Implement lint

vite.config.mjs

@@ -16,6 +16,7 @@ export default defineConfig(({ mode }) => {
 		publicDir: false,
 		plugins: [
 			livetrailPublicAssets(),
+			livetrailLint(isDev),
 			vue()
 		],
 		build: {
@@ -62,6 +63,37 @@ export default defineConfig(({ mode }) => {
 	};
 });
 
+function livetrailLint(isDev) {
+	return {
+		name: 'livetrail-lint',
+		apply: 'build',
+		//In `--watch` mode Vite re-runs the whole plugin pipeline (including
+		//buildStart) on every rebuild it triggers from a file change, so this
+		//alone gives re-linting on every save with no separate watchChange
+		//wiring needed.
+		async buildStart() {
+			await runLint(isDev);
+		}
+	};
+}
+
+async function runLint(isDev) {
+	const { ESLint } = await import('eslint');
+	const eslint = new ESLint({ cwd: ROOT });
+	const results = await eslint.lintFiles(['src']);
+
+	const formatter = await eslint.loadFormatter('stylish');
+	const output = await formatter.format(results);
+	if (output) process.stdout.write(output + '\n');
+
+	//Dev keeps watching regardless - the point is fast feedback, not a gate.
+	//Prod aborts the build so bad code can't ship.
+	const hasErrors = results.some((result) => result.errorCount > 0);
+	if (hasErrors && !isDev) {
+		throw new Error('ESLint found errors in src/ - aborting production build.');
+	}
+}
+
 function livetrailPublicAssets() {
 	return {
 		name: 'livetrail-public-assets',