Allow regexp-quote to return its argument

* src/search.c (Fregexp_quote): Only allocate a new string if needed.
* doc/lispref/searching.texi (Regexp Functions):
* etc/NEWS (Incompatible Lisp Changes): Document.

3 files changed, 13 insertions, 4 deletions

diff --git a/doc/lispref/searching.texi b/doc/lispref/searching.texi
index 1286b63446a..65f56b490fd 100644
--- a/doc/lispref/searching.texi
+++ b/doc/lispref/searching.texi
@@ -1562,6 +1562,9 @@ whitespace:
  (concat "\\s-" (regexp-quote string) "\\s-"))
 @end group
 @end example
+
+The returned string may be @var{string} itself if it does not contain
+any special characters.
 @end defun
 
 @cindex optimize regexp
diff --git a/etc/NEWS b/etc/NEWS
index 3072d4081b8..96b2cb129bd 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -2157,6 +2157,10 @@ valid event type.
 be specified in image specs representing the entire bitmap as a single
 bool vector.
 
++++
+** 'regexp-quote' may return its argument string.
+If the argument needs no quoting, it can be returned instead of a copy.
+
 
 * Lisp Changes in Emacs 27.1
 
diff --git a/src/search.c b/src/search.c
index 1e57d2ecbe5..9d95dcbca58 100644
--- a/src/search.c
+++ b/src/search.c
@@ -3138,10 +3138,12 @@ DEFUN ("regexp-quote", Fregexp_quote, Sregexp_quote, 1, 1, 0,
     }
 
   Lisp_Object result
-    = make_specified_string (temp,
-                             SCHARS (string) + backslashes_added,
-                             out - temp,
-                             STRING_MULTIBYTE (string));
+    = (backslashes_added > 0
+       ? make_specified_string (temp,
+                                SCHARS (string) + backslashes_added,
+                                out - temp,
+                                STRING_MULTIBYTE (string))
+       : string);
   SAFE_FREE ();
   return result;
 }