>>>
class JsonCodec {
  const JsonCodec({
      Object? reviver(Object? key, Object? value)?,
      Object? toEncodable(dynamic object)?})
      : _reviver = reviver,
        _toEncodable = toEncodable;
}
<<<
class JsonCodec {
  const JsonCodec({
    Object? reviver(Object? key, Object? value)?,
    Object? toEncodable(dynamic object)?,
  }) : _reviver = reviver,
       _toEncodable = toEncodable;
}
>>>
class JsonUtf8Encoder {
  JsonUtf8Encoder(
      [String? indent, dynamic toEncodable(dynamic object)?, int? bufferSize])
      : _indent = _utf8Encode(indent),
        _toEncodable = toEncodable,
        _bufferSize = bufferSize ?? _defaultBufferSize;
}
<<<
class JsonUtf8Encoder {
  JsonUtf8Encoder([
    String? indent,
    dynamic toEncodable(dynamic object)?,
    int? bufferSize,
  ]) : _indent = _utf8Encode(indent),
       _toEncodable = toEncodable,
       _bufferSize = bufferSize ?? _defaultBufferSize;
}
>>> comma between parameters
mandatory(f()?,i) {}
optional([f()?,i]) {}
named({f()?,i}) {}
<<<
mandatory(f()?, i) {}
optional([f()?, i]) {}
named({f()?, i}) {}
>>> trailing commas
mandatory(f()?,) {}
optional([f()?,]) {}
named({f()?,}) {}
<<<
mandatory(f()?) {}
optional([f()?]) {}
named({f()?}) {}
>>> constructor initializer trailing comma
class C {
  C(f()?,) : field = 3;
}
<<<
class C {
  C(f()?) : field = 3;
}