Add Kotlin as a optional dependency of core module.

[ikhoon]

If Kotlin dependency is added to an optional dependency, we can provide Kotlin-specific extension methods and DSL for each module. For example:

// WebClientExtensions.kt
inline fun <reified T> WebClientRequestPreparation.asJson():
        FutureTransformingRequestPreparation<ResponseEntity<T>> {
    return asJson(object : TypeReference<T>() {})
}

val response: ResponseEntity<Item> = 
  client.prepare()
        .get("/example")
        .asJson<Item>()  // Simply specify the target type parameter.
        .execute()

[jimexist]

by the way i added kotlin support in thrift some time ago, could benefit from that once libthrift and compiler 0.17.0 is released in Q3 2022

[ikhoon]

It looks to support Kotlin Coroutines. Awesome! ❤️ https://github.com/apache/thrift/blob/master/compiler/cpp/src/thrift/generate/t_kotlin_generator.cc#L1393

[jimexist]

It looks to support Kotlin Coroutines. Awesome! ❤️ https://github.com/apache/thrift/blob/master/compiler/cpp/src/thrift/generate/t_kotlin_generator.cc#L1393

yes i intended to only support suspend functions, but then (for the default implementation) delegate to jdk8 bridge for suspend function <=> async client operations, so that the generated code can still work with the existing Java libthrift library alone, i.e. there's no libthrift-kotlin library.

i can see that in armeria the thrift client is actually not based on the default implementation but rather via dynamic proxy and delegate in order to work upon HTTP protocol, so ideally this can be done similarly for kotlin