How to set Java language version?

[asarkar]

Nowhere in the Building Java with Mill, was I able to find a way to set the language/target version. Gradle does it as follows:

java {
    toolchain {
        languageVersion = JavaLanguageVersion.of(17)
    }
}

Surely there's a way to specify this in the build file regardless of the compiler version used for the build, right?

[asarkar]

I found the answer by digging around in c3p0/build.mill, but IMO, users would benefit from this being shown in the mill docs. None of the example Java builds target a specific JVM version, which is rare for a non-hobbyist project.

val JavaVersion = "17"
override def javacOptions = Seq("--release", JavaVersion)

[lefou]

We have a scalaVersion in ScalaModule and a kotlinVersion/kotlinLanguageVersion in KotlinModule. It sounds reasonable to manages the respective compiler options for Java as well, and add a javaVersion task. But there are some subtleties when using the --release option. E.g. you can't use --add-exports or --source and --target simultaneously. And if we add a javaReleaseVersion, a javaSourceVersion and a javaTargetVersion, we have to validate their correct combinations and fail accordingly, which could even depend on the version of the used JDK.

Just documenting how you can (and should) configure it via javacOptions seems to be the most maintainable option for now.

[lefou]

FTR, https://docs.oracle.com/en/java/javase/17/docs/specs/man/javac.html

[asarkar]

@lefou Would you mind converting this discussion into a docs update ticket then?

[lefou]

• Document, how to set Java language version #4935