IGListBindingSectionController no longer asserts when reloading the entire section. (#1213)

Summary:
Issue fixed: #1174

- [X] All tests pass. Demo project builds and runs.
- [x] I added tests, an experiment, or detailed why my change isn't tested.
- [X] I added an entry to the `CHANGELOG.md` for any breaking changes, enhancements, or bug fixes.
- [X] I have reviewed the [contributing guide](https://github.com/Instagram/IGListKit/blob/master/.github/CONTRIBUTING.md)
Pull Request resolved: https://github.com/Instagram/IGListKit/pull/1213

Differential Revision: D9003398

Pulled By: rnystrom

fbshipit-source-id: 2c68f42e21abaea9191f26309668d866544f80b4

CHANGELOG.md

@@ -12,6 +12,8 @@ The changelog for `IGListKit`. Also see the [releases](https://github.com/instag
 
 - Added `IGListCollectionScrollingTraits` for exposing `UICollectionView` scrolling traits to section controllers via `IGListCollectionContext`. [Adam Stern](https://github.com/adamastern) (tbd)
 
+-  `IGListBindingSectionController` no longer asserts when reloading the entire section. A warning message is now logged if the entire section is going to be reloaded. [Jeff Bailey](https://github.com/jeffbailey) (#1213)
+
 ### Fixes
 
 - Experimental fix to get the `UICollectionView` for batch updating immediately before applying the update. [Ryan Nystrom](https://github.com/rnystrom) (tbd)

Source/IGListBindingSectionController.m

@@ -115,9 +115,12 @@ typedef NS_ENUM(NSInteger, IGListDiffingSectionState) {
         NSArray *viewModels = [self.dataSource sectionController:self viewModelsForObject:object];
         self.viewModels = objectsWithDuplicateIdentifiersRemoved(viewModels);
     } else {
-        IGAssert([oldObject isEqualToDiffableObject:object],
-                 @"Unequal objects %@ and %@ will cause IGListBindingSectionController to reload the entire section",
-                 oldObject, object);
+#if IGLK_LOGGING_ENABLED
+        if (![oldObject isEqualToDiffableObject:object]) {
+            IGLKLog(@"Warning: Unequal objects %@ and %@ will cause IGListBindingSectionController to reload the entire section",
+                    oldObject, object);
+        }
+#endif
         [self updateAnimated:YES completion:nil];
     }
 }

Tests/Objects/IGTestDiffingObject.m

@@ -28,8 +28,18 @@
     return self.key;
 }
 
-- (BOOL)isEqualToDiffableObject:(id<IGListDiffable>)object {
-    return YES;
+- (BOOL)isEqualToDiffableObject:(id)object {
+    if (object == self) {
+        return YES;
+    }
+    if ([object isKindOfClass:[IGTestDiffingObject class]]) {
+        /* A simple equality test that only looks at the number of objects for the key.
+           It does not currently test the equality of each of the objects. */
+        IGTestDiffingObject *testDiffingObject = (IGTestDiffingObject *)object;
+        return self.objects.count == testDiffingObject.objects.count;
+    }
+    
+    return NO;
 }
 
 @end