Change ignoreFiles to be extendable

docs/user-guide/configure.md

@@ -385,8 +385,6 @@ If the globs are absolute paths, they are used as is. If they are relative, they
 - the config's filepath, if the config is a file that Stylelint found a loaded;
 - or `process.cwd()`.
 
-The `ignoreFiles` property is stripped from extended configs: only the root-level config can ignore files.
-
 _Note that this is not an efficient method for ignoring lots of files._ If you want to ignore a lot of files efficiently, use [`.stylelintignore`](ignore-code.md) or adjust your files globs.
 
 ## `processors`

lib/__tests__/ignore.test.js

@@ -245,8 +245,8 @@ test('extending a config that ignores files', async () => {
 	// empty-block.css found
 	expect(results[0].source).toContain('empty-block.css');
 
-	// empty-block.css linted
-	expect(results[0].warnings).toHaveLength(1);
+	// empty-block.css not linted
+	expect(results[0].warnings).toHaveLength(0);
 
 	// invalid-hex.css found
 	expect(results[1].source).toContain('invalid-hex.css');

lib/augmentConfig.js

@@ -58,9 +58,9 @@ async function augmentConfigExtended(stylelint, cosmiconfigResult) {
 	}
 
 	const configDir = path.dirname(cosmiconfigResult.filepath || '');
-	const { ignoreFiles, ...cleanedConfig } = cosmiconfigResult.config;
+	const { config } = cosmiconfigResult;
 
-	const augmentedConfig = await augmentConfigBasic(stylelint, cleanedConfig, configDir);
+	const augmentedConfig = await augmentConfigBasic(stylelint, config, configDir);
 
 	return {
 		config: augmentedConfig,