CHANGED TO MIRROR

Assets/Mirror/Editor/EnterPlayModeSettingsCheck.cs

@@ -0,0 +1,52 @@
+// Unity 2019.3 has an experimental 'disable domain reload on play'
+// feature. keeping any global state between sessions will break
+// Mirror and most of our user's projects. don't allow it for now.
+// https://blogs.unity3d.com/2019/11/05/enter-play-mode-faster-in-unity-2019-3/
+using UnityEditor;
+using UnityEngine;
+
+namespace Mirror
+{
+    public class EnterPlayModeSettingsCheck : MonoBehaviour
+    {
+        [InitializeOnLoadMethod]
+        static void OnInitializeOnLoad()
+        {
+#if UNITY_2019_3_OR_NEWER
+            // We can't support experimental "Enter Play Mode Options" mode
+            // Check immediately on load, and before entering play mode, and warn the user
+            CheckPlayModeOptions();
+#endif
+
+            // Hook this event to see if we have a good weave every time
+            // user attempts to enter play mode or tries to do a build
+            EditorApplication.playModeStateChanged += OnPlayModeStateChanged;
+        }
+
+        static void OnPlayModeStateChanged(PlayModeStateChange state)
+        {
+            // Per Unity docs, this fires "when exiting edit mode before the Editor is in play mode".
+            // This doesn't fire when closing the editor.
+            if (state == PlayModeStateChange.ExitingEditMode)
+            {
+#if UNITY_2019_3_OR_NEWER
+                // We can't support experimental "Enter Play Mode Options" mode
+                // Check and prevent entering play mode if enabled
+                CheckPlayModeOptions();
+#endif
+            }
+        }
+
+#if UNITY_2019_3_OR_NEWER
+        static void CheckPlayModeOptions()
+        {
+            // enabling the checkbox is enough. it controls all the other settings.
+            if (EditorSettings.enterPlayModeOptionsEnabled)
+            {
+                Debug.LogError("Enter Play Mode Options are not supported by Mirror. Please disable 'ProjectSettings -> Editor -> Enter Play Mode Settings (Experimental)'.");
+                EditorApplication.isPlaying = false;
+            }
+        }
+#endif
+    }
+}