anchor.diff:  
     void writeFormalParameter(ParameterElement element) {
       if (element.isRequiredPositional) {
  -      _writeWithoutDelimiters(element);
  +      _writeWithoutDelimiters(element, forElement: true);
       } else if (element.isOptionalPositional) {
         _write('[');
  -      _writeWithoutDelimiters(element);
  +      _writeWithoutDelimiters(element, forElement: true);
         _write(']');
       } else if (element.isNamed) {
         _write('{');
  -      _writeWithoutDelimiters(element);
  +      _writeWithoutDelimiters(element, forElement: true);
         _write('}');
       }
     }
  
positive.code:     _writeType(type.returnType);
      _write(' Function');
      _writeTypeParameters(type.typeFormals);
      _writeFormalParameters(
        type.parameters,
        withNamesOfPositional: false,
        withDefaultValueCode: false,
      );
      _writeNullability(type.nullabilitySuffix);
    }
  
  
negative.code:       } else if (parameter.isNamed) {
          openGroup(_WriteFormalParameterKind.named, '{', '}');
        }
        _writeWithoutDelimiters(parameter, forElement: forElement);
      }
  
      _write(lastClose);
  