Martin Gaens: I have a home-manager config which is either managed on its own or within NixOS, which I use across 2 different computer. I am using the extraSpecialArgs in flake.nix or home-manager.users.nicolas._module.args when embedded in a NixOS configuration, to set some configuration managed externally.

Note, there is nothing about special args, I might have as well set an option by adding an extra module in homeManager's flake.nix and done the same within the configuration embedded in NixOS.

I can either use my home manager as a standalone entry in my flake.nix:

    homeConfigurations.nicolas = home-manager.lib.homeManagerConfiguration {
      extraSpecialArgs = inputs // {
        inNixOS = false;
      };
      pkgs = import nixpkgs-unstable {
        system = "x86_64-linux";
        overlays = [ self.overlays.openpnp ];
      };
      modules = [ ./users/nicolas/home.nix ];
    };

Or as a module to import in my NixOS configuration:

{ home-manager, ...}@inputs:

{
  imports = [
    home-manager.nixosModules.home-manager
  ];

  home-manager = {
    users.nicolas.imports = [ ./home.nix ];
    users.nicolas._module.args = {
      inNixOS = true;
    } // inputs;
  };
}

The inNixOS argument is nothing special, this is just an extra attribute I give as argument to the home-manager modules to tune it differently.