Function suggestTurbopack

packages/next-codemod/bin/upgrade.ts:486–557

(
  packageJson: any,
  targetNextVersion: string
)

 *    showing the current dev command as the initial value.
 */
async function suggestTurbopack(
  packageJson: any,
  targetNextVersion: string
): Promise<void> {
  const devScript: string | undefined = packageJson.scripts?.['dev']
  // Turbopack flag was changed from `--turbo` to `--turbopack` in v15.0.1-canary.3
  // PR: https://github.com/vercel/next.js/pull/71657
  // Release: https://github.com/vercel/next.js/releases/tag/v15.0.1-canary.3
  const isAfterTurbopackFlagChange =
    compareVersions(targetNextVersion, '15.0.1-canary.3') >= 0
  const turboPackFlag = isAfterTurbopackFlagChange ? '--turbopack' : '--turbo'

  if (!devScript) {
    console.log(
      `${pc.yellow('⚠')} No "dev" script found in your package.json. Skipping Turbopack suggestion.`
    )
    return
  }

  if (devScript.includes('next dev')) {
    // covers "--turbopack" as well
    if (devScript.includes('--turbo')) {
      if (isAfterTurbopackFlagChange && !devScript.includes('--turbopack')) {
        console.log() // new line
        console.log(
          `${pc.green('✔')} Replaced "--turbo" with "--turbopack" in your dev script.`
        )
        console.log() // new line
        packageJson.scripts['dev'] = devScript.replace('--turbo', '--turbopack')
        return
      }
      return
    }

    const responseTurbopack = await prompts(
      {
        type: 'confirm',
        name: 'enable',
        message: `Enable Turbopack for ${pc.bold('next dev')}?`,
        initial: true,
      },
      { onCancel }
    )

    if (!responseTurbopack.enable) {
      return
    }

    packageJson.scripts['dev'] = devScript.replace(
      'next dev',
      `next dev ${turboPackFlag}`
    )
    return
  }

  console.log(
    `${pc.yellow('⚠')} Could not find "${pc.bold('next dev')}" in your dev script.`
  )