Output

Build pipeline

Den converts den.hosts and den.homes declarations into flake outputs through a unified pipeline:

graph LR
  H[den.hosts] --> B[build]
  M[den.homes] --> B
  B --> F[flake.*Configurations]

Host instantiation

For each host in den.hosts, Den calls:

host.instantiate {
  modules = [
    host.mainModule
    { nixpkgs.hostPlatform = lib.mkDefault host.system; }
  ];
}

host.mainModule is internally computed by resolving the host’s aspect with its context (den.ctx.host), collecting all class-specific config and dispatched includes.

The result is placed at flake.<intoAttr> — by default flake.nixosConfigurations.<name> or flake.darwinConfigurations.<name>.

Home instantiation

For each home in den.homes, Den calls:

home.instantiate {
  pkgs = home.pkgs;
  modules = [ home.mainModule ];
}

The result lands at flake.homeConfigurations.<name> by default.

`outputs.nix` — flake-parts compatibility

When inputs.flake-parts is absent, Den defines its own options.flake option so that output generation works identically with or without flake-parts.

This means Den can produce nixosConfigurations, darwinConfigurations, homeConfigurations, and any custom output attribute regardless of whether flake-parts is loaded.

Custom output paths

Override intoAttr on any host or home to place outputs at a custom path:

den.hosts.x86_64-linux.myhost = {
  intoAttr = [ "nixosConfigurations" "custom-name" ];
};

Use intoAttr = [ ] to skip placing the configuration.

Custom instantiation

Override instantiate to use a different builder or add specialArgs:

den.hosts.x86_64-linux.myhost = {
  instantiate = inputs.nixos-unstable.lib.nixosSystem;
};

Flake outputs like `packages`, `checks`, etc.

Den aspects can directly contribute to packages and similar flake outputs.

The following example are for packages but same applies for checks, devShells, legacyPackages and other per system outputs.

Define flake.packages output.

This is only needed if you don’t use flake-parts and will have more than one package, because the Nix module system needs to know how to merge both output definitions:
modules/outputs.nix
```
{ inputs, ... }:
{
  imports = [ inputs.den.flakeOutputs.packages ];
}
```

Allow aspects to produce packages.

# ANY Host or User aspect can produce outputs:
den.ctx.flake-system.into.host = { system }:
  map (host: { inherit host; })
  (lib.attrValues den.hosts.${system});

# ONLY foo aspect can produce packages:
den.ctx.flake-packages.includes = [ den.aspects.foo ];

Use the packages class on your aspects:

den.aspects.foo = {
   packages = { pkgs, ... }: { inherit (pkgs) hello; };
};

See forward-flake-level.nix for all examples.

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