text: /**
   * 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 {Thenable, Wakeable} from 'shared/ReactTypes';
  import type {Fiber, FiberRoot} from './ReactInternalTypes';
  import type {Lanes, Lane} from './ReactFiberLane.new';
  import type {Interaction} from 'scheduler/src/Tracing';
  import type {SuspenseState} from './ReactFiberSuspenseComponent.new';
  import type {StackCursor} from './ReactFiberStack.new';
  import type {FunctionComponentUpdateQueue} from './ReactFiberHooks.new';
  import type {Flags} from './ReactFiberFlags';
  
  import {
    warnAboutDeprecatedLifecycles,
    enableSuspenseServerRenderer,
    replayFailedUnitOfWorkWithInvokeGuardedCallback,
    enableProfilerTimer,
    enableProfilerCommitHooks,
    enableProfilerNestedUpdatePhase,
    enableProfilerNestedUpdateScheduledHook,
    enableSchedulerTracing,
    warnAboutUnmockedScheduler,
    deferRenderPhaseUpdateToNextBatch,
    enableDebugTracing,
    enableSchedulingProfiler,
    disableSchedulerTimeoutInWorkLoop,
    enableStrictEffects,
    skipUnmountedBoundaries,
  } from 'shared/ReactFeatureFlags';
  import ReactSharedInternals from 'shared/ReactSharedInternals';
  import invariant from 'shared/invariant';
  
  import {
    scheduleCallback,
    cancelCallback,
    shouldYield,
    requestPaint,
    now,
    ImmediatePriority as ImmediateSchedulerPriority,
    UserBlockingPriority as UserBlockingSchedulerPriority,
    NormalPriority as NormalSchedulerPriority,
    IdlePriority as IdleSchedulerPriority,
  } from './Scheduler';
  import {
    flushSyncCallbackQueue,
    scheduleSyncCallback,
  } from './ReactFiberSyncTaskQueue.new';
  import {
    NoFlags as NoHookEffect,
    Passive as HookPassive,
  } from './ReactHookEffectTags';
  import {
    logCommitStarted,
    logCommitStopped,
    logLayoutEffectsStarted,
    logLayoutEffectsStopped,
    logPassiveEffectsStarted,
    logPassiveEffectsStopped,
    logRenderStarted,
    logRenderStopped,
  } from './DebugTracing';
  import {
    markCommitStarted,
    markCommitStopped,
    markLayoutEffectsStarted,
    markLayoutEffectsStopped,
    markPassiveEffectsStarted,
    markPassiveEffectsStopped,
    markRenderStarted,
    markRenderYielded,
    markRenderStopped,
  } from './SchedulingProfiler';
  
  // The scheduler is imported here *only* to detect whether it's been mocked
  import * as Scheduler from 'scheduler';
  
  import {__interactionsRef, __subscriberRef} from 'scheduler/tracing';
  
  import {
    resetAfterCommit,
    scheduleTimeout,
    cancelTimeout,
    noTimeout,
    warnsIfNotActing,
    afterActiveInstanceBlur,
    clearContainer,
    getCurrentEventPriority,
    supportsMicrotasks,
    errorHydratingContainer,
    scheduleMicrotask,
  } from './ReactFiberHostConfig';
  
  import {
    createWorkInProgress,
    assignFiberPropertiesInDEV,
  } from './ReactFiber.new';
  import {
    NoMode,
    StrictLegacyMode,
    ProfileMode,
    ConcurrentMode,
  } from './ReactTypeOfMode';
  import {
    HostRoot,
    IndeterminateComponent,
    ClassComponent,
    SuspenseComponent,
    SuspenseListComponent,
    FunctionComponent,
    ForwardRef,
    MemoComponent,
    SimpleMemoComponent,
    Profiler,
  } from './ReactWorkTags';
  import {LegacyRoot} from './ReactRootTags';
  import {
    NoFlags,
    Placement,
    PassiveStatic,
    Incomplete,
    HostEffectMask,
    Hydrating,
    BeforeMutationMask,
    MutationMask,
    LayoutMask,
    PassiveMask,
    MountPassiveDev,
    MountLayoutDev,
  } from './ReactFiberFlags';
  import {
    NoLanes,
    NoLane,
    SyncLane,
    NoTimestamp,
    claimNextTransitionLane,
    claimNextRetryLane,
    includesSomeLane,
    isSubsetOfLanes,
    mergeLanes,
    removeLanes,
    pickArbitraryLane,
    includesNonIdleWork,
    includesOnlyRetries,
    includesOnlyTransitions,
    getNextLanes,
    markStarvedLanesAsExpired,
    getLanesToRetrySynchronouslyOnError,
    getMostRecentEventTime,
    markRootUpdated,
    markRootSuspended as markRootSuspended_dontCallThisOneDirectly,
    markRootPinged,
    markRootExpired,
    markRootFinished,
    areLanesExpired,
    getHighestPriorityLane,
  } from './ReactFiberLane.new';
  import {
    DiscreteEventPriority,
    ContinuousEventPriority,
    DefaultEventPriority,
    IdleEventPriority,
    getCurrentUpdatePriority,
    setCurrentUpdatePriority,
    lowerEventPriority,
    lanesToEventPriority,
  } from './ReactEventPriorities.new';
  import {requestCurrentTransition, NoTransition} from './ReactFiberTransition';
  import {beginWork as originalBeginWork} from './ReactFiberBeginWork.new';
  import {completeWork} from './ReactFiberCompleteWork.new';
  import {unwindWork, unwindInterruptedWork} from './ReactFiberUnwindWork.new';
  import {
    throwException,
    createRootErrorUpdate,
    createClassErrorUpdate,
  } from './ReactFiberThrow.new';
  import {
    commitBeforeMutationEffects,
    commitLayoutEffects,
    commitMutationEffects,
    commitPassiveEffectDurations,
    commitPassiveMountEffects,
    commitPassiveUnmountEffects,
    invokeLayoutEffectMountInDEV,
    invokePassiveEffectMountInDEV,
    invokeLayoutEffectUnmountInDEV,
    invokePassiveEffectUnmountInDEV,
  } from './ReactFiberCommitWork.new';
  import {enqueueUpdate} from './ReactUpdateQueue.new';
  import {resetContextDependencies} from './ReactFiberNewContext.new';
  import {
    resetHooksAfterThrow,
    ContextOnlyDispatcher,
    getIsUpdatingOpaqueValueInRenderPhaseInDEV,
  } from './ReactFiberHooks.new';
  import {createCapturedValue} from './ReactCapturedValue';
  import {
    push as pushToStack,
    pop as popFromStack,
    createCursor,
  } from './ReactFiberStack.new';
  import {enqueueInterleavedUpdates} from './ReactFiberInterleavedUpdates.new';
  
  import {
    markNestedUpdateScheduled,
    recordCommitTime,
    resetNestedUpdateFlag,
    startProfilerTimer,
    stopProfilerTimerIfRunningAndRecordDelta,
    syncNestedUpdateFlag,
  } from './ReactProfilerTimer.new';
  
  // DEV stuff
  import getComponentNameFromFiber from 'react-reconciler/src/getComponentNameFromFiber';
  import ReactStrictModeWarnings from './ReactStrictModeWarnings.new';
  import {
    isRendering as ReactCurrentDebugFiberIsRenderingInDEV,
    current as ReactCurrentFiberCurrent,
    resetCurrentFiber as resetCurrentDebugFiberInDEV,
    setCurrentFiber as setCurrentDebugFiberInDEV,
  } from './ReactCurrentFiber';
  import {
    invokeGuardedCallback,
    hasCaughtError,
    clearCaughtError,
  } from 'shared/ReactErrorUtils';
  import {
    onCommitRoot as onCommitRootDevTools,
    onPostCommitRoot as onPostCommitRootDevTools,
  } from './ReactFiberDevToolsHook.new';
  import {onCommitRoot as onCommitRootTestSelector} from './ReactTestSelectors';
  
  // Used by `act`
  import enqueueTask from 'shared/enqueueTask';
  
  const ceil = Math.ceil;
  
  const {
    ReactCurrentDispatcher,
    ReactCurrentOwner,
    ReactCurrentBatchConfig,
    IsSomeRendererActing,
  } = ReactSharedInternals;
  
  type ExecutionContext = number;
  
  export const NoContext = /*             */ 0b000000;
  const BatchedContext = /*               */ 0b000001;
  const EventContext = /*                 */ 0b000010;
  const LegacyUnbatchedContext = /*       */ 0b000100;
  const RenderContext = /*                */ 0b001000;
  const CommitContext = /*                */ 0b010000;
  export const RetryAfterError = /*       */ 0b100000;
  
  type RootExitStatus = 0 | 1 | 2 | 3 | 4 | 5;
  const RootIncomplete = 0;
  const RootFatalErrored = 1;
  const RootErrored = 2;
  const RootSuspended = 3;
  const RootSuspendedWithDelay = 4;
  const RootCompleted = 5;
  
  // Describes where we are in the React execution stack
  let executionContext: ExecutionContext = NoContext;
  // The root we're working on
  let workInProgressRoot: FiberRoot | null = null;
  // The fiber we're working on
  let workInProgress: Fiber | null = null;
  // The lanes we're rendering
  let workInProgressRootRenderLanes: Lanes = NoLanes;
  
  // Stack that allows components to change the render lanes for its subtree
  // This is a superset of the lanes we started working on at the root. The only
  // case where it's different from `workInProgressRootRenderLanes` is when we
  // enter a subtree that is hidden and needs to be unhidden: Suspense and
  // Offscreen component.
  //
  // Most things in the work loop should deal with workInProgressRootRenderLanes.
  // Most things in begin/complete phases should deal with subtreeRenderLanes.
  export let subtreeRenderLanes: Lanes = NoLanes;
  const subtreeRenderLanesCursor: StackCursor<Lanes> = createCursor(NoLanes);
  
  // Whether to root completed, errored, suspended, etc.
  let workInProgressRootExitStatus: RootExitStatus = RootIncomplete;
  // A fatal error, if one is thrown
  let workInProgressRootFatalError: mixed = null;
  // "Included" lanes refer to lanes that were worked on during this render. It's
  // slightly different than `renderLanes` because `renderLanes` can change as you
  // enter and exit an Offscreen tree. This value is the combination of all render
  // lanes for the entire render phase.
  let workInProgressRootIncludedLanes: Lanes = NoLanes;
  // The work left over by components that were visited during this render. Only
  // includes unprocessed updates, not work in bailed out children.
  let workInProgressRootSkippedLanes: Lanes = NoLanes;
  // Lanes that were updated (in an interleaved event) during this render.
  let workInProgressRootUpdatedLanes: Lanes = NoLanes;
  // Lanes that were pinged (in an interleaved event) during this render.
  let workInProgressRootPingedLanes: Lanes = NoLanes;
  
  // The most recent time we committed a fallback. This lets us ensure a train
  // model where we don't commit new loading states in too quick succession.
  let globalMostRecentFallbackTime: number = 0;
  const FALLBACK_THROTTLE_MS: number = 500;
  
  // The absolute time for when we should start giving up on rendering
  // more and prefer CPU suspense heuristics instead.
  let workInProgressRootRenderTargetTime: number = Infinity;
  // How long a render is supposed to take before we start following CPU
  // suspense heuristics and opt out of rendering more content.
  const RENDER_TIMEOUT_MS = 500;
  
  function resetRenderTimer() {
    workInProgressRootRenderTargetTime = now() + RENDER_TIMEOUT_MS;
  }
  
  export function getRenderTargetTime(): number {
    return workInProgressRootRenderTargetTime;
  }
  
  let hasUncaughtError = false;
  let firstUncaughtError = null;
  let legacyErrorBoundariesThatAlreadyFailed: Set<mixed> | null = null;
  
  // Only used when enableProfilerNestedUpdateScheduledHook is true;
  // to track which root is currently committing layout effects.
  let rootCommittingMutationOrLayoutEffects: FiberRoot | null = null;
  
  let rootDoesHavePassiveEffects: boolean = false;
  let rootWithPendingPassiveEffects: FiberRoot | null = null;
  let pendingPassiveEffectsLanes: Lanes = NoLanes;
  let pendingPassiveProfilerEffects: Array<Fiber> = [];
  
  // Use these to prevent an infinite loop of nested updates
  const NESTED_UPDATE_LIMIT = 50;
  let nestedUpdateCount: number = 0;
  let rootWithNestedUpdates: FiberRoot | null = null;
  
  const NESTED_PASSIVE_UPDATE_LIMIT = 50;
  let nestedPassiveUpdateCount: number = 0;
  
  // Marks the need to reschedule pending interactions at these lanes
  // during the commit phase. This enables them to be traced across components
  // that spawn new work during render. E.g. hidden boundaries, suspended SSR
  // hydration or SuspenseList.
  // TODO: Can use a bitmask instead of an array
  let spawnedWorkDuringRender: null | Array<Lane | Lanes> = null;
  
  // If two updates are scheduled within the same event, we should treat their
  // event times as simultaneous, even if the actual clock time has advanced
  // between the first and second call.
  let currentEventTime: number = NoTimestamp;
  let currentEventTransitionLane: Lanes = NoLanes;
  
  // Dev only flag that tracks if passive effects are currently being flushed.
  // We warn about state updates for unmounted components differently in this case.
  let isFlushingPassiveEffects = false;
  
  export function getWorkInProgressRoot(): FiberRoot | null {
    return workInProgressRoot;
  }
  
  export function requestEventTime() {
    if ((executionContext & (RenderContext | CommitContext)) !== NoContext) {
      // We're inside React, so it's fine to read the actual time.
      return now();
    }
    // We're not inside React, so we may be in the middle of a browser event.
    if (currentEventTime !== NoTimestamp) {
      // Use the same start time for all updates until we enter React again.
      return currentEventTime;
    }
    // This is the first update since React yielded. Compute a new start time.
    currentEventTime = now();
    return currentEventTime;
  }
  
  export function getCurrentTime() {
    return now();
  }
  
  export function requestUpdateLane(fiber: Fiber): Lane {
    // Special cases
    const mode = fiber.mode;
    if ((mode & ConcurrentMode) === NoMode) {
      return (SyncLane: Lane);
    } else if (
      !deferRenderPhaseUpdateToNextBatch &&
      (executionContext & RenderContext) !== NoContext &&
      workInProgressRootRenderLanes !== NoLanes
    ) {
      // This is a render phase update. These are not officially supported. The
      // old behavior is to give this the same "thread" (expiration time) as
      // whatever is currently rendering. So if you call `setState` on a component
      // that happens later in the same render, it will flush. Ideally, we want to
      // remove the special case and treat them as if they came from an
      // interleaved event. Regardless, this pattern is not officially supported.
      // This behavior is only a fallback. The flag only exists until we can roll
      // out the setState warning, since existing code might accidentally rely on
      // the current behavior.
      return pickArbitraryLane(workInProgressRootRenderLanes);
    }
  
    const isTransition = requestCurrentTransition() !== NoTransition;
    if (isTransition) {
      // The algorithm for assigning an update to a lane should be stable for all
      // updates at the same priority within the same event. To do this, the
      // inputs to the algorithm must be the same.
      //
      // The trick we use is to cache the first of each of these inputs within an
      // event. Then reset the cached values once we can be sure the event is
      // over. Our heuristic for that is whenever we enter a concurrent work loop.
      if (currentEventTransitionLane === NoLane) {
        // All transitions within the same event are assigned the same lane.
        currentEventTransitionLane = claimNextTransitionLane();
      }
      return currentEventTransitionLane;
    }
  
    // Updates originating inside certain React methods, like flushSync, have
    // their priority set by tracking it with a context variable.
    //
    // The opaque type returned by the host config is internally a lane, so we can
    // use that directly.
    // TODO: Move this type conversion to the event priority module.
    const updateLane: Lane = (getCurrentUpdatePriority(): any);
    if (updateLane !== NoLane) {
      return updateLane;
    }
  
    // This update originated outside React. Ask the host environement for an
    // appropriate priority, based on the type of event.
    //
    // The opaque type returned by the host config is internally a lane, so we can
    // use that directly.
    // TODO: Move this type conversion to the event priority module.
    const eventLane: Lane = (getCurrentEventPriority(): any);
    return eventLane;
  }
  
  function requestRetryLane(fiber: Fiber) {
    // This is a fork of `requestUpdateLane` designed specifically for Suspense
    // "retries" — a special update that attempts to flip a Suspense boundary
    // from its placeholder state to its primary/resolved state.
  
    // Special cases
    const mode = fiber.mode;
    if ((mode & ConcurrentMode) === NoMode) {
      return (SyncLane: Lane);
    }
  
    return claimNextRetryLane();
  }
  
  export function scheduleUpdateOnFiber(
    fiber: Fiber,
    lane: Lane,
    eventTime: number,
  ): FiberRoot | null {
    checkForNestedUpdates();
    warnAboutRenderPhaseUpdatesInDEV(fiber);
  
    const root = markUpdateLaneFromFiberToRoot(fiber, lane);
    if (root === null) {
      warnAboutUpdateOnUnmountedFiberInDEV(fiber);
      return null;
    }
  
    // Mark that the root has a pending update.
    markRootUpdated(root, lane, eventTime);
  
    if (enableProfilerTimer && enableProfilerNestedUpdateScheduledHook) {
      if (
        (executionContext & CommitContext) !== NoContext &&
        root === rootCommittingMutationOrLayoutEffects
      ) {
        if (fiber.mode & ProfileMode) {
          let current = fiber;
          while (current !== null) {
            if (current.tag === Profiler) {
              const {id, onNestedUpdateScheduled} = current.memoizedProps;
              if (typeof onNestedUpdateScheduled === 'function') {
                if (enableSchedulerTracing) {
                  onNestedUpdateScheduled(id, root.memoizedInteractions);
                } else {
                  onNestedUpdateScheduled(id);
                }
              }
            }
            current = current.return;
          }
        }
      }
    }
  
    // TODO: Consolidate with `isInterleavedUpdate` check
    if (root === workInProgressRoot) {
      // Received an update to a tree that's in the middle of rendering. Mark
      // that there was an interleaved update work on this root. Unless the
      // `deferRenderPhaseUpdateToNextBatch` flag is off and this is a render
      // phase update. In that case, we don't treat render phase updates as if
      // they were interleaved, for backwards compat reasons.
      if (
        deferRenderPhaseUpdateToNextBatch ||
        (executionContext & RenderContext) === NoContext
      ) {
        workInProgressRootUpdatedLanes = mergeLanes(
          workInProgressRootUpdatedLanes,
          lane,
        );
      }
      if (workInProgressRootExitStatus === RootSuspendedWithDelay) {
        // The root already suspended with a delay, which means this render
        // definitely won't finish. Since we have a new update, let's mark it as
        // suspended now, right before marking the incoming update. This has the
        // effect of interrupting the current render and switching to the update.
        // TODO: Make sure this doesn't override pings that happen while we've
        // already started rendering.
        markRootSuspended(root, workInProgressRootRenderLanes);
      }
    }
  
    if (lane === SyncLane) {
      if (
        // Check if we're inside unbatchedUpdates
        (executionContext & LegacyUnbatchedContext) !== NoContext &&
        // Check if we're not already rendering
        (executionContext & (RenderContext | CommitContext)) === NoContext
      ) {
        // Register pending interactions on the root to avoid losing traced interaction data.
        schedulePendingInteractions(root, lane);
  
        // This is a legacy edge case. The initial mount of a ReactDOM.render-ed
        // root inside of batchedUpdates should be synchronous, but layout updates
        // should be deferred until the end of the batch.
        performSyncWorkOnRoot(root);
      } else {
        ensureRootIsScheduled(root, eventTime);
        schedulePendingInteractions(root, lane);
        if (
          executionContext === NoContext &&
          (fiber.mode & ConcurrentMode) === NoMode
        ) {
          // Flush the synchronous work now, unless we're already working or inside
          // a batch. This is intentionally inside scheduleUpdateOnFiber instead of
          // scheduleCallbackForFiber to preserve the ability to schedule a callback
          // without immediately flushing it. We only do this for user-initiated
          // updates, to preserve historical behavior of legacy mode.
          resetRenderTimer();
          flushSyncCallbackQueue();
        }
      }
    } else {
      // Schedule other updates after in case the callback is sync.
      ensureRootIsScheduled(root, eventTime);
      schedulePendingInteractions(root, lane);
    }
  
    return root;
  }
  
  // This is split into a separate function so we can mark a fiber with pending
  // work without treating it as a typical update that originates from an event;
  // e.g. retrying a Suspense boundary isn't an update, but it does schedule work
  // on a fiber.
  function markUpdateLaneFromFiberToRoot(
    sourceFiber: Fiber,
    lane: Lane,
  ): FiberRoot | null {
    // Update the source fiber's lanes
    sourceFiber.lanes = mergeLanes(sourceFiber.lanes, lane);
    let alternate = sourceFiber.alternate;
    if (alternate !== null) {
      alternate.lanes = mergeLanes(alternate.lanes, lane);
    }
    if (__DEV__) {
      if (
        alternate === null &&
        (sourceFiber.flags & (Placement | Hydrating)) !== NoFlags
      ) {
        warnAboutUpdateOnNotYetMountedFiberInDEV(sourceFiber);
      }
    }
    // Walk the parent path to the root and update the child lanes.
    let node = sourceFiber;
    let parent = sourceFiber.return;
    while (parent !== null) {
      parent.childLanes = mergeLanes(parent.childLanes, lane);
      alternate = parent.alternate;
      if (alternate !== null) {
        alternate.childLanes = mergeLanes(alternate.childLanes, lane);
      } else {
        if (__DEV__) {
          if ((parent.flags & (Placement | Hydrating)) !== NoFlags) {
            warnAboutUpdateOnNotYetMountedFiberInDEV(sourceFiber);
          }
        }
      }
      node = parent;
      parent = parent.return;
    }
    if (node.tag === HostRoot) {
      const root: FiberRoot = node.stateNode;
      return root;
    } else {
      return null;
    }
  }
  
  export function isInterleavedUpdate(fiber: Fiber, lane: Lane) {
    return (
      // TODO: Optimize slightly by comparing to root that fiber belongs to.
      // Requires some refactoring. Not a big deal though since it's rare for
      // concurrent apps to have more than a single root.
      workInProgressRoot !== null &&
      (fiber.mode & ConcurrentMode) !== NoMode &&
      // If this is a render phase update (i.e. UNSAFE_componentWillReceiveProps),
      // then don't treat this as an interleaved update. This pattern is
      // accompanied by a warning but we haven't fully deprecated it yet. We can
      // remove once the deferRenderPhaseUpdateToNextBatch flag is enabled.
      (deferRenderPhaseUpdateToNextBatch ||
        (executionContext & RenderContext) === NoContext)
    );
  }
  
  // Use this function to schedule a task for a root. There's only one task per
  // root; if a task was already scheduled, we'll check to make sure the priority
  // of the existing task is the same as the priority of the next level that the
  // root has work on. This function is called on every update, and right before
  // exiting a task.
  function ensureRootIsScheduled(root: FiberRoot, currentTime: number) {
    const existingCallbackNode = root.callbackNode;
  
    // Check if any lanes are being starved by other work. If so, mark them as
    // expired so we know to work on those next.
    markStarvedLanesAsExpired(root, currentTime);
  
    // Determine the next lanes to work on, and their priority.
    const nextLanes = getNextLanes(
      root,
      root === workInProgressRoot ? workInProgressRootRenderLanes : NoLanes,
    );
  
    if (nextLanes === NoLanes) {
      // Special case: There's nothing to work on.
      if (existingCallbackNode !== null) {
        cancelCallback(existingCallbackNode);
      }
      root.callbackNode = null;
      root.callbackPriority = NoLane;
      return;
    }
  
    // We use the highest priority lane to represent the priority of the callback.
    const newCallbackPriority = getHighestPriorityLane(nextLanes);
  
    // Check if there's an existing task. We may be able to reuse it.
    const existingCallbackPriority = root.callbackPriority;
    if (existingCallbackPriority === newCallbackPriority) {
      if (__DEV__) {
        // If we're going to re-use an existing task, it needs to exist.
        // Assume that discrete update microtasks are non-cancellable and null.
        // TODO: Temporary until we confirm this warning is not fired.
        if (
          existingCallbackNode == null &&
          existingCallbackPriority !== SyncLane
        ) {
          console.error(
            'Expected scheduled callback to exist. This error is likely caused by a bug in React. Please file an issue.',
          );
        }
      }
      // The priority hasn't changed. We can reuse the existing task. Exit.
      return;
    }
  
    if (existingCallbackNode != null) {
      // Cancel the existing callback. We'll schedule a new one below.
      cancelCallback(existingCallbackNode);
    }
  
    // Schedule a new callback.
    let newCallbackNode;
    if (newCallbackPriority === SyncLane) {
      // Special case: Sync React callbacks are scheduled on a special
      // internal queue
      scheduleSyncCallback(performSyncWorkOnRoot.bind(null, root));
      if (supportsMicrotasks) {
        // Flush the queue in a microtask.
        scheduleMicrotask(flushSyncCallbackQueue);
      } else {
        // Flush the queue in an Immediate task.
        scheduleCallback(ImmediateSchedulerPriority, flushSyncCallbackQueue);
      }
      newCallbackNode = null;
    } else {
      let schedulerPriorityLevel;
      switch (lanesToEventPriority(nextLanes)) {
        case DiscreteEventPriority:
          schedulerPriorityLevel = ImmediateSchedulerPriority;
          break;
        case ContinuousEventPriority:
          schedulerPriorityLevel = UserBlockingSchedulerPriority;
          break;
        case DefaultEventPriority:
          schedulerPriorityLevel = NormalSchedulerPriority;
          break;
        case IdleEventPriority:
          schedulerPriorityLevel = IdleSchedulerPriority;
          break;
        default:
          schedulerPriorityLevel = NormalSchedulerPriority;
          break;
      }
      newCallbackNode = scheduleCallback(
        schedulerPriorityLevel,
        performConcurrentWorkOnRoot.bind(null, root),
      );
    }
  
    root.callbackPriority = newCallbackPriority;
    root.callbackNode = newCallbackNode;
  }
  
  // This is the entry point for every concurrent task, i.e. anything that
  // goes through Scheduler.
  function performConcurrentWorkOnRoot(root, didTimeout) {
    if (enableProfilerTimer && enableProfilerNestedUpdatePhase) {
      resetNestedUpdateFlag();
    }
  
    // Since we know we're in a React event, we can clear the current
    // event time. The next update will compute a new event time.
    currentEventTime = NoTimestamp;
    currentEventTransitionLane = NoLanes;
  
    invariant(
      (executionContext & (RenderContext | CommitContext)) === NoContext,
      'Should not already be working.',
    );
  
    // Flush any pending passive effects before deciding which lanes to work on,
    // in case they schedule additional work.
    const originalCallbackNode = root.callbackNode;
    const didFlushPassiveEffects = flushPassiveEffects();
    if (didFlushPassiveEffects) {
      // Something in the passive effect phase may have canceled the current task.
      // Check if the task node for this root was changed.
      if (root.callbackNode !== originalCallbackNode) {
        // The current task was canceled. Exit. We don't need to call
        // `ensureRootIsScheduled` because the check above implies either that
        // there's a new task, or that there's no remaining work on this root.
        return null;
      } else {
        // Current task was not canceled. Continue.
      }
    }
  
    // Determine the next expiration time to work on, using the fields stored
    // on the root.
    let lanes = getNextLanes(
      root,
      root === workInProgressRoot ? workInProgressRootRenderLanes : NoLanes,
    );
    if (lanes === NoLanes) {
      // Defensive coding. This is never expected to happen.
      return null;
    }
  
    // TODO: We only check `didTimeout` defensively, to account for a Scheduler
    // bug we're still investigating. Once the bug in Scheduler is fixed,
    // we can remove this, since we track expiration ourselves.
    if (!disableSchedulerTimeoutInWorkLoop && didTimeout) {
      // Something expired. Flush synchronously until there's no expired
      // work left.
      markRootExpired(root, lanes);
      // This will schedule a synchronous callback.
      ensureRootIsScheduled(root, now());
      return null;
    }
  
    let exitStatus = renderRootConcurrent(root, lanes);
    if (exitStatus !== RootIncomplete) {
      if (exitStatus === RootErrored) {
        executionContext |= RetryAfterError;
  
        // If an error occurred during hydration,
        // discard server response and fall back to client side render.
        if (root.hydrate) {
          root.hydrate = false;
          if (__DEV__) {
            errorHydratingContainer(root.containerInfo);
          }
          clearContainer(root.containerInfo);
        }
  
        // If something threw an error, try rendering one more time. We'll render
        // synchronously to block concurrent data mutations, and we'll includes
        // all pending updates are included. If it still fails after the second
        // attempt, we'll give up and commit the resulting tree.
        lanes = getLanesToRetrySynchronouslyOnError(root);
        if (lanes !== NoLanes) {
          exitStatus = renderRootSync(root, lanes);
        }
      }
  
      if (exitStatus === RootFatalErrored) {
        const fatalError = workInProgressRootFatalError;
        prepareFreshStack(root, NoLanes);
        markRootSuspended(root, lanes);
        ensureRootIsScheduled(root, now());
        throw fatalError;
      }
  
      // We now have a consistent tree. The next step is either to commit it,
      // or, if something suspended, wait to commit it after a timeout.
      const finishedWork: Fiber = (root.current.alternate: any);
      root.finishedWork = finishedWork;
      root.finishedLanes = lanes;
      finishConcurrentRender(root, exitStatus, lanes);
    }
  
    ensureRootIsScheduled(root, now());
    if (root.callbackNode === originalCallbackNode) {
      // The task node scheduled for this root is the same one that's
      // currently executed. Need to return a continuation.
      return performConcurrentWorkOnRoot.bind(null, root);
    }
    return null;
  }
  
  function finishConcurrentRender(root, exitStatus, lanes) {
    switch (exitStatus) {
      case RootIncomplete:
      case RootFatalErrored: {
        invariant(false, 'Root did not complete. This is a bug in React.');
      }
      // Flow knows about invariant, so it complains if I add a break
      // statement, but eslint doesn't know about invariant, so it complains
      // if I do. eslint-disable-next-line no-fallthrough
      case RootErrored: {
        // We should have already attempted to retry this tree. If we reached
        // this point, it errored again. Commit it.
        commitRoot(root);
        break;
      }
      case RootSuspended: {
        markRootSuspended(root, lanes);
  
        // We have an acceptable loading state. We need to figure out if we
        // should immediately commit it or wait a bit.
  
        if (
          includesOnlyRetries(lanes) &&
          // do not delay if we're inside an act() scope
          !shouldForceFlushFallbacksInDEV()
        ) {
          // This render only included retries, no updates. Throttle committing
          // retries so that we don't show too many loading states too quickly.
          const msUntilTimeout =
            globalMostRecentFallbackTime + FALLBACK_THROTTLE_MS - now();
          // Don't bother with a very short suspense time.
          if (msUntilTimeout > 10) {
            const nextLanes = getNextLanes(root, NoLanes);
            if (nextLanes !== NoLanes) {
              // There's additional work on this root.
              break;
            }
            const suspendedLanes = root.suspendedLanes;
            if (!isSubsetOfLanes(suspendedLanes, lanes)) {
              // We should prefer to render the fallback of at the last
              // suspended level. Ping the last suspended level to try
              // rendering it again.
              // FIXME: What if the suspended lanes are Idle? Should not restart.
              const eventTime = requestEventTime();
              markRootPinged(root, suspendedLanes, eventTime);
              break;
            }
  
            // The render is suspended, it hasn't timed out, and there's no
            // lower priority work to do. Instead of committing the fallback
            // immediately, wait for more data to arrive.
            root.timeoutHandle = scheduleTimeout(
              commitRoot.bind(null, root),
              msUntilTimeout,
            );
            break;
          }
        }
        // The work expired. Commit immediately.
        commitRoot(root);
        break;
      }
      case RootSuspendedWithDelay: {
        markRootSuspended(root, lanes);
  
        if (includesOnlyTransitions(lanes)) {
          // This is a transition, so we should exit without committing a
          // placeholder and without scheduling a timeout. Delay indefinitely
          // until we receive more data.
          break;
        }
  
        if (!shouldForceFlushFallbacksInDEV()) {
          // This is not a transition, but we did trigger an avoided state.
          // Schedule a placeholder to display after a short delay, using the Just
          // Noticeable Difference.
          // TODO: Is the JND optimization worth the added complexity? If this is
          // the only reason we track the event time, then probably not.
          // Consider removing.
  
          const mostRecentEventTime = getMostRecentEventTime(root, lanes);
          const eventTimeMs = mostRecentEventTime;
          const timeElapsedMs = now() - eventTimeMs;
          const msUntilTimeout = jnd(timeElapsedMs) - timeElapsedMs;
  
          // Don't bother with a very short suspense time.
          if (msUntilTimeout > 10) {
            // Instead of committing the fallback immediately, wait for more data
            // to arrive.
            root.timeoutHandle = scheduleTimeout(
              commitRoot.bind(null, root),
              msUntilTimeout,
            );
            break;
          }
        }
  
        // Commit the placeholder.
        commitRoot(root);
        break;
      }
      case RootCompleted: {
        // The work completed. Ready to commit.
        commitRoot(root);
        break;
      }
      default: {
        invariant(false, 'Unknown root exit status.');
      }
    }
  }
  
  function markRootSuspended(root, suspendedLanes) {
    // When suspending, we should always exclude lanes that were pinged or (more
    // rarely, since we try to avoid it) updated during the render phase.
    // TODO: Lol maybe there's a better way to factor this besides this
    // obnoxiously named function :)
    suspendedLanes = removeLanes(suspendedLanes, workInProgressRootPingedLanes);
    suspendedLanes = removeLanes(suspendedLanes, workInProgressRootUpdatedLanes);
    markRootSuspended_dontCallThisOneDirectly(root, suspendedLanes);
  }
  
  // This is the entry point for synchronous tasks that don't go
  // through Scheduler
  function performSyncWorkOnRoot(root) {
    if (enableProfilerTimer && enableProfilerNestedUpdatePhase) {
      syncNestedUpdateFlag();
    }
  
    invariant(
      (executionContext & (RenderContext | CommitContext)) === NoContext,
      'Should not already be working.',
    );
  
    flushPassiveEffects();
  
    let lanes;
    let exitStatus;
    if (
      root === workInProgressRoot &&
      areLanesExpired(root, workInProgressRootRenderLanes)
    ) {
      // There's a partial tree, and at least one of its lanes has expired. Finish
      // rendering it before rendering the rest of the expired work.
      lanes = workInProgressRootRenderLanes;
      exitStatus = renderRootSync(root, lanes);
    } else {
      lanes = getNextLanes(root, NoLanes);
      exitStatus = renderRootSync(root, lanes);
    }
  
    if (root.tag !== LegacyRoot && exitStatus === RootErrored) {
      executionContext |= RetryAfterError;
  
      // If an error occurred during hydration,
      // discard server response and fall back to client side render.
      if (root.hydrate) {
        root.hydrate = false;
        if (__DEV__) {
          errorHydratingContainer(root.containerInfo);
        }
        clearContainer(root.containerInfo);
      }
  
      // If something threw an error, try rendering one more time. We'll render
      // synchronously to block concurrent data mutations, and we'll includes
      // all pending updates are included. If it still fails after the second
      // attempt, we'll give up and commit the resulting tree.
      lanes = getLanesToRetrySynchronouslyOnError(root);
      if (lanes !== NoLanes) {
        exitStatus = renderRootSync(root, lanes);
      }
    }
  
    if (exitStatus === RootFatalErrored) {
      const fatalError = workInProgressRootFatalError;
      prepareFreshStack(root, NoLanes);
      markRootSuspended(root, lanes);
      ensureRootIsScheduled(root, now());
      throw fatalError;
    }
  
    // We now have a consistent tree. Because this is a sync render, we
    // will commit it even if something suspended.
    const finishedWork: Fiber = (root.current.alternate: any);
    root.finishedWork = finishedWork;
    root.finishedLanes = lanes;
    commitRoot(root);
  
    // Before exiting, make sure there's a callback scheduled for the next
    // pending level.
    ensureRootIsScheduled(root, now());
  
    return null;
  }
  
  // TODO: Do we still need this API? I think we can delete it. Was only used
  // internally.
  export function flushRoot(root: FiberRoot, lanes: Lanes) {
    if (lanes !== NoLanes) {
      markRootExpired(root, lanes);
      ensureRootIsScheduled(root, now());
      if ((executionContext & (RenderContext | CommitContext)) === NoContext) {
        resetRenderTimer();
        flushSyncCallbackQueue();
      }
    }
  }
  
  export function getExecutionContext(): ExecutionContext {
    return executionContext;
  }
  
  export function flushDiscreteUpdates() {
    // TODO: Should be able to flush inside batchedUpdates, but not inside `act`.
    // However, `act` uses `batchedUpdates`, so there's no way to distinguish
    // those two cases. Need to fix this before exposing flushDiscreteUpdates
    // as a public API.
    if (
      (executionContext & (BatchedContext | RenderContext | CommitContext)) !==
      NoContext
    ) {
      if (__DEV__) {
        if ((executionContext & RenderContext) !== NoContext) {
          console.error(
            'unstable_flushDiscreteUpdates: Cannot flush updates when React is ' +
              'already rendering.',
          );
        }
      }
      // We're already rendering, so we can't synchronously flush pending work.
      // This is probably a nested event dispatch triggered by a lifecycle/effect,
      // like `el.focus()`. Exit.
      return;
    }
    flushSyncCallbackQueue();
    // If the discrete updates scheduled passive effects, flush them now so that
    // they fire before the next serial event.
    flushPassiveEffects();
  }
  
  export function deferredUpdates<A>(fn: () => A): A {
    const previousPriority = getCurrentUpdatePriority();
    const prevTransition = ReactCurrentBatchConfig.transition;
    try {
      ReactCurrentBatchConfig.transition = 0;
      setCurrentUpdatePriority(DefaultEventPriority);
      return fn();
    } finally {
      setCurrentUpdatePriority(previousPriority);
      ReactCurrentBatchConfig.transition = prevTransition;
    }
  }
  
  export function batchedUpdates<A, R>(fn: A => R, a: A): R {
    const prevExecutionContext = executionContext;
    executionContext |= BatchedContext;
    try {
      return fn(a);
    } finally {
      executionContext = prevExecutionContext;
      if (executionContext === NoContext) {
        // Flush the immediate callbacks that were scheduled during this batch
        resetRenderTimer();
        flushSyncCallbackQueue();
      }
    }
  }
  
  export function batchedEventUpdates<A, R>(fn: A => R, a: A): R {
    const prevExecutionContext = executionContext;
    executionContext |= EventContext;
    try {
      return fn(a);
    } finally {
      executionContext = prevExecutionContext;
      if (executionContext === NoContext) {
        // Flush the immediate callbacks that were scheduled during this batch
        resetRenderTimer();
        flushSyncCallbackQueue();
      }
    }
  }
  
  export function discreteUpdates<A, B, C, D, R>(
    fn: (A, B, C, D) => R,
    a: A,
    b: B,
    c: C,
    d: D,
  ): R {
    const previousPriority = getCurrentUpdatePriority();
    const prevTransition = ReactCurrentBatchConfig.transition;
    try {
      ReactCurrentBatchConfig.transition = 0;
      setCurrentUpdatePriority(DiscreteEventPriority);
      return fn(a, b, c, d);
    } finally {
      setCurrentUpdatePriority(previousPriority);
      ReactCurrentBatchConfig.transition = prevTransition;
      if (executionContext === NoContext) {
        // Flush the immediate callbacks that were scheduled during this batch
        resetRenderTimer();
        flushSyncCallbackQueue();
      }
    }
  }
  
  export function unbatchedUpdates<A, R>(fn: (a: A) => R, a: A): R {
    const prevExecutionContext = executionContext;
    executionContext &= ~BatchedContext;
    executionContext |= LegacyUnbatchedContext;
    try {
      return fn(a);
    } finally {
      executionContext = prevExecutionContext;
      if (executionContext === NoContext) {
        // Flush the immediate callbacks that were scheduled during this batch
        resetRenderTimer();
        flushSyncCallbackQueue();
      }
    }
  }
  
  export function flushSync<A, R>(fn: A => R, a: A): R {
    const prevExecutionContext = executionContext;
    executionContext |= BatchedContext;
  
    const prevTransition = ReactCurrentBatchConfig.transition;
    const previousPriority = getCurrentUpdatePriority();
    try {
      ReactCurrentBatchConfig.transition = 0;
      setCurrentUpdatePriority(DiscreteEventPriority);
      if (fn) {
        return fn(a);
      } else {
        return (undefined: $FlowFixMe);
      }
    } finally {
      setCurrentUpdatePriority(previousPriority);
      ReactCurrentBatchConfig.transition = prevTransition;
      executionContext = prevExecutionContext;
      // Flush the immediate callbacks that were scheduled during this batch.
      // Note that this will happen even if batchedUpdates is higher up
      // the stack.
      if ((executionContext & (RenderContext | CommitContext)) === NoContext) {
        flushSyncCallbackQueue();
      } else {
        if (__DEV__) {
          console.error(
            'flushSync was called from inside a lifecycle method. React cannot ' +
              'flush when React is already rendering. Consider moving this call to ' +
              'a scheduler task or micro task.',
          );
        }
      }
    }
  }
  
  export function flushControlled(fn: () => mixed): void {
    const prevExecutionContext = executionContext;
    executionContext |= BatchedContext;
    const prevTransition = ReactCurrentBatchConfig.transition;
    const previousPriority = getCurrentUpdatePriority();
    try {
      ReactCurrentBatchConfig.transition = 0;
      setCurrentUpdatePriority(DiscreteEventPriority);
      fn();
    } finally {
      setCurrentUpdatePriority(previousPriority);
      ReactCurrentBatchConfig.transition = prevTransition;
  
      executionContext = prevExecutionContext;
      if (executionContext === NoContext) {
        // Flush the immediate callbacks that were scheduled during this batch
        resetRenderTimer();
        flushSyncCallbackQueue();
      }
    }
  }
  
  export function pushRenderLanes(fiber: Fiber, lanes: Lanes) {
    pushToStack(subtreeRenderLanesCursor, subtreeRenderLanes, fiber);
    subtreeRenderLanes = mergeLanes(subtreeRenderLanes, lanes);
    workInProgressRootIncludedLanes = mergeLanes(
      workInProgressRootIncludedLanes,
      lanes,
    );
  }
  
  export function popRenderLanes(fiber: Fiber) {
    subtreeRenderLanes = subtreeRenderLanesCursor.current;
    popFromStack(subtreeRenderLanesCursor, fiber);
  }
  
  function prepareFreshStack(root: FiberRoot, lanes: Lanes) {
    root.finishedWork = null;
    root.finishedLanes = NoLanes;
  
    const timeoutHandle = root.timeoutHandle;
    if (timeoutHandle !== noTimeout) {
      // The root previous suspended and scheduled a timeout to commit a fallback
      // state. Now that we have additional work, cancel the timeout.
      root.timeoutHandle = noTimeout;
      // $FlowFixMe Complains noTimeout is not a TimeoutID, despite the check above
      cancelTimeout(timeoutHandle);
    }
  
    if (workInProgress !== null) {
      let interruptedWork = workInProgress.return;
      while (interruptedWork !== null) {
        unwindInterruptedWork(interruptedWork, workInProgressRootRenderLanes);
        interruptedWork = interruptedWork.return;
      }
    }
    workInProgressRoot = root;
    workInProgress = createWorkInProgress(root.current, null);
    workInProgressRootRenderLanes = subtreeRenderLanes = workInProgressRootIncludedLanes = lanes;
    workInProgressRootExitStatus = RootIncomplete;
    workInProgressRootFatalError = null;
    workInProgressRootSkippedLanes = NoLanes;
    workInProgressRootUpdatedLanes = NoLanes;
    workInProgressRootPingedLanes = NoLanes;
  
    enqueueInterleavedUpdates();
  
    if (enableSchedulerTracing) {
      spawnedWorkDuringRender = null;
    }
  
    if (__DEV__) {
      ReactStrictModeWarnings.discardPendingWarnings();
    }
  }
  
  function handleError(root, thrownValue): void {
    do {
      let erroredWork = workInProgress;
      try {
        // Reset module-level state that was set during the render phase.
        resetContextDependencies();
        resetHooksAfterThrow();
        resetCurrentDebugFiberInDEV();
        // TODO: I found and added this missing line while investigating a
        // separate issue. Write a regression test using string refs.
        ReactCurrentOwner.current = null;
  
        if (erroredWork === null || erroredWork.return === null) {
          // Expected to be working on a non-root fiber. This is a fatal error
          // because there's no ancestor that can handle it; the root is
          // supposed to capture all errors that weren't caught by an error
          // boundary.
          workInProgressRootExitStatus = RootFatalErrored;
          workInProgressRootFatalError = thrownValue;
          // Set `workInProgress` to null. This represents advancing to the next
          // sibling, or the parent if there are no siblings. But since the root
          // has no siblings nor a parent, we set it to null. Usually this is
          // handled by `completeUnitOfWork` or `unwindWork`, but since we're
          // intentionally not calling those, we need set it here.
          // TODO: Consider calling `unwindWork` to pop the contexts.
          workInProgress = null;
          return;
        }
  
        if (enableProfilerTimer && erroredWork.mode & ProfileMode) {
          // Record the time spent rendering before an error was thrown. This
          // avoids inaccurate Profiler durations in the case of a
          // suspended render.
          stopProfilerTimerIfRunningAndRecordDelta(erroredWork, true);
        }
  
        throwException(
          root,
          erroredWork.return,
          erroredWork,
          thrownValue,
          workInProgressRootRenderLanes,
        );
        completeUnitOfWork(erroredWork);
      } catch (yetAnotherThrownValue) {
        // Something in the return path also threw.
        thrownValue = yetAnotherThrownValue;
        if (workInProgress === erroredWork && erroredWork !== null) {
          // If this boundary has already errored, then we had trouble processing
          // the error. Bubble it to the next boundary.
          erroredWork = erroredWork.return;
          workInProgress = erroredWork;
        } else {
          erroredWork = workInProgress;
        }
        continue;
      }
      // Return to the normal work loop.
      return;
    } while (true);
  }
  
  function pushDispatcher() {
    const prevDispatcher = ReactCurrentDispatcher.current;
    ReactCurrentDispatcher.current = ContextOnlyDispatcher;
    if (prevDispatcher === null) {
      // The React isomorphic package does not include a default dispatcher.
      // Instead the first renderer will lazily attach one, in order to give
      // nicer error messages.
      return ContextOnlyDispatcher;
    } else {
      return prevDispatcher;
    }
  }
  
  function popDispatcher(prevDispatcher) {
    ReactCurrentDispatcher.current = prevDispatcher;
  }
  
  function pushInteractions(root) {
    if (enableSchedulerTracing) {
      const prevInteractions: Set<Interaction> | null = __interactionsRef.current;
      __interactionsRef.current = root.memoizedInteractions;
      return prevInteractions;
    }
    return null;
  }
  
  function popInteractions(prevInteractions) {
    if (enableSchedulerTracing) {
      __interactionsRef.current = prevInteractions;
    }
  }
  
  export function markCommitTimeOfFallback() {
    globalMostRecentFallbackTime = now();
  }
  
  export function markSkippedUpdateLanes(lane: Lane | Lanes): void {
    workInProgressRootSkippedLanes = mergeLanes(
      lane,
      workInProgressRootSkippedLanes,
    );
  }
  
  export function renderDidSuspend(): void {
    if (workInProgressRootExitStatus === RootIncomplete) {
      workInProgressRootExitStatus = RootSuspended;
    }
  }
  
  export function renderDidSuspendDelayIfPossible(): void {
    if (
      workInProgressRootExitStatus === RootIncomplete ||
      workInProgressRootExitStatus === RootSuspended
    ) {
      workInProgressRootExitStatus = RootSuspendedWithDelay;
    }
  
    // Check if there are updates that we skipped tree that might have unblocked
    // this render.
    if (
      workInProgressRoot !== null &&
      (includesNonIdleWork(workInProgressRootSkippedLanes) ||
        includesNonIdleWork(workInProgressRootUpdatedLanes))
    ) {
      // Mark the current render as suspended so that we switch to working on
      // the updates that were skipped. Usually we only suspend at the end of
      // the render phase.
      // TODO: We should probably always mark the root as suspended immediately
      // (inside this function), since by suspending at the end of the render
      // phase introduces a potential mistake where we suspend lanes that were
      // pinged or updated while we were rendering.
      markRootSuspended(workInProgressRoot, workInProgressRootRenderLanes);
    }
  }
  
  export function renderDidError() {
    if (workInProgressRootExitStatus !== RootCompleted) {
      workInProgressRootExitStatus = RootErrored;
    }
  }
  
  // Called during render to determine if anything has suspended.
  // Returns false if we're not sure.
  export function renderHasNotSuspendedYet(): boolean {
    // If something errored or completed, we can't really be sure,
    // so those are false.
    return workInProgressRootExitStatus === RootIncomplete;
  }
  
  function renderRootSync(root: FiberRoot, lanes: Lanes) {
    const prevExecutionContext = executionContext;
    executionContext |= RenderContext;
    const prevDispatcher = pushDispatcher();
  
    // If the root or lanes have changed, throw out the existing stack
    // and prepare a fresh one. Otherwise we'll continue where we left off.
    if (workInProgressRoot !== root || workInProgressRootRenderLanes !== lanes) {
      prepareFreshStack(root, lanes);
      startWorkOnPendingInteractions(root, lanes);
    }
  
    const prevInteractions = pushInteractions(root);
  
    if (__DEV__) {
      if (enableDebugTracing) {
        logRenderStarted(lanes);
      }
    }
  
    if (enableSchedulingProfiler) {
      markRenderStarted(lanes);
    }
  
    do {
      try {
        workLoopSync();
        break;
      } catch (thrownValue) {
        handleError(root, thrownValue);
      }
    } while (true);
    resetContextDependencies();
    if (enableSchedulerTracing) {
      popInteractions(((prevInteractions: any): Set<Interaction>));
    }
  
    executionContext = prevExecutionContext;
    popDispatcher(prevDispatcher);
  
    if (workInProgress !== null) {
      // This is a sync render, so we should have finished the whole tree.
      invariant(
        false,
        'Cannot commit an incomplete root. This error is likely caused by a ' +
          'bug in React. Please file an issue.',
      );
    }
  
    if (__DEV__) {
      if (enableDebugTracing) {
        logRenderStopped();
      }
    }
  
    if (enableSchedulingProfiler) {
      markRenderStopped();
    }
  
    // Set this to null to indicate there's no in-progress render.
    workInProgressRoot = null;
    workInProgressRootRenderLanes = NoLanes;
  
    return workInProgressRootExitStatus;
  }
  
  // The work loop is an extremely hot path. Tell Closure not to inline it.
  /** @noinline */
  function workLoopSync() {
    // Already timed out, so perform work without checking if we need to yield.
    while (workInProgress !== null) {
      performUnitOfWork(workInProgress);
    }
  }
  
  function renderRootConcurrent(root: FiberRoot, lanes: Lanes) {
    const prevExecutionContext = executionContext;
    executionContext |= RenderContext;
    const prevDispatcher = pushDispatcher();
  
    // If the root or lanes have changed, throw out the existing stack
    // and prepare a fresh one. Otherwise we'll continue where we left off.
    if (workInProgressRoot !== root || workInProgressRootRenderLanes !== lanes) {
      resetRenderTimer();
      prepareFreshStack(root, lanes);
      startWorkOnPendingInteractions(root, lanes);
    }
  
    const prevInteractions = pushInteractions(root);
  
    if (__DEV__) {
      if (enableDebugTracing) {
        logRenderStarted(lanes);
      }
    }
  
    if (enableSchedulingProfiler) {
      markRenderStarted(lanes);
    }
  
    do {
      try {
        workLoopConcurrent();
        break;
      } catch (thrownValue) {
        handleError(root, thrownValue);
      }
    } while (true);
    resetContextDependencies();
    if (enableSchedulerTracing) {
      popInteractions(((prevInteractions: any): Set<Interaction>));
    }
  
    popDispatcher(prevDispatcher);
    executionContext = prevExecutionContext;
  
    if (__DEV__) {
      if (enableDebugTracing) {
        logRenderStopped();
      }
    }
  
    // Check if the tree has completed.
    if (workInProgress !== null) {
      // Still work remaining.
      if (enableSchedulingProfiler) {
        markRenderYielded();
      }
      return RootIncomplete;
    } else {
      // Completed the tree.
      if (enableSchedulingProfiler) {
        markRenderStopped();
      }
  
      // Set this to null to indicate there's no in-progress render.
      workInProgressRoot = null;
      workInProgressRootRenderLanes = NoLanes;
  
      // Return the final exit status.
      return workInProgressRootExitStatus;
    }
  }
  
  /** @noinline */
  function workLoopConcurrent() {
    // Perform work until Scheduler asks us to yield
    while (workInProgress !== null && !shouldYield()) {
      performUnitOfWork(workInProgress);
    }
  }
  
  function performUnitOfWork(unitOfWork: Fiber): void {
    // The current, flushed, state of this fiber is the alternate. Ideally
    // nothing should rely on this, but relying on it here means that we don't
    // need an additional field on the work in progress.
    const current = unitOfWork.alternate;
    setCurrentDebugFiberInDEV(unitOfWork);
  
    let next;
    if (enableProfilerTimer && (unitOfWork.mode & ProfileMode) !== NoMode) {
      startProfilerTimer(unitOfWork);
      next = beginWork(current, unitOfWork, subtreeRenderLanes);
      stopProfilerTimerIfRunningAndRecordDelta(unitOfWork, true);
    } else {
      next = beginWork(current, unitOfWork, subtreeRenderLanes);
    }
  
    resetCurrentDebugFiberInDEV();
    unitOfWork.memoizedProps = unitOfWork.pendingProps;
    if (next === null) {
      // If this doesn't spawn new work, complete the current work.
      completeUnitOfWork(unitOfWork);
    } else {
      workInProgress = next;
    }
  
    ReactCurrentOwner.current = null;
  }
  
  function completeUnitOfWork(unitOfWork: Fiber): void {
    // Attempt to complete the current unit of work, then move to the next
    // sibling. If there are no more siblings, return to the parent fiber.
    let completedWork = unitOfWork;
    do {
      // The current, flushed, state of this fiber is the alternate. Ideally
      // nothing should rely on this, but relying on it here means that we don't
      // need an additional field on the work in progress.
      const current = completedWork.alternate;
      const returnFiber = completedWork.return;
  
      // Check if the work completed or if something threw.
      if ((completedWork.flags & Incomplete) === NoFlags) {
        setCurrentDebugFiberInDEV(completedWork);
        let next;
        if (
          !enableProfilerTimer ||
          (completedWork.mode & ProfileMode) === NoMode
        ) {
          next = completeWork(current, completedWork, subtreeRenderLanes);
        } else {
          startProfilerTimer(completedWork);
          next = completeWork(current, completedWork, subtreeRenderLanes);
          // Update render duration assuming we didn't error.
          stopProfilerTimerIfRunningAndRecordDelta(completedWork, false);
        }
        resetCurrentDebugFiberInDEV();
  
        if (next !== null) {
          // Completing this fiber spawned new work. Work on that next.
          workInProgress = next;
          return;
        }
      } else {
        // This fiber did not complete because something threw. Pop values off
        // the stack without entering the complete phase. If this is a boundary,
        // capture values if possible.
        const next = unwindWork(completedWork, subtreeRenderLanes);
  
        // Because this fiber did not complete, don't reset its expiration time.
  
        if (next !== null) {
          // If completing this work spawned new work, do that next. We'll come
          // back here again.
          // Since we're restarting, remove anything that is not a host effect
          // from the effect tag.
          next.flags &= HostEffectMask;
          workInProgress = next;
          return;
        }
  
        if (
          enableProfilerTimer &&
          (completedWork.mode & ProfileMode) !== NoMode
        ) {
          // Record the render duration for the fiber that errored.
          stopProfilerTimerIfRunningAndRecordDelta(completedWork, false);
  
          // Include the time spent working on failed children before continuing.
          let actualDuration = completedWork.actualDuration;
          let child = completedWork.child;
          while (child !== null) {
            actualDuration += child.actualDuration;
            child = child.sibling;
          }
          completedWork.actualDuration = actualDuration;
        }
  
        if (returnFiber !== null) {
          // Mark the parent fiber as incomplete and clear its subtree flags.
          returnFiber.flags |= Incomplete;
          returnFiber.subtreeFlags = NoFlags;
          returnFiber.deletions = null;
        }
      }
  
      const siblingFiber = completedWork.sibling;
      if (siblingFiber !== null) {
        // If there is more work to do in this returnFiber, do that next.
        workInProgress = siblingFiber;
        return;
      }
      // Otherwise, return to the parent
      completedWork = returnFiber;
      // Update the next thing we're working on in case something throws.
      workInProgress = completedWork;
    } while (completedWork !== null);
  
    // We've reached the root.
    if (workInProgressRootExitStatus === RootIncomplete) {
      workInProgressRootExitStatus = RootCompleted;
    }
  }
  
  function commitRoot(root) {
    // TODO: This no longer makes any sense. We already wrap the mutation and
    // layout phases. Should be able to remove.
    const previousUpdateLanePriority = getCurrentUpdatePriority();
    const prevTransition = ReactCurrentBatchConfig.transition;
    try {
      ReactCurrentBatchConfig.transition = 0;
      setCurrentUpdatePriority(DiscreteEventPriority);
      commitRootImpl(root, previousUpdateLanePriority);
    } finally {
      ReactCurrentBatchConfig.transition = prevTransition;
      setCurrentUpdatePriority(previousUpdateLanePriority);
    }
  
    return null;
  }
  
  function commitRootImpl(root, renderPriorityLevel) {
    do {
      // `flushPassiveEffects` will call `flushSyncUpdateQueue` at the end, which
      // means `flushPassiveEffects` will sometimes result in additional
      // passive effects. So we need to keep flushing in a loop until there are
      // no more pending effects.
      // TODO: Might be better if `flushPassiveEffects` did not automatically
      // flush synchronous work at the end, to avoid factoring hazards like this.
      flushPassiveEffects();
    } while (rootWithPendingPassiveEffects !== null);
    flushRenderPhaseStrictModeWarningsInDEV();
  
    invariant(
      (executionContext & (RenderContext | CommitContext)) === NoContext,
      'Should not already be working.',
    );
  
    const finishedWork = root.finishedWork;
    const lanes = root.finishedLanes;
  
    if (__DEV__) {
      if (enableDebugTracing) {
        logCommitStarted(lanes);
      }
    }
  
    if (enableSchedulingProfiler) {
      markCommitStarted(lanes);
    }
  
    if (finishedWork === null) {
      if (__DEV__) {
        if (enableDebugTracing) {
          logCommitStopped();
        }
      }
  
      if (enableSchedulingProfiler) {
        markCommitStopped();
      }
  
      return null;
    }
    root.finishedWork = null;
    root.finishedLanes = NoLanes;
  
    invariant(
      finishedWork !== root.current,
      'Cannot commit the same tree as before. This error is likely caused by ' +
        'a bug in React. Please file an issue.',
    );
  
    // commitRoot never returns a continuation; it always finishes synchronously.
    // So we can clear these now to allow a new callback to be scheduled.
    root.callbackNode = null;
    root.callbackPriority = NoLane;
  
    // Update the first and last pending times on this root. The new first
    // pending time is whatever is left on the root fiber.
    let remainingLanes = mergeLanes(finishedWork.lanes, finishedWork.childLanes);
    markRootFinished(root, remainingLanes);
  
    if (root === workInProgressRoot) {
      // We can reset these now that they are finished.
      workInProgressRoot = null;
      workInProgress = null;
      workInProgressRootRenderLanes = NoLanes;
    } else {
      // This indicates that the last root we worked on is not the same one that
      // we're committing now. This most commonly happens when a suspended root
      // times out.
    }
  
    // If there are pending passive effects, schedule a callback to process them.
    // Do this as early as possible, so it is queued before anything else that
    // might get scheduled in the commit phase. (See #16714.)
    // TODO: Delete all other places that schedule the passive effect callback
    // They're redundant.
    if (
      (finishedWork.subtreeFlags & PassiveMask) !== NoFlags ||
      (finishedWork.flags & PassiveMask) !== NoFlags
    ) {
      if (!rootDoesHavePassiveEffects) {
        rootDoesHavePassiveEffects = true;
        scheduleCallback(NormalSchedulerPriority, () => {
          flushPassiveEffects();
          return null;
        });
      }
    }
  
    // Check if there are any effects in the whole tree.
    // TODO: This is left over from the effect list implementation, where we had
    // to check for the existence of `firstEffect` to satsify Flow. I think the
    // only other reason this optimization exists is because it affects profiling.
    // Reconsider whether this is necessary.
    const subtreeHasEffects =
      (finishedWork.subtreeFlags &
        (BeforeMutationMask | MutationMask | LayoutMask | PassiveMask)) !==
      NoFlags;
    const rootHasEffect =
      (finishedWork.flags &
        (BeforeMutationMask | MutationMask | LayoutMask | PassiveMask)) !==
      NoFlags;
  
    if (subtreeHasEffects || rootHasEffect) {
      const prevTransition = ReactCurrentBatchConfig.transition;
      ReactCurrentBatchConfig.transition = 0;
      const previousPriority = getCurrentUpdatePriority();
      setCurrentUpdatePriority(DiscreteEventPriority);
  
      const prevExecutionContext = executionContext;
      executionContext |= CommitContext;
      const prevInteractions = pushInteractions(root);
  
      // Reset this to null before calling lifecycles
      ReactCurrentOwner.current = null;
  
      // The commit phase is broken into several sub-phases. We do a separate pass
      // of the effect list for each phase: all mutation effects come before all
      // layout effects, and so on.
  
      // The first phase a "before mutation" phase. We use this phase to read the
      // state of the host tree right before we mutate it. This is where
      // getSnapshotBeforeUpdate is called.
      const shouldFireAfterActiveInstanceBlur = commitBeforeMutationEffects(
        root,
        finishedWork,
      );
  
      if (enableProfilerTimer) {
        // Mark the current commit time to be shared by all Profilers in this
        // batch. This enables them to be grouped later.
        recordCommitTime();
      }
  
      if (enableProfilerTimer && enableProfilerNestedUpdateScheduledHook) {
        // Track the root here, rather than in commitLayoutEffects(), because of ref setters.
        // Updates scheduled during ref detachment should also be flagged.
        rootCommittingMutationOrLayoutEffects = root;
      }
  
      // The next phase is the mutation phase, where we mutate the host tree.
      commitMutationEffects(root, finishedWork);
  
      if (shouldFireAfterActiveInstanceBlur) {
        afterActiveInstanceBlur();
      }
      resetAfterCommit(root.containerInfo);
  
      // The work-in-progress tree is now the current tree. This must come after
      // the mutation phase, so that the previous tree is still current during
      // componentWillUnmount, but before the layout phase, so that the finished
      // work is current during componentDidMount/Update.
      root.current = finishedWork;
  
      // The next phase is the layout phase, where we call effects that read
      // the host tree after it's been mutated. The idiomatic use case for this is
      // layout, but class component lifecycles also fire here for legacy reasons.
      if (__DEV__) {
        if (enableDebugTracing) {
          logLayoutEffectsStarted(lanes);
        }
      }
      if (enableSchedulingProfiler) {
        markLayoutEffectsStarted(lanes);
      }
      commitLayoutEffects(finishedWork, root, lanes);
      if (__DEV__) {
        if (enableDebugTracing) {
          logLayoutEffectsStopped();
        }
      }
  
      if (enableSchedulingProfiler) {
        markLayoutEffectsStopped();
      }
  
      if (enableProfilerTimer && enableProfilerNestedUpdateScheduledHook) {
        rootCommittingMutationOrLayoutEffects = null;
      }
  
      // Tell Scheduler to yield at the end of the frame, so the browser has an
      // opportunity to paint.
      requestPaint();
  
      if (enableSchedulerTracing) {
        popInteractions(((prevInteractions: any): Set<Interaction>));
      }
      executionContext = prevExecutionContext;
  
      // Reset the priority to the previous non-sync value.
      setCurrentUpdatePriority(previousPriority);
      ReactCurrentBatchConfig.transition = prevTransition;
    } else {
      // No effects.
      root.current = finishedWork;
      // Measure these anyway so the flamegraph explicitly shows that there were
      // no effects.
      // TODO: Maybe there's a better way to report this.
      if (enableProfilerTimer) {
        recordCommitTime();
      }
    }
  
    const rootDidHavePassiveEffects = rootDoesHavePassiveEffects;
  
    if (rootDoesHavePassiveEffects) {
      // This commit has passive effects. Stash a reference to them. But don't
      // schedule a callback until after flushing layout work.
      rootDoesHavePassiveEffects = false;
      rootWithPendingPassiveEffects = root;
      pendingPassiveEffectsLanes = lanes;
    }
  
    // Read this again, since an effect might have updated it
    remainingLanes = root.pendingLanes;
  
    // Check if there's remaining work on this root
    if (remainingLanes !== NoLanes) {
      if (enableSchedulerTracing) {
        if (spawnedWorkDuringRender !== null) {
          const expirationTimes = spawnedWorkDuringRender;
          spawnedWorkDuringRender = null;
          for (let i = 0; i < expirationTimes.length; i++) {
            scheduleInteractions(
              root,
              expirationTimes[i],
              root.memoizedInteractions,
            );
          }
        }
        schedulePendingInteractions(root, remainingLanes);
      }
    } else {
      // If there's no remaining work, we can clear the set of already failed
      // error boundaries.
      legacyErrorBoundariesThatAlreadyFailed = null;
    }
  
    if (__DEV__ && enableStrictEffects) {
      if (!rootDidHavePassiveEffects) {
        commitDoubleInvokeEffectsInDEV(root.current, false);
      }
    }
  
    if (enableSchedulerTracing) {
      if (!rootDidHavePassiveEffects) {
        // If there are no passive effects, then we can complete the pending interactions.
        // Otherwise, we'll wait until after the passive effects are flushed.
        // Wait to do this until after remaining work has been scheduled,
        // so that we don't prematurely signal complete for interactions when there's e.g. hidden work.
        finishPendingInteractions(root, lanes);
      }
    }
  
    if (includesSomeLane(remainingLanes, (SyncLane: Lane))) {
      if (enableProfilerTimer && enableProfilerNestedUpdatePhase) {
        markNestedUpdateScheduled();
      }
  
      // Count the number of times the root synchronously re-renders without
      // finishing. If there are too many, it indicates an infinite update loop.
      if (root === rootWithNestedUpdates) {
        nestedUpdateCount++;
      } else {
        nestedUpdateCount = 0;
        rootWithNestedUpdates = root;
      }
    } else {
      nestedUpdateCount = 0;
    }
  
    onCommitRootDevTools(finishedWork.stateNode, renderPriorityLevel);
  
    if (__DEV__) {
      onCommitRootTestSelector();
    }
  
    // Always call this before exiting `commitRoot`, to ensure that any
    // additional work on this root is scheduled.
    ensureRootIsScheduled(root, now());
  
    if (hasUncaughtError) {
      hasUncaughtError = false;
      const error = firstUncaughtError;
      firstUncaughtError = null;
      throw error;
    }
  
    if ((executionContext & LegacyUnbatchedContext) !== NoContext) {
      if (__DEV__) {
        if (enableDebugTracing) {
          logCommitStopped();
        }
      }
  
      if (enableSchedulingProfiler) {
        markCommitStopped();
      }
  
      // This is a legacy edge case. We just committed the initial mount of
      // a ReactDOM.render-ed root inside of batchedUpdates. The commit fired
      // synchronously, but layout updates should be deferred until the end
      // of the batch.
      return null;
    }
  
    // If the passive effects are the result of a discrete render, flush them
    // synchronously at the end of the current task so that the result is
    // immediately observable. Otherwise, we assume that they are not
    // order-dependent and do not need to be observed by external systems, so we
    // can wait until after paint.
    // TODO: We can optimize this by not scheduling the callback earlier. Since we
    // currently schedule the callback in multiple places, will wait until those
    // are consolidated.
    if (
      includesSomeLane(pendingPassiveEffectsLanes, SyncLane) &&
      root.tag !== LegacyRoot
    ) {
      flushPassiveEffects();
    }
  
    // If layout work was scheduled, flush it now.
    flushSyncCallbackQueue();
  
    if (__DEV__) {
      if (enableDebugTracing) {
        logCommitStopped();
      }
    }
  
    if (enableSchedulingProfiler) {
      markCommitStopped();
    }
  
    return null;
  }
  
  export function flushPassiveEffects(): boolean {
    // Returns whether passive effects were flushed.
    if (pendingPassiveEffectsLanes !== NoLanes) {
      const renderPriority = lanesToEventPriority(pendingPassiveEffectsLanes);
      const priority = lowerEventPriority(DefaultEventPriority, renderPriority);
      const prevTransition = ReactCurrentBatchConfig.transition;
      const previousPriority = getCurrentUpdatePriority();
      try {
        ReactCurrentBatchConfig.transition = 0;
        setCurrentUpdatePriority(priority);
        return flushPassiveEffectsImpl();
      } finally {
        setCurrentUpdatePriority(previousPriority);
        ReactCurrentBatchConfig.transition = prevTransition;
      }
    }
    return false;
  }
  
  export function enqueuePendingPassiveProfilerEffect(fiber: Fiber): void {
    if (enableProfilerTimer && enableProfilerCommitHooks) {
      pendingPassiveProfilerEffects.push(fiber);
      if (!rootDoesHavePassiveEffects) {
        rootDoesHavePassiveEffects = true;
        scheduleCallback(NormalSchedulerPriority, () => {
          flushPassiveEffects();
          return null;
        });
      }
    }
  }
  
  function flushPassiveEffectsImpl() {
    if (rootWithPendingPassiveEffects === null) {
      return false;
    }
  
    const root = rootWithPendingPassiveEffects;
    const lanes = pendingPassiveEffectsLanes;
    rootWithPendingPassiveEffects = null;
    pendingPassiveEffectsLanes = NoLanes;
  
    invariant(
      (executionContext & (RenderContext | CommitContext)) === NoContext,
      'Cannot flush passive effects while already rendering.',
    );
  
    if (__DEV__) {
      if (enableDebugTracing) {
        logPassiveEffectsStarted(lanes);
      }
    }
  
    if (enableSchedulingProfiler) {
      markPassiveEffectsStarted(lanes);
    }
  
    if (__DEV__) {
      isFlushingPassiveEffects = true;
    }
  
    const prevExecutionContext = executionContext;
    executionContext |= CommitContext;
    const prevInteractions = pushInteractions(root);
  
    commitPassiveUnmountEffects(root.current);
    commitPassiveMountEffects(root, root.current);
  
    // TODO: Move to commitPassiveMountEffects
    if (enableProfilerTimer && enableProfilerCommitHooks) {
      const profilerEffects = pendingPassiveProfilerEffects;
      pendingPassiveProfilerEffects = [];
      for (let i = 0; i < profilerEffects.length; i++) {
        const fiber = ((profilerEffects[i]: any): Fiber);
        commitPassiveEffectDurations(root, fiber);
      }
    }
  
    if (enableSchedulerTracing) {
      popInteractions(((prevInteractions: any): Set<Interaction>));
      finishPendingInteractions(root, lanes);
    }
  
    if (__DEV__) {
      isFlushingPassiveEffects = false;
    }
  
    if (__DEV__) {
      if (enableDebugTracing) {
        logPassiveEffectsStopped();
      }
    }
  
    if (enableSchedulingProfiler) {
      markPassiveEffectsStopped();
    }
  
    if (__DEV__ && enableStrictEffects) {
      commitDoubleInvokeEffectsInDEV(root.current, true);
    }
  
    executionContext = prevExecutionContext;
  
    flushSyncCallbackQueue();
  
    // If additional passive effects were scheduled, increment a counter. If this
    // exceeds the limit, we'll fire a warning.
    nestedPassiveUpdateCount =
      rootWithPendingPassiveEffects === null ? 0 : nestedPassiveUpdateCount + 1;
  
    // TODO: Move to commitPassiveMountEffects
    onPostCommitRootDevTools(root);
    if (enableProfilerTimer && enableProfilerCommitHooks) {
      const stateNode = root.current.stateNode;
      stateNode.effectDuration = 0;
      stateNode.passiveEffectDuration = 0;
    }
  
    return true;
  }
  
  export function isAlreadyFailedLegacyErrorBoundary(instance: mixed): boolean {
    return (
      legacyErrorBoundariesThatAlreadyFailed !== null &&
      legacyErrorBoundariesThatAlreadyFailed.has(instance)
    );
  }
  
  export function markLegacyErrorBoundaryAsFailed(instance: mixed) {
    if (legacyErrorBoundariesThatAlreadyFailed === null) {
      legacyErrorBoundariesThatAlreadyFailed = new Set([instance]);
    } else {
      legacyErrorBoundariesThatAlreadyFailed.add(instance);
    }
  }
  
  function prepareToThrowUncaughtError(error: mixed) {
    if (!hasUncaughtError) {
      hasUncaughtError = true;
      firstUncaughtError = error;
    }
  }
  export const onUncaughtError = prepareToThrowUncaughtError;
  
  function captureCommitPhaseErrorOnRoot(
    rootFiber: Fiber,
    sourceFiber: Fiber,
    error: mixed,
  ) {
    const errorInfo = createCapturedValue(error, sourceFiber);
    const update = createRootErrorUpdate(rootFiber, errorInfo, (SyncLane: Lane));
    enqueueUpdate(rootFiber, update, (SyncLane: Lane));
    const eventTime = requestEventTime();
    const root = markUpdateLaneFromFiberToRoot(rootFiber, (SyncLane: Lane));
    if (root !== null) {
      markRootUpdated(root, SyncLane, eventTime);
      ensureRootIsScheduled(root, eventTime);
      schedulePendingInteractions(root, SyncLane);
    }
  }
  
  export function captureCommitPhaseError(
    sourceFiber: Fiber,
    nearestMountedAncestor: Fiber | null,
    error: mixed,
  ) {
    if (sourceFiber.tag === HostRoot) {
      // Error was thrown at the root. There is no parent, so the root
      // itself should capture it.
      captureCommitPhaseErrorOnRoot(sourceFiber, sourceFiber, error);
      return;
    }
  
    let fiber = null;
    if (skipUnmountedBoundaries) {
      fiber = nearestMountedAncestor;
    } else {
      fiber = sourceFiber.return;
    }
  
    while (fiber !== null) {
      if (fiber.tag === HostRoot) {
        captureCommitPhaseErrorOnRoot(fiber, sourceFiber, error);
        return;
      } else if (fiber.tag === ClassComponent) {
        const ctor = fiber.type;
        const instance = fiber.stateNode;
        if (
          typeof ctor.getDerivedStateFromError === 'function' ||
          (typeof instance.componentDidCatch === 'function' &&
            !isAlreadyFailedLegacyErrorBoundary(instance))
        ) {
          const errorInfo = createCapturedValue(error, sourceFiber);
          const update = createClassErrorUpdate(
            fiber,
            errorInfo,
            (SyncLane: Lane),
          );
          enqueueUpdate(fiber, update, (SyncLane: Lane));
          const eventTime = requestEventTime();
          const root = markUpdateLaneFromFiberToRoot(fiber, (SyncLane: Lane));
          if (root !== null) {
            markRootUpdated(root, SyncLane, eventTime);
            ensureRootIsScheduled(root, eventTime);
            schedulePendingInteractions(root, SyncLane);
          }
          return;
        }
      }
      fiber = fiber.return;
    }
  
    if (__DEV__) {
      // TODO: Until we re-land skipUnmountedBoundaries (see #20147), this warning
      // will fire for errors that are thrown by destroy functions inside deleted
      // trees. What it should instead do is propagate the error to the parent of
      // the deleted tree. In the meantime, do not add this warning to the
      // allowlist; this is only for our internal use.
      console.error(
        'Internal React error: Attempted to capture a commit phase error ' +
          'inside a detached tree. This indicates a bug in React. Likely ' +
          'causes include deleting the same fiber more than once, committing an ' +
          'already-finished tree, or an inconsistent return pointer.\n\n' +
          'Error message:\n\n%s',
        error,
      );
    }
  }
  
  export function pingSuspendedRoot(
    root: FiberRoot,
    wakeable: Wakeable,
    pingedLanes: Lanes,
  ) {
    const pingCache = root.pingCache;
    if (pingCache !== null) {
      // The wakeable resolved, so we no longer need to memoize, because it will
      // never be thrown again.
      pingCache.delete(wakeable);
    }
  
    const eventTime = requestEventTime();
    markRootPinged(root, pingedLanes, eventTime);
  
    if (
      workInProgressRoot === root &&
      isSubsetOfLanes(workInProgressRootRenderLanes, pingedLanes)
    ) {
      // Received a ping at the same priority level at which we're currently
      // rendering. We might want to restart this render. This should mirror
      // the logic of whether or not a root suspends once it completes.
  
      // TODO: If we're rendering sync either due to Sync, Batched or expired,
      // we should probably never restart.
  
      // If we're suspended with delay, or if it's a retry, we'll always suspend
      // so we can always restart.
      if (
        workInProgressRootExitStatus === RootSuspendedWithDelay ||
        (workInProgressRootExitStatus === RootSuspended &&
          includesOnlyRetries(workInProgressRootRenderLanes) &&
          now() - globalMostRecentFallbackTime < FALLBACK_THROTTLE_MS)
      ) {
        // Restart from the root.
        prepareFreshStack(root, NoLanes);
      } else {
        // Even though we can't restart right now, we might get an
        // opportunity later. So we mark this render as having a ping.
        workInProgressRootPingedLanes = mergeLanes(
          workInProgressRootPingedLanes,
          pingedLanes,
        );
      }
    }
  
    ensureRootIsScheduled(root, eventTime);
    schedulePendingInteractions(root, pingedLanes);
  }
  
  function retryTimedOutBoundary(boundaryFiber: Fiber, retryLane: Lane) {
    // The boundary fiber (a Suspense component or SuspenseList component)
    // previously was rendered in its fallback state. One of the promises that
    // suspended it has resolved, which means at least part of the tree was
    // likely unblocked. Try rendering again, at a new expiration time.
    if (retryLane === NoLane) {
      // TODO: Assign this to `suspenseState.retryLane`? to avoid
      // unnecessary entanglement?
      retryLane = requestRetryLane(boundaryFiber);
    }
    // TODO: Special case idle priority?
    const eventTime = requestEventTime();
    const root = markUpdateLaneFromFiberToRoot(boundaryFiber, retryLane);
    if (root !== null) {
      markRootUpdated(root, retryLane, eventTime);
      ensureRootIsScheduled(root, eventTime);
      schedulePendingInteractions(root, retryLane);
    }
  }
  
  export function retryDehydratedSuspenseBoundary(boundaryFiber: Fiber) {
    const suspenseState: null | SuspenseState = boundaryFiber.memoizedState;
    let retryLane = NoLane;
    if (suspenseState !== null) {
      retryLane = suspenseState.retryLane;
    }
    retryTimedOutBoundary(boundaryFiber, retryLane);
  }
  
  export function resolveRetryWakeable(boundaryFiber: Fiber, wakeable: Wakeable) {
    let retryLane = NoLane; // Default
    let retryCache: WeakSet<Wakeable> | Set<Wakeable> | null;
    if (enableSuspenseServerRenderer) {
      switch (boundaryFiber.tag) {
        case SuspenseComponent:
          retryCache = boundaryFiber.stateNode;
          const suspenseState: null | SuspenseState = boundaryFiber.memoizedState;
          if (suspenseState !== null) {
            retryLane = suspenseState.retryLane;
          }
          break;
        case SuspenseListComponent:
          retryCache = boundaryFiber.stateNode;
          break;
        default:
          invariant(
            false,
            'Pinged unknown suspense boundary type. ' +
              'This is probably a bug in React.',
          );
      }
    } else {
      retryCache = boundaryFiber.stateNode;
    }
  
    if (retryCache !== null) {
      // The wakeable resolved, so we no longer need to memoize, because it will
      // never be thrown again.
      retryCache.delete(wakeable);
    }
  
    retryTimedOutBoundary(boundaryFiber, retryLane);
  }
  
  // Computes the next Just Noticeable Difference (JND) boundary.
  // The theory is that a person can't tell the difference between small differences in time.
  // Therefore, if we wait a bit longer than necessary that won't translate to a noticeable
  // difference in the experience. However, waiting for longer might mean that we can avoid
  // showing an intermediate loading state. The longer we have already waited, the harder it
  // is to tell small differences in time. Therefore, the longer we've already waited,
  // the longer we can wait additionally. At some point we have to give up though.
  // We pick a train model where the next boundary commits at a consistent schedule.
  // These particular numbers are vague estimates. We expect to adjust them based on research.
  function jnd(timeElapsed: number) {
    return timeElapsed < 120
      ? 120
      : timeElapsed < 480
      ? 480
      : timeElapsed < 1080
      ? 1080
      : timeElapsed < 1920
      ? 1920
      : timeElapsed < 3000
      ? 3000
      : timeElapsed < 4320
      ? 4320
      : ceil(timeElapsed / 1960) * 1960;
  }
  
  function checkForNestedUpdates() {
    if (nestedUpdateCount > NESTED_UPDATE_LIMIT) {
      nestedUpdateCount = 0;
      rootWithNestedUpdates = null;
      invariant(
        false,
        'Maximum update depth exceeded. This can happen when a component ' +
          'repeatedly calls setState inside componentWillUpdate or ' +
          'componentDidUpdate. React limits the number of nested updates to ' +
          'prevent infinite loops.',
      );
    }
  
    if (__DEV__) {
      if (nestedPassiveUpdateCount > NESTED_PASSIVE_UPDATE_LIMIT) {
        nestedPassiveUpdateCount = 0;
        console.error(
          'Maximum update depth exceeded. This can happen when a component ' +
            "calls setState inside useEffect, but useEffect either doesn't " +
            'have a dependency array, or one of the dependencies changes on ' +
            'every render.',
        );
      }
    }
  }
  
  function flushRenderPhaseStrictModeWarningsInDEV() {
    if (__DEV__) {
      ReactStrictModeWarnings.flushLegacyContextWarning();
  
      if (warnAboutDeprecatedLifecycles) {
        ReactStrictModeWarnings.flushPendingUnsafeLifecycleWarnings();
      }
    }
  }
  
  function commitDoubleInvokeEffectsInDEV(
    fiber: Fiber,
    hasPassiveEffects: boolean,
  ) {
    if (__DEV__ && enableStrictEffects) {
      // TODO (StrictEffects) Should we set a marker on the root if it contains strict effects
      // so we don't traverse unnecessarily? similar to subtreeFlags but just at the root level.
      // Maybe not a big deal since this is DEV only behavior.
  
      setCurrentDebugFiberInDEV(fiber);
      invokeEffectsInDev(fiber, MountLayoutDev, invokeLayoutEffectUnmountInDEV);
      if (hasPassiveEffects) {
        invokeEffectsInDev(
          fiber,
          MountPassiveDev,
          invokePassiveEffectUnmountInDEV,
        );
      }
  
      invokeEffectsInDev(fiber, MountLayoutDev, invokeLayoutEffectMountInDEV);
      if (hasPassiveEffects) {
        invokeEffectsInDev(fiber, MountPassiveDev, invokePassiveEffectMountInDEV);
      }
      resetCurrentDebugFiberInDEV();
    }
  }
  
  function invokeEffectsInDev(
    firstChild: Fiber,
    fiberFlags: Flags,
    invokeEffectFn: (fiber: Fiber) => void,
  ): void {
    if (__DEV__ && enableStrictEffects) {
      // We don't need to re-check StrictEffectsMode here.
      // This function is only called if that check has already passed.
  
      let current = firstChild;
      let subtreeRoot = null;
      while (current !== null) {
        const primarySubtreeFlag = current.subtreeFlags & fiberFlags;
        if (
          current !== subtreeRoot &&
          current.child !== null &&
          primarySubtreeFlag !== NoFlags
        ) {
          current = current.child;
        } else {
          if ((current.flags & fiberFlags) !== NoFlags) {
            invokeEffectFn(current);
          }
  
          if (current.sibling !== null) {
            current = current.sibling;
          } else {
            current = subtreeRoot = current.return;
          }
        }
      }
    }
  }
  
  let didWarnStateUpdateForNotYetMountedComponent: Set<string> | null = null;
  function warnAboutUpdateOnNotYetMountedFiberInDEV(fiber) {
    if (__DEV__) {
      if ((executionContext & RenderContext) !== NoContext) {
        // We let the other warning about render phase updates deal with this one.
        return;
      }
  
      if (!(fiber.mode & ConcurrentMode)) {
        return;
      }
  
      const tag = fiber.tag;
      if (
        tag !== IndeterminateComponent &&
        tag !== HostRoot &&
        tag !== ClassComponent &&
        tag !== FunctionComponent &&
        tag !== ForwardRef &&
        tag !== MemoComponent &&
        tag !== SimpleMemoComponent
      ) {
        // Only warn for user-defined components, not internal ones like Suspense.
        return;
      }
  
      // We show the whole stack but dedupe on the top component's name because
      // the problematic code almost always lies inside that component.
      const componentName = getComponentNameFromFiber(fiber) || 'ReactComponent';
      if (didWarnStateUpdateForNotYetMountedComponent !== null) {
        if (didWarnStateUpdateForNotYetMountedComponent.has(componentName)) {
          return;
        }
        didWarnStateUpdateForNotYetMountedComponent.add(componentName);
      } else {
        didWarnStateUpdateForNotYetMountedComponent = new Set([componentName]);
      }
  
      const previousFiber = ReactCurrentFiberCurrent;
      try {
        setCurrentDebugFiberInDEV(fiber);
        console.error(
          "Can't perform a React state update on a component that hasn't mounted yet. " +
            'This indicates that you have a side-effect in your render function that ' +
            'asynchronously later calls tries to update the component. Move this work to ' +
            'useEffect instead.',
        );
      } finally {
        if (previousFiber) {
          setCurrentDebugFiberInDEV(fiber);
        } else {
          resetCurrentDebugFiberInDEV();
        }
      }
    }
  }
  
  let didWarnStateUpdateForUnmountedComponent: Set<string> | null = null;
  function warnAboutUpdateOnUnmountedFiberInDEV(fiber) {
    if (__DEV__) {
      const tag = fiber.tag;
      if (
        tag !== HostRoot &&
        tag !== ClassComponent &&
        tag !== FunctionComponent &&
        tag !== ForwardRef &&
        tag !== MemoComponent &&
        tag !== SimpleMemoComponent
      ) {
        // Only warn for user-defined components, not internal ones like Suspense.
        return;
      }
  
      if ((fiber.flags & PassiveStatic) !== NoFlags) {
        const updateQueue: FunctionComponentUpdateQueue | null = (fiber.updateQueue: any);
        if (updateQueue !== null) {
          const lastEffect = updateQueue.lastEffect;
          if (lastEffect !== null) {
            const firstEffect = lastEffect.next;
  
            let effect = firstEffect;
            do {
              if (effect.destroy !== undefined) {
                if ((effect.tag & HookPassive) !== NoHookEffect) {
                  return;
                }
              }
              effect = effect.next;
            } while (effect !== firstEffect);
          }
        }
      }
      // We show the whole stack but dedupe on the top component's name because
      // the problematic code almost always lies inside that component.
      const componentName = getComponentNameFromFiber(fiber) || 'ReactComponent';
      if (didWarnStateUpdateForUnmountedComponent !== null) {
        if (didWarnStateUpdateForUnmountedComponent.has(componentName)) {
          return;
        }
        didWarnStateUpdateForUnmountedComponent.add(componentName);
      } else {
        didWarnStateUpdateForUnmountedComponent = new Set([componentName]);
      }
  
      if (isFlushingPassiveEffects) {
        // Do not warn if we are currently flushing passive effects!
        //
        // React can't directly detect a memory leak, but there are some clues that warn about one.
        // One of these clues is when an unmounted React component tries to update its state.
        // For example, if a component forgets to remove an event listener when unmounting,
        // that listener may be called later and try to update state,
        // at which point React would warn about the potential leak.
        //
        // Warning signals are the most useful when they're strong.
        // (So we should avoid false positive warnings.)
        // Updating state from within an effect cleanup function is sometimes a necessary pattern, e.g.:
        // 1. Updating an ancestor that a component had registered itself with on mount.
        // 2. Resetting state when a component is hidden after going offscreen.
      } else {
        const previousFiber = ReactCurrentFiberCurrent;
        try {
          setCurrentDebugFiberInDEV(fiber);
          console.error(
            "Can't perform a React state update on an unmounted component. This " +
              'is a no-op, but it indicates a memory leak in your application. To ' +
              'fix, cancel all subscriptions and asynchronous tasks in %s.',
            tag === ClassComponent
              ? 'the componentWillUnmount method'
              : 'a useEffect cleanup function',
          );
        } finally {
          if (previousFiber) {
            setCurrentDebugFiberInDEV(fiber);
          } else {
            resetCurrentDebugFiberInDEV();
          }
        }
      }
    }
  }
  
  let beginWork;
  if (__DEV__ && replayFailedUnitOfWorkWithInvokeGuardedCallback) {
    const dummyFiber = null;
    beginWork = (current, unitOfWork, lanes) => {
      // If a component throws an error, we replay it again in a synchronously
      // dispatched event, so that the debugger will treat it as an uncaught
      // error See ReactErrorUtils for more information.
  
      // Before entering the begin phase, copy the work-in-progress onto a dummy
      // fiber. If beginWork throws, we'll use this to reset the state.
      const originalWorkInProgressCopy = assignFiberPropertiesInDEV(
        dummyFiber,
        unitOfWork,
      );
      try {
        return originalBeginWork(current, unitOfWork, lanes);
      } catch (originalError) {
        if (
          originalError !== null &&
          typeof originalError === 'object' &&
          typeof originalError.then === 'function'
        ) {
          // Don't replay promises. Treat everything else like an error.
          throw originalError;
        }
  
        // Keep this code in sync with handleError; any changes here must have
        // corresponding changes there.
        resetContextDependencies();
        resetHooksAfterThrow();
        // Don't reset current debug fiber, since we're about to work on the
        // same fiber again.
  
        // Unwind the failed stack frame
        unwindInterruptedWork(unitOfWork, workInProgressRootRenderLanes);
  
        // Restore the original properties of the fiber.
        assignFiberPropertiesInDEV(unitOfWork, originalWorkInProgressCopy);
  
        if (enableProfilerTimer && unitOfWork.mode & ProfileMode) {
          // Reset the profiler timer.
          startProfilerTimer(unitOfWork);
        }
  
        // Run beginWork again.
        invokeGuardedCallback(
          null,
          originalBeginWork,
          null,
          current,
          unitOfWork,
          lanes,
        );
  
        if (hasCaughtError()) {
          const replayError = clearCaughtError();
          if (
            typeof replayError === 'object' &&
            replayError !== null &&
            replayError._suppressLogging &&
            typeof originalError === 'object' &&
            originalError !== null &&
            !originalError._suppressLogging
          ) {
            // If suppressed, let the flag carry over to the original error which is the one we'll rethrow.
            originalError._suppressLogging = true;
          }
        }
        // We always throw the original error in case the second render pass is not idempotent.
        // This can happen if a memoized function or CommonJS module doesn't throw after first invokation.
        throw originalError;
      }
    };
  } else {
    beginWork = originalBeginWork;
  }
  
  let didWarnAboutUpdateInRender = false;
  let didWarnAboutUpdateInRenderForAnotherComponent;
  if (__DEV__) {
    didWarnAboutUpdateInRenderForAnotherComponent = new Set();
  }
  
  function warnAboutRenderPhaseUpdatesInDEV(fiber) {
    if (__DEV__) {
      if (
        ReactCurrentDebugFiberIsRenderingInDEV &&
        (executionContext & RenderContext) !== NoContext &&
        !getIsUpdatingOpaqueValueInRenderPhaseInDEV()
      ) {
        switch (fiber.tag) {
          case FunctionComponent:
          case ForwardRef:
          case SimpleMemoComponent: {
            const renderingComponentName =
              (workInProgress && getComponentNameFromFiber(workInProgress)) ||
              'Unknown';
            // Dedupe by the rendering component because it's the one that needs to be fixed.
            const dedupeKey = renderingComponentName;
            if (!didWarnAboutUpdateInRenderForAnotherComponent.has(dedupeKey)) {
              didWarnAboutUpdateInRenderForAnotherComponent.add(dedupeKey);
              const setStateComponentName =
                getComponentNameFromFiber(fiber) || 'Unknown';
              console.error(
                'Cannot update a component (`%s`) while rendering a ' +
                  'different component (`%s`). To locate the bad setState() call inside `%s`, ' +
                  'follow the stack trace as described in https://reactjs.org/link/setstate-in-render',
                setStateComponentName,
                renderingComponentName,
                renderingComponentName,
              );
            }
            break;
          }
          case ClassComponent: {
            if (!didWarnAboutUpdateInRender) {
              console.error(
                'Cannot update during an existing state transition (such as ' +
                  'within `render`). Render methods should be a pure ' +
                  'function of props and state.',
              );
              didWarnAboutUpdateInRender = true;
            }
            break;
          }
        }
      }
    }
  }
  
  // a 'shared' variable that changes when act() opens/closes in tests.
  export const IsThisRendererActing = {current: (false: boolean)};
  
  export function warnIfNotScopedWithMatchingAct(fiber: Fiber): void {
    if (__DEV__) {
      if (
        warnsIfNotActing === true &&
        IsSomeRendererActing.current === true &&
        IsThisRendererActing.current !== true
      ) {
        const previousFiber = ReactCurrentFiberCurrent;
        try {
          setCurrentDebugFiberInDEV(fiber);
          console.error(
            "It looks like you're using the wrong act() around your test interactions.\n" +
              'Be sure to use the matching version of act() corresponding to your renderer:\n\n' +
              '// for react-dom:\n' +
              // Break up imports to avoid accidentally parsing them as dependencies.
              'import {act} fr' +
              "om 'react-dom/test-utils';\n" +
              '// ...\n' +
              'act(() => ...);\n\n' +
              '// for react-test-renderer:\n' +
              // Break up imports to avoid accidentally parsing them as dependencies.
              'import TestRenderer fr' +
              "om 'react-test-renderer';\n" +
              'const {act} = TestRenderer;\n' +
              '// ...\n' +
              'act(() => ...);',
          );
        } finally {
          if (previousFiber) {
            setCurrentDebugFiberInDEV(fiber);
          } else {
            resetCurrentDebugFiberInDEV();
          }
        }
      }
    }
  }
  
  export function warnIfNotCurrentlyActingEffectsInDEV(fiber: Fiber): void {
    if (__DEV__) {
      if (
        warnsIfNotActing === true &&
        (fiber.mode & StrictLegacyMode) !== NoMode &&
        IsSomeRendererActing.current === false &&
        IsThisRendererActing.current === false
      ) {
        console.error(
          'An update to %s ran an effect, but was not wrapped in act(...).\n\n' +
            'When testing, code that causes React state updates should be ' +
            'wrapped into act(...):\n\n' +
            'act(() => {\n' +
            '  /* fire events that update state */\n' +
            '});\n' +
            '/* assert on the output */\n\n' +
            "This ensures that you're testing the behavior the user would see " +
            'in the browser.' +
            ' Learn more at https://reactjs.org/link/wrap-tests-with-act',
          getComponentNameFromFiber(fiber),
        );
      }
    }
  }
  
  function warnIfNotCurrentlyActingUpdatesInDEV(fiber: Fiber): void {
    if (__DEV__) {
      if (
        warnsIfNotActing === true &&
        executionContext === NoContext &&
        IsSomeRendererActing.current === false &&
        IsThisRendererActing.current === false
      ) {
        const previousFiber = ReactCurrentFiberCurrent;
        try {
          setCurrentDebugFiberInDEV(fiber);
          console.error(
            'An update to %s inside a test was not wrapped in act(...).\n\n' +
              'When testing, code that causes React state updates should be ' +
              'wrapped into act(...):\n\n' +
              'act(() => {\n' +
              '  /* fire events that update state */\n' +
              '});\n' +
              '/* assert on the output */\n\n' +
              "This ensures that you're testing the behavior the user would see " +
              'in the browser.' +
              ' Learn more at https://reactjs.org/link/wrap-tests-with-act',
            getComponentNameFromFiber(fiber),
          );
        } finally {
          if (previousFiber) {
            setCurrentDebugFiberInDEV(fiber);
          } else {
            resetCurrentDebugFiberInDEV();
          }
        }
      }
    }
  }
  
  export const warnIfNotCurrentlyActingUpdatesInDev = warnIfNotCurrentlyActingUpdatesInDEV;
  
  // In tests, we want to enforce a mocked scheduler.
  let didWarnAboutUnmockedScheduler = false;
  // TODO Before we release concurrent mode, revisit this and decide whether a mocked
  // scheduler is the actual recommendation. The alternative could be a testing build,
  // a new lib, or whatever; we dunno just yet. This message is for early adopters
  // to get their tests right.
  
  export function warnIfUnmockedScheduler(fiber: Fiber) {
    if (__DEV__) {
      if (
        didWarnAboutUnmockedScheduler === false &&
        Scheduler.unstable_flushAllWithoutAsserting === undefined
      ) {
        if (fiber.mode & ConcurrentMode) {
          didWarnAboutUnmockedScheduler = true;
          console.error(
            'In Concurrent or Sync modes, the "scheduler" module needs to be mocked ' +
              'to guarantee consistent behaviour across tests and browsers. ' +
              'For example, with jest: \n' +
              // Break up requires to avoid accidentally parsing them as dependencies.
              "jest.mock('scheduler', () => require" +
              "('scheduler/unstable_mock'));\n\n" +
              'For more info, visit https://reactjs.org/link/mock-scheduler',
          );
        } else if (warnAboutUnmockedScheduler === true) {
          didWarnAboutUnmockedScheduler = true;
          console.error(
            'Starting from React v18, the "scheduler" module will need to be mocked ' +
              'to guarantee consistent behaviour across tests and browsers. ' +
              'For example, with jest: \n' +
              // Break up requires to avoid accidentally parsing them as dependencies.
              "jest.mock('scheduler', () => require" +
              "('scheduler/unstable_mock'));\n\n" +
              'For more info, visit https://reactjs.org/link/mock-scheduler',
          );
        }
      }
    }
  }
  
  function computeThreadID(root: FiberRoot, lane: Lane | Lanes) {
    // Interaction threads are unique per root and expiration time.
    // NOTE: Intentionally unsound cast. All that matters is that it's a number
    // and it represents a batch of work. Could make a helper function instead,
    // but meh this is fine for now.
    return (lane: any) * 1000 + root.interactionThreadID;
  }
  
  export function markSpawnedWork(lane: Lane | Lanes) {
    if (!enableSchedulerTracing) {
      return;
    }
    if (spawnedWorkDuringRender === null) {
      spawnedWorkDuringRender = [lane];
    } else {
      spawnedWorkDuringRender.push(lane);
    }
  }
  
  function scheduleInteractions(
    root: FiberRoot,
    lane: Lane | Lanes,
    interactions: Set<Interaction>,
  ) {
    if (!enableSchedulerTracing) {
      return;
    }
  
    if (interactions.size > 0) {
      const pendingInteractionMap = root.pendingInteractionMap;
      const pendingInteractions = pendingInteractionMap.get(lane);
      if (pendingInteractions != null) {
        interactions.forEach(interaction => {
          if (!pendingInteractions.has(interaction)) {
            // Update the pending async work count for previously unscheduled interaction.
            interaction.__count++;
          }
  
          pendingInteractions.add(interaction);
        });
      } else {
        pendingInteractionMap.set(lane, new Set(interactions));
  
        // Update the pending async work count for the current interactions.
        interactions.forEach(interaction => {
          interaction.__count++;
        });
      }
  
      const subscriber = __subscriberRef.current;
      if (subscriber !== null) {
        const threadID = computeThreadID(root, lane);
        subscriber.onWorkScheduled(interactions, threadID);
      }
    }
  }
  
  function schedulePendingInteractions(root: FiberRoot, lane: Lane | Lanes) {
    // This is called when work is scheduled on a root.
    // It associates the current interactions with the newly-scheduled expiration.
    // They will be restored when that expiration is later committed.
    if (!enableSchedulerTracing) {
      return;
    }
  
    scheduleInteractions(root, lane, __interactionsRef.current);
  }
  
  function startWorkOnPendingInteractions(root: FiberRoot, lanes: Lanes) {
    // This is called when new work is started on a root.
    if (!enableSchedulerTracing) {
      return;
    }
  
    // Determine which interactions this batch of work currently includes, So that
    // we can accurately attribute time spent working on it, And so that cascading
    // work triggered during the render phase will be associated with it.
    const interactions: Set<Interaction> = new Set();
    root.pendingInteractionMap.forEach((scheduledInteractions, scheduledLane) => {
      if (includesSomeLane(lanes, scheduledLane)) {
        scheduledInteractions.forEach(interaction =>
          interactions.add(interaction),
        );
      }
    });
  
    // Store the current set of interactions on the FiberRoot for a few reasons:
    // We can re-use it in hot functions like performConcurrentWorkOnRoot()
    // without having to recalculate it. We will also use it in commitWork() to
    // pass to any Profiler onRender() hooks. This also provides DevTools with a
    // way to access it when the onCommitRoot() hook is called.
    root.memoizedInteractions = interactions;
  
    if (interactions.size > 0) {
      const subscriber = __subscriberRef.current;
      if (subscriber !== null) {
        const threadID = computeThreadID(root, lanes);
        try {
          subscriber.onWorkStarted(interactions, threadID);
        } catch (error) {
          // If the subscriber throws, rethrow it in a separate task
          scheduleCallback(ImmediateSchedulerPriority, () => {
            throw error;
          });
        }
      }
    }
  }
  
  function finishPendingInteractions(root, committedLanes) {
    if (!enableSchedulerTracing) {
      return;
    }
  
    const remainingLanesAfterCommit = root.pendingLanes;
  
    let subscriber;
  
    try {
      subscriber = __subscriberRef.current;
      if (subscriber !== null && root.memoizedInteractions.size > 0) {
        // FIXME: More than one lane can finish in a single commit.
        const threadID = computeThreadID(root, committedLanes);
        subscriber.onWorkStopped(root.memoizedInteractions, threadID);
      }
    } catch (error) {
      // If the subscriber throws, rethrow it in a separate task
      scheduleCallback(ImmediateSchedulerPriority, () => {
        throw error;
      });
    } finally {
      // Clear completed interactions from the pending Map.
      // Unless the render was suspended or cascading work was scheduled,
      // In which case– leave pending interactions until the subsequent render.
      const pendingInteractionMap = root.pendingInteractionMap;
      pendingInteractionMap.forEach((scheduledInteractions, lane) => {
        // Only decrement the pending interaction count if we're done.
        // If there's still work at the current priority,
        // That indicates that we are waiting for suspense data.
        if (!includesSomeLane(remainingLanesAfterCommit, lane)) {
          pendingInteractionMap.delete(lane);
  
          scheduledInteractions.forEach(interaction => {
            interaction.__count--;
  
            if (subscriber !== null && interaction.__count === 0) {
              try {
                subscriber.onInteractionScheduledWorkCompleted(interaction);
              } catch (error) {
                // If the subscriber throws, rethrow it in a separate task
                scheduleCallback(ImmediateSchedulerPriority, () => {
                  throw error;
                });
              }
            }
          });
        }
      });
    }
  }
  
  // `act` testing API
  //
  // TODO: This is mostly a copy-paste from the legacy `act`, which does not have
  // access to the same internals that we do here. Some trade offs in the
  // implementation no longer make sense.
  
  let isFlushingAct = false;
  let isInsideThisAct = false;
  
  function shouldForceFlushFallbacksInDEV() {
    // Never force flush in production. This function should get stripped out.
    return __DEV__ && actingUpdatesScopeDepth > 0;
  }
  
  const flushMockScheduler = Scheduler.unstable_flushAllWithoutAsserting;
  const isSchedulerMocked = typeof flushMockScheduler === 'function';
  
  // Returns whether additional work was scheduled. Caller should keep flushing
  // until there's no work left.
  function flushActWork(): boolean {
    if (flushMockScheduler !== undefined) {
      const prevIsFlushing = isFlushingAct;
      isFlushingAct = true;
      try {
        return flushMockScheduler();
      } finally {
        isFlushingAct = prevIsFlushing;
      }
    } else {
      // No mock scheduler available. However, the only type of pending work is
      // passive effects, which we control. So we can flush that.
      const prevIsFlushing = isFlushingAct;
      isFlushingAct = true;
      try {
        let didFlushWork = false;
        while (flushPassiveEffects()) {
          didFlushWork = true;
        }
        return didFlushWork;
      } finally {
        isFlushingAct = prevIsFlushing;
      }
    }
  }
  
  function flushWorkAndMicroTasks(onDone: (err: ?Error) => void) {
    try {
      flushActWork();
      enqueueTask(() => {
        if (flushActWork()) {
          flushWorkAndMicroTasks(onDone);
        } else {
          onDone();
        }
      });
    } catch (err) {
      onDone(err);
    }
  }
  
  // we track the 'depth' of the act() calls with this counter,
  // so we can tell if any async act() calls try to run in parallel.
  
  let actingUpdatesScopeDepth = 0;
  let didWarnAboutUsingActInProd = false;
  
  export function act(callback: () => Thenable<mixed>): Thenable<void> {
    if (!__DEV__) {
      if (didWarnAboutUsingActInProd === false) {
        didWarnAboutUsingActInProd = true;
        // eslint-disable-next-line react-internal/no-production-logging
        console.error(
          'act(...) is not supported in production builds of React, and might not behave as expected.',
        );
      }
    }
  
    const previousActingUpdatesScopeDepth = actingUpdatesScopeDepth;
    actingUpdatesScopeDepth++;
  
    const previousIsSomeRendererActing = IsSomeRendererActing.current;
    const previousIsThisRendererActing = IsThisRendererActing.current;
    const previousIsInsideThisAct = isInsideThisAct;
    IsSomeRendererActing.current = true;
    IsThisRendererActing.current = true;
    isInsideThisAct = true;
  
    function onDone() {
      actingUpdatesScopeDepth--;
      IsSomeRendererActing.current = previousIsSomeRendererActing;
      IsThisRendererActing.current = previousIsThisRendererActing;
      isInsideThisAct = previousIsInsideThisAct;
      if (__DEV__) {
        if (actingUpdatesScopeDepth > previousActingUpdatesScopeDepth) {
          // if it's _less than_ previousActingUpdatesScopeDepth, then we can assume the 'other' one has warned
          console.error(
            'You seem to have overlapping act() calls, this is not supported. ' +
              'Be sure to await previous act() calls before making a new one. ',
          );
        }
      }
    }
  
    let result;
    try {
      result = batchedUpdates(callback);
    } catch (error) {
      // on sync errors, we still want to 'cleanup' and decrement actingUpdatesScopeDepth
      onDone();
      throw error;
    }
  
    if (
      result !== null &&
      typeof result === 'object' &&
      typeof result.then === 'function'
    ) {
      // setup a boolean that gets set to true only
      // once this act() call is await-ed
      let called = false;
      if (__DEV__) {
        if (typeof Promise !== 'undefined') {
          //eslint-disable-next-line no-undef
          Promise.resolve()
            .then(() => {})
            .then(() => {
              if (called === false) {
                console.error(
                  'You called act(async () => ...) without await. ' +
                    'This could lead to unexpected testing behaviour, interleaving multiple act ' +
                    'calls and mixing their scopes. You should - await act(async () => ...);',
                );
              }
            });
        }
      }
  
      // in the async case, the returned thenable runs the callback, flushes
      // effects and  microtasks in a loop until flushPassiveEffects() === false,
      // and cleans up
      return {
        then(resolve, reject) {
          called = true;
          result.then(
            () => {
              if (
                actingUpdatesScopeDepth > 1 ||
                (isSchedulerMocked === true &&
                  previousIsSomeRendererActing === true)
              ) {
                onDone();
                resolve();
                return;
              }
              // we're about to exit the act() scope,
              // now's the time to flush tasks/effects
              flushWorkAndMicroTasks((err: ?Error) => {
                onDone();
                if (err) {
                  reject(err);
                } else {
                  resolve();
                }
              });
            },
            err => {
              onDone();
              reject(err);
            },
          );
        },
      };
    } else {
      if (__DEV__) {
        if (result !== undefined) {
          console.error(
            'The callback passed to act(...) function ' +
              'must return undefined, or a Promise. You returned %s',
            result,
          );
        }
      }
  
      // flush effects until none remain, and cleanup
      try {
        if (
          actingUpdatesScopeDepth === 1 &&
          (isSchedulerMocked === false || previousIsSomeRendererActing === false)
        ) {
          // we're about to exit the act() scope,
          // now's the time to flush effects
          flushActWork();
        }
        onDone();
      } catch (err) {
        onDone();
        throw err;
      }
  
      // in the sync case, the returned thenable only warns *if* await-ed
      return {
        then(resolve) {
          if (__DEV__) {
            console.error(
              'Do not await the result of calling act(...) with sync logic, it is not a Promise.',
            );
          }
          resolve();
        },
      };
    }
  }
  