apple-browsers: Skill for Claude Code

Add or change a feature flag

Flags live in FeatureFlag.swift in iOS/LocalPackages/FeatureFlags-iOS/Sources/FeatureFlags/ and macOS/LocalPackages/FeatureFlags-macOS/Sources/FeatureFlags/. Copy the shape of the neighbouring cases; the steps below cover what the neighbours don't show.

1. Get the flag's Asana task URL from the user. The flag case carries it as a /// doc comment, and so does its subfeature.
2. Add the subfeature the remote config controls:
   • iOS only: iOSBrowserConfigSubfeature.swift, next to FeatureFlag.swift.
   • macOS only: MacOSBrowserConfigSubfeature in SharedPackages/BrowserServicesKit/Sources/PrivacyConfig/Features/PrivacyFeature.swift.
   • A feature with its own parent, such as AIChatSubfeature: that parent's enum in the same PrivacyFeature.swift.
3. Add the flag case and its Config(...) entry in the config switch. source is .remoteReleasable(<Subfeature>.case), or .disabled to switch the flag off everywhere.
   • defaultValue applies only while the remote config doesn't list the subfeature. Once the config lists it, the config decides for everyone, internal users included. .internalOnly is the usual starting point.
   • Keep supportsLocalOverriding at its default true unless the flag must not be toggled from the debug menu. macOS UI tests crash at launch when they set a flag that doesn't allow it.
   • macOS: pass category: (FeatureFlagCategory.swift) to group the flag in the debug menu.
4. Gate the code with featureFlagger.isFeatureOn(.flag) on an injected FeatureFlagger; on iOS, default the parameter to AppDependencyProvider.shared.featureFlagger. When the flag picks between two UI implementations that bind at launch, read it once at startup instead, as FireModeCapability.resolve(using:) does in MainCoordinator, so a mid-session toggle can't leave the UI half-switched.
5. Experiment (A/B/N):
   • Nest a <Name>Cohort: String, FeatureFlagCohortDescribing enum in FeatureFlag and pass it as cohortType:.
   • featureFlagger.resolveCohort(for: .flag) enrolls the device, so call it only where the user meets the difference. Anywhere else, read with assignedCohort(for:), which never enrolls.
   • Fire metrics with PixelKit.fireExperimentPixel (PixelExperimentKit), and declare them under the experiment in {iOS,macOS}/PixelDefinitions/pixels/native_experiments.json5.
6. Test both states with the platform's mock: on iOS, MockFeatureFlagger(enabledFeatureFlags: [.flag]) from iOS/SharedTestUtils; on macOS and in SharedPackages, the PrivacyConfig MockFeatureFlagger with featuresStub[flag.rawValue] set.
7. Tell the user that the rollout happens in the duckduckgo/privacy-configuration repository, under the subfeature name from step 2. The embedded config files in this repository are generated copies, so editing them turns nothing on.

Done when the flag compiles on every platform it targets, both of its states are tested, and the user has the subfeature name to add to privacy-configuration.