Make rsvp promises/A+ spec-1.1 compliant

lib/rsvp/promise.js

@@ -61,12 +61,8 @@ var invokeCallback = function(type, promise, callback, event) {
     succeeded = true;
   }
 
-  if (objectOrFunction(value) && isFunction(value.then)) {
-    value.then(function(value) {
-      resolve(promise, value);
-    }, function(error) {
-      reject(promise, error);
-    });
+  if (handleThenable(promise, value)) {
+    return;
   } else if (hasCallback && succeeded) {
     resolve(promise, value);
   } else if (failed) {
@@ -111,11 +107,27 @@ Promise.prototype = {
 EventTarget.mixin(Promise.prototype);
 
 function resolve(promise, value) {
-
   if (promise === value) {
     fulfill(promise, value);
-  } else if (objectOrFunction(value) && isFunction(value.then)) {
-    value.then(function(val) {
+  } else if (!handleThenable(promise, value)) {
+    fulfill(promise, value);
+  }
+}
+
+function handleThenable(promise, value) {
+  var then = null;
+
+  if (objectOrFunction(value)) {
+    try {
+      then = value.then;
+    } catch(e) {
+      reject(promise, e);
+      return true;
+    }
+
+    if (isFunction(then)) {
+      try {
+        then.call(value, function(val) {
           if (value !== val) {
             resolve(promise, val);
           } else {
@@ -124,9 +136,14 @@ function resolve(promise, value) {
         }, function(val) {
           reject(promise, val);
         });
-  } else {
-    fulfill(promise, value);
+      } catch (e) {
+        reject(promise, e);
+      }
+      return true;
     }
+  }
+
+  return false;
 }
 
 function fulfill(promise, value) {