[SPARK-3256] Added support for :cp <jar> that was broken in Scala 2.10.x for REPL

As seen with [SI-6502](https://issues.scala-lang.org/browse/SI-6502) of Scala, the _:cp_ command was broken in Scala 2.10.x. As the Spark shell is a friendly wrapper on top of the Scala REPL, it is also affected by this problem.

My solution was to alter the internal classpath and invalidate any new entries. I also had to add the ability to add new entries to the parent classloader of the interpreter (SparkIMain's global).

The advantage of this versus wiping the interpreter and replaying all of the commands is that you don't have to worry about rerunning heavy Spark-related commands (going to the cluster) or potentially reloading data that might have changed. Instead, you get to work from where you left off.

Until this is fixed upstream for 2.10.x, I had to use reflection to alter the internal compiler classpath.

The solution now looks like this:
![screen shot 2014-08-13 at 3 46 02 pm](https://cloud.githubusercontent.com/assets/2481802/3912625/f02b1440-232c-11e4-9bf6-bafb3e352d14.png)

Author: Chip Senkbeil <rcsenkbe@us.ibm.com>

Closes #1929 from rcsenkbeil/FixReplClasspathSupport and squashes the following commits:

f420cbf [Chip Senkbeil] Added SparkContext.addJar calls to support executing code on remote clusters
a826795 [Chip Senkbeil] Updated AddUrlsToClasspath to use 'new Run' suggestion over hackish compiler error
2ff1d86 [Chip Senkbeil] Added compilation failure on symbols hack to get Scala classes to load correctly
a220639 [Chip Senkbeil] Added support for :cp <jar> that was broken in Scala 2.10.x for REPL

2 files changed, 73 insertions, 11 deletions

diff --git a/repl/src/main/scala/org/apache/spark/repl/SparkILoop.scala b/repl/src/main/scala/org/apache/spark/repl/SparkILoop.scala
index 65788f4646..53df599cf8 100644
--- a/repl/src/main/scala/org/apache/spark/repl/SparkILoop.scala
+++ b/repl/src/main/scala/org/apache/spark/repl/SparkILoop.scala
@@ -8,7 +8,11 @@
 package org.apache.spark.repl
 
 
+import java.net.URL
+
+import scala.reflect.io.AbstractFile
 import scala.tools.nsc._
+import scala.tools.nsc.backend.JavaPlatform
 import scala.tools.nsc.interpreter._
 
 import scala.tools.nsc.interpreter.{ Results => IR }
@@ -22,11 +26,10 @@ import scala.tools.util.{ Javap }
 import scala.annotation.tailrec
 import scala.collection.mutable.ListBuffer
 import scala.concurrent.ops
-import scala.tools.nsc.util.{ ClassPath, Exceptional, stringFromWriter, stringFromStream }
+import scala.tools.nsc.util._
 import scala.tools.nsc.interpreter._
-import scala.tools.nsc.io.{ File, Directory }
+import scala.tools.nsc.io.{File, Directory}
 import scala.reflect.NameTransformer._
-import scala.tools.nsc.util.ScalaClassLoader
 import scala.tools.nsc.util.ScalaClassLoader._
 import scala.tools.util._
 import scala.language.{implicitConversions, existentials}
@@ -711,22 +714,24 @@ class SparkILoop(in0: Option[BufferedReader], protected val out: JPrintWriter,
         added = true
         addedClasspath = ClassPath.join(addedClasspath, f.path)
         totalClasspath = ClassPath.join(settings.classpath.value, addedClasspath)
+        intp.addUrlsToClassPath(f.toURI.toURL)
+        sparkContext.addJar(f.toURI.toURL.getPath)
       }
     }
-    if (added) replay()
   }
 
   def addClasspath(arg: String): Unit = {
     val f = File(arg).normalize
     if (f.exists) {
       addedClasspath = ClassPath.join(addedClasspath, f.path)
-      val totalClasspath = ClassPath.join(settings.classpath.value, addedClasspath)
-      echo("Added '%s'.  Your new classpath is:\n\"%s\"".format(f.path, totalClasspath))
-      replay()
+      intp.addUrlsToClassPath(f.toURI.toURL)
+      sparkContext.addJar(f.toURI.toURL.getPath)
+      echo("Added '%s'.  Your new classpath is:\n\"%s\"".format(f.path, intp.global.classPath.asClasspathString))
     }
     else echo("The path '" + f + "' doesn't seem to exist.")
   }
 
+
   def powerCmd(): Result = {
     if (isReplPower) "Already in power mode."
     else enablePowerMode(false)
diff --git a/repl/src/main/scala/org/apache/spark/repl/SparkIMain.scala b/repl/src/main/scala/org/apache/spark/repl/SparkIMain.scala
index 84b57cd2dc..6ddb6accd6 100644
--- a/repl/src/main/scala/org/apache/spark/repl/SparkIMain.scala
+++ b/repl/src/main/scala/org/apache/spark/repl/SparkIMain.scala
@@ -7,11 +7,14 @@
 
 package org.apache.spark.repl
 
+import java.io.File
+
 import scala.tools.nsc._
+import scala.tools.nsc.backend.JavaPlatform
 import scala.tools.nsc.interpreter._
 
 import Predef.{ println => _, _ }
-import util.stringFromWriter
+import scala.tools.nsc.util.{MergedClassPath, stringFromWriter, ScalaClassLoader, stackTraceString}
 import scala.reflect.internal.util._
 import java.net.URL
 import scala.sys.BooleanProp
@@ -21,7 +24,6 @@ import reporters._
 import symtab.Flags
 import scala.reflect.internal.Names
 import scala.tools.util.PathResolver
-import scala.tools.nsc.util.ScalaClassLoader
 import ScalaClassLoader.URLClassLoader
 import scala.tools.nsc.util.Exceptional.unwrap
 import scala.collection.{ mutable, immutable }
@@ -34,7 +36,6 @@ import scala.reflect.runtime.{ universe => ru }
 import scala.reflect.{ ClassTag, classTag }
 import scala.tools.reflect.StdRuntimeTags._
 import scala.util.control.ControlThrowable
-import util.stackTraceString
 
 import org.apache.spark.{Logging, HttpServer, SecurityManager, SparkConf}
 import org.apache.spark.util.Utils
@@ -130,6 +131,9 @@ import org.apache.spark.util.Utils
     private var _classLoader: AbstractFileClassLoader = null                              // active classloader
     private val _compiler: Global                     = newCompiler(settings, reporter)   // our private compiler
 
+    private trait ExposeAddUrl extends URLClassLoader { def addNewUrl(url: URL) = this.addURL(url) }
+    private var _runtimeClassLoader: URLClassLoader with ExposeAddUrl = null              // wrapper exposing addURL
+
     private val nextReqId = {
       var counter = 0
       () => { counter += 1 ; counter }
@@ -308,6 +312,57 @@ import org.apache.spark.util.Utils
       }
     }
 
+    /**
+     * Adds any specified jars to the compile and runtime classpaths.
+     *
+     * @note Currently only supports jars, not directories
+     * @param urls The list of items to add to the compile and runtime classpaths
+     */
+    def addUrlsToClassPath(urls: URL*): Unit = {
+      new Run // Needed to force initialization of "something" to correctly load Scala classes from jars
+      urls.foreach(_runtimeClassLoader.addNewUrl) // Add jars/classes to runtime for execution
+      updateCompilerClassPath(urls: _*)           // Add jars/classes to compile time for compiling
+    }
+
+    protected def updateCompilerClassPath(urls: URL*): Unit = {
+      require(!global.forMSIL) // Only support JavaPlatform
+
+      val platform = global.platform.asInstanceOf[JavaPlatform]
+
+      val newClassPath = mergeUrlsIntoClassPath(platform, urls: _*)
+
+      // NOTE: Must use reflection until this is exposed/fixed upstream in Scala
+      val fieldSetter = platform.getClass.getMethods
+        .find(_.getName.endsWith("currentClassPath_$eq")).get
+      fieldSetter.invoke(platform, Some(newClassPath))
+
+      // Reload all jars specified into our compiler
+      global.invalidateClassPathEntries(urls.map(_.getPath): _*)
+    }
+
+    protected def mergeUrlsIntoClassPath(platform: JavaPlatform, urls: URL*): MergedClassPath[AbstractFile] = {
+      // Collect our new jars/directories and add them to the existing set of classpaths
+      val allClassPaths = (
+        platform.classPath.asInstanceOf[MergedClassPath[AbstractFile]].entries ++
+        urls.map(url => {
+          platform.classPath.context.newClassPath(
+            if (url.getProtocol == "file") {
+              val f = new File(url.getPath)
+              if (f.isDirectory)
+                io.AbstractFile.getDirectory(f)
+              else
+                io.AbstractFile.getFile(f)
+            } else {
+              io.AbstractFile.getURL(url)
+            }
+          )
+        })
+      ).distinct
+
+      // Combine all of our classpaths (old and new) into one merged classpath
+      new MergedClassPath(allClassPaths, platform.classPath.context)
+    }
+
     /** Parent classloader.  Overridable. */
     protected def parentClassLoader: ClassLoader =
       SparkHelper.explicitParentLoader(settings).getOrElse( this.getClass.getClassLoader() )
@@ -356,7 +411,9 @@ import org.apache.spark.util.Utils
     private def makeClassLoader(): AbstractFileClassLoader =
       new TranslatingClassLoader(parentClassLoader match {
         case null   => ScalaClassLoader fromURLs compilerClasspath
-        case p      => new URLClassLoader(compilerClasspath, p)
+        case p      =>
+          _runtimeClassLoader = new URLClassLoader(compilerClasspath, p) with ExposeAddUrl
+          _runtimeClassLoader
       })
 
     def getInterpreterClassLoader() = classLoader