Type inferencing fails for closure over view bound because of ETA expansion

[felixmulder]

import scala.collection.mutable

case class Foo[K, V <% Ordered[V]]()
extends mutable.HashMap[K,V] {
  this.toSeq.sortWith(_._2 > _._2)
}

yields:

-- Error: local/priv.scala:5:22 ------------------------------------------------
5 |  this.toSeq.sortWith(_._2 > _._2)
  |                      ^
  |                    missing parameter type for parameter _$1, expected = ?
-- Error: local/priv.scala:5:29 ------------------------------------------------
5 |  this.toSeq.sortWith(_._2 > _._2)
  |                             ^
  |                    missing parameter type for parameter _$2, expected = ?

I think it's the ETA expansion, because when I change code so that it's annotated:

import scala.collection.mutable

case class Foo[K, V <% Ordered[V]]()
extends mutable.HashMap[K,V] {
  this.toSeq.sortWith { case ((_, v1), (_, v2) => v1 > v2 }
}

Dotty fails with:

-- Error: local/priv.scala:5:24 ------------------------------------------------
5 |  this.toSeq.sortWith { case ((_, v1), (_, v2)) => v1 > v2 }
  |                        ^
  |     missing parameter type for parameter x$1 of expanded function x$1 =>
  |       x$1 @unchecked match
  |         {
  |           case ((_, v1), (_, v2)) =>
  |             v1 > v2
  |         }, expected = ?
-- [E007] Type Mismatch Error: local/priv.scala:5:51 ---------------------------
5 |  this.toSeq.sortWith { case ((_, v1), (_, v2)) => v1 > v2 }
  |                                                   ^^
  |found:    Nothing(v1)
  |required: ?{ > : ? }
  |
  |
  |Note that implicit conversions cannot be applied because they are ambiguous;
  | both method Float2float in object Predef and method Byte2byte in object Predef convert from Nothing(v1) to ?{ > : FunProto(v2):? }

[nicolasstucki]

Note that now we write it as

case class Foo[K, V]()(implicit conv: ImplicitConverter[V, Ordered[V]])

[smarter]

Already fixed, regression test in #5800.