Closes #3984 by the most arduous and indirect r...

Closes #3984 by the most arduous and indirect route imaginable:
abstracts the common code out of the TrieIterators in HashMap and
HashSet. When I raised this flag to find out if anyone would open
fire, all was quiet on the western front. Although I wouldn't want
to write code like this as an everyday thing, I think it serves as a
nice showcase for some of the abstraction challenges we're up against:
performance looks the same and I will never again have to fix the same
bug in two places. Review by rompf.

1 files changed, 33 insertions, 2 deletions

diff --git a/test/files/run/bug3984.scala b/test/files/run/bug3984.scala
index 3e4d2edf53..0747b0ee25 100644
--- a/test/files/run/bug3984.scala
+++ b/test/files/run/bug3984.scala
@@ -1,4 +1,4 @@
-object Test {
+object SetBug {
   import scala.collection.immutable.{ Set => ImmutSet }
   import scala.collection.mutable.{ Set => MutSet }
 
@@ -6,16 +6,47 @@ object Test {
     override def hashCode: Int = h
   }
 
-  def main (args: Array[String]) {
+  def run() {
     var is = ImmutSet.empty[IH]
     var ms = MutSet.empty[IH]
     for (ih <- List(IH(2,0),IH(0,0),IH(4,4),IH(6,4),IH(-8,1520786080))) {
       is = is + ih
       ms = ms + ih
     }
+    assert(is == ms)
     val x = IH(6,4)
     is = is - x
     ms = ms - x
     assert(is == ms)
   }
 }
+
+object MapBug {
+  import scala.collection.immutable.{ Map => ImmutMap }
+  import scala.collection.mutable.{ Map => MutMap }
+
+  case class IH (i: Int, h: Int) {
+    override def hashCode: Int = h
+  }
+
+  def run() {
+    var im = ImmutMap.empty[IH,IH]
+    var mm = MutMap.empty[IH,IH]
+    for (ih <- List(IH(2,0),IH(0,0),IH(4,4),IH(6,4),IH(-8,1520786080))) {
+      im = im + ((ih,ih))
+      mm = mm + ((ih,ih))
+    }
+    assert(im == mm)
+    val x = IH(6,4)
+    im = im - x
+    mm = mm - x
+    assert(im == mm)
+  }
+}
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    SetBug.run()
+    MapBug.run()
+  }
+}