gh-145921: Add PyObject_GetItemData to the limited C API and stable ABI

Move PyObject_GetItemData and PyObject_GetItemData_DuringGC from the
unstable CPython API (Include/cpython/object.h) to the limited C API
(Include/object.h), gated on Py_LIMITED_API >= 3.15, and declare them
as part of the stable ABI in Misc/stable_abi.toml.

Author: wjakob

Doc/c-api/object.rst

@@ -624,6 +624,10 @@ Object Protocol
 
    .. versionadded:: 3.12
 
+   .. versionchanged:: 3.15
+
+      Added to the limited C API.
+
 .. c:function:: int PyObject_VisitManagedDict(PyObject *obj, visitproc visit, void *arg)
 
    Visit the managed dictionary of *obj*.

Doc/data/stable_abi.dat

@@ -441,9 +441,6 @@ PyAPI_FUNC(void) _PyTrash_thread_destroy_chain(PyThreadState *tstate);
 #define Py_TRASHCAN_END
 
 
-PyAPI_FUNC(void *) PyObject_GetItemData(PyObject *obj);
-PyAPI_FUNC(void *) PyObject_GetItemData_DuringGC(PyObject *obj);
-
 PyAPI_FUNC(int) PyObject_VisitManagedDict(PyObject *obj, visitproc visit, void *arg);
 PyAPI_FUNC(void) PyObject_ClearManagedDict(PyObject *obj);
 

Include/cpython/object.h

@@ -355,6 +355,9 @@ PyAPI_FUNC(PyObject *) PyType_FromMetaclass(PyTypeObject*, PyObject*, PyType_Spe
 PyAPI_FUNC(void *) PyObject_GetTypeData(PyObject *obj, PyTypeObject *cls);
 PyAPI_FUNC(Py_ssize_t) PyType_GetTypeDataSize(PyTypeObject *cls);
 #endif
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= _Py_PACK_VERSION(3, 15)
+PyAPI_FUNC(void *) PyObject_GetItemData(PyObject *obj);
+#endif
 #if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= 0x030E0000
 PyAPI_FUNC(int) PyType_GetBaseByToken(PyTypeObject *, void *, PyTypeObject **);
 #define Py_TP_USE_SPEC NULL
@@ -781,6 +784,7 @@ PyAPI_FUNC(PyObject *) PyType_GetModuleByToken(PyTypeObject *type,
                                                const void *token);
 PyAPI_FUNC(void *) PyObject_GetTypeData_DuringGC(PyObject *obj,
                                                  PyTypeObject *cls);
+PyAPI_FUNC(void *) PyObject_GetItemData_DuringGC(PyObject *obj);
 PyAPI_FUNC(void *) PyType_GetModuleState_DuringGC(PyTypeObject *);
 PyAPI_FUNC(int) PyType_GetBaseByToken_DuringGC(PyTypeObject *,
                                                void *, PyTypeObject **);

Include/object.h

@@ -0,0 +1,2 @@
+Add :c:func:`PyObject_GetItemData` and
+:c:func:`PyObject_GetItemData_DuringGC` to the limited C API and stable ABI.

Lib/test/test_stable_abi_ctypes.py

@@ -2666,8 +2666,13 @@
 [function.Py_SET_SIZE]
     # Before 3.15, this was a macro that accessed the PyObject member
     added = '3.15'
+[function.PyObject_GetItemData]
+    # Before 3.15, this was only available in the unstable CPython API
+    added = '3.15'
 [function.PyObject_GetTypeData_DuringGC]
     added = '3.15'
+[function.PyObject_GetItemData_DuringGC]
+    added = '3.15'
 [function.PyType_GetModuleState_DuringGC]
     added = '3.15'
 [function.PyModule_GetState_DuringGC]