gh-91320: Add _Py_reinterpret_cast() macro (#91959)

Fix C++ compiler warnings about "old-style cast"
(g++ -Wold-style-cast) in the Python C API.  Use C++
reinterpret_cast<> and static_cast<> casts when the Python C API is
used in C++.

Example of fixed warning:

    Include/object.h:107:43: error: use of old-style cast to
    ‘PyObject*’ {aka ‘struct _object*’} [-Werror=old-style-cast]
    #define _PyObject_CAST(op) ((PyObject*)(op))

Add _Py_reinterpret_cast() and _Py_static_cast() macros.

1 files changed, 3 insertions, 1 deletions

diff --git a/Include/methodobject.h b/Include/methodobject.h
index 959e775..2046ab9 100644
--- a/Include/methodobject.h
+++ b/Include/methodobject.h
@@ -42,7 +42,9 @@ typedef PyObject *(*PyCMethod)(PyObject *, PyTypeObject *, PyObject *const *,
 // used to prevent a compiler warning. If the function has a single parameter,
 // it triggers an undefined behavior when Python calls it with 2 parameters
 // (bpo-33012).
-#define _PyCFunction_CAST(func) ((PyCFunction)(void(*)(void))(func))
+#define _PyCFunction_CAST(func) \
+    _Py_reinterpret_cast(PyCFunction, \
+        _Py_reinterpret_cast(void(*)(void), (func)))
 
 PyAPI_FUNC(PyCFunction) PyCFunction_GetFunction(PyObject *);
 PyAPI_FUNC(PyObject *) PyCFunction_GetSelf(PyObject *);