fix: skip calling respond for server-side fetch on prerendered pages (#13377)

When using server-side fetch for internal requests, if a server route
is matched from the server `manifest.js`, it gets called without making
a real HTTP request.

However, prerendered routes are not included on this list! This is fine
when routes are prerendered with `export const prerender = true;`, but
will cause issues with a non-prerendered route also matches the same
URL as any prerendered routes.

This commit adds `prerendered_routes: Set<string>` to the `manifest.js`,
which skips calling the non-prerendered route.

Fixes #12778
Fixes #12739

Author: aloisklink

.changeset/nine-llamas-fetch.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: skip hooks for server fetch to prerendered routes

.changeset/slow-penguins-play.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: default server fetch to use prerendered paths

packages/kit/src/core/adapt/builder.js

@@ -138,6 +138,7 @@ export function create_builder({
 						generateManifest: ({ relativePath }) =>
 							generate_manifest({
 								build_data,
+								prerendered: [],
 								relative_path: relativePath,
 								routes: Array.from(filtered)
 							})
@@ -185,6 +186,7 @@ export function create_builder({
 		generateManifest({ relativePath, routes: subset }) {
 			return generate_manifest({
 				build_data,
+				prerendered: prerendered.paths,
 				relative_path: relativePath,
 				routes: subset
 					? subset.map((route) => /** @type {import('types').RouteData} */ (lookup.get(route)))

packages/kit/src/core/generate_manifest/index.js

@@ -14,11 +14,12 @@ import { find_server_assets } from './find_server_assets.js';
  * build process, to power routing, etc.
  * @param {{
  *   build_data: import('types').BuildData;
+ *   prerendered: string[];
  *   relative_path: string;
  *   routes: import('types').RouteData[];
  * }} opts
  */
-export function generate_manifest({ build_data, relative_path, routes }) {
+export function generate_manifest({ build_data, prerendered, relative_path, routes }) {
 	/**
 	 * @type {Map<any, number>} The new index of each node in the filtered nodes array
 	 */
@@ -113,6 +114,7 @@ export function generate_manifest({ build_data, relative_path, routes }) {
 						`;
 					}).filter(Boolean).join(',\n')}
 				],
+				prerendered_routes: new Set(${s(prerendered)}),
 				matchers: async () => {
 					${Array.from(
 						matchers,

packages/kit/src/exports/public.d.ts

@@ -1297,6 +1297,7 @@ export interface SSRManifest {
 		client: NonNullable<BuildData['client']>;
 		nodes: SSRNodeLoader[];
 		routes: SSRRoute[];
+		prerendered_routes: Set<string>;
 		matchers: () => Promise<Record<string, ParamMatcher>>;
 		/** A `[file]: size` map of all assets imported by server code */
 		server_assets: Record<string, number>;

packages/kit/src/exports/vite/dev/index.js

@@ -222,6 +222,7 @@ export async function dev(vite, vite_config, svelte_config) {
 						return result;
 					};
 				}),
+				prerendered_routes: new Set(),
 				routes: compact(
 					manifest_data.routes.map((route) => {
 						if (!route.page && !route.endpoint) return null;

packages/kit/src/exports/vite/index.js

@@ -795,6 +795,7 @@ Tips:
 					manifest_path,
 					`export const manifest = ${generate_manifest({
 						build_data,
+						prerendered: [],
 						relative_path: '.',
 						routes: manifest_data.routes
 					})};\n`
@@ -917,6 +918,7 @@ Tips:
 					manifest_path,
 					`export const manifest = ${generate_manifest({
 						build_data,
+						prerendered: [],
 						relative_path: '.',
 						routes: manifest_data.routes
 					})};\n`
@@ -948,6 +950,7 @@ Tips:
 					`${out}/server/manifest.js`,
 					`export const manifest = ${generate_manifest({
 						build_data,
+						prerendered: prerendered.paths,
 						relative_path: '.',
 						routes: manifest_data.routes.filter((route) => prerender_map.get(route.id) !== true)
 					})};\n`

packages/kit/src/runtime/server/fetch.js

@@ -112,6 +112,18 @@ export function create_fetch({ event, options, manifest, state, get_cookie_heade
 					return await fetch(request);
 				}
 
+				if (
+					manifest._.prerendered_routes.has(decoded) ||
+					(decoded.at(-1) === '/' && manifest._.prerendered_routes.has(decoded.slice(0, -1)))
+				) {
+					// The path of something prerendered could match a different route
+					// that is still in the manifest, leading to the wrong route being loaded.
+					// We therefore bail early here. The prerendered logic is different for
+					// each adapter, (except maybe for prerendered redirects)
+					// so we need to make an actual HTTP request.
+					return await fetch(request);
+				}
+
 				if (credentials !== 'omit') {
 					const cookie = get_cookie_header(url, request.headers.get('cookie'));
 					if (cookie) {

packages/kit/test/apps/basics/src/hooks.server.js

@@ -1,3 +1,4 @@
+import { building, dev } from '$app/environment';
 import { error, isHttpError, redirect } from '@sveltejs/kit';
 import { sequence } from '@sveltejs/kit/hooks';
 import fs from 'node:fs';
@@ -136,6 +137,15 @@ export const handle = sequence(
 
 		return resolve(event);
 	},
+	async ({ event, resolve }) => {
+		if (!dev && !building && event.url.pathname === '/prerendering/prerendered-endpoint/api') {
+			error(
+				500,
+				`Server hooks should not be called for prerendered endpoints: isSubRequest=${event.isSubRequest}`
+			);
+		}
+		return resolve(event);
+	},
 	async ({ event, resolve }) => {
 		if (['/non-existent-route', '/non-existent-route-loop'].includes(event.url.pathname)) {
 			event.locals.url = new URL(event.request.url);

packages/kit/test/apps/basics/src/routes/prerendering/prerendered-endpoint/api-with-param/[option]/+server.js

@@ -0,0 +1,23 @@
+import { building, dev } from '$app/environment';
+import { error, json } from '@sveltejs/kit';
+
+export const prerender = 'auto';
+
+export function entries() {
+	return [
+		{
+			option: 'prerendered'
+		}
+	];
+}
+
+export async function GET({ params: { option } }) {
+	if ((await entries()).find((entry) => entry.option === option)) {
+		if (dev || building) {
+			return json({ message: 'Im prerendered and called from a non-prerendered +page.server.js' });
+		} else {
+			error(500, 'I should not be called at runtime because I am prerendered');
+		}
+	}
+	return json({ message: 'Im not prerendered' });
+}