IllegalAccessError in CpsTransformer accessing AsmClassGenerator#isThisExpression() on Java 25

[NotMyFault]

jenkinsci/github-plugin#782 fails on JDK 25 with IllegalAccessError when CpsTransformer tries to access AsmClassGenerator.isThisExpression().

For more details, see https://ci.jenkins.io/job/Plugins/job/github-plugin/job/PR-782/4/testReport/

[dwnusbaum]

See https://github.com/jenkinsci/github-plugin/pull/782/changes#r2657851536, but in short, that PR is picking up Groovy 5.x, which causes the problem.

Updating Groovy would be its own project and comes with nontrivial risk due to the very tight coupling between Groovy internals and https://github.com/jenkinsci/groovy-sandbox (used by https://github.com/jenkinsci/script-security-plugin) as well as groovy-cps here. See jenkinsci/jenkins#19976, jenkinsci/jenkins#22806, jenkinsci/jenkins#18083, jenkinsci/jenkins#16730, and linked issues for further discussion.

[NotMyFault]

See jenkinsci/github-plugin#782 (changes), but in short, that PR is picking up Groovy 5.x, which causes the problem.

Thanks for the pointer! Yeah, I followed these discussions back then, but couldn't figure out that groovy 5 is the issue here, albeit that makes sense, given the method named is private in groovy 5.