don't undo if only converting prefab assets

- also show warning if exporting prefab instance with object overrides
- warn that overwriting on export cannot be undone

Author: vkovec

com.unity.formats.fbx/Editor/ConvertToNestedPrefab.cs

@@ -113,6 +113,26 @@ public static ExportSettings ExportSettings
             get { return ExportSettings.instance; }
         }
 
+        /// <summary>
+        /// Return true if the given set contains only prefab assets on disk,
+        /// and nothing from the scene.
+        /// </summary>
+        /// <returns></returns>
+        internal static bool SetContainsOnlyPrefabAssets(Object[] toConvert)
+        {
+            foreach (var obj in toConvert)
+            {
+                var go = ModelExporter.GetGameObject(obj);
+                if (go != null && !PrefabUtility.IsPartOfPrefabAsset(go))
+                {
+                    // return as soon as we find something that is not part of a prefab asset
+                    // on disk
+                    return false;
+                }
+            }
+            return true;
+        }
+
         /// <summary>
         /// Create instantiated model prefabs from a selection of objects.
         ///
@@ -153,9 +173,14 @@ public static GameObject[] CreateInstantiatedModelPrefab(
                 return toExport.ToArray();
             }
 
-            Undo.IncrementCurrentGroup();
-            int groupIndex = Undo.GetCurrentGroup();
-            Undo.SetCurrentGroupName(UndoConversionCreateObject);
+            bool onlyPrefabAssets = ConvertToNestedPrefab.SetContainsOnlyPrefabAssets(unityGameObjectsToConvert);
+            int groupIndex = -1;
+            if (!onlyPrefabAssets)
+            {
+                Undo.IncrementCurrentGroup();
+                groupIndex = Undo.GetCurrentGroup();
+                Undo.SetCurrentGroupName(UndoConversionCreateObject);
+            }
             var converted = new List<GameObject>();
             var exportOptions = ExportSettings.instance.ConvertToPrefabSettings.info;
             foreach (var go in toExport)
@@ -166,8 +191,11 @@ public static GameObject[] CreateInstantiatedModelPrefab(
                     converted.Add(convertedGO);
                 }
             }
-            Undo.CollapseUndoOperations(groupIndex);
-            Undo.IncrementCurrentGroup();
+            if (!onlyPrefabAssets && groupIndex >= 0)
+            {
+                Undo.CollapseUndoOperations(groupIndex);
+                Undo.IncrementCurrentGroup();
+            }
             return converted.ToArray();
         }
 

com.unity.formats.fbx/Editor/ConvertToPrefabEditorWindow.cs

@@ -191,9 +191,15 @@ protected override bool Export()
                 return true;
             }
 
-            Undo.IncrementCurrentGroup();
-            int groupIndex = Undo.GetCurrentGroup();
-            Undo.SetCurrentGroupName(ConvertToNestedPrefab.UndoConversionCreateObject);
+            bool onlyPrefabAssets = ConvertToNestedPrefab.SetContainsOnlyPrefabAssets(GetToExport());
+            int groupIndex = -1;
+            // no need to undo if we aren't converting anything that's in the scene
+            if (!onlyPrefabAssets)
+            {
+                Undo.IncrementCurrentGroup();
+                groupIndex = Undo.GetCurrentGroup();
+                Undo.SetCurrentGroupName(ConvertToNestedPrefab.UndoConversionCreateObject);
+            }
             foreach (var obj in GetToExport())
             {
                 // Convert, automatically choosing a file path that won't clobber any existing files.
@@ -202,8 +208,11 @@ protected override bool Export()
                     go, fbxDirectoryFullPath: fbxDirPath, prefabDirectoryFullPath: prefabDirPath, exportOptions: ExportSettings.instance.ConvertToPrefabSettings.info
                 );
             }
-            Undo.CollapseUndoOperations(groupIndex);
-            Undo.IncrementCurrentGroup();
+            if (!onlyPrefabAssets && groupIndex >= 0)
+            {
+                Undo.CollapseUndoOperations(groupIndex);
+                Undo.IncrementCurrentGroup();
+            }
             return true;
         }
 

com.unity.formats.fbx/Editor/ExportModelEditorWindow.cs

@@ -156,6 +156,31 @@ public void OnPresetSelectionChanged()
             this.Repaint ();
         }
 
+        protected bool SelectionContainsPrefabInstanceWithAddedObjects()
+        {
+            var exportSet = GetToExport();
+            Queue<Object> queue = new Queue<Object>(exportSet);
+            while (queue.Count > 0)
+            {
+                var go = ModelExporter.GetGameObject(queue.Dequeue());
+                if (!go)
+                {
+                    continue;
+                }
+
+                if(PrefabUtility.IsAnyPrefabInstanceRoot(go) && PrefabUtility.GetAddedGameObjects(go).Count > 0)
+                {
+                    return true;
+                }
+
+                foreach (Transform child in go.transform)
+                {
+                    queue.Enqueue(child.gameObject);
+                }
+            }
+            return false;
+        }
+
         protected abstract bool Export ();
 
         /// <summary>
@@ -399,6 +424,13 @@ protected void OnGUI ()
                 InnerEditor.OnInspectorGUI ();
             }
 
+            // if we are exporting or converting a prefab with overrides, then show a warning
+            if (SelectionContainsPrefabInstanceWithAddedObjects())
+            {
+                EditorGUILayout.Space();
+                EditorGUILayout.HelpBox("Prefab instance overrides will be exported", MessageType.Warning, true);
+            }
+
             GUILayout.FlexibleSpace ();
 
             GUILayout.BeginHorizontal ();
@@ -430,7 +462,7 @@ protected bool OverwriteExistingFile(string filePath){
             if (System.IO.File.Exists (filePath)) {
                 bool overwrite = UnityEditor.EditorUtility.DisplayDialog (
                     string.Format("{0} Warning", ModelExporter.PACKAGE_UI_NAME), 
-                    string.Format("File {0} already exists.", filePath), 
+                    string.Format("File {0} already exists.\nOverwrite cannot be undone", filePath), 
                     "Overwrite", "Cancel");
                 if (!overwrite) {
                     if (GUI.changed) {