fix: properly apply oneOf

example/zfs-with-vdevs.nix

@@ -90,7 +90,7 @@
             special = {
               members = [ "z" ];
             };
-            cache = "cache";
+            cache = [ "cache" ];
           };
         };
 

example/zfs.nix

@@ -100,3 +100,4 @@
     };
   };
 }
+

lib/types/zfs.nix

@@ -53,4 +53,3 @@
     };
   };
 }
-

lib/types/zpool.nix

@@ -25,7 +25,9 @@ in
     };
     mode = lib.mkOption {
       default = "";
-      type = (lib.types.enum modeOptions) // (lib.types.attrsOf (diskoLib.subType {
+      type = (lib.types.oneOf [
+        (lib.types.enum modeOptions)
+        (lib.types.attrsOf (diskoLib.subType {
           types = {
             topology =
               let
@@ -90,7 +92,8 @@ in
                 });
           };
           extraArgs.parent = config;
-      }));
+        }))
+      ]);
       description = "Mode of the ZFS pool";
     };
     options = lib.mkOption {