(match-substitute-replacement): New function.

lisp/subr.el

@@ -2709,6 +2709,24 @@ STRING should be given if the last search was by `string-match' on STRING."
 	(buffer-substring-no-properties (match-beginning num)
 					(match-end num)))))
 
+
+(defun match-substitute-replacement (replacement
+				     &optional fixedcase literal string subexp)
+  "Return REPLACEMENT as it will be inserted by `replace-match'.
+In other words, all back-references in the form `\\&' and `\\N'
+are substituted with actual strings matched by the last search.
+Optional FIXEDCASE, LITERAL, STRING and SUBEXP have the same
+meaning as for `replace-match'."
+  (let ((match (match-string 0 string)))
+    (save-match-data
+      (set-match-data (mapcar (lambda (x)
+				(if (numberp x)
+				    (- x (match-beginning 0))
+				  x))
+			      (match-data t)))
+      (replace-match replacement fixedcase literal match subexp))))
+
+
 (defun looking-back (regexp &optional limit greedy)
   "Return non-nil if text before point matches regular expression REGEXP.
 Like `looking-at' except matches before point, and is slower.