Feature Flag System

const Disable = false

/**
 * Enables the application to opt-in for preview features based on runtime
 * checks. This is backed by the GITHUB_DESKTOP_PREVIEW_FEATURES environment
 * variable, which is checked for non-development environments.
 */
function enableDevelopmentFeatures(): boolean {
  if (Disable) {
    return false
  }

  if (__DEV__) {
    return true
  }

  if (process.env.GITHUB_DESKTOP_PREVIEW_FEATURES === '1') {
    return true
  }

  return false
}

/** Should the app enable beta features? */
function enableBetaFeatures(): boolean {
  return enableDevelopmentFeatures() || __RELEASE_CHANNEL__ === 'beta'
}

/** Should we show a pull-requests quick view? */
export function enablePullRequestQuickView(): boolean {
  return enableDevelopmentFeatures()
}

import { enablePullRequestQuickView } from '../lib/feature-flag'

class MyComponent extends React.Component {
  render() {
    if (enablePullRequestQuickView()) {
      return <PullRequestQuickView />
    } else {
      return <StandardPullRequestView />
    }
  }
}

/** Should we show a pull-requests quick view? */
export function enablePullRequestQuickView(): boolean {
  return enableDevelopmentFeatures()
}

export function enableReadmeOverwriteWarning(): boolean {
  return enableBetaFeatures()
}

/** Should the app detect Windows Subsystem for Linux as a valid shell? */
export function enableWSLDetection(): boolean {
  return enableBetaFeatures()
}

/**
 * Should we allow x64 apps running under ARM translation to auto-update to
 * ARM64 builds?
 */
export function enableUpdateFromEmulatedX64ToARM64(): boolean {
  if (__DARWIN__) {
    return true  // Always enabled on macOS
  }

  return enableBetaFeatures()
}

export const enableCommitMessageGeneration = (account: Account) => {
  return (
    (account.features ?? []).includes(
      'desktop_copilot_generate_commit_message'
    ) &&
    // IMPORTANT: Do not remove this feature flag without replacing its usages
    // with a check for the `isCopilotDesktopEnabled` property on the account.
    account.isCopilotDesktopEnabled
  )
}

export const enableCustomIntegration = () => true

export const enableResizingToolbarButtons = () => true

export const enableHooksEnvironment = () => true

npm start  # All features enabled automatically

// Good: Clear, descriptive names
export function enablePullRequestQuickView(): boolean
export function enableWSLDetection(): boolean
export function enableReadmeOverwriteWarning(): boolean

// Bad: Vague or unclear names
export function newFeature(): boolean
export function feature1(): boolean

export function enableMyFeature(): boolean {
  return enableDevelopmentFeatures()
}

export const enableMyFeature = () => true

export function enableMyFeature(): boolean {
  if (__DARWIN__) {
    return true
  }
  return enableBetaFeatures()
}

export const enableMyFeature = (account: Account) => {
  return account.features?.includes('my_feature_flag')
}

// Good: Clear separation
if (enableNewEditor()) {
  return <NewEditor />
} else {
  return <LegacyEditor />
}

// Bad: Mixed logic
const editorType = enableNewEditor() ? 'new' : 'legacy'
const config = { ...baseConfig, type: editorType }

# Search for feature flag usage
grep -r "enableMyFeature" app/src/

# Search in TypeScript files only  
find app/src -name "*.ts*" -exec grep -l "enableMyFeature" {} \;

const Disable = false

function enableDevelopmentFeatures(): boolean {
  if (Disable) {
    return false  // Immediately disable all features
  }
  // ... rest of logic
}

describe('feature flags', () => {
  it('enables preview features in development', () => {
    // Mock __DEV__ = true
    expect(enableDevelopmentFeatures()).toBe(true)
  })

  it('respects environment variable', () => {
    process.env.GITHUB_DESKTOP_PREVIEW_FEATURES = '1'
    expect(enableDevelopmentFeatures()).toBe(true)
  })
})