Subject: Re: [bug#30351] [PATCH] gnu: mcron2: Correct and enhance the wrap phase.

From: [email-masked] (Ludovic Courtès)
Date: Fri, 09 Feb 2018 11:09:47 +0100

Hi Maxim,

Maxim Cournoyer <[email-masked]> skribis:

> As a follow up to my previous patch to mcron2, this completes the wrap
> phases and fix a small issue where the mcron modules were installed to
> share/guile/site/2.0 instead of 2.2.

Good catch.  I’ve committed that change separately.

BTW, I encourage you to submit changes to [email-masked].  Mcron is
now maintained by Mathieu Lirzin, who is familiar with current Guile and
certainly interested in receiving improvements like this.

(Another thing that should be done would be install .go files in
$libdir/guile/2.2/site-ccache.)

> For those using dyndns services, a job like the following should now
> work without having to propagate Guile or GnuTLS in your user/system
> profile[0]:

[...]

>>>From 385343b1370d87e6104ebe2ef473bf2d1e31f2f2 Mon Sep 17 00:00:00 2001
> From: Maxim Cournoyer <[email-masked]>
> Date: Sun, 4 Feb 2018 14:05:40 -0500
> Subject: [PATCH] gnu: mcron2: Correct and enhance the wrap phase.
>
> * gnu/packages/guile.scm (mcron2)[inputs]: Rename "guile-2.2" to just "guile".
> [phases]: Install mcron2 modules to guile/site/2.2 instead of guile/site/2.0.
> Add Guile 2.2 and GnuTLS modules to the wrap phase.

[...]

>             (add-after 'install 'wrap-mcron
> -             (lambda* (#:key outputs #:allow-other-keys)
> -               ;; Wrap the 'mcron' command to refer to the right
> -               ;; modules.
> -               (let* ((out  (assoc-ref outputs "out"))
> -                      (bin  (string-append out "/bin"))
> -                      (site (string-append
> -                             out "/share/guile/site")))
> -                 (match (scandir site)
> -                   (("." ".." version)
> -                    (let ((modules (string-append site "/" version)))
> -                      (wrap-program (string-append bin "/mcron")
> -                        `("GUILE_LOAD_PATH" ":" prefix
> -                          (,modules))
> -                        `("GUILE_LOAD_COMPILED_PATH" ":" prefix
> -                          (,modules)))
> -                      #t))))))))))))
> +             (lambda* (#:key inputs outputs #:allow-other-keys)
> +               ;; Wrap the 'mcron' command to refer to the right modules. We
> +               ;; also include Guile 2.2 modules and GnuTLS, so that Guile
> +               ;; libraries can be used in mcron jobs without having to
> +               ;; propagate those in a user profile.
> +               (let* ((site-dir "/share/guile/site/2.2")
> +                      (ccache-dir "/lib/guile/2.2/ccache")
> +                      (mcron  (assoc-ref outputs "out"))
> +                      (mcron-bin (string-append mcron "/bin/mcron"))
> +                      (mcron-modules (string-append mcron site-dir))
> +                      (guile (assoc-ref inputs "guile"))
> +                      (guile-modules (string-append guile site-dir))
> +                      (guile-ccache (string-append guile ccache-dir))
> +                      (gnutls (assoc-ref inputs "gnutls"))
> +                      (gnutls-modules (string-append gnutls site-dir))
> +                      (gnutls-ccache (string-append gnutls ccache-dir)))
> +                 (wrap-program mcron-bin
> +                   `("GUILE_LOAD_PATH" ":" prefix
> +                     (,mcron-modules ,guile-modules ,gnutls-modules))
> +                   `("GUILE_LOAD_COMPILED_PATH" ":" prefix
> +                     (,mcron-modules ,guile-ccache ,gnutls-ccache)))
> +                 #t)))))))))

A couple of issues here: the ‘scandir’ trick above allowed us to not
hard-code “2.2”.  I think it’d be nice to try to preserve such things;
it’ll be less pain down the road.

Second issue is about adding GnuTLS to the search path: it’s not the
right place for that.  What if someone wants Guile-JSON?  And Guile-Git?
And…  You get the idea.  :-)

Instead I’d suggest writing your mcron job along these lines:

  #~(begin
      (add-to-load-path (string-append #+gnutls "/share/guile/site/"
                                       (effective-version)))
      (use-modules (web client))
      …)

(See (guix download) for an example of this hack.)

The extra boilerplate is admittedly not great, so I’d like to add a
‘with-extensions’ or ‘with-imported-packages’ form that would be like
’with-imported-modules’ but for Guile “extensions” like GnuTLS.

Last thing: it’s not necessary to put Guile’s own module directories in
the search path.  They’re already there by default.

So overall I think I’m arguing for the status quo.  Would that work for
you?

Thanks,
Ludo’.