Could not determine the dependencies of task '...' - Cannot convert kotlin.Unit to a task

Help/Discuss
1

I’ve migrated all my groovy stuff to kotlin, the compiler is happy so far, but at runtime some of my tasks in different subprojects are now failing with this message:

E.g.:

* What went wrong:
Could not determine the dependencies of task ':subproject:assemble'.
> Cannot convert kotlin.Unit to a task.
  The following types/formats are supported:
    - A String or CharSequence task name or path
    - A Task instance
    - A TaskReference instance
    - A Buildable instance
    - A TaskDependency instance
    - A Provider that represents a task output
    - A Provider instance that returns any of these types
    - A Closure instance that returns any of these types
    - A Callable instance that returns any of these types
    - An Iterable, Collection, Map or array instance that contains any of these types

“–stacktrace” is not helpful either - is there some way to find the explicit location where gradle does have a kotlin.Unit instead of a task now - the project is huge and without a hint it’s somewhat difficult to fix it?

2

Hard to say from the information you gave.
Somewhere you call a method that historically accepts Object (probably dependsOn in your case), but now with something that returns Unit which cannot be converted to a task.

3

Sorry, I did not had anything more, because there was no hint where it is failing, but with try/error I found this:

I had the following code:

val cycloneDxBom =
    tasks.cyclonedxBom {
...
   }

the task itself is from the cyclonedx gradle plugin and used that in a builtBy:

artifacts.add("cycloneDxReport", layout.buildDirectory.file("reports/cyclonedx-backend-$version.xml")) {
    builtBy(cycloneDxBom)
}

Compiler was happy, but at runtime I had that error message from above.

I’ve changed it to:

tasks {
    cyclonedxBom {
    ...
   }
}



artifacts.add("cycloneDxReport", layout.buildDirectory.file("reports/cyclonedx-backend-$version.xml")) {
    builtBy(tasks.named("cyclonedxBom"))
}

Now it is building again. Seems I can’t assign that task to a val and use it - obviously as it is failing - although I am not sure why not and why the compiler is happy about that usage.

4

Yes you can, if you would have, but you didn’t :slight_smile:
You assigned the result of calling tasks.cyconledxBom { ... } which is syntactic sugar for tasks.cyconledxBom.configure { ... } which is a void method, so in Kotlin results in Unit, not the task or task provider.

val cycloneDxBom = tasks.cyclonedxBom
cyclonedxBom {
    ...
}

would have worked.
Or also

val cycloneDxBom by tasks.existing(TypeOfTheTask::class) {
    ...
}

Or also

tasks.cyclonedxBom {
    ...
}
...
builtBy(tasks.cycloneDxBom)

…

1 Like
5

grummel - now I need some sugar too, that is such a bummer, a little bit of embarrassing :wink: - you’re right of cause argl - thanks for that feedback.

1 Like