gh-106084: Remove _PyObject_RealIsInstance() function (#106106)

Remove the following functions from the public C API:

* _PyObject_RealIsInstance()
* _PyObject_RealIsSubclass()
* _Py_add_one_to_index_F()
* _Py_add_one_to_index_C()

Move _PyObject_RealIsInstance() and _PyObject_RealIsSubclass() to the
internal C API (pycore_abstract.h) and no longer export their symbols
(in libpython).

Make _Py_add_one_to_index_F() and _Py_add_one_to_index_C() functions
static: no longer export them.

Include/cpython/abstract.h

@@ -147,18 +147,10 @@ PyAPI_FUNC(Py_ssize_t) PyObject_LengthHint(PyObject *o, Py_ssize_t);
 
 /* === Mapping protocol ================================================= */
 
-PyAPI_FUNC(int) _PyObject_RealIsInstance(PyObject *inst, PyObject *cls);
-
-PyAPI_FUNC(int) _PyObject_RealIsSubclass(PyObject *derived, PyObject *cls);
-
-/* For internal use by buffer API functions */
-PyAPI_FUNC(void) _Py_add_one_to_index_F(int nd, Py_ssize_t *index,
-                                        const Py_ssize_t *shape);
-PyAPI_FUNC(void) _Py_add_one_to_index_C(int nd, Py_ssize_t *index,
-                                        const Py_ssize_t *shape);
-
-/* Convert Python int to Py_ssize_t. Do nothing if the argument is None. */
+// Convert Python int to Py_ssize_t. Do nothing if the argument is None.
+// Cannot be moved to the internal C API: used by Argument Clinic.
 PyAPI_FUNC(int) _Py_convert_optional_to_ssize_t(PyObject *, void *);
 
-/* Same as PyNumber_Index but can return an instance of a subclass of int. */
+// Same as PyNumber_Index but can return an instance of a subclass of int.
+// Cannot be moved to the internal C API: used by Argument Clinic.
 PyAPI_FUNC(PyObject *) _PyNumber_Index(PyObject *o);

Include/internal/pycore_abstract.h

@@ -41,6 +41,13 @@ extern int _PyObject_HasLen(PyObject *o);
 extern Py_ssize_t _PySequence_IterSearch(PyObject *seq,
                                          PyObject *obj, int operation);
 
+/* === Mapping protocol ================================================= */
+
+extern int _PyObject_RealIsInstance(PyObject *inst, PyObject *cls);
+
+extern int _PyObject_RealIsSubclass(PyObject *derived, PyObject *cls);
+
+
 #ifdef __cplusplus
 }
 #endif

Objects/abstract.c

@@ -517,7 +517,7 @@ PyBuffer_GetPointer(const Py_buffer *view, const Py_ssize_t *indices)
 }
 
 
-void
+static void
 _Py_add_one_to_index_F(int nd, Py_ssize_t *index, const Py_ssize_t *shape)
 {
     int k;
@@ -533,7 +533,7 @@ _Py_add_one_to_index_F(int nd, Py_ssize_t *index, const Py_ssize_t *shape)
     }
 }
 
-void
+static void
 _Py_add_one_to_index_C(int nd, Py_ssize_t *index, const Py_ssize_t *shape)
 {
     int k;

Objects/descrobject.c

@@ -1,6 +1,7 @@
 /* Descriptors -- a new, flexible way to describe attributes */
 
 #include "Python.h"
+#include "pycore_abstract.h"      // _PyObject_RealIsSubclass()
 #include "pycore_ceval.h"         // _Py_EnterRecursiveCallTstate()
 #include "pycore_object.h"        // _PyObject_GC_UNTRACK()
 #include "pycore_pystate.h"       // _PyThreadState_GET()

Objects/exceptions.c

@@ -7,6 +7,7 @@
 #define PY_SSIZE_T_CLEAN
 #include <Python.h>
 #include <stdbool.h>
+#include "pycore_abstract.h"      // _PyObject_RealIsSubclass()
 #include "pycore_ceval.h"         // _Py_EnterRecursiveCall
 #include "pycore_pyerrors.h"      // struct _PyErr_SetRaisedException
 #include "pycore_exceptions.h"    // struct _Py_exc_state