add service-worker-index.html

fixes #422

src/api/export.ts

@@ -94,7 +94,9 @@ async function _export({
 		const is_html = type === 'text/html';
 
 		if (is_html) {
-			file = file === '' ? 'index.html' : `${file}/index.html`;
+			if (pathname !== '/service-worker-index.html') {
+				file = file === '' ? 'index.html' : `${file}/index.html`;
+			}
 			body = minify_html(body);
 		}
 
@@ -113,7 +115,10 @@ async function _export({
 	});
 
 	async function handle(url: URL) {
-		const pathname = (url.pathname.replace(root.pathname, '') || '/');
+		let pathname = url.pathname;
+		if (pathname !== '/service-worker-index.html') {
+		  pathname = pathname.replace(root.pathname, '') || '/'
+		}
 
 		if (seen.has(pathname)) return;
 		seen.add(pathname);
@@ -138,7 +143,7 @@ async function _export({
 		const range = ~~(r.status / 100);
 
 		if (range === 2) {
-			if (type === 'text/html') {
+			if (type === 'text/html' && pathname !== '/service-worker-index.html') {
 				const urls: URL[] = [];
 
 				const cleaned = clean_html(body);
@@ -181,6 +186,7 @@ async function _export({
 
 	return ports.wait(port)
 		.then(() => handle(root))
+		.then(() => handle(resolve(root.href, 'service-worker-index.html')))
 		.then(() => proc.kill())
 		.catch(err => {
 			proc.kill();

src/core/create_manifests.ts

@@ -45,17 +45,15 @@ export function create_serviceworker_manifest({ manifest_data, output, client_fi
 	client_files: string[];
 	static_files: string;
 }) {
-	let files: string[];
+	let files: string[] = ['/service-worker-index.html'];
 
 	if (fs.existsSync(static_files)) {
-		files = walk(static_files);
+		files = files.concat(walk(static_files));
 	} else {
 		// TODO remove in a future version
 		if (fs.existsSync('assets')) {
 			throw new Error(`As of Sapper 0.21, the assets/ directory should become static/`);
 		}
-
-		files = [];
 	}
 
 	let code = `