feature-flags

작성자: facebook

React 기능 플래그를 채널 전반에 걸쳐 관리하고, 조건부로 게이트 테스트를 수행하며, 플래그별 테스트 실패를 디버깅합니다. 네 개의 플래그 파일이 기본값과 채널별 오버라이드(canary, www, React Native, test renderer)를 제어하며, __VARIANT__ 플래그는 두 상태 모두에서 테스트되는 게이트키퍼를 시뮬레이션합니다. @gate flagName 프래그마를 사용하여 플래그를 사용할 수 없을 때 테스트를 완전히 건너뛰거나, 동작이 다를 때 인라인 gate()를 사용하여 어설션을 분기합니다. 새 플래그를 추가하려면 메인 파일과 모든 포크 파일에 항목을 입력해야 합니다.

npx skills add https://github.com/facebook/react --skill feature-flags

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React Feature Flags

Flag Files

File	Purpose
`packages/shared/ReactFeatureFlags.js`	Default flags (canary), `__EXPERIMENTAL__` overrides
`packages/shared/forks/ReactFeatureFlags.www.js`	www channel, `__VARIANT__` overrides
`packages/shared/forks/ReactFeatureFlags.native-fb.js`	React Native, `__VARIANT__` overrides
`packages/shared/forks/ReactFeatureFlags.test-renderer.js`	Test renderer

Gating Tests

`@gate` pragma (test-level)

Use when the feature is completely unavailable without the flag:

// @gate enableViewTransition
it('supports view transitions', () => {
  // This test only runs when enableViewTransition is true
  // and is SKIPPED (not failed) when false
});

`gate()` inline (assertion-level)

Use when the feature exists but behavior differs based on flag:

it('renders component', async () => {
  await act(() => root.render(<App />));

  if (gate(flags => flags.enableNewBehavior)) {
    expect(container.textContent).toBe('new output');
  } else {
    expect(container.textContent).toBe('legacy output');
  }
});

Adding a New Flag

Add to ReactFeatureFlags.js with default value
Add to each fork file (*.www.js, *.native-fb.js, etc.)
If it should vary in www/RN, set to __VARIANT__ in the fork file
Gate tests with @gate flagName or inline gate()

Checking Flag States

Use /flags to view states across channels. See the flags skill for full command options.

`VARIANT` Flags (GKs)

Flags set to __VARIANT__ simulate gatekeepers - tested twice (true and false):

/test www <pattern>              # __VARIANT__ = true
/test www variant false <pattern> # __VARIANT__ = false

Debugging Channel-Specific Failures

Run /flags --diff <channel1> <channel2> to compare values
Check @gate conditions - test may be gated to specific channels
Run /test <channel> <pattern> to isolate the failure
Verify flag exists in all fork files if newly added

Common Mistakes

Forgetting both variants - Always test www AND www variant false for __VARIANT__ flags
Using @gate for behavior differences - Use inline gate() if both paths should run
Missing fork files - New flags must be added to ALL fork files, not just the main one
Wrong gate syntax - It's gate(flags => flags.name), not gate('name')