Fix Json encoding of non-string map keys

Author: ghostdogpr

json/src/main/scala/proteus/json/package.scala

@@ -75,12 +75,10 @@ implicit def jsonWriterCodec[A](using codec: ProtobufCodec[A], registry: Registr
                     val it      = c.deconstructor.deconstruct(b.asInstanceOf[m[k, v]])
                     val builder = List.newBuilder[Json]
                     while (it.hasNext) {
-                      val v = it.next
-                      builder +=
-                        Json.obj(
-                          loop(c.deconstructor.getKey(v), c.element.fields(0).asInstanceOf[SimpleField[?]].codec, offset).asString.getOrElse("") ->
-                            loop(c.deconstructor.getValue(v), c.element.fields(1).asInstanceOf[SimpleField[?]].codec, offset)
-                        )
+                      val v     = it.next
+                      val key   = loop(c.deconstructor.getKey(v), c.element.fields(0).asInstanceOf[SimpleField[?]].codec, offset)
+                      val value = loop(c.deconstructor.getValue(v), c.element.fields(1).asInstanceOf[SimpleField[?]].codec, offset)
+                      builder += Json.obj(key.asString.getOrElse(key.noSpaces) -> value)
                     }
                     Json.arr(builder.result()*)
                   case Bytes                   => Json.fromString("<bytes>")

json/src/test/scala/proteus/json/JsonSpec.scala

@@ -184,6 +184,12 @@ object JsonSpec extends ZIOSpecDefault {
         val result   = instance.asJson.noSpaces
         assertTrue(result == """{"data":[{"one":1},{"two":2}]}""" || result == """{"data":[{"two":2},{"one":1}]}""")
       },
+      test("toJson serializes Map[Int, Int]") {
+        case class MapMessage(data: Map[Int, Int]) derives Schema, ProtobufCodec
+        val instance = MapMessage(Map(1 -> 1, 2 -> 2))
+        val result   = instance.asJson.noSpaces
+        assertTrue(result == """{"data":[{"1":1},{"2":2}]}""" || result == """{"data":[{"2":2},{"1":1}]}""")
+      },
       test("toJson serializes empty Map") {
         case class MapMessage(data: Map[String, String]) derives Schema, ProtobufCodec
         val instance = MapMessage(Map.empty)