Thanks for telling me :). On a serious note though, anything can work with source generators but it doesn't match the style of coding that we'd like (moving everything to be declarative isn't the path we want to go down for certain APIs). Also source generators don't compose, so any source generation that we would want to use would need to take advantage of the JSON source generator (if we wanted to keep things NativeAOT safe). Right now most of the APIs you use in ASP.NET Core are imperative and source generators cannot change the callsite so you need to resort to method declarations and attributes everywhere.
That's not an optimization, that's a programming model change.
Well in system text json the api keeps the same and you „only“ need to pass an autogenerated meta object its basically the same api you just need to pass another object instead of an generic Parameter. But yeah its a change.
