Compiler errors when using `IAsyncEnumerable<T>` with .NET Standard 2.1 enabled

[JesseTG]

Describe the bug

Any project that uses IAsyncEnumerable<T> with ML-Agents imported and .NET Standard 2.1 enabled will cause compiler errors.

Context

The type System.Collections.Generic.IAsyncEnumerable<T> is available in both the included System.Interactive.Async assembly (which is used by Grpc.Core) and in .NET Standard 2.1. Since around Unity 2021.3, Unity includes IAsyncEnumerable<T> as part of its .NET Standard 2.1 support; as a consequence, the compiler can't decide whether to import IAsyncEnumerable<T> from netstandard or from System.Interactive.Async.

This issue probably occurs with other types in System.Interactive.Async, but I only checked this one.

To Reproduce

1. Install ML-Agents
2. Write or install any code that uses IAsyncEnumerable<T> (in my case, this package)
3. Let the Unity editor try to compile your project.

Console logs / stack traces

It depends on the exact library, but here's an example from Razensoft.Mapper:

[CompilerError] The type 'IAsyncEnumerable<T>' exists in both 'System.Interactive.Async, Version=3.0.1000.0, Culture=neutral, PublicKeyToken=94bc3704cddfc263' and 'netstandard, Version=2.1.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'
Compiler Error at Library\PackageCache\com.razensoft.mapper@1.0.4\Runtime\Extensions\MapEnumerableAsync.cs:26 column 13
24:   public static async IAsyncEnumerable<TDestination> MapEnumerableAsync<TSource, TDestination>(
25:       this IMapper<TSource, TDestination> mapper,
-->26:       IAsyncEnumerable<TSource> source,
27:       [EnumeratorCancellation] CancellationToken cancellationToken = default)
28:       where TDestination : new()

Environment:

• Unity Version: 2022.1.19f1
• OS + version: Windows 10
• ML-Agents version: 2.3.0-exp.2
• Torch version: Not relevant
• Environment: Not relevant

Proposed Fix

I see a couple of possible fixes:

• Add the define constraint !NET_STANDARD_2_1 to the included System.Interactive.Async assembly. This way, Grpc.Core will use netstandard when available.
• Disable auto-referencing in System.Interactive.Async. Grpc.Core can continue to use that library this way, if you don't mind pulling in redundant library code.

Workaround

I see two workarounds:

• Modify ML-Agents with the aforementioned proposed fix. (This worked for me.)
• Manually override references in any assembly definition that uses APIs offered by System.Interactive.Async, such that these asmdefs don't seek it out. (This also worked, but you'd have to do it for every offending assembly.)

[Eelam]

Did you try ML-Agents version: 2.2.1-exp.1

[JesseTG]

@Eelam Yes, the error persists.

[JesseTG]

Any thoughts on this? This is making it difficult for me to use ML-Agents.

[Alex-Geornoiu]

Hi, I have the same error "The type 'IAsyncEnumerable' exists in both 'System.Interactive.Async, Version=3.0.1000.0, Culture=neutral, PublicKeyToken=94bc3704cddfc263' and 'netstandard, Version=2.1.0.0"
I tried the reactive framework, adding alias for System.Interactive.Async, but Unity just resets them afterwards back to global, I tried to decompile the dll and add that constraint but I failed, I even went and copy pasted your System.Interactive.Async.dll file into my place but that didn't work either.
For context, I also have a ML Agents game in Unity version 2022.2.6f1, and now I tried adding a chat gpt NPC to start the game with, using OpenAI-API-dotnet from OkGoDoIt. Thanks so much for all the help!

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