Provide easy access to git branch name in (single branch) Pipeline build

Hello,

I'm the maintainer of a maven-plugin (https://github.com/ktoso/maven-git-commit-id-plugin ) that exposes certain repository information as properties into the build. A user of of this plugin reported that the branch name is not available with a single branch pipeline build under jenkins. From the plugin perspective we rely (especially for the branch identifier) on the environment properties that are being exposed by the [Git Plugin|https://github.com/ktoso/maven-git-commit-id-plugin ]. In particular we use the GIT_LOCAL_BRANCH or GIT_BRANCH . Unfortunately with Jenkins LTS 2.73.1 (2017-09-13) those environment variables are not available and thus making it impossible to retrieve the branch name.

Thank you for your time.

Note:

During my initial debugging I noticed that a user could this get to work when using a parameterized build which is not really beautiful since the parameter used need to be set to GIT_LOCAL_BRANCH or GIT_BRANCH since its then automatically exposed as environment variable (would consider this a dirty hack)...

pipeline {
    agent any
    parameters {
        string(defaultValue: 'master', description: 'branch', name: 'GIT_BRANCH')
    }
    
    stages {
        stage('Clone sources') {
            steps {
                git branch: "${params.GIT_BRANCH}", url: 'https://github.com/ktoso/maven-git-commit-id-plugin.git'
            }
        }
        
        stage('Build printenv'){
            steps {
                sh 'printenv'
            }
        }
    }
}

 
Original issue: https://github.com/ktoso/maven-git-commit-id-plugin/issues/325