fixes #1796

tests/gc/cyclecollector.nim

@@ -0,0 +1,21 @@
+
+# Program to detect bug #1796 reliably
+
+type
+  Node = ref object
+    a, b: Node
+    leaf: string
+
+proc createCycle(leaf: string): Node =
+  new result
+  result.a = result
+  shallowCopy result.leaf, leaf
+
+proc main =
+  for i in 0 .. 100_000:
+    var leaf = "this is the leaf. it allocates"
+    let x = createCycle(leaf)
+    let y = createCycle(leaf)
+  echo "done ", getOccupiedMem()
+
+main()