TL;DR:

git clean -fdx should be git clean -ffdx as per this advice

Problem / Steps To Reproduce

If a build creates a git repository in a subdirectory of the workspace, the option to "clean after checkout" will skip it. This is expected behavior of git that you can verify quite easily:

# assuming we are ubuntu@jenkins-agent:/tmp/jenkins-blah/workspace/some-job
 
some-job$ mkdir foo

some-job$ cd foo

some-job/foo$ git init
Initialized empty Git repository in /tmp/jenkins-blah/workspace/some-job/foo/.git/

some-job/foo$ cd .. 

some-job$ git clean -fdx
Skipping repository foo/

some-job$ git clean -ffdx
Removing foo/

Expected behavior

Git plugin cleans the workspace by removing the foo directory that has been initialized with its own git repository

some-job$ git clean -ffdx
Removing foo/

Actual behavior

Git plugin silently fails to clean the workspace because the git command it runs succeeds with a warning message that the directory containing another repository was skipped:

some-job$ git clean -fdx
Skipping repository foo/

Suggested fix

Use the -f option twice with git: git -ffdx to force removal of directories that contain git repositories.

Possible problems with git -ffdx

I'm not sure whether simply making this change will affect subdirectories; it shouldn't, but I haven't tested.

Issues that are NOT this issue:

• JENKINS-21369 (because my git clean command succeeds)
• JENKINS-23694 (because that's about submodules that are expected)