fix(router-core): avoid false notFound matches for proxied loader data (#7156)

* fix(router-core): avoid false notFound matches for proxied loader data

* test(react-start): cover proxied loader data notFound regression

* test(react-start): move notFound regression to rsc direct loader

* chore: add changeset

Author: brenelz

.changeset/spotty-geckos-repeat.md

@@ -0,0 +1,5 @@
+---
+'@tanstack/router-core': patch
+---
+
+avoid false notFound matches for proxied loader data

e2e/react-start/rsc/src/routeTree.gen.ts

@@ -33,6 +33,7 @@ import { Route as RscFormsRouteImport } from './routes/rsc-forms'
 import { Route as RscFlightApiRouteImport } from './routes/rsc-flight-api'
 import { Route as RscExternalRouteImport } from './routes/rsc-external'
 import { Route as RscErrorRouteImport } from './routes/rsc-error'
+import { Route as RscDirectLoaderRouteImport } from './routes/rsc-direct-loader'
 import { Route as RscDeferredComponentRouteImport } from './routes/rsc-deferred-component'
 import { Route as RscDeferredRouteImport } from './routes/rsc-deferred'
 import { Route as RscCssPreloadComplexRouteImport } from './routes/rsc-css-preload-complex'
@@ -171,6 +172,11 @@ const RscErrorRoute = RscErrorRouteImport.update({
   path: '/rsc-error',
   getParentRoute: () => rootRouteImport,
 } as any)
+const RscDirectLoaderRoute = RscDirectLoaderRouteImport.update({
+  id: '/rsc-direct-loader',
+  path: '/rsc-direct-loader',
+  getParentRoute: () => rootRouteImport,
+} as any)
 const RscDeferredComponentRoute = RscDeferredComponentRouteImport.update({
   id: '/rsc-deferred-component',
   path: '/rsc-deferred-component',
@@ -270,6 +276,7 @@ export interface FileRoutesByFullPath {
   '/rsc-css-preload-complex': typeof RscCssPreloadComplexRoute
   '/rsc-deferred': typeof RscDeferredRoute
   '/rsc-deferred-component': typeof RscDeferredComponentRoute
+  '/rsc-direct-loader': typeof RscDirectLoaderRoute
   '/rsc-error': typeof RscErrorRoute
   '/rsc-external': typeof RscExternalRoute
   '/rsc-flight-api': typeof RscFlightApiRoute
@@ -313,6 +320,7 @@ export interface FileRoutesByTo {
   '/rsc-css-preload-complex': typeof RscCssPreloadComplexRoute
   '/rsc-deferred': typeof RscDeferredRoute
   '/rsc-deferred-component': typeof RscDeferredComponentRoute
+  '/rsc-direct-loader': typeof RscDirectLoaderRoute
   '/rsc-error': typeof RscErrorRoute
   '/rsc-external': typeof RscExternalRoute
   '/rsc-flight-api': typeof RscFlightApiRoute
@@ -357,6 +365,7 @@ export interface FileRoutesById {
   '/rsc-css-preload-complex': typeof RscCssPreloadComplexRoute
   '/rsc-deferred': typeof RscDeferredRoute
   '/rsc-deferred-component': typeof RscDeferredComponentRoute
+  '/rsc-direct-loader': typeof RscDirectLoaderRoute
   '/rsc-error': typeof RscErrorRoute
   '/rsc-external': typeof RscExternalRoute
   '/rsc-flight-api': typeof RscFlightApiRoute
@@ -402,6 +411,7 @@ export interface FileRouteTypes {
     | '/rsc-css-preload-complex'
     | '/rsc-deferred'
     | '/rsc-deferred-component'
+    | '/rsc-direct-loader'
     | '/rsc-error'
     | '/rsc-external'
     | '/rsc-flight-api'
@@ -445,6 +455,7 @@ export interface FileRouteTypes {
     | '/rsc-css-preload-complex'
     | '/rsc-deferred'
     | '/rsc-deferred-component'
+    | '/rsc-direct-loader'
     | '/rsc-error'
     | '/rsc-external'
     | '/rsc-flight-api'
@@ -488,6 +499,7 @@ export interface FileRouteTypes {
     | '/rsc-css-preload-complex'
     | '/rsc-deferred'
     | '/rsc-deferred-component'
+    | '/rsc-direct-loader'
     | '/rsc-error'
     | '/rsc-external'
     | '/rsc-flight-api'
@@ -532,6 +544,7 @@ export interface RootRouteChildren {
   RscCssPreloadComplexRoute: typeof RscCssPreloadComplexRoute
   RscDeferredRoute: typeof RscDeferredRoute
   RscDeferredComponentRoute: typeof RscDeferredComponentRoute
+  RscDirectLoaderRoute: typeof RscDirectLoaderRoute
   RscErrorRoute: typeof RscErrorRoute
   RscExternalRoute: typeof RscExternalRoute
   RscFlightApiRoute: typeof RscFlightApiRoute
@@ -733,6 +746,13 @@ declare module '@tanstack/react-router' {
       preLoaderRoute: typeof RscErrorRouteImport
       parentRoute: typeof rootRouteImport
     }
+    '/rsc-direct-loader': {
+      id: '/rsc-direct-loader'
+      path: '/rsc-direct-loader'
+      fullPath: '/rsc-direct-loader'
+      preLoaderRoute: typeof RscDirectLoaderRouteImport
+      parentRoute: typeof rootRouteImport
+    }
     '/rsc-deferred-component': {
       id: '/rsc-deferred-component'
       path: '/rsc-deferred-component'
@@ -868,6 +888,7 @@ const rootRouteChildren: RootRouteChildren = {
   RscCssPreloadComplexRoute: RscCssPreloadComplexRoute,
   RscDeferredRoute: RscDeferredRoute,
   RscDeferredComponentRoute: RscDeferredComponentRoute,
+  RscDirectLoaderRoute: RscDirectLoaderRoute,
   RscErrorRoute: RscErrorRoute,
   RscExternalRoute: RscExternalRoute,
   RscFlightApiRoute: RscFlightApiRoute,

e2e/react-start/rsc/src/routes/rsc-direct-loader.tsx

@@ -0,0 +1,55 @@
+import { createFileRoute } from '@tanstack/react-router'
+import { createServerFn } from '@tanstack/react-start'
+import { renderServerComponent } from '@tanstack/react-start/rsc'
+import { pageStyles } from '~/utils/styles'
+import {
+  serverBadge,
+  serverBox,
+  serverHeader,
+  timestamp,
+} from '~/utils/serverStyles'
+
+const getDirectLoaderServerComponent = createServerFn({
+  method: 'GET',
+}).handler(async () => {
+  const serverTimestamp = Date.now()
+
+  return renderServerComponent(
+    <div style={serverBox} data-testid="rsc-direct-loader-content">
+      <div style={serverHeader}>
+        <span style={serverBadge}>SERVER RENDERED</span>
+        <span style={timestamp} data-testid="rsc-direct-loader-timestamp">
+          Fetched: {new Date(serverTimestamp).toLocaleTimeString()}
+        </span>
+      </div>
+
+      <h2 data-testid="rsc-direct-loader-heading">Direct loader RSC</h2>
+      <p>
+        This route returns a server component directly from its loader without
+        wrapping it in an object.
+      </p>
+    </div>,
+  )
+})
+
+export const Route = createFileRoute('/rsc-direct-loader')({
+  loader: () => getDirectLoaderServerComponent(),
+  component: RscDirectLoaderComponent,
+})
+
+function RscDirectLoaderComponent() {
+  const ServerComponent = Route.useLoaderData()
+
+  return (
+    <div style={pageStyles.container}>
+      <h1 data-testid="rsc-direct-loader-title" style={pageStyles.title}>
+        Direct Loader Return
+      </h1>
+      <p style={pageStyles.description}>
+        The loader returns the server component itself. This guards against
+        mistaking proxied loader data for a notFound result.
+      </p>
+      {ServerComponent}
+    </div>
+  )
+}

e2e/react-start/rsc/tests/rsc-direct-loader.spec.ts

@@ -0,0 +1,21 @@
+import { expect } from '@playwright/test'
+import { test } from '@tanstack/router-e2e-utils'
+
+test.describe('RSC Direct Loader Tests', () => {
+  test('direct loader return does not trigger notFound handling', async ({
+    page,
+  }) => {
+    const response = await page.goto('/rsc-direct-loader')
+    await page.waitForURL('/rsc-direct-loader')
+
+    expect(response?.status()).toBe(200)
+
+    await expect(page.getByTestId('rsc-direct-loader-title')).toHaveText(
+      'Direct Loader Return',
+    )
+    await expect(page.getByTestId('rsc-direct-loader-content')).toBeVisible()
+    await expect(page.getByTestId('rsc-direct-loader-heading')).toHaveText(
+      'Direct loader RSC',
+    )
+  })
+})

examples/react/start-rscs/src/routes/pokemon-rsc.tsx

@@ -4,13 +4,13 @@ import { getPokemonList } from '~/pokemon/server-functions'
 export const Route = createFileRoute('/pokemon-rsc')({
   loader: async () => {
     const { Renderable } = await getPokemonList()
-    return { PokemonList: Renderable }
+    return Renderable
   },
   component: PokemonPage,
 })
 
 function PokemonPage() {
-  const { PokemonList } = Route.useLoaderData()
+  const PokemonList = Route.useLoaderData()
 
   return (
     <div className="py-10">

packages/router-core/src/not-found.ts

@@ -37,5 +37,5 @@ export function notFound(options: NotFoundError = {}) {
 
 /** Determine if a value is a TanStack Router not-found error. */
 export function isNotFound(obj: any): obj is NotFoundError {
-  return !!obj?.isNotFound
+  return obj?.isNotFound === true
 }

packages/router-core/tests/load.test.ts

@@ -82,6 +82,42 @@ describe('redirect resolution', () => {
   )
 })
 
+describe('notFound detection', () => {
+  test('does not treat arbitrary proxy property access as notFound', async () => {
+    const rootRoute = new BaseRootRoute({})
+    const fooRoute = new BaseRoute({
+      getParentRoute: () => rootRoute,
+      path: '/foo',
+      loader: () =>
+        new Proxy(
+          {},
+          {
+            get(_target, prop) {
+              if (prop === 'isNotFound') return 'truthy-but-not-true'
+              return undefined
+            },
+            has() {
+              return true
+            },
+          },
+        ),
+    })
+
+    const routeTree = rootRoute.addChildren([fooRoute])
+
+    const router = createTestRouter({
+      routeTree,
+      history: createMemoryHistory({ initialEntries: ['/foo'] }),
+      isServer: true,
+    })
+
+    await router.load()
+
+    expect(router.state.matches.at(-1)?.status).toBe('success')
+    expect(router.state.matches.at(-1)?.error).toBeUndefined()
+  })
+})
+
 describe('beforeLoad skip or exec', () => {
   const setup = ({ beforeLoad }: { beforeLoad?: BeforeLoad }) => {
     const rootRoute = new BaseRootRoute({})