[request] better typescript type for next.config.js NextConfig

[bluelovers]

Feature request

Is your feature request related to a problem? Please describe.

i only see this, but any not a good type

declare type NextConfig = any;

if have a type/interface for this
we can more easy write a next.config or a config plugin

Describe the solution you'd like

A clear and concise description of what you want to happen.

Describe alternatives you've considered

A clear and concise description of any alternative solutions or features you've considered.

Additional context

Add any other context or screenshots about the feature request here.

[eps1lon]

Just leaving my use case here after #8044 was closed without much considerations:

Is your feature request related to a problem? Please describe.

Documentation for config is incomplete and spread out. In-editor autocomplete solves this via types.

Describe the solution you'd like

Export types of next.config.js so that people can use JSDOC to get autcomplete for the config via

/**
 * @type {import('next').Config}
 */
const config = {
  // your config here
};
module.exports = config;

Describe alternatives you've considered

Declare the types locally starting from https://github.com/zeit/next.js/blob/287961ed9142a53f8e9a23bafb2f31257339ea98/packages/next/next-server/server/config.ts#L12-L65

[jgoux]

I just used a similar approach for typing relay's configuration file :

// @ts-check

/**
 * @type import("relay-compiler/lib/bin/RelayCompilerMain").Config
 */
module.exports = {
  // free auto-complete and type-checking yay!
};

It's a great addition for discoverability.

[bluelovers]

they don't want type for it
#10275

[Timer]

See #13429

[eps1lon]

See #13429

It doesn't look like that PR adds a public type. It was suggested (#13429 (comment)) but it's not apparent how I would import the config type.

[Rowno]

Gatsby exposes really good types for their config, which allows you to strongly type the JavaScript config file using JSDoc as described above.

[lfades]

This is not one of our current priorities but I'm open to review a PR that adds types for Next.js configurations (similar to #13429 which was closed due to being quite outdated)