change ReactBatchConfig.transition

Previously, ReactBatchConfig.transition was an number (1 = there is a transition, 0 = there isn't one). This PR changes this to a transition object (object = there is a transition, null = there isn't one) in preparation for transition tracing changes.

packages/react-dom/src/events/ReactDOMEventListener.js

@@ -117,7 +117,7 @@ function dispatchDiscreteEvent(
 ) {
   const previousPriority = getCurrentUpdatePriority();
   const prevTransition = ReactCurrentBatchConfig.transition;
-  ReactCurrentBatchConfig.transition = 0;
+  ReactCurrentBatchConfig.transition = null;
   try {
     setCurrentUpdatePriority(DiscreteEventPriority);
     dispatchEvent(domEventName, eventSystemFlags, container, nativeEvent);
@@ -135,7 +135,7 @@ function dispatchContinuousEvent(
 ) {
   const previousPriority = getCurrentUpdatePriority();
   const prevTransition = ReactCurrentBatchConfig.transition;
-  ReactCurrentBatchConfig.transition = 0;
+  ReactCurrentBatchConfig.transition = null;
   try {
     setCurrentUpdatePriority(ContinuousEventPriority);
     dispatchEvent(domEventName, eventSystemFlags, container, nativeEvent);

packages/react-reconciler/src/ReactFiberHooks.new.js

@@ -1928,7 +1928,7 @@ function mountDeferredValue<T>(value: T): T {
   const [prevValue, setValue] = mountState(value);
   mountEffect(() => {
     const prevTransition = ReactCurrentBatchConfig.transition;
-    ReactCurrentBatchConfig.transition = 1;
+    ReactCurrentBatchConfig.transition = {};
     try {
       setValue(value);
     } finally {
@@ -1942,7 +1942,7 @@ function updateDeferredValue<T>(value: T): T {
   const [prevValue, setValue] = updateState(value);
   updateEffect(() => {
     const prevTransition = ReactCurrentBatchConfig.transition;
-    ReactCurrentBatchConfig.transition = 1;
+    ReactCurrentBatchConfig.transition = {};
     try {
       setValue(value);
     } finally {
@@ -1956,7 +1956,7 @@ function rerenderDeferredValue<T>(value: T): T {
   const [prevValue, setValue] = rerenderState(value);
   updateEffect(() => {
     const prevTransition = ReactCurrentBatchConfig.transition;
-    ReactCurrentBatchConfig.transition = 1;
+    ReactCurrentBatchConfig.transition = {};
     try {
       setValue(value);
     } finally {
@@ -1975,20 +1975,27 @@ function startTransition(setPending, callback) {
   setPending(true);
 
   const prevTransition = ReactCurrentBatchConfig.transition;
-  ReactCurrentBatchConfig.transition = 1;
+  ReactCurrentBatchConfig.transition = {};
+  const currentTransition = ReactCurrentBatchConfig.transition;
+
+  if (__DEV__) {
+    ReactCurrentBatchConfig.transition._updatedFibers = new Set();
+  }
+
   try {
     setPending(false);
     callback();
   } finally {
     setCurrentUpdatePriority(previousPriority);
+
     ReactCurrentBatchConfig.transition = prevTransition;
     if (__DEV__) {
       if (
-        prevTransition !== 1 &&
+        prevTransition === null &&
         warnOnSubscriptionInsideStartTransition &&
-        ReactCurrentBatchConfig._updatedFibers
+        currentTransition._updatedFibers
       ) {
-        const updatedFibersCount = ReactCurrentBatchConfig._updatedFibers.size;
+        const updatedFibersCount = currentTransition._updatedFibers.size;
         if (updatedFibersCount > 10) {
           console.warn(
             'Detected a large number of updates inside startTransition. ' +
@@ -1996,7 +2003,7 @@ function startTransition(setPending, callback) {
               'Otherwise concurrent mode guarantees are off the table.',
           );
         }
-        ReactCurrentBatchConfig._updatedFibers.clear();
+        currentTransition._updatedFibers.clear();
       }
     }
   }

packages/react-reconciler/src/ReactFiberHooks.old.js

@@ -1928,7 +1928,7 @@ function mountDeferredValue<T>(value: T): T {
   const [prevValue, setValue] = mountState(value);
   mountEffect(() => {
     const prevTransition = ReactCurrentBatchConfig.transition;
-    ReactCurrentBatchConfig.transition = 1;
+    ReactCurrentBatchConfig.transition = {};
     try {
       setValue(value);
     } finally {
@@ -1942,7 +1942,7 @@ function updateDeferredValue<T>(value: T): T {
   const [prevValue, setValue] = updateState(value);
   updateEffect(() => {
     const prevTransition = ReactCurrentBatchConfig.transition;
-    ReactCurrentBatchConfig.transition = 1;
+    ReactCurrentBatchConfig.transition = {};
     try {
       setValue(value);
     } finally {
@@ -1956,7 +1956,7 @@ function rerenderDeferredValue<T>(value: T): T {
   const [prevValue, setValue] = rerenderState(value);
   updateEffect(() => {
     const prevTransition = ReactCurrentBatchConfig.transition;
-    ReactCurrentBatchConfig.transition = 1;
+    ReactCurrentBatchConfig.transition = {};
     try {
       setValue(value);
     } finally {
@@ -1975,20 +1975,27 @@ function startTransition(setPending, callback) {
   setPending(true);
 
   const prevTransition = ReactCurrentBatchConfig.transition;
-  ReactCurrentBatchConfig.transition = 1;
+  ReactCurrentBatchConfig.transition = {};
+  const currentTransition = ReactCurrentBatchConfig.transition;
+
+  if (__DEV__) {
+    ReactCurrentBatchConfig.transition._updatedFibers = new Set();
+  }
+
   try {
     setPending(false);
     callback();
   } finally {
     setCurrentUpdatePriority(previousPriority);
+
     ReactCurrentBatchConfig.transition = prevTransition;
     if (__DEV__) {
       if (
-        prevTransition !== 1 &&
+        prevTransition === null &&
         warnOnSubscriptionInsideStartTransition &&
-        ReactCurrentBatchConfig._updatedFibers
+        currentTransition._updatedFibers
       ) {
-        const updatedFibersCount = ReactCurrentBatchConfig._updatedFibers.size;
+        const updatedFibersCount = currentTransition._updatedFibers.size;
         if (updatedFibersCount > 10) {
           console.warn(
             'Detected a large number of updates inside startTransition. ' +
@@ -1996,7 +2003,7 @@ function startTransition(setPending, callback) {
               'Otherwise concurrent mode guarantees are off the table.',
           );
         }
-        ReactCurrentBatchConfig._updatedFibers.clear();
+        currentTransition._updatedFibers.clear();
       }
     }
   }

packages/react-reconciler/src/ReactFiberTracingMarkerComponent.new.js

@@ -0,0 +1,13 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+import type {Fiber} from 'react-reconciler/src/ReactInternalTypes';
+
+export type Transition = {
+  _updatedFibers?: Set<Fiber>,
+};

packages/react-reconciler/src/ReactFiberTransition.js

@@ -8,11 +8,12 @@
  */
 
 import ReactSharedInternals from 'shared/ReactSharedInternals';
+import type {Transition} from './ReactFiberTracingMarkerComponent.new';
 
 const {ReactCurrentBatchConfig} = ReactSharedInternals;
 
-export const NoTransition = 0;
+export const NoTransition = null;
 
-export function requestCurrentTransition(): number {
+export function requestCurrentTransition(): Transition | null {
   return ReactCurrentBatchConfig.transition;
 }

packages/react-reconciler/src/ReactFiberWorkLoop.new.js

@@ -401,9 +401,14 @@ export function requestUpdateLane(fiber: Fiber): Lane {
     if (
       __DEV__ &&
       warnOnSubscriptionInsideStartTransition &&
-      ReactCurrentBatchConfig._updatedFibers
+      ReactCurrentBatchConfig.transition !== null
     ) {
-      ReactCurrentBatchConfig._updatedFibers.add(fiber);
+      const transition = ReactCurrentBatchConfig.transition;
+      if (!transition._updatedFibers) {
+        transition._updatedFibers = new Set();
+      }
+
+      transition._updatedFibers.add(fiber);
     }
     // The algorithm for assigning an update to a lane should be stable for all
     // updates at the same priority within the same event. To do this, the
@@ -1246,7 +1251,7 @@ export function deferredUpdates<A>(fn: () => A): A {
   const previousPriority = getCurrentUpdatePriority();
   const prevTransition = ReactCurrentBatchConfig.transition;
   try {
-    ReactCurrentBatchConfig.transition = 0;
+    ReactCurrentBatchConfig.transition = null;
     setCurrentUpdatePriority(DefaultEventPriority);
     return fn();
   } finally {
@@ -1285,7 +1290,7 @@ export function discreteUpdates<A, B, C, D, R>(
   const previousPriority = getCurrentUpdatePriority();
   const prevTransition = ReactCurrentBatchConfig.transition;
   try {
-    ReactCurrentBatchConfig.transition = 0;
+    ReactCurrentBatchConfig.transition = null;
     setCurrentUpdatePriority(DiscreteEventPriority);
     return fn(a, b, c, d);
   } finally {
@@ -1320,7 +1325,7 @@ export function flushSync(fn) {
   const prevTransition = ReactCurrentBatchConfig.transition;
   const previousPriority = getCurrentUpdatePriority();
   try {
-    ReactCurrentBatchConfig.transition = 0;
+    ReactCurrentBatchConfig.transition = null;
     setCurrentUpdatePriority(DiscreteEventPriority);
     if (fn) {
       return fn();
@@ -1355,7 +1360,7 @@ export function flushControlled(fn: () => mixed): void {
   const prevTransition = ReactCurrentBatchConfig.transition;
   const previousPriority = getCurrentUpdatePriority();
   try {
-    ReactCurrentBatchConfig.transition = 0;
+    ReactCurrentBatchConfig.transition = null;
     setCurrentUpdatePriority(DiscreteEventPriority);
     fn();
   } finally {
@@ -1893,7 +1898,7 @@ function commitRoot(root: FiberRoot, recoverableErrors: null | Array<mixed>) {
   const previousUpdateLanePriority = getCurrentUpdatePriority();
   const prevTransition = ReactCurrentBatchConfig.transition;
   try {
-    ReactCurrentBatchConfig.transition = 0;
+    ReactCurrentBatchConfig.transition = null;
     setCurrentUpdatePriority(DiscreteEventPriority);
     commitRootImpl(root, recoverableErrors, previousUpdateLanePriority);
   } finally {
@@ -2028,7 +2033,7 @@ function commitRootImpl(
 
   if (subtreeHasEffects || rootHasEffect) {
     const prevTransition = ReactCurrentBatchConfig.transition;
-    ReactCurrentBatchConfig.transition = 0;
+    ReactCurrentBatchConfig.transition = null;
     const previousPriority = getCurrentUpdatePriority();
     setCurrentUpdatePriority(DiscreteEventPriority);
 
@@ -2283,7 +2288,7 @@ export function flushPassiveEffects(): boolean {
     const prevTransition = ReactCurrentBatchConfig.transition;
     const previousPriority = getCurrentUpdatePriority();
     try {
-      ReactCurrentBatchConfig.transition = 0;
+      ReactCurrentBatchConfig.transition = null;
       setCurrentUpdatePriority(priority);
       return flushPassiveEffectsImpl();
     } finally {

packages/react-reconciler/src/ReactFiberWorkLoop.old.js

@@ -401,9 +401,14 @@ export function requestUpdateLane(fiber: Fiber): Lane {
     if (
       __DEV__ &&
       warnOnSubscriptionInsideStartTransition &&
-      ReactCurrentBatchConfig._updatedFibers
+      ReactCurrentBatchConfig.transition !== null
     ) {
-      ReactCurrentBatchConfig._updatedFibers.add(fiber);
+      const transition = ReactCurrentBatchConfig.transition;
+      if (!transition._updatedFibers) {
+        transition._updatedFibers = new Set();
+      }
+
+      transition._updatedFibers.add(fiber);
     }
     // The algorithm for assigning an update to a lane should be stable for all
     // updates at the same priority within the same event. To do this, the
@@ -1246,7 +1251,7 @@ export function deferredUpdates<A>(fn: () => A): A {
   const previousPriority = getCurrentUpdatePriority();
   const prevTransition = ReactCurrentBatchConfig.transition;
   try {
-    ReactCurrentBatchConfig.transition = 0;
+    ReactCurrentBatchConfig.transition = null;
     setCurrentUpdatePriority(DefaultEventPriority);
     return fn();
   } finally {
@@ -1285,7 +1290,7 @@ export function discreteUpdates<A, B, C, D, R>(
   const previousPriority = getCurrentUpdatePriority();
   const prevTransition = ReactCurrentBatchConfig.transition;
   try {
-    ReactCurrentBatchConfig.transition = 0;
+    ReactCurrentBatchConfig.transition = null;
     setCurrentUpdatePriority(DiscreteEventPriority);
     return fn(a, b, c, d);
   } finally {
@@ -1320,7 +1325,7 @@ export function flushSync(fn) {
   const prevTransition = ReactCurrentBatchConfig.transition;
   const previousPriority = getCurrentUpdatePriority();
   try {
-    ReactCurrentBatchConfig.transition = 0;
+    ReactCurrentBatchConfig.transition = null;
     setCurrentUpdatePriority(DiscreteEventPriority);
     if (fn) {
       return fn();
@@ -1355,7 +1360,7 @@ export function flushControlled(fn: () => mixed): void {
   const prevTransition = ReactCurrentBatchConfig.transition;
   const previousPriority = getCurrentUpdatePriority();
   try {
-    ReactCurrentBatchConfig.transition = 0;
+    ReactCurrentBatchConfig.transition = null;
     setCurrentUpdatePriority(DiscreteEventPriority);
     fn();
   } finally {
@@ -1893,7 +1898,7 @@ function commitRoot(root: FiberRoot, recoverableErrors: null | Array<mixed>) {
   const previousUpdateLanePriority = getCurrentUpdatePriority();
   const prevTransition = ReactCurrentBatchConfig.transition;
   try {
-    ReactCurrentBatchConfig.transition = 0;
+    ReactCurrentBatchConfig.transition = null;
     setCurrentUpdatePriority(DiscreteEventPriority);
     commitRootImpl(root, recoverableErrors, previousUpdateLanePriority);
   } finally {
@@ -2028,7 +2033,7 @@ function commitRootImpl(
 
   if (subtreeHasEffects || rootHasEffect) {
     const prevTransition = ReactCurrentBatchConfig.transition;
-    ReactCurrentBatchConfig.transition = 0;
+    ReactCurrentBatchConfig.transition = null;
     const previousPriority = getCurrentUpdatePriority();
     setCurrentUpdatePriority(DiscreteEventPriority);
 
@@ -2283,7 +2288,7 @@ export function flushPassiveEffects(): boolean {
     const prevTransition = ReactCurrentBatchConfig.transition;
     const previousPriority = getCurrentUpdatePriority();
     try {
-      ReactCurrentBatchConfig.transition = 0;
+      ReactCurrentBatchConfig.transition = null;
       setCurrentUpdatePriority(priority);
       return flushPassiveEffectsImpl();
     } finally {

packages/react/src/ReactCurrentBatchConfig.js

@@ -7,22 +7,17 @@
  * @flow
  */
 
-import type {Fiber} from 'react-reconciler/src/ReactInternalTypes';
+import type {Transition} from 'react-reconciler/src/ReactFiberTracingMarkerComponent.new';
 
 type BatchConfig = {
-  transition: number,
-  _updatedFibers?: Set<Fiber>,
+  transition: Transition | null,
 };
 /**
  * Keeps track of the current batch's configuration such as how long an update
  * should suspend for if it needs to.
  */
 const ReactCurrentBatchConfig: BatchConfig = {
-  transition: 0,
+  transition: null,
 };
 
-if (__DEV__) {
-  ReactCurrentBatchConfig._updatedFibers = new Set();
-}
-
 export default ReactCurrentBatchConfig;

packages/react/src/ReactStartTransition.js

@@ -12,18 +12,24 @@ import {warnOnSubscriptionInsideStartTransition} from 'shared/ReactFeatureFlags'
 
 export function startTransition(scope: () => void) {
   const prevTransition = ReactCurrentBatchConfig.transition;
-  ReactCurrentBatchConfig.transition = 1;
+  ReactCurrentBatchConfig.transition = {};
+  const currentTransition = ReactCurrentBatchConfig.transition;
+
+  if (__DEV__) {
+    ReactCurrentBatchConfig.transition._updatedFibers = new Set();
+  }
   try {
     scope();
   } finally {
     ReactCurrentBatchConfig.transition = prevTransition;
+
     if (__DEV__) {
       if (
-        prevTransition !== 1 &&
+        prevTransition === null &&
         warnOnSubscriptionInsideStartTransition &&
-        ReactCurrentBatchConfig._updatedFibers
+        currentTransition._updatedFibers
       ) {
-        const updatedFibersCount = ReactCurrentBatchConfig._updatedFibers.size;
+        const updatedFibersCount = currentTransition._updatedFibers.size;
         if (updatedFibersCount > 10) {
           console.warn(
             'Detected a large number of updates inside startTransition. ' +
@@ -31,7 +37,7 @@ export function startTransition(scope: () => void) {
               'Otherwise concurrent mode guarantees are off the table.',
           );
         }
-        ReactCurrentBatchConfig._updatedFibers.clear();
+        currentTransition._updatedFibers.clear();
       }
     }
   }