Question IL2CPP regression - fails to resolve generic code that used to compile

I have some generic code in our project that's started spitting out IL2CPP errors on build. This is a regression, as the code used to work in older versions.

Bug report is #1427322

Specifically, the last version the bug is not present in is:
2020.3.32f1

The bug is present in:
2020.3.33f1
2021.3.0.f1

The bug is not present in 2022.0.1f1, probably due to the changes to IL2CPP there.

The repro project contains four files, which is as far as I managed to strip the project down:

Code (csharp):

1.  // IHasObject.cs
2. public interface IHasObject {
3.     object obj { get; }
4. }
5.  
6. // ShapeTrigger.cs
7. using UnityEngine;
8.  
9. public class ShapeTrigger<THasObject, TTrigger> : ScriptableObject
10.     where TTrigger : ShapeTrigger<THasObject, TTrigger>
11.     where THasObject    : IHasObject {
12.  
13.     public ShapeTriggerParent<THasObject, TTrigger> parent;
14. }
15.  
16. //ShapeTriggerParent.cs
17. using UnityEngine;
18.  
19. public class ShapeTriggerParent <THasObject, TTrigger> : ScriptableObject
20.     where TTrigger   : ShapeTrigger<THasObject, TTrigger>
21.     where THasObject : IHasObject {
22.  
23.     public THasObject data;
24. }
25.  
26. //RainArea.cs
27. public class RainArea : ShapeTriggerParent<RainArea.RainTriggerData, RainArea.RainTrigger> {
28.  
29.     public class RainTrigger : ShapeTrigger<RainTriggerData, RainTrigger> { }
30.  
31.     public class RainTriggerData : IHasObject {
32.         public object obj => null;
33.     }
34. }
35.  
36.  

 

Sure!

Code (csharp):

1. Field 'THasObject ShapeTriggerParent`2::data' from 'PATH_TO_PROJECT\Poroject_ShapeTriggerParent2020\Library\ScriptAssemblies\Assembly-CSharp.dll', exception Failed to resolve THasObject
2. UnityEngine.GUIUtility:ProcessEvent (int,intptr,bool&)

and

Code (csharp):

1. Field 'THasObject ShapeTriggerParent`2::data' from 'PATH_TO_PROJECT\Poroject_ShapeTriggerParent2020\Library\PlayerScriptAssemblies\Assembly-CSharp.dll', exception Failed to resolve THasObject
2. UnityEngine.GUIUtility:ProcessEvent (int,intptr,bool&)

The build still finishes when building to Windows Intel 64-bit. I haven't actually looked into what happens if we try to use any of the code, but I assume trying to grab data from a field that doesn't resolve would cause bad things.
On at least one console, the build doesn't complete, though we get the same error (and some others, but we're investigating this first).

 

I just upgraded my Unity version today and I'm having a similar compilation issue. When compiling with IL2cpp I get this error:

Field 'T TerrainGeneration.TerrainDetail`1::generationOptions' from '...\Library\ScriptAssemblies\Assembly-CSharp.dll', exception Failed to resolve GenerationOptionType

The type its complaining about is defined like this:

public abstract class TerrainGenerationEngine<GenerationOptionType> : TerrainGenerationEngine

  where GenerationOptionType : IGeneratorOptions

{

    ...

}

IGeneratorOptions is an interface.

TerrainGenerationEngine (with no generic parameter) is abstract and extends MonoBehaviour.

Going to try to downgrade for now. If you need more info let me know

 

I'm seeing the same thing with the UIWidgets package (version 1.14.2) from the store. We just upgraded to 2021.3.0.2f1 and now we get :
Field 'TPoint UIWidgets.TracksViewBase`2::valueAtCenter' from 'D:\Perforce\StoryEngine_Rick\StoryEngine\Library\ScriptAssemblies\ThirdParty.Runtime.dll', exception Failed to resolve TPoint
(a half dozen times) on code that used to compile fine. I've tried rebuilding assets, deleting my library and rebuilding, etc. and it doesn't help.

 

I'm facing the same problem on Unity 2021.3.1f1 and 2021.3.2f1, the build process is failing when I try to build for Android. When I build the project on Unity 2021.2.17f1 this problem don't occurs.

 

Hello @JoshPeterson,

Do you have some news about this problem?

 

@JoshPeterson This issue (or a really similar one) also happens without IL2CPP. All that is needed for us is a specific set of generics usage while building for win64. Our case number is 1426750. For us this happened while trying to upgrade from 21.2.13f1 to 21.3.2f1

 

I made the same mistake after upgrading the unity version,
These are the 10 mistakes every time,
The timing is addressable packaging and build

 

@JoshPeterson anything more to share about this bug?

 

Hello we are facing same issue
Is there any workaround for this?

 

I deleted these codes and everything went back to normal. Take a look, it may help you.

 

It'd be great to get those details. Mostly wondering if the bug is likely to be an easy fix, or if we should rewrite a bunch of our code to be less generic.

 

Seems that at least for us (without IL2CPP) the bug is fixed in 2021.3.4f1

• Scripting: Fixed a case where the type of generic fields inside generic classes would fail to get resolved when building the project. (1415422)

 

It seems like 2021.3.4f1 might have fixed this issue! We're at least not getting any errors on PC on either mono or il2cpp, will be testing consoles next

 

For anyone wondering if they want to update to this version. Be advised that https://issuetracker.unity3d.com/is...is-overlapping-in-the-inspector-when-expanded is back. So if you have a lot of arrays of serialized classes in it wait for this to be fixed (again ...)

[Edit]
Seems the actual issue is linked under known issues https://issuetracker.unity3d.com/is...n-for-arrays-that-use-custom-property-drawers for those that want to track when it is fixed.

 

@rarepop99 Will the fix come out in 2020 LTS ?
We are currently running 2020.3.35f1 and are having the same issues