issue with localePath in monorepo when deployed to Vercel

[jakubHynek]

Describe the bug

We have this project structure, where I need to deploy one app from monorepo to Vercel, I created simpified reprocudction in GitHub repo.
The problem is with next-i18next.config.js and localePath. When I use path.resolve('./public/locales'), then the serverless function on Vercel can't find the locale files, when I use path.resolve('./packages/parent/public/locales'), then the pre-rendering function can't find the locale files, so there is this problem in recognizing if the config is in getStaticProps or getServerSideProps and I cant get it to work. Right now the config looks like this:

/* next-i18next.config.js */
const path = require('path');

module.exports = {
    i18n: {
      defaultLocale: 'cs',
      locales: ['en', 'cs'],
      localePath: process.env.VERCEL ? path.resolve('./packages/parent/public/locales') : path.resolve('./public/locales')
    },
  };

I tried to play with process.browser and typeof window === 'undefined' but that did not help.

When path.resolve('./public/locales') it crashes when trying to load SSR rendered page with error:

info  - Loaded env from /var/task/.env
2021-11-29T13:47:12.977Z	0e7d42ba-aaae-4c84-bb41-96a5a3fb6847	ERROR	Error: ENOENT: no such file or directory, scandir '/var/task/public/locales/en'
    at Object.readdirSync (fs.js:1047:3)
    at getLocaleNamespaces (/var/task/node_modules/next-i18next/dist/commonjs/config/createConfig.js:175:23)
    at /var/task/node_modules/next-i18next/dist/commonjs/config/createConfig.js:181:20
    at Array.map (<anonymous>)
    at getNamespaces (/var/task/node_modules/next-i18next/dist/commonjs/config/createConfig.js:180:44)
    at createConfig (/var/task/node_modules/next-i18next/dist/commonjs/config/createConfig.js:221:29)
    at _callee$ (/var/task/node_modules/next-i18next/dist/commonjs/serverSideTranslations.js:199:53)
    at tryCatch (/var/task/node_modules/regenerator-runtime/runtime.js:63:40)
    at Generator.invoke [as _invoke] (/var/task/node_modules/regenerator-runtime/runtime.js:294:22)
    at Generator.next (/var/task/node_modules/regenerator-runtime/runtime.js:119:21) {
  errno: -2,
  syscall: 'scandir',
  path: '/var/task/public/locales/en',
  page: '/'
}
RequestId: 0e7d42ba-aaae-4c84-bb41-96a5a3fb6847 Error: Runtime exited with error: exit status 1
Runtime.ExitError

When path.resolve('./package/parent/public/locales') it crashes during build with exit message:

Error occurred prerendering page "/en". Read more: https://nextjs.org/docs/messages/prerender-error
Error: ENOENT: no such file or directory, scandir '/vercel/path0/packages/parent/packages/parent/public/locales/en'
     at Object.readdirSync (fs.js:1047:3)
     at getLocaleNamespaces (/vercel/path0/node_modules/next-i18next/dist/commonjs/config/createConfig.js:175:23)
     at /vercel/path0/node_modules/next-i18next/dist/commonjs/config/createConfig.js:181:20
     at Array.map (<anonymous>)
     at getNamespaces (/vercel/path0/node_modules/next-i18next/dist/commonjs/config/createConfig.js:180:44)
     at createConfig (/vercel/path0/node_modules/next-i18next/dist/commonjs/config/createConfig.js:221:29)
     at _callee$ (/vercel/path0/node_modules/next-i18next/dist/commonjs/serverSideTranslations.js:199:53)
     at tryCatch (/vercel/path0/node_modules/regenerator-runtime/runtime.js:63:40)
     at Generator.invoke [as _invoke] (/vercel/path0/node_modules/regenerator-runtime/runtime.js:294:22)
     at Generator.next (/vercel/path0/node_modules/regenerator-runtime/runtime.js:119:21)}
RequestId: 1d6d712f-02d3-4029-8277-7bf418949555 Error: Runtime exited with error: exit status 1
Runtime.ExitError

Occurs in next-i18next version

^9.2.0

Steps to reproduce

Reproduction repository:

https://github.com/jakubHynek/lerna-monorepo

There is packages/parent which is basic next app created with yarn create next-app --typescript

packages/child not important for this issue - exports one basic function

Steps

yarn install

npx vercel

• follow the steps of Vercel initialization

• setup vercel project on their site:
  FRAMEWORK PRESET: Next.js
  BUILD COMMAND: yarn workspace parent run build
  OUTPUT DIRECTORY: packages/parent/.next
  leave Root Directory setting empty

• either crash at build or at server side rendered page

[isaachinman]

@jakubHynek This package's repo itself is a monorepo, and the simple example is deployed on Vercel. You may need to change this setting:

[jakubHynek]

So much pain for this mistake. Thank you very much!