fix potential null pointer in lightweight checkout and support fetching Jenkinsfile from directory

[jetersen]

As project can be nullable due to it's transient nature it is safer to use projectPath

I also updated lastModified to use the commit date for the SCMFileSystem

[jetersen]

@stephenc Would you mind taking a look :)

I might be able to throw a similar PR over to https://github.com/jenkinsci/gitea-plugin/blob/master/src/main/java/org/jenkinsci/plugin/gitea/GiteaSCMFile.java :)

[stephenc]

LGTM (though I am not familiar with the finer print of the gitllab api)

👍 to a PR for gitea

[jetersen]

The gitlab API does not offer a whole lot of file typing like GitHub API does

This is what GitLab file options provide

https://gitlab.com/api/v4/projects/13555154/repository/tree?ref=folder
https://gitlab.com/api/v4/projects/13555154/repository/files/Jenkinsfile?ref=folder

See API docs here:
https://docs.gitlab.com/ee/api/repositories.html#list-repository-tree
https://docs.gitlab.com/ee/api/repository_files.html#get-file-from-repository

[baymac]

Thanks @Casz for fixing this. LGTM.

[jetersen]

needs testing as lightweight checkout still fails for merge requests.

[baymac]

@jetersen Light checkout doesn't work as expected for MRs. https://issues.jenkins-ci.org/browse/JENKINS-62343?focusedCommentId=390912&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-390912 Could you fix it or point in the direction to fix it?

[baymac]

@jetersen Pinging again to get updates on this. FYI light weight checkout works in bitbucket branch source and not in gitlab branch source.