Function useFiber

packages/react-reconciler/src/ReactChildFiber.js:483–490

(fiber: Fiber, pendingProps: mixed)

  }

  function useFiber(fiber: Fiber, pendingProps: mixed): Fiber {
    // We currently set sibling to null and index to 0 here because it is easy
    // to forget to do before returning it. E.g. for the single child case.
    const clone = createWorkInProgress(fiber, pendingProps);
    clone.index = 0;
    clone.sibling = null;
    return clone;
  }

  function placeChild(
    newFiber: Fiber,