Getting a StreamJsonRpc.RemoteInvocationException when invoking a server->client RPC on Mono.

[ILikePizza555]

Minimal source code that reproduces this error: https://github.com/ILikePizza555/StreamJsonRPCTest

This happens on MacOS on the latest version of Mono (6.4.0.198).

Output of the project is

Entered RequestDataFromServerRPC
Entered RequestDataFromClientRPC
RPC Exception: StreamJsonRpc.RemoteInvocationException: Attempted to access an element as a type incompatible with the array.
  at StreamJsonRpc.JsonRpc.InvokeCoreAsync[TResult] (System.Nullable`1[T] id, System.String targetName, System.Collections.Generic.IReadOnlyList`1[T] arguments, System.Threading.CancellationToken cancellationToken, System.Boolean isParameterObject) [0x0018d] in <ab9df841741b4f729c437e4366755293>:0 
  at SJRTest.Server.RequestDataFromClientRPC (System.String key, System.Threading.CancellationToken ct) [0x0009b] in <33bed87fd5be4d728d3def5bfad1c0af>:0 
Result: 

Obviously, the expected behavior is to not have the exception. The fact that the application does not print out Entered DictionaryDataCallback indicates that this exception is thrown before the method is called.

[AArnott]

I am pleased to say this reproduces on Windows with the mono runtime as well.
I'll try to get our unit tests running on mono so we can offer better mono support. But please do file a bug against mono as well and link to this issue so we can track. (I did this already).

[AArnott]

Mono is struggling to run our unit tests for a variety of reasons. For just our JsonRpcJsonHeadersTests class, 31 of 145 tests fail, including with the exception that this issue tracks.

[AArnott]

I found an even smaller repro for your project. I've sent a PR.

But really it's just this:

static void Main(string[] args)
{
    var m = typeof(Program).GetMethod(nameof(Foo), BindingFlags.Static | BindingFlags.NonPublic);
    ParameterInfo[] a = m.GetParameters();
    Span<ParameterInfo> s = a.AsSpan(0, 0); // a's runtime type is RuntimeParameterInfo[]
}

static void Foo() { }

[AArnott]

I filed mono/mono#17993 to track the defect on mono

[AArnott]

I also filed mono/mono#17994 to track the only other defect on mono that I found.