inner class of enum companion not visible from the enum, unless companion is declared after

[yuriy-yarosh]

Compiler version

3.0.2 and 3.1.0-RC2

Minimized code

object StatusCode:
  enum Matcher:
    case ServerError extends Matcher
  end Matcher
end StatusCode

enum StatusCode(code: Int, m: StatusCode.Matcher):
  case InternalServerError extends StatusCode(500, StatusCode.Matcher.ServerError)
end StatusCode

object Main {
  def main(args: Array[String]): Unit = {
    println(StatusCode.InternalServerError)
  }
}

Output

-- Error:
7 |enum StatusCode(code: Int, m: StatusCode.Matcher):
  |                              ^^^^^^^^^^^^^^^^^^
  |                         type Matcher is not a member of object StatusCode

Expectation

When putting the object declaration after the enum declaration it does compile, like so

enum StatusCode(code: Int, m: StatusCode.Matcher):
  case InternalServerError extends StatusCode(500, StatusCode.Matcher.ServerError)
end StatusCode

object StatusCode:
  enum Matcher:
    case ServerError extends Matcher
  end Matcher
end StatusCode

object Main {
  def main(args: Array[String]): Unit = {
    println(StatusCode.InternalServerError)
  }
}

Which is really frustrating.

[yuriy-yarosh]

thanks for the more concise naming @bishabosha, glad that it got some attention.

[bishabosha]

minimised to just an inner class causing the issue:

object StatusCode:                                                                                               
  class Matcher

enum StatusCode(m: StatusCode.Matcher):
  case InternalServerError extends StatusCode(???)

again it is fixed by changing the order:

enum StatusCode(m: StatusCode.Matcher):
  case InternalServerError extends StatusCode(???)

object StatusCode:                                                                                               
  class Matcher

[anatoliykmetyuk]

I traced it to this line (not the root cause):

https://github.com/lampepfl/dotty/blob/ee137ff4bd06139b343034221ef81dffb0fc9825/compiler/src/dotty/tools/dotc/core/SymDenotations.scala#L2042

info appears to be the type of the object StatusCode, and info.decls, the list of the declaration in that object, doesn't contain class Matcher. Probably caused by earlier incorrect typing of that companion object.

[odersky]

Yes, that describes the symptom, but not the cause.