Data Adapter: Only trigger model type update if the record live array…

… count actually changed

Fixes emberjs/ember-inspector#690

The issue:

In some cases, Ember Data's `peekAll` triggers `arrayContentDidChange` on the record array manager's live record array even if the records didn't change.
One example case is when we call `unloadRecord` and then `peekAll` within the same run loop.
The `peekAll` will trigger the array observer's `didChange` callback (with zero changes).
This is generally harmless as long as we guard against that in our data adapter.
Without the guard, we risk causing an infinite recursion because our `didChange` observer itself calls `peekAll`, which in the above scenario will re-trigger
the observer and so on.

(cherry picked from commit 7bd47da)

packages/ember-extension-support/lib/data_adapter.js

@@ -294,8 +294,12 @@ export default EmberObject.extend({
     }
 
     let observer = {
-      didChange() {
-        run.scheduleOnce('actions', this, onChange);
+      didChange(array, idx, removedCount, addedCount) {
+        // Only re-fetch records if the record count changed
+        // (which is all we care about as far as model types are concerned).
+        if (removedCount > 0 || addedCount > 0) {
+          run.scheduleOnce('actions', this, onChange);
+        }
       },
       willChange() { return this; }
     };

packages/ember-extension-support/tests/data_adapter_test.js

@@ -140,6 +140,33 @@ moduleFor('Data Adapter', class extends ApplicationTestCase {
     });
   }
 
+  ['@test Model Types Updated but Unchanged Do not Trigger Callbacks']() {
+    expect(0);
+    let records = emberA([1, 2, 3]);
+    this.add('data-adapter:main', DataAdapter.extend({
+      getRecords(klass, name) {
+        return records;
+      }
+    }));
+    this.add('model:post', PostClass);
+
+    return this.visit('/').then(() => {
+      adapter = this.applicationInstance.lookup('data-adapter:main');
+
+      function modelTypesAdded(types) {
+        run(() => {
+          records.arrayContentDidChange(0, 0, 0);
+        });
+      }
+
+      function modelTypesUpdated(types) {
+        ok(false, "modelTypesUpdated should not be triggered if the array didn't change");
+      }
+
+      adapter.watchModelTypes(modelTypesAdded, modelTypesUpdated);
+    });
+  }
+
   ['@test Records Added']() {
     let countAdded = 1;
     let post = PostClass.create();