feat: support linting from the last tag

Author: Ben Quarmby

Diff for: @commitlint/cli/src/cli.ts

@@ -90,6 +90,11 @@ const cli = yargs(process.argv.slice(2))
 				'lower end of the commit range to lint; applies if edit=false',
 			type: 'string',
 		},
+		'from-last-tag': {
+			description:
+				'uses the last tag as the lower end of the commit range to lint; applies if edit=false and from is not set',
+			type: 'boolean',
+		},
 		'git-log-args': {
 			description:
 				"additional git log arguments as space separated string, example '--first-parent --cherry-pick'",
@@ -237,6 +242,7 @@ async function main(args: MainArgs): Promise<void> {
 		: read({
 				to: flags.to,
 				from: flags.from,
+				fromLastTag: flags['from-last-tag'],
 				last: flags.last,
 				edit: flags.edit,
 				cwd: flags.cwd,
@@ -395,6 +401,7 @@ function checkFromEdit(flags: CliFlags): boolean {
 function checkFromHistory(flags: CliFlags): boolean {
 	return (
 		typeof flags.from === 'string' ||
+		typeof flags['from-last-tag'] === 'boolean' ||
 		typeof flags.to === 'string' ||
 		typeof flags.last === 'boolean'
 	);

Diff for: @commitlint/cli/src/types.ts

@@ -8,6 +8,7 @@ export interface CliFlags {
 	help?: boolean;
 	'help-url'?: string;
 	from?: string;
+	'from-last-tag'?: boolean;
 	'git-log-args'?: string;
 	last?: boolean;
 	format?: string;

Diff for: @commitlint/read/src/read.ts

@@ -9,17 +9,42 @@ import {execa} from 'execa';
 interface GetCommitMessageOptions {
 	cwd?: string;
 	from?: string;
+	fromLastTag?: boolean;
 	to?: string;
 	last?: boolean;
 	edit?: boolean | string;
 	gitLogArgs?: string;
 }
 
+async function getLastTag() {
+	const {stdout} = await execa('git', [
+		'describe',
+		'--abbrev=40',
+		'--always',
+		'--first-parent',
+		'--long',
+		'--tags',
+	]);
+
+	if (stdout.length === 40) {
+		// Hash only means no last tag. Use that as the from ref.
+		return stdout;
+	}
+
+	// Description will be in the format: <tag>-<count>-g<hash>
+	// Example: v3.2.0-11-g9057371a52adaae5180d93fe4d0bb808d874b9fb
+	// Minus zero based (1), dash (1), "g" prefix (1), hash (40) = -43
+	const tagSlice = stdout.lastIndexOf('-', stdout.length - 43);
+
+	return stdout.slice(0, tagSlice);
+}
+
 // Get commit messages
 export default async function getCommitMessages(
 	settings: GetCommitMessageOptions
 ): Promise<string[]> {
-	const {cwd, from, to, last, edit, gitLogArgs} = settings;
+	const {cwd, fromLastTag, to, last, edit, gitLogArgs} = settings;
+	let from = settings.from;
 
 	if (edit) {
 		return getEditCommit(cwd, edit);
@@ -38,6 +63,10 @@ export default async function getCommitMessages(
 		return [output];
 	}
 
+	if (!from && fromLastTag) {
+		from = await getLastTag();
+	}
+
 	let gitOptions: GitOptions = {from, to};
 	if (gitLogArgs) {
 		gitOptions = {

Diff for: docs/reference/cli.md

@@ -22,6 +22,8 @@ Options:
   -H, --help-url       help url in error message                        [string]
   -f, --from           lower end of the commit range to lint; applies if
                        edit=false                                       [string]
+      --from-last-tag  uses the last tag as the lower end of the commit range to
+                       lint; applies if edit=false and from is not set [boolean]
   -o, --format         output format of the results                     [string]
   -p, --parser-preset  configuration preset to use for
                        conventional-commits-parser                      [string]