The following is a quote from Macros: the Plan for Scala 3 from more than 3 years ago:
For instance, one will be able to define a macro annotation @json that adds a JSON serializer to a type.
Any idea how/if this is actually possible in Scala 3?
More generally, is there anything in Scala 3 that can provide "Macro Annotations" functionality? The following is a quote from Macro Annotations - Scala 2.13:
Unlike in the previous versions of macro paradise, macro annotations in 2.0 are done right in the sense that they: 1) apply not just to classes and objects, but to arbitrary definitions, 2) allow expansions of classes to modify or even create companion objects
As of June 2021, macro annotations are not supported in Scala 3, and they are not mentioned anywhere in the doc.
Right now, if you'd like to generate methods, classes or objects, I believe you have to use scalameta or write a compiler plugin.
Obviously, this situation might change in the future, macro annotations were not part of Scala 2 at the beginning either.