Recursive serialization with custom formatter only writes last member about messagepack-csharp

[pygmypenguin]

If you want to repo the exception I included in Additional Context, here is the modified version of DataWrapper and it's associated formatter:

[MessagePackObject]
public class DataWrapper {
  [Key(0)]
  [MessagePackFormatter(typeof(IdFormatter))]
  public int Id { get; set; }
  [Key(1)]
  public IChildType? Value { get; set; }
}

public class IdFormatter : IMessagePackFormatter<int> {
  public void Serialize(ref MessagePackWriter writer, int value, MessagePackSerializerOptions options) {

    writer.WriteArrayHeader(2);
    writer.WriteExtensionFormat(new ExtensionResult(88, BitConverter.GetBytes(value)));
  }
  public int Deserialize(ref MessagePackReader reader, MessagePackSerializerOptions options) => throw new NotImplementedException();
}

[pygmypenguin]

I've found my own issue; I need to use the overload version of MessagePackSerializer.Serialize that accepts ref MessagePackWriter writer as an argument. This implementation of Serialize fixes my issue:

  public void Serialize(ref MessagePackWriter writer, DataWrapper value, MessagePackSerializerOptions options) {
    if (value.Value == null) {
      return;
    }

    writer.WriteArrayHeader(2);
    writer.WriteExtensionFormat(new ExtensionResult(88, BitConverter.GetBytes(value.Id)));
    MessagePackSerializer.Serialize(value.Value.GetType(), ref writer, value.Value, options);
  }

closing this issue.