System.Reflection.MetadataLoadContext doesn't support function pointer types

[vargaz]

To reproduce: run the attached project
Version: master
Expected result: works
Actual result:

Unhandled exception. System.NotSupportedException: Parsing function pointer types in signatures is not supported.
   at System.Reflection.TypeLoading.Ecma.EcmaModule.GetFunctionPointerType(MethodSignature`1 signature)
   at System.Reflection.Metadata.Ecma335.SignatureDecoder`2.DecodeType(BlobReader& blobReader, Boolean allowTypeSpecifications, Int32 typeCode)
   at System.Reflection.Metadata.Ecma335.SignatureDecoder`2.DecodeMethodSignature(BlobReader& blobReader)
   at System.Reflection.TypeLoading.Ecma.EcmaMethodDecoder.SpecializeMethodSig(IRoMethodBase roMethodBase)
   at System.Reflection.TypeLoading.RoDefinitionMethod`1.ComputeMethodSig()
   at System.Reflection.TypeLoading.RoMethod.get_MethodSig()
   at System.Reflection.TypeLoading.RoMethod.get_ReturnParameter()
   at System.Reflection.TypeLoading.RoMethod.get_ReturnType()

[vargaz]

test.tar.gz

[marek-safar]

Hmm how is Roslyn reading such metadata?

@jaredpar @MichalStrehovsky

[MichalStrehovsky]

This looks like a bug in System.Reflection.MetadataLoadContext. It's a library built on top of System.Reflection.Metadata that provides additional abstractions over the metadata. Roslyn only uses S.R.Metadata, not this extra layer with the missing implementation.

[steveharter]

This looks like a bug in System.Reflection.MetadataLoadContext

It is apparently by design since it throws an explicit NotSupportedException when detecting a function pointer.

This overlaps with #11354 where we don't return function pointer type from standard reflection either and need a way to represent that.

Doing a typeof(delegate*<void>) (for example) returns System.IntPtr as the type, so it would be expected that MLC return IntPtr as the type. However, that doesn't allow inspection of the parameters or return type, and there is not an existing "function pointer" type in .NET that we can readily use instead.