Merge pull request scala#4693 from scala/revert-3791-ticket/8346

Revert "SI-8346 Rebuild invariant sets in #toSet, avoiding CCE"

Author: SethTisue

src/library/scala/collection/immutable/HashSet.scala

@@ -162,13 +162,6 @@ class HashSet[A] extends AbstractSet[A]
   def - (e: A): HashSet[A] =
     nullToEmpty(removed0(e, computeHash(e), 0))
 
-  /** Returns this $coll as an immutable set.
-   *  
-   *  A new set will not be built; lazy collections will stay lazy.
-   */
-  @deprecatedOverriding("Immutable sets should do nothing on toSet but return themselves cast as a Set.", "2.11.0")
-  override def toSet[B >: A]: Set[B] = this.asInstanceOf[Set[B]]
-
   override def filter(p: A => Boolean) = {
     val buffer = new Array[HashSet[A]](bufferSize(size))
     nullToEmpty(filter0(p, false, 0, buffer, 0))

src/library/scala/collection/immutable/ListSet.scala

@@ -138,13 +138,6 @@ class ListSet[A] extends AbstractSet[A]
 
   override def stringPrefix = "ListSet"
 
-  /** Returns this $coll as an immutable set.
-   *  
-   *  A new set will not be built; lazy collections will stay lazy.
-   */
-  @deprecatedOverriding("Immutable sets should do nothing on toSet but return themselves cast as a Set.", "2.11.0")
-  override def toSet[B >: A]: Set[B] = this.asInstanceOf[Set[B]]
-
   /** Represents an entry in the `ListSet`.
    */
   protected class Node(override val head: A) extends ListSet[A] with Serializable {

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

@@ -35,7 +35,12 @@ trait Set[A] extends Iterable[A]
   override def companion: GenericCompanion[Set] = Set
 
 
-  override def toSet[B >: A]: Set[B] = to[({type l[a] = immutable.Set[B]})#l] // for bincompat; remove in dev
+  /** Returns this $coll as an immutable map.
+   *  
+   *  A new map will not be built; lazy collections will stay lazy.
+   */
+  @deprecatedOverriding("Immutable sets should do nothing on toSet but return themselves cast as a Set.", "2.11.0")
+  override def toSet[B >: A]: Set[B] = this.asInstanceOf[Set[B]]
 
   override def seq: Set[A] = this
   protected override def parCombiner = ParSet.newCombiner[A] // if `immutable.SetLike` gets introduced, please move this there!
@@ -57,7 +62,6 @@ object Set extends ImmutableSetFactory[Set] {
     def - (elem: Any): Set[Any] = this
     def iterator: Iterator[Any] = Iterator.empty
     override def foreach[U](f: Any =>  U): Unit = {}
-    override def toSet[B >: Any]: Set[B] = this.asInstanceOf[Set[B]]
   }
   private[collection] def emptyInstance: Set[Any] = EmptySet
 
@@ -88,8 +92,6 @@ object Set extends ImmutableSetFactory[Set] {
       if (f(elem1)) Some(elem1)
       else None
     }
-    @deprecatedOverriding("Immutable sets should do nothing on toSet but return themselves cast as a Set.", "2.11.0")
-    override def toSet[B >: A]: Set[B] = this.asInstanceOf[Set[B]]
   }
 
   /** An optimized representation for immutable sets of size 2 */
@@ -121,8 +123,6 @@ object Set extends ImmutableSetFactory[Set] {
       else if (f(elem2)) Some(elem2)
       else None
     }
-    @deprecatedOverriding("Immutable sets should do nothing on toSet but return themselves cast as a Set.", "2.11.0")
-    override def toSet[B >: A]: Set[B] = this.asInstanceOf[Set[B]]
   }
 
   /** An optimized representation for immutable sets of size 3 */
@@ -156,8 +156,6 @@ object Set extends ImmutableSetFactory[Set] {
       else if (f(elem3)) Some(elem3)
       else None
     }
-    @deprecatedOverriding("Immutable sets should do nothing on toSet but return themselves cast as a Set.", "2.11.0")
-    override def toSet[B >: A]: Set[B] = this.asInstanceOf[Set[B]]
   }
 
   /** An optimized representation for immutable sets of size 4 */
@@ -193,8 +191,6 @@ object Set extends ImmutableSetFactory[Set] {
       else if (f(elem4)) Some(elem4)
       else None
     }
-    @deprecatedOverriding("Immutable sets should do nothing on toSet but return themselves cast as a Set.", "2.11.0")
-    override def toSet[B >: A]: Set[B] = this.asInstanceOf[Set[B]]
   }
 }