Map java.util.UUID to ID instead of String

core/src/main/scala/caliban/schema/Schema.scala

@@ -108,7 +108,7 @@ trait GenericSchema[R] extends DerivationSchema[R] {
   implicit val unitSchema: Schema[Any, Unit]             = scalarSchema("Unit", None, _ => ObjectValue(Nil))
   implicit val booleanSchema: Schema[Any, Boolean]       = scalarSchema("Boolean", None, BooleanValue)
   implicit val stringSchema: Schema[Any, String]         = scalarSchema("String", None, StringValue)
-  implicit val uuidSchema: Schema[Any, UUID]             = stringSchema.contramap(_.toString)
+  implicit val uuidSchema: Schema[Any, UUID]             = scalarSchema("ID", None, uuid => StringValue(uuid.toString))
   implicit val intSchema: Schema[Any, Int]               = scalarSchema("Int", None, IntValue(_))
   implicit val longSchema: Schema[Any, Long]             = scalarSchema("Long", None, IntValue(_))
   implicit val bigIntSchema: Schema[Any, BigInt]         = scalarSchema("BigInt", None, IntValue(_))

core/src/test/scala/caliban/schema/SchemaSpec.scala

@@ -1,5 +1,7 @@
 package caliban.schema
 
+import java.util.UUID
+
 import scala.concurrent.Future
 import caliban.introspection.adt.{ __DeprecatedArgs, __Type, __TypeKind }
 import caliban.schema.SchemaSpecUtils._
@@ -37,6 +39,12 @@ object SchemaSpec
             Types.collectTypes(introspect[Queries]).keys,
             contains("BInput") && contains("CInput")
           )
+        },
+        test("UUID field should be converted to ID") {
+          assert(
+            introspect[IDSchema].fields(__DeprecatedArgs()).toList.flatten.headOption.map(_.`type`()),
+            isSome(hasField[__Type, String]("id", _.ofType.flatMap(_.name).get, equalTo("ID")))
+          )
         }
       )
     )
@@ -45,6 +53,7 @@ object SchemaSpecUtils {
   case class EffectfulFieldSchema(q: Task[Int])
   case class InfallibleFieldSchema(q: UIO[Int])
   case class FutureFieldSchema(q: Future[Int])
+  case class IDSchema(id: UUID)
 
   def introspect[Q](implicit schema: Schema[Any, Q]): __Type = schema.toType()
 }

vuepress/docs/docs/schema.md

@@ -10,7 +10,7 @@ The table below shows how common Scala types are converted to GraphQL types.
 | Float              | Float                                            |
 | Double             | Float                                            |
 | String             | String                                           |
-| java.util.UUID     | String                                           |
+| java.util.UUID     | ID                                               |
 | Unit               | Unit (custom scalar)                             |
 | Long               | Long (custom scalar)                             |
 | BigInt             | BigInt (custom scalar)                           |