Gradle Kotlin DSL: Define Kotlin version in unique place

For describing Gradle build scripts, we can use Kotlin via build.gradle.kts files. It's a common problem to globally define the Kotlin version to be used, both in the dependencies and also in the build plugin section (It's rather uncommon to have different versions in use for the given case).

Consider the following code (Gradle 4.3.1):

plugins {
    var pluginVersion = "1.2.30"
    kotlin("jvm").version(kotlinVersion)
    // more
}

var dependencyVersion = "1.2.30"
dependencies {
    compile(kotlin("stdlib", kotlinVersion))
    compile(kotlin("reflect", kotlinVersion))
    testCompile(kotlin("test", kotlinVersion))
    // more
}

As you can see, the kotlin version (1.2.30 in this case) is defined twice: dependencyVersion and pluginVersion, which very often does not differ. Due to DSL restrictions, it is impossible to access the pluginVersion from outside the plugins block or access the dependencyVersion from within the plugins block.

How can the version string, "1.2.30" be extracted to a single place?

In later versions of Gradle you no longer need to specify the version of your kotlin(stdlib|reflect|test) dependencies, the Kotlin plugin will automatically configure them for you.

As for extracting the dependency to a single place, there are two main patterns:

• define the constants you want to share in an object within buildSrc/src/main/kotlin/ and use that object in your build script, code from buildSrc is available to the whole script including the plugins block

• use a system property, you can define a system property in gradle.properties by prefixing its name with systemProp. and you can access system properties via System.getProperties(), for example:

  // build.gradle.kts
  plugins {
    val kotlinVersion by System.getProperties()
    println("Kotlin version is $kotlinVersion")
  }
  
  // gradle.properties
  systemProp.kotlinVersion=1.2.20