Merge 83fd2f6 into cd800d5

core/src/main/scala-3/pureconfig/generic/derivation/ConfigReaderDerivation.scala

@@ -2,6 +2,7 @@ package pureconfig
 package generic
 package derivation
 
+import scala.compiletime.summonFrom
 import scala.deriving.Mirror
 
 trait ConfigReaderDerivation extends CoproductConfigReaderDerivation with ProductConfigReaderDerivation {
@@ -12,6 +13,15 @@ trait ConfigReaderDerivation extends CoproductConfigReaderDerivation with Produc
         case given Mirror.SumOf[A] => derivedSum
       }
   }
+
+  /** Summons a `ConfigReader` for a given type `A`. It first tries to find an existing given instance of
+    * `ConfigReader[A]`. If none is found, it tries to derive one using this `ConfigReaderDerivation` instance. This
+    * method differs from `derived` in that the latter doesn't try to find an existing instance first.
+    */
+  protected inline def summonConfigReader[A] = summonFrom {
+    case reader: ConfigReader[A] => reader
+    case given Mirror.Of[A] => ConfigReader.derived[A]
+  }
 }
 
 object ConfigReaderDerivation {

core/src/main/scala-3/pureconfig/generic/derivation/CoproductConfigReaderDerivation.scala

@@ -7,7 +7,7 @@ import scala.deriving.Mirror
 
 import pureconfig.error.{CannotConvert, ConfigReaderFailures}
 import pureconfig.generic.derivation.ConfigReaderDerivation
-import pureconfig.generic.derivation.WidenType.widen
+import pureconfig.generic.derivation.Utils._
 
 trait CoproductConfigReaderDerivation(fieldMapping: ConfigFieldMapping, optionField: String) {
   self: ConfigReaderDerivation =>
@@ -33,8 +33,7 @@ trait CoproductConfigReaderDerivation(fieldMapping: ConfigFieldMapping, optionFi
         } yield result
 
       val readers =
-        Labels
-          .transformed[m.MirroredElemLabels](fieldMapping)
+        transformedLabels[A](fieldMapping)
           .zip(deriveForSubtypes[m.MirroredElemTypes, A])
           .toMap
     }
@@ -46,11 +45,5 @@ trait CoproductConfigReaderDerivation(fieldMapping: ConfigFieldMapping, optionFi
     }
 
   inline def deriveForSubtype[A0, A]: ConfigReader[A] =
-    summonFrom {
-      case reader: ConfigReader[A0] =>
-        reader.map(widen[A0, A](_))
-
-      case given Mirror.Of[A0] =>
-        ConfigReader.derived[A0].map(widen[A0, A](_))
-    }
+    summonConfigReader[A0].map(widen[A0, A](_))
 }

core/src/main/scala-3/pureconfig/generic/derivation/EnumConfigReaderDerivation.scala

@@ -6,7 +6,7 @@ import scala.compiletime.{constValue, erasedValue, error, summonInline}
 import scala.deriving.Mirror
 
 import pureconfig.error.{CannotConvert, ConfigReaderFailures}
-import pureconfig.generic.derivation.WidenType.widen
+import pureconfig.generic.derivation.Utils._
 
 type EnumConfigReader[A] = EnumConfigReaderDerivation.Default.EnumConfigReader[A]
 
@@ -53,7 +53,7 @@ trait EnumConfigReaderDerivation(transformName: String => String) {
         inline transformName: String => String,
         inline value: String
     )(using m: Mirror.SumOf[A]) = {
-      val ord = Labels.transformed[m.MirroredElemLabels](transformName).indexOf(value)
+      val ord = transformedLabels[A](transformName).indexOf(value)
       Option.when(ord >= 0)(ord)
     }
   }

core/src/main/scala-3/pureconfig/generic/derivation/ProductConfigReaderDerivation.scala

@@ -8,7 +8,7 @@ import scala.deriving.Mirror
 import scala.util.chaining.*
 
 import pureconfig.error.{ConfigReaderFailures, ConvertFailure, KeyNotFound, UnknownKey, WrongSizeList}
-import pureconfig.generic.derivation.WidenType.widen
+import pureconfig.generic.derivation.Utils._
 
 trait ProductConfigReaderDerivation(fieldMapping: ConfigFieldMapping) { self: ConfigReaderDerivation =>
   inline def derivedProduct[A](using m: Mirror.ProductOf[A]): ConfigReader[A] =
@@ -38,8 +38,7 @@ trait ProductConfigReaderDerivation(fieldMapping: ConfigFieldMapping) { self: Co
             for {
               objCur <- cur.asObjectCursor
               result <-
-                Labels
-                  .transformed[m.MirroredElemLabels](fieldMapping)
+                transformedLabels[A](fieldMapping)
                   .pipe(labels =>
                     readTuple[m.MirroredElemTypes, 0](
                       labels.map(objCur.atKeyOrUndefined(_)),
@@ -74,10 +73,4 @@ trait ProductConfigReaderDerivation(fieldMapping: ConfigFieldMapping) { self: Co
       case _: EmptyTuple =>
         Right(widen[EmptyTuple, T](EmptyTuple))
     }
-
-  inline def summonConfigReader[A] =
-    summonFrom {
-      case reader: ConfigReader[A] => reader
-      case given Mirror.Of[A] => ConfigReader.derived[A]
-    }
 }

core/src/main/scala-3/pureconfig/generic/derivation/Utils.scala

@@ -0,0 +1,35 @@
+package pureconfig.generic
+package derivation
+
+import scala.compiletime.{constValue, erasedValue, summonFrom, summonInline}
+import scala.deriving.Mirror
+
+object Utils {
+
+  /** Asserts in compile time that a given value of type `A` is also of type `B`.
+    *
+    * @param a
+    *   the value whose type to assert
+    * @return
+    *   `a` with a widened type.
+    */
+  inline def widen[A, B](a: A): A & B =
+    inline a match { case b: B => b }
+
+  /** Materializes the labels of a `A` (e.g. product element names, coproduct options) as a list of strings with an
+    * optional compile-time transformation. The function is guaranteed to return a constant list.
+    *
+    * @param transform
+    *   the function to transform keys with
+    * @return
+    *   the list of transformed labels.
+    */
+  inline def transformedLabels[A](inline transform: String => String)(using m: Mirror.Of[A]): List[String] =
+    transformedLabelsTuple[m.MirroredElemLabels](transform)
+
+  private inline def transformedLabelsTuple[T <: Tuple](inline transform: String => String): List[String] =
+    inline erasedValue[T] match {
+      case _: (h *: t) => transform(constValue[h & String]) :: transformedLabelsTuple[t](transform)
+      case _: EmptyTuple => Nil
+    }
+}