feat(cli): add format option for report output

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

@@ -0,0 +1,6 @@
+module.exports = {
+	formatter: 'custom-formatter',
+	rules: {
+		'type-enum': [2, 'never', ['foo']]
+	}
+};

@commitlint/cli/src/cli.js

@@ -1,7 +1,6 @@
 #!/usr/bin/env node
 require('babel-polyfill'); // eslint-disable-line import/no-unassigned-import
 
-const format = require('@commitlint/format');
 const load = require('@commitlint/load');
 const lint = require('@commitlint/lint');
 const read = require('@commitlint/read');
@@ -63,6 +62,12 @@ const flags = {
 		description: 'lower end of the commit range to lint; applies if edit=false',
 		type: 'string'
 	},
+	format: {
+		alias: 'o',
+		default: null,
+		description: 'output format of the results',
+		type: 'string'
+	},
 	'parser-preset': {
 		alias: 'p',
 		description: 'configuration preset to use for conventional-commits-parser',
@@ -135,6 +140,7 @@ async function main(options) {
 	const loaded = await load(getSeed(flags), loadOpts);
 	const parserOpts = selectParserOpts(loaded.parserPreset);
 	const opts = parserOpts ? {parserOpts} : {parserOpts: {}};
+	const format = loadFormatter(loaded, flags);
 
 	// Strip comments if reading from `.git/COMMIT_EDIT_MSG`
 	if (range.edit) {
@@ -248,6 +254,19 @@ function selectParserOpts(parserPreset) {
 	return parserPreset.parserOpts;
 }
 
+function loadFormatter(config, flags) {
+	const moduleName = flags.format || config.formatter;
+	let modulePath;
+
+	try {
+		modulePath = require.resolve(`${moduleName}`);
+	} catch (error) {
+		throw new Error(`Using format ${moduleName}, but cannot find the module.`);
+	}
+
+	return require(modulePath);
+}
+
 // Catch unhandled rejections globally
 process.on('unhandledRejection', (reason, promise) => {
 	console.log('Unhandled Rejection at: Promise ', promise, ' reason: ', reason);

@commitlint/cli/src/cli.test.js

@@ -239,6 +239,30 @@ test('should not print full commit message when input succeeds', async t => {
 	t.is(actual.code, 0);
 });
 
+test('should fail for invalid formatters from configuration', async t => {
+	const cwd = await git.bootstrap('fixtures/custom-formatter');
+	const actual = await cli([], {cwd})('foo: bar');
+	t.true(
+		actual.stderr.includes(
+			`Using format custom-formatter, but cannot find the module`
+		)
+	);
+	t.is(actual.stdout, '');
+	t.is(actual.code, 1);
+});
+
+test('should fail for invalid formatters from flags', async t => {
+	const cwd = await git.bootstrap('fixtures/custom-formatter');
+	const actual = await cli(['--format', 'through-flag'], {cwd})('foo: bar');
+	t.true(
+		actual.stderr.includes(
+			`Using format through-flag, but cannot find the module`
+		)
+	);
+	t.is(actual.stdout, '');
+	t.is(actual.code, 1);
+});
+
 async function writePkg(payload, options) {
 	const pkgPath = path.join(options.cwd, 'package.json');
 	const pkg = JSON.parse(await sander.readFile(pkgPath));