os/modules/core/nix.nix

{
  config,
  pkgs,
  lib,
  inputs,
  ...
}: {
  nix = {
    # Use default version alias for nix package
    package = pkgs.nix;
    gc.automatic = true;
    optimise.automatic = true;
    settings = {
      # Improve nix store disk usage
      auto-optimise-store = true;
      # Prevents impurities in builds
      sandbox = true;
      # give root and @wheel special privileges with nix
      trusted-users = ["root" "@wheel"];
      # This is just a representation of the nix default
      system-features = ["nixos-test" "benchmark" "big-parallel" "kvm"];
    };
    # Generally useful nix option defaults
    extraOptions = lib.mkForce ''
      min-free = 536870912
      keep-outputs = true
      keep-derivations = true
      fallback = true
    '';
  };
}