@kou I'll get that job running and then merge this.

I mean I'll get it running and then let you merge this. 😀

@kou Please hold off on release... I may have found one more bug running HexaPDF tests.

The setup-ruby logic for JRuby on Windows must not be fully choosing Java 21, so when it tries to compile the extension it's still using an older version. This fixes it.

@headius Could you make a PR to setup-ruby to fix that? It would be good to avoid adding many actions/setup-java everywhere just to workaround this bug.

Mmh, it should work fine since https://github.com/ruby/setup-ruby/blob/eaecf785f6a34567a6d97f686bbb7bccc1ac1e5c/ruby-builder.js#L59 is done on Windows too.
And this is the failing job: https://github.com/ruby/strscan/actions/runs/14805467215/job/41572923725
But as we see on this line JAVA_HOME is set correctly.

I suppose rake compile for Java extensions might need $JAVA_HOME/bin to be in PATH, and not just having JAVA_HOME set then (makes sense if e.g. it calls out to javac).
So I guess then we should add $JAVA_HOME/bin in PATH too in setup-ruby for JRuby (a bit unfortunate as it might cause unintended side effects but I don't see another solution), PR welcome.

It seems that rake-compiler uses $JAVA_HOME/bin/javac: https://github.com/rake-compiler/rake-compiler/blob/6ac2e3d4fc2504595d51792d57af56024cf4c5d4/lib/rake/javaextensiontask.rb#L111-L113

Good point. Maybe the mix of / and \ then?
i.e. File.join always uses /, even on Windows, IIRC.
So it might be javac_path = 'C:\hostedtoolcache\windows\Java_Temurin-Hotspot_jdk\21.0.7-6.0\x64/bin/javac' and that might/probably fail the File.exist? check.

In fact in the failed job we do see:

mkdir -p tmp/java/strscan
javac -target 1.8 -source 1.8 -Xlint -d tmp/java/strscan -cp D:/jruby-10.0.0.0/lib/jruby.jar ext/jruby/org/jruby/ext/strscan/RubyStringScanner.java ext/jruby/org/jruby/ext/strscan/StringScannerLibrary.java

clearly that's javac without JAVA_HOME/bin in front.

Ah, RbConfig::CONFIG["EXEEXT"] may be related. Could you try rake-compiler 1.3.1?

#155