Parallel checkout in declarative Jenkins pipeline on multiple nodes

Question

I'm developing a declarative Jenkins pipeline for CI builds, triggered from Gitlab. What I have now:

// variable definitions

pipeline {
    agent none

    parameters {
            string(defaultValue: 'develop',
                description: 'Commit ID or branch name to build', 
                name: 'branch', 
                trim: false)
    }

    stages {
        stage('Checkout') {
            parallel {
                stage ('Windows') {
                    agent {
                        label 'build' && 'windows'
                    }

                    steps {
                        script {

                            def checkout_ext = [[$class: 'CleanCheckout'],
                                                [$class: 'CleanBeforeCheckout']] // calls git clean -fdx and git reset --hard

                            if (env.gitlabActionType == "MERGE"){   
                                  checkout_ext.add([$class: 'PreBuildMerge', 
                                                    options: [ mergeRemote: "origin",
                                                              mergeTarget: "${env.gitlabTargetBranch}"]])
                            }
                        }

                        checkout([
                                $class: 'GitSCM', 
                                branches: [[name: "${params.branch}"]],
                                userRemoteConfigs: [[ url: "${git_url}",                                          credentialsId: "${git_credentials_id}" ]],
                                extensions:   checkout_ext 
                        ])
                    }
                }

                stage('Linux') {
                    agent {
                        label 'build' && 'linux'
                    }
                    steps {
                        script {

                            def checkout_ext = [[$class: 'CleanCheckout'], 
                                                [$class: 'CleanBeforeCheckout']] // calls git clean -fdx and git reset --hard

                            if (env.gitlabActionType == "MERGE"){   
                               checkout_ext.add([$class: 'PreBuildMerge', 
                                                 options: [ mergeRemote: "origin",
                                                 mergeTarget: "${env.gitlabTargetBranch}"]])
                            }
                        }

                        checkout([
                                $class: 'GitSCM', 
                                branches: [[name: "${params.branch}"]],
                                userRemoteConfigs: [[ url: "${git_url}", credentialsId: "${git_credentials_id}"]],
                                extensions:   checkout_ext 
                        ])
                    }
                }
            }
        }
    }
}

Checkout stage is somewhat complex. If gitlabActionType is MERGE , then first try to merge into a target branch, to make sure that merge request does not break anything in it.

This code is the same for both OSes. I'd like to avoid code duplication, but cannot figure out correct syntax for that.

I have tried moving definition of checkout steps to the global variable, but have got syntax errors.

def checkout_step = {
    script {
   ...
    }
    checkout (... )
}

pipeline {
...
   stages {
        stage('Checkout') {
            parallel {
                stage ('Windows') {
                    agent {
                        label 'build' && 'windows'
                    }

                    steps {
                        checkout_step
                    }
                }
                stage ('Linux') {
                    agent {
                        label 'build' && 'linux'
                    }

                    steps {
                        checkout_step
                    }
                }
            }
        }
    }
}

If add steps , there's also an error:

def checkout_step = steps {
    script {
   ...
    }
    checkout (... )
}

pipeline {
...
   stages {
        stage('Checkout') {
            parallel {
                stage ('Windows') {
                    agent {
                        label 'build' && 'windows'
                    }

                    checkout_step

                }
                stage ('Linux') {
                    agent {
                        label 'build' && 'linux'
                    }

                    checkout_step

                }
            }
        }
    }
}

Answer 1

Have found solution here

git_url = "git@gitserver.corp.com:group/repo.git"
git_credentials_id = 'aaaaaaa-bbbb-cccc-dddd-eefefefefef'


def checkout_tasks(os_labels) {
    tasks = [:]

    for (int i = 0; i < os_labels.size(); i++) {
        def os = os_labels[i]
        tasks["${os}"] = {
            node("build && ${os}"){

                def checkout_ext = [[$class: 'CleanCheckout'], [$class: 'CleanBeforeCheckout']] // calls git clean -fdx and git reset --hard

                if (env.gitlabActionType == "MERGE"){   
                    checkout_ext.add([
                            $class: 'PreBuildMerge', 
                            options: [ 
                            mergeRemote: "origin", 
                            mergeTarget: "${env.gitlabTargetBranch}" 
                            ]
                    ])
                         /* using this extension requires .gitconfig with section [user for Jenkins]
                            Example
                            [user]
                            email = jenkins@builder
                            name = Jenkins

                          */
                }

                checkout([
                        $class: 'GitSCM', 
                        branches: [[name: "${params.branch}"]],
                        userRemoteConfigs: [[
                            url: "${git_url}", 
                            credentialsId: "${git_credentials_id}"
                        ]],
                        extensions:  checkout_ext 
                ])

            }
        }
    }
    return tasks
}


pipeline {
    agent none

    parameters {
        string(defaultValue: 'develop',
               description: 'Commit ID or branch name to build', 
               name: 'branch', 
               trim: false)
    }

    stages {
        stage('Checkout') {
            steps {
                script {
                    def OSes = ["windows", "linux"]
                    parallel checkout_tasks(OSes)
                }
            }
        }
   }
}

It is important also to declare git_url and git_credentials_id without def , so that functions can read them.

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