Make PYBIND11_MODULE name usable with define

[tzh1043]

The name in the PYBIND11_MODULE(name, variable) #define can not be used with a preprocessor define.

Given a simple cpp file define_module_name.cpp, where MODULENAME is defined elsewhere, and preprocess it.

// define_module_name.cpp, preprocessor command (add your pybind11/python -I flags!):
// c++ -E -o define_module_name.ii -DMODULENAME=my_module_name define_module_name.cpp
#include <pybind11/pybind11.h>
#include <pybind11/embed.h>

PYBIND11_MODULE(MODULENAME, m) { }
PYBIND11_EMBEDDED_MODULE(MODULENAME, m) { }

The result in define_module_name.ii will contain both my_module_name and MODULENAME:

PyObject *PyInit_my_module_name()

static void pybind11_init_MODULENAME(pybind11::module &);
auto m = pybind11::module("MODULENAME");
pybind11_init_MODULENAME(m);
void pybind11_init_MODULENAME(pybind11::module &m) { }

This commit fixes this by adding one level of macro indirection.

[jagerman]

Minor nitpick: this isn't actually string concatenation; perhaps rename to just PYBIND11_CONCAT?

[jagerman]

Minor style consistency issue: need a space after a comma.

[jagerman]

Same here.

[jagerman]

Looks good to me; I left a couple comments for minor cosmetic details.

[jagerman]

This is a pretty small change and seems worth including in 2.2.1.

[dean0x7d]

LGTM. I just have two whitespace nitpicks.

[dean0x7d]

Remove whitespace between docs and definition.

[dean0x7d]

Same here.

[dean0x7d]

Merged, thanks!