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

[Ben de Groot]

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?
>
> --
> Best regards,
> Michał Górny
>

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.

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

-- 
Cheers,

Ben | yngwin
Gentoo developer
Gentoo Qt project lead, Gentoo Wiki admin