Provide validate types only response function

[aexol]

Sometimes it would we useful to validate response type. The function should also give a way to transform the validated type:

import { getUserOrThrow } from '@/src/auth.js';
import { createResolvers } from '@/src/axolotl.js';
import { GraphQLError } from 'graphql';

export const Mutation = createResolvers({
  Mutation: {
    public:() => {
      return {}
    },
    user:async ([,,context],args,validate) => {
      const authHeader = context.request.headers.get("Authorization")
      if(!authHeader) throw new GraphQLError("You must be logged in to use this resolver")
      return validate(getUserOrThrow(authHeader))
    }
  },
})

This should be identity function only used for type check without real validation of response only to help developer experience

const validate = <Z={}>(o:T extends OUR_RESPONSE_TYPE):T => o

Overloading would look like that

import { getUserOrThrow } from '@/src/auth.js';
import { createResolvers } from '@/src/axolotl.js';
import { GraphQLError } from 'graphql';

export const Mutation = createResolvers({
  Mutation: {
    public:() => {
      return {}
    },
    user:async ([,,context],args,validate) => {
      const authHeader = context.request.headers.get("Authorization")
      if(!authHeader) throw new GraphQLError("You must be logged in to use this resolver")
      return validate<ReturnType<typeof validate> & { smth:string }>(getUserOrThrow(authHeader))
    }
  },
})