PYBIND11_NUMPY_DTYPE and X macros

[davidemollica]

Hi, I am trying to create a custom dtype using X macros like this:

#include <pybind11/pybind11.h>
#include <pybind11/numpy.h>

#define FOR_FIELDS(X) \
    X(float, a)\
    X(float, b)\
    X(float, c)

#define DEFINE_FIELD(type, name) type name;
struct MyStruct {FOR_FIELDS(DEFINE_FIELD)};
#undef DEFINE_FIELD

PYBIND11_MODULE(testmodule, m) {

    #define DEFINE_FIELD(type, name) ,name
    PYBIND11_NUMPY_DTYPE(MyStruct FOR_FIELDS(DEFINE_FIELD));
    #undef DEFINE_FIELD

    // PYBIND11_NUMPY_DTYPE(MyStruct, a, b, c);
}

#undef FOR_FIELDS

The preprocessor output, relative to the PYBIND11_NUMPY_DTYPE macro, is

::pybind11::detail::npy_format_descriptor<MyStruct ,a ,b ,c>::register_dtype(
    ::std::vector<::pybind11::detail::field_descriptor>{
        ::pybind11::detail::field_descriptor {
            "a", 
            __builtin_offsetof (MyStruct, a)
            , sizeof(decltype(std::declval<MyStruct>().a)),
            ::pybind11::format_descriptor<decltype(std::declval<MyStruct>().a)>::format(),
            ::pybind11::detail::npy_format_descriptor< decltype(std::declval<MyStruct>().a)>::dtype()
        },
        ::pybind11::detail::field_descriptor { 
            "b", 
            __builtin_offsetof (MyStruct, b)
            , sizeof(decltype(std::declval<MyStruct>().b)),
            ::pybind11::format_descriptor<decltype(std::declval<MyStruct>().b)>::format(),
            ::pybind11::detail::npy_format_descriptor< decltype(std::declval<MyStruct>().b)>::dtype()
        },
        ::pybind11::detail::field_descriptor { 
            "c", 
            __builtin_offsetof (MyStruct, c)
            , sizeof(decltype(std::declval<MyStruct>().c)),
            ::pybind11::format_descriptor<decltype(std::declval<MyStruct>().c)>::format(),
            ::pybind11::detail::npy_format_descriptor< decltype(std::declval<MyStruct>().c)>::dtype()
        },
        ::pybind11::detail::field_descriptor {
            "", 
            __builtin_offsetof (MyStruct, ), 
            sizeof(decltype(std::declval<MyStruct>().)),
            ::pybind11::format_descriptor<decltype(std::declval<MyStruct>().)>::format(),
            ::pybind11::detail::npy_format_descriptor< decltype(std::declval<MyStruct>().)>::dtype() 
        }
    }
);

As you can see, there is a spurious empty field "" (the last one), while the struct is correct:

struct MyStruct {float a; float b; float c;};

Is this a bug or am I missing something?

Thanks!