Smol experimental macro to help with enum conversions

src/test/scala/io/moia/protos/teleproto/EnumMacros.scala

@@ -0,0 +1,59 @@
+package io.moia.protos.teleproto
+
+import scalapb.GeneratedEnum
+import scala.quoted.*
+import scala.deriving.Mirror
+import io.moia.food.food.Meal.Color.COLOR_BLUE.name
+
+object EnumMacros:
+
+  inline def fromProtobufToEnum[I <: GeneratedEnum, O](using M: Mirror.SumOf[O]): I => O =
+    ${ fromProtobufToEnumImpl[I, O] }
+
+  private def fromProtobufToEnumImpl[I <: GeneratedEnum: Type, O: Type](using Quotes): Expr[I => O] =
+    import quotes.reflect.*
+
+    def recGetLabels[T: Type]: List[String] =
+      Type.of[T] match
+        case '[EmptyTuple] => Nil
+        case '[label *: labelsTail] =>
+          val label = Type
+            .valueOfConstant[label]
+            .getOrElse {
+              report.errorAndAbort(s"Couldn't get the value of the label for type ${TypeRepr.of[label].show}.")
+            }
+            .asInstanceOf[String]
+          label :: recGetLabels[labelsTail]
+
+    val labelsOfEnumMembers =
+      Expr.summon[Mirror.SumOf[O]] match
+        case None =>
+          report.errorAndAbort("Couldn't summon the mirror of the enum.")
+        case Some(mirror) =>
+          mirror match
+            case '{ $m: Mirror.Sum { type MirroredElemLabels = elementLabels } } =>
+              recGetLabels[elementLabels]
+            case _ => report.errorAndAbort("Couln't get the labels of the enum members.")
+
+    val labelOfInputType = TypeRepr.of[I].show.split('.').last // last element of FQCN
+    val inputType        = Expr(labelOfInputType)
+
+    val O   = TypeRepr.of[O]
+    val sym = O.typeSymbol
+
+    // this will work *only* for Scala 3 enums
+    // look here: https://github.com/scalalandio/chimney/blob/master/chimney-macro-commons/src/main/scala-3/io/scalaland/chimney/internal/compiletime/datatypes/SealedHierarchiesPlatform.scala
+    // for a more general solution that works with any sealed hierarchy
+    def spawnInstance(label: Expr[String]): Expr[O] =
+      Apply(Select.unique(Ref(sym.companionModule), "valueOf"), List(label.asTerm)).asExprOf[O]
+
+    '{ (i: I) =>
+      {
+        val name: String  = i.name
+        val prefix        = $inputType + "_"
+        val withoutPrefix = name.toLowerCase.replace(prefix.toLowerCase, "")
+        val capitalized   = withoutPrefix.split('_').map(_.capitalize).mkString
+
+        ${ spawnInstance('capitalized) }
+      }
+    }

src/test/scala/io/moia/protos/teleproto/ProtocolBuffersRoundTripTest.scala

@@ -13,22 +13,9 @@ import scala.reflect.ClassTag
 class ProtocolBuffersRoundTripTest extends UnitTest with ScalaCheckPropertyChecks {
   import ProtocolBuffersRoundTripTest.*
 
-  def fn[T <: GeneratedEnum](e: T)(implicit classTag: ClassTag[T]): Color = {
-    val name: String = e.name // "COLOR_YELLOW"
-
-    val className = classTag.runtimeClass.getSimpleName // "Color"
-
-    val x = className + "_" // "Color_"
-
-    val y = name.toLowerCase.replace(x.toLowerCase, "") // "yellow"
-
-    val z = y.split('_').map(_.capitalize).mkString // "Yellow"
-
-    Color.valueOf(z) // Yellow
-  }
-
   given PartialTransformer[food.Meal.Color, Color] =
-    PartialTransformer.fromFunction(fn)
+    // types have to be provided explicitly!
+    PartialTransformer.fromFunction(EnumMacros.fromProtobufToEnum[food.Meal.Color, Color])
 
 //  given PartialTransformer[food.Meal.Color, Color] = PartialTransformer
 //    .define[food.Meal.Color, Color]
@@ -77,6 +64,18 @@ class ProtocolBuffersRoundTripTest extends UnitTest with ScalaCheckPropertyCheck
 
   val mealGen: Gen[Meal] = Gen.oneOf(fruitBasketGen, lunchBoxGen).map(Meal.apply)
 
+  "Macro transform for enums" should {
+    "convert from Protocol Buffers to model" in {
+      val fun: food.Meal.Color => Color = EnumMacros.fromProtobufToEnum[food.Meal.Color, Color]
+
+      fun(food.Meal.Color.COLOR_YELLOW) shouldBe Color.Yellow
+      fun(food.Meal.Color.COLOR_RED) shouldBe Color.Red
+      fun(food.Meal.Color.COLOR_ORANGE) shouldBe Color.Orange
+      fun(food.Meal.Color.COLOR_PINK) shouldBe Color.Pink
+      fun(food.Meal.Color.COLOR_BLUE) shouldBe Color.Blue
+    }
+  }
+
   "ProtocolBuffers" should {
     "generate writer and reader that round trip successfully" in {
       forAll(mealGen) { meal =>