Implicit BuildFrom Not In Scope With Exclusive Range

[adamgfraser]

reproduction steps

Using Scala 2.13.3,

import scala.concurrent._
import scala.concurrent.ExecutionContext.global
  
implicit val ec = global
  
Future.traverse(1 until 10)(a => Future.unit)
// Cannot construct a collection of type scala.collection.immutable.AbstractSeq[Unit] with elements of type Unit based on a collection of type scala.collection.immutable.AbstractSeq[Int].

problem

There is no implicit CanBuildFrom in scope here when the range is exclusive, even though there is when the range is inclusive. I would expect we should be able to build something here, especially when we can in seemingly the same situation if we just do 1 to 10 instead of 1 until 10.

[som-snytt]

Duplicates #11875 and others. "Fixed in dotty." Workaround is to provide type args or use Range.inclusive.