I'm trying to patch a factory method on the HashMap class, but I cannot refer to the type variables in the patch:

   class HashMap<K, V> {
     external factory HashMap();
     ...
   }

   patch class HashMap<K, V> {
     patch factory HashMap() {
       .... cannot refer to K or V ...
     }
   }

The error message is something like this:

   sdk/lib/collection/hash_map.dart:23:15:
      Internal error: Cannot find value origin class(HashMap).K

and it is apparently reported on the non-patched class.