[kotlin-client] update Kotlin and libraries versions

[WonderCsabo]

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@dr4ke616 @karismann @Zomzog @andrewemery @4brunu @yutaka0m @stefankoppier @e5l

[wing328]

thanks for the pr

can you review the build failure when you've time?

[WonderCsabo]

https://github.com/OpenAPITools/openapi-generator/actions/runs/17399819940/job/49390120768

For me it seems the echo server is not started. These are the logs for the Run echo server step:

Run git clone https://github.com/wing328/http-echo-server -b openapi-generator-test-server
  git clone https://github.com/wing328/http-echo-server -b openapi-generator-test-server
  (cd http-echo-server && npm install && npm start &)
  shell: /usr/bin/bash -e {0}
  env:
    JAVA_HOME: /opt/hostedtoolcache/Java_Temurin-Hotspot_jdk/17.0.16-8/x64
    JAVA_HOME_17_X64: /opt/hostedtoolcache/Java_Temurin-Hotspot_jdk/17.0.16-8/x64
    GRADLE_BUILD_ACTION_SETUP_COMPLETED: true
    GRADLE_BUILD_ACTION_CACHE_RESTORED: true
    DEVELOCITY_INJECTION_INIT_SCRIPT_NAME: gradle-actions.inject-develocity.init.gradle
    DEVELOCITY_AUTO_INJECTION_CUSTOM_VALUE: gradle-actions
    GITHUB_DEPENDENCY_GRAPH_ENABLED: false
Cloning into 'http-echo-server'...

https://github.com/OpenAPITools/openapi-generator/actions/runs/17399819930/

All of the jobs have this error:

Gradle requires JVM 17 or later to run. Your build is currently configured to use JVM 11.

I updated Gradle to 9.0.0. Should i downgrade it for now?

[wing328]

I updated Gradle to 9.0.0. Should i downgrade it for now?

good question. gradle 8.x active support was ended like a month ago: https://endoflife.date/gradle

shall we take this opportunity to only support gradle 9.x moving forward?

i think it's a good idea but let see if the Kotlin technical committee members have a different opinion on this.

[WonderCsabo]

I also vote for supporting Gradle 9.x . However we need to change the CI to run JVM 17, i will need a little help with that.

[wing328]

https://github.com/OpenAPITools/openapi-generator/actions/runs/17402841036/workflow?pr=21866#L79

you will need to change that to 17

ref: .github/workflows/samples-kotlin-client.yaml

[WonderCsabo]

@wing328 i changed it to Java 17, it works. Thanks!

I still have an issue with the echo server. Can you check it pls?

Also there is an unrelated build error on one of the Circle CI runs.

[WonderCsabo]

@wing328 can you check these if you have time? ⬆️

[wing328]

here is the feedback from Gradle team:

I discussed it a bit more within the team and this is what we propose:
We think you should continue to support Gradle 8 for some time. You can still upgrade your build to Gradle 9, though, then you'd need to add tests for Gradle 8 support and possibly make sure you compile to target Java 8. For Gradle plugins written in Kotlin using Gradle 9 to build a plugin that runs on Gradle 8 is problematic, since the Kotlin versions are not backward compatible. So we would avoid doing that.

ref: https://openapi-generator.slack.com/archives/CLSB0U0R5/p1757653266058709?thread_ts=1755862642.667769&cid=CLSB0U0R5

[wing328]

circle ci failure not related to this change

[wing328]

thanks for the PR 🙏

let's give it a try