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fix: prerender errors during development #16507

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fix: prerender errors during development #16507

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63f8d46
check page option instead of prerenderer options
teemingc Jul 24, 2026
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5 changes: 5 additions & 0 deletions .changeset/silent-bushes-grow.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
---
'@sveltejs/kit': patch
---

fix: surface prerender errors during development
7 changes: 5 additions & 2 deletions packages/kit/src/runtime/server/page/index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -122,7 +122,10 @@ export async function render_page(
// renders an empty 'shell' page if SSR is turned off and if there is
// no server data to prerender. As a result, the load functions and rendering
// only occur client-side.
if (ssr === false && !(state.prerendering && should_prerender_data)) {
if (
ssr === false &&
!((state.prerendering || state.prerender_default === true) && should_prerender_data)
) {
// if the user makes a request through a non-enhanced form, the returned value is lost
// because there is no SSR or client-side handling of the response
if (DEV && action_result && !event.request.headers.has('x-sveltekit-action')) {
Expand Down Expand Up @@ -173,7 +176,7 @@ export async function render_page(

const data_serializer = server_data_serializer(event, event_state, options);
const data_serializer_json =
state.prerendering && should_prerender_data
(state.prerendering || state.prerender_default === true) && should_prerender_data
? server_data_serializer_json(event, event_state, options)
: null;

Expand Down
2 changes: 1 addition & 1 deletion packages/kit/src/runtime/server/page/load_data.js
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Original file line number Diff line number Diff line change
Expand Up @@ -67,7 +67,7 @@ export async function load_server_data({ event, event_state, state, node, parent
}
);

if (state.prerendering) {
if (state.prerendering || state.prerender_default === true) {
disable_search(url);
}

Expand Down
19 changes: 12 additions & 7 deletions packages/kit/src/runtime/server/page/render.js
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Original file line number Diff line number Diff line change
Expand Up @@ -58,7 +58,7 @@ export async function render_response({
data_serializer,
error_components
}) {
if (state.prerendering) {
if (state.prerendering || state.prerender_default === true) {
if (options.csp.mode === 'nonce') {
throw new Error('Cannot use prerendering if config.csp.mode === "nonce"');
}
Expand Down Expand Up @@ -106,7 +106,7 @@ export async function render_response({
let base_expression = s(paths.base);

const csp = new Csp(options.csp, {
prerender: !!state.prerendering
prerender: !!(state.prerendering || state.prerender_default === true)
});

// if appropriate, use relative paths for greater portability
Expand Down Expand Up @@ -310,7 +310,7 @@ export async function render_response({
* @param {string[]} attributes
*/
const add_preload = (path, attributes) => {
if (options.link_header_preload && !state.prerendering) {
if (options.link_header_preload && !(state.prerendering || state.prerender_default === true)) {
link_headers.add(`<${encodeURI(path)}>; ${attributes.join('; ')}; nopush`);
} else {
head.add_link_tag(path, attributes);
Expand Down Expand Up @@ -351,7 +351,11 @@ export async function render_response({
if (page_config.ssr && page_config.csr) {
body += `\n\t\t\t${fetched
.map((item) =>
serialize_data(item, resolve_opts.filterSerializedResponseHeaders, !!state.prerendering)
serialize_data(
item,
resolve_opts.filterSerializedResponseHeaders,
!!(state.prerendering || state.prerender_default === true)
)
)
.join('\n\t\t\t')}`;
}
Expand All @@ -363,7 +367,8 @@ export async function render_response({
// import the env.js module so that it evaluates before any user code can evaluate.
// TODO revert to using top-level await once https://bugs.webkit.org/show_bug.cgi?id=242740 is fixed
// https://github.com/sveltejs/kit/pull/11601
const load_env_eagerly = client.uses_env_dynamic_public && !!state.prerendering;
const load_env_eagerly =
client.uses_env_dynamic_public && (state.prerendering || state.prerender_default === true);

if (load_env_eagerly) {
modulepreloads.add(`${paths.app_dir}/env.js`);
Expand Down Expand Up @@ -568,14 +573,14 @@ export async function render_response({
'content-type': 'text/html'
});

if (state.prerendering) {
if (state.prerendering || state.prerender_default === true) {
// TODO read headers set with setHeaders and convert into http-equiv where possible
const csp_headers = csp.csp_provider.get_meta();
if (csp_headers) {
head.add_http_equiv(csp_headers);
}

if (state.prerendering.cache) {
if (state.prerendering?.cache) {
head.add_http_equiv(
`<meta http-equiv="cache-control" content="${state.prerendering.cache}">`
);
Expand Down
2 changes: 1 addition & 1 deletion packages/kit/src/runtime/server/respond.js
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Original file line number Diff line number Diff line change
Expand Up @@ -435,7 +435,7 @@ export async function internal_respond(request, options, manifest, state) {
prerender = node.prerender ?? prerender;
} else if (page_nodes) {
config = page_nodes.get_config() ?? config;
prerender = page_nodes.prerender();
prerender = state.prerender_default = page_nodes.prerender();

@Rich-Harris Rich-Harris Jul 25, 2026

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is there any value in doing something like this immediately after this block, rather than adding prerender_default?

if (DEV && prerender) {
  state.prerendering = {
    dependencies: new Map(),
    remote_responses: new Map()
  };
}

It's a bit of a kludge but it would mean we didn't need to worry about forgetting the

|| state.prerender_default === true

part of

if (state.prerendering || state.prerender_default === true) {...}

Or does that not work for whatever reason?

@Nic-Polumeyv Nic-Polumeyv Jul 25, 2026 •
edited
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I checked. event_state is created earlier in respond with prerendering: state.prerendering, so the request store would keep undefined unless that becomes a getter (or gets the same assignment). #16508 makes it a bit less cumbersome.

@Rich-Harris Rich-Harris Jul 25, 2026

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That's true. But I think that itself is a problem — we have SSRState and EventState that overlap on prerender, and many functions that take both as arguments.

This was never intentional, just an artifact of organic software development — they should probably be unified into a single object. There are lots of adjacent tidy-ups that would be beneficial. But those would all be slightly disruptive changes that we should hold off on until the PR queue is emptier (specifically of things like #16464 and #15574), and as such I think we should hit pause on both this and #16508.

}

if (state.emulator?.platform) {
Expand Down
1 change: 1 addition & 0 deletions packages/kit/src/types/internal.d.ts
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Expand Up @@ -233,6 +233,7 @@ export interface PrerenderDependency {
body: null | string | Uint8Array;
}

/** Internal context for the prerendering process */
export interface PrerenderOptions {
cache?: string; // including this here is a bit of a hack, but it makes it easy to add <meta http-equiv>
fallback?: boolean;
Expand Down
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