bug(typedef): AppType typedef changed in 12.3

Verify canary release

• I verified that the issue exists in the latest Next.js canary release

Provide environment information

    Operating System:
      Platform: darwin
      Arch: arm64
      Version: Darwin Kernel Version 21.6.0: Wed Aug 10 14:28:23 PDT 2022; root:xnu-8020.141.5~2/RELEASE_ARM64_T6000
    Binaries:
      Node: 16.15.1
      npm: 8.11.0
      Yarn: 1.22.19
      pnpm: 7.10.0
    Relevant packages:
      next: 12.3.0
      eslint-config-next: 12.3.0
      react: 18.2.0
      react-dom: 18.2.0

What browser are you using? (if relevant)

No response

How are you deploying your application? (if relevant)

No response

Describe the Bug

When bumping version to Next 12.3.0 we ran into some troubles with the AppType typedefinition:

The AppType typedefinition and specifically the pageProps seems to have been broken in 12.3.0 and the pageProps now evaluates to {}:

Expected Behavior

I am not sure if this is a bug or if it’s intended, but this change is not present in the changelog and seems to be a “breaking” one worth noting. Maybe we are required to augment some part to make it work with 3rd party dependencies?

Link to reproduction

https://github.com/juliusmarminge/apptype-repro

To Reproduce

Create a new next-app (using reproduction template):

npx create-next-app -e reproduction-template

Install NextAuth:

nom install next-auth

Create pages/_app.tsx with the following content:

import { SessionProvider } from "next-auth/react";
import type { AppType } from "next/dist/shared/lib/utils";

const MyApp: AppType = ({ Component, pageProps }) => {
  return (
    <SessionProvider session={pageProps.session}>
      <Component {...pageProps} />
    </SessionProvider>
  );
};

Hover pageProps, it evaluates to {} and the pageProps.session will error. This was not an issue in 12.2.5.

[juliusmarminge]

Appears to be related to this typedef change

12.2:

export declare type AppInitialProps = {

    pageProps: any;

};

export declare type AppPropsType<R extends NextRouter = NextRouter, P = {}> = AppInitialProps & {

    Component: NextComponentType<NextPageContext, any, P>;

    router: R;

    __N_SSG?: boolean;

    __N_SSP?: boolean;

    __N_RSC?: boolean;

};

12.3:

export declare type AppInitialProps<P = any> = {

    pageProps: P;

};

export declare type AppPropsType<R extends NextRouter = NextRouter, P = {}> = AppInitialProps<P> & {

    Component: NextComponentType<NextPageContext, any, any>;

    router: R;

    __N_SSG?: boolean;

    __N_SSP?: boolean;

    __N_RSC?: boolean;

};

To be clear i think this is a very good improvement and seems like it would allow for a more typesafe usage in the root app.

Maybe the AppType should be a generic like NextPage, or React.FC and letting me pass in the props like

const MyApp: AppType<{ session: Session }> = ...

[balazsorban44]

Yes, it makes more sense as a feature request, I started working on it already. See #40391