using SelfType to mixin compiler options

[lostiniceland]

In my evaluation project it would be great to define a SelfType in order to mixin compiler-options.

trait KotlinCompilerOptions  {
  this: KotlinModule =>

  override def kotlinVersion: T[String] = Versions.kotlin

  override def kotlincPluginMvnDeps: T[Seq[Dep]] = Seq(
    mvn"org.jetbrains.kotlin:kotlin-allopen-compiler-plugin:${kotlinVersion()}",
    mvn"org.jetbrains.kotlin:kotlin-noarg-compiler-plugin:${kotlinVersion()}"
  )

  override def kotlincOptions = Seq(
    "-jvm-target=21",
    "-P",
    "plugin:org.jetbrains.kotlin.allopen:preset=spring",
    "-P",
    "plugin:org.jetbrains.kotlin.noarg:preset=jpa",
  )
}

object app extends KotlinMavenModule with KotlinCompilerOptions{
   object test extends KotlinMavenTests with KotlinCompilerOptions
}
// another use-case would be for JavacCompilerOptions which are needed by multiple modules but not all

Unfortunately this seem not possible because the Task.Simple macro is not able to work with this.
Task{} members must be defs defined in a Module class/trait/object body

Removing the type annotations fixes the self-type definition but breaks when doing the actual mixin because now the types differ (String != T[String])

Since the macro seems not to be able to wrap the parameters I tried creating a Task.Anon, but this is not the proper type
Found: mill.api.Task[String] Required: mill.api.Task.Simple[String]

I am not sure if this is a bug (should KotlinMavenTests not inherit the settings I've made on KotlinMavenModule), a missing feature, or if I am completely wrong here.

[lihaoyi]

@lostiniceland can you do

trait KotlinCompilerOptions  extends mill.Module{
  this: KotlinModule =>

That might make the members must be defs defined in a Module error go away

[lefou]

Beside the extends mill.Module hint @lihaoyi gave, a proper mix-in should not blindly overwrite tasks but add or filter to their super-tasks. Otherwise they're not really composable.

[lostiniceland]

Beside the extends mill.Module hint @lihaoyi gave, a proper mix-in should not blindly overwrite tasks but add or filter to their super-tasks. Otherwise they're not really composable.

True. Propably going for composition is the better alternative. I've marked @lihaoyi answer nevertheless since it fixed the actual compiler issue.