fix: mtt-4516 NetworkList change inside OnNetworkSpawn

com.unity.netcode.gameobjects/Runtime/Core/NetworkBehaviour.cs

@@ -476,6 +476,15 @@ internal void VisibleOnNetworkSpawn()
             {
                 Debug.LogException(e);
             }
+
+            InitializeVariables();
+            if (IsServer)
+            {
+                // Since we just spawned the object and since user code might have modified their NetworkVariable, esp.
+                // NetworkList, we need to mark the object as free of updates.
+                // This should happen for all objects on the machine triggering the spawn.
+                PostNetworkVariableWrite(true);
+            }
         }
 
         internal void InternalOnNetworkDespawn()
@@ -622,12 +631,24 @@ internal void PreNetworkVariableWrite()
             NetworkVariableIndexesToResetSet.Clear();
         }
 
-        internal void PostNetworkVariableWrite()
+        internal void PostNetworkVariableWrite(bool forced = false)
         {
-            // mark any variables we wrote as no longer dirty
-            for (int i = 0; i < NetworkVariableIndexesToReset.Count; i++)
+            if (forced)
+            {
+                // Mark every variable as no longer dirty. We just spawned the object and whatever the game code did
+                // during OnNetworkSpawn has been sent and needs to be cleared
+                for (int i = 0; i < NetworkVariableFields.Count; i++)
+                {
+                    NetworkVariableFields[i].ResetDirty();
+                }
+            }
+            else
             {
-                NetworkVariableFields[NetworkVariableIndexesToReset[i]].ResetDirty();
+                // mark any variables we wrote as no longer dirty
+                for (int i = 0; i < NetworkVariableIndexesToReset.Count; i++)
+                {
+                    NetworkVariableFields[NetworkVariableIndexesToReset[i]].ResetDirty();
+                }
             }
 
             MarkVariablesDirty(false);

com.unity.netcode.gameobjects/Runtime/Core/NetworkBehaviourUpdater.cs

@@ -75,10 +75,7 @@ internal void NetworkBehaviourUpdate(NetworkManager networkManager)
                 // Now, reset all the no-longer-dirty variables
                 foreach (var dirtyobj in m_DirtyNetworkObjects)
                 {
-                    for (int k = 0; k < dirtyobj.ChildNetworkBehaviours.Count; k++)
-                    {
-                        dirtyobj.ChildNetworkBehaviours[k].PostNetworkVariableWrite();
-                    }
+                    dirtyobj.PostNetworkVariableWrite();
                 }
                 m_DirtyNetworkObjects.Clear();
             }

com.unity.netcode.gameobjects/Runtime/Core/NetworkObject.cs

@@ -1094,6 +1094,14 @@ public unsafe void Deserialize(FastBufferReader reader)
             }
         }
 
+        internal void PostNetworkVariableWrite()
+        {
+            for (int k = 0; k < ChildNetworkBehaviours.Count; k++)
+            {
+                ChildNetworkBehaviours[k].PostNetworkVariableWrite();
+            }
+        }
+
         internal SceneObject GetMessageSceneObject(ulong targetClientId)
         {
             var obj = new SceneObject

com.unity.netcode.gameobjects/Runtime/NetworkVariable/Collections/NetworkList.cs

@@ -12,7 +12,6 @@ namespace Unity.Netcode
     public class NetworkList<T> : NetworkVariableBase where T : unmanaged, IEquatable<T>
     {
         private NativeList<T> m_List = new NativeList<T>(64, Allocator.Persistent);
-        private NativeList<T> m_ListAtLastReset = new NativeList<T>(64, Allocator.Persistent);
         private NativeList<NetworkListEvent<T>> m_DirtyEvents = new NativeList<NetworkListEvent<T>>(64, Allocator.Persistent);
 
         /// <summary>
@@ -53,7 +52,6 @@ public override void ResetDirty()
             if (m_DirtyEvents.Length > 0)
             {
                 m_DirtyEvents.Clear();
-                m_ListAtLastReset.CopyFrom(m_List.AsArray());
             }
         }
 
@@ -135,26 +133,10 @@ public override void WriteDelta(FastBufferWriter writer)
         /// <inheritdoc />
         public override void WriteField(FastBufferWriter writer)
         {
-            // The listAtLastReset mechanism was put in place to deal with duplicate adds
-            // upon initial spawn. However, it causes issues with in-scene placed objects
-            // due to difference in spawn order. In order to address this, we pick the right
-            // list based on the type of object.
-            bool isSceneObject = m_NetworkBehaviour.NetworkObject.IsSceneObject != false;
-            if (isSceneObject)
+            writer.WriteValueSafe((ushort)m_List.Length);
+            for (int i = 0; i < m_List.Length; i++)
             {
-                writer.WriteValueSafe((ushort)m_ListAtLastReset.Length);
-                for (int i = 0; i < m_ListAtLastReset.Length; i++)
-                {
-                    NetworkVariableSerialization<T>.Write(writer, ref m_ListAtLastReset.ElementAt(i));
-                }
-            }
-            else
-            {
-                writer.WriteValueSafe((ushort)m_List.Length);
-                for (int i = 0; i < m_List.Length; i++)
-                {
-                    NetworkVariableSerialization<T>.Write(writer, ref m_List.ElementAt(i));
-                }
+                NetworkVariableSerialization<T>.Write(writer, ref m_List.ElementAt(i));
             }
         }
 
@@ -528,7 +510,6 @@ public int LastModifiedTick
         public override void Dispose()
         {
             m_List.Dispose();
-            m_ListAtLastReset.Dispose();
             m_DirtyEvents.Dispose();
         }
     }

com.unity.netcode.gameobjects/Tests/Runtime/NetworkShowHideTests.cs

@@ -37,6 +37,17 @@ public override void OnNetworkSpawn()
             {
                 ClientTargetedNetworkObjects.Add(this);
             }
+
+            if (IsServer)
+            {
+                MyListSetOnSpawn.Add(45);
+            }
+            else
+            {
+                Debug.Assert(MyListSetOnSpawn.Count == 1);
+                Debug.Assert(MyListSetOnSpawn[0] == 45);
+            }
+
             base.OnNetworkSpawn();
         }
 
@@ -50,11 +61,14 @@ public override void OnNetworkDespawn()
         }
 
         public NetworkVariable<int> MyNetworkVariable;
+        public NetworkList<int> MyListSetOnSpawn;
 
         private void Awake()
         {
             MyNetworkVariable = new NetworkVariable<int>();
             MyNetworkVariable.OnValueChanged += Changed;
+
+            MyListSetOnSpawn = new NetworkList<int>();
         }
 
         public void Changed(int before, int after)