Add --print-config option

Co-authored-by: teehemkay <tmk@exidia.com>
Signed-off-by: Anders Kaseorg <andersk@mit.edu>

cli-main.js

@@ -31,6 +31,7 @@ const cli = meow(`
 	  --cwd=<dir>       Working directory for files
 	  --stdin           Validate/fix code from stdin
 	  --stdin-filename  Specify a filename for the --stdin option
+	  --print-config    Print the ESLint configuration for the given file
 
 	Examples
 	  $ xo
@@ -41,6 +42,7 @@ const cli = meow(`
 	  $ xo --plugin=react
 	  $ xo --plugin=html --extension=html
 	  $ echo 'const x=true' | xo --stdin --fix
+	  $ xo --print-config=index.js
 
 	Tips
 	  - Add XO to your project with \`npm init xo\`.
@@ -103,6 +105,9 @@ const cli = meow(`
 		cwd: {
 			type: 'string'
 		},
+		printConfig: {
+			type: 'string'
+		},
 		stdin: {
 			type: 'boolean'
 		},
@@ -174,7 +179,21 @@ if (options.nodeVersion) {
 }
 
 (async () => {
-	if (options.stdin) {
+	if (options.printConfig) {
+		if (input.length > 0) {
+			console.error('The `print-config` option must be used with exactly one file name');
+			process.exit(1);
+		}
+
+		if (options.stdin) {
+			console.error('The `print-config` option is not supported on stdin');
+			process.exit(1);
+		}
+
+		options.filename = options.printConfig;
+		const config = xo.getConfig(options);
+		console.log(JSON.stringify(config, null, '\t'));
+	} else if (options.stdin) {
 		const stdin = await getStdin();
 
 		if (options.stdinFilename) {

index.js

@@ -57,6 +57,13 @@ const globFiles = async (patterns, {ignores, extensions, cwd}) => (
 		{ignore: ignores, gitignore: true, cwd}
 	)).filter(file => extensions.includes(path.extname(file).slice(1))).map(file => path.resolve(cwd, file));
 
+const getConfig = options => {
+	const {options: foundOptions, prettierOptions} = mergeWithFileConfig(normalizeOptions(options));
+	options = buildConfig(foundOptions, prettierOptions);
+	const engine = new eslint.CLIEngine(options);
+	return engine.getConfigForFile(options.filename);
+};
+
 const lintText = (string, options) => {
 	const {options: foundOptions, prettierOptions} = mergeWithFileConfig(normalizeOptions(options));
 	options = buildConfig(foundOptions, prettierOptions);
@@ -121,6 +128,7 @@ module.exports = {
 	getFormatter: eslint.CLIEngine.getFormatter,
 	getErrorResults: eslint.CLIEngine.getErrorResults,
 	outputFixes: eslint.CLIEngine.outputFixes,
+	getConfig,
 	lintText,
 	lintFiles
 };

readme.md

@@ -72,6 +72,7 @@ $ xo --help
     --cwd=<dir>       Working directory for files
     --stdin           Validate/fix code from stdin
     --stdin-filename  Specify a filename for the --stdin option
+    --print-config    Print the ESLint configuration for the given file
 
   Examples
     $ xo
@@ -82,6 +83,7 @@ $ xo --help
     $ xo --plugin=react
     $ xo --plugin=html --extension=html
     $ echo 'const x=true' | xo --stdin --fix
+    $ xo --print-config=index.js
 
   Tips
     - Add XO to your project with `npm init xo`.

test/cli-main.js

@@ -167,3 +167,21 @@ test('extension option', async t => {
 	t.is(reports.length, 1);
 	t.true(reports[0].filePath.endsWith('.unknown'));
 });
+
+test('invalid print-config option with stdin', async t => {
+	const msg = 'The `print-config` option is not supported on stdin';
+	try {
+		await main(['--print-config', 'x.js', '--stdin'], {input: 'console.log()\n'});
+	} catch (error) {
+		t.is(error.stderr.trim(), msg);
+	}
+});
+
+test('print-config option requires a single filename', async t => {
+	const msg = 'The `print-config` option must be used with exactly one file name';
+	try {
+		await main(['--print-config', 'x.js', 'y.js']);
+	} catch (error) {
+		t.is(error.stderr.trim(), msg);
+	}
+});

test/print-config.js

@@ -0,0 +1,26 @@
+import path from 'path';
+import test from 'ava';
+import execa from 'execa';
+import tempWrite from 'temp-write';
+import fn from '..';
+
+process.chdir(__dirname);
+
+const main = (arguments_, options) => execa(path.join(__dirname, '../cli-main.js'), arguments_, options);
+
+const hasUnicornPlugin = config => config.plugins.includes('unicorn');
+const hasPrintConfigGlobal = config => Object.keys(config.globals).includes('printConfig');
+
+test('getConfig', async t => {
+	const filepath = await tempWrite('console.log()\n', 'x.js');
+	const options = {filename: filepath, globals: ['printConfig']};
+	const result = fn.getConfig(options);
+	t.true(hasUnicornPlugin(result) && hasPrintConfigGlobal(result));
+});
+
+test('print-config option', async t => {
+	const filepath = await tempWrite('console.log()\n', 'x.js');
+	const {stdout} = await main(['--global=printConfig', '--print-config', filepath]);
+	const result = JSON.parse(stdout);
+	t.true(hasUnicornPlugin(result) && hasPrintConfigGlobal(result));
+});