bpo-40170: PyObject_NEW() becomes an alias to PyObject_New() (GH-19379)

The PyObject_NEW() macro becomes an alias to the PyObject_New()
macro, and the PyObject_NEW_VAR() macro becomes an alias to the
PyObject_NewVar() macro, to hide implementation details. They no
longer access directly the PyTypeObject.tp_basicsize member.

Exclude _PyObject_SIZE() and _PyObject_VAR_SIZE() macros from
the limited C API.

Replace PyObject_NEW() with PyObject_New() and replace
PyObject_NEW_VAR() with PyObject_NewVar().

2 files changed, 59 insertions, 61 deletions

diff --git a/Include/cpython/objimpl.h b/Include/cpython/objimpl.h
index 2f802e9..832622c 100644
--- a/Include/cpython/objimpl.h
+++ b/Include/cpython/objimpl.h
@@ -6,6 +6,56 @@
 extern "C" {
 #endif
 
+#define _PyObject_SIZE(typeobj) ( (typeobj)->tp_basicsize )
+
+/* _PyObject_VAR_SIZE returns the number of bytes (as size_t) allocated for a
+   vrbl-size object with nitems items, exclusive of gc overhead (if any).  The
+   value is rounded up to the closest multiple of sizeof(void *), in order to
+   ensure that pointer fields at the end of the object are correctly aligned
+   for the platform (this is of special importance for subclasses of, e.g.,
+   str or int, so that pointers can be stored after the embedded data).
+
+   Note that there's no memory wastage in doing this, as malloc has to
+   return (at worst) pointer-aligned memory anyway.
+*/
+#if ((SIZEOF_VOID_P - 1) & SIZEOF_VOID_P) != 0
+#   error "_PyObject_VAR_SIZE requires SIZEOF_VOID_P be a power of 2"
+#endif
+
+#define _PyObject_VAR_SIZE(typeobj, nitems)     \
+    _Py_SIZE_ROUND_UP((typeobj)->tp_basicsize + \
+        (nitems)*(typeobj)->tp_itemsize,        \
+        SIZEOF_VOID_P)
+
+
+/* This example code implements an object constructor with a custom
+   allocator, where PyObject_New is inlined, and shows the important
+   distinction between two steps (at least):
+       1) the actual allocation of the object storage;
+       2) the initialization of the Python specific fields
+      in this storage with PyObject_{Init, InitVar}.
+
+   PyObject *
+   YourObject_New(...)
+   {
+       PyObject *op;
+
+       op = (PyObject *) Your_Allocator(_PyObject_SIZE(YourTypeStruct));
+       if (op == NULL)
+       return PyErr_NoMemory();
+
+       PyObject_Init(op, &YourTypeStruct);
+
+       op->ob_field = value;
+       ...
+       return op;
+   }
+
+   Note that in C++, the use of the new operator usually implies that
+   the 1st step is performed automatically for you, so in a C++ class
+   constructor you would start directly with PyObject_Init/InitVar. */
+
+
 /* Inline functions trading binary compatibility for speed:
    PyObject_INIT() is the fast version of PyObject_Init(), and
    PyObject_INIT_VAR() is the fast version of PyObject_InitVar().
diff --git a/Include/objimpl.h b/Include/objimpl.h
index 4591925..6e7549c 100644
--- a/Include/objimpl.h
+++ b/Include/objimpl.h
@@ -122,12 +122,18 @@ PyAPI_FUNC(PyVarObject *) PyObject_InitVar(PyVarObject *,
 PyAPI_FUNC(PyObject *) _PyObject_New(PyTypeObject *);
 PyAPI_FUNC(PyVarObject *) _PyObject_NewVar(PyTypeObject *, Py_ssize_t);
 
-#define PyObject_New(type, typeobj) \
-                ( (type *) _PyObject_New(typeobj) )
+#define PyObject_New(type, typeobj) ((type *)_PyObject_New(typeobj))
+
+// Alias to PyObject_New(). In Python 3.8, PyObject_NEW() called directly
+// PyObject_MALLOC() with _PyObject_SIZE().
+#define PyObject_NEW(type, typeobj) PyObject_New(type, typeobj)
+
 #define PyObject_NewVar(type, typeobj, n) \
                 ( (type *) _PyObject_NewVar((typeobj), (n)) )
 
-#define _PyObject_SIZE(typeobj) ( (typeobj)->tp_basicsize )
+// Alias to PyObject_New(). In Python 3.8, PyObject_NEW() called directly
+// PyObject_MALLOC() with _PyObject_VAR_SIZE().
+#define PyObject_NEW_VAR(type, typeobj, n) PyObject_NewVar(type, typeobj, n)
 
 
 #ifdef Py_LIMITED_API
@@ -143,64 +149,6 @@ PyAPI_FUNC(PyVarObject *) _PyObject_NewVar(PyTypeObject *, Py_ssize_t);
 #endif
 
 
-/* _PyObject_VAR_SIZE returns the number of bytes (as size_t) allocated for a
-   vrbl-size object with nitems items, exclusive of gc overhead (if any).  The
-   value is rounded up to the closest multiple of sizeof(void *), in order to
-   ensure that pointer fields at the end of the object are correctly aligned
-   for the platform (this is of special importance for subclasses of, e.g.,
-   str or int, so that pointers can be stored after the embedded data).
-
-   Note that there's no memory wastage in doing this, as malloc has to
-   return (at worst) pointer-aligned memory anyway.
-*/
-#if ((SIZEOF_VOID_P - 1) & SIZEOF_VOID_P) != 0
-#   error "_PyObject_VAR_SIZE requires SIZEOF_VOID_P be a power of 2"
-#endif
-
-#define _PyObject_VAR_SIZE(typeobj, nitems)     \
-    _Py_SIZE_ROUND_UP((typeobj)->tp_basicsize + \
-        (nitems)*(typeobj)->tp_itemsize,        \
-        SIZEOF_VOID_P)
-
-#define PyObject_NEW(type, typeobj) \
-( (type *) PyObject_Init( \
-    (PyObject *) PyObject_MALLOC( _PyObject_SIZE(typeobj) ), (typeobj)) )
-
-#define PyObject_NEW_VAR(type, typeobj, n) \
-( (type *) PyObject_InitVar( \
-      (PyVarObject *) PyObject_MALLOC(_PyObject_VAR_SIZE((typeobj),(n)) ),\
-      (typeobj), (n)) )
-
-/* This example code implements an object constructor with a custom
-   allocator, where PyObject_New is inlined, and shows the important
-   distinction between two steps (at least):
-       1) the actual allocation of the object storage;
-       2) the initialization of the Python specific fields
-      in this storage with PyObject_{Init, InitVar}.
-
-   PyObject *
-   YourObject_New(...)
-   {
-       PyObject *op;
-
-       op = (PyObject *) Your_Allocator(_PyObject_SIZE(YourTypeStruct));
-       if (op == NULL)
-       return PyErr_NoMemory();
-
-       PyObject_Init(op, &YourTypeStruct);
-
-       op->ob_field = value;
-       ...
-       return op;
-   }
-
-   Note that in C++, the use of the new operator usually implies that
-   the 1st step is performed automatically for you, so in a C++ class
-   constructor you would start directly with PyObject_Init/InitVar
-*/
-
-
-
 /*
  * Garbage Collection Support
  * ==========================