PreviousConnectingVisitor: Utilize WeakReference (#730)

Author: staabm

src/Ast/ExpressionFinder.php

@@ -134,6 +134,10 @@ private function findFirstPreviousOfNode(Node $node, callable $filter): ?Node
         // move to previous expression
         $previousStatement = $node->getAttribute(PreviousConnectingVisitor::ATTRIBUTE_PREVIOUS);
         if (null !== $previousStatement) {
+            if ($previousStatement instanceof \WeakReference) {
+                $previousStatement = $previousStatement->get();
+            }
+
             if (! $previousStatement instanceof Node) {
                 throw new ShouldNotHappenException();
             }

src/Ast/PreviousConnectingVisitor.php

@@ -39,7 +39,7 @@ public function enterNode(Node $node)
             && ! $this->previous instanceof Node\Stmt\ClassLike
             && ! $this->previous instanceof VirtualNode
         ) {
-            $node->setAttribute(self::ATTRIBUTE_PREVIOUS, $this->previous);
+            $node->setAttribute(self::ATTRIBUTE_PREVIOUS, \WeakReference::create($this->previous));
         }
 
         return null;