In reply to @infinisil:matrix.org
Before, config.user and config.default had the same priority. The conflict happened one level above

Finally, you have effectively

{
  out = lib.mkMerge [
    config.default
    config.user
  ];
}

Finally, you have effectively

{
  out = lib.mkMerge [
      { a = 1; b = 2; }
      { b = 3; }
  ];
}

Both of which are without priority, so it recurses into the attrs and conflicts because two bs

I recently stumbled upon similar issue when working on home-manager. https://discourse.nixos.org/t/is-it-possible-to-define-systemd-services-in-a-submodule/39538/5

The idea is that enabling https://nix-community.github.io/home-manager/options.xhtml#opt-programs.bash.enableCompletion should set environment.pathsToLink = [ "/share/bash-completion" ];.

I think that module system is missing an option to pass config options recursively up to all ancestors.

I'm reading through the module system deep dive on nix.dev and am wondering if there is a behavioral difference between setting an options default behavior in the config attribute vs the default attribute in mkOption.

this

{
  pkgs,
  lib,
  config,
  ...
}: {
  options = {
    scripts.output = lib.mkOption {
      type = lib.types.package;
    };
  };
  config = {
    scripts.output = pkgs.writeShellApplication {
      name = "map";
      runtimeInputs = with pkgs; [curl feh];
      text = ''
        ${./map} ${lib.concatStringsSep " "
          config.requestParams} | feh -
      '';
    };
  };
}

vs this

{
  pkgs,
  lib,
  config,
  ...
}: {
  options = {
    scripts.output = lib.mkOption {
      type = lib.types.package;
      default = pkgs.writeShellApplication {
        name = "map";
        runtimeInputs = with pkgs; [curl feh];
        text = ''
          ${./map} ${lib.concatStringsSep " "
            config.requestParams} | feh -
        '';
      };
    };
  };
}