Fix EventChannel.filter and .filterIsInstance when chained, fix #953

mirai-core-api/src/commonMain/kotlin/event/EventChannel.kt

@@ -28,6 +28,7 @@ import net.mamoe.mirai.internal.event.ListenerRegistry
 import net.mamoe.mirai.internal.event.registerEventHandler
 import net.mamoe.mirai.utils.MiraiExperimentalApi
 import net.mamoe.mirai.utils.MiraiLogger
+import net.mamoe.mirai.utils.cast
 import java.util.function.Consumer
 import kotlin.coroutines.CoroutineContext
 import kotlin.coroutines.EmptyCoroutineContext
@@ -129,11 +130,12 @@ public open class EventChannel<out BaseEvent : Event> @JvmOverloads internal con
      */
     @JvmSynthetic
     public fun filter(filter: suspend (event: BaseEvent) -> Boolean): EventChannel<BaseEvent> {
+        val parent = this
         return object : EventChannel<BaseEvent>(baseEventClass, defaultCoroutineContext) {
             private inline val innerThis get() = this
 
             override fun <E : Event> (suspend (E) -> ListeningStatus).intercepted(): suspend (E) -> ListeningStatus {
-                return { ev ->
+                val thisIntercepted: suspend (E) -> ListeningStatus = { ev ->
                     val filterResult = try {
                         @Suppress("UNCHECKED_CAST")
                         baseEventClass.isInstance(ev) && filter(ev as BaseEvent)
@@ -141,9 +143,10 @@ public open class EventChannel<out BaseEvent : Event> @JvmOverloads internal con
                         if (e is ExceptionInEventChannelFilterException) throw e // wrapped by another filter
                         throw ExceptionInEventChannelFilterException(ev, innerThis, cause = e)
                     }
-                    if (filterResult) this.invoke(ev)
+                    if (filterResult) this@intercepted.invoke(ev)
                     else ListeningStatus.LISTENING
                 }
+                return parent.run { thisIntercepted.intercepted() }
             }
         }
     }
@@ -203,16 +206,7 @@ public open class EventChannel<out BaseEvent : Event> @JvmOverloads internal con
      * @see filter 获取更多信息
      */
     public fun <E : Event> filterIsInstance(kClass: KClass<out E>): EventChannel<E> {
-        return object : EventChannel<E>(kClass, defaultCoroutineContext) {
+        return filter { kClass.isInstance(it) }.cast()
-            private inline val innerThis get() = this
-
-            override fun <E1 : Event> (suspend (E1) -> ListeningStatus).intercepted(): suspend (E1) -> ListeningStatus {
-                return { ev ->
-                    if (kClass.isInstance(ev)) this.invoke(ev)
-                    else ListeningStatus.LISTENING
-                }
-            }
-        }
     }
 
     /**

mirai-core-api/src/jvmTest/kotlin/event/EventChannelTest.kt

@@ -9,17 +9,62 @@
 
 package net.mamoe.mirai.event
 
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.runBlocking
 import net.mamoe.mirai.event.events.FriendEvent
 import net.mamoe.mirai.event.events.GroupEvent
 import net.mamoe.mirai.event.events.GroupMessageEvent
 import net.mamoe.mirai.event.events.MessageEvent
 import org.junit.jupiter.api.Test
+import java.lang.IllegalStateException
+import kotlin.coroutines.resume
+import kotlin.coroutines.resumeWithException
+import kotlin.coroutines.suspendCoroutine
+import kotlin.test.assertEquals
+import kotlin.test.assertFailsWith
 
 internal class EventChannelTest {
     suspend fun suspendCall() {
 
     }
 
+    data class TE(
+        val x: Int
+    ) : AbstractEvent()
+
+    @Test
+    fun testFilter() {
+        runBlocking {
+            val received = suspendCoroutine<Int> { cont ->
+                GlobalEventChannel
+                    .filterIsInstance<TE>()
+                    .filter {
+                        true
+                    }
+                    .filter {
+                        it.x == 2
+                    }
+                    .filter {
+                        true
+                    }
+                    .subscribeOnce<TE> {
+                        cont.resume(it.x)
+                    }
+
+                launch {
+                    println("Broadcast 1")
+                    TE(1).broadcast()
+                    println("Broadcast 2")
+                    TE(2).broadcast()
+                    println("Broadcast done")
+                }
+            }
+
+            assertEquals(2, received)
+        }
+    }
+
+
     @Suppress("UNUSED_VARIABLE")
     @Test
     fun testVariance() {