Patternmatcher fails to bind `_: _*` correctly

[felixmulder]

When transforming:

val List(_: _*) = List(1)

_ is evaluated to be an Int instead of a Seq[Int].

[DarkDimius]

val List(x: _*) = List(1)
is handled correctly, but
val List(_: _*) = List(1)
isn't

[DarkDimius]

As far as I see, the issue stems from the fact that desugaring performed by typer is ambiguous:

object Test {
  def main(args: Array[String]): Unit = {
   val List(_: _*) = (List(1) : Any)
   /*  case List.unapplySeq[Any'](_: scala.collection.Seq[Any]):
            scala.collection.immutable.List[Any']          => () */

   val List(_: Seq[Any]) = (List(List()) : Any)
   /* case List.unapplySeq[Any'](_: Seq[Any]):
            scala.collection.immutable.List[Any']  => () */
  }
}

both matches here are desugared into the very same tree.

@odersky has found the very same issue from a different side: TreeInfo.isWildcardStarArg assumes that the _: _* case should be matching:

case Typed(_, tpt: TypeTree) => tpt.hasType && tpt.tpe.isRepeatedParam

but it does not, as tpt will not be Int* but will be Seq[Int] instead.