fix: ignore empty commit messages conventional-changelog#615

bypass rules for completely empty commit messages (only of blank
lines/comments in message)

Author: Carl Tompkins

@commitlint/lint/src/lint.test.ts

@@ -283,3 +283,34 @@ test('returns original message with commit header, body and footer, parsing comm
 
 	expect(report.input).toBe(expected);
 });
+
+test('positive on comment-only commit message', async () => {
+	const actual = await lint(
+		// '# This is empty\n#This is also a comment',
+		'# comment!',
+		{
+			'header-max-length': [2, 'always', 72]
+		},
+		{
+			parserOpts: {
+				commentChar: '#'
+			}
+		}
+	);
+	expect(actual.valid).toBe(true);
+});
+
+test('positive on blank lines and comment commit message', async () => {
+	const actual = await lint(
+		'\n# Comment\n# Another comment\n',
+		{
+			'header-max-length': [2, 'always', 72]
+		},
+		{
+			parserOpts: {
+				commentChar: '#'
+			}
+		}
+	);
+	expect(actual.valid).toBe(true);
+});

@commitlint/lint/src/lint.ts

@@ -9,14 +9,15 @@ import {
 	LintOptions,
 	LintRuleOutcome,
 	Rule,
-	RuleSeverity
+	RuleSeverity,
+	LintOutcome
 } from '@commitlint/types';
 
 export default async function lint(
 	message: string,
 	rawRulesConfig?: LintRuleConfig,
 	rawOpts?: LintOptions
-) {
+): Promise<LintOutcome> {
 	const opts = rawOpts
 		? rawOpts
 		: {defaultIgnores: undefined, ignores: undefined};
@@ -36,6 +37,20 @@ export default async function lint(
 
 	// Parse the commit message
 	const parsed = await parse(message, undefined, opts.parserOpts);
+	if (
+		parsed.header === null &&
+		parsed.body === null &&
+		parsed.footer === null
+	) {
+		// Commit is empty, skip
+		return {
+			valid: true,
+			errors: [],
+			warnings: [],
+			input: message
+		};
+	}
+
 	const allRules: Map<string, Rule<unknown> | Rule<never>> = new Map(
 		Object.entries(defaultRules)
 	);