Merge pull request #4703 from Ichoran/issue/8346

SI-8346  Re-established soundness of toSet (element type widening)

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

@@ -194,6 +194,7 @@ class HashSet[A] extends AbstractSet[A]
 
   protected def writeReplace(): AnyRef = new HashSet.SerializationProxy(this)
 
+  override def toSet[B >: A]: Set[B] = this.asInstanceOf[HashSet[B]]
 }
 
 /** $factoryInfo

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

@@ -179,4 +179,6 @@ class ListSet[A] extends AbstractSet[A]
 
     override def tail: ListSet[A] = self
   }
+
+  override def toSet[B >: A]: Set[B] = this.asInstanceOf[ListSet[B]]
 }

src/library/scala/collection/immutable/MapLike.scala

@@ -113,6 +113,11 @@ self =>
     override def - (elem: A): immutable.Set[A] =
       if (this(elem)) immutable.Set[A]() ++ this - elem
       else this
+
+    // ImmutableDefaultKeySet is only protected, so we won't warn on override.
+    // Someone could override in a way that makes widening not okay
+    // (e.g. by overriding +, though the version in this class is fine)
+    override def toSet[B >: A]: Set[B] = this.asInstanceOf[Set[B]]
   }
 
   /** This function transforms all the values of mappings contained

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

@@ -35,12 +35,22 @@ trait Set[A] extends Iterable[A]
   override def companion: GenericCompanion[Set] = Set
 
 
-  /** Returns this $coll as an immutable map.
-   *  
-   *  A new map will not be built; lazy collections will stay lazy.
+  /** Returns this $coll as an immutable set, perhaps accepting a
+   *  wider range of elements.  Since it already is an
+   *  immutable set, it will only be rebuilt if the underlying structure
+   *  cannot be expanded to include arbitrary element types.
+   *  For instance, `BitSet` and `SortedSet` will be rebuilt, as
+   *  they require `Int` and sortable elements respectively.
+   *
+   *  When in doubt, the set will be rebuilt.  Rebuilt sets never
+   *  need to be rebuilt again.
    */
-  @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 toSet[B >: A]: Set[B] = {
+      // This way of building sets typically has the best benchmarks, surprisingly!
+    val sb = Set.newBuilder[B]
+    foreach(sb += _)
+    sb.result()
+  }
 
   override def seq: Set[A] = this
   protected override def parCombiner = ParSet.newCombiner[A] // if `immutable.SetLike` gets introduced, please move this there!
@@ -62,6 +72,7 @@ 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
 
@@ -92,6 +103,10 @@ object Set extends ImmutableSetFactory[Set] {
       if (f(elem1)) Some(elem1)
       else None
     }
+    // Why is Set1 non-final?  Need to fix that!
+    @deprecatedOverriding("This immutable set should do nothing on toSet but cast itself to a Set with a wider element type.", "2.11.8")
+    override def toSet[B >: A]: Set[B] = this.asInstanceOf[Set1[B]]
+
   }
 
   /** An optimized representation for immutable sets of size 2 */
@@ -123,6 +138,9 @@ object Set extends ImmutableSetFactory[Set] {
       else if (f(elem2)) Some(elem2)
       else None
     }
+    // Why is Set2 non-final?  Need to fix that!
+    @deprecatedOverriding("This immutable set should do nothing on toSet but cast itself to a Set with a wider element type.", "2.11.8")
+    override def toSet[B >: A]: Set[B] = this.asInstanceOf[Set2[B]]
   }
 
   /** An optimized representation for immutable sets of size 3 */
@@ -156,6 +174,9 @@ object Set extends ImmutableSetFactory[Set] {
       else if (f(elem3)) Some(elem3)
       else None
     }
+    // Why is Set3 non-final?  Need to fix that!
+    @deprecatedOverriding("This immutable set should do nothing on toSet but cast itself to a Set with a wider element type.", "2.11.8")
+    override def toSet[B >: A]: Set[B] = this.asInstanceOf[Set3[B]]
   }
 
   /** An optimized representation for immutable sets of size 4 */
@@ -191,6 +212,9 @@ object Set extends ImmutableSetFactory[Set] {
       else if (f(elem4)) Some(elem4)
       else None
     }
+    // Why is Set4 non-final?  Need to fix that!
+    @deprecatedOverriding("This immutable set should do nothing on toSet but cast itself to a Set with a wider element type.", "2.11.8")
+    override def toSet[B >: A]: Set[B] = this.asInstanceOf[Set4[B]]
   }
 }
 

src/library/scala/collection/immutable/SortedMap.scala

@@ -53,6 +53,12 @@ self =>
       val map = self.rangeImpl(from, until)
       new map.DefaultKeySortedSet
     }
+    override def toSet[C >: A]: Set[C] = {
+      // This way of building sets typically has the best benchmarks, surprisingly!
+      val sb = Set.newBuilder[C]
+      foreach(sb += _)
+      sb.result()
+    }
   }
 
   /** Add a key/value pair to this map.

test/junit/scala/collection/immutable/SetTests.scala

@@ -0,0 +1,81 @@
+package scala.collection.immutable
+
+import org.junit.Assert._
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.junit.runners.JUnit4
+
+@RunWith(classOf[JUnit4])
+class SetTests {
+  @Test
+  def test_SI8346_toSet_soundness(): Unit = {
+    val any2stringadd = "Disabled string conversions so as not to get confused!"
+
+    def any[A](set: Set[A]): Set[Any] = {
+      val anyset = set.toSet[Any]
+      assert((anyset + "fish") contains "fish")
+      anyset
+    }
+
+    // Make sure default immutable Set does not rebuild itself on widening with toSet
+    // Need to cover 0, 1, 2, 3, 4 elements as special cases
+    var si = Set.empty[Int]
+    assert(si eq si.toSet[Any])
+    for (i <- 1 to 5) {
+      val s1 = Set(Array.range(1, i+1): _*)
+      val s2 = si + i
+      val s1a = any(s1)
+      val s2a = any(s2)
+      assert(s1 eq s1a)
+      assert(s2 eq s2a)
+      si = s2
+    }
+
+    // Make sure BitSet correctly rebuilds itself on widening with toSet
+    // Need to cover empty, values 0-63, values 0-127 as special cases
+    val bitsets = Seq(BitSet.empty, BitSet(23), BitSet(23, 99), BitSet(23, 99, 141))
+    bitsets.foreach{ b =>
+      val ba = any(b)
+      assert(b ne ba)
+      assertEquals(b, ba)
+    }
+
+    // Make sure HashSet (and by extension, its implementing class HashTrieSet)
+    // does not rebuild itself on widening by toSet
+    val hashset = HashSet(1, 3, 5, 7)
+    val hashseta = any(hashset)
+    assert(hashset eq hashseta)
+
+    // Make sure ListSet does not rebuild itself on widening by toSet
+    // (Covers Node also, since it subclasses ListSet)
+    val listset = ListSet(1, 3, 5, 7)
+    val listseta = any(listset)
+    assert(listset eq listseta)
+
+    // Make sure SortedSets correctly rebuild themselves on widening with toSet
+    // Covers TreeSet and keySet of SortedMap also
+    val sortedsets = Seq(
+      SortedSet.empty[Int], SortedSet(5), SortedSet(1,2,3,5,4),
+      SortedMap(1 -> "cod", 2 -> "herring").keySet
+    )
+    sortedsets.foreach{ set => 
+      val seta = any(set)
+      assert(set ne seta)
+      assertEquals(set, seta)
+    }
+
+    // Make sure ValueSets correctly rebuild themselves on widening with toSet
+    object WeekDay extends Enumeration {
+      type WeekDay = Value
+      val Mon, Tue, Wed, Thu, Fri, Sat, Sun = Value
+    }
+    val valuesa = any(WeekDay.values)
+    assert(WeekDay.values ne valuesa)
+    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)
+    assert(mapset eq mapseta)
+  }
+}