Unexpected finalization of uncancelable resource

Scala version: 2.13.6 Cats-effect version: 3.2.9

Minimal example:

import cats.effect.{IO, IOApp, Resource}
import cats.effect.syntax.monadCancel._

object Main extends IOApp.Simple {

  def resource(prefix: String): Resource[IO, Unit] =
    Resource.makeCase(IO.unit) {
      case (_, Resource.ExitCase.Succeeded) => IO.println(s"[$prefix]. Release. Success")
      case (_, Resource.ExitCase.Errored(e)) => IO.println(s"[$prefix]. Release. Error: $e")
      case (_, Resource.ExitCase.Canceled) => IO.println(s"[$prefix]. Release. Canceled")
    }

  def run: IO[Unit] =
    for {
      r1 <- resource("general").use(_ => IO.raiseError(new RuntimeException("oops"))).attempt

      // emulate error
      r2 <- resource("uncancelable").uncancelable.use(_ => IO.raiseError(new RuntimeException("oops"))).attempt

      // emulate cancelation
      d <- IO.deferred[Unit]
      fiber <- resource("uncancelable cancel").uncancelable.use(_ => d.complete(()) >> IO.never).start
      _ <- d.get // wait till `use` hit `never`
      _ <- fiber.cancel
      
      _ <- IO.println("r1: " + r1)
      _ <- IO.println("r2: " + r2)
    } yield ()

}

The output:

[general]. Release. Error: java.lang.RuntimeException: oops
[uncancelable]. Release. Success
[uncancelable cancel]. Release. Success

r1: Left(java.lang.RuntimeException: oops)
r2: Left(java.lang.RuntimeException: oops)

For some reason, a resource that has been marked as uncancelable always has ExitCase.Succeeded during the release stage. Even though it has been canceled or completed with an error.

Resource.uncancelable[IO, Unit](_ => resource("uncancelable")) has the same behavior.

[TimWSpence]

If nobody objects, I’m going to have a go at this. I haven’t really dealt with Resource internals before so it should be interesting 😅

[djspiewak]

Give it a shot! 😃 Really this is about implementing an allocatedFull that is dual to applyFull