Type-challenges - 20 Medium Promise.all (https://github.com/type-challenges/type-challenges/blob/main/questions/00020-medium-promise-all/README.md)

Promise-all.ts

type PromiseAllType<P> = 
  P extends []
    ? []
    : P extends [Promise<infer T> | infer T, ...infer F]
      ? [T, ...PromiseAllType<F>]
      : never

declare function PromiseAll<P extends any[]>(args: readonly [...P]): Promise<PromiseAllType<P>>

const promise1 = Promise.resolve(3);
const promise2 = 42;
const promise3 = new Promise<string>((resolve, reject) => {
  setTimeout(resolve, 100, 'foo');
});

// expected to be `Promise<[number, 42, string]>`
const p = PromiseAll([promise1, promise2, promise3] as const)