Make FlowCollector fun interface, remove redundant extensions (Kotlin…

…#3047)

* It also saves us from the copy-without-imports problem

Addresses Kotlin#3037

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

@@ -919,8 +919,6 @@ public final class kotlinx/coroutines/flow/FlowKt {
 	public static final fun catch (Lkotlinx/coroutines/flow/Flow;Lkotlin/jvm/functions/Function3;)Lkotlinx/coroutines/flow/Flow;
 	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;

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

@@ -8,10 +8,25 @@ package kotlinx.coroutines.flow
  * [FlowCollector] is used as an intermediate or a terminal collector of the flow and represents
  * an entity that accepts values emitted by the [Flow].
  *
- * This interface should usually not be implemented directly, but rather used as a receiver in a [flow] builder when implementing a custom operator.
+ * This interface should usually not be implemented directly, but rather used as a receiver in a [flow] builder when implementing a custom operator,
+ * or with SAM-conversion.
  * Implementations of this interface are not thread-safe.
+ *
+ * Example of usage:
+ *
+ * ```
+ * val flow = getMyEvents()
+ * try {
+ *     flow.collect { value ->
+ *         println("Received $value")
+ *     }
+ *     println("My events are consumed successfully")
+ * } catch (e: Throwable) {
+ *     println("Exception from the flow: $e")
+ * }
+ * ```
  */
-public interface FlowCollector<in T> {
+public fun interface FlowCollector<in T> {
 
     /**
      * Collects the value emitted by the upstream.

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

@@ -50,42 +50,6 @@ public fun <T> Flow<T>.launchIn(scope: CoroutineScope): Job = scope.launch {
     collect() // tail-call
 }
 
-/**
- * Terminal flow operator that collects the given flow with a provided [action].
- * If any exception occurs during collect or in the provided flow, this exception is rethrown from this method.
- *
- * Example of use:
- *
- * ```
- * val flow = getMyEvents()
- * try {
- *     flow.collect { value ->
- *         println("Received $value")
- *     }
- *     println("My events are consumed successfully")
- * } catch (e: Throwable) {
- *     println("Exception from the flow: $e")
- * }
- * ```
- */
-public suspend inline fun <T> Flow<T>.collect(crossinline action: suspend (value: T) -> Unit): Unit =
-    collect(object : FlowCollector<T> {
-        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.