feat: Support returning default flags for None identities

Author: khvn26

flag_engine/segments/evaluator.py

@@ -109,7 +109,7 @@ def get_evaluation_result(context: EvaluationContext) -> EvaluationResult:
                     segment_feature_contexts[feature_key] = override_feature_context
 
     identity_key = get_context_value(context, "$.identity.key")
-    flags: typing.List[FlagResult] = [
+    flags: list[FlagResult] = [
         (
             {
                 "enabled": segment_feature_context["enabled"],
@@ -140,7 +140,7 @@ def get_evaluation_result(context: EvaluationContext) -> EvaluationResult:
 
 def get_flag_result_from_feature_context(
     feature_context: FeatureContext,
-    key: SupportsStr,
+    key: typing.Optional[SupportsStr],
 ) -> FlagResult:
     """
     Get a feature value from the feature context
@@ -150,7 +150,7 @@ def get_flag_result_from_feature_context(
     :param key: the key to get the value for
     :return: the value for the key in the feature context
     """
-    if variants := feature_context.get("variants"):
+    if key is not None and (variants := feature_context.get("variants")):
         percentage_value = get_hashed_percentage_for_object_ids(
             [feature_context["key"], key]
         )

tests/unit/segments/test_segments_evaluator.py

@@ -984,7 +984,7 @@ def test_get_evaluation_result__identity_override__returns_expected(
         ),
     ),
 )
-def test_get_flag_result_from_feature_context__call_return_expected(
+def test_get_flag_result_from_feature_context__calls_returns_expected(
     percentage_value: int,
     expected_result: FlagResult,
     mocker: MockerFixture,
@@ -1031,6 +1031,52 @@ def test_get_flag_result_from_feature_context__call_return_expected(
     )
 
 
+def test_get_flag_result_from_feature_context__null_key__calls_returns_expected(
+    mocker: MockerFixture,
+) -> None:
+    # Given
+    expected_feature_context_key = "2"
+    expected_key = None
+
+    # we mock the function which gets the percentage value for an identity to
+    # return a deterministic value so we know which value to expect
+    get_hashed_percentage_for_object_ids_mock = mocker.patch(
+        "flag_engine.segments.evaluator.get_hashed_percentage_for_object_ids",
+    )
+
+    # and have a feature context with some multivariate feature options and associated values
+    feature_context: FeatureContext = {
+        "key": expected_feature_context_key,
+        "feature_key": "1",
+        "enabled": False,
+        "name": "my_feature",
+        "value": "control",
+        "variants": [
+            {"value": "foo", "weight": 30},
+            {"value": "bar", "weight": 30},
+        ],
+    }
+
+    # When
+    result = get_flag_result_from_feature_context(
+        feature_context=feature_context,
+        key=expected_key,
+    )
+
+    # Then
+    # the value of the feature state is correct based on the percentage value returned
+    assert result == {
+        "enabled": False,
+        "feature_key": "1",
+        "name": "my_feature",
+        "reason": "DEFAULT",
+        "value": "control",
+    }
+
+    # the function is not called as there is no key to hash against
+    get_hashed_percentage_for_object_ids_mock.assert_not_called()
+
+
 @pytest.mark.parametrize(
     "property",
     [