Implement findDescendantNode without cloning the tree (#39356)

Summary:
Pull Request resolved: #39356

changelog: [internal]

`findDescendantNode` shouldn't clone the tree.

Reviewed By: javache

Differential Revision: D49095341

fbshipit-source-id: 4cd6aa6f9ba0f96d708e6a6c6b0cd55f03d8b5b1

packages/react-native/ReactCommon/react/renderer/mounting/tests/StateReconciliationTest.cpp

@@ -36,23 +36,31 @@ class DummyShadowTreeDelegate : public ShadowTreeDelegate {
  bool mountSynchronously) const override{};
 };
 
-inline const ShadowNode* findDescendantNode(
+namespace {
+const ShadowNode* findDescendantNode(
  const ShadowNode& shadowNode,
  const ShadowNodeFamily& family) {
- const ShadowNode* result = nullptr;
- shadowNode.cloneTree(family, [&](const ShadowNode& oldShadowNode) {
- result = &oldShadowNode;
- return oldShadowNode.clone({});
- });
- return result;
+ if (&shadowNode.getFamily() == &family) {
+ return &shadowNode;
+ }
+
+ for (auto childNode : shadowNode.getChildren()) {
+ auto descendant = findDescendantNode(*childNode, family);
+ if (descendant != nullptr) {
+ return descendant;
+ }
+ }
+
+ return nullptr;
 }
 
-inline const ShadowNode* findDescendantNode(
+const ShadowNode* findDescendantNode(
  const ShadowTree& shadowTree,
  const ShadowNodeFamily& family) {
  return findDescendantNode(
  *shadowTree.getCurrentRevision().rootShadowNode, family);
 }
+} // namespace
 
 TEST(StateReconciliationTest, testStateReconciliation) {
  auto builder = simpleComponentBuilder();