Vague error message with async functions

[DanielRosenwasser]

async function foo() {
    return "hi";
}

First thing I get is An async function must have a valid awaitable return type.

From a UX perspective, this is very confusing. If you add es2015.promise to your lib, it goes away.

[normalser]

Yea, I got confused by this in the past #10805
Especially that in one project it worked fine (that used older types for Bluebird) and in new project with latest Bluebird typings (which stopped exporting global definition for Promise) it was throwing this error with example taken from docs. Some more info for users in this error would be beneficial.

and if you do import * as Promise from 'bluebird' - you get error TS2529: Duplicate identifier 'Promise'. Compiler reserves name 'Promise' in top level scope of a module containing async functions

so not too clear for users

[blvd20]

Is there another way to solve this problem now?