[SPARK-15436][SQL] Remove DescribeFunction and ShowFunctions

## What changes were proposed in this pull request?
This patch removes the last two commands defined in the catalyst module: DescribeFunction and ShowFunctions. They were unnecessary since the parser could just generate DescribeFunctionCommand and ShowFunctionsCommand directly.

## How was this patch tested?
Created a new SparkSqlParserSuite.

Author: Reynold Xin <rxin@databricks.com>

Closes #13292 from rxin/SPARK-15436.

4 files changed, 101 insertions, 8 deletions

diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/SparkSqlParser.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/SparkSqlParser.scala
index f85d6062e8..57f534cd9e 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/SparkSqlParser.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/SparkSqlParser.scala
@@ -24,7 +24,7 @@ import org.antlr.v4.runtime.{ParserRuleContext, Token}
 import org.antlr.v4.runtime.tree.TerminalNode
 
 import org.apache.spark.sql.SaveMode
-import org.apache.spark.sql.catalyst.TableIdentifier
+import org.apache.spark.sql.catalyst.{FunctionIdentifier, TableIdentifier}
 import org.apache.spark.sql.catalyst.catalog._
 import org.apache.spark.sql.catalyst.parser._
 import org.apache.spark.sql.catalyst.parser.SqlBaseParser._
@@ -494,6 +494,37 @@ class SparkSqlAstBuilder(conf: SQLConf) extends AstBuilder {
   }
 
   /**
+   * Create a plan for a DESCRIBE FUNCTION command.
+   */
+  override def visitDescribeFunction(ctx: DescribeFunctionContext): LogicalPlan = withOrigin(ctx) {
+    import ctx._
+    val functionName =
+      if (describeFuncName.STRING() != null) {
+        FunctionIdentifier(string(describeFuncName.STRING()), database = None)
+      } else if (describeFuncName.qualifiedName() != null) {
+        visitFunctionName(describeFuncName.qualifiedName)
+      } else {
+        FunctionIdentifier(describeFuncName.getText, database = None)
+      }
+    DescribeFunctionCommand(functionName, EXTENDED != null)
+  }
+
+  /**
+   * Create a plan for a SHOW FUNCTIONS command.
+   */
+  override def visitShowFunctions(ctx: ShowFunctionsContext): LogicalPlan = withOrigin(ctx) {
+    import ctx._
+    if (qualifiedName != null) {
+      val name = visitFunctionName(qualifiedName)
+      ShowFunctionsCommand(name.database, Some(name.funcName))
+    } else if (pattern != null) {
+      ShowFunctionsCommand(None, Some(string(pattern)))
+    } else {
+      ShowFunctionsCommand(None, None)
+    }
+  }
+
+  /**
    * Create a [[CreateFunctionCommand]] command.
    *
    * For example:
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/SparkStrategies.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/SparkStrategies.scala
index c46cecc71f..e40525287a 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/SparkStrategies.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/SparkStrategies.scala
@@ -416,12 +416,6 @@ private[sql] abstract class SparkStrategies extends QueryPlanner[SparkPlan] {
             c.child)
         ExecutedCommandExec(cmd) :: Nil
 
-      case logical.ShowFunctions(db, pattern) =>
-        ExecutedCommandExec(ShowFunctionsCommand(db, pattern)) :: Nil
-
-      case logical.DescribeFunction(function, extended) =>
-        ExecutedCommandExec(DescribeFunctionCommand(function, extended)) :: Nil
-
       case _ => Nil
     }
   }
diff --git a/sql/core/src/test/scala/org/apache/spark/sql/execution/SparkSqlParserSuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/execution/SparkSqlParserSuite.scala
new file mode 100644
index 0000000000..e2858bb475
--- /dev/null
+++ b/sql/core/src/test/scala/org/apache/spark/sql/execution/SparkSqlParserSuite.scala
@@ -0,0 +1,68 @@
+/*
+ * 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.execution
+
+import org.apache.spark.sql.catalyst.FunctionIdentifier
+import org.apache.spark.sql.catalyst.parser.ParseException
+import org.apache.spark.sql.catalyst.plans.PlanTest
+import org.apache.spark.sql.catalyst.plans.logical.LogicalPlan
+import org.apache.spark.sql.execution.command.{DescribeFunctionCommand, ShowFunctionsCommand}
+import org.apache.spark.sql.internal.SQLConf
+
+/**
+ * Parser test cases for rules defined in [[SparkSqlParser]].
+ *
+ * See [[org.apache.spark.sql.catalyst.parser.PlanParserSuite]] for rules
+ * defined in the Catalyst module.
+ */
+class SparkSqlParserSuite extends PlanTest {
+
+  private lazy val parser = new SparkSqlParser(new SQLConf)
+
+  private def assertEqual(sqlCommand: String, plan: LogicalPlan): Unit = {
+    comparePlans(parser.parsePlan(sqlCommand), plan)
+  }
+
+  private def intercept(sqlCommand: String, messages: String*): Unit = {
+    val e = intercept[ParseException](parser.parsePlan(sqlCommand))
+    messages.foreach { message =>
+      assert(e.message.contains(message))
+    }
+  }
+
+  test("show functions") {
+    assertEqual("show functions", ShowFunctionsCommand(None, None))
+    assertEqual("show functions foo", ShowFunctionsCommand(None, Some("foo")))
+    assertEqual("show functions foo.bar", ShowFunctionsCommand(Some("foo"), Some("bar")))
+    assertEqual("show functions 'foo\\\\.*'", ShowFunctionsCommand(None, Some("foo\\.*")))
+    intercept("show functions foo.bar.baz", "Unsupported function name")
+  }
+
+  test("describe function") {
+    assertEqual("describe function bar",
+      DescribeFunctionCommand(FunctionIdentifier("bar", database = None), isExtended = false))
+    assertEqual("describe function extended bar",
+      DescribeFunctionCommand(FunctionIdentifier("bar", database = None), isExtended = true))
+    assertEqual("describe function foo.bar",
+      DescribeFunctionCommand(
+        FunctionIdentifier("bar", database = Option("foo")), isExtended = false))
+    assertEqual("describe function extended f.bar",
+      DescribeFunctionCommand(FunctionIdentifier("bar", database = Option("f")), isExtended = true))
+  }
+
+}
diff --git a/sql/core/src/test/scala/org/apache/spark/sql/execution/command/DDLCommandSuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/execution/command/DDLCommandSuite.scala
index eab1f55712..850fca5852 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/execution/command/DDLCommandSuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/execution/command/DDLCommandSuite.scala
@@ -33,7 +33,7 @@ import org.apache.spark.sql.types.{IntegerType, StringType, StructType}
 
 // TODO: merge this with DDLSuite (SPARK-14441)
 class DDLCommandSuite extends PlanTest {
-  private val parser = new SparkSqlParser(new SQLConf)
+  private lazy val parser = new SparkSqlParser(new SQLConf)
 
   private def assertUnsupported(sql: String, containsThesePhrases: Seq[String] = Seq()): Unit = {
     val e = intercept[ParseException] {