New instantiating type for polymorphic serializer

plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/GeneratorHelpers.kt

@@ -37,6 +37,7 @@ import org.jetbrains.kotlin.types.typeUtil.makeNotNullable
 import org.jetbrains.kotlinx.serialization.compiler.backend.common.findTypeSerializerOrContext
 import org.jetbrains.kotlinx.serialization.compiler.backend.jvm.contextSerializerId
 import org.jetbrains.kotlinx.serialization.compiler.backend.jvm.enumSerializerId
+import org.jetbrains.kotlinx.serialization.compiler.backend.jvm.polymorphicSerializerId
 import org.jetbrains.kotlinx.serialization.compiler.backend.jvm.referenceArraySerializerId
 import org.jetbrains.kotlinx.serialization.compiler.resolve.*
 
@@ -466,7 +467,7 @@ interface IrBuilderExtension {
         } else {
             var serializerClass = serializerClassOriginal
             var args: List<IrExpression> = when (serializerClassOriginal.classId) {
-                contextSerializerId -> listOf(classReference(kType))
+                contextSerializerId, polymorphicSerializerId -> listOf(classReference(kType))
                 enumSerializerId -> {
                     serializerClass = serializableDescriptor.getClassFromInternalSerializationPackage("CommonEnumSerializer")
                     kType.toClassDescriptor!!.let { enumDesc ->

plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/js/JsCodegenUtil.kt

@@ -35,6 +35,7 @@ import org.jetbrains.kotlinx.serialization.compiler.backend.common.findTypeSeria
 import org.jetbrains.kotlinx.serialization.compiler.backend.common.primaryPropertiesDescriptorsMap
 import org.jetbrains.kotlinx.serialization.compiler.backend.jvm.contextSerializerId
 import org.jetbrains.kotlinx.serialization.compiler.backend.jvm.enumSerializerId
+import org.jetbrains.kotlinx.serialization.compiler.backend.jvm.polymorphicSerializerId
 import org.jetbrains.kotlinx.serialization.compiler.backend.jvm.referenceArraySerializerId
 import org.jetbrains.kotlinx.serialization.compiler.resolve.*
 
@@ -133,6 +134,8 @@ internal fun SerializerJsTranslator.serializerTower(property: SerializableProper
         ?.let { expr -> if (property.type.isMarkedNullable) JsNew(nullableSerClass, listOf(expr)) else expr }
 }
 
+private val classIdsWhichNeedKClass = setOf(enumSerializerId, contextSerializerId, polymorphicSerializerId)
+
 internal fun SerializerJsTranslator.serializerInstance(
     serializerClass: ClassDescriptor?,
     module: ModuleDescriptor,
@@ -148,7 +151,7 @@ internal fun SerializerJsTranslator.serializerInstance(
     if (serializerClass.kind == ClassKind.OBJECT) {
         return context.serializerObjectGetter(serializerClass)
     } else {
-        var args = if (serializerClass.classId == enumSerializerId || serializerClass.classId == contextSerializerId)
+        var args = if (serializerClass.classId in classIdsWhichNeedKClass)
             listOf(ExpressionVisitor.getObjectKClass(context, kType.toClassDescriptor!!))
         else kType.arguments.map {
             val argSer = findTypeSerializerOrContext(module, it.type, sourceElement = serializerClass.findPsi())

plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/jvm/JVMCodegenUtil.kt

@@ -264,7 +264,7 @@ internal fun AbstractSerialGenerator.stackValueSerializerInstance(codegen: Class
         // instantiate all arg serializers on stack
         val signature = StringBuilder("(")
         when (serializer.classId) {
-            enumSerializerId, contextSerializerId -> {
+            enumSerializerId, contextSerializerId, polymorphicSerializerId -> {
                 // a special way to instantiate enum -- need a enum KClass reference
                 // GENERIC_ARGUMENT forces boxing in order to obtain KClass
                 aconst(codegen.typeMapper.mapType(kType, null, TypeMappingMode.GENERIC_ARGUMENT))