trace sdk: add StatusData

[iRevive]

Reference	Link
Spec	https://opentelemetry.io/docs/specs/otel/trace/api/#set-status
Java implementation	StatusData.java

[iRevive]

The spec says:

Description MUST only be used with the Error StatusCode value.

Should we encode StatusData as ADT instead? For example:

sealed abstract class StatusData(val code: StatusCode, description: Option[String])

object StatusData {
  case object Ok extends StatusData(StatusCode.Ok, None)
  case object Unset extends StatusData(StatusCode.Unset, None)
  final case class Error(desc: Option[String]) extends StatusData(StatusCode.Error, desc)
}

[armanbilge]

Sure, I might do something like this.

sealed abstract class StatusData(val code: StatusCode) {
  def description: Option[String]
}

object StatusData {
  case object Ok extends StatusData(StatusCode.Ok) {
    def description: None.type = None
  }
  case object Unset extends StatusData(StatusCode.Unset) {
    def description: None.type = None
  }
  final case class Error(description: Option[String]) extends StatusData(StatusCode.Error)
}

[iRevive]

These apply methods will be needed there:

https://github.com/typelevel/otel4s/pull/325/files#diff-b00a1cedc0fb0cc94255f20aea84be95187a261e07f8ad033de3375f70d43f8cR97-R103

[iRevive]

Technically, we can move them to the SdkSpanBackend

[NthPortal]

would it be better to leave out description entirely if it's None?

[iRevive]

I agree, thanks

[NthPortal]

this isn't really const for Error, and isn't testing that the other two are constant (should assert(StatusData(...) eq expected))

[iRevive]

I renamed the test