2 files changed, 11 insertions, 7 deletions
diff --git a/src/library/scala/Symbol.scala b/src/library/scala/Symbol.scala
index 723c05a30c..4fead7a50c 100644
--- a/src/library/scala/Symbol.scala
+++ b/src/library/scala/Symbol.scala
@@ -69,6 +69,11 @@ private[scala] abstract class UniquenessCache[K, V >: Null]
         val res = cached()
         if (res != null) res
         else {
+          // If we don't remove the old String key from the map, we can
+          // wind up with one String as the key and a different String as
+          // as the name field in the Symbol, which can lead to surprising
+          // GC behavior and duplicate Symbols. See SI-6706.
+          map remove name
           val sym = valueFromKey(name)
           map.put(name, new WeakReference(sym))
           sym
diff --git a/src/library/scala/collection/mutable/FlatHashTable.scala b/src/library/scala/collection/mutable/FlatHashTable.scala
index c0299479f3..91e95e039b 100644
--- a/src/library/scala/collection/mutable/FlatHashTable.scala
+++ b/src/library/scala/collection/mutable/FlatHashTable.scala
@@ -110,24 +110,23 @@ trait FlatHashTable[A] extends FlatHashTable.HashUtils[A] {
 
   /** Finds an entry in the hash table if such an element exists. */
   protected def findEntry(elem: A): Option[A] = {
-    var h = index(elemHashCode(elem))
-    var entry = table(h)
-    while (null != entry && entry != elem) {
-      h = (h + 1) % table.length
-      entry = table(h)
-    }
+    val entry = findEntryImpl(elem)
     if (null == entry) None else Some(entry.asInstanceOf[A])
   }
 
   /** Checks whether an element is contained in the hash table. */
   protected def containsEntry(elem: A): Boolean = {
+    null != findEntryImpl(elem)
+  }
+
+  private def findEntryImpl(elem: A): AnyRef = {
     var h = index(elemHashCode(elem))
     var entry = table(h)
     while (null != entry && entry != elem) {
       h = (h + 1) % table.length
       entry = table(h)
     }
-    null != entry
+    entry
   }
 
   /** Add entry if not yet in table.