zimoun <zimon.toutoune@gmail.com> writes:

> You want something like that:
>
> --8<---------------cut here---------------start------------->8---
> (define-public debian-archive-keyring
>   (package
>     (name "debian-archive-keyring")
>     (version "2019.1")
>     (source ...)
>     (build-system copy-build-system)
>     (arguments
>      '(#:install-plan
>        (lambda* (#:key outputs #:allow-other-keys)
>                 (let* ((out (assoc-ref outputs "out"))
>                        (apt (string-append out "/etc/apt/trusted.gpg.d/"))
>                        (key (string-append out "/share/keyrings/")))
>                   (install-file "keyrings/debian-archive-keyring.gpg" key)
>                   (install-file "keyrings/debian-archive-removed-keys.gpg" key)
>                   (for-each (lambda (file)
>                               (install-file file apt))
>                             (find-files "trusted.gpg" "\\.gpg$")))
>                 #t)))))
> --8<---------------cut here---------------end--------------->8---

Actually we could simplify the install plan with something like

--8<---------------cut here---------------start------------->8---
#:install-plan
(("source1" "target1")
 ("source-dir2/" "target-dir2" #:exclude ("foo")))
--8<---------------cut here---------------end--------------->8---

Regarding the data fetching, if I understand your point I think it
should be handled in a separate issue.

Cheers!

-- 
Pierre Neidhardt
https://ambrevar.xyz/