Pattern to programmatically set config values? Runtime config not available in serverless, why?

[eric-burel]

Hi guys,
I still struggle to answer 2 questions in Next 9.4, regarding config:

• What's the preferred pattern to set a public setting, compute dynamically in JavaScript? Example use case: I want to make package.json version available to the client.
  Intuitively I've written this:

const withPkgInfo = (nextConfig) => {
  nextConfig.publicRuntimeConfig.pkgInfo = {
    version: packageJSON.version
  }
}

Note that I can't get this info from environment, hence the idea of using public config.

Which raises even more questions:

• publicRuntimeConfig is not available in serverless environment. Why? I don't see the point/technical reason for this.
• I could set the nextConfig.env value instead. But it's now unclear how to handle public variables this way. Should I name do nextConfig.env.NEXT_PUBLIC_VERSION = packageJSON.version for instance? Is it safe?

I've raised similar question in the .env support RFC but it wasn't the most appropriate place, so I am opening a separate discussion.

Edit: Second use case for the server is passing CORS whitelist.
You may want to preprocess the environment variable, by splitting the array, before including it in the config. It's not doable at this point.

[eric-burel]

Specifically, in the documentation for next.config.js env field, it's recommended to use .env variables, which is indeed more ergonomic when the end user knows the variable, but not valid when it has to be fetched programatically on build time.