[BUG] Arrow result continuation broken

[ulfryk]

Affected version: 1.1.2
Affected scope: arrow.core.continuations
Kotlin version: 1.7.21

Using result { … } comprehension and binding invokations of suspended functions/methods inside causes unexpected behaviour. Nested Result<Result<X>> values are returned in runtime - despite having Result<X> type in compile time.

Bug affects result { … } and result.eager { … }.
It does NOT affect nullable { … } / nullable.eager { … } or either { … } / either.eager { … }.

Code to reproduce an issue:

import arrow.core.continuations.result
import kotlinx.coroutines.delay

suspend fun main() {
    val ok = result { "whatever" }
    println("The OK Result is: $ok")

    val a = getV()
    println("The A Result is: $a")

    val b = result {
        delay(1)
        "whatever"
    }
    println("The B Result is: $b")

    val c = result {
        getV().bind()
    }
    println("The C Result is: $c")

    val d = result {
        val v = getV().bind()

        v + "__cont"
    }
    println("The D Result is: $d")

}

private suspend fun getV() = result {
    delay(1)
    "whatever"
}

Result of running above code:

The OK Result is: Success(whatever)
The A Result is: Success(Success(whatever))
The B Result is: Success(Success(whatever))
The C Result is: Success(Success(Success(whatever)))
Exception in thread "main" java.lang.ClassCastException: class kotlin.Result cannot be cast to class java.lang.String (kotlin.Result is in unnamed module of loader 'app'; java.lang.String is in module java.base of loader 'bootstrap')
	at com.fiatrepublic.pomerania.oauth2server.pkceimpl.EffectsIssueKt$main$$inlined$invoke-gIAlu-s$4$3.invokeSuspend(Effect.kt:0)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
	at arrow.core.continuations.FoldContinuation.resumeWith(Effect.kt:713)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:46)
	at kotlinx.coroutines.DispatchedTaskKt.resume(DispatchedTask.kt:178)
	at kotlinx.coroutines.DispatchedTaskKt.dispatch(DispatchedTask.kt:166)
	at kotlinx.coroutines.CancellableContinuationImpl.dispatchResume(CancellableContinuationImpl.kt:397)
	at kotlinx.coroutines.CancellableContinuationImpl.resumeImpl(CancellableContinuationImpl.kt:431)
	at kotlinx.coroutines.CancellableContinuationImpl.resumeImpl$default(CancellableContinuationImpl.kt:420)
	at kotlinx.coroutines.CancellableContinuationImpl.resumeUndispatched(CancellableContinuationImpl.kt:518)
	at kotlinx.coroutines.EventLoopImplBase$DelayedResumeTask.run(EventLoop.common.kt:500)
	at kotlinx.coroutines.EventLoopImplBase.processNextEvent(EventLoop.common.kt:284)
	at kotlinx.coroutines.DefaultExecutor.run(DefaultExecutor.kt:108)
	at java.base/java.lang.Thread.run(Thread.java:830)

Process finished with exit code 1

[nomisRev]

Hey @ulfryk,

Thank you for the bug report, including reproducible examples 🙏
I saw you mentioned Affected version: 1.1.2, is this also reproducible in 1.1.3 and/or 1.1.4-rc.3?

[ulfryk]

Hey @nomisRev,

Checked other versions - 1.1.3 has same issue :( but 1.1.4-rc.3 seems to have it fixed 🎉 :

1.1.3

The OK Result is: Success(whatever)
The A Result is: Success(Success(whatever))
The B Result is: Success(Success(whatever))
The C Result is: Success(Success(Success(whatever)))
Exception in thread "main" java.lang.ClassCastException: class kotlin.Result cannot be cast to class java.lang.String (kotlin.Result is in unnamed module of loader 'app'; java.lang.String is in module java.base of loader 'bootstrap')
	at com.fiatrepublic.pomerania.oauth2server.pkceimpl.ArrowIssuesKt$main$$inlined$invoke-gIAlu-s$4.invokeSuspend(result.kt:0)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
	at arrow.core.continuations.FoldContinuation.resumeWith(Effect.kt:756)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:46)
	at kotlinx.coroutines.DispatchedTaskKt.resume(DispatchedTask.kt:178)
	at kotlinx.coroutines.DispatchedTaskKt.dispatch(DispatchedTask.kt:166)
	at kotlinx.coroutines.CancellableContinuationImpl.dispatchResume(CancellableContinuationImpl.kt:397)
	at kotlinx.coroutines.CancellableContinuationImpl.resumeImpl(CancellableContinuationImpl.kt:431)
	at kotlinx.coroutines.CancellableContinuationImpl.resumeImpl$default(CancellableContinuationImpl.kt:420)
	at kotlinx.coroutines.CancellableContinuationImpl.resumeUndispatched(CancellableContinuationImpl.kt:518)
	at kotlinx.coroutines.EventLoopImplBase$DelayedResumeTask.run(EventLoop.common.kt:500)
	at kotlinx.coroutines.EventLoopImplBase.processNextEvent(EventLoop.common.kt:284)
	at kotlinx.coroutines.DefaultExecutor.run(DefaultExecutor.kt:108)
	at java.base/java.lang.Thread.run(Thread.java:830)

Process finished with exit code 1

1.1.4-4c.3

The OK Result is: Success(whatever)
The A Result is: Success(whatever)
The B Result is: Success(whatever)
The C Result is: Success(whatever)
The D Result is: Success(whatever__cont)

Process finished with exit code 0

[nomisRev]

@ulfryk thanks for letting us know ☺️ We're currently rolling out 1.1.4, and will be released this week.
Will close this issue after it's officially released.

[nomisRev]

This fix has been released ☺️ Closing the issue.