[SPARK-14508][BUILD] Add a new ScalaStyle Rule `OmitBracesInCase`

## What changes were proposed in this pull request?

According to the [Spark Code Style Guide](https://cwiki.apache.org/confluence/display/SPARK/Spark+Code+Style+Guide) and [Scala Style Guide](http://docs.scala-lang.org/style/control-structures.html#curlybraces), we had better enforce the following rule.
  ```
  case: Always omit braces in case clauses.
  ```
This PR makes a new ScalaStyle rule, 'OmitBracesInCase', and enforces it to the code.

## How was this patch tested?

Pass the Jenkins tests (including Scala style checking)

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #12280 from dongjoon-hyun/SPARK-14508.

5 files changed, 10 insertions, 20 deletions

diff --git a/examples/src/main/scala/org/apache/spark/examples/CassandraCQLTest.scala b/examples/src/main/scala/org/apache/spark/examples/CassandraCQLTest.scala
index 973b005f91..ca4eea2356 100644
--- a/examples/src/main/scala/org/apache/spark/examples/CassandraCQLTest.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/CassandraCQLTest.scala
@@ -106,9 +106,8 @@ object CassandraCQLTest {
 
     println("Count: " + casRdd.count)
     val productSaleRDD = casRdd.map {
-      case (key, value) => {
+      case (key, value) =>
         (ByteBufferUtil.string(value.get("prod_id")), ByteBufferUtil.toInt(value.get("quantity")))
-      }
     }
     val aggregatedRDD = productSaleRDD.reduceByKey(_ + _)
     aggregatedRDD.collect().foreach {
@@ -116,11 +115,10 @@ object CassandraCQLTest {
     }
 
     val casoutputCF = aggregatedRDD.map {
-      case (productId, saleCount) => {
+      case (productId, saleCount) =>
         val outKey = Collections.singletonMap("prod_id", ByteBufferUtil.bytes(productId))
         val outVal = Collections.singletonList(ByteBufferUtil.bytes(saleCount))
         (outKey, outVal)
-      }
     }
 
     casoutputCF.saveAsNewAPIHadoopFile(
diff --git a/examples/src/main/scala/org/apache/spark/examples/CassandraTest.scala b/examples/src/main/scala/org/apache/spark/examples/CassandraTest.scala
index 6a8f73ad00..eff840d36e 100644
--- a/examples/src/main/scala/org/apache/spark/examples/CassandraTest.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/CassandraTest.scala
@@ -90,9 +90,8 @@ object CassandraTest {
 
     // Let us first get all the paragraphs from the retrieved rows
     val paraRdd = casRdd.map {
-      case (key, value) => {
+      case (key, value) =>
         ByteBufferUtil.string(value.get(ByteBufferUtil.bytes("para")).value())
-      }
     }
 
     // Lets get the word count in paras
@@ -103,7 +102,7 @@ object CassandraTest {
     }
 
     counts.map {
-      case (word, count) => {
+      case (word, count) =>
         val colWord = new org.apache.cassandra.thrift.Column()
         colWord.setName(ByteBufferUtil.bytes("word"))
         colWord.setValue(ByteBufferUtil.bytes(word))
@@ -122,7 +121,6 @@ object CassandraTest {
         mutations.get(1).setColumn_or_supercolumn(new ColumnOrSuperColumn())
         mutations.get(1).column_or_supercolumn.setColumn(colCount)
         (outputkey, mutations)
-      }
     }.saveAsNewAPIHadoopFile("casDemo", classOf[ByteBuffer], classOf[List[Mutation]],
       classOf[ColumnFamilyOutputFormat], job.getConfiguration)
 
diff --git a/examples/src/main/scala/org/apache/spark/examples/LocalALS.scala b/examples/src/main/scala/org/apache/spark/examples/LocalALS.scala
index af5f216f28..fa10101955 100644
--- a/examples/src/main/scala/org/apache/spark/examples/LocalALS.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/LocalALS.scala
@@ -104,16 +104,14 @@ object LocalALS {
   def main(args: Array[String]) {
 
     args match {
-      case Array(m, u, f, iters) => {
+      case Array(m, u, f, iters) =>
         M = m.toInt
         U = u.toInt
         F = f.toInt
         ITERATIONS = iters.toInt
-      }
-      case _ => {
+      case _ =>
         System.err.println("Usage: LocalALS <M> <U> <F> <iters>")
         System.exit(1)
-      }
     }
 
     showWarning()
diff --git a/examples/src/main/scala/org/apache/spark/examples/ml/OneVsRestExample.scala b/examples/src/main/scala/org/apache/spark/examples/ml/OneVsRestExample.scala
index a0bb5dabf4..0b5d31c0ff 100644
--- a/examples/src/main/scala/org/apache/spark/examples/ml/OneVsRestExample.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/ml/OneVsRestExample.scala
@@ -118,17 +118,15 @@ object OneVsRestExample {
     val inputData = sqlContext.read.format("libsvm").load(params.input)
     // compute the train/test split: if testInput is not provided use part of input.
     val data = params.testInput match {
-      case Some(t) => {
+      case Some(t) =>
         // compute the number of features in the training set.
         val numFeatures = inputData.first().getAs[Vector](1).size
         val testData = sqlContext.read.option("numFeatures", numFeatures.toString)
           .format("libsvm").load(t)
         Array[DataFrame](inputData, testData)
-      }
-      case None => {
+      case None =>
         val f = params.fracTest
         inputData.randomSplit(Array(1 - f, f), seed = 12345)
-      }
     }
     val Array(train, test) = data.map(_.cache())
 
diff --git a/examples/src/main/scala/org/apache/spark/examples/mllib/DecisionTreeRunner.scala b/examples/src/main/scala/org/apache/spark/examples/mllib/DecisionTreeRunner.scala
index c263f4f595..ee811d3aa1 100644
--- a/examples/src/main/scala/org/apache/spark/examples/mllib/DecisionTreeRunner.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/mllib/DecisionTreeRunner.scala
@@ -180,7 +180,7 @@ object DecisionTreeRunner {
     }
     // For classification, re-index classes if needed.
     val (examples, classIndexMap, numClasses) = algo match {
-      case Classification => {
+      case Classification =>
         // classCounts: class --> # examples in class
         val classCounts = origExamples.map(_.label).countByValue()
         val sortedClasses = classCounts.keys.toList.sorted
@@ -209,7 +209,6 @@ object DecisionTreeRunner {
           println(s"$c\t$frac\t${classCounts(c)}")
         }
         (examples, classIndexMap, numClasses)
-      }
       case Regression =>
         (origExamples, null, 0)
       case _ =>
@@ -225,7 +224,7 @@ object DecisionTreeRunner {
         case "libsvm" => MLUtils.loadLibSVMFile(sc, testInput, numFeatures)
       }
       algo match {
-        case Classification => {
+        case Classification =>
           // classCounts: class --> # examples in class
           val testExamples = {
             if (classIndexMap.isEmpty) {
@@ -235,7 +234,6 @@ object DecisionTreeRunner {
             }
           }
           Array(examples, testExamples)
-        }
         case Regression =>
           Array(examples, origTestExamples)
       }