SI-7149 Use a WeakHashSet for type uniqueness

Currently type uniqueness is done via a HashSet[Type], but
that means the Types live through an entire compile session, even
ones that are used once. The result is a huge amount of unnecessarily
retained memory. This commit uses a WeakHashSet instead so that Types
and their WeakReferences are cleaned up when no longer in use.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/reflect/scala/reflect/internal/Types.scala b/src/reflect/scala/reflect/internal/Types.scala
index cd9f3d23c9..cfa6f927b5 100644
--- a/src/reflect/scala/reflect/internal/Types.scala
+++ b/src/reflect/scala/reflect/internal/Types.scala
@@ -3935,13 +3935,13 @@ trait Types extends api.Types { self: SymbolTable =>
 // Hash consing --------------------------------------------------------------
 
   private val initialUniquesCapacity = 4096
-  private var uniques: util.HashSet[Type] = _
+  private var uniques: util.WeakHashSet[Type] = _
   private var uniqueRunId = NoRunId
 
   protected def unique[T <: Type](tp: T): T = {
     if (Statistics.canEnable) Statistics.incCounter(rawTypeCount)
     if (uniqueRunId != currentRunId) {
-      uniques = util.HashSet[Type]("uniques", initialUniquesCapacity)
+      uniques = util.WeakHashSet[Type](initialUniquesCapacity)
       perRunCaches.recordCache(uniques)
       uniqueRunId = currentRunId
     }