Exception when importing a C++/CLI assembly using "operator -"

[maxun]

Environment

• Pythonnet version: >= 3.0.0 ( version < 3.0.0 are ok)
• Python version: 3.9, 3.10, 3.11, 3.12...
• Operating System: Windows x64
• .NET Runtime: 4.6.2 .net framework

Details

Importing a .net assembly written in C++/CLI using a very specific way to define an operator result in an exception:

Python 3.11.4 | packaged by Anaconda, Inc. | (main, Jul  5 2023, 13:47:18) [MSC v.1916 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import clr
>>> clr.AddReference(r"C:\Users\laure\source\repos\Operator\x64\Release\Operator.dll")
<System.Reflection.RuntimeAssembly object at 0x0000029709E3D680>
>>> import Operator
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<frozen importlib._bootstrap>", line 1176, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1147, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 676, in _load_unlocked
  File "<frozen importlib._bootstrap>", line 573, in module_from_spec
  File "<string>", line 15, in create_module
System.IndexOutOfRangeException: Index was outside the bounds of the array.
   at Python.Runtime.OperatorMethod.IsReverse(MethodBase method)
   at Python.Runtime.OperatorMethod.FilterMethods(MethodBase[] methods, MethodBase[]& forwardMethods, MethodBase[]& reverseMethods)
   at Python.Runtime.ClassManager.GetClassInfo(Type type, ClassBase impl)
   at Python.Runtime.ClassManager.InitClassBase(Type type, ClassBase impl, ReflectedClrType pyType)
   at Python.Runtime.ReflectedClrType.GetOrCreate(Type type)
   at Python.Runtime.ModuleObject.GetAttribute(String name, Boolean guess)
   at Python.Runtime.ModuleObject.LoadNames()
   at Python.Runtime.ImportHook.Import(String modname)
   at Python.Runtime.CLRModule._load_clr_module(PyObject spec)

This can be reproduce with the minimal code (C++/CLI):

namespace Operator
{
	public ref class Matrix
	{
	public:
		Matrix^ operator - ()
		{
			return gcnew Matrix();
		}
	};
}

See Operator.zip

Investigation

It seems there is two way to define the operator- in C++/CLI:

Matrix^ operator - ()

And

static Matrix^ operator - (Matrix^ m)

There is no issue when using the second form. Actually in C# only the equivalent of the second form is possible. It explains why this bug is very uncommon.

Source of the exception

The code in pythonnet code triggering this exception (src/runtime/Types/OperatorMethod.cs)

public static bool IsReverse(MethodBase method)
        {
            Type primaryType = method.IsOpsHelper()
                ? method.DeclaringType.GetGenericArguments()[0]
                : method.DeclaringType;
            Type leftOperandType = method.GetParameters()[0].ParameterType;
            return leftOperandType != primaryType;
        }

The exception is thrown because GetGenericArguments return an empty list.

[filmor]

I'll have a look. Especially for edge cases like these, PRs are appreciated. I don't have an MSVC build setup available right now.

[maxun]

Here is the assembly so you do not need to recompile it with MSVC:

Operator.zip

I am not sure about the purpose of this IsReverse function but adding a trivial check should fix this bug.