Grpc-dotnet: System.Interactive.Async dependency is problematic (transitive)

[mgravell]

Currently, the lib takes a transitive dependency on System.Interactive.Async v3.2.0" via Grpc.Core.

This is problematic because it defines IAsyncEnumerable<T> etc, which means that anyone taking a dep on this lib cannot use async-enumerable:

error CS0433: The type 'IAsyncEnumerable' exists in both 'System.Interactive.Async, Version=3.2.0.0, Culture=neutral, PublicKeyToken=94bc3704cddfc263' and 'System.Runtime, Version=4.2.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'

The ideal fix here would be if there was a preview of Grpc.Core that took a dep on v4.0.0 (preview); as I understand it, v4.0.0 unifies the types to avoid this problem - but of course v4.0.0 is preview as long as core 3 is preview; so it would need to be a preview of Grpc.Core too, etc. But that's probably all correct.

The main point of this issue is to make it explicit that it would be a bad idea to release Grpc-Dotnet with it taking a transitive dependency that breaks async enumerables.

Of course, if we can co-ordinate with Grpc.Core to get a preview build that works correctly with them, that's even better - it would allow a full test of more scenarios, and would prevent the risk of accidentally deploying with a dangerously broken API.

[mgravell]

In case you're wondering about the context here: my code-first stuff implements API re-shaping. The following already works:

``` c#
[ServiceContract(Name = "Greet.Greeter")]
public interface IGreeter
{
ValueTask SayHelloAsync(HelloRequest request);
}

but I'd ideally like it to also work to detect client/server/duplex streaming APIs via `IAsyncEnumerable<T>`, i.e.

``` c#
IAsyncEnumerable<SomeReply> FullDuplex(IAsyncEnumerable<SomeRequest> whatever);

I can't begin to look at this as long as the transitive dependency problem is there.

(the key point of API re-shaping is that it allows a single interface to be shared at both client and server, with the server implementing the interface, and the client getting a proxy; i.e. my server here is a class SomeServer : IGreeter)

[JamesNK]

I've already brought this up here - https://github.com/grpc/grpc/pull/19059

You should add a comment that this is important to resolve.

[mgravell]

Awesome, thanks. Chimed in.

[JamesNK]

By the way you can work around this. It's not user friendly, and not a good long term solution but it will unblock you. I'll look up a sample I wrote.

[JamesNK]

Put this in your csproj:

  <!--
    System.Interactive.Async contains IAsyncEnumerable<T> that conflicts with .NET Core version
    Give assembly an alias so .NET Core version can be referenced in C#
  -->
  <Target Name="ChangeAliasesOfReactiveExtensions" BeforeTargets="FindReferenceAssembliesForReferences;ResolveReferences">
    <ItemGroup>
      <ReferencePath Condition="'%(FileName)' == 'System.Interactive.Async'">
        <Aliases>ix</Aliases>
      </ReferencePath>
    </ItemGroup>
  </Target>

[mgravell]

Oren sent me.that via twitter. I didn't realise it was yours, but nice: thanks!

[JamesNK]

Covered by https://github.com/grpc/grpc/pull/19059