[DRAFT] gh-105059: In C++, Py_INCREF() uses a function call

[vstinner]

In C++, Py_INCREF() and Py_DECREF() are now implemented as function calls. Moreover, in C++, PyObject.ob_refcnt type is just Py_ssize_t: don't use an anonymous union to avoid compiler warnings (anonymous unions were added to C11).

• Issue: object.h uses an anonymous union in a struct (older C incompatible) #105059

[vstinner]

In the issue #105387, I modified Py_INCREF() and Py_DECREF() to implement them as opaque function calls in the limited C API version 3.12 and newer (and when Python is built in debug mode): commit b542972

We can consider to do something similar in C++ and/or in C without anonymous union (ex: ISO C89). This PR implements this idea for C++: in C++, PyObject.ob_refcnt type is again the simple Py_ssize_t, and Py_INCREF() and Py_DECREF() are implemented as function calls.

Well, I wrote this PR to show that we now have this technical solution, but it has a cost on performance. I don't know if it's acceptable for Python 3.12. Alternatives are discussed in issue #105059 and PR #105275.

cc @eduardo-elizondo

[vstinner]

C without anonymous union (ex: ISO C89)

C compiler configured for C99 in pedantic mode also emits a compiler warning (which may be treated as error) in Include/object.h because of the PyObject.ob_refcnt anonymous union: #105059 (comment)

[vstinner]

Abandoned in favor of PR #105767. C++ is unaffected by the issue: #105059 (comment)