[SPARK-16458][SQL] SessionCatalog should support `listColumns` for temporary tables

## What changes were proposed in this pull request?

Temporary tables are used frequently, but `spark.catalog.listColumns` does not support those tables. This PR make `SessionCatalog` supports temporary table column listing.

**Before**
```scala
scala> spark.range(10).createOrReplaceTempView("t1")

scala> spark.catalog.listTables().collect()
res1: Array[org.apache.spark.sql.catalog.Table] = Array(Table[name=`t1`, tableType=`TEMPORARY`, isTemporary=`true`])

scala> spark.catalog.listColumns("t1").collect()
org.apache.spark.sql.AnalysisException: Table `t1` does not exist in database `default`.;
```

**After**
```
scala> spark.catalog.listColumns("t1").collect()
res2: Array[org.apache.spark.sql.catalog.Column] = Array(Column[name='id', description='id', dataType='bigint', nullable='false', isPartition='false', isBucket='false'])
```
## How was this patch tested?

Pass the Jenkins tests including a new testcase.

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #14114 from dongjoon-hyun/SPARK-16458.

1 files changed, 25 insertions, 7 deletions

diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/catalog/SessionCatalog.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/catalog/SessionCatalog.scala
index d88b5ffc05..c0ebb2b1fa 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/catalog/SessionCatalog.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/catalog/SessionCatalog.scala
@@ -22,7 +22,7 @@ import javax.annotation.concurrent.GuardedBy
 import scala.collection.mutable
 
 import org.apache.hadoop.conf.Configuration
-import org.apache.hadoop.fs.{FileSystem, Path}
+import org.apache.hadoop.fs.Path
 
 import org.apache.spark.internal.Logging
 import org.apache.spark.sql.AnalysisException
@@ -253,9 +253,27 @@ class SessionCatalog(
   def getTableMetadata(name: TableIdentifier): CatalogTable = {
     val db = formatDatabaseName(name.database.getOrElse(getCurrentDatabase))
     val table = formatTableName(name.table)
-    requireDbExists(db)
-    requireTableExists(TableIdentifier(table, Some(db)))
-    externalCatalog.getTable(db, table)
+    val tid = TableIdentifier(table)
+    if (isTemporaryTable(name)) {
+      CatalogTable(
+        identifier = tid,
+        tableType = CatalogTableType.VIEW,
+        storage = CatalogStorageFormat.empty,
+        schema = tempTables(table).output.map { c =>
+          CatalogColumn(
+            name = c.name,
+            dataType = c.dataType.catalogString,
+            nullable = c.nullable,
+            comment = Option(c.name)
+          )
+        },
+        properties = Map(),
+        viewText = None)
+    } else {
+      requireDbExists(db)
+      requireTableExists(TableIdentifier(table, Some(db)))
+      externalCatalog.getTable(db, table)
+    }
   }
 
   /**
@@ -432,10 +450,10 @@ class SessionCatalog(
   def tableExists(name: TableIdentifier): Boolean = synchronized {
     val db = formatDatabaseName(name.database.getOrElse(currentDb))
     val table = formatTableName(name.table)
-    if (name.database.isDefined || !tempTables.contains(table)) {
-      externalCatalog.tableExists(db, table)
+    if (isTemporaryTable(name)) {
+      true
     } else {
-      true // it's a temporary table
+      externalCatalog.tableExists(db, table)
     }
   }