[ASCollectionView] synchronous mode

CHANGELOG.md

@@ -1,6 +1,7 @@
 ## master
 
 * Add your own contributions to the next release on the line below this with your name.
+- Add a synchronous mode to ASCollectionNode, for colletion view data source debugging. [Hannah Troisi](https://github.com/hannahmbanana)
 - Fixed an issue where GIFs with placeholders never had their placeholders uncover the GIF. [Garrett Moon](https://github.com/garrettmoon)
 - [Yoga] Implement ASYogaLayoutSpec, a simplified integration strategy for Yoga-powered layout calculation. [Scott Goodson](https://github.com/appleguy)
 - Fixed an issue where calls to setNeedsDisplay and setNeedsLayout would stop working on loaded nodes. [Garrett Moon](https://github.com/garrettmoon)

Source/ASCollectionNode+Beta.h

@@ -40,6 +40,23 @@ NS_ASSUME_NONNULL_BEGIN
 
 @property (nonatomic, weak) id<ASBatchFetchingDelegate> batchFetchingDelegate;
 
+/**
+ * When this mode is enabled, ASCollectionView matches the timing of UICollectionView as closely as possible, 
+ * ensuring that all reload and edit operations are performed on the main thread as blocking calls. 
+ *
+ * This mode is useful for applications that are debugging issues with their collection view implementation. 
+ * In particular, some applications do not properly conform to the API requirement of UICollectionView, and these 
+ * applications may experience difficulties with ASCollectionView. Providing this mode allows for developers to 
+ * work towards resolving technical debt in their collection view data source, while ramping up asynchronous 
+ * collection layout.
+ *
+ * NOTE: Because this mode results in expensive operations like cell layout being performed on the main thread, 
+ * it should be used as a tool to resolve data source conformance issues with Apple collection view API.
+ *
+ * @default defaults to NO.
+ */
+@property (nonatomic, assign) BOOL usesSynchronousDataLoading;
+
 - (instancetype)initWithFrame:(CGRect)frame collectionViewLayout:(UICollectionViewLayout *)layout layoutFacilitator:(nullable id<ASCollectionViewLayoutFacilitatorProtocol>)layoutFacilitator;
 
 - (instancetype)initWithLayoutDelegate:(id<ASCollectionLayoutDelegate>)layoutDelegate layoutFacilitator:(nullable id<ASCollectionViewLayoutFacilitatorProtocol>)layoutFacilitator;

Source/ASCollectionNode.mm

@@ -464,6 +464,16 @@ - (void)setBatchFetchingDelegate:(id<ASBatchFetchingDelegate>)batchFetchingDeleg
   return _batchFetchingDelegate;
 }
 
+- (BOOL)usesSynchronousDataLoading
+{
+  return self.view.usesSynchronousDataLoading;
+}
+
+- (void)setUsesSynchronousDataLoading:(BOOL)usesSynchronousDataLoading
+{
+  self.view.usesSynchronousDataLoading = usesSynchronousDataLoading;
+}
+
 #pragma mark - Range Tuning
 
 - (ASRangeTuningParameters)tuningParametersForRangeType:(ASLayoutRangeType)rangeType

Source/ASCollectionView.mm

@@ -767,6 +767,16 @@ - (NSArray *)visibleNodes
   return visibleNodes;
 }
 
+- (BOOL)usesSynchronousDataLoading
+{
+  return self.dataController.usesSynchronousDataLoading;
+}
+
+- (void)setUsesSynchronousDataLoading:(BOOL)usesSynchronousDataLoading
+{
+  self.dataController.usesSynchronousDataLoading = usesSynchronousDataLoading;
+}
+
 #pragma mark Internal
 
 - (void)_configureCollectionViewLayout:(nonnull UICollectionViewLayout *)layout

Source/Details/ASCollectionInternal.h

@@ -31,6 +31,11 @@ NS_ASSUME_NONNULL_BEGIN
 @property (nonatomic, strong, readonly) ASDataController *dataController;
 @property (nonatomic, strong, readonly) ASRangeController *rangeController;
 
+/**
+ * @see ASCollectionNode+Beta.h for full documentation.
+ */
+@property (nonatomic, assign) BOOL usesSynchronousDataLoading;
+
 /**
  * Attempt to get the view-layer index path for the item with the given index path.
  *

Source/Details/ASDataController.h

@@ -227,6 +227,11 @@ extern NSString * const ASCollectionInvalidUpdateException;
 @property (nonatomic, strong, readonly) ASEventLog *eventLog;
 #endif
 
+/**
+ * @see ASCollectionNode+Beta.h for full documentation.
+ */
+@property (nonatomic, assign) BOOL usesSynchronousDataLoading;
+
 /** @name Data Updating */
 
 - (void)updateWithChangeSet:(_ASHierarchyChangeSet *)changeSet;

Source/Details/ASDataController.mm

@@ -582,6 +582,10 @@ - (void)updateWithChangeSet:(_ASHierarchyChangeSet *)changeSet
       }];
     }];
   });
+
+  if (_usesSynchronousDataLoading) {
+    dispatch_group_wait(_editingTransactionGroup, DISPATCH_TIME_FOREVER);
+  }
 }
 
 /**