[NativeAOT] Enum.GetValues(Type) should have an aot safe implementation

[LakshanF]

We have annotated the above API, public static System.Array GetValues(System.Type enumType), as dangerous (RequiresDynamicCode("It might not be possible to create an array of the enum type at runtime. Use the GetValues<TEnum> overload instead.")).

Consider removing the RDC and providing a native AOT safe implementation.

[agocke]

Looks like this already exists as Enum.GetValues<Type>

[LakshanF]

I think we still need an implementation when the source of the type is not known and not able to use the generic one

[MichalPetryka]

Well the issue is that AOT generally requires the type to be known since it can't generate code for every enum possible. So I'm not sure if this would be possible without keeping metadata about every enum.

[MichalStrehovsky]

The problem is with creating the array type at runtime, not with "what values to fill in". We keep enough metadata to be able to fill it in.

We are discussing "fixing" this by having the API return the underlying type of the array. The signature is Array GetValues(Type). It currently returns SomeInt32Enum[] for SomeInt32Enum. But it could also return int[] and still satisfy the contract. There's an upper bound on primitive type arrays and we can pregenerate that.

We did this in the early days of .NET Native. Backtracked on that, but nobody remembers why. We want to try again :).

[Suchiman]

@MichalStrehovsky couldn't the TypeLoader dynamically typeload SomeInt32Enum[] by basing it off the underlying type? Given that they have identical layouts and calling conventions, etc.

[MichalStrehovsky]

@MichalStrehovsky couldn't the TypeLoader dynamically typeload SomeInt32Enum[] by basing it off the underlying type? Given that they have identical layouts and calling conventions, etc.

It would probably leak out from the implementation of generic interfaces on the arrays. Maybe something like cast to IEnumerator(SomeEnum), do GetEnumerator and on the returned enumerator call the non-generic IEnumerator.Current. It would return a boxed Int because it's hardcoded in code. We need shared code over enums to get around that.