Function updateSlots

packages/runtime-core/src/componentSlots.ts:207–252

(
  instance: ComponentInternalInstance,
  children: VNodeNormalizedChildren,
  optimized: boolean,
)

}

export const updateSlots = (
  instance: ComponentInternalInstance,
  children: VNodeNormalizedChildren,
  optimized: boolean,
): void => {
  const { vnode, slots } = instance
  let needDeletionCheck = true
  let deletionComparisonTarget = EMPTY_OBJ
  if (vnode.shapeFlag & ShapeFlags.SLOTS_CHILDREN) {
    const type = (children as RawSlots)._
    if (type) {
      // compiled slots.
      if (__DEV__ && isHmrUpdating) {
        // Parent was HMR updated so slot content may have changed.
        // force update slots and mark instance for hmr as well
        assignSlots(slots, children as Slots, optimized)
        trigger(instance, TriggerOpTypes.SET, '$slots')
      } else if (optimized && type === SlotFlags.STABLE) {
        // compiled AND stable.
        // no need to update, and skip stale slots removal.
        needDeletionCheck = false
      } else {
        // compiled but dynamic (v-if/v-for on slots) - update slots, but skip
        // normalization.
        assignSlots(slots, children as Slots, optimized)
      }
    } else {
      needDeletionCheck = !(children as RawSlots).$stable
      normalizeObjectSlots(children as RawSlots, slots, instance)
    }
    deletionComparisonTarget = children as RawSlots
  } else if (children) {
    // non slot object children (direct value) passed to a component
    normalizeVNodeSlots(instance, children)
    deletionComparisonTarget = { default: 1 }
  }

  // delete stale slots
  if (needDeletionCheck) {
    for (const key in slots) {
      if (!isInternalKey(key) && deletionComparisonTarget[key] == null) {
        delete slots[key]
      }
    }
  }
}