handle circular dependencies in dynamic imports (#5619)

* handle circular dependencies in dynamic imports - closes #5399

* add test

Author: Rich-Harris

.changeset/eleven-crews-knock.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+Handle circular dependencies in dynamic imports

packages/kit/src/vite/build/utils.js

@@ -35,6 +35,9 @@ export async function create_build(config) {
  * @param {boolean} add_dynamic_css
  */
 export function find_deps(manifest, entry, add_dynamic_css) {
+	/** @type {Set<string>} */
+	const seen = new Set();
+
 	/** @type {Set<string>} */
 	const imports = new Set();
 
@@ -46,9 +49,11 @@ export function find_deps(manifest, entry, add_dynamic_css) {
 	 * @param {boolean} add_js
 	 */
 	function traverse(file, add_js) {
+		if (seen.has(file)) return;
+		seen.add(file);
+
 		const chunk = manifest[file];
 
-		if (imports.has(chunk.file)) return;
 		if (add_js) imports.add(chunk.file);
 
 		if (chunk.css) {

packages/kit/test/apps/basics/src/routes/cyclical-dynamic-import/_is_even.js

@@ -0,0 +1,5 @@
+export async function is_even(num) {
+	const { is_odd } = await import('./_is_odd.js');
+	if (num === 0) return true;
+	return is_odd(num - 1);
+}

packages/kit/test/apps/basics/src/routes/cyclical-dynamic-import/_is_odd.js

@@ -0,0 +1,5 @@
+export async function is_odd(num) {
+	const { is_even } = await import('./_is_even.js');
+	if (num === 1) return true;
+	return is_even(num - 1);
+}

packages/kit/test/apps/basics/src/routes/cyclical-dynamic-import/index.svelte

@@ -0,0 +1,8 @@
+<script>
+	import { onMount } from 'svelte';
+
+	onMount(async () => {
+		const { is_even } = await import('./_is_even.js');
+		console.log(is_even(5));
+	});
+</script>