bug#40567: mpd-service-type needs a pre-existing user in system and does not works with a new user defined in config.scm

[Leo Famulari]

On Sun, Apr 12, 2020 at 09:55:15AM +0530, R Veera Kumar wrote:
> This is to report:
> mpd-service-type needs a pre-existing user in system and does not works
> with a new user defined in config.scm. Running guix system reconfigure 
> gives some getpw error.
> 
> Guix system reconfigure works fine if we add temporarily a user with useradd.

I suppose the service was written with the assumption that one would
choose their own user as the MPD user, since they likely own the music
library.

We could make the MPD service extend accounts-service-type to handle
user accounts for a "system user" but it depends on the expectations of
MPD users, or at least people using this service.

At least, we could add a more informative error message.