Use Kotlin's bom to provide dependency management for Kotlin

[wilkinsona]

Thanks to @sdeleuze, it looks like Kotlin is going to provide a bom. As part of our Kotlin story in 2.0, we should import the bom in spring-boot-dependencies.

[sdeleuze]

I would suggest renaming this issue to "Provide dependency management for Kotlin", add for the moment kotlin-reflect, kotlin-stdlib, kotlin-stdlib-jre7 and kotlin-stdlib-jre8 artifacts to dependency management (enough for most use cases) since it is needed for #10511 (see sdeleuze@8eb684f). If a Kotlin BOM is released before 2.0 GA (see KT-18398, I have recently highlighted again the priority of that issue to Kotlin team) we will switch to the BOM, else staying with that for now will help most Kotlin developers to avoid mixing different versions of Kotlin artifacts (occurs frequently with kotlin-reflect).

[sdeleuze]

@wilkinsona Damned it seems we almost got it for Boot 2.0 but that will be for Boot 2.1 ;-) Could you please have a look to https://github.com/cy6erGn0m/kotlin-bom/blob/master/kotlin-lang/pom.xml, @cy6erGn0m would like some feedbacks and I prefer to ask to the real expert on that topic!

[snicoll]

Thanks for the ping @sdeleuze, I've created cy6erGn0m/kotlin-bom#1

[wilkinsona]

Kotlin has a bom in 1.3 so we should be able to do this in 2.2.

[oliemansm]

When will je be upgrading the Kotlin version to 1.3?

We're using Spring Boot 2.1.0 starter right now, which sets the Kotlin version to 1.2.71, while the graphql-java-tools lib we use requires (and explicitly sets) 1.3.10. However, Spring Boot appears to be overriding that version, so right now the only way to fix that is by setting the required Kotlin version manually in our Spring Boot project to override the version specified by Spring Boot.

Bottom line: would be ideal if Spring Boot would be upgraded to use Kotlin 1.3.* as well.

[wilkinsona]

As shown by this issue being assigned to the 2.2.x milestone and my comment above, we intend to upgrade to Kotlin 1.3 in Spring Boot 2.2.

[snicoll]

However, Spring Boot appears to be overriding that version

The Spring Boot parent and dependency management sets a version for Kotlin, yes. You can easily override that as described in the documentation

[sdeleuze]

@oliemansm Spring Boot plugin is expected to leverage the Kotlin version defined with the kotlin.version property, and Gradle plugin even directly uses the version of the Kotlin plugin.

[oliemansm]

Thanks all

[ilya-g]

@wilkinsona Note that Kotlin will have bom only starting from 1.3.20, which hasn't been released yet. Although you can try the eap version, which has been published recently:
https://mvnrepository.com/artifact/org.jetbrains.kotlin/kotlin-bom/1.3.20-eap-25
https://dl.bintray.com/kotlin/kotlin-eap/org/jetbrains/kotlin/kotlin-bom/1.3.20-eap-25/

[sdeleuze]

After discussion with @mp911de I have created KT-30042 to ask Coroutines artifacts to be added in the kotlin-bom since most Coroutines are on library side and use a different version scheme (currently Coroutines 1.1.1 is designed to work with Kotlin 1.3.21).