Fix and test case for #408. Review by community.

2 files changed, 21 insertions, 6 deletions

diff --git a/src/library/scala/collection/immutable/HashSet.scala b/src/library/scala/collection/immutable/HashSet.scala
index 25a8059b0c..2320187be9 100644
--- a/src/library/scala/collection/immutable/HashSet.scala
+++ b/src/library/scala/collection/immutable/HashSet.scala
@@ -115,17 +115,20 @@ class HashSet[A] extends Set[A]
 
   private def makeCopy(last: HashSet[A]) {
     def undo(m: HashSet[A]) {
-      if (m ne last) {
-        undo(m.later)
-        if (m.deleted) addEntry(m.changedElem)
-        else removeEntry(m.changedElem)
-      }
+      if (m.deleted) addEntry(m.changedElem)
+      else removeEntry(m.changedElem)
     }
     table = new scala.Array[AnyRef](last.table.length)
     scala.Array.copy(last.table, 0, table, 0, table.length)
     tableSize = last.tableSize
     threshold = last.threshold
-    undo(this)
+
+    // we need to work from the end of the list but non-tail-recursion
+    // potentially blows the stack, so instead we create a stack on the heap.
+    // See ticket #408.
+    val toUndo = new mutable.Stack[HashSet[A]]
+    toUndo pushAll ((Iterator iterate this)(_.later) takeWhile (_ ne last))
+    toUndo foreach undo
     later = null
   }
 
diff --git a/test/files/run/bug408.scala b/test/files/run/bug408.scala
new file mode 100644
index 0000000000..9e51e881ed
--- /dev/null
+++ b/test/files/run/bug408.scala
@@ -0,0 +1,12 @@
+object Test
+{
+  val a = scala.collection.immutable.Set.empty ++ (0 to 100000)
+  val b = scala.collection.immutable.Set.empty ++ (0 to 100000)
+
+  def main(args: Array[String]): Unit = {
+    a -- b
+    a -- b
+    a -- b
+    a -- b
+  }
+}