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

[Maxime Devos]

Ludovic Courtès schreef op di 15-03-2022 om 14:50 [+0100]:
> $ ./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.

These collisions happen because the bag of a package contains of multiple
variants of bash: the default canonical bash-minimal, from (gnu packages
commencement), not directly visible (i.e., with "guix show" and
'specification->package'), which is overidden by the bash-minimal from
native-inputs, which is visible from specification->package and as a public
variable, and as I understand it, the bash-minimal supposed to end up
in the references of non-bootstrap packages.

For these kind of collisions, I think the non-canonical package (that's
actually visible with "guix show FOO") is preferred here, so perhaps
the canonical variants can be filtered out whenever that would resolve
a collision?

That seems also 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’.

Special-casing -D like this also seems like a hack to me.  I'm not sure
which hack is better, though I prefer this one and the ‘filter out
canonical packages’ above the original ‘just disable collision
checking’.

Greetings,
Maxime.

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