nixos: fix setups where users.users.<id>.name is not <id>

[taliyahwebb]

TL;DR

This PR is pretty similar to #252 but achives a few extra goals.

• evaluated which "name" should be used where (more on that in # Description)
• documents the behavior around names in the option descriptions
• properly tested all apparent cases (see feature matrix in # Testing)

It is properly tested, test cases and results see below.

In Depth

Description

Guideline for which "name" should be used where

• the name as in the module (users.users.<name>) for nixos whenever its a submodule name
• the name as in the final linux system (users.users.<user>.name) whenever it's a .name option
• since groups are only ever set as .group those are always final group names and never resolved from users.groups.<group>.name

Testing

I have tested and verified the following cases:

• "same" = where: users.users.<user>.name == "<user>"
• "diff" = where: users.users.<user>.name != "<user>" (in this case I assume home-manager.users.<user>.home.username == users.users.<user>.name if not that's prob wrong in of it self)

Support Matrix Before PR

same	diff	case description
✅	✅	environment.persistence dirs without explicit user config (1)
✅	✅	environment.persistence dirs with explicit user config (2)
✅	❌ (runtime, dir is owned by root instead)	environment.persistence.users.<user> dirs without explicit user config (3)
✅	❌ (eval error, cant find associated group when making homedir)	environment.persistence.users.<user> dirs with explicit user config (4)
✅	❌ (eval error, cant find associated group when making homedir)	home.persistence dirs without explicit user config (5)
✅	❌ (eval error, cant find associated group when making homedir)	home.persistence dirs with explicit user config (6)
✅	❌ (eval error, cant find associated group when making homedir)	explicit group (only one case since this was barely touched) (7)

Support Matrix After PR

same	diff	case description
✅	✅	environment.persistence dirs without explicit user config (1)
✅	✅	environment.persistence dirs with explicit user config (2)
✅	✅	environment.persistence.users.<user> dirs without explicit user config (3)
✅	✅	environment.persistence.users.<user> dirs with explicit user config (4)
✅	✅	home.persistence dirs without explicit user config (5)
✅	✅	home.persistence dirs with explicit user config (6)
✅	✅	explicit group (7)

Numbered Test Cases

In the diff cases this was used

 users.users.someuser.name = "otheruser";

In the tests the permissions of dirs and parent dirs was verified to be ok

1

environment.persistence."/persistence" = {
  directories = [
    "/var/lib/nixos"
  ];
};

2

environment.persistence."/persistence" = {
  directories = [
    { directory = "/data"; user = config.users.users.someuser.name; }
  ];
};

3

environment.persistence."/persistence" = {
  users.someuser = {
    directories = [
      "data"
    ];
  };
};

4

environment.persistence."/persistence" = {
  users.someuser = {
    directories = [
      { directory = "data"; user = config.users.users.someuser.name; }
    ];
  };
};

5

home.persistence."/persistence" = {
    directories = [
      "data"
    ];
};

6

home.persistence."/persistence" = {
    directories = [
      { directory = "data"; user = config.users.users.someuser.name; }
    ];
};

7

home.persistence."/persistence" = {
    directories = [
      { directory = "data"; user = config.users.users.someuser.name; group = "wheel"; }
    ];
};