NixOS module

To use Home Manager as a NixOS module, a bare-minimum flake.nix would be as follows:

{
  description = "NixOS configuration";

  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
    home-manager.url = "github:nix-community/home-manager";
  };

  outputs = inputs@{ nixpkgs, home-manager, ... }: {
    nixosConfigurations = {
      hostname = nixpkgs.lib.nixosSystem {
        system = "x86_64-linux";
        modules = [
          ./configuration.nix
          home-manager.nixosModules.home-manager
          {
            home-manager.useGlobalPkgs = true;
            home-manager.useUserPackages = true;
            home-manager.extraSpecialArgs = { inherit inputs; };
            home-manager.users.jdoe = ./home.nix;
          }
        ];
      };
    };
  };
}

Use home-manager.extraSpecialArgs to pass arguments from your flake to home.nix and any imported Home Manager modules. For example, the configuration above makes the complete inputs attrset available to modules, so they can declare arguments such as { inputs, ... }:.

The lower-level mechanism behind this is _module.args. Set _module.args.<name> from inside a module only when you need to provide a module argument from within the module graph itself. For values that originate outside the module graph, such as flake inputs, prefer home-manager.extraSpecialArgs.

Use home-manager.sharedModules for Home Manager modules or settings that should be imported by every user declared in home-manager.users.

The Home Manager configuration is then part of the NixOS configuration and is automatically rebuilt with the system when using the appropriate command for the system, such as

$ nixos-rebuild switch --flake /etc/nixos

You can use the above flake.nix as a template in /etc/nixos by

$ nix flake new /etc/nixos -t github:nix-community/home-manager#nixos