Inferred Promise type breaks ordering of completions

🔎 Search Terms

promise, generic, completion, inference

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about promise/completions (found nothing)

⏯ Playground Link

https://www.typescriptlang.org/play?#code/JYOwLgpgTgZghgYwgAgGIHt0B4AqA+ZCAD0hABMBnZABSnQFtgKJcCBvAKGWQHofkcACybIKg9AFcANmVHiA7sgkAHZDGBQKYZHCnoQAc2TzgYQcgRwwCQQBpkZiCHvqQuqQE97EawDouapgAFACUAFzIINJSANwcAL4cHFI+yAaYZBEY2ADaALp4cRx8yACSIMgAagDKyADC6GQQ9mBQHg4eyqAGYcU8fdxpGf5JMBIgCGDA+sgARnBkrEFEETjhaJisyJzcUD4SUBVRUlI6VHAgHnGJSSXlVbUNTS1tHV2GvXwD3PNkQfkhXxAA

💻 Code

interface Foo<T> extends Promise<T> {
  // This should show up first along with catch, then, finally, etc.
  foo(): null;
}

let good: Foo<[]>;

async () => {
  // In VS Code, try typing:
  //
  //   good.
}

function bad<T>(x: T): Foo<T> {
  return null as any;
}


async () => {
  // In VS Code, try typing:
  //
  //   bad([]).
}

🙁 Actual behavior

If a generic is used to infer the type contained in the Promise, then the completions ordering is lost.

This is the correct ordering, foo shows up towards the top:

But if the function returning the Promise subclass is used, the ordering is lost:

🙂 Expected behavior

The methods declared on the Promise and its subclasses / subinterfaces should show up before the "after adding await" properties of whatever is contained in the Promise.

Additional information about the issue

I'd be willing to work on fixing this with some guidance, if it's feasible.

Start by running the linked TypeScript Playground reproduction and compare completions for good versus bad([]). Trace the completion behavior for the Promise subtype and generic inference; done means foo and Promise methods appear before properties added from the contained value in both cases.