configuration.nix

{
  imports = [ ./users.nix ];

  x.users.alice.editor = "hx";
  x.users.bob.editor = "vi";
  x.users.clive.editor = "code";

  boot.loader.grub.enable = false;
  fileSystems."/" = { device = "/dev/sda1"; };
}

gistfile1.txt

❯ nix-build '<nixpkgs/nixos>' -I nixos-config=example.nix
trace: warning: system.stateVersion is not set, defaulting to 23.11. Read why this matters on https://nixos.org/manual/nixos/stable/options.html#opt-system.stateVersion.
trace: warning: I am alice and my editor is hx
trace: warning: I am bob and my editor is vi
trace: warning: I am clive and my editor is code

users.nix

{ config, lib, ... }:
let
  userOptions = {
    options = {
      editor = lib.mkOption {
        type = lib.types.str;
      };
    };
  };
in
{
  options = {
    x.users = lib.mkOption {
      type = lib.types.attrsOf (lib.types.submoduleWith {
        modules = [ userOptions ];
      });
    };
  };

  config.warnings = lib.mapAttrsToList (name: cfg: "I am ${name} and my editor is ${cfg.editor}") config.x.users;
}