When referencing another project that has excel functions >=16 arguments, "a non-collectible assembly may not reference a collectible assembly." error is thrown

[speksen-kb01]

Hello,

Reference project here. I stripped down everything and am using barebones excel-dna:
https://github.com/speksen-kb01/exceldna-minimal-noncollectible-assembly-error

The problem

I am referencing another project in my addin project, and in the referenced project there is an Enum. I have defined two functions that takes this enum as an argument. In the first case, there are less than 16 arguments for a function and it is successfully registered. However when the argument count goes over 16+, I am encountering the "a non-collectible assembly may not reference a collectible assembly" error.

What I am trying to do

I am trying to make a self-updating addin, following this stackoverflow answer:
https://stackoverflow.com/a/30377635
This registration error is caused by .dna file in my project, where I have referenced my other project as an external reference. If you delete this line, everything works and registration is working file as well. This however, locks the dll file, which makes me unable to update this dll file.

What I tried

Using DisableAssemblyContextUnload="true"

This actually makes all the assemblies collectible so there are no non-collectible assemblies generated, this solves the issue. However, it breaks the auto-update. After the dlls are updated, you need to reload your xll file to make your changes applied:

dynamic app = ExcelDnaUtil.Application;
app.RegisterXLL(ExcelDnaUtil.XllPath);

Then RegisterXLL throws this:
Exception thrown: 'System.InvalidOperationException' in Microsoft.CSharp.dll: 'Cannot unload non-collectible AssemblyLoadContext.'

Replacing the references with primitive types

Another solution is to replace Enum type with a string type, and parse it inside the function. This totally works and have no issues, even if you have more than 16+ arguments as long as you don't reference another class or enum for those arguments. Although I'd like to have the option to give out [ExcelHandle]s to my functions, by creating an excel function CreateModelX and returning a handle X from it. I'd have to parse my class from a string or some primitive object[,] otherwise.

Is there any way I can have all these features and not give up on any one of them? I don't really want to disable hot reloading since it is really convinient for the user

[Sergey-Vlasov]

This error is not specific to a reference project. It also happens if the problematic function is in the main add-in dll.

The error occurs inside Expression.Lambda construction. When the number of method arguments is more than 16, it tries to emit a new delegate type. It fails when there is a type from a collectable assembly.

I’ve statically predefined potential delegate types and passed a suitable one to Expression.Lambda construction. It resolved the problem.

[speksen-kb01]

Thank you. I see that there are tests for referencing Enums but did not see for Class 'es (handles as parameters). Would it be safe to assume the current changes also work if I have a Class as 17th parameter?

[Sergey-Vlasov]

@speksen-kb01

Yes, it should work for classes as well.

If you have a test case, I will add a corresponding unit test.