How do I get the new async semantics working in VS2017 RC?

Question

Quoting from Visual Studio 2017 RC Release Notes

Language Extensions and Analyzers

This release includes some proposed new langua

Answer 1

There is nothing else you need to do to enable task-like returns. The issue here is that the diagonstic message for this feature hasn't been updated yet. Here is a link to the tracking issue:

https://github.com/dotnet/roslyn/issues/12621