Global configuration for JVM for bloop

[romanowski]

Is your feature request related to a problem? Please describe.

Scala CLI wants to stick to default, LTS JDK - for now it is Java 17. Some users wants to use newer versions like 18 or 19 and Scala CLI should have a easy way to configure that.

Describe the solution you'd like

A global setting that specify default JDK for bloop. It should accept same arguments as --jvm. Also it should not allow JDK lower then 17.

Additionally, we should update the error, warning and info messages about JDK that we report.

Additional context

Inspired by @milessabin comment.

[SethTisue]

@MaciejG604 and I are looking at this at today's Tooling Spree

It should accept same arguments as --jvm

It's not clear to me if that's the right design, or if the right design is to be like --java-home. What if the JVM the user wants to use is somewhere where Coursier doesn't know about?

[SethTisue]

Note that --bloop-jvm does already exist. I hadn't realized that until just now.

But what we don't have is --bloop-java-home, to cover the case where Coursier doesn't know about the JVM the user wants to use.

So the main task in front of us is:

• add bloop-jvm config setting (corresponding to --bloop-jvm)

but we should also consider

• add --bloop-java-home
• add bloop-java-home config setting

[SethTisue]

We have apparently-working WIP code for the config setting, but there's a strange thing where scala-cli bloop and scala-cli bloop start seem to have independent implementations (in Bloop and BloopStart). What we have works for bloop, do we just copy-and-paste the same code into BloopStart? Seems strange that a duplicate would be required

We also need to do some error checking and handling for whether the requested Java version is 17+. Do we do that at the time the user sets the config, or check it at the time Bloop starts, or both?

We need to write a test. For now, we are testing it manually with:

./mill -i scala config bloop-jvm zulu:17
scala-cli --power bloop exit
./mill -i scala --power bloop
./mill -i scala --power bloop about

which prints a message such as:

Running on Java JDK v17.0.14 (/Users/tisue/Library/Caches/Coursier/arc/https/cdn.azul.com/zulu/bin/zulu17.56.15-ca-jdk17.0.14-macosx_aarch64.tar.gz/zulu17.56.15-ca-jdk17.0.14-macosx_aarch64/zulu-17.jdk/Contents/Home)

[SethTisue]

wip code: https://github.com/SethTisue/scala-cli/commits/issue-1386/

[Gedochao]

What we have works for bloop, do we just copy-and-paste the same code into BloopStart?

Yeah.... that's awkward, but likely what we need to do. Some abstraction might be a good idea (just leave a TODO comment, if you don't want to refactor).

We also need to do some error checking and handling for whether the requested Java version is 17+. Do we do that at the time the user sets the config, or check it at the time Bloop starts, or both?

Both.