bug#42510: ‘guix pack -RR’ can lead to profile collisions

[Ludovic Courtès]

Hi,

‘guix pack -RR’ produces package variants that can lead to profile
collision in the presence of propagated inputs:

--8<---------------cut here---------------start------------->8---
$ guix describe
Generacio 151   Jul 20 2020 11:16:29    (nuna)
  guix cd0c426
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: master
    commit: cd0c4268d74e58fcfe9c729183d90665f4abbb09
$ guix pack -RR python-scipy python-numpy --no-grafts
guix pack: error: profile contains conflicting entries for python-numpy
guix pack: error:   first entry: python-numpy@1.17.3 
/gnu/store/603imkkh2bqs01z8ik0b2ndgpdz0jghk-python-numpy-1.17.3
guix pack: error:    ... propagated from python-scipy@1.3.2
guix pack: error:   second entry: python-numpy@1.17.3 
/gnu/store/0fjdgihg6r3m2d6qfbkis4vg0017ilkj-python-numpy-1.17.3R
hint: Try upgrading both `python-scipy' and `python-numpy', or remove one of 
them from the profile.
--8<---------------cut here---------------end--------------->8---

Here the “R” variant conflicts with the regular one.

Ludo’.