fix: observers not being cleared on despawning NetworkObject (#2009)

Author: NoelStephensUnity

com.unity.netcode.gameobjects/CHANGELOG.md

@@ -20,7 +20,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 ### Removed
 
 ### Fixed
-
+- Fixed issue where `NetworkObject.Observers` was not being cleared when despawned. (#2009)
 - Fixed `NetworkAnimator` could not run in the server authoritative mode. (#2003)
 - Fixed issue where late joining clients would get a soft synchronization error if any in-scene placed NetworkObjects were parented under another `NetworkObject`. (#1985)
 - Fixed issue where `NetworkBehaviourReference` would throw a type cast exception if using `NetworkBehaviourReference.TryGet` and the component type was not found. (#1984)

com.unity.netcode.gameobjects/Runtime/Spawning/NetworkSpawnManager.cs

@@ -811,6 +811,9 @@ internal void OnDespawnObject(NetworkObject networkObject, bool destroyGameObjec
                 SpawnedObjectsList.Remove(networkObject);
             }
 
+            // Always clear out the observers list when despawned
+            networkObject.Observers.Clear();
+
             var gobj = networkObject.gameObject;
             if (destroyGameObject && gobj != null)
             {

testproject/Assets/Tests/Runtime/RpcObserverTests.cs

@@ -140,6 +140,51 @@ private IEnumerator RunRpcObserverTest(List<ulong> nonObservers)
             }
         }
 
+        /// <summary>
+        /// Validates that when a NetworkObject is despawned but not destroyed
+        /// and then re-spawned that the observer list is cleared
+        /// </summary>
+        [UnityTest]
+        public IEnumerator DespawnRespawnObserverTest()
+        {
+            var nonObservers = new List<ulong>();
+            m_ServerRpcObserverObject.ResetTest();
+            // Wait for all clients to report they have spawned an instance of our test prefab
+            yield return WaitForConditionOrTimeOut(m_ServerRpcObserverObject.AllClientsSpawned);
+
+            m_ServerRpcObserverObject.ObserverMessageClientRpc();
+
+            yield return WaitForConditionOrTimeOut(m_ServerRpcObserverObject.AllObserversReceivedRPC);
+            Assert.False(s_GlobalTimeoutHelper.TimedOut, $"Timed out waiting for all clients to receive message!\n" +
+                $"Clients that received the message:{m_ServerRpcObserverObject.GetClientIdsAsString()}");
+            Assert.False(m_ServerRpcObserverObject.NonObserversReceivedRPC(nonObservers), $"Non-observers ({m_ServerRpcObserverObject.GetClientIdsAsString(nonObservers)}) received the RPC message!");
+
+            m_ServerRpcObserverObject.NetworkObject.Despawn(false);
+
+            Assert.True(m_ServerRpcObserverObject.NetworkObject.Observers.Count == 0, $"Despawned {m_ServerRpcObserverObject.name} but it still has {m_ServerRpcObserverObject.NetworkObject.Observers.Count} observers!");
+
+            for (int i = 4; i < NumberOfClients; i++)
+            {
+                nonObservers.Add(m_ClientNetworkManagers[i].LocalClientId);
+                m_ServerNetworkManager.DisconnectClient(m_ClientNetworkManagers[i].LocalClientId);
+            }
+
+            yield return s_DefaultWaitForTick;
+            m_ServerRpcObserverObject.ResetTest();
+            m_ServerRpcObserverObject.NetworkObject.Spawn();
+            m_ServerRpcObserverObject.ObserverMessageClientRpc();
+            yield return WaitForConditionOrTimeOut(m_ServerRpcObserverObject.AllObserversReceivedRPC);
+            Assert.False(s_GlobalTimeoutHelper.TimedOut, $"Timed out waiting for all clients to receive message!\n" +
+                $"Clients that received the message:{m_ServerRpcObserverObject.GetClientIdsAsString()}");
+            Assert.False(m_ServerRpcObserverObject.NonObserversReceivedRPC(nonObservers), $"Non-observers ({m_ServerRpcObserverObject.GetClientIdsAsString(nonObservers)}) received the RPC message!");
+
+            // Always verify the host received the RPC
+            if (m_UseHost)
+            {
+                Assert.True(m_ServerRpcObserverObject.HostReceivedMessage, $"Host failed to receive the ClientRpc with the following observers: {m_ServerRpcObserverObject.GetClientIdsAsString()}!");
+            }
+        }
+
         protected override IEnumerator OnTearDown()
         {
             // Make sure to dispose of the native array