where can I ask questions about binary compatibili...

# announcements

[Tasos Stamadianos]

where can I ask questions about binary compatibility and JVM/JDK versions?

[gildor]

Binary compatibility of Kotlin? This channel is fine for that

[Tasos Stamadianos]

awesome. I think i should have been more specific with my question. Say I'm using a library which is built against Kotlin 1.2.x, but I'm on Kotlin 1.3.x. When I include this lib as a dependency, I get a warning advising me against keeping different versions of runtime JAR files in my classpath. I'm aware that this is likely due to the library in question including Kotlin stdlib as a dependency. Is there a way to fix this? And in a broader scope, if a lib is built against a previous version but does not include the stdlib from that version, will it work with newer Kotlin versions?

[fred.deschenes]

https://kotlinlang.org/docs/reference/compatibility-guide-13.html

[fred.deschenes]

as far as I can see, as long as you include the new libs you should be fine

[Tasos Stamadianos]

oh i've never seen this page, thanks

[ilya.gorbunov]

@Tasos Stamadianos Which build system do you use? Gradle, Maven?
In general there should be only one version of the standard library in the classpath and it should be consistent with the other kotlin runtime libraries such as kotlin-reflect. Could you show the entire warning telling what artifacts have conflicting versions?

[Tasos Stamadianos]

Hi @ilya.gorbunov, thanks for chiming in 🙂 my error is as follows:

Runtime JAR files in the classpath should have the same version. These files were found in the classpath:
    /home/tasos/.gradle/caches/modules-2/files-2.1/org.jetbrains.kotlin/kotlin-stdlib-jdk8/1.2.71/5470d1f752cd342edb77e1062bac07e838d2cea4/kotlin-stdlib-jdk8-1.2.71.jar (version 1.2)
    /home/tasos/.gradle/caches/modules-2/files-2.1/org.jetbrains.kotlin/kotlin-stdlib-jdk7/1.2.71/4ce93f539e2133f172f1167291a911f83400a5d0/kotlin-stdlib-jdk7-1.2.71.jar (version 1.2)
    /home/tasos/.gradle/caches/modules-2/files-2.1/org.jetbrains.kotlin/kotlin-stdlib/1.3.10/b178c1501609c6e4ee8be635513cb023a466457d/kotlin-stdlib-1.3.10.jar (version 1.3)
    /home/tasos/.gradle/caches/modules-2/files-2.1/org.jetbrains.kotlin/kotlin-stdlib-common/1.3.10/1b19d99229dcedad7caf50534dce38fe82845269/kotlin-stdlib-common-1.3.10.jar (version 1.3)

I narrowed down the dependency causing this issue to the popular Javalin HTTP framework, which has an issue referencing Kotlin 1.3 support here: https://github.com/tipsy/javalin/issues/434

thanks!!

[Tasos Stamadianos]

it looks like this is likely to happen whenever I use a dependency built against an older version of Kotlin

[ilya.gorbunov]

It looks like you depend on kotlin-stdlib:1.3.10 and Javalin depens on kotlin-stdlib-jdk8:1.2.71 which itselfs depends transitively on kotlin-stdlib:1.2.71. Gradle resolves that transitive dependency version conflict by choosing the highest version of kotlin-stdlib, but it's ok from gradle's standpoint to leave 1.2.71 version of stdlib-jdk8.

You can resolve this warning by depending explicitly on kotlin-stdlib-jdk8:1.3.10.

[Tasos Stamadianos]

ah okay, so changing:
implementation("org.jetbrains.kotlin:kotlin-stdlib-jdk8")
to:
implementation("org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.3.10")
will fix it?

[Tasos Stamadianos]

this is in my build.gradle.kts

[Tasos Stamadianos]

right now it does not specify a version

[ilya.gorbunov]

If you omit version, it should be inferred from the kotlin plugin version.

[Tasos Stamadianos]

okay, i included the version but the warning remains

[ilya.gorbunov]

That's interesting, could you share build.gradle or at least dependencies section?

[Tasos Stamadianos]

wait, it might be due to inclusion of another lib that's depending on an old version of reflection

[Tasos Stamadianos]

one moment

[Tasos Stamadianos]

okay, i fixed it by explicitly specifying the reflect lib version

[Tasos Stamadianos]

thanks for your help 🙂

[Tasos Stamadianos]

out of curiosity, how is binary compatibility handled in this case?

[ilya.gorbunov]

You can substitute older versions with newer ones. However it's important to keep versions of kotlin core libraries consistent. To make it easier we're going to provide a bill-of-materials (BOM) artifact in 1.3.20, which lists all these libraries versions to keep them in sync (see https://youtrack.jetbrains.com/issue/KT-18398).
This BOM artifact can be used in Maven to pin versions of your dependencies, and AFAIK in Gradle since 5.0.