This is already included in workflow-cps-plugin (core Pipeline) version 2.29 released on March 3.

https://wiki.jenkins-ci.org/display/JENKINS/Pipeline+Groovy+Plugin

I just downloaded the very latest Jenkins, updated all plugins and created a Multibranch Pipeline job configuring Bitbucket as the SCM supplying my Bitbucket Server Web credentials and I still get an "@script" clone for each branch identified as well as a clone for the pipeline checkout step.  

I've got an updated Jenkins and plugins too and I've experimenting the same issue using a Multibranch job with Bitbucket as a source.

I have a repo of 2,6GB with 2 branches and in the Jenkins Master workspace directory I found:
2,6G part_of_the_branch_name_1-UBEA5XUZNXNXC3VOM6COTGUSIEU26KDGQPKDMGV36VVYRJ6MBLRQ@script
2,6G part_of_the_branch_name_1-BMHC5R4EOUCRCXQQ77PBNZ2YTY6J5NEQLJ5DXELS3CWYZLG3BJQA@script

I'm assuming that the famous JENKINS-33273 issue is not applied in the Bitbucket sources case.
Would if be possible to make a lightweight "checkout" of the Jenkinsfile with something like https://bitbucketServer.url/projects/project-name/repos/repo-name/browse/Jenkinsfile?raw ???

Nowadays, as it is working right now is making my CI/CD environment un-maintainable.

I have a similar situation, my Bitbucket Git Repo is 3GB, it takes at least 1hr to clone with jenkins and Bitbucket on the same LAN.

The bitbucket-branch-source-plugin has resolved the initial scan for the branches with the Jenkinsfile's,

I am now looking at how to minimize the time required to checkout the individual Jenkinsfile's, using the BitBucket REST API to checkout the raw contents of the Jenkinsfile looks like a potential option?

https://api.bitbucket.org/1.0/repositories/\{accountname}/{repo_slug}/raw/{revision}/{path}

With an updated Jenkins instance, I have a weir behavior.

I created 2 projects : 

• a Bitbucket Team/Project and
• a Multibranch Pipeline.

The first one still create this "script" folder (my repo is 4 Go) so I experience the same issue described above.

But the Multibranch pipeline works perfectly without creating the script folder.

So I don't think it's Github or Bitbucket related...

I still want to use this Bitbucket plugin because of the PR integration (build status pushed to Bibucket).

Just adding my observations to this:

On the master node, for every branch of every repo, I also get different behavior when using GitSCMSource vs BitbucketSCMSource plugins.

• GitSCMSource: No "@script" folder, Jenkinsfile fetched directly from Git without requiring a checkout, but shared libraries put in the "@libs" folder when using:
  <sources class="jenkins.branch.MultiBranchProject$BranchSourceList">
     <data>
        <jenkins.branch.BranchSource>
           <source class="jenkins.plugins.git.GitSCMSource">
              ...
• ..causing a minimal footprint

• BitbucketSCMSource: Git clone with full history (sometimes years of history) and checkout (minus LFS objects, also no submodules) in workspace "@script" folder when using:
  <sources class="jenkins.branch.MultiBranchProject$BranchSourceList">
     <data>
        <jenkins.branch.BranchSource plugin="branch-api">
           <source plugin="cloudbees-bitbucket-branch-source" class="com.cloudbees.jenkins.plugins.bitbucket.BitbucketSCMSource">
              ...
• ..causing a huge footprint, hundreds of megabytes and for some projects several GBs for every branch in every repo