Function setBlockTracking

packages/runtime-core/src/vnode.ts:315–322

(value: number, inVOnce = false)

 * @private
 */
export function setBlockTracking(value: number, inVOnce = false): void {
  isBlockTreeEnabled += value
  if (value < 0 && currentBlock && inVOnce) {
    // mark current block so it doesn't take fast path and skip possible
    // nested components during unmount
    currentBlock.hasOnce = true
  }
}

function setupBlock(vnode: VNode) {
  // save current block children on the block vnode