Rework extension system

modules/extends.nix

@@ -3,13 +3,42 @@
 with lib;
 
 let
- mkExtend = name: mkOption {
- type = types.coercedTo (types.uniq types.anything) toList (types.listOf (types.uniq types.anything));
+ mkExtend = type: mkOption {
+ type = types.attrsOf (types.submodule ({ name, config, ... }: {
+ options = {
+ type = mkOption {
+ type = types.optionType;
+ description = ''
+ Type of the extionsion option.
+ '';
+ };
+ description = mkOption {
+ type = types.nullOr types.str;
+ default = null;
+ description = ''
+ Description of the extension option.
+ '';
+ };
+ default = mkOption {
+ type = types.nullOr config.type;
+ default = null;
+ description = ''
+ Default value for the extension option.
+ '';
+ };
+ };
+ }));
  description = ''
- Extensions options defined for elements of type ${name}
+ Extensions options defined for elements of type ${type}
  '';
  default = { };
  };
+
+ mkOptions = type: mapAttrs
+ (name: option: mkOption {
+ inherit (option) type description default;
+ })
+ config.extends.${type};
 in
 {
  options = {
@@ -29,7 +58,10 @@ in
  # TODO: Use types.optionType instead and leverage mkMerge to merge a custome module with the base definition
  extend = name: base:
  assert assertMsg (config.extends ? "${name}") "Undeclared extension: ${name}";
- types.submodule ([ base ] ++ config.extends."${name}");
+ types.submodule [
+ base
+ { options = mkOptions name; }
+ ];
  };
  };
 }