Choose appropriate minimum JDK for JRuby versions

[headius]

JRuby 10 is just about to be released, and master (now hosting 10) will become jruby-head once we unlock jruby-dev-builder (ruby/jruby-dev-builder#9). JRuby 10, unlike 9.4, depends on JDK 21 minimum. Because GHA defaults JAVA_HOME to a Java 17 install, we need to adjust that for all setup-ruby use on JRuby >= 10-snapshot.

Users of JRuby 10 should not have to perform an additional step to choose the proper JDK level, and we can't flip jruby-head builds to 10 until this is fixed.

I am not familiar enough with the codebase or GHA to know where to put this code. The basic requirement is to detect that we're setting up a JRuby version (head or 10+) that requires JDK 21, and alter the JAVA_HOME environment variable to point at the contents of the platform-appropriate JAVA_HOME_21_* variable (see https://github.com/actions/runner-images/discussions/9266 for some discussion on that).

[eregon]

I am not familiar enough with the codebase or GHA to know where to put this code

Please take a look and make a PR yourself, it should be fairly simple.
See

setup-ruby/index.js

Lines 55 to 59 in 277ba2a

	if (platform.startsWith('windows-') && engine === 'ruby' && !common.isSelfHostedRunner()) {
	installer = require('./windows')
	} else {
	installer = require('./ruby-builder')
	}

so the installer for JRuby is always ruby-builder.js: https://github.com/ruby/setup-ruby/blob/master/ruby-builder.js
It seems best to set JAVA_HOME just after

setup-ruby/ruby-builder.js

Line 50 in 277ba2a

common.setupPath([path.join(rubyPrefix, 'bin')])

As said in #684 (comment) the logic should be:

IOW I think ideally we would detect if JAVA_HOME is the default, if it is switch to JAVA_HOME_21_X64 instead if available, for all other cases do nothing.

Regardless of the JRuby version if possible, to make it simpler (older JRuby should run fine on JDK 21, maybe even faster).

[headius]

Regardless of the JRuby version if possible

I am reluctant to switch all existing JRuby 9.4 users to Java 21. It will run fine, and may be faster, but they did not opt into such a change.

However, if it becomes a problem people are concerned about, we can address it then. Hopefully most will not notice.

[eregon]

PR merged, thanks.

[NC-piercej]

We are seeing GitHub Actions failures on ubuntu-latest and jruby-head after this change:

Run ruby/setup-ruby@v1
Modifying PATH
  Entries added to PATH to use selected Ruby:
    /home/runner/.rubies/jruby-head/bin
Downloading Ruby
  https://github.com/ruby/jruby-dev-builder/releases/latest/download/jruby-head-ubuntu-24.04.tar.gz
  Took   1.38 seconds
Extracting  Ruby
  /usr/bin/tar -xz -C /home/runner/.rubies -f /home/runner/work/_temp/ab607910-b37c-4b92-85
  Took   0.42 seconds
Print Ruby version
  /home/runner/.rubies/jruby-head/bin/ruby --version
  Unrecognized VM option 'AutoCreateSharedArchive'
  Error: Could not create the Java Virtual Machine.
  Error: A fatal exception has occurred. Program will exit.
  Took   0.38 seconds
Error: The process '/home/runner/.rubies/jruby-head/bin/ruby' failed with exit code 1

Seems to be related?

[headius]

Yeah sorry about that... issues that only came up once everything was released. We're working on it in #722.

You may be able to work around it yourself by using setup-java to install Java 21, or reset env JAVA_HOME to JAVA_HOME_21_X64.

[headius]

work around it yourself

Doing these things before setup-ruby, that is.

[headius]

You can also switch to JRuby 9.4 builds which is where the 9.4 maintenance line can be tested now. jruby-head is now JRuby 10, requiring Java 21 and supporting up to Ruby 3.4 features.

[eregon]

Fixed by #722 and released as https://github.com/ruby/setup-ruby/releases/tag/v1.225.0