TBH, I'm not sure what the distinction of the Component multi-branch-project-plugin (not Pipeline) is. I am using the multibranch plugin with pipeline Jenkinsfiles but this issue seems to be more about multi-branch than it does about Pipeline.
In any case, as everyone realises, PRs and branches come and go in the MBPP model.
What's happening though is that the workspaces that are created to build and test these PRs and branches are being left lying around, piling up, using up free disk space. There does not seem to be any mechanism to clean these up (on the slaves, to be clear) when a PR is closed and/or a branch is deleted.
Sure, I could just get all delete-happy in the workspace dirs of my slaves but that is not really productive. I don't want to go deleting workspaces for branches and/or PRs that are still open and thus still being used.
What's the solution here?