bug.scala

val template = s"""
  |trait RouteTrait extends ExtendedController with SimpleRouter with OptionalAuthElement with AuthConfigImpl with Circe {
  |  def routes: Router.Routes = {
  |
  |    case GET(p"/pets" ? q_o"tags=$$tags" ? q_o"limit=$$limit") => AsyncStack { implicit request =>
  |      constructResult(findPets(tags, limit))
  |    }
  |
  |    case POST(p"/pets") => AsyncStack(circe.json) { implicit request =>
  |      constructResult(addPet())
  |    }
  |
  |    case GET(p"/pets/$${int(id)}") => AsyncStack { implicit request =>
  |      constructResult(findPetById(id))
  |    }
  |  
  |    case DELETE(p"/pets/$${int(id)}") => AsyncStack { implicit request =>
  |      constructResult(deletePet(id))
  |    }
  |
  |  }
  |
  |  def findPets(tags: Option[String], limit: Option[String])(implicit request: RequestWithAttributes[AnyContent]): HttpResult[Result]
  |  def addPet()(implicit request: RequestWithAttributes[AnyContent]): HttpResult[Result]
  |  def findPetById(id: Int)(implicit request: RequestWithAttributes[AnyContent]): HttpResult[Result]
  |  def deletePet(id: Int)(implicit request: RequestWithAttributes[AnyContent]): HttpResult[Result]
  |}
  """.stripMargin.trim

val source =
  s"""
     |trait RouteTrait {
     |
     |}
   """.stripMargin

import scala.meta._

val templateTree = template.parse[Source].get.collect {
  case c @q"..$mods trait $tname[..$tparams] extends $template" =>
    c
}.headOption.get

val sourceTree = source.parse[Source].get.transform {
  case c @q"..$mods trait $tname[..$tparams] extends $template" =>
    templateTree
}

sourceTree.syntax

Output:

trait RouteTrait extends ExtendedController with SimpleRouter with OptionalAuthElement with AuthConfigImpl with Circe {
  def routes: Router.Routes = {
    case GET(p""/pets"" ? q_o""tags="${tags}""" ? q_o""limit="${limit}""") =>
      AsyncStack { implicit request => 
        constructResult(findPets(tags, limit))
      }
    case POST(p""/pets"") =>
      AsyncStack(circe.json) { implicit request => 
        constructResult(addPet())
      }
    case GET(p""/pets/"${int(id)}""") =>
      AsyncStack { implicit request => 
        constructResult(findPetById(id))
      }
    case DELETE(p""/pets/"${int(id)}""") =>
      AsyncStack { implicit request => 
        constructResult(deletePet(id))
      }
  }
  def findPets(tags: Option[String], limit: Option[String])(implicit request: RequestWithAttributes[AnyContent]): HttpResult[Result]
  def addPet()(implicit request: RequestWithAttributes[AnyContent]): HttpResult[Result]
  def findPetById(id: Int)(implicit request: RequestWithAttributes[AnyContent]): HttpResult[Result]
  def deletePet(id: Int)(implicit request: RequestWithAttributes[AnyContent]): HttpResult[Result]
}