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.

3 files changed, 50 insertions, 2 deletions

diff --git a/bincompat-backward.whitelist.conf b/bincompat-backward.whitelist.conf
index c016b52241..38d26c7fb7 100644
--- a/bincompat-backward.whitelist.conf
+++ b/bincompat-backward.whitelist.conf
@@ -279,6 +279,30 @@ filter {
         {
             matchName="scala.reflect.internal.util.WeakReferenceWithEquals"
             problemName=MissingClassProblem
+        },
+               {
+            matchName="scala.reflect.internal.SymbolTable.scala$reflect$internal$Types$$uniques"
+            problemName=IncompatibleResultTypeProblem
+        },
+        {
+            matchName="scala.reflect.internal.SymbolTable.scala$reflect$internal$Types$$uniques_="
+            problemName=IncompatibleMethTypeProblem
+        },
+        {
+            matchName="scala.reflect.internal.Types.scala$reflect$internal$Types$$uniques"
+            problemName=IncompatibleResultTypeProblem
+        },
+        {
+            matchName="scala.reflect.internal.Types.scala$reflect$internal$Types$$uniques_="
+            problemName=IncompatibleMethTypeProblem
+        },
+        {
+            matchName="scala.reflect.internal.Types.scala$reflect$internal$Types$$uniques"
+            problemName=MissingMethodProblem
+        },
+        {
+            matchName="scala.reflect.internal.Types.scala$reflect$internal$Types$$uniques_="
+            problemName=MissingMethodProblem
         }
     ]
 }
diff --git a/bincompat-forward.whitelist.conf b/bincompat-forward.whitelist.conf
index d1a19534db..a64eb0ba5d 100644
--- a/bincompat-forward.whitelist.conf
+++ b/bincompat-forward.whitelist.conf
@@ -1383,6 +1383,30 @@ filter {
         {
             matchName="scala.reflect.internal.util.WeakHashSet.reduceOption"
             problemName=MissingMethodProblem
+        },
+        {
+            matchName="scala.reflect.internal.SymbolTable.scala$reflect$internal$Types$$uniques"
+            problemName=IncompatibleResultTypeProblem
+        },
+        {
+            matchName="scala.reflect.internal.SymbolTable.scala$reflect$internal$Types$$uniques_="
+            problemName=IncompatibleMethTypeProblem
+        },
+        {
+            matchName="scala.reflect.internal.Types.scala$reflect$internal$Types$$uniques"
+            problemName=IncompatibleResultTypeProblem
+        },
+        {
+            matchName="scala.reflect.internal.Types.scala$reflect$internal$Types$$uniques_="
+            problemName=IncompatibleMethTypeProblem
+        },
+        {
+            matchName="scala.reflect.internal.Types.scala$reflect$internal$Types$$uniques"
+            problemName=MissingMethodProblem
+        },
+        {
+            matchName="scala.reflect.internal.Types.scala$reflect$internal$Types$$uniques_="
+            problemName=MissingMethodProblem
         }
     ]
 }
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
     }