Kotlin compilation error with spring-cloud-function 4.2.0-

[bnasslahsen]

Describe the bug
Kotlin compilation error with spring-cloud-function 4.2.0

Versions of the framework:

• Spring Boot 3.4.0
• Spring Cloud: 2024.0.0
• Kotlin: 1.9.25
• Java: 17

Sample
To reproduce:

1. Generate the project from https://start.spring.io/#!type=maven-project&language=kotlin&platformVersion=3.4.0&packaging=jar&jvmVersion=17&groupId=com.example&artifactId=demo&name=demo&description=Demo%20project%20for%20Spring%20Boot&packageName=com.example.demo&dependencies=web,cloud-function
2. unzip and compile the project:

./mvnw compile

Current behavior
Compilation error:

[ERROR] Failed to execute goal org.jetbrains.kotlin:kotlin-maven-plugin:1.9.25:compile (compile) on project springdoc-openapi-starter-common: Compilation failure
[ERROR] /opt/repository/org/springframework/cloud/spring-cloud-function-context/4.2.0/spring-cloud-function-context-4.2.0.jar!/META-INF/spring-cloud-function-context.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.
[ERROR] -> [Help 1]

Expected behavior
No compilation error

Added minimal reproducer project just in case:
demo3.zip

[olegz]

We do not specify Kotlin version anywhere in s-c-function, so it is pulled transitively.
Yes I was able to reproduce the issue with your reproducer (thank you) and it appears that something has changed upstream (perhaps in boot) since if you upgrade cloud version to 2024.0.1-SNAPSHOT, everything compiles just fine.

Please let me know, so I can close this issue

[spencergibb]

See #1015. In my tests, I see the kotlin-maven-plugin using a 2.1.0 plugin. There might be some times it gets 2.1.0 and other times it doesn't.

[olegz]

Seems like it is indeed random, so we need to be explicit about it. . .
Thank you @spencergibb for adding it - 0a43fc9

[bnasslahsen]

Wonderful, thanks @olegz and @spencergibb!
Looking forward to 4.2.1—maybe it’ll arrive just in time for Christmas!