Add type parameters to partial structures

[thewilloftheshadow]

Add type parameters to Partial structures so that things like fetchGuild() will return Guilds that are for sure not partial, since we fetched the data before

(Maintainers, see https://discord.com/channels/1280628625904894072/1284942028685443144/1284955904822870168)

[apteryxxyz]

I'm gonna post the mock I made as reference.

import { APIUser } from 'discord-api-types/v10'

// i tried using boolean before, but went with this due to issues with the value type being expanded to boolean
// tho as im making this comment i realised might be able to add const to the type parameter
export class User<D extends string | APIUser> {
    private _data: Partial<APIUser>

    constructor(data: D) {
        if (typeof data === 'string') this._data = { id: data }
        else this._data = data
    }

    get id() {
        return this._data.id!
    }

    get globalName(): D extends string ? undefined : string {
        // would have to always type case due to the condition, tho i think only internally, user wont have to
        return (this._data.global_name || undefined) as never
    }
}

const user = new User('aaaaa')
user.globalName
//     ^? undefined

const user2 = new User({} as APIUser)
user2.globalName
//      ^? string

[apteryxxyz]

I tried a bunch of ways of using IsPartial extends boolean , but at the moment can only get D extends string | APIUser to work, bit annoying but oh well