To reduce hidden class checks we need to read the batch config once w…

…hich requires inlining the requestCurrentTransition implementation.

packages/react-reconciler/src/ReactFiberHooks.js

@@ -152,7 +152,7 @@ import {requestTransitionLane} from './ReactFiberRootScheduler';
 import {isCurrentTreeHidden} from './ReactFiberHiddenContext';
 import {
   notifyTransitionCallbacks,
-  requestCurrentTransition,
+  registerTransitionUpdateHandler,
 } from './ReactFiberTransition';
 
 const {ReactCurrentDispatcher, ReactCurrentBatchConfig} = ReactSharedInternals;
@@ -3343,7 +3343,10 @@ function dispatchOptimisticSetState<S, A>(
   queue: UpdateQueue<S, A>,
   action: A,
 ): void {
-  const transition = requestCurrentTransition();
+  const transition = ReactCurrentBatchConfig.transition;
+  if (transition !== null) {
+    registerTransitionUpdateHandler(transition);
+  }
 
   if (__DEV__) {
     if (transition === null) {

packages/react-reconciler/src/ReactFiberTransition.js

@@ -33,21 +33,15 @@ import {
   CacheContext,
 } from './ReactFiberCacheComponent';
 
-import ReactSharedInternals from 'shared/ReactSharedInternals';
 import {entangleAsyncAction} from './ReactFiberAsyncAction';
 
-const {ReactCurrentBatchConfig} = ReactSharedInternals;
-
 export const NoTransition = null;
 
-export function requestCurrentTransition(): BatchConfigTransition | null {
-  const transition = ReactCurrentBatchConfig.transition;
-  if (transition !== null) {
-    // Whenever a transition update is scheduled, register a callback on the
-    // transition object so we can get the return value of the scope function.
-    transition._callbacks.add(handleAsyncAction);
-  }
-  return transition;
+export function registerTransitionUpdateHandler(
+  transition: BatchConfigTransition,
+) {
+  // $FlowFixMe[incompatible-call]: Thenable<mixed> is not compatible with mixed. Previously this was anytyped so it was always a type error just hidden
+  transition._callbacks.add(handleAsyncAction);
 }
 
 function handleAsyncAction(

packages/react-reconciler/src/ReactFiberWorkLoop.js

@@ -163,7 +163,7 @@ import {
   lowerEventPriority,
   lanesToEventPriority,
 } from './ReactEventPriorities';
-import {requestCurrentTransition} from './ReactFiberTransition';
+import {registerTransitionUpdateHandler} from './ReactFiberTransition';
 import {
   SelectiveHydrationException,
   beginWork,
@@ -621,17 +621,19 @@ export function requestUpdateLane(fiber: Fiber): Lane {
     return pickArbitraryLane(workInProgressRootRenderLanes);
   }
 
-  const transition = requestCurrentTransition();
+  const transition = ReactCurrentBatchConfig.transition;
+  const eventPriority = ReactCurrentBatchConfig.eventPriority;
+
   if (transition !== null) {
     if (__DEV__) {
-      const batchConfigTransition = ReactCurrentBatchConfig.transition;
-      if (!batchConfigTransition._updatedFibers) {
-        batchConfigTransition._updatedFibers = new Set();
+      if (!transition._updatedFibers) {
+        transition._updatedFibers = new Set();
       }
 
-      batchConfigTransition._updatedFibers.add(fiber);
+      transition._updatedFibers.add(fiber);
     }
 
+    registerTransitionUpdateHandler(transition);
     const actionScopeLane = peekEntangledActionLane();
     return actionScopeLane !== NoLane
       ? // We're inside an async action scope. Reuse the same lane.
@@ -644,7 +646,7 @@ export function requestUpdateLane(fiber: Fiber): Lane {
 
   // If there is an eventPriority scoped to React's internals we use it.
   // The opaque type used for EventPriority matches the Lane so we cast it
-  let updateLane: Lane = (ReactCurrentBatchConfig.eventPriority: any);
+  let updateLane: Lane = (eventPriority: any);
   if (updateLane !== NoLane) {
     return updateLane;
   }