Require either `async override` or `override async` (don't allow both)

[Skalman]

Bug Report

🔎 Search Terms

class async override

🕗 Version & Regression Information

• This changed between versions 4.2.0 and nightly

⏯ Playground Link

Playground link with relevant code

💻 Code

class Base {
    method1() {}
    method2() {}
}

class Test extends Base {
    public override async method1() {
        return Promise.resolve(1);
    }

    public async override method2() {
        return Promise.resolve(1);
    }
}

🙁 Actual behavior

No errors

🙂 Expected behavior

Possibly error on either override async or async override.

My understanding (from #43533) is that you prefer requiring a specific modifier order. If that's the case, I would have expected an error here.

[dsherret]

For some more information on which one should be chosen if one should be chosen, C# supports both forms, but override async is used about 12x more than async override in open source projects. Also, doing override async would keep in line with having the readonly keyword appear after override as mentioned in that linked issue, Additionally, override async is winning big time in this poll I did.

Right now, it seems like the declare keyword is the only modifier whose order isn't enforced.

[fbartho]

just like public/private, override is something of an internal annotation (for implementors), while async is a more external annotation (for consumers).

Therefore, it makes sense to me to spell it as public override readonly async someMethod() which follows a consistent direction of moving along a spectrum from implementor-relevant towards consumer-focused (left-to-right).

[fbartho]

To put it another way:

• async applies to the right to someMethod()
• readonly applies to the instance (what you can do to an instance)
• override and public both apply outwards to the class or meta level

So working from the outside in meta -> instance -> method becomes public override readonly async someMethod()

(Not sure if this phrasing makes more sense to people)

[andrewbranch]

The order of override and static is also not currently enforced.