anchor.diff:          token = next;
           break;
         }
  -      var type = FormalParameterKind.optionalPositional;
  -      token = parseFormalParameter(token, type, kind).next;
  +      token = parseFormalParameter(
  +              token, FormalParameterKind.optionalPositional, kind)
  +          .next;
         ++parameterCount;
       } while (optional(',', token));
       if (parameterCount == 0) {
  
positive.code:         token = next;
          break;
        }
        var type = FormalParameterKind.optionalNamed;
        token = parseFormalParameter(token, type, kind).next;
        ++parameterCount;
      } while (optional(',', token));
      if (parameterCount == 0) {
  
negative.code:           // Supply a non-empty method name so that it does not accidently
            // match the default constructor.
            token = insertSyntheticIdentifier(
                token, context, '#synthetic_field_name_${token.offset}');
          }
        }
      } else if (token.type.isBuiltIn && !context.isBuiltInIdentifierAllowed) {
  