On 06/29/2017 04:20 AM, Adam Williamson wrote:
On Thu, 2017-06-29 at 12:11 +1000, Nick Coghlan wrote:
On 29 June 2017 at 11:39, Adam Williamson <adamw...@fedoraproject.org> wrote:
On Wed, 2017-06-28 at 16:21 +0200, Iryna Shcherbina wrote:
2) Using `python-` instead of `python2-` in the dependencies for the
Python 2 binary RPM [2].
I'm not sure this list is terribly useful, because of the above. There
are thousands of packages that do this, because the 'python2-' provide
is not available on some older Fedora release, or on EPEL (and the
package is maintained for EPEL as well as Fedora). Sprinkling "if (some
release number condition) then Requires: python2-foo else Requires:
python-foo" all over your spec is a giant PITA and I for one am not
very interested in doing it.
IMHO, if there is going to be some kind of requirement that all Python
requires be explicitly versioned, there needs to be a co-ordinated
effort to make sure the versioned Provides are available across at
least EL6, EL7, and all supported Fedora releases *first*.
This was the key concern I raised in response to the initial email,
and our conclusion at the time was:
1. This case does need to be addressed
2. Adding an opaque dependency on buildroot configuration settings
wouldn't be a particularly nice way to handle it, since it forces
every package to switch concurrently, rather than each maintainer
getting to decide when to move from the Python 2 stack to the Python 3
stack for themselves (and that unilateral shift is already going to
happen for unqualified dependency declarations when the virtual
%python_provides macro moves from the Python 2 stack to the Python 3
stack)
3. Ideally, the recommended approach would work for arbitrary RHEL &
CentOS based buildroots, not just those with the EPEL RPM macros
available
The most straightforward solution we came up with was for affected
packages to define their own "%py_prefix" macro that selects the stack
they want to use based on the Python version:
```
# The block below would become the conventional
# "Python stack compatibility" dance for
# EL6, EL7, and Fedora
# Each package can decide for itself which version of
# Fedora had a sufficiently complete Py3 stack for
# them to be able to switch over
# Current EL releases & older Fedora use "python-*"
%if 0%{?el6} || 0%{?el7} || 0%{?fedora} < 25
%define py_prefix python
%if 0%{?el6} || 0%{?el7}
BuildRequires: python-devel
%else
BuildRequires: python2-devel
%endif
%else
# Newer Fedora releases use "pythonX-*"
# A Py2-only project would use "python2" here
%define py_prefix python3
BuildRequires: python3-devel
%endif
# Dependency declarations use stack selected above
BuildRequires: %{py_prefix}-builddep1
BuildRequires: %{py_prefix}-builddep2
Requires: %{py_prefix}-runtimedep1
Requires: %{py_prefix}-runtimedep2
```
Erf, well, that seems kinda icky but manageable. Is it really better
than just coming up with some kind of script to at least add the
appropriate "Provides: python2-foo" to all packages (or at least a
large subset of the most commonly-used packages) in EL6/EL7/F24,
though? I mean, that doesn't seem beyond the bounds of possibility, to
just find everything that provides 'python-foo' and make it also
provide 'python2-foo'...
Adding python2-foo is the second half of this proposal.
We don't want to do that by *just* adding "Provides: python2-foo" to all
packages, because if everyone did that, we'd need to ask them to change
again in a few years.
Would it be reasonable to do this in phases: first ask everyone to add
python2- provides, then ask everyone to use them? Yes, and in fact, we
already did that: the python2- prefix has been recommended in the
guidelines for a quite a long time. But many packagers won't do the
change until it starts being necessary.
Rebuilding lots of packages in EL6 is practically impossible, actually.
However, some subset of commonly-used packages do have the python2-
prefixed provides even in EL6. The very example above is misleading:
EL6's packages do provide python2-devel.
--
Petr Viktorin
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