[Feature Request] next.config.js export can be a Promise

[remorses]

Feature request

Is your feature request related to a problem? Please describe.

I need to do asynchronous setup before running the nextjs compilation, such as creating some additional pages, currently i cannot run asynchronous code because the config export must be an object or a function and not a promise

Describe the solution you'd like

The module.exports object can be a promise

// next.config.js
module.exports = new Promise((resolve) => {
    asyncWork().then(
        resolve({
            pageExtensions: ['js', 'jsx', 'ts', 'tsx'],
        }),
    )
})

Nextjs will wait for the promise to finish before compiling

Describe alternatives you've considered

I considered making a webpack plugin or a webpack loader but the pages files created during webpack compilation are not used by nextjs

[jescalan]

We made this plugin to bake in some tasks before build, in case it is helpful: https://github.com/hashicorp/prebuild-webpack-plugin

Another option would be to append an npm script to whatever your "start" command is, like so in package.json

"scripts": {
  "dev": "node some_script.js && next dev"
}

[remorses]

Thank you @jescalan for the suggestions

Unfortunately pages generated after nextjs reads the config are not taken in consideration so using a webpack plugin doesn’t work

I will use an external script temporarily and maybe open a PR