Do not redundantly recurse during updateFromPrefab with larger prefab instance hierarchies

Ensure that external prefab game object references are broken on prefab deserialization (not tested if this works)

BansheeCore/Include/BsGameObjectManager.h

@@ -110,7 +110,7 @@ namespace BansheeEngine
 		//  - 1. Resolves all GameObjectHandles on deserialization
 		//    - We can't just resolve them as we go because during deserialization not all objects
 		//      have necessarily been created.
-		//  - 2. Maps serialized IDs to actual in-engine ids. 
+		//  - 2. Maps serialized IDs to actual in-engine IDs. 
 
 		/**
 		 * @brief	Needs to be called whenever GameObject deserialization starts. Must be followed

BansheeCore/Include/BsPrefab.h

@@ -29,13 +29,9 @@ namespace BansheeEngine
 		 *			scene object hierarchy. The returned hierarchy will be parented
 		 *			to world root by default.
 		 *			
-		 * @param	onlyClone	If true the internal prefab hierarchy will be cloned and returned, but not actually 
-		 * 						instantiated. Caller must ensure to call ::instantiate on the returned scene object. 
-		 * 						If false the returned scene object will be instantiated before returning.
-		 * 						
-		 * @returns	Clone of the prefab's scene object hierarchy.
+		 * @returns	Instantiated clone of the prefab's scene object hierarchy.
 		 */
-		HSceneObject instantiate(bool onlyClone = false);
+		HSceneObject instantiate();
 
 		/**
 		 * @brief	Replaces the contents of this prefab with new contents
@@ -52,6 +48,13 @@ namespace BansheeEngine
 		 */
 		HSceneObject _getRoot() const { return mRoot; }
 
+		/**
+		 * @brief	Creates the clone of the prefab's current hierarchy but doesn't instantiate it.
+		 *			
+		 * @returns	Clone of the prefab's scene object hierarchy.
+		 */
+		HSceneObject _clone();
+
 		/**
 		 * @brief	Returns a hash value that can be used for determining if a prefab changed
 		 *			by comparing it to a previously saved hash.

BansheeCore/Include/BsPrefabRTTI.h

@@ -27,6 +27,14 @@ namespace BansheeEngine
 			addPlainField("mNextLinkId", 2, &PrefabRTTI::getNextLinkId, &PrefabRTTI::setNextLinkId);
 		}
 
+		virtual void onDeserializationStarted(IReflectable* ptr) override
+		{
+			// Make sure external IDs are broken because we do some ID matching when dealing with prefabs and keeping
+			// the invalid external references could cause it to match invalid objects in case they end up having the
+			// same ID.
+			GameObjectManager::instance().setDeserializationMode(GODM_UseNewIds | GODM_BreakExternal);
+		}
+
 		virtual const String& getRTTIName() override
 		{
 			static String name = "Prefab";

BansheeCore/Source/BsPrefab.cpp

@@ -108,7 +108,7 @@ namespace BansheeEngine
 		mHash++;
 	}
 
-	HSceneObject Prefab::instantiate(bool onlyClone)
+	HSceneObject Prefab::instantiate()
 	{
 		if (mRoot == nullptr)
 			return HSceneObject();
@@ -136,16 +136,21 @@ namespace BansheeEngine
 		}
 #endif
 
-		mRoot->mPrefabHash = mHash;
-
-		HSceneObject clone = mRoot->clone();
-
-		if (!onlyClone)
-			clone->instantiate();
+		HSceneObject clone = _clone();
+		clone->instantiate();
 		
 		return clone;
 	}
 
+	HSceneObject Prefab::_clone()
+	{
+		if (mRoot == nullptr)
+			return HSceneObject();
+
+		mRoot->mPrefabHash = mHash;
+		return mRoot->clone();
+	}
+
 	RTTITypeBase* Prefab::getRTTIStatic()
 	{
 		return PrefabRTTI::instance();

BansheeCore/Source/BsPrefabDiff.cpp

@@ -382,7 +382,7 @@ namespace BansheeEngine
 			String uuid;
 		};
 
-		// When renaming it is important to rename the instance and not the prefab, since the diff will otherwise
+		// When renaming it is important to rename the prefab and not the instance, since the diff will otherwise
 		// contain prefab's IDs, but will be used for the instance.
 
 		Stack<StackEntry> todo;

BansheeCore/Source/BsPrefabUtility.cpp

@@ -103,7 +103,7 @@ namespace BansheeEngine
 				PrefabDiffPtr prefabDiff = current->mPrefabDiff;
 
 				current->destroy(true);
-				HSceneObject newInstance = prefabLink->instantiate(true);
+				HSceneObject newInstance = prefabLink->_clone();
 
 				// When restoring instance IDs it is important to make all the new handles point to the old GameObjectInstanceData.
 				// This is because old handles will have different GameObjectHandleData and we have no easy way of accessing it to