Non-literal default argument interferes with module locality

[cnx-tcsikos]

Hi All!

I'm experiencing an issue with default arguments, where even though std::vector<uint8_t> is defined with py::module_local(), its definitions in the two modules conflicts with the following error:
ImportError: generic_type: type "vector_uint8_t" is already registered!

This only happens if default argument is a non-literal value. If py::arg("a") = std::vector<uint8_t>(1,2,3,4), everything works.

Consider the following setup:

lib_dep.cpp

class MyClass : public Common
{
public:
  MyClass(const std::vector<uint8_t>& a = CreateDefaultValue()){}
  static std::vector<uint8_t>CreateDefaultValue() { return {1,2,3,4};}
...
};

PYBIND11_MAKE_OPAQUE(std::vector<uint8_t>);

PYBIND11_MODULE(lib_dep, mod)
{
  py::bind_vector<std::vector<uint8_t>>(mod, "vector_uint8_t", py::module_local());
  py::implicitly_convertible<py::list, std::vector<uint8_t>>();

  py::class_<MyClass, std::shared_ptr<MyClass>,Common>(mod, "MyClass")
    .def(py::init<const std::vector<uint16_t>&>(), py::arg("a") = MyClass::CreateDefaultValue)
    ...;
  ...
}

lib_super

class Common{...};

PYBIND11_MAKE_OPAQUE(std::vector<uint8_t>);

PYBIND11_MODULE(lib_super, mod)
{
  py::bind_vector<std::vector<uint8_t>>(mod, "vector_uint8_t", py::module_local());
  py::implicitly_convertible<py::list, std::vector<uint8_t>>();

  py::class_<Common...
  ...
}