short-circuit RSVP.resolve is resolving RSVP.Promise

browser/rsvp.js

@@ -566,12 +566,15 @@ define("rsvp/resolve",
     "use strict";
     var Promise = __dependency1__.Promise;
 
-
     function objectOrFunction(x) {
       return typeof x === "function" || (typeof x === "object" && x !== null);
     }
 
     function resolve(thenable){
+      if (thenable instanceof Promise) {
+        return thenable;
+      }
+
       var promise = new Promise(function(resolve, reject){
         var then;
 

browser/rsvp/resolve.amd.js

@@ -4,12 +4,15 @@ define(
     "use strict";
     var Promise = __dependency1__.Promise;
 
-
     function objectOrFunction(x) {
       return typeof x === "function" || (typeof x === "object" && x !== null);
     }
 
     function resolve(thenable){
+      if (thenable instanceof Promise) {
+        return thenable;
+      }
+
       var promise = new Promise(function(resolve, reject){
         var then;
 

lib/rsvp/resolve.js

 import { Promise } from "rsvp/promise";
 
-
 function objectOrFunction(x) {
   return typeof x === "function" || (typeof x === "object" && x !== null);
 }
 
 function resolve(thenable){
+  if (thenable instanceof Promise) {
+    return thenable;
+  }
+
   var promise = new Promise(function(resolve, reject){
     var then;
 

tests/extension-tests.js

@@ -613,6 +613,12 @@ describe("RSVP extensions", function() {
       assert(RSVP.resolve);
     });
 
+    specify("it short circuits if RSVP.promise", function(){
+
+      var deferred = new RSVP.defer();
+      assert.equal(RSVP.resolve(deferred.promise), deferred.promise);
+    });
+
     describe("1. If x is a promise, adopt its state ", function(){
       specify("1.1 If x is pending, promise must remain pending until x is fulfilled or rejected.", function(done){
         var expectedValue, resolver, thenable, wrapped;