Mixed Groovy/Kotlin DSL multiproject build, How can Kotlin read ext variables

Question

I'm exploring converting our Groovy DSL based build files to Kotlin and would like to do this incrementally. However, I can't figure out how to read ext variables set in the top level build.gradle in a sub-project build.gradle.kts.

My experimental repository is available here

It has this layout:

.
├── README.md
├── build.gradle
├── gradle
│   └── wrapper
│       ├── gradle-wrapper.jar
│       └── gradle-wrapper.properties
├── gradlew
├── groovy
│   └── build.gradle
├── kts
│   ├── build.gradle.kts
│   └── src
│       └── main
│           └── java
│               └── xyz
│                   └── abc
│                       └── def
│                           └── Main.java
└── settings.gradle

The top level file defines an ext variable containing common library versions like so:

plugins {
    id("java")
}

ext.libraries = [ shared: "xyz.abc.def:art:1.2" ]

There are two sub-projects, one using the Groovy DSL and one using the Kotlin DSL. They both attempt to declare a dependency on libraries.shared.

╰─➤  cat groovy/build.gradle 
plugins {
    id("java")
}

dependencies {
    implementation(libraries.shared)
}

╰─➤  cat kts/build.gradle.kts 
plugins {
    id("java")
}

dependencies {
    implementation(libraries.shared)
}

settings.gradle includes both projects.

╰─➤  cat settings.gradle 
include "groovy"
include "kts"

When I run ./gradlew projects I get this error:

  Line 6:     implementation(libraries.shared)
                             ^ Unresolved reference: libraries

When the include for the kts sub-project is commented out it succeeds, displaying the groovy sub-project.

I've tried a number of different things to reference the libraries, such as project.extra or extra but so far haven't hit anything that works.

EDIT:

After digging around in the Gradle API docs I came up with this, which works but is absolutely horrid.

implementation((project.getParent()!!.extra.properties["libraries"]!! as HashMap).get("shared")!!);

timyates_6509 · Answer

You could use this in the kotlin script

plugins {
    java
}

val libraries: Map by rootProject.extra

repositories {
    mavenCentral()
}

dependencies {
    implementation(libraries["shared"]!!)
}

Edit

If you are using a current (7 at time of writing) version of Gradle, you could try out the new version catalogues feature -- which is in preview at time of writing, so may be a bumpy road to take...

To do this, you can remove your ext.libraries from your root project, and replace it with this in settings.gradle

enableFeaturePreview('VERSION_CATALOGS')

dependencyResolutionManagement {
    versionCatalogs {
        libs {
            alias('shared').to('com.bloidonia:ascii-image:1.1')
        }
    }
}

Then in both Groovy and Kotlin DSL build scripts, you can reference these dependencies via:

    implementation(libs.shared)

Edit 2 -- after some coffee

Ahhh, so I think this answers Jeff's question in the comments, and shows an alternative

Yes, we could add a function to ext in the root Project like so:

ext.libraries = [ shared: "com.bloidonia:ascii-image:1.1" ]
ext.library = { String name ->
    ext.libraries."$name"
}

And then in the Kotlin project, we can do:

val library: groovy.lang.Closure by rootProject.extra

dependencies {
    implementation(library("shared"))
}

Mixed Groovy/Kotlin DSL multiproject build, How can Kotlin read ext variables

1 Answers

Edit

Edit 2 -- after some coffee