SPARK-4297 [BUILD] Build warning fixes omnibus

There are a number of warnings generated in a normal, successful build right now. They're mostly Java unchecked cast warnings, which can be suppressed. But there's a grab bag of other Scala language warnings and so on that can all be easily fixed. The forthcoming PR fixes about 90% of the build warnings I see now.

Author: Sean Owen <sowen@cloudera.com>

Closes #3157 from srowen/SPARK-4297 and squashes the following commits:

8c9e469 [Sean Owen] Suppress unchecked cast warnings, and several other build warning fixes

5 files changed, 9 insertions, 6 deletions

diff --git a/core/pom.xml b/core/pom.xml
index 1feb00b3a7..c5c41b2b5d 100644
--- a/core/pom.xml
+++ b/core/pom.xml
@@ -352,9 +352,9 @@
           </execution>
         </executions>
         <configuration>
-          <tasks>
+          <target>
             <unzip src="../python/lib/py4j-0.8.2.1-src.zip" dest="../python/build" />
-          </tasks>
+          </target>
         </configuration>
       </plugin>
       <plugin>
diff --git a/core/src/main/scala/org/apache/spark/scheduler/TaskResultGetter.scala b/core/src/main/scala/org/apache/spark/scheduler/TaskResultGetter.scala
index 819b51e12a..4896ec845b 100644
--- a/core/src/main/scala/org/apache/spark/scheduler/TaskResultGetter.scala
+++ b/core/src/main/scala/org/apache/spark/scheduler/TaskResultGetter.scala
@@ -19,6 +19,7 @@ package org.apache.spark.scheduler
 
 import java.nio.ByteBuffer
 
+import scala.language.existentials
 import scala.util.control.NonFatal
 
 import org.apache.spark._
diff --git a/core/src/test/java/org/apache/spark/JavaAPISuite.java b/core/src/test/java/org/apache/spark/JavaAPISuite.java
index e5bdad6bda..5ce299d058 100644
--- a/core/src/test/java/org/apache/spark/JavaAPISuite.java
+++ b/core/src/test/java/org/apache/spark/JavaAPISuite.java
@@ -184,6 +184,7 @@ public class JavaAPISuite implements Serializable {
     Assert.assertEquals(new Tuple2<Integer, Integer>(3, 2), sortedPairs.get(2));
   }
 
+  @SuppressWarnings("unchecked")
   @Test
   public void repartitionAndSortWithinPartitions() {
     List<Tuple2<Integer, Integer>> pairs = new ArrayList<Tuple2<Integer, Integer>>();
@@ -491,6 +492,7 @@ public class JavaAPISuite implements Serializable {
     Assert.assertEquals(33, sum);
   }
 
+  @SuppressWarnings("unchecked")
   @Test
   public void aggregateByKey() {
     JavaPairRDD<Integer, Integer> pairs = sc.parallelizePairs(
@@ -1556,7 +1558,7 @@ public class JavaAPISuite implements Serializable {
   @Test
   public void testRegisterKryoClasses() {
     SparkConf conf = new SparkConf();
-    conf.registerKryoClasses(new Class[]{ Class1.class, Class2.class });
+    conf.registerKryoClasses(new Class<?>[]{ Class1.class, Class2.class });
     Assert.assertEquals(
         Class1.class.getName() + "," + Class2.class.getName(),
         conf.get("spark.kryo.classesToRegister"));
diff --git a/core/src/test/scala/org/apache/spark/metrics/InputOutputMetricsSuite.scala b/core/src/test/scala/org/apache/spark/metrics/InputOutputMetricsSuite.scala
index ca226fd4e6..f8bcde12a3 100644
--- a/core/src/test/scala/org/apache/spark/metrics/InputOutputMetricsSuite.scala
+++ b/core/src/test/scala/org/apache/spark/metrics/InputOutputMetricsSuite.scala
@@ -24,14 +24,14 @@ import org.apache.spark.deploy.SparkHadoopUtil
 import org.apache.spark.scheduler.{SparkListenerTaskEnd, SparkListener}
 
 import org.scalatest.FunSuite
-import org.scalatest.matchers.ShouldMatchers
+import org.scalatest.Matchers
 
 import org.apache.hadoop.conf.Configuration
 import org.apache.hadoop.fs.{Path, FileSystem}
 
 import scala.collection.mutable.ArrayBuffer
 
-class InputOutputMetricsSuite extends FunSuite with SharedSparkContext with ShouldMatchers {
+class InputOutputMetricsSuite extends FunSuite with SharedSparkContext with Matchers {
   test("input metrics when reading text file with single split") {
     val file = new File(getClass.getSimpleName + ".txt")
     val pw = new PrintWriter(new FileWriter(file))
diff --git a/core/src/test/scala/org/apache/spark/scheduler/DAGSchedulerSuite.scala b/core/src/test/scala/org/apache/spark/scheduler/DAGSchedulerSuite.scala
index 436eea4f1f..d6ec9e129c 100644
--- a/core/src/test/scala/org/apache/spark/scheduler/DAGSchedulerSuite.scala
+++ b/core/src/test/scala/org/apache/spark/scheduler/DAGSchedulerSuite.scala
@@ -739,7 +739,7 @@ class DAGSchedulerSuite extends TestKit(ActorSystem("DAGSchedulerSuite")) with F
 
   test("accumulator not calculated for resubmitted result stage") {
     //just for register
-    val accum = new Accumulator[Int](0, SparkContext.IntAccumulatorParam)
+    val accum = new Accumulator[Int](0, AccumulatorParam.IntAccumulatorParam)
     val finalRdd = new MyRDD(sc, 1, Nil)
     submit(finalRdd, Array(0))
     completeWithAccumulator(accum.id, taskSets(0), Seq((Success, 42)))