com-lihaoyi / mill-moduledefs   0.10.9

MIT License GitHub

Scalac compiler plugin to support Mill modules

Scala versions: 2.13



The Mill build tool module structure is highly tied to the organizational structure of the Scala programming language. Project modules are modelled as Scala objects, Module targets are modelled as Scala defs.

Mill targets are also modelled as free applicatives, which among other things makes the Mill task graph introspectable. To hide some boilerplate code needed to nicely write tasks like defs, Mill uses some Scala macros and a Scalac compiler plugin.

In this project, you’ll find the compiler plugin and some shared code.


Artifacts of this project are released to Maven Central.

def ivyDeps = Agg(
// Enable the plugin in the Scala compiler
def scalacPluginIvyDeps = Agg(

Project Layout

This project contains two modules:

  • moduledefs - Some shared code to be used in the Mill classpath. The artifactName is mill-moduledefs.

  • moduledefs/plugin - A Scalac compiler plugin to be used when compiling Mill projects. The artifactName is scalac-mill-moduledefs-plugin.

Development and Releases

This code is expected to change rarely.

It should be especially kept stable within the same Mill major version.


Publishing is automated via GitHub Actions and implemented in the publishToSonatype command.

def publishToSonatype(
    sonatypeCreds: String,
    gpgArgs: String = PublishModule.defaultGpgArgs.mkString(","),
    dryRun: Boolean = false,
    artifactsFile: Option[String] = None
): Command[Unit]

You need to update the version manually, before creatign the git tag!

All git tags are automatically published. The tag should reflect the version number.

Re-publish for a new Scala Release

The most frequently expected changes are releases for newer Scala version. This is especially needed, as compiler plugins are tied to the exact Scala compiler version.

Hence, this build aims to be flexible enough, to release an already tagged version for newer Scalac releases after the fact.

As an example, to release an already published version 0.10.9 for a new Scala version 2.13.10, follow these steps:

  1. Create a branch release-0.10.9 from the git tag 0.10.9.

  2. Add the new Scala version to the build setup. Make sure you don’t change the actual code, so it stays compatible to the original tag.

  3. Add a file PUBLISH_ONLY containing a selector for the artifacts to publish. If you need more than one selector, place each on a new line.

    Example file PUBLISH_ONLY
  4. Commit your changes.

  5. Tag your commit with 0.10.9-for-2.13.10. This will trigger the publish-sonatype workflow in GHA.

  6. If appropriate, update the Readme/Changelog in the main branch.


This project is published under the MIT License.


0.10.9 - 2022-11-10

First stable release from this repository. No feature additions and removals since release 0.10.8 from the Mill repository.

  • 2023-06-03: Published for Scala 2.13.11

  • 2023-09-07: Published for Scala 2.13.12

  • 2024-02-27: Published for Scala 2.13.13

0.10.9-alpha-1 - 2022-10-17

Initial release from this repository. Intended for testing only.

Older Releases

Older versions of this project were developed in the Mill git repository and were packaged as ordinary Scala artifact mill-moduledefs (without the full Scala version suffix). Refer to issue #2035, to learn why we split the projects.