Document how to declare a PostCSS plugin in an ES6/TypeScript module

It’s currently unclear how to properly declare a PostCSS module using ES6 module syntax (which TypeScript also uses idiomatically). The suggested module.exports isn’t idiomatic in these systems.

[nex3]

Okay, I’ve found an incantation that works:

// eslint-disable-next-line @typescript-eslint/no-namespace
namespace plugin {
  export interface Options { … }
}

const plugin: PluginCreator<olugin.Options> = (opts = {}) => { … };
plugin.postcss = true;

export = plugin;

It would be nice if there were an alternative way to declare these plugins that was more module-system friendly—allowing the PluginCreator to be defined as the top-level postcss field, for example.

[romainmenke]

That was from before my time as a maintainer of these plugins so I would have to start digging through old commits.

Most likely this happened :

• someone had an issue with some plugin in esm, deno, webpack, …
• conditional exports were setup with the dual distibution of esm and cjs
• someone fixed the actual issue by changing/adding the rollup config

I don’t dare removing it now 😃