Fix duplicate doobie/util/package.scala for Scala 3

Author: jatcwang

modules/core/src/main/scala-3/doobie/util/GetPlatform.scala

@@ -7,6 +7,7 @@ package doobie.util
 import scala.deriving.Mirror
 import scala.compiletime.constValue
 import scala.reflect.Enum
+import doobie.util.derivation.{summonSingletonCases, summonLabels}
 
 trait GetPlatform {
   private def of[A](name: String, cases: List[A], labels: List[String]): Get[A] =

modules/core/src/main/scala-3/doobie/util/PutPlatform.scala

@@ -7,6 +7,7 @@ package doobie.util
 import scala.compiletime.constValue
 import scala.deriving.Mirror
 import scala.reflect.Enum
+import doobie.util.derivation.{summonSingletonCases, summonLabels}
 
 trait PutPlatform {
   inline final def deriveEnumString[A <: Enum](using mirror: Mirror.SumOf[A]): Put[A] =

modules/core/src/main/scala-3/doobie/util/derivation.scala

@@ -0,0 +1,24 @@
+// Copyright (c) 2013-2020 Rob Norris and Contributors
+// This software is licensed under the MIT License (MIT).
+// For more information see LICENSE or https://opensource.org/licenses/MIT
+
+package doobie.util
+
+import scala.compiletime.{constValue, erasedValue, error, summonInline}
+import scala.deriving.Mirror
+
+private[util] object derivation:
+
+  inline final def summonLabels[T <: Tuple]: List[String] =
+    inline erasedValue[T] match
+      case _: EmptyTuple => Nil
+      case _: (t *: ts)  => constValue[t].asInstanceOf[String] :: summonLabels[ts]
+
+  inline final def summonSingletonCases[T <: Tuple, A](inline typeName: String): List[A] =
+    inline erasedValue[T] match
+      case _: EmptyTuple => Nil
+      case _: (h *: t)   =>
+        inline summonInline[Mirror.Of[h]] match
+          case m: Mirror.Singleton => m.fromProduct(EmptyTuple).asInstanceOf[A] :: summonSingletonCases[t, A](typeName)
+          case m: Mirror           =>
+            error("Enum " + typeName + " contains non singleton case " + constValue[m.MirroredLabel])