bug#74015: 'guix shell --export-manifest' fails for some transformations

[Simon Tournier <zimon.toutoune@gmail.com>]

Hi,

On Sun, 10 Nov 2024 at 12:38, Ludovic Courtès <ludo@gnu.org> wrote:

>> $ guix shell -m manifest.scm --export-manifest
>
> ‘--export-manifest’ is meant to “translate” a command line, which it can
> do faithfully; there’s no way it could possibly “recreate” what
> ‘manifest.scm’, which may contain arbitrary Scheme code (and someone who
> already has a ‘manifest.scm’ file probably doesn’t need
> ‘--export-manifest’).

Yes, one might need. :-)

As I explained: « That’s annoying in some context as “guix pack
--save-provenance” [1].  Even, it defeats the idea of a self-contained
reproducible binary container. »

For sure, I understand it’s hard to capture this kind of transformation.
Still, an improvement appears to me possible (see below).

1: https://hpc.guix.info/blog/2021/10/when-docker-images-become-fixed-point


> It’s necessarily a lossy process.

This is where I disagree. :-) I mean, yes I agree that building
profile/manifest is somehow a lossy process because some Scheme is
potentially evaluated on the road.  However, I am proposing: Aside the
profile ’manifest’ file (lossy process), we could store all the
manifests provided by the command line.  Something as:

    /gnu/store/xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx-profile/manifest
    /gnu/store/xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx-profile/manifest.orig1
    /gnu/store/xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx-profile/manifest.orig2
    …

where manifest.orig1 and manifest.orig2 are the copy of files ’foo.scm’
and ’bar.scm’ from:

    -m foo.scm -m bar.scm

This way, the option --export-manifest could be improved, eventually.

In other word, I think that saving as-is the manifests costs almost
nothing and it paves the way to more robust self-contained binary packs.

Well, maybe this extra work could be only done when there is an option
’--save-provenance’ applied.

> I would close it as not-a-bug; WDYT?

I still think it’s a feature that it’s possible to improve.

Cheers,
simon