Extending kotlinx.serialization functionality with Arrow Meta

Migrating from Jackson to kotlinx.serialization may be quite a challenge due to differences in approaches. One of them is not having a global naming strategy. But can we solve this? Sure, we can with Arrow Meta.

Arrow Meta is a functional companion to Kotlin's compiler. This library opens a way to write compiler plugins, linters and other source transformations.

In this talk, we are going to cover the following:

Setup a multi module project for compiler plugin development with gradle
Overview of Arrow Meta features
Use case: Adding a global naming strategy to Kotlin Serialization

Transcript

1. Extending kotlinx.serialization functionality with Arrow Meta Karin-Aleksandra Monoid Kotland, 2021
2. About Senior Software Engineer Background in Kotlin & Scala (both front and backend) Living in Berlin with two cats
3. Agenda • Why? • What is Arrow Meta • Sample project: description • Diving into details • Showtime!
4. Project stack Just backend with Ktor + Arrow Jackson was kind of "default" Smooth but not Kotlin-first
5. Kotlinx.serialization Pros Kotlin-first No boilerplate for sealed classes Cons Not a lot of serializers out of the box Nuances with transients in abstract classes No global naming strategy
6. Global naming strategy UPPER_SNAKE_CASE -> camelCase USER_NAME -> userName
7. val objectMapperUpperCamelCase = jacksonObjectMapper() .apply { propertyNamingStrategy = PropertyNamingStrategies.UPPER_SNAKE_CASE }
8. Global naming strategy @SerialName("USER_NAME") val userName: String
9. What is Arrow Meta?
10. Functional companion to Kotlin's Compiler
11. GIF source: https://github.com/arrow-kt/arrow-meta
12. Source repository https://github.com/paranoidmonoid/kotlin-serial-name
13. Setting: a Zoo • various animals (actually, only cats and dogs) • various sources (= 3rd party services) • various standards of documentation (in JSON format with different naming policies)
14. A generic cat @Serializable data class Cat( val name: String, val age: Int, val ownerName: String, val breed: String )
15. Project setup create-plugin use-plugin
16. create-plugin • Dependencies: "io.arrow-kt:compiler-plugin:$ARROW_META_VERSION" • Jar wrapper
17. use-plugin Dependent task: tasks.withType(<..>.tasks.KotlinCompile) { compileTask -> compileTask.dependsOn ":create-plugin:assemble" }
18. Create an extension function val Meta.serialNameGenerator: CliPlugin get() = TODO()
19. Create an extension function val Meta.serialNameGenerator: CliPlugin get() = "Serial Name Plugin" { meta(TODO("add plugin logic")) }
20. Register your extension class SerialNamePlugin : Meta { @ExperimentalContracts override fun intercept( ctx: CompilerContext ): List<CliPlugin> = listOf( serialNameGenerator ) }
21. Decide the phase • classDeclaration - class signature (name, annotations, parameters etc.) • finallySection - finally block • destructuringDeclaration - like in val (first, second) = listOf(first, second) • classBody - functions, properties, companions And others
22. Decide the phase • classDeclaration - class signature (name, annotations, parameters etc.) • finallySection - finally block • destructuringDeclaration - like in val (first, second) = listOf(first, second) • classBody - functions, properties, companions And others
23. Decide the phase classDeclaration(this, { isAnnotatedWith("@Serializable".toRegex()) }) { ... }
24. Add transformations val paramList = value.getValueParameters().map { """@kotlinx.serialization.SerialName |(\"${it.name?.toSnakeCase()}\") |${it.text}""".trimMargin() } val paramListString = paramList.joinToString(", ", "(", ")")
25. Add transformations val paramList = value.getValueParameters().map { """@kotlinx.serialization.SerialName |(\"${it.name?.toSnakeCase()}\") |${it.text}""".trimMargin() }
26. Add transformations val newDeclaration = """ |$`@annotations` |$kind$name$`(typeParameters)` |$paramListString { |$body |} """.trimMargin() Transform.Companion.replace(classElement, newDeclaration.`class`.syntheticScope)
27. Transformations val skip = value.getValueParameters().all { it.isAnnotatedWith(".*SerialName.*".toRegex()) } Transform.Companion.replace(classElement, if (skip) this else newDeclaration.`class`.syntheticScope )
28. Result Showtime!
29. Resources • https://meta.arrow-kt.io/ • https://github.com/arrow-kt/arrow-meta-examples • https://paranoidmonoid.github.io/articles/Kotlin%20and%20friends/Naming%20 strategy%20plugin