[SPARK-5211][SQL]Restore HiveMetastoreTypes.toDataType

jira: https://issues.apache.org/jira/browse/SPARK-5211

Author: Yin Huai <yhuai@databricks.com>

Closes #4026 from yhuai/SPARK-5211 and squashes the following commits:

15ee32b [Yin Huai] Remove extra line.
c6c1651 [Yin Huai] Get back HiveMetastoreTypes.toDataType.

sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveMetastoreCatalog.scala

@@ -39,7 +39,7 @@ import org.apache.spark.sql.catalyst.expressions._
 import org.apache.spark.sql.catalyst.plans.logical
 import org.apache.spark.sql.catalyst.plans.logical._
 import org.apache.spark.sql.catalyst.rules._
-import org.apache.spark.sql.sources.{LogicalRelation, ResolvedDataSource}
+import org.apache.spark.sql.sources.{DDLParser, LogicalRelation, ResolvedDataSource}
 import org.apache.spark.sql.types._
 import org.apache.spark.util.Utils
 
@@ -558,6 +558,12 @@ private[hive] case class MetastoreRelation
 }
 
 object HiveMetastoreTypes {
+  protected val ddlParser = new DDLParser
+
+  def toDataType(metastoreType: String): DataType = synchronized {
+    ddlParser.parseType(metastoreType)
+  }
+
   def toMetastoreType(dt: DataType): String = dt match {
     case ArrayType(elementType, _) => s"array<${toMetastoreType(elementType)}>"
     case StructType(fields) =>

sql/hive/src/test/scala/org/apache/spark/sql/hive/HiveMetastoreCatalogSuite.scala

@@ -19,7 +19,6 @@ package org.apache.spark.sql.hive
 
 import org.scalatest.FunSuite
 
-import org.apache.spark.sql.sources.DDLParser
 import org.apache.spark.sql.test.ExamplePointUDT
 import org.apache.spark.sql.types.StructType
 
@@ -28,9 +27,7 @@ class HiveMetastoreCatalogSuite extends FunSuite {
   test("struct field should accept underscore in sub-column name") {
     val metastr = "struct<a: int, b_1: string, c: string>"
 
-    val ddlParser = new DDLParser
-
-    val datatype = ddlParser.parseType(metastr)
+    val datatype = HiveMetastoreTypes.toDataType(metastr)
     assert(datatype.isInstanceOf[StructType])
   }