Why cannot be `const val` used in build.gradle.kts

Question

I'd like to define a version constant in guild.gradle.kts file so that it can be used even in the plugins block. The plugins block requires restricted syntax :

«plugin version» must be constant, literal, strings

Following the restriction I tried to define the a version constant:

const val kotlinVersion = "1.3.72"

plugins {
    java
    kotlin("jvm") version kotlinVersion
}

However this fails with message

Const 'val' are only allowed on top level or in objects

even though the declaration seem to meet all const requirements . Why cannot be const val used in build.gradle.kts?

Answer 1

Even though it seems like your build script is top level, it isn't. The gradle docs mentions this when explaining the lifecycle of the build:

Finally, evaluate each Project by executing its build.gradle file, if present, against the project.

(source ) This means that in your kotlin build scripts, the receiver type (ie this ) is KotlinBuildScript which is eventually a subclass of Project . I don't know the details about how it's evaluated, but I can imagine it would be equivalent to what you can do in Kotlin with receiver types:

fun Project.evaluate(buildScript: Project.() -> Unit) = this.evaluate()

So your build script is really just the inside of a closure, hence why you can't use const val .