Fabric: Implementing cloneAndReplaceChild() for ViewShadowNode

Summary:
First, LayoutableShadowNode::cloneAndReplaceChild() is now pure virtual. The default implementation was useless and confusing.
Second, cloneAndReplaceChild() is now fully implemented for ViewShadowNode, so fancy Yoga Concurrent layout *should* work now.

Reviewed By: mdvacca

Differential Revision: D7376352

fbshipit-source-id: 1199a37e64535c8592a2a5480e60139f61d02006

ReactCommon/fabric/core/layout/LayoutableShadowNode.cpp

@@ -93,9 +93,5 @@ void LayoutableShadowNode::layoutChildren(LayoutContext layoutContext) {
   // Default implementation does nothing.
 }
 
-SharedLayoutableShadowNode LayoutableShadowNode::cloneAndReplaceChild(const SharedLayoutableShadowNode &child) {
-  return child;
-}
-
 } // namespace react
 } // namespace facebook

ReactCommon/fabric/core/layout/LayoutableShadowNode.h

@@ -93,9 +93,8 @@ class LayoutableShadowNode:
   /*
    * In case layout algorithm needs to mutate this (probably sealed) node,
    * it has to clone and replace it in the hierarchy before to do so.
-   * Default implementation does nothing and returns `child`.
    */
-  virtual SharedLayoutableShadowNode cloneAndReplaceChild(const SharedLayoutableShadowNode &child);
+  virtual SharedLayoutableShadowNode cloneAndReplaceChild(const SharedLayoutableShadowNode &child) = 0;
 
   /*
    * Sets layout metrics for the shadow node.

ReactCommon/fabric/view/ViewShadowNode.cpp

@@ -7,6 +7,8 @@
 
 #include "ViewShadowNode.h"
 
+#include <algorithm>
+
 #include <fabric/debug/DebugStringConvertibleItem.h>
 
 namespace facebook {
@@ -87,6 +89,31 @@ SharedLayoutableShadowNodeList ViewShadowNode::getChildren() const {
   return sharedLayoutableShadowNodeList;
 }
 
+SharedLayoutableShadowNode ViewShadowNode::cloneAndReplaceChild(const SharedLayoutableShadowNode &child) {
+  ensureUnsealed();
+
+  // We cannot mutate `children_` in place here because it is a *shared*
+  // data structure which means other `ShadowNodes` might refer to its old value.
+  // So, we have to clone this and only then mutate.
+  auto nonConstChildrenCopy = SharedShadowNodeList(*children_);
+
+  auto viewShadowNodeChild = std::dynamic_pointer_cast<const ViewShadowNode>(child);
+  assert(viewShadowNodeChild);
+
+  auto viewShadowNodeChildClone = std::make_shared<const ViewShadowNode>(viewShadowNodeChild);
+
+  std::replace(
+    nonConstChildrenCopy.begin(),
+    nonConstChildrenCopy.end(),
+    std::static_pointer_cast<const ShadowNode>(viewShadowNodeChild),
+    std::static_pointer_cast<const ShadowNode>(viewShadowNodeChildClone)
+  );
+
+  children_ = std::make_shared<const SharedShadowNodeList>(nonConstChildrenCopy);
+
+  return std::static_pointer_cast<const LayoutableShadowNode>(viewShadowNodeChildClone);
+}
+
 #pragma mark - DebugStringConvertible
 
 SharedDebugStringConvertibleList ViewShadowNode::getDebugProps() const {

ReactCommon/fabric/view/ViewShadowNode.h

@@ -57,6 +57,7 @@ class ViewShadowNode:
 #pragma mark - LayoutableShadowNode
 
   SharedLayoutableShadowNodeList getChildren() const override;
+  SharedLayoutableShadowNode cloneAndReplaceChild(const SharedLayoutableShadowNode &child) override;
 };
 
 } // namespace react