Promise.then cancel on non cancellable thenable fixed

lib/rsvp/promise.js

@@ -201,7 +201,9 @@ function handleThenable(promise, value) {
 
       if (isFunction(then)) {
         promise.on('promise:cancelled', function(event) {
-          value.cancel();
+          if (isFunction(value.cancel)) {
+            value.cancel();
+          }
         });
         then.call(value, function(val) {
           if (resolved) { return true; }

test/tests/extension_test.js

@@ -1591,6 +1591,88 @@ describe("`cancel` on promise created by then", function () {
 
 });
 
+describe("`cancel` on thenable created by then", function () {
+  it('should cancel the pending fulfilled promise', function (done) {
+    var cancel_called = false,
+      promise = new RSVP.Promise(function (resolve) {resolve();}),
+      promise2 = promise.then(function () {
+        return {"then": function() {}, "cancel": function () {
+          cancel_called = true;
+        }};
+      });
+
+    setTimeout(function() {
+      promise2.cancel("Foo");
+      setTimeout(function() {
+        assert.equal(cancel_called, true);
+        assert.equal(promise2.isFulfilled, undefined);
+        assert.equal(promise2.isRejected, true);
+        assert(promise2.rejectedReason instanceof RSVP.CancellationError);
+        done();
+      }, 20);
+    }, 20);
+  });
+
+  it('should cancel the pending rejected promise', function (done) {
+    var cancel_called = false,
+      promise = new RSVP.Promise(function (resolve, reject) {reject();}),
+      promise2 = promise.then(undefined, function () {
+        return {"then": function() {}, "cancel": function () {
+          cancel_called = true;
+        }};
+      });
+
+    setTimeout(function() {
+      promise2.cancel("Foo");
+      setTimeout(function() {
+        assert.equal(cancel_called, true);
+        assert.equal(promise2.isFulfilled, undefined);
+        assert.equal(promise2.isRejected, true);
+        assert(promise2.rejectedReason instanceof RSVP.CancellationError);
+        done();
+      }, 20);
+    }, 20);
+  });
+});
+
+describe("`cancel` on non cancellable thenable created by then", function () {
+  it('should cancel the pending fulfilled promise', function (done) {
+    var cancel_called = false,
+      promise = new RSVP.Promise(function (resolve) {resolve();}),
+      promise2 = promise.then(function () {
+        return {"then": function() {}};
+      });
+
+    setTimeout(function() {
+      promise2.cancel("Foo");
+      setTimeout(function() {
+        assert.equal(promise2.isFulfilled, undefined);
+        assert.equal(promise2.isRejected, true);
+        assert(promise2.rejectedReason instanceof RSVP.CancellationError);
+        done();
+      }, 20);
+    }, 20);
+  });
+
+  it('should cancel the pending rejected promise', function (done) {
+    var cancel_called = false,
+      promise = new RSVP.Promise(function (resolve, reject) {reject();}),
+      promise2 = promise.then(undefined, function () {
+        return {"then": function() {}};
+      });
+
+    setTimeout(function() {
+      promise2.cancel("Foo");
+      setTimeout(function() {
+        assert.equal(promise2.isFulfilled, undefined);
+        assert.equal(promise2.isRejected, true);
+        assert(promise2.rejectedReason instanceof RSVP.CancellationError);
+        done();
+      }, 20);
+    }, 20);
+  });
+});
+
 describe("`always` on a promise", function () {
   it('should be a function', function () {
     var promise = new RSVP.Promise(function (done, fail) {});