bug#54350: Profile collisions are ignored, installing multiple versions of the same package is silently broken

["Ludovic Courtès" <ludo@gnu.org>]

Hi,

Maxime Devos <maximedevos@telenet.be> skribis:

> $ guix shell --pure bash pango@1.42 pango@1.48
> $ ~/.guix-profile/bin/ls -l $GUIX_ENVIRONMENT/lib/libpango*.so
>
> Result:
> [...]/lib/libpango-1.0.so -> [...]-pango-1.42.4/lib/libpango-1.0.so
> [...]/lib/libpangocairo-1.0.so -> [...]-pango-1.42.4/lib/libpangocairo-1.0.so
> [...]/lib/libpangoft2-1.0.so -> [...]-1.42.4/lib/libpangoft2-1.0.so
> [...]/lib/libpangoxft-1.0.so -> [...]-pango-1.42.4/lib/libpangoxft-1.0.so
>
> Question: how does this even work?  Aren't error messages about profile
> collisions a thing?

Unlike ‘guix package’, ‘guix environment/shell’ explicitly disables
collision checks—see #:allow-collisions? in environment.scm.

The rationale back then was that if you do:

  guix shell -D guile

then you likely end up with profile collisions, like so (I modified the
code to do #:allow-collisions? #f):

--8<---------------cut here---------------start------------->8---
$ ./pre-inst-env guix shell -D guile -n
guix shell: error: profile contains conflicting entries for bash-minimal
guix shell: error:   first entry: bash-minimal@5.1.8 /gnu/store/chfwin3a4qp1znnpsjbmydr2jbzk0d6y-bash-minimal-5.1.8
guix shell: error:   second entry: bash-minimal@5.1.8 /gnu/store/4y5m9lb8k3qkb1y9m02sw9w9a6hacd16-bash-minimal-5.1.8
hint: You cannot have two different versions or variants of `bash-minimal' in the same profile.
--8<---------------cut here---------------end--------------->8---

These collisions are harmless but frequent in package development
environments, which is why ‘guix environment’ had to turn off those
checks (commit afd06f605bf88a796acefc7ed598b43879346a6b).

That’s a bit of a hack though.

What we could do, as a mitigation, is to enable collision checks unless
there’s at least one ‘-D’ flag.  We’d also need to introduce
‘--allow-collisions’ for ‘guix shell’.

WDYT?

Thanks,
Ludo’.