Actualize 'serializer not found' platform-specific message (#2339)

Fixes #1248

Author: sandwwraith

core/jsMain/src/kotlinx/serialization/internal/Platform.kt

@@ -40,8 +40,8 @@ internal actual fun <T : Any, E : T?> ArrayList<E>.toNativeArrayImpl(eClass: KCl
 
 internal actual fun KClass<*>.platformSpecificSerializerNotRegistered(): Nothing {
     throw SerializationException(
-        "${notRegisteredMessage()}\n" +
-                "On Kotlin/JS explicitly declared serializer should be used for interfaces and enums without @Serializable annotation"
+        notRegisteredMessage() +
+                "To get enum serializer on Kotlin/JS, it should be annotated with @Serializable annotation."
     )
 }
 

core/nativeMain/src/kotlinx/serialization/internal/Platform.kt

@@ -19,8 +19,9 @@ internal actual inline fun BooleanArray.getChecked(index: Int): Boolean {
 
 internal actual fun KClass<*>.platformSpecificSerializerNotRegistered(): Nothing {
     throw SerializationException(
-        "${notRegisteredMessage()}\n" +
-                "On Kotlin/Native explicitly declared serializer should be used for interfaces and enums without @Serializable annotation"
+        notRegisteredMessage() +
+            "To get enum serializer on Kotlin/Native, it should be annotated with @Serializable annotation.\n" +
+            "To get interface serializer on Kotlin/Native, use PolymorphicSerializer() constructor function.\n"
     )
 }
 

docs/builtin-classes.md

@@ -166,6 +166,8 @@ In JSON an enum gets encoded as a string.
 {"name":"kotlinx.serialization","status":"SUPPORTED"}
 ```   
 
+> Note: On Kotlin/JS and Kotlin/Native, `@Serializable` annotation is needed for enum class if you want to use it as a root object — i.e. use `encodeToString<Status>(Status.SUPPORTED)`.
+
 <!--- TEST -->
 
 ### Serial names of enum entries

docs/polymorphism.md

@@ -408,6 +408,8 @@ fun main() {
 {"type":"owned","name":"kotlinx.coroutines","owner":"kotlin"}
 ```
 
+> Note: On Kotlin/Native, you should use `format.encodeToString(PolymorphicSerializer(Project::class), data))` instead due to limited reflection capabilities.
+
 <!--- TEST LINES_START -->
 
 ### Property of an interface type