I'm looking into migrating a Groovy codebase to Ko...

# gradle

[Rob Elliot]

I'm looking into migrating a Groovy codebase to Kotlin.

I was doing OK with having the Kotlin code depend on the Groovy code, but after some thought I think the migration will be easier if the Groovy code depends on the Kotlin code. I'm struggling to get compileGroovy to see the Kotlin classes though. Could anyone give me some pointers?

[Rob Elliot]

For reference, this was the build.groovy config I used to get Kotlin depending on Groovy:

tasks.named('compileGroovy') {
    // Groovy only needs the declared dependencies
    // (and not longer the output of compileJava)
    classpath = sourceSets.main.compileClasspath
}

tasks.named('compileKotlin') {
    // Kotlin also depends on the result of Groovy compilation
    // (which automatically makes it depend of compileGroovy)
    classpath += files(sourceSets.main.groovy.classesDirectory)
}

tasks.named('compileTestGroovy') {
    // Groovy only needs the declared dependencies
    // (and not longer the output of compileJava)
    classpath = sourceSets.test.compileClasspath
}

tasks.named('compileTestKotlin') {
    // Kotlin also depends on the result of Groovy compilation
    // (which automatically makes it depend of compileGroovy)
    classpath += files(sourceSets.test.groovy.classesDirectory)
}

[August Lilleaas]

how do you access the Kotlin classes? Just in case you weren’t aware, many classes (only exception is kotlin files with a single class with the same name as the file) will get a “Kt” suffix

[Rob Elliot]

The classes have the correct names. The problem is that the Kotlin classes are not on the Groovy compile classpath.

[Rob Elliot]

I presume I need something along the lines of:

tasks.named('compileGroovy') {
    classpath = [
        sourceSets.main.compileClasspath,
        sourceSets.main.kotlin.classesDirectory
    ]
}

but classesDirectory is not a property of sourceSets.main.kotlin.

[Vampire]

There is an example of how to change the lanugage dependency order in the manual

[Vampire]

https://docs.gradle.org/current/userguide/building_java_projects.html#sub:compile_deps_jvm_lang

[Vampire]

It is for changing the order between Groovy and Java, but I guess for Groovy and Kotlin it should be largely the same.

[Vampire]

Ah now I see your problem. There is no source directory set named "kotlin" like for "groovy"

[Rob Elliot]

Insofar as I understand that page, it would mean this:

tasks.named('compileKotlin') {
    classpath = sourceSets.main.compileClasspath
}

tasks.named('compileGroovy') {
    classpath += files(sourceSets.main.kotlin.classesDirectory)
}

but sourceSets.main.kotlin.classesDirectory doesn't seem to exist.

[Rob Elliot]

What you said

[Vampire]

Try it with .java. instead of .kotlin..
Iirc, that's the way to go.

[Rob Elliot]

compileGroovy is still reporting unable to resolve class XXX for all my Kotlin classes. A build/classes/kotlin directory exists with my compiled Kotlin classes, so I guess compileKotlin does have its own independent output? Or would it have added it to sourceSets.main.java.classesDirectory?

I do find it hard to navigate the Gradle model to work out what to do in these circumstances. Unfortunately googling anything involving the words gradle, groovy and kotlin inevitably brings up reams of results about the gradle DSL.

[Rob Elliot]

The following seems to work:

tasks.named('compileGroovy') {
    classpath += files(tasks.compileKotlin.destinationDir)
}

[Rob Elliot]

(The task dependencies are already correct, as Groovy depends on Java and Java depends on Kotlin)

[Rob Elliot]

Oh no, that only worked with Kotlin 1.6... 1.7 doesn't have tasks.compileKotlin.destinationDir.

[Rob Elliot]

OK, so with Kotlin 1.7 (& gradle 7.5.1) this works:

tasks.named('compileGroovy') {
    classpath += files(tasks.compileKotlin.destinationDirectory)
}

tasks.named('compileTestGroovy') {
    classpath += files(tasks.compileTestKotlin.destinationDirectory)
}

If this is wrong™ please let me know.