[bug#54918] [WIP] make guix-service-type more extendable

[Ludovic Courtès]

Hi Justin,

Justin Veilleux <terramorpha@cock.li> skribis:

> I realize that this change isn't trivial as it breaks some people's
> os.scm and requires updating the documentation, but I think it is a
> very low hanging fruit in terms of functionality.

I think the risk of breakage is low: the previous extension mechanism
had only one use case, qemu-binfmt.  That use case is now gone, so we
should be fine.

> +(define-record-type* <guix-extension>
> +  guix-extension make-guix-extension
> +  guix-extension?
> +  (authorized-keys guix-extension-authorized-keys ;list of gexps
> +                    (default '()))
> +  (substitute-urls guix-extension-substitute-urls ;list of strings
> +                    (default '()))
> +  (chroot-directories guix-extension-chroot-directories ;list of 
> file-like/strings
> +                      (default '())))

I like this approach!

Together with update documentation and a changelog, it LGTM.  Could you
send an updated patch?

Thanks,
Ludo’.