Improve performance of MessageChain.get, MessageChain.contains. Add relevant tests.

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

@@ -209,8 +209,10 @@ public sealed interface MessageChain :
      *
      * @see MessageChain.getOrFail 在找不到此类型的元素时抛出 [NoSuchElementException]
      */
-    public operator fun <M : SingleMessage> get(key: MessageKey<M>): M? =
-        asSequence().mapNotNull { key.safeCast.invoke(it) }.firstOrNull()
+    public operator fun <M : SingleMessage> get(key: MessageKey<M>): M? {
+        @Suppress("UNCHECKED_CAST")
+        return firstOrNull { key.safeCast.invoke(it) != null } as M?
+    }
 
     /**
      * 当存在 [ConstrainSingle.key] 为 [key] 的 [SingleMessage] 实例时返回 `true`.
@@ -239,7 +241,7 @@ public sealed interface MessageChain :
      * @see MessageChain.getOrFail 在找不到此类型的元素时抛出 [NoSuchElementException]
      */
     public operator fun <M : SingleMessage> contains(key: MessageKey<M>): Boolean =
-        asSequence().any { key.safeCast.invoke(it) != null }
+        any { key.safeCast.invoke(it) != null }
 
     @MiraiExperimentalApi
     override fun appendMiraiCodeTo(builder: StringBuilder) {

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2019-2020 Mamoe Technologies and contributors.
+ * Copyright 2019-2021 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.
@@ -12,6 +12,7 @@ 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.assertSame
 
 
 private open class TestStandaloneConstrainSingleMessage : ConstrainSingle, MessageContent {
@@ -98,4 +99,26 @@ internal class MessageKeyTest {
         assertEquals<Any?>(constrainSingle, chain[TestStandaloneConstrainSingleMessage])
         assertEquals(1, chain.size)
     }
+
+    @Test
+    fun `can get from MessageChain`() {
+        val cons = TestStandaloneConstrainSingleMessage()
+        assertSame(cons, messageChainOf(cons)[TestStandaloneConstrainSingleMessage])
+    }
+
+    @Test
+    fun `can get from MessageChain2`() {
+        val cons = TestStandaloneConstrainSingleMessage()
+        assertSame(cons, messageChainOf(PlainText("test"), AtAll, cons)[TestStandaloneConstrainSingleMessage])
+    }
+
+    @Test
+    fun `get can be null`() {
+        assertEquals(null, messageChainOf()[TestStandaloneConstrainSingleMessage])
+    }
+
+    @Test
+    fun `get can be null2`() {
+        assertEquals(null, messageChainOf(PlainText("test"), AtAll)[TestStandaloneConstrainSingleMessage])
+    }
 }