[SPARK-13442][SQL] Make type inference recognize boolean types

## What changes were proposed in this pull request?

https://issues.apache.org/jira/browse/SPARK-13442

This PR adds the support for inferring `BooleanType` for schema.
It supports to infer case-insensitive `true` / `false` as `BooleanType`.

Unittests were added for `CSVInferSchemaSuite` and `CSVSuite` for end-to-end test.

## How was the this patch tested?

This was tested with unittests and with `dev/run_tests` for coding style

Author: hyukjinkwon <gurwls223@gmail.com>

Closes #11315 from HyukjinKwon/SPARK-13442.

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/csv/CSVInferSchema.scala

@@ -87,6 +87,7 @@ private[csv] object CSVInferSchema {
         case LongType => tryParseLong(field)
         case DoubleType => tryParseDouble(field)
         case TimestampType => tryParseTimestamp(field)
+        case BooleanType => tryParseBoolean(field)
         case StringType => StringType
         case other: DataType =>
           throw new UnsupportedOperationException(s"Unexpected data type $other")
@@ -117,6 +118,14 @@ private[csv] object CSVInferSchema {
   def tryParseTimestamp(field: String): DataType = {
     if ((allCatch opt Timestamp.valueOf(field)).isDefined) {
       TimestampType
+    } else {
+      tryParseBoolean(field)
+    }
+  }
+
+  def tryParseBoolean(field: String): DataType = {
+    if ((allCatch opt field.toBoolean).isDefined) {
+      BooleanType
     } else {
       stringType()
     }

sql/core/src/test/resources/bool.csv

+bool
+"True"
+"False"
+
+"true"

sql/core/src/test/scala/org/apache/spark/sql/execution/datasources/csv/CSVInferSchemaSuite.scala

@@ -30,6 +30,8 @@ class InferSchemaSuite extends SparkFunSuite {
     assert(CSVInferSchema.inferField(NullType, "3.5") == DoubleType)
     assert(CSVInferSchema.inferField(NullType, "test") == StringType)
     assert(CSVInferSchema.inferField(NullType, "2015-08-20 15:57:00") == TimestampType)
+    assert(CSVInferSchema.inferField(NullType, "True") == BooleanType)
+    assert(CSVInferSchema.inferField(NullType, "FAlSE") == BooleanType)
   }
 
   test("String fields types are inferred correctly from other types") {
@@ -40,6 +42,9 @@ class InferSchemaSuite extends SparkFunSuite {
     assert(CSVInferSchema.inferField(DoubleType, "test") == StringType)
     assert(CSVInferSchema.inferField(LongType, "2015-08-20 14:57:00") == TimestampType)
     assert(CSVInferSchema.inferField(DoubleType, "2015-08-20 15:57:00") == TimestampType)
+    assert(CSVInferSchema.inferField(LongType, "True") == BooleanType)
+    assert(CSVInferSchema.inferField(IntegerType, "FALSE") == BooleanType)
+    assert(CSVInferSchema.inferField(TimestampType, "FALSE") == BooleanType)
   }
 
   test("Timestamp field types are inferred correctly from other types") {
@@ -48,6 +53,11 @@ class InferSchemaSuite extends SparkFunSuite {
     assert(CSVInferSchema.inferField(LongType, "2015-08 14:49:00") == StringType)
   }
 
+  test("Boolean fields types are inferred correctly from other types") {
+    assert(CSVInferSchema.inferField(LongType, "Fale") == StringType)
+    assert(CSVInferSchema.inferField(DoubleType, "TRUEe") == StringType)
+  }
+
   test("Type arrays are merged to highest common type") {
     assert(
       CSVInferSchema.mergeRowTypes(Array(StringType),
@@ -67,6 +77,7 @@ class InferSchemaSuite extends SparkFunSuite {
     assert(CSVInferSchema.inferField(IntegerType, "\\N", "\\N") == IntegerType)
     assert(CSVInferSchema.inferField(DoubleType, "\\N", "\\N") == DoubleType)
     assert(CSVInferSchema.inferField(TimestampType, "\\N", "\\N") == TimestampType)
+    assert(CSVInferSchema.inferField(BooleanType, "\\N", "\\N") == BooleanType)
   }
 
   test("Merging Nulltypes should yeild Nulltype.") {

sql/core/src/test/scala/org/apache/spark/sql/execution/datasources/csv/CSVSuite.scala

@@ -43,6 +43,7 @@ class CSVSuite extends QueryTest with SharedSQLContext with SQLTestUtils {
   private val emptyFile = "empty.csv"
   private val commentsFile = "comments.csv"
   private val disableCommentsFile = "disable_comments.csv"
+  private val boolFile = "bool.csv"
   private val simpleSparseFile = "simple_sparse.csv"
 
   private def testFile(fileName: String): String = {
@@ -118,6 +119,18 @@ class CSVSuite extends QueryTest with SharedSQLContext with SQLTestUtils {
     verifyCars(cars, withHeader = true, checkTypes = true)
   }
 
+  test("test inferring booleans") {
+    val result = sqlContext.read
+      .format("csv")
+      .option("header", "true")
+      .option("inferSchema", "true")
+      .load(testFile(boolFile))
+
+    val expectedSchema = StructType(List(
+      StructField("bool", BooleanType, nullable = true)))
+    assert(result.schema === expectedSchema)
+  }
+
   test("test with alternative delimiter and quote") {
     val cars = sqlContext.read
       .format("csv")