Subject: Re: [bug#72136] [PATCH 1/2] gnu: coreutils-minimal: Don't support targets with no system.

From: Ludovic Courtès <[email-masked]>
Date: Thu, 18 Jul 2024 11:33:49 +0200

Hello,

Christopher Baines <[email-masked]> skribis:

> Since I believe coreutils-minimal will fail to build for these targets, this
> will catch this early and display a clear message for both this package and
> packages using it as an input.
>
> * gnu/packages/base.scm (coreutils-minimal)[native-inputs]: Check the target
> if there is one.
>
> Change-Id: Id37cf6ac0b63226261a85a00699dfd06188c1475

[...]

> +    (native-inputs
> +     (begin
> +       (let ((target (%current-target-system)))
> +         (when target
> +           (unless (platform-system (lookup-platform-by-target target))
> +             (raise
> +              (condition
> +               (&package-unsupported-target-error
> +                (package this-package)
> +                (target target)))))))
> +       '()))

I understand the rationale, but this raises a few issues IMO:

  1. This is abusing the ‘native-inputs’ field.

  2. It’s the kind of thing that should be purely declarative, much like
     ‘supported-systems’.

  3. So far, we do not keep track of the supported cross-compilation
     targets of each package, and I think it’s probably better that way:
     the set of cross-compilation targets is pretty much open-ended and
     we only check them on a best-effort basis, for select packages
     (typically those listed in ‘packages-to-cross-build’ in (gnu ci)
     and/or ‘etc/release-manifest.scm’).  I think we’d rather not start
     annotating packages for supported cross-compilation target.

That said, the initial problem remains: how can we ensure that the Data
Service does not attempt to compute cross-build derivations that don’t
make sense, such as Coreutils on bare-metal targets like ‘avr’?

My take is that we should bake knowledge about what makes sense to be
tested somewhere.  It could be either arranging so (gnu ci) can be used
by the Data Service (it’s currently used by Cuirass), or
‘etc/release-manifest.scm’, or even just a hard-coded listed of
supported targets—we’re talking about a list of ten triplets or so,
that’s okay.

Or perhaps there’s room for something nicer in (guix platforms), but I
don’t see how we could determine whether a given package is eligible for
a bare-metal target.

Thoughts?

Ludo’.