Hello Ludo,

Thanks for your explanation :)

> This is expected: packages in ‘%final-inputs’ (those returned by
> ‘canonical-package’) are rooted in the bootstrap graph and cannot be
> cross-compiled.

Looking at canonical-package in (gnu packages commencement), I see that
there's already a switch on (%current-target-system). The given package
is directly returned if (%current-target-system) is set, which appears
to be what we want!

--8<---------------cut here---------------start------------->8---
         ;; In general we want CANON, except if we're cross-compiling: CANON
         ;; uses explicit inputs, so it is "anchored" in the bootstrapped
         ;; process, with dependencies on things that cannot be
         ;; cross-compiled.
         (if (%current-target-system)
             package
             canon))
--8<---------------cut here---------------end--------------->8---

But, this doesn't work as expected. I guess it is because of
(%current-target-system) evaluation time.

As I'm not fully understand everything here, I would propose to define a
gexp-compiler for "canonical-packages", but there's maybe a better thing
to do?

Anyway, the snippet below works fine with a gexp-compiler (patch
attached) and doesn't work with the current implementation of
canonical-package.

--8<---------------cut here---------------start------------->8---
(use-modules (guix)
             (gnu packages base))

(run-with-store (open-connection)
  (mlet* %store-monad
      ((gexp    -> #~(#$(canonical-package grep)))
       (drv     (gexp->script "test.scm" gexp
                               #:target "aarch64-linux-gnu"))
       (build   (built-derivations (list drv))))
    (return #t)))
--8<---------------cut here---------------end--------------->8---

WDYT?

Thanks,

Mathieu