nixos/modules/base/nix.nix

{ nix-index-database, nixpkgs-unstable, nixpkgs, ... }: {
  imports = [
    nix-index-database.nixosModules.nix-index
  ];

  nix = {
    # https://nixos.wiki/wiki/Storage_optimization
    gc = {
      # Automatically run the nix garbage collector, removing files from
      # the store that are not referenced by any generation.
      # https://nixos.org/manual/nix/stable/package-management/garbage-collection
      automatic = true;
      dates = "weekly";
      options = "--delete-older-than 7d";
    };

    settings = {
      # Automatically optimise the store after each build. Store optimisation
      # reduces nix store space by 25-35% by finding identical files and
      # hard-linking them to each other.
      # https://nixos.org/manual/nix/unstable/command-ref/nix-store/optimise.html
      auto-optimise-store = true;

      # Enable flakes
      experimental-features = [ "nix-command" "flakes" ];

      # Timeout connections to the binary cache instead of waiting forever
      connect-timeout = 5;
    };

    # The nix registry is used to refer to flakes using symbolic identifiers
    # when running commands such as `nix run nixpkgs#hello`. By default,
    # the global registry from [1] is used, which aliases `nixpkgs` to the
    # nixpkgs-unstable branch. We overwrite the default global `nixpkgs`
    # registry with one which refers to the same nixpkgs as the rest of
    # the system, aligning it with flake.lock.
    # [1] https://github.com/NixOS/flake-registry/blob/master/flake-registry.json
    registry = {
      nixpkgs.flake = nixpkgs;
      nixpkgs-unstable.flake = nixpkgs-unstable;
    };
  };

  # https://github.com/nix-community/comma
  programs.nix-index-database.comma.enable = true;
  programs.command-not-found.enable = false;
}