Got this debugging another error. Filing here for reference. Original code: https://phabricator.intern.facebook.com/P59317705
isRendering = false;
  }
  function completeRoot(
    root: FiberRoot,
    finishedWork: Fiber,
    expirationTime: ExpirationTime,
  ): void {
    
    const firstBatch = root.firstBatch;
    if (firstBatch !== null && firstBatch._expirationTime <= expirationTime) {
      if (completedBatches === null) {
        completedBatches = [firstBatch];
      } else {
        completedBatches.push(firstBatch);
      }
      if (firstBatch._defer) {
        
        
        root.finishedWork = finishedWork;
        root.remainingExpirationTime = NoWork;
        return;
      }
    }
    
    root.finishedWork = null;
    root.remainingExpirationTime = commitRoot(finishedWork);
  }
  
  
  function shouldYield() {