pythongh-120600: Make Py_TYPE() opaque in limited C API 3.14

In the limited C API 3.14 and newer, Py_TYPE() and Py_SET_TYPE() are
now implemented as opaque function calls to hide implementation
details.

Add _Py_TYPE() and _Py_SET_TYPE() private functions.

Author: vstinner

Doc/whatsnew/3.14.rst

@@ -286,6 +286,12 @@ New Features
 Porting to Python 3.14
 ----------------------
 
+* In the limited C API 3.14 and newer, :c:func:`Py_TYPE` and
+  :c:func:`Py_SET_TYPE` are now implemented as opaque function calls to hide
+  implementation details.
+  (Contributed by Victor Stinner in :gh:`120600`.)
+
+
 Deprecated
 ----------
 

Include/object.h

@@ -244,9 +244,15 @@ _Py_IsOwnedByCurrentThread(PyObject *ob)
 }
 #endif
 
+PyAPI_FUNC(PyTypeObject*) _Py_TYPE(PyObject *ob);
+
 // bpo-39573: The Py_SET_TYPE() function must be used to set an object type.
 static inline PyTypeObject* Py_TYPE(PyObject *ob) {
-#ifdef Py_GIL_DISABLED
+#if defined(Py_LIMITED_API) && Py_LIMITED_API+0 >= 0x030e0000
+    // Stable ABI implements Py_TYPE() as a function call
+    // on limited C API version 3.14 and newer.
+    return _Py_TYPE(ob);
+#elif defined(Py_GIL_DISABLED)
     return (PyTypeObject *)_Py_atomic_load_ptr_relaxed(&ob->ob_type);
 #else
     return ob->ob_type;
@@ -277,8 +283,14 @@ static inline int Py_IS_TYPE(PyObject *ob, PyTypeObject *type) {
 #endif
 
 
+PyAPI_FUNC(void) _Py_SET_TYPE(PyObject *ob, PyTypeObject *type);
+
 static inline void Py_SET_TYPE(PyObject *ob, PyTypeObject *type) {
-#ifdef Py_GIL_DISABLED
+#if defined(Py_LIMITED_API) && Py_LIMITED_API+0 >= 0x030e0000
+    // Stable ABI implements Py_SET_TYPE() as a function call
+    // on limited C API version 3.14 and newer.
+    return _Py_SET_TYPE(ob, type);
+#elif defined(Py_GIL_DISABLED)
     _Py_atomic_store_ptr(&ob->ob_type, type);
 #else
     ob->ob_type = type;

Lib/test/test_stable_abi_ctypes.py

@@ -0,0 +1,3 @@
+In the limited C API 3.14 and newer, :c:func:`Py_TYPE` and
+:c:func:`Py_SET_TYPE` are now implemented as opaque function calls to hide
+implementation details. Patch by Victor Stinner.

Misc/NEWS.d/next/C API/2024-06-16-22-58-47.gh-issue-120600.TJdf0w.rst

@@ -2507,3 +2507,9 @@
     added = '3.13'
 [function.PyEval_GetFrameLocals]
     added = '3.13'
+[function._Py_TYPE]
+    added = '3.14'
+    abi_only = true
+[function._Py_SET_TYPE]
+    added = '3.14'
+    abi_only = true

Misc/stable_abi.toml

@@ -3001,3 +3001,17 @@ Py_GetConstantBorrowed(unsigned int constant_id)
     // All constants are immortal
     return Py_GetConstant(constant_id);
 }
+
+
+// Py_TYPE() implementation for the stable ABI
+PyTypeObject* _Py_TYPE(PyObject *ob)
+{
+    return Py_TYPE(ob);
+}
+
+
+// Py_SET_TYPE() implementation for the stable ABI
+void _Py_SET_TYPE(PyObject *ob, PyTypeObject *type)
+{
+    Py_SET_TYPE(ob, type);
+}