Custom Nix Classes

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

What Are Custom Classes?

Den natively supports nixos, darwin, and homeManager classes. But you can create your own classes that forward their settings into any target submodule. This is exactly how Home-Manager integration works internally.

The forward Battery

den._.forward creates an aspect that takes configs from a source class and inserts them into a target class at a specified path.

Example: Custom Class to NixOS

Forward a custom class into NixOS top-level:

{ den, lib, ... }:
let
  forwarded = { class, aspect-chain }:
    den._.forward {
      each = lib.singleton class;
      fromClass = _: "custom";
      intoClass = _: "nixos";
      intoPath = _: [ ];
      fromAspect = _: lib.head aspect-chain;
    };
in {
  den.aspects.igloo = {
    includes = [ forwarded ];
    custom.networking.hostName = "from-custom-class";
  };
}

Example: Forward into a Subpath

Insert configs into a nested submodule:

den.aspects.igloo = {
  includes = [ forwarded ];
  nixos.imports = [
    { options.fwd-box = lib.mkOption {
        type = lib.types.submoduleWith { modules = [ myModule ]; };
    }; }
  ];
  src.items = [ "from-src-class" ];
};

With intoPath = _: [ "fwd-box" ], the src class configs merge into nixos.fwd-box.

How Home-Manager Uses Forward

Den’s Home-Manager integration is built on forward:

den._.forward {
  each = lib.singleton true;
  fromClass = _: "homeManager";
  intoClass = _: host.class;
  intoPath = _: [ "home-manager" "users" user.userName ];
  fromAspect = _: userAspect;
}

This takes all homeManager class configs from user aspects and inserts them into home-manager.users.<name> on the host’s OS configuration.

Use Cases

User environments: Forward a user class into users.users.<name>
Containerization: Forward a container class into systemd-nspawn configs
VM configs: Forward a vm class into microvm or QEMU settings
Custom tools: Forward into any Nix-configurable system (NixVim, etc.)

Creating Your Own

The forward function parameters:

Parameter	Description
`each`	List of items to iterate over
`fromClass`	Source class name (string)
`intoClass`	Target class name (string)
`intoPath`	Attribute path in target (list of strings)
`fromAspect`	Source aspect to read from