1726363 - Always return rejected promise from async callback when throwing

Status: RESOLVED DUPLICATE of bug 1726595

(Core :: DOM: Bindings (WebIDL), enhancement)

Description

[Kagami Rosylight [:saschanaz] (they/them)]

Say that there is a callback type that returns a promise:

interface LockManager {
  Promise<any> request(DOMString name,
                       LockGrantedCallback callback);
};

callback LockGrantedCallback = Promise<any> (Lock? lock);

Currently the way to get the result from aCallback.Call() for the following each case is different:

locks.request("foo", () => { throw new Error("error"); });
locks.request("foo", async () => { throw new Error("error"); });

1. Call() will pass the exception to its ErrorResult argument and the return value is nullptr.
2. Call() will return a rejected promise.

I don't think there is a good reason to differentiate 1 and 2, and it would be great if Call() always return a promise in this case, just as general return values are always wrapped by Promises.