Function upgradePendingLanesToSync

packages/react-reconciler/src/ReactFiberLane.js:1053–1068

(
  root: FiberRoot,
  lanesToUpgrade: Lanes,
)

}

export function upgradePendingLanesToSync(
  root: FiberRoot,
  lanesToUpgrade: Lanes,
) {
  // Same as upgradePendingLaneToSync but accepts multiple lanes, so it's a
  // bit slower.
  root.pendingLanes |= SyncLane;
  root.entangledLanes |= SyncLane;
  let lanes = lanesToUpgrade;
  while (lanes) {
    const index = pickArbitraryLaneIndex(lanes);
    const lane = 1 << index;
    root.entanglements[SyncLaneIndex] |= lane;
    lanes &= ~lane;
  }
}

export function markHiddenUpdate(
  root: FiberRoot,