Empty Span

[kubukoz]

Hello! I've been using something like this to make Trace[IO] bearable:

def defaultSpan[F[_]: Applicative](ep: EntryPoint[F]): Span[F] =
  new Span[F] {
    def put(fields: (String, TraceValue)*): F[Unit] = Applicative[F].unit

    def kernel: F[Kernel] = Applicative[F].pure(Kernel(Map.empty))

    def span(name: String): Resource[F, Span[F]] = ep.root(name)

    def traceId: F[Option[String]] = Applicative[F].pure(None)

    def spanId: F[Option[String]] = Applicative[F].pure(None)

    def traceUri: F[Option[URI]] = Applicative[F].pure(None)

  }

The idea is that Trace.ioTrace requires a default Span that it starts from. The combined usage looks like this:

Trace.ioTrace(Spans.defaultSpan(ep)).flatMap { implicit ioTrace: Trace[IO] =>
  ...
}

You can do it once per app, at startup, and pass the Trace[IO] instance everywhere, which is very convenient and doesn't require any wrapping in Kleisli.

I'd happily contribute something similar, or even provide a shortcut that goes from EntryPoint[IO] straight to IO[Trace[IO]] (to avoid the question of what span to use as the default). Does this seem like a good idea?

[skirsdeda]

👍 Great idea! I was trying to find a sane way to use Trace[IO] with skunk Session being initialized only once in AWS Lambda for multiple requests (using feral). Thanks so much for posting this here :)