Enum type is lost when used in attribute

[Novakov]

Description
Enum type is lost (casted to int32) when used in attribute named argument of type obj.

http://stackoverflow.com/questions/35732830/how-to-preserve-value-type-in-enum

Repro Steps
Create attribute with named argument of type obj. Add that attribute and assign enum value to named argument.

type MyAttribute() =
    inherit Attribute()

    let mutable prop = null

    member this.Prop
        with get(): obj = prop
        and  set(value) = prop <- value


type MyEnum = 
    | A = 1
    | B = 2

[<My(Prop = MyEnum.B)>]
type MyClass = class
    end

let test () =
   let t = typeof<MyClass>
   let a = t.GetCustomAttributes(false).[0] :?> MyAttribute

   let e = a.Prop
   Convert.ToString(e, Globalization.CultureInfo.CurrentCulture)

Expected
test function should return "B". In IL value should be stored as enum.

Actual
test function returns 2. In IL value is stored as int32 - enum type is lost

Version: Microsoft (R) F# Compiler version 14.0.23413.0

[gsomix]

Hey, any news on it? Thanks!

[abelbraaksma]

Why is this actually marked as feature request? Is it by design that the type information is lost, or is it because the underlying type of the enum is int?

[isaevdan]

As for me this looks like a bug, and this does not happen in similar C# code

[cartermp]

@dsyme to comment on the labeling, I personally think it's a bug

[dsyme]

Yes, it can be considered a bug, though it's fix might need an RFC

The translation from Enums to constants is done too early. IIRC the only reason I didn't fix it was a concern that quotations actually see the constant, not the field, and because it would mean storing more information in the TAST which we have to do very carefully w.rt. compat.

We can fix this, but it may need a new quotation node that refines "Const" - that is, the node will continue to match "BasicPatterns.Const" but there is an additional "BasicPatterns.EnumConst" or something that sees this refined information.