Unable to serialize generics in Scala

[inmyth]

I have been unable to serialize a generic class using GenericTest as reference. I have below a very simple class in Scala. To imitate the Java test code I don't use Option or case class.

  @CompiledJson
  class Abc[A] {
    var test: A = _
  }

  val dslJson = new DslJson[Any](new DslJson.Settings()
                .allowArrayFormat(true).includeServiceLoader())
  val writer = dslJson.newWriter
  var model = new Abc[String]
  model.test = "aaa"
  val t = new TypeDefinition[Abc[String]]() {}.`type`
  val os = new ByteArrayOutputStream
  writer.reset(os)
  val res = dslJson.serialize(writer, t, model)     
  writer.flush()

res always returns false signifying failed serialization. Perhaps you could help point out the problem ? Thank you.

[zapov]

Unfortunately, thats currently expected behavior.
Generics are supported only via annotation processor.
Scala version currently uses only reflection features.
Scala tooling is not really annotation processor friendly, and while technically you could run it, in practice I have not seen people do it.

Ideally Scala version will get some kind of compilation support... but community should help out with that.

[inmyth]

I see. I guess at the time being, generics are only supported in Java version ?

[zapov]

Yes

[inmyth]

So I tried recoding it in Java but it still didn't work. Finally I copied and ran GenericTest but all tests failed. I was using dsl-json-java8, version: 1.8.3 (version 1.8.4 was not yet available at Maven). This is one result I get from testSerializeAndDeserializeGeneric . Basically dslJson.serialize would still return false and the resulting json returns an empty string.

java.io.IOException: Unexpected end of JSON input

	at com.dslplatform.json.JsonReader.read(JsonReader.java:304)
	at com.dslplatform.json.JsonReader.getNextToken(JsonReader.java:747)
	at com.dslplatform.json.DslJson.deserialize(DslJson.java:1550)
	at com.mypackage.json.dsl.GenericTest.testSerializeAndDeserializeGeneric(GenericTest.java:67)

[zapov]

If you write your example as a test in GenericTest does it work then? If not, can you make a PR?

I suspect that you need to initialize library via new DslJson<>(Settings.withRuntime()) before it behaves as you expect.

[inmyth]

I copied the file without changing anything. DslJson is initialialized like this

private final DslJson<Object> dslJson = new DslJson<>(new DslJson.Settings<>()
.allowArrayFormat(true).includeServiceLoader());

And I tried cloning the project. It failed to build with the same reason as when I did it with my own test. Basically dsl-json version 1.8.4 is not available and artifact dsl-json-integration-tests-java8-external-models doesn't exist. As the last version was pushed very recent like a week ago, maybe it has something to do with it ?

[zapov]

dsl-json 1.8.4 is not released, but you should be able to build it locally by going to root project and running

mvn clean install

That should build the entire project including the external-models.
What happens if you do that?

[inmyth]

Still failed with error

DSL Platform JSON (core) 1.8.4 ..................... FAILURE [ 10.291 s]
java.lang.NoClassDefFoundError: org/junit/runner/notification/RunNotifier
	at java.lang.Class.getDeclaredConstructors0(Native Method)
Caused by: java.lang.ClassNotFoundException: org.junit.runner.notification.RunNotifier
	at java.net.URLClassLoader.findClass(URLClassLoader.java:382)

though test-compile works.

[wadejensen]

Would be very keen for generics support in Scala.

[zapov]

Yes, it would be nice to resolve such minor TODOs: https://github.com/ngs-doo/dsl-json/blob/master/scala/src/main/scala/com/dslplatform/json/runtime/ScalaClassAnalyzer.scala#L20

I don't have much time ATM, but I suspect it would not be complicated to add that support for reflection.

[zapov]

There is now basic support for generics in Scala: https://github.com/ngs-doo/dsl-json/blob/master/scala/src/test/scala/com/dslplatform/json/GenericsTest.scala

Will be included in 1.8.5

[zapov]

v1.8.5 released