bpo-39573: Convert Py_REFCNT and Py_SIZE to functions (GH-20429)

Convert Py_REFCNT() and Py_SIZE() macros to static inline functions.
They cannot be used as l-value anymore: use Py_SET_REFCNT() and
Py_SET_SIZE() to set an object reference count and size.

Replace &Py_SIZE(self) with &((PyVarObject*)self)->ob_size
in arraymodule.c.

This change is backward incompatible on purpose, to prepare the C API
for an opaque PyObject structure.

2 files changed, 19 insertions, 9 deletions

diff --git a/Doc/c-api/structures.rst b/Doc/c-api/structures.rst
index 5535f42..b2392fa 100644
--- a/Doc/c-api/structures.rst
+++ b/Doc/c-api/structures.rst
@@ -88,13 +88,13 @@ the definition of all other Python objects.
    .. versionadded:: 3.9
 
 
-.. c:macro:: Py_REFCNT(o)
+.. c:function:: Py_ssize_t Py_REFCNT(const PyObject *o)
 
-   This macro is used to access the :attr:`ob_refcnt` member of a Python
-   object.
-   It expands to::
+   Get the reference count of the Python object *o*.
 
-      (((PyObject*)(o))->ob_refcnt)
+   .. versionchanged:: 3.10
+      :c:func:`Py_REFCNT()` is changed to the inline static function.
+      Use :c:func:`Py_SET_REFCNT()` to set an object reference count.
 
 
 .. c:function:: void Py_SET_REFCNT(PyObject *o, Py_ssize_t refcnt)
@@ -104,12 +104,13 @@ the definition of all other Python objects.
    .. versionadded:: 3.9
 
 
-.. c:macro:: Py_SIZE(o)
+.. c:function:: Py_ssize_t Py_SIZE(const PyVarObject *o)
 
-   This macro is used to access the :attr:`ob_size` member of a Python object.
-   It expands to::
+   Get the size of the Python object *o*.
 
-      (((PyVarObject*)(o))->ob_size)
+   .. versionchanged:: 3.10
+      :c:func:`Py_SIZE()` is changed to the inline static function.
+      Use :c:func:`Py_SET_SIZE()` to set an object size.
 
 
 .. c:function:: void Py_SET_SIZE(PyVarObject *o, Py_ssize_t size)
diff --git a/Doc/whatsnew/3.10.rst b/Doc/whatsnew/3.10.rst
index fabd9a2..9edef1e 100644
--- a/Doc/whatsnew/3.10.rst
+++ b/Doc/whatsnew/3.10.rst
@@ -138,6 +138,15 @@ Porting to Python 3.10
   see :c:func:`Py_SET_TYPE()` (available since Python 3.9).
   (Contributed by Dong-hee Na in :issue:`39573`.)
 
+* Since :c:func:`Py_REFCNT()` is changed to the inline static function,
+  ``Py_REFCNT(obj) = new_refcnt`` must be replaced with ``Py_SET_REFCNT(obj, new_refcnt)``:
+  see :c:func:`Py_SET_REFCNT()` (available since Python 3.9).
+  (Contributed by Victor Stinner in :issue:`39573`.)
+
+* Since :c:func:`Py_SIZE()` is changed to the inline static function,
+  ``Py_SIZE(obj) = new_size`` must be replaced with ``Py_SET_SIZE(obj, new_size)``:
+  see :c:func:`Py_SET_SIZE()` (available since Python 3.9).
+  (Contributed by Victor Stinner in :issue:`39573`.)
 
 Removed
 -------