Warn against external usages of SparkSubmitDriverBootstrapper

Author: andrewor14

bin/spark-class

@@ -167,7 +167,8 @@ if [ -n "$SPARK_SUBMIT_BOOTSTRAP_DRIVER" ]; then
   export CLASSPATH
   export JAVA_OPTS
   export OUR_JAVA_MEM
-  shift
+  export SPARK_CLASS=1
+  shift # Ignore main class and use our own
   exec "$RUNNER" org.apache.spark.deploy.SparkSubmitDriverBootstrapper "$@"
 else
   # Note: The format of this command is closely echoed in SparkSubmitDriverBootstrapper.scala

core/src/main/scala/org/apache/spark/deploy/SparkSubmitDriverBootstrapper.scala

@@ -37,6 +37,13 @@ private[spark] object SparkSubmitDriverBootstrapper {
   // Any changes made there must be reflected in this file.
 
   def main(args: Array[String]): Unit = {
+
+    // This should be called only from `bin/spark-class`
+    if (!sys.env.contains("SPARK_CLASS")) {
+      System.err.println("SparkSubmitDriverBootstrapper must be called from `bin/spark-class`!")
+      System.exit(1)
+    }
+
     val submitArgs = args
     val runner = sys.env("RUNNER")
     val classpath = sys.env("CLASSPATH")