Context

👋 .NET 10 is bringing support for Runtime-Async. I started playing around with it in an IcedTasks PR. However, I noticed some of benchmarks being off considerably. One of the requirements is having MethodImplOptions.Async set. I manually added the atttribute, but it doesn't get written to the IL.

Repro steps

Provide the steps required to reproduce the problem:

    [<MethodImpl(MethodImplOptions.Async)>]
    let fsharp_tenBindAsync_TaskBuilderRuntime () =
        IcedTasks.Polyfill.TasksRuntime.TaskBuilder.task {
            do! taskYield ()
            return 100
        }

see that the compiled DLL doesn't contain it in the IL/decompiled c#

    public static Task<int> fsharp_tenBindAsync_TaskBuilderRuntime()
    {
      YieldAwaitable.YieldAwaiter awaiter1 = Task.Yield().GetAwaiter();
      if (!awaiter1.IsCompleted)
        AsyncHelpers.UnsafeAwaitAwaiter<YieldAwaitable.YieldAwaiter>(awaiter1);
      awaiter1.GetResult();
      ValueTaskAwaiter<int> awaiter11 = ValueTask.FromResult<int>(100).GetAwaiter();
      if (!awaiter11.IsCompleted)
        AsyncHelpers.UnsafeAwaitAwaiter<ValueTaskAwaiter<int>>(awaiter11);
      return Task.FromResult<int>(awaiter11.GetResult());
    }

ilprint seems to need to have detection and output for it done. However, the current detection relies on MethodImpl being in netstandard2.0, since this is part of net10.0, there would have to be some compat layer here.

Secondly, as a separate discussion point. Having people manually add this attribute would be extremely inconvenient. What options do you see as possible for a CE to add attributes to the methods that get written out? (We can move to a separate discussion if needed)

Expected behavior

MethodImpl is preserved

Actual behavior

MethodImpl is not preserved

Known workarounds

Hand editing the IL?

Related information

Provide any related information (optional):

• Operating system
• .NET Runtime kind (.NET Core, .NET Framework, Mono)
• Editing Tools (e.g. Visual Studio Version, Visual Studio)