No way to extract CustomAttribute from interfaces in SR.Metadata

[glennawatson]

Hi,

I am making a public api approval tool for my application. I am adding support for C# 8 nullable contexts. I have one issue remaining which seems to be having bugs with SR.Metadata

I have the following class in my test suite:

 public class DerivedNullableInterface2 : IEnumerable<IEnumerable<string?>>
    {
        public IEnumerator<IEnumerable<string?>> GetEnumerator()
        {
            throw new NotImplementedException();
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            throw new NotImplementedException();
        }
    }

It generates the following IL for the NullableAttribute:

.class auto ansi nested public beforefieldinit DerivedNullableInterface2
       extends [netstandard]System.Object
       implements class [netstandard]System.Collections.Generic.IEnumerable`1<class [netstandard]System.Collections.Generic.IEnumerable`1<string>>,
                  [netstandard]System.Collections.IEnumerable
{
  .interfaceimpl type class [netstandard]System.Collections.Generic.IEnumerable`1<class [netstandard]System.Collections.Generic.IEnumerable`1<string>>
  .custom instance void System.Runtime.CompilerServices.NullableAttribute::.ctor(uint8[]) = ( 01 00 03 00 00 00 00 00 02 00 00 ) 
} // end of class DerivedNullableInterface2

I would assume the .custom after the `interfaceimpl would be available in the InterfaceImplementation custom attributes.

However, although I can see the NullableAttribute generated in the MetadataReader main list of CustomAttributes I don't see it associated with the interface.

I made my own test code against the SR.Metadata to find the parent of the attribute (which in my example has row number 1).

public void GetParentTest(MetadataReader reader)
{
             var interestedAttribute = reader.CustomAttributes.First();
            var handle = reader.CustomAttributeTable.GetParent(interestedAttribute);           
}

The handle returned is a Parameter (despite being the valid .custom in the above generated IL), with a row number also of 1.

[jnm2]

/cc @tmat

[nguerrera]

There are two NullableAttribute applications. One is applied to return Parameter of GetEnumerator method and another is applied to InterfaceImplementation of IEnumerable<IEnumerable<IEnumerable<string>> .

reader.CustomAttributes.First()could be any attribute, why do you expect it to be a particular one?

using var peReader = new PEReader(File.OpenRead(Assembly.GetExecutingAssembly().Location));
var mdReader = peReader.GetMetadataReader();

foreach (var attributeHandle in mdReader.CustomAttributes)
{
    var attribute = mdReader.GetCustomAttribute(attributeHandle);
    var ctorHandle = attribute.Constructor;

    EntityHandle attributeTypeHandle = ctorHandle.Kind switch
    {
        HandleKind.MethodDefinition => mdReader.GetMethodDefinition((MethodDefinitionHandle)ctorHandle).GetDeclaringType(),
        HandleKind.MemberReference => mdReader.GetMemberReference((MemberReferenceHandle)ctorHandle).Parent,
        _ => throw new InvalidOperationException(),
    };

    StringHandle attributeTypeNameHandle = attributeTypeHandle.Kind switch
    {
        HandleKind.TypeDefinition => mdReader.GetTypeDefinition((TypeDefinitionHandle)attributeTypeHandle).Name,
        HandleKind.TypeReference => mdReader.GetTypeReference((TypeReferenceHandle)attributeTypeHandle).Name,
        _ => throw new InvalidOperationException(),
    };

    if (mdReader.StringComparer.Equals(attributeTypeNameHandle, "NullableAttribute"))
    {
        Console.WriteLine(attribute.Parent.Kind);
    }
}

Parameter
InterfaceImplementation

[glennawatson]

That's solely because it's the one matching the .custom implementation above rather than a fixed test..

The point is I'm not getting inside the InterfaceImplementation any attributes coming through with the above sample.

[glennawatson]

so I am unable to get the IEnumerable<IEnumerable<IEnumerable<string?>> nullability.

[nguerrera]

See my sample. I don't think it is correct that the first attribute is the one you are looking for. The one applied to a Parameter is applied to the return value of GetEnumerator.

From ILSpy decompilation:

	[return: System.Runtime.CompilerServices.Nullable(new byte[]
	{
		1,
		1,
		2
	})]
	public IEnumerator<IEnumerable<string>> GetEnumerator()

From IL:

  .method public hidebysig newslot virtual final 
          instance class [System.Runtime]System.Collections.Generic.IEnumerator`1<class [System.Runtime]System.Collections.Generic.IEnumerable`1<string>> 
          GetEnumerator() cil managed
  {
    .param [0]
    .custom instance void System.Runtime.CompilerServices.NullableAttribute::.ctor(uint8[]) = ( 01 00 03 00 00 00 01 01 02 00 00 ) 

I can find the one on the InterfaceImplementation, it's just a different attribute application.

[glennawatson]

Yes,

My original code was

Get interface implementations for type DerivedInterface2, Get custom attributes for InterfaceImplementation, InterfaceImplementation CustomAttribute is empty.

The first item is a red hearing and not related to this item.

I solely did it for @jnm2 suggestion on gitter.

[glennawatson]

to be honest @nguerrera I have found this interaction extremely rude. Given that @terrajobst has been attempting to help me with the issue and @jnm2 without much success.

[nguerrera]

I apologize that this sounded rude. I am trying to help here too. I didn't have the prior context, and I took time out of my weekend to investigate here with the sample above.

[nguerrera]

I'm digging further based on your updated information.

[glennawatson]

yeah sorry about that. Just iteration upon iteration so the code has gotten away from my initial problem.

https://github.com/glennawatson/MetadataPublicApiGenerator/blob/4d24e8dcbc305aeeb378d55ac0f445d88fc1a9b4/src/MetadataPublicApiGenerator/Extensions/TypeExtensions.cs#L52

So that's my attempt so far, there is a bit of a wrapper around the InterfaceImplementation here

https://github.com/glennawatson/MetadataPublicApiGenerator/blob/master/src/LightweightMetadata/TypeWrappers/InterfaceImplementationWrapper.cs#L29

So that interface implementation is correctly the IEnumerable<....> but the custom attributes doesn't seem to be producing anything in the interface implementation

[nguerrera]

Get interface implementations for type DerivedInterface2, Get custom attributes for InterfaceImplementation, InterfaceImplementation CustomAttribute is empty.

This was my attempt to repro that path:

using var peReader = new PEReader(File.OpenRead(Assembly.GetExecutingAssembly().Location));
var mdReader = peReader.GetMetadataReader();

foreach (var typeDefinitionHandle in mdReader.TypeDefinitions)
{
    var typeDefinition = mdReader.GetTypeDefinition(typeDefinitionHandle);
            
    foreach (var interfaceImplementationHandle in typeDefinition.GetInterfaceImplementations())
    {
        var interfaceImplementation = mdReader.GetInterfaceImplementation(interfaceImplementationHandle);

        foreach (var attribute in interfaceImplementation.GetCustomAttributes())
        {
            var typeName = mdReader.GetString(typeDefinition.Name);

            Console.WriteLine($"Found attribute on InterfaceImplementation by {typeName}");
        }
    }
}

But it worked for me. Above prints:

Found attribute on InterfaceImplementation by DerivedNullableInterface2

I will look at the code links above next.

[nguerrera]

I can't spot an obvious issue in the linked code. Are you able to reduce what you are seeing into steps that I can run? I can debug it from there.

[nguerrera]

There are two InterfaceImplementations, one of IEnumerable<IEnumerable<string>> and one of non-generic IEnumerable. Is it possible you are looking at the second one?

[nguerrera]

The point is I'm not getting inside the InterfaceImplementation any attributes coming through with the above sample.

Sorry, I missed this before. Are you saying that when you run my code snippets above, you don't get the same results?

What is dotnet --info in that case? I am currently using 3.0 preview 7 on my home machine.

[glennawatson]

sorry, preview6, after upgrading I am now getting more consistent results with what you have above.

[glennawatson]

Thanks for your help regardless, I appreciate you helping on your day off

[nguerrera]

No problem, glad it worked out. :)