Mode.scala

import enumeratum._

sealed trait Mode extends EnumEntry

@SwaggerEnum
object Mode extends Enum[Mode] {
  override def values = findValues
  
  case object Initial extends Mode
  case object Initial extends Mode
}

@ApiModel
case class Foobar(
  @ApiModelProperty(dataType = "string", allowableValues = Mode.swaggerValues)
  mode: Mode
)

swagger.scala

package com.zendesk.walmart

import scala.meta._
import scala.annotation.StaticAnnotation
import scala.collection.immutable.Seq

abstract class SwaggerEnum extends StaticAnnotation {
  inline def apply(defn: Any): Any = meta {
    defn match {
      case q"object $name extends ..$parents { ..$body }" => {
        SwaggerEnumMacros.expandEnum(name, parents, body)
      }
      case _ => {
        abort("must annotate an object.")
      }
    }
  }
}

object SwaggerEnumMacros {
  def expandEnum(name: Term.Name, parents: Seq[Ctor.Call], body: Seq[Stat]): Defn = {
    val q"$pname[..$ptargs](...$pargss)" = parents match {
      case head :: Nil => head
      case _ => abort("Must annotate an Enum[A]")
    }
    val values = body.collect {
      case q"$mods object $name extends ..$parents" => name
    }
    val reference = Lit.String(values.map(_.value).sorted.mkString(","))
    q"""object $name extends ..$parents {
          final val swaggerValues = $reference
          ..$body
        }"""
  }
}