style: throw instructive error for non-existent rules

Author: marionebl

@commitlint/core/src/lint.js

@@ -16,6 +16,20 @@ export default async (message, rules = {}, opts = {}) => {
 	// Parse the commit message
 	const parsed = await parse(message, undefined, opts.parserOpts);
 
+	// Find invalid rules configs
+	const missing = Object.keys(rules).filter(
+		name => typeof implementations[name] !== 'function'
+	);
+
+	if (missing.length > 0) {
+		const names = Object.keys(implementations);
+		throw new RangeError(
+			`Found missing rule names: ${missing.join(
+				', '
+			)}. Supported rule names are: ${names.join(', ')}`
+		);
+	}
+
 	// Validate against all rules
 	const results = entries(rules)
 		.filter(entry => {
@@ -32,6 +46,7 @@ export default async (message, rules = {}, opts = {}) => {
 			}
 
 			const rule = implementations[name];
+
 			const [valid, message] = rule(parsed, when, value);
 
 			return {

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

@@ -52,3 +52,11 @@ test('positive on stub message and opts', async t => {
 	);
 	t.true(actual.valid);
 });
+
+test('should throw for invalid rule names', async t => {
+	const error = await t.throws(
+		lint('foo', {foo: [2, 'always'], bar: [1, 'never']})
+	);
+
+	t.is(error.message.indexOf('Found invalid rule names: foo, bar'), 0);
+});