Merge pull request #233 from sangria-graphql/fix_ambiguous_implicits

fix ambiguous implicits in scala 3

src/main/scala/sangria/marshalling/FromInput.scala

@@ -9,7 +9,7 @@ trait FromInput[Val] {
   def fromResult(node: marshaller.Node): Val
 }
 
-object FromInput {
+object FromInput extends LowPriorityFromInput {
   private object ScalarFromInput extends FromInput[Any] {
     val marshaller: CoercedScalaResultMarshaller = CoercedScalaResultMarshaller.default
     def fromResult(node: marshaller.Node): marshaller.Node = node
@@ -59,10 +59,14 @@ object FromInput {
 
   implicit def optionInput[T](implicit ev: FromInput[T]): FromInput[Option[T]] =
     ev.asInstanceOf[FromInput[Option[T]]]
-  implicit def seqInput[T](implicit ev: FromInput[T]): SeqFromInput[T] = new SeqFromInput[T](ev)
   implicit def iterableInput[T](implicit ev: FromInput[T]): IterableFromInput[T, Iterable] =
     new IterableFromInput[T, Iterable](ev)
 
   trait CoercedScalaResult
   trait InputObjectResult
 }
+
+trait LowPriorityFromInput {
+  import FromInput.SeqFromInput
+  implicit def seqInput[T](implicit ev: FromInput[T]): SeqFromInput[T] = new SeqFromInput[T](ev)
+}

src/test/scala/sangria/marshalling/FromInputSpec.scala

@@ -0,0 +1,73 @@
+package sangria.marshalling
+
+import org.scalatest.wordspec.AnyWordSpec
+
+class FromInputSpec extends AnyWordSpec {
+
+  "FromInput" should {
+    "provide default FromInput for Map[String, Any]" in {
+      val fromInput = implicitly[FromInput[Map[String, Any]]]
+
+      assert(fromInput != null)
+    }
+
+    "provide default FromInput for Seq" in {
+      import FromInputSpec.FromInputStringInstance.stringFromInput
+
+      val fromInput = implicitly[FromInput[Seq[String]]]
+
+      assert(fromInput != null)
+    }
+
+    "provide default FromInput for Iterable" in {
+      import FromInputSpec.FromInputStringInstance.stringFromInput
+
+      val fromInput = implicitly[FromInput[Iterable[String]]]
+
+      assert(fromInput != null)
+    }
+
+    "provide default FromInput for Option" in {
+      import FromInputSpec.FromInputStringInstance.stringFromInput
+
+      val fromInput = implicitly[FromInput[Option[String]]]
+
+      assert(fromInput != null)
+    }
+
+    "provide default FromInput for Option of Seq" in {
+      import FromInputSpec.FromInputStringInstance.stringFromInput
+
+      val fromInput = implicitly[FromInput[Option[Seq[String]]]]
+
+      assert(fromInput != null)
+    }
+
+    "resolve covariant Seq" in {
+      import FromInputSpec.InputType._
+      import FromInputSpec.FromInputStringInstance.stringFromInput
+
+      val fromInput = instance(OptionInputType(SeqInputType(StringInputType)))
+
+      assert(fromInput != null)
+    }
+  }
+}
+
+object FromInputSpec {
+  object FromInputStringInstance {
+    implicit val stringFromInput: FromInput[String] = new FromInput[String] {
+      override val marshaller: ResultMarshaller = CoercedScalaResultMarshaller.default
+      override def fromResult(node: marshaller.Node): String = "hello"
+    }
+  }
+
+  trait InputType[+T]
+  object InputType {
+    case class OptionInputType[T](t: InputType[T]) extends InputType[Option[T]]
+    case class SeqInputType[T](t: InputType[T]) extends InputType[Seq[T]]
+    case object StringInputType extends InputType[String]
+
+    def instance[T](t: InputType[T])(implicit fromInput: FromInput[T]): FromInput[T] = fromInput
+  }
+}