Nullability mismatch reported for generic return type of implementation of unannotated method

[cston]

A warning is reported for IEnumerable<T>.GetEnumerator():

using System.Collections;
using System.Collections.Generic;
using System.Runtime.CompilerServices;
[module: NonNullTypes]
class Enumerable<T> : IEnumerable<T>
{
    IEnumerator<T> IEnumerable<T>.GetEnumerator() => throw null; // warning
    IEnumerator IEnumerable.GetEnumerator() => throw null;
}

(7,35): warning CS8616: Nullability of reference types in return type doesn't match
    implemented member 'IEnumerator<T> IEnumerable<T>.GetEnumerator()'.

[cston]

Fixed in #30913?

[DavidArno]

Did #30913 make it into VS2019 preview 1? If it did, this problem still persists as I'm getting the same warning testing C# 8 beta there.

[alrz]

@DavidArno The merged PR is targeting preview 2 branch.

[DavidArno]

@alrz, thanks. I couldn't work that out for myself, so glad you were on hand to work it out for me! 😁

[jskeet]

One thing to note is that at least in my experience, this only occurs for explicit interface implementation. So this would be fine:

public IEnumerator<T> GetEnumerator() => throw null;