[SPARK-25918][SQL] LOAD DATA LOCAL INPATH should handle a relative path

## What changes were proposed in this pull request?

Unfortunately, it seems that we missed this in 2.4.0. In Spark 2.4, if the default file system is not the local file system, `LOAD DATA LOCAL INPATH` only works in case of absolute paths. This PR aims to fix it to support relative paths. This is a regression in 2.4.0.

```scala
$ ls kv1.txt
kv1.txt

scala> spark.sql("LOAD DATA LOCAL INPATH 'kv1.txt' INTO TABLE t")
org.apache.spark.sql.AnalysisException: LOAD DATA input path does not exist: kv1.txt;
```

## How was this patch tested?

Pass the Jenkins

Closes apache#22927 from dongjoon-hyun/SPARK-LOAD.

Authored-by: Dongjoon Hyun <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>

Author: dongjoon-hyun

sql/core/src/main/scala/org/apache/spark/sql/execution/command/tables.scala

@@ -376,7 +376,8 @@ object LoadDataCommand {
    * @return qualified path object
    */
   private[sql] def makeQualified(defaultUri: URI, workingDir: Path, path: Path): Path = {
-    val pathUri = if (path.isAbsolute()) path.toUri() else new Path(workingDir, path).toUri()
+    val newPath = new Path(workingDir, path)
+    val pathUri = if (path.isAbsolute()) path.toUri() else newPath.toUri()
     if (pathUri.getScheme == null || pathUri.getAuthority == null &&
         defaultUri.getAuthority != null) {
       val scheme = if (pathUri.getScheme == null) defaultUri.getScheme else pathUri.getScheme
@@ -393,7 +394,7 @@ object LoadDataCommand {
           throw new IllegalArgumentException(e)
       }
     } else {
-      path
+      newPath
     }
   }
 }

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

@@ -20,11 +20,13 @@ package org.apache.spark.sql.hive.execution
 import java.io.File
 
 import com.google.common.io.Files
+import org.apache.hadoop.fs.{FileContext, FsConstants, Path}
 
 import org.apache.spark.sql.{AnalysisException, QueryTest, Row, SaveMode}
 import org.apache.spark.sql.catalyst.TableIdentifier
 import org.apache.spark.sql.catalyst.analysis.NoSuchTableException
 import org.apache.spark.sql.catalyst.catalog.{CatalogStorageFormat, CatalogTable, CatalogTableType}
+import org.apache.spark.sql.execution.command.LoadDataCommand
 import org.apache.spark.sql.hive.test.TestHiveSingleton
 import org.apache.spark.sql.test.SQLTestUtils
 import org.apache.spark.sql.types.StructType
@@ -439,4 +441,11 @@ class HiveCommandSuite extends QueryTest with SQLTestUtils with TestHiveSingleto
     }
   }
 
+  test("SPARK-25918: LOAD DATA LOCAL INPATH should handle a relative path") {
+    val localFS = FileContext.getLocalFSFileContext()
+    val workingDir = localFS.getWorkingDirectory
+    val r = LoadDataCommand.makeQualified(
+      FsConstants.LOCAL_FS_URI, workingDir, new Path("kv1.txt"))
+    assert(r === new Path(s"$workingDir/kv1.txt"))
+  }
 }