Add AtAll

mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/AtAll.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 net.mamoe.mirai.message.data
+
+/**
+ * "@全体成员"
+ *
+ * @see At at 单个群成员
+ */
+object AtAll : Message {
+    override fun toString(): String = "@全体成员"
+
+    // 自动为消息补充 " "
+
+    override fun followedBy(tail: Message): MessageChain {
+        if(tail is PlainText && tail.stringValue.startsWith(' ')){
+            return super.followedBy(tail)
+        }
+        return super.followedBy(PlainText(" ")) + tail
+    }
+}
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