[SPARK-56447][SHELL] Fix spark-shell REPL classpath initialization error

bin/spark-shell

@@ -37,13 +37,6 @@ export _SPARK_CMD_USAGE="Usage: ./bin/spark-shell [options]
 Scala REPL options, Spark Classic only:
   -I <file>                   preload <file>, enforcing line-by-line interpretation"
 
-# SPARK-4161: scala does not assume use of the java classpath,
-# so we need to add the "-Dscala.usejavacp=true" flag manually. We
-# do this specifically for the Spark shell because the scala REPL
-# has its own class loader, and any additional classpath specified
-# through spark.driver.extraClassPath is not automatically propagated.
-SPARK_SUBMIT_OPTS="$SPARK_SUBMIT_OPTS -Dscala.usejavacp=true"
-
 function main() {
   export SPARK_SCALA_SHELL=1
   # In case of Spark Connect shell, the main class (and resource) is replaced in

bin/spark-shell2.cmd

@@ -28,16 +28,5 @@ set _SPARK_CMD_USAGE=Usage: .\bin\spark-shell.cmd [options]^%LF%%LF%^%LF%%LF%^
 Scala REPL options:^%LF%%LF%^
   -I ^<file^>                   preload ^<file^>, enforcing line-by-line interpretation
 
-rem SPARK-4161: scala does not assume use of the java classpath,
-rem so we need to add the "-Dscala.usejavacp=true" flag manually. We
-rem do this specifically for the Spark shell because the scala REPL
-rem has its own class loader, and any additional classpath specified
-rem through spark.driver.extraClassPath is not automatically propagated.
-if "x%SPARK_SUBMIT_OPTS%"=="x" (
-  set SPARK_SUBMIT_OPTS=-Dscala.usejavacp=true
-  goto run_shell
-)
-set SPARK_SUBMIT_OPTS="%SPARK_SUBMIT_OPTS% -Dscala.usejavacp=true"
-
 :run_shell
 "%SPARK_HOME%\bin\spark-submit2.cmd" --class org.apache.spark.repl.Main --name "Spark shell" %*

repl/src/main/scala/org/apache/spark/repl/Main.scala

@@ -65,13 +65,15 @@ object Main extends Logging {
   // Visible for testing
   private[repl] def doMain(args: Array[String], _interp: SparkILoop): Unit = {
     interp = _interp
-    val jars = Utils
+    val userJars = Utils
       .getLocalUserJarsForShell(conf)
       // Remove file:///, file:// or file:/ scheme if exists for each jar
       .map { x =>
         if (x.startsWith("file:")) new File(new URI(x)).getPath else x
       }
       .mkString(File.pathSeparator)
+    val jvmClasspath = sys.props.getOrElse("java.class.path", "")
+    val jars = Seq(userJars, jvmClasspath).filter(_.nonEmpty).mkString(File.pathSeparator)
     val interpArguments = List(
       "-Yrepl-class-based",
       "-Yrepl-outdir",

repl/src/test/scala/org/apache/spark/repl/ReplSuite.scala

@@ -72,6 +72,27 @@ class ReplSuite extends SparkFunSuite {
   def runInterpreterInPasteMode(master: String, input: String): String =
     runInterpreter(master, ":paste\n" + input + 4.toChar) // 4 is the ascii code of CTRL + D
 
+  test("SPARK-56447: spark-shell REPL initializes without explicit -classpath argument") {
+    // Regression test for SPARK-56447: doMain must include java.class.path in the REPL
+    // classpath even when the caller does not pass -classpath explicitly. Before the fix,
+    // the Scala compiler mirror failed to find `object scala` because the JVM classpath
+    // was not propagated to the REPL settings.
+    // spark.repl.local.jars is not set, so userJars is intentionally empty;
+    // the classpath must be derived from java.class.path alone.
+    Main.sparkContext = null
+    Main.sparkSession = null
+    Main.conf.set("spark.master", "local")
+
+    val in = new BufferedReader(new StringReader("spark.version\n"))
+    val out = new StringWriter()
+    Main.doMain(Array.empty, new SparkILoop(in, new PrintWriter(out)))
+
+    val output = out.toString
+    assertDoesNotContain("object scala in compiler mirror not found", output)
+    assertDoesNotContain("Failed to initialize compiler", output)
+    assertContains("res0: String =", output)
+  }
+
   def assertContains(message: String, output: String): Unit = {
     val isContain = output.contains(message)
     assert(isContain,