allow cjs config files on type module projects

[mrdaniellewis]

↪️ Pull Request

Allow plugins with .js config files to also work with a .cjs extension.

If you have a project with "type": "module" then currently it is impossible to have a javascript config file for a plugin. Either you get a error telling you require isn't allowed using modules, or if you use modules you get an error telling you modules can't be used with require. If you use a cjs file you get a JSON parse error.

This PR allows loadConfig to load a cjs file as js file instead of trying to load it as a json file.

It also updates all plugins that accept a js config file to also accept a cjs config file.

Also see previously reported #6830

💻 Examples

For example if you use the pug transformer, you can now have a config file called:

pug.config.cjs.

Previously it would only allow pug.config.js

🚨 Test instructions

Create a project with "type": "module" in the package.json.

Attempt to use a javascript config file with, for example, a pug template.

// .pugrc.js
module.exports = {
  filters: {
    'custom-filter': function (text, options) {
      return 'FILTERED: ' + text;
    }
  }
}

// index.pug
:custom-filter()
    Hello!

If the .pugrc.js is renamed .pugrc.cjs this will now work without an error.

✔️ PR Todo

• Added/updated unit tests for this change
• Filled out test instructions (In case there aren't any unit tests)
• Included links to related issues/PRs

[devongovett]

Makes sense to me

[optimistiks]

https://github.com/parcel-bundler/parcel/blob/v2/packages/transformers/postcss/src/loadConfig.js#L98

It seems it should check for .cjs here as well