[ASDisplayNode] Add support for setting non-fatal error block

AsyncDisplayKit/ASDisplayNode.h

@@ -55,6 +55,12 @@ typedef void (^ASDisplayNodeContextModifier)(CGContextRef context);
  */
 typedef ASLayoutSpec * _Nonnull(^ASLayoutSpecBlock)(__kindof ASDisplayNode * _Nonnull node, ASSizeRange constrainedSize);
 
+/**
+ * AsyncDisplayKit non-fatal error block. This block can be used for handling non-fatal errors. Useful for reporting
+ * errors that happens in production.
+ */
+typedef void (^ASDisplayNodeNonFatalErrorBlock)(__kindof NSError * _Nonnull error);
+
 /**
  * Interface state is available on ASDisplayNode and ASViewController, and
  * allows checking whether a node is in an interface situation where it is prudent to trigger certain
@@ -252,6 +258,16 @@ extern NSInteger const ASDefaultDrawingPriority;
  */
 @property (readonly) ASInterfaceState interfaceState;
 
+/**
+ * @abstract Class property that allows to set a block that can be called on non-fatal errors. This
+ * property can be useful for cases when Async Display Kit can recover from an abnormal behavior, but
+ * still gives the opportunity to use a reporting mechanism to catch occurrences in production. In
+ * development, Async Display Kit will assert instead of calling this block.
+ *
+ * @warning This method is not thread-safe.
+ */
+@property (nonatomic, class, copy) ASDisplayNodeNonFatalErrorBlock nonFatalErrorBlock;
+
 
 /** @name Managing dimensions */
 

AsyncDisplayKit/ASDisplayNode.mm

@@ -63,6 +63,8 @@
   #define TIME_SCOPED(outVar)
 #endif
 
+static ASDisplayNodeNonFatalErrorBlock _nonFatalErrorBlock = nil;
+
 // Forward declare CALayerDelegate protocol as the iOS 10 SDK moves CALayerDelegate from a formal delegate to a protocol.
 // We have to forward declare the protocol as this place otherwise it will not compile compiling with an Base SDK < iOS 10
 @protocol CALayerDelegate;
@@ -2259,6 +2261,20 @@ - (void)subnodeDisplayDidFinish:(ASDisplayNode *)subnode
   return (id)kCFNull;
 }
 
+#pragma mark - Error Handling
+
++ (void)setNonFatalErrorBlock:(ASDisplayNodeNonFatalErrorBlock)nonFatalErrorBlock
+{
+  if (_nonFatalErrorBlock != nonFatalErrorBlock) {
+    _nonFatalErrorBlock = [nonFatalErrorBlock copy];
+  }
+}
+
++ (ASDisplayNodeNonFatalErrorBlock)nonFatalErrorBlock
+{
+  return _nonFatalErrorBlock;
+}
+
 #pragma mark - Converting to and from the Node's Coordinate System
 
 - (CATransform3D)_transformToAncestor:(ASDisplayNode *)ancestor

Base/ASAssert.h

@@ -59,3 +59,19 @@
 #define ASDisplayNodeCAssertPositiveReal(description, num) ASDisplayNodeCAssert(num >= 0 && num <= CGFLOAT_MAX, @"%@ must be a real positive integer.", description)
 #define ASDisplayNodeCAssertInfOrPositiveReal(description, num) ASDisplayNodeCAssert(isinf(num) || (num >= 0 && num <= CGFLOAT_MAX), @"%@ must be infinite or a real positive integer.", description)
 
+#define ASDisplayNodeErrorDomain @"ASDisplayNodeErrorDomain"
+#define ASDisplayNodeNonFatalErrorCode 1
+
+#define ASDisplayNodeAssertNonFatal(condition, desc, ...)                                                                         \
+  ASDisplayNodeAssert(condition, desc, ##__VA_ARGS__);                                                                            \
+  if (condition ==  NO) {                                                                                                         \
+    ASDisplayNodeNonFatalErrorBlock block = [ASDisplayNode nonFatalErrorBlock];                                                   \
+    if (block != nil) {                                                                                                           \
+      NSDictionary *userInfo = nil;                                                                                               \
+      if (desc.length > 0) {                                                                                                      \
+        userInfo = @{ NSLocalizedDescriptionKey : desc };                                                                         \
+      }                                                                                                                           \
+      NSError *error = [NSError errorWithDomain:ASDisplayNodeErrorDomain code:ASDisplayNodeNonFatalErrorCode userInfo:userInfo];  \
+      block(error);                                                                                                               \
+    }                                                                                                                             \
+  }