Promise constructor's return type doesn't unwrap nested promises

[bsimonjc]

Bug Report

🔎 Search Terms

promise constructor

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about Promises

⏯ Playground Link

Playground link with relevant code

💻 Code

const nestedPromise = (function() {
    return new Promise<Promise<number>>(resolve1 => {

        resolve1(new Promise<number>(resolve2 => {
            resolve2(5);
        }));

    })
})();

// according to TS, `result` should be a Promise<number>, but at runtime, it's actually just a number
nestedPromise.then(result => console.log('first', result, typeof result));
//                 ^?

// when using Promise.resolve(), the type is correct
const nestedPromiseResolve = (function() { return Promise.resolve(Promise.resolve(Promise.resolve(5)))})();
nestedPromiseResolve.then(result => console.log('second', result, typeof result));
//                        ^?

🙁 Actual behavior

Return type of the promise constructor doesn't unwrap nested promises

🙂 Expected behavior

The return type of the promise constructor should match the runtime behavior

The current constructor type is { new <T>(executor: (resolve: (value: T | PromiseLike<T>) => void, reject: (reason?: any) => void) => void): Promise<T>; }

Shouldn't the return type actually be Promise<Awaited<T>> like it is for Promise.resolve()? Is there something I'm missing here?

[Artxe2]

This definitely seems wrong. Is there any work planned to fix this? The following behaviors that appear to be bugs are as follows.

// it's correct
const resolve: Promise<number> = Promise.resolve(Promise.resolve(Promise.resolve(0)))

async function pr<T>(v: T) {
  return v
}
// it's should be Promise<number>
const promise: Promise<Promise<Promise<number>>> = pr(pr(pr(0)))

const a: any = 0
;(a as Promise<Promise<Promise<number>>>).then(
  // value is should be number
  (value: Promise<Promise<number>>) => {}
)

Playground