-Improved performance issue fix for deeply nested LINQ to JSON objects

Src/Newtonsoft.Json.Tests/Linq/JArrayTests.cs

@@ -20,6 +20,15 @@ namespace Newtonsoft.Json.Tests.Linq
       Assert.AreEqual(0, a.Count);
     }
 
+    [Test]
+    public void AddToSelf()
+    {
+      JArray a = new JArray();
+      a.Add(a);
+
+      Assert.IsFalse(ReferenceEquals(a[0], a));
+    }
+
     [Test]
     public void Contains()
     {

Src/Newtonsoft.Json.Tests/PerformanceTests.cs

@@ -703,6 +703,21 @@ namespace Newtonsoft.Json.Tests
         }, "JObject.ToString");
     }
 
+    [Test]
+    public void RecursiveLoop()
+    {
+      JArray a1 = new JArray();
+      JArray a2 = new JArray();
+      JArray a3 = new JArray();
+      JArray a4 = new JArray();
+
+      a1.Add(a2);
+      a2.Add(a3);
+      a3.Add(a4);
+
+
+    }
+
     [Test]
     public void NestedJToken()
     {
@@ -716,7 +731,7 @@ namespace Newtonsoft.Json.Tests
         for (int j = 0; j < i; j++)
         {
           JArray temp = new JArray();
-          ija.AddAndSkipParentCheck(temp);
+          ija.Add(temp);
           ija = temp;
         }
         ija.Add(1);

Src/Newtonsoft.Json/Linq/JContainer.cs

@@ -266,27 +266,16 @@ namespace Newtonsoft.Json.Linq
       if (item == null)
         return new JValue((object) null);
 
-      if (item.Parent != null)
-      {
+      if (skipParentCheck)
+        return item;
+
+      // to avoid a token having multiple parents or creating a recursive loop, create a copy if...
+      // the item already has a parent
+      // the item is being added to itself
+      // the item is being added to the root parent of itself
+      if (item.Parent != null || item == this || (item.HasValues && Root == item))
         item = item.CloneToken();
-      }
-      else
-      {
-        // check whether attempting to add a token to itself
-        // not possible with a value, only a container
-        if (item is JContainer && !skipParentCheck)
-        {
-          JContainer parent = this;
-          while (parent.Parent != null)
-          {
-            parent = parent.Parent;
-          }
-          if (item == parent)
-          {
-            item = item.CloneToken();
-          }
-        }
-      }
+
       return item;
     }