Add feature flag for Presto expand data

docs/installation.rst

@@ -1185,7 +1185,8 @@ You can enable or disable features with flag from ``superset_config.py``:
 
      DEFAULT_FEATURE_FLAGS = {
          'CLIENT_CACHE': False,
-         'ENABLE_EXPLORE_JSON_CSRF_PROTECTION': False
+         'ENABLE_EXPLORE_JSON_CSRF_PROTECTION': False,
+         'PRESTO_EXPAND_DATA': False,
      }
 
 Here is a list of flags and descriptions:
@@ -1195,3 +1196,7 @@ Here is a list of flags and descriptions:
   * For some security concerns, you may need to enforce CSRF protection on all query request to explore_json endpoint. In Superset, we use `flask-csrf <https://sjl.bitbucket.io/flask-csrf/>`_ add csrf protection for all POST requests, but this protection doesn't apply to GET method.
 
   * When ENABLE_EXPLORE_JSON_CSRF_PROTECTION is set to true, your users cannot make GET request to explore_json. The default value for this feature False (current behavior), explore_json accepts both GET and POST request. See `PR 7935 <https://github.com/apache/incubator-superset/pull/7935>`_ for more details.
+
+* PRESTO_EXPAND_DATA
+
+  * When this feature is enabled, nested types in Presto will be expanded into extra columns and/or arrays. This is experimental, and doesn't work with all nested types.

superset/config.py

@@ -208,6 +208,7 @@
     # Experimental feature introducing a client (browser) cache
     "CLIENT_CACHE": False,
     "ENABLE_EXPLORE_JSON_CSRF_PROTECTION": False,
+    "PRESTO_EXPAND_DATA": False,
 }
 
 # A function that receives a dict of all feature flags

superset/db_engine_specs/presto.py

@@ -30,6 +30,7 @@
 from sqlalchemy.engine.result import RowProxy
 from sqlalchemy.sql.expression import ColumnClause
 
+from superset import is_feature_enabled
 from superset.db_engine_specs.base import BaseEngineSpec
 from superset.exceptions import SupersetTemplateException
 from superset.models.sql_types.presto_sql_types import type_map as presto_type_map
@@ -749,6 +750,9 @@ def expand_data(
         :return: list of all columns(selected columns and their nested fields),
                  expanded data set, listed of nested fields
         """
+        if not is_feature_enabled("PRESTO_EXPAND_DATA"):
+            return columns, data, []
+
         all_columns: List[dict] = []
         # Get the list of all columns (selected fields and their nested fields)
         for column in columns:

tests/db_engine_specs_test.py

@@ -614,6 +614,9 @@ def test_presto_remove_processed_array_columns(self):
         }
         self.assertEqual(array_col_hierarchy, expected_array_col_hierarchy)
 
+    @mock.patch.dict(
+        "superset._feature_flags", {"PRESTO_EXPAND_DATA": True}, clear=True
+    )
     def test_presto_expand_data_with_simple_structural_columns(self):
         cols = [
             {"name": "row_column", "type": "ROW(NESTED_OBJ VARCHAR)"},
@@ -644,6 +647,9 @@ def test_presto_expand_data_with_simple_structural_columns(self):
         self.assertEqual(actual_data, expected_data)
         self.assertEqual(actual_expanded_cols, expected_expanded_cols)
 
+    @mock.patch.dict(
+        "superset._feature_flags", {"PRESTO_EXPAND_DATA": True}, clear=True
+    )
     def test_presto_expand_data_with_complex_row_columns(self):
         cols = [
             {
@@ -684,6 +690,9 @@ def test_presto_expand_data_with_complex_row_columns(self):
         self.assertEqual(actual_data, expected_data)
         self.assertEqual(actual_expanded_cols, expected_expanded_cols)
 
+    @mock.patch.dict(
+        "superset._feature_flags", {"PRESTO_EXPAND_DATA": True}, clear=True
+    )
     def test_presto_expand_data_with_complex_array_columns(self):
         cols = [
             {"name": "int_column", "type": "BIGINT"},