Jetpack Compose version:

androidx.compose.compiler:compiler:1.5.6
androidx.compose:compose-bom:2023.10.01

Jetpack Compose component used: compiler and runtime

Android Studio Build:

Hedgehog | 2023.1.1
Build #AI-231.9392.1.2311.11076708, built on November 9, 2023

Kotlin version: 1.9.21

I encountered this crash upgrading Kotlin from 1.9.20 to 1.9.21. When I switched our project to Kotlin 1.9.21, one of our compositions started to crash.

I isolated the crash to this minimal sample:

import androidx.compose.runtime.Composable
import app.cash.molecule.RecompositionMode.Immediate
import app.cash.molecule.moleculeFlow
import kotlinx.coroutines.flow.first
import kotlinx.coroutines.runBlocking
import org.junit.Test

class ImbalanceTest {

  @Composable
  fun goBoom(): Boolean {
    run {
      if (true) {
        return@run
      } else {
        Unit::toString
        return@run
      }
    }

    return true
  }

  @Test fun test() {
    val flow = moleculeFlow(Immediate) {
      goBoom()
    }
    runBlocking {
      flow.first()
    }
  }
}

This sample uses Molecule to start the composition in a test case. I don’t believe Molecule is necessary to reproduce this.

Stack trace (if applicable):

Compose Runtime internal error. Unexpected or incorrect use of the Compose internal runtime API (Start/end imbalance). Please report to Google or use https://goo.gle/compose-feedback
androidx.compose.runtime.ComposeRuntimeError: Compose Runtime internal error. Unexpected or incorrect use of the Compose internal runtime API (Start/end imbalance). Please report to Google or use https://goo.gle/compose-feedback
	at app//androidx.compose.runtime.ComposerKt.composeRuntimeError(Composer.kt:4557)
	at app//androidx.compose.runtime.ComposerImpl.finalizeCompose(Composer.kt:4743)
	at app//androidx.compose.runtime.ComposerImpl.endRoot(Composer.kt:1456)
	at app//androidx.compose.runtime.ComposerImpl.doCompose(Composer.kt:3355)
	at app//androidx.compose.runtime.ComposerImpl.composeContent$runtime_release(Composer.kt:3273)
	at app//androidx.compose.runtime.CompositionImpl.composeContent(Composition.kt:588)
	at app//androidx.compose.runtime.Recomposer.composeInitial$runtime_release(Recomposer.kt:1013)
	at app//androidx.compose.runtime.CompositionImpl.setContent(Composition.kt:520)
	at app//app.cash.molecule.MoleculeKt.launchMolecule(molecule.kt:200)
	at app//app.cash.molecule.MoleculeKt.launchMolecule$default(molecule.kt:165)
	at app//app.cash.molecule.MoleculeKt$immediateClockFlow$1$1$1.invokeSuspend(molecule.kt:66)
	at app//app.cash.molecule.MoleculeKt$immediateClockFlow$1$1$1.invoke(molecule.kt)
	at app//app.cash.molecule.MoleculeKt$immediateClockFlow$1$1$1.invoke(molecule.kt)
	at app//kotlinx.coroutines.intrinsics.UndispatchedKt.startCoroutineUndispatched(Undispatched.kt:44)
	at app//kotlinx.coroutines.CoroutineStart.invoke(CoroutineStart.kt:112)
	at app//kotlinx.coroutines.AbstractCoroutine.start(AbstractCoroutine.kt:126)
	at app//kotlinx.coroutines.BuildersKt__Builders_commonKt.launch(Builders.common.kt:56)
	at app//kotlinx.coroutines.BuildersKt.launch(Unknown Source)
	at app//app.cash.molecule.MoleculeKt$immediateClockFlow$1$1.invokeSuspend(molecule.kt:65)
	at app//app.cash.molecule.MoleculeKt$immediateClockFlow$1$1.invoke(molecule.kt)
	at app//app.cash.molecule.MoleculeKt$immediateClockFlow$1$1.invoke(molecule.kt)
	at app//kotlinx.coroutines.intrinsics.UndispatchedKt.startUndispatchedOrReturn(Undispatched.kt:78)
	at app//kotlinx.coroutines.CoroutineScopeKt.coroutineScope(CoroutineScope.kt:264)
	at app//app.cash.molecule.MoleculeKt$immediateClockFlow$1.invokeSuspend(molecule.kt:61)
	at app//app.cash.molecule.MoleculeKt$immediateClockFlow$1.invoke(molecule.kt)
	at app//app.cash.molecule.MoleculeKt$immediateClockFlow$1.invoke(molecule.kt)
	at app//kotlinx.coroutines.flow.SafeFlow.collectSafely(Builders.kt:61)
	at app//kotlinx.coroutines.flow.AbstractFlow.collect(Flow.kt:230)
	at app//kotlinx.coroutines.flow.FlowKt__ReduceKt.first(Reduce.kt:198)
	at app//kotlinx.coroutines.flow.FlowKt.first(Unknown Source)
	at app//com.squareup.cash.ImbalanceTest$test$1.invokeSuspend(ImbalanceTest.kt:32)

I believe the return@run lines are particularly problematic here. Replacing those lines with Unit prevents the crash.

I believe this is related to another bug from August 2021. https://issuetracker.google.com/issues/195242921