SPARK-1488. Resolve scalac feature warnings during build

For your consideration: scalac currently notes a number of feature warnings during compilation:

```
[warn] there were 65 feature warning(s); re-run with -feature for details
```

Warnings are like:

```
[warn] /Users/srowen/Documents/spark/core/src/main/scala/org/apache/spark/SparkContext.scala:1261: implicit conversion method rddToPairRDDFunctions should be enabled
[warn] by making the implicit value scala.language.implicitConversions visible.
[warn] This can be achieved by adding the import clause 'import scala.language.implicitConversions'
[warn] or by setting the compiler option -language:implicitConversions.
[warn] See the Scala docs for value scala.language.implicitConversions for a discussion
[warn] why the feature should be explicitly enabled.
[warn]   implicit def rddToPairRDDFunctions[K: ClassTag, V: ClassTag](rdd: RDD[(K, V)]) =
[warn]                ^
```

scalac is suggesting that it's just best practice to explicitly enable certain language features by importing them where used.

This PR simply adds the imports it suggests (and squashes one other Java warning along the way). This leaves just deprecation warnings in the build.

Author: Sean Owen <sowen@cloudera.com>

Closes #404 from srowen/SPARK-1488 and squashes the following commits:

8598980 [Sean Owen] Quiet scalac warnings about language features by explicitly importing language features.
39bc831 [Sean Owen] Enable -feature in scalac to emit language feature warnings

28 files changed, 33 insertions, 3 deletions

diff --git a/core/src/main/scala/org/apache/spark/SparkContext.scala b/core/src/main/scala/org/apache/spark/SparkContext.scala
index 456070fa7c..3ddc0d5eee 100644
--- a/core/src/main/scala/org/apache/spark/SparkContext.scala
+++ b/core/src/main/scala/org/apache/spark/SparkContext.scala
@@ -25,6 +25,7 @@ import java.util.UUID.randomUUID
 import scala.collection.{Map, Set}
 import scala.collection.generic.Growable
 import scala.collection.mutable.{ArrayBuffer, HashMap}
+import scala.language.implicitConversions
 import scala.reflect.{ClassTag, classTag}
 import org.apache.hadoop.conf.Configuration
 import org.apache.hadoop.fs.Path
diff --git a/core/src/main/scala/org/apache/spark/api/java/JavaDoubleRDD.scala b/core/src/main/scala/org/apache/spark/api/java/JavaDoubleRDD.scala
index 537f410b0c..4330cef396 100644
--- a/core/src/main/scala/org/apache/spark/api/java/JavaDoubleRDD.scala
+++ b/core/src/main/scala/org/apache/spark/api/java/JavaDoubleRDD.scala
@@ -19,6 +19,7 @@ package org.apache.spark.api.java
 
 import java.lang.{Double => JDouble}
 
+import scala.language.implicitConversions
 import scala.reflect.ClassTag
 
 import org.apache.spark.Partitioner
diff --git a/core/src/main/scala/org/apache/spark/api/java/JavaPairRDD.scala b/core/src/main/scala/org/apache/spark/api/java/JavaPairRDD.scala
index a41c7dbda2..e5b2c8a5e7 100644
--- a/core/src/main/scala/org/apache/spark/api/java/JavaPairRDD.scala
+++ b/core/src/main/scala/org/apache/spark/api/java/JavaPairRDD.scala
@@ -21,6 +21,7 @@ import java.util.{Comparator, List => JList}
 import java.lang.{Iterable => JIterable}
 
 import scala.collection.JavaConversions._
+import scala.language.implicitConversions
 import scala.reflect.ClassTag
 
 import com.google.common.base.Optional
diff --git a/core/src/main/scala/org/apache/spark/api/java/JavaRDD.scala b/core/src/main/scala/org/apache/spark/api/java/JavaRDD.scala
index 01d9357a25..327c1552dc 100644
--- a/core/src/main/scala/org/apache/spark/api/java/JavaRDD.scala
+++ b/core/src/main/scala/org/apache/spark/api/java/JavaRDD.scala
@@ -17,6 +17,7 @@
 
 package org.apache.spark.api.java
 
+import scala.language.implicitConversions
 import scala.reflect.ClassTag
 
 import org.apache.spark._
diff --git a/core/src/main/scala/org/apache/spark/api/java/JavaSparkContext.scala b/core/src/main/scala/org/apache/spark/api/java/JavaSparkContext.scala
index 7fbefe1cb0..e6a3f06b0e 100644
--- a/core/src/main/scala/org/apache/spark/api/java/JavaSparkContext.scala
+++ b/core/src/main/scala/org/apache/spark/api/java/JavaSparkContext.scala
@@ -22,6 +22,7 @@ import java.util.{Map => JMap}
 
 import scala.collection.JavaConversions
 import scala.collection.JavaConversions._
+import scala.language.implicitConversions
 import scala.reflect.ClassTag
 
 import com.google.common.base.Optional
diff --git a/core/src/main/scala/org/apache/spark/deploy/FaultToleranceTest.scala b/core/src/main/scala/org/apache/spark/deploy/FaultToleranceTest.scala
index f4eb1601be..47dbcd87c3 100644
--- a/core/src/main/scala/org/apache/spark/deploy/FaultToleranceTest.scala
+++ b/core/src/main/scala/org/apache/spark/deploy/FaultToleranceTest.scala
@@ -25,6 +25,7 @@ import scala.collection.mutable.ListBuffer
 import scala.concurrent.{Await, future, promise}
 import scala.concurrent.ExecutionContext.Implicits.global
 import scala.concurrent.duration._
+import scala.language.postfixOps
 import scala.sys.process._
 
 import org.json4s._
diff --git a/core/src/main/scala/org/apache/spark/deploy/master/Master.scala b/core/src/main/scala/org/apache/spark/deploy/master/Master.scala
index 6c58e741df..81f990bfa6 100644
--- a/core/src/main/scala/org/apache/spark/deploy/master/Master.scala
+++ b/core/src/main/scala/org/apache/spark/deploy/master/Master.scala
@@ -23,6 +23,7 @@ import java.util.Date
 import scala.collection.mutable.{ArrayBuffer, HashMap, HashSet}
 import scala.concurrent.Await
 import scala.concurrent.duration._
+import scala.language.postfixOps
 import scala.util.Random
 
 import akka.actor._
diff --git a/core/src/main/scala/org/apache/spark/deploy/worker/Worker.scala b/core/src/main/scala/org/apache/spark/deploy/worker/Worker.scala
index 52c164ca3c..dd0a1360ab 100755
--- a/core/src/main/scala/org/apache/spark/deploy/worker/Worker.scala
+++ b/core/src/main/scala/org/apache/spark/deploy/worker/Worker.scala
@@ -23,6 +23,7 @@ import java.util.Date
 
 import scala.collection.mutable.HashMap
 import scala.concurrent.duration._
+import scala.language.postfixOps
 
 import akka.actor._
 import akka.remote.{DisassociatedEvent, RemotingLifecycleEvent}
diff --git a/core/src/main/scala/org/apache/spark/network/ConnectionManager.scala b/core/src/main/scala/org/apache/spark/network/ConnectionManager.scala
index cfee41c613..dcbbc18531 100644
--- a/core/src/main/scala/org/apache/spark/network/ConnectionManager.scala
+++ b/core/src/main/scala/org/apache/spark/network/ConnectionManager.scala
@@ -33,6 +33,7 @@ import scala.collection.mutable.SynchronizedQueue
 
 import scala.concurrent.{Await, ExecutionContext, Future, Promise}
 import scala.concurrent.duration._
+import scala.language.postfixOps
 
 import org.apache.spark._
 import org.apache.spark.util.{SystemClock, Utils}
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 c6e79557f0..9ff76892ae 100644
--- a/core/src/main/scala/org/apache/spark/rdd/CoGroupedRDD.scala
+++ b/core/src/main/scala/org/apache/spark/rdd/CoGroupedRDD.scala
@@ -20,6 +20,7 @@ package org.apache.spark.rdd
 import java.io.{IOException, ObjectOutputStream}
 
 import scala.collection.mutable.ArrayBuffer
+import scala.language.existentials
 
 import org.apache.spark.{InterruptibleIterator, Partition, Partitioner, SparkEnv, TaskContext}
 import org.apache.spark.{Dependency, OneToOneDependency, ShuffleDependency}
diff --git a/core/src/main/scala/org/apache/spark/rdd/CoalescedRDD.scala b/core/src/main/scala/org/apache/spark/rdd/CoalescedRDD.scala
index 44401a6634..c45b759f00 100644
--- a/core/src/main/scala/org/apache/spark/rdd/CoalescedRDD.scala
+++ b/core/src/main/scala/org/apache/spark/rdd/CoalescedRDD.scala
@@ -21,6 +21,7 @@ import java.io.{IOException, ObjectOutputStream}
 
 import scala.collection.mutable
 import scala.collection.mutable.ArrayBuffer
+import scala.language.existentials
 import scala.reflect.ClassTag
 
 import org.apache.spark._
diff --git a/core/src/main/scala/org/apache/spark/scheduler/DAGSchedulerEvent.scala b/core/src/main/scala/org/apache/spark/scheduler/DAGSchedulerEvent.scala
index 7367c08b5d..0800c5684c 100644
--- a/core/src/main/scala/org/apache/spark/scheduler/DAGSchedulerEvent.scala
+++ b/core/src/main/scala/org/apache/spark/scheduler/DAGSchedulerEvent.scala
@@ -20,6 +20,7 @@ package org.apache.spark.scheduler
 import java.util.Properties
 
 import scala.collection.mutable.Map
+import scala.language.existentials
 
 import org.apache.spark._
 import org.apache.spark.executor.TaskMetrics
diff --git a/core/src/main/scala/org/apache/spark/scheduler/ResultTask.scala b/core/src/main/scala/org/apache/spark/scheduler/ResultTask.scala
index 0b381308b6..0e8d551e4b 100644
--- a/core/src/main/scala/org/apache/spark/scheduler/ResultTask.scala
+++ b/core/src/main/scala/org/apache/spark/scheduler/ResultTask.scala
@@ -21,6 +21,7 @@ import java.io._
 import java.util.zip.{GZIPInputStream, GZIPOutputStream}
 
 import scala.collection.mutable.HashMap
+import scala.language.existentials
 
 import org.apache.spark._
 import org.apache.spark.rdd.{RDD, RDDCheckpointData}
diff --git a/core/src/main/scala/org/apache/spark/scheduler/ShuffleMapTask.scala b/core/src/main/scala/org/apache/spark/scheduler/ShuffleMapTask.scala
index 23f3b3e824..02b62de7e3 100644
--- a/core/src/main/scala/org/apache/spark/scheduler/ShuffleMapTask.scala
+++ b/core/src/main/scala/org/apache/spark/scheduler/ShuffleMapTask.scala
@@ -21,6 +21,7 @@ import java.io._
 import java.util.zip.{GZIPInputStream, GZIPOutputStream}
 
 import scala.collection.mutable.HashMap
+import scala.language.existentials
 
 import org.apache.spark._
 import org.apache.spark.executor.ShuffleWriteMetrics
diff --git a/core/src/main/scala/org/apache/spark/scheduler/TaskSchedulerImpl.scala b/core/src/main/scala/org/apache/spark/scheduler/TaskSchedulerImpl.scala
index acd152dda8..a3439b525f 100644
--- a/core/src/main/scala/org/apache/spark/scheduler/TaskSchedulerImpl.scala
+++ b/core/src/main/scala/org/apache/spark/scheduler/TaskSchedulerImpl.scala
@@ -25,6 +25,7 @@ import scala.concurrent.duration._
 import scala.collection.mutable.ArrayBuffer
 import scala.collection.mutable.HashMap
 import scala.collection.mutable.HashSet
+import scala.language.postfixOps
 import scala.util.Random
 
 import org.apache.spark._
diff --git a/core/src/main/scala/org/apache/spark/ui/JettyUtils.scala b/core/src/main/scala/org/apache/spark/ui/JettyUtils.scala
index 3ae147a36c..750f5a501c 100644
--- a/core/src/main/scala/org/apache/spark/ui/JettyUtils.scala
+++ b/core/src/main/scala/org/apache/spark/ui/JettyUtils.scala
@@ -22,6 +22,7 @@ import javax.servlet.DispatcherType
 import javax.servlet.http.{HttpServlet, HttpServletRequest, HttpServletResponse}
 
 import scala.annotation.tailrec
+import scala.language.implicitConversions
 import scala.util.{Failure, Success, Try}
 import scala.xml.Node
 
diff --git a/core/src/main/scala/org/apache/spark/util/TimeStampedWeakValueHashMap.scala b/core/src/main/scala/org/apache/spark/util/TimeStampedWeakValueHashMap.scala
index b65017d680..f5be5856c2 100644
--- a/core/src/main/scala/org/apache/spark/util/TimeStampedWeakValueHashMap.scala
+++ b/core/src/main/scala/org/apache/spark/util/TimeStampedWeakValueHashMap.scala
@@ -21,6 +21,7 @@ import java.lang.ref.WeakReference
 import java.util.concurrent.atomic.AtomicInteger
 
 import scala.collection.mutable
+import scala.language.implicitConversions
 
 import org.apache.spark.Logging
 
diff --git a/core/src/main/scala/org/apache/spark/util/Vector.scala b/core/src/main/scala/org/apache/spark/util/Vector.scala
index 1a647fa1c9..c6cab82c3e 100644
--- a/core/src/main/scala/org/apache/spark/util/Vector.scala
+++ b/core/src/main/scala/org/apache/spark/util/Vector.scala
@@ -17,6 +17,7 @@
 
 package org.apache.spark.util
 
+import scala.language.implicitConversions
 import scala.util.Random
 
 import org.apache.spark.util.random.XORShiftRandom
diff --git a/core/src/test/scala/org/apache/spark/ConnectionManagerSuite.scala b/core/src/test/scala/org/apache/spark/ConnectionManagerSuite.scala
index 80f7ec00c7..df6b2604c8 100644
--- a/core/src/test/scala/org/apache/spark/ConnectionManagerSuite.scala
+++ b/core/src/test/scala/org/apache/spark/ConnectionManagerSuite.scala
@@ -25,7 +25,7 @@ import org.apache.spark.network.{ConnectionManager, Message, ConnectionManagerId
 import scala.concurrent.Await
 import scala.concurrent.TimeoutException
 import scala.concurrent.duration._
-
+import scala.language.postfixOps
 
 /**
   * Test the ConnectionManager with various security settings.
diff --git a/core/src/test/scala/org/apache/spark/ContextCleanerSuite.scala b/core/src/test/scala/org/apache/spark/ContextCleanerSuite.scala
index e50981cf6f..5a83100908 100644
--- a/core/src/test/scala/org/apache/spark/ContextCleanerSuite.scala
+++ b/core/src/test/scala/org/apache/spark/ContextCleanerSuite.scala
@@ -20,6 +20,8 @@ package org.apache.spark
 import java.lang.ref.WeakReference
 
 import scala.collection.mutable.{HashSet, SynchronizedSet}
+import scala.language.existentials
+import scala.language.postfixOps
 import scala.util.Random
 
 import org.scalatest.{BeforeAndAfter, FunSuite}
diff --git a/core/src/test/scala/org/apache/spark/DriverSuite.scala b/core/src/test/scala/org/apache/spark/DriverSuite.scala
index 7f59bdcce4..de4bd90c8f 100644
--- a/core/src/test/scala/org/apache/spark/DriverSuite.scala
+++ b/core/src/test/scala/org/apache/spark/DriverSuite.scala
@@ -29,6 +29,8 @@ import org.scalatest.time.SpanSugar._
 
 import org.apache.spark.util.Utils
 
+import scala.language.postfixOps
+
 class DriverSuite extends FunSuite with Timeouts {
 
   test("driver should exit after finishing") {
diff --git a/core/src/test/scala/org/apache/spark/PipedRDDSuite.scala b/core/src/test/scala/org/apache/spark/PipedRDDSuite.scala
index 867b28cc0d..dfe057515e 100644
--- a/core/src/test/scala/org/apache/spark/PipedRDDSuite.scala
+++ b/core/src/test/scala/org/apache/spark/PipedRDDSuite.scala
@@ -19,8 +19,6 @@ package org.apache.spark
 
 import java.io.File
 
-import com.google.common.io.Files
-
 import org.scalatest.FunSuite
 
 import org.apache.spark.rdd.{HadoopRDD, PipedRDD, HadoopPartition}
@@ -28,6 +26,7 @@ import org.apache.hadoop.mapred.{JobConf, TextInputFormat, FileSplit}
 import org.apache.hadoop.fs.Path
 
 import scala.collection.Map
+import scala.language.postfixOps
 import scala.sys.process._
 import scala.util.Try
 
diff --git a/core/src/test/scala/org/apache/spark/rdd/AsyncRDDActionsSuite.scala b/core/src/test/scala/org/apache/spark/rdd/AsyncRDDActionsSuite.scala
index 3b833f2e41..28197657e9 100644
--- a/core/src/test/scala/org/apache/spark/rdd/AsyncRDDActionsSuite.scala
+++ b/core/src/test/scala/org/apache/spark/rdd/AsyncRDDActionsSuite.scala
@@ -22,6 +22,7 @@ import java.util.concurrent.Semaphore
 import scala.concurrent.{Await, TimeoutException}
 import scala.concurrent.duration.Duration
 import scala.concurrent.ExecutionContext.Implicits.global
+import scala.language.postfixOps
 
 import org.scalatest.{BeforeAndAfterAll, FunSuite}
 import org.scalatest.concurrent.Timeouts
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 db4df1d121..35a7ac9d04 100644
--- a/core/src/test/scala/org/apache/spark/scheduler/DAGSchedulerSuite.scala
+++ b/core/src/test/scala/org/apache/spark/scheduler/DAGSchedulerSuite.scala
@@ -19,6 +19,7 @@ package org.apache.spark.scheduler
 
 import scala.Tuple2
 import scala.collection.mutable.{HashSet, HashMap, Map}
+import scala.language.reflectiveCalls
 
 import org.scalatest.{BeforeAndAfter, FunSuite}
 
diff --git a/core/src/test/scala/org/apache/spark/storage/BlockManagerSuite.scala b/core/src/test/scala/org/apache/spark/storage/BlockManagerSuite.scala
index e10ec7d262..907428db80 100644
--- a/core/src/test/scala/org/apache/spark/storage/BlockManagerSuite.scala
+++ b/core/src/test/scala/org/apache/spark/storage/BlockManagerSuite.scala
@@ -33,6 +33,9 @@ import org.apache.spark.scheduler.LiveListenerBus
 import org.apache.spark.serializer.{JavaSerializer, KryoSerializer}
 import org.apache.spark.util.{AkkaUtils, ByteBufferInputStream, SizeEstimator, Utils}
 
+import scala.language.implicitConversions
+import scala.language.postfixOps
+
 class BlockManagerSuite extends FunSuite with BeforeAndAfter with PrivateMethodTester {
   private val conf = new SparkConf(false)
   var store: BlockManager = null
diff --git a/core/src/test/scala/org/apache/spark/storage/DiskBlockManagerSuite.scala b/core/src/test/scala/org/apache/spark/storage/DiskBlockManagerSuite.scala
index 808ddfdcf4..9b29e2a8a5 100644
--- a/core/src/test/scala/org/apache/spark/storage/DiskBlockManagerSuite.scala
+++ b/core/src/test/scala/org/apache/spark/storage/DiskBlockManagerSuite.scala
@@ -20,6 +20,7 @@ package org.apache.spark.storage
 import java.io.{File, FileWriter}
 
 import scala.collection.mutable
+import scala.language.reflectiveCalls
 
 import com.google.common.io.Files
 import org.scalatest.{BeforeAndAfterEach, FunSuite}
diff --git a/core/src/test/scala/org/apache/spark/ui/UISuite.scala b/core/src/test/scala/org/apache/spark/ui/UISuite.scala
index b85c483ca2..ed02b0ba00 100644
--- a/core/src/test/scala/org/apache/spark/ui/UISuite.scala
+++ b/core/src/test/scala/org/apache/spark/ui/UISuite.scala
@@ -21,6 +21,7 @@ import java.net.ServerSocket
 import javax.servlet.http.HttpServletRequest
 
 import scala.io.Source
+import scala.language.postfixOps
 import scala.util.{Failure, Success, Try}
 
 import org.eclipse.jetty.server.Server
diff --git a/core/src/test/scala/org/apache/spark/util/random/XORShiftRandomSuite.scala b/core/src/test/scala/org/apache/spark/util/random/XORShiftRandomSuite.scala
index 39199a1a17..0865c6386f 100644
--- a/core/src/test/scala/org/apache/spark/util/random/XORShiftRandomSuite.scala
+++ b/core/src/test/scala/org/apache/spark/util/random/XORShiftRandomSuite.scala
@@ -22,6 +22,8 @@ import org.scalatest.matchers.ShouldMatchers
 
 import org.apache.spark.util.Utils.times
 
+import scala.language.reflectiveCalls
+
 class XORShiftRandomSuite extends FunSuite with ShouldMatchers {
 
   def fixture = new {