Prevent negative spaces for items and supplementaries

Summary:
If a negative height/width comes down, cap it to `0.0`.

Issue fixed: #566

Also fixes t16455632 internally.

- [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.
Closes https://github.com/Instagram/IGListKit/pull/583

Differential Revision: D4797520

Pulled By: jessesquires

fbshipit-source-id: 3eeec5244a445bb451460286b4f006ca0d9c67d1

CHANGELOG.md

@@ -90,6 +90,8 @@ This release closes the [3.0.0 milestone](https://github.com/Instagram/IGListKit
 
 - Fix a potential crash when a section is moved and deleted at the same time. [Ryan Nystrom](https://github.com/rnystrom) [(#577)](https://github.com/Instagram/IGListKit/pull/577)
 
+- Prevent section controllers and supplementary sources from returning negative sizes that crash `UICollectionViewFlowLayout`. [Ryan Nystrom](https://github.com/rnystrom) [(#583)](https://github.com/Instagram/IGListKit/pull/583)
+
 2.1.0
 -----
 

Source/IGListAdapter.m

@@ -458,14 +458,16 @@
     IGAssertMainThread();
 
     IGListSectionController <IGListSectionType> *sectionController = [self sectionControllerForSection:indexPath.section];
-    return [sectionController sizeForItemAtIndex:indexPath.item];
+    const CGSize size = [sectionController sizeForItemAtIndex:indexPath.item];
+    return CGSizeMake(MAX(size.width, 0.0), MAX(size.height, 0.0));
 }
 
 - (CGSize)sizeForSupplementaryViewOfKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)indexPath {
     IGAssertMainThread();
     id <IGListSupplementaryViewSource> supplementaryViewSource = [self supplementaryViewSourceAtIndexPath:indexPath];
     if ([[supplementaryViewSource supportedElementKinds] containsObject:elementKind]) {
-        return [supplementaryViewSource sizeForSupplementaryViewOfKind:elementKind atIndex:indexPath.item];
+        const CGSize size = [supplementaryViewSource sizeForSupplementaryViewOfKind:elementKind atIndex:indexPath.item];
+        return CGSizeMake(MAX(size.width, 0.0), MAX(size.height, 0.0));
     }
     return CGSizeZero;
 }

Tests/IGListAdapterTests.m

@@ -1083,4 +1083,32 @@ XCTAssertEqual(CGSizeEqualToSize(size, s), YES); \
     IGAssertEqualSize([self.adapter containerSizeForSectionController:controller], 98, 98);
 }
 
+- (void)test_whenSectionControllerReturnsNegativeSize_thatAdapterReturnsZero {
+    self.dataSource.objects = @[@1];
+    IGListTestSection *section = [self.adapter sectionControllerForObject:self.dataSource.objects[0]];
+    section.size = CGSizeMake(-1, -1);
+    const CGSize size = [self.adapter sizeForItemAtIndexPath:[NSIndexPath indexPathForItem:0 inSection:0]];
+    XCTAssertEqual(size.width, 0.0);
+    XCTAssertEqual(size.height, 0.0);
+}
+
+- (void)test_whenSupplementarySourceReturnsNegativeSize_thatAdapterReturnsZero {
+    self.dataSource.objects = @[@1];
+    [self.adapter reloadDataWithCompletion:nil];
+    
+    IGTestSupplementarySource *supplementarySource = [IGTestSupplementarySource new];
+    supplementarySource.collectionContext = self.adapter;
+    supplementarySource.supportedElementKinds = @[UICollectionElementKindSectionFooter];
+    supplementarySource.size = CGSizeMake(-1, -1);
+    
+    IGListSectionController<IGListSectionType> *controller = [self.adapter sectionControllerForObject:@1];
+    controller.supplementaryViewSource = supplementarySource;
+    supplementarySource.sectionController = controller;
+    
+    const CGSize size = [self.adapter sizeForSupplementaryViewOfKind:UICollectionElementKindSectionHeader
+                                                         atIndexPath:[NSIndexPath indexPathForItem:0 inSection:0]];
+    XCTAssertEqual(size.width, 0.0);
+    XCTAssertEqual(size.height, 0.0);
+}
+
 @end

Tests/Objects/IGListTestSection.h

@@ -16,6 +16,8 @@
 
 @property (nonatomic, assign) NSInteger items;
 
+@property (nonatomic, assign) CGSize size;
+
 @property (nonatomic, assign) BOOL wasSelected;
 
 @end

Tests/Objects/IGListTestSection.m

@@ -11,6 +11,13 @@
 
 @implementation IGListTestSection
 
+- (instancetype)init {
+    if (self = [super init]) {
+        _size = CGSizeMake(100, 10);
+    }
+    return self;
+}
+
 - (NSArray <Class> *)cellClasses {
     return @[UICollectionViewCell.class];
 }
@@ -20,7 +27,7 @@
 }
 
 - (CGSize)sizeForItemAtIndex:(NSInteger)index {
-    return CGSizeMake(100, 10);
+    return self.size;
 }
 
 - (UICollectionViewCell *)cellForItemAtIndex:(NSInteger)index {

Tests/Objects/IGTestStoryboardSupplementarySource.m

@@ -26,10 +26,4 @@
     return CGSizeMake([self.collectionContext containerSize].width, 45);
 }
 
-- (CGSize)estimatedSizeForSupplementaryViewOfKind:(NSString *)elementKind
-                                          atIndex:(NSInteger)index {
-    return CGSizeZero;
-}
-
-
 @end

Tests/Objects/IGTestSupplementarySource.h

@@ -15,6 +15,8 @@
 
 @property (nonatomic, assign) BOOL dequeueFromNib;
 
+@property (nonatomic, assign) CGSize size;
+
 @property (nonatomic, strong, readwrite) NSArray<NSString *> *supportedElementKinds;
 
 @property (nonatomic, weak) id<IGListCollectionContext> collectionContext;

Tests/Objects/IGTestSupplementarySource.m

@@ -13,6 +13,13 @@
 
 @implementation IGTestSupplementarySource
 
+- (instancetype)init {
+    if (self = [super init]) {
+        _size = CGSizeMake(100, 10);
+    }
+    return self;
+}
+
 #pragma mark - IGListSupplementaryViewSource
 
 - (UICollectionReusableView *)viewForSupplementaryElementOfKind:(NSString *)elementKind
@@ -34,12 +41,7 @@
 }
 
 - (CGSize)sizeForSupplementaryViewOfKind:(NSString *)elementKind atIndex:(NSInteger)index {
-    return CGSizeMake([self.collectionContext containerSize].width, 10);
-}
-
-- (CGSize)estimatedSizeForSupplementaryViewOfKind:(NSString *)elementKind
-                                          atIndex:(NSInteger)index {
-    return CGSizeZero;
+    return self.size;
 }
 
 @end