The problem

Using Scala 2 macros, we have built an RPC framework that can automatically generate implementations of arbitrary traits. These implementations are effectively network proxies that translate every method call into a network request. When the request is received by the RPC server, a reverse translation is performed and a real implementation of this trait is invoked.

A very simplified example of this mechanism:

trait RawRpc {
  def invoke(methodName: String, parameters: Map[String, Json]): Future[Json]
}
object RawRpc {
  def asReal[RealRpc](rawRpc: RawRpc): RealRpc = macro ...
  def asRaw[RealRpc](realRpc: RealRpc): RawRpc = macro ...
}

The asReal macro needs to do the following:

• enumerate all (abstract) methods of RealRpc
• for every parameter of every method, find a typeclass instance that would allow it to serialize it into Json
• for every method's result type, find a typeclass instance that would allow it to deserialize it from Json (assuming that the result type is a Future)
• generate an implementation of every method that forwards it to rawRpc
• inspect annotations on methods and parameters in order to treat them in some special way

The asRaw macro needs similar capabilities in order to perform a reverse translation.

Situation in Scala 3

It's unclear to me whether something like this is possible with Scala 3. Looking at the Quotes API, it should in principle be possible if I was able to generate arbitrary trees, starting with ClassDef. However, it seems that currently ClassDef.apply is commented out and marked as TODO.

So my questions are:

• First of all, is this a valid use case for Scala 3 metaprogramming?
• If yes, can this be done with Quotes API?
• Are there any serious obstacles preventing methods like ClassDef.apply from being exposed?

(Note: I asked this question briefly on Gitter and it was recommended to me to create an issue.)