feat(rules): add async promise based rules methods into lint

Author: ogomozov-godaddy

@commitlint/lint/src/index.js

@@ -119,7 +119,7 @@ export default async (message, rules = {}, opts = {}) => {
 	}
 
 	// Validate against all rules
-	const results = toPairs(rules)
+	const results = await Promise.all(toPairs(rules)
 		.filter(entry => {
 			const [, [level]] = toPairs(entry);
 			return level > 0;
@@ -134,17 +134,25 @@ export default async (message, rules = {}, opts = {}) => {
 			}
 
 			const rule = mergedImplementations[name];
-
-			const [valid, message] = rule(parsed, when, value);
-
-			return {
-				level,
-				valid,
-				name,
-				message
-			};
+			const ruleOutput = rule(parsed, when, value);
+			if (ruleOutput instanceof Promise) {
+				return ruleOutput.then(([valid, message]) => ({
+					level,
+					valid,
+					name,
+					message
+				}));
+			} else {
+				const [valid, message] = ruleOutput;
+				return Promise.resolve({
+					level,
+					valid,
+					name,
+					message
+				});
+			}
 		})
-		.filter(Boolean);
+		.filter(Boolean));
 
 	const errors = results.filter(result => result.level === 2 && !result.valid);
 	const warnings = results.filter(

@commitlint/lint/src/index.test.js

@@ -252,6 +252,26 @@ test('passes for custom plugin rule', async t => {
 	t.true(report.valid);
 });
 
+test('passes for custom plugin rule if rule is a Promise', async t => {
+	const report = await lint(
+		'somehting #1',
+		{
+			'plugin-rule': [2, 'never']
+		},
+		{
+			plugins: {
+				'plugin-example': {
+					rules: {
+						'plugin-rule': () => Promise.resolve([true])
+					}
+				}
+			}
+		}
+	);
+
+	t.true(report.valid);
+});
+
 test('returns original message only with commit header', async t => {
 	const message = 'foo: bar';
 	const report = await lint(message);