vant/packages/vant-use/src/useRelation/useParent.ts

import {
  inject,
  computed,
  onUnmounted,
  getCurrentInstance,
  ComponentPublicInstance,
  ComponentInternalInstance,
} from 'vue';

type ParentProvide<T> = T & {
  link(child: ComponentInternalInstance): void;
  unlink(child: ComponentInternalInstance): void;
  children: ComponentPublicInstance[];
  internalChildren: ComponentInternalInstance[];
};

export function useParent<T>(key: string | symbol) {
  const parent = inject<ParentProvide<T> | null>(key, null);

  if (parent) {
    const instance = getCurrentInstance();

    if (instance) {
      const { link, unlink, internalChildren, ...rest } = parent;

      link(instance);

      onUnmounted(() => {
        unlink(instance);
      });

      const index = computed(() => internalChildren.indexOf(instance));

      return {
        parent: rest,
        index,
      };
    }
  }

  return {};
}