bpo-40170: Remove PyIndex_Check() macro (GH-19428)

Always declare PyIndex_Check() as an opaque function to hide
implementation details: remove PyIndex_Check() macro. The macro
accessed directly the PyTypeObject.tp_as_number member.

Author: vstinner

Include/cpython/abstract.h

@@ -335,12 +335,6 @@ PyAPI_FUNC(void) PyBuffer_Release(Py_buffer *view);
     (Py_TYPE(obj)->tp_iternext != NULL && \
      Py_TYPE(obj)->tp_iternext != &_PyObject_NextNotImplemented)
 
-/* === Number Protocol ================================================== */
-
-#define PyIndex_Check(obj)                              \
-    (Py_TYPE(obj)->tp_as_number != NULL &&            \
-     Py_TYPE(obj)->tp_as_number->nb_index != NULL)
-
 /* === Sequence protocol ================================================ */
 
 /* Assume tp_as_sequence and sq_item exist and that 'i' does not

Misc/NEWS.d/next/C API/2020-04-04-23-51-59.bpo-40170.uXQ701.rst

@@ -0,0 +1,3 @@
+Always declare :c:func:`PyIndex_Check` as an opaque function to hide
+implementation details: remove ``PyIndex_Check()`` macro. The macro accessed
+directly the :c:member:`PyTypeObject.tp_as_number` member.

Objects/abstract.c

@@ -1309,8 +1309,6 @@ PyNumber_Absolute(PyObject *o)
 }
 
 
-#undef PyIndex_Check
-
 int
 PyIndex_Check(PyObject *obj)
 {