AOTSupportScanner ignores Odin-serialized ISerializationCallbackReceivers when serialized by SerializeReference attribute

[Gahwon Lee]

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[CreateAssetMenu]
public class RefTest : SerializedScriptableObject
{
    [SerializeReference]
    public object Value = new RefSerialized();

    [Serializable]
    public class RefSerialized : ISerializationCallbackReceiver
    {
        [NonSerialized]
        public HashSet<int> Value;

        [SerializeField]
        [HideInInspector]
        private byte[] _serializationData;

        void ISerializationCallbackReceiver.OnBeforeSerialize()
        {
            _serializationData = SerializationUtility.SerializeValue(Value, DataFormat.Binary);
        }

        void ISerializationCallbackReceiver.OnAfterDeserialize()
        {
            Value = SerializationUtility.DeserializeValue<HashSet<int>>(_serializationData, DataFormat.Binary);
        }
    }
}

What happened?

Under Odin Preferences > AOT Generation (or during build), the Scan Project button does not fully detect necessary Types:

When a field is marked with the [SerializeReference] attribute, Odin does not look at the value during AOT scanning. This results in it missing Types that it needs to codegen for IL2CPP stripping.

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How can we reproduce it?

1. Take the provided code and create the RefTest ScriptableObject in a Resources folder.
2. Attempt AOT Generation Scan Project.
3. Notice that the type HashSet<int> was not added to the list of serialized Types.

Note that the issue happens regardless of whether RefTest derives ScriptableObject or SerializedScriptableObject.

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What version of Unity are you using? What version of Odin are you using? (See "Tools > Odin Inspector > About")

Tested with two versions:

• Unity 2020.1.3f1 with Odin 2.1.12
• Unity 2020.1.6f1 with Odin 3.0.3

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Do you have Editor Only mode enabled?

No

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What operating system are you on?

Windows 10 Pro

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I think this issue can be solved by first getting all SerializeReference FieldInfos using UnityEditor.TypeCache.GetFieldsWithAttribute<SerializeReference>, and then scanning for all objects of the declared types. I would really appreciate it if you also backport this fix to Odin 2.1.x, please. Thank you in advance!