Implement GetInterfaceMap

[Suchiman]

Copy pasted from https://github.com/dotnet/runtime/blob/master/src/coreclr/src/System.Private.CoreLib/src/System/RuntimeType.CoreCLR.cs#L2609 and then made to work.

[Suchiman]

The original code also says

// If the impl is null, then virtual stub dispatch is active.
RuntimeMethodHandleInternal classRtMethodHandle = GetTypeHandleInternal().GetInterfaceMethodImplementation(ifaceRtTypeHandle, ifaceRtMethodHandle);

but VSD is always active for interfaces and impl appears to be non null?

[Suchiman]

Ok, best of both worlds i hope. Not modifying existing code and no switches for now.
I don't suppose there's an easier / better way to get to the VirtualResolveData?

[MichalStrehovsky]

RuntimeAugments.IsAssignableFrom might be better because it also covers variance:

interface IFoo<in T>
{
    void Frob();
}



class Foo : IFoo<object>
{
    public void Frob() { }
}

class Program
{
    static void Main()
    {
        var m = typeof(Foo).GetInterfaceMap(typeof(IFoo<string>));
        Console.WriteLine(m.InterfaceMethods[0].DeclaringType);
        Console.WriteLine(m.TargetMethods[0].DeclaringType);
    }
}

[Suchiman]

On the other hand, it bails on

interface IFoo<in T>
{
    void Frob();
}

class Foo<T> : IFoo<object>
{
    public void Frob() { }
}

class Program
{
    static void Main()
    {
        var m = typeof(Foo<>).GetInterfaceMap(typeof(IFoo<string>));
        Console.WriteLine(m.InterfaceMethods[0].DeclaringType);
        Console.WriteLine(m.TargetMethods[0].DeclaringType);
    }
}

due to

corert/src/Runtime.Base/src/System/Runtime/TypeCast.cs

Lines 493 to 497 in 0185f47

	// Special case: Generic Type definitions are not assignable in a mrt sense
	// in any way. Assignability of those types is handled by reflection logic.
	// Call this case out first and here so that these only somewhat filled in
	// types do not leak into the rest of the type casting logic.
	if (pTargetType->IsGenericTypeDefinition || pSourceType->IsGenericTypeDefinition)

while CoreCLR does not.

[jkotas]

Could you please add a comment that lists all known cases that CoreCLR handles, but this implementation does not?

[jkotas]

Thanks

[jkotas]

Thank you!

[MichalStrehovsky]

Thank you @Suchiman! I didn't expect we would be able to get this far without extra tables generated by the compiler.