Change RENAME behavior when src and dst keys are the same.

Fixes issue #2392.

src/db.c

@@ -688,16 +688,20 @@ void shutdownCommand(redisClient *c) {
 void renameGenericCommand(redisClient *c, int nx) {
     robj *o;
     long long expire;
+    int samekey = 0;
 
-    /* To use the same key as src and dst is probably an error */
+    /* When source and dest key is the same, no operation is performed,
-    if (sdscmp(c->argv[1]->ptr,c->argv[2]->ptr) == 0) {
+     * if the key exists, however we still return an error on unexisting key. */
-        addReply(c,shared.sameobjecterr);
+    if (sdscmp(c->argv[1]->ptr,c->argv[2]->ptr) == 0) samekey = 1;
-        return;
-    }
 
     if ((o = lookupKeyWriteOrReply(c,c->argv[1],shared.nokeyerr)) == NULL)
         return;
 
+    if (samekey) {
+        addReply(c,nx ? shared.czero : shared.ok);
+        return;
+    }
+
     incrRefCount(o);
     expire = getExpire(c->db,c->argv[1]);
     if (lookupKeyWrite(c->db,c->argv[2]) != NULL) {

tests/unit/basic.tcl

@@ -368,7 +368,18 @@ start_server {tags {"basic"}} {
         format $err
     } {ERR*}
 
-    test {RENAME where source and dest key is the same} {
+    test {RENAME where source and dest key are the same (existing)} {
+        r set mykey foo
+        r rename mykey mykey
+    } {OK}
+
+    test {RENAMENX where source and dest key are the same (existing)} {
+        r set mykey foo
+        r renamenx mykey mykey
+    } {0}
+
+    test {RENAME where source and dest key are the same (non existing)} {
+        r del mykey
         catch {r rename mykey mykey} err
         format $err
     } {ERR*}