This DEV-only field was added in 836331ba5f69f2cc53b273ec073fae116db14302 by @sebmarkbage but it's not being used anymore to my knowledge.
workInProgress: Fiber,
  nextChildren: any,
  renderLanes: Lanes,
) {
  
  
  
  
  
  
  
  
  workInProgress.child = reconcileChildFibers(
    workInProgress,
    current.child,
    null,
    renderLanes,
  );
  
  
  
  
  workInProgress.child = reconcileChildFibers(
    workInProgress,
    null,
    nextChildren,
    renderLanes,
  );
}
function updateForwardRef(