Currently, Lightweight checkout to obtain the Jenkinsfile for pull request builds works only if: Discover pull requests from origin strategy is set to The current pull request revision, which has some limitations - the pull request can't be behind the target branch's revision (HEAD).

This is also mentioned here: https://issues.jenkins.io/browse/JENKINS-33273?focusedId=335013&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-335013

If it's set to the default Merging the pull request with the current target branch revision (which doesn't have the above limitation) a full git clone is performed at the Jenkins controller which is much more expensive, takes longer, consumes more of the Bitbucket rate limits and a lot of disk space for large projects - and because this space isn't managed by Jenkins in any way, we have to run some additional cleanup scripts to at least keep things in control somehow.

Would it be possible to improve the retrieval of Jenkinsfile for pull request builds so that the Lighweight checkout would work even with the default pull request discovery strategy?