ConfiguredAsyncEnumerable in netcoreapp3.0 preview is not acceptable with await foreach (CS8142)?

[yyjdelete]

Version Used: The one in VS2019 Preview1 and dotnet sdk 3.0.100-preview-009812

Steps to Reproduce:

1. using System.Threading.Tasks;
2. await foreach (var z in /IAsyncEnumerable/.ConfigureAwait(false))

Expected Behavior:
See this on https://github.com/dotnet/csharplang/blob/master/proposals/async-streams.md but seems not see this on #24037, is it still available?

Actual Behavior:
CS8412

[jaredpar]

@yyjdelete can you clarify what error you're getting here? It's unclear from the bug what the actual error is.

[yyjdelete]

Expected Behavior:

Build successful with no errors.

Actual Behavior:

Error CS8412 Async foreach requires that the return type 'ConfiguredAsyncEnumerable.Enumerator' of 'ConfiguredAsyncEnumerable.GetAsyncEnumerator()' must have a suitable public 'MoveNextAsync' method and public 'Current' property

Nightly builds of dotnet-sdk/roslyn is not tested.

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp3.0</TargetFramework>
    <LangVersion>8.0</LangVersion>
  </PropertyGroup>

</Project>

using System;
using System.Collections.Generic;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello World!");
        }

        public async Task Test2()
        {
            await foreach(var x in Test())
            {
            }

            await foreach (var x in Test().ConfigureAwait(false))
            {
            }
        }

        public IAsyncEnumerable<int> Test() => null;
    }
}

[jcouv]

Thanks for reporting this and for the details. A fix is pending review for preview2.

[jcouv]

Fix merged for preview2.
Note there is a related issue which is not fixed yet. When you use ConfigureAwait in an await foreach loop, we'll don't call its DisposeAsync() method. Tracked by #32316