Add [RCTShadowView isCSSLeaf] for skipping css tree of children

Summary: RCTShadowText currently overrides a couple methods from RCTShadowView to reset the count of the cssNode children to 0. This diff instead moves that logic into RCTShadowView behind a configurable flag making it easier to reason about.

Reviewed By: javache

Differential Revision: D3586434

fbshipit-source-id: 4389a8119dc49e3fc4357174c87c0c69287ae385

Libraries/Text/RCTShadowText.m

@@ -81,6 +81,11 @@ - (NSString *)description
   return [[superDescription substringToIndex:superDescription.length - 1] stringByAppendingFormat:@"; text: %@>", [self attributedString].string];
 }
 
+- (BOOL)isCSSLeafNode
+{
+  return YES;
+}
+
 - (void)contentSizeMultiplierDidChange:(NSNotification *)note
 {
   [self dirtyLayout];
@@ -443,18 +448,6 @@ - (void)_setParagraphStyleOnAttributedString:(NSMutableAttributedString *)attrib
   }
 }
 
-- (void)insertReactSubview:(RCTShadowView *)subview atIndex:(NSInteger)atIndex
-{
-  [super insertReactSubview:subview atIndex:atIndex];
-  self.cssNode->children_count = 0;
-}
-
-- (void)removeReactSubview:(RCTShadowView *)subview
-{
-  [super removeReactSubview:subview];
-  self.cssNode->children_count = 0;
-}
-
 - (void)setBackgroundColor:(UIColor *)backgroundColor
 {
   super.backgroundColor = backgroundColor;

React/Views/RCTShadowView.h

@@ -189,6 +189,13 @@ typedef void (^RCTApplierBlock)(NSDictionary<NSNumber *, UIView *> *viewRegistry
 - (void)dirtyLayout NS_REQUIRES_SUPER;
 - (BOOL)isLayoutDirty;
 
+/**
+ * Return whether or not this node acts as a leaf node in the eyes of CSSLayout. For example
+ * RCTShadowText has children which it does not want CSSLayout to lay out so in the eyes of
+ * CSSLayout it is a leaf node.
+ */
+- (BOOL)isCSSLeafNode;
+
 - (void)dirtyPropagation NS_REQUIRES_SUPER;
 - (BOOL)isPropagationDirty;
 

React/Views/RCTShadowView.m

@@ -320,6 +320,11 @@ - (BOOL)isLayoutDirty
   return _layoutLifecycle != RCTUpdateLifecycleComputed;
 }
 
+- (BOOL)isCSSLeafNode
+{
+  return NO;
+}
+
 - (void)dirtyPropagation
 {
   if (_propagationLifecycle != RCTUpdateLifecycleDirtied) {
@@ -354,7 +359,7 @@ - (void)setTextComputed
 - (void)insertReactSubview:(RCTShadowView *)subview atIndex:(NSInteger)atIndex
 {
   [_reactSubviews insertObject:subview atIndex:atIndex];
-  _cssNode->children_count = (int)_reactSubviews.count;
+  _cssNode->children_count = [self isCSSLeafNode] ? 0 : (int)_reactSubviews.count;
   subview->_superview = self;
   _didUpdateSubviews = YES;
   [self dirtyText];
@@ -370,7 +375,7 @@ - (void)removeReactSubview:(RCTShadowView *)subview
   _didUpdateSubviews = YES;
   subview->_superview = nil;
   [_reactSubviews removeObject:subview];
-  _cssNode->children_count = (int)_reactSubviews.count;
+  _cssNode->children_count = [self isCSSLeafNode] ? 0 : (int)_reactSubviews.count;
 }
 
 - (NSArray<RCTShadowView *> *)reactSubviews