fix(rules): ignore comments in signed-off-by (#2098)

Fix `signed-off-by` rule to ignore lines starting with `#`.

These lines are comments. They are added by `git commit` at the end of
the commit message template to show which files are included in
the commit, and removed from the actual commit message.

Before this change, the rule `signed-off-by` was rejecting pretty much
all commit messages created by `git commit` from the command line.

With this change in place, the rule ignores commits and accepts commit
message created by `git commit` from the command line.

Signed-off-by: Miroslav Bajtoš <mbajtoss@gmail.com>

@commitlint/rules/src/signed-off-by.test.ts

@@ -7,6 +7,15 @@ const messages = {
 	without: `test: subject\nbody\nfooter\n\n`,
 	inSubject: `test: subject Signed-off-by:\nbody\nfooter\n\n`,
 	inBody: `test: subject\nbody Signed-off-by:\nfooter\n\n`,
+	withSignoffAndComments: `test: subject
+
+message body
+
+Signed-off-by:
+
+# Please enter the commit message for your changes. Lines starting
+# with '#' will be ignored, and an empty message aborts the commit.
+`,
 };
 
 const parsed = {
@@ -15,6 +24,7 @@ const parsed = {
 	without: parse(messages.without),
 	inSubject: parse(messages.inSubject),
 	inBody: parse(messages.inBody),
+	withSignoffAndComments: parse(messages.withSignoffAndComments),
 };
 
 test('empty against "always signed-off-by" should fail', async () => {
@@ -57,6 +67,16 @@ test('without against "never signed-off-by" should succeed', async () => {
 	expect(actual).toEqual(expected);
 });
 
+test('trailing comments should be ignored', async () => {
+	const [actual] = signedOffBy(
+		await parsed.withSignoffAndComments,
+		'always',
+		'Signed-off-by:'
+	);
+	const expected = true;
+	expect(actual).toEqual(expected);
+});
+
 test('inSubject against "always signed-off-by" should fail', async () => {
 	const [actual] = signedOffBy(
 		await parsed.inSubject,

@commitlint/rules/src/signed-off-by.ts

@@ -7,7 +7,14 @@ export const signedOffBy: SyncRule<string> = (
 	when = 'always',
 	value = ''
 ) => {
-	const lines = toLines(parsed.raw).filter(Boolean);
+	const lines = toLines(parsed.raw).filter(
+		(ln) =>
+			// skip comments
+			!ln.startsWith('#') &&
+			// ignore empty lines
+			Boolean(ln)
+	);
+
 	const last = lines[lines.length - 1];
 
 	const negated = when === 'never';