ext in buildscript can not be recognised by Gradle

Question

In these days, I am trying to write some codes to experience the Spring reactive features and kotlin extension in Spring 5, and I also prepared a gradle Kotlin DSL build.gradle.kt to configure the gradle build.

The build.gradle.kt is converted from Spring Boot template codes generated by http://start.spring.io.

But the ext in the buildscript can not be detected by Gradle.

buildscript {
  ext { }
}

The ext will cause Gradle build error.

To make the variables in classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlinVersion") and compile("org.jetbrains.kotlin:kotlin-stdlib-jre8:$kotlinVersion") work, I added the variables in the hard way.

val kotlinVersion = "1.1.4"
val springBootVersion = "2.0.0.M3"

But I have to declare them in global top location and duplicate them in the buildscript.

Code: https://github.com/hantsy/spring-reactive-sample/blob/master/kotlin-gradle/build.gradle.kts

Is there a graceful approach to make ext work?

Update: There are some ugly approaches:

1. From Gradle Kotlin DSL example, https://github.com/gradle/kotlin-dsl/tree/master/samples/project-properties, declares the properties in gradel.properties.

   kotlinVersion = 1.1.4
   springBootVersion = 2.0.0.M3
   

   And use it in build.gradle.kts.

   buildScript{
      val kotlinVersion by project
   
   }
    val kotlinVersion by project //another declare out of buildscript block.
   

2. Similar with above declare them in buildScript block:

   buildScript{
      extra["kotlinVersion"] = "1.1.4"
      extra["springBootVersion"] = "2.0.0.M3"
      val kotlinVersion: String by extra
   
   }
    val kotlinVersion: String by extra//another declare out of buildscript block.
   

How can I avoid the duplication of val kotlinVersion: String by extra?

Answer 1

Global properties in kotlin-gradle-dsl:
https://stackoverflow.com/a/53594357/3557894

---

Kotlin version is embedded into kotlin-gradle-dsl.
You can use dependecies with embedded version as follows:

implementation(embeddedKotlin("stdlib-jdk7"))

classpath(embeddedKotlin("gradle-plugin"))

Answer 2

What is working for me is using ext in allprojects instead of buildscript, so in your top-level build.gradle.kts

allprojects {
  ext {
    set("supportLibraryVersion", "26.0.1")
  }
}

then you can use it in build.gradle.kts files in modules like this:

val supportLibraryVersion = ext.get("supportLibraryVersion") as String

Answer 3

With Kotlin DSL ext has been changed to extra and it can be used under buildscript.

Eg :-

buildscript {
    // Define versions in a single place
    extra.apply{
        set("minSdkVersion", 26)
        set("targetSdkVersion", 27)
    }
}