[Bug] Dynamic Route Type Error: params inferred as Promise in .next/types for [userId] page

[blessibles]

Link to the code that reproduces this issue

https://github.com/blessibles/blessibles-cursor

To Reproduce

1. Create a dynamic route at src/app/admin/user/[userId]/page.tsx
2. Run npm run build
3. Observe the type error referencing .next/types/app/admin/user/[userId]/page.ts

Current vs. Expected behavior

When building a dynamic route at src/app/admin/user/[userId]/page.tsx, the build fails with a type error:

Type '{ params: { userId: string; }; }' is missing the following properties from type 'Promise': then, catch, finally, [Symbol.toStringTag]

The generated .next/types/app/admin/user/[userId]/page.ts expects params to be a Promise, which is not correct for a dynamic route page.

This error persists even after:

• Removing all type annotations and using only inline types
• Deleting .next, node_modules, and lock files
• Creating a brand new Next.js project and copying only the source files
• Renaming the dynamic route folder
• Deleting stale type files in .next/types

The error always references the same generated type file, even after all caches are cleared and the route is renamed.

Expected:
The build should succeed, and the generated types should expect params to be an object, not a Promise, for a dynamic route page.

Provide environment information

Operating system: Windows 11
App dir: admin
Dynamic route: src/app/admin/user/[userId]/page.tsx
Node.js: v22.16.0   
Next.js: 15.3.3
Typescript: 5.8.3

Which area(s) are affected? (Select all that apply)

Not sure

Which stage(s) are affected? (Select all that apply)

next build (local)

Additional context

This error is reproducible in a fresh Next.js project with only the relevant files copied over. All troubleshooting steps from the official docs and community have been exhausted.

With the help of an expert assistant, I have systematically tried all of the following:

• Removed all explicit type annotations from the page and used only inline types.

• Deleted all build artifacts and caches: .next, .next/types, node_modules, package-lock.json.

• Performed a full clean install of all dependencies.

• Renamed the dynamic route folder (e.g., from [userId] to [uid] and [userPageId]).

• Deleted stale type files in .next/types.

• Moved the page to a new dynamic route in a fresh folder.

• Created a brand new Next.js project using npx create-next-app, copied only the source files and configs, and tried building there.

• Tried disabling type checking with // @ts-nocheck and NEXT_IGNORE_TYPE_ERRORS=true.

• Checked for custom or global type definitions that could interfere (none found).

• Confirmed all versions of Next.js and TypeScript are compatible and up to date.

  **The attached ZIP file contains:

  • src/app/admin/user/[userId]/page.tsx
  • .next/types/app/admin/user/[userId]/page.ts
  • package.json
  • tsconfig.json**

The error persists in all cases, and always references the same generated type file, even after all caches are cleared and the route is renamed.

Zipped.zip

[icyJoseph]

Hi,

Next 15 introduced breaking changes, documented here:

• https://nextjs.org/blog/next-15#async-request-apis-breaking-change
• https://nextjs.org/docs/app/api-reference/file-conventions/page#params-optional

You need to change your code to:

// src/app/admin/user/[userId]/page.tsx

export async function Page({ params }: { params: Promise<{ userId: string }> }) {
  const { userId } = await params
}

[icyJoseph]

@blessibles I see a fix was attempted, but there was a crucial detail left out, that this page is use client:

// src/app/admin/user/[userId]/page.tsx
'use client'

import { use } from 'react';

// other code

export default function Page({ params }: { params: Promise<{ userId: string }> }) {
  const { userId } = use (params);
  const [user, setUser] = useState<User | null>(null);

This was also documented, in one of the links I left above, https://nextjs.org/docs/app/api-reference/file-conventions/page#reading-searchparams-and-params-in-client-components

[blessibles]

Thank you! I just applied this 😊 From: Joseph ***@***.***> Sent: Wednesday, June 11, 2025 1:00 PM To: vercel/next.js ***@***.***> Cc: blessibles ***@***.***>; Mention ***@***.***> Subject: Re: [vercel/next.js] [Bug] Dynamic Route Type Error: params inferred as Promise in .next/types for [userId] page (Issue #80296) <https://avatars.githubusercontent.com/u/21013447?s=20&v=4> icyJoseph left a comment (vercel/next.js#80296) <#80296 (comment)> @blessibles <https://github.com/blessibles> I see a fix was attempted, but there was a crucial detail left out, that this page is use client: // src/app/admin/user/[userId]/page.tsx 'use client' import { use } from 'react'; // other code export default function Page({ params }: { params: Promise<{ userId: string }> }) { const { userId } = use (params); const [user, setUser] = useState<User | null>(null); This was also documented, in one of the links I left above, https://nextjs.org/docs/app/api-reference/file-conventions/page#reading-searchparams-and-params-in-client-components — Reply to this email directly, view it on GitHub <#80296 (comment)> , or unsubscribe <https://github.com/notifications/unsubscribe-auth/BSUHZ5XG33ZMOXS7UMOZLH33DBVDFAVCNFSM6AAAAAB63J3L76VHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDSNRTG4YDSNZSGI> . You are receiving this because you were mentioned. <https://github.com/notifications/beacon/BSUHZ5SZ2NMRZ7OGEA4CQF33DBVDFA5CNFSM6AAAAAB63J3L76WGG33NNVSW45C7OR4XAZNMJFZXG5LFINXW23LFNZ2KUY3PNVWWK3TUL5UWJTVQU2PRU.gif> Message ID: ***@***.*** ***@***.***> >

[icyJoseph]

I will move this into a discussion thread. I think the root issue has been identified.