Incompatible with Kotlin 1.9.x

[artdk]

Spring framework will not fully support Kotlin 2.x until version 7.0 (projected to be released in Q4 2025) and as a result many users are sticking with Kotlin 1.9.x until the Spring 7.0 release
Because this library is compiled with Kotlin 2.1, it cannot be used with older versions of Kotlin and results in this error:
.m2/repository/dev/hsbrysk/caffeine-coroutines/2.0.1/caffeine-coroutines-2.0.1.jar!/META-INF/caffeine-coroutines.kotlin_module: Module was compiled with an incompatible version of Kotlin. The binary version of its metadata is 2.1.0, expected version is 1.9.0.

Are there any plans to compile it with a lower Kotlin version for wider compatibility?

I tested the downgrade and all it requires is a downgrade of kotlin-coroutines, and some extra casting which is not handled by smart casting in Kotlin <2

For additional context here is a similar issue in the openai-java SDK: openai/openai-java#320

[be-hase]

Sorry for the late reply.

I'm also a Spring Boot user, so I'm quite familiar with it.
Honestly, Kotlin 1.9 is too outdated, so I don't plan to support it — sorry about that.

Spring has also mentioned that you can use Kotlin 2.x as long as you’re careful with dependencies.
spring-projects/spring-framework#33629 (comment)

In fact, I’m using Spring with Kotlin 2.x at work as well, and I haven’t encountered any particular issues.

[be-hase]

Maybe, version 1.2.1 should work with Kotlin 1.9 as well.
https://github.com/be-hase/caffeine-coroutines/releases/tag/v1.2.1

(Actually, I tried downgrading, but since Caffeine has migrated to jspecify, it requires Kotlin 2.1, so I gave up.
ref: #63

[artdk]

Thanks for the reply!
Unfortunately for organizational reasons we cannot upgrade to Kotlin 2.x until it is fully supported in Spring, so for now we will use 1.2.0 as 1.2.1 also requires Kotlin 2.x and look forward to upgrading in Q4

Thanks for your work maintaining this fantastic library though

[be-hase]

thanks !