fix: prevent cold dev route loader requests from failing during SPA

.changeset/floppy-pandas-count.md

@@ -0,0 +1,5 @@
+---
+'@qwik.dev/router': patch
+---
+
+fix: prevent cold dev route loader requests from failing during SPA navigation

packages/qwik-router/src/middleware/request-handler/handlers/loader-handler.ts

@@ -1,3 +1,4 @@
+import { isDev } from '@qwik.dev/core';
 import { _serialize } from '@qwik.dev/core/internal';
 import {
   FULLPATH_HEADER,
@@ -42,7 +43,9 @@ export function loaderHandler(
       return;
     }
 
-    setLoaderData(requestEv, routeLoaders, loaderPaths);
+    const activeRouteLoaders =
+      isDev && !routeLoaders.includes(loader) ? [...routeLoaders, loader] : routeLoaders;
+    setLoaderData(requestEv, activeRouteLoaders, loaderPaths);
 
     const loaderRequestEv = createLoaderRequestEventFactory(requestEv)(loader);
 

packages/qwik-router/src/middleware/request-handler/handlers/loader-handler.unit.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it, vi } from 'vitest';
-import { FULLPATH_HEADER } from '../../../runtime/src/route-loaders';
+import { FULLPATH_HEADER, routeLoaderQrl } from '../../../runtime/src/route-loaders';
 import { getLoaderName, IsQLoader, QLoaderId } from '../request-path';
 import { loaderHandler } from './loader-handler';
 
@@ -120,6 +120,21 @@ describe('loaderHandler', () => {
     expect(requestEv.send).toHaveBeenCalledWith(200, expect.any(String));
   });
 
+  it('runs a dev registered loader that was not exported by the route module', async () => {
+    const requestEv = createRequestEv();
+    const qrl = {
+      call: vi.fn(async () => 'registered-loader-value'),
+      getHash: () => 'loader-id',
+      getSymbol: () => 'loader-id',
+    };
+    routeLoaderQrl(qrl as any);
+
+    await loaderHandler([])(requestEv as any);
+
+    expect(qrl.call).toHaveBeenCalledOnce();
+    expect(requestEv.send).toHaveBeenCalledWith(200, expect.any(String));
+  });
+
   it('treats empty normalized eTags as absent', async () => {
     const requestEv = createRequestEv();
     const cacheKey = vi.fn(() => null);

packages/qwik-router/src/runtime/src/prefetch-route.ts

@@ -1,5 +1,5 @@
 import * as qwikRouterConfig from '@qwik-router-config';
-import { isBrowser } from '@qwik.dev/core';
+import { isBrowser, isDev } from '@qwik.dev/core';
 // @ts-expect-error no types for preloader yet
 import { p as preload } from '@qwik.dev/core/preloader';
 import { ensureSlash } from '../../utils/pathname';
@@ -25,7 +25,7 @@ export async function prefetchRoute(
   manifestHash?: string,
   prefetchBundle = true
 ) {
-  if (!isBrowser) {
+  if (!isBrowser || isDev) {
     return;
   }
 

packages/qwik-router/src/runtime/src/route-loaders.ts

@@ -169,6 +169,24 @@ const isRequestEvent = (value: unknown): value is RequestEvent =>
 const isLoaderInternal = (value: unknown): value is LoaderInternal =>
   typeof value === 'function' && (value as LoaderInternal).__brand === 'server_loader';
 
+const getDevRouteLoaderRegistry = () => {
+  if (!isDev || !isServer) {
+    return undefined;
+  }
+  const registryKey = Symbol.for('qwik.dev.router.route-loaders');
+  return ((globalThis as any)[registryKey] ||= new Map<string, LoaderInternal>()) as Map<
+    string,
+    LoaderInternal
+  >;
+};
+
+const registerDevRouteLoader = (loader: LoaderInternal) => {
+  if (!isDev) {
+    return;
+  }
+  getDevRouteLoaderRegistry()?.set(loader.__id, loader);
+};
+
 /**
  * Fetch a single loader's data from the server.
  *
@@ -203,7 +221,7 @@ export const fetchRouteLoaderData = async (
   const url = `${pathBase}${getLoaderName(loaderId, manifestHash)}${search}`;
 
   const headers: Record<string, string> = {};
-  if (pageUrl && pageUrl.pathname !== pathBase && !globalThis.__STRICT_LOADERS__) {
+  if (pageUrl && pageUrl.pathname !== pathBase) {
     headers[FULLPATH_HEADER] = pageUrl.pathname;
   }
 
@@ -621,8 +639,7 @@ export const ensureRouteLoaderSignals = (
   for (let i = 0; i < loaders.length; i++) {
     const loader = loaders[i];
     // Dev-only safety net for the first SPA nav: the route module isn't transformed yet, so the
-    // client trie has no _R loader hash and the loader would resolve to undefined. Seed the page
-    // path (where the loader runs), only filling genuine gaps so a trie-resolved path is kept.
+    // client trie has no _R loader hash and the loader would resolve to undefined.
     if (isDev && !isServer) {
       if (routeLoaderCtx.pagePathname && routeLoaderCtx.loaderPaths[loader.__id] === undefined) {
         routeLoaderCtx.loaderPaths[loader.__id] = routeLoaderCtx.pagePathname;
@@ -648,7 +665,11 @@ export const resolveRouteLoaderByHash = (
   routeLoaders: readonly LoaderInternal[],
   loaderId: string
 ) => {
-  return routeLoaders.find((loader) => loader.__id === loaderId);
+  // Cold dev q-loader requests can know an id before route-local scans see the loader object.
+  return (
+    routeLoaders.find((loader) => loader.__id === loaderId) ??
+    (isDev ? getDevRouteLoaderRegistry()?.get(loaderId) : undefined)
+  );
 };
 
 /** Run a loader and return its raw value. Errors/redirects propagate as exceptions. */
@@ -828,6 +849,9 @@ export const routeLoaderQrl = ((
   loader.__search = search;
   loader.__allowStale = allowStale;
   Object.freeze(loader);
+  if (isDev) {
+    registerDevRouteLoader(loader);
+  }
   return loader;
 }) as LoaderConstructorQRL;
 

packages/qwik-router/src/runtime/src/use-endpoint.unit.ts

@@ -4,10 +4,13 @@ import { getLoaderName } from '../../middleware/request-handler/request-path';
 import { FULLPATH_HEADER, fetchRouteLoaderData } from './route-loaders';
 import { submitAction } from './use-endpoint';
 
+const previousStrictLoaders = globalThis.__STRICT_LOADERS__;
+
 describe('submitAction', () => {
   afterEach(() => {
     vi.restoreAllMocks();
     vi.unstubAllGlobals();
+    globalThis.__STRICT_LOADERS__ = previousStrictLoaders;
   });
 
   const makeJsonResponse = async (payload: object, status = 200) =>
@@ -129,6 +132,29 @@ describe('fetchRouteLoaderData', () => {
     );
   });
 
+  it('sends X-Qwik-fullpath for strict root loader requests on deeper page paths', async () => {
+    globalThis.__STRICT_LOADERS__ = true;
+    const fetchSpy = vi.fn().mockResolvedValue(
+      new Response('', {
+        status: 404,
+      })
+    );
+    vi.stubGlobal('fetch', fetchSpy);
+
+    await fetchRouteLoaderData('root-loader', '/', 'manifest-hash', {
+      pageUrl: new URL('http://localhost/products/123/?view=full'),
+    });
+
+    expect(fetchSpy).toHaveBeenCalledWith(
+      `/${getLoaderName('root-loader', 'manifest-hash')}?view=full`,
+      expect.objectContaining({
+        headers: {
+          [FULLPATH_HEADER]: '/products/123/',
+        },
+      })
+    );
+  });
+
   it('converts unfollowed HTTP redirects into loader redirects', async () => {
     vi.stubGlobal(
       'fetch',