Fix: parameter on AppType incorrectly applied to pageProps instead of props

[Jah-yee]

Good day

Bug Description

When using AppType<MyInitialProps>, the type parameter was incorrectly applied only to MyApp.props.pageProps via AppInitialProps<PageProps>, instead of directly to MyApp.props.

This caused a TypeScript error on props.foo (which exists at runtime) while incorrectly showing no error on pageProps.foo (which does not exist at runtime).

Root Cause

In AppPropsType<Router, PageProps>, the PageProps type parameter was only used within AppInitialProps<PageProps> which wraps it in a pageProps property. The raw PageProps was not included in the props intersection.

Fix

Changed AppPropsType from:

export type AppPropsType<Router, PageProps = {}> = AppInitialProps<PageProps> & {
  Component: ...
}

to:

export type AppPropsType<Router, PageProps = {}> = AppInitialProps<PageProps> & PageProps & {
  Component: ...
}

This ensures that when AppType<P> is used, the parameter P is correctly applied to props directly (via both AppInitialProps for pageProps and the intersection with PageProps itself).

Files Changed

• packages/next/src/shared/lib/utils.ts: Added PageProps to the intersection in AppPropsType

Thank you for your attention. If there are any issues or suggestions, please leave a comment and I will address them promptly.

Warmly, RoomWithOutRoof

[vercel]

Adding & PageProps to AppPropsType causes the PageProps type parameter to incorrectly leak onto the top-level component props, breaking the common AppProps<P> pattern where P should only describe pageProps.