Allow underscore in struct field column name

Correcting for PR comments: remove changes to q-file, add a separate unittest

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

@@ -201,7 +201,7 @@ object HiveMetastoreTypes extends RegexParsers {
     }
 
   protected lazy val structField: Parser[StructField] =
-    "[a-zA-Z0-9]*".r ~ ":" ~ dataType ^^ {
+    "[a-zA-Z0-9_]*".r ~ ":" ~ dataType ^^ {
       case name ~ _ ~ tpe => StructField(name, tpe, nullable = true)
     }
 

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

@@ -0,0 +1,32 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.hive
+
+import org.scalatest.FunSuite
+
+import org.apache.spark.sql.catalyst.types.{DataType, StructType}
+
+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 datatype = HiveMetastoreTypes.toDataType(metastr)
+    assert(datatype.isInstanceOf[StructType])
+  }
+}