Re: [gentoo-python] python-r1 <-> python.eclass package dependencies

[Michał Górny]

On Sun, 11 Nov 2012 14:29:20 +0800
Ben de Groot <yngwin@g.o> wrote:

> On 11 November 2012 00:43, Michał Górny <mgorny@g.o> wrote:
>
> > Hello,
> >
> > As some of you are aware already, there is a significant difference
> > in handling Python implementation choice between python.eclass
> > and python-r1 / p-d-ng.
> >
> > The python.eclass packages use USE_PYTHON (undocumented variable)
> > or the eselected Python2+3, and store that choice implicitly.
> > Everything works on the assumption that implementations don't change
> > or user runs python-updater.
> >
> > The python-r1 / p-d-ng packages use explicit USE flags to choose
> > implementation. The choice is thus explicitly exported and other
> > packages can use USE dependencies to enforce matching implementations.
> >
> > The problems arise whenever python-r1 package depends on package using
> > the python.eclass, or the other way round. There is no clear way to
> > enforce the same implementations being used, so everything falls down
> > to user.
> >
> > In order to solve the most common problems due to that, I have
> > published a news item explaining how PYTHON_TARGETS work and what needs
> > to be done with them.
> >
> > In the discussion with other Gentoo Python devs, it was assumed that
> > USE_PYTHON should not be considered public and thus not be described
> > in the message. Sadly, it seems that this resulted in people actually
> > trying to disable Python3 using PYTHON_TARGETS and seeing random
> > failures due to python.eclass enforcing it anyway.
> >
> >
> > I believe we should thoroughly think what should be done now in order
> > to solve the issues best for the transition time. Here are a few
> > solutions I can think of.
> >
> > 1) lard both eclasses with USE_PYTHON <-> PYTHON_TARGETS consistency
> > checks. This should be pretty easy for python-r1, harder for
> > python.eclass (anyone volunteering to touch it in thick gloves?).
> >
> > In other words, we just warn users whenever they need to do something
> > to ensure things work.
> >
> >
> > 2) make python.eclass respect PYTHON_TARGETS.
> >
> > Sadly, due to PMS limitations we can't tell if PYTHON_TARGETS was set
> > by user or has the default value. So we either can:
> >
> > a) stop using USE_PYTHON and eselect defaults, start using
> > PYTHON_TARGETS only, pull in correct Python versions, tell users to run
> > python-updater;
> >
> > b) prefer PYTHON_TARGETS over USE_PYTHON and the default (but only
> > if PYTHON_TARGETS != default PYTHON_TARGETS, so we're on thin ice here).
> >
> >
> > 3) make python.eclass respect and export PYTHON_TARGETS in IUSE.
> >
> > Like the above but instead of running the fragile and broken
> > python-updater, we simply force rebuild of all packages. People can
> > start using USE-deps in the meantime, everyone becomes a bit happier
> > in the further plane. Sadly, this means every Python package is going
> > to need being rebuilt.
> >
> >
> > Please also note that 2 & 3 mean mass-changing behavior of stable
> > packages. Not something I'd do in a short timeframe where the issue
> > should be best fixed.
> >
> > Any other ideas? Any +1, -1s?
> I'm sorry if I missed something, but I don't see why USE_PYTHON should be
> considered not public. That has been the only mechanism until now (in
> combination with package.mask) to get a consistent system without redundant
> multiple python versions.

Well, the most important reason is that I don't think USE_PYTHON is
pretty much documented *anywhere*.

> I think it is easiest to tell users to set USE_PYTHON as well, until
> python.eclass is finally phased out.

Yes, that's what the warning would say.

-- 
Best regards,
Michał Górny