Re: significance of collisions in 'guix environment'?

[Leo Famulari]

On Tue, Nov 08, 2016 at 05:09:11PM +0000, Paul Garlick wrote:
> $ ./pre-inst-env guix environment --pure gmsh
> warning: collision encountered:
> /gnu/store/m6s3bz6a2sv7015z78sfzdk5ngkzdwwg-gfortran-
> 4.9.3/libexec/gcc/x86_64-unknown-linux-gnu/4.9.3/liblto_plugin.so.0.0.0 
> /gnu/store/frrj3bfbmg5vrd0flh9cf8j64h7cr2v4-gcc-
> 4.9.3/libexec/gcc/x86_64-unknown-linux-gnu/4.9.3/liblto_plugin.so.0.0.0
> warning: arbitrarily choosing
> /gnu/store/m6s3bz6a2sv7015z78sfzdk5ngkzdwwg-gfortran-
> 4.9.3/libexec/gcc/x86_64-unknown-linux-gnu/4.9.3/liblto_plugin.so.0.0.0

[...]

> There are 14 gfortran-related messages and a message regarding ld-
> wrapper and binutils.

The ld-wrapper collision is harmless. See http://bugs.gnu.org/22659

> How should these messages be interpreted?  Could there be duplication
> in the package inputs?  

These are filesystem paths that collide when generating a profile. A
profile is a bunch of symlinks, forming a union of various directories
in /gnu/store.

The collision warnings mean that of the store directories linked to from
your profile, more than one provide a given path.

For example, GNU Parallel and moreutils both have a path "bin/parallel":
/gnu/store/7ggbvsql79s5i05a3v8cbn48kdrzf7nc-parallel-20151222/bin/parallel
/gnu/store/ax4ppgzmx5cjqr813l3djgzhiniam1yz-moreutils-0.57/bin/parallel

If you wanted to install both in your profile, those two paths would
both become: ~/.guix-profile/bin/parallel

To resolve the conflict, the first one is chosen and the rest are not
included in the profile.

In general, we have to investigate collisions on a case by case basis;
some are harmless, some are not.

Avoiding harmful collisions is a use case for creating profiles with
`guix package --profiles`.

> I have noticed that Gmsh lists gfortran and lapack as propagated-inputs 
> and lapack also lists gfortran as an input.

I wonder if this could be improved to eliminate the collisions, but I
don't have experience with those packages.