Add .old prefix to reconciler modules

packages/legacy-events/PluginModuleType.js

@@ -7,7 +7,7 @@
  * @flow
  */
 
-import type {Fiber} from 'react-reconciler/src/ReactFiber';
+import type {Fiber} from 'react-reconciler/src/ReactFiber.old';
 import type {
   DispatchConfig,
   ReactSyntheticEvent,

packages/legacy-events/ReactSyntheticEventType.js

@@ -8,7 +8,7 @@
  * @flow
  */
 
-import type {Fiber} from 'react-reconciler/src/ReactFiber';
+import type {Fiber} from 'react-reconciler/src/ReactFiber.old';
 import type {EventPriority} from 'shared/ReactTypes';
 import type {TopLevelType} from './TopLevelEventTypes';
 

packages/react-debug-tools/src/ReactDebugHooks.js

@@ -17,12 +17,15 @@ import type {
   ReactEventResponderListener,
   ReactScopeMethods,
 } from 'shared/ReactTypes';
-import type {Fiber} from 'react-reconciler/src/ReactFiber';
+import type {Fiber} from 'react-reconciler/src/ReactFiber.old';
 import type {OpaqueIDType} from 'react-reconciler/src/ReactFiberHostConfig';
 
-import type {Hook, TimeoutConfig} from 'react-reconciler/src/ReactFiberHooks';
-import type {Dispatcher as DispatcherType} from 'react-reconciler/src/ReactFiberHooks';
-import type {SuspenseConfig} from 'react-reconciler/src/ReactFiberSuspenseConfig';
+import type {
+  Hook,
+  TimeoutConfig,
+  Dispatcher as DispatcherType,
+} from 'react-reconciler/src/ReactFiberHooks.old';
+import type {SuspenseConfig} from 'react-reconciler/src/ReactFiberSuspenseConfig.old';
 import {NoMode} from 'react-reconciler/src/ReactTypeOfMode';
 
 import ErrorStackParser from 'error-stack-parser';

packages/react-devtools-shared/src/backend/console.js

@@ -10,7 +10,7 @@
 import {getInternalReactConstants} from './renderer';
 import describeComponentFrame from './describeComponentFrame';
 
-import type {Fiber} from 'react-reconciler/src/ReactFiber';
+import type {Fiber} from 'react-reconciler/src/ReactFiber.old';
 import type {ReactRenderer} from './types';
 
 const APPEND_STACK_TO_METHODS = ['error', 'trace', 'warn'];

packages/react-devtools-shared/src/backend/renderer.js

@@ -50,7 +50,7 @@ import {
   registerRenderer as registerRendererWithConsole,
 } from './console';
 
-import type {Fiber} from 'react-reconciler/src/ReactFiber';
+import type {Fiber} from 'react-reconciler/src/ReactFiber.old';
 import type {
   ChangeDescription,
   CommitDataBackend,

packages/react-devtools-shared/src/backend/types.js

@@ -9,7 +9,7 @@
 
 import type {ReactContext} from 'shared/ReactTypes';
 import type {Source} from 'shared/ReactElementType';
-import type {Fiber} from 'react-reconciler/src/ReactFiber';
+import type {Fiber} from 'react-reconciler/src/ReactFiber.old';
 import type {
   ComponentFilter,
   ElementType,

packages/react-dom/src/client/ReactDOMComponentTree.js

@@ -7,7 +7,7 @@
  * @flow
  */
 
-import type {Fiber} from 'react-reconciler/src/ReactFiber';
+import type {Fiber} from 'react-reconciler/src/ReactFiber.old';
 import type {
   Container,
   TextInstance,

packages/react-dom/src/client/ReactDOMRoot.js

@@ -12,7 +12,7 @@ import type {RootTag} from 'react-reconciler/src/ReactRootTags';
 import type {ReactNodeList} from 'shared/ReactTypes';
 // TODO: This type is shared between the reconciler and ReactDOM, but will
 // eventually be lifted out to the renderer.
-import type {FiberRoot} from 'react-reconciler/src/ReactFiberRoot';
+import type {FiberRoot} from 'react-reconciler/src/ReactFiberRoot.old';
 import {findHostInstanceWithNoPortals} from 'react-reconciler/src/ReactFiberReconciler';
 
 export type RootType = {

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

@@ -11,7 +11,7 @@ import type {AnyNativeEvent} from 'legacy-events/PluginModuleType';
 import type {DOMTopLevelEventType} from 'legacy-events/TopLevelEventTypes';
 import type {ElementListenerMap} from '../events/DOMEventListenerMap';
 import type {EventSystemFlags} from './EventSystemFlags';
-import type {Fiber} from 'react-reconciler/src/ReactFiber';
+import type {Fiber} from 'react-reconciler/src/ReactFiber.old';
 import type {PluginModule} from 'legacy-events/PluginModuleType';
 import type {ReactSyntheticEvent} from 'legacy-events/ReactSyntheticEventType';
 import type {TopLevelType} from 'legacy-events/TopLevelEventTypes';

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

@@ -15,7 +15,7 @@ import type {
 } from '../events/DOMEventListenerMap';
 import type {EventSystemFlags} from './EventSystemFlags';
 import type {EventPriority, ReactScopeMethods} from 'shared/ReactTypes';
-import type {Fiber} from 'react-reconciler/src/ReactFiber';
+import type {Fiber} from 'react-reconciler/src/ReactFiber.old';
 import type {PluginModule} from 'legacy-events/PluginModuleType';
 import type {
   ReactSyntheticEvent,

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

@@ -31,7 +31,7 @@ import {
   flushDiscreteUpdatesIfNeeded,
   executeUserEventHandler,
 } from './ReactDOMUpdateBatching';
-import type {Fiber} from 'react-reconciler/src/ReactFiber';
+import type {Fiber} from 'react-reconciler/src/ReactFiber.old';
 import {enableDeprecatedFlareAPI} from 'shared/ReactFeatureFlags';
 import invariant from 'shared/invariant';
 

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

@@ -9,7 +9,7 @@
 
 import type {AnyNativeEvent} from 'legacy-events/PluginModuleType';
 import type {EventPriority} from 'shared/ReactTypes';
-import type {FiberRoot} from 'react-reconciler/src/ReactFiberRoot';
+import type {FiberRoot} from 'react-reconciler/src/ReactFiberRoot.old';
 import type {Container, SuspenseInstance} from '../client/ReactDOMHostConfig';
 import type {DOMTopLevelEventType} from 'legacy-events/TopLevelEventTypes';
 

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

@@ -12,7 +12,7 @@ import type {Container, SuspenseInstance} from '../client/ReactDOMHostConfig';
 import type {DOMTopLevelEventType} from 'legacy-events/TopLevelEventTypes';
 import type {ElementListenerMap} from '../events/DOMEventListenerMap';
 import type {EventSystemFlags} from './EventSystemFlags';
-import type {FiberRoot} from 'react-reconciler/src/ReactFiberRoot';
+import type {FiberRoot} from 'react-reconciler/src/ReactFiberRoot.old';
 
 import {
   enableDeprecatedFlareAPI,

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

@@ -12,7 +12,7 @@ import type {
   DOMTopLevelEventType,
 } from 'legacy-events/TopLevelEventTypes';
 import type {ReactSyntheticEvent} from 'legacy-events/ReactSyntheticEventType';
-import type {Fiber} from 'react-reconciler/src/ReactFiber';
+import type {Fiber} from 'react-reconciler/src/ReactFiber.old';
 import type {PluginModule} from 'legacy-events/PluginModuleType';
 import type {EventSystemFlags} from './EventSystemFlags';
 

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

@@ -7,7 +7,7 @@
  * @flow
  */
 
-import type {Fiber} from 'react-reconciler/src/ReactFiber';
+import type {Fiber} from 'react-reconciler/src/ReactFiber.old';
 import type {ReactSyntheticEvent} from 'legacy-events/ReactSyntheticEventType';
 
 import {HostComponent} from 'react-reconciler/src/ReactWorkTags';
@@ -82,7 +82,7 @@ function accumulateEnterLeaveListenersForEvent(
     return;
   }
   const dispatchListeners = [];
-  const dispatchInstances = [];
+  const dispatchInstances: Array<Fiber | null> = [];
   const dispatchCurrentTargets = [];
 
   let instance = target;

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

@@ -7,6 +7,7 @@
  * @flow
  */
 
+import type {Fiber} from 'react-reconciler/src/ReactFiber.old';
 import type {DOMTopLevelEventType} from 'legacy-events/TopLevelEventTypes';
 import type {ReactSyntheticEvent} from 'legacy-events/ReactSyntheticEventType';
 
@@ -17,7 +18,7 @@ export default function accumulateEventTargetListeners(
   currentTarget: EventTarget,
 ): void {
   const dispatchListeners = [];
-  const dispatchInstances = [];
+  const dispatchInstances: Array<Fiber | null> = [];
   const dispatchCurrentTargets = [];
 
   const eventTypeMap = eventTargetEventListenerStore.get(currentTarget);

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

@@ -7,6 +7,7 @@
  * @flow
  */
 
+import type {Fiber} from 'react-reconciler/src/ReactFiber.old';
 import type {DOMTopLevelEventType} from 'legacy-events/TopLevelEventTypes';
 import type {ReactSyntheticEvent} from 'legacy-events/ReactSyntheticEventType';
 
@@ -30,7 +31,7 @@ export default function accumulateTwoPhaseListeners(
 ): void {
   const phasedRegistrationNames = event.dispatchConfig.phasedRegistrationNames;
   const dispatchListeners = [];
-  const dispatchInstances = [];
+  const dispatchInstances: Array<Fiber | null> = [];
   const dispatchCurrentTargets = [];
 
   const {bubbled, captured} = phasedRegistrationNames;

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

@@ -6,7 +6,7 @@
  * @flow
  */
 
-import type {Fiber} from 'react-reconciler/src/ReactFiber';
+import type {Fiber} from 'react-reconciler/src/ReactFiber.old';
 import type {Props} from '../client/ReactDOMHostConfig';
 
 import invariant from 'shared/invariant';

packages/react-dom/src/server/ReactPartialRendererHooks.js

@@ -10,7 +10,7 @@
 import type {
   Dispatcher as DispatcherType,
   TimeoutConfig,
-} from 'react-reconciler/src/ReactFiberHooks';
+} from 'react-reconciler/src/ReactFiberHooks.old';
 import type {ThreadID} from './ReactThreadIDAllocator';
 import type {OpaqueIDType} from 'react-reconciler/src/ReactFiberHostConfig';
 
@@ -21,7 +21,7 @@ import type {
   ReactContext,
   ReactEventResponderListener,
 } from 'shared/ReactTypes';
-import type {SuspenseConfig} from 'react-reconciler/src/ReactFiberSuspenseConfig';
+import type {SuspenseConfig} from 'react-reconciler/src/ReactFiberSuspenseConfig.old';
 import type {ReactDOMListenerMap} from '../shared/ReactDOMTypes';
 
 import {validateContextBounds} from './ReactPartialRendererContext';

packages/react-native-renderer/src/ReactFabricEventEmitter.js

@@ -8,7 +8,7 @@
  */
 
 import type {AnyNativeEvent} from 'legacy-events/PluginModuleType';
-import type {Fiber} from 'react-reconciler/src/ReactFiber';
+import type {Fiber} from 'react-reconciler/src/ReactFiber.old';
 import type {PluginModule} from 'legacy-events/PluginModuleType';
 import type {ReactSyntheticEvent} from 'legacy-events/ReactSyntheticEventType';
 import type {TopLevelType} from 'legacy-events/TopLevelEventTypes';

packages/react-native-renderer/src/ReactNativeEventEmitter.js

@@ -8,7 +8,7 @@
  */
 
 import type {AnyNativeEvent} from 'legacy-events/PluginModuleType';
-import type {Fiber} from 'react-reconciler/src/ReactFiber';
+import type {Fiber} from 'react-reconciler/src/ReactFiber.old';
 import type {PluginModule} from 'legacy-events/PluginModuleType';
 import type {ReactSyntheticEvent} from 'legacy-events/ReactSyntheticEventType';
 import type {TopLevelType} from 'legacy-events/TopLevelEventTypes';

packages/react-native-renderer/src/ReactNativeFiberInspector.js

@@ -7,7 +7,7 @@
  * @flow
  */
 
-import type {Fiber} from 'react-reconciler/src/ReactFiber';
+import type {Fiber} from 'react-reconciler/src/ReactFiber.old';
 import type {TouchedViewDataAtPoint, InspectorData} from './ReactNativeTypes';
 
 import {

packages/react-native-renderer/src/ReactNativeGetListener.js

@@ -6,7 +6,7 @@
  * @flow
  */
 
-import type {Fiber} from 'react-reconciler/src/ReactFiber';
+import type {Fiber} from 'react-reconciler/src/ReactFiber.old';
 
 import invariant from 'shared/invariant';
 import {getFiberCurrentPropsFromNode} from 'legacy-events/EventPluginUtils';

packages/react-noop-renderer/src/createReactNoop.js

@@ -14,7 +14,7 @@
  * environment.
  */
 
-import type {Fiber} from 'react-reconciler/src/ReactFiber';
+import type {Fiber} from 'react-reconciler/src/ReactFiber.old';
 import type {UpdateQueue} from 'react-reconciler/src/ReactUpdateQueue';
 import type {ReactNodeList} from 'shared/ReactTypes';
 import type {RootTag} from 'react-reconciler/src/ReactRootTags';

packages/react-reconciler/src/ReactCapturedValue.js

@@ -7,7 +7,7 @@
  * @flow
  */
 
-import type {Fiber} from './ReactFiber';
+import type {Fiber} from './ReactFiber.old';
 
 import {getStackByFiberInDevAndProd} from './ReactFiberComponentStack';
 

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

@@ -11,8 +11,8 @@ import type {ReactElement} from 'shared/ReactElementType';
 import type {ReactPortal} from 'shared/ReactTypes';
 import type {BlockComponent} from 'react/src/ReactBlock';
 import type {LazyComponent} from 'react/src/ReactLazy';
-import type {Fiber} from './ReactFiber';
-import type {ExpirationTime} from './ReactFiberExpirationTime';
+import type {Fiber} from './ReactFiber.old';
+import type {ExpirationTime} from './ReactFiberExpirationTime.old';
 
 import getComponentName from 'shared/getComponentName';
 import {Placement, Deletion} from './ReactSideEffectTags';
@@ -42,11 +42,11 @@ import {
   createFiberFromFragment,
   createFiberFromText,
   createFiberFromPortal,
-} from './ReactFiber';
-import {emptyRefsObject} from './ReactFiberClassComponent';
+} from './ReactFiber.old';
+import {emptyRefsObject} from './ReactFiberClassComponent.old';
 import {getStackByFiberInDevAndProd} from './ReactFiberComponentStack';
 import {getCurrentFiberStackInDev} from './ReactCurrentFiber';
-import {isCompatibleFamilyForHotReloading} from './ReactFiberHotReloading';
+import {isCompatibleFamilyForHotReloading} from './ReactFiberHotReloading.old';
 import {StrictMode} from './ReactTypeOfMode';
 
 let didWarnAboutMaps;

packages/react-reconciler/src/ReactCurrentFiber.js

@@ -7,7 +7,7 @@
  * @flow
  */
 
-import type {Fiber} from './ReactFiber';
+import type {Fiber} from './ReactFiber.old';
 
 import ReactSharedInternals from 'shared/ReactSharedInternals';
 import {getStackByFiberInDevAndProd} from './ReactFiberComponentStack';

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

@@ -17,14 +17,14 @@ import type {
   ReactFundamentalComponent,
   ReactScope,
 } from 'shared/ReactTypes';
-import type {RootTag} from 'react-reconciler/src/ReactRootTags';
+import type {RootTag} from './ReactRootTags';
 import type {WorkTag} from './ReactWorkTags';
 import type {TypeOfMode} from './ReactTypeOfMode';
 import type {SideEffectTag} from './ReactSideEffectTags';
-import type {ExpirationTime} from './ReactFiberExpirationTime';
-import type {UpdateQueue} from './ReactUpdateQueue';
-import type {ContextDependency} from './ReactFiberNewContext';
-import type {HookType} from './ReactFiberHooks';
+import type {ExpirationTime} from './ReactFiberExpirationTime.old';
+import type {UpdateQueue} from './ReactUpdateQueue.old';
+import type {ContextDependency} from './ReactFiberNewContext.old';
+import type {HookType} from './ReactFiberHooks.old';
 import type {SuspenseInstance} from './ReactFiberHostConfig';
 
 import invariant from 'shared/invariant';
@@ -36,7 +36,7 @@ import {
   throwEarlyForMysteriousError,
 } from 'shared/ReactFeatureFlags';
 import {NoEffect, Placement} from './ReactSideEffectTags';
-import {ConcurrentRoot, BlockingRoot} from 'react-reconciler/src/ReactRootTags';
+import {ConcurrentRoot, BlockingRoot} from './ReactRootTags';
 import {
   IndeterminateComponent,
   ClassComponent,
@@ -63,13 +63,13 @@ import {
 } from './ReactWorkTags';
 import getComponentName from 'shared/getComponentName';
 
-import {isDevToolsPresent} from './ReactFiberDevToolsHook';
+import {isDevToolsPresent} from './ReactFiberDevToolsHook.old';
 import {
   resolveClassForHotReloading,
   resolveFunctionForHotReloading,
   resolveForwardRefForHotReloading,
-} from './ReactFiberHotReloading';
-import {NoWork} from './ReactFiberExpirationTime';
+} from './ReactFiberHotReloading.old';
+import {NoWork} from './ReactFiberExpirationTime.old';
 import {
   NoMode,
   ConcurrentMode,

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

@@ -10,15 +10,15 @@
 import type {ReactProviderType, ReactContext} from 'shared/ReactTypes';
 import type {BlockComponent} from 'react/src/ReactBlock';
 import type {LazyComponent as LazyComponentType} from 'react/src/ReactLazy';
-import type {Fiber} from './ReactFiber';
-import type {FiberRoot} from './ReactFiberRoot';
-import type {ExpirationTime} from './ReactFiberExpirationTime';
+import type {Fiber} from './ReactFiber.old';
+import type {FiberRoot} from './ReactFiberRoot.old';
+import type {ExpirationTime} from './ReactFiberExpirationTime.old';
 import type {
   SuspenseState,
   SuspenseListRenderState,
   SuspenseListTailMode,
-} from './ReactFiberSuspenseComponent';
-import type {SuspenseContext} from './ReactFiberSuspenseContext';
+} from './ReactFiberSuspenseComponent.old';
+import type {SuspenseContext} from './ReactFiberSuspenseContext.old';
 
 import checkPropTypes from 'shared/checkPropTypes';
 
@@ -73,7 +73,7 @@ import {
 import invariant from 'shared/invariant';
 import shallowEqual from 'shared/shallowEqual';
 import getComponentName from 'shared/getComponentName';
-import ReactStrictModeWarnings from './ReactStrictModeWarnings';
+import ReactStrictModeWarnings from './ReactStrictModeWarnings.old';
 import {REACT_LAZY_TYPE, getIteratorFn} from 'shared/ReactSymbols';
 import {
   getCurrentFiberOwnerNameInDevOrNull,
@@ -83,24 +83,24 @@ import {
   resolveFunctionForHotReloading,
   resolveForwardRefForHotReloading,
   resolveClassForHotReloading,
-} from './ReactFiberHotReloading';
+} from './ReactFiberHotReloading.old';
 
 import {
   mountChildFibers,
   reconcileChildFibers,
   cloneChildFibers,
-} from './ReactChildFiber';
+} from './ReactChildFiber.old';
 import {
   processUpdateQueue,
   cloneUpdateQueue,
   initializeUpdateQueue,
-} from './ReactUpdateQueue';
+} from './ReactUpdateQueue.old';
 import {
   NoWork,
   Never,
   Sync,
   computeAsyncExpiration,
-} from './ReactFiberExpirationTime';
+} from './ReactFiberExpirationTime.old';
 import {
   ConcurrentMode,
   NoMode,
@@ -117,7 +117,7 @@ import {
 } from './ReactFiberHostConfig';
 import type {SuspenseInstance} from './ReactFiberHostConfig';
 import {shouldSuspend} from './ReactFiberReconciler';
-import {pushHostContext, pushHostContainer} from './ReactFiberHostContext';
+import {pushHostContext, pushHostContainer} from './ReactFiberHostContext.old';
 import {
   suspenseStackCursor,
   pushSuspenseContext,
@@ -127,8 +127,8 @@ import {
   setDefaultShallowSuspenseContext,
   addSubtreeSuspenseContext,
   setShallowSuspenseContext,
-} from './ReactFiberSuspenseContext';
-import {findFirstSuspended} from './ReactFiberSuspenseComponent';
+} from './ReactFiberSuspenseContext.old';
+import {findFirstSuspended} from './ReactFiberSuspenseComponent.old';
 import {
   pushProvider,
   propagateContextChange,
@@ -136,9 +136,9 @@ import {
   prepareToReadContext,
   calculateChangedBits,
   scheduleWorkOnParentPath,
-} from './ReactFiberNewContext';
-import {renderWithHooks, bailoutHooks} from './ReactFiberHooks';
-import {stopProfilerTimerIfRunning} from './ReactProfilerTimer';
+} from './ReactFiberNewContext.old';
+import {renderWithHooks, bailoutHooks} from './ReactFiberHooks.old';
+import {stopProfilerTimerIfRunning} from './ReactProfilerTimer.old';
 import {
   getMaskedContext,
   getUnmaskedContext,
@@ -147,14 +147,14 @@ import {
   isContextProvider as isLegacyContextProvider,
   pushTopLevelContextObject,
   invalidateContextProvider,
-} from './ReactFiberContext';
+} from './ReactFiberContext.old';
 import {
   enterHydrationState,
   reenterHydrationStateFromDehydratedSuspenseInstance,
   resetHydrationState,
   tryToClaimNextHydratableInstance,
   warnIfHydrating,
-} from './ReactFiberHydrationContext';
+} from './ReactFiberHydrationContext.old';
 import {
   adoptClassInstance,
   applyDerivedStateFromProps,
@@ -162,15 +162,15 @@ import {
   mountClassInstance,
   resumeMountClassInstance,
   updateClassInstance,
-} from './ReactFiberClassComponent';
-import {resolveDefaultProps} from './ReactFiberLazyComponent';
+} from './ReactFiberClassComponent.old';
+import {resolveDefaultProps} from './ReactFiberLazyComponent.old';
 import {
   resolveLazyComponentTag,
   createFiberFromTypeAndProps,
   createFiberFromFragment,
   createWorkInProgress,
   isSimpleFunctionComponent,
-} from './ReactFiber';
+} from './ReactFiber.old';
 import {
   markSpawnedWork,
   requestCurrentTimeForUpdate,
@@ -179,7 +179,7 @@ import {
   renderDidSuspendDelayIfPossible,
   markUnprocessedUpdateTime,
   getWorkInProgressRoot,
-} from './ReactFiberWorkLoop';
+} from './ReactFiberWorkLoop.old';
 
 import {disableLogs, reenableLogs} from 'shared/ConsolePatchingDev';
 

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

@@ -7,9 +7,9 @@
  * @flow
  */
 
-import type {Fiber} from './ReactFiber';
-import type {ExpirationTime} from './ReactFiberExpirationTime';
-import type {UpdateQueue} from './ReactUpdateQueue';
+import type {Fiber} from './ReactFiber.old';
+import type {ExpirationTime} from './ReactFiberExpirationTime.old';
+import type {UpdateQueue} from './ReactUpdateQueue.old';
 
 import * as React from 'react';
 import {Update, Snapshot} from './ReactSideEffectTags';
@@ -18,15 +18,15 @@ import {
   disableLegacyContext,
   warnAboutDeprecatedLifecycles,
 } from 'shared/ReactFeatureFlags';
-import ReactStrictModeWarnings from './ReactStrictModeWarnings';
-import {isMounted} from 'react-reconciler/src/ReactFiberTreeReflection';
+import ReactStrictModeWarnings from './ReactStrictModeWarnings.old';
+import {isMounted} from './ReactFiberTreeReflection';
 import {get as getInstance, set as setInstance} from 'shared/ReactInstanceMap';
 import shallowEqual from 'shared/shallowEqual';
 import getComponentName from 'shared/getComponentName';
 import invariant from 'shared/invariant';
 import {REACT_CONTEXT_TYPE, REACT_PROVIDER_TYPE} from 'shared/ReactSymbols';
 
-import {resolveDefaultProps} from './ReactFiberLazyComponent';
+import {resolveDefaultProps} from './ReactFiberLazyComponent.old';
 import {StrictMode} from './ReactTypeOfMode';
 
 import {
@@ -39,22 +39,22 @@ import {
   ForceUpdate,
   initializeUpdateQueue,
   cloneUpdateQueue,
-} from './ReactUpdateQueue';
-import {NoWork} from './ReactFiberExpirationTime';
+} from './ReactUpdateQueue.old';
+import {NoWork} from './ReactFiberExpirationTime.old';
 import {
   cacheContext,
   getMaskedContext,
   getUnmaskedContext,
   hasContextChanged,
   emptyContextObject,
-} from './ReactFiberContext';
-import {readContext} from './ReactFiberNewContext';
+} from './ReactFiberContext.old';
+import {readContext} from './ReactFiberNewContext.old';
 import {
   requestCurrentTimeForUpdate,
   computeExpirationForFiber,
   scheduleUpdateOnFiber,
-} from './ReactFiberWorkLoop';
-import {requestCurrentSuspenseConfig} from './ReactFiberSuspenseConfig';
+} from './ReactFiberWorkLoop.old';
+import {requestCurrentSuspenseConfig} from './ReactFiberSuspenseConfig.old';
 
 import {disableLogs, reenableLogs} from 'shared/ConsolePatchingDev';
 

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

@@ -15,13 +15,13 @@ import type {
   ChildSet,
   UpdatePayload,
 } from './ReactFiberHostConfig';
-import type {Fiber} from './ReactFiber';
-import type {FiberRoot} from './ReactFiberRoot';
-import type {ExpirationTime} from './ReactFiberExpirationTime';
-import type {SuspenseState} from './ReactFiberSuspenseComponent';
-import type {FunctionComponentUpdateQueue} from './ReactFiberHooks';
+import type {Fiber} from './ReactFiber.old';
+import type {FiberRoot} from './ReactFiberRoot.old';
+import type {ExpirationTime} from './ReactFiberExpirationTime.old';
+import type {SuspenseState} from './ReactFiberSuspenseComponent.old';
+import type {FunctionComponentUpdateQueue} from './ReactFiberHooks.old';
 import type {Wakeable} from 'shared/ReactTypes';
-import type {ReactPriorityLevel} from './SchedulerWithReactIntegration';
+import type {ReactPriorityLevel} from './SchedulerWithReactIntegration.old';
 
 import {unstable_wrap as Schedule_tracing_wrap} from 'scheduler/tracing';
 import {
@@ -72,18 +72,18 @@ import {
 import getComponentName from 'shared/getComponentName';
 import invariant from 'shared/invariant';
 
-import {onCommitUnmount} from './ReactFiberDevToolsHook';
+import {onCommitUnmount} from './ReactFiberDevToolsHook.old';
 import {getStackByFiberInDevAndProd} from './ReactFiberComponentStack';
-import {resolveDefaultProps} from './ReactFiberLazyComponent';
+import {resolveDefaultProps} from './ReactFiberLazyComponent.old';
 import {
   getCommitTime,
   recordLayoutEffectDuration,
   recordPassiveEffectDuration,
   startLayoutEffectTimer,
   startPassiveEffectTimer,
-} from './ReactProfilerTimer';
+} from './ReactProfilerTimer.old';
 import {ProfileMode} from './ReactTypeOfMode';
-import {commitUpdateQueue} from './ReactUpdateQueue';
+import {commitUpdateQueue} from './ReactUpdateQueue.old';
 import {
   getPublicInstance,
   supportsMutation,
@@ -120,19 +120,22 @@ import {
   enqueuePendingPassiveHookEffectMount,
   enqueuePendingPassiveHookEffectUnmount,
   enqueuePendingPassiveProfilerEffect,
-} from './ReactFiberWorkLoop';
+} from './ReactFiberWorkLoop.old';
 import {
   NoEffect as NoHookEffect,
   HasEffect as HookHasEffect,
   Layout as HookLayout,
   Passive as HookPassive,
 } from './ReactHookEffectTags';
-import {didWarnAboutReassigningProps} from './ReactFiberBeginWork';
-import {runWithPriority, NormalPriority} from './SchedulerWithReactIntegration';
+import {didWarnAboutReassigningProps} from './ReactFiberBeginWork.old';
+import {
+  runWithPriority,
+  NormalPriority,
+} from './SchedulerWithReactIntegration.old';
 import {
   updateDeprecatedEventListeners,
   unmountDeprecatedResponderListeners,
-} from './ReactFiberDeprecatedEvents';
+} from './ReactFiberDeprecatedEvents.old';
 
 let didWarnAboutUndefinedSnapshotBeforeUpdate: Set<mixed> | null = null;
 if (__DEV__) {

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

@@ -7,13 +7,13 @@
  * @flow
  */
 
-import type {Fiber} from './ReactFiber';
-import type {ExpirationTime} from './ReactFiberExpirationTime';
+import type {Fiber} from './ReactFiber.old';
+import type {ExpirationTime} from './ReactFiberExpirationTime.old';
 import type {
   ReactFundamentalComponentInstance,
   ReactScopeInstance,
 } from 'shared/ReactTypes';
-import type {FiberRoot} from './ReactFiberRoot';
+import type {FiberRoot} from './ReactFiberRoot.old';
 import type {
   Instance,
   Type,
@@ -24,11 +24,11 @@ import type {
 import type {
   SuspenseState,
   SuspenseListRenderState,
-} from './ReactFiberSuspenseComponent';
-import type {SuspenseContext} from './ReactFiberSuspenseContext';
-import {resetWorkInProgressVersions as resetMutableSourceWorkInProgressVersions} from './ReactMutableSource';
+} from './ReactFiberSuspenseComponent.old';
+import type {SuspenseContext} from './ReactFiberSuspenseContext.old';
+import {resetWorkInProgressVersions as resetMutableSourceWorkInProgressVersions} from './ReactMutableSource.old';
 
-import {now} from './SchedulerWithReactIntegration';
+import {now} from './SchedulerWithReactIntegration.old';
 
 import {
   IndeterminateComponent,
@@ -88,7 +88,7 @@ import {
   popHostContext,
   getHostContext,
   popHostContainer,
-} from './ReactFiberHostContext';
+} from './ReactFiberHostContext.old';
 import {
   suspenseStackCursor,
   InvisibleParentSuspenseContext,
@@ -98,21 +98,21 @@ import {
   setShallowSuspenseContext,
   ForceSuspenseFallback,
   setDefaultShallowSuspenseContext,
-} from './ReactFiberSuspenseContext';
-import {findFirstSuspended} from './ReactFiberSuspenseComponent';
+} from './ReactFiberSuspenseContext.old';
+import {findFirstSuspended} from './ReactFiberSuspenseComponent.old';
 import {
   isContextProvider as isLegacyContextProvider,
   popContext as popLegacyContext,
   popTopLevelContextObject as popTopLevelLegacyContextObject,
-} from './ReactFiberContext';
-import {popProvider} from './ReactFiberNewContext';
+} from './ReactFiberContext.old';
+import {popProvider} from './ReactFiberNewContext.old';
 import {
   prepareToHydrateHostInstance,
   prepareToHydrateHostTextInstance,
   prepareToHydrateHostSuspenseInstance,
   popHydrationState,
   resetHydrationState,
-} from './ReactFiberHydrationContext';
+} from './ReactFiberHydrationContext.old';
 import {
   enableSchedulerTracing,
   enableSuspenseCallback,
@@ -127,12 +127,12 @@ import {
   renderDidSuspend,
   renderDidSuspendDelayIfPossible,
   renderHasNotSuspendedYet,
-} from './ReactFiberWorkLoop';
-import {createFundamentalStateInstance} from './ReactFiberFundamental';
-import {Never} from './ReactFiberExpirationTime';
-import {resetChildFibers} from './ReactChildFiber';
-import {updateDeprecatedEventListeners} from './ReactFiberDeprecatedEvents';
-import {createScopeMethods} from './ReactFiberScope';
+} from './ReactFiberWorkLoop.old';
+import {createFundamentalStateInstance} from './ReactFiberFundamental.old';
+import {Never} from './ReactFiberExpirationTime.old';
+import {resetChildFibers} from './ReactChildFiber.old';
+import {updateDeprecatedEventListeners} from './ReactFiberDeprecatedEvents.old';
+import {createScopeMethods} from './ReactFiberScope.old';
 
 function markUpdate(workInProgress: Fiber) {
   // Tag the fiber with an update effect. This turns a Placement into

packages/react-reconciler/src/ReactFiberComponentStack.js

@@ -7,7 +7,7 @@
  * @flow
  */
 
-import type {Fiber} from './ReactFiber';
+import type {Fiber} from './ReactFiber.old';
 
 import {
   HostComponent,

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

@@ -7,17 +7,17 @@
  * @flow
  */
 
-import type {Fiber} from './ReactFiber';
-import type {StackCursor} from './ReactFiberStack';
+import type {Fiber} from './ReactFiber.old';
+import type {StackCursor} from './ReactFiberStack.old';
 
-import {isFiberMounted} from 'react-reconciler/src/ReactFiberTreeReflection';
+import {isFiberMounted} from './ReactFiberTreeReflection';
 import {disableLegacyContext} from 'shared/ReactFeatureFlags';
 import {ClassComponent, HostRoot} from './ReactWorkTags';
 import getComponentName from 'shared/getComponentName';
 import invariant from 'shared/invariant';
 import checkPropTypes from 'shared/checkPropTypes';
 
-import {createCursor, push, pop} from './ReactFiberStack';
+import {createCursor, push, pop} from './ReactFiberStack.old';
 
 let warnedAboutMissingGetChildContext;
 

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

@@ -7,7 +7,7 @@
  * @flow
  */
 
-import type {Fiber} from './ReactFiber';
+import type {Fiber} from './ReactFiber.old';
 import type {Container, Instance} from './ReactFiberHostConfig';
 import type {
   ReactEventResponder,
@@ -19,7 +19,7 @@ import {
   DEPRECATED_mountResponderInstance,
   DEPRECATED_unmountResponderInstance,
 } from './ReactFiberHostConfig';
-import {NoWork} from './ReactFiberExpirationTime';
+import {NoWork} from './ReactFiberExpirationTime.old';
 
 import {REACT_RESPONDER_TYPE} from 'shared/ReactSymbols';
 

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

@@ -8,12 +8,12 @@
  */
 
 import {enableProfilerTimer} from 'shared/ReactFeatureFlags';
-import {getCurrentTime} from './ReactFiberWorkLoop';
-import {inferPriorityFromExpirationTime} from './ReactFiberExpirationTime';
+import {getCurrentTime} from './ReactFiberWorkLoop.old';
+import {inferPriorityFromExpirationTime} from './ReactFiberExpirationTime.old';
 
-import type {Fiber} from './ReactFiber';
-import type {FiberRoot} from './ReactFiberRoot';
-import type {ExpirationTime} from './ReactFiberExpirationTime';
+import type {Fiber} from './ReactFiber.old';
+import type {FiberRoot} from './ReactFiberRoot.old';
+import type {ExpirationTime} from './ReactFiberExpirationTime.old';
 import type {ReactNodeList} from 'shared/ReactTypes';
 
 import {DidCapture} from './ReactSideEffectTags';

packages/react-reconciler/src/ReactFiberErrorDialog.js

@@ -7,7 +7,7 @@
  * @flow
  */
 
-import type {Fiber} from './ReactFiber';
+import type {Fiber} from './ReactFiber.old';
 import type {CapturedValue} from './ReactCapturedValue';
 
 // This module is forked in different environments.

packages/react-reconciler/src/ReactFiberErrorLogger.js

@@ -7,7 +7,7 @@
  * @flow
  */
 
-import type {Fiber} from './ReactFiber';
+import type {Fiber} from './ReactFiber.old';
 import type {CapturedValue} from './ReactCapturedValue';
 
 import {showErrorDialog} from './ReactFiberErrorDialog';

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

@@ -7,7 +7,7 @@
  * @flow
  */
 
-import type {ReactPriorityLevel} from './SchedulerWithReactIntegration';
+import type {ReactPriorityLevel} from './SchedulerWithReactIntegration.old';
 
 import {MAX_SIGNED_31_BIT_INT} from './MaxInts';
 
@@ -16,7 +16,7 @@ import {
   UserBlockingPriority,
   NormalPriority,
   IdlePriority,
-} from './SchedulerWithReactIntegration';
+} from './SchedulerWithReactIntegration.old';
 
 export type ExpirationTime = number;
 

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

@@ -7,7 +7,7 @@
  * @flow
  */
 
-import type {Fiber} from './ReactFiber';
+import type {Fiber} from './ReactFiber.old';
 import type {
   ReactFundamentalImpl,
   ReactFundamentalComponentInstance,

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

@@ -16,12 +16,12 @@ import type {
   ReactEventResponderListener,
   ReactScopeMethods,
 } from 'shared/ReactTypes';
-import type {Fiber} from './ReactFiber';
-import type {ExpirationTime} from './ReactFiberExpirationTime';
+import type {Fiber} from './ReactFiber.old';
+import type {ExpirationTime} from './ReactFiberExpirationTime.old';
 import type {HookEffectTag} from './ReactHookEffectTags';
-import type {SuspenseConfig} from './ReactFiberSuspenseConfig';
-import type {ReactPriorityLevel} from './SchedulerWithReactIntegration';
-import type {FiberRoot} from './ReactFiberRoot';
+import type {SuspenseConfig} from './ReactFiberSuspenseConfig.old';
+import type {ReactPriorityLevel} from './SchedulerWithReactIntegration.old';
+import type {FiberRoot} from './ReactFiberRoot.old';
 import type {
   OpaqueIDType,
   ReactListenerEvent,
@@ -32,11 +32,11 @@ import type {
 import ReactSharedInternals from 'shared/ReactSharedInternals';
 import {enableUseEventAPI} from 'shared/ReactFeatureFlags';
 
-import {markRootExpiredAtTime} from './ReactFiberRoot';
-import {NoWork, Sync} from './ReactFiberExpirationTime';
+import {markRootExpiredAtTime} from './ReactFiberRoot.old';
+import {NoWork, Sync} from './ReactFiberExpirationTime.old';
 import {NoMode, BlockingMode} from './ReactTypeOfMode';
-import {readContext} from './ReactFiberNewContext';
-import {createDeprecatedResponderListener} from './ReactFiberDeprecatedEvents';
+import {readContext} from './ReactFiberNewContext.old';
+import {createDeprecatedResponderListener} from './ReactFiberDeprecatedEvents.old';
 import {
   Update as UpdateEffect,
   Passive as PassiveEffect,
@@ -57,7 +57,7 @@ import {
   warnIfNotScopedWithMatchingAct,
   markRenderEventTimeAndConfig,
   markUnprocessedUpdateTime,
-} from './ReactFiberWorkLoop';
+} from './ReactFiberWorkLoop.old';
 import {
   registerEvent,
   mountEventListener as mountHostEventListener,
@@ -68,15 +68,15 @@ import {
 import invariant from 'shared/invariant';
 import getComponentName from 'shared/getComponentName';
 import is from 'shared/objectIs';
-import {markWorkInProgressReceivedUpdate} from './ReactFiberBeginWork';
-import {requestCurrentSuspenseConfig} from './ReactFiberSuspenseConfig';
+import {markWorkInProgressReceivedUpdate} from './ReactFiberBeginWork.old';
+import {requestCurrentSuspenseConfig} from './ReactFiberSuspenseConfig.old';
 import {
   UserBlockingPriority,
   NormalPriority,
   runWithPriority,
   getCurrentPriorityLevel,
-} from './SchedulerWithReactIntegration';
-import {getIsHydrating} from './ReactFiberHydrationContext';
+} from './SchedulerWithReactIntegration.old';
+import {getIsHydrating} from './ReactFiberHydrationContext.old';
 import {
   makeClientId,
   makeClientIdInDEV,
@@ -89,8 +89,8 @@ import {
   setPendingExpirationTime,
   setWorkInProgressVersion,
   warnAboutMultipleRenderersDEV,
-} from './ReactMutableSource';
-import {getRootHostContainer} from './ReactFiberHostContext';
+} from './ReactMutableSource.old';
+import {getRootHostContainer} from './ReactFiberHostContext.old';
 import {getIsRendering} from './ReactCurrentFiber';
 
 const {ReactCurrentDispatcher, ReactCurrentBatchConfig} = ReactSharedInternals;

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

@@ -7,14 +7,14 @@
  * @flow
  */
 
-import type {Fiber} from './ReactFiber';
-import type {StackCursor} from './ReactFiberStack';
+import type {Fiber} from './ReactFiber.old';
+import type {StackCursor} from './ReactFiberStack.old';
 import type {Container, HostContext} from './ReactFiberHostConfig';
 
 import invariant from 'shared/invariant';
 
 import {getChildHostContext, getRootHostContext} from './ReactFiberHostConfig';
-import {createCursor, push, pop} from './ReactFiberStack';
+import {createCursor, push, pop} from './ReactFiberStack.old';
 
 declare class NoContextT {}
 const NO_CONTEXT: NoContextT = ({}: any);

packages/react-reconciler/src/ReactFiberHotReloading.js

@@ -7,476 +7,66 @@
  * @flow
  */
 
-import type {ReactElement} from 'shared/ReactElementType';
-import type {Fiber} from './ReactFiber';
-import type {FiberRoot} from './ReactFiberRoot';
-import type {Instance} from './ReactFiberHostConfig';
-import type {ReactNodeList} from 'shared/ReactTypes';
+import {enableNewReconciler} from 'shared/ReactFeatureFlags';
+
+export type {
+  Family,
+  RefreshUpdate,
+  SetRefreshHandler,
+  ScheduleRefresh,
+  ScheduleRoot,
+  FindHostInstancesForRefresh,
+} from './ReactFiberHotReloading';
 
 import {
-  flushSync,
-  scheduleUpdateOnFiber,
-  flushPassiveEffects,
-} from './ReactFiberWorkLoop';
-import {updateContainer, syncUpdates} from './ReactFiberReconciler';
-import {emptyContextObject} from './ReactFiberContext';
-import {Sync} from './ReactFiberExpirationTime';
+  setRefreshHandler as setRefreshHandler_old,
+  resolveFunctionForHotReloading as resolveFunctionForHotReloading_old,
+  resolveClassForHotReloading as resolveClassForHotReloading_old,
+  resolveForwardRefForHotReloading as resolveForwardRefForHotReloading_old,
+  isCompatibleFamilyForHotReloading as isCompatibleFamilyForHotReloading_old,
+  markFailedErrorBoundaryForHotReloading as markFailedErrorBoundaryForHotReloading_old,
+  scheduleRefresh as scheduleRefresh_old,
+  scheduleRoot as scheduleRoot_old,
+  findHostInstancesForRefresh as findHostInstancesForRefresh_old,
+} from './ReactFiberHotReloading.old';
+
+// TODO: Update these to point to the fork.
 import {
-  ClassComponent,
-  FunctionComponent,
-  ForwardRef,
-  HostComponent,
-  HostPortal,
-  HostRoot,
-  MemoComponent,
-  SimpleMemoComponent,
-} from './ReactWorkTags';
-import {
-  REACT_FORWARD_REF_TYPE,
-  REACT_MEMO_TYPE,
-  REACT_LAZY_TYPE,
-} from 'shared/ReactSymbols';
+  setRefreshHandler as setRefreshHandler_new,
+  resolveFunctionForHotReloading as resolveFunctionForHotReloading_new,
+  resolveClassForHotReloading as resolveClassForHotReloading_new,
+  resolveForwardRefForHotReloading as resolveForwardRefForHotReloading_new,
+  isCompatibleFamilyForHotReloading as isCompatibleFamilyForHotReloading_new,
+  markFailedErrorBoundaryForHotReloading as markFailedErrorBoundaryForHotReloading_new,
+  scheduleRefresh as scheduleRefresh_new,
+  scheduleRoot as scheduleRoot_new,
+  findHostInstancesForRefresh as findHostInstancesForRefresh_new,
+} from './ReactFiberHotReloading.old';
 
-export type Family = {|
-  current: any,
-|};
-
-export type RefreshUpdate = {|
-  staleFamilies: Set<Family>,
-  updatedFamilies: Set<Family>,
-|};
-
-// Resolves type to a family.
-type RefreshHandler = any => Family | void;
-
-// Used by React Refresh runtime through DevTools Global Hook.
-export type SetRefreshHandler = (handler: RefreshHandler | null) => void;
-export type ScheduleRefresh = (root: FiberRoot, update: RefreshUpdate) => void;
-export type ScheduleRoot = (root: FiberRoot, element: ReactNodeList) => void;
-export type FindHostInstancesForRefresh = (
-  root: FiberRoot,
-  families: Array<Family>,
-) => Set<Instance>;
-
-let resolveFamily: RefreshHandler | null = null;
-// $FlowFixMe Flow gets confused by a WeakSet feature check below.
-let failedBoundaries: WeakSet<Fiber> | null = null;
-
-export const setRefreshHandler = (handler: RefreshHandler | null): void => {
-  if (__DEV__) {
-    resolveFamily = handler;
-  }
-};
-
-export function resolveFunctionForHotReloading(type: any): any {
-  if (__DEV__) {
-    if (resolveFamily === null) {
-      // Hot reloading is disabled.
-      return type;
-    }
-    const family = resolveFamily(type);
-    if (family === undefined) {
-      return type;
-    }
-    // Use the latest known implementation.
-    return family.current;
-  } else {
-    return type;
-  }
-}
-
-export function resolveClassForHotReloading(type: any): any {
-  // No implementation differences.
-  return resolveFunctionForHotReloading(type);
-}
-
-export function resolveForwardRefForHotReloading(type: any): any {
-  if (__DEV__) {
-    if (resolveFamily === null) {
-      // Hot reloading is disabled.
-      return type;
-    }
-    const family = resolveFamily(type);
-    if (family === undefined) {
-      // Check if we're dealing with a real forwardRef. Don't want to crash early.
-      if (
-        type !== null &&
-        type !== undefined &&
-        typeof type.render === 'function'
-      ) {
-        // ForwardRef is special because its resolved .type is an object,
-        // but it's possible that we only have its inner render function in the map.
-        // If that inner render function is different, we'll build a new forwardRef type.
-        const currentRender = resolveFunctionForHotReloading(type.render);
-        if (type.render !== currentRender) {
-          const syntheticType = {
-            $$typeof: REACT_FORWARD_REF_TYPE,
-            render: currentRender,
-          };
-          if (type.displayName !== undefined) {
-            (syntheticType: any).displayName = type.displayName;
-          }
-          return syntheticType;
-        }
-      }
-      return type;
-    }
-    // Use the latest known implementation.
-    return family.current;
-  } else {
-    return type;
-  }
-}
-
-export function isCompatibleFamilyForHotReloading(
-  fiber: Fiber,
-  element: ReactElement,
-): boolean {
-  if (__DEV__) {
-    if (resolveFamily === null) {
-      // Hot reloading is disabled.
-      return false;
-    }
-
-    const prevType = fiber.elementType;
-    const nextType = element.type;
-
-    // If we got here, we know types aren't === equal.
-    let needsCompareFamilies = false;
-
-    const $$typeofNextType =
-      typeof nextType === 'object' && nextType !== null
-        ? nextType.$$typeof
-        : null;
-
-    switch (fiber.tag) {
-      case ClassComponent: {
-        if (typeof nextType === 'function') {
-          needsCompareFamilies = true;
-        }
-        break;
-      }
-      case FunctionComponent: {
-        if (typeof nextType === 'function') {
-          needsCompareFamilies = true;
-        } else if ($$typeofNextType === REACT_LAZY_TYPE) {
-          // We don't know the inner type yet.
-          // We're going to assume that the lazy inner type is stable,
-          // and so it is sufficient to avoid reconciling it away.
-          // We're not going to unwrap or actually use the new lazy type.
-          needsCompareFamilies = true;
-        }
-        break;
-      }
-      case ForwardRef: {
-        if ($$typeofNextType === REACT_FORWARD_REF_TYPE) {
-          needsCompareFamilies = true;
-        } else if ($$typeofNextType === REACT_LAZY_TYPE) {
-          needsCompareFamilies = true;
-        }
-        break;
-      }
-      case MemoComponent:
-      case SimpleMemoComponent: {
-        if ($$typeofNextType === REACT_MEMO_TYPE) {
-          // TODO: if it was but can no longer be simple,
-          // we shouldn't set this.
-          needsCompareFamilies = true;
-        } else if ($$typeofNextType === REACT_LAZY_TYPE) {
-          needsCompareFamilies = true;
-        }
-        break;
-      }
-      default:
-        return false;
-    }
-
-    // Check if both types have a family and it's the same one.
-    if (needsCompareFamilies) {
-      // Note: memo() and forwardRef() we'll compare outer rather than inner type.
-      // This means both of them need to be registered to preserve state.
-      // If we unwrapped and compared the inner types for wrappers instead,
-      // then we would risk falsely saying two separate memo(Foo)
-      // calls are equivalent because they wrap the same Foo function.
-      const prevFamily = resolveFamily(prevType);
-      if (prevFamily !== undefined && prevFamily === resolveFamily(nextType)) {
-        return true;
-      }
-    }
-    return false;
-  } else {
-    return false;
-  }
-}
-
-export function markFailedErrorBoundaryForHotReloading(fiber: Fiber) {
-  if (__DEV__) {
-    if (resolveFamily === null) {
-      // Hot reloading is disabled.
-      return;
-    }
-    if (typeof WeakSet !== 'function') {
-      return;
-    }
-    if (failedBoundaries === null) {
-      failedBoundaries = new WeakSet();
-    }
-    failedBoundaries.add(fiber);
-  }
-}
-
-export const scheduleRefresh: ScheduleRefresh = (
-  root: FiberRoot,
-  update: RefreshUpdate,
-): void => {
-  if (__DEV__) {
-    if (resolveFamily === null) {
-      // Hot reloading is disabled.
-      return;
-    }
-    const {staleFamilies, updatedFamilies} = update;
-    flushPassiveEffects();
-    flushSync(() => {
-      scheduleFibersWithFamiliesRecursively(
-        root.current,
-        updatedFamilies,
-        staleFamilies,
-      );
-    });
-  }
-};
-
-export const scheduleRoot: ScheduleRoot = (
-  root: FiberRoot,
-  element: ReactNodeList,
-): void => {
-  if (__DEV__) {
-    if (root.context !== emptyContextObject) {
-      // Super edge case: root has a legacy _renderSubtree context
-      // but we don't know the parentComponent so we can't pass it.
-      // Just ignore. We'll delete this with _renderSubtree code path later.
-      return;
-    }
-    flushPassiveEffects();
-    syncUpdates(() => {
-      updateContainer(element, root, null, null);
-    });
-  }
-};
-
-function scheduleFibersWithFamiliesRecursively(
-  fiber: Fiber,
-  updatedFamilies: Set<Family>,
-  staleFamilies: Set<Family>,
-) {
-  if (__DEV__) {
-    const {alternate, child, sibling, tag, type} = fiber;
-
-    let candidateType = null;
-    switch (tag) {
-      case FunctionComponent:
-      case SimpleMemoComponent:
-      case ClassComponent:
-        candidateType = type;
-        break;
-      case ForwardRef:
-        candidateType = type.render;
-        break;
-      default:
-        break;
-    }
-
-    if (resolveFamily === null) {
-      throw new Error('Expected resolveFamily to be set during hot reload.');
-    }
-
-    let needsRender = false;
-    let needsRemount = false;
-    if (candidateType !== null) {
-      const family = resolveFamily(candidateType);
-      if (family !== undefined) {
-        if (staleFamilies.has(family)) {
-          needsRemount = true;
-        } else if (updatedFamilies.has(family)) {
-          if (tag === ClassComponent) {
-            needsRemount = true;
-          } else {
-            needsRender = true;
-          }
-        }
-      }
-    }
-    if (failedBoundaries !== null) {
-      if (
-        failedBoundaries.has(fiber) ||
-        (alternate !== null && failedBoundaries.has(alternate))
-      ) {
-        needsRemount = true;
-      }
-    }
-
-    if (needsRemount) {
-      fiber._debugNeedsRemount = true;
-    }
-    if (needsRemount || needsRender) {
-      scheduleUpdateOnFiber(fiber, Sync);
-    }
-    if (child !== null && !needsRemount) {
-      scheduleFibersWithFamiliesRecursively(
-        child,
-        updatedFamilies,
-        staleFamilies,
-      );
-    }
-    if (sibling !== null) {
-      scheduleFibersWithFamiliesRecursively(
-        sibling,
-        updatedFamilies,
-        staleFamilies,
-      );
-    }
-  }
-}
-
-export const findHostInstancesForRefresh: FindHostInstancesForRefresh = (
-  root: FiberRoot,
-  families: Array<Family>,
-): Set<Instance> => {
-  if (__DEV__) {
-    const hostInstances = new Set();
-    const types = new Set(families.map(family => family.current));
-    findHostInstancesForMatchingFibersRecursively(
-      root.current,
-      types,
-      hostInstances,
-    );
-    return hostInstances;
-  } else {
-    throw new Error(
-      'Did not expect findHostInstancesForRefresh to be called in production.',
-    );
-  }
-};
-
-function findHostInstancesForMatchingFibersRecursively(
-  fiber: Fiber,
-  types: Set<any>,
-  hostInstances: Set<Instance>,
-) {
-  if (__DEV__) {
-    const {child, sibling, tag, type} = fiber;
-
-    let candidateType = null;
-    switch (tag) {
-      case FunctionComponent:
-      case SimpleMemoComponent:
-      case ClassComponent:
-        candidateType = type;
-        break;
-      case ForwardRef:
-        candidateType = type.render;
-        break;
-      default:
-        break;
-    }
-
-    let didMatch = false;
-    if (candidateType !== null) {
-      if (types.has(candidateType)) {
-        didMatch = true;
-      }
-    }
-
-    if (didMatch) {
-      // We have a match. This only drills down to the closest host components.
-      // There's no need to search deeper because for the purpose of giving
-      // visual feedback, "flashing" outermost parent rectangles is sufficient.
-      findHostInstancesForFiberShallowly(fiber, hostInstances);
-    } else {
-      // If there's no match, maybe there will be one further down in the child tree.
-      if (child !== null) {
-        findHostInstancesForMatchingFibersRecursively(
-          child,
-          types,
-          hostInstances,
-        );
-      }
-    }
-
-    if (sibling !== null) {
-      findHostInstancesForMatchingFibersRecursively(
-        sibling,
-        types,
-        hostInstances,
-      );
-    }
-  }
-}
-
-function findHostInstancesForFiberShallowly(
-  fiber: Fiber,
-  hostInstances: Set<Instance>,
-): void {
-  if (__DEV__) {
-    const foundHostInstances = findChildHostInstancesForFiberShallowly(
-      fiber,
-      hostInstances,
-    );
-    if (foundHostInstances) {
-      return;
-    }
-    // If we didn't find any host children, fallback to closest host parent.
-    let node = fiber;
-    while (true) {
-      switch (node.tag) {
-        case HostComponent:
-          hostInstances.add(node.stateNode);
-          return;
-        case HostPortal:
-          hostInstances.add(node.stateNode.containerInfo);
-          return;
-        case HostRoot:
-          hostInstances.add(node.stateNode.containerInfo);
-          return;
-      }
-      if (node.return === null) {
-        throw new Error('Expected to reach root first.');
-      }
-      node = node.return;
-    }
-  }
-}
-
-function findChildHostInstancesForFiberShallowly(
-  fiber: Fiber,
-  hostInstances: Set<Instance>,
-): boolean {
-  if (__DEV__) {
-    let node: Fiber = fiber;
-    let foundHostInstances = false;
-    while (true) {
-      if (node.tag === HostComponent) {
-        // We got a match.
-        foundHostInstances = true;
-        hostInstances.add(node.stateNode);
-        // There may still be more, so keep searching.
-      } else if (node.child !== null) {
-        node.child.return = node;
-        node = node.child;
-        continue;
-      }
-      if (node === fiber) {
-        return foundHostInstances;
-      }
-      while (node.sibling === null) {
-        if (node.return === null || node.return === fiber) {
-          return foundHostInstances;
-        }
-        node = node.return;
-      }
-      node.sibling.return = node.return;
-      node = node.sibling;
-    }
-  }
-  return false;
-}
+export const setRefreshHandler = enableNewReconciler
+  ? setRefreshHandler_new
+  : setRefreshHandler_old;
+export const resolveFunctionForHotReloading = enableNewReconciler
+  ? resolveFunctionForHotReloading_new
+  : resolveFunctionForHotReloading_old;
+export const resolveClassForHotReloading = enableNewReconciler
+  ? resolveClassForHotReloading_new
+  : resolveClassForHotReloading_old;
+export const resolveForwardRefForHotReloading = enableNewReconciler
+  ? resolveForwardRefForHotReloading_new
+  : resolveForwardRefForHotReloading_old;
+export const isCompatibleFamilyForHotReloading = enableNewReconciler
+  ? isCompatibleFamilyForHotReloading_new
+  : isCompatibleFamilyForHotReloading_old;
+export const markFailedErrorBoundaryForHotReloading = enableNewReconciler
+  ? markFailedErrorBoundaryForHotReloading_new
+  : markFailedErrorBoundaryForHotReloading_old;
+export const scheduleRefresh = enableNewReconciler
+  ? scheduleRefresh_new
+  : scheduleRefresh_old;
+export const scheduleRoot = enableNewReconciler
+  ? scheduleRoot_new
+  : scheduleRoot_old;
+export const findHostInstancesForRefresh = enableNewReconciler
+  ? findHostInstancesForRefresh_new
+  : findHostInstancesForRefresh_old;

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

@@ -0,0 +1,482 @@
+/**
+ * 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 {ReactElement} from 'shared/ReactElementType';
+import type {Fiber} from './ReactFiber.old';
+import type {FiberRoot} from './ReactFiberRoot.old';
+import type {Instance} from './ReactFiberHostConfig';
+import type {ReactNodeList} from 'shared/ReactTypes';
+
+import {
+  flushSync,
+  scheduleUpdateOnFiber,
+  flushPassiveEffects,
+} from './ReactFiberWorkLoop.old';
+import {updateContainer, syncUpdates} from './ReactFiberReconciler.old';
+import {emptyContextObject} from './ReactFiberContext.old';
+import {Sync} from './ReactFiberExpirationTime.old';
+import {
+  ClassComponent,
+  FunctionComponent,
+  ForwardRef,
+  HostComponent,
+  HostPortal,
+  HostRoot,
+  MemoComponent,
+  SimpleMemoComponent,
+} from './ReactWorkTags';
+import {
+  REACT_FORWARD_REF_TYPE,
+  REACT_MEMO_TYPE,
+  REACT_LAZY_TYPE,
+} from 'shared/ReactSymbols';
+
+export type Family = {|
+  current: any,
+|};
+
+export type RefreshUpdate = {|
+  staleFamilies: Set<Family>,
+  updatedFamilies: Set<Family>,
+|};
+
+// Resolves type to a family.
+type RefreshHandler = any => Family | void;
+
+// Used by React Refresh runtime through DevTools Global Hook.
+export type SetRefreshHandler = (handler: RefreshHandler | null) => void;
+export type ScheduleRefresh = (root: FiberRoot, update: RefreshUpdate) => void;
+export type ScheduleRoot = (root: FiberRoot, element: ReactNodeList) => void;
+export type FindHostInstancesForRefresh = (
+  root: FiberRoot,
+  families: Array<Family>,
+) => Set<Instance>;
+
+let resolveFamily: RefreshHandler | null = null;
+// $FlowFixMe Flow gets confused by a WeakSet feature check below.
+let failedBoundaries: WeakSet<Fiber> | null = null;
+
+export const setRefreshHandler = (handler: RefreshHandler | null): void => {
+  if (__DEV__) {
+    resolveFamily = handler;
+  }
+};
+
+export function resolveFunctionForHotReloading(type: any): any {
+  if (__DEV__) {
+    if (resolveFamily === null) {
+      // Hot reloading is disabled.
+      return type;
+    }
+    const family = resolveFamily(type);
+    if (family === undefined) {
+      return type;
+    }
+    // Use the latest known implementation.
+    return family.current;
+  } else {
+    return type;
+  }
+}
+
+export function resolveClassForHotReloading(type: any): any {
+  // No implementation differences.
+  return resolveFunctionForHotReloading(type);
+}
+
+export function resolveForwardRefForHotReloading(type: any): any {
+  if (__DEV__) {
+    if (resolveFamily === null) {
+      // Hot reloading is disabled.
+      return type;
+    }
+    const family = resolveFamily(type);
+    if (family === undefined) {
+      // Check if we're dealing with a real forwardRef. Don't want to crash early.
+      if (
+        type !== null &&
+        type !== undefined &&
+        typeof type.render === 'function'
+      ) {
+        // ForwardRef is special because its resolved .type is an object,
+        // but it's possible that we only have its inner render function in the map.
+        // If that inner render function is different, we'll build a new forwardRef type.
+        const currentRender = resolveFunctionForHotReloading(type.render);
+        if (type.render !== currentRender) {
+          const syntheticType = {
+            $$typeof: REACT_FORWARD_REF_TYPE,
+            render: currentRender,
+          };
+          if (type.displayName !== undefined) {
+            (syntheticType: any).displayName = type.displayName;
+          }
+          return syntheticType;
+        }
+      }
+      return type;
+    }
+    // Use the latest known implementation.
+    return family.current;
+  } else {
+    return type;
+  }
+}
+
+export function isCompatibleFamilyForHotReloading(
+  fiber: Fiber,
+  element: ReactElement,
+): boolean {
+  if (__DEV__) {
+    if (resolveFamily === null) {
+      // Hot reloading is disabled.
+      return false;
+    }
+
+    const prevType = fiber.elementType;
+    const nextType = element.type;
+
+    // If we got here, we know types aren't === equal.
+    let needsCompareFamilies = false;
+
+    const $$typeofNextType =
+      typeof nextType === 'object' && nextType !== null
+        ? nextType.$$typeof
+        : null;
+
+    switch (fiber.tag) {
+      case ClassComponent: {
+        if (typeof nextType === 'function') {
+          needsCompareFamilies = true;
+        }
+        break;
+      }
+      case FunctionComponent: {
+        if (typeof nextType === 'function') {
+          needsCompareFamilies = true;
+        } else if ($$typeofNextType === REACT_LAZY_TYPE) {
+          // We don't know the inner type yet.
+          // We're going to assume that the lazy inner type is stable,
+          // and so it is sufficient to avoid reconciling it away.
+          // We're not going to unwrap or actually use the new lazy type.
+          needsCompareFamilies = true;
+        }
+        break;
+      }
+      case ForwardRef: {
+        if ($$typeofNextType === REACT_FORWARD_REF_TYPE) {
+          needsCompareFamilies = true;
+        } else if ($$typeofNextType === REACT_LAZY_TYPE) {
+          needsCompareFamilies = true;
+        }
+        break;
+      }
+      case MemoComponent:
+      case SimpleMemoComponent: {
+        if ($$typeofNextType === REACT_MEMO_TYPE) {
+          // TODO: if it was but can no longer be simple,
+          // we shouldn't set this.
+          needsCompareFamilies = true;
+        } else if ($$typeofNextType === REACT_LAZY_TYPE) {
+          needsCompareFamilies = true;
+        }
+        break;
+      }
+      default:
+        return false;
+    }
+
+    // Check if both types have a family and it's the same one.
+    if (needsCompareFamilies) {
+      // Note: memo() and forwardRef() we'll compare outer rather than inner type.
+      // This means both of them need to be registered to preserve state.
+      // If we unwrapped and compared the inner types for wrappers instead,
+      // then we would risk falsely saying two separate memo(Foo)
+      // calls are equivalent because they wrap the same Foo function.
+      const prevFamily = resolveFamily(prevType);
+      if (prevFamily !== undefined && prevFamily === resolveFamily(nextType)) {
+        return true;
+      }
+    }
+    return false;
+  } else {
+    return false;
+  }
+}
+
+export function markFailedErrorBoundaryForHotReloading(fiber: Fiber) {
+  if (__DEV__) {
+    if (resolveFamily === null) {
+      // Hot reloading is disabled.
+      return;
+    }
+    if (typeof WeakSet !== 'function') {
+      return;
+    }
+    if (failedBoundaries === null) {
+      failedBoundaries = new WeakSet();
+    }
+    failedBoundaries.add(fiber);
+  }
+}
+
+export const scheduleRefresh: ScheduleRefresh = (
+  root: FiberRoot,
+  update: RefreshUpdate,
+): void => {
+  if (__DEV__) {
+    if (resolveFamily === null) {
+      // Hot reloading is disabled.
+      return;
+    }
+    const {staleFamilies, updatedFamilies} = update;
+    flushPassiveEffects();
+    flushSync(() => {
+      scheduleFibersWithFamiliesRecursively(
+        root.current,
+        updatedFamilies,
+        staleFamilies,
+      );
+    });
+  }
+};
+
+export const scheduleRoot: ScheduleRoot = (
+  root: FiberRoot,
+  element: ReactNodeList,
+): void => {
+  if (__DEV__) {
+    if (root.context !== emptyContextObject) {
+      // Super edge case: root has a legacy _renderSubtree context
+      // but we don't know the parentComponent so we can't pass it.
+      // Just ignore. We'll delete this with _renderSubtree code path later.
+      return;
+    }
+    flushPassiveEffects();
+    syncUpdates(() => {
+      updateContainer(element, root, null, null);
+    });
+  }
+};
+
+function scheduleFibersWithFamiliesRecursively(
+  fiber: Fiber,
+  updatedFamilies: Set<Family>,
+  staleFamilies: Set<Family>,
+) {
+  if (__DEV__) {
+    const {alternate, child, sibling, tag, type} = fiber;
+
+    let candidateType = null;
+    switch (tag) {
+      case FunctionComponent:
+      case SimpleMemoComponent:
+      case ClassComponent:
+        candidateType = type;
+        break;
+      case ForwardRef:
+        candidateType = type.render;
+        break;
+      default:
+        break;
+    }
+
+    if (resolveFamily === null) {
+      throw new Error('Expected resolveFamily to be set during hot reload.');
+    }
+
+    let needsRender = false;
+    let needsRemount = false;
+    if (candidateType !== null) {
+      const family = resolveFamily(candidateType);
+      if (family !== undefined) {
+        if (staleFamilies.has(family)) {
+          needsRemount = true;
+        } else if (updatedFamilies.has(family)) {
+          if (tag === ClassComponent) {
+            needsRemount = true;
+          } else {
+            needsRender = true;
+          }
+        }
+      }
+    }
+    if (failedBoundaries !== null) {
+      if (
+        failedBoundaries.has(fiber) ||
+        (alternate !== null && failedBoundaries.has(alternate))
+      ) {
+        needsRemount = true;
+      }
+    }
+
+    if (needsRemount) {
+      fiber._debugNeedsRemount = true;
+    }
+    if (needsRemount || needsRender) {
+      scheduleUpdateOnFiber(fiber, Sync);
+    }
+    if (child !== null && !needsRemount) {
+      scheduleFibersWithFamiliesRecursively(
+        child,
+        updatedFamilies,
+        staleFamilies,
+      );
+    }
+    if (sibling !== null) {
+      scheduleFibersWithFamiliesRecursively(
+        sibling,
+        updatedFamilies,
+        staleFamilies,
+      );
+    }
+  }
+}
+
+export const findHostInstancesForRefresh: FindHostInstancesForRefresh = (
+  root: FiberRoot,
+  families: Array<Family>,
+): Set<Instance> => {
+  if (__DEV__) {
+    const hostInstances = new Set();
+    const types = new Set(families.map(family => family.current));
+    findHostInstancesForMatchingFibersRecursively(
+      root.current,
+      types,
+      hostInstances,
+    );
+    return hostInstances;
+  } else {
+    throw new Error(
+      'Did not expect findHostInstancesForRefresh to be called in production.',
+    );
+  }
+};
+
+function findHostInstancesForMatchingFibersRecursively(
+  fiber: Fiber,
+  types: Set<any>,
+  hostInstances: Set<Instance>,
+) {
+  if (__DEV__) {
+    const {child, sibling, tag, type} = fiber;
+
+    let candidateType = null;
+    switch (tag) {
+      case FunctionComponent:
+      case SimpleMemoComponent:
+      case ClassComponent:
+        candidateType = type;
+        break;
+      case ForwardRef:
+        candidateType = type.render;
+        break;
+      default:
+        break;
+    }
+
+    let didMatch = false;
+    if (candidateType !== null) {
+      if (types.has(candidateType)) {
+        didMatch = true;
+      }
+    }
+
+    if (didMatch) {
+      // We have a match. This only drills down to the closest host components.
+      // There's no need to search deeper because for the purpose of giving
+      // visual feedback, "flashing" outermost parent rectangles is sufficient.
+      findHostInstancesForFiberShallowly(fiber, hostInstances);
+    } else {
+      // If there's no match, maybe there will be one further down in the child tree.
+      if (child !== null) {
+        findHostInstancesForMatchingFibersRecursively(
+          child,
+          types,
+          hostInstances,
+        );
+      }
+    }
+
+    if (sibling !== null) {
+      findHostInstancesForMatchingFibersRecursively(
+        sibling,
+        types,
+        hostInstances,
+      );
+    }
+  }
+}
+
+function findHostInstancesForFiberShallowly(
+  fiber: Fiber,
+  hostInstances: Set<Instance>,
+): void {
+  if (__DEV__) {
+    const foundHostInstances = findChildHostInstancesForFiberShallowly(
+      fiber,
+      hostInstances,
+    );
+    if (foundHostInstances) {
+      return;
+    }
+    // If we didn't find any host children, fallback to closest host parent.
+    let node = fiber;
+    while (true) {
+      switch (node.tag) {
+        case HostComponent:
+          hostInstances.add(node.stateNode);
+          return;
+        case HostPortal:
+          hostInstances.add(node.stateNode.containerInfo);
+          return;
+        case HostRoot:
+          hostInstances.add(node.stateNode.containerInfo);
+          return;
+      }
+      if (node.return === null) {
+        throw new Error('Expected to reach root first.');
+      }
+      node = node.return;
+    }
+  }
+}
+
+function findChildHostInstancesForFiberShallowly(
+  fiber: Fiber,
+  hostInstances: Set<Instance>,
+): boolean {
+  if (__DEV__) {
+    let node: Fiber = fiber;
+    let foundHostInstances = false;
+    while (true) {
+      if (node.tag === HostComponent) {
+        // We got a match.
+        foundHostInstances = true;
+        hostInstances.add(node.stateNode);
+        // There may still be more, so keep searching.
+      } else if (node.child !== null) {
+        node.child.return = node;
+        node = node.child;
+        continue;
+      }
+      if (node === fiber) {
+        return foundHostInstances;
+      }
+      while (node.sibling === null) {
+        if (node.return === null || node.return === fiber) {
+          return foundHostInstances;
+        }
+        node = node.return;
+      }
+      node.sibling.return = node.return;
+      node = node.sibling;
+    }
+  }
+  return false;
+}

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

@@ -7,7 +7,7 @@
  * @flow
  */
 
-import type {Fiber} from './ReactFiber';
+import type {Fiber} from './ReactFiber.old';
 import type {
   Instance,
   TextInstance,
@@ -16,7 +16,7 @@ import type {
   Container,
   HostContext,
 } from './ReactFiberHostConfig';
-import type {SuspenseState} from './ReactFiberSuspenseComponent';
+import type {SuspenseState} from './ReactFiberSuspenseComponent.old';
 
 import {
   HostComponent,
@@ -30,7 +30,7 @@ import invariant from 'shared/invariant';
 import {
   createFiberFromHostInstanceForDeletion,
   createFiberFromDehydratedFragment,
-} from './ReactFiber';
+} from './ReactFiber.old';
 import {
   shouldSetTextContent,
   supportsHydration,
@@ -55,7 +55,7 @@ import {
   didNotFindHydratableSuspenseInstance,
 } from './ReactFiberHostConfig';
 import {enableSuspenseServerRenderer} from 'shared/ReactFeatureFlags';
-import {Never, NoWork} from './ReactFiberExpirationTime';
+import {Never, NoWork} from './ReactFiberExpirationTime.old';
 
 // The deepest Fiber on the stack involved in a hydration context.
 // This may have been an insertion or a hydration.

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

@@ -8,9 +8,9 @@
  */
 
 import type {ReactContext} from 'shared/ReactTypes';
-import type {Fiber} from './ReactFiber';
-import type {StackCursor} from './ReactFiberStack';
-import type {ExpirationTime} from './ReactFiberExpirationTime';
+import type {Fiber} from './ReactFiber.old';
+import type {StackCursor} from './ReactFiberStack.old';
+import type {ExpirationTime} from './ReactFiberExpirationTime.old';
 
 export type ContextDependency<T> = {
   context: ReactContext<T>,
@@ -20,7 +20,7 @@ export type ContextDependency<T> = {
 };
 
 import {isPrimaryRenderer} from './ReactFiberHostConfig';
-import {createCursor, push, pop} from './ReactFiberStack';
+import {createCursor, push, pop} from './ReactFiberStack.old';
 import {MAX_SIGNED_31_BIT_INT} from './MaxInts';
 import {
   ContextProvider,
@@ -30,13 +30,9 @@ import {
 
 import invariant from 'shared/invariant';
 import is from 'shared/objectIs';
-import {
-  createUpdate,
-  enqueueUpdate,
-  ForceUpdate,
-} from 'react-reconciler/src/ReactUpdateQueue';
-import {NoWork} from './ReactFiberExpirationTime';
-import {markWorkInProgressReceivedUpdate} from './ReactFiberBeginWork';
+import {createUpdate, enqueueUpdate, ForceUpdate} from './ReactUpdateQueue.old';
+import {NoWork} from './ReactFiberExpirationTime.old';
+import {markWorkInProgressReceivedUpdate} from './ReactFiberBeginWork.old';
 import {enableSuspenseServerRenderer} from 'shared/ReactFeatureFlags';
 
 const valueCursor: StackCursor<mixed> = createCursor(null);

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

@@ -7,9 +7,9 @@
  * @flow
  */
 
-import type {Fiber} from './ReactFiber';
-import type {FiberRoot} from './ReactFiberRoot';
-import type {RootTag} from 'react-reconciler/src/ReactRootTags';
+import type {Fiber} from './ReactFiber.old';
+import type {FiberRoot} from './ReactFiberRoot.old';
+import type {RootTag} from './ReactRootTags';
 import type {
   Instance,
   TextInstance,
@@ -19,16 +19,16 @@ import type {
 import type {RendererInspectionConfig} from './ReactFiberHostConfig';
 import {FundamentalComponent} from './ReactWorkTags';
 import type {ReactNodeList, Thenable} from 'shared/ReactTypes';
-import type {ExpirationTime} from './ReactFiberExpirationTime';
+import type {ExpirationTime} from './ReactFiberExpirationTime.old';
 import type {
   SuspenseHydrationCallbacks,
   SuspenseState,
-} from './ReactFiberSuspenseComponent';
+} from './ReactFiberSuspenseComponent.old';
 
 import {
   findCurrentHostFiber,
   findCurrentHostFiberWithNoPortals,
-} from 'react-reconciler/src/ReactFiberTreeReflection';
+} from './ReactFiberTreeReflection';
 import {get as getInstance} from 'shared/ReactInstanceMap';
 import {
   HostComponent,
@@ -46,9 +46,9 @@ import {
   processChildContext,
   emptyContextObject,
   isContextProvider as isLegacyContextProvider,
-} from './ReactFiberContext';
-import {createFiberRoot} from './ReactFiberRoot';
-import {injectInternals, onScheduleRoot} from './ReactFiberDevToolsHook';
+} from './ReactFiberContext.old';
+import {createFiberRoot} from './ReactFiberRoot.old';
+import {injectInternals, onScheduleRoot} from './ReactFiberDevToolsHook.old';
 import {
   requestCurrentTimeForUpdate,
   computeExpirationForFiber,
@@ -67,8 +67,8 @@ import {
   warnIfNotScopedWithMatchingAct,
   warnIfUnmockedScheduler,
   IsThisRendererActing,
-} from './ReactFiberWorkLoop';
-import {createUpdate, enqueueUpdate} from './ReactUpdateQueue';
+} from './ReactFiberWorkLoop.old';
+import {createUpdate, enqueueUpdate} from './ReactUpdateQueue.old';
 import {getStackByFiberInDevAndProd} from './ReactFiberComponentStack';
 import {
   isRendering as ReactCurrentFiberIsRendering,
@@ -79,14 +79,14 @@ import {
   Sync,
   ContinuousHydration,
   computeInteractiveExpiration,
-} from './ReactFiberExpirationTime';
-import {requestCurrentSuspenseConfig} from './ReactFiberSuspenseConfig';
+} from './ReactFiberExpirationTime.old';
+import {requestCurrentSuspenseConfig} from './ReactFiberSuspenseConfig.old';
 import {
   scheduleRefresh,
   scheduleRoot,
   setRefreshHandler,
   findHostInstancesForRefresh,
-} from './ReactFiberHotReloading';
+} from './ReactFiberHotReloading.old';
 
 // used by isTestEnvironment builds
 import enqueueTask from 'shared/enqueueTask';

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

@@ -7,26 +7,26 @@
  * @flow
  */
 
-import type {Fiber} from './ReactFiber';
-import type {ExpirationTime} from './ReactFiberExpirationTime';
-import type {RootTag} from 'react-reconciler/src/ReactRootTags';
+import type {Fiber} from './ReactFiber.old';
+import type {ExpirationTime} from './ReactFiberExpirationTime.old';
+import type {RootTag} from './ReactRootTags';
 import type {TimeoutHandle, NoTimeout} from './ReactFiberHostConfig';
 import type {Wakeable} from 'shared/ReactTypes';
 import type {Interaction} from 'scheduler/src/Tracing';
-import type {SuspenseHydrationCallbacks} from './ReactFiberSuspenseComponent';
-import type {ReactPriorityLevel} from './SchedulerWithReactIntegration';
+import type {SuspenseHydrationCallbacks} from './ReactFiberSuspenseComponent.old';
+import type {ReactPriorityLevel} from './SchedulerWithReactIntegration.old';
 
 import {noTimeout} from './ReactFiberHostConfig';
-import {createHostRootFiber} from './ReactFiber';
-import {NoWork} from './ReactFiberExpirationTime';
+import {createHostRootFiber} from './ReactFiber.old';
+import {NoWork} from './ReactFiberExpirationTime.old';
 import {
   enableSchedulerTracing,
   enableSuspenseCallback,
 } from 'shared/ReactFeatureFlags';
 import {unstable_getThreadID} from 'scheduler/tracing';
-import {NoPriority} from './SchedulerWithReactIntegration';
-import {initializeUpdateQueue} from './ReactUpdateQueue';
-import {clearPendingUpdates as clearPendingMutableSourceUpdates} from './ReactMutableSource';
+import {NoPriority} from './SchedulerWithReactIntegration.old';
+import {initializeUpdateQueue} from './ReactUpdateQueue.old';
+import {clearPendingUpdates as clearPendingMutableSourceUpdates} from './ReactMutableSource.old';
 
 export type PendingInteractionMap = Map<ExpirationTime, Set<Interaction>>;
 

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

@@ -7,7 +7,7 @@
  * @flow
  */
 
-import type {Fiber} from './ReactFiber';
+import type {Fiber} from './ReactFiber.old';
 import type {
   ReactScope,
   ReactScopeInstance,

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

@@ -7,7 +7,7 @@
  * @flow
  */
 
-import type {Fiber} from './ReactFiber';
+import type {Fiber} from './ReactFiber.old';
 
 export type StackCursor<T> = {|current: T|};
 

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

@@ -7,9 +7,9 @@
  * @flow
  */
 
-import type {Fiber} from './ReactFiber';
+import type {Fiber} from './ReactFiber.old';
 import type {SuspenseInstance} from './ReactFiberHostConfig';
-import type {ExpirationTime} from './ReactFiberExpirationTime';
+import type {ExpirationTime} from './ReactFiberExpirationTime.old';
 import {SuspenseComponent, SuspenseListComponent} from './ReactWorkTags';
 import {NoEffect, DidCapture} from './ReactSideEffectTags';
 import {

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

@@ -7,10 +7,10 @@
  * @flow
  */
 
-import type {Fiber} from './ReactFiber';
-import type {StackCursor} from './ReactFiberStack';
+import type {Fiber} from './ReactFiber.old';
+import type {StackCursor} from './ReactFiberStack.old';
 
-import {createCursor, push, pop} from './ReactFiberStack';
+import {createCursor, push, pop} from './ReactFiberStack.old';
 
 export opaque type SuspenseContext = number;
 export opaque type SubtreeSuspenseContext: SuspenseContext = number;

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

@@ -7,13 +7,13 @@
  * @flow
  */
 
-import type {Fiber} from './ReactFiber';
-import type {FiberRoot} from './ReactFiberRoot';
-import type {ExpirationTime} from './ReactFiberExpirationTime';
+import type {Fiber} from './ReactFiber.old';
+import type {FiberRoot} from './ReactFiberRoot.old';
+import type {ExpirationTime} from './ReactFiberExpirationTime.old';
 import type {CapturedValue} from './ReactCapturedValue';
-import type {Update} from './ReactUpdateQueue';
+import type {Update} from './ReactUpdateQueue.old';
 import type {Wakeable} from 'shared/ReactTypes';
-import type {SuspenseContext} from './ReactFiberSuspenseContext';
+import type {SuspenseContext} from './ReactFiberSuspenseContext.old';
 
 import getComponentName from 'shared/getComponentName';
 import {
@@ -30,7 +30,7 @@ import {
   LifecycleEffectMask,
 } from './ReactSideEffectTags';
 import {NoMode, BlockingMode} from './ReactTypeOfMode';
-import {shouldCaptureSuspense} from './ReactFiberSuspenseComponent';
+import {shouldCaptureSuspense} from './ReactFiberSuspenseComponent.old';
 
 import {createCapturedValue} from './ReactCapturedValue';
 import {
@@ -39,24 +39,24 @@ import {
   CaptureUpdate,
   ForceUpdate,
   enqueueUpdate,
-} from './ReactUpdateQueue';
+} from './ReactUpdateQueue.old';
 import {getStackByFiberInDevAndProd} from './ReactFiberComponentStack';
-import {markFailedErrorBoundaryForHotReloading} from './ReactFiberHotReloading';
+import {markFailedErrorBoundaryForHotReloading} from './ReactFiberHotReloading.old';
 import {
   suspenseStackCursor,
   InvisibleParentSuspenseContext,
   hasSuspenseContext,
-} from './ReactFiberSuspenseContext';
+} from './ReactFiberSuspenseContext.old';
 import {
   renderDidError,
   onUncaughtError,
   markLegacyErrorBoundaryAsFailed,
   isAlreadyFailedLegacyErrorBoundary,
   pingSuspendedRoot,
-} from './ReactFiberWorkLoop';
+} from './ReactFiberWorkLoop.old';
 import {logCapturedError} from './ReactFiberErrorLogger';
 
-import {Sync} from './ReactFiberExpirationTime';
+import {Sync} from './ReactFiberExpirationTime.old';
 
 const PossiblyWeakMap = typeof WeakMap === 'function' ? WeakMap : Map;
 

packages/react-reconciler/src/ReactFiberTreeReflection.js

@@ -7,9 +7,9 @@
  * @flow
  */
 
-import type {Fiber} from './ReactFiber';
+import type {Fiber} from './ReactFiber.old';
 import type {Container, SuspenseInstance} from './ReactFiberHostConfig';
-import type {SuspenseState} from './ReactFiberSuspenseComponent';
+import type {SuspenseState} from './ReactFiberSuspenseComponent.old';
 
 import invariant from 'shared/invariant';
 

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

@@ -7,11 +7,11 @@
  * @flow
  */
 
-import type {Fiber} from './ReactFiber';
-import type {ExpirationTime} from './ReactFiberExpirationTime';
-import type {SuspenseState} from './ReactFiberSuspenseComponent';
+import type {Fiber} from './ReactFiber.old';
+import type {ExpirationTime} from './ReactFiberExpirationTime.old';
+import type {SuspenseState} from './ReactFiberSuspenseComponent.old';
 
-import {resetWorkInProgressVersions as resetMutableSourceWorkInProgressVersions} from './ReactMutableSource';
+import {resetWorkInProgressVersions as resetMutableSourceWorkInProgressVersions} from './ReactMutableSource.old';
 import {
   ClassComponent,
   HostRoot,
@@ -24,15 +24,15 @@ import {
 import {DidCapture, NoEffect, ShouldCapture} from './ReactSideEffectTags';
 import {enableSuspenseServerRenderer} from 'shared/ReactFeatureFlags';
 
-import {popHostContainer, popHostContext} from './ReactFiberHostContext';
-import {popSuspenseContext} from './ReactFiberSuspenseContext';
-import {resetHydrationState} from './ReactFiberHydrationContext';
+import {popHostContainer, popHostContext} from './ReactFiberHostContext.old';
+import {popSuspenseContext} from './ReactFiberSuspenseContext.old';
+import {resetHydrationState} from './ReactFiberHydrationContext.old';
 import {
   isContextProvider as isLegacyContextProvider,
   popContext as popLegacyContext,
   popTopLevelContextObject as popTopLevelLegacyContextObject,
-} from './ReactFiberContext';
-import {popProvider} from './ReactFiberNewContext';
+} from './ReactFiberContext.old';
+import {popProvider} from './ReactFiberNewContext.old';
 
 import invariant from 'shared/invariant';
 

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

@@ -8,14 +8,14 @@
  */
 
 import type {Wakeable} from 'shared/ReactTypes';
-import type {Fiber} from './ReactFiber';
-import type {FiberRoot} from './ReactFiberRoot';
-import type {ExpirationTime} from './ReactFiberExpirationTime';
-import type {ReactPriorityLevel} from './SchedulerWithReactIntegration';
+import type {Fiber} from './ReactFiber.old';
+import type {FiberRoot} from './ReactFiberRoot.old';
+import type {ExpirationTime} from './ReactFiberExpirationTime.old';
+import type {ReactPriorityLevel} from './SchedulerWithReactIntegration.old';
 import type {Interaction} from 'scheduler/src/Tracing';
-import type {SuspenseConfig} from './ReactFiberSuspenseConfig';
-import type {SuspenseState} from './ReactFiberSuspenseComponent';
-import type {Effect as HookEffect} from './ReactFiberHooks';
+import type {SuspenseConfig} from './ReactFiberSuspenseConfig.old';
+import type {SuspenseState} from './ReactFiberSuspenseComponent.old';
+import type {Effect as HookEffect} from './ReactFiberHooks.old';
 
 import {
   warnAboutDeprecatedLifecycles,
@@ -49,7 +49,7 @@ import {
   IdlePriority,
   flushSyncCallbackQueue,
   scheduleSyncCallback,
-} from './SchedulerWithReactIntegration';
+} from './SchedulerWithReactIntegration.old';
 
 // The scheduler is imported here *only* to detect whether it's been mocked
 import * as Scheduler from 'scheduler';
@@ -65,14 +65,17 @@ import {
   warnsIfNotActing,
 } from './ReactFiberHostConfig';
 
-import {createWorkInProgress, assignFiberPropertiesInDEV} from './ReactFiber';
+import {
+  createWorkInProgress,
+  assignFiberPropertiesInDEV,
+} from './ReactFiber.old';
 import {
   isRootSuspendedAtTime,
   markRootSuspendedAtTime,
   markRootFinishedAtTime,
   markRootUpdatedAtTime,
   markRootExpiredAtTime,
-} from './ReactFiberRoot';
+} from './ReactFiberRoot.old';
 import {
   NoMode,
   StrictMode,
@@ -91,7 +94,7 @@ import {
   SimpleMemoComponent,
   Block,
 } from './ReactWorkTags';
-import {LegacyRoot} from 'react-reconciler/src/ReactRootTags';
+import {LegacyRoot} from './ReactRootTags';
 import {
   NoEffect,
   PerformedWork,
@@ -122,15 +125,15 @@ import {
   LOW_PRIORITY_EXPIRATION,
   Batched,
   Idle,
-} from './ReactFiberExpirationTime';
-import {beginWork as originalBeginWork} from './ReactFiberBeginWork';
-import {completeWork} from './ReactFiberCompleteWork';
-import {unwindWork, unwindInterruptedWork} from './ReactFiberUnwindWork';
+} from './ReactFiberExpirationTime.old';
+import {beginWork as originalBeginWork} from './ReactFiberBeginWork.old';
+import {completeWork} from './ReactFiberCompleteWork.old';
+import {unwindWork, unwindInterruptedWork} from './ReactFiberUnwindWork.old';
 import {
   throwException,
   createRootErrorUpdate,
   createClassErrorUpdate,
-} from './ReactFiberThrow';
+} from './ReactFiberThrow.old';
 import {
   commitBeforeMutationLifeCycles as commitBeforeMutationEffectOnFiber,
   commitLifeCycles as commitLayoutEffectOnFiber,
@@ -142,14 +145,14 @@ import {
   commitAttachRef,
   commitPassiveEffectDurations,
   commitResetTextContent,
-} from './ReactFiberCommitWork';
-import {enqueueUpdate} from './ReactUpdateQueue';
-import {resetContextDependencies} from './ReactFiberNewContext';
+} from './ReactFiberCommitWork.old';
+import {enqueueUpdate} from './ReactUpdateQueue.old';
+import {resetContextDependencies} from './ReactFiberNewContext.old';
 import {
   resetHooksAfterThrow,
   ContextOnlyDispatcher,
   getIsUpdatingOpaqueValueInRenderPhaseInDEV,
-} from './ReactFiberHooks';
+} from './ReactFiberHooks.old';
 import {createCapturedValue} from './ReactCapturedValue';
 
 import {
@@ -158,11 +161,11 @@ import {
   startPassiveEffectTimer,
   startProfilerTimer,
   stopProfilerTimerIfRunningAndRecordDelta,
-} from './ReactProfilerTimer';
+} from './ReactProfilerTimer.old';
 
 // DEV stuff
 import getComponentName from 'shared/getComponentName';
-import ReactStrictModeWarnings from './ReactStrictModeWarnings';
+import ReactStrictModeWarnings from './ReactStrictModeWarnings.old';
 import {getStackByFiberInDevAndProd} from './ReactFiberComponentStack';
 import {
   isRendering as ReactCurrentDebugFiberIsRenderingInDEV,
@@ -174,7 +177,7 @@ import {
   hasCaughtError,
   clearCaughtError,
 } from 'shared/ReactErrorUtils';
-import {onCommitRoot} from './ReactFiberDevToolsHook';
+import {onCommitRoot} from './ReactFiberDevToolsHook.old';
 
 const ceil = Math.ceil;
 

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

@@ -7,12 +7,12 @@
  * @flow
  */
 
-import type {ExpirationTime} from 'react-reconciler/src/ReactFiberExpirationTime';
-import type {FiberRoot} from 'react-reconciler/src/ReactFiberRoot';
+import type {ExpirationTime} from './ReactFiberExpirationTime.old';
+import type {FiberRoot} from './ReactFiberRoot.old';
 import type {MutableSource, MutableSourceVersion} from 'shared/ReactTypes';
 
 import {isPrimaryRenderer} from './ReactFiberHostConfig';
-import {NoWork} from './ReactFiberExpirationTime';
+import {NoWork} from './ReactFiberExpirationTime.old';
 
 // Work in progress version numbers only apply to a single render,
 // and should be reset before starting a new render.

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

@@ -7,7 +7,7 @@
  * @flow
  */
 
-import type {Fiber} from './ReactFiber';
+import type {Fiber} from './ReactFiber.old';
 
 import {
   enableProfilerTimer,

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

@@ -7,7 +7,7 @@
  * @flow
  */
 
-import type {Fiber} from './ReactFiber';
+import type {Fiber} from './ReactFiber.old';
 
 import {getStackByFiberInDevAndProd} from './ReactFiberComponentStack';
 

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

@@ -84,16 +84,16 @@
 // regardless of priority. Intermediate state may vary according to system
 // resources, but the final state is always the same.
 
-import type {Fiber} from './ReactFiber';
-import type {ExpirationTime} from './ReactFiberExpirationTime';
-import type {SuspenseConfig} from './ReactFiberSuspenseConfig';
-import type {ReactPriorityLevel} from './SchedulerWithReactIntegration';
+import type {Fiber} from './ReactFiber.old';
+import type {ExpirationTime} from './ReactFiberExpirationTime.old';
+import type {SuspenseConfig} from './ReactFiberSuspenseConfig.old';
+import type {ReactPriorityLevel} from './SchedulerWithReactIntegration.old';
 
-import {NoWork, Sync} from './ReactFiberExpirationTime';
+import {NoWork, Sync} from './ReactFiberExpirationTime.old';
 import {
   enterDisallowedContextReadInDEV,
   exitDisallowedContextReadInDEV,
-} from './ReactFiberNewContext';
+} from './ReactFiberNewContext.old';
 import {Callback, ShouldCapture, DidCapture} from './ReactSideEffectTags';
 
 import {debugRenderPhaseSideEffectsForStrictMode} from 'shared/ReactFeatureFlags';
@@ -102,10 +102,10 @@ import {StrictMode} from './ReactTypeOfMode';
 import {
   markRenderEventTimeAndConfig,
   markUnprocessedUpdateTime,
-} from './ReactFiberWorkLoop';
+} from './ReactFiberWorkLoop.old';
 
 import invariant from 'shared/invariant';
-import {getCurrentPriorityLevel} from './SchedulerWithReactIntegration';
+import {getCurrentPriorityLevel} from './SchedulerWithReactIntegration.old';
 
 import {disableLogs, reenableLogs} from 'shared/ConsolePatchingDev';
 

packages/react-reconciler/src/__tests__/ReactIncrementalErrorReplay-test.internal.js

@@ -18,11 +18,14 @@ describe('ReactIncrementalErrorReplay-test', () => {
     // We almost always try to avoid such tests, but here the cost of
     // the list getting out of sync (and causing subtle bugs in rare cases)
     // is higher than the cost of maintaining the test.
-    const {
-      // This is the method we're going to test.
-      // If this is no longer used, you can delete this test file.
-      assignFiberPropertiesInDEV,
-    } = require('../ReactFiber');
+
+    // This is the method we're going to test.
+    // If this is no longer used, you can delete this test file.;
+
+    const assignFiberPropertiesInDEV = require('shared/ReactFeatureFlags')
+      ? // TODO: Update this to point to the new module, once it exists
+        require('../ReactFiber.old').assignFiberPropertiesInDEV
+      : require('../ReactFiber.old').assignFiberPropertiesInDEV;
 
     // Get a real fiber.
     const realFiber = ReactTestRenderer.create(<div />).root._currentFiber();

packages/react-reconciler/src/forks/ReactFiberErrorDialog.native.js

@@ -7,7 +7,7 @@
  * @flow
  */
 
-import type {Fiber} from '../ReactFiber';
+import type {Fiber} from '../ReactFiber.old';
 import type {CapturedValue} from '../ReactCapturedValue';
 
 import {ClassComponent} from '../ReactWorkTags';

packages/react-reconciler/src/forks/ReactFiberErrorDialog.www.js

@@ -7,7 +7,7 @@
  * @flow
  */
 
-import type {Fiber} from '../ReactFiber';
+import type {Fiber} from '../ReactFiber.old';
 import type {CapturedValue} from '../ReactCapturedValue';
 
 import {ClassComponent} from '../ReactWorkTags';

packages/react-refresh/src/ReactFreshRuntime.js

@@ -8,7 +8,7 @@
  */
 
 import type {Instance} from 'react-reconciler/src/ReactFiberHostConfig';
-import type {FiberRoot} from 'react-reconciler/src/ReactFiberRoot';
+import type {FiberRoot} from 'react-reconciler/src/ReactFiberRoot.old';
 import type {
   Family,
   RefreshUpdate,

packages/react-test-renderer/src/ReactTestRenderer.js

@@ -7,8 +7,8 @@
  * @flow
  */
 
-import type {Fiber} from 'react-reconciler/src/ReactFiber';
-import type {FiberRoot} from 'react-reconciler/src/ReactFiberRoot';
+import type {Fiber} from 'react-reconciler/src/ReactFiber.old';
+import type {FiberRoot} from 'react-reconciler/src/ReactFiberRoot.old';
 import type {Instance, TextInstance} from './ReactTestHostConfig';
 
 import * as Scheduler from 'scheduler/unstable_mock';

packages/react/src/ReactBatchConfig.js

@@ -7,7 +7,7 @@
  * @flow
  */
 
-import type {SuspenseConfig} from 'react-reconciler/src/ReactFiberSuspenseConfig';
+import type {SuspenseConfig} from 'react-reconciler/src/ReactFiberSuspenseConfig.old';
 
 import ReactCurrentBatchConfig from './ReactCurrentBatchConfig';
 

packages/react/src/ReactCurrentBatchConfig.js

@@ -7,7 +7,7 @@
  * @flow
  */
 
-import type {SuspenseConfig} from 'react-reconciler/src/ReactFiberSuspenseConfig';
+import type {SuspenseConfig} from 'react-reconciler/src/ReactFiberSuspenseConfig.old';
 
 /**
  * Keeps track of the current batch's configuration such as how long an update

packages/react/src/ReactCurrentDispatcher.js

@@ -7,7 +7,7 @@
  * @flow
  */
 
-import type {Dispatcher} from 'react-reconciler/src/ReactFiberHooks';
+import type {Dispatcher} from 'react-reconciler/src/ReactFiberHooks.old';
 
 /**
  * Keeps track of the current dispatcher.

packages/react/src/ReactCurrentOwner.js

@@ -7,7 +7,7 @@
  * @flow
  */
 
-import type {Fiber} from 'react-reconciler/src/ReactFiber';
+import type {Fiber} from 'react-reconciler/src/ReactFiber.old';
 
 /**
  * Keeps track of the current owner.

scripts/flow/react-native-host-hooks.js

@@ -18,7 +18,7 @@ import type {
 } from 'react-native-renderer/src/ReactNativeTypes';
 import type {RNTopLevelEventType} from 'legacy-events/TopLevelEventTypes';
 import type {CapturedError} from 'react-reconciler/src/ReactCapturedValue';
-import type {Fiber} from 'react-reconciler/src/ReactFiber';
+import type {Fiber} from 'react-reconciler/src/ReactFiber.old';
 
 type DeepDifferOptions = {|+unsafelyIgnoreFunctions?: boolean|};
 

scripts/rollup/forks.js

@@ -281,6 +281,27 @@ const forks = Object.freeze({
     return 'react-reconciler/src/ReactFiberReconciler.old.js';
   },
 
+  'react-reconciler/src/ReactFiberHotReloading': (
+    bundleType,
+    entry,
+    dependencies,
+    moduleType,
+    bundle
+  ) => {
+    if (bundle.enableNewReconciler) {
+      switch (bundleType) {
+        case FB_WWW_DEV:
+        case FB_WWW_PROD:
+        case FB_WWW_PROFILING:
+          // Use the forked version of the reconciler
+          // TODO: Update this to point to the new module, once it exists
+          return 'react-reconciler/src/ReactFiberHotReloading.old.js';
+      }
+    }
+    // Otherwise, use the non-forked version.
+    return 'react-reconciler/src/ReactFiberHotReloading.old.js';
+  },
+
   // Different dialogs for caught errors.
   'react-reconciler/src/ReactFiberErrorDialog': (bundleType, entry) => {
     switch (bundleType) {