Attribute argument of a type containing function pointer fails with TypeLoadException during reflection

[jjonescz]

Version Used: dotnet/roslyn@34180c3 (2022-12-20)

Discovered while working on dotnet/roslyn#66073.

Steps to Reproduce:

[Theory, CombinatorialData, WorkItem(65594, "https://github.com/dotnet/roslyn/issues/65594")]
public void Attribute_TypedDefault_Enum([CombinatorialValues("class", "struct")] string kind)
{
    var source = $$"""
        using System;
        using System.Linq;
        
        var attr = typeof(C).CustomAttributes.Single(d => d.AttributeType == typeof(A));
        var arg = attr.ConstructorArguments.Single();
        Console.WriteLine((int)arg.Value == 0);
        
        class A : Attribute
        {
            public A(B<delegate*<void>[]>.E e) { }
        }

        {{kind}} B<T>
        {
            public enum E { }
        }

        [A(default)]
        class C { }
        """;

    var verifier = CompileAndVerify(source, expectedOutput: "True", symbolValidator: static module =>
    {
        var c = module.GlobalNamespace.GetTypeMember("C");
        var attr = c.GetAttributes().Single(d => d.AttributeClass?.Name == "A");
        Assert.Empty(attr.ConstructorArguments);
    });
    verifier.VerifyDiagnostics();
}

Expected Behavior: The test succeeds.

Actual Behavior: At runtime, it fails with:

System.TypeLoadException: Could not load type '(fnptr)' from assembly 'System.Private.CoreLib, Version=7.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e'.
   at System.RuntimeTypeHandle.GetTypeByNameUsingCARules(String name, RuntimeModule scope)
   at System.Reflection.CustomAttributeTypedArgument.ResolveType(RuntimeModule scope, String typeName)
   at System.Reflection.CustomAttributeTypedArgument..ctor(RuntimeModule scope, CustomAttributeEncodedArgument encodedArg)
   at System.Reflection.RuntimeCustomAttributeData.get_ConstructorArguments()
   at Program.<Main>$(String[] args)

Changing A's constructor to take parameter of a different type, e.g., B<int>.E instead of B<delegate*<void>[]>.E, makes the test pass. (Although I wouldn't expect the symbol validator to discover empty attribute constructor arguments, but that's a different issue - dotnet/roslyn#66370.)

Note This issue is mentioned in tests (dotnet/roslyn#66073).

[jcouv]

Assigned to @jjonescz for initial investigation (confirm whether this is a runtime/reflection issue). Thanks

[jjonescz]

@jcouv Yes, this seems to be runtime issue. The emitted metadata look correct. Here is an IL repro:

[Fact]
public void Issue66187()
{
    var ilSource = """
        .class public auto ansi beforefieldinit A
            extends [mscorlib]System.Attribute
        {
            .method public hidebysig specialname rtspecialname 
                instance void .ctor (
                    valuetype B`1/E<method void *()[]> e
                ) cil managed 
            {
                .maxstack 8
                ret
            }
        }

        .class public auto ansi beforefieldinit B`1<T>
            extends System.Object
        {
            .class nested public auto ansi sealed E<T>
                extends [mscorlib]System.Enum
            {
                .param type T
                .field public specialname rtspecialname int32 value__
            }
        }

        .class public auto ansi beforefieldinit C
            extends System.Object
        {
            .custom instance void A::.ctor(valuetype B`1/E<method void *()[]>) = (
                01 00 00 00 00 00 00 00
            )
        }
        """;
    var source = """
        using System;
        using System.Linq;

        var attr = typeof(C).CustomAttributes.Single(d => d.AttributeType == typeof(A));
        var arg = attr.ConstructorArguments.Single();
        Console.WriteLine((int?)arg.Value == 0);
        """;
    var comp = CreateCompilationWithIL(source, ilSource).VerifyDiagnostics();
    CompileAndVerify(comp, expectedOutput: "True");
}

Fails with:

System.TypeLoadException : Could not load type '(fnptr)' from assembly 'System.Private.CoreLib, Version=7.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e'.
Stack Trace:
     at System.RuntimeTypeHandle.GetTypeByNameUsingCARules(String name, RuntimeModule scope)
     at System.Reflection.CustomAttributeTypedArgument.ResolveType(RuntimeModule scope, String typeName)
     at System.Reflection.CustomAttributeTypedArgument..ctor(RuntimeModule scope, CustomAttributeEncodedArgument encodedArg)
     at System.Reflection.RuntimeCustomAttributeData.get_ConstructorArguments()
  (4,0): at Program.<Main>$(String[] args)

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[ghost]

Tagging subscribers to this area: @dotnet/area-system-reflection
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Version Used: 34180c3974c46fe354740d7f5fddd17244474612 (2022-12-20)

Discovered while working on dotnet/roslyn#66073.

Steps to Reproduce:

[Theory, CombinatorialData, WorkItem(65594, "https://github.com/dotnet/roslyn/issues/65594")]
public void Attribute_TypedDefault_Enum([CombinatorialValues("class", "struct")] string kind)
{
    var source = $$"""
        using System;
        using System.Linq;
        
        var attr = typeof(C).CustomAttributes.Single(d => d.AttributeType == typeof(A));
        var arg = attr.ConstructorArguments.Single();
        Console.WriteLine((int)arg.Value == 0);
        
        class A : Attribute
        {
            public A(B<delegate*<void>[]>.E e) { }
        }

        {{kind}} B<T>
        {
            public enum E { }
        }

        [A(default)]
        class C { }
        """;

    var verifier = CompileAndVerify(source, expectedOutput: "True", symbolValidator: static module =>
    {
        var c = module.GlobalNamespace.GetTypeMember("C");
        var attr = c.GetAttributes().Single(d => d.AttributeClass?.Name == "A");
        Assert.Empty(attr.ConstructorArguments);
    });
    verifier.VerifyDiagnostics();
}

Expected Behavior: The test succeeds.

Actual Behavior: At runtime, it fails with:

System.TypeLoadException: Could not load type '(fnptr)' from assembly 'System.Private.CoreLib, Version=7.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e'.
   at System.RuntimeTypeHandle.GetTypeByNameUsingCARules(String name, RuntimeModule scope)
   at System.Reflection.CustomAttributeTypedArgument.ResolveType(RuntimeModule scope, String typeName)
   at System.Reflection.CustomAttributeTypedArgument..ctor(RuntimeModule scope, CustomAttributeEncodedArgument encodedArg)
   at System.Reflection.RuntimeCustomAttributeData.get_ConstructorArguments()
   at Program.<Main>$(String[] args)

Changing A's constructor to take parameter of a different type, e.g., B<int>.E instead of B<delegate*<void>[]>.E, makes the test pass. (Although I wouldn't expect the symbol validator to discover empty attribute constructor arguments, but that's probably a different issue.)

Note This issue is mentioned in code.

Author:	jjonescz
Assignees:	-
Labels:	bug, area-System.Reflection, untriaged
Milestone:	-

[steveharter]

Function pointers are not currently supported as a reflectable type othan than IntPtr; see #11354.

We are working on adding support in 8.0, although resolving a function pointer from a string may not be supported in 8.0 either as shown in the provided call stack
System.Reflection.CustomAttributeTypedArgument.ResolveType(RuntimeModule scope, String typeName).

Keeping in 8.0 for re-assessment once the core function pointer work is in.

[steveharter]

This issue still occurs in v8 RC1:

namespace ConsoleApp172
{
    internal class Program
    {
        static void Main(string[] args)
        {
            var attr = typeof(C).CustomAttributes.Single(d => d.AttributeType == typeof(A));

            // throws:
            var arg = attr.ConstructorArguments.Single();

            Console.WriteLine((int)arg.Value == 0);
        }
    }

    class A : Attribute
    {
        public A(B<delegate*<void>[]>.E e) { }
        
        // This works:
        // public A(B<void*[]>.E e) { }
    }

    class B<T>
    {
        public enum E { }
    }

    [A(default)]
    class C { }
}

Moving to v9 based on priority.

[steveharter]

Closing; this works in latest v9 (Preview 1+). It did not work in v8.

I don't have the fix that allowed this to work - previously, the attribute data string could not be properly deserialized: 'Could not load type 'System.Void()' from assembly 'System.Private.CoreLib, Version=9.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e'.'

The enum type is based on int so arg.Value.GetType will be int\Int32, so this LOC could be added to the test above:

Console.WriteLine(arg.Value.GetType() == typeof(int));

The actual benefit from this is very low to none. The original failing test in the PR description is "combinatorial" and I can't think of a useful real-world scenario since:

• A function pointer type can't be used in an attribute (an array of function pointers was selected in the combinatorial test data).
• A function pointer cannot be used as a generic parameter (by design; no C# support anyway).