Add support to Next.js for multiple "app environments" .env files (development, preview, staging, production)

loadAppEnv.js

// loadAppEnv.js
const fs = require('fs')
const dotenvFlow = require('dotenv-flow')

// This module loads .env files from the config/ directory based the "app
// environment" that it is being built for or is running in (e.g. development,
// preview, staging, beta, canary, production, etc..). The "app environment"
// is determined by APP_ENV (if defined) or NODE_ENV. It exports a set of
// environment variables which should be passed to Next.js as the env config.
//
// We do not place .env files in the project root because Next.js loads those
// based on NODE_ENV and is limited to just "development", "production", and
// "test". By using a distinct environment variable we can more easily create
// a "production" build (minified JavaScript, etc...) that uses "development"
// or "staging" application settings. This solution was based on the "proposed
// workaround" described in the following Next.js RFC:
//  - https://github.com/vercel/next.js/discussions/25764

function throwErrorIfConflictingFilesDetected() {
  // we throw an exception if .env files are found in the project root since
  // they can conflict with ours. Someone probably just didn't realize we
  // store .env files in ./config
  fileNames = [
    '.env',
    '.env.local',
    '.env.development',
    '.env.development.local',
    '.env.production',
    '.env.production.local',
    '.env.test',
    '.env.test.local',
  ]
  fileNames.forEach((path) => {
    if (fs.existsSync(path)) {
      throw new Error(
        `env file detected in project root: ${path}. This project requires all .env files to be stored in ./config`
      )
    }
  })
}

function loadAppEnv() {
  throwErrorIfConflictingFilesDetected()
  dotenvFlow.config({
    path: 'config',
    node_env: process.env.APP_ENV || process.env.NODE_ENV || 'development',
  })
}

loadAppEnv()

next.config.js

// next.config.js
require('./loadAppEnv')

module.exports = {
  //...
}

thank you very much! Saved my day

Doesnt this need a return env in line 53?

@asp3 hmmm... I think you're right. However, it seems that code isn't even needed. Maybe it used to be needed but isn't any more. Will update.

Why is this no longer needed? Support for runtime configs is still needed, right?

@tappin-kr the comments on Feb 5 and Feb 7 were related to a different revision so you can ignore. I still use the above code.