Serializable meta-annotation

core/commonMain/src/kotlinx/serialization/Annotations.kt

@@ -73,6 +73,48 @@ public annotation class Serializable(
     val with: KClass<out KSerializer<*>> = KSerializer::class // Default value indicates that auto-generated serializer is used
 )
 
+/**
+ * The meta-annotation for adding behaviour of [Serializable] to custom annotations.
+ * Applying [MetaSerializable] to the annotation class instructs the serialization plugin to treat this annotation
+ * as [Serializable].
+ *
+ * ```
+ * @MetaSerializable
+ * @Target(AnnotationTarget.CLASS)
+ * annotation class MySerializable
+ *
+ * @MySerializable
+ * class MyData(val myData: AnotherData, val intProperty: Int, ...)
+ *
+ * // Produces JSON string using the generated serializer
+ * val jsonString = Json.encodeToJson(MyData.serializer(), instance)
+ * ```
+ *
+ * All annotations marked with [MetaSerializable] are saved in the generated [SerialDescriptor]
+ * as if they are annotated [SerialInfo].
+ *
+ * ```
+ * @MetaSerializable
+ * @Target(AnnotationTarget.CLASS)
+ * annotation class MySerializable(val data: String)
+ *
+ * @MySerializable("some_data")
+ * class MyData(val myData: AnotherData, val intProperty: Int, ...)
+ *
+ * val serializer = MyData.serializer()
+ * serializer.descriptor.annotations.filterIsInstance<MySerializable>().first().data // <- returns "some_data"
+ * ```
+ *
+ * @see Serializable
+ * @see SerialInfo
+ * @see UseSerializers
+ * @see Serializer
+ */
+@Target(AnnotationTarget.ANNOTATION_CLASS)
+//@Retention(AnnotationRetention.RUNTIME) // Runtime is the default retention, also see KT-41082
+@ExperimentalSerializationApi
+public annotation class MetaSerializable
+
 /**
  * Instructs the serialization plugin to turn this class into serializer for specified class [forClass].
  * However, it would not be used automatically. To apply it on particular class or property,

core/commonTest/src/kotlinx/serialization/MetaSerializableTest.kt

@@ -0,0 +1,56 @@
+package kotlinx.serialization
+
+import kotlin.reflect.KClass
+import kotlin.test.Test
+
+// TODO: for this test to work, kotlin dependency should be updated
+// to serialization plugin with @MetaSerializable support
+class MetaSerializableTest {
+
+    @MetaSerializable
+    @Target(AnnotationTarget.CLASS, AnnotationTarget.PROPERTY)
+    annotation class MySerializable
+
+    @MetaSerializable
+    @Target(AnnotationTarget.CLASS, AnnotationTarget.PROPERTY)
+    annotation class MySerializableWithInfo(
+        val value: Int,
+        val kclass: KClass<*>
+    )
+
+    @MySerializable
+    class Project1(val name: String, val language: String)
+
+    @MySerializableWithInfo(123, String::class)
+    class Project2(val name: String, val language: String)
+
+    @MySerializableWithInfo(123, String::class)
+    @Serializable
+    class Project3(val name: String, val language: String)
+
+    @Serializable
+    class Wrapper(
+        @MySerializableWithInfo(234, Int::class) val project: Project3
+    )
+
+    @Test
+    fun testMetaSerializable() {
+//        val serializer = serializer<Project1>()
+//        assertNotNull(serializer)
+    }
+
+    @Test
+    fun testMetaSerializableWithInfo() {
+//        val info = serializer<Project2>().descriptor.annotations.filterIsInstance<MySerializableWithInfo>().first()
+//        assertEquals(123, info.value)
+//        assertEquals(String::class, info.kclass)
+    }
+
+    @Test
+    fun testMetaSerializableOnProperty() {
+//        val info = serializer<Wrapper>().descriptor
+//            .getElementAnnotations(0).filterIsInstance<MySerializableWithInfo>().first()
+//        assertEquals(234, info.value)
+//        assertEquals(Int::class, info.kclass)
+    }
+}