current: Fiber | null,
  workInProgress: Fiber,
): void {
  invariant(
    current === null || workInProgress.child === current.child,
    'Resuming work not yet implemented.',
  );
  if (workInProgress.child === null) {
    return;
  }
  let currentChild = workInProgress.child;
  let newChild = createWorkInProgress(
    currentChild,
    currentChild.pendingProps,
    currentChild.expirationTime,
  );
  workInProgress.child = newChild;
  newChild.return = workInProgress;
  while (currentChild.sibling !== null) {
    currentChild = currentChild.sibling;
    newChild = newChild.sibling = createWorkInProgress(
      currentChild,
      currentChild.pendingProps,
      currentChild.expirationTime,
    );
    newChild.return = workInProgress;
  }
  newChild.sibling = null;
}