How to resolve the issue when Jenkins does not display pull requests and merge requests, as well as branches in GitLab CI?

If Jenkins does not display pull requests (PR), merge requests (MR), and branches from GitLab CI, possible reasons and solutions:

1. Check Jenkins integration with GitLab:

   • Ensure that the GitLab plugin for Jenkins is installed and properly configured.
   • Verify that Jenkins has correct access to the GitLab repository (tokens, SSH keys).

2. Configure webhooks in GitLab:

   • Add a webhook in the GitLab project settings to notify Jenkins about PR/MR events and pushes.
   • The webhook should point to the correct Jenkins URL and be active.

3. Configure Jenkins Pipeline or Multibranch Pipeline:

   • Use a Multibranch Pipeline that automatically detects branches and MRs.
   • Check that the source settings specify the correct branch and MR filters.

4. Access rights:

   • Jenkins user must have read rights for branches and MRs in GitLab.

5. Check Jenkins logs:

   • Logs may show errors when attempting to fetch data from GitLab.

6. Plugin and Jenkins versions:

   • Update GitLab and Jenkins plugins to the latest stable versions.

Example of setting up a Multibranch Pipeline for GitLab:

pipeline {
    agent any
    stages {
        stage('Build') {
            steps {
                echo "Building branch ${env.BRANCH_NAME}"
            }
        }
    }
}

In Jenkins, in the Multibranch Pipeline section, specify the GitLab repository and configure branch and MR scanning.