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| 1 | +# Version-Gated Feature Flags |
| 2 | + |
| 3 | +Canonical guide for evaluating remote feature flags that include a minimum app version. Applies to all teams (Ramp, Perps, Money, Predict, platform selectors, etc.). |
| 4 | + |
| 5 | +## SSOT |
| 6 | + |
| 7 | +| Concern | Location | |
| 8 | +| ------------------------------------ | -------------------------------------------------------------------------------------- | |
| 9 | +| Version comparison + flag validation | [`app/util/remoteFeatureFlag/index.ts`](../../app/util/remoteFeatureFlag/index.ts) | |
| 10 | +| Raw flag storage | `RemoteFeatureFlagController.remoteFeatureFlags` (no client version gating) | |
| 11 | +| Boolean for UI / hooks | Selectors under `app/selectors/featureFlagController/` or `**/selectors/featureFlags/` | |
| 12 | + |
| 13 | +**Always use** `validatedVersionGatedFeatureFlag` in selectors. **Never** duplicate `hasMinimumRequiredVersion` or `validatedVersionGatedFeatureFlag` in feature modules. |
| 14 | + |
| 15 | +`hasMinimumRequiredVersion` is a lower-level helper used inside `validatedVersionGatedFeatureFlag`. Import it from the util only when you need a standalone version check — do not reimplement it. |
| 16 | + |
| 17 | +## Flag shapes |
| 18 | + |
| 19 | +### Standard (preferred) |
| 20 | + |
| 21 | +LaunchDarkly JSON: |
| 22 | + |
| 23 | +```json |
| 24 | +{ |
| 25 | + "enabled": true, |
| 26 | + "minimumVersion": "7.65.0" |
| 27 | +} |
| 28 | +``` |
| 29 | + |
| 30 | +Progressive-rollout wrappers (`{ name, value: { enabled, minimumVersion } }`) are normalized automatically. |
| 31 | + |
| 32 | +### Non-standard configs |
| 33 | + |
| 34 | +Some flags use different property names (e.g. `depositConfig` uses `active` instead of `enabled`). **Map** to the canonical shape before calling the helper: |
| 35 | + |
| 36 | +```typescript |
| 37 | +validatedVersionGatedFeatureFlag({ |
| 38 | + enabled: depositConfig.active ?? false, |
| 39 | + minimumVersion: depositConfig.minimumVersion ?? '', |
| 40 | +}) ?? false; |
| 41 | +``` |
| 42 | + |
| 43 | +### Multi-version flags (controller-processed) |
| 44 | + |
| 45 | +`RemoteFeatureFlagController` resolves flags shaped as `{ versions: { "7.53.0": value, "7.60.0": value } }` at fetch time using `clientVersion`. Consumers read the **processed** value from state — no `validatedVersionGatedFeatureFlag` call needed for that shape. |
| 46 | + |
| 47 | +## Implementation pattern |
| 48 | + |
| 49 | +### 1. Selector (required) |
| 50 | + |
| 51 | +```typescript |
| 52 | +import { createSelector } from 'reselect'; |
| 53 | +import { selectRemoteFeatureFlags } from '../index'; // adjust path |
| 54 | +import { |
| 55 | + validatedVersionGatedFeatureFlag, |
| 56 | + type VersionGatedFeatureFlag, |
| 57 | +} from '../../../util/remoteFeatureFlag'; |
| 58 | + |
| 59 | +export const selectMyFeatureEnabled = createSelector( |
| 60 | + selectRemoteFeatureFlags, |
| 61 | + (remoteFeatureFlags) => { |
| 62 | + const localFlag = process.env.MM_MY_FEATURE_ENABLED === 'true'; |
| 63 | + const remoteFlag = |
| 64 | + remoteFeatureFlags?.myFeature as unknown as VersionGatedFeatureFlag; |
| 65 | + |
| 66 | + return validatedVersionGatedFeatureFlag(remoteFlag) ?? localFlag; |
| 67 | + }, |
| 68 | +); |
| 69 | +``` |
| 70 | + |
| 71 | +- Remote flag wins when valid; `undefined` from the helper triggers env/local fallback. |
| 72 | +- When `OVERRIDE_REMOTE_FEATURE_FLAGS=true`, the helper returns `undefined` so local overrides apply. |
| 73 | + |
| 74 | +### 2. Hook or component |
| 75 | + |
| 76 | +```typescript |
| 77 | +const isEnabled = useSelector(selectMyFeatureEnabled); |
| 78 | +``` |
| 79 | + |
| 80 | +Do not call `getVersion()`, `compare-versions`, or local version helpers in hooks/components. |
| 81 | + |
| 82 | +## Version source |
| 83 | + |
| 84 | +`validatedVersionGatedFeatureFlag` compares against the **native binary version** from `react-native-device-info`'s `getVersion()` — not `package.json`. After a version bump, do a clean native rebuild if gating behaves unexpectedly. |
| 85 | + |
| 86 | +## Forbidden |
| 87 | + |
| 88 | +- Local `function hasMinimumRequiredVersion(...)` copies |
| 89 | +- Inline `compareVersions.compare(getVersion(), minimumVersion, '>=')` for feature flags |
| 90 | +- Duplicate util files under `app/components/UI/**/utils/` or `app/core/redux/slices/**/` |
| 91 | + |
| 92 | +## Related |
| 93 | + |
| 94 | +- [Perps feature flags](../perps/perps-feature-flags.md) — team-specific examples |
| 95 | +- [Compliance OFAC gating](../compliance.md#feature-flag) — real selector using this pattern |
| 96 | +- [`.cursor/rules/version-gated-feature-flags.mdc`](../../.cursor/rules/version-gated-feature-flags.mdc) — Cursor agent rule |
| 97 | +- External: [MetaMask remote feature flags](https://github.com/MetaMask/contributor-docs/blob/main/docs/remote-feature-flags.md) |
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