bug#29255: "Profile contains conflicting entries" could be more helpful

[Ben Sturmfels]

Hi Folks,

When trying to install "python-twine", installation failed with the
following error:

$ guix package --install python-twine
The following package will be installed:
   python-twine 1.9.1   
/gnu/store/fh72qswc2gpj1c1xb2gm23hfs1vx4lk2-python-twine-1.9.1

guix package: error: profile contains conflicting entries for 
python-requests:out
guix package: error:   first entry: address@hidden:out 
/gnu/store/4paqanwmdw2d7ss9hdq7d34b43ycjgsv-python-requests-2.13.0
guix package: error:    ... propagated from address@hidden
guix package: error:   second entry: address@hidden:out 
/gnu/store/z4jqf8p2z73dscrjmbpwamdvyfdaqkgx-python-requests-2.13.0


This was quite baffling - it wasn’t clear to me why there was a
conflict, whether it was related to something I'd done and what I could
do to fix it.

If I understand correctly, the cause is that I had manually installed
"python-requests" at some stage and that only one version can be
available in my profile, and that "python-twine" depended on a different
version.

I believe the action I need to take to resolve the conflict is:

  guix package --install python-twine --upgrade python-requests


So I think the bug is that the user interface could be more helpful here.
It should probably either tell you what happened and what you can do to
fix it, or offer to resolve the conflict/perform the upgrade for you.

Regards,
Ben