Last time I checked, admittedly several years ago, Lombok was abusing the fact that the AST esposed to the annotation processors was mutable (exposing a deep immutable view over a complex data structure is not something that you do easily nor efficiently in Java to this day, so I'm not blaming javac here). The compiler estensionions were not really forbidden in any meaningful way to do what Lombok is doing, and given the difference in tooling and effort required for a new language I don't really blame them either. That said, going against the whishes of the JSL has its risks, but I can understand Lombok's choice. I still push against Lombok in the projects I work on since how it works makes me unconfortable.