python-distlib vs python-distlib/next

[Ricardo Wurmus <rekado@elephly.net>]

Hi,

commit ce6efff6eca0ed88cb9538803f5d1252c91a3b5e updated 
virtualenv.  As part of this change python-distlib was replaced 
with python-distlib/next.

This broke the *installation* (not the build) of other packages 
such as python-pygenometracks.  The reason is that the closure of 
python-pygenometracks would include both python-distlib and 
python-distlib/next.  Guix would then prevent the installation of 
python-pygenometracks into user profiles:

> guix package: error: profile contains conflicting entries for 
> python-distlib
> guix package: error:   first entry: python-distlib@0.3.1 
> /gnu/store/mypg42bass5n61liwyq7llrwla4w8bny-python-distlib-0.3.1
> guix package: error:    ... propagated from 
> python-virtualenv@20.2.1
> guix package: error:    ... propagated from python-tox@3.20.0
> guix package: error:    ... propagated from 
> python-argh@0.26.2-1.dcd3253
> guix package: error:    ... propagated from 
> python-gffutils@0.9-1.4034c54
> guix package: error:    ... propagated from 
> python-pygenometracks@3.3
> guix package: error:   second entry: python-distlib@0.3.0 
> /gnu/store/fwya18dazamh2cjdkgh5wpxi7lqn4fcm-python-distlib-0.3.0
> guix package: error:    ... propagated from 
> python-sortedcontainers@2.1.0
> guix package: error:    ... propagated from 
> python-intervaltree@3.0.2
> guix package: error:    ... propagated from 
> python-pygenometracks@3.3

We can’t easily detect these problems because they only strike at 
installation time.  This means that we may not do partial upgrades 
in the Python world due to the quirks of propagation.  There may 
be other packages that are broken in a similar fashion right now.

How can we make this more robust and avoid problems like this in 
the future?

(I worked around this problem for pygenometracks by removing 
python-tox from the propagated inputs of python-argh.)

-- 
Ricardo