[Python-Dev] No longer enable Py_TRACE_REFS by default in debug build

[Victor Stinner]

Hi,

When Python is built in debug mode, PyObject gets 2 new fields:
_ob_prev and _ob_next. These fields change the offset of following
fields in the PyObject structure and so breaks the ABI.

I propose to modify the debug build (Py_DEBUG) to no longer imply
Py_TRACE_REFS. Antoine Pitrou proposed this idea when the C API was
discussed to get a stable ABI.

https://bugs.python.org/issue36465
https://github.com/python/cpython/pull/12615

This change makes the debug build ABI closer to the release build ABI,
but I am not sure how to compare these two ABI. Technically, C
extensions still need to be recompiled.

What do you think?

--

I also wrote a PR to remove all code related to Py_TRACE_REFS:
https://github.com/python/cpython/pull/12614

I don't think that it's right approach. I prefer to keep this special
build around to see if anyone needs it, and wait one or two Python
releases to decide what to do with it.

Victor
-- 
Night gathers, and now my watch begins. It shall not end until my death.