[SPARK-37444][SQL] ALTER NAMESPACE ... SET LOCATION should handle empty location consistently across v1 and v2 command

### What changes were proposed in this pull request?

Currently, there is an inconsistency when handling an empty location for `ALTER NAMESPACE .. SET LOCATION` between v1 and v2 command. In v1 command, an empty string location will result in the `IllegalArgumentException` exception thrown whereas v2 uses the empty string as it is.

This PR proposes to make the behavior consistent by following the v1 command behavior.

### Why are the changes needed?

To make the behavior consistent and the reason for following v1 behavior is that "Spark should be responsible to qualify the user-specified path using its spark/hadoop configs, before passing the path to v2 sources": #34610 (comment)

### Does this PR introduce _any_ user-facing change?

Yes, now the empty string location will result in the `IllegalArgumentException` exception thrown even for v2 catalogs.

### How was this patch tested?

Added a new test

Closes #34686 from imback82/empty_location_fix.

Authored-by: Terry Kim <yuminkim@gmail.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>

Author: imback82

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

@@ -19,6 +19,7 @@ package org.apache.spark.sql.catalyst.catalog
 
 import java.net.URI
 
+import org.apache.hadoop.conf.Configuration
 import org.apache.hadoop.fs.Path
 import org.apache.hadoop.util.Shell
 
@@ -258,6 +259,24 @@ object CatalogUtils {
     new Path(str).toUri
   }
 
+  def makeQualifiedNamespacePath(
+      locationUri: URI,
+      warehousePath: String,
+      hadoopConf: Configuration): URI = {
+    if (locationUri.isAbsolute) {
+      locationUri
+    } else {
+      val fullPath = new Path(warehousePath, CatalogUtils.URIToString(locationUri))
+      makeQualifiedPath(fullPath.toUri, hadoopConf)
+    }
+  }
+
+  def makeQualifiedPath(path: URI, hadoopConf: Configuration): URI = {
+    val hadoopPath = new Path(path)
+    val fs = hadoopPath.getFileSystem(hadoopConf)
+    fs.makeQualified(hadoopPath).toUri
+  }
+
   private def normalizeColumnName(
       tableName: String,
       tableCols: Seq[String],

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

@@ -210,9 +210,7 @@ class SessionCatalog(
    * FileSystem is changed.
    */
   private def makeQualifiedPath(path: URI): URI = {
-    val hadoopPath = new Path(path)
-    val fs = hadoopPath.getFileSystem(hadoopConf)
-    fs.makeQualified(hadoopPath).toUri
+    CatalogUtils.makeQualifiedPath(path, hadoopConf)
   }
 
   private def requireDbExists(db: String): Unit = {
@@ -254,12 +252,7 @@ class SessionCatalog(
   }
 
   private def makeQualifiedDBPath(locationUri: URI): URI = {
-    if (locationUri.isAbsolute) {
-      locationUri
-    } else {
-      val fullPath = new Path(conf.warehousePath, CatalogUtils.URIToString(locationUri))
-      makeQualifiedPath(fullPath.toUri)
-    }
+    CatalogUtils.makeQualifiedNamespacePath(locationUri, conf.warehousePath, hadoopConf)
   }
 
   def dropDatabase(db: String, ignoreIfNotExists: Boolean, cascade: Boolean): Unit = {

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/v2/DataSourceV2Strategy.scala

@@ -22,6 +22,7 @@ import scala.collection.mutable
 
 import org.apache.spark.sql.{SparkSession, Strategy}
 import org.apache.spark.sql.catalyst.analysis.{ResolvedDBObjectName, ResolvedNamespace, ResolvedPartitionSpec, ResolvedTable}
+import org.apache.spark.sql.catalyst.catalog.CatalogUtils
 import org.apache.spark.sql.catalyst.expressions
 import org.apache.spark.sql.catalyst.expressions.{And, Attribute, DynamicPruning, EmptyRow, Expression, Literal, NamedExpression, PredicateHelper, SubqueryExpression}
 import org.apache.spark.sql.catalyst.planning.PhysicalOperation
@@ -38,6 +39,7 @@ import org.apache.spark.sql.errors.{QueryCompilationErrors, QueryExecutionErrors
 import org.apache.spark.sql.execution.{FilterExec, LeafExecNode, LocalTableScanExec, ProjectExec, RowDataSourceScanExec, SparkPlan}
 import org.apache.spark.sql.execution.datasources.{DataSourceStrategy, PushableColumn, PushableColumnBase}
 import org.apache.spark.sql.execution.streaming.continuous.{WriteToContinuousDataSource, WriteToContinuousDataSourceExec}
+import org.apache.spark.sql.internal.StaticSQLConf.WAREHOUSE_PATH
 import org.apache.spark.sql.sources.{BaseRelation, TableScan}
 import org.apache.spark.sql.types.{BooleanType, StringType}
 import org.apache.spark.sql.util.CaseInsensitiveStringMap
@@ -311,10 +313,13 @@ class DataSourceV2Strategy(session: SparkSession) extends Strategy with Predicat
       AlterNamespaceSetPropertiesExec(catalog.asNamespaceCatalog, ns, properties) :: Nil
 
     case SetNamespaceLocation(ResolvedNamespace(catalog, ns), location) =>
+      val warehousePath = session.sharedState.conf.get(WAREHOUSE_PATH)
+      val nsPath = CatalogUtils.makeQualifiedNamespacePath(
+        CatalogUtils.stringToURI(location), warehousePath, session.sharedState.hadoopConf)
       AlterNamespaceSetPropertiesExec(
         catalog.asNamespaceCatalog,
         ns,
-        Map(SupportsNamespaces.PROP_LOCATION -> location)) :: Nil
+        Map(SupportsNamespaces.PROP_LOCATION -> CatalogUtils.URIToString(nsPath))) :: Nil
 
     case CommentOnNamespace(ResolvedNamespace(catalog, ns), comment) =>
       AlterNamespaceSetPropertiesExec(

sql/core/src/test/scala/org/apache/spark/sql/connector/DataSourceV2SQLSuite.scala

@@ -1294,13 +1294,25 @@ class DataSourceV2SQLSuite
       assert(descriptionDf.collect() === Seq(
         Row("Namespace Name", "ns2"),
         Row(SupportsNamespaces.PROP_COMMENT.capitalize, "test namespace"),
-        Row(SupportsNamespaces.PROP_LOCATION.capitalize, "/tmp/ns_test_2"),
+        Row(SupportsNamespaces.PROP_LOCATION.capitalize, "file:/tmp/ns_test_2"),
         Row(SupportsNamespaces.PROP_OWNER.capitalize, defaultUser),
         Row("Properties", ""))
       )
     }
   }
 
+  test("SPARK-37444: ALTER NAMESPACE .. SET LOCATION using v2 catalog with empty location") {
+    val ns = "testcat.ns1.ns2"
+    withNamespace(ns) {
+      sql(s"CREATE NAMESPACE IF NOT EXISTS $ns COMMENT " +
+        "'test namespace' LOCATION '/tmp/ns_test_1'")
+      val e = intercept[IllegalArgumentException] {
+        sql(s"ALTER DATABASE $ns SET LOCATION ''")
+      }
+      assert(e.getMessage.contains("Can not create a Path from an empty string"))
+    }
+  }
+
   private def testShowNamespaces(
       sqlText: String,
       expected: Seq[String]): Unit = {