Fabric: RootShadowNode::layoutIfNeeded

Summary:
Reasons:
 * The name of the method now better represent what it's doing;
 * It exposes information about "dirty" state of the node without opening actual `LayoutableShadowNode` protected APIs;
 * It's a tiny bit faster now because it checks the flag before calling Yoga.

Changelog: [Internal] Fabric-specific internal change.

Reviewed By: sammy-SC

Differential Revision: D19596282

fbshipit-source-id: 3d87d9d5ba20bb8e360683f149b5ebf90beecd65

Author: shergin

ReactCommon/fabric/components/root/RootShadowNode.cpp

@@ -15,9 +15,14 @@ namespace react {
 
 const char RootComponentName[] = "RootView";
 
-void RootShadowNode::layout(
+bool RootShadowNode::layoutIfNeeded(
     std::vector<LayoutableShadowNode const *> *affectedNodes) {
   SystraceSection s("RootShadowNode::layout");
+
+  if (getIsLayoutClean()) {
+    return false;
+  }
+
   ensureUnsealed();
 
   auto layoutContext = getProps()->layoutContext;
@@ -31,6 +36,8 @@ void RootShadowNode::layout(
     setLayoutMetrics(layoutMetricsFromYogaNode(yogaNode_));
     setHasNewLayout(false);
   }
+
+  return true;
 }
 
 RootShadowNode::Unshared RootShadowNode::clone(

ReactCommon/fabric/components/root/RootShadowNode.h

@@ -35,9 +35,11 @@ class RootShadowNode final
   using Unshared = std::shared_ptr<RootShadowNode>;
 
   /*
-   * Layouts the shadow tree.
+   * Layouts the shadow tree if needed.
+   * Returns `false` if the three is already laid out.
    */
-  void layout(std::vector<LayoutableShadowNode const *> *affectedNodes = {});
+  bool layoutIfNeeded(
+      std::vector<LayoutableShadowNode const *> *affectedNodes = {});
 
   /*
    * Clones the node with given `layoutConstraints` and `layoutContext`.
@@ -58,9 +60,6 @@ class RootShadowNode final
       ShadowNodeFamily const &shadowNodeFamily,
       std::function<ShadowNode::Unshared(ShadowNode const &oldShadowNode)>
           callback) const;
-
- private:
-  using YogaLayoutableShadowNode::layout;
 };
 
 } // namespace react

ReactCommon/fabric/mounting/ShadowTree.cpp

@@ -169,7 +169,7 @@ bool ShadowTree::tryCommit(ShadowTreeCommitTransaction transaction) const {
   affectedLayoutableNodes.reserve(1024);
 
   telemetry.willLayout();
-  newRootShadowNode->layout(&affectedLayoutableNodes);
+  newRootShadowNode->layoutIfNeeded(&affectedLayoutableNodes);
   telemetry.didLayout();
 
   newRootShadowNode->sealRecursive();

ReactCommon/fabric/mounting/tests/ShadowTreeLifeCycleTest.cpp

@@ -92,7 +92,7 @@ static void testShadowNodeTreeLifeCycle(
 
       // Laying out the tree.
       std::const_pointer_cast<RootShadowNode>(nextRootNode)
-          ->layout(&affectedLayoutableNodes);
+          ->layoutIfNeeded(&affectedLayoutableNodes);
 
       nextRootNode->sealRecursive();
       allNodes.push_back(nextRootNode);

ReactCommon/fabric/uimanager/Scheduler.cpp

@@ -234,7 +234,7 @@ Size Scheduler::measureSurface(
             [&](RootShadowNode::Shared const &oldRootShadowNode) {
               auto rootShadowNode =
                   oldRootShadowNode->clone(layoutConstraints, layoutContext);
-              rootShadowNode->layout();
+              rootShadowNode->layoutIfNeeded();
               size = rootShadowNode->getLayoutMetrics().frame.size;
               return nullptr;
             });