lib.types.attrTag: expose suboptions at correct level (#419081)

lib/tests/modules/types-attrTag.nix

@@ -7,7 +7,7 @@
 let
   inherit (lib) mkOption types;
   forceDeep = x: builtins.deepSeq x x;
-  mergedSubOption = (options.merged.type.getSubOptions options.merged.loc).extensible."merged.<name>";
+  mergedSubOption = (options.merged.type.getSubOptions options.merged.loc).extensible;
 in
 {
   options = {

lib/types.nix

@@ -919,12 +919,7 @@ let
           description = "attribute-tagged union";
           descriptionClass = "noun";
           getSubOptions =
-            prefix:
-            mapAttrs (tagName: tagOption: {
-              "${lib.showOption prefix}" = tagOption // {
-                loc = prefix ++ [ tagName ];
-              };
-            }) tags;
+            prefix: mapAttrs (tagName: tagOption: tagOption // { loc = prefix ++ [ tagName ]; }) tags;
           check = v: isAttrs v && length (attrNames v) == 1 && tags ? ${head (attrNames v)};
           merge =
             loc: defs: