Function markSpawnedDeferredLane

packages/react-reconciler/src/ReactFiberLane.js:991–1020

(
  root: FiberRoot,
  spawnedLane: Lane,
  entangledLanes: Lanes,
)

}

function markSpawnedDeferredLane(
  root: FiberRoot,
  spawnedLane: Lane,
  entangledLanes: Lanes,
) {
  // This render spawned a deferred task. Mark it as pending.
  root.pendingLanes |= spawnedLane;
  root.suspendedLanes &= ~spawnedLane;

  // Entangle the spawned lane with the DeferredLane bit so that we know it
  // was the result of another render. This lets us avoid a useDeferredValue
  // waterfall — only the first level will defer.
  // TODO: Now that there is a reserved set of transition lanes that are used
  // exclusively for deferred work, we should get rid of this special
  // DeferredLane bit; the same information can be inferred by checking whether
  // the lane is one of the TransitionDeferredLanes. The only reason this still
  // exists is because we need to also do the same for OffscreenLane. That
  // requires additional changes because there are more places around the
  // codebase that treat OffscreenLane as a magic value; would need to check
  // for a new OffscreenDeferredLane, too. Will leave this for a follow-up.
  const spawnedLaneIndex = laneToIndex(spawnedLane);
  root.entangledLanes |= spawnedLane;
  root.entanglements[spawnedLaneIndex] |=
    DeferredLane |
    // If the parent render task suspended, we must also entangle those lanes
    // with the spawned task, so that the deferred task includes all the same
    // updates that the parent task did. We can exclude any lane that is not
    // used for updates (e.g. Offscreen).
    (entangledLanes & UpdateLanes);
}

export function markRootEntangled(root: FiberRoot, entangledLanes: Lanes) {
  // In addition to entangling each of the given lanes with each other, we also