updateHostRoot

function updateHostRoot(current, workInProgress, renderLanes) {
  pushHostRootContext(workInProgress);

  const nextProps = workInProgress.pendingProps;
  const prevState = workInProgress.memoizedState;
  const prevChildren = prevState.element;
  cloneUpdateQueue(current, workInProgress);
  processUpdateQueue(workInProgress, nextProps, null, renderLanes);

  const nextState: RootState = workInProgress.memoizedState;
  const root: FiberRoot = workInProgress.stateNode;
  pushRootTransition(workInProgress, root, renderLanes);

  const nextChildren = nextState.element;
  if (supportsHydration && prevState.isDehydrated) {
    const overrideState: RootState = {
      element: nextChildren,
      isDehydrated: false,
      cache: nextState.cache,
    };
    const updateQueue: UpdateQueue<RootState> = (workInProgress.updateQueue: any);
    updateQueue.baseState = overrideState;
    workInProgress.memoizedState = overrideState;

    if (workInProgress.flags & ForceClientRender) {
      const recoverableError = createCapturedValueAtFiber(
        new Error(
          'There was an error while hydrating. Because the error happened outside ' +
            'of a Suspense boundary, the entire root will switch to ' +
            'client rendering.',
        ),
        workInProgress,
      );
      return mountHostRootWithoutHydrating(
        current,
        workInProgress,
        nextChildren,
        renderLanes,
        recoverableError,
      );
    } else if (nextChildren !== prevChildren) {
      const recoverableError = createCapturedValueAtFiber(
        new Error(
          'This root received an early update, before anything was able ' +
            'hydrate. Switched the entire root to client rendering.',
        ),
        workInProgress,
      );
      return mountHostRootWithoutHydrating(
        current,
        workInProgress,
        nextChildren,
        renderLanes,
        recoverableError,
      );
    } else {
      // The outermost shell has not hydrated yet. Start hydrating.
      enterHydrationState(workInProgress);
      if (enableUseMutableSource) {
        const mutableSourceEagerHydrationData =
          root.mutableSourceEagerHydrationData;
        if (mutableSourceEagerHydrationData != null) {
          for (let i = 0; i < mutableSourceEagerHydrationData.length; i += 2) {
            const mutableSource = ((mutableSourceEagerHydrationData[
              i
            ]: any): MutableSource<any>);
            const version = mutableSourceEagerHydrationData[i + 1];
            setWorkInProgressVersion(mutableSource, version);
          }
        }
      }

      const child = mountChildFibers(
        workInProgress,
        null,
        nextChildren,
        renderLanes,
      );
      workInProgress.child = child;

      let node = child;
      while (node) {
        node.flags = (node.flags & ~Placement) | Hydrating;
        node = node.sibling;
      }
    }
  } else {
    resetHydrationState();
    if (nextChildren === prevChildren) {
      return bailoutOnAlreadyFinishedWork(current, workInProgress, renderLanes);
    }
    reconcileChildren(current, workInProgress, nextChildren, renderLanes);
  }
  return workInProgress.child;
}