Sample crashes with Flow serialization issue

[swankjesse]

I’m running the emoji search sample and it’s bitrotted.

2022-08-15 12:46:38.358 6126-6151/com.example.zipline.emojisearch.debug E/Zipline: java.lang.Exception: SerializationException: Class 'ChannelFlowBuilder' is not registered for polymorphic serialization in the scope of 'Flow'.
    Mark the base class as 'sealed' or register the serializer explicitly.
        at captureStack (../../../../../runtime/coreRuntime.kt:86)
        at SerializationException_init_$Create$_0 (kotlinx-serialization-kotlinx-serialization-core-js-ir.js)
        at throwSubtypeNotRegistered_0 (../../../../../Z:/BuildAgent/work/b2fef8360e1bcf3d/core/commonMain/src/kotlinx/serialization/internal/AbstractPolymorphicSerializer.kt:102)
        at throwSubtypeNotRegistered (../../../../../Z:/BuildAgent/work/b2fef8360e1bcf3d/core/commonMain/src/kotlinx/serialization/internal/AbstractPolymorphicSerializer.kt:113)
        at findPolymorphicSerializer (../../../../../Z:/BuildAgent/work/b2fef8360e1bcf3d/core/commonMain/src/kotlinx/serialization/PolymorphicSerializer.kt:109)
        at <anonymous> (../../../../../Z:/BuildAgent/work/b2fef8360e1bcf3d/core/commonMain/src/kotlinx/serialization/internal/AbstractPolymorphicSerializer.kt:32)
        at <anonymous> (../../../../../Polymorphic.kt:89)
        at <anonymous> (../../../../../Z:/BuildAgent/work/b2fef8360e1bcf3d/core/commonMain/src/kotlinx/serialization/encoding/AbstractEncoder.kt:80)
        at <anonymous> (../../../../../commonMainSources/libraries/stdlib/src/kotlin/util/Preconditions.kt:287)
        at <anonymous> (zipline-root-zipline.js)
        at <anonymous> (../../../../../Polymorphic.kt:89)
        at <anonymous> (../../../../../Z:/BuildAgent/work/b2fef8360e1bcf3d/core/commonMain/src/kotlinx/serialization/encoding/AbstractEncoder.kt:80)
        at <anonymous> (../../../../../Z:/BuildAgent/work/b2fef8360e1bcf3d/core/commonMain/src/kotlinx/serialization/encoding/Encoding.kt:287)
        at <anonymous> (zipline-root-zipline.js)
        at <anonymous> (../../../../../Polymorphic.kt:89)
        at encodeToDynamic_0 (../../../../../DynamicEncoders.kt:42)
        at encodeToDynamic (../../../../../Dynamics.kt)
        at encodeToStringFast (../../../../../jsonJs.kt)
        at <anonymous> (../../../../../CallCodec.kt:56)
        at <anonymous> (../../../../../OutboundCallHandler.kt:52)
        at <anonymous> (../../../../../SuspendCallback.kt)
        at <anonymous> (zipline-root-zipline.js)
        at <anonymous> (../../../../../InboundService.kt:713)
        at <anonymous> (../../../../../InboundService.kt)
        at l (zipline-root-zipline.js)
        at <anonymous> (../../../../../src/kotlin/coroutines_13/IntrinsicsJs.kt:163)
        at <anonymous> (../../../../../src/kotlin/coroutines_13/CoroutineImpl.kt:55)
        at <anonymous> (kotlin-kotlin-stdlib-js-ir.js)
        at <anonymous> (../../../../../DispatchedTask.kt:10131)
        at <anonymous> (../../../../../commonMainSources/libraries/stdlib/src/kotlin/util/Standard.kt:153)
        at <anonymous> (../../../../../JSDispatcher.kt:19)
        at apply (native)
        at <anonymous> (../../../../../GlobalBridge.kt:70)
        at <anonymous> (../../../../../platform.kt)
        at <anonymous> (zipline-root-zipline.js)
        at <anonymous> (../../../../../InboundService.kt:835)
        at <anonymous> (../../../../../Endpoint.kt:79)
        at <anonymous> (zipline-root-zipline.js)
        at <anonymous> (../../../../../GlobalBridge.kt)
        at <anonymous> (zipline-root-zipline.js)
        at app.cash.zipline.internal.JsPlatform$Companion$Adapter$GeneratedOutboundService.runJob(platform.kt:37)
        at app.cash.zipline.internal.CoroutineEventLoop$DelayedJob$run$1.invokeSuspend(CoroutineEventLoop.kt:59)
        at app.cash.zipline.internal.CoroutineEventLoop$DelayedJob$run$1.invoke(Unknown Source:8)
        at app.cash.zipline.internal.CoroutineEventLoop$DelayedJob$run$1.invoke(Unknown Source:4)
        at kotlinx.coroutines.intrinsics.UndispatchedKt.startCoroutineUndispatched(Undispatched.kt:55)
        at kotlinx.coroutines.BuildersKt__Builders_commonKt.startCoroutineImpl(Builders.common.kt:198)
        at kotlinx.coroutines.BuildersKt.startCoroutineImpl(Unknown Source:1)
        at kotlinx.coroutines.AbstractCoroutine.start(AbstractCoroutine.kt:134)
        at kotlinx.coroutines.BuildersKt__Builders_commonKt.launch(Builders.common.kt:56)
        at kotlinx.coroutines.BuildersKt.launch(Unknown Source:1)
2022-08-15 12:46:38.358 6126-6151/com.example.zipline.emojisearch.debug E/Zipline:     at kotlinx.coroutines.BuildersKt__Builders_commonKt.launch$default(Builders.common.kt:47)
        at kotlinx.coroutines.BuildersKt.launch$default(Unknown Source:1)
        at app.cash.zipline.internal.CoroutineEventLoop$DelayedJob.run(CoroutineEventLoop.kt:57)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
        at java.lang.Thread.run(Thread.java:920)

[JakeWharton]

Once fixed, if you write a quick Espresso test I'll set up the CI for it.

[swankjesse]

I think the core issue is we have special serialization support for Flow, and we have other special serialization support for the result of a suspend fun, but we don’t have anything for the combination of these features.

The frustrating part here is that Kotlin serialization doesn’t compose the way I want it to for type parameters. In particular I can’t find a way to mark the type parameter as contextual. I can probably find a work around but ugh.

[JakeWharton]

Hmm. There should (almost) never be a reason to have a suspend function that returns a Flow as the async operation can be moved into the flow itself to occur upon collection.

Should we just ban it?

[swankjesse]

Good idea on the immediate problem. I think I’m still in a bad place with the way the serialization of types composes.

[swankjesse]

Fix will be the same as #602