HIVE-29461: Iceberg: HIVE_METASTORE_WAREHOUSE_EXTERNAL is ignored when initializing HiveCatalog

HiveCatalog.initialize() propagated CatalogProperties.WAREHOUSE_LOCATION to the
Hadoop configuration but ignored the equivalent external-warehouse property, so
getExternalWarehouseLocation() and convertToDatabase() failed with an NPE
("Warehouse location is not set: hive.metastore.warehouse.external.dir=null")
whenever a caller reached HiveCatalog through the standard Iceberg
Catalog.initialize(name, properties) API without separately mutating the
Configuration. Callers worked around this either by re-setting the value on the
Configuration before initialize() (HMSCatalogFactory) or by relying on a
side-channel setConf() carrying the value through (IcebergSummaryHandler), and
in both cases used a different, undocumented property key
("external-warehouse" vs "externalwarehouse").

Add HiveCatalog.EXTERNAL_WAREHOUSE_LOCATION ("external-warehouse") as the
canonical catalog property and propagate it from initialize() to
hive.metastore.warehouse.external.dir, mirroring the existing handling for
WAREHOUSE_LOCATION (including LocationUtil.stripTrailingSlash). Update the two
in-tree callers to use the constant and drop HMSCatalogFactory's redundant
configuration.set() workaround. The unhyphenated key in IcebergSummaryHandler
was effectively dead code (HiveCatalog never read it) and is replaced rather
than retained.

Adds testInitializeCatalogWithExternalWarehouseProperty mirroring
testInitializeCatalogWithProperties to lock in the propagation behavior.

Author: 1fanwang

iceberg/iceberg-catalog/src/main/java/org/apache/iceberg/hive/HiveCatalog.java

@@ -78,6 +78,13 @@ public class HiveCatalog extends BaseMetastoreViewCatalog
   public static final String LIST_ALL_TABLES = "list-all-tables";
   public static final String LIST_ALL_TABLES_DEFAULT = "false";
 
+  /**
+   * Catalog property for the external (unmanaged) warehouse location, propagated by
+   * {@link #initialize(String, Map)} to {@code hive.metastore.warehouse.external.dir}.
+   * Mirrors {@link CatalogProperties#WAREHOUSE_LOCATION} which targets the managed warehouse.
+   */
+  public static final String EXTERNAL_WAREHOUSE_LOCATION = "external-warehouse";
+
   public static final String HMS_TABLE_OWNER = "hive.metastore.table.owner";
   public static final String HMS_DB_OWNER = "hive.metastore.database.owner";
   public static final String HMS_DB_OWNER_TYPE = "hive.metastore.database.owner-type";
@@ -115,6 +122,11 @@ public void initialize(String inputName, Map<String, String> properties) {
           LocationUtil.stripTrailingSlash(properties.get(CatalogProperties.WAREHOUSE_LOCATION)));
     }
 
+    if (properties.containsKey(EXTERNAL_WAREHOUSE_LOCATION)) {
+      this.conf.set(HiveConf.ConfVars.HIVE_METASTORE_WAREHOUSE_EXTERNAL.varname,
+          LocationUtil.stripTrailingSlash(properties.get(EXTERNAL_WAREHOUSE_LOCATION)));
+    }
+
     this.listAllTables = Boolean.parseBoolean(properties.getOrDefault(LIST_ALL_TABLES, LIST_ALL_TABLES_DEFAULT));
 
     String fileIOImpl = properties.get(CatalogProperties.FILE_IO_IMPL);

iceberg/iceberg-catalog/src/test/java/org/apache/iceberg/hive/TestHiveCatalog.java

@@ -283,6 +283,22 @@ public void testInitializeCatalogWithProperties() {
         .isEqualTo("/user/hive/testwarehouse");
   }
 
+  @Test
+  public void testInitializeCatalogWithExternalWarehouseProperty() {
+    Map<String, String> properties = Maps.newHashMap();
+    properties.put("warehouse", "/user/hive/testwarehouse/");
+    properties.put(HiveCatalog.EXTERNAL_WAREHOUSE_LOCATION, "/user/hive/external/");
+    HiveCatalog hiveCatalog = new HiveCatalog();
+    hiveCatalog.initialize("hive", properties);
+
+    // Both warehouse properties should be propagated to the Hadoop configuration
+    // and trailing slashes should be stripped (matching the managed warehouse behavior).
+    assertThat(hiveCatalog.getConf().get("hive.metastore.warehouse.dir"))
+        .isEqualTo("/user/hive/testwarehouse");
+    assertThat(hiveCatalog.getConf().get("hive.metastore.warehouse.external.dir"))
+        .isEqualTo("/user/hive/external");
+  }
+
   @Test
   public void testCreateTableTxnBuilder() throws Exception {
     Schema schema = getTestSchema();

iceberg/iceberg-handler/src/main/java/org/apache/iceberg/metasummary/IcebergSummaryHandler.java

@@ -64,7 +64,7 @@ public void initialize(String catalogName, boolean jsonFormat, MetaSummarySchema
     LOG.info("Initializing iceberg summary handler with warehouse:{}，external warehouse:{}，uris:{}",
         mgdWarehouse, extWarehouse, uris);
     propertiesMap.put("warehouse", mgdWarehouse);
-    propertiesMap.put("externalwarehouse", extWarehouse);
+    propertiesMap.put(HiveCatalog.EXTERNAL_WAREHOUSE_LOCATION, extWarehouse);
     propertiesMap.put("uri", uris);
     PrivilegedAction<HiveCatalog> action = () -> {
       HiveCatalog hiveCatalog = new HiveCatalog();

standalone-metastore/metastore-rest-catalog/src/main/java/org/apache/iceberg/rest/HMSCatalogFactory.java

@@ -85,9 +85,7 @@ private Catalog createCatalog() {
     }
     final String configExtWarehouse = MetastoreConf.getVar(configuration, MetastoreConf.ConfVars.WAREHOUSE_EXTERNAL);
     if (configExtWarehouse != null) {
-      properties.put("external-warehouse", configExtWarehouse);
-      // HiveCatalog reads this property directly from Configuration, not from properties map
-      configuration.set(MetastoreConf.ConfVars.WAREHOUSE_EXTERNAL.getHiveName(), configExtWarehouse);
+      properties.put(HiveCatalog.EXTERNAL_WAREHOUSE_LOCATION, configExtWarehouse);
     }
     if (configuration.get(SERVLET_ID_KEY) != null) {
       // For the testing purpose. HiveCatalog caches a metastore client in a static field. As our tests can spin up