Managed type system has trouble resolving virtual methods

[MichalStrehovsky]

I assume this is a regression from #51764.

In the \src\tests\JIT\Generics\Instantiation\Interfaces\Class05.cs test, we have a situation where:

public interface IGen<T>
{
    void _Init(T fld1);
    bool InstVerify(System.Type t1);
}

public interface IGenSub2DStringArray : IGen<string[,]> { }

public class Gen2DStringArray : IGenSub2DStringArray
{
    public void _Init(string[,] fld1)
    {
    }
}

When the managed type system tries to find implementation of IGen<string[]>._Init on Gen2DStringArray, it will try to match up the signature of _Init between those two types. The signatures don't match because the signature of _Init on Gen2DStringArray has EmbeddedSignatureData of type ArrayShape with contents 1.2.2.1||0,0, while the signature on the interface doesn't have an ArrayShape. The Equals check on the signature fails at callstack:

>	ILCompiler.TypeSystem.dll!Internal.TypeSystem.MethodSignature.Equals(Internal.TypeSystem.MethodSignature otherSignature, bool allowCovariantReturn) Line 220	C#
 	ILCompiler.TypeSystem.dll!Internal.TypeSystem.MethodSignature.Equals(Internal.TypeSystem.MethodSignature otherSignature) Line 185	C#
 	ILCompiler.TypeSystem.dll!Internal.TypeSystem.MetadataVirtualMethodAlgorithm.FindMatchingVirtualMethodOnTypeByNameAndSig(Internal.TypeSystem.MethodDesc targetMethod, Internal.TypeSystem.DefType currentType, bool reverseMethodSearch, System.Func<Internal.TypeSystem.MethodDesc, Internal.TypeSystem.MethodDesc, bool> nameSigMatchMethodIsValidCandidate) Line 340	C#
 	ILCompiler.TypeSystem.dll!Internal.TypeSystem.MetadataVirtualMethodAlgorithm.ResolveInterfaceMethodToVirtualMethodOnType(Internal.TypeSystem.MethodDesc interfaceMethod, Internal.TypeSystem.MetadataType currentType) Line 601	C#
 	ILCompiler.TypeSystem.dll!Internal.TypeSystem.MetadataVirtualMethodAlgorithm.ResolveInterfaceMethodToVirtualMethodOnType(Internal.TypeSystem.MethodDesc interfaceMethod, Internal.TypeSystem.TypeDesc currentType) Line 565	C#
 	ILCompiler.TypeSystem.dll!Internal.TypeSystem.TypeSystemHelpers.ResolveInterfaceMethodToVirtualMethodOnType(Internal.TypeSystem.TypeDesc type, Internal.TypeSystem.MethodDesc interfaceMethod) Line 275	C#

There are more tests where this is failing, but I assume in crossgen2 this only means a failure to devirtualize in these tests. The failure mode is more brutal in NativeAOT.

But this can result in incorrect devirtualization with crossgen2 if there's a matching signature in one of the base types - I assume we don't have tests for that.

Cc @dotnet/crossgen-contrib

[MichalStrehovsky]

Might have been fixed with #52796 but needs verification.

[davidwrighton]

Sigh. #53796 didn't fix this one. Looking into this more deeply. The fix here is likely to be confusing.