Specify system JVM as default JVM

[aschofie]

scala-cli has the capability-- and the requirement-- of downloading and managing its own JVMs. I believe we should be able to direct it to use a manually-installed JVM, or indeed whatever JVM is on the PATH and JAVA_HOME. This should be able to be specified in a config file, environment variables, and as a command-line option.

[MaciejG604]

There is a way to do this with --java-home option and using javaHome directive, but no config entry.
E.g: //> using javaHome /Library/Java/JavaVirtualMachines/adoptopenjdk-11.jdk/Contents/Home
or --java-home /Library/Java/JavaVirtualMachines/adoptopenjdk-11.jdk/Contents/Home

However, JVM 17 is mandatory when using Bloop and it will be installed if the one provided has a lower version. You can opt for using scalac instead of Bloop with option server=false. Note that the bsp command always uses Bloop.

[som-snytt]

My experience is the opposite at #2126 running under my ambient JDK 20 makes it use the wrong -java-output-version; it looks like I figured out to either downgrade my JDK or use --jdk.

I haven't overcome the friction yet to have much experience with the tool, though I am eager to (at some point).

Thanks for the extra pointers.

[som-snytt]

Another input is that we'd like to use standard directives in tests on scala/scala, to replace // scalac: -Werror style pragmas. It would nice to have a standard way to say // javaVersion: 9+ or on scala 3 // test: -jdk:9 (or similar). That is, use the ambient or system JDK, but if it doesn't satisfy a version requirement, abort nicely. Maybe further convergence of scala-cli test and frameworks is possible.

[nartamonov]

scala-cli has the capability-- and the requirement-- of downloading and managing its own JVMs

Moreover, this requirement is completely opaque in the documentation. Encountered this behavior and was puzzled why scala-cli does not use a system-wide JDK. Searches for documentation have yielded nothing. The default value is not specified for the directive using jvm' or --jvm` argument.