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For information / discussion: Add support for Scala 3 enums #1176

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12 changes: 10 additions & 2 deletions play-json/shared/src/main/scala-3/play/api/libs/json/JsMacroImpl.scala
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Expand Up @@ -241,8 +241,12 @@ object JsMacroImpl { // TODO: debug
TypeRepr.of[String]
)

val termSym = tpr.termSymbol
val typeSym = tpr.typeSymbol
val isCase = termSym.flags.is(Flags.Case)

val tpeCaseName: Expr[String] = '{
${ config }.typeNaming(${ Expr(typeName(tpr.typeSymbol)) })
${ config }.typeNaming(${ Expr(typeName(if isCase then termSym else typeSym)) })
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@DavidGregory084 DavidGregory084 Jun 25, 2025

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By using the termSymbol we get the fully qualified name of the enum case rather than the name of the enum as our type discriminator.

}

val resolve = resolver[Reads, sub](
Expand Down Expand Up @@ -595,8 +599,12 @@ object JsMacroImpl { // TODO: debug
subTpr
)

val termSym = tpr.termSymbol
val typeSym = tpr.typeSymbol
val isCase = termSym.flags.is(Flags.Case)

val tpeCaseName: Expr[String] = '{
${ config }.typeNaming(${ Expr(typeName(tpr.typeSymbol)) })
${ config }.typeNaming(${ Expr(typeName(if isCase then termSym else typeSym)) })
}

val resolve = resolver[Writes, sub](
Expand Down
61 changes: 18 additions & 43 deletions play-json/shared/src/main/scala-3/play/api/libs/json/QuotesHelper.scala
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Expand Up @@ -4,12 +4,11 @@

package play.api.libs.json

import scala.deriving.Mirror
import scala.util.Try as TryResult
import scala.util.Success as TrySuccess
import scala.util.Failure as TryFailure

import scala.deriving.Mirror.ProductOf

import scala.quoted.Expr
import scala.quoted.Quotes
import scala.quoted.Type
Expand Down Expand Up @@ -43,51 +42,27 @@ private[json] trait QuotesHelper {
* Class `Lorem` is listed through `SubFoo`,
* but `SubFoo` itself is not returned.
*/
final def knownSubclasses(tpr: TypeRepr): Option[List[TypeRepr]] =
tpr.classSymbol.flatMap { cls =>
@annotation.tailrec
def subclasses(
children: List[Tree],
out: List[TypeRepr]
): List[TypeRepr] = {
val childTpr = children.headOption.collect {
case tpd: Typed =>
tpd.tpt.tpe

case vd: ValDef =>
vd.tpt.tpe
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@DavidGregory084 DavidGregory084 Jun 25, 2025

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I don't know what to do here to get the singleton Type that the compiler-generated Mirror gives us


case cd: ClassDef =>
cd.constructor.returnTpt.tpe

}

childTpr match {
case Some(child) => {
val tpeSym = child.typeSymbol

if (tpeSym.flags.is(Flags.Abstract) &&
tpeSym.flags.is(Flags.Sealed) &&
!(child <:< anyValTpe)) ||
(tpeSym.flags.is(Flags.Sealed) &&
tpeSym.flags.is(Flags.Trait))
then {
// Ignore sub-trait itself, but check the sub-sub-classes
subclasses(tpeSym.children.map(_.tree) ::: children.tail, out)
} else {
subclasses(children.tail, child :: out)
}
final def knownSubclasses(tpr: TypeRepr): Option[List[TypeRepr]] = {
def gatherNestedSubtypes[Parent: Type, Elems: Type](using Quotes): List[TypeRepr] =
Type.of[Elems] match {
case '[elem *: elems] =>
Expr.summon[Mirror.Of[elem]] match {
case Some('{ $sum: Mirror.SumOf[elem] { type MirroredElemTypes = elementTypes } }) =>
gatherNestedSubtypes[elem, elementTypes] ++ gatherNestedSubtypes[Parent, elems]
case _ =>
TypeRepr.of[elem] :: gatherNestedSubtypes[Parent, elems]
}

case _ =>
out.reverse
}
case '[EmptyTuple] => Nil
}

val types = subclasses(cls.children.map(_.tree), Nil)

if types.isEmpty then None else Some(types)
tpr.asType match {
case '[t] =>
Expr.summon[Mirror.Of[t]].collect {
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@DavidGregory084 DavidGregory084 Jun 25, 2025

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I think that a less WIP implementation of this should probably use Implicits.search so that it could surface any implicit search error messages to the user

case '{ $sum: Mirror.SumOf[t] { type MirroredElemTypes = elementTypes } } =>
gatherNestedSubtypes[t, elementTypes]
}
}
}

@annotation.tailrec
private def withElems[U <: Product](
Expand Down
49 changes: 49 additions & 0 deletions play-json/shared/src/test/scala-3/play/api/libs/json/MacroScala3Spec.scala
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Expand Up @@ -4,12 +4,14 @@

package play.api.libs.json

import org.scalatest.EitherValues
import org.scalatest.matchers.must.Matchers
import org.scalatest.wordspec.AnyWordSpec

final class MacroScala3Spec
extends AnyWordSpec
with Matchers
with EitherValues
with org.scalatestplus.scalacheck.ScalaCheckPropertyChecks {
"Case class" should {
"not be handled" when {
Expand Down Expand Up @@ -57,6 +59,44 @@ final class MacroScala3Spec
}
}
}

"Scala 3 enum" should {
"be handled" when {
"declared with no-arg cases" in {
given Format[Color.Red.type] = Json.format[Color.Red.type]
given Format[Color.Green.type] = Json.format[Color.Green.type]
given Format[Color.Blue.type] = Json.format[Color.Blue.type]
val format = Json.format[Color]

val redJson = Json.obj("_type" -> "play.api.libs.json.Color.Red")
format.writes(Color.Red).mustEqual(redJson)
format.reads(redJson).asEither.value.mustEqual(Color.Red)

val greenJson = Json.obj("_type" -> "play.api.libs.json.Color.Green")
format.writes(Color.Green).mustEqual(greenJson)
format.reads(greenJson).asEither.value.mustEqual(Color.Green)

val blueJson = Json.obj("_type" -> "play.api.libs.json.Color.Blue")
format.writes(Color.Blue).mustEqual(blueJson)
format.reads(blueJson).asEither.value.mustEqual(Color.Blue)
}
}

"declared with single-arg case" in {
given Format[IntOption.Some] = Json.format[IntOption.Some]
given Format[IntOption.None.type] = Json.format[IntOption.None.type]
given format: Format[IntOption] = Json.format[IntOption]

val someValue = IntOption.Some(1)
val someJson = Json.obj("_type" -> "play.api.libs.json.IntOption.Some", "value" -> 1)
format.writes(someValue).mustEqual(someJson)
format.reads(someJson).asEither.value.mustEqual(someValue)

val noneJson = Json.obj("_type" -> "play.api.libs.json.IntOption.None")
format.writes(IntOption.None).mustEqual(noneJson)
format.reads(noneJson).asEither.value.mustEqual(IntOption.None)
}
}
}

final class CustomNoProductOf(val name: String, val age: Int)
Expand All @@ -66,3 +106,12 @@ object CustomNoProductOf {
given Conversion[CustomNoProductOf, Tuple2[String, Int]] =
(v: CustomNoProductOf) => v.name -> v.age
}

enum Color {
case Red, Green, Blue
}

enum IntOption {
case Some(value: Int)
case None
}
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