Function updateHostRoot

packages/react-reconciler/src/ReactFiberBeginWork.js:1798–1914

(
  current: null | Fiber,
  workInProgress: Fiber,
  renderLanes: Lanes,
)

}

function updateHostRoot(
  current: null | Fiber,
  workInProgress: Fiber,
  renderLanes: Lanes,
) {
  pushHostRootContext(workInProgress);

  if (current === null) {
    throw new Error('Should have a current fiber. This is a bug in React.');
  }

  const nextProps = workInProgress.pendingProps;
  const prevState: RootState = 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);

  if (enableTransitionTracing) {
    pushRootMarkerInstance(workInProgress);
  }

  const nextCache: Cache = nextState.cache;
  pushCacheProvider(workInProgress, nextCache);
  if (nextCache !== prevState.cache) {
    // The root cache refreshed.
    propagateContextChange(workInProgress, CacheContext, renderLanes);
  }

  // This would ideally go inside processUpdateQueue, but because it suspends,
  // it needs to happen after the `pushCacheProvider` call above to avoid a
  // context stack mismatch. A bit unfortunate.
  suspendIfUpdateReadFromEntangledAsyncAction();

  // Caution: React DevTools currently depends on this property
  // being called "element".
  const nextChildren = nextState.element;
  if (supportsHydration && prevState.isDehydrated) {
    // This is a hydration root whose shell has not yet hydrated. We should
    // attempt to hydrate.

    // Flip isDehydrated to false to indicate that when this render
    // finishes, the root will no longer be dehydrated.
    const overrideState: RootState = {
      element: nextChildren,
      isDehydrated: false,
      cache: nextState.cache,
    };
    const updateQueue: UpdateQueue<RootState> =
      (workInProgress.updateQueue: any);
    // `baseState` can always be the last state because the root doesn't
    // have reducer functions so it doesn't need rebasing.
    updateQueue.baseState = overrideState;
    workInProgress.memoizedState = overrideState;