Stop using `ELEMENT_TYPE_INTERNAL` for generic instantiations

[SeeminglyScience]

$longToBytes = il { [byte[]]([long]) } {
    .locals init {
        [Span[byte]] $span
    }

    ldarga.s 0
    sizeof { [long] }
    call { [Span[byte]] [Runtime.InteropServices.MemoryMarshal]::CreateSpan([g[byte]], [ref] [byte], [int]) }
    stloc.auto $span
    ldloca.auto $span
    call { [byte[]] [Span[byte]].ToArray() }
    ret
}

$longToBytes.Invoke(20l)

Get-Error

Exception             :
    Type           : System.Management.Automation.MethodInvocationException
    ErrorRecord    :
        Exception             :
            Type    : System.Management.Automation.ParentContainsErrorRecordException
            Message : Exception calling "Invoke" with "1" argument(s): "Could not load type 'Microsoft.CodeAnalysis.EmbeddedAttribute'
from assembly 'ILAssembler, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' due to value type mismatch."
            HResult : -2146233087
        CategoryInfo          : NotSpecified: (:) [], ParentContainsErrorRecordException
        FullyQualifiedErrorId : TypeLoadException
        InvocationInfo        :
            ScriptLineNumber : 1
            OffsetInLine     : 1
            HistoryId        : -1
            Line             : $longToBytes.Invoke(20l)
            PositionMessage  : At line:1 char:1
                               + $longToBytes.Invoke(20l)
                               + ~~~~~~~~~~~~~~~~~~~~~~~~
            CommandOrigin    : Internal
        ScriptStackTrace      : at <ScriptBlock>, <No file>: line 1
    TargetSite     :
        Name          : ConvertToMethodInvocationException
        DeclaringType : System.Management.Automation.ExceptionHandlingOps, System.Management.Automation, Version=7.1.0.0, Culture=neutral,
PublicKeyToken=31bf3856ad364e35
        MemberType    : Method
        Module        : System.Management.Automation.dll
    StackTrace     :
   at System.Management.Automation.ExceptionHandlingOps.ConvertToMethodInvocationException(Exception exception, Type typeToThrow, String
methodName, Int32 numArgs, MemberInfo memberInfo)
   at CallSite.Target(Closure , CallSite , Object , Int64 )
   at System.Dynamic.UpdateDelegates.UpdateAndExecute2[T0,T1,TRet](CallSite site, T0 arg0, T1 arg1)
   at System.Management.Automation.Interpreter.DynamicInstruction`3.Run(InterpretedFrame frame)
   at System.Management.Automation.Interpreter.EnterTryCatchFinallyInstruction.Run(InterpretedFrame frame)
    Message        : Exception calling "Invoke" with "1" argument(s): "Could not load type 'Microsoft.CodeAnalysis.EmbeddedAttribute' from
assembly 'ILAssembler, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' due to value type mismatch."
    Data           : System.Collections.ListDictionaryInternal
    InnerException :
        Type       : System.TypeLoadException
        Message    : Could not load type 'Microsoft.CodeAnalysis.EmbeddedAttribute' from assembly 'ILAssembler, Version=1.0.0.0,
Culture=neutral, PublicKeyToken=null' due to value type mismatch.
        TypeName   : Microsoft.CodeAnalysis.EmbeddedAttribute
        TargetSite : Byte[] Invoke(Int64)
        StackTrace :
   at Invoke(Int64 )
   at CallSite.Target(Closure , CallSite , Object , Int64 )
        Source     : ILAssembler
        HResult    : -2146233054
    Source         : System.Management.Automation
    HResult        : -2146233087
CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
FullyQualifiedErrorId : TypeLoadException
InvocationInfo        :
    ScriptLineNumber : 1
    OffsetInLine     : 1
    HistoryId        : -1
    Line             : $longToBytes.Invoke(20l)
    PositionMessage  : At line:1 char:1
                       + $longToBytes.Invoke(20l)
                       + ~~~~~~~~~~~~~~~~~~~~~~~~
    CommandOrigin    : Internal
ScriptStackTrace      : at <ScriptBlock>, <No file>: line 1

[SeeminglyScience]

Turns out it's any generic instantiation. There doesn't appear to be anything wrong with the signature that I'm encoding, so I am leaning towards it being a bug with DynamicILInfo. I'll need to do more research and possibly open an issue on dotnet/runtime.

Until then, I've worked around the issue by using the unsupported element type ELEMENT_TYPE_INTERNAL to embed the type handle directly into the signature.

ILAssembler/src/ILAssembler/EncoderExtensions.cs

Lines 48 to 66 in 7e1a7ce

	// The supported way of declaring a generic instantiation isn't
	// working correctly in a locals sig. Unsure if it's something
	// we're doing wrong or if it's a problem with the DynamicILInfo
	// API. As a workaround, we're depending on an implementation
	// detail used by the runtime to embed a type handle directly
	// as a pointer.
	//
	// The proper implementation is commented below this.
	//
	// https://github.com/SeeminglyScience/ILAssembler/issues/42
	const byte ELEMENT_TYPE_INTERNAL = 0x21;
	encoder.Builder.WriteByte(ELEMENT_TYPE_INTERNAL);
	IntPtr rawHandle = type.TypeHandle.Value;
	unsafe
	{
	encoder.Builder.WriteBytes(
	(byte*)&rawHandle,
	sizeof(IntPtr));
	}