[ASCollectionNode] Add scrollableDirections method to ASCollectionViewLayoutInspecting p… (#2381)

* Add scrollableDirections method to ASCollectionViewLayoutInspecting protocol

ASViewController's default method will not always return the correct scrollable
directions in cases where size changes may not have been applied. This allows
us to ignore this issue for a little while longer by allowing the layout
inspector to explicitly vend this.

* Better header, thanks @maicki!

AsyncDisplayKit/ASCollectionView.mm

@@ -178,6 +178,7 @@ static NSString * const kCellReuseIdentifier = @"_ASCollectionViewCell";
   struct {
     unsigned int layoutInspectorDidChangeCollectionViewDataSource:1;
     unsigned int layoutInspectorDidChangeCollectionViewDelegate:1;
+    unsigned int layoutInspectorScrollableDirections:1;
   } _layoutInspectorFlags;
 }
 
@@ -454,6 +455,7 @@ static NSString * const kCellReuseIdentifier = @"_ASCollectionViewCell";
   
   _layoutInspectorFlags.layoutInspectorDidChangeCollectionViewDataSource = [_layoutInspector respondsToSelector:@selector(didChangeCollectionViewDataSource:)];
   _layoutInspectorFlags.layoutInspectorDidChangeCollectionViewDelegate = [_layoutInspector respondsToSelector:@selector(didChangeCollectionViewDelegate:)];
+  _layoutInspectorFlags.layoutInspectorScrollableDirections = [_layoutInspector respondsToSelector:@selector(scrollableDirections)];
 }
 
 - (void)setTuningParameters:(ASRangeTuningParameters)tuningParameters forRangeType:(ASLayoutRangeType)rangeType
@@ -844,19 +846,9 @@ static NSString * const kCellReuseIdentifier = @"_ASCollectionViewCell";
 
 - (ASScrollDirection)scrollableDirections
 {
-  if ([self.collectionViewLayout asdk_isFlowLayout]) {
+  if (_layoutInspectorFlags.layoutInspectorScrollableDirections) {
-    return [self flowLayoutScrollableDirections:(UICollectionViewFlowLayout *)self.collectionViewLayout];
+    return [self.layoutInspector scrollableDirections];
   } else {
-    return [self nonFlowLayoutScrollableDirections];
-  }
-}
-
-- (ASScrollDirection)flowLayoutScrollableDirections:(UICollectionViewFlowLayout *)flowLayout {
-  return (flowLayout.scrollDirection == UICollectionViewScrollDirectionHorizontal) ? ASScrollDirectionHorizontalDirections : ASScrollDirectionVerticalDirections;
-}
-
-- (ASScrollDirection)nonFlowLayoutScrollableDirections
-{
     ASScrollDirection scrollableDirection = ASScrollDirectionNone;
     CGFloat totalContentWidth = self.contentSize.width + self.contentInset.left + self.contentInset.right;
     CGFloat totalContentHeight = self.contentSize.height + self.contentInset.top + self.contentInset.bottom;
@@ -869,6 +861,11 @@ static NSString * const kCellReuseIdentifier = @"_ASCollectionViewCell";
     }
     return scrollableDirection;
   }
+}
+
+- (ASScrollDirection)flowLayoutScrollableDirections:(UICollectionViewFlowLayout *)flowLayout {
+  return (flowLayout.scrollDirection == UICollectionViewScrollDirectionHorizontal) ? ASScrollDirectionHorizontalDirections : ASScrollDirectionVerticalDirections;
+}
 
 - (void)layoutSubviews
 {

AsyncDisplayKit/Details/ASCollectionViewFlowLayoutInspector.h

@@ -12,6 +12,7 @@
 
 #import <Foundation/Foundation.h>
 #import <AsyncDisplayKit/ASDimension.h>
+#import <AsyncDisplayKit/ASScrollDirection.h>
 
 @class ASCollectionView;
 @protocol ASCollectionDataSource;
@@ -52,6 +53,11 @@ NS_ASSUME_NONNULL_BEGIN
  */
 - (void)didChangeCollectionViewDataSource:(nullable id<ASCollectionDataSource>)dataSource;
 
+/**
+ * Return the directions in which your collection view can scroll
+ */
+- (ASScrollDirection)scrollableDirections;
+
 #pragma mark Deprecated Methods
 
 /**

AsyncDisplayKit/Details/ASCollectionViewFlowLayoutInspector.m

@@ -176,6 +176,11 @@ static inline ASSizeRange NodeConstrainedSizeForScrollDirection(ASCollectionView
   return [self layoutHasSupplementaryViewOfKind:kind inSection:section collectionView:collectionView] ? 1 : 0;
 }
 
+- (ASScrollDirection)scrollableDirections
+{
+  return (self.layout.scrollDirection == UICollectionViewScrollDirectionHorizontal) ? ASScrollDirectionHorizontalDirections : ASScrollDirectionVerticalDirections;
+}
+
 #pragma mark - Private helpers
 
 - (CGSize)sizeForSupplementaryViewOfKind:(NSString *)kind inSection:(NSUInteger)section collectionView:(ASCollectionView *)collectionView