feat: check stage before entering prompt

@commitlint/cli/fixtures/custom-formatter/formatters/custom.js

@@ -1,3 +1,3 @@
-module.exports = function (report) {
+module.exports = function(_report) {
 	return 'custom-formatter-ok';
-}
+};

@commitlint/load/fixtures/formatter-local-module/formatters/custom.js

@@ -1,3 +1,3 @@
-module.exports = function (report) {
+module.exports = function(_report) {
 	return 'ok';
-}
+};

@commitlint/load/src/index.js

@@ -54,7 +54,8 @@ export default async (seed = {}, options = {cwd: process.cwd()}) => {
 
 	// Resolve config-relative formatter module
 	if (typeof config.formatter === 'string') {
-		preset.formatter = resolveFrom.silent(base, config.formatter) || config.formatter;
+		preset.formatter =
+			resolveFrom.silent(base, config.formatter) || config.formatter;
 	}
 
 	// Execute rule config functions if needed

@commitlint/prompt-cli/cli.js

@@ -1,7 +1,7 @@
 #!/usr/bin/env node
 const execa = require('execa');
 const meow = require('meow');
-const prompter = require('@commitlint/prompt').prompter;
+const {prompter} = require('@commitlint/prompt');
 
 const HELP = `
 	Usage
@@ -18,7 +18,20 @@ main(meow(HELP)).catch(err => {
 });
 
 function main() {
-	return prompt();
+	return isStageEmpty()
+		.then(empty => {
+			if (empty) {
+				console.log(
+					`Nothing to commit. Stage your changes via "git add" execute "commit" again`
+				);
+				process.exit(1);
+			}
+		})
+		.then(() => prompt());
+}
+
+function isStageEmpty() {
+	return execa('git', ['diff', '--cached']).then(r => r.stdout === '');
 }
 
 function commit(message) {

@commitlint/prompt-cli/cli.test.js

@@ -0,0 +1,25 @@
+import path from 'path';
+import {git} from '@commitlint/test';
+import test from 'ava';
+import execa from 'execa';
+import stream from 'string-to-stream';
+
+const bin = path.join(__dirname, './cli.js');
+
+const cli = (args, options) => {
+	return (input = '') => {
+		const c = execa(bin, args, {
+			capture: ['stdout'],
+			cwd: options.cwd,
+			env: options.env
+		});
+		stream(input).pipe(c.stdin);
+		return c.catch(err => err);
+	};
+};
+
+test('should print warning if stage is empty', async t => {
+	const cwd = await git.bootstrap();
+	const actual = await cli([], {cwd})('foo: bar');
+	t.true(actual.stdout.includes('Nothing to commit.'));
+});

@commitlint/prompt-cli/package.json

@@ -13,7 +13,8 @@
     "commit": "$npm_package_bin_commit",
     "deps": "dep-check",
     "pkg": "pkg-check --skip-main",
-    "lint": "xo"
+    "lint": "xo",
+    "test": "ava -c 4 --verbose"
   },
   "xo": false,
   "repository": {
@@ -31,12 +32,15 @@
   },
   "homepage": "https://github.com/marionebl/commitlint#readme",
   "devDependencies": {
+    "@commitlint/test": "^7.1.2",
     "@commitlint/utils": "^7.1.2",
+    "ava": "^0.25.0",
     "xo": "0.20.3"
   },
   "dependencies": {
     "@commitlint/prompt": "^7.2.1",
     "execa": "0.9.0",
-    "meow": "3.7.0"
+    "meow": "3.7.0",
+    "string-to-stream": "^1.1.1"
   }
 }