How to configure Jenkins to detect and handle pull-requests, merge requests, and branches from GitLab CI/CD?

To configure Jenkins for handling pull-requests, merge requests, and branches from GitLab CI/CD, the GitLab Branch Source plugin or GitLab Plugin are usually used.

Main steps:

1. Install the appropriate plugin in Jenkins.
2. Create a Multibranch Pipeline or GitLab Project, specifying the GitLab repository URL and credentials.
3. Configure the Jenkinsfile in the repository, which describes the build and tests.
4. Enable branch and merge request (pull-requests) detection in the project settings.
5. Set up webhooks in GitLab so that Jenkins receives notifications and triggers builds when branches or merge requests are created or updated.

Example Jenkinsfile for handling a merge request:

pipeline {
    agent any
    stages {
        stage('Build') {
            steps {
                echo "Building branch ${env.BRANCH_NAME}"
                // build commands
            }
        }
        stage('Test') {
            steps {
                echo 'Running tests'
                // testing commands
            }
        }
    }
}

Thus, Jenkins automatically detects new branches and merge requests, triggers builds and tests, ensuring integration with GitLab CI/CD.