fix: Reasons for environment default flags by bakirFS · Pull Request #347 · Flagsmith/flagsmith-engine

bakirFS · 2026-09-30T09:36:31Z

Closes #341

When a flag falls back to its environment default, the engine always returned the DEFAULT reason.

Now:

STATIC if no segment overrides the feature
DEFAULT if the feature has segment overrides, but none matched

coderabbitai · 2026-09-30T09:36:46Z

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📝 Walkthrough

Walkthrough

Feature evaluation now assigns DEFAULT when segment overrides target a feature and STATIC when they do not. Dependency resolution applies the same distinction through its feature-to-segment index when no override matches. Unit tests update expected reasons and cover an unmatched segment override. The engine test-data subproject reference also changes.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Severity of issue fixed: Low

Merge Risk: ⚪ Minimal · up to fdf04

The fallback reasons align with the requested STATIC versus DEFAULT distinction. The test-data revision discrepancy does not change fixture contents; this change is mergeable subject to normal checks.

Architecture Summary

Architecture risk: 🔵 Low · up to fdf04

The change affects 2 systems.

Changed systems: tests, flag_engine

Architecture concerns
No architecture-level concerns identified.

Review details

Systems and components

observed — tests (service) was modified; 2 changed files map to changed impact.
observed — flag_engine (service) was modified; 1 changed file maps to changed impact.

Before / after behavior

observed — Modified behavior in flag_engine/segments/evaluator.py: evaluate_features now collects feature names targeted by segment overrides before evaluating features.
observed — Modified behavior in flag_engine/segments/evaluator.py: Fallback reasons now come from get_fallback_reason rather than always being DEFAULT; features targeted by any segment get DEFAULT, while untargeted features get STATIC. The new helper gathers override feature names across all segments and applies that rule.
observed — Modified behavior in flag_engine/segments/evaluator.py: Adds get_targeted_feature_names to collect override names from segment contexts and get_fallback_reason to return DEFAULT for targeted features and STATIC otherwise.
observed — Modified behavior in flag_engine/segments/evaluator.py: When dependency resolution finds no matching segment override, the fallback reason now uses the feature’s segment-key index: DEFAULT if it appears in that index, otherwise STATIC, replacing the unconditional DEFAULT.

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Actionable comments posted: 1

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flag_engine/segments/evaluator.py
tests/unit/test_engine.py

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github-actions · 2026-09-30T13:29:37Z

File	Coverage		Missing
All files	`100%`	✅

Minimum allowed coverage is 100%

Generated by 🐒 cobertura-action against fdf0448

codspeed · 2026-09-30T13:30:18Z

Merging this PR will not alter performance

✅ 1 untouched benchmark

_{Comparing fix/reason-environment-default (fdf0448) with main (31dc381)}

khvn26

Just a couple changes needed.

khvn26 · 2026-10-06T15:27:48Z

+def test_get_evaluation_result__unmatched_segment_override__returns_default_reason(
+    context: EvaluationContext,
+) -> None:
+    # Given
+    context["segments"] = {
+        "1": {
+            "key": "1",
+            "name": "unmatched_segment",
+            "rules": [
+                {
+                    "type": "ALL",
+                    "conditions": [
+                        {"property": "foo", "operator": "EQUAL", "value": "no match"}
+                    ],
+                }
+            ],
+            "overrides": [
+                {
+                    "key": "4",
+                    "name": "feature_1",
+                    "enabled": False,
+                    "value": "segment_override",
+                }
+            ],
+        }
+    }
+
+    # When
+    result = get_evaluation_result(context)
+
+    # Then
+    assert result["flags"]["feature_1"]["reason"] == "DEFAULT"
+    assert result["flags"]["feature_2"]["reason"] == "STATIC"


Remove this; engine-test-data covers it.

khvn26 · 2026-10-06T15:28:14Z

Please pin to https://github.com/Flagsmith/engine-test-data/releases/tag/v3.12.0.

khvn26 · 2026-10-06T15:31:27Z

+    """
+    Get the reason for a flag evaluated to its environment default.
+
+    `DEFAULT` if the feature has targeting rules that did not match,


DEFAULT if the feature has targeting rules that did not match,

@matthewelwell is this the behaviour we're looking for? I was under the impression that we'd decided to reserve DEFAULT for SDK-side defaults?

The implementation is correct (I checked the issue body with @aepfli back in September)

In that case, we need another PR to engine-test-data adding a test case for DEFAULT.

@bakirFS

bakirFS added 2 commits September 28, 2026 13:19

started work

95ecea7

simplified syntax

1549b48

bakirFS requested a review from a team as a code owner September 30, 2026 09:36

bakirFS requested review from emyller and removed request for a team September 30, 2026 09:36

coderabbitai Bot reviewed Sep 30, 2026

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Comment thread tests/unit/test_engine.py

bakirFS mentioned this pull request Sep 30, 2026

feat: expect STATIC reason for features without segment overrides Flagsmith/engine-test-data#61

Merged

deps: Point engine-test-data at aceb9e1 (pending release)

fdf0448

khvn26 changed the title ~~fix: reason environment default~~ fix: Reasons for environment default Oct 6, 2026

flagsmith-engineering Bot assigned emyller Oct 6, 2026

khvn26 changed the title ~~fix: Reasons for environment default~~ fix: Reasons for environment default flags Oct 6, 2026

khvn26 requested changes Oct 6, 2026

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khvn26 reviewed Oct 6, 2026

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fix: Reasons for environment default flags - #347

fix: Reasons for environment default flags#347
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bakirFS commented Sep 30, 2026

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bakirFS commented Sep 30, 2026

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Merging this PR will not alter performance

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coderabbitai Bot commented Sep 30, 2026 •

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