await: rethrow error when there is no catch block, fixes sveltejs#5129

src/runtime/internal/await_block.ts

@@ -59,6 +59,10 @@ export function handle_promise(promise, info) {
 			update(info.then, 1, info.value, value);
 			set_current_component(null);
 		}, error => {
+			if (info.current === info.catch && info.error === undefined) {
+				// when no catch block is present
+				throw error;
+			}
 			set_current_component(current_component);
 			update(info.catch, 2, info.error, error);
 			set_current_component(null);

test/runtime/samples/await-without-catch/_config.js

@@ -0,0 +1,44 @@
+let fulfil;
+
+let promise = new Promise(f => {
+	fulfil = f;
+});
+
+export default {
+	props: {
+		promise
+	},
+
+	html: `
+		<p>loading...</p>
+	`,
+
+	test({ assert, component, target }) {
+		fulfil(42);
+
+		return promise
+		.then(() => {
+			assert.htmlEqual(target.innerHTML, `
+				<p>loaded</p>
+			`);
+
+			let reject;
+
+			promise = new Promise((f, r) => {
+				reject = r;
+			});
+
+			component.promise = promise;
+
+			assert.htmlEqual(target.innerHTML, `
+				<p>loading...</p>
+			`);
+
+			reject(new Error('this error should be thrown'));
+			return promise;
+		})
+		.catch((err) => {
+			assert.equal(err.message, 'this error should be thrown');
+		});
+	}
+};

test/runtime/samples/await-without-catch/main.svelte

@@ -0,0 +1,9 @@
+<script>
+	export let promise;
+</script>
+
+{#await promise}
+	<p>loading...</p>
+{:then value}
+	<p>loaded</p>
+{/await}