Add extensions option

cli.js

@@ -42,6 +42,7 @@ const cli = meow(`
 	  --extend        Extend defaults with a custom config  [Can be set multiple times]
 	  --open          Open files with issues in your editor
 	  --quiet         Show only errors and no warnings
+	  --extension     Additional extension to lint [Can be set multiple times]
 
 	Examples
 	  $ xo
@@ -51,6 +52,7 @@ const cli = meow(`
 	  $ xo --env=node --env=mocha
 	  $ xo --init --esnext
 	  $ xo --plugin=react
+	  $ xo --plugin=html --extension=html
 
 	Tips
 	  Put options in package.json instead of using flags so other tools can read it.

index.js

@@ -28,14 +28,16 @@ exports.lintFiles = (patterns, opts) => {
 	opts = optionsManager.preprocess(opts);
 
 	if (patterns.length === 0) {
-		patterns = '**/*.{js,jsx}';
+		patterns = '**/*';
 	}
 
 	return globby(patterns, {ignore: opts.ignores}).then(paths => {
-		// when users are silly and don't specify an extension in the glob pattern
+		// filter out unwanted file extensions
+		// for silly users that don't specify an extension in the glob pattern
 		paths = paths.filter(x => {
-			const ext = path.extname(x);
-			return ext === '.js' || ext === '.jsx';
+			// Remove dot before the actual extension
+			const ext = path.extname(x).replace('.', '');
+			return opts.extensions.indexOf(ext) !== -1;
 		});
 
 		if (!(opts.overrides && opts.overrides.length > 0)) {

options-manager.js

@@ -22,6 +22,11 @@ const DEFAULT_IGNORE = [
 	'dist/**'
 ];
 
+const DEFAULT_EXTENSION = [
+	'js',
+	'jsx'
+];
+
 const DEFAULT_CONFIG = {
 	useEslintrc: false,
 	cache: true,
@@ -45,7 +50,8 @@ function normalizeOpts(opts) {
 		'ignore',
 		'plugin',
 		'rule',
-		'extend'
+		'extend',
+		'extension'
 	].forEach(singular => {
 		const plural = singular + 's';
 		let value = opts[plural] || opts[singular];
@@ -195,6 +201,7 @@ function preprocess(opts) {
 	opts = mergeWithPkgConf(opts);
 	opts = normalizeOpts(opts);
 	opts.ignores = DEFAULT_IGNORE.concat(opts.ignores || []);
+	opts.extensions = DEFAULT_EXTENSION.concat(opts.extensions || []);
 	return opts;
 }
 

readme.md

@@ -49,6 +49,7 @@ $ xo --help
     --extend        Extend defaults with a custom config  [Can be set multiple times]
     --open          Open files with issues in your editor
     --quiet         Show only errors and no warnings
+    --extension     Additional extension to lint [Can be set multiple times]
 
   Examples
     $ xo
@@ -58,6 +59,7 @@ $ xo --help
     $ xo --env=node --env=mocha
     $ xo --init --esnext
     $ xo --plugin=react
+    $ xo --plugin=html --extension=html
 
   Tips
     Put options in package.json instead of using flags so other tools can read it.
@@ -197,6 +199,12 @@ Type: `Array`, `string`
 
 Use one or more [shareable configs](http://eslint.org/docs/developer-guide/shareable-configs.html) to override any of the default rules (like `rules` above).
 
+### extensions
+
+Type: `Array`
+
+Allow more extensions to be linted besides `.js` and `.jsx`. Make sure they're supported by ESLint or an ESLint plugin.
+
 
 ## Config Overrides
 

test/api.js

@@ -77,3 +77,16 @@ test('lintText() - overrides support', async t => {
 	const indexResults = fn.lintText(await readFile(bar, 'utf8'), {filename: index, cwd}).results;
 	t.is(indexResults[0].errorCount, 0, indexResults[0]);
 });
+
+test('.lintFiles() - only accepts whitelisted extensions', async t => {
+	// Markdown files will always produce linter errors and will not be going away
+	const mdGlob = path.join(__dirname, '..', '*.md');
+
+	// No files should be linted = no errors
+	const noOptionsResults = await fn.lintFiles(mdGlob, {});
+	t.is(noOptionsResults.errorCount, 0);
+
+	// Markdown files linted (with no plugin for it) = errors
+	const moreExtensionsResults = await fn.lintFiles(mdGlob, {extensions: ['md']});
+	t.true(moreExtensionsResults.errorCount > 0);
+});

test/options-manager.js

@@ -12,7 +12,8 @@ test('normalizeOpts: makes all the opts plural and arrays', t => {
 		ignore: 'test.js',
 		plugin: 'my-plugin',
 		rule: {'my-rule': 'foo'},
-		extend: 'foo'
+		extend: 'foo',
+		extension: 'html'
 	});
 
 	t.deepEqual(opts, {
@@ -21,7 +22,8 @@ test('normalizeOpts: makes all the opts plural and arrays', t => {
 		ignores: ['test.js'],
 		plugins: ['my-plugin'],
 		rules: {'my-rule': 'foo'},
-		extends: ['foo']
+		extends: ['foo'],
+		extensions: ['html']
 	});
 });