Restore ImmutableKeySet test

Co-authored-by: Georgi Krastev <[email protected]>

Author: som-snytt

src/library/scala/collection/immutable/Map.scala

@@ -142,7 +142,7 @@ trait MapOps[K, +V, +CC[X, +Y] <: MapOps[X, Y, CC, _], +C <: MapOps[K, V, CC, C]
   override def keySet: Set[K] = new ImmutableKeySet
 
   /** The implementation class of the set returned by `keySet` */
-  protected class ImmutableKeySet extends AbstractSet[K] with GenKeySet with DefaultSerializable {
+  protected[immutable] class ImmutableKeySet extends AbstractSet[K] with GenKeySet with DefaultSerializable {
     def incl(elem: K): Set[K] = if (this(elem)) this else empty ++ this + elem
     def excl(elem: K): Set[K] = if (this(elem)) empty ++ this - elem else this
   }

src/library/scala/collection/immutable/Set.scala

@@ -106,8 +106,8 @@ object Set extends IterableFactory[Set] {
       case s: Set2[E]    => s
       case s: Set3[E]    => s
       case s: Set4[E]    => s
-      //case s: MapOps[E @unchecked, _, _, _]#ImmutableKeySet => s
       case s: HashMap[E @unchecked, _]#HashKeySet => s
+      case s: MapOps[E, Any, Map, Map[E, Any]]#ImmutableKeySet @unchecked => s
       // We also want `SortedSet` (and subclasses, such as `BitSet`)
       // to rebuild themselves, to avoid element type widening issues.
       case _ => newBuilder[E].addAll(it).result()

test/junit/scala/collection/FactoriesTest.scala

@@ -203,7 +203,7 @@ class FactoriesTest {
       im.Set(1),
       im.HashSet("a", "b", "c"),
       im.ListSet('c', 'd'),
-      //im.Map("a" -> 1, "b" -> 1, "c" -> 1).keySet,      // MapOps$ImmutableKeySet
+      im.Map("a" -> 1, "b" -> 1, "c" -> 1).keySet,      // MapOps$ImmutableKeySet
       im.HashMap("a" -> 1, "b" -> 1, "c" -> 1).keySet,  // HashKeySet
     )
 

test/junit/scala/collection/immutable/SetTest.scala

@@ -73,9 +73,9 @@ class SetTest {
     assertEquals(WeekDay.values, valuesa)
 
     // Make sure regular Map keySets do not rebuild themselves on widening with toSet
-    //val mapset = Map(1 -> "cod", 2 -> "herring").keySet
-    //val mapseta = any(mapset)
-    //assertSame(mapset, mapseta) // WIP see Set.from
+    val mapset = Map(1 -> "cod", 2 -> "herring").keySet
+    val mapseta = any(mapset)
+    assertSame(mapset, mapseta) // WIP see Set.from
   }
 
   @deprecated("Uses deprecated API", since="2.13")