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

  • Updated

Use case

In most cases, builds will use the variable CF_BRANCH to reference the branch associated with a git triggered build.

In a pull request triggered build, CF_BRANCH specifically refers to the source branch, and another variable CF_PULL_REQUEST_TARGET refers to the target branch. You may need to use the target branch instead in your merge build.

Solution

  • Create a separate pipeline that uses ${{CF_PULL_REQUEST_TARGET}} instead of the standard ${{CF_BRANCH}}
    or
  • Add the following step before your clone step to check if CF_PULL_REQUEST_TARGET exists, and if it does assign its value to CF_BRANCH:
 update_branch_var:
   type: freestyle
   description: "Updating clone branch var to PR target branch"
   stage: 'clone'
   arguments:
     image: 'alpine:3.8'
     commands:
        - cf_export CF_BRANCH='${{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 in a PR-initiated build. By updating its value to the value of CF_PULL_REQUEST_TARGET the target will be pulled instead. This variable only exists for PR triggered builds, and if not present the build will clone the source branch instead.

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