feature-flags

What this skill does

When applied, it prepends a system prompt before your request is sent — no extra calls and no change to how you are billed beyond the added tokens.

---
name: feature-flags
description: Use when feature flag tests fail, flags need updating, understanding @gate pragmas, debugging channel-specific test failures, or adding new flags to React.
---

# 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:

```javascript
// @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:

```javascript
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

1. Add to `ReactFeatureFlags.js` with default value
2. Add to each fork file (`*.www.js`, `*.native-fb.js`, etc.)
3. If it should vary in www/RN, set to `__VARIANT__` in the fork file
4. 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):

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

## Debugging Channel-Specific Failures

1. Run `

Use this skill

{
  "model": "gpt-4o-mini",
  "skill": "imp-eac289a8-aed5-4627-add4-f533c7a9ae90",
  "messages": [{ "role": "user", "content": "…" }]
}

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