gh-141726: Add PyDict_SetDefaultRef to the Stable ABI

Include/cpython/dictobject.h

@@ -39,16 +39,6 @@ Py_DEPRECATED(3.14) PyAPI_FUNC(PyObject *) _PyDict_GetItemStringWithError(PyObje
 PyAPI_FUNC(PyObject *) PyDict_SetDefault(
     PyObject *mp, PyObject *key, PyObject *defaultobj);
 
-// Inserts `key` with a value `default_value`, if `key` is not already present
-// in the dictionary.  If `result` is not NULL, then the value associated
-// with `key` is returned in `*result` (either the existing value, or the now
-// inserted `default_value`).
-// Returns:
-//   -1 on error
-//    0 if `key` was not present and `default_value` was inserted
-//    1 if `key` was present and `default_value` was not inserted
-PyAPI_FUNC(int) PyDict_SetDefaultRef(PyObject *mp, PyObject *key, PyObject *default_value, PyObject **result);
-
 /* Get the number of items of a dictionary. */
 static inline Py_ssize_t PyDict_GET_SIZE(PyObject *op) {
     PyDictObject *mp;

Include/dictobject.h

@@ -68,6 +68,18 @@ PyAPI_FUNC(int) PyDict_GetItemRef(PyObject *mp, PyObject *key, PyObject **result
 PyAPI_FUNC(int) PyDict_GetItemStringRef(PyObject *mp, const char *key, PyObject **result);
 #endif
 
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= 0x030F0000
+// Inserts `key` with a value `default_value`, if `key` is not already present
+// in the dictionary.  If `result` is not NULL, then the value associated
+// with `key` is returned in `*result` (either the existing value, or the now
+// inserted `default_value`).
+// Returns:
+//   -1 on error
+//    0 if `key` was not present and `default_value` was inserted
+//    1 if `key` was present and `default_value` was not inserted
+PyAPI_FUNC(int) PyDict_SetDefaultRef(PyObject *mp, PyObject *key, PyObject *default_value, PyObject **result);
+#endif
+
 #if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= 0x030A0000
 PyAPI_FUNC(PyObject *) PyObject_GenericGetDict(PyObject *, void *);
 #endif

Misc/NEWS.d/next/C_API/2025-11-18-18-36-15.gh-issue-141726.ILrhyK.rst

@@ -0,0 +1 @@
+Add :c:func:`PyDict_SetDefaultRef` to the Stable ABI.

Misc/stable_abi.toml

@@ -2639,3 +2639,5 @@
     added = '3.15'
 [const.Py_mod_token]
     added = '3.15'
+[function.PyDict_SetDefaultRef]
+    added = '3.15'