Add a default parameter to Database feature flags is_enabled.

This fixes an issue with an inconsistent interface where `check_cache`
and `default` collide.

Related #98

src/platform/BL_Python/platform/feature_flag/caching_feature_flag_router.py

@@ -70,6 +70,9 @@ def feature_is_enabled(self, name: str, default: bool = False) -> bool:
         """
         self._validate_name(name)
 
+        if type(default) != bool:
+            raise TypeError("`default` must be a boolean.")
+
         return self._feature_flags.get(name, default)
 
     def feature_is_cached(self, name: str):

src/platform/BL_Python/platform/feature_flag/db_feature_flag_router.py

@@ -1,6 +1,6 @@
 from abc import ABC
 from logging import Logger
-from typing import Type, cast
+from typing import Type, cast, overload
 
 from injector import inject
 from sqlalchemy import Boolean, Column, Unicode
@@ -103,7 +103,16 @@ def set_feature_is_enabled(self, name: str, is_enabled: bool):
         self._session.commit()
         super().set_feature_is_enabled(name, is_enabled)
 
-    def feature_is_enabled(self, name: str, check_cache: bool = True) -> bool:  # type: ignore reportIncompatibleMethodOverride
+    @overload
+    def feature_is_enabled(self, name: str, default: bool = False) -> bool: ...
+    @overload
+    def feature_is_enabled(
+        self, name: str, default: bool, check_cache: bool = True
+    ) -> bool: ...
+    @override
+    def feature_is_enabled(
+        self, name: str, default: bool = False, check_cache: bool = True
+    ) -> bool:
         """
         Determine whether a feature flag is enabled or disabled.
         This method returns False if the feature flag does not exist in the database.
@@ -112,13 +121,13 @@ def feature_is_enabled(self, name: str, check_cache: bool = True) -> bool:  # ty
         for the specified feature flag. It is only cached if the value is
         pulled from the database. If the flag does not exist, no value is cached.
 
-        name: The feature flag to check.
-
-        check_cache: Whether to use the cached value if it is cached. The default is `True`.
+        :param str name: The feature flag to check.
+        :param bool default: The default value to return when a flag does not exist.
+        :param bool check_cache: Whether to use the cached value if it is cached. The default is `True`.
             If the cache is not checked, the new value pulled from the database will be cached.
         """
         if check_cache and super().feature_is_cached(name):
-            return super().feature_is_enabled(name)
+            return super().feature_is_enabled(name, default)
 
         feature_flag = (
             self._session.query(self._feature_flag)
@@ -128,9 +137,9 @@ def feature_is_enabled(self, name: str, check_cache: bool = True) -> bool:  # ty
 
         if feature_flag is None:
             self._logger.warn(
-                f'Feature flag {name} not found in database. Returning "False" by default.'
+                f'Feature flag {name} not found in database. Returning "{default}" by default.'
             )
-            return False
+            return default
 
         is_enabled = cast(bool, feature_flag.enabled)
 

src/platform/test/unit/feature_flags/test_db_feature_flag_router.py

@@ -67,17 +67,21 @@ def test__feature_is_enabled__defaults_to_false(feature_flag_session: Session):
     assert is_enabled == False
 
 
-def test__feature_is_enabled__defaults_to_false_when_flag_does_not_exist(
+@pytest.mark.parametrize("default", [True, False])
+def test__feature_is_enabled__uses_default_when_flag_does_not_exist(
+    default: bool,
     feature_flag_session: Session,
 ):
     logger = logging.getLogger("FeatureFlagLogger")
     db_feature_flag_router = DBFeatureFlagRouter(
         FeatureFlag, feature_flag_session, logger
     )
 
-    is_enabled = db_feature_flag_router.feature_is_enabled(_FEATURE_FLAG_TEST_NAME)
+    is_enabled = db_feature_flag_router.feature_is_enabled(
+        _FEATURE_FLAG_TEST_NAME, default
+    )
 
-    assert is_enabled == False
+    assert is_enabled == default
 
 
 def test__feature_is_enabled__disallows_empty_name(feature_flag_session: Session):
@@ -187,7 +191,7 @@ def test__feature_is_enabled__checks_cache(
     db_feature_flag_router = DBFeatureFlagRouter(FeatureFlag, session_mock, logger)
 
     _ = db_feature_flag_router.feature_is_enabled(
-        _FEATURE_FLAG_TEST_NAME, check_cache[0]
+        _FEATURE_FLAG_TEST_NAME, False, check_cache[0]
     )
 
     assert feature_is_enabled_mock.call_count == check_cache[1]
@@ -210,7 +214,7 @@ def test__feature_is_enabled__sets_cache(
     db_feature_flag_router = DBFeatureFlagRouter(FeatureFlag, session_mock, logger)
 
     _ = db_feature_flag_router.feature_is_enabled(
-        _FEATURE_FLAG_TEST_NAME, check_cache[0]
+        _FEATURE_FLAG_TEST_NAME, False, check_cache[0]
     )
 
     assert set_feature_is_enabled_mock.call_count == check_cache[1]