Make a serialization upgrade path for maxStep. (#3424) (#3434)

- Test comment out as we need a package that is only verified for 2019.2.

Author: surfnerd

Project/ProjectSettings/EditorBuildSettings.asset

@@ -4,5 +4,8 @@
 EditorBuildSettings:
   m_ObjectHideFlags: 0
   serializedVersion: 2
-  m_Scenes: []
+  m_Scenes:
+  - enabled: 1
+    path: Packages/com.unity.ml-agents/Tests/Runtime/SerializeTestScene.unity
+    guid: 60783bd849bd242eeb66243542762b23
   m_configObjects: {}

com.unity.ml-agents/Runtime/Agent.cs

@@ -106,11 +106,25 @@ internal struct AgentAction
         "docs/Learning-Environment-Design-Agents.md")]
     [Serializable]
     [RequireComponent(typeof(BehaviorParameters))]
-    public abstract class Agent : MonoBehaviour
+    public abstract class Agent : MonoBehaviour, ISerializationCallbackReceiver
     {
         IPolicy m_Brain;
         BehaviorParameters m_PolicyFactory;
 
+        /// This code is here to make the upgrade path for users using maxStep
+        /// easier.  We will hook into the Serialization code and make sure that
+        /// agentParameters.maxStep and this.maxStep are in sync.
+        [Serializable]
+        internal struct AgentParameters
+        {
+            public int maxStep;
+        }
+
+        [SerializeField] [HideInInspector]
+        internal AgentParameters agentParameters;
+        [SerializeField] [HideInInspector]
+        internal bool hasUpgradedFromAgentParameters;
+
         /// <summary>
         /// The maximum number of steps the agent takes before being done.
         /// </summary>
@@ -187,6 +201,26 @@ void OnEnable()
             LazyInitialize();
         }
 
+
+        public void OnBeforeSerialize()
+        {
+            if (maxStep == 0 && maxStep != agentParameters.maxStep && !hasUpgradedFromAgentParameters)
+            {
+                maxStep = agentParameters.maxStep;
+
+            }
+            hasUpgradedFromAgentParameters = true;
+        }
+
+        public void OnAfterDeserialize()
+        {
+            if (maxStep == 0 && maxStep != agentParameters.maxStep && !hasUpgradedFromAgentParameters)
+            {
+                maxStep = agentParameters.maxStep;
+            }
+            hasUpgradedFromAgentParameters = true;
+        }
+
         /// Helper method for the <see cref="OnEnable"/> event, created to
         /// facilitate testing.
         public void LazyInitialize()
@@ -215,7 +249,6 @@ public void LazyInitialize()
             ResetData();
             InitializeAgent();
             InitializeSensors();
-
         }
 
         /// Monobehavior function that is called when the attached GameObject

com.unity.ml-agents/Tests/Runtime.meta

@@ -0,0 +1,51 @@
+// using System.Collections;
+// using NUnit.Framework;
+// #if UNITY_EDITOR
+// using UnityEditor.SceneManagement;
+// using UnityEngine.TestTools;
+// #endif
+// using UnityEngine;
+// using UnityEngine.SceneManagement;
+//
+// namespace Tests
+// {
+//     [TestFixture]
+//     public class SerializationTest
+//     {
+//
+//         [SetUp]
+//         public void Setup()
+//         {
+//             SceneManager.LoadScene("Packages/com.unity.ml-agents/Tests/Runtime/SerializeTestScene");
+//         }
+//
+//         /// <summary>
+//         /// Test that the serialized agent in the scene, which has its agent parameter value serialized,
+//         /// properly deserializes it to Agent.maxStep.
+//         /// </summary>
+//         [UnityTest]
+//         public IEnumerator SerializationTestSimplePasses()
+//         {
+//             // Use the Assert class to test conditions
+//             var gameObjects = SceneManager.GetActiveScene().GetRootGameObjects();
+//             if (SceneManager.GetActiveScene().name != "SerializeTestScene")
+//             {
+//                 yield return null;
+//             }
+//
+//             GameObject agent = null;
+//             foreach (var go in gameObjects)
+//             {
+//                 if (go.name == "Agent")
+//                 {
+//                     agent = go;
+//                     break;
+//                 }
+//             }
+//             Assert.NotNull(agent);
+//             var agentComponent = agent.GetComponent<SerializeAgent>();
+//             Assert.True(agentComponent.maxStep == 5000);
+//
+//         }
+//     }
+// }

com.unity.ml-agents/Tests/Runtime/SerializationTest.cs

@@ -0,0 +1,12 @@
+using System.Collections;
+using System.Collections.Generic;
+using UnityEngine;
+using MLAgents;
+
+public class SerializeAgent : Agent
+{
+    public override float[] Heuristic()
+    {
+        return new[] {0f};
+    }
+}