fix: keep resolve relative to initial base during prerender (#14533)

* fix: keep resolve relative to initial base during prerender

* test: cover resolve helper relative link in prerender

* chore: changeset

* Update packages/kit/src/runtime/app/paths/internal/server.js

* Update packages/kit/src/runtime/app/paths/server.js

* Update packages/kit/src/runtime/app/paths/server.js

---------

Co-authored-by: Simon H <[email protected]>

Author: LeeWxx

.changeset/famous-fans-cheer.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: keep resolve relative to initial base during prerender

packages/kit/src/runtime/app/paths/internal/server.js

@@ -5,6 +5,12 @@ export const relative = __SVELTEKIT_PATHS_RELATIVE__;
 
 const initial = { base, assets };
 
+/**
+ * `base` could be overridden during rendering to be relative;
+ * this one's the original non-relative base path
+ */
+export const initial_base = initial.base;
+
 /**
  * @param {{ base: string, assets: string }} paths
  */

packages/kit/src/runtime/app/paths/server.js

@@ -1,4 +1,4 @@
-import { base, assets, relative } from './internal/server.js';
+import { base, assets, relative, initial_base } from './internal/server.js';
 import { resolve_route } from '../../../utils/routing.js';
 import { try_get_request_store } from '@sveltejs/kit/internal/server';
 
@@ -16,7 +16,8 @@ export function resolve(id, params) {
 		const store = try_get_request_store();
 
 		if (store && !store.state.prerendering?.fallback) {
-			const segments = store.event.url.pathname.slice(base.length).split('/').slice(2);
+			const after_base = store.event.url.pathname.slice(initial_base.length);
+			const segments = after_base.split('/').slice(2);
 			const prefix = segments.map(() => '..').join('/') || '.';
 
 			return prefix + resolved;

packages/kit/test/prerendering/basics/src/routes/resolve-relative/lv1/+page.svelte

@@ -0,0 +1 @@
+<h1>level 1</h1>

packages/kit/test/prerendering/basics/src/routes/resolve-relative/lv1/lv2/+page.svelte

@@ -0,0 +1,5 @@
+<script>
+	import { resolve } from '$app/paths';
+</script>
+
+<a id="resolved-link" href={resolve('/resolve-relative/lv1')}>go up</a>

packages/kit/test/prerendering/basics/test/tests.spec.js

@@ -200,6 +200,11 @@ test('prerenders binary data', async () => {
 	assert.equal(Buffer.compare(read('fetch-image/image.png', null), read('image.png', null)), 0);
 });
 
+test('generates relative link for resolve helper during prerender', () => {
+	const content = read('resolve-relative/lv1/lv2.html');
+	expect(content).toMatch('href="../../resolve-relative/lv1"');
+});
+
 test('fetches data from local endpoint', () => {
 	const data = JSON.parse(read('origin/__data.json'));