Function updateSlot

packages/react-reconciler/src/ReactChildFiber.js:811–939

(
    returnFiber: Fiber,
    oldFiber: Fiber | null,
    newChild: any,
    lanes: Lanes,
  )

  }

  function updateSlot(
    returnFiber: Fiber,
    oldFiber: Fiber | null,
    newChild: any,
    lanes: Lanes,
  ): Fiber | null {
    // Update the fiber if the keys match, otherwise return null.
    const key = oldFiber !== null ? oldFiber.key : null;

    if (
      (typeof newChild === 'string' && newChild !== '') ||
      typeof newChild === 'number' ||
      typeof newChild === 'bigint'
    ) {
      // Text nodes don't have keys. If the previous node is implicitly keyed
      // we can continue to replace it without aborting even if it is not a text
      // node.
      if (key !== null) {
        return null;
      }
      return updateTextNode(
        returnFiber,
        oldFiber,
        // $FlowFixMe[unsafe-addition] Flow doesn't want us to use `+` operator with string and bigint
        '' + newChild,
        lanes,
      );
    }

    if (typeof newChild === 'object' && newChild !== null) {
      switch (newChild.$$typeof) {
        case REACT_ELEMENT_TYPE: {
          if (newChild.key === key) {
            const prevDebugInfo = pushDebugInfo(newChild._debugInfo);
            const updated = updateElement(
              returnFiber,
              oldFiber,
              newChild,
              lanes,
            );
            currentDebugInfo = prevDebugInfo;
            return updated;
          } else {
            return null;
          }
        }
        case REACT_PORTAL_TYPE: {
          if (newChild.key === key) {
            return updatePortal(returnFiber, oldFiber, newChild, lanes);
          } else {
            return null;
          }
        }
        case REACT_LAZY_TYPE: {
          const prevDebugInfo = pushDebugInfo(newChild._debugInfo);
          const resolvedChild = resolveLazy((newChild: any));
          const updated = updateSlot(
            returnFiber,