Restrict custom functions to be defined only in public static classes.

[schabannes]

This fixes a couple of issues/limitations of the .nt.cs files:

• It shouldn't consider a generic class as it can't set the generic parameter: The fix is to filter out generic class.
• It shouldn't consider generic static methods: To get around this whithout going too deep into scriban (and writing a custom filter) we only restrict the custom function to be in a public static class. All other 'classic' extension methods can be in an internal static class.

Note: the VS plugin need to be updated to apply the same restriction on code completion.

[NeVeSpl]

But let's start from the beginning, what problems are you trying to solve here?

I see only one, Scriban does not work with custom functions that are generic, am I missing something else?

[schabannes]

Yes, that is correct it's all related to generic class that will break the compilation of the .nt.cs files. The fix is the extra where clause '!x.ContainsGenericParameters', the second condition (public+static) avoid exposing non Scriban custom function (e.g. extension methods). However it will be a breaking change (quite small to fix, but still breaking). We could put that behind a feature switch (adding one extra settings to the GlobalConfig) or remove it.

I don't know the impact on your VS plugin though.

[NeVeSpl]

So basically you want to fix problems that no one has, by introducing breaking changes to every existing *.nt.cs. file. :D

I hope that it is very clear how bad that idea is.

From my perspective adding information to documentation about generics would be enough.

I would consider adding emitting some warnings/errors if someone would use generic class/methods, but this is so a rare use case that I am not sure it is worth doing it.