gh-128629: Add Py_PACK_VERSION and Py_PACK_FULL_VERSION

[encukou]

• Issue: Add Py_PACK_VERSION macros #128629

---

📚 Documentation preview 📚: https://cpython-previews--128630.org.readthedocs.build/

[vstinner]

You need more complicated code for Free Threading, something like:

#include "pyconfig.h"  // Py_GIL_DISABLED
#ifndef Py_GIL_DISABLED
#  define Py_LIMITED_API 0x030e0000  // Added in 3.14
#endif

[vstinner]

What's the purpose of testing the API through ctypes? It should be the same as testing _testlimitedcapi, no?

[encukou]

It tests the exported function.
(Unlike most similar API, these are macros even in limited API. This tests the case of not using the C headers at all.)

[vstinner]

The _testcapi module tests Py_INCREF() macro and function this way:

#define TEST_REFCOUNT() \
    do { \
        PyObject *obj = PyList_New(0); \
        if (obj == NULL) { \
            return NULL; \
        } \
        assert(Py_REFCNT(obj) == 1); \
        \
        /* test Py_NewRef() */ \
        PyObject *ref = Py_NewRef(obj); \
        assert(ref == obj); \
        assert(Py_REFCNT(obj) == 2); \
        Py_DECREF(ref); \
        \
        /* test Py_XNewRef() */ \
        PyObject *xref = Py_XNewRef(obj); \
        assert(xref == obj); \
        assert(Py_REFCNT(obj) == 2); \
        Py_DECREF(xref); \
        \
        assert(Py_XNewRef(NULL) == NULL); \
        \
        Py_DECREF(obj); \
        Py_RETURN_NONE; \
    } while (0)


// Test Py_NewRef() and Py_XNewRef() macros
static PyObject*
test_refcount_macros(PyObject *self, PyObject *Py_UNUSED(ignored))
{
    TEST_REFCOUNT();
}

#undef Py_NewRef
#undef Py_XNewRef

// Test Py_NewRef() and Py_XNewRef() functions, after undefining macros.
static PyObject*
test_refcount_funcs(PyObject *self, PyObject *Py_UNUSED(ignored))
{
    TEST_REFCOUNT();
}

Maybe you can do something similar to avoid ctypes.

[encukou]

The C tests do something similar, with #undef Py_PACK_FULL_VERSION.
(But if I had misspelled that #undef, the test would quietly be ineffective.)

Also, I don't particularly want to avoid ctypes :)

[vstinner]

LGTM

[vstinner]

Why not just Py_PATCHLEVEL_H, as done in other header files?

[encukou]

Because I don't want to add this define to public API. It's a private detail, users don't need this; we should be able to, for example, merge this code into another header and remove patchlevel.h.

[encukou]

Thank you for the reviews!