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

Binary compatibility of Kotlin? This channel is fine for that

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?

oh i've never seen this page, thanks

@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?

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!!

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

.

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?

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

okay, i included the version but the warning remains

That's interesting, could you share

build.gradle

or at least

dependencies

section?

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

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.