[🐞] beta.40: ancestor layout's routeLoader$ gets empty params + truncated request.url when resolving a route nested under it

[ixcans]

Which component is this bug report for?

Qwik Router

Describe the bug

On @qwik.dev/router@2.0.0-beta.40, when a routeLoader$ is declared in a layout.tsx that lives at a dynamic [param] segment, and the actual request being served is for a route nested one level deeper than that layout, the layout's own loader receives:

• params — an empty object (missing the param the child route resolves correctly)
• url.pathname — truncated to the layout's own segment (e.g. /x/ instead of /x/sub/)
• request.url — also truncated the same way (not just a derived value — the raw Request itself)

...while the child route's own routeLoader$, running in the same request, sees the correct full params/url/request.url.

This is absent on 2.0.0-beta.35 (confirmed via bisection — identical repro, only the Qwik version pin changed). It is not adapter-specific — I reproduced it both on a custom Bun-based SSR adapter and on Qwik Router's own official node-server adapter running under plain Node.js, byte-for-byte identically. It does not reproduce under vite dev (live/unbundled SSR) — only in the built/production SSR bundle path both adapters share. It is also not limited to a literal first/"cold" request — it reproduces deterministically on repeated requests to an already-warm server process too; the only thing that avoids it is a client-side <Link>/useNavigate() transition, which never goes through this server-side document-request path at all.

Suspected regression source: beta.40's sole substantial change, the Vite 8 + Rolldown migration (#8909) — bisection confirms the bug is new in beta.40 relative to beta.35, and no other change of similar scope shipped in between.

Real-world impact: found while investigating a production app (a per-tenant dashboard) where this silently redirected users away from any deep-linked, bookmarked, or refreshed page — the entire nested-route tree was affected. The app reverted from beta.40 back to beta.35 because of this.

Related but distinct (same general subsystem/symptom family, different trigger — not duplicates): #8859 (a client-side SPA-action re-fetch missing a route-path header, landing a loader at / — different mechanism, pre-dates beta.40) and #8856 (merged in beta.39, touches getLoaderRequestEvent()'s per-loader RequestEvent field overriding — same code area, but scoped to a different, client-triggered path, and predates the Vite8/Rolldown migration so it can't be this regression).

Reproduction

https://github.com/ixcans/qwik-router-layout-params-repro

Scaffolded from the official Qwik CLI (npm create qwik@beta empty app) with zero added business logic — three small route files, 58 lines total:

// src/routes/[slug]/layout.tsx
import { Slot, component$ } from "@qwik.dev/core";
import { routeLoader$ } from "@qwik.dev/router";

export const useSlugParam = routeLoader$((ev) => {
  console.error(
    "[LAYOUT useSlugParam] params=%s pathname=%s request.url=%s",
    JSON.stringify(ev.params), ev.url.pathname, ev.request.url,
  );
  return ev.params.slug ?? null;
});

export default component$(() => <Slot />);

// src/routes/[slug]/sub/index.tsx
import { component$ } from "@qwik.dev/core";
import { routeLoader$, useLocation } from "@qwik.dev/router";
import { useSlugParam } from "../layout";

export const useSubParam = routeLoader$((ev) => {
  console.error(
    "[CHILD  useSubParam] params=%s pathname=%s request.url=%s",
    JSON.stringify(ev.params), ev.url.pathname, ev.request.url,
  );
  return ev.params.slug ?? null;
});

export default component$(() => {
  const layoutSlug = useSlugParam();
  const childSlug = useSubParam();
  const loc = useLocation();
  return (
    <div>
      <div>layoutSlug: {JSON.stringify(layoutSlug.value)}</div>
      <div>childSlug: {JSON.stringify(childSlug.value)}</div>
      <div>useLocation().params: {JSON.stringify(loc.params)}</div>
    </div>
  );
});

npm install
npm run build
npm run build.preview
npm run preview -- --open=false

Then make a fresh request (curl, or a browser hard-navigation — not a client-side link click) to /x/sub/ (any literal value in place of x).

Steps to reproduce

1. Clone https://github.com/ixcans/qwik-router-layout-params-repro
2. npm install && npm run build && npm run build.preview && npm run preview -- --open=false
3. curl http://localhost:<printed-port>/x/sub/
4. Check the server's stderr for the two log lines

Expected behavior

Both loaders should observe the same, correct params/url.pathname/request.url for the request actually being served.

Actual behavior

[LAYOUT useSlugParam] params={} pathname=/x/ request.url=http://localhost:PORT/x/
[CHILD  useSubParam] params={"slug":"x"} pathname=/x/sub/ request.url=http://localhost:PORT/x/sub/

Rendered page: layoutSlug: null, childSlug: "x". Requesting the bare /x/ (no nested sub) does not reproduce this — the layout loader sees correct params there. The corruption is specific to an ancestor layout resolving in the same request as a route nested deeper under it.

Confirmed absent on 2.0.0-beta.35 with the identical repro (only the version pin changed).

System Info

@qwik.dev/core: 2.0.0-beta.40
@qwik.dev/router: 2.0.0-beta.40
vite: 8.0.16
Tested on both a custom Bun-based SSR adapter and Qwik Router's official node-server adapter (Node.js), same result on both.

Additional information

No existing issue found covering this exact bug after a thorough search (issues, PRs, discussions, and every issue filed since beta.40 shipped) — happy to help narrow this down further if useful.

[wmertens]

This is fully intentional and was part of the big routeLoader refactor, specifically mentioned in changelog and docs.

If you use the full path in a loader, the result will depend on it. However, during SPA requests the loader is fetched on its own path, so the result caches the wrong data.

Instead, you must (re)export the loader from the deepest route(s) that you need it from, and it will get the full path for the route.

[ixcans]

Re-export works for the "need the full nested path" case — thanks for confirming the mechanism.

Worth being explicit about what #8945 actually changes, since it's easy to misread as relitigating this closure — it isn't. #8945 doesn't touch the pathname/caching behavior at all. It only fixes params being unconditionally emptied even when the loader's own scoped path already resolved them (e.g. a loader at /[tenantSlug]/ rendering /acme/agents/ should still get { tenantSlug: 'acme' } at its own path, no re-export needed). That makes the default case correct with zero app-side workaround, while leaving the shared-caching behavior you described fully intact for routes that don't need the full path.

The re-export workaround itself remains necessary for the deeper case. Worth being precise about why the failure mode matters, since "you have to remember to add it" isn't much of a complaint on its own — an opt-in mechanism requiring opt-in isn't a bug. The actual problem: the re-exporting-loaders docs describe what happens when you skip a re-export as "it will not run or throw exception" — a loud, safe failure by design. What actually happens for an ancestor-layout loader is neither: it runs, returns params: {}, and nothing errors anywhere. That's a mismatch between the documented failure mode and the actual one, not just an easy-to-forget requirement. At 45+ leaf routes in a real app, that gap between "should fail loud" and "fails silent" is exactly how this shipped to production unnoticed. Cache-sharing is a separate, smaller cost: the re-export also makes that loader's canonical path leaf-specific, applied to every route that needs it whether or not caching matters there.

One syntax gotcha too: only export { X } from '../layout' triggers it. import { X } from '../layout'; export { X }; is semantically identical in plain JS but has no effect.

[wmertens]

Fixed by #8945 (ancestor layout loaders keep the route params). The truncated request.url is intended: to get the full URL, re-export the loader from the deepest route. Please reopen if you still see empty params on beta.45 or later.

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