3.7: instance member function becomes instance member property in type references [outcome: fixed since 3.7.0-dev.20191016]

[bre1470]

TypeScript Version: 3.7.0-dev.20191002

Search Terms: instance member property

Code

declare global {
    class A {
        public f(): void;
    }
    class BA extends A {
        public f(): void;
    }
    class CA extends A {
        public f(): void;
    }
    class D extends CA {
        public f: BA['f']; // errors with 3.7
    }
}

export default undefined;

Expected behavior: use declarations without error

Actual behavior: errors with Class 'CA' defines instance member function 'f', but extended class 'D' defines it as instance member property.

Playground Link: https://www.typescriptlang.org/play/?ts=Nightly#code/CYUwxgNghgTiAEBzCB7ARlC8DeAoeB8kUAzifAII76G0AOArmhAJZjwBmAFAJQBc8AG4oWwANw0CAX0lFoZeACEqIAB4AXEADtg5Knlr0mrdt35CR42TNrEFAYRUbtuytUOFGzNp14DhohK0NoR25AAi8GqaOuSO7h7wXiacAsoA2gDkHJkAumLwAPSFUTAwKDDkAO4s6gAW8ADMAHQA7Na4MrhgKFokKBAgzaiIXJkAEiAQqAA08FUVEMAAhJk8ErhqdBXq8KAcUAwQuww6IBwsWiBWQA (compiles there without error)

Related Issues: -

[NoPhaseNoKill]

I'm getting the same issue, namely when using react lifecycle methods that have an arrow function.

componentWillMount = () => {...}

/*Throws 'Class component'' Props<State, any> defines instance member function componentDidMount, but extended class 'X ' defines it as an instance member property
*/

Error is fixed with:
componentWillMount() {....}

The problem with the workaround, is that to my knowledge it will change what is bound to context of 'this' under certain scenarios. Could someone please clarify on this?

[bre1470]

In your case the this scope might change as arrow functions use the outer scope as they do not have their own.

[seansfkelley]

This is still the case in 3.7.0-beta. Original issue: #17113.

Edit: this is fixed in nightly already and is working for me.

[bre1470]

Confirmed. The issue is solved for me as well since 3.7.0-dev.20191016.