Make `SingleMessage` not extending `CharSequence` for clearer semantics

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

@@ -178,12 +178,6 @@ class ForwardMessage @JvmOverloads constructor(
 
     @MiraiExperimentalAPI
     override fun contentToString(): String = contentToString
-    override val length: Int get() = contentToString.length
-    override fun get(index: Int): Char = contentToString[length]
-    override fun subSequence(startIndex: Int, endIndex: Int): CharSequence =
-        contentToString.subSequence(startIndex, endIndex)
-
-    override fun compareTo(other: String): Int = contentToString.compareTo(other)
 }
 
 

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

@@ -140,13 +140,7 @@ data class PokeMessage internal constructor(
     private val stringValue = "[mirai:poke:$type,$id]"
 
     override fun toString(): String = stringValue
-    override val length: Int get() = stringValue.length
-    override fun get(index: Int): Char = stringValue[index]
-    override fun subSequence(startIndex: Int, endIndex: Int): CharSequence =
-        stringValue.subSequence(startIndex, endIndex)
-
     override fun contentToString(): String = "[戳一戳]"
-    override fun compareTo(other: String): Int = stringValue.compareTo(other)
     //businessType=0x00000001(1)
     //pbElem=08 01 18 00 20 FF FF FF FF 0F 2A 00 32 00 38 00 50 00
     //serviceType=0x00000002(2)
@@ -231,13 +225,7 @@ data class VipFace internal constructor(
     private val stringValue = "[mirai:vipface:$kind,$count]"
 
     override fun toString(): String = stringValue
-    override val length: Int get() = stringValue.length
-    override fun get(index: Int): Char = stringValue[index]
-    override fun subSequence(startIndex: Int, endIndex: Int): CharSequence =
-        stringValue.subSequence(startIndex, endIndex)
-
     override fun contentToString(): String = "[${kind.name}]x$count"
-    override fun compareTo(other: String): Int = stringValue.compareTo(other)
 }
 
 
@@ -299,11 +287,6 @@ sealed class FlashImage : MessageContent, HummerMessage() {
         }
 
     override fun toString(): String = stringValue!!
-    override val length: Int get() = stringValue!!.length
-    override fun get(index: Int) = stringValue!![index]
-    override fun subSequence(startIndex: Int, endIndex: Int) = stringValue!!.subSequence(startIndex, endIndex)
-    override fun compareTo(other: String) = other.compareTo(stringValue!!)
-
     override fun contentToString(): String = "[闪照]"
 }
 

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

@@ -110,6 +110,7 @@ val FRIEND_IMAGE_ID_REGEX_2 = Regex("""/[0-9]*-[0-9]*-[0-9a-zA-Z]{32}""")
  *
  * `{01E9451B-70ED-EAE3-B37C-101F1EEBF5B5}.mirai`
  */
+@Suppress("RegExpRedundantEscape") // This is required on Android
 @SinceMirai("0.39.2")
 // Java: MessageUtils.GROUP_IMAGE_ID_REGEX
 val GROUP_IMAGE_ID_REGEX = Regex("""\{.{8}-(.{4}-){3}.{12}\}\.mirai""")
@@ -117,6 +118,7 @@ val GROUP_IMAGE_ID_REGEX = Regex("""\{.{8}-(.{4}-){3}.{12}\}\.mirai""")
 /**
  * 在 `0.39.0` 前的图片的正则表示
  */
+@Suppress("RegExpRedundantEscape") // This is required on Android
 @Deprecated("Only for temporal use",
     replaceWith = ReplaceWith("GROUP_IMAGE_ID_REGEX", "net.mamoe.mirai.message.data.GROUP_IMAGE_ID_REGEX"))
 @SinceMirai("0.39.2")
@@ -323,12 +325,6 @@ sealed class AbstractImage : Image {
             field = "[mirai:image:$imageId]"
             field
         }
-    override val length: Int get() = _stringValue!!.length
-    override fun get(index: Int): Char = _stringValue!![index]
-    override fun subSequence(startIndex: Int, endIndex: Int): CharSequence =
-        _stringValue!!.subSequence(startIndex, endIndex)
-
-    override fun compareTo(other: String): Int = _stringValue!!.compareTo(other)
     final override fun toString(): String = _stringValue!!
     final override fun contentToString(): String = "[图片]"
 }

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

@@ -279,7 +279,7 @@ interface Message { // must be interface. Don't consider any changes.
 @SinceMirai("0.39.3")
 fun Message.isContentEmpty(): Boolean = when (this) {
     is MessageMetadata -> true
-    is PlainText -> this.isEmpty()
+    is PlainText -> this.stringValue.isEmpty()
     is MessageChain -> this.all { it.isContentEmpty() }
     else -> false
 }
@@ -312,7 +312,7 @@ inline fun Message.repeat(count: Int): MessageChain {
 inline operator fun Message.times(count: Int): MessageChain = this.repeat(count)
 
 @Suppress("OverridingDeprecatedMember")
-interface SingleMessage : Message, CharSequence, Comparable<String> {
+interface SingleMessage : Message {
     @PlannedRemoval("1.0.0")
     @JvmSynthetic
     @Deprecated(
@@ -352,12 +352,7 @@ interface SingleMessage : Message, CharSequence, Comparable<String> {
  *
  * @see ConstrainSingle 约束一个 [MessageChain] 中只存在这一种类型的元素
  */
-interface MessageMetadata : SingleMessage {
-    override val length: Int get() = 0
-    override fun get(index: Int): Char = ""[index] // produce uniform exception
-    override fun subSequence(startIndex: Int, endIndex: Int): CharSequence = "".subSequence(startIndex, endIndex)
-    override fun compareTo(other: String): Int = "".compareTo(other)
-}
+interface MessageMetadata : SingleMessage
 
 /**
  * 约束一个 [MessageChain] 中只存在这一种类型的元素. 新元素将会替换旧元素, 保持原顺序.

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

@@ -86,11 +86,6 @@ interface RichMessage : MessageContent {
     }
 
     val content: String
-
-    override val length: Int get() = content.length
-    override fun get(index: Int): Char = content[index]
-    override fun subSequence(startIndex: Int, endIndex: Int): CharSequence = content.subSequence(startIndex, endIndex)
-    override fun compareTo(other: String): Int = content.compareTo(other)
 }
 
 /**