Completed CombinedMessage redesigning and constraining on concatenation

compatibility-validator/build.gradle.kts

@@ -7,6 +7,11 @@ plugins {
 
 description = "Binary and source compatibility validator for mirai-core and mirai-core-qqandroid"
 
+repositories {
+    mavenCentral()
+    jcenter()
+}
+
 kotlin {
     sourceSets {
         all {
@@ -17,7 +22,19 @@ kotlin {
         main {
             dependencies {
                 api(kotlin("stdlib"))
-                api(project(":mirai-core-qqandroid"))
+                runtimeOnly(project(":mirai-core-qqandroid"))
+                compileOnly("net.mamoe:mirai-core-qqandroid-jvm:0.33.0")
+                api(kotlinx("coroutines-core", Versions.Kotlin.coroutines))
+            }
+        }
+
+        test {
+            dependencies {
+                api(kotlin("stdlib"))
+                api(kotlin("test"))
+                api(kotlin("test-junit"))
+                runtimeOnly(project(":mirai-core-qqandroid"))
+                compileOnly("net.mamoe:mirai-core-qqandroid-jvm:0.33.0")
                 api(kotlinx("coroutines-core", Versions.Kotlin.coroutines))
             }
         }

compatibility-validator/src/main/kotlin/compatibility/testKotlinCompatibility.kt

+/*
+ * Copyright 2020 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/master/LICENSE
+ */
+
+package compatibility
+
+fun main() {
+
+}
\ No newline at end of file

compatibility-validator/src/test/kotlin/compatibility/CombinedMessageTest.kt

+package compatibility
+
+import net.mamoe.mirai.message.data.*
+import net.mamoe.mirai.utils.MiraiInternalAPI
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+@OptIn(MiraiInternalAPI::class)
+internal class CombinedMessageTest {
+
+
+    @Test
+    fun testAsSequence() {
+        var message: Message = "Hello ".toMessage()
+        message += "World"
+
+        assertEquals(
+            "Hello World",
+            (message as CombinedMessage).asSequence().joinToString(separator = "")
+        )
+    }
+
+    @Test
+    fun testAsSequence2() {
+        var message: Message = "Hello ".toMessage()
+        message += listOf(
+            PlainText("W"),
+            PlainText("o"),
+            PlainText("r") + PlainText("ld")
+        ).asMessageChain()
+
+        assertEquals(
+            "Hello World",
+            (message as CombinedMessage).asSequence().joinToString(separator = "")
+        )
+    }
+}
+
+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()
+}
+
+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
+    }
+    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())
+    }
+}
\ No newline at end of file

compatibility-validator/src/test/kotlin/compatibility/TestKotlinCompatibility.kt

+/*
+ * Copyright 2020 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/master/LICENSE
+ */
+
+package compatibility
+
+import net.mamoe.mirai.message.data.Message
+import net.mamoe.mirai.message.data.PlainText
+import org.junit.Test
+
+
+internal class TestKotlinCompatibility {
+
+    @Test
+    fun testMessageChain() {
+        val x = PlainText("te") + PlainText("st")
+
+        println(Message::class.java.declaredMethods.joinToString("\n"))
+        println()
+        println(x::class.java.declaredMethods.joinToString("\n"))
+    }
+}
\ No newline at end of file

mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/QQAndroidBot.common.kt

@@ -56,6 +56,7 @@ import kotlin.coroutines.CoroutineContext
 import kotlin.jvm.JvmSynthetic
 import kotlin.math.absoluteValue
 import kotlin.random.Random
+import net.mamoe.mirai.qqandroid.network.protocol.data.jce.FriendInfo as JceFriendInfo
 
 @OptIn(ExperimentalContracts::class)
 internal fun Bot.asQQAndroidBot(): QQAndroidBot {
@@ -98,8 +99,9 @@ internal abstract class QQAndroidBotBase constructor(
 
     override val friends: ContactList<QQ> = ContactList(LockFreeLinkedList())
 
-    override lateinit var nick: String
-        internal set
+    override val nick: String get() = selfInfo.nick
+
+    internal lateinit var selfInfo: JceFriendInfo
 
     override val selfQQ: QQ by lazy {
         @OptIn(LowLevelAPI::class)

mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/contact/QQImpl.kt

@@ -51,7 +51,7 @@ import kotlin.jvm.JvmSynthetic
 internal inline class FriendInfoImpl(
     private val jceFriendInfo: net.mamoe.mirai.qqandroid.network.protocol.data.jce.FriendInfo
 ) : FriendInfo {
-    override val nick: String get() = jceFriendInfo.nick ?: ""
+    override val nick: String get() = jceFriendInfo.nick
     override val uin: Long get() = jceFriendInfo.friendUin
 }
 

mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/network/QQAndroidBotNetworkHandler.kt

@@ -223,8 +223,8 @@ internal class QQAndroidBotNetworkHandler(bot: QQAndroidBot) : BotNetworkHandler
                         }
 
                         // self info
-                        data.selfInfo?.apply {
-                            bot.nick = nick ?: ""
+                        data.selfInfo?.run {
+                            bot.selfInfo = this
 //                            bot.remark = remark ?: ""
 //                            bot.sex = sex
                         }

mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/network/protocol/data/jce/FriendList.kt

@@ -109,7 +109,7 @@ internal class FriendInfo(
     @JceId(11) val sqqOnLineStateV2: Byte? = null,
     @JceId(12) val sShowName: String? = "",
     @JceId(13) val isRemark: Byte? = null,
-    @JceId(14) val nick: String? = "",
+    @JceId(14) val nick: String = "",
     @JceId(15) val specialFlag: Byte? = null,
     @JceId(16) val vecIMGroupID: ByteArray? = null,
     @JceId(17) val vecMSFGroupID: ByteArray? = null,

mirai-core/src/commonMain/kotlin/net.mamoe.mirai/Bot.kt

@@ -87,6 +87,7 @@ expect abstract class Bot() : CoroutineScope, LowLevelBotAPIAccessor {
     /**
      * 昵称
      */
+    @SinceMirai("0.33.1")
     abstract val nick: String
 
     /**

mirai-core/src/commonMain/kotlin/net.mamoe.mirai/event/subscribeMessages.kt

@@ -24,7 +24,7 @@ import net.mamoe.mirai.message.ContactMessage
 import net.mamoe.mirai.message.FriendMessage
 import net.mamoe.mirai.message.GroupMessage
 import net.mamoe.mirai.message.data.Message
-import net.mamoe.mirai.message.data.first
+import net.mamoe.mirai.message.data.firstIsInstance
 import net.mamoe.mirai.utils.SinceMirai
 import kotlin.contracts.ExperimentalContracts
 import kotlin.contracts.InvocationKind
@@ -700,7 +700,7 @@ open class MessageSubscribersBuilder<M : ContactMessage, out Ret, R : RR, RR>(
     @MessageDsl
     @SinceMirai("0.30.0")
     inline fun <reified N : Message> has(noinline onEvent: @MessageDsl suspend M.(N) -> R): Ret =
-        content({ message.any { it is N } }, { onEvent.invoke(this, message.first()) })
+        content({ message.any { it is N } }, { onEvent.invoke(this, message.firstIsInstance()) })
 
     /**
      * 如果 [mapper] 返回值非空, 就执行 [onEvent]

mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/MessagePacket.kt

@@ -357,8 +357,8 @@ suspend inline fun <reified M : Message> ContactMessage.nextMessageContaining(
 ): M {
     return subscribingGet<ContactMessage, ContactMessage>(timeoutMillis) {
         takeIf { this.isContextIdenticalWith(this@nextMessageContaining) }
-            .takeIf { this.message.any<M>() }
-    }.message.first()
+            .takeIf { this.message.anyIsInstance<M>() }
+    }.message.firstIsInstance()
 }
 
 @JvmSynthetic
@@ -370,8 +370,8 @@ inline fun <reified M : Message> ContactMessage.nextMessageContainingAsync(
         @Suppress("RemoveExplicitTypeArguments")
         subscribingGet<ContactMessage, ContactMessage>(timeoutMillis) {
             takeIf { this.isContextIdenticalWith(this@nextMessageContainingAsync) }
-                .takeIf { this.message.any<M>() }
-        }.message.first<M>()
+                .takeIf { this.message.anyIsInstance<M>() }
+        }.message.firstIsInstance<M>()
     }
 }
 
@@ -391,8 +391,8 @@ suspend inline fun <reified M : Message> ContactMessage.nextMessageContainingOrN
 ): M? {
     return subscribingGetOrNull<ContactMessage, ContactMessage>(timeoutMillis) {
         takeIf { this.isContextIdenticalWith(this@nextMessageContainingOrNull) }
-            .takeIf { this.message.any<M>() }
-    }?.message?.first()
+            .takeIf { this.message.anyIsInstance<M>() }
+    }?.message?.firstIsInstance()
 }
 
 @JvmSynthetic
@@ -403,8 +403,8 @@ inline fun <reified M : Message> ContactMessage.nextMessageContainingOrNullAsync
     return this.bot.async(coroutineContext) {
         subscribingGetOrNull<ContactMessage, ContactMessage>(timeoutMillis) {
             takeIf { this.isContextIdenticalWith(this@nextMessageContainingOrNullAsync) }
-                .takeIf { this.message.any<M>() }
-        }?.message?.first<M>()
+                .takeIf { this.message.anyIsInstance<M>() }
+        }?.message?.firstIsInstance<M>()
     }
 }
 

mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/At.kt

@@ -17,6 +17,7 @@ package net.mamoe.mirai.message.data
 import net.mamoe.mirai.LowLevelAPI
 import net.mamoe.mirai.contact.Member
 import net.mamoe.mirai.contact.nameCardOrNick
+import net.mamoe.mirai.utils.MiraiInternalAPI
 import kotlin.jvm.JvmMultifileClass
 import kotlin.jvm.JvmName
 import kotlin.jvm.JvmStatic
@@ -56,6 +57,7 @@ private constructor(val target: Long, val display: String) :
     }
 
     // 自动为消息补充 " "
+    @OptIn(MiraiInternalAPI::class)
     @Suppress("INAPPLICABLE_JVM_NAME")
     @Deprecated("for binary compatibility", level = DeprecationLevel.HIDDEN)
     @JvmName("followedBy")
@@ -67,7 +69,7 @@ private constructor(val target: Long, val display: String) :
         return followedByInternalForBinaryCompatibility(PlainText(" ") + tail)
     }
 
-    override fun followedBy(tail: Message): Message {
+    override fun followedBy(tail: Message): MessageChain {
         if (tail is PlainText && tail.stringValue.startsWith(' ')) {
             return super.followedBy(tail)
         }

mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/AtAll.kt

@@ -12,6 +12,7 @@
 
 package net.mamoe.mirai.message.data
 
+import net.mamoe.mirai.utils.MiraiInternalAPI
 import net.mamoe.mirai.utils.SinceMirai
 import kotlin.jvm.JvmMultifileClass
 import kotlin.jvm.JvmName
@@ -42,6 +43,7 @@ object AtAll :
     override fun contentToString(): String = display
 
     // 自动为消息补充 " "
+    @OptIn(MiraiInternalAPI::class)
     @Deprecated("for binary compatibility", level = DeprecationLevel.HIDDEN)
     @Suppress("INAPPLICABLE_JVM_NAME")
     @JvmName("followedBy")
@@ -53,7 +55,7 @@ object AtAll :
         return followedByInternalForBinaryCompatibility(PlainText(" ") + tail)
     }
 
-    override fun followedBy(tail: Message): Message {
+    override fun followedBy(tail: Message): MessageChain {
         if (tail is PlainText && tail.stringValue.startsWith(' ')) {
             return super.followedBy(tail)
         }

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

@@ -14,11 +14,13 @@ package net.mamoe.mirai.message.data
 
 import net.mamoe.mirai.utils.MiraiExperimentalAPI
 import net.mamoe.mirai.utils.MiraiInternalAPI
+import net.mamoe.mirai.utils.PlannedRemoval
 import kotlin.jvm.JvmMultifileClass
 import kotlin.jvm.JvmName
+import kotlin.jvm.JvmSynthetic
 
 /**
- * 链接的两个消息.
+ * 快速链接的两个消息 (避免构造新的 list).
  *
  * 不要直接构造 [CombinedMessage], 使用 [Message.plus]
  * 要连接多个 [Message], 使用 [buildMessageChain]
@@ -27,64 +29,68 @@ import kotlin.jvm.JvmName
  *
  * Left-biased list
  */
+@MiraiInternalAPI("this API is going to be internal")
 class CombinedMessage
-@Deprecated(message = "use Message.plus", level = DeprecationLevel.ERROR)
-@MiraiInternalAPI("CombinedMessage 构造器可能会在将来被改动") constructor(
-    @MiraiExperimentalAPI("CombinedMessage.left 可能会在将来被改动")
-    val left: SingleMessage,
-    @MiraiExperimentalAPI("CombinedMessage.tail 可能会在将来被改动")
-    val tail: SingleMessage
-) : Iterable<SingleMessage>, Message {
-
-    /*
-    // 不要把它用作 local function, 会编译错误
-    @OptIn(MiraiExperimentalAPI::class)
-    private suspend fun SequenceScope<Message>.yieldCombinedOrElements(message: Message) {
-        when (message) {
-            is CombinedMessage -> {
-                // fast path, 避免创建新的 iterator, 也不会挂起协程
-                yieldCombinedOrElements(message.left)
-                yieldCombinedOrElements(message.tail)
-            }
-            is Iterable<*> -> {
-                // 更好的性能, 因为协程不会挂起.
-                // 这可能会导致爆栈 (十万个元素), 但作为消息序列足够了.
-                message.forEach {
-                    yieldCombinedOrElements(
-                        it as? Message ?: error(
-                            "A Message implementing Iterable must implement Iterable<Message>, " +
-                                    "whereas got ${it!!::class.simpleName}"
-                        )
-                    )
-                }
-            }
-            else -> {
-                check(message is SingleMessage) {
-                    "unsupported Message type. " +
-                            "A Message must be a CombinedMessage, a Iterable<Message> or a SingleMessage"
-                }
-                yield(message)
-            }
-        }
-    }
-    */
-
+internal constructor(
+    internal val left: Message, // 必须已经完成 constrain single
+    internal val tail: Message
+) : Message, MessageChain {
     @OptIn(MiraiExperimentalAPI::class)
     fun asSequence(): Sequence<SingleMessage> = sequence {
-        yield(left)
-        yield(tail)
+        yieldCombinedOrElementsFlatten(this@CombinedMessage)
     }
 
     override fun iterator(): Iterator<SingleMessage> {
         return asSequence().iterator()
     }
 
+    @PlannedRemoval("1.0.0")
+    @Deprecated(
+        "有歧义, 自行使用 contentToString() 比较",
+        ReplaceWith("this.contentToString() == other"),
+        DeprecationLevel.HIDDEN
+    )
+    override fun contains(sub: String): Boolean {
+        return contentToString().contains(sub)
+    }
+
+    override val size: Int = when {
+        left === EmptyMessageChain && tail !== EmptyMessageChain -> 1
+        left === EmptyMessageChain && tail === EmptyMessageChain -> 0
+        left !== EmptyMessageChain && tail === EmptyMessageChain -> 1
+        left !== EmptyMessageChain && tail !== EmptyMessageChain -> 2
+        else -> error("stub")
+    }
+
     @OptIn(MiraiExperimentalAPI::class)
     override fun toString(): String {
         return tail.toString() + left.toString()
     }
 
     override fun contentToString(): String {
-        return toString()
+        return left.contentToString() + tail.contentToString()
+    }
+}
+
+@JvmSynthetic
+// 不要把它用作 local function, 会编译错误
+@OptIn(MiraiExperimentalAPI::class, MiraiInternalAPI::class)
+private suspend fun SequenceScope<SingleMessage>.yieldCombinedOrElementsFlatten(message: Message) {
+    when (message) {
+        is CombinedMessage -> {
+            // fast path, 避免创建新的 iterator, 也不会挂起协程
+            yieldCombinedOrElementsFlatten(message.left)
+            yieldCombinedOrElementsFlatten(message.tail)
+        }
+        is MessageChain -> {
+            yieldAll(message)
+        }
+        else -> {
+            check(message is SingleMessage) {
+                "unsupported Message type: ${message::class}" +
+                        "A Message must be a CombinedMessage, a Iterable<Message> or a SingleMessage"
+            }
+            yield(message)
+        }
     }
 }

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

@@ -15,6 +15,7 @@ import net.mamoe.mirai.contact.Contact
 import net.mamoe.mirai.message.MessageReceipt
 import net.mamoe.mirai.utils.MiraiExperimentalAPI
 import net.mamoe.mirai.utils.MiraiInternalAPI
+import net.mamoe.mirai.utils.PlannedRemoval
 import net.mamoe.mirai.utils.SinceMirai
 import kotlin.jvm.JvmName
 import kotlin.jvm.JvmSynthetic
@@ -24,16 +25,16 @@ import kotlin.jvm.JvmSynthetic
  * 采用这样的消息模式是因为 QQ 的消息多元化, 一条消息中可包含 [纯文本][PlainText], [图片][Image] 等.
  *
  * [消息][Message] 分为
- * - [MessageMetadata] 消息元数据, 包括: [消息来源][MessageSource]
- * - [MessageContent] 单个消息, 包括: [纯文本][PlainText], [@群员][At], [@全体成员][AtAll] 等.
- * - [CombinedMessage] 通过 [plus] 连接的两个消息. 可通过 [asMessageChain] 转换为 [MessageChain]
- * - [MessageChain] 不可变消息链, 链表形式链接的多个 [SingleMessage] 实例.
+ * - [SingleMessage]:
+ *   - [MessageMetadata] 消息元数据, 包括: [消息来源][MessageSource], [引用回复][QuoteReply].
+ *   - [MessageContent] 含内容的消息, 包括: [纯文本][PlainText], [@群员][At], [@全体成员][AtAll] 等.
+ * - [MessageChain]: 不可变消息链, 链表形式链接的多个 [SingleMessage] 实例.
  *
  * #### 在 Kotlin 使用 [Message]:
  * 这与使用 [String] 的使用非常类似.
  *
- * 比较 [Message] 与 [String] (使用 infix [Message.eq]):
- *  `if(event eq "你好") qq.sendMessage(event)`
+ * 比较 [SingleMessage] 与 [String]:
+ *  `if(message.contentToString() == "你好") qq.sendMessage(event)`
  *
  * 连接 [Message] 与 [Message], [String], (使用 operator [Message.plus]):
  *  ```kotlin
@@ -65,6 +66,7 @@ import kotlin.jvm.JvmSynthetic
  *
  * @see Contact.sendMessage 发送消息
  */
+@OptIn(MiraiInternalAPI::class)
 interface Message {
     /**
      * 类型 Key.
@@ -75,25 +77,16 @@ interface Message {
      */
     interface Key<out M : Message> {
         /**
-         * 此 [Key] 指代的 [Message] 类型名. 一般为 `class.simpleName`
+         * 此 [Key] 指代的 [Message] 类型名. 一般为 `class.simpleName`, 如 "QuoteReply", "PlainText"
          */
         @SinceMirai("0.34.0")
         val typeName: String
     }
 
-    infix fun eq(other: Message): Boolean = this.toString() == other.toString()
-
-    /**
-     * 将 [toString] 与 [other] 比较
-     */
-    infix fun eq(other: String): Boolean = this.toString() == other
-
-    operator fun contains(sub: String): Boolean = false
-
     /**
      * 把 `this` 连接到 [tail] 的头部. 类似于字符串相加.
      *
-     * 连接后无法保证 [ConstrainSingle] 的元素单独存在. 需在
+     * 连接后可以保证 [ConstrainSingle] 的元素单独存在.
      *
      * 例:
      * ```kotlin
@@ -111,17 +104,67 @@ interface Message {
     @Suppress("DEPRECATION_ERROR")
     @OptIn(MiraiInternalAPI::class)
     @JvmSynthetic // in java they should use `plus` instead
-    fun followedBy(tail: Message): Message {
-        TODO()
-        if (this is SingleMessage && tail is SingleMessage) {
+    fun followedBy(tail: Message): MessageChain {
+        when {
+            this is SingleMessage && tail is SingleMessage -> {
                 if (this is ConstrainSingle<*> && tail is ConstrainSingle<*>) {
-                return if (this.key == tail.key) {
+                    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)) {
+                    val iterator = this.iterator()
+                    var tailUsed = false
+                    return MessageChainImplByCollection(
+                        constrainSingleMessagesImpl {
+                            if (iterator.hasNext()) {
+                                iterator.next()
+                            } else if (!tailUsed) {
+                                tailUsed = true
                                 tail
-                } else {
-                    CombinedMessage(this, tail)
+                            } else null
                         }
+                    )
                 }
 
+                return CombinedMessage(this, tail)
+            }
+
+            else -> { // both chain
+                this as MessageChain
+                tail as MessageChain
+
+                var iterator = this.iterator()
+                var tailUsed = false
+                return MessageChainImplByCollection(
+                    constrainSingleMessagesImpl {
+                        if (iterator.hasNext()) {
+                            iterator.next()
+                        } else if (!tailUsed) {
+                            tailUsed = true
+                            iterator = tail.iterator()
+                            iterator.next()
+                        } else null
+                    }
+                )
+            }
         }
     }
 
@@ -147,43 +190,79 @@ interface Message {
     @SinceMirai("0.34.0")
     fun contentToString(): String
 
-    operator fun plus(another: Message): Message = this.followedBy(another)
+    operator fun plus(another: Message): MessageChain = this.followedBy(another)
 
-    // avoid resolution ambiguity
-    operator fun plus(another: SingleMessage): Message = this.followedBy(another)
+    // don't remove! avoid resolution ambiguity between `CharSequence` and `Message`
+    operator fun plus(another: SingleMessage): MessageChain = this.followedBy(another)
 
-    operator fun plus(another: String): Message = this.followedBy(another.toMessage())
+    operator fun plus(another: String): MessageChain = this.followedBy(another.toMessage())
 
     // `+ ""` will be resolved to `plus(String)` instead of `plus(CharSeq)`
-    operator fun plus(another: CharSequence): Message = this.followedBy(another.toString().toMessage())
-
+    operator fun plus(another: CharSequence): MessageChain = this.followedBy(another.toString().toMessage())
 
+    //////////////////////////////////////
     // FOR BINARY COMPATIBILITY UNTIL 1.0.0
+    //////////////////////////////////////
+
+    @PlannedRemoval("1.0.0")
+    @JvmSynthetic
+    @Deprecated(
+        "有歧义, 自行使用 contentToString() 比较",
+        ReplaceWith("this.contentToString() == other"),
+        DeprecationLevel.HIDDEN
+    )
+    infix fun eq(other: Message): Boolean = this.toString() == other.toString()
 
+    /**
+     * 将 [contentToString] 与 [other] 比较
+     */
+    @PlannedRemoval("1.0.0")
+    @JvmSynthetic
+    @Deprecated(
+        "有歧义, 自行使用 contentToString() 比较",
+        ReplaceWith("this.contentToString() == other"),
+        DeprecationLevel.HIDDEN
+    )
+    infix fun eq(other: String): Boolean = this.contentToString() == other
+
+    @PlannedRemoval("1.0.0")
+    @JvmSynthetic
+    @Deprecated(
+        "有歧义, 自行使用 contentToString() 比较",
+        ReplaceWith("this.contentToString() == other"),
+        DeprecationLevel.HIDDEN
+    )
+    operator fun contains(sub: String): Boolean = false
+
+    @PlannedRemoval("1.0.0")
     @Suppress("INAPPLICABLE_JVM_NAME")
     @JvmName("followedBy")
     @Deprecated("for binary compatibility", level = DeprecationLevel.HIDDEN)
     @JvmSynthetic
     fun followedBy1(tail: Message): CombinedMessage = this.followedByInternalForBinaryCompatibility(tail)
 
+    @PlannedRemoval("1.0.0")
     @Suppress("INAPPLICABLE_JVM_NAME")
     @JvmName("plus")
     @Deprecated("for binary compatibility", level = DeprecationLevel.HIDDEN)
     @JvmSynthetic
     fun plus1(another: Message): CombinedMessage = this.followedByInternalForBinaryCompatibility(another)
 
+    @PlannedRemoval("1.0.0")
     @Suppress("INAPPLICABLE_JVM_NAME")
     @JvmName("plus")
     @Deprecated("for binary compatibility", level = DeprecationLevel.HIDDEN)
     @JvmSynthetic
     fun plus1(another: SingleMessage): CombinedMessage = this.followedByInternalForBinaryCompatibility(another)
 
+    @PlannedRemoval("1.0.0")
     @Suppress("INAPPLICABLE_JVM_NAME")
     @JvmName("plus")
     @Deprecated("for binary compatibility", level = DeprecationLevel.HIDDEN)
     @JvmSynthetic
     fun plus1(another: String): CombinedMessage = this.followedByInternalForBinaryCompatibility(another.toMessage())
 
+    @PlannedRemoval("1.0.0")
     @Suppress("INAPPLICABLE_JVM_NAME")
     @JvmName("plus")
     @Deprecated("for binary compatibility", level = DeprecationLevel.HIDDEN)
@@ -192,24 +271,24 @@ interface Message {
         this.followedByInternalForBinaryCompatibility(another.toString().toMessage())
 }
 
+
+@OptIn(MiraiInternalAPI::class)
+private fun Message.hasDuplicationOfConstrain(key: Message.Key<*>): Boolean {
+    return when (this) {
+        is SingleMessage -> (this as? ConstrainSingle<*>)?.key == key
+        is CombinedMessage -> return this.left.hasDuplicationOfConstrain(key) || this.tail.hasDuplicationOfConstrain(key)
+        is SingleMessageChainImpl -> (this.delegate as? ConstrainSingle<*>)?.key == key
+        is MessageChainImplByCollection -> this.delegate.any { (it as? ConstrainSingle<*>)?.key == key }
+        is MessageChainImplBySequence -> this.any { (it as? ConstrainSingle<*>)?.key == key }
+        else -> error("stub")
+    }
+}
+
 @OptIn(MiraiInternalAPI::class)
 @JvmSynthetic
 @Suppress("DEPRECATION_ERROR")
 internal fun Message.followedByInternalForBinaryCompatibility(tail: Message): CombinedMessage {
-    TODO()
-    if (this is ConstrainSingle<*>) {
-
-    }
-
-    if (this is SingleMessage && tail is SingleMessage) {
-        if (this is ConstrainSingle<*> && tail is ConstrainSingle<*>
-            && this.key == tail.key
-        ) return CombinedMessage(EmptyMessageChain, tail)
-        return CombinedMessage(left = this, tail = tail)
-    } else {
-
-        //    return CombinedMessage(left = this.constrain)
-    }
+    return CombinedMessage(EmptyMessageChain, this.followedBy(tail))
 }
 
 @JvmSynthetic
@@ -218,7 +297,8 @@ suspend inline fun <C : Contact> Message.sendTo(contact: C): MessageReceipt<C> {
     return contact.sendMessage(this) as MessageReceipt<C>
 }
 
-fun Message.repeat(count: Int): MessageChain {
+// inline: for future removal
+inline fun Message.repeat(count: Int): MessageChain {
     if (this is ConstrainSingle<*>) {
         // fast-path
         return SingleMessageChainImpl(this)
@@ -231,7 +311,21 @@ fun Message.repeat(count: Int): MessageChain {
 @JvmSynthetic
 inline operator fun Message.times(count: Int): MessageChain = this.repeat(count)
 
-interface SingleMessage : Message, CharSequence, Comparable<String>
+@Suppress("OverridingDeprecatedMember")
+interface SingleMessage : Message, CharSequence, Comparable<String> {
+    override operator fun contains(sub: String): Boolean = sub in this.contentToString()
+
+    /**
+     * 比较两个消息的 [contentToString]
+     */
+    override infix fun eq(other: Message): Boolean = this.contentToString() == other.contentToString()
+
+    /**
+     * 将 [contentToString] 与 [other] 比较
+     */
+    override infix fun eq(other: String): Boolean = this.contentToString() == other
+
+}
 
 /**
  * 消息元数据, 即不含内容的元素.
@@ -251,7 +345,7 @@ interface MessageMetadata : SingleMessage {
  */
 @SinceMirai("0.34.0")
 @MiraiExperimentalAPI
-interface ConstrainSingle<M : Message> : SingleMessage {
+interface ConstrainSingle<M : Message> : MessageMetadata {
     val key: Message.Key<M>
 }
 
@@ -263,6 +357,7 @@ interface MessageContent : SingleMessage
 /**
  * 将 [this] 发送给指定联系人
  */
+@JvmSynthetic
 @Suppress("UNCHECKED_CAST")
 suspend inline fun <C : Contact> MessageChain.sendTo(contact: C): MessageReceipt<C> =
     contact.sendMessage(this) as MessageReceipt<C>
\ No newline at end of file

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

@@ -40,10 +40,16 @@ import kotlin.reflect.KProperty
  * @see flatten 扁平化
  */
 interface MessageChain : Message, Iterable<SingleMessage> {
+    @PlannedRemoval("1.0.0")
+    @Deprecated(
+        "有歧义, 自行使用 contentToString() 比较",
+        ReplaceWith("this.contentToString() == other"),
+        DeprecationLevel.HIDDEN
+    )
     override operator fun contains(sub: String): Boolean
 
     /**
-     * 元素数量
+     * 元素数量. [EmptyMessageChain] 不参加计数.
      */
     @SinceMirai("0.31.1")
     val size: Int
@@ -104,20 +110,20 @@ inline fun MessageChain.foreachContent(block: (Message) -> Unit) {
  * 获取第一个 [M] 类型的 [Message] 实例
  */
 @JvmSynthetic
-inline fun <reified M : Message?> MessageChain.firstOrNull(): M? = this.firstOrNull { it is M } as M?
+inline fun <reified M : Message?> MessageChain.firstIsInstanceOrNull(): M? = this.firstOrNull { it is M } as M?
 
 /**
  * 获取第一个 [M] 类型的 [Message] 实例
  * @throws [NoSuchElementException] 如果找不到该类型的实例
  */
 @JvmSynthetic
-inline fun <reified M : Message> MessageChain.first(): M = this.first { it is M } as M
+inline fun <reified M : Message> MessageChain.firstIsInstance(): M = this.first { it is M } as M
 
 /**
  * 获取第一个 [M] 类型的 [Message] 实例
  */
 @JvmSynthetic
-inline fun <reified M : Message> MessageChain.any(): Boolean = this.any { it is M }
+inline fun <reified M : Message> MessageChain.anyIsInstance(): Boolean = this.any { it is M }
 
 
 /**
@@ -127,35 +133,35 @@ inline fun <reified M : Message> MessageChain.any(): Boolean = this.any { it is
 @JvmSynthetic
 @Suppress("UNCHECKED_CAST")
 fun <M : Message> MessageChain.firstOrNull(key: Message.Key<M>): M? = when (key) {
-    At -> firstOrNull<At>()
-    AtAll -> firstOrNull<AtAll>()
-    PlainText -> firstOrNull<PlainText>()
-    Image -> firstOrNull<Image>()
-    OnlineImage -> firstOrNull<OnlineImage>()
-    OfflineImage -> firstOrNull<OfflineImage>()
-    GroupImage -> firstOrNull<GroupImage>()
-    FriendImage -> firstOrNull<FriendImage>()
-    Face -> firstOrNull<Face>()
-    QuoteReply -> firstOrNull<QuoteReply>()
-    MessageSource -> firstOrNull<MessageSource>()
-    OnlineMessageSource -> firstOrNull<OnlineMessageSource>()
-    OfflineMessageSource -> firstOrNull<OfflineMessageSource>()
-    OnlineMessageSource.Outgoing -> firstOrNull<OnlineMessageSource.Outgoing>()
-    OnlineMessageSource.Outgoing.ToGroup -> firstOrNull<OnlineMessageSource.Outgoing.ToGroup>()
-    OnlineMessageSource.Outgoing.ToFriend -> firstOrNull<OnlineMessageSource.Outgoing.ToFriend>()
-    OnlineMessageSource.Incoming -> firstOrNull<OnlineMessageSource.Incoming>()
-    OnlineMessageSource.Incoming.FromGroup -> firstOrNull<OnlineMessageSource.Incoming.FromGroup>()
-    OnlineMessageSource.Incoming.FromFriend -> firstOrNull<OnlineMessageSource.Incoming.FromFriend>()
-    OnlineMessageSource -> firstOrNull<OnlineMessageSource>()
-    XmlMessage -> firstOrNull<XmlMessage>()
-    JsonMessage -> firstOrNull<JsonMessage>()
-    RichMessage -> firstOrNull<RichMessage>()
-    LightApp -> firstOrNull<LightApp>()
-    PokeMessage -> firstOrNull<PokeMessage>()
-    HummerMessage -> firstOrNull<HummerMessage>()
-    FlashImage -> firstOrNull<FlashImage>()
-    GroupFlashImage -> firstOrNull<GroupFlashImage>()
-    FriendFlashImage -> firstOrNull<FriendFlashImage>()
+    At -> firstIsInstanceOrNull<At>()
+    AtAll -> firstIsInstanceOrNull<AtAll>()
+    PlainText -> firstIsInstanceOrNull<PlainText>()
+    Image -> firstIsInstanceOrNull<Image>()
+    OnlineImage -> firstIsInstanceOrNull<OnlineImage>()
+    OfflineImage -> firstIsInstanceOrNull<OfflineImage>()
+    GroupImage -> firstIsInstanceOrNull<GroupImage>()
+    FriendImage -> firstIsInstanceOrNull<FriendImage>()
+    Face -> firstIsInstanceOrNull<Face>()
+    QuoteReply -> firstIsInstanceOrNull<QuoteReply>()
+    MessageSource -> firstIsInstanceOrNull<MessageSource>()
+    OnlineMessageSource -> firstIsInstanceOrNull<OnlineMessageSource>()
+    OfflineMessageSource -> firstIsInstanceOrNull<OfflineMessageSource>()
+    OnlineMessageSource.Outgoing -> firstIsInstanceOrNull<OnlineMessageSource.Outgoing>()
+    OnlineMessageSource.Outgoing.ToGroup -> firstIsInstanceOrNull<OnlineMessageSource.Outgoing.ToGroup>()
+    OnlineMessageSource.Outgoing.ToFriend -> firstIsInstanceOrNull<OnlineMessageSource.Outgoing.ToFriend>()
+    OnlineMessageSource.Incoming -> firstIsInstanceOrNull<OnlineMessageSource.Incoming>()
+    OnlineMessageSource.Incoming.FromGroup -> firstIsInstanceOrNull<OnlineMessageSource.Incoming.FromGroup>()
+    OnlineMessageSource.Incoming.FromFriend -> firstIsInstanceOrNull<OnlineMessageSource.Incoming.FromFriend>()
+    OnlineMessageSource -> firstIsInstanceOrNull<OnlineMessageSource>()
+    XmlMessage -> firstIsInstanceOrNull<XmlMessage>()
+    JsonMessage -> firstIsInstanceOrNull<JsonMessage>()
+    RichMessage -> firstIsInstanceOrNull<RichMessage>()
+    LightApp -> firstIsInstanceOrNull<LightApp>()
+    PokeMessage -> firstIsInstanceOrNull<PokeMessage>()
+    HummerMessage -> firstIsInstanceOrNull<HummerMessage>()
+    FlashImage -> firstIsInstanceOrNull<FlashImage>()
+    GroupFlashImage -> firstIsInstanceOrNull<GroupFlashImage>()
+    FriendFlashImage -> firstIsInstanceOrNull<FriendFlashImage>()
     else -> null
 } as M?
 
@@ -191,7 +197,8 @@ inline fun <M : Message> MessageChain.any(key: Message.Key<M>): Boolean = firstO
  * val image: Image by message
  */
 @JvmSynthetic
-inline operator fun <reified T : Message> MessageChain.getValue(thisRef: Any?, property: KProperty<*>): T = this.first()
+inline operator fun <reified T : Message> MessageChain.getValue(thisRef: Any?, property: KProperty<*>): T =
+    this.firstIsInstance()
 
 /**
  * 可空的委托
@@ -215,7 +222,8 @@ inline class OrNullDelegate<out R : Message?>(private val value: Any?) {
  * @see orElse 提供一个不存在则使用默认值的委托
  */
 @JvmSynthetic
-inline fun <reified T : Message> MessageChain.orNull(): OrNullDelegate<T?> = OrNullDelegate(this.firstOrNull<T>())
+inline fun <reified T : Message> MessageChain.orNull(): OrNullDelegate<T?> =
+    OrNullDelegate(this.firstIsInstanceOrNull<T>())
 
 /**
  * 提供一个类型的 [Message] 的委托, 若不存在这个类型的 [Message] 则委托会提供 `null`
@@ -234,7 +242,7 @@ inline fun <reified T : Message> MessageChain.orNull(): OrNullDelegate<T?> = OrN
 inline fun <reified T : Message?> MessageChain.orElse(
     lazyDefault: () -> T
 ): OrNullDelegate<T> =
-    OrNullDelegate<T>(this.firstOrNull<T>() ?: lazyDefault())
+    OrNullDelegate<T>(this.firstIsInstanceOrNull<T>() ?: lazyDefault())
 
 // endregion delegate
 
@@ -250,6 +258,7 @@ inline fun <reified T : Message?> MessageChain.orElse(
 @JvmName("newChain")
 @JsName("newChain")
 @Suppress("UNCHECKED_CAST")
+@OptIn(MiraiInternalAPI::class)
 fun Message.asMessageChain(): MessageChain = when (this) {
     is MessageChain -> this
     is CombinedMessage -> (this as Iterable<Message>).asMessageChain()
@@ -281,6 +290,7 @@ fun Iterable<SingleMessage>.asMessageChain(): MessageChain =
 inline fun MessageChain.asMessageChain(): MessageChain = this // 避免套娃
 
 @JvmSynthetic
+@OptIn(MiraiInternalAPI::class)
 fun CombinedMessage.asMessageChain(): MessageChain {
     @OptIn(MiraiExperimentalAPI::class)
     if (left is SingleMessage && this.tail is SingleMessage) {
@@ -377,6 +387,7 @@ inline fun Sequence<SingleMessage>.flatten(): Sequence<SingleMessage> = this //
  * - 其他: 返回 `sequenceOf(this)`
  */
 fun Message.flatten(): Sequence<SingleMessage> {
+    @OptIn(MiraiInternalAPI::class)
     return when (this) {
         is MessageChain -> this.asSequence()
         is CombinedMessage -> this.flatten() // already constrained single.
@@ -385,6 +396,7 @@ fun Message.flatten(): Sequence<SingleMessage> {
 }
 
 @JvmSynthetic // make Java user happier with less methods
+@OptIn(MiraiInternalAPI::class)
 fun CombinedMessage.flatten(): Sequence<SingleMessage> {
     // already constrained single.
     @Suppress("UNCHECKED_CAST")
@@ -400,17 +412,12 @@ inline fun MessageChain.flatten(): Sequence<SingleMessage> = this.asSequence() /
 /**
  * 不含任何元素的 [MessageChain]
  */
-object EmptyMessageChain : MessageChain, Iterator<SingleMessage>, @MiraiExperimentalAPI SingleMessage {
+object EmptyMessageChain : MessageChain, Iterator<SingleMessage> {
     override fun contains(sub: String): Boolean = sub.isEmpty()
     override val size: Int get() = 0
     override fun toString(): String = ""
     override fun contentToString(): String = ""
 
-    override val length: Int get() = 0
-    override fun get(index: Int): Char = ""[index]
-    override fun subSequence(startIndex: Int, endIndex: Int): CharSequence = "".subSequence(startIndex, endIndex)
-    override fun compareTo(other: String): Int = "".compareTo(other)
-
     override fun iterator(): Iterator<SingleMessage> = this
     override fun hasNext(): Boolean = false
     override fun next(): SingleMessage = throw NoSuchElementException("EmptyMessageChain is empty.")
@@ -495,20 +502,21 @@ internal inline fun <T> List<T>.indexOfFirst(offset: Int, predicate: (T) -> Bool
  */
 @PublishedApi
 internal class MessageChainImplByCollection constructor(
-    private val delegate: Collection<SingleMessage> // 必须 constrainSingleMessages, 且为 immutable
+    internal val delegate: Collection<SingleMessage> // 必须 constrainSingleMessages, 且为 immutable
 ) : Message, Iterable<SingleMessage>, MessageChain {
     override val size: Int get() = delegate.size
     override fun iterator(): Iterator<SingleMessage> = delegate.iterator()
+
     private var toStringTemp: String? = null
-    override fun toString(): String =
-        toStringTemp ?: this.delegate.joinToString("") { it.toString() }.also { toStringTemp = it }
+        get() = field ?: this.delegate.joinToString("") { it.toString() }.also { field = it }
 
-    private var contentToStringTemp: String? = null
-    override fun contentToString(): String =
-        contentToStringTemp ?: this.delegate.joinToString("") { it.contentToString() }.also { contentToStringTemp = it }
+    override fun toString(): String = toStringTemp!!
 
+    private var contentToStringTemp: String? = null
+        get() = field ?: this.delegate.joinToString("") { it.contentToString() }.also { field = it }
 
-    override operator fun contains(sub: String): Boolean = delegate.any { it.contains(sub) }
+    override fun contentToString(): String = contentToStringTemp!!
+    override operator fun contains(sub: String): Boolean = sub in contentToStringTemp!!
 }
 
 /**
@@ -525,17 +533,17 @@ internal class MessageChainImplBySequence constructor(
      */
     private val collected: List<SingleMessage> by lazy { delegate.constrainSingleMessages() }
     override fun iterator(): Iterator<SingleMessage> = collected.iterator()
+
     private var toStringTemp: String? = null
-    override fun toString(): String =
-        toStringTemp ?: this.collected.joinToString("") { it.toString() }.also { toStringTemp = it }
+        get() = field ?: this.joinToString("") { it.toString() }.also { field = it }
 
-    private var contentToStringTemp: String? = null
-    override fun contentToString(): String =
-        contentToStringTemp ?: this.collected.joinToString("") { it.contentToString() }
-            .also { contentToStringTemp = it }
+    override fun toString(): String = toStringTemp!!
 
+    private var contentToStringTemp: String? = null
+        get() = field ?: this.joinToString("") { it.contentToString() }.also { field = it }
 
-    override operator fun contains(sub: String): Boolean = collected.any { it.contains(sub) }
+    override fun contentToString(): String = contentToStringTemp!!
+    override operator fun contains(sub: String): Boolean = sub in contentToStringTemp!!
 }
 
 /**
@@ -543,7 +551,7 @@ internal class MessageChainImplBySequence constructor(
  */
 @PublishedApi
 internal class SingleMessageChainImpl constructor(
-    private val delegate: SingleMessage
+    internal val delegate: SingleMessage
 ) : Message, Iterable<SingleMessage>, MessageChain {
     override val size: Int get() = 1
     override fun toString(): String = this.delegate.toString()

mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/PlainText.kt

@@ -30,7 +30,6 @@ class PlainText(val stringValue: String) :
     @Suppress("unused")
     constructor(charSequence: CharSequence) : this(charSequence.toString())
 
-    override operator fun contains(sub: String): Boolean = sub in stringValue
     override fun toString(): String = stringValue
     override fun contentToString(): String = stringValue
 

mirai-core/src/commonMain/kotlin/net.mamoe.mirai/utils/BotConfiguration.kt

@@ -97,30 +97,6 @@ open class BotConfiguration {
     fun fileBasedDeviceInfo(filename: String = "device.json") {
         deviceInfo = getFileBasedDeviceInfoSupplier(filename)
     }
-
-
-    @PlannedRemoval("0.34.0")
-    @Deprecated(
-        "use fileBasedDeviceInfo(filepath", level = DeprecationLevel.ERROR,
-        replaceWith = ReplaceWith("fileBasedDeviceInfo")
-    )
-    operator fun FileBasedDeviceInfo.unaryPlus() {
-        fileBasedDeviceInfo(this.filepath)
-    }
-}
-
-/**
- * 使用文件系统存储设备信息.
- */
-@PlannedRemoval("0.34.0")
-@Deprecated(
-    "use fileBasedDeviceInfo(filepath", level = DeprecationLevel.ERROR
-)
-inline class FileBasedDeviceInfo(val filepath: String) {
-    /**
-     * 使用 "device.json" 存储设备信息
-     */
-    companion object ByDeviceDotJson
 }
 
 @OptIn(ExperimentalMultiplatform::class)

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

 package net.mamoe.mirai.message.data
 
+import net.mamoe.mirai.utils.MiraiInternalAPI
 import kotlin.test.Test
 import kotlin.test.assertEquals
-import kotlin.time.ExperimentalTime
-import kotlin.time.measureTime
 
+@OptIn(MiraiInternalAPI::class)
 internal class CombinedMessageTest {
 
+
     @Test
     fun testAsSequence() {
         var message: Message = "Hello ".toMessage()
@@ -32,84 +33,6 @@ internal class CombinedMessageTest {
             (message as CombinedMessage).asSequence().joinToString(separator = "")
         )
     }
-
-    private val toAdd = "1".toMessage()
-
-    @OptIn(ExperimentalTime::class)
-    @Test
-    fun speedTest() = repeat(100) {
-        var count = 1L
-
-        repeat(Int.MAX_VALUE) {
-            count++
-        }
-
-        var combineMessage: Message = toAdd
-
-        println(
-            "init combine ok " + measureTime {
-                repeat(1000) {
-                    combineMessage += toAdd
-                }
-            }.inMilliseconds
-        )
-
-        val list = mutableListOf<Message>()
-        println(
-            "init messageChain ok " + measureTime {
-                repeat(1000) {
-                    list += toAdd
-                }
-            }.inMilliseconds
-        )
-
-        measureTime {
-            list.joinToString(separator = "")
-        }.let { time ->
-            println("list foreach: ${time.inMilliseconds} ms")
-        }
-
-        measureTime {
-            (combineMessage as CombinedMessage).iterator().joinToString(separator = "")
-        }.let { time ->
-            println("combined iterate: ${time.inMilliseconds} ms")
-        }
-
-        measureTime {
-            (combineMessage as CombinedMessage).asSequence().joinToString(separator = "")
-        }.let { time ->
-            println("combined sequence: ${time.inMilliseconds} ms")
-        }
-
-        repeat(5) {
-            println()
-        }
-    }
-
-    @OptIn(ExperimentalTime::class)
-    @Test
-    fun testFastIteration() {
-        println("start!")
-        println("start!")
-        println("start!")
-        println("start!")
-
-        var combineMessage: Message = toAdd
-
-        println(
-            "init combine ok " + measureTime {
-                repeat(1000) {
-                    combineMessage += toAdd
-                }
-            }.inMilliseconds
-        )
-
-        measureTime {
-            (combineMessage as CombinedMessage).iterator().joinToString(separator = "")
-        }.let { time ->
-            println("combine: ${time.inMilliseconds} ms")
-        }
-    }
 }
 
 fun <T> Iterator<T>.joinToString(
@@ -140,7 +63,7 @@ fun <T, A : Appendable> Iterator<T>.joinTo(
             buffer.appendElement(element, transform)
         } else break
     }
-    if (limit >= 0 && count > limit) buffer.append(truncated)
+    if (limit in 0 until count) buffer.append(truncated)
     buffer.append(postfix)
     return buffer
 }

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

@@ -10,9 +10,11 @@
 package net.mamoe.mirai.message.data
 
 import net.mamoe.mirai.utils.MiraiExperimentalAPI
+import net.mamoe.mirai.utils.MiraiInternalAPI
 import kotlin.test.Test
 import kotlin.test.assertEquals
 import kotlin.test.assertSame
+import kotlin.test.assertTrue
 
 
 @OptIn(MiraiExperimentalAPI::class)
@@ -25,7 +27,7 @@ internal class TestConstrainSingleMessage : ConstrainSingle<TestConstrainSingleM
     override fun toString(): String = "<TestConstrainSingleMessage#${super.hashCode()}>"
 
     override fun contentToString(): String {
-        TODO("Not yet implemented")
+        return ""
     }
 
     override val key: Message.Key<TestConstrainSingleMessage>
@@ -46,16 +48,75 @@ internal class TestConstrainSingleMessage : ConstrainSingle<TestConstrainSingleM
     }
 }
 
+@OptIn(MiraiExperimentalAPI::class)
 internal class ConstrainSingleTest {
 
-    @OptIn(MiraiExperimentalAPI::class)
+    @OptIn(MiraiInternalAPI::class)
+    @Test
+    fun testCombine() {
+        val result = PlainText("te") + PlainText("st")
+        assertTrue(result is CombinedMessage)
+        assertEquals("te", result.left.contentToString())
+        assertEquals("st", result.tail.contentToString())
+        assertEquals(2, result.size)
+        assertEquals("test", result.contentToString())
+    }
+
     @Test
-    fun testConstrainSingleInPlus() {
+    fun testSinglePlusChain() {
+        val result = PlainText("te") + buildMessageChain {
+            add(TestConstrainSingleMessage())
+            add("st")
+        }
+        assertTrue(result is MessageChainImplByCollection)
+        assertEquals(3, result.size)
+        assertEquals(result.contentToString(), "test")
+    }
+
+    @Test
+    fun testSinglePlusChainConstrain() {
+        val chain = buildMessageChain {
+            add(TestConstrainSingleMessage())
+            add("st")
+        }
+        val result = TestConstrainSingleMessage() + chain
+        assertSame(chain, result)
+        assertEquals(2, result.size)
+        assertEquals(result.contentToString(), "st")
+        assertTrue { result.first() is TestConstrainSingleMessage }
+    }
+
+    @Test
+    fun testSinglePlusSingle() {
+        val new = TestConstrainSingleMessage()
+        val combined = (TestConstrainSingleMessage() + new)
+
+        assertTrue(combined is SingleMessageChainImpl)
+        assertSame(new, combined.delegate)
+    }
+
+    @Test
+    fun testChainPlusSingle() {
         val new = TestConstrainSingleMessage()
-        val combined = (TestConstrainSingleMessage() + new) as CombinedMessage
 
-        assertEquals(combined.left, EmptyMessageChain)
-        assertSame(combined.tail, new)
+        val result = buildMessageChain {
+            add(" ")
+            add(Face(Face.hao))
+            add(TestConstrainSingleMessage())
+            add(
+                PlainText("ss")
+                        + " "
+            )
+        } + buildMessageChain {
+            add(PlainText("p "))
+            add(new)
+            add(PlainText("test"))
+        }
+
+        assertEquals(7, result.size)
+        assertEquals(" [表情]ss p test", result.contentToString())
+        result as MessageChainImplByCollection
+        assertSame(new, result.delegate.toTypedArray()[2])
     }
 
     @Test // net.mamoe.mirai/message/data/MessageChain.kt:441