I haven't worked with annotations much in Java or ...

# getting-started

[Sean Proctor]

I haven't worked with annotations much in Java or Kotlin. I've come across a bug, that I believe is in generated code.

@Serializable
data class FooInput {
    val id: OptionalInput<@Serializable(with = UUIDSerializer::class) UUID> = OptionalInput.Undefined
}

How does the annotation in the type parameter work? It seems like it's discarded which causes the bug, but kotlinx.serialization looks a bit like magic to me.

[Dominaezzz]

What's the bug?

[Dominaezzz]

Is optional input marked serialisable?

[Sean Proctor]

yes. https://github.com/ExpediaGroup/graphql-kotlin/blob/master/clients/graphql-kotlin-[…]xpediagroup/graphql/client/serialization/types/OptionalInput.kt

[Sean Proctor]

The serializer tries to inspect the properties of UUID which raises an exception.

[Sean Proctor]

specifically java.lang.IllegalAccessException: class kotlin.reflect.jvm.internal.calls.CallerImpl$FieldGetter cannot access a member of class java.util.UUID (in module java.base) with modifiers "private final"

[Dominaezzz]

You can't use that annotation the way you have. The custom serialiser for optional input doesn't support it.

[Dominaezzz]

The compiler plugin will try and inject the uuid serialiser into the optional input serialiser ctor and fail.

[Sean Proctor]

Yeah, makes sense. That code I pasted is generated by the gradle plugin

[Sean Proctor]

Is it obvious how that should work and I'm not understanding, or should I wait for the maintainers of the graphql library to look at it and come up with a solution?

[Dominaezzz]

No, I don't see how that is supposed to work. It needs fixing.

[ephemient]

it should work if you define a serializer that accepts the type, for example

class TypedOptionalInputSerializer<T : Any>(
    private val delegate: KSerializer<T>
) : KSerializer<OptionalInput<T>> {
    override val descriptor: SerialDescriptor = delegate.descriptor.nullable

    override fun serialize(encoder: Encoder, value: OptionalInput<T>) {
        encoder.encodeNullableSerializableValue(
            delegate,
            when (value) {
                is OptionalInput.Undefined -> null
                is OptionalInput.Defined -> value.value
            }
        )
    }

    override fun deserialize(decoder: Decoder): OptionalInput<T> =
        OptionalInput.Defined(decoder.decodeNullableSerializableValue(delegate.nullable))
}

@Serializable
data class FooInput {
    val id: @Serializable(with = TypedOptionalInputSerializer::class) OptionalInput<@Serializable(with = UUIDSerializer::class) UUID> = OptionalInput.Undefined
}

(untested but something along those lines)

[ephemient]

their default OptionalInput serializer only works reasonably for primitives and Map/List of…, and otherwise falls back to reflection; I think it's a terrible idea but not my project 🤷

[Sean Proctor]

Thanks. That looks promising. Would it be possible for TypedOptionalInputSerializer to have a default delegate of AnyKSerializer so it falls back to the current behavior? I guess I can try to work our a set of changes for this. Thanks again for your help