Macro annotation to eliminate case class repetition

Extends.scala

import scala.annotation.{StaticAnnotation, compileTimeOnly}
import scala.language.experimental.macros
import scala.reflect.macros.whitebox.Context

@compileTimeOnly("use macro paradise")
class Extends[T](defaults: Any*) extends StaticAnnotation {
  def macroTransform(annottees: Any*): Any = macro Extends.impl
}

object Extends {
  def impl(c: Context)(annottees: c.Expr[Any]*): c.Expr[Any] = {
    import c.universe._

    val targetTrait: Tree = c.prefix.tree match {
      case q"new $name[$typ]" => typ
    }

    val tpe: Type = c.typecheck(q"0.asInstanceOf[$targetTrait]").tpe

    val values: List[TermSymbol] = tpe.members.collect { case d if d.isTerm => d.asTerm }.filter(t => t.isStable && t.isMethod && t.isAbstract).toList.reverse

    def extractClassNameAndFields(classDecl: ClassDef): (TypeName, Seq[Tree], Seq[Tree], Seq[Tree]) = {
      try {
        val q"case class $className(..$fields) extends ..$bases { ..$body }" = classDecl
        (className, fields, bases, body)
      } catch {
        case _: MatchError => c.abort(c.enclosingPosition, "Annotation is only supported on case classes")
      }
    }

    def modifiedFields(fields: List[ValDef]): List[ValDef] = {
      val newParams = values.map { v =>
        ValDef(Modifiers(Flag.CASEACCESSOR), v.name, TypeTree(v.typeSignature.typeConstructor), EmptyTree)
      }
      newParams ++ fields
    }

    def modifiedClass(classDecl: ClassDef): Expr[_] = {
      val (className, fields, bases, body) = extractClassNameAndFields(classDecl)
      val ctor = modifiedFields(fields.asInstanceOf[List[ValDef]])
      c.Expr(q"case class $className(..$ctor) extends $targetTrait with ..$bases { ..$body }")
    }

    annottees.map(_.tree) match {
      case (classDecl: ClassDef) :: Nil => modifiedClass(classDecl)
      case _ => c.abort(c.enclosingPosition, "Invalid annottee")
    }
  }
}