Mill downloading a JVM even though I have one

[bishabosha]

Version: 1.1.0-RC3-156-47444a

I downloaded the bootstrap script from https://repo1.maven.org/maven2/com/lihaoyi/mill-dist/1.1.0-RC3-156-47444a/mill-dist-1.1.0-RC3-156-47444a-mill.sh and ran ./mill version and now it started downloading a JVM (Azul Zulu 21):

in the same shell environment i already had a JVM installed:

java --version
openjdk 21.0.8 2025-07-15 LTS
OpenJDK Runtime Environment Temurin-21.0.8+9 (build 21.0.8+9-LTS)
OpenJDK 64-Bit Server VM Temurin-21.0.8+9 (build 21.0.8+9-LTS, mixed mode, sharing)

echo $JAVA_HOME
/Users/jamie/.sdkman/candidates/java/current

[lefou]

I think Mill should be more smart about this situation. If the installed and initially used JVM meet the configured specification, we should just re-use it.

E.g. if the .mill-jvm-version says 21, your installed Temurin-21.0.8+9 should be sufficient. If the config is more precise and doesn't match (e.g. "21.0.9" or "zulu:21"), downloading a JVM is probably ok. Maybe, we need more fine-grained configuration for such situations.

Currently, the only way to avoid that is to set mill-jvm-version to system.