Redesign MessageChain hierarchy: Add LinearMessageChainImpl and CombinedMessage

mirai-core-api/compatibility-validation/android/api/android.api

@@ -3608,7 +3608,7 @@ public final class net/mamoe/mirai/message/data/Dice$Key : net/mamoe/mirai/messa
 	public final fun serializer ()Lkotlinx/serialization/KSerializer;
 }
 
-public final class net/mamoe/mirai/message/data/EmptyMessageChain : java/util/List, kotlin/jvm/internal/markers/KMappedMarker, net/mamoe/mirai/message/data/MessageChain {
+public final class net/mamoe/mirai/message/data/EmptyMessageChain : java/util/List, kotlin/jvm/internal/markers/KMappedMarker, net/mamoe/mirai/message/data/MessageChain, net/mamoe/mirai/message/data/MessageChainImpl {
 	public static final field INSTANCE Lnet/mamoe/mirai/message/data/EmptyMessageChain;
 	public synthetic fun add (ILjava/lang/Object;)V
 	public fun add (ILnet/mamoe/mirai/message/data/SingleMessage;)V
@@ -3624,6 +3624,7 @@ public final class net/mamoe/mirai/message/data/EmptyMessageChain : java/util/Li
 	public fun equals (Ljava/lang/Object;)Z
 	public synthetic fun get (I)Ljava/lang/Object;
 	public fun get (I)Lnet/mamoe/mirai/message/data/SingleMessage;
+	public fun getHasConstrainSingle ()Z
 	public fun getSize ()I
 	public fun hashCode ()I
 	public final fun indexOf (Ljava/lang/Object;)I

mirai-core-api/compatibility-validation/jvm/api/jvm.api

@@ -3608,7 +3608,7 @@ public final class net/mamoe/mirai/message/data/Dice$Key : net/mamoe/mirai/messa
 	public final fun serializer ()Lkotlinx/serialization/KSerializer;
 }
 
-public final class net/mamoe/mirai/message/data/EmptyMessageChain : java/util/List, kotlin/jvm/internal/markers/KMappedMarker, net/mamoe/mirai/message/data/MessageChain {
+public final class net/mamoe/mirai/message/data/EmptyMessageChain : java/util/List, kotlin/jvm/internal/markers/KMappedMarker, net/mamoe/mirai/message/data/MessageChain, net/mamoe/mirai/message/data/MessageChainImpl {
 	public static final field INSTANCE Lnet/mamoe/mirai/message/data/EmptyMessageChain;
 	public synthetic fun add (ILjava/lang/Object;)V
 	public fun add (ILnet/mamoe/mirai/message/data/SingleMessage;)V
@@ -3624,6 +3624,7 @@ public final class net/mamoe/mirai/message/data/EmptyMessageChain : java/util/Li
 	public fun equals (Ljava/lang/Object;)Z
 	public synthetic fun get (I)Ljava/lang/Object;
 	public fun get (I)Lnet/mamoe/mirai/message/data/SingleMessage;
+	public fun getHasConstrainSingle ()Z
 	public fun getSize ()I
 	public fun hashCode ()I
 	public final fun indexOf (Ljava/lang/Object;)I

mirai-core-api/src/commonMain/kotlin/internal/message/MessageSerializersImpl.kt

@@ -92,7 +92,7 @@ private val builtInSerializersModule by lazy {
 
 //        contextual(SingleMessage::class, SingleMessage.Serializer)
         contextual(MessageChain::class, MessageChain.Serializer)
-        contextual(MessageChainImpl::class, MessageChainImpl.serializer())
+        contextual(LinearMessageChainImpl::class, LinearMessageChainImpl.serializer())
 
         contextual(ShowImageFlag::class, ShowImageFlag.Serializer)
 

mirai-core-api/src/commonMain/kotlin/message/data/CombinedMessage.kt

@@ -0,0 +1,207 @@
+/*
+ * Copyright 2019-2022 Mamoe Technologies and contributors.
+ *
+ * 此源代码的使用受 GNU AFFERO GENERAL PUBLIC LICENSE version 3 许可证的约束, 可以在以下链接找到该许可证.
+ * Use of this source code is governed by the GNU AGPLv3 license that can be found through the following link.
+ *
+ * https://github.com/mamoe/mirai/blob/dev/LICENSE
+ */
+
+package net.mamoe.mirai.message.data
+
+import net.mamoe.mirai.message.data.visitor.MessageVisitor
+import net.mamoe.mirai.message.data.visitor.RecursiveMessageVisitor
+import net.mamoe.mirai.message.data.visitor.accept
+import net.mamoe.mirai.utils.MiraiInternalApi
+
+/**
+ * One after one, hierarchically.
+ * @since 2.12
+ */
+@MiraiInternalApi
+public class CombinedMessage @MessageChainConstructor constructor(
+    @MiraiInternalApi public val element: Message,
+    @MiraiInternalApi public val tail: Message,
+    @MiraiInternalApi public override val hasConstrainSingle: Boolean
+) : MessageChainImpl, List<SingleMessage> {
+    override fun <D, R> accept(visitor: MessageVisitor<D, R>, data: D): R {
+        return visitor.visitCombinedMessage(this, data)
+    }
+
+    override fun <D> acceptChildren(visitor: MessageVisitor<D, *>, data: D) {
+        element.accept(visitor, data)
+        tail.accept(visitor, data)
+    }
+
+    override val size: Int by lazy {
+        if (slowList.isInitialized()) return@lazy slowList.value.size
+        var size = 0
+        val visitor = object : RecursiveMessageVisitor<Unit>() {
+            override fun visitMessageChain(messageChain: MessageChain, data: Unit) {
+                if (messageChain is DirectSizeAccess) {
+                    size += messageChain.size
+                    return
+                }
+                return super.visitMessageChain(messageChain, data)
+            }
+
+            override fun visitSingleMessage(message: SingleMessage, data: Unit) {
+                size++
+            }
+        }
+        element.accept(visitor)
+        tail.accept(visitor)
+        size
+    }
+
+    override fun isEmpty(): Boolean {
+        if (slowList.isInitialized()) return slowList.value.isEmpty()
+        return element is MessageChain && element.isEmpty() && tail is MessageChain && tail.isEmpty()
+    }
+
+    override fun contains(element: SingleMessage): Boolean {
+        if (slowList.isInitialized()) return slowList.value.contains(element)
+        if (this.element == element) return true
+        if (this.tail == element) return true
+        if (this.element is MessageChain && this.element.contains(element)) return true
+        if (this.tail is MessageChain && this.tail.contains(element)) return true
+        return false
+    }
+
+
+    private val toStringTemp: String by lazy {
+        if (slowList.isInitialized()) return@lazy slowList.value.toString()
+        buildString {
+            accept(object : RecursiveMessageVisitor<Unit>() {
+                override fun visitSingleMessage(message: SingleMessage, data: Unit) {
+                    append(message.toString())
+                }
+
+                override fun visitMessageChain(messageChain: MessageChain, data: Unit) {
+                    if (messageChain is DirectToStringAccess) {
+                        append(messageChain.toString())
+                    } else {
+                        super.visitMessageChain(messageChain, data)
+                    }
+                }
+            })
+        }
+    }
+
+    private val contentToStingTemp: String by lazy {
+        if (slowList.isInitialized()) return@lazy slowList.value.contentToString()
+        buildString {
+            accept(object : RecursiveMessageVisitor<Unit>() {
+                override fun visitSingleMessage(message: SingleMessage, data: Unit) {
+                    append(message.contentToString())
+                }
+
+                override fun visitMessageChain(messageChain: MessageChain, data: Unit) {
+                    if (messageChain is DirectToStringAccess) {
+                        append(messageChain.contentToString())
+                    } else {
+                        super.visitMessageChain(messageChain, data)
+                    }
+                }
+            })
+        }
+    }
+
+    override fun toString(): String = toStringTemp
+    override fun contentToString(): String = contentToStingTemp
+
+    override fun containsAll(elements: Collection<SingleMessage>): Boolean {
+        if (slowList.isInitialized()) return slowList.value.containsAll(elements)
+        if (elements.isEmpty()) return true
+        if (this.isEmpty()) return false
+        val remaining = elements.toMutableList()
+        accept(object : RecursiveMessageVisitor<Unit>() {
+            override fun isFinished(): Boolean = remaining.isEmpty()
+            override fun visitSingleMessage(message: SingleMessage, data: Unit) {
+                remaining.remove(message)
+            }
+        })
+        return remaining.isEmpty()
+    }
+
+    override fun iterator(): Iterator<SingleMessage> {
+        if (slowList.isInitialized()) return slowList.value.iterator()
+        suspend fun SequenceScope<SingleMessage>.yieldMessage(element: Message) {
+            when (element) {
+                is SingleMessage -> {
+                    yield(element)
+                }
+                is MessageChain -> {
+                    yieldAll(element.iterator())
+                }
+            }
+        }
+
+        return iterator {
+            yieldMessage(element)
+            yieldMessage(tail)
+        }
+    }
+
+    override fun subList(fromIndex: Int, toIndex: Int): List<SingleMessage> {
+        if (slowList.isInitialized()) return slowList.value.subList(fromIndex, toIndex)
+        if (fromIndex < 0 || fromIndex > toIndex) throw IndexOutOfBoundsException("fromIndex: $fromIndex, toIndex: $toIndex")
+
+        return buildList {
+            accept(object : RecursiveMessageVisitor<Unit>() {
+                private var currentIndex = 0
+                override fun isFinished(): Boolean = currentIndex >= toIndex
+
+                override fun visitSingleMessage(message: SingleMessage, data: Unit) {
+                    if (isFinished()) return
+                    if (currentIndex >= fromIndex) {
+                        add(message)
+                    }
+                    currentIndex++
+                }
+            })
+        }
+    }
+
+
+    override fun equals(other: Any?): Boolean {
+        if (this === other) return true
+        if (javaClass != other?.javaClass) return false
+
+        other as CombinedMessage
+
+        if (element != other.element) return false
+        if (tail != other.tail) return false
+        if (hasConstrainSingle != other.hasConstrainSingle) return false
+
+        return true
+    }
+
+    override fun hashCode(): Int {
+        var result = element.hashCode()
+        result = 31 * result + tail.hashCode()
+        result = 31 * result + hasConstrainSingle.hashCode()
+        return result
+    }
+
+
+    ///////////////////////////////////////////////////////////////////////////
+    // slow operations
+    ///////////////////////////////////////////////////////////////////////////
+
+    internal val slowList: Lazy<MessageChain> = lazy {
+        sequenceOf(element, tail).toMessageChain()
+    }
+
+    // [MessageChain] implements [RandomAccess] so we should ensure that property here.
+    override fun get(index: Int): SingleMessage = slowList.value[index]
+    override fun indexOf(element: SingleMessage): Int = slowList.value.indexOf(element)
+    override fun lastIndexOf(element: SingleMessage): Int = slowList.value.lastIndexOf(element)
+    override fun listIterator(): ListIterator<SingleMessage> = slowList.value.listIterator()
+    override fun listIterator(index: Int): ListIterator<SingleMessage> = slowList.value.listIterator(index)
+
+
+}
+
+internal interface DirectSizeAccess : MessageChain
+internal interface DirectToStringAccess : MessageChain

mirai-core-api/src/commonMain/kotlin/message/data/Message.kt

@@ -240,7 +240,20 @@ public interface Message {
      * @see plus `+` 操作符重载
      */
     @JvmSynthetic // in java they should use `plus` instead
-    public fun followedBy(tail: Message): MessageChain = followedByImpl(tail)
+    public fun followedBy(tail: Message): MessageChain {
+        var constrainSingleCount = 0
+        if (this.hasConstrainSingle) constrainSingleCount++
+        if (tail.hasConstrainSingle) constrainSingleCount++
+        return if (constrainSingleCount == 0) {
+            // Future optimize:
+            // When constrainSingleCount == 1, see if we can connect by CombinedMessage,
+            // this need some kind of replacement of `hasConstrainSingle` with more information about MessageKeys.
+            @OptIn(MessageChainConstructor::class)
+            CombinedMessage(this, tail, false)
+        } else {
+            LinearMessageChainImpl.combineCreate(this, tail)
+        }
+    }
 
     /** 将 [another] 按顺序连接到这个消息的尾部. */
     public operator fun plus(another: MessageChain): MessageChain = this + another as Message
@@ -277,14 +290,14 @@ public interface Message {
 
     /**
      * @suppress 这是内部 API, 不要在任何情况下调用
-     * @since MESSAGE_VISITOR
+     * @since 2.12
      */
     @MiraiInternalApi
     public fun <D, R> accept(visitor: MessageVisitor<D, R>, data: D): R = visitor.visitMessage(this, data)
 
     /**
      * @suppress 这是内部 API, 不要在任何情况下调用
-     * @since MESSAGE_VISITOR
+     * @since 2.12
      */
     @MiraiInternalApi
     public fun <D> acceptChildren(visitor: MessageVisitor<D, *>, data: D) {

mirai-core-api/src/commonMain/kotlin/message/data/MessageChain.kt

@@ -143,6 +143,11 @@ import net.mamoe.mirai.console.compiler.common.ResolveContext.Kind.RESTRICTED_AB
  * 例如用户发送了两条内容相同的消息, 但其中一条带有引用回复而另一条没有, 则两条消息的索引可能有变化 (当然内容顺序不会改变, 只是 [QuoteReply] 的位置有可能会变化).
  * 因此在使用直接索引访问时要格外注意兼容性, 故不推荐这种访问方案.
  *
+ * ### 避免索引访问以提高性能
+ *
+ * 自 2.12 起, [MessageChain] 内部结构有性能优化. 该优化大幅降低元素数量多的 [MessageChain] 的连接的时间复杂度.
+ * 性能优化默认生效, 但若使用 [get], [subList] 等 [List] 于 [Collection] 之外的方法时则会让该优化失效 (相比 2.12 以前不会丢失性能, 只是没有优化).
+ *
  * ## 撤回和引用
  *
  * 要撤回消息, 查看 [MessageSource]
@@ -253,11 +258,6 @@ public sealed interface MessageChain :
     @MiraiInternalApi
     override fun <D, R> accept(visitor: MessageVisitor<D, R>, data: D): R = visitor.visitMessageChain(this, data)
 
-    @MiraiInternalApi
-    override fun <D> acceptChildren(visitor: MessageVisitor<D, *>, data: D) {
-        forEach { it.accept(visitor, data) }
-    }
-
     /**
      * 将 [MessageChain] 作为 `List<SingleMessage>` 序列化. 使用 [多态序列化][Polymorphic].
      *
@@ -349,7 +349,7 @@ public sealed interface MessageChain :
 /**
  * 返回一个不含任何元素的 [MessageChain].
  *
- * @since 2.11
+ * @since 2.12
  */
 // Java: MessageUtils.emptyMessageChain()
 @Suppress("DEPRECATION")
@@ -363,14 +363,18 @@ public fun emptyMessageChain(): MessageChain = EmptyMessageChain
     "Please use emptyMessageChain()",
     replaceWith = ReplaceWith("emptyMessageChain()", "net.mamoe.mirai.message.data.emptyMessageChain")
 )
-@DeprecatedSinceMirai(warningSince = "2.11")
-public object EmptyMessageChain : MessageChain, List<SingleMessage> by emptyList() {
+@DeprecatedSinceMirai(warningSince = "2.12")
+public object EmptyMessageChain : MessageChain, List<SingleMessage> by emptyList(), MessageChainImpl {
     override val size: Int get() = 0
 
     override fun toString(): String = ""
     override fun contentToString(): String = ""
     override fun serializeToMiraiCode(): String = ""
 
+    @MiraiInternalApi
+    override val hasConstrainSingle: Boolean
+        get() = false
+
     @MiraiExperimentalApi
     override fun appendMiraiCodeTo(builder: StringBuilder) {
     }
@@ -486,7 +490,7 @@ public inline fun messageChainOf(vararg messages: Message): MessageChain = messa
  */
 @JvmName("newChain")
 public fun Sequence<Message>.toMessageChain(): MessageChain =
-    createMessageChainImplOptimized(this.constrainSingleMessages())
+    LinearMessageChainImpl.create(ConstrainSingleHelper.constrainSingleMessages(this))
 
 /**
  * 扁平化 [this] 并创建一个 [MessageChain].
@@ -525,11 +529,8 @@ public inline fun Array<out Message>.toMessageChain(): MessageChain = this.asSeq
 @JvmName("newChain")
 public fun Message.toMessageChain(): MessageChain = when (this) {
     is MessageChain -> (this as List<SingleMessage>).toMessageChain()
-    else -> MessageChainImpl(
-        listOf(
-            this as? SingleMessage ?: error("Message is either MessageChain nor SingleMessage: $this")
-        )
-    )
+    is SingleMessage -> LinearMessageChainImpl.create(listOf(this), this is ConstrainSingle)
+    else -> error("Message is either MessageChain nor SingleMessage: $this")
 }
 
 

mirai-core-api/src/commonMain/kotlin/message/data/MessageChainBuilder.kt

@@ -1,10 +1,10 @@
 /*
- * Copyright 2019-2021 Mamoe Technologies and contributors.
+ * Copyright 2019-2022 Mamoe Technologies and contributors.
  *
- *  此源代码的使用受 GNU AFFERO GENERAL PUBLIC LICENSE version 3 许可证的约束, 可以在以下链接找到该许可证.
- *  Use of this source code is governed by the GNU AGPLv3 license that can be found through the following link.
+ * 此源代码的使用受 GNU AFFERO GENERAL PUBLIC LICENSE version 3 许可证的约束, 可以在以下链接找到该许可证.
+ * Use of this source code is governed by the GNU AGPLv3 license that can be found through the following link.
  *
- *  https://github.com/mamoe/mirai/blob/master/LICENSE
+ * https://github.com/mamoe/mirai/blob/dev/LICENSE
  */
 
 @file:JvmMultifileClass
@@ -176,7 +176,7 @@ public class MessageChainBuilder private constructor(
     // avoid resolution to extensions
     public fun asMessageChain(): MessageChain {
         this.flushCache()
-        return createMessageChainImplOptimized(this.constrainSingleMessages())
+        return this.toMessageChain()
     }
 
     /** 同 [asMessageChain] */

mirai-core-api/src/commonMain/kotlin/message/data/impl.kt

@@ -17,8 +17,10 @@ import kotlinx.serialization.Serializable
 import net.mamoe.mirai.message.data.Image.Key.IMAGE_ID_REGEX
 import net.mamoe.mirai.message.data.Image.Key.IMAGE_RESOURCE_ID_REGEX_1
 import net.mamoe.mirai.message.data.Image.Key.IMAGE_RESOURCE_ID_REGEX_2
-import net.mamoe.mirai.utils.MiraiExperimentalApi
+import net.mamoe.mirai.message.data.visitor.MessageVisitor
+import net.mamoe.mirai.utils.MiraiInternalApi
 import net.mamoe.mirai.utils.asImmutable
+import net.mamoe.mirai.utils.castOrNull
 import net.mamoe.mirai.utils.replaceAllKotlin
 
 // region image
@@ -27,18 +29,6 @@ import net.mamoe.mirai.utils.replaceAllKotlin
 //// IMPLEMENTATIONS ////
 /////////////////////////
 
-@Suppress("unused", "UNUSED_PARAMETER")
-private fun Message.hasDuplicationOfConstrain(key: MessageKey<*>): Boolean {
-    return true
-    /*
-     return when (this) {
-         is SingleMessage -> (this as? ConstrainSingle)?.key == key
-         is CombinedMessage -> return this.left.hasDuplicationOfConstrain(key) || this.tail.hasDuplicationOfConstrain(key)
-         is MessageChainImplByCollection -> this.delegate.any { (it as? ConstrainSingle)?.key == key }
-         else -> error("stub")
-     }*/
-}
-
 @JvmSynthetic
 internal fun Message.contentEqualsStrictImpl(another: Message, ignoreCase: Boolean): Boolean {
     if (!this.contentToString().equals(another.contentToString(), ignoreCase = ignoreCase)) return false
@@ -65,117 +55,89 @@ internal fun Message.contentEqualsStrictImpl(another: Message, ignoreCase: Boole
     }
 }
 
-@JvmSynthetic
-internal fun Message.followedByImpl(tail: Message): MessageChain {
-    return MessageChainImplBySequence(this.toMessageChain().asSequence() + tail.toMessageChain().asSequence())
-    /*
-    when {
-        this is SingleMessage && tail is SingleMessage -> {
-            if (this is ConstrainSingle && tail is ConstrainSingle) {
-                if (this.key == tail.key)
-                    return SingleMessageChainImpl(tail)
-            }
-            return CombinedMessage(this, tail)
-        }
 
-        this is SingleMessage -> { // tail is not
-            tail as MessageChain
-
-            if (this is ConstrainSingle) {
-                val key = this.key
-                if (tail.any { (it as? ConstrainSingle)?.key == key }) {
-                    return tail
-                }
-            }
-            return CombinedMessage(this, tail)
-        }
-
-        tail is SingleMessage -> {
-            this as MessageChain
-
-            if (tail is ConstrainSingle && this.hasDuplicationOfConstrain(tail.key)) {
-                return MessageChainImplByCollection(constrainSingleMessagesImpl(this.asSequence() + tail))
-            }
-
-            return CombinedMessage(this, tail)
-        }
-
-        else -> { // both chain
-            this as MessageChain
-            tail as MessageChain
-
-            return MessageChainImplByCollection(
-                constrainSingleMessagesImpl(this.asSequence() + tail)
-            )
-        }
-    }*/
+internal sealed interface MessageChainImpl : MessageChain {
+    /**
+     * 去重算法 v1 - 2.12:
+     * 在连接时若只有 0-1 方包含 [ConstrainSingle], 则使用 [CombinedMessage] 优化性能. 否则使用旧版复杂去重算法构造 [LinearMessageChainImpl].
+     */
+    @MiraiInternalApi
+    val hasConstrainSingle: Boolean
 }
 
-
-@JvmSynthetic
-internal fun Sequence<SingleMessage>.constrainSingleMessages(): List<SingleMessage> =
-    constrainSingleMessagesImpl(this)
-
-/**
- * - [Sequence.toMutableList]
- * - Replace in-place with marker null
- */
-@MiraiExperimentalApi
-@JvmSynthetic
-internal fun constrainSingleMessagesImpl(sequence: Sequence<SingleMessage>): List<SingleMessage> {
-    val list: MutableList<SingleMessage?> = sequence.toMutableList()
-
-    for (singleMessage in list.asReversed()) {
-        if (singleMessage is ConstrainSingle) {
-            val key = singleMessage.key.topmostKey
-            val firstOccurrence = list.first { it != null && key.isInstance(it) } // may be singleMessage itself
-            list.replaceAllKotlin {
-                when {
-                    it == null -> null
-                    it === firstOccurrence -> singleMessage
-                    key.isInstance(it) -> null // remove duplicates
-                    else -> it
-                }
-            }
-        }
+internal val Message.hasConstrainSingle: Boolean
+    get() {
+        if (this is SingleMessage) return this is ConstrainSingle
+        // now `this` is MessageChain
+        return this.castOrNull<MessageChainImpl>()?.hasConstrainSingle ?: true // for external type, assume they do
+    }
+
+/**
+ * @see ConstrainSingleHelper.constrainSingleMessages
+ */
+internal data class ConstrainSingleData(
+    val value: List<SingleMessage>,
+    val hasConstrainSingle: Boolean,
+)
+
+internal object ConstrainSingleHelper {
+    @JvmName("constrainSingleMessages_Sequence")
+    internal fun constrainSingleMessages(sequence: Sequence<Message>): ConstrainSingleData =
+        constrainSingleMessages(sequence.flatMap { it.toMessageChain() })
+
+    internal fun constrainSingleMessages(sequence: Sequence<SingleMessage>): ConstrainSingleData =
+        constrainSingleMessagesImpl(sequence)
+
+    /**
+     * - [Sequence.toMutableList]
+     * - Replace in-place with marker null
+     */
+    private fun constrainSingleMessagesImpl(sequence: Sequence<SingleMessage>): ConstrainSingleData {
+        val list: MutableList<SingleMessage?> = sequence.toMutableList()
+
+        var hasConstrainSingle = false
+        for (singleMessage in list.asReversed()) {
+            if (singleMessage is ConstrainSingle) {
+                hasConstrainSingle = true
+                val key = singleMessage.key.topmostKey
+                val firstOccurrence = list.first { it != null && key.isInstance(it) } // may be singleMessage itself
+                list.replaceAllKotlin {
+                    when {
+                        it == null -> null
+                        it === firstOccurrence -> singleMessage
+                        key.isInstance(it) -> null // remove duplicates
+                        else -> it
+                    }
+                }
+            }
+        }
+
+        return ConstrainSingleData(list.filterNotNull().asImmutable(), hasConstrainSingle)
     }
 
-    return list.filterNotNull().asImmutable()
 }
 
-@JvmSynthetic
-internal fun Iterable<SingleMessage>.constrainSingleMessages(): List<SingleMessage> =
-    constrainSingleMessagesImpl(this.asSequence())
-
-@JvmName("constrainSingleMessages_Sequence")
-@JvmSynthetic
-internal fun Sequence<Message>.constrainSingleMessages(): List<SingleMessage> =
-    this.flatMap { it.toMessageChain() }.constrainSingleMessages()
-
-
 @JvmSynthetic
 @Suppress("UNCHECKED_CAST", "DEPRECATION_ERROR", "DEPRECATION")
 internal fun <M : SingleMessage> MessageChain.getImpl(key: MessageKey<M>): M? {
     return this.asSequence().mapNotNull { key.safeCast.invoke(it) }.firstOrNull()
 }
 
-/**
- * @return [EmptyMessageChain] if [delegate] is empty, otherwise [MessageChainImpl]
- */
-internal fun createMessageChainImplOptimized(delegate: List<SingleMessage>): MessageChain {
-    return if (delegate.isEmpty()) emptyMessageChain()
-    else MessageChainImpl(delegate)
-}
+@RequiresOptIn
+internal annotation class MessageChainConstructor
+
 
 /**
  * 使用 [Collection] 作为委托的 [MessageChain]
  */
 @Suppress("SERIALIZER_TYPE_INCOMPATIBLE")
 @Serializable(MessageChain.Serializer::class)
-internal data class MessageChainImpl constructor(
+internal class LinearMessageChainImpl @MessageChainConstructor private constructor(
     @JvmField
-    internal val delegate: List<SingleMessage> // 必须 constrainSingleMessages, 且为 immutable
-) : Message, MessageChain, List<SingleMessage> by delegate {
+    internal val delegate: List<SingleMessage>,
+    override val hasConstrainSingle: Boolean
+) : Message, MessageChain, List<SingleMessage> by delegate, MessageChainImpl,
+    DirectSizeAccess, DirectToStringAccess {
     override val size: Int get() = delegate.size
     override fun iterator(): Iterator<SingleMessage> = delegate.iterator()
 
@@ -186,13 +148,81 @@ internal data class MessageChainImpl constructor(
     override fun contentToString(): String = contentToStringTemp
 
     override fun hashCode(): Int = delegate.hashCode()
-    override fun equals(other: Any?): Boolean = other is MessageChainImpl && other.delegate == this.delegate
-}
+    override fun equals(other: Any?): Boolean = other is LinearMessageChainImpl && other.delegate == this.delegate
 
-@Suppress("FunctionName") // source compatibility with 1.x
-internal fun MessageChainImplBySequence(
-    delegate: Sequence<SingleMessage> // 可以有重复 ConstrainSingle
-): MessageChain = createMessageChainImplOptimized(delegate.constrainSingleMessages())
+    override fun <D> acceptChildren(visitor: MessageVisitor<D, *>, data: D) {
+        for (singleMessage in delegate) {
+            singleMessage.accept(visitor, data)
+        }
+    }
+
+    companion object {
+        fun combineCreate(message: Message, tail: Message): MessageChain {
+            return create(
+                ConstrainSingleHelper.constrainSingleMessages(
+                    message.toMessageChain().asSequence() + tail.toMessageChain().asSequence()
+                )
+            )
+            /*
+            when {
+                this is SingleMessage && tail is SingleMessage -> {
+                    if (this is ConstrainSingle && tail is ConstrainSingle) {
+                        if (this.key == tail.key)
+                            return SingleMessageChainImpl(tail)
+                    }
+                    return CombinedMessage(this, tail)
+                }
+
+                this is SingleMessage -> { // tail is not
+                    tail as MessageChain
+
+                    if (this is ConstrainSingle) {
+                        val key = this.key
+                        if (tail.any { (it as? ConstrainSingle)?.key == key }) {
+                            return tail
+                        }
+                    }
+                    return CombinedMessage(this, tail)
+                }
+
+                tail is SingleMessage -> {
+                    this as MessageChain
+
+                    if (tail is ConstrainSingle && this.hasDuplicationOfConstrain(tail.key)) {
+                        return MessageChainImplByCollection(constrainSingleMessagesImpl(this.asSequence() + tail))
+                    }
+
+                    return CombinedMessage(this, tail)
+                }
+
+                else -> { // both chain
+                    this as MessageChain
+                    tail as MessageChain
+
+                    return MessageChainImplByCollection(
+                        constrainSingleMessagesImpl(this.asSequence() + tail)
+                    )
+                }
+            }*/
+        }
+
+        /**
+         * @param delegate must be immutable
+         */
+        @OptIn(MessageChainConstructor::class)
+        fun create(delegate: List<SingleMessage>, hasConstrainSingle: Boolean): MessageChain {
+            return if (delegate.isEmpty()) {
+                emptyMessageChain()
+            } else {
+                LinearMessageChainImpl(delegate, hasConstrainSingle)
+            }
+        }
+
+        fun create(data: ConstrainSingleData): MessageChain {
+            return create(data.value, data.hasConstrainSingle)
+        }
+    }
+}
 
 
 //////////////////////

mirai-core-api/src/commonMain/kotlin/message/data/visitor/MessageVisitor.kt

@@ -11,158 +11,232 @@ package net.mamoe.mirai.message.data.visitor
 
 import net.mamoe.mirai.message.data.*
 import net.mamoe.mirai.utils.MiraiInternalApi
+import net.mamoe.mirai.utils.NotStableForInheritance
 
 /**
  * @suppress 这是内部 API, 请不要调用
- * @since MESSAGE_VISITOR
+ * @since 2.12
  */
 @MiraiInternalApi
+@NotStableForInheritance
 public interface MessageVisitor<in D, out R> {
     public fun visitMessage(message: Message, data: D): R
 
+    public fun visitSingleMessage(message: SingleMessage, data: D): R
+    public fun visitMessageChain(messageChain: MessageChain, data: D): R
+    public fun visitCombinedMessage(message: CombinedMessage, data: D): R
 
-    public fun visitSingleMessage(message: SingleMessage, data: D): R {
+    public fun visitMessageContent(message: MessageContent, data: D): R
+    public fun visitMessageMetadata(message: MessageMetadata, data: D): R
+
+    public fun visitMessageOrigin(message: MessageOrigin, data: D): R
+    public fun visitMessageSource(message: MessageSource, data: D): R
+    public fun visitQuoteReply(message: QuoteReply, data: D): R
+    public fun visitCustomMessageMetadata(message: CustomMessageMetadata, data: D): R
+    public fun visitShowImageFlag(message: ShowImageFlag, data: D): R
+
+
+    public fun visitPlainText(message: PlainText, data: D): R
+    public fun visitAt(message: At, data: D): R
+    public fun visitAtAll(message: AtAll, data: D): R
+
+    @Suppress("DEPRECATION_ERROR")
+    public fun visitVoice(message: net.mamoe.mirai.message.data.Voice, data: D): R
+    public fun visitAudio(message: Audio, data: D): R
+    public fun visitHummerMessage(message: HummerMessage, data: D): R
+    public fun visitFlashImage(message: FlashImage, data: D): R
+    public fun visitPokeMessage(message: PokeMessage, data: D): R
+    public fun visitVipFace(message: VipFace, data: D): R
+    public fun visitMarketFace(message: MarketFace, data: D): R
+    public fun visitDice(message: Dice, data: D): R
+    public fun visitFace(message: Face, data: D): R
+    public fun visitFileMessage(message: FileMessage, data: D): R
+    public fun visitImage(message: Image, data: D): R
+    public fun visitForwardMessage(message: ForwardMessage, data: D): R
+    public fun visitMusicShare(message: MusicShare, data: D): R
+
+    public fun visitRichMessage(message: RichMessage, data: D): R
+    public fun visitServiceMessage(message: ServiceMessage, data: D): R
+    public fun visitSimpleServiceMessage(message: SimpleServiceMessage, data: D): R
+    public fun visitLightApp(message: LightApp, data: D): R
+    public fun visitAbstractServiceMessage(message: AbstractServiceMessage, data: D): R
+
+    public fun visitUnsupportedMessage(message: UnsupportedMessage, data: D): R
+}
+
+/**
+ * @suppress 这是内部 API, 请不要调用
+ * @since 2.12
+ */
+@MiraiInternalApi
+public abstract class AbstractMessageVisitor<in D, out R> : MessageVisitor<D, R> {
+    public override fun visitSingleMessage(message: SingleMessage, data: D): R {
         return visitMessage(message, data)
     }
 
-    public fun visitMessageChain(messageChain: MessageChain, data: D): R {
+    public override fun visitMessageChain(messageChain: MessageChain, data: D): R {
         return visitMessage(messageChain, data)
     }
 
+    public override fun visitCombinedMessage(message: CombinedMessage, data: D): R {
+        return visitMessageChain(message, data)
+    }
 
-    public fun visitMessageContent(message: MessageContent, data: D): R {
+
+    public override fun visitMessageContent(message: MessageContent, data: D): R {
         return visitSingleMessage(message, data)
     }
 
-    public fun visitMessageMetadata(message: MessageMetadata, data: D): R {
+    public override fun visitMessageMetadata(message: MessageMetadata, data: D): R {
         return visitSingleMessage(message, data)
     }
 
 
-    public fun visitMessageOrigin(message: MessageOrigin, data: D): R {
+    public override fun visitMessageOrigin(message: MessageOrigin, data: D): R {
         return visitMessageMetadata(message, data)
     }
 
-    public fun visitMessageSource(message: MessageSource, data: D): R {
+    public override fun visitMessageSource(message: MessageSource, data: D): R {
         return visitMessageMetadata(message, data)
     }
 
-    public fun visitQuoteReply(message: QuoteReply, data: D): R {
+    public override fun visitQuoteReply(message: QuoteReply, data: D): R {
         return visitMessageMetadata(message, data)
     }
 
-    public fun visitCustomMessageMetadata(message: CustomMessageMetadata, data: D): R {
+    public override fun visitCustomMessageMetadata(message: CustomMessageMetadata, data: D): R {
         return visitMessageMetadata(message, data)
     }
 
-    public fun visitShowImageFlag(message: ShowImageFlag, data: D): R {
+    public override fun visitShowImageFlag(message: ShowImageFlag, data: D): R {
         return visitMessageMetadata(message, data)
     }
 
 
-    public fun visitPlainText(message: PlainText, data: D): R {
+    public override fun visitPlainText(message: PlainText, data: D): R {
         return visitMessageContent(message, data)
     }
 
-    public fun visitAt(message: At, data: D): R {
+    public override fun visitAt(message: At, data: D): R {
         return visitMessageContent(message, data)
     }
 
-    public fun visitAtAll(message: AtAll, data: D): R {
+    public override fun visitAtAll(message: AtAll, data: D): R {
         return visitMessageContent(message, data)
     }
 
     @Suppress("DEPRECATION_ERROR")
-    public fun visitVoice(message: Voice, data: D): R {
+    public override fun visitVoice(message: net.mamoe.mirai.message.data.Voice, data: D): R {
         return visitMessageContent(message, data)
     }
 
-    public fun visitAudio(message: Audio, data: D): R {
+    public override fun visitAudio(message: Audio, data: D): R {
         return visitMessageContent(message, data)
     }
 
-    public fun visitHummerMessage(message: HummerMessage, data: D): R {
+    public override fun visitHummerMessage(message: HummerMessage, data: D): R {
         return visitMessageContent(message, data)
     }
 
-    public fun visitFlashImage(message: FlashImage, data: D): R {
+    public override fun visitFlashImage(message: FlashImage, data: D): R {
         return visitHummerMessage(message, data)
     }
 
-    public fun visitPokeMessage(message: PokeMessage, data: D): R {
+    public override fun visitPokeMessage(message: PokeMessage, data: D): R {
         return visitHummerMessage(message, data)
     }
 
-    public fun visitVipFace(message: VipFace, data: D): R {
+    public override fun visitVipFace(message: VipFace, data: D): R {
         return visitHummerMessage(message, data)
     }
 
-    public fun visitMarketFace(message: MarketFace, data: D): R {
+    public override fun visitMarketFace(message: MarketFace, data: D): R {
         return visitHummerMessage(message, data)
     }
 
-    public fun visitDice(message: Dice, data: D): R {
+    public override fun visitDice(message: Dice, data: D): R {
         return visitMarketFace(message, data)
     }
 
-    public fun visitFace(message: Face, data: D): R {
+    public override fun visitFace(message: Face, data: D): R {
         return visitMessageContent(message, data)
     }
 
-    public fun visitFileMessage(message: FileMessage, data: D): R {
+    public override fun visitFileMessage(message: FileMessage, data: D): R {
         return visitMessageContent(message, data)
     }
 
-    public fun visitImage(message: Image, data: D): R {
+    public override fun visitImage(message: Image, data: D): R {
         return visitMessageContent(message, data)
     }
 
-    public fun visitForwardMessage(message: ForwardMessage, data: D): R {
+    public override fun visitForwardMessage(message: ForwardMessage, data: D): R {
         return visitMessageContent(message, data)
     }
 
-    public fun visitMusicShare(message: MusicShare, data: D): R {
+    public override fun visitMusicShare(message: MusicShare, data: D): R {
         return visitMessageContent(message, data)
     }
 
-    public fun visitUnsupportedMessage(message: UnsupportedMessage, data: D): R {
+    public override fun visitUnsupportedMessage(message: UnsupportedMessage, data: D): R {
         return visitMessageContent(message, data)
     }
 
 
-    public fun visitRichMessage(message: RichMessage, data: D): R {
+    public override fun visitRichMessage(message: RichMessage, data: D): R {
         return visitMessageContent(message, data)
     }
 
-    public fun visitServiceMessage(message: ServiceMessage, data: D): R {
+    public override fun visitServiceMessage(message: ServiceMessage, data: D): R {
         return visitRichMessage(message, data)
     }
 
-    public fun visitSimpleServiceMessage(message: SimpleServiceMessage, data: D): R {
+    public override fun visitSimpleServiceMessage(message: SimpleServiceMessage, data: D): R {
         return visitServiceMessage(message, data)
     }
 
-    public fun visitLightApp(message: LightApp, data: D): R {
+    public override fun visitLightApp(message: LightApp, data: D): R {
         return visitRichMessage(message, data)
     }
 
-    public fun visitAbstractServiceMessage(message: AbstractServiceMessage, data: D): R {
+    public override fun visitAbstractServiceMessage(message: AbstractServiceMessage, data: D): R {
         return visitServiceMessage(message, data)
     }
 }
 
 /**
  * @suppress 这是内部 API, 请不要调用
- * @since 2.11
+ * @since 2.12
  */
 @MiraiInternalApi
-public interface MessageVisitorUnit<in D> : MessageVisitor<D, Unit> {
+public abstract class RecursiveMessageVisitor<D> : MessageVisitorUnit<D>() {
+    protected open fun isFinished(): Boolean = false
+
+    override fun visitMessage(message: Message, data: D) {
+        if (isFinished()) return
+        message.acceptChildren(this, data)
+    }
+}
+
+/**
+ * @suppress 这是内部 API, 请不要调用
+ * @since 2.12
+ */
+@MiraiInternalApi
+public abstract class MessageVisitorUnit<in D> : AbstractMessageVisitor<D, Unit>() {
     override fun visitMessage(message: Message, data: D): Unit = Unit
 }
 
 /**
  * @suppress 这是内部 API, 请不要调用
- * @since 2.11
+ * @since 2.12
  */
 @MiraiInternalApi
-public fun <R> Message.accept(visitor: MessageVisitor<Unit, R>): R = this.accept(visitor, Unit)
+public fun <R> Message.accept(visitor: MessageVisitor<Unit, R>): R = this.accept(visitor, Unit)
+
+/**
+ * @suppress 这是内部 API, 请不要调用
+ * @since 2.12
+ */
+@MiraiInternalApi
+public fun Message.acceptChildren(visitor: MessageVisitor<Unit, *>): Unit = this.acceptChildren(visitor, Unit)

mirai-core-api/src/commonTest/kotlin/message.data/CombinedMessageTest.kt

@@ -1,85 +1,220 @@
 /*
- * Copyright 2019-2021 Mamoe Technologies and contributors.
+ * Copyright 2019-2022 Mamoe Technologies and contributors.
  *
- *  此源代码的使用受 GNU AFFERO GENERAL PUBLIC LICENSE version 3 许可证的约束, 可以在以下链接找到该许可证.
- *  Use of this source code is governed by the GNU AGPLv3 license that can be found through the following link.
+ * 此源代码的使用受 GNU AFFERO GENERAL PUBLIC LICENSE version 3 许可证的约束, 可以在以下链接找到该许可证.
+ * Use of this source code is governed by the GNU AGPLv3 license that can be found through the following link.
  *
- *  https://github.com/mamoe/mirai/blob/master/LICENSE
+ * https://github.com/mamoe/mirai/blob/dev/LICENSE
  */
-package  net.mamoe.mirai.message.data
+package net.mamoe.mirai.message.data
 
+import net.mamoe.mirai.message.data.visitor.MessageVisitorUnit
+import net.mamoe.mirai.message.data.visitor.RecursiveMessageVisitor
+import net.mamoe.mirai.message.data.visitor.accept
+import net.mamoe.mirai.message.data.visitor.acceptChildren
 import kotlin.test.Test
 import kotlin.test.assertEquals
+import kotlin.test.assertFalse
+import kotlin.test.assertIs
 
 
+@OptIn(MessageChainConstructor::class)
 internal class CombinedMessageTest {
-
+    private fun linearMessageChainOf(vararg values: SingleMessage) =
+        LinearMessageChainImpl.create(values.toList(), values.any { it.hasConstrainSingle })
 
     @Test
-    fun testAsSequence() {
-        var message: Message = PlainText("Hello ")
-        message += "World"
+    fun singlePlusSingleCreatesCombinedMessage() {
+        kotlin.run {
+            val chain = PlainText("fo").plus(PlainText("o"))
+            assertIs<CombinedMessage>(chain)
+            assertEquals(PlainText("fo"), chain.element)
+            assertEquals(PlainText("o"), chain.tail)
+            assertEquals(false, chain.hasConstrainSingle)
+        }
+        kotlin.run {
+            val chain = PlainText("fo").plus(LightApp("c"))
+            assertIs<LinearMessageChainImpl>(chain)
+            assertEquals(LightApp("c"), chain.single())
+            assertEquals(true, chain.hasConstrainSingle)
+        }
+    }
 
+    @Test
+    fun singlePlusChainCreatesCombinedMessage() {
+        val chain = PlainText("fo").plus(linearMessageChainOf(PlainText("o")))
+        assertIs<CombinedMessage>(chain)
+        assertEquals(PlainText("fo"), chain.element)
+        assertEquals(linearMessageChainOf(PlainText("o")), chain.tail)
+        assertEquals(false, chain.hasConstrainSingle)
+    }
+
+    @Test
+    fun chainPlusSingleCreatesCombinedMessage() {
+        val chain = linearMessageChainOf(PlainText("o")).plus(PlainText("fo"))
+        assertIs<CombinedMessage>(chain)
+        assertEquals(linearMessageChainOf(PlainText("o")), chain.element)
+        assertEquals(PlainText("fo"), chain.tail)
+        assertEquals(false, chain.hasConstrainSingle)
+    }
+
+    private fun createTestInstance(): CombinedMessage {
+        return CombinedMessage(
+            buildMessageChain {
+                +PlainText("bar")
+                +emptyMessageChain()
+                +buildMessageChain {
+                    +AtAll
+                    +PlainText("zoo")
+                }
+            },
+            buildMessageChain {
+                +buildMessageChain {
+                    +At(2)
+                }
+                +At(1)
+            },
+            false
+        )
+    }
+
+    private fun createComplexCombined() = CombinedMessage(
+        PlainText("foo"),
+        createTestInstance(),
+        false
+    )
+
+    private val complexCombined = createComplexCombined()
+    ///////////////////////////////////////////////////////////////////////////
+    // properties
+    ///////////////////////////////////////////////////////////////////////////
+
+    @Test
+    fun sizeTest() {
+        assertEquals(0, CombinedMessage(messageChainOf(), messageChainOf(), false).size)
         assertEquals(
-            "Hello World",
-            message.toMessageChain().asSequence().joinToString(separator = "")
+            0,
+            CombinedMessage(messageChainOf(), CombinedMessage(messageChainOf(), messageChainOf(), false), false).size
+        )
+
+        createTestInstance().run {
+            assertEquals(5, size)
+            assertFalse { slowList.isInitialized() }
+        }
+    }
+
+    @Test
+    fun slowListTest() {
+        assertEquals(messageChainOf(), CombinedMessage(messageChainOf(), messageChainOf(), false).slowList.value)
+        assertEquals(
+            listOf(
+                PlainText("foo"),
+                PlainText("bar"),
+                AtAll,
+                PlainText("zoo"),
+                At(2),
+                At(1),
+            ),
+            complexCombined.slowList.value.toList()
         )
     }
 
     @Test
-    fun testAsSequence2() {
-        var message: Message = PlainText("Hello ")
-        message += listOf(
-            PlainText("W"),
-            PlainText("o"),
-            PlainText("r") + PlainText("ld")
-        ).toMessageChain()
+    fun consistencyTest() {
+        val first = createTestInstance()
+        val second = createTestInstance()
+        assertEquals(first, second)
+        assertEquals(first.hashCode(), second.hashCode())
+        assertEquals(first.toString(), second.toString())
+        assertEquals(first.contentToString(), second.contentToString())
+        assertEquals(first.size, second.size)
+    }
 
+    ///////////////////////////////////////////////////////////////////////////
+    // functions
+    ///////////////////////////////////////////////////////////////////////////
+
+    @Test
+    fun subList() {
         assertEquals(
-            "Hello World",
-            message.toMessageChain().asSequence().joinToString(separator = "")
+            createComplexCombined().slowList.value.subList(2, 4),
+            complexCombined.subList(2, 4)
+        )
+        assertFalse {
+            complexCombined.slowList.isInitialized()
+        }
+        complexCombined.slowList.value // initialize
+        assertEquals(
+            createComplexCombined().slowList.value.subList(2, 4),
+            complexCombined.subList(2, 4)
         )
     }
-}
 
-fun <T> Iterator<T>.joinToString(
-    separator: CharSequence = ", ",
-    prefix: CharSequence = "",
-    postfix: CharSequence = "",
-    limit: Int = -1,
-    truncated: CharSequence = "...",
-    transform: ((T) -> CharSequence)? = null
-): String {
-    return joinTo(StringBuilder(), separator, prefix, postfix, limit, truncated, transform).toString()
-}
+    ///////////////////////////////////////////////////////////////////////////
+    // visiting
+    ///////////////////////////////////////////////////////////////////////////
 
-fun <T, A : Appendable> Iterator<T>.joinTo(
-    buffer: A,
-    separator: CharSequence = ", ",
-    prefix: CharSequence = "",
-    postfix: CharSequence = "",
-    limit: Int = -1,
-    truncated: CharSequence = "...",
-    transform: ((T) -> CharSequence)? = null
-): A {
-    buffer.append(prefix)
-    var count = 0
-    for (element in this) {
-        if (++count > 1) buffer.append(separator)
-        if (limit < 0 || count <= limit) {
-            buffer.appendElement(element, transform)
-        } else break
+    @Test
+    fun acceptChildrenTest() {
+        val list = buildList {
+            complexCombined.acceptChildren(object : MessageVisitorUnit<Unit>() {
+                override fun visitMessage(message: Message, data: Unit) {
+                    add(message)
+                    super.visitMessage(message, data)
+                }
+            })
+        }
+        assertEquals(
+            listOf(
+                PlainText("foo"),
+                createTestInstance()
+            ),
+            list
+        )
     }
-    if (limit in 0 until count) buffer.append(truncated)
-    buffer.append(postfix)
-    return buffer
-}
 
-internal fun <T> Appendable.appendElement(element: T, transform: ((T) -> CharSequence)?) {
-    when {
-        transform != null -> append(transform(element))
-        element is CharSequence? -> append(element)
-        element is Char -> append(element)
-        else -> append(element.toString())
+    @OptIn(MessageChainConstructor::class)
+    @Test
+    fun acceptChildrenRecursiveTest() {
+        val list = buildList {
+            complexCombined.accept(object : RecursiveMessageVisitor<Unit>() {
+                override fun visitMessage(message: Message, data: Unit) {
+                    println("visitMessage: (${message::class.simpleName}) $message")
+                    super.visitMessage(message, data)
+                }
+
+                override fun visitSingleMessage(message: SingleMessage, data: Unit) {
+                    add(message)
+                    super.visitSingleMessage(message, data)
+                }
+            })
+        }
+        assertEquals(
+            listOf(
+                PlainText("foo"),
+                PlainText("bar"),
+                AtAll,
+                PlainText("zoo"),
+                At(2),
+                At(1),
+            ),
+            list
+        )
+    }
+
+    @Test
+    fun hierarchicalIterator() {
+        assertEquals(
+            listOf(
+                PlainText("foo"),
+                PlainText("bar"),
+                AtAll,
+                PlainText("zoo"),
+                At(2),
+                At(1),
+            ),
+            complexCombined.iterator().asSequence().toList()
+        )
+        assertFalse { complexCombined.slowList.isInitialized() }
     }
 }

mirai-core-api/src/commonTest/kotlin/message.data/ConstrainSingleHelperTest.kt

@@ -0,0 +1,177 @@
+/*
+ * Copyright 2019-2022 Mamoe Technologies and contributors.
+ *
+ * 此源代码的使用受 GNU AFFERO GENERAL PUBLIC LICENSE version 3 许可证的约束, 可以在以下链接找到该许可证.
+ * Use of this source code is governed by the GNU AGPLv3 license that can be found through the following link.
+ *
+ * https://github.com/mamoe/mirai/blob/dev/LICENSE
+ */
+
+package net.mamoe.mirai.message.data
+
+import net.mamoe.mirai.utils.safeCast
+import org.junit.jupiter.api.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFalse
+import kotlin.test.assertTrue
+
+internal class ConstrainSingleHelperTest {
+
+    @Test
+    fun linearPlains() {
+        val list = listOf(PlainText("1"), PlainText("2"))
+        ConstrainSingleHelper.constrainSingleMessages(list.asSequence()).run {
+            assertEquals(list, value)
+            assertFalse { hasConstrainSingle }
+        }
+    }
+
+    @Test
+    fun linearNonConstrains() {
+        val list = listOf(PlainText("1"), At(2))
+        ConstrainSingleHelper.constrainSingleMessages(list.asSequence()).run {
+            assertEquals(list, value)
+            assertFalse { hasConstrainSingle }
+        }
+    }
+
+    @Test
+    fun hierarchicalNonConstrains() {
+        val list = listOf(PlainText("1"), (PlainText("1") + At(2)))
+        ConstrainSingleHelper.constrainSingleMessages(list.asSequence()).run {
+            assertEquals(listOf(PlainText("1"), PlainText("1"), At(2)), value)
+            assertFalse { hasConstrainSingle }
+        }
+    }
+
+    @Test
+    fun singleConstrain() {
+        val list = listOf(Dice(2))
+        ConstrainSingleHelper.constrainSingleMessages(list.asSequence()).run {
+            assertEquals(list, value)
+            assertTrue { hasConstrainSingle }
+        }
+    }
+
+    @Test
+    fun linearDuplicatedConstrains() {
+        val list = listOf(Dice(2), Dice(3))
+        ConstrainSingleHelper.constrainSingleMessages(list.asSequence()).run {
+            assertEquals(1, value.size)
+            assertEquals(Dice(3), value.first())
+            assertTrue { hasConstrainSingle }
+        }
+    }
+
+    @Test
+    fun linearMultipleDuplicatedConstrains() {
+        val list = listOf(PlainText("a"), LightApp("aa"), Dice(2), Dice(3), LightApp("bb"), PlainText("c"))
+        ConstrainSingleHelper.constrainSingleMessages(list.asSequence()).run {
+            assertEquals(1, value.size)
+            assertEquals(listOf(LightApp("bb")), value)
+            assertTrue { hasConstrainSingle }
+        }
+    }
+
+    @Test
+    fun hierarchicalDuplicatedConstrains() {
+        val list = listOf(
+            MySingle(1), // before first MessageContent that can be replaced by the last ConstrainSingle
+            PlainText("a"),
+            LightApp("aa"),
+            LinearMessageChainImpl.create( // without processing ConstrainSingle
+                listOf(
+                    PlainText("ab"),
+                    LightApp("aab"),
+                    Dice(5),
+                    Dice(3),
+                    LightApp("bbb"),
+                    PlainText("cb")
+                ), true
+            ),
+            Dice(3),
+            LightApp("bb"), // last ConstrainSingle
+            PlainText("c")
+        )
+        ConstrainSingleHelper.constrainSingleMessages(list.asSequence()).run {
+            assertEquals(2, value.size)
+            assertEquals(listOf(MySingle(1), LightApp("bb")), value)
+            assertTrue { hasConstrainSingle }
+        }
+    }
+
+    @Test
+    fun hierarchicalDuplicatedConstrains3() {
+        val list = listOf(
+            PlainText("a"),
+            LightApp("aa"),
+            LinearMessageChainImpl.create( // without processing ConstrainSingle
+                listOf(
+                    PlainText("ab"),
+                    LightApp("aab"),
+                    Dice(5),
+                    Dice(3),
+                    LightApp("bbb"),
+                    PlainText("cb")
+                ), true
+            ),
+            Dice(3),
+            MySingle(1), // after first MessageContent that can be replaced by the last ConstrainSingle
+            LightApp("bb"), // last ConstrainSingle
+            PlainText("c")
+        )
+        ConstrainSingleHelper.constrainSingleMessages(list.asSequence()).run {
+            assertEquals(2, value.size)
+            assertEquals(listOf(LightApp("bb"), MySingle(1)), value)
+            assertTrue { hasConstrainSingle }
+        }
+    }
+
+    @Test
+    fun hierarchicalDuplicatedConstrains2() {
+        val list = listOf(
+            PlainText("a"),
+            LightApp("aa"),
+            Dice(3),
+            LightApp("bb"),
+            PlainText("c"),
+            LinearMessageChainImpl.create( // without processing ConstrainSingle
+                listOf(
+                    PlainText("a"),
+                    LightApp("aa"),
+                    Dice(2),
+                    MySingle(1), // after first MessageContent that can be replaced by the last ConstrainSingle
+                    Dice(3),
+                    LightApp("foo"), // last ConstrainSingle
+                    PlainText("c")
+                ), true
+            ),
+        )
+        ConstrainSingleHelper.constrainSingleMessages(list.asSequence()).run {
+            assertEquals(2, value.size)
+            assertEquals(listOf(LightApp("foo"), MySingle(1)), value)
+            assertTrue { hasConstrainSingle }
+        }
+    }
+}
+
+private class MySingle(
+    val value: Int
+) : MessageMetadata, ConstrainSingle {
+    override val key: MessageKey<MySingle>
+        get() = Key
+
+    override fun toString(): String {
+        return "MySingle@${this.hashCode()}"
+    }
+
+    override fun equals(other: Any?): Boolean {
+        return other is MySingle && other.value == this.value
+    }
+
+    override fun hashCode(): Int {
+        return value
+    }
+
+    private object Key : AbstractMessageKey<MySingle>({ it.safeCast() })
+}

mirai-core-api/src/commonTest/kotlin/message.data/ConstrainSingleTest.kt

@@ -1,10 +1,10 @@
 /*
- * Copyright 2019-2021 Mamoe Technologies and contributors.
+ * Copyright 2019-2022 Mamoe Technologies and contributors.
  *
- *  此源代码的使用受 GNU AFFERO GENERAL PUBLIC LICENSE version 3 许可证的约束, 可以在以下链接找到该许可证.
- *  Use of this source code is governed by the GNU AGPLv3 license that can be found through the following link.
+ * 此源代码的使用受 GNU AFFERO GENERAL PUBLIC LICENSE version 3 许可证的约束, 可以在以下链接找到该许可证.
+ * Use of this source code is governed by the GNU AGPLv3 license that can be found through the following link.
  *
- *  https://github.com/mamoe/mirai/blob/master/LICENSE
+ * https://github.com/mamoe/mirai/blob/dev/LICENSE
  */
 package  net.mamoe.mirai.message.data
 
@@ -72,7 +72,7 @@ internal class ConstrainSingleTest {
 
         assertEquals(7, result.size)
         assertEquals(" [OK]ss p test", result.contentToString())
-        result as MessageChainImpl
+        result as LinearMessageChainImpl
         assertSame(new, result.delegate.toTypedArray()[2])
     }
 
@@ -85,7 +85,8 @@ internal class ConstrainSingleTest {
             last
         )
 
-        val result = sequence.constrainSingleMessages()
+        val (result, has) = ConstrainSingleHelper.constrainSingleMessages(sequence)
+        assertTrue { has }
         assertEquals(result.count(), 1)
         assertSame(result.single(), last)
     }
@@ -100,7 +101,8 @@ internal class ConstrainSingleTest {
             last
         )
 
-        val result = sequence.constrainSingleMessages()
+        val (result, has) = ConstrainSingleHelper.constrainSingleMessages(sequence)
+        assertTrue { has }
         assertEquals(result.count(), 2)
         assertSame(result.first(), last)
     }

mirai-core-api/src/commonTest/kotlin/message.data/LinearMessageChainImplTest.kt

@@ -0,0 +1,87 @@
+/*
+ * Copyright 2019-2022 Mamoe Technologies and contributors.
+ *
+ * 此源代码的使用受 GNU AFFERO GENERAL PUBLIC LICENSE version 3 许可证的约束, 可以在以下链接找到该许可证.
+ * Use of this source code is governed by the GNU AGPLv3 license that can be found through the following link.
+ *
+ * https://github.com/mamoe/mirai/blob/dev/LICENSE
+ */
+
+package net.mamoe.mirai.message.data
+
+import net.mamoe.mirai.message.data.visitor.MessageVisitorUnit
+import net.mamoe.mirai.message.data.visitor.acceptChildren
+import org.junit.jupiter.api.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertIs
+
+internal class LinearMessageChainImplTest {
+
+    private val complexLinearChain = buildMessageChain {
+        +PlainText("foo")
+        +buildMessageChain {
+            +PlainText("bar")
+            +emptyMessageChain()
+            +buildMessageChain {
+                +AtAll
+                +PlainText("zoo")
+            }
+        }
+        +buildMessageChain {
+            +buildMessageChain {
+                +At(2)
+            }
+            +At(1)
+        }
+    }
+
+    @Test
+    fun buildMessageChainCreatesLinearMessageChainImpl() {
+        assertIs<LinearMessageChainImpl>(complexLinearChain)
+    }
+
+    @Test
+    fun hierarchicalIterator() {
+        assertEquals(
+            listOf(
+                PlainText("foo"),
+                PlainText("bar"),
+                AtAll,
+                PlainText("zoo"),
+                At(2),
+                At(1),
+            ),
+            complexLinearChain.iterator().asSequence().toList()
+        )
+    }
+
+    @Test
+    fun sizeTest() {
+        assertEquals(0, messageChainOf().size)
+        assertEquals(6, complexLinearChain.size)
+        assertEquals(6, complexLinearChain.count())
+    }
+
+    @Test
+    fun acceptChildrenTest() {
+        val list = buildList {
+            complexLinearChain.acceptChildren(object : MessageVisitorUnit<Unit>() {
+                override fun visitMessage(message: Message, data: Unit) {
+                    add(message)
+                    super.visitMessage(message, data)
+                }
+            })
+        }
+        assertEquals(
+            listOf(
+                PlainText("foo"),
+                PlainText("bar"),
+                AtAll,
+                PlainText("zoo"),
+                At(2),
+                At(1),
+            ),
+            list
+        )
+    }
+}

mirai-core-api/src/commonTest/kotlin/message.data/MessageChainImplTest.kt

@@ -0,0 +1,25 @@
+/*
+ * Copyright 2019-2022 Mamoe Technologies and contributors.
+ *
+ * 此源代码的使用受 GNU AFFERO GENERAL PUBLIC LICENSE version 3 许可证的约束, 可以在以下链接找到该许可证.
+ * Use of this source code is governed by the GNU AGPLv3 license that can be found through the following link.
+ *
+ * https://github.com/mamoe/mirai/blob/dev/LICENSE
+ */
+
+package net.mamoe.mirai.message.data
+
+import org.junit.jupiter.api.Test
+import kotlin.test.assertIs
+
+internal class MessageChainImplTest {
+    @OptIn(MessageChainConstructor::class)
+    @Test
+    fun allInternalImplementationsOfMessageChainAreMessageChainImpl() {
+        assertIs<MessageChainImpl>(CombinedMessage(AtAll, AtAll, false))
+        assertIs<MessageChainImpl>(emptyMessageChain())
+        val linear = LinearMessageChainImpl.create(listOf(AtAll), true)
+        assertIs<LinearMessageChainImpl>(linear)
+        assertIs<MessageChainImpl>(linear)
+    }
+}

mirai-core-api/src/commonTest/kotlin/message.data/MessageVisitorTest.kt

@@ -0,0 +1,461 @@
+/*
+ * Copyright 2019-2022 Mamoe Technologies and contributors.
+ *
+ * 此源代码的使用受 GNU AFFERO GENERAL PUBLIC LICENSE version 3 许可证的约束, 可以在以下链接找到该许可证.
+ * Use of this source code is governed by the GNU AGPLv3 license that can be found through the following link.
+ *
+ * https://github.com/mamoe/mirai/blob/dev/LICENSE
+ */
+
+package net.mamoe.mirai.message.data
+
+import net.mamoe.mirai.contact.FileSupported
+import net.mamoe.mirai.message.data.visitor.AbstractMessageVisitor
+import net.mamoe.mirai.message.data.visitor.accept
+import net.mamoe.mirai.utils.MiraiExperimentalApi
+import org.junit.jupiter.api.Test
+import kotlin.test.assertContentEquals
+
+internal class MessageVisitorTest {
+    object GetCalledMethodNames : AbstractMessageVisitor<Unit, Array<String>>() {
+        override fun visitMessage(message: Message, data: Unit): Array<String> {
+            return arrayOf("visitMessage")
+        }
+
+        override fun visitSingleMessage(message: SingleMessage, data: Unit): Array<String> {
+            return arrayOf("visitSingleMessage") + super.visitSingleMessage(message, data)
+        }
+
+        override fun visitMessageChain(messageChain: MessageChain, data: Unit): Array<String> {
+            return arrayOf("visitMessageChain") + super.visitMessageChain(messageChain, data)
+        }
+
+        override fun visitCombinedMessage(message: CombinedMessage, data: Unit): Array<String> {
+            return arrayOf("visitCombinedMessage") + super.visitCombinedMessage(message, data)
+        }
+
+        override fun visitMessageContent(message: MessageContent, data: Unit): Array<String> {
+            return arrayOf("visitMessageContent") + super.visitMessageContent(message, data)
+        }
+
+        override fun visitMessageMetadata(message: MessageMetadata, data: Unit): Array<String> {
+            return arrayOf("visitMessageMetadata") + super.visitMessageMetadata(message, data)
+        }
+
+        override fun visitMessageOrigin(message: MessageOrigin, data: Unit): Array<String> {
+            return arrayOf("visitMessageOrigin") + super.visitMessageOrigin(message, data)
+        }
+
+        override fun visitMessageSource(message: MessageSource, data: Unit): Array<String> {
+            return arrayOf("visitMessageSource") + super.visitMessageSource(message, data)
+        }
+
+        override fun visitQuoteReply(message: QuoteReply, data: Unit): Array<String> {
+            return arrayOf("visitQuoteReply") + super.visitQuoteReply(message, data)
+        }
+
+        override fun visitCustomMessageMetadata(message: CustomMessageMetadata, data: Unit): Array<String> {
+            return arrayOf("visitCustomMessageMetadata") + super.visitCustomMessageMetadata(message, data)
+        }
+
+        override fun visitShowImageFlag(message: ShowImageFlag, data: Unit): Array<String> {
+            return arrayOf("visitShowImageFlag") + super.visitShowImageFlag(message, data)
+        }
+
+        override fun visitPlainText(message: PlainText, data: Unit): Array<String> {
+            return arrayOf("visitPlainText") + super.visitPlainText(message, data)
+        }
+
+        override fun visitAt(message: At, data: Unit): Array<String> {
+            return arrayOf("visitAt") + super.visitAt(message, data)
+        }
+
+        override fun visitAtAll(message: AtAll, data: Unit): Array<String> {
+            return arrayOf("visitAtAll") + super.visitAtAll(message, data)
+        }
+
+        @Suppress("DEPRECATION_ERROR")
+        override fun visitVoice(message: Voice, data: Unit): Array<String> {
+            return arrayOf("visitVoice") + super.visitVoice(message, data)
+        }
+
+        override fun visitAudio(message: Audio, data: Unit): Array<String> {
+            return arrayOf("visitAudio") + super.visitAudio(message, data)
+        }
+
+        override fun visitHummerMessage(message: HummerMessage, data: Unit): Array<String> {
+            return arrayOf("visitHummerMessage") + super.visitHummerMessage(message, data)
+        }
+
+        override fun visitFlashImage(message: FlashImage, data: Unit): Array<String> {
+            return arrayOf("visitFlashImage") + super.visitFlashImage(message, data)
+        }
+
+        override fun visitPokeMessage(message: PokeMessage, data: Unit): Array<String> {
+            return arrayOf("visitPokeMessage") + super.visitPokeMessage(message, data)
+        }
+
+        override fun visitVipFace(message: VipFace, data: Unit): Array<String> {
+            return arrayOf("visitVipFace") + super.visitVipFace(message, data)
+        }
+
+        override fun visitMarketFace(message: MarketFace, data: Unit): Array<String> {
+            return arrayOf("visitMarketFace") + super.visitMarketFace(message, data)
+        }
+
+        override fun visitDice(message: Dice, data: Unit): Array<String> {
+            return arrayOf("visitDice") + super.visitDice(message, data)
+        }
+
+        override fun visitFace(message: Face, data: Unit): Array<String> {
+            return arrayOf("visitFace") + super.visitFace(message, data)
+        }
+
+        override fun visitFileMessage(message: FileMessage, data: Unit): Array<String> {
+            return arrayOf("visitFileMessage") + super.visitFileMessage(message, data)
+        }
+
+        override fun visitImage(message: Image, data: Unit): Array<String> {
+            return arrayOf("visitImage") + super.visitImage(message, data)
+        }
+
+        override fun visitForwardMessage(message: ForwardMessage, data: Unit): Array<String> {
+            return arrayOf("visitForwardMessage") + super.visitForwardMessage(message, data)
+        }
+
+        override fun visitMusicShare(message: MusicShare, data: Unit): Array<String> {
+            return arrayOf("visitMusicShare") + super.visitMusicShare(message, data)
+        }
+
+        override fun visitUnsupportedMessage(message: UnsupportedMessage, data: Unit): Array<String> {
+            return arrayOf("visitUnsupportedMessage") + super.visitUnsupportedMessage(message, data)
+        }
+
+        override fun visitRichMessage(message: RichMessage, data: Unit): Array<String> {
+            return arrayOf("visitRichMessage") + super.visitRichMessage(message, data)
+        }
+
+        override fun visitServiceMessage(message: ServiceMessage, data: Unit): Array<String> {
+            return arrayOf("visitServiceMessage") + super.visitServiceMessage(message, data)
+        }
+
+        override fun visitSimpleServiceMessage(message: SimpleServiceMessage, data: Unit): Array<String> {
+            return arrayOf("visitSimpleServiceMessage") + super.visitSimpleServiceMessage(message, data)
+        }
+
+        override fun visitLightApp(message: LightApp, data: Unit): Array<String> {
+            return arrayOf("visitLightApp") + super.visitLightApp(message, data)
+        }
+
+        override fun visitAbstractServiceMessage(message: AbstractServiceMessage, data: Unit): Array<String> {
+            return arrayOf("visitAbstractServiceMessage") + super.visitAbstractServiceMessage(message, data)
+        }
+    }
+
+    @OptIn(MessageChainConstructor::class)
+    @Test
+    fun visitMessageChain() {
+        assertContentEquals(
+            arrayOf(
+                "visitMessageChain",
+                "visitMessage",
+            ),
+            messageChainOf(PlainText("1")).accept(GetCalledMethodNames)
+        )
+        assertContentEquals(
+            arrayOf(
+                "visitMessageChain",
+                "visitMessage",
+            ),
+            emptyMessageChain().accept(GetCalledMethodNames)
+        )
+        assertContentEquals(
+            arrayOf(
+                "visitCombinedMessage",
+                "visitMessageChain",
+                "visitMessage",
+            ),
+            CombinedMessage(AtAll, AtAll, false).accept(GetCalledMethodNames)
+        )
+    }
+
+    @Test
+    fun visitSingleMessageContent() {
+        assertContentEquals(
+            arrayOf(
+                "visitMessage",
+            ),
+            object : Message {
+                @Suppress("RedundantOverride") // false positive
+                override fun toString(): String = super.toString()
+                override fun contentToString(): String = super.toString()
+            }.accept(GetCalledMethodNames)
+        )
+
+        assertContentEquals(
+            arrayOf(
+                "visitSingleMessage",
+                "visitMessage",
+            ),
+            object : SingleMessage {
+                @Suppress("RedundantOverride") // false positive
+                override fun toString(): String = super.toString()
+                override fun contentToString(): String = super.toString()
+            }.accept(GetCalledMethodNames)
+        )
+
+        assertContentEquals(
+            arrayOf(
+                "visitMessageContent",
+                "visitSingleMessage",
+                "visitMessage",
+            ),
+            object : MessageContent {
+                @Suppress("RedundantOverride") // false positive
+                override fun toString(): String = super.toString()
+                override fun contentToString(): String = super.toString()
+            }.accept(GetCalledMethodNames)
+        )
+
+        assertContentEquals(
+            arrayOf(
+                "visitPlainText",
+                "visitMessageContent",
+                "visitSingleMessage",
+                "visitMessage",
+            ),
+            PlainText("1").accept(GetCalledMethodNames)
+        )
+
+        assertContentEquals(
+            arrayOf(
+                "visitAt",
+                "visitMessageContent",
+                "visitSingleMessage",
+                "visitMessage",
+            ),
+            At(1).accept(GetCalledMethodNames)
+        )
+
+        assertContentEquals(
+            arrayOf(
+                "visitAtAll",
+                "visitMessageContent",
+                "visitSingleMessage",
+                "visitMessage",
+            ),
+            AtAll.accept(GetCalledMethodNames)
+        )
+
+        assertContentEquals(
+            arrayOf(
+                "visitVoice",
+                "visitMessageContent",
+                "visitSingleMessage",
+                "visitMessage",
+            ),
+            @Suppress("DEPRECATION_ERROR")
+            Voice("", byteArrayOf(), 1, 1, "").accept(GetCalledMethodNames)
+        )
+
+        assertContentEquals(
+            arrayOf(
+                "visitAudio",
+                "visitMessageContent",
+                "visitSingleMessage",
+                "visitMessage",
+            ),
+            object : OfflineAudio {
+                override val filename: String get() = ""
+                override val fileMd5: ByteArray get() = byteArrayOf()
+                override val fileSize: Long get() = 1
+                override val codec: AudioCodec get() = AudioCodec.AMR
+                override val extraData: ByteArray? get() = null
+                override fun toString(): String = "test"
+            }.accept(GetCalledMethodNames)
+        )
+
+        assertContentEquals(
+            arrayOf(
+                "visitFlashImage",
+                "visitHummerMessage",
+                "visitMessageContent",
+                "visitSingleMessage",
+                "visitMessage",
+            ),
+            FlashImage(createImage()).accept(GetCalledMethodNames)
+        )
+
+        assertContentEquals(
+            arrayOf(
+                "visitPokeMessage",
+                "visitHummerMessage",
+                "visitMessageContent",
+                "visitSingleMessage",
+                "visitMessage",
+            ),
+            PokeMessage.BiXin.accept(GetCalledMethodNames)
+        )
+
+        assertContentEquals(
+            arrayOf(
+                "visitVipFace",
+                "visitHummerMessage",
+                "visitMessageContent",
+                "visitSingleMessage",
+                "visitMessage",
+            ),
+            VipFace(VipFace.AiXin, 1).accept(GetCalledMethodNames)
+        )
+
+        assertContentEquals(
+            arrayOf(
+                "visitMarketFace",
+                "visitHummerMessage",
+                "visitMessageContent",
+                "visitSingleMessage",
+                "visitMessage",
+            ),
+            object : MarketFace {
+                override val name: String get() = "f"
+                override val id: Int get() = 1
+                override fun toString(): String = "ok"
+            }.accept(GetCalledMethodNames)
+        )
+
+        assertContentEquals(
+            arrayOf(
+                "visitDice",
+                "visitMarketFace",
+                "visitHummerMessage",
+                "visitMessageContent",
+                "visitSingleMessage",
+                "visitMessage",
+            ),
+            Dice(1).accept(GetCalledMethodNames)
+        )
+
+
+        assertContentEquals(
+            arrayOf(
+                "visitFace",
+                "visitMessageContent",
+                "visitSingleMessage",
+                "visitMessage",
+            ),
+            Face(Face.AI_NI).accept(GetCalledMethodNames)
+        )
+
+        assertContentEquals(
+            arrayOf(
+                "visitFileMessage",
+                "visitMessageContent",
+                "visitSingleMessage",
+                "visitMessage",
+            ),
+            object : FileMessage {
+                override val id: String get() = ""
+                override val internalId: Int get() = 1
+                override val name: String get() = ""
+                override val size: Long get() = 1
+
+                override suspend fun toAbsoluteFile(contact: FileSupported): Nothing =
+                    throw UnsupportedOperationException()
+
+                override fun toString(): String = ""
+            }.accept(GetCalledMethodNames)
+        )
+
+        assertContentEquals(
+            arrayOf(
+                "visitImage",
+                "visitMessageContent",
+                "visitSingleMessage",
+                "visitMessage",
+            ),
+            createImage().accept(GetCalledMethodNames)
+        )
+
+        assertContentEquals(
+            arrayOf(
+                "visitForwardMessage",
+                "visitMessageContent",
+                "visitSingleMessage",
+                "visitMessage",
+            ),
+            ForwardMessage(listOf(), "", "", "", "", listOf()).accept(GetCalledMethodNames)
+        )
+
+        assertContentEquals(
+            arrayOf(
+                "visitMusicShare",
+                "visitMessageContent",
+                "visitSingleMessage",
+                "visitMessage",
+            ),
+            MusicShare(
+                kind = MusicKind.NeteaseCloudMusic,
+                title = "ファッション",
+                summary = "rinahamu/Yunomi",
+                brief = "",
+                jumpUrl = "https://music.163.com/song/1338728297/?userid=324076307",
+                pictureUrl = "https://p2.music.126.net/y19E5SadGUmSR8SZxkrNtw==/109951163785855539.jpg",
+                musicUrl = "https://music.163.com/song/media/outer/url?id=1338728297&userid=324076307"
+            ).accept(GetCalledMethodNames)
+        )
+
+        assertContentEquals(
+            arrayOf(
+                "visitUnsupportedMessage",
+                "visitMessageContent",
+                "visitSingleMessage",
+                "visitMessage",
+            ),
+            object : UnsupportedMessage {
+                override val struct: ByteArray get() = byteArrayOf()
+                override fun toString(): String = "test"
+            }.accept(GetCalledMethodNames)
+        )
+
+        assertContentEquals(
+            arrayOf(
+                "visitSimpleServiceMessage",
+                "visitServiceMessage",
+                "visitRichMessage",
+                "visitMessageContent",
+                "visitSingleMessage",
+                "visitMessage",
+            ),
+            SimpleServiceMessage(1, "str").accept(GetCalledMethodNames)
+        )
+
+        assertContentEquals(
+            arrayOf(
+                "visitLightApp",
+                "visitRichMessage",
+                "visitMessageContent",
+                "visitSingleMessage",
+                "visitMessage",
+            ),
+            LightApp("str").accept(GetCalledMethodNames)
+        )
+    }
+}
+
+private fun createImage(): Image {
+    return object : Image {
+        override val imageId: String get() = "{88914B32-B758-74ED-B00D-CAA6D2A5D7F6}.jpg"
+        override val width: Int get() = 1
+        override val height: Int get() = 1
+        override val size: Long get() = 1
+        override val imageType: ImageType get() = ImageType.APNG
+
+        override fun toString(): String = "test"
+        override fun contentToString(): String = "test"
+
+        @MiraiExperimentalApi
+        override fun appendMiraiCodeTo(builder: StringBuilder) {
+        }
+
+    }
+}

mirai-core/src/commonMain/kotlin/contact/SendMessageHandler.kt

@@ -319,9 +319,7 @@ internal suspend fun <C : Contact> SendMessageHandler<C>.transformSpecialMessage
             )
             forward.nodeList.forEach { tmp.addAll(it.messageChain) }
 
-            // toMessageChain will lose some element
-            @Suppress("INVISIBLE_MEMBER")
-            createMessageChainImplOptimized(tmp).verifyLength(forward, contact)
+            tmp.verifyLength(forward, contact)
         }
 
         val resId = getMiraiImpl().uploadMessageHighway(

mirai-core/src/commonMain/kotlin/contact/util.kt

@@ -30,7 +30,7 @@ internal fun Contact.logMessageSent(message: Message) {
     }
 }
 
-internal fun MessageChain.countImages(): Int = this.count { it is Image }
+internal fun Iterable<SingleMessage>.countImages(): Int = this.count { it is Image }
 
 private val logger by lazy { MiraiLogger.Factory.create(SendMessageHandler::class) }
 
@@ -55,14 +55,14 @@ internal fun Message.verifySendingValid() {
     }
 }
 
-internal fun MessageChain.verifyLength(
+internal fun Iterable<SingleMessage>.verifyLength(
     originalMessage: Message, target: Contact,
 ): Int {
     val chain = this
     val length = estimateLength(target, 15001)
     if (length > 15000 || countImages() > 50) {
         throw MessageTooLargeException(
-            target, originalMessage, this,
+            target, originalMessage, this.toMessageChain(),
             "message(${
                 chain.joinToString("", limit = 10).let { rsp ->
                     if (rsp.length > 100) {

mirai-core/src/commonMain/kotlin/message/RefinableMessage.kt

@@ -156,8 +156,9 @@ internal object LightMessageRefiner : MessageRefiner() {
         val source = this.sourceOrNull?.safeCast<IncomingMessageSourceInternal>() ?: return this
         val originalMessage = this
         source.originalMessageLazy = lazy {
-            @Suppress("INVISIBLE_MEMBER")
-            createMessageChainImplOptimized(originalMessage.filterNot { it is MessageSource })
+            originalMessage.filterNot { it is MessageSource }.toMessageChain()
+//            @Suppress("INVISIBLE_MEMBER")
+//            createMessageChainImplOptimized(originalMessage.filterNot { it is MessageSource })
         }
         return this
     }

mirai-core/src/commonMain/kotlin/utils/type.kt

@@ -44,7 +44,7 @@ internal fun String.toIpV4Long(): Long {
     }
 }
 
-internal fun MessageChain.estimateLength(target: ContactOrBot, upTo: Int): Int =
+internal fun Iterable<SingleMessage>.estimateLength(target: ContactOrBot, upTo: Int): Int =
     sumUpTo(upTo) { it, up ->
         it.estimateLength(target, up)
     }

mirai-core/src/commonTest/kotlin/message/CleanupRubbishMessageElementsTest.kt

@@ -151,8 +151,7 @@ internal class CleanupRubbishMessageElementsTest {
     }
 
     private fun noMessageSource(c: MessageChain): MessageChain {
-        @Suppress("INVISIBLE_MEMBER", "INVISIBLE_REFERENCE")
-        return createMessageChainImplOptimized(c.filterNot { it is MessageSource })
+        return c.filterNot { it is MessageSource }.toMessageChain()
     }
 
     //endregion