[SPARK-6202] [SQL] enable variable substitution on test framework

Author: Daoyuan Wang <daoyuan.wang@intel.com>

Closes #4930 from adrian-wang/testvs and squashes the following commits:

2ce590f [Daoyuan Wang] add explicit function types
b1d68bf [Daoyuan Wang] only substitute for parseSql
9c4a950 [Daoyuan Wang] add a comment explaining
18fb481 [Daoyuan Wang] enable variable substitute on test framework

sql/hive/src/main/scala/org/apache/spark/sql/hive/test/TestHive.scala

@@ -23,6 +23,7 @@ import java.util.{Set => JavaSet}
 import org.apache.hadoop.hive.ql.exec.FunctionRegistry
 import org.apache.hadoop.hive.ql.io.avro.{AvroContainerInputFormat, AvroContainerOutputFormat}
 import org.apache.hadoop.hive.ql.metadata.Table
+import org.apache.hadoop.hive.ql.parse.VariableSubstitution
 import org.apache.hadoop.hive.ql.processors._
 import org.apache.hadoop.hive.serde2.RegexSerDe
 import org.apache.hadoop.hive.serde2.`lazy`.LazySimpleSerDe
@@ -153,8 +154,13 @@ class TestHiveContext(sc: SparkContext) extends HiveContext(sc) {
 
   val describedTable = "DESCRIBE (\\w+)".r
 
+  val vs = new VariableSubstitution()
+
+  // we should substitute variables in hql to pass the text to parseSql() as a parameter.
+  // Hive parser need substituted text. HiveContext.sql() does this but return a DataFrame,
+  // while we need a logicalPlan so we cannot reuse that.
   protected[hive] class HiveQLQueryExecution(hql: String)
-    extends this.QueryExecution(HiveQl.parseSql(hql)) {
+    extends this.QueryExecution(HiveQl.parseSql(vs.substitute(hiveconf, hql))) {
     def hiveExec(): Seq[String] = runSqlHive(hql)
     override def toString: String = hql + "\n" + super.toString
   }