Use Batteries

import { Aside } from ‘@astrojs/starlight/components’;

What Are Batteries?

Batteries are pre-built aspects shipped with Den. They are opt-in — you explicitly include them where needed. They are replaceable — you can write your own alternative.

Access batteries via den._. (shorthand for den.provides.).

define-user

Defines a user at both OS and Home-Manager levels:

den.default.includes = [ den._.define-user ];

Sets users.users.<name>, home.username, and home.homeDirectory automatically for NixOS, Darwin, and standalone Home-Manager.

primary-user

Makes a user an administrator:

den.aspects.vic.includes = [ den._.primary-user ];

On NixOS: adds wheel and networkmanager groups. On Darwin: sets system.primaryUser. On WSL: sets wsl.defaultUser if host has a wsl attribute.

user-shell

Sets a user’s default shell at OS and HM levels:

den.aspects.vic.includes = [ (den._.user-shell "fish") ];

Enables the shell program on both NixOS/Darwin and Home-Manager, and sets it as the user’s default shell.

unfree

Enables unfree packages by name:

den.aspects.my-laptop.includes = [ (den._.unfree [ "discord" "slack" ]) ];

Works for any class — NixOS, Darwin, Home-Manager.

tty-autologin

Enables automatic tty login for a given username:

den.aspects.my-laptop.includes = [ (den._.tty-autologin "root") ];

import-tree

Recursively imports non-dendritic Nix files by class:

den.ctx.host.includes = [ (den._.import-tree._.host ./hosts) ];
den.ctx.user.includes = [ (den._.import-tree._.user ./users) ];

Given a directory structure like ./hosts/my-laptop/_nixos/, it auto-imports files under the matching class directory. Useful for migration.

inputs’ and self’ (flake-parts)

Provide per-system inputs' and self' to NixOS/HM modules:

den.default.includes = [ den._.inputs' den._.self' ];

den.aspects.igloo.nixos = { inputs', ... }: {
  environment.systemPackages = [ inputs'.nixpkgs.legacyPackages.hello ];
};

forward

Create custom Nix classes that forward configs into target submodules:

den.aspects.igloo.includes = [
  ({ class, aspect-chain }:
    den._.forward {
      each = lib.singleton class;
      fromClass = _: "custom";
      intoClass = _: "nixos";
      intoPath = _: [ ];
      fromAspect = _: lib.head aspect-chain;
    })
];

This is how Home-Manager integration is implemented internally.

Writing Your Own

Any aspect can serve as a battery. Publish it in a namespace for others:

{ den, ... }: {
  den.provides.my-battery = den.lib.parametric {
    includes = [
      ({ host, ... }: { nixos.my-setting = host.name; })
    ];
  };
}