za.co.absa.spline.common.EnumerationMacros.scala Maven / Gradle / Ivy

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/*
 * Copyright 2017 ABSA Group Limited
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package za.co.absa.spline.common

import scala.language.experimental.macros
import scala.reflect.macros.blackbox

/**
  * A macro to produce a TreeSet of all instances of a sealed trait.
  *
  * Based on Travis Brown's and user673551 work:
  * https://stackoverflow.com/a/24705126/96766
  */
object EnumerationMacros {
  def sealedInstancesOf[A]: Set[A] = macro sealedInstancesOf_impl[A]

  def sealedInstancesOf_impl[A: c.WeakTypeTag](c: blackbox.Context): c.Expr[Set[A]] = {
    import c.universe._

    val symbol = weakTypeOf[A].typeSymbol

    if (!symbol.isClass || !symbol.asClass.isSealed)
      c.abort(c.enclosingPosition, "Can only enumerate values of a sealed trait or class.")
    else {
      val siblingSubclasses: List[Symbol] =
        scala.util.Try {
          val enclosingModule = c.internal.enclosingOwner.asInstanceOf[ModuleDef]
          enclosingModule.impl.body.filter { x =>
            scala.util.Try(x.symbol.asModule.moduleClass.asClass.baseClasses.contains(symbol)) getOrElse false
          }.map(_.symbol)
        } getOrElse Nil

      val children = symbol.asClass.knownDirectSubclasses.toList ::: siblingSubclasses
      if (!children.forall(x => x.isModuleClass || x.isModule))
        c.abort(c.enclosingPosition, "All children must be objects.")
      else
        c.Expr[Set[A]] {
          val sourceModuleRef = (sym: Symbol) => Ident(
            if (sym.isModule) sym
            else sym.asInstanceOf[scala.reflect.internal.Symbols#Symbol].sourceModule.asInstanceOf[Symbol])

          Apply(
            Select(reify(Set).tree, TermName("apply")),
            children.map(sourceModuleRef)
          )
        }
    }
  }
}