Right now code built with C# 8.0 / .NET Core 3.1 always gives the following error for code I've tried (tried all versions and a manual compile from source):

System.InvalidOperationException: No design time or full build available

FYI, I am in the process of developing a tool that will take Go code and convert it to C#: go2cs

dotnet-try would be perfect for this by doing head-to-head comparisons of original Go code and converted C# code: