Mill 1.1.0-RC1 and onwards to 1.1.0

[lihaoyi]

I have released Mill 1.1.0-RC1, with an eye to releasing 1.1.0 final in December. The two big features of Mill 1.1.0 is support for config-based modules defined in build.mill.yaml files, and single-file .java, .scala, or .kt scripts with YAML build headers. These are discussed more in the changelog below and linked documentation:

• Changelog

The current plan is to synchronize the 1.1.0 release with the Scala 3.8 release also expected by end of the year, such that Mill 1.1.0 will be the first Mill version on Scala 3.8.0. Until then, that gives users 1-2 months to try out the new features and report and issues or bugs, and for us maintainers to polish up the 1.1.0 release.

Please leave any comments, feedback or discussion in this thread

[lefou]

Although Mill supports Scala 3.8, I don't think we want switch our code-base to Scala 3.8, since it will drop support for all Java runtimes lower than Java 17. Of course, we encourage the use of the newest JVM/JDK/Scala version, I think we want to keep that Java 11 compatibility a bit longer. I don't see any feature we can't implement because we stay on Scala 3.7.x.

We might want to cross-back-publish mill-moduledefs for newer Scala versions, so users can bump Scala/JVM version in their builds.

[lihaoyi]

One issue with staying on 3.7.x is that we may lose compatibility with newer JVM versions; AFAIK 3.7.4 is going to be the last point release since it's not LTS, so next time if Java 26 or 27 etc. come out there may not be any 3.7.x release usable together with it. And we can't feasibly downgrade to 3.3.x since we do make use of newer features such as named tuples

The Java 11 vs 17 thing is definitely an issue, I wonder if there's anything we can do there, e.g. allowing user modules to run with Java 11 while Mill itself runs with Java 17. I believe that's what Maven4 and Gradle do, so we would just be following suit

[re-thc]

Spring Boot 3 (not the upcoming 4) already requires Java 17. Same as recent Maven / Gradle releases. 17 sounds good here. It's currently 2 LTS versions behind. Good enough.

[lefou]

Since the build tools must run as long, as the last part of a potentially large toolchain is migrated, we should avoid breaking legacy platform support for as long as possible.

Regarding support for newer Java versions. I'm asking to compile with Scala 3.7.x, not to run with it. All we need to support Java 11 is use Scala 3.7.x for compiling Mill. We also need to bump some dependencies like asm or classgraph to support newer Java versions, e.g. when scanning for main classes.

This should not prevent users to "run" our bytecode on more recent Java or Scala versions.

[He-Pin]

I suggest we keep 1.1.0 as the last version supports Java 11, and the next version of Mill will go with Java 17.