systemd-unit-overrides.nix

{ config, lib, pkgs, modulesPath, ... }: let
  systemdLib = import "${modulesPath}/system/boot/systemd-lib.nix" { inherit config lib pkgs; };

  # Apply a list of overrideAttrs functions to a drv
  applyOverrides = drv: overrides: lib.foldl' (drv': override: lib.extendDerivation true (override drv') drv') drv overrides;
in {
  options.systemd.units = lib.mkOption {
    type = lib.types.attrsOf (lib.types.submodule ({ name, config, ... }: {
      options = {
        overrides = lib.mkOption {
          description = "Overrides to apply to the unit file derivation";
          # TOREM 21.05
          #type = lib.types.listOf (lib.types.functionTo lib.types.attrs);
          type = lib.types.listOf lib.types.unspecified;
          default = [];
          example = [ (oA: {
            patches = (oA.patches or []) ++ [ "$somepatch" ];
          }) ];
        };
      };

      config = {
        unit = applyOverrides (systemdLib.makeUnit name config) config.overrides;
      };
    }));
  };
}