Migration window does not properly check (and upgrade) dependencies

[thalbern]

Describe the bug

Bug (or missing feature) on upgrading the following scenario:

• Create a prefab with a component that will soon be deprecated (eg BoundingBox)
• Set up some values in the prefab
• Create new scene
• Add instance of that prefab
• Modify values on the instance.
• Try upgrading the scene / the prefab / the project.

In all scenarios the data / gameobject will be migrated but the result is going to be not as expected.

Scenario 1: Upgrading just the scene:

• bounding box on gameobject instance will be removed and new bounds control will be added
• all values will be ported over and nothing will be inherited from the prefab as this version of bounds control is only local to this instance

Expected result: we should after upgrading still conserve the original intend of having the component inherited from the prefab and only some values overridden.

Scenario 2: Upgrading just the prefab:

• bounding box on prefab will be migrated and new bounds control will be added
• prefab result is as expected
• instance in scene will only have the values from the newly added bounds control in the prefab but will have lost all it's overrides from the previous bounding box.

Expected result: On prefab upgrades the tool should automatically show all dependencies in all scenes and inform the user / give them a choice to upgrade the instances in those scenes as well so they're not loosing any data. The obsolete / deprecated component in the prefab can only be removed after successful upgrade/migration of all the instances/dependent game objects.

Note: consider several prefab hierarchies for this as well!

Scenario 3: Upgrading the whole project:

Can result in scenario 1 or 2 randomly depending on which file was found first by the tool.

[thalbern]

Throwing some code snippet here that might be useful for discovering the hierarchy of an instance that needs upgrading:

var boundingBox = gameObject.GetComponent<BoundingBox>();

            // we are based on one or more prefabs so we have to upgrade them first before upgrading our current gameobject
            Boo.Lang.List<PrefabInfo> prefabPaths = new Boo.Lang.List<PrefabInfo>();
            var rootPrefabInstance = boundingBox;
            while (HasPrefab(rootPrefabInstance))
            {
                BoundingBox prefabBox = PrefabUtility.GetCorrespondingObjectFromSource(rootPrefabInstance);
                string prefabPath = PrefabUtility.GetPrefabAssetPathOfNearestInstanceRoot(prefabBox);
                prefabPaths.Add(new PrefabInfo(prefabPath, prefabBox));
                rootPrefabInstance = prefabBox;
            }

            // update prefab hierarchy
            for (int i = prefabPaths.Count - 1; i >= 0; ++i)
            {
                GameObject prefabRoot = PrefabUtility.LoadPrefabContents(prefabPaths[i].path);
                MigrateStage(prefabPaths[i].box);
                UnityEditor.PrefabUtility.SaveAsPrefabAsset(prefabRoot, prefabPaths[i].path);
                PrefabUtility.UnloadPrefabContents(prefabRoot);
            }

            // update actual instance
            MigrateStage(boundingBox);

            // remove bounding box
            if (rootPrefabInstance != boundingBox && prefabPaths.Count != 0)
            {
                int rootIndex = prefabPaths.Count - 1;
                GameObject prefabRoot = PrefabUtility.LoadPrefabContents(prefabPaths[rootIndex].path);
                prefabPaths[rootIndex].box.enabled = false;
                UnityEditor.PrefabUtility.SaveAsPrefabAsset(prefabRoot, prefabPaths[rootIndex].path);
                PrefabUtility.UnloadPrefabContents(prefabRoot);
            }
            else
            {
                Object.DestroyImmediate(boundingBox);
            }

[stale[bot]]

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