Subject: bug#45570: operating-system definitions allow duplicate passwd and group entries

From: Jason Conroy <[email-masked]>
Date: Thu, 31 Dec 2020 13:14:19 -0500

When an operating-system contains multiple users or groups with the same
name, instantiating it with `guix system` does not cause a validation
failure, nor are the duplicate entries filtered from the resulting /etc
files.

This duplication can happen in a few different ways:

- both entries are manually included in the "users" or "groups" fields of
the operating-system
- a manually-specified entry collides with an entry defined by a service
(via an account-service-type extension)
- multiple services define entries that collide with each other

Steps to reproduce: call "guix system container" with the attached
operating-system definition.