How-to: Clone target instead of source branch on pull request

Use case

You want to use the target of the branch in a merge, and not the source.

Solution

• Create a new pipeline that uses ${{CF_PULL_REQUEST_TARGET}} instead of the standard ${{CF_BRANCH}} or
• Add the following step before your clone step:

 update_branch_var:
   type: freestyle
   description: "Updating clone branch var to PR target branch"
   stage: 'clone'
   arguments:
     image: 'alpine:3.8'
     commands:
        - cf_export CF_BRANCH='${{CF_PULL_REQUEST_TARGET}}'
    when:
        condition:
          all:
           whenTargetExists: 'includes("${{CF_PULL_REQUEST_TARGET}}", "{{CF_PULL_REQUEST_TARGET}}") == false'

Notes CF_BRANCH is the source branch. By updating this value to the value of CF_PULL_REQUEST_TARGET the target will be pulled. If this variable is not present it will clone the source branch instead.