PyUnstable_SetImmortal() is not available on the limited C API

Author: vstinner

docs/api.rst

@@ -349,6 +349,8 @@ Python 3.14
 
    Not available on PyPy. ``Py_REFCNT()`` semantics is different on PyPy.
 
+   Not available on the limited C API.
+
 .. c:function:: void PyUnstable_EnableTryIncRef(PyObject *op)
 
    See `PyUnstable_EnableTryIncRef() documentation <https://docs.python.org/dev/c-api/object.html#c.PyUnstable_EnableTryIncRef>`__.

pythoncapi_compat.h

@@ -2543,7 +2543,9 @@ static inline int PyUnstable_Object_IsUniquelyReferenced(PyObject *obj)
 // gh-128926 added PyUnstable_TryIncRef() and PyUnstable_EnableTryIncRef() to
 // Python 3.14. Adapted from _Py_TryIncref() and _PyObject_SetMaybeWeakref().
 // Not available on PyPy: Py_REFCNT() semantics is different on PyPy.
-#if PY_VERSION_HEX < _Py_PACK_VERSION(3, 14) && !defined(PYPY_VERSION)
+// Not available on the limited C API.
+#if (PY_VERSION_HEX < _Py_PACK_VERSION(3, 14) \
+     && !defined(PYPY_VERSION) && !defined(Py_LIMITED_API))
 static inline int PyUnstable_TryIncRef(PyObject *op)
 {
 #ifndef Py_GIL_DISABLED

tests/test_pythoncapi_compat_cext.c

@@ -2593,6 +2593,7 @@ test_try_incref(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
 #endif  // !defined(PYPY_VERSION) && !defined(Py_LIMITED_API)
 
 
+// Test PyUnstable_SetImmortal()
 #if (_Py_PACK_VERSION(3, 13) <= PY_VERSION_HEX \
      && !defined(PYPY_VERSION) && !defined(Py_LIMITED_API))
 static PyObject *