close #3954, no review

3 files changed, 22 insertions, 1 deletions

diff --git a/src/library/scala/collection/mutable/SetLike.scala b/src/library/scala/collection/mutable/SetLike.scala
index 39ab1ff634..6264d1fbc2 100644
--- a/src/library/scala/collection/mutable/SetLike.scala
+++ b/src/library/scala/collection/mutable/SetLike.scala
@@ -79,7 +79,7 @@ trait SetLike[A, +This <: SetLike[A, This] with Set[A]]
   def add(elem: A): Boolean = {
     val r = contains(elem)
     this += elem
-    r
+    !r
   }
 
   /** Removes an element from this set.
diff --git a/test/files/run/colltest.check b/test/files/run/colltest.check
index be930f06ce..1ad81a1350 100644
--- a/test/files/run/colltest.check
+++ b/test/files/run/colltest.check
@@ -1 +1,7 @@
+true
+false
+true
+false
+true
+false
 succeeded for 10 iterations.
diff --git a/test/files/run/colltest.scala b/test/files/run/colltest.scala
index b6577006f4..b635c4e531 100644
--- a/test/files/run/colltest.scala
+++ b/test/files/run/colltest.scala
@@ -46,5 +46,20 @@ class TestSet(s0: Set[Int], s1: Set[Int]) {
   Console.println("succeeded for "+Iterations+" iterations.")
 }
 object Test extends Application {
+  def t3954 {
+    import scala.collection.mutable
+    import scala.collection.immutable
+    val result = new mutable.ImmutableSetAdaptor(immutable.ListSet.empty[Int])
+    println(result.add(1))
+    println(result.add(1))
+    val result2 = new mutable.HashSet[Int]
+    println(result2.add(1))
+    println(result2.add(1))
+    val result3 = new java.util.HashSet[Int]()
+    println(result3.add(1))
+    println(result3.add(1))
+  }
+  t3954
+
   new TestSet(HashSet.empty, new scala.collection.mutable.LinkedHashSet)
 }