title: How to get ext.* variables into plugins block in build.gradle.kts
body: <p>My build file looks like this:</p>
  
  <pre><code>val nexusBaseUri: String by extra
  val gradle_version: String by extra
  val kotlin_version: String by extra
  
  buildscript {
      val nexusBaseUri by extra { "https://mynexusserver/nexus" }
      val gradle_version by extra { "4.1" }
      val kotlin_version by extra { "1.1.4-3" }
      val springBoot_version by extra { "2.0.0.M3" }
  
      repositories {
          maven { url = uri("$nexusBaseUri/repository/public") }
          jcenter()
          maven { url = uri("http://repo.spring.io/snapshot") }
          maven { url = uri("http://repo.spring.io/milestone") }
      }
      dependencies {
          classpath("org.springframework.boot:spring-boot-gradle-plugin:$springBoot_version")
          classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version")
          classpath("org.jetbrains.kotlin:kotlin-allopen:$kotlin_version")
      }
  }
  
  plugins {
      application
      // vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
      // the following line causes a problem
      // vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
      kotlin("jvm", kotlin_version)
  }
  
  apply {
      plugin("kotlin-spring")
      plugin("org.springframework.boot")
      plugin("io.spring.dependency-management")
  }
  
  application {
      mainClassName = "eqip.fid.FdmlInterpreterDeveloperAppKt"
  }
  
  repositories {
      maven { url = uri("$nexusBaseUri/content/groups/public") }
      jcenter()
      maven { url = uri("http://repo.spring.io/snapshot") }
      maven { url = uri("http://repo.spring.io/milestone") }
  }
  
  dependencies {
      compile(kotlin("stdlib"))
      compile("org.springframework.boot:spring-boot-starter-web")
  }
  
  tasks {
      "wrapper"(Wrapper::class) {
          gradleVersion = gradle_version
      }
  }
  </code></pre>
  
  <p>The error I get in IntelliJ IDEA is</p>
  
  <blockquote>
    <p>'val kotlin_version: String' can't be called in this context by implicit receiver. Use the explicit one if necessary</p>
  </blockquote>
  
  <p>How do I fix this?</p>