Warnings after updating kotlin to Kotlin 1.4

[patrykpacewicz]

Describe the bug

Yesterday was released Kotlin 1.4.0.

• https://blog.jetbrains.com/kotlin/2020/08/kotlin-1-4-released-with-a-focus-on-quality-and-performance/

Today I updated my code to work with Kotlin 1.4 and this is the error that I received

> Task :compileKotlin
w: Runtime JAR files in the classpath should have the same version. These files were found in the classpath:
    /Users/.../.gradle/caches/modules-2/files-2.1/org.jetbrains.kotlin/kotlin-stdlib-jdk8/1.4.0/e3765b66f0610afc92053ff1a93a87a544fca2b/kotlin-stdlib-jdk8-1.4.0.jar (version 1.4)
    /Users/.../.gradle/caches/modules-2/files-2.1/org.jetbrains.kotlin/kotlin-stdlib-jdk7/1.4.0/9cc187c3dfaf6e4001bdf962e3cdadff7690261b/kotlin-stdlib-jdk7-1.4.0.jar (version 1.4)
    /Users/.../.gradle/caches/modules-2/files-2.1/org.jetbrains.kotlin/kotlin-reflect/1.3.72/86613e1a669a701b0c660bfd2af4f82a7ae11fca/kotlin-reflect-1.3.72.jar (version 1.3)
    /Users/.../.gradle/caches/modules-2/files-2.1/org.jetbrains.kotlin/kotlin-stdlib/1.4.0/63e75298e93d4ae0b299bb869cf0c627196f8843/kotlin-stdlib-1.4.0.jar (version 1.4)
    /Users/.../.gradle/caches/modules-2/files-2.1/org.jetbrains.kotlin/kotlin-stdlib-common/1.4.0/1c752cce0ead8d504ccc88a4fed6471fd83ab0dd/kotlin-stdlib-common-1.4.0.jar (version 1.4)
w: Consider providing an explicit dependency on kotlin-reflect 1.4 to prevent strange errors
w: Some runtime JAR files in the classpath have an incompatible version. Consider removing them from the classpath

It is caused by using kotlin-reflect version 1.3 in jackson-module-kotlin

To Reproduce
It is very easy to reproduce, we need build.gradle

plugins {
    id "org.jetbrains.kotlin.jvm" version "1.4.0"
}

repositories { mavenCentral() }

dependencies {
    api "org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.4.0"
    api "com.fasterxml.jackson.module:jackson-module-kotlin:2.11.2"
}

and App.kt

fun main() {
  println("Hello World!")
}

Versions

• Kotlin: '1.4.0'
• Jackson-module-kotlin: '2.11.2'

[daviddenton]

This isn't really a bug. It's pretty standard behaviour caused when new versions of Kotlin are released which use JARs compiled under older versions. What's needed is actually a new version of this lib built against 1.4. There's already an issue open to collate that work here: #356 😄

[dinomite]

Yep, we can track this is #356