File loading error -- warbler_jar

[redconfetti]

I’m testing a Rails 8.0.4 app on JRuby 10.0.4.0 using warbler from the master branch (as of April 7, 2026), and running into a build failure.

I've forked a previous reports minimal test app (from #560) for this test. The app is completely minimal and exists specifically to demonstrate this problem. You can find it here:

https://github.com/sis-berkeley-edu/warbler_test

Environment:

• JRuby: 10.0.4.0
• Rails: 8.0.4
• Java: OpenJDK 21.0.8
• Tomcat: 9.0.117
• OS: macOS Sequoia 15.7.3 (Apple Silicon)
• jruby-rack: master branch from jruby/jruby-rack
• warbler: master branch from jruby/warbler

When I try to run a build with this test app, I get:

$ rails war
bin/rails aborted!
LoadError: cannot load such file -- warbler_jar (LoadError)
/Users/jason.c.miller/Developer/warbler_test/Rakefile:8:in '<main>'
bin/rails:4:in '<main>'
(See full trace by running task with --trace)

When I try to run a build from another project I receive:

$ bundle exec warble
bundler: failed to load command: warble (/Users/jason.c.miller/.rbenv/versions/jruby-10.0.4.0/lib/ruby/gems/shared/bin/warble)
org/jruby/RubyKernel.java:1193:in 'require': cannot load such file -- warbler_jar (LoadError)
        from /Users/jason.c.miller/.rbenv/versions/jruby-10.0.4.0/lib/ruby/stdlib/bundled_gems.rb:81:in 'block in replace_require'
        from /Users/jason.c.miller/.rbenv/versions/jruby-10.0.4.0/lib/ruby/gems/shared/bundler/gems/warbler-95db95756ebd/lib/warbler/jar.rb:336:in '<class:Jar>'
        from /Users/jason.c.miller/.rbenv/versions/jruby-10.0.4.0/lib/ruby/gems/shared/bundler/gems/warbler-95db95756ebd/lib/warbler/jar.rb:19:in '<module:Warbler>'
        from /Users/jason.c.miller/.rbenv/versions/jruby-10.0.4.0/lib/ruby/gems/shared/bundler/gems/warbler-95db95756ebd/lib/warbler/jar.rb:12:in '<main>'

[chadlwilson]

Running off master has been broken since #579 so somewhat deliberate. 😓

I don't know of any practical workaround. You'd effectively need to bundle to a known path and then go into the bundled version and run a build that does the Java compile and puts the jar in the known place.

@headius in lieu of addressing the root cause, could we please cut a warbler 2.1.1 release off master get these changes out? https://github.com/jruby/warbler/blob/master/CHANGELOG.md#211-unreleased

This would allow @redconfetti to use a published/Rubygems warbler to work with jruby-rack master, since the version constraint has been relaxed to allow it.