Add handling for attempting to repair lost program asset references

- Add handling for when Unity sucks and drops program asset references. This handling has been added to both fix behaviours in the scene and behaviours in prefabs used by the scene.

Assets/UdonSharp/Editor/UdonSharpEditorManager.cs

@@ -464,6 +464,8 @@ static void RunAllUpdates(List<UdonBehaviour> allBehaviours = null)
             if (allBehaviours == null)
                 allBehaviours = GetAllUdonBehaviours();
 
+            RepairPrefabProgramAssets(allBehaviours);
+            RepairProgramAssetLinks(allBehaviours);
             UpdateSerializedProgramAssets(allBehaviours);
             UpdatePublicVariables(allBehaviours);
             UpdateSyncModes(allBehaviours);
@@ -531,6 +533,148 @@ static List<UdonBehaviour> GetAllUdonBehaviours(Scene scene)
             return behaviourList;
         }
 
+        static void RepairPrefabProgramAssets(List<UdonBehaviour> dependencyRoots)
+        {
+            Dictionary<AbstractSerializedUdonProgramAsset, UdonSharpProgramAsset> udonSharpProgramAssetLookup =
+                new Dictionary<AbstractSerializedUdonProgramAsset, UdonSharpProgramAsset>();
+
+            foreach (UdonSharpProgramAsset programAsset in UdonSharpProgramAsset.GetAllUdonSharpPrograms())
+                udonSharpProgramAssetLookup.Add(programAsset.SerializedProgramAsset, programAsset);
+
+            FieldInfo serializedAssetField = typeof(UdonBehaviour).GetField("serializedProgramAsset", BindingFlags.NonPublic | BindingFlags.Instance);
+            FieldInfo serializedObjectReferencesField = typeof(UdonBehaviour).GetField("publicVariablesUnityEngineObjects", BindingFlags.NonPublic | BindingFlags.Instance);
+
+            HashSet<UnityEngine.Object> dependencies = new HashSet<UnityEngine.Object>();
+
+            // Yes, this is not as thorough as AssetDatabase.GetDependencies, it is however much faster and catches the important cases.
+            foreach (UdonBehaviour dependencyRoot in dependencyRoots)
+            {
+                var behaviourDependencies = ((List<UnityEngine.Object>)serializedObjectReferencesField.GetValue(dependencyRoot))?.Where(e => e != null);
+
+                if (behaviourDependencies != null)
+                    dependencies.UnionWith(behaviourDependencies);
+            }
+
+            HashSet<string> prefabsToRepair = new HashSet<string>();
+            List<UdonBehaviour> foundBehaviours = new List<UdonBehaviour>();
+
+            foreach (UnityEngine.Object dependencyObject in dependencies)
+            {
+                if (!PrefabUtility.IsPartOfAnyPrefab(dependencyObject))
+                    continue;
+
+                GameObject prefabRoot = null;
+
+                if (dependencyObject is GameObject dependencyGameObject && PrefabUtility.IsPartOfPrefabAsset(dependencyGameObject))
+                {
+                    prefabRoot = dependencyGameObject;
+                }
+
+                if (prefabRoot)
+                    prefabRoot.GetComponentsInChildren<UdonBehaviour>(true, foundBehaviours);
+                else
+                    foundBehaviours.Clear();
+
+                if (foundBehaviours.Count == 0)
+                    continue;
+
+                foreach (UdonBehaviour behaviour in foundBehaviours)
+                {
+                    if (behaviour.programSource != null)
+                        continue;
+
+                    if (serializedAssetField.GetValue(behaviour) != null)
+                    {
+                        prefabsToRepair.Add(AssetDatabase.GetAssetPath(prefabRoot));
+                        break;
+                    }
+                }
+            }
+
+            foundBehaviours.Clear();
+
+            foreach (string repairPrefab in prefabsToRepair)
+            {
+                GameObject prefabRoot = PrefabUtility.LoadPrefabContents(repairPrefab);
+
+                if (PrefabUtility.IsPartOfImmutablePrefab(prefabRoot))
+                {
+                    PrefabUtility.UnloadPrefabContents(prefabRoot);
+                    continue;
+                }
+
+                try
+                {
+                    prefabRoot.GetComponentsInChildren<UdonBehaviour>(true, foundBehaviours);
+
+                    foreach (UdonBehaviour behaviour in foundBehaviours)
+                    {
+                        if (behaviour.programSource != null)
+                            continue;
+
+                        AbstractSerializedUdonProgramAsset serializedUdonProgramAsset =
+                            (AbstractSerializedUdonProgramAsset) serializedAssetField.GetValue(behaviour);
+
+                        if (serializedUdonProgramAsset == null)
+                            continue;
+
+                        if (udonSharpProgramAssetLookup.TryGetValue(serializedUdonProgramAsset,
+                            out UdonSharpProgramAsset foundProgramAsset))
+                        {
+                            SerializedObject serializedBehaviour = new SerializedObject(behaviour);
+                            serializedBehaviour.FindProperty(nameof(UdonBehaviour.programSource)).objectReferenceValue = foundProgramAsset;
+                            serializedBehaviour.ApplyModifiedPropertiesWithoutUndo();
+
+                            Debug.LogWarning($"Repaired reference to {foundProgramAsset} on prefab {prefabRoot}", prefabRoot);
+                        }
+                    }
+
+                    PrefabUtility.SaveAsPrefabAsset(prefabRoot, repairPrefab);
+                }
+                finally
+                {
+                    PrefabUtility.UnloadPrefabContents(prefabRoot);
+                }
+            }
+        }
+
+        static void RepairProgramAssetLinks(List<UdonBehaviour> udonBehaviours)
+        {
+            Dictionary<AbstractSerializedUdonProgramAsset, UdonSharpProgramAsset> udonSharpProgramAssetLookup =
+                new Dictionary<AbstractSerializedUdonProgramAsset, UdonSharpProgramAsset>();
+
+            foreach (UdonSharpProgramAsset programAsset in UdonSharpProgramAsset.GetAllUdonSharpPrograms())
+                udonSharpProgramAssetLookup.Add(programAsset.SerializedProgramAsset, programAsset);
+
+            foreach (UdonBehaviour behaviour in udonBehaviours)
+            {
+                if (behaviour.programSource != null)
+                    continue;
+
+                SerializedObject serializedBehaviour = new SerializedObject(behaviour);
+                SerializedProperty serializedProgramProperty = serializedBehaviour.FindProperty("serializedProgramAsset");
+
+                AbstractSerializedUdonProgramAsset serializedUdonProgramAsset =
+                    (AbstractSerializedUdonProgramAsset) serializedProgramProperty.objectReferenceValue;
+
+                if (serializedUdonProgramAsset != null)
+                {
+                    if (udonSharpProgramAssetLookup.TryGetValue(serializedUdonProgramAsset,
+                        out UdonSharpProgramAsset foundProgramAsset))
+                    {
+                        serializedBehaviour.FindProperty(nameof(UdonBehaviour.programSource)).objectReferenceValue = foundProgramAsset;
+                        serializedBehaviour.ApplyModifiedPropertiesWithoutUndo();
+
+                        Debug.LogWarning($"Repaired reference to {foundProgramAsset} on {behaviour}");
+                    }
+                }
+                else
+                {
+                    Debug.LogWarning($"Empty UdonBehaviour found on {behaviour.gameObject}", behaviour);
+                }
+            }
+        }
+
         static FieldInfo _serializedAssetField;
         static void UpdateSerializedProgramAssets(List<UdonBehaviour> udonBehaviours)
         {