gh-89653: PEP 670: Functions don't cast pointers (#91697)

In the limited C API version 3.11 and newer, the following functions
no longer cast their object pointer argument with _PyObject_CAST() or
_PyObject_CAST_CONST():

* Py_REFCNT(), Py_TYPE(), Py_SIZE()
* Py_SET_REFCNT(), Py_SET_TYPE(), Py_SET_SIZE()
* Py_IS_TYPE()
* Py_INCREF(), Py_DECREF()
* Py_XINCREF(), Py_XDECREF()
* Py_NewRef(), Py_XNewRef()
* PyObject_TypeCheck()
* PyType_Check()
* PyType_CheckExact()

Split Py_DECREF() implementation in 3 versions to make the code more
readable.

Update the xxlimited.c extension, which uses the limited C API
version 3.11, to pass PyObject* to these functions.

3 files changed, 119 insertions, 56 deletions

diff --git a/Include/cpython/unicodeobject.h b/Include/cpython/unicodeobject.h
index 992588c..2712c58 100644
--- a/Include/cpython/unicodeobject.h
+++ b/Include/cpython/unicodeobject.h
@@ -256,14 +256,18 @@ PyAPI_FUNC(int) _PyUnicode_CheckConsistency(
 static inline unsigned int PyUnicode_CHECK_INTERNED(PyObject *op) {
     return _PyASCIIObject_CAST(op)->state.interned;
 }
-#define PyUnicode_CHECK_INTERNED(op) PyUnicode_CHECK_INTERNED(_PyObject_CAST(op))
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
+#  define PyUnicode_CHECK_INTERNED(op) PyUnicode_CHECK_INTERNED(_PyObject_CAST(op))
+#endif
 
 /* Fast check to determine whether an object is ready. Equivalent to:
    PyUnicode_IS_COMPACT(op) || _PyUnicodeObject_CAST(op)->data.any */
 static inline unsigned int PyUnicode_IS_READY(PyObject *op) {
     return _PyASCIIObject_CAST(op)->state.ready;
 }
-#define PyUnicode_IS_READY(op) PyUnicode_IS_READY(_PyObject_CAST(op))
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
+#  define PyUnicode_IS_READY(op) PyUnicode_IS_READY(_PyObject_CAST(op))
+#endif
 
 /* Return true if the string contains only ASCII characters, or 0 if not. The
    string may be compact (PyUnicode_IS_COMPACT_ASCII) or not, but must be
@@ -272,21 +276,27 @@ static inline unsigned int PyUnicode_IS_ASCII(PyObject *op) {
     assert(PyUnicode_IS_READY(op));
     return _PyASCIIObject_CAST(op)->state.ascii;
 }
-#define PyUnicode_IS_ASCII(op) PyUnicode_IS_ASCII(_PyObject_CAST(op))
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
+#  define PyUnicode_IS_ASCII(op) PyUnicode_IS_ASCII(_PyObject_CAST(op))
+#endif
 
 /* Return true if the string is compact or 0 if not.
    No type checks or Ready calls are performed. */
 static inline unsigned int PyUnicode_IS_COMPACT(PyObject *op) {
     return _PyASCIIObject_CAST(op)->state.compact;
 }
-#define PyUnicode_IS_COMPACT(op) PyUnicode_IS_COMPACT(_PyObject_CAST(op))
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
+#  define PyUnicode_IS_COMPACT(op) PyUnicode_IS_COMPACT(_PyObject_CAST(op))
+#endif
 
 /* Return true if the string is a compact ASCII string (use PyASCIIObject
    structure), or 0 if not.  No type checks or Ready calls are performed. */
 static inline int PyUnicode_IS_COMPACT_ASCII(PyObject *op) {
     return (_PyASCIIObject_CAST(op)->state.ascii && PyUnicode_IS_COMPACT(op));
 }
-#define PyUnicode_IS_COMPACT_ASCII(op) PyUnicode_IS_COMPACT_ASCII(_PyObject_CAST(op))
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
+#  define PyUnicode_IS_COMPACT_ASCII(op) PyUnicode_IS_COMPACT_ASCII(_PyObject_CAST(op))
+#endif
 
 enum PyUnicode_Kind {
 /* String contains only wstr byte characters.  This is only possible
@@ -326,7 +336,9 @@ static inline void* PyUnicode_DATA(PyObject *op) {
     }
     return _PyUnicode_NONCOMPACT_DATA(op);
 }
-#define PyUnicode_DATA(op) PyUnicode_DATA(_PyObject_CAST(op))
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
+#  define PyUnicode_DATA(op) PyUnicode_DATA(_PyObject_CAST(op))
+#endif
 
 /* Return pointers to the canonical representation cast to unsigned char,
    Py_UCS2, or Py_UCS4 for direct character access.
@@ -344,7 +356,9 @@ static inline Py_ssize_t PyUnicode_GET_LENGTH(PyObject *op) {
     assert(PyUnicode_IS_READY(op));
     return _PyASCIIObject_CAST(op)->length;
 }
-#define PyUnicode_GET_LENGTH(op) PyUnicode_GET_LENGTH(_PyObject_CAST(op))
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
+#  define PyUnicode_GET_LENGTH(op) PyUnicode_GET_LENGTH(_PyObject_CAST(op))
+#endif
 
 /* Write into the canonical representation, this function does not do any sanity
    checks and is intended for usage in loops.  The caller should cache the
@@ -405,8 +419,10 @@ static inline Py_UCS4 PyUnicode_READ_CHAR(PyObject *unicode, Py_ssize_t index)
     assert(kind == PyUnicode_4BYTE_KIND);
     return PyUnicode_4BYTE_DATA(unicode)[index];
 }
-#define PyUnicode_READ_CHAR(unicode, index) \
-    PyUnicode_READ_CHAR(_PyObject_CAST(unicode), (index))
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
+#  define PyUnicode_READ_CHAR(unicode, index) \
+       PyUnicode_READ_CHAR(_PyObject_CAST(unicode), (index))
+#endif
 
 /* Return a maximum character value which is suitable for creating another
    string based on op.  This is always an approximation but more efficient
@@ -428,8 +444,10 @@ static inline Py_UCS4 PyUnicode_MAX_CHAR_VALUE(PyObject *op)
     assert(kind == PyUnicode_4BYTE_KIND);
     return 0x10ffffU;
 }
-#define PyUnicode_MAX_CHAR_VALUE(op) \
-    PyUnicode_MAX_CHAR_VALUE(_PyObject_CAST(op))
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
+#  define PyUnicode_MAX_CHAR_VALUE(op) \
+       PyUnicode_MAX_CHAR_VALUE(_PyObject_CAST(op))
+#endif
 
 /* === Public API ========================================================= */
 
@@ -465,7 +483,9 @@ static inline int PyUnicode_READY(PyObject *op)
     }
     return _PyUnicode_Ready(op);
 }
-#define PyUnicode_READY(op) PyUnicode_READY(_PyObject_CAST(op))
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
+#  define PyUnicode_READY(op) PyUnicode_READY(_PyObject_CAST(op))
+#endif
 
 /* Get a copy of a Unicode string. */
 PyAPI_FUNC(PyObject*) _PyUnicode_Copy(
@@ -606,7 +626,9 @@ static inline Py_ssize_t PyUnicode_WSTR_LENGTH(PyObject *op)
         return _PyCompactUnicodeObject_CAST(op)->wstr_length;
     }
 }
-#define PyUnicode_WSTR_LENGTH(op) PyUnicode_WSTR_LENGTH(_PyObject_CAST(op))
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
+#  define PyUnicode_WSTR_LENGTH(op) PyUnicode_WSTR_LENGTH(_PyObject_CAST(op))
+#endif
 
 /* Returns the deprecated Py_UNICODE representation's size in code units
    (this includes surrogate pairs as 2 units).
@@ -625,7 +647,9 @@ static inline Py_ssize_t PyUnicode_GET_SIZE(PyObject *op)
     return PyUnicode_WSTR_LENGTH(op);
     _Py_COMP_DIAG_POP
 }
-#define PyUnicode_GET_SIZE(op) PyUnicode_GET_SIZE(_PyObject_CAST(op))
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
+#  define PyUnicode_GET_SIZE(op) PyUnicode_GET_SIZE(_PyObject_CAST(op))
+#endif
 
 Py_DEPRECATED(3.3)
 static inline Py_ssize_t PyUnicode_GET_DATA_SIZE(PyObject *op)
@@ -635,7 +659,9 @@ static inline Py_ssize_t PyUnicode_GET_DATA_SIZE(PyObject *op)
     return PyUnicode_GET_SIZE(op) * Py_UNICODE_SIZE;
     _Py_COMP_DIAG_POP
 }
-#define PyUnicode_GET_DATA_SIZE(op) PyUnicode_GET_DATA_SIZE(_PyObject_CAST(op))
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
+#  define PyUnicode_GET_DATA_SIZE(op) PyUnicode_GET_DATA_SIZE(_PyObject_CAST(op))
+#endif
 
 /* Alias for PyUnicode_AsUnicode().  This will create a wchar_t/Py_UNICODE
    representation on demand.  Using this macro is very inefficient now,
@@ -655,7 +681,9 @@ static inline Py_UNICODE* PyUnicode_AS_UNICODE(PyObject *op)
     return PyUnicode_AsUnicode(op);
     _Py_COMP_DIAG_POP
 }
-#define PyUnicode_AS_UNICODE(op) PyUnicode_AS_UNICODE(_PyObject_CAST(op))
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
+#  define PyUnicode_AS_UNICODE(op) PyUnicode_AS_UNICODE(_PyObject_CAST(op))
+#endif
 
 Py_DEPRECATED(3.3)
 static inline const char* PyUnicode_AS_DATA(PyObject *op)
@@ -665,7 +693,9 @@ static inline const char* PyUnicode_AS_DATA(PyObject *op)
     return (const char *)PyUnicode_AS_UNICODE(op);
     _Py_COMP_DIAG_POP
 }
-#define PyUnicode_AS_DATA(op) PyUnicode_AS_DATA(_PyObject_CAST(op))
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
+#  define PyUnicode_AS_DATA(op) PyUnicode_AS_DATA(_PyObject_CAST(op))
+#endif
 
 
 /* --- _PyUnicodeWriter API ----------------------------------------------- */
diff --git a/Include/object.h b/Include/object.h
index 8a45ddb..5622305 100644
--- a/Include/object.h
+++ b/Include/object.h
@@ -123,44 +123,58 @@ PyAPI_FUNC(int) Py_Is(PyObject *x, PyObject *y);
 static inline Py_ssize_t Py_REFCNT(PyObject *ob) {
     return ob->ob_refcnt;
 }
-#define Py_REFCNT(ob) Py_REFCNT(_PyObject_CAST(ob))
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
+#  define Py_REFCNT(ob) Py_REFCNT(_PyObject_CAST(ob))
+#endif
 
 
 // bpo-39573: The Py_SET_TYPE() function must be used to set an object type.
 static inline PyTypeObject* Py_TYPE(PyObject *ob) {
     return ob->ob_type;
 }
-#define Py_TYPE(ob) Py_TYPE(_PyObject_CAST(ob))
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
+#  define Py_TYPE(ob) Py_TYPE(_PyObject_CAST(ob))
+#endif
 
 // bpo-39573: The Py_SET_SIZE() function must be used to set an object size.
 static inline Py_ssize_t Py_SIZE(PyVarObject *ob) {
     return ob->ob_size;
 }
-#define Py_SIZE(ob) Py_SIZE(_PyVarObject_CAST(ob))
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
+#  define Py_SIZE(ob) Py_SIZE(_PyVarObject_CAST(ob))
+#endif
 
 
 static inline int Py_IS_TYPE(PyObject *ob, PyTypeObject *type) {
     return Py_TYPE(ob) == type;
 }
-#define Py_IS_TYPE(ob, type) Py_IS_TYPE(_PyObject_CAST(ob), type)
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
+#  define Py_IS_TYPE(ob, type) Py_IS_TYPE(_PyObject_CAST(ob), type)
+#endif
 
 
 static inline void Py_SET_REFCNT(PyObject *ob, Py_ssize_t refcnt) {
     ob->ob_refcnt = refcnt;
 }
-#define Py_SET_REFCNT(ob, refcnt) Py_SET_REFCNT(_PyObject_CAST(ob), refcnt)
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
+#  define Py_SET_REFCNT(ob, refcnt) Py_SET_REFCNT(_PyObject_CAST(ob), refcnt)
+#endif
 
 
 static inline void Py_SET_TYPE(PyObject *ob, PyTypeObject *type) {
     ob->ob_type = type;
 }
-#define Py_SET_TYPE(ob, type) Py_SET_TYPE(_PyObject_CAST(ob), type)
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
+#  define Py_SET_TYPE(ob, type) Py_SET_TYPE(_PyObject_CAST(ob), type)
+#endif
 
 
 static inline void Py_SET_SIZE(PyVarObject *ob, Py_ssize_t size) {
     ob->ob_size = size;
 }
-#define Py_SET_SIZE(ob, size) Py_SET_SIZE(_PyVarObject_CAST(ob), size)
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
+#  define Py_SET_SIZE(ob, size) Py_SET_SIZE(_PyVarObject_CAST(ob), size)
+#endif
 
 
 /*
@@ -247,7 +261,9 @@ PyAPI_FUNC(int) PyType_IsSubtype(PyTypeObject *, PyTypeObject *);
 static inline int PyObject_TypeCheck(PyObject *ob, PyTypeObject *type) {
     return Py_IS_TYPE(ob, type) || PyType_IsSubtype(Py_TYPE(ob), type);
 }
-#define PyObject_TypeCheck(ob, type) PyObject_TypeCheck(_PyObject_CAST(ob), type)
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
+#  define PyObject_TypeCheck(ob, type) PyObject_TypeCheck(_PyObject_CAST(ob), type)
+#endif
 
 PyAPI_DATA(PyTypeObject) PyType_Type; /* built-in 'type' */
 PyAPI_DATA(PyTypeObject) PyBaseObject_Type; /* built-in 'object' */
@@ -485,39 +501,43 @@ static inline void Py_INCREF(PyObject *op)
     op->ob_refcnt++;
 #endif
 }
-#define Py_INCREF(op) Py_INCREF(_PyObject_CAST(op))
-
-static inline void Py_DECREF(
-#if defined(Py_REF_DEBUG) && !(defined(Py_LIMITED_API) && Py_LIMITED_API+0 >= 0x030A0000)
-    const char *filename, int lineno,
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
+#  define Py_INCREF(op) Py_INCREF(_PyObject_CAST(op))
 #endif
-    PyObject *op)
-{
+
+
 #if defined(Py_REF_DEBUG) && defined(Py_LIMITED_API) && Py_LIMITED_API+0 >= 0x030A0000
-    // Stable ABI for Python 3.10 built in debug mode.
+// Stable ABI for limited C API version 3.10 of Python debug build
+static inline void Py_DECREF(PyObject *op) {
     _Py_DecRef(op);
-#else
-    // Non-limited C API and limited C API for Python 3.9 and older access
-    // directly PyObject.ob_refcnt.
-#ifdef Py_REF_DEBUG
+}
+#define Py_DECREF(op) Py_DECREF(_PyObject_CAST(op))
+
+#elif defined(Py_REF_DEBUG)
+static inline void Py_DECREF(const char *filename, int lineno, PyObject *op)
+{
     _Py_RefTotal--;
-#endif
     if (--op->ob_refcnt != 0) {
-#ifdef Py_REF_DEBUG
         if (op->ob_refcnt < 0) {
             _Py_NegativeRefcount(filename, lineno, op);
         }
-#endif
     }
     else {
         _Py_Dealloc(op);
     }
-#endif
 }
-#if defined(Py_REF_DEBUG) && !(defined(Py_LIMITED_API) && Py_LIMITED_API+0 >= 0x030A0000)
-#  define Py_DECREF(op) Py_DECREF(__FILE__, __LINE__, _PyObject_CAST(op))
+#define Py_DECREF(op) Py_DECREF(__FILE__, __LINE__, _PyObject_CAST(op))
+
 #else
-#  define Py_DECREF(op) Py_DECREF(_PyObject_CAST(op))
+static inline void Py_DECREF(PyObject *op)
+{
+    // Non-limited C API and limited C API for Python 3.9 and older access
+    // directly PyObject.ob_refcnt.
+    if (--op->ob_refcnt == 0) {
+        _Py_Dealloc(op);
+    }
+}
+#define Py_DECREF(op) Py_DECREF(_PyObject_CAST(op))
 #endif
 
 
@@ -571,8 +591,9 @@ static inline void Py_XINCREF(PyObject *op)
         Py_INCREF(op);
     }
 }
-
-#define Py_XINCREF(op) Py_XINCREF(_PyObject_CAST(op))
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
+#  define Py_XINCREF(op) Py_XINCREF(_PyObject_CAST(op))
+#endif
 
 static inline void Py_XDECREF(PyObject *op)
 {
@@ -580,8 +601,9 @@ static inline void Py_XDECREF(PyObject *op)
         Py_DECREF(op);
     }
 }
-
-#define Py_XDECREF(op) Py_XDECREF(_PyObject_CAST(op))
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
+#  define Py_XDECREF(op) Py_XDECREF(_PyObject_CAST(op))
+#endif
 
 // Create a new strong reference to an object:
 // increment the reference count of the object and return the object.
@@ -605,8 +627,13 @@ static inline PyObject* _Py_XNewRef(PyObject *obj)
 // Py_NewRef() and Py_XNewRef() are exported as functions for the stable ABI.
 // Names overridden with macros by static inline functions for best
 // performances.
-#define Py_NewRef(obj) _Py_NewRef(_PyObject_CAST(obj))
-#define Py_XNewRef(obj) _Py_XNewRef(_PyObject_CAST(obj))
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
+#  define Py_NewRef(obj) _Py_NewRef(_PyObject_CAST(obj))
+#  define Py_XNewRef(obj) _Py_XNewRef(_PyObject_CAST(obj))
+#else
+#  define Py_NewRef(obj) _Py_NewRef(obj)
+#  define Py_XNewRef(obj) _Py_XNewRef(obj)
+#endif
 
 
 /*
@@ -749,14 +776,18 @@ PyType_HasFeature(PyTypeObject *type, unsigned long feature)
 static inline int PyType_Check(PyObject *op) {
     return PyType_FastSubclass(Py_TYPE(op), Py_TPFLAGS_TYPE_SUBCLASS);
 }
-#define PyType_Check(op) PyType_Check(_PyObject_CAST(op))
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
+#  define PyType_Check(op) PyType_Check(_PyObject_CAST(op))
+#endif
 
 #define _PyType_CAST(op) (assert(PyType_Check(op)), (PyTypeObject*)(op))
 
 static inline int PyType_CheckExact(PyObject *op) {
     return Py_IS_TYPE(op, &PyType_Type);
 }
-#define PyType_CheckExact(op) PyType_CheckExact(_PyObject_CAST(op))
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
+#  define PyType_CheckExact(op) PyType_CheckExact(_PyObject_CAST(op))
+#endif
 
 #ifdef __cplusplus
 }
diff --git a/Modules/xxlimited.c b/Modules/xxlimited.c
index 16d1b83..c36bf5c 100644
--- a/Modules/xxlimited.c
+++ b/Modules/xxlimited.c
@@ -110,12 +110,13 @@ newXxoObject(PyObject *module)
 /* Xxo finalization */
 
 static int
-Xxo_traverse(XxoObject *self, visitproc visit, void *arg)
+Xxo_traverse(PyObject *self_obj, visitproc visit, void *arg)
 {
     // Visit the type
-    Py_VISIT(Py_TYPE(self));
+    Py_VISIT(Py_TYPE(self_obj));
 
     // Visit the attribute dict
+    XxoObject *self = (XxoObject *)self_obj;
     Py_VISIT(self->x_attr);
     return 0;
 }
@@ -128,13 +129,14 @@ Xxo_clear(XxoObject *self)
 }
 
 static void
-Xxo_finalize(XxoObject *self)
+Xxo_finalize(PyObject *self_obj)
 {
+    XxoObject *self = (XxoObject *)self_obj;
     Py_CLEAR(self->x_attr);
 }
 
 static void
-Xxo_dealloc(XxoObject *self)
+Xxo_dealloc(PyObject *self)
 {
     Xxo_finalize(self);
     PyTypeObject *tp = Py_TYPE(self);