bug#33286: Add 'list-formats' to 'guix pack'

[Maxim Cournoyer <maxim.cournoyer@gmail.com>]

Hello,

Efraim Flashner <efraim@flashner.co.il> writes:

> On Tue, Nov 06, 2018 at 04:31:59PM +0100, Ludovic Courtès wrote:
>> Hello,
>> 
>> Efraim Flashner <efraim@flashner.co.il> skribis:
>> 
>> > From af9a132a662f1d703df1c32278a45d2adca146ed Mon Sep 17 00:00:00 2001
>> > From: Efraim Flashner <efraim@flashner.co.il>
>> > Date: Tue, 6 Nov 2018 11:50:48 +0200
>> > Subject: [PATCH] pack: List the available formats.
>> >
>> > * guix/scripts/pack.scm (show-formats): New variable.
>> > (%options, show-help): Add 'list-formats' option.
>> 
>> [...]
>> 
>> > @@ -551,6 +552,18 @@ please email '~a'~%")
>> >      (squashfs . ,squashfs-image)
>> >      (docker  . ,docker-image)))
>> >  
>> > +(define (show-formats)
>> > +  ;; Print the supported pack formats.
>> > +  (display (G_ "The supported formats for 'guix pack' are:"))
>> > +  (newline)
>> > +  (display (G_ "
>> > +  tarball       A self-contained tarball, ready to run on another machine."))
>> > +  (display (G_ "
>> > +  squashfs      A squashfs image, ready for 'cluster engines' and the like."))
>> 
>> I’d write “Squashfs image suitable for Singularity” and remove “A” from
>> each.
>> 
>> Also, since we have the ‘%formats’ alist right above, what about
>> adjusting it so that it contains each format description, and then
>> ‘show-formats’ would just traverse it?

[...]

> I do like the idea, but I haven't been able to get it to work. In the
> mean time I've committed this as db08ea40873ae20507bc40d34a56dea1b8ce8f0e
> so we at least get the benefits of having it here.

Closing.

Thank you!

Maxim