`No main class specified or found` when overriding `zincWorker`

[dontgitit]

Hello,

I put together a very simple hello world app, but experienced strange behavior once I added a zincWorker override; my main class could no longer be detected. The full sample app can be found here. Commenting out this line makes the app run as expected.

Let me know if any additional info is needed.

[lefou]

I can reproduce it.

build.sc

import mill.scalalib._
import mill.define.ModuleRef

object ZincWorkerJava21 extends ZincWorkerModule {
  def jvmId = "temurin:21.0.6"
}

object foo extends ScalaModule {
  def scalaVersion = "3.6.3"
  // commenting out the zincWorker makes the app run
  override def zincWorker = ModuleRef(ZincWorkerJava21)
  // alternatively, uncomment this for an explicit main class
  //  def mainClass = Some("Foo")
}

.mill-version

0.12.8

foo/src/Foo.scala

object Foo {
  def main(args: Array[String]): Unit = println("hello world")
}

> mill --version
Mill Build Tool version 0.12.8
Java version: 21.0.5, vendor: Eclipse Adoptium, runtime: /opt/openjdk-bin-21.0.5_p11
Default locale: de_DE, platform encoding: UTF-8
OS name: "Linux", version: 6.6.74-gentoo-x86_64, arch: amd64

> mill foo.run
[build.sc-61/65] compile
[build.sc-61] [info] compiling 1 Scala source to /tmp/mill-2/out/mill-build/compile.dest/classes ...
[build.sc-61] [info] done compiling
[58/66] foo.compile
[58] [info] compiling 1 Scala source to /tmp/mill-2/out/foo/compile.dest/classes ...
[58] [info] done compiling
[66/66] ============================== foo.run ============================== 62s
1 tasks failed
foo.finalMainClass No main class specified or found