fix invalidateLayout crash

Summary:
Pretty sure in `-invalidateLayout`, we should calculate the `NSIndexPaths` after the delay. Otherwise, those `NSIndexPaths` might be incorrect after the update.

Before this change, running `test_whenInvalidatingInsideBatchUpdate_andRemoveThatSectionController_thatCollectionViewDoesntCrash` crashes with:
> Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'attempting to invalidate an item at an invalid indexPath: <NSIndexPath: 0x9566e79c2077363c> {length = 2, path = 1 - 0} globalIndex: 1 numItems: 1'

Reviewed By: candance

Differential Revision: D23742819

fbshipit-source-id: 39496d04025ff3554673313df3c7516c33c305d4

Source/IGListKit/IGListAdapter.m

@@ -1271,6 +1271,17 @@
 
 - (void)invalidateLayoutForSectionController:(IGListSectionController *)sectionController
                                   completion:(void (^)(BOOL finished))completion {
+    __weak __typeof__(self) weakSelf = self;
+
+    // do not call -[UICollectionView performBatchUpdates:completion:] while already updating. defer it until completed.
+    [self _deferBlockBetweenBatchUpdates:^{
+        // Note that we calculate the `NSIndexPaths` after the batch update, otherwise they're be wrong.
+        [weakSelf _invalidateLayoutForSectionController:sectionController completion:completion];
+    }];
+}
+
+- (void)_invalidateLayoutForSectionController:(IGListSectionController *)sectionController
+                                   completion:(void (^)(BOOL finished))completion {
     const NSInteger section = [self sectionForSectionController:sectionController];
     if (section == NSNotFound) {
         // The section controller is not in the map, which can happen if the associated object was deleted or after a full reload.
@@ -1291,14 +1302,9 @@
     UICollectionViewLayoutInvalidationContext *context = [[[layout.class invalidationContextClass] alloc] init];
     [context invalidateItemsAtIndexPaths:indexPaths];
 
-    __weak __typeof__(_collectionView) weakCollectionView = _collectionView;
-
-    // do not call -[UICollectionView performBatchUpdates:completion:] while already updating. defer it until completed.
-    [self _deferBlockBetweenBatchUpdates:^{
-        [weakCollectionView performBatchUpdates:^{
-            [layout invalidateLayoutWithContext:context];
-        } completion:completion];
-    }];
+    [_collectionView performBatchUpdates:^{
+        [layout invalidateLayoutWithContext:context];
+    } completion:completion];
 }
 
 #pragma mark - IGListBatchContext

Tests/IGListAdapterE2ETests.m

@@ -1597,6 +1597,39 @@
     }];
 }
 
+- (void)test_whenInvalidatingInsideBatchUpdate_andRemoveThatSectionController_thatCollectionViewDoesntCrash {
+    IGTestObject *foo = genTestObject(@1, @"Foo");
+    IGTestObject *bar = genTestObject(@0, @"Bar");
+    self.dataSource.objects = @[foo, bar];
+
+    UICollectionView *collectionView = [[UICollectionView alloc] initWithFrame:self.window.frame collectionViewLayout:[UICollectionViewFlowLayout new]];
+    [self.window addSubview:collectionView];
+    IGListAdapterUpdater *updater = [IGListAdapterUpdater new];
+    IGListAdapter *adapter = [[IGListAdapter alloc] initWithUpdater:updater viewController:nil];
+    adapter.dataSource = self.dataSource;
+    adapter.collectionView = collectionView;
+    [collectionView layoutIfNeeded];
+
+    IGTestDelegateController *sectionToRemove = [adapter sectionControllerForObject:bar];
+
+    self.dataSource.objects = @[foo];
+
+    XCTestExpectation *expectation = genExpectation;
+    [adapter performUpdatesAnimated:YES completion:^(BOOL finished) {
+        XCTAssertTrue(finished);
+        [expectation fulfill];
+    }];
+
+    XCTestExpectation *expectation2 = genExpectation;
+    [sectionToRemove.collectionContext invalidateLayoutForSectionController:sectionToRemove completion:^(BOOL finished) {
+        // That section-controller is about to be removed, so this should not finish.
+        XCTAssertFalse(finished);
+        [expectation2 fulfill];
+    }];
+
+    [self waitForExpectationsWithTimeout:30 handler:nil];
+}
+
 - (void)test_whenAddingMultipleUpdateListeners_withPerformUpdatesAnimated_thatEventsReceived {
     [self setupWithObjects:@[
                              genTestObject(@1, @1)

Tests/IGListExperimentalAdapterE2ETests.m

@@ -2005,6 +2005,39 @@
     }];
 }
 
+- (void)test_whenInvalidatingInsideBatchUpdate_andRemoveThatSectionController_thatCollectionViewDoesntCrash {
+    IGTestObject *foo = genTestObject(@1, @"Foo");
+    IGTestObject *bar = genTestObject(@0, @"Bar");
+    self.dataSource.objects = @[foo, bar];
+
+    UICollectionView *collectionView = [[UICollectionView alloc] initWithFrame:self.window.frame collectionViewLayout:[UICollectionViewFlowLayout new]];
+    [self.window addSubview:collectionView];
+    IGListExperimentalAdapterUpdater *updater = [IGListExperimentalAdapterUpdater new];
+    IGListAdapter *adapter = [[IGListAdapter alloc] initWithUpdater:updater viewController:nil];
+    adapter.dataSource = self.dataSource;
+    adapter.collectionView = collectionView;
+    [collectionView layoutIfNeeded];
+
+    IGTestDelegateController *sectionToRemove = [adapter sectionControllerForObject:bar];
+
+    self.dataSource.objects = @[foo];
+
+    XCTestExpectation *expectation = genExpectation;
+    [adapter performUpdatesAnimated:YES completion:^(BOOL finished) {
+        XCTAssertTrue(finished);
+        [expectation fulfill];
+    }];
+
+    XCTestExpectation *expectation2 = genExpectation;
+    [sectionToRemove.collectionContext invalidateLayoutForSectionController:sectionToRemove completion:^(BOOL finished) {
+        // That section-controller is about to be removed, so this should not finish.
+        XCTAssertFalse(finished);
+        [expectation2 fulfill];
+    }];
+
+    [self waitForExpectationsWithTimeout:30 handler:nil];
+}
+
 - (void)test_whenPerformingBatchSectionUpdate_thatTransactionObjectsGetsDeallocated {
     __weak IGListUpdateTransactionBuilder *transactionBuilder = nil;
     __block __weak IGListUpdateTransactionBuilder *lastTransactionBuilder = nil;