Fix crash when requesting OOB layout attributes

Summary: There's a small crash showing up when requesting an index path that doesn't exist. It's totally valid that this could be requested from a product and not the infra. Should fail gracefully.

Differential Revision: D4911349

fbshipit-source-id: eee8891cf9400b3c3cd5539e839296f393f82354

Source/IGListCollectionViewLayout.mm

@@ -175,6 +175,14 @@ - (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSInde
         return attributes;
     }
 
+    // avoid OOB errors
+    const NSInteger section = indexPath.section;
+    const NSInteger item = indexPath.item;
+    if (section >= _sectionData.size()
+        || item >= _sectionData[section].itemBounds.size()) {
+        return nil;
+    }
+
     attributes = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];
     attributes.frame = _sectionData[indexPath.section].itemBounds[indexPath.item];
     adjustZIndexForAttributes(attributes);
@@ -192,8 +200,13 @@ - (UICollectionViewLayoutAttributes *)layoutAttributesForSupplementaryViewOfKind
         return attributes;
     }
 
-    UICollectionView *collectionView = self.collectionView;
+    // avoid OOB errors
     const NSInteger section = indexPath.section;
+    if (section >= _sectionData.size()) {
+        return nil;
+    }
+
+    UICollectionView *collectionView = self.collectionView;
     const IGListSectionEntry entry = _sectionData[section];
     const CGFloat minY = CGRectGetMinY(entry.bounds);
 

Tests/IGListCollectionViewLayoutTests.m

@@ -694,4 +694,34 @@ - (void)test_ {
     IGAssertEqualFrame([self cellForSection:5 item:0].frame, 277, 139, 136, 136);
 }
 
+- (void)test_whenQueryingAttributes_withSectionOOB_thatReturnsNil {
+    [self setUpWithStickyHeaders:NO topInset:0 stretchToEdge:YES];
+    [self prepareWithData:@[
+                            [[IGLayoutTestSection alloc] initWithInsets:UIEdgeInsetsZero
+                                                            lineSpacing:0
+                                                       interitemSpacing:0
+                                                           headerHeight:0
+                                                                  items:@[
+                                                                          [[IGLayoutTestItem alloc] initWithSize:CGSizeMake(33, 33)],
+                                                                          [[IGLayoutTestItem alloc] initWithSize:CGSizeMake(65, 33)],
+                                                                          ]],
+                            ]];
+    XCTAssertNil([self.layout layoutAttributesForItemAtIndexPath:quickPath(4, 0)]);
+}
+
+- (void)test_whenQueryingAttributes_withItemOOB_thatReturnsNil {
+    [self setUpWithStickyHeaders:NO topInset:0 stretchToEdge:YES];
+    [self prepareWithData:@[
+                            [[IGLayoutTestSection alloc] initWithInsets:UIEdgeInsetsZero
+                                                            lineSpacing:0
+                                                       interitemSpacing:0
+                                                           headerHeight:0
+                                                                  items:@[
+                                                                          [[IGLayoutTestItem alloc] initWithSize:CGSizeMake(33, 33)],
+                                                                          [[IGLayoutTestItem alloc] initWithSize:CGSizeMake(65, 33)],
+                                                                          ]],
+                            ]];
+    XCTAssertNil([self.layout layoutAttributesForItemAtIndexPath:quickPath(0, 4)]);
+}
+
 @end