AsyncEnumerable.Empty not accessible with the 7.* preview nugets

[Tragetaschen]

Which library version?

7.0.0-preview.1.g24680b5469

What are the platform(s), environment(s) and related component version(s)?

.NET 10, but lower versions with the System.Linq.AsyncEnumerable compat nuget as well.

What is the use case or problem?

While there are mostly extension methods in the System.Linq.AsyncEnumerable type, the static Empty<TResult>() method is meant to be called via the static class name directly.
This currently results in an ambiguous type error:

Do you have a code snippet or project that reproduces the problem?

public class C {
  public IAsyncEnumerable<int> M() => AsyncEnumerable.Empty<int>();
}

What is the expected outcome?

The code should compile without errors

What is the actual outcome?

The type 'AsyncEnumerable' exists in both 'System.Linq.Async, Version=7.0.0.0, Culture=neutral, PublicKeyToken=94bc3704cddfc263' and 'System.Linq.AsyncEnumerable, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'

[Tragetaschen]

As workaround, you can create a local iterator

private async IAsyncEnumerable<int> Empty() {
    yield break;
}

[julealgon]

@Tragetaschen this was likely an intentional removal since it is now (.NET10 coming up next month) available as part of the BCL:

• https://learn.microsoft.com/en-us/dotnet/api/system.linq.asyncenumerable.empty?view=net-9.0-pp

[Tragetaschen]

Huh? No.

It's still there and contains "the weird stuff" that didn't make it into .NET 10. See #2240

As the error shows, there are two AsyncEnumerable types sitting in the System.Linq namespace. One from the BCL and one in System.Linq.Async. For the extension methods, this is fine as the C# compiler doesn't care, but when you need to explicitly name the type in source code, it's ambiguous now.