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bpo-44874: deprecate Py_TRASHCAN_SAFE_BEGIN and Py_TRASHCAN_SAFE_END #27693

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Merged
ambv merged 6 commits into from
Aug 18, 2021
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bpo-44874: deprecate Py_TRASHCAN_SAFE_BEGIN and Py_TRASHCAN_SAFE_END #27693

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6772bdf
bpo-44874: deprecate Py_TRASHCAN_SAFE_BEGIN and Py_TRASHCAN_SAFE_END
iritkatriel Aug 9, 2021
62d64e7
📜🤖 Added by blurb_it.
blurb-it[bot] Aug 9, 2021
d4de5cd
add compiler warning
iritkatriel Aug 17, 2021
f58b627
add migration instructions to news file
iritkatriel Aug 18, 2021
dc5cd34
Increase example readability
ambv Aug 18, 2021
9d2d76d
Move porting instructions to What's New in Python 3.11
ambv Aug 18, 2021
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41 changes: 41 additions & 0 deletions Doc/whatsnew/3.11.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -304,6 +304,47 @@ New Features
Porting to Python 3.11
----------------------

* The old trashcan macros (``Py_TRASHCAN_SAFE_BEGIN``/``Py_TRASHCAN_SAFE_END``)
are now deprecated. They should be replaced by the new macros
``Py_TRASHCAN_BEGIN`` and ``Py_TRASHCAN_END``.

A tp_dealloc function that has the old macros, such as::

static void
mytype_dealloc(mytype *p)
{
PyObject_GC_UnTrack(p);
Py_TRASHCAN_SAFE_BEGIN(p);
...
Py_TRASHCAN_SAFE_END
}

should migrate to the new macros as follows::

static void
mytype_dealloc(mytype *p)
{
PyObject_GC_UnTrack(p);
Py_TRASHCAN_BEGIN(p, mytype_dealloc)
...
Py_TRASHCAN_END
}

Note that ``Py_TRASHCAN_BEGIN`` has a second argument which
should be the deallocation function it is in.

To support older Python versions in the same codebase, you
can define the following macros and use them throughout
the code (credit: these were copied from the ``mypy`` codebase)::

#if PY_MAJOR_VERSION >= 3 && PY_MINOR_VERSION >= 8
# define CPy_TRASHCAN_BEGIN(op, dealloc) Py_TRASHCAN_BEGIN(op, dealloc)
# define CPy_TRASHCAN_END(op) Py_TRASHCAN_END
#else
# define CPy_TRASHCAN_BEGIN(op, dealloc) Py_TRASHCAN_SAFE_BEGIN(op)
# define CPy_TRASHCAN_END(op) Py_TRASHCAN_SAFE_END(op)
#endif

* The :c:func:`PyType_Ready` function now raises an error if a type is defined
with the :const:`Py_TPFLAGS_HAVE_GC` flag set but has no traverse function
(:c:member:`PyTypeObject.tp_traverse`).
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17 changes: 13 additions & 4 deletions Include/cpython/object.h
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Expand Up @@ -534,7 +534,16 @@ PyAPI_FUNC(int) _PyTrash_cond(PyObject *op, destructor dealloc);
Py_TRASHCAN_BEGIN_CONDITION(op, \
_PyTrash_cond(_PyObject_CAST(op), (destructor)dealloc))

/* For backwards compatibility, these macros enable the trashcan
* unconditionally */
#define Py_TRASHCAN_SAFE_BEGIN(op) Py_TRASHCAN_BEGIN_CONDITION(op, 1)
#define Py_TRASHCAN_SAFE_END(op) Py_TRASHCAN_END
/* The following two macros, Py_TRASHCAN_SAFE_BEGIN and
* Py_TRASHCAN_SAFE_END, are deprecated since version 3.11 and
* will be removed in the future.
* Use Py_TRASHCAN_BEGIN and Py_TRASHCAN_END instead.
*/
Py_DEPRECATED(3.11) typedef int UsingDeprecatedTrashcanMacro;
#define Py_TRASHCAN_SAFE_BEGIN(op) \
do { \
UsingDeprecatedTrashcanMacro cond=1; \
Py_TRASHCAN_BEGIN_CONDITION(op, cond);
#define Py_TRASHCAN_SAFE_END(op) \
Py_TRASHCAN_END; \
} while(0);
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core and Builtins/2021-08-09-19-05-20.bpo-44874.oOcfU4.rst
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@@ -0,0 +1 @@
Deprecate the old trashcan macros (``Py_TRASHCAN_SAFE_BEGIN``/``Py_TRASHCAN_SAFE_END``). They should be replaced by the new macros ``Py_TRASHCAN_BEGIN`` and ``Py_TRASHCAN_END``.