feature-flags

por facebook

Gestiona los feature flags de React a través de canales, prueba condicionalmente las gate tests y depura fallos de prueba específicos de flags. Cuatro archivos de flags controlan los valores predeterminados y las anulaciones específicas de canal (canary, www, React Native, test renderer) con flags __VARIANT__ que simulan gatekeepers probados en ambos estados. Usa la pragma @gate flagName para omitir pruebas por completo cuando un flag no está disponible, o gate() en línea para bifurcar aserciones cuando el comportamiento difiere. Agregar un nuevo flag requiere entradas en el archivo principal más todos los archivos fork;...

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')