How to parametrize Kotlin version in the plugins block of a build.gradle.kts script?

Short answer:

There is currenlty no way of accessing anything of the outer scope from inside the lambda passed to plugins.

Long answer:

In case you use IntelliJ it will show you a bit more information:

'val kotlinVersion: String' can't be called in this context by implicit receiver. Use the explicit one if necessary.

The outer scope (this@Build_gradle) where you define kotlinVersion is not avaiable in the this@plugins scope so you have to define kotlinVersion inside the plugins lambda.

Since the extra delegate isn't available there either you can't use it:

plugins {
    val kotlinVersion = "1.3.61"
    // ...
}

---

Unfortunately using a label does not work:

val kotlinVersion by extra ("1.3.61")

plugins {
    // ... Unresolved reference: kotlinVersion 
    kotlin("jvm") version this@Build_gradle.kotlinVersion
}