Extend option defined in other package

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1

I’m currently in the process of writing a module to host virtualisation options (e.g. Docker) for my NixOS config.

To enable that, I set virtualisation.docker.enable = true;. Since ideally, I want to be able to only import the module into my config without having to make any extra declarations, I’m searching for a way to extend the users.users.<my-username>.extraGroups option by the "docker" group. I define the extraGroups option in my configuration.nix, which also imports the module. I wondered how I would extend the extraGroups option in my module, while keeping the values that are already specified in my configuration.nix.

See my files here, shortened for readability:

configuration.nix:

{ inputs, lib, config, pkgs, ... }: {
  imports = [
    ./virtualisation.nix
  ];

  users.users.<my-username> = {
    extraGroups = [ "networkmanager" "wheel" ];
  };
}

virtualisation.nix:

{ pkgs, ... }: {
  virtualisation.docker.enable = true;
  # TODO: add user to docker group
}
2

NixOS’s module system merges the configurations set in different modules and usually does the right thing. You can just put
``

{ pkgs, ... }: {
  virtualisation.docker.enable = true;
  users.users.<my-username> = {
    extraGroups = [ "docker" ];
  };
}

in your virtualisation.nix and in will do what you want.

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