`unreachable code after return statement` warning

What version of Next.js are you using?

11.0.1

What version of Node.js are you using?

14.17.0

What browser are you using?

Firefox

What operating system are you using?

Fedora 34

How are you deploying your application?

next start

Describe the Bug

The browser prints the unreachable code after return statement warning. This only happens in production and not with next dev. The error refers to the last return statement of this piece of code so it has something to do with the i18n routing.

Expected Behavior

It doesn’t print the error

To Reproduce

Create a new application with yarn create next-app. Set the following configuration in next.config.js:

module.exports = {
  reactStrictMode: true,
  i18n: {
    defaultLocale: "en",
    locales: ["en"],
  },
}

Run yarn build && yarn start.

[timneutkens]

@smitssjors if you move the last return false into an else it’ll be correctly tree shaken 👍

E.g. this:

export function getDomainLocale(
  path: string,
  locale?: string | false,
  locales?: string[],
  domainLocales?: DomainLocale[]
) {
  if (process.env.__NEXT_I18N_SUPPORT) {
    locale = locale || normalizeLocalePath(path, locales).detectedLocale

    const detectedDomain = detectDomainLocale(domainLocales, undefined, locale)

    if (detectedDomain) {
      return `http${detectedDomain.http ? '' : 's'}://${detectedDomain.domain}${
        basePath || ''
      }${locale === detectedDomain.defaultLocale ? '' : `/${locale}`}${path}`
    }
    return false
  } else {
  	return false
  }
}

Feel free to open a PR changing this. I’ve already verified this will shake it away on https://try.terser.org/

Reference code that is passed to Terser (sort of, it's not exactly this)

// write or paste code here

export function getDomainLocale(
  path,
  locale,
  locales,
  domainLocales
) {
  if (true) {
    locale = locale || normalizeLocalePath(path, locales).detectedLocale

    const detectedDomain = detectDomainLocale(domainLocales, undefined, locale)

    if (detectedDomain) {
      return `http${detectedDomain.http ? '' : 's'}://${detectedDomain.domain}${
        basePath || ''
      }${locale === detectedDomain.defaultLocale ? '' : `/${locale}`}${path}`
    }
    return false
  } else {
  	return false
  }
}

[balazsorban44]

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