Function completeWork

packages/react-reconciler/src/ReactFiberCompleteWork.js:1049–2040

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

}

function completeWork(
  current: Fiber | null,
  workInProgress: Fiber,
  renderLanes: Lanes,
): Fiber | null {
  const newProps = workInProgress.pendingProps;
  // Note: This intentionally doesn't check if we're hydrating because comparing
  // to the current tree provider fiber is just as fast and less error-prone.
  // Ideally we would have a special version of the work loop only
  // for hydration.
  popTreeContext(workInProgress);
  switch (workInProgress.tag) {
    case IncompleteFunctionComponent: {
      if (disableLegacyMode) {
        break;
      }
      // Fallthrough
    }
    case LazyComponent:
    case SimpleMemoComponent:
    case FunctionComponent:
    case ForwardRef:
    case Fragment:
    case Mode:
    case Profiler:
    case ContextConsumer:
    case MemoComponent:
      bubbleProperties(workInProgress);
      return null;
    case ClassComponent: {
      const Component = workInProgress.type;
      if (isLegacyContextProvider(Component)) {
        popLegacyContext(workInProgress);
      }
      bubbleProperties(workInProgress);
      return null;
    }
    case HostRoot: {
      const fiberRoot = (workInProgress.stateNode: FiberRoot);

      if (enableTransitionTracing) {
        const transitions = getWorkInProgressTransitions();
        // We set the Passive flag here because if there are new transitions,
        // we will need to schedule callbacks and process the transitions,
        // which we do in the passive phase
        if (transitions !== null) {
          workInProgress.flags |= Passive;
        }
      }

      let previousCache: Cache | null = null;
      if (current !== null) {
        previousCache = current.memoizedState.cache;
      }
      const cache: Cache = workInProgress.memoizedState.cache;
      if (cache !== previousCache) {
        // Run passive effects to retain/release the cache.
        workInProgress.flags |= Passive;