Introduce SharedFlow collect overload and override that return Nothing (Kotlin#2803)

* Introduce SharedFlow collect overload and override that return Nothing
* Override will ensure the proper implementation of the interface
* collect extension is added as the very basic lint helper

Fixes Kotlin#2789
Fixes Kotlin#2502

Co-authored-by: dkhalanskyjb <[email protected]>

Author: 2 people

kotlinx-coroutines-core/api/kotlinx-coroutines-core.api

@@ -902,6 +902,7 @@ public final class kotlinx/coroutines/flow/FlowKt {
 	public static final fun channelFlow (Lkotlin/jvm/functions/Function2;)Lkotlinx/coroutines/flow/Flow;
 	public static final fun collect (Lkotlinx/coroutines/flow/Flow;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
 	public static final fun collect (Lkotlinx/coroutines/flow/Flow;Lkotlin/jvm/functions/Function2;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
+	public static final fun collect (Lkotlinx/coroutines/flow/SharedFlow;Lkotlin/jvm/functions/Function2;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
 	public static final fun collectIndexed (Lkotlinx/coroutines/flow/Flow;Lkotlin/jvm/functions/Function3;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
 	public static final fun collectLatest (Lkotlinx/coroutines/flow/Flow;Lkotlin/jvm/functions/Function2;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
 	public static final fun combine (Lkotlinx/coroutines/flow/Flow;Lkotlinx/coroutines/flow/Flow;Lkotlin/jvm/functions/Function3;)Lkotlinx/coroutines/flow/Flow;
@@ -1063,6 +1064,7 @@ public abstract interface class kotlinx/coroutines/flow/MutableStateFlow : kotli
 }
 
 public abstract interface class kotlinx/coroutines/flow/SharedFlow : kotlinx/coroutines/flow/Flow {
+	public abstract fun collect (Lkotlinx/coroutines/flow/FlowCollector;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
 	public abstract fun getReplayCache ()Ljava/util/List;
 }
 

kotlinx-coroutines-core/common/src/flow/SharedFlow.kt

@@ -129,6 +129,19 @@ public interface SharedFlow<out T> : Flow<T> {
      * A snapshot of the replay cache.
      */
     public val replayCache: List<T>
+
+    /**
+     * Accepts the given [collector] and [emits][FlowCollector.emit] values into it.
+     * This method should never be used directly. To emit values from a shared flow into a specific collector, either `collector.emitAll(flow)` or `collect { ... }` extension
+     * should be used.
+     *
+     * **A shared flow never completes**. A call to [Flow.collect] or any other terminal operator
+     * on a shared flow never completes normally.
+     *
+     * @see [Flow.collect]
+     */
+    @InternalCoroutinesApi
+    override suspend fun collect(collector: FlowCollector<T>): Nothing
 }
 
 /**
@@ -344,7 +357,7 @@ internal open class SharedFlowImpl<T>(
         get() = buffer!!.getBufferAt(replayIndex + replaySize - 1) as T
 
     @Suppress("UNCHECKED_CAST")
-    override suspend fun collect(collector: FlowCollector<T>) {
+    override suspend fun collect(collector: FlowCollector<T>): Nothing {
         val slot = allocateSlot()
         try {
             if (collector is SubscribedFlowCollector) collector.onSubscription()

kotlinx-coroutines-core/common/src/flow/StateFlow.kt

@@ -380,7 +380,7 @@ private class StateFlowImpl<T>(
         throw UnsupportedOperationException("MutableStateFlow.resetReplayCache is not supported")
     }
 
-    override suspend fun collect(collector: FlowCollector<T>) {
+    override suspend fun collect(collector: FlowCollector<T>): Nothing {
         val slot = allocateSlot()
         try {
             if (collector is SubscribedFlowCollector) collector.onSubscription()

kotlinx-coroutines-core/common/src/flow/terminal/Collect.kt

@@ -73,6 +73,19 @@ public suspend inline fun <T> Flow<T>.collect(crossinline action: suspend (value
         override suspend fun emit(value: T) = action(value)
     })
 
+/**
+ * Terminal flow operator that collects the given [SharedFlow] with the provided [action].
+ * If any exception occurs during `collect` or in the provided flow, this exception is rethrown from this method.
+ *
+ * This is a counterpart of a regular [Flow.collect] extension, only different in the return type
+ * so that any code below `collect` produces a compilation warning.
+ */
+public suspend inline fun <T> SharedFlow<T>.collect(crossinline action: suspend (value: T) -> Unit): Nothing {
+    collect(object : FlowCollector<T> {
+        override suspend fun emit(value: T) = action(value)
+    })
+}
+
 /**
  * Terminal flow operator that collects the given flow with a provided [action] that takes the index of an element (zero-based) and the element.
  * If any exception occurs during collect or in the provided flow, this exception is rethrown from this method.