austinderek · austinderek · Jul 28, 2025
diff --git a/packages/next/src/server/app-render/work-unit-async-storage.external.ts b/packages/next/src/server/app-render/work-unit-async-storage.external.ts
@@ -246,6 +246,13 @@ export interface PrivateUseCacheStore extends CommonUseCacheStore {
    * access the request cookies.
    */
   readonly cookies: ReadonlyRequestCookies
+
+  /**
+   * Private caches don't currently need to track root params in the cache key
+   * because they're not persisted anywhere, so we can allow root params access
+   * (unlike public caches)
+   */
+  readonly rootParams: Params
 }
 
 export type UseCacheStore = PublicUseCacheStore | PrivateUseCacheStore

diff --git a/packages/next/src/server/request/root-params.ts b/packages/next/src/server/request/root-params.ts
@@ -41,7 +41,6 @@ export async function unstable_rootParams(): Promise<Params> {
 
   switch (workUnitStore.type) {
     case 'cache':
-    case 'private-cache':
     case 'unstable-cache': {
       throw new Error(
         `Route ${workStore.route} used \`unstable_rootParams()\` inside \`"use cache"\` or \`unstable_cache\`. Support for this API inside cache scopes is planned for a future version of Next.js.`
@@ -56,6 +55,7 @@ export async function unstable_rootParams(): Promise<Params> {
         workStore,
         workUnitStore
       )
+    case 'private-cache':
     case 'request':
       return Promise.resolve(workUnitStore.rootParams)
     default:
@@ -228,7 +228,6 @@ export function getRootParam(paramName: string): Promise<ParamValue> {
 
   switch (workUnitStore.type) {
     case 'unstable-cache':
-    case 'private-cache':
     case 'cache': {
       throw new Error(
         `Route ${workStore.route} used ${apiName} inside \`"use cache"\` or \`unstable_cache\`. Support for this API inside cache scopes is planned for a future version of Next.js.`
@@ -245,6 +244,7 @@ export function getRootParam(paramName: string): Promise<ParamValue> {
         apiName
       )
     }
+    case 'private-cache':
     case 'request': {
       break
     }

diff --git a/packages/next/src/server/use-cache/use-cache-wrapper.ts b/packages/next/src/server/use-cache/use-cache-wrapper.ts
@@ -187,14 +187,15 @@ function createUseCacheStore(
       explicitExpire: undefined,
       explicitStale: undefined,
       tags: null,
-      hmrRefreshHash:
-        outerWorkUnitStore && getHmrRefreshHash(workStore, outerWorkUnitStore),
-      isHmrRefresh: outerWorkUnitStore?.isHmrRefresh ?? false,
-      serverComponentsHmrCache: outerWorkUnitStore?.serverComponentsHmrCache,
+      hmrRefreshHash: getHmrRefreshHash(workStore, outerWorkUnitStore),
+      isHmrRefresh: outerWorkUnitStore.isHmrRefresh ?? false,
+      serverComponentsHmrCache: outerWorkUnitStore.serverComponentsHmrCache,
       forceRevalidate: shouldForceRevalidate(workStore, outerWorkUnitStore),
-      draftMode:
-        outerWorkUnitStore &&
-        getDraftModeProviderForCacheScope(workStore, outerWorkUnitStore),
+      draftMode: getDraftModeProviderForCacheScope(
+        workStore,
+        outerWorkUnitStore
+      ),
+      rootParams: outerWorkUnitStore.rootParams,
       cookies: outerWorkUnitStore.cookies,
     }
   } else {

diff --git a/...app-dir/app-root-params-getters/fixtures/use-cache-private/app/[lang]/[locale]/layout.tsx b/...app-dir/app-root-params-getters/fixtures/use-cache-private/app/[lang]/[locale]/layout.tsx
@@ -0,0 +1,16 @@
+import { ReactNode } from 'react'
+
+export default function Root({ children }: { children: ReactNode }) {
+  return (
+    <html>
+      <body>{children}</body>
+    </html>
+  )
+}
+
+export function generateStaticParams() {
+  // the param values are not accessed in tests,
+  // we just need a value here to avoid errors in PPR/cacheComponents
+  // where we need to provide at least one set of values for root params
+  return [{ lang: 'foo', locale: 'bar' }]
+}
diff --git a/...-params-getters/fixtures/use-cache-private/app/[lang]/[locale]/use-cache-private/page.tsx b/...-params-getters/fixtures/use-cache-private/app/[lang]/[locale]/use-cache-private/page.tsx
@@ -0,0 +1,34 @@
+import { lang, locale } from 'next/root-params'
+import { connection } from 'next/server'
+import { Suspense } from 'react'
+
+export default async function Page() {
+  return (
+    <Suspense fallback="Loading...">
+      <Runtime />
+    </Suspense>
+  )
+}
+
+async function Runtime() {
+  await connection()
+
+  const rootParams = await getCachedParams()
+  const data = await fetch(
+    'https://next-data-api-endpoint.vercel.app/api/random'
+  ).then((res) => res.text())
+
+  return (
+    <p>
+      <span id="param">
+        {rootParams.lang} {rootParams.locale}
+      </span>{' '}
+      <span id="random">{data}</span>
+    </p>
+  )
+}
+
+async function getCachedParams() {
+  'use cache: private'
+  return { lang: await lang(), locale: await locale() }
+}
diff --git a/test/e2e/app-dir/app-root-params-getters/fixtures/use-cache-private/next.config.ts b/test/e2e/app-dir/app-root-params-getters/fixtures/use-cache-private/next.config.ts
@@ -0,0 +1,10 @@
+import type { NextConfig } from 'next'
+
+const nextConfig: NextConfig = {
+  experimental: {
+    useCache: true,
+    rootParams: true,
+  },
+}
+
+export default nextConfig
diff --git a/test/e2e/app-dir/app-root-params-getters/use-cache.test.ts b/test/e2e/app-dir/app-root-params-getters/use-cache.test.ts
@@ -5,7 +5,6 @@ import { createSandbox } from 'development-sandbox'
 describe('app-root-param-getters - cache - at runtime', () => {
   const { next, isNextDev, skipped } = nextTestSetup({
     files: join(__dirname, 'fixtures', 'use-cache-runtime'),
-    skipStart: true,
     // this test asserts on build failure logs, which aren't currently observable in `next.cliOutput`.
     skipDeployment: true,
   })
@@ -39,19 +38,6 @@ describe('app-root-param-getters - cache - at runtime', () => {
       )
     })
   } else {
-    beforeAll(async () => {
-      try {
-        await next.start()
-      } catch (err) {
-        // if (isPPREnabled) {
-        //   throw err
-        // } else {
-        //   // in PPR/cacheComponents, we expect the build to fail,
-        //   // so we swallow the error and let the tests assert on the logs
-        // }
-      }
-    })
-
     it('should error when using root params within a "use cache" - start', async () => {
       await next.render$('/en/us/use-cache')
       expect(next.cliOutput).toInclude(
@@ -68,6 +54,30 @@ describe('app-root-param-getters - cache - at runtime', () => {
   }
 })
 
+describe('app-root-param-getters - private cache', () => {
+  const { next, isNextDev } = nextTestSetup({
+    files: join(__dirname, 'fixtures', 'use-cache-private'),
+  })
+
+  if (isNextDev) {
+    it('should allow using root params within a "use cache: private" - dev', async () => {
+      await using sandbox = await createSandbox(
+        next,
+        undefined,
+        '/en/us/use-cache-private'
+      )
+      const { session, browser } = sandbox
+      await session.assertNoRedbox()
+      expect(await browser.elementById('param').text()).toBe('en us')
+    })
+  } else {
+    it('should allow using root params within a "use cache: private" - start', async () => {
+      const browser = await next.browser('/en/us/use-cache-private')
+      expect(await browser.elementById('param').text()).toBe('en us')
+    })
+  }
+})
+
 describe('app-root-param-getters - cache - at build', () => {
   const { next, isNextDev } = nextTestSetup({
     files: join(__dirname, 'fixtures', 'use-cache-build'),