SprayJsonSupport not working for Future[List[obj]] under Scala 3

[csar]

val fut = Future.successful(List(Dummy(1),Dummy(2))) complete(fut)

fails to compile under Scala 3.x - works as expected under 2.13.x

Minimal project to show the issue

[raboof]

By spelling out the implicit more, uh, explicitly:

implicitly[ToResponseMarshaller[Future[List[Dummy]]]]

We get a better error message:

[error]    |no implicit argument of type akka.http.scaladsl.marshalling.ToResponseMarshaller[
[error]    |  concurrent.Future[List[Dummy]]
[error]    |] was found for parameter e of method implicitly in object Predef.
[error]    |I found:
[error]    |
[error]    |    akka.http.scaladsl.marshalling.Marshaller.futureMarshaller[A, B](
[error]    |      akka.http.scaladsl.marshalling.Marshaller.liftMarshaller[T](
[error]    |        Run.sprayJsonMarshaller[T](
[error]    |          /* ambiguous: both method immIterableFormat in trait CollectionFormats and method linearSeqFormat in trait CollectionFormats match type spray.json.RootJsonWriter[T] */
[error]    |            summon[spray.json.RootJsonWriter[T]]
[error]    |        , /* missing */summon[spray.json.JsonPrinter])
[error]    |      )
[error]    |    )

This is still rather hard to read, but it says it correctly found 'futureMarshaller', 'liftMarshaller' and sprayJsonMarshaller, but is having trouble finding the right parameters to call sprayJsonMarshaller with.

You can work around this problem for now by performing this step 'manually':

implicit val jsonMarshaller: ToEntityMarshaller[List[Dummy]] = sprayJsonMarshaller(listFormat)

or:

implicit val jsonMarshaller: ToEntityMarshaller[List[Dummy]] = sprayJsonMarshaller(linearSeqFormat)

or:

implicit val jsonMarshaller: ToEntityMarshaller[List[Dummy]] = sprayJsonMarshaller(immIterableFormat)

Not sure why Scala 2 didn't consider these ambiguous and Scala 3 does... especially since with:

implicitly[RootJsonWriter[List[Dummy]]]

both Scala 2 and Scala 3 select an implicit without errors.

[csar]

This still persists with 10.6.0 - any progress?