Recursive Promise unwrapper for TypeScript

Await.ts

// Works exactly as `await`/`then` in JavaScript, but for types!
// Of course, it can’t handle deep nesting (≥45±n levels) due to
// TypeScript limitations. But 45 is enough.

// License: MIT.

type Await<a> = {
    0: Await<a extends PromiseLike<infer b> ? b : never>,
    1: a,
}[a extends PromiseLike<any> ? 0 : 1];

type A = Await<Promise<Promise<Promise<Promise<number>>>>>; // number