breezy fails to build on Python 3.10: issue with Py_REFCNT()

[Victor Stinner]

On Python 3.10, Py_REFCNT() macro can no longer be used as an l-value, whereas breezy/_static_tuple_c.c uses it to set the reference count of an object:
    Py_REFCNT(self) -= 1;
and
    Py_REFCNT(self) = 2;

The new Py_SET_REFCNT() function must be used instead. For backward compatibility, this macro can be used to define Py_SET_REFCNT() on Python 3.8 and older.

#if PY_VERSION_HEX < 0x030900A4
# define Py_SET_REFCNT(obj, refcnt) ((Py_REFCNT(obj) = (refcnt)), (void)0)
#endif

Then replace:
    Py_REFCNT(self) -= 1;
with:
    Py_SET_REFCNT(self, Py_REFCNT(self) - 1);

And replace:
    Py_REFCNT(self) = 2;
with:
    Py_SET_REFCNT(self, 2);

Copy of What's New in Python 3.10:
"""
Since 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 Py_SET_REFCNT() (available since Python 3.9). For backward compatibility, this macro can be used:

#if PY_VERSION_HEX < 0x030900A4
# define Py_SET_REFCNT(obj, refcnt) ((Py_REFCNT(obj) = (refcnt)), (void)0)
#endif
"""

Python issue where the Py_REFCNT() macro has been changed:
https://bugs.python.org/issue39573

Downstream Fedora issue for breezy on Python 3.10:
https://bugzilla.redhat.com/show_bug.cgi?id=1890880

[Victor Stinner (vstinner)]

I attach a fix as a patch.

I failed to create a brz branch.

The "bzr push lp:~vstinner/brz/brz" command fails with:

<email address hidden>: Permission denied (publickey).
ConnectionReset reading response for b'BzrDir.open_2.1', retrying
<email address hidden>: Permission denied (publickey).

"ssh -v <email address hidden>" fails with:

debug1: Offering public key: /home/vstinner/.ssh/id_rsa RSA SHA256:2Ikqg/9eDjHfxObh+4wk6E4u5JhguaHpFG/V04e0yIo agent
debug1: send_pubkey_test: no mutual signature algorithm

I tested 2 different RSA keys (registered in my Launchpad account).

[Jelmer Vernooij (jelmer)]

On Thu, Nov 19, 2020 at 12:36:20PM -0000, Victor Stinner wrote:
> I attach a fix as a patch.

> ** Patch added: "Port brz to Python 3.10"
> https://bugs.launchpad.net/brz/+bug/1904868/+attachment/5435974/+files/brz-python310.patch
Thanks for the patch - I'll submit that to the 3.1 and 3.2 series for
Breezy.

> I failed to create a brz branch.
>
> The "bzr push lp:~vstinner/brz/brz" command fails with:
>
> <email address hidden>: Permission denied (publickey).
> ConnectionReset reading response for b'BzrDir.open_2.1', retrying
> <email address hidden>: Permission denied (publickey).

>
> "ssh -v <email address hidden>" fails with:
>
> debug1: Offering public key: /home/vstinner/.ssh/id_rsa RSA SHA256:2Ikqg/9eDjHfxObh+4wk6E4u5JhguaHpFG/V04e0yIo agent
> debug1: send_pubkey_test: no mutual signature algorithm
>
> I tested 2 different RSA keys (registered in my Launchpad account).
Not really sure what's going on there - if you care about debugging
this further, the best place to ask is probably
https://answers.launchpad.net/launchpad or the launchpad users list.

I know Launchpad uses some variant of the twisted SSH implementation,
but I am fuzzy on the details.

Breezy has integration for Launchpad (and other hosting platforms)
and is hosted on Launchpad, but is otherwise a separate project.

Jelmer

[Victor Stinner (vstinner)]

> New → Fix Committed

Great, that was quick! Thank you :-)