Unity editor script that warns the user when an AnimatorController asset changes on disk.

AnimatorControllerChangeDetector.cs

using System;
using System.Collections;
using System.Collections.Generic;
using UnityEditor;

// Detect when .controller assets are modified on disk, and give the user a warning so they
// can restart Unity to pick up the changes.
//
// Workaround for bug #1133706 (AnimatorController assets are not reimported if they contain
// attached StateMachineBehaviour).
public class AnimatorControllerChangeDetector : AssetPostprocessor
{
    static DateTime lastSaveTime;

    static bool IsAnimatorControllerAsset(string assetPath)
    {
        return assetPath.EndsWith(".controller");
    }

    public class SaveProcessor : UnityEditor.AssetModificationProcessor
    {
        static string[] OnWillSaveAssets(string[] paths)
        {
            lastSaveTime = DateTime.Now;
            return paths;
        }
    }

    public class AssetProcessor : AssetPostprocessor
    {
        static void OnPostprocessAllAssets(string[] importedAssets, string[] deletedAssets, string[] movedAssets, string[] movedFromAssetPaths)
        {
            // Ignore changes due to save.  This is obviously a pretty wild hack, but we can't match up
            // whether an asset import is due to save or not, as this function may be called multiple
            // times for a single asset save.
            if ((DateTime.Now - lastSaveTime) < TimeSpan.FromSeconds(1))
                return;

            bool hasModifications = false;
            foreach (string asset in importedAssets)
            {
                if (IsAnimatorControllerAsset(asset))
                {
                    hasModifications = true;
                    UnityEngine.Debug.LogWarning($"{asset} has changed on disk; restart Unity");
                }
            }
            
            if (hasModifications)
                EditorUtility.DisplayDialog("Files changed on disk", "AnimatorController assets have changed on disk, and Unity may not have reloaded them.  Recommend you restart Unity.", "Hooray");
        }
    }
}