MemberNotNullWhen does not work when overridden in derived interface

[Ilchert]

Version Used:
SDK 9.0.101
Steps to Reproduce:

1. Mark overridden property as MemberNotNullWhen from base interface
2. Roslyn ignores this attribute

sharplab

string Get(IResponse<string> s) {
        if(s.IsSuccess)
            return s.Content; // warning CS8603: Possible null reference return.
        return  "default";
    }

interface IResponse
{
     bool IsSuccess {get;}
}

interface IResponse<T>:IResponse
{
    [MemberNotNullWhen(true,nameof(Content))]
     abstract bool IResponse.IsSuccess {get;}
     T? Content {get;}
}

Diagnostic Id:
warning CS8603: Possible null reference return.

Expected Behavior:
Should not trigger warning.

Actual Behavior:
As far I understand MemberNotNullWhen can reference only properties/methods from same class. Like in the example. But in this case, it ignores the attribute on IsSuccess override.

[RikkiGibson]

I think when the IsSuccess declaration is an explicit interface implementation, that member is not "seen" at the use site. Only the signature of the implemented member is seen. So if you want attributes and such to have an effect at the use site you may want to do something like this: SharpLab

using System.Diagnostics.CodeAnalysis;

string Get(IResponse<string> s) {
        if(s.IsSuccess)
            return s.Content; // ok
        return  "default";
    }

interface IResponse
{
     bool IsSuccess {get;}
}

interface IResponse<T>:IResponse
{
    bool IResponse.IsSuccess => IsSuccess;

    [MemberNotNullWhen(true,nameof(Content))]
     abstract new bool IsSuccess {get;}
     T? Content {get;}
}

[RikkiGibson]

Closing out as answered. Feel free to follow up with any more questions or concerns. Thanks!