gh-134989: Fix Py_RETURN_NONE in the limited C API (GH-135165)

Fix Py_RETURN_NONE, Py_RETURN_TRUE and Py_RETURN_FALSE macros in the
limited C API 3.11 and older:
Don't treat Py_None, Py_True and Py_False as immortal.

Author: vstinner

Include/boolobject.h

@@ -34,9 +34,16 @@ PyAPI_FUNC(int) Py_IsTrue(PyObject *x);
 PyAPI_FUNC(int) Py_IsFalse(PyObject *x);
 #define Py_IsFalse(x) Py_Is((x), Py_False)
 
-/* Macros for returning Py_True or Py_False, respectively */
-#define Py_RETURN_TRUE return Py_True
-#define Py_RETURN_FALSE return Py_False
+/* Macros for returning Py_True or Py_False, respectively.
+ * Only treat Py_True and Py_False as immortal in the limited C API 3.12
+ * and newer. */
+#if defined(Py_LIMITED_API) && Py_LIMITED_API+0 < 0x030c0000
+#  define Py_RETURN_TRUE return Py_NewRef(Py_True)
+#  define Py_RETURN_FALSE return Py_NewRef(Py_False)
+#else
+#  define Py_RETURN_TRUE return Py_True
+#  define Py_RETURN_FALSE return Py_False
+#endif
 
 /* Function to return a bool from a C long */
 PyAPI_FUNC(PyObject *) PyBool_FromLong(long);

Include/object.h

@@ -660,8 +660,13 @@ PyAPI_DATA(PyObject) _Py_NoneStruct; /* Don't use this directly */
 PyAPI_FUNC(int) Py_IsNone(PyObject *x);
 #define Py_IsNone(x) Py_Is((x), Py_None)
 
-/* Macro for returning Py_None from a function */
-#define Py_RETURN_NONE return Py_None
+/* Macro for returning Py_None from a function.
+ * Only treat Py_None as immortal in the limited C API 3.12 and newer. */
+#if defined(Py_LIMITED_API) && Py_LIMITED_API+0 < 0x030c0000
+#  define Py_RETURN_NONE return Py_NewRef(Py_None)
+#else
+#  define Py_RETURN_NONE return Py_None
+#endif
 
 /*
 Py_NotImplemented is a singleton used to signal that an operation is

Misc/NEWS.d/next/C_API/2025-06-05-11-06-07.gh-issue-134989.74p4ud.rst

@@ -0,0 +1,3 @@
+Fix ``Py_RETURN_NONE``, ``Py_RETURN_TRUE`` and ``Py_RETURN_FALSE`` macros in
+the limited C API 3.11 and older: don't treat ``Py_None``, ``Py_True`` and
+``Py_False`` as immortal. Patch by Victor Stinner.