More reliable way to get git branch name

Jenkinsfile

@@ -131,14 +131,10 @@ def SphinxDoc() {
   node('linux && cpu') {
     unstash name: 'srcs'
     echo "Running sphinx-doc..."
-    def branch_name = sh (
-      script: 'git rev-parse --abbrev-ref HEAD',
-      returnStdout: true
-    ).trim()
     //container_type = "lint"
     //docker_binary = "docker"
     //sh """#!/bin/bash
-    //CI_DOCKER_EXTRA_PARAMS_INIT='-e SPHINX_GIT_BRANCH=${args.branch_name}' ${dockerRun} ${container_type} ${docker_binary} make -C doc html
+    //CI_DOCKER_EXTRA_PARAMS_INIT='-e SPHINX_GIT_BRANCH=${BRANCH_NAME}' ${dockerRun} ${container_type} ${docker_binary} make -C doc html
     //"""
   }
 }
@@ -183,24 +179,16 @@ def BuildJVMSpark(args) {
 def BuildJVMDoc() {
   node('linux && cpu') {
     unstash name: 'srcs'
-    def commit_id = sh (
-      script: 'git rev-parse HEAD',
-      returnStdout: true
-    ).trim()
-    def branch_name = sh (
-      script: 'git rev-parse --abbrev-ref HEAD',
-      returnStdout: true
-    ).trim()
     echo "Building JVM doc..."
     container_type = "jvm"
     docker_binary = "docker"
     s3Download file: 'tests/ci_build/maven-repo-cache.tar.bz2', bucket: 'xgboost-ci-jenkins-artifacts', force: true, path: 'maven-repo-cache.tar.bz2'
     sh """
-    ${dockerRun} ${container_type} ${docker_binary} tests/ci_build/build_jvm_doc.sh ${commit_id}
+    ${dockerRun} ${container_type} ${docker_binary} tests/ci_build/build_jvm_doc.sh ${BRANCH_NAME}
     """
-    archiveArtifacts artifacts: "jvm-packages/${commit_id}.tar.bz2", allowEmptyArchive: true
+    archiveArtifacts artifacts: "jvm-packages/${BRANCH_NAME}.tar.bz2", allowEmptyArchive: true
     echo 'Deploying doc...'
-    s3Upload file: "jvm-packages/${commit_id}.tar.bz2", bucket: 'xgboost-docs', acl: 'PublicRead', path: "${branch_name}.tar.bz2"
+    s3Upload file: "jvm-packages/${BRANCH_NAME}.tar.bz2", bucket: 'xgboost-docs', acl: 'PublicRead', path: "${BRANCH_NAME}.tar.bz2"
   }
 }
 

tests/ci_build/build_jvm_doc.sh

@@ -1,7 +1,7 @@
 #!/bin/bash
 
 if [ $# -ne 1 ]; then
-  echo "Usage: $0 [commit id]"
+  echo "Usage: $0 [branch name]"
   exit 1
 fi
 
@@ -13,7 +13,7 @@ set -x
 
 cd jvm-packages
 
-commit_id=$1
+branch_name=$1
 
 # Install JVM packages in local Maven repository
 mvn install -DskipTests
@@ -30,8 +30,8 @@ cp -rv xgboost4j-spark/target/site/scaladocs/ ./tmp/scaladocs/xgboost4j-spark/
 cp -rv xgboost4j-flink/target/site/scaladocs/ ./tmp/scaladocs/xgboost4j-flink/
 
 cd tmp
-tar cvjf ${commit_id}.tar.bz2 javadocs/ scaladocs/
-mv ${commit_id}.tar.bz2 ..
+tar cvjf ${branch_name}.tar.bz2 javadocs/ scaladocs/
+mv ${branch_name}.tar.bz2 ..
 cd ..
 rm -rfv tmp/