Inference issue with nested async boundaries

[fwbrasil]

The inference of Boundary when two operations are directly nested like Async.run(Async.timeout(1.second)(v)) is failing to compile. Background: #797 (comment)

[hearnadam]

I believe the issue is caused by using automatically propagating Boundaries between functions where the type may have changed, eg timeout (adds a failure type).

The fix is to derive the boundary within the function where the type already contains the expected value. The only issue is that the function must now be inline to expose Ctx type to the underlying macro.

    inline def timeout[E, A: Flat, Ctx](after: Duration)(v: => A < (Abort[E] & Async & Ctx))(
        using frame: Frame
    ): A < (Abort[E | Timeout] & Async & Ctx) =
        if !after.isFinite then v
        else
            summon[Boundary[Ctx, Async & Abort[E | Timeout]]] { (trace, context) =>
                Clock.use { clock =>
                    IO.Unsafe {
                        val sleepFiber = clock.unsafe.sleep(after)
                        val task       = IOTask[Ctx, E | Timeout, A](v, trace, context)
                        sleepFiber.onComplete(_ => discard(task.complete(Result.fail(Timeout(frame)))))
                        task.onComplete(_ => discard(sleepFiber.interrupt()))
                        Async.get(task)
                    }
                }
            }
    end timeout

[hearnadam]

/bounty $75 for a fix that doesn't require inlining the full body of each function

[algora-pbc]

💎 $75 bounty • Kyo

Steps to solve:

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