Question Managed Plugin Unresolved System.ValueTuple On Build

We have imported a managed plugin into Unity 2021.3 LTS for a UWP project. We have the API compatibility level set to .NETStandard 2.1 in Player settings. We are running into a build error with that plugin where the Unity linker can’t resolve the Item2 field on System.ValueTuple.

According to the Unity documentation here:

“By default, IL2CPP targets .NET 2.0 API compatiblity level. That means it does not support managed plugins targeting .NET 4.5 or consuming any of Windows Runtime APIs. All managed plugins must be targeting .NET 4.5 or equivalent API when using this compatiblity level. You can switch to .NET 4.6 API compatibilty level in Player settings if you wish to lift these restrictions.”

This statement is confusing to me as the second and third sentence seem to contradict each other. Regardless, I have tried switching the API compatibility level between .NET Framework and .NET Standard 2.1, but both fail with the same exception (attached to thread). Interestingly, ValueTuple does resolve and work fine in C# scripts.

My assumption at this time is that this structure simply won’t work in a managed plugin, but I would love confirmation of that and some more understanding on what the restrictions are for managed plugins. It would also be great to understand if there is an alternative way to consume this managed plugin, such as referencing it from the generated solution instead of putting it through Unity's build process.

Thank you for your help and time.

 

The assembly was created to be a plugin for UWP, so, like UWP, the assembly is compiled against a .NET Core variant.

Our target platform is UWP for our application. What sort of options do we have to get around this issue and still utilize the unmodified plugin with our application?

 

Thanks for your replies! No, I cannot share the plugin with you unfortunately. The UniversalWindowPlatform version in use is 6.2.14. UniversalWindowPlatform 5.2.2 is unfortunately very old and also has high security vulnerabilities.

I believe it is complaining about code similar to this in the plugin:

Code (CSharp):

1. (T obj, bool isActive)[] array = new (T obj, bool isActive)[totalSize];
2. for (int index = 0; index < totalSize; ++index)
3. {
4.     array[index].isActive = false;
5. }

 

Thanks for the reply. I wouldn't expect Unity to fix this particular issue. I was trying to understand what the limitations are when it comes to managed plugins. And I think I understand more now what the issue is thanks to your responses.

The managed plugin is a Windows Runtime Component (winmd) that is created to be used as a UWP library. When you create one of these in Visual Studio 2022, it sets the UniversalWindowsPlatform as 6.2.14 and the target platform as .NET Core 5.0. In .NET Core 5.0, ValueTuple is in the System.Runtime assembly, compared to .NET Framework 4.8 (mscorlib) and .NET Standard 2.0/2.1 (netstandard).

To recap then, imported managed plugins should be compiled against .NET Framework 4.8 or .NET Standard 2.0/2.1. I wouldn't recommend UniversalWindowsPlatform 5.2.2 given the reasons I stated in this thread.

Thanks so much for your help.