bug#19795: Allow for stateless users and groups in GuixSD

[Alex Sassmannshausen <alex.sassmannshausen@gmail.com>]

Hello,

My 2c:

In short +1!

Thompson, David writes:

> Currently, removing a user account from the users list in an OS config
> does not remove the user account from a system when 'guix system
> reconfigure' is run.  I think that user accounts not specified in the
> user accounts list should be invalidated and that /etc/passwd and
> other files be fully rebuilt each time.  In other words, I want a
> stateless /etc/passwd, not a stateful one.

I would love this functionality: it feels intuitive for a functional
package manager.

> As Mark brought up on IRC, this proposed change in behavior may very
> well surprise and frustrate another subset of users, so perhaps the
> existing behavior should be preserved, with a bit that can be flipped
> for stateless user accounts.

I agree that perhaps statefulness should be the default for now, as that
seems the "common way to do things".

Alex