth arg KEEP-ALL is non-nil, add NEWELT to history even
+if it is empty or a duplicate."
   (unless maxelt
     (setq maxelt (or (get history-var 'history-length)
                      history-length)))
   (let ((history (symbol-value history-var))
         tail)
-    (if history-delete-duplicates
-        (setq history (delete newelt history)))
-    (setq history (cons newelt history))
-    (when (integerp maxelt)
-      (if (= 0 maxelt)
-          (setq history nil)
-        (setq tail (nthcdr (1- maxelt) history))
-        (when (consp tail)
-          (setcdr tail nil))))
+    (when (and (listp history)
+               (or keep-all
+                   (not (stringp newelt))
+                   (> (length newelt) 0))
+               (or keep-all
+                   (not (equal (car history) newelt))))
+      (if history-delete-duplicates
+          (delete newelt history))
+      (setq history (cons newelt history))
+      (when (integerp maxelt)
+        (if (= 0 maxelt)
+            (setq history nil)
+          (setq tail (nthcdr (1- maxelt) history))
+          (when (consp tail)
+            (setcdr tail nil)))))
     (set history-var history)))