Add support JS objects for extends config option

[ybiquitous]

What is the problem you're trying to solve?

First, assume that there is a pure ESM package for a sharable config named foo-config:

foo-config/package.json:

{
  "name": "foo-config",
  "version": "1.0.0",
  "type": "module",
  "main": "index.js"
}

foo-config/index.js:

export default {
	rules: {
		'color-no-invalid-hex': true,
	},
};

Next, consider a case using foo-config via npm:

package.json:

{
  "dependencies": {
    "foo-config": "^1.0.0",
    "stylelint": "^15.8.0"
  }
}

.stylelintrc.mjs:

import foo from 'foo-config';

export default {
	// Not working => Error [ERR_REQUIRE_ESM]: require() of ES Module ...
	extends: 'foo-config',

	// Still not working => TypeError: Expected `moduleId` to be of type `string`, got `object`
	extends: foo,
};

Running stylelint like this raises the errors above:

echo 'a { color: #f4 }' | npx stylelint --stdin

This means that Stylelint cannot use a pure ESM sharable config with the extends option.

Related: #5291

What solution would you like to see?

I expect Stylelint to work even when using JS objects with extends instead of strings (e.g., package name or path). For example:

$ echo 'a { color: #f4 }' | npx stylelint --stdin

<input css qXAh0i>
 1:12  ✖  Unexpected invalid hex color "#f4"  color-no-invalid-hex

1 problem (1 error, 0 warnings)

I find it works by applying the following patch:

--- a/lib/augmentConfig.js
+++ b/lib/augmentConfig.js
@@ -178,7 +178,13 @@ async function extendConfig(stylelint, config, configDir, rootConfigDir, filePat
 	let resultConfig = originalWithoutExtends;
 
 	for (const extendLookup of normalizedExtends) {
-		const extendResult = await loadExtendedConfig(stylelint, configDir, extendLookup);
+		let extendResult;
+
+		if (typeof extendLookup === 'string') {
+			extendResult = await loadExtendedConfig(stylelint, configDir, extendLookup);
+		} else if (typeof extendLookup === 'object' && extendLookup !== null) {
+			extendResult = { config: extendLookup };
+		}
 
 		if (extendResult) {
 			let extendResultConfig = extendResult.config;

This patch simply uses JS objects if they are passed.

What do you think about this idea? Is there some pitfall?

---

For your information, I refer to the current spec of extends:

stylelint/docs/user-guide/configure.md

Lines 215 to 219 in 16754b1

	The value of `"extends"` is a "locater" (or an array of "locaters") that is ultimately `require()`d. It can fit whatever format works with Node's `require.resolve()` algorithm. That means a "locater" can be:
	- the name of a module in `node_modules` (e.g. `stylelint-config-standard`; that module's `main` file must be a valid JSON configuration)
	- an absolute path to a file (which makes sense if you're creating a JS object in a Node.js context and passing it in) with a `.js` or `.json` extension.
	- a relative path to a file with a `.js` or `.json` extension, relative to the referencing configuration (e.g. if configA has `extends: "../configB"`, we'll look for `configB` relative to configA).