Handle no previous Git tags (#322)

Fixes #316

lib/git-util.js

@@ -1,6 +1,22 @@
 'use strict';
 const execa = require('execa');
 
+const latestTag = () => execa.stdout('git', ['describe', '--abbrev=0']);
+const firstCommit = () => execa.stdout('git', ['rev-list', '--max-parents=0', 'HEAD']);
+
+exports.latestTagOrFirstCommit = async () => {
+	let latest;
+	try {
+		// In case a previous tag exists, we use it to compare the current repo status to.
+		latest = await latestTag();
+	} catch (_) {
+		// Otherwise, we fallback to using the first commit for comparison.
+		latest = await firstCommit();
+	}
+
+	return latest;
+};
+
 exports.hasUpstream = async () => {
 	const {stdout} = await execa('git', ['status', '--short', '--branch', '--porcelain=2']);
 	return /^# branch\.upstream [\w\-/]+$/m.test(stdout);

lib/ui.js

@@ -5,6 +5,7 @@ const chalk = require('chalk');
 const githubUrlFromGit = require('github-url-from-git');
 const isScoped = require('is-scoped');
 const util = require('./util');
+const {latestTagOrFirstCommit} = require('./git-util');
 const version = require('./version');
 
 const prettyVersionDiff = (oldVersion, inc) => {
@@ -30,8 +31,8 @@ const prettyVersionDiff = (oldVersion, inc) => {
 };
 
 const printCommitLog = async repoUrl => {
-	const {stdout: latestTag} = await execa('git', ['describe', '--abbrev=0']);
-	const {stdout: log} = await execa('git', ['log', '--format=%s %h', `${latestTag}..HEAD`]);
+	const latest = await latestTagOrFirstCommit();
+	const {stdout: log} = await execa('git', ['log', '--format=%s %h', `${latest}..HEAD`]);
 
 	if (!log) {
 		return false;
@@ -46,7 +47,7 @@ const printCommitLog = async repoUrl => {
 		})
 		.join('\n');
 
-	const commitRange = util.linkifyCommitRange(repoUrl, `${latestTag}...master`);
+	const commitRange = util.linkifyCommitRange(repoUrl, `${latest}...master`);
 
 	console.log(`${chalk.bold('Commits:')}\n${history}\n\n${chalk.bold('Commit Range:')}\n${commitRange}\n`);