Type.GetInterfaceMap(Type) does not throw for open generic types

[Xriuk]

Description

According to the docs:

Exceptions
ArgumentException
...
The current instance or interfaceType argument is an open generic type; that is, the ContainsGenericParameters property returns true.

The current instance I guess it refers to the type on which the method is called, which in my examples below is always an open type, and it does not throw for that.
While the interfaceType argument only throws if I manually write it as an open generic, while if I retrieve it through reflection it does not.

Reproduction Steps

See fiddle: https://dotnetfiddle.net/8698i5

Expected behavior

According to the docs it should always throw

Actual behavior

It throws only if both types are specified as open generics through typeof() and not via reflection

Regression?

No response

Known Workarounds

No response

Configuration

No response

Other information

No response

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Issue Details

---

Description

According to the docs:

Exceptions
ArgumentException
...
The current instance or interfaceType argument is an open generic type; that is, the ContainsGenericParameters property returns true.

The current instance I guess it refers to the type on which the method is called, which in my examples below is always an open type, and it does not throw for that.
While the interfaceType argument only throws if I manually write it as an open generic, while if I retrieve it through reflection it does not.

Reproduction Steps

See fiddle: https://dotnetfiddle.net/8698i5

Expected behavior

According to the docs it should always throw

Actual behavior

It throws only if both types are specified as open generics through typeof() and not via reflection

Regression?

No response

Known Workarounds

No response

Configuration

No response

Other information

No response

Author:	Xriuk
Assignees:	-
Labels:	area-System.Reflection
Milestone:	-

[buyaa-n]

According to the docs:

Exceptions
ArgumentException
...
The current instance or interfaceType argument is an open generic type; that is, the ContainsGenericParameters property returns true.

I don't see such throwing logic anywhere in the validation section:
https://github.com/dotnet/runtime/blob/1f9764f23332f19b2f3f7af22d875a8b27d5030b/src/coreclr/System.Private.CoreLib/src/System/RuntimeType.CoreCLR.cs#L2724-L2743

According to the docs it should always throw

I don't think it should always throw, it looks like a doc bug, it produces valid interface map

public interface MyGenericInterface<T>
{
    void DoIt(T t);
}

public class MyGenericClass<T> : MyGenericInterface<T>
{
    public void DoIt(T t)
    {
        throw new NotImplementedException();
    }
}

public class Program
{
    public static void Main()
    {
        // This produces valid interface map:
        InterfaceMapping map = typeof(MyGenericClass<>).GetInterfaceMap(typeof(MyGenericClass<>).GetInterfaces().First());

        // This throws because of the validation on row 2736 'TypeHandle.VerifyInterfaceIsImplemented(ifaceRtTypeHandle);' 
        // Not because 'ContainsGenericParameters' property returns true
        map = typeof(MyGenericClass<>).GetInterfaceMap(typeof(MyGenericInterface<>));
    }
}