Add regression test for coroutines issue KT-49294

compiler/testData/codegen/box/coroutines/kt49294.kt

@@ -0,0 +1,95 @@
+// WITH_STDLIB
+// IGNORE_BACKEND: JVM
+// IGNORE_LIGHT_ANALYSIS
+// FILE: 1.kt
+
+@file:OptIn(ExperimentalTypeInference::class)
+
+import kotlin.experimental.*
+
+fun interface FlowCollector<in T> {
+    suspend fun emit(value: T)
+}
+
+interface SendChannel<in E> {
+    suspend fun send(element: E)
+}
+
+suspend fun <T> Flow<T>.toList(): List<T> {
+    val destination = ArrayList<T>()
+    collect { value ->
+        destination.add(value)
+    }
+    return destination
+}
+
+fun <T> flow(@BuilderInference block: suspend FlowCollector<T>.() -> Unit): Flow<T> = SafeFlow(block)
+
+private class SafeFlow<T>(private val block: suspend FlowCollector<T>.() -> Unit) : Flow<T> {
+    override suspend fun collect(collector: FlowCollector<T>) {
+        collector.block()
+    }
+}
+
+fun <T> channelFlow(@BuilderInference block: suspend SendChannel<T>.() -> Unit): Flow<T> =
+    ChannelFlowBuilder(block)
+
+private open class ChannelFlowBuilder<T>(
+    private val block: suspend SendChannel<T>.() -> Unit
+) : ChannelFlow<T>() {
+    override suspend fun collectTo(scope: SendChannel<T>) =
+        block(scope)
+}
+
+abstract class ChannelFlow<T> : Flow<T> {
+    protected abstract suspend fun collectTo(scope: SendChannel<T>)
+
+    override suspend fun collect(collector: FlowCollector<T>): Unit {
+        collectTo(object : SendChannel<T> {
+            override suspend fun send(element: T) {}
+        })
+    }
+}
+
+interface Flow<out T> {
+    suspend fun collect(collector: FlowCollector<T>)
+}
+
+inline fun <T, R> Flow<T>.map(crossinline transform: suspend (value: T) -> R): Flow<R> = flow {
+    collect { value ->
+        emit(transform(value))
+    }
+}
+
+fun <T, R> Flow<T>.flatMapMerge(transform: suspend (value: T) -> Flow<R>): Flow<R> =
+    map(transform).flattenMerge()
+
+fun <T> Flow<Flow<T>>.flattenMerge(): Flow<T> =
+    ChannelFlowMerge(this)
+
+// FILE: 2.kt
+
+class ChannelFlowMerge<T>(val flow: Flow<Flow<T>>) : ChannelFlow<T>() {
+    override suspend fun collectTo(scope: SendChannel<T>) {
+        flow.collect {}
+    }
+}
+
+// FILE: 3.kt
+
+import kotlin.coroutines.*
+
+fun box(): String {
+    val l: suspend Any.() -> Unit = {
+        flow { emit(1) }.flatMapMerge {
+            channelFlow {
+                val value = channelFlow { send(1) }
+                send(value)
+            }
+        }.toList()
+    }
+    l.startCoroutine(Any(), Continuation(EmptyCoroutineContext) {
+        it.getOrThrow()
+    })
+    return "OK"
+}