How to import only types from Next

[DoroGi]

Goals

To be able to import next types like ReadonlyRequestCookies or the type of a monkey-patched Fetch, without the need to import the whole next.

Non-Goals

No response

Background

I am writing a typescript function, in an npm package, that accepts as input the result of next cookies() function and performs some extraction/manipulations.
The function would be something similar to:
const extractCustomCookies = (cookies: ReadonlyRequestCookies) => cookies.get('customCookie');

I tried installing next as a devDependency, but I saw that the type cannot be imported.
Also a few random types seems to break in other parts of my npm package, like some useContext now seems to use a canary version of react.

Proposal

I propose to discuss a way to provide next types only to whoever need them to create wrapper functions

[icyJoseph]

Could you do:

import type { cookies } from 'next/headers'

type Args = Parameters<typeof cookies>
type Result = Awaited<Result<typeof cookies>>

Stuff like that should work. It tells TS that during compile time, after type verification, it can drop that import from the process.

I think, I've used the triple slash directive on a package that needed the extended fetch from Next.js: https://www.typescriptlang.org/docs/handbook/triple-slash-directives.html

Look at your project next-env.d.ts or whatever it is called:

/// <reference types="next" />

But, I think my suggestion above should do the trick