WriteDelta does not work correctly for NetworkVariable<List<Class>> due to incorrect handling of duplicates in ListSerializer

[harayuu9]

Title

WriteDelta does not work correctly for NetworkVariable<List<Class>> due to incorrect handling of duplicates in ListSerializer

Description

The Duplicate method in the ListSerializer does not make copies of the instances within the list. As a result, when the number of elements in the list changes, it marks the list as Dirty correctly, but changes to the contents of the class instances within the list do not trigger the Dirty state.
The Class in question implements INetworkSerializable and IEquatable as expected, so this behavior is unexpected. Since a simple solution isn’t apparent, I recommend adding a managed version of NetworkList. Additionally, implementing an ILPP error for cases like this would be beneficial.

Reproduce Steps

1. Create a class containing a NetworkVariable<List<Class>>.
2. Add elements to the list and confirm that it correctly triggers the Dirty state.
3. Modify a property of an instance within the list.
4. Observe that it does not trigger the Dirty state.

Actual Outcome

Modifying the properties of instances within the list does not trigger WriteDelta, and the list does not enter the Dirty state.

Expected Outcome

Modifying the properties of instances within the list should trigger the Dirty state for the list as a whole.

Screenshots

(If applicable, add screenshots to help explain your problem)

Environment

• OS: Windows
• Unity Version: 2023.1
• Netcode Version: 1.9.1

Additional Context

Additional context related to the problem is provided below.
Please include logs or code snippets, and if possible, attach a minimal Unity project that reproduces the issue.

[harayuu9]

It doesn’t seem to be an issue with the Dirty flag not being set; rather, it appears to be a problem with WriteDelta in ListSerializer not writing correctly. As an experiment, I replaced WriteDelta with Write(writer, ref value); and similarly modified the Read method, which resolved the issue. Since you have to manually set the Dirty flag for Lists, I still recommend using the Managed version of NetworkList.

[NoelStephensUnity]

@harayuu9
#3081 should get back ported soon to NGO v1.x.x and will be in the NGO v1.12.0 update.
I believe the updates in that PR will resolve the issue you are experiencing with using NetworkVariable<List<Class>>.

[harayuu9]

@NoelStephensUnity
Thank you, I'll check it out when it's backported.