[SPARK-16220][SQL] Revert Change to Bring Back SHOW FUNCTIONS Functionality

## What changes were proposed in this pull request?

- Fix tests regarding show functions functionality
- Revert `catalog.ListFunctions` and `SHOW FUNCTIONS` to return to `Spark 1.X` functionality.

Cherry picked changes from this PR: https://github.com/apache/spark/pull/13413/files

## How was this patch tested?

Unit tests.

Author: Bill Chambers <bill@databricks.com>
Author: Bill Chambers <wchambers@ischool.berkeley.edu>

Closes #13916 from anabranch/master.

python/pyspark/sql/tests.py

@@ -1509,7 +1509,17 @@ class SQLTests(ReusedPySparkTestCase):
         spark.sql("CREATE DATABASE some_db")
         functions = dict((f.name, f) for f in spark.catalog.listFunctions())
         functionsDefault = dict((f.name, f) for f in spark.catalog.listFunctions("default"))
-        self.assertEquals(len(functions), 0)
+        self.assertTrue(len(functions) > 200)
+        self.assertTrue("+" in functions)
+        self.assertTrue("like" in functions)
+        self.assertTrue("month" in functions)
+        self.assertTrue("to_unix_timestamp" in functions)
+        self.assertTrue("current_database" in functions)
+        self.assertEquals(functions["+"], Function(
+            name="+",
+            description=None,
+            className="org.apache.spark.sql.catalyst.expressions.Add",
+            isTemporary=True))
         self.assertEquals(functions, functionsDefault)
         spark.catalog.registerFunction("temp_func", lambda x: str(x))
         spark.sql("CREATE FUNCTION func1 AS 'org.apache.spark.data.bricks'")

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/catalog/SessionCatalog.scala

@@ -855,8 +855,7 @@ class SessionCatalog(
       .map { f => FunctionIdentifier(f, Some(dbName)) }
     val loadedFunctions = StringUtils.filterPattern(functionRegistry.listFunction(), pattern)
       .map { f => FunctionIdentifier(f) }
-    (dbFunctions ++ loadedFunctions)
-      .filterNot(f => FunctionRegistry.functionSet.contains(f.funcName))
+    dbFunctions ++ loadedFunctions
   }
 
 

sql/core/src/test/scala/org/apache/spark/sql/SQLQuerySuite.scala

@@ -80,13 +80,10 @@ class SQLQuerySuite extends QueryTest with SharedSQLContext {
     val functions = Array("ilog", "logi", "logii", "logiii", "crc32i", "cubei", "cume_disti",
       "isize", "ispace", "to_datei", "date_addi", "current_datei")
 
-    assert(sql("SHOW functions").collect().isEmpty)
-
     createFunction(functions)
 
     checkAnswer(sql("SHOW functions"), getFunctions("*"))
-    assert(sql("SHOW functions").collect().size === functions.size)
-    assert(sql("SHOW functions").collect().toSet === functions.map(Row(_)).toSet)
+    assert(sql("SHOW functions").collect().size > 200)
 
     Seq("^c*", "*e$", "log*", "*date*").foreach { pattern =>
       // For the pattern part, only '*' and '|' are allowed as wildcards.

sql/core/src/test/scala/org/apache/spark/sql/internal/CatalogSuite.scala

@@ -174,7 +174,8 @@ class CatalogSuite
   }
 
   test("list functions") {
-    assert(spark.catalog.listFunctions().collect().isEmpty)
+    assert(Set("+", "current_database", "window").subsetOf(
+      spark.catalog.listFunctions().collect().map(_.name).toSet))
     createFunction("my_func1")
     createFunction("my_func2")
     createTempFunction("my_temp_func")
@@ -191,7 +192,8 @@ class CatalogSuite
   }
 
   test("list functions with database") {
-    assert(spark.catalog.listFunctions("default").collect().isEmpty)
+    assert(Set("+", "current_database", "window").subsetOf(
+      spark.catalog.listFunctions().collect().map(_.name).toSet))
     createDatabase("my_db1")
     createDatabase("my_db2")
     createFunction("my_func1", Some("my_db1"))

sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/SQLQuerySuite.scala

@@ -187,6 +187,11 @@ class SQLQuerySuite extends QueryTest with SQLTestUtils with TestHiveSingleton {
   }
 
   test("show functions") {
+    val allBuiltinFunctions = FunctionRegistry.builtin.listFunction().toSet[String].toList.sorted
+    val allFunctions = sql("SHOW functions").collect().map(r => r(0))
+    allBuiltinFunctions.foreach { f =>
+      assert(allFunctions.contains(f))
+    }
     withTempDatabase { db =>
       def createFunction(names: Seq[String]): Unit = {
         names.foreach { name =>