[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, 14 insertions, 28 deletions

diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Cast.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Cast.scala
index d842ffdc66..0f8876a9e6 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Cast.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Cast.scala
@@ -898,7 +898,7 @@ case class Cast(child: Expression, dataType: DataType) extends UnaryExpression w
     val result = ctx.freshName("result")
     val tmpRow = ctx.freshName("tmpRow")
 
-    val fieldsEvalCode = fieldsCasts.zipWithIndex.map { case (cast, i) => {
+    val fieldsEvalCode = fieldsCasts.zipWithIndex.map { case (cast, i) =>
       val fromFieldPrim = ctx.freshName("ffp")
       val fromFieldNull = ctx.freshName("ffn")
       val toFieldPrim = ctx.freshName("tfp")
@@ -920,7 +920,6 @@ case class Cast(child: Expression, dataType: DataType) extends UnaryExpression w
           }
         }
        """
-      }
     }.mkString("\n")
 
     (c, evPrim, evNull) =>
diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala
index affd1bdb32..8d8cc152ff 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala
@@ -97,11 +97,11 @@ class EquivalentExpressions {
   def debugString(all: Boolean = false): String = {
     val sb: mutable.StringBuilder = new StringBuilder()
     sb.append("Equivalent expressions:\n")
-    equivalenceMap.foreach { case (k, v) => {
+    equivalenceMap.foreach { case (k, v) =>
       if (all || v.length > 1) {
         sb.append("  " + v.mkString(", ")).append("\n")
       }
-    }}
+    }
     sb.toString()
   }
 }
diff --git a/sql/catalyst/src/test/scala/org/apache/spark/sql/RandomDataGenerator.scala b/sql/catalyst/src/test/scala/org/apache/spark/sql/RandomDataGenerator.scala
index 8207d64798..711e870711 100644
--- a/sql/catalyst/src/test/scala/org/apache/spark/sql/RandomDataGenerator.scala
+++ b/sql/catalyst/src/test/scala/org/apache/spark/sql/RandomDataGenerator.scala
@@ -196,12 +196,11 @@ object RandomDataGenerator {
       case ShortType => randomNumeric[Short](
         rand, _.nextInt().toShort, Seq(Short.MinValue, Short.MaxValue, 0.toShort))
       case NullType => Some(() => null)
-      case ArrayType(elementType, containsNull) => {
+      case ArrayType(elementType, containsNull) =>
         forType(elementType, nullable = containsNull, rand).map {
           elementGenerator => () => Seq.fill(rand.nextInt(MAX_ARR_SIZE))(elementGenerator())
         }
-      }
-      case MapType(keyType, valueType, valueContainsNull) => {
+      case MapType(keyType, valueType, valueContainsNull) =>
         for (
           keyGenerator <- forType(keyType, nullable = false, rand);
           valueGenerator <-
@@ -221,8 +220,7 @@ object RandomDataGenerator {
             keys.zip(values).toMap
           }
         }
-      }
-      case StructType(fields) => {
+      case StructType(fields) =>
         val maybeFieldGenerators: Seq[Option[() => Any]] = fields.map { field =>
           forType(field.dataType, nullable = field.nullable, rand)
         }
@@ -232,8 +230,7 @@ object RandomDataGenerator {
         } else {
           None
         }
-      }
-      case udt: UserDefinedType[_] => {
+      case udt: UserDefinedType[_] =>
         val maybeSqlTypeGenerator = forType(udt.sqlType, nullable, rand)
         // Because random data generator at here returns scala value, we need to
         // convert it to catalyst value to call udt's deserialize.
@@ -253,7 +250,6 @@ object RandomDataGenerator {
         } else {
           None
         }
-      }
       case unsupportedType => None
     }
     // Handle nullability by wrapping the non-null value generator:
@@ -277,7 +273,7 @@ object RandomDataGenerator {
     val fields = mutable.ArrayBuffer.empty[Any]
     schema.fields.foreach { f =>
       f.dataType match {
-        case ArrayType(childType, nullable) => {
+        case ArrayType(childType, nullable) =>
           val data = if (f.nullable && rand.nextFloat() <= PROBABILITY_OF_NULL) {
             null
           } else {
@@ -294,10 +290,8 @@ object RandomDataGenerator {
             arr
           }
           fields += data
-        }
-        case StructType(children) => {
+        case StructType(children) =>
           fields += randomRow(rand, StructType(children))
-        }
         case _ =>
           val generator = RandomDataGenerator.forType(f.dataType, f.nullable, rand)
           assert(generator.isDefined, "Unsupported type")
diff --git a/sql/core/src/test/scala/org/apache/spark/sql/DataFrameSuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/DataFrameSuite.scala
index 86c6405522..e953a6e8ef 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/DataFrameSuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/DataFrameSuite.scala
@@ -1153,14 +1153,12 @@ class DataFrameSuite extends QueryTest with SharedSQLContext {
   private def verifyNonExchangingAgg(df: DataFrame) = {
     var atFirstAgg: Boolean = false
     df.queryExecution.executedPlan.foreach {
-      case agg: TungstenAggregate => {
+      case agg: TungstenAggregate =>
         atFirstAgg = !atFirstAgg
-      }
-      case _ => {
+      case _ =>
         if (atFirstAgg) {
           fail("Should not have operators between the two aggregations")
         }
-      }
     }
   }
 
@@ -1170,12 +1168,11 @@ class DataFrameSuite extends QueryTest with SharedSQLContext {
   private def verifyExchangingAgg(df: DataFrame) = {
     var atFirstAgg: Boolean = false
     df.queryExecution.executedPlan.foreach {
-      case agg: TungstenAggregate => {
+      case agg: TungstenAggregate =>
         if (atFirstAgg) {
           fail("Should not have back to back Aggregates")
         }
         atFirstAgg = true
-      }
       case e: ShuffleExchange => atFirstAgg = false
       case _ =>
     }
diff --git a/sql/core/src/test/scala/org/apache/spark/sql/execution/vectorized/ColumnarBatchSuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/execution/vectorized/ColumnarBatchSuite.scala
index 8a551cd78c..31b63f2ce1 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/execution/vectorized/ColumnarBatchSuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/execution/vectorized/ColumnarBatchSuite.scala
@@ -612,23 +612,20 @@ class ColumnarBatchSuite extends SparkFunSuite {
             val a2 = r2.getList(v._2).toArray
             assert(a1.length == a2.length, "Seed = " + seed)
             childType match {
-              case DoubleType => {
+              case DoubleType =>
                 var i = 0
                 while (i < a1.length) {
                   assert(doubleEquals(a1(i).asInstanceOf[Double], a2(i).asInstanceOf[Double]),
                     "Seed = " + seed)
                   i += 1
                 }
-              }
-              case FloatType => {
+              case FloatType =>
                 var i = 0
                 while (i < a1.length) {
                   assert(doubleEquals(a1(i).asInstanceOf[Float], a2(i).asInstanceOf[Float]),
                     "Seed = " + seed)
                   i += 1
                 }
-              }
-
               case t: DecimalType =>
                 var i = 0
                 while (i < a1.length) {
@@ -640,7 +637,6 @@ class ColumnarBatchSuite extends SparkFunSuite {
                   }
                   i += 1
                 }
-
               case _ => assert(a1 === a2, "Seed = " + seed)
             }
           case StructType(childFields) =>