Close #369 - [refined4s-circe] Add KeyEncoder and KeyDecoder to…

… `refined4s.modules.circe.derivation.generic.auto`

modules/refined4s-circe/shared/src/main/scala/refined4s/modules/circe/derivation/generic/auto.scala

@@ -1,6 +1,6 @@
 package refined4s.modules.circe.derivation.generic
 
-import io.circe.{Decoder, Encoder}
+import io.circe.{Decoder, Encoder, KeyDecoder, KeyEncoder}
 import refined4s.modules.cats.syntax.contraCoercible
 import refined4s.{Coercible, RefinedCtor}
 
@@ -17,5 +17,34 @@ trait auto {
 
   inline given derivedRefinedDecoder[A, B](using refinedCtor: RefinedCtor[B, A], decoder: Decoder[A]): Decoder[B] =
     decoder.emap(refinedCtor.create)
+
+  inline given derivedKeyEncoder[A, B](using coercible: Coercible[A, B], encoder: KeyEncoder[B]): KeyEncoder[A] =
+    contraCoercible(encoder)
+
+  inline given derivedNewtypeKeyDecoder[A, B](using coercible: Coercible[A, B], decoder: KeyDecoder[A]): KeyDecoder[B] =
+    Coercible.unsafeWrapTC(decoder)
+
+  inline given derivedRefinedKeyDecoder[A, B](using refinedCtor: RefinedCtor[B, A], decoder: KeyDecoder[A]): KeyDecoder[B] with {
+    override def apply(key: String): Option[B] =
+      decoder.apply(key).flatMap(refinedCtor.create(_).toOption)
+  }
+
+  /** Without this, Circe's decode uses an incorrect Decoder for the value.
+    * @example
+    * {{{
+    *   // when
+    *   decode[Map[PortNumber, Int]]("""{ "0": 65536 }""")
+    *
+    *   // The expected result is
+    *   Map(PortNumber(0), 65536)
+    *
+    *   // But the actual result is
+    *   // Either[DecodingFailure, Map[PortNumber, Int]] =
+    *   //   Left(DecodingFailure(Invalid value: [65536]. It has to be Int between 0 and 65535 (0 <= PortNumber <= 65535), List(DownField(0))))
+    *   // The KeyDecoder is fine here, but the value Decoder `decode` uses is not Decoder[Int] but Decoder[PortNumber].
+    * }}}
+    */
+  inline given derivedMapDecoder[A, B](using KeyDecoder[A], Decoder[B]): Decoder[Map[A, B]] = io.circe.Decoder.decodeMap
+
 }
 object auto extends auto