Circe Enumeratum knownDirectSubclasses compile time error

[CharlesAHunt]

Error during compilation of a CirceEnum: knownDirectSubclasses observed before subclass registered

Using:

• Scala - 2.12.1
• enumeratum - 1.5.3
• enumeratum-circe - 1.5.3

Enumeratum ADT looks like:

import enumeratum._
sealed trait Role extends EnumEntry
case object Role extends CirceEnum[Role] with Enum[Role] {
  case object Service extends Role
  case object User extends Role
  val values = findValues
}

For this case, two errors are produced:

[error] knownDirectSubclasses of Role observed before subclass Service registered
[error] knownDirectSubclasses of Role observed before subclass User registered

[lloydmeta]

Hi,

Thanks for posting your issue. Strangely, it seems to work on my computer.

Welcome to the Ammonite Repl 0.8.1
(Scala 2.12.1 Java 1.8.0_101)
@ import $ivy.`com.beachape::enumeratum-circe:1.5.3` 
import $ivy.$                                     
@ {
  import enumeratum._
  sealed trait Role extends EnumEntry
  case object Role extends CirceEnum[Role] with Enum[Role] {
    case object Service extends Role
    case object User extends Role
    val values = findValues
  }
  } 
import enumeratum._

defined trait Role
defined object Role
@ Role.values 
res2: collection.immutable.IndexedSeq[Role] = Vector(Service, User)
@ import io.circe.Json 
import io.circe.Json
@ import io.circe.syntax._ 
import io.circe.syntax._
@ Role.values.foreach { r => println(r.asJson) } 
"Service"
"User"

Are you by any chance using any auto-deriving codecs (perhaps via import) from Circe itself or another helper library? Enumeratum purposely avoids using knownDirectSubclasses because it was buggy in the past (it was supposedly improved recently, but I haven't checked), so I don't think the error comes from this codebase.

[CharlesAHunt]

I am. Looks like that is actually the source of the problem. Thanks!

[lloydmeta]

No problem. Glad I could help :)

[callicles]

@CharlesAHunt What was the issue? facing the same one

[callicles]

Got it, for the next guy that may fall on this error. I have solved by importing the module containing the Enum at the root of my app (extend App) I think that forces the compiler to compile it before the issue is risen (Hypothesis).

[lloydmeta]

Cool, glad you got it figured out.

I'm not sure, but I think the issue was originally resolved by not using full-auto-derivation, and instead using one of the other methods of Codec generation described in the Circe codec guide.

[jukwaa1]

I've just hit the same issue -- does this mean that Circe full automatic derivation can't be used with Enumeratum?

[lloydmeta]

Not necessarily; I think there may be cases where you can use it, but it isn't related to Enumeratum per se.

That error is thrown by knownDirectSubclasses, a method called at compile time by macros used by Circe automatic derivation (which might be calling it via Shapeless). This method was hopelessly broken for a few years (see SI-7046), and recently fixed "95%" by Miles sometime last year.

Essentially, it isn't a perfect fix, so I guess depending on the project, your file layout, the weather, the stars, you might be in the 5% case, where knownDirectSubclasses throws this kind of error. I kid because I don't know when it fails, but as you can see, you're certainly not alone.

Enumeratum was written when that method was pretty much completely borked, so it purposely avoids using it to avoid this problem.

[zergin]

For other poor souls trying to get it to work. For me the fix was to force imports order:

import TextType._
import io.circe.generic.auto._
import de.heikoseeberger.akkahttpcirce.CirceSupport

where TextType extends EnumEntry. It does not matter weather enumerated types are used or not in the class (for me they're not). The only thing that triggered working code path was to have all enumerated types imported before io.circe.generic.auto._.

This seems to work for both generic akka-http application and unit tests with isolated Circe encoding/decoding.

[witi83]

Workaround works for me, thank you!

FWIW, this issue is not reproducible with Scala 2.11.8 (starts with 2.11.9). Maybe Miles' partial fix is the underlying cause of this issue.

[joan38]

Rename your Enum trait to AWhatwver.
It just needs to start with a letter high enough in the alphabetical order.
What a joke.

Using 2.12.2
See: circe/circe#639

[lloydmeta]

Thanks everyone, I've just managed to reproduce this error and used @CharlesAHunt's Role example. I was previously unable to do so because 1. my files were not in the right (or is it wrong?) order for the bug to manifest or 2. I was using Scastie and putting everything in the right order anyways.

In any case I've added my minimal reproduction repo to @joan38 's ticket but I'll link to it here as well just as a reference:

1. https://github.com/lloydmeta/circe-auto-derive-repro
2. On Scastie too https://scastie.scala-lang.org/lloydmeta/0resq7ZBTkSH3smuWnXVUA