Pull Request policy for "Merging" with target polluting workspace disk space on Jenkins master with commits in detached head

[lgcCerti]

Jenkins and plugins versions report

Environment

Jenkins: 2.440.2
OS: Linux - 5.4.0-170-generic
Java: 17.0.10 - Private Build (OpenJDK 64-Bit Server VM)
---
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ws-cleanup:0.45

What Operating System are you using (both controller, and any agents involved in the problem)?

Distributor ID: Ubuntu
Description: Ubuntu 20.04.6 LTS

Reproduction steps

1. Create a Repository on bitbucket with a Jenkinsfile that Jenkins has access to and create a task for that repository
2. Create a new branch with changes and push to the remote bitbucket
3. Configure Branch source to "Merge" with target before running the pipeline
   
4. Commit to the main branch with changes and push to remote bitbucket
5. Create a pull request on the repository
6. Jenkins will create the detached head of the merge and run the pipeline
7. Jenkins will leave this detached head in the workspace of Jenkins Master, cluttering its workspace in its @script folders

Expected Results

Merged head being removed from the Jenkins Master after the operation is finished.
Clean Workspace commands working to remove these files from Jenkins Master.

Actual Results

Jenkins Master being cluttered with detached heads until the disc space explodes.

Anything else?

An option to clear the script workspace for configuration could help a lot.

Are you interested in contributing a fix?

There may be already a fix but I haven't seen it.

[schiasileon]

Hi, we have the same problem on our build systems, cluttering up jenkins controller nodes in k8s as the controller workspaces do not get cleaned up. This leads to us having to perform several manual cleanups weekly.

This can really 'explode' the disk usage, as we have several repos that are > 1GB with several hundreds of PR builds a day.

[nfalco79]

Expected Results

Merged head being removed from the Jenkins Master after the operation is finished.

The expectation is not correct, the strategy is about what checkout, Any kind of workspace cleanup are delegated to traits like
Check out to matching local branch or Check out to matching local branch ( I do not think Clean after checkout will work for you).
Let me know if one of these traits works.

[nfalco79]

Did you configure in your project "localBranch" trait?

The Git plugin checks code out to a detached head. Configure
LocalBranch to force checkout to a specific local branch.
Configure this extension as null or as "**" to signify that
the local branch name should be the same as the remote branch
name sans the remote repository prefix (origin for example).

This should resolve your issue.

[nfalco79]

Duplicate https://issues.jenkins.io/browse/JENKINS-44734

[KalleOlaviNiemitalo]

I don't see how this is a duplicate of JENKINS-44734. The problem there was that the detached HEAD made it more difficult to push new commits from Jenkins to Bitbucket, and the advice was to add a trait that makes Git use a named branch instead. Here, the problem is that multiple workspaces are created in the Jenkins controller and not automatically cleaned up soon enough and they consume too much disk space. How does it matter for workspace creation or cleanup whether HEAD is detached or a branch?

[nfalco79]

If you add "checkout to local branch" trait, you can also use the "Prune stale remote-tracking branches" trait