[SPARK-9262][build] Treat Scala compiler warnings as errors

I've seen a few cases in the past few weeks that the compiler is throwing warnings that are caused by legitimate bugs. This patch upgrades warnings to errors, except deprecation warnings.

Note that ideally we should be able to mark deprecation warnings as errors as well. However, due to the lack of ability to suppress individual warning messages in the Scala compiler, we cannot do that (since we do need to access deprecated APIs in Hadoop).

Most of the work are done by ericl.

Author: Reynold Xin <rxin@databricks.com>
Author: Eric Liang <ekl@databricks.com>

Closes #7598 from rxin/warnings and squashes the following commits:

beb311b [Reynold Xin] Fixed tests.
542c031 [Reynold Xin] Fixed one more warning.
87c354a [Reynold Xin] Fixed all non-deprecation warnings.
78660ac [Eric Liang] first effort to fix warnings

5 files changed, 7 insertions, 7 deletions

diff --git a/core/src/main/scala/org/apache/spark/api/r/RBackendHandler.scala b/core/src/main/scala/org/apache/spark/api/r/RBackendHandler.scala
index 9658e9a696..a5de10fe89 100644
--- a/core/src/main/scala/org/apache/spark/api/r/RBackendHandler.scala
+++ b/core/src/main/scala/org/apache/spark/api/r/RBackendHandler.scala
@@ -20,6 +20,7 @@ package org.apache.spark.api.r
 import java.io.{ByteArrayInputStream, ByteArrayOutputStream, DataInputStream, DataOutputStream}
 
 import scala.collection.mutable.HashMap
+import scala.language.existentials
 
 import io.netty.channel.ChannelHandler.Sharable
 import io.netty.channel.{ChannelHandlerContext, SimpleChannelInboundHandler}
diff --git a/core/src/main/scala/org/apache/spark/rdd/CoGroupedRDD.scala b/core/src/main/scala/org/apache/spark/rdd/CoGroupedRDD.scala
index 658e8c8b89..130b58882d 100644
--- a/core/src/main/scala/org/apache/spark/rdd/CoGroupedRDD.scala
+++ b/core/src/main/scala/org/apache/spark/rdd/CoGroupedRDD.scala
@@ -94,13 +94,14 @@ class CoGroupedRDD[K](@transient var rdds: Seq[RDD[_ <: Product2[K, _]]], part:
   }
 
   override def getDependencies: Seq[Dependency[_]] = {
-    rdds.map { rdd: RDD[_ <: Product2[K, _]] =>
+    rdds.map { rdd: RDD[_] =>
       if (rdd.partitioner == Some(part)) {
         logDebug("Adding one-to-one dependency with " + rdd)
         new OneToOneDependency(rdd)
       } else {
         logDebug("Adding shuffle dependency with " + rdd)
-        new ShuffleDependency[K, Any, CoGroupCombiner](rdd, part, serializer)
+        new ShuffleDependency[K, Any, CoGroupCombiner](
+          rdd.asInstanceOf[RDD[_ <: Product2[K, _]]], part, serializer)
       }
     }
   }
@@ -133,7 +134,7 @@ class CoGroupedRDD[K](@transient var rdds: Seq[RDD[_ <: Product2[K, _]]], part:
     // A list of (rdd iterator, dependency number) pairs
     val rddIterators = new ArrayBuffer[(Iterator[Product2[K, Any]], Int)]
     for ((dep, depNum) <- dependencies.zipWithIndex) dep match {
-      case oneToOneDependency: OneToOneDependency[Product2[K, Any]] =>
+      case oneToOneDependency: OneToOneDependency[Product2[K, Any]] @unchecked =>
         val dependencyPartition = split.narrowDeps(depNum).get.split
         // Read them from the parent
         val it = oneToOneDependency.rdd.iterator(dependencyPartition, context)
diff --git a/core/src/main/scala/org/apache/spark/util/JsonProtocol.scala b/core/src/main/scala/org/apache/spark/util/JsonProtocol.scala
index a078f14af5..c600319d9d 100644
--- a/core/src/main/scala/org/apache/spark/util/JsonProtocol.scala
+++ b/core/src/main/scala/org/apache/spark/util/JsonProtocol.scala
@@ -94,6 +94,8 @@ private[spark] object JsonProtocol {
         logStartToJson(logStart)
       case metricsUpdate: SparkListenerExecutorMetricsUpdate =>
         executorMetricsUpdateToJson(metricsUpdate)
+      case blockUpdated: SparkListenerBlockUpdated =>
+        throw new MatchError(blockUpdated)  // TODO(ekl) implement this
     }
   }
 
diff --git a/core/src/main/scala/org/apache/spark/util/SerializableConfiguration.scala b/core/src/main/scala/org/apache/spark/util/SerializableConfiguration.scala
index 30bcf1d2f2..3354a92327 100644
--- a/core/src/main/scala/org/apache/spark/util/SerializableConfiguration.scala
+++ b/core/src/main/scala/org/apache/spark/util/SerializableConfiguration.scala
@@ -20,8 +20,6 @@ import java.io.{ObjectInputStream, ObjectOutputStream}
 
 import org.apache.hadoop.conf.Configuration
 
-import org.apache.spark.util.Utils
-
 private[spark]
 class SerializableConfiguration(@transient var value: Configuration) extends Serializable {
   private def writeObject(out: ObjectOutputStream): Unit = Utils.tryOrIOException {
diff --git a/core/src/main/scala/org/apache/spark/util/SerializableJobConf.scala b/core/src/main/scala/org/apache/spark/util/SerializableJobConf.scala
index afbcc6efc8..cadae472b3 100644
--- a/core/src/main/scala/org/apache/spark/util/SerializableJobConf.scala
+++ b/core/src/main/scala/org/apache/spark/util/SerializableJobConf.scala
@@ -21,8 +21,6 @@ import java.io.{ObjectInputStream, ObjectOutputStream}
 
 import org.apache.hadoop.mapred.JobConf
 
-import org.apache.spark.util.Utils
-
 private[spark]
 class SerializableJobConf(@transient var value: JobConf) extends Serializable {
   private def writeObject(out: ObjectOutputStream): Unit = Utils.tryOrIOException {