[BUGFIX beta] mixin/arrays firstObject/lastObject notifications only …

…when cached

Basically the contents of https://gist.github.com/mmun/877bad33158578a8609b

packages/ember-runtime/lib/mixins/array.js

@@ -7,6 +7,8 @@
 // HELPERS
 //
 import { symbol } from 'ember-utils';
+
+import { peekMeta } from 'ember-metal';
 import Ember, { // ES6TODO: Ember.A
   get,
   computed,
@@ -136,19 +138,22 @@ export function arrayContentDidChange(array, startIdx, removeAmt, addAmt) {
   sendEvent(array, '@array:change', [array, startIdx, removeAmt, addAmt]);
 
   let length = get(array, 'length');
-  let cachedFirst = cacheFor(array, 'firstObject');
-  let cachedLast = cacheFor(array, 'lastObject');
 
-  if (objectAt(array, 0) !== cachedFirst) {
-    propertyWillChange(array, 'firstObject');
-    propertyDidChange(array, 'firstObject');
-  }
+  let meta = peekMeta(array);
+  let cache = meta && meta.readableCache();
 
-  if (objectAt(array, length - 1) !== cachedLast) {
-    propertyWillChange(array, 'lastObject');
-    propertyDidChange(array, 'lastObject');
+  if (cache) {
+    if (cache.firstObject !== undefined &&
+        objectAt(array, 0) !== cacheFor.get(cache, 'firstObject')) {
+      propertyWillChange(array, 'firstObject');
+      propertyDidChange(array, 'firstObject');
+    }
+    if (cache.lastObject !== undefined &&
+        objectAt(array, length - 1) !== cacheFor.get(cache, 'lastObject')) {
+      propertyWillChange(array, 'lastObject');
+      propertyDidChange(array, 'lastObject');
+    }
   }
-
   return array;
 }
 

packages/ember-runtime/tests/suites/mutable_array/replace.js

@@ -22,6 +22,23 @@ suite.test('[].replace(0,0,\'X\') => [\'X\'] + notify', function() {
   equal(observer.timesCalled('lastObject'), 1, 'should have notified lastObject once');
 });
 
+suite.test('[].replace(0,0,"X") => ["X"] + avoid calling objectAt and notifying fistObject/lastObject when not in cache', function() {
+  var obj, exp, observer;
+  var called = 0;
+  exp = this.newFixture(1);
+  obj = this.newObject([]);
+  obj.objectAt = function() {
+    called++;
+  };
+  observer = this.newObserver(obj, 'firstObject', 'lastObject');
+
+  obj.replace(0, 0, exp);
+
+  equal(called, 0, 'should NOT have called objectAt upon replace when firstObject/lastObject are not cached');
+  equal(observer.validate('firstObject'), false, 'should NOT have notified firstObject since not cached');
+  equal(observer.validate('lastObject'), false, 'should NOT have notified lastObject since not cached');
+});
+
 suite.test('[A,B,C,D].replace(1,2,X) => [A,X,D] + notify', function() {
   let before  = this.newFixture(4);
   let replace = this.newFixture(1);