Editor helper for finding (and try to fix) missing Udon references when updating 2018 project to 2019

FixSceneReference.cs

using UnityEngine;
using UnityEditor;
using UnityEditor.Experimental.SceneManagement;
using System.Collections.Generic;
using VRC.SDKBase;
using VRC.Udon;

using UnityObject = UnityEngine.Object;

public class FixSceneReference : EditorWindow {
  const string PROGRAM_SOURCE_PROP = "programSource";
  const string SERIALIZED_ASSET_PROP = "serializedProgramAsset";

  UdonBehaviour[] searchResult;
  Dictionary<UdonBehaviour, UdonBehaviour> prefabMapping = new Dictionary<UdonBehaviour, UdonBehaviour>();
  Vector2 scrollPos;
  bool showMissingOnly;
  UdonBehaviour assignTarget;

  int currentPickerWindow;
  [MenuItem("Tools/Fix Scene UdonBehaviour References")]
  public static void GetWindow() => GetWindow<FixSceneReference>();

  void OnGUI() {
    if (GUILayout.Button("Find Assets")) {
      searchResult = FindObjectsOfType<UdonBehaviour>();
      prefabMapping.Clear();
      scrollPos = Vector2.zero;
    }
    showMissingOnly = EditorGUILayout.ToggleLeft("Show Missing Only", showMissingOnly);
    if (searchResult != null && searchResult.Length > 0) {
      if (GUILayout.Button("Fix All")) {
        foreach (var dest in searchResult) FixOne(dest);
      }
      scrollPos = EditorGUILayout.BeginScrollView(scrollPos);
      EditorGUILayout.BeginVertical();
      var contentColor = GUI.contentColor;
      var options = new GUILayoutOption[] { GUILayout.Height(EditorGUIUtility.singleLineHeight), GUILayout.ExpandWidth(false) };
      foreach (var dest in searchResult) {
        UnityObject progSource = dest.programSource;
        if (progSource != null && showMissingOnly) continue;
        EditorGUILayout.BeginHorizontal();
        if (progSource == null) progSource = dest;
        if (GUILayout.Button(EditorGUIUtility.ObjectContent(progSource, progSource.GetType()), EditorStyles.label, options)) {
          EditorGUIUtility.PingObject(dest);
        }
        GUILayout.FlexibleSpace();
        UdonBehaviour src = dest, last = dest;
        GUI.contentColor = dest.programSource == null ? Color.red : Color.green;
        EditorGUILayout.SelectableLabel(dest.GetInstanceID().ToString(), EditorStyles.textField, options);
        while (prefabMapping.TryGetValue(src, out src)) {
          GUI.contentColor = src.programSource == null ? Color.red : Color.green;
          EditorGUILayout.SelectableLabel(src.GetInstanceID().ToString(), EditorStyles.textField, options);
          if (GUILayout.Button("Ping", EditorStyles.miniButton, options))
            EditorGUIUtility.PingObject(src);
          last = src;
        }
        GUI.contentColor = contentColor;
        if (GUILayout.Button("Fetch Prefab", EditorStyles.miniButton, options)) {
          src = PrefabUtility.GetCorrespondingObjectFromSource(last);
          if (src != null) prefabMapping[last] = src;
        }
        if (GUILayout.Button("Auto Fix", EditorStyles.miniButtonLeft, options)) {
          FixOne(dest);
        }
        if (GUILayout.Button("Manual Fix", EditorStyles.miniButtonRight, options)) {
          assignTarget = dest;
          ShowPicker();
        }
        EditorGUILayout.EndHorizontal();
      }
      GUI.contentColor = contentColor;
      GUILayout.FlexibleSpace();
      EditorGUILayout.EndVertical();
      EditorGUILayout.EndScrollView();
    }
    if (assignTarget != null && Event.current.commandName == "ObjectSelectorUpdated" &&　EditorGUIUtility.GetObjectPickerControlID() == currentPickerWindow) {
      currentPickerWindow = -1;
      if (EditorGUIUtility.GetObjectPickerObject() is AbstractUdonProgramSource destObj) {
        var destSo = new SerializedObject(assignTarget);
        destSo.FindProperty(PROGRAM_SOURCE_PROP).objectReferenceValue = destObj;
        destSo.FindProperty(SERIALIZED_ASSET_PROP).objectReferenceValue = destObj.SerializedProgramAsset;
        destSo.ApplyModifiedProperties();
      }
    }
  }

  public static void FixOne(UdonBehaviour dest) {
    if (dest.programSource != null) return;
    var destSo = new SerializedObject(dest);
    var destProgSoruceProp = destSo.FindProperty(PROGRAM_SOURCE_PROP);
    var destSerializedAssetProp = destSo.FindProperty(SERIALIZED_ASSET_PROP);
    bool replaced = false;
    var parent = dest;
    while (!replaced && parent != null) {
      var assetPath = PrefabUtility.GetPrefabAssetPathOfNearestInstanceRoot(parent);
      parent = PrefabUtility.GetCorrespondingObjectFromSource(parent);
      var siblingPath = GetSiblingPath(dest);
      if (string.IsNullOrEmpty(assetPath)) continue;
      var go = PrefabUtility.LoadPrefabContents(assetPath);
      if (go == null) continue;
      foreach (var x in RecursiveFind<UdonBehaviour>(go))
        if (CompareSiblingPath(GetSiblingPath(x), siblingPath)) {
          var so = new SerializedObject(x);
          var progSoruce = so.FindProperty(PROGRAM_SOURCE_PROP).objectReferenceValue;
          if (progSoruce != null) {
            destProgSoruceProp.objectReferenceValue = progSoruce;
            replaced = true;
          }
          var serializedAsset = so.FindProperty(SERIALIZED_ASSET_PROP).objectReferenceValue;
          if (serializedAsset != null) {
            destSerializedAssetProp.objectReferenceValue = serializedAsset;
            replaced = true;
          }
          destSo.ApplyModifiedProperties();
          break;
        }
      PrefabUtility.UnloadPrefabContents(go);
    }
  }

  public static int[] GetSiblingPath(Component target) {
    var result = new List<int>();
    var transform = target.transform;
    while (transform != null) {
      var parent = transform.parent;
      if (parent == null) break;
      result.Add(transform.GetSiblingIndex());
      transform = parent;
    }
    return result.ToArray();
  }

  public static bool CompareSiblingPath(int[] src, int[] dest) {
    for (int i = 0, l = Mathf.Min(src.Length, dest.Length); i < l; i++) {
      if (src[i] != dest[i]) return false;
    }
    return true;
  }

  public static T[] RecursiveFind<T>(GameObject root) where T : Component {
    var stack = new Stack<Transform>();
    var result = new List<T>();
    stack.Push(root.transform);
    while (stack.Count > 0) {
      var current = stack.Pop();
      result.AddRange(current.GetComponents<T>());
      for (int i = 0, l = current.childCount; i < l; i++)
        stack.Push(current.GetChild(i));
    }
    return result.ToArray();
  }

  void ShowPicker() {
     currentPickerWindow = GUIUtility.GetControlID(FocusType.Passive) + 100;
     EditorGUIUtility.ShowObjectPicker<AbstractUdonProgramSource>(null, false, "", currentPickerWindow);
  }
}