Function trackPostponedBoundary

packages/react-server/src/ReactFizzServer.js:3848–3889

(
  request: Request,
  trackedPostpones: PostponedHoles,
  boundary: SuspenseBoundary,
)

}

function trackPostponedBoundary(
  request: Request,
  trackedPostpones: PostponedHoles,
  boundary: SuspenseBoundary,
): ReplaySuspenseBoundary {
  boundary.status = POSTPONED;
  // We need to eagerly assign it an ID because we'll need to refer to
  // it before flushing and we know that we can't inline it.
  boundary.rootSegmentID = request.nextSegmentId++;

  const boundaryKeyPath = boundary.trackedContentKeyPath;
  if (boundaryKeyPath === null) {
    throw new Error(
      'It should not be possible to postpone at the root. This is a bug in React.',
    );
  }

  const fallbackReplayNode = boundary.trackedFallbackNode;

  const children: Array<ReplayNode> = [];
  const boundaryNode: void | ReplayNode =
    trackedPostpones.workingMap.get(boundaryKeyPath);
  if (boundaryNode === undefined) {
    const suspenseBoundary: ReplaySuspenseBoundary = [
      boundaryKeyPath[1],
      boundaryKeyPath[2],
      children,
      null,
      fallbackReplayNode,
      boundary.rootSegmentID,
    ];
    trackedPostpones.workingMap.set(boundaryKeyPath, suspenseBoundary);
    addToReplayParent(suspenseBoundary, boundaryKeyPath[0], trackedPostpones);
    return suspenseBoundary;
  } else {
    // Upgrade to ReplaySuspenseBoundary.
    const suspenseBoundary: ReplaySuspenseBoundary = (boundaryNode: any);
    suspenseBoundary[4] = fallbackReplayNode;
    suspenseBoundary[5] = boundary.rootSegmentID;
    return suspenseBoundary;
  }
}

function trackPostpone(
  request: Request,