So my understanding is that you need to use the techniques for using unsupported plugins with job DSL to configure traits... at least until we get around to adding the @Symbol annotations (
JENKINS-45504)... of course that is currently blocked on JENKINS-45503 because for reasons documented in those issues.
Having said all that, we did retain the setter for extensions (just marked deprecated is all) and that setter will create the matching traits, so the only thing I can think is that you may be hitting the ref trimming... in which case all you need to do is add the trait that allows specifying an additional refspec to fetch and ensure that the master branch refspec is always fetched from the remote so that the merge extension / trait can work...
Mark Waite I think we need to hear back on how this "no longer works" to determine if:
- The jobs are not getting configured correctly; or
- The configured jobs are failing because of the missing refspec for origin; or
- Something else