Add context getter

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

@@ -43,7 +43,7 @@ internal abstract class QQAndroidBotBase constructor(
     context: Context,
     account: BotAccount,
     configuration: BotConfiguration
-) : BotImpl<QQAndroidBotNetworkHandler>(account, configuration) {
+) : BotImpl<QQAndroidBotNetworkHandler>(context, account, configuration) {
     val client: QQAndroidClient =
         QQAndroidClient(
             context,

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

@@ -44,7 +44,8 @@ abstract class Bot : CoroutineScope {
          * 复制一份此时的 [Bot] 实例列表.
          */
         @JvmStatic
-        val instances: List<WeakRef<Bot>> get() = BotImpl.instances.toList()
+        val instances: List<WeakRef<Bot>>
+            get() = BotImpl.instances.toList()
 
         /**
          * 遍历每一个 [Bot] 实例
@@ -58,6 +59,14 @@ abstract class Bot : CoroutineScope {
         fun instanceWhose(qq: Long): Bot = BotImpl.instanceWhose(qq = qq)
     }
 
+    /**
+     * [Bot] 运行的 [Context].
+     *
+     * 在 JVM 的默认实现为 `class ContextImpl : Context`
+     * 在 Android 实现为 `android.content.Context`
+     */
+    abstract val context: Context
+
     /**
      * 账号信息
      */

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

@@ -32,6 +32,7 @@ import kotlin.coroutines.CoroutineContext
 @UseExperimental(MiraiExperimentalAPI::class)
 @MiraiInternalAPI
 abstract class BotImpl<N : BotNetworkHandler> constructor(
+    context: Context,
     account: BotAccount,
     val configuration: BotConfiguration
 ) : Bot(), CoroutineScope {
@@ -39,6 +40,7 @@ abstract class BotImpl<N : BotNetworkHandler> constructor(
     override val coroutineContext: CoroutineContext =
         configuration.parentCoroutineContext + botJob + (configuration.parentCoroutineContext[CoroutineExceptionHandler]
             ?: CoroutineExceptionHandler { _, e -> logger.error("An exception was thrown under a coroutine of Bot", e) })
+    override val context: Context by context.unsafeWeakRef()
 
     @Suppress("CanBePrimaryConstructorProperty") // for logger
     final override val account: BotAccount = account