Polymorphic open support

[williamboxhall]

Huge disclaimer: I don't know kotlinx or avro4k internals at all so there's a good chance this implementation is not on the right track. It was also done under delivery time pressure so forgive me for not doing deeper homework on this. Happy to take any pointers on how to improve it.

This PR adds support for open / unsealed / abstract classes, configured like so:

val module = SerializersModule {
   polymorphic(UnsealedPolymorphicRoot::class) {
      subclass(UnsealedChildOne::class)
      subclass(UnsealedChildTwo::class)
   }
}
val schema = Avro(serializersModule = module).schema(UnsealedPolymorphicRoot.serializer())

For now it explicitly doesn't support polymorphic defaults - this is a feature someone could build on top if they want to.

[williamboxhall]

Not sure on the process here but tagging @thake if he has a little bit of time 🙏🏻

[thake]

@williamboxhall thanks for your contribution :) That was fast. I just had a quick look at the code. Can you add 2 more tests to the patch before I go into a deeper review? The first one tests the serialization/deserialization and the second one tests the schema for polymorphic references.

[williamboxhall]

The first one tests the serialization/deserialization

This makes sense, happy to do it. Is there another good test I can use as a reference for this?

the second one tests the schema for polymorphic references

I don't quite follow what you mean by this, would you be able to explain in a little bit more detail please?

[thake]

Thanks for driving this feature :+1:

For serialization/deserialization you can have a look at https://github.com/avro-kotlin/avro4k/blob/master/src/test/kotlin/com/github/avrokotlin/avro4k/io/SealedClassIoTest.kt

I thought about a test where a schema for the class ReferencingPolymorphicRoot in the following code snippet:

@Serializable
abstract class UnsealedPolymorphicRoot

@Serializable
data class UnsealedChildOne(val one: String) : UnsealedPolymorphicRoot()

@Serializable
data class UnsealedChildTwo(val two: String) : UnsealedPolymorphicRoot()

@Serializable
data class ReferencingPolymorphicRoot(
  @Polymorphic
  val root : UnsealedPolymorphicRoot
)

[williamboxhall]

@thake I've just pushed up the additional tests you ask for, and, shamefully, the missing encoder/decoder support for the polymorphic types (my previous code generated the avro schema properly but not the actual encode/decode 🤦🏻‍♂️). I think everything's all good now.

Note that @Polymorphic is not actually required in order for the nested type to serialize properly so I've deliberately omitted it (it's harmless when added, however)

[thake]

@williamboxhall Can I make some adjustments to your PR? I would like to remove some code duplication. Unfortunately, I do not seem to have write access to the PR branch in your fork.

[williamboxhall]

@thake I'll work on getting you added as a contributor to our fork but there's a bit of internal bureaucracy to get people added so it might take a couple of days. Another option could be for you to pull my branch back in under avro-kotlin/avro4k to make a couple of modifications.

[williamboxhall]

Another option could be to add me as a branch contributor to avro-kotlin/avro4k and I can push my branch upstream to there

[williamboxhall]

Update: @thake we've added you as a non-master branch contributor on our fork avro-kotlin/avro4k. You probably have to "accept" the invitation somewhere before you can push upstream though - hopefully you have a notification about it somewhere in github

[thake]

Unfortunately, it still does not work. Have you followed https://docs.github.com/en/github/collaborating-with-pull-requests/working-with-forks/allowing-changes-to-a-pull-request-branch-created-from-a-fork to grant access?

[williamboxhall]

@thake we couldn't follow that process because I am not the organization owner - I think for that to work I'd need to close my PR and get my org owner to open it, then tick that box.

However, my org owner adding you as a contributor should work, and I think the problem is that you haven't "accepted" the invitation yet:

There should be somewhere you can go in github, or you may have received a notification, allowing you to accept this invitation, which should open up access. Let me know if you can't figure it out and I'll just re-fork this in my personal repo and push the changes up there and give you access.

[williamboxhall]

https://github.community/t/where-do-i-see-all-incoming-invitations-collaborator/661

This page says you either need to access from the email notification or navigate to our forked repo (https://github.com/cultureamp/avro4k) in order to accept the invitation.

[williamboxhall]

@thake I've created a new fork in my personal repo so if you can't get things working here, we can just do things over there where I have more control and have already enabled edits my maintainers: https://github.com/avro-kotlin/avro4k/pull/110

[thake]

Continuing in PR #110