Make sure collection have unique ListDiffable objects on initial data…

Summary:
… source setup too

Issue fixed: #815

- [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)
Closes https://github.com/Instagram/IGListKit/pull/993

Reviewed By: jeremycohen

Differential Revision: D6264886

Pulled By: rnystrom

fbshipit-source-id: 5159b7989f1d17fd0a7522d986ed6abf012da77f

CHANGELOG.md

@@ -16,6 +16,8 @@ The changelog for `IGListKit`. Also see the [releases](https://github.com/instag
 
 ### Fixes
 
+- Duplicate objects for initial data source setup filtered out. [Mikhail Vashlyaev](https://github.com/yemodin) [(#993](https://github.com/Instagram/IGListKit/pull/993)
+
 - Weakly reference the `UICollectionView` in coalescence so that it can be released if the rest of system is destroyed. [Ryan Nystrom](https://github.com/rnystrom) [(#tbd)](https://github.com/Instagram/IGListKit/pull/tbd)
 
 - Fix bug with `-[IGListAdapter scrollToObject:supplementaryKinds:scrollDirection:scrollPosition:animated:]` where the content inset of the collection view was incorrectly being applied to the final offset. [Ryan Nystrom](https://github.com/rnystrom) [(#tbd)](https://github.com/Instagram/IGListKit/pull/tbd)

Source/Common/Internal/IGListArrayUtilsInternal.h

@@ -24,7 +24,7 @@ static NSArray *objectsWithDuplicateIdentifiersRemoved(NSArray<id<IGListDiffable
             [identifiers addObject:diffIdentifier];
             [uniqueObjects addObject:object];
         } else {
-            IGLKLog(@"WARNING: Object %@ already appeared in objects array", object);
+            IGLKLog(@"WARNING: Diff identifier %@ for object %@ already appeared in objects array", diffIdentifier, object);
         }
     }
     return uniqueObjects;

Source/IGListAdapter.m

@@ -15,6 +15,7 @@
 
 #import "IGListSectionControllerInternal.h"
 #import "IGListDebugger.h"
+#import "IGListArrayUtilsInternal.h"
 
 @implementation IGListAdapter {
     NSMapTable<UICollectionReusableView *, IGListSectionController *> *_viewSectionControllerMap;
@@ -143,7 +144,8 @@
 - (void)updateAfterPublicSettingsChange {
     id<IGListAdapterDataSource> dataSource = _dataSource;
     if (_collectionView != nil && dataSource != nil) {
-        [self updateObjects:[[dataSource objectsForListAdapter:self] copy] dataSource:dataSource];
+        NSArray *uniqueObjects = objectsWithDuplicateIdentifiersRemoved([dataSource objectsForListAdapter:self]);
+        [self updateObjects:uniqueObjects dataSource:dataSource];
     }
 }
 
@@ -359,13 +361,13 @@
         return;
     }
 
-    NSArray *newItems = [[dataSource objectsForListAdapter:self] copy];
+    NSArray *uniqueObjects = objectsWithDuplicateIdentifiersRemoved([dataSource objectsForListAdapter:self]);
 
     __weak __typeof__(self) weakSelf = self;
     [self.updater reloadDataWithCollectionView:collectionView reloadUpdateBlock:^{
         // purge all section controllers from the item map so that they are regenerated
         [weakSelf.sectionMap reset];
-        [weakSelf updateObjects:newItems dataSource:dataSource];
+        [weakSelf updateObjects:uniqueObjects dataSource:dataSource];
     } completion:^(BOOL finished) {
         [weakSelf notifyDidUpdate:IGListAdapterUpdateTypeReloadData animated:NO];
         if (completion) {
@@ -563,11 +565,8 @@
     IGParameterAssert(dataSource != nil);
 
 #if DEBUG
-    NSCountedSet *identifiersSet = [NSCountedSet new];
     for (id object in objects) {
-        [identifiersSet addObject:[object diffIdentifier]];
         IGAssert([object isEqualToDiffableObject:object], @"Object instance %@ not equal to itself. This will break infra map tables.", object);
-        IGAssert([identifiersSet countForObject:[object diffIdentifier]] <= 1, @"Diff identifier %@ for object %@ occurs more than once. Identifiers must be unique!", [object diffIdentifier], object);
     }
 #endif
 

Tests/IGListAdapterTests.m

@@ -1491,9 +1491,11 @@
     XCTAssertEqual(collectionView1.dataSource, adapter2);
 }
 
-- (void)test_whenPassingNonUniqueIdentifiers_adapterShouldAssert {
+- (void)test_whenPassingNonUniqueIdentifiers_adapterReloadShouldSkipDuplicates {
     self.dataSource.objects = @[@0, @1, @2, @0];
-    XCTAssertThrows([self.adapter reloadDataWithCompletion:nil]);
+    [self.adapter reloadDataWithCompletion:nil];
+
+    XCTAssertEqual(self.adapter.objects.count, 3);
 }
 
 - (void)test_whenPrefetchingEnabled_thatSetterDisables {

Tests/IGListDebuggerTests.m

@@ -45,7 +45,7 @@
     adapter3.collectionView = collectionView;
 
     NSArray *descriptions = [IGListDebugger adapterDescriptions];
-    XCTAssertEqual(descriptions.count, 4);
+    XCTAssertEqual(descriptions.count, 3);
 }
 
 @end