Add --fix-dry-run flag

Fixes #663

Author: sindresorhus

cli.ts

@@ -20,6 +20,7 @@ const cli = meow(
 
   Options
     --fix             Automagically fix issues
+    --fix-dry-run     Automagically fix issues without saving the changes to the file system
     --reporter        Reporter to use
     --space           Use space indent instead of tabs [Default: 2]
     --config          Path to a XO configuration file
@@ -51,6 +52,10 @@ const cli = meow(
 				type: 'boolean',
 				default: false,
 			},
+			fixDryRun: {
+				type: 'boolean',
+				default: false,
+			},
 			reporter: {
 				type: 'string',
 			},
@@ -116,7 +121,7 @@ const baseXoConfigOptions: XoConfigOptions = {
 };
 
 const linterOptions: LinterOptions = {
-	fix: cliOptions.fix,
+	fix: cliOptions.fix || cliOptions.fixDryRun,
 	cwd: (cliOptions.cwd && path.resolve(cliOptions.cwd)) ?? process.cwd(),
 	quiet: cliOptions.quiet,
 	ts: true,
@@ -201,7 +206,7 @@ if (cliOptions.stdin) {
 		}
 	}
 
-	if (cliOptions.fix) {
+	if (linterOptions.fix) {
 		const xo = new Xo(linterOptions, baseXoConfigOptions);
 		const {results: [result]} = await xo.lintText(stdin, {
 			filePath: cliOptions.stdinFilename,

readme.md

@@ -58,6 +58,7 @@ $ xo --help
 
 	Options
 		--fix             Automagically fix issues
+		--fix-dry-run     Automagically fix issues without saving the changes to the file system
 		--reporter        Reporter to use
 		--space           Use space indent instead of tabs [Default: 2]
 		--config          Path to a XO configuration file

test/cli.test.ts

@@ -43,6 +43,15 @@ test('xo --fix', async t => {
 	t.is(fileContent, dedent`console.log('hello');\n`);
 });
 
+test('xo --fix-dry-run', async t => {
+	const filePath = path.join(t.context.cwd, 'test.js');
+	const original = dedent`console.log('hello')\n`;
+	await fs.writeFile(filePath, original, 'utf8');
+	await t.notThrowsAsync($`node ./dist/cli --cwd ${t.context.cwd} --fix-dry-run`);
+	const fileContent = await fs.readFile(filePath, 'utf8');
+	t.is(fileContent, original, 'File should not be modified with --fix-dry-run');
+});
+
 test('xo --fix --space', async t => {
 	const filePath = path.join(t.context.cwd, 'test.js');
 	await fs.writeFile(filePath, dedent`function test() {\n   return true;\n}\n`, 'utf8');
@@ -162,6 +171,11 @@ test('xo --stdin --fix', async t => {
 	t.is(stdout, 'const x = true;');
 });
 
+test('xo --stdin --fix-dry-run', async t => {
+	const {stdout} = await $`echo ${'const x = true'}`.pipe`node ./dist/cli --cwd=${t.context.cwd} --stdin --fix-dry-run`;
+	t.is(stdout, 'const x = true;');
+});
+
 test('xo --stdin --stdin-filename=test.js', async t => {
 	const {stdout} = await $`echo ${'const x = true'}`.pipe`node ./dist/cli --cwd=${t.context.cwd} --stdin --stdin-filename=test.js`;
 	t.true(stdout.includes('test.js'));