Support arrays of RawRepresentable types

[tonyarnold]

I'm currently using a simple Set of enumerations to represent the role of a user in a certain context within my model, ie:

enum Role: Int16 {
     case licenseManager = 0
     case billingManager = 1
     case owner = 2
}

I would love to be able to declare the following:

// Model
class User: Model {
    @Field("roles")
    var roles: Set<Role>
}

// Migration 
.field("roles", .array(of: .int16), .required)

And have it be queryable, and saved to the database with a column type of smallint[].

Right now, I have to resort to workarounds like:

class User: Model {
    var roles: Set<Role> {
        get {
            Set(rolesRawValues.compactMap { Role(rawValue: $0) })
        }
        set {
            rolesRawValues = Set(newValue.map(\.rawValue))
        }
    }

    @Field("roles")
    var rolesRawValues: Set<Int16>
}

Which makes my Fluent queries end up looking like:

User.query(on: database)
  .filter(\.$rolesRawValues, .custom("@>"), [Role.owner.rawValue])

It's not ideal.

It would be great if this were supported out of the box. I can see that in a few places arrays of Strings have been special cased - include @Enum, but there's no support for other implicitly Codable types like Int and friends.