let
  function =
    name: value:
    let
      result = if builtins.isAttrs value then { ... }: value else value;
      result' = builtins.trace "result ${name}=${builtins.typeOf result}" result;
    in
    assert builtins.isFunction result';
    result;

  config =
    {
      user ? { },
      home-manager ? { },
    }@set:
    builtins.mapAttrs function { inherit user home-manager; };

in
name: value:
let
  result =
    if builtins.isFunction value then
      config { user = value; }
    else if
      builtins.any (attr: builtins.hasAttr attr value) [
        "user"
        "home-manager"
      ]
    then
      config value
    else
      config { user = value; };
in
result