Code sharing between system and home services (was Re: On the naming of System and Home services modules.)

[Xinglu Chen <public@yoctocell.xyz>]

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On Thu, Sep 23 2021, Ludovic Courtès wrote:

> Hi,
>
> Xinglu Chen <public@yoctocell.xyz> skribis:
>
>> Some services might be useful to have in both Guix System and Guix Home;
>> for instance, Guix System currently has a service for configuring
>> Syncthing, and I think it makes sense to also have one for Guix Home,
>> this would mean that people not using Guix System (me :-)) could also
>> have Guix manage Syncthing.  With the current approach, we would have to
>> copy and paste quite a bit of code, and if the Syncthing service for
>> Guix System changes, then the one for Guix Home might have to change as
>> well.
>
> Silly question, but why do we need to have two different configuration
> record types in the first place?

The problem is that the configuration records for system and home
service don’t necessarily have the same fields.  The Syncthing service
for Guix System has a ‘user’ and a ‘group’ field, which is not really of
any use in Guix Home, as the only user would be the user invoking ‘guix
home’.

> Sharing configuration between Home and System sounds important to me: it
> means users can easily move services from one to the other, which is
> pretty big deal.  It also means we’d have much less code to maintain.

Agreed, that’s what I would like to see as well.

> Would that be feasible?  (Apologies if this has already been
> discussed!)

Since it might not make sense to have the same records fields for a
system service and home service, I proposed (in the mail you replied to)
a ‘define-configuration’ form that would generate a configuration record
for a system service and optionally one for a home service, without
having to maintain two records separately.

--8<---------------cut here---------------start------------->8---
(define-configuration syncthing-configuration
  (package
   (package syncthing)
   "Syncthing package to use.")
  (arguments
   (list-of-strings ’())
   "Command line arguments to pass to the Syncthing package.")
  (log-flags
   (integer 0)
   "Sum of logging flags.")
  (user
   (maybe-string 'disabled)
   "The user as which the Syncthing service is to be run."
   (home-service? #f))  ; not for Guix Home
  (group
   (string "users")
   "The group as which the Syncthing service is to be run."
   (home-service? #f))  ; likewise ^^
  (home
   (maybe-string 'disabled)
   "Common configuration and data directory.")
  (home-service? #t))
--8<---------------cut here---------------end--------------->8---

It would generate <syncthing-configuration> and
<home-syncthing-configuration>.  The only difference being that
<home-syncthing-configuration> doesn’t have a ‘user’ and a ‘group’
field.

It’s probably going to be quite complicated, so it would be good to get
some feedback/thoughts on it.  Cc Maxim since he has done some work with
(gnu services configuration).

Also, it’s probably time to properly document (gnu services
configuration) in the manual.  ;-)

> Also, I proposed earlier a possible way to generate a Home service type
> from the corresponding System service type—or, IOW, to generate a Home
> service type graph from the System graph.  Does that sound feasible?

I am not sure exactly what you mean here, could you elaborate?


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