test/upcast.cpp does not compile since python 3.10

[e-kwsm]

revision: 3e7be69

Since Python 3.10, compilation of test/upcast.cpp fails.

python/test/upcast.cpp

Lines 16 to 17 in 3e7be69

	BOOST_TEST(&Py_REFCNT(boost::python::upcast<PyObject>(&o)) == &Py_REFCNT(&o));
	BOOST_TEST(&Py_REFCNT(boost::python::upcast<PyObject>(&y)) == &Py_REFCNT(&y));

$ g++ -Iinclude -I/opt/miniconda3/envs/py310/include/python3.10 test/upcast.cpp
In file included from /usr/include/boost/detail/lightweight_test.hpp:15,
 from ./test/upcast.cpp:7:
./test/upcast.cpp: In function 'int main()':
/opt/miniconda3/envs/py310/include/python3.10/object.h:133:33: error: lvalue required as unary '&' operand
 133 | #define Py_REFCNT(ob) _Py_REFCNT(_PyObject_CAST_CONST(ob))
 | ~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
./test/upcast.cpp:16:17: note: in expansion of macro 'Py_REFCNT'
 16 | BOOST_TEST(&Py_REFCNT(boost::python::upcast<PyObject>(&o)) == &Py_REFCNT(&o));
 | ^~~~~~~~~
/opt/miniconda3/envs/py310/include/python3.10/object.h:133:33: error: lvalue required as unary '&' operand
 133 | #define Py_REFCNT(ob) _Py_REFCNT(_PyObject_CAST_CONST(ob))
 | ~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
./test/upcast.cpp:16:68: note: in expansion of macro 'Py_REFCNT'
 16 | BOOST_TEST(&Py_REFCNT(boost::python::upcast<PyObject>(&o)) == &Py_REFCNT(&o));
 | ^~~~~~~~~
/opt/miniconda3/envs/py310/include/python3.10/object.h:133:33: error: lvalue required as unary '&' operand
 133 | #define Py_REFCNT(ob) _Py_REFCNT(_PyObject_CAST_CONST(ob))
 | ~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
./test/upcast.cpp:17:17: note: in expansion of macro 'Py_REFCNT'
 17 | BOOST_TEST(&Py_REFCNT(boost::python::upcast<PyObject>(&y)) == &Py_REFCNT(&y));
 | ^~~~~~~~~
/opt/miniconda3/envs/py310/include/python3.10/object.h:133:33: error: lvalue required as unary '&' operand
 133 | #define Py_REFCNT(ob) _Py_REFCNT(_PyObject_CAST_CONST(ob))
 | ~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
./test/upcast.cpp:17:68: note: in expansion of macro 'Py_REFCNT'
 17 | BOOST_TEST(&Py_REFCNT(boost::python::upcast<PyObject>(&y)) == &Py_REFCNT(&y));
 | ^~~~~~~~~

$ g++ -Iinclude -I/usr/include/python3.13 test/upcast.cpp
In file included from /usr/include/boost/detail/lightweight_test.hpp:15,
 from test/upcast.cpp:7:
test/upcast.cpp: In function 'int main()':
/usr/include/python3.13/object.h:330:34: error: lvalue required as unary '&' operand
 330 | # define Py_REFCNT(ob) Py_REFCNT(_PyObject_CAST(ob))
 | ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~
test/upcast.cpp:16:17: note: in expansion of macro 'Py_REFCNT'
 16 | BOOST_TEST(&Py_REFCNT(boost::python::upcast<PyObject>(&o)) == &Py_REFCNT(&o));
 | ^~~~~~~~~
/usr/include/python3.13/object.h:330:34: error: lvalue required as unary '&' operand
 330 | # define Py_REFCNT(ob) Py_REFCNT(_PyObject_CAST(ob))
 | ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~
test/upcast.cpp:16:68: note: in expansion of macro 'Py_REFCNT'
 16 | BOOST_TEST(&Py_REFCNT(boost::python::upcast<PyObject>(&o)) == &Py_REFCNT(&o));
 | ^~~~~~~~~
/usr/include/python3.13/object.h:330:34: error: lvalue required as unary '&' operand
 330 | # define Py_REFCNT(ob) Py_REFCNT(_PyObject_CAST(ob))
 | ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~
test/upcast.cpp:17:17: note: in expansion of macro 'Py_REFCNT'
 17 | BOOST_TEST(&Py_REFCNT(boost::python::upcast<PyObject>(&y)) == &Py_REFCNT(&y));
 | ^~~~~~~~~
/usr/include/python3.13/object.h:330:34: error: lvalue required as unary '&' operand
 330 | # define Py_REFCNT(ob) Py_REFCNT(_PyObject_CAST(ob))
 | ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~
test/upcast.cpp:17:68: note: in expansion of macro 'Py_REFCNT'
 17 | BOOST_TEST(&Py_REFCNT(boost::python::upcast<PyObject>(&y)) == &Py_REFCNT(&y));
 | ^~~~~~~~~

This is because Py_REFCNT() is changed to the inline static function.

Unfortunately, the CI images use python upto 3.8, so the issue has not been found.