Merge pull request #12100 from rwjblue/fix-alias-volatility

Fix issue with `Ember.computed.alias` volatility.

packages/ember-metal/lib/chains.js

@@ -15,7 +15,7 @@ function isObject(obj) {
 }
 
 function isVolatile(obj) {
-  return !(isObject(obj) && obj.isDescriptor && !obj._volatile);
+  return !(isObject(obj) && obj.isDescriptor && obj._volatile === false);
 }
 
 function ChainWatchers(obj) {

packages/ember-runtime/tests/system/array_proxy/length_test.js

@@ -0,0 +1,72 @@
+import ArrayProxy from 'ember-runtime/system/array_proxy';
+import Object from 'ember-runtime/system/object';
+import { observer } from 'ember-metal/mixin';
+import { computed } from 'ember-metal/computed';
+import { A as a } from 'ember-runtime/system/native_array';
+
+QUnit.module('Ember.ArrayProxy - content change (length)');
+
+QUnit.test('array proxy + aliasedProperty complex test', function() {
+  var aCalled, bCalled, cCalled, dCalled, eCalled;
+
+  aCalled = bCalled = cCalled = dCalled = eCalled = 0;
+
+  var obj = Object.extend({
+    colors: computed.reads('model'),
+    length: computed.reads('colors.length'),
+
+    a: observer('length', function() {
+      aCalled++;
+    }),
+
+    b: observer('colors.length', function() {
+      bCalled++;
+    }),
+
+    c: observer('colors.content.length', function() {
+      cCalled++;
+    }),
+
+    d: observer('colors.[]', function() {
+      dCalled++;
+    }),
+
+    e: observer('colors.content.[]', function() {
+      eCalled++;
+    })
+  }).create();
+
+  obj.set('model', ArrayProxy.create({
+    content: a([
+      'red',
+      'yellow',
+      'blue'
+    ])
+  })
+  );
+
+  equal(obj.get('colors.content.length'), 3);
+  equal(obj.get('colors.length'), 3);
+  equal(obj.get('length'), 3);
+
+  equal(aCalled, 1, 'expected observer `length` to be called ONCE');
+  equal(bCalled, 1, 'expected observer `colors.length` to be called ONCE');
+  equal(cCalled, 1, 'expected observer `colors.content.length` to be called ONCE');
+  equal(dCalled, 1, 'expected observer `colors.[]` to be called ONCE');
+  equal(eCalled, 1, 'expected observer `colors.content.[]` to be called ONCE');
+
+  obj.get('colors').pushObjects([
+    'green',
+    'red'
+  ]);
+
+  equal(obj.get('colors.content.length'), 5);
+  equal(obj.get('colors.length'), 5);
+  equal(obj.get('length'), 5);
+
+  equal(aCalled, 2, 'expected observer `length` to be called TWICE');
+  equal(bCalled, 2, 'expected observer `colors.length` to be called TWICE');
+  equal(cCalled, 2, 'expected observer `colors.content.length` to be called TWICE');
+  equal(dCalled, 2, 'expected observer `colors.[]` to be called TWICE');
+  equal(eCalled, 2, 'expected observer `colors.content.[]` to be called TWICE');
+});