Fix BigQuery namespace miss handling

Report unsupported multipart namespace identifiers as NoSuchNamespaceError so CLI describe can continue to the table candidate without hiding unexpected catalog errors.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: kevinjqliu

pyiceberg/catalog/bigquery_metastore.py

@@ -335,7 +335,7 @@ def load_view(self, identifier: str | Identifier) -> View:
 
     @override
     def load_namespace_properties(self, namespace: str | Identifier) -> Properties:
-        dataset_name = self.identifier_to_database(namespace)
+        dataset_name = self.identifier_to_database(namespace, NoSuchNamespaceError)
 
         try:
             dataset = self.client.get_dataset(DatasetReference(project=self.project_id, dataset_id=dataset_name))

tests/catalog/test_bigquery_metastore.py

@@ -17,13 +17,14 @@
 import os
 from unittest.mock import MagicMock
 
+import pytest
 from google.api_core.exceptions import NotFound
 from google.cloud.bigquery import Dataset, DatasetReference, Table, TableReference
 from google.cloud.bigquery.external_config import ExternalCatalogDatasetOptions, ExternalCatalogTableOptions
 from pytest_mock import MockFixture
 
 from pyiceberg.catalog.bigquery_metastore import ICEBERG_TABLE_TYPE_VALUE, TABLE_TYPE_PROP, BigQueryMetastoreCatalog
-from pyiceberg.exceptions import NoSuchTableError
+from pyiceberg.exceptions import NoSuchNamespaceError, NoSuchTableError
 from pyiceberg.schema import Schema
 
 
@@ -178,3 +179,15 @@ def test_list_namespaces(mocker: MockFixture) -> None:
     assert ("dataset1",) in namespaces
     assert ("dataset2",) in namespaces
     client_mock.list_datasets.assert_called_once()
+
+
+def test_load_namespace_properties_rejects_multipart_namespace(mocker: MockFixture) -> None:
+    client_mock = MagicMock()
+    mocker.patch("pyiceberg.catalog.bigquery_metastore.Client", return_value=client_mock)
+    mocker.patch.dict(os.environ, values={"PYICEBERG_LEGACY_CURRENT_SNAPSHOT_ID": "True"})
+    catalog = BigQueryMetastoreCatalog("test_catalog", **{"gcp.bigquery.project-id": "my-project"})
+
+    with pytest.raises(NoSuchNamespaceError, match="hierarchical namespaces are not supported"):
+        catalog.load_namespace_properties(("dataset", "table"))
+
+    client_mock.get_dataset.assert_not_called()