solution.ts

//
// ────────────────────────────────── SOLUTION ─────────────────────────────────
//

type MyAwaited<T extends PromiseLike<any | PromiseLike<any>>> =
	T extends PromiseLike<infer U>
		? U extends PromiseLike<any>
			? MyAwaited<U>
			: U
		: never

//
// ──────────────────────────────────── TEST ───────────────────────────────────
//

import type { Equal, Expect } from '@type-challenges/utils'

type X = Promise<string>
type Y = Promise<{ field: number }>
type Z = Promise<Promise<string | number>>
type Z1 = Promise<Promise<Promise<string | boolean>>>
type T = { then: (onfulfilled: (arg: number) => any) => any }

type cases = [
	Expect<Equal<MyAwaited<X>, string>>,
	Expect<Equal<MyAwaited<Y>, { field: number }>>,
	Expect<Equal<MyAwaited<Z>, string | number>>,
	Expect<Equal<MyAwaited<Z1>, string | boolean>>,
	Expect<Equal<MyAwaited<T>, number>>
]

// @ts-expect-error
type error = MyAwaited<number>