Ensure parallel map Closed error propagation
#1393
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…to map-par-closed-bug
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| // Recurring task with a delay between | ||
| // executions | ||
| val b: Fiber[Unit, Any] < Sync = | ||
| val b: Fiber[Unit, Abort[Nothing]] < Sync = |
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I think It'd be important to not track Abort[Nothing] here. Sorry, I think I indicated that it'd be fine to remove Reducible from Fiber.init but I thought this would still be Any since the underlying impl is IOPromiseBase[Any, A < (Async & S)] but I'm not sure it's possible.
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I think it may still be possible to get rid of Reducible without tracking Abort[Nothing]. I'll give it a try
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We can pull it off by adding a reduce method to Fiber and Fiber.Unsafe
| */ | ||
| def apply[A, S](effect: A < (Abort[EG] & S)): A < (Abort[EG | Masked] & S) | ||
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| given tag: ConcreteTag[Masked] |
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it seems this doesn't need to be in the abstract class?
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I couldn't make it work without it here. If you need to call Abort.run[mask.Masked] within a withMask effect, this is the only way I can figure out to make the ConcreteTag available to the compiler.
| def apply[A, S](effect: A < (Abort[EG] & S)): A < (Abort[EG | Masked] & S) = | ||
| Abort.runPartial[E](effect).map: | ||
| case Result.Success(a) => a | ||
| case Result.Failure(e) => Abort.fail(Wr(e)) |
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Nice insight :) I'm wondering if we could have a more generic version of this mechanism since it's essentially temporarily swapping the tag. I couldn't test it and there's some type safety challenges but I wonder if this could be a good path:
sealed trait Mask[E] extends ArrowEffect[Const[Any], Const[Any]]
object Mask:
def apply[E <: ArrowEffect[?, ?]](using Frame)[A, S](v: A < (E & S))(using eTag: Tag[E], maskTag: Tag[Mask[E]]): A < (Mask[E] & S) =
ArrowEffect.handle(eTag, v) {
[C] => (input, cont) => ArrowEffect.suspendWith(maskTag, input)(cont)
}
def run[E <: ArrowEffect[?, ?]](using Frame)[A, S](v: A < (Mask[E] & S))(using eTag: Tag[E], maskTag: Tag[Mask[E]]): A < (E & S) =
ArrowEffect.handle(maskTag, v) {
[C] => (input: Any, cont) => ArrowEffect.suspendWith(eTag, input)(cont)
}It seems it should work to prevent E suspensions from being handled until Mask.run. Ah, but there's also the challenge that Abort still uses erased tags, though.
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I tried something like this too, but I actually need to preserve the Abort so that I can do error handling. So I can't mask Abort[E] as Mask[Abort[E]], but it would have to be Abort[E] -> Abort[Mask[E]]. That's why we need a specialized approach for abort.
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given that Abort[E1] & Abort[E2] is equivalent to Abort[E1 | E2], it seems Mask[Abort[E1]] would work to mask the appropriate failures? That's considering a scenario where Abort doesn't use erased tags
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Mask[Abort[E1]] would mask the failure, but I would not be able to then call Abort.run and handle the masked case separately from the unmasked case. The use case is that I'm given some effect A < (Abort[E] & S), and I don't know whether Closed is a subtype of E. I need to compose this with an effect of type Unit < Abort[Closed] effect and then handle all errors on it. I need to do something different depending on whether the failure comes from the Closed abort on the second effect or whether it's a failure E from the first effect, which may very well include Closed from some other resource.
) <!-- PRs require an approval from any of the core contributors, other than the PR author. Include this header if applicable: Fixes #issue1, #issue2, ... --> Prerequisite for #1393. See [discussion](#1393 (comment)). ### Problem <!-- Explain here the context, and why you're making this change. What is the problem you're trying to solve? --> The derivation macro for `ConcreteTag` currently does not search for given `ConcreteTag` instances for components `A` and `B` in composite types like `A | B` or `A & B`. This forces users to require implicit evidence for the full composite type in cases where only one of the types is generic (e.g., `def someMethod[E](A < Abort[E | Closed])(using ConcreteTag[E | Closed]) ...`). This creates a more severe problem when one of the types in the intersection isn't known in the type signature, like when one of the types is a dependent type. ### Solution <!-- Describe your solution. Focus on helping reviewers understand your technical approach and implementation decisions. --> Add an implicit search in the `createSingle` method of the `ConcreteTag` derivation macro to look for a given instance prior to trying to construct it from the `TypeRepr`. ### Notes <!-- Add any important additional information as bullet points, such as: - Implementation details reviewers should know about - Open questions and concerns - Limitations --> Also updated some names which hadn't been updated from the previous name `SafeClassTag`.
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@hearnadam @ahoy-jon since Flavio has stepped out, could one of you take a look at this? I think I have addressed all the issues. Regardless of whether we adopt a more general |
| * [[Fiber.Unsafe]] for low-level operations requiring [[AllowUnsafe]] | ||
| */ | ||
| opaque type Fiber[+A, -S] = IOPromiseBase[Any, A < (Async & S)] | ||
| opaque type Fiber[+A, -S <: Abort[Nothing]] = IOPromiseBase[Any, A < (Async & S)] |
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Maybe we should make this change separately? We probably need Scalafix rule? @ahoy-jon
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I think this is quite old 🙂
| * A Fiber that is immediately completed with the provided Result | ||
| */ | ||
| def fromResult[E, A, S](result: Result[E, A < S])(using reduce: Reducible[Abort[E]]): Fiber[A, reduce.SReduced & S] = | ||
| def fromResult[E, A, S](result: Result[E, A < S]): Fiber[A, Abort[E] & S] = |
| reduce: Reducible[Abort[E]], | ||
| frame: Frame | ||
| ): Fiber[A, reduce.SReduced & S2] < (Sync & S & Scope) = | ||
| using frame: Frame |
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these don't need to be named anymore, since you are not using reduce anymore.
3 participants
Fixes #1387
Problem
For concurrent stream transformations using
Channeland/orMeter, there is a bug (#1387) where if the transformation effectffails withAbort[Closed], that failure is interpreted as end-of-stream.Solution
Added
Abort.withMaskwhich allows you to mask anAbortfailure type that may or may not be within a generic type intersection to protect it from being handled accidentally.Notes
A couple significant changes to make this work:
ConcreteTagderivation now does an implicit search forcreateSingleso that the tag for a union can be derived from tags of single typesFiber.initand otherAsyncmethods do not useReducibleto eliminateAbort[Nothing]. Instead, theStype parameter inFiberis constrained to being a subtype ofAbort[Nothing]to reflect the coupling ofFiberto failures.