Fix #4188: Test case

Author: odersky

tests/pos/i4188/Test_2.scala

@@ -0,0 +1,9 @@
+package collections
+
+import decorators._
+
+object Test {
+  def test(map: Map[Int, String]) = {
+    MapDecorator(map.view)
+  }
+}

tests/pos/i4188/collections_1.scala

@@ -0,0 +1,43 @@
+package collections
+
+object collections {
+  type AnyConstr[X] = Any
+}
+
+import collections._
+
+trait Iterable[+A] extends IterableOps[A, Iterable, Iterable[A]]
+
+trait IterableOps[+A, +CC[_], +C]
+
+trait Map[K, +V] extends MapOps[K, V, Map, Map[K, V]]
+
+trait MapOps[K, +V, +CC[_, _] <: IterableOps[_, AnyConstr, _], +C]
+  extends IterableOps[(K, V), Iterable, C] {
+  def view: MapView[K, V] = ???
+}
+
+trait View[+A] extends Iterable[A] with IterableOps[A, View, View[A]]
+
+trait MapView[K, +V]
+  extends MapOps[K, V, ({ type l[X, Y] = View[(X, Y)] })#l, View[(K, V)]]
+  with View[(K, V)]
+
+class MapDecorator[C, M <: HasMapOps[C]]
+
+trait HasMapOps[C] {
+
+  /** The type of keys */
+  type K
+
+  /** The type of values */
+  type V
+
+  type A = (K, V)
+}
+
+object decorators {
+  def MapDecorator[C](coll: C)(implicit map: HasMapOps[C]): MapDecorator[C, map.type] = ???
+
+  implicit def mapHasMapOps[CC[X, +Y] <: MapOps[X, Y, ({ type l[X, +Y] = IterableOps[_, AnyConstr, _] })#l, _], K0, V0]: HasMapOps[CC[K0, V0]] { type K = K0; type V = V0 } = ???
+}