从Scala 3.3.0-RC 2开始，出现了宏注解（由Nicolas Stucki实现）。

• 宏注解（第1部分）* https://github.com/lampepfl/dotty/pull/16392
• 宏注解类修改（第2部分）* https://github.com/lampepfl/dotty/pull/16454
• 启用从宏注解返回类（第3部分）* https://github.com/lampepfl/dotty/pull/16534
  新定义在宏展开外不可见。

添加辅助构造函数的宏注解应如下：

• build.sbt*

scalaVersion := "3.3.0-RC3"

import scala.annotation.{MacroAnnotation, experimental}
import scala.quoted.*

object Macros:
  @experimental
  class entity extends MacroAnnotation:
    def transform(using Quotes)(tree: quotes.reflect.Definition): List[quotes.reflect.Definition] =
      import quotes.reflect.*

      tree match
        case ClassDef(name, constr, parents, selfOpt, body) =>
          val constrSym = Symbol.newMethod(tree.symbol, "<init>", MethodType(Nil)(_ => Nil, _ => TypeRepr.of[Unit]))
          val constrDef = DefDef(constrSym, _ => Some(
            Apply(Select.unique(New(Inferred(tree.symbol.typeRef)), "<init>"), List('{0}.asTerm, '{null}.asTerm))
          ))

          val res = List(ClassDef.copy(tree)(name, constr, parents, selfOpt, body :+ constrDef))
          println(res.map(_.show))
          res

        case _ => report.errorAndAbort("@entity can annotate only classes")

import Macros.entity
import scala.annotation.experimental

object App:
  @entity @experimental
  class Student(val id: Long, val name: String)

//scalac: List(@scala.annotation.experimental @Macros.entity class Student(val id: scala.Long, val name: scala.Predef.String) {
//  def this() = new App.Student(0, null)
//})

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