Restrict auto-implementing serializers methods to certain type of classes

plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/resolve/KSerializationUtil.kt

@@ -34,6 +34,12 @@ import org.jetbrains.kotlin.types.typeUtil.supertypes
 import org.jetbrains.kotlinx.serialization.compiler.resolve.SerialEntityNames.KSERIALIZER_CLASS
 import org.jetbrains.kotlinx.serialization.compiler.resolve.SerializationPackages.packageFqName
 
+fun isAllowedToHaveAutoGeneratedSerializerMethods(classDescriptor: ClassDescriptor): Boolean {
+    // it is either GeneratedSerializer implementation
+    // or user implementation which does not have type parameters (to be able to correctly initialize descriptor)
+    return classDescriptor.typeConstructor.supertypes.any(::isGeneratedKSerializer) ||
+            (classDescriptor.typeConstructor.supertypes.any(::isKSerializer) && classDescriptor.declaredTypeParameters.isEmpty())
+}
 
 fun isKSerializer(type: KotlinType?): Boolean =
     type != null && KotlinBuiltIns.isConstructedFromGivenClass(type, SerialEntityNames.KSERIALIZER_NAME_FQ)

plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/resolve/KSerializerDescriptorResolver.kt

@@ -136,6 +136,9 @@ object KSerializerDescriptorResolver {
         name: Name,
         result: MutableSet<PropertyDescriptor>
     ) {
+        // Do not auto-generate anything for user serializers
+        if (!isAllowedToHaveAutoGeneratedSerializerMethods(thisDescriptor)) return
+
         val classDescriptor = getSerializableClassDescriptorBySerializer(thisDescriptor) ?: return
         if (name == SerialEntityNames.SERIAL_DESC_FIELD_NAME && result.none(thisDescriptor::checkSerializableClassPropertyResult) &&
             fromSupertypes.none { thisDescriptor.checkSerializableClassPropertyResult(it) && it.modality == Modality.FINAL }
@@ -168,6 +171,9 @@ object KSerializerDescriptorResolver {
         name: Name,
         result: MutableCollection<SimpleFunctionDescriptor>
     ) {
+        // Do not auto-generate anything for user serializers
+        if (!isAllowedToHaveAutoGeneratedSerializerMethods(thisDescriptor)) return
+
         val classDescriptor = getSerializableClassDescriptorBySerializer(thisDescriptor) ?: return
 
         fun shouldAddSerializerFunction(checkParameters: (FunctionDescriptor) -> Boolean): Boolean {