feat: 🚀 Support parameterized types in ClassTagExtensions

[gaeljw]

Aims to solve #503 by enriching ClassTagExtensions as ScalaObjectMapper is being deprecated/removed for Scala 3.

The idea is to use a home-made typeclass JavaTypeable in combination with ClassTags.
An instance of JavaTypeable being provided for all non-generic types and generic types up to 5 type parameters.

This compiles and pass the tests in ClassTagExtensionsTest.

---

However I see at least one caveat to this implementation: if using a generic class with more type parameters than "allowed" (3 for now in this MR), the error provided to the user is not very clean:

private case class Uber[A,B,C,D](a: A, b: B, c: C, d: D)

mapper.readValue[Uber[Int, String, Double, Float]](...)

// Gives:
java.lang.IllegalArgumentException: Cannot create TypeBindings for class com.fasterxml.jackson.module.scala.ScalaObjectMapperTest$Uber with 3 type parameters: class expects 4
   at com.fasterxml.jackson.databind.type.TypeBindings.create(TypeBindings.java:113)

This is because a JavaTypeable[Uber[B,C,D]] is provided instead of a more regular "implicit not found" error. I don't know if there's a way around that 🤷

This might be acceptable though if we provide the typeclass for up to 10 or even 22 type parameters as it would occur on a very rare basis?

[pjfanning]

@gaeljw thanks - would it be possible to retarget this PR to the 2.13 branch? - the master branch is for a future unscheduled release

[pjfanning]

I'm not sure if this won't break binary compatibility for existing ScalaObjectMapper users. We don't make any promises about binary compatibility in jackson-module-scala v2 but we've recently started doing MIMA checks.

One possibility would be to put the new code in an existing class called ClassTagExtensions - that class is not very useful as is so I'd happily replace it - so users can opt in to using your new code but would have to make an explicit change to their code to use it.

[gaeljw]

would it be possible to retarget this PR to the 2.13 branch? - the master branch is for a future unscheduled release

Done :)

I'm not sure if this won't break binary compatibility for existing ScalaObjectMapper users.

I'm 100% sure it breaks binary compatibility indeed.

One possibility would be to put the new code in an existing class called ClassTagExtensions

Indeed, I had not see this class, my proposal makes more sense in ClassTagExtensions then and keep the removal of ScalaObjectMapper for Scala 3 users If I understand correctly.

[pjfanning]

@gaeljw that's what I am proposing - it's awkward to balance the expectations of users who want binary compatibility and those who want to continue to support ScalaObjectMapper for Scala 3 users.

One other option (that I would prefer slightly less than the existing proposal) is that we already have scala version specific src dirs and could keep ScalaObjectMapper as is in scala 2.x source but use your version in scala 3.x source.

[gaeljw]

I'll think about the different options in the coming days and will update the PR next week probably :)

[gaeljw]

Finally had some time to update the PR.

The suggested code now lives in ClassTagExtensions.

[gaeljw]

Not sure why the build is failing for Scala 2.13. Output is incomplete on TravisCI 🤷

[pjfanning]

Thanks very much @gaeljw - I'll merge and see what happens with the build

[tmunk123]

@pjfanning I'm currently using Scala 2.11.12 and fasterXML 2.13.1. When I compile, I see the following:

C:\temp\IdeaProjects\dataservices\Db2ZAI\src\com\ibm\analytics\db2zai\utils\Db2ZAIJSONUtil.scala:15:40
trait ScalaObjectMapper in package scala is deprecated: ScalaObjectMapper is deprecated because Manifests are not supported in Scala3, you might want to use ClassTagExtensions as a replacement
    val mapr = new ObjectMapper() with ScalaObjectMapper

Will this deprecation warning be resolved/fixed once we move to Scala 2.12.x or later?

[gaeljw]

@tmunk123 please read the documentation: https://github.com/FasterXML/jackson-module-scala#classtagextensions

The deprecation will not disappear, you have to change your code.