Add JSDoc to config options

packages/next/server/config-shared.ts

@@ -43,13 +43,56 @@ export interface TypeScriptConfig {
   tsconfigPath?: string
 }
 
+export interface WebpackConfigContext {
+  /** Next.js root directory */
+  dir: string
+  /** Indicates if the compilation will be done in development */
+  dev: boolean
+  /** It's `true` for server-side compilation, and `false` for client-side compilation */
+  isServer: boolean
+  /**  The build id, used as a unique identifier between builds */
+  buildId: string
+  config: NextConfigComplete
+  /** Default loaders used internally by Next.js */
+  defaultLoaders: {
+    /** Default babel-loader configuration */
+    babel: any
+  }
+  /** Number of total Next.js pages */
+  totalPages: number
+  /** The webpack configuration */
+  webpack: any
+}
+
+export interface NextJsWebpackConfig {
+  (
+    /** Existing Webpack config */
+    config: any,
+    context: WebpackConfigContext
+  ): any
+}
+
 export type NextConfig = { [key: string]: any } & {
   i18n?: I18NConfig | null
 
   eslint?: ESLintConfig
   typescript?: TypeScriptConfig
 
+  /**
+   * Headers allow you to set custom HTTP headers for an incoming request path.
+   *
+   * Refer to complete [Headers configuration documentations](https://nextjs.org/docs/api-reference/next.config.js/headers)
+   */
   headers?: () => Promise<Header[]>
+
+  /**
+   * Rewrites allow you to map an incoming request path to a different destination path.
+   *
+   * Rewrites act as a URL proxy and mask the destination path, making it appear the user hasn't changed their location on the site.
+   * In contrast, redirects will reroute to a new page and show the URL changes
+   *
+   * Refer to complete [Rewrites configuration documentations](https://nextjs.org/docs/api-reference/next.config.js/rewrites)
+   */
   rewrites?: () => Promise<
     | Rewrite[]
     | {
@@ -58,34 +101,98 @@ export type NextConfig = { [key: string]: any } & {
         fallback: Rewrite[]
       }
   >
+
+  /**
+   * Redirects allow you to redirect an incoming request path to a different destination path.
+   *
+   * Redirects are only available on the Node.js environment and do not affect client-side routing.
+   *
+   * Refer to complete [Redirects configuration documentations](https://nextjs.org/docs/api-reference/next.config.js/redirects)
+   */
   redirects?: () => Promise<Redirect[]>
 
+  /**
+   * Webpack 5 is now the default for all Next.js applications. If you did not have custom webpack configuration your application is already using webpack 5.
+   * If you do have custom webpack configuration you can refer to the [Next.js webpack 5 documentation](https://nextjs.org/docs/messages/webpack5) for upgrading guidance.
+   */
   webpack5?: false
+
+  /**
+   * Moment.js includes translations for a lot of locales by default. Next.js now automatically excludes these locales by default
+   * to optimize bundle size for applications using Moment.js.
+   *
+   * To load a specific locale use this snippet:
+   *
+   * ```js
+   * import moment from 'moment'
+   * import 'moment/locale/ja'
+   *
+   * moment.locale('ja')
+   * ```
+   *
+   * You can opt-out of this new default by adding `excludeDefaultMomentLocales: false` to `next.config.js` if you do not want the new behavior,
+   * do note it's highly recommended to not disable this new optimization as it significantly reduces the size of Moment.js.
+   */
   excludeDefaultMomentLocales?: boolean
 
-  webpack?:
-    | ((
-        config: any,
-        context: {
-          dir: string
-          dev: boolean
-          isServer: boolean
-          buildId: string
-          config: NextConfigComplete
-          defaultLoaders: { babel: any }
-          totalPages: number
-          webpack: any
-        }
-      ) => any)
-    | null
+  /**
+   * Before continuing to add custom webpack configuration to your application make sure Next.js doesn't already support your use-case
+   *
+   * Refer to complete [Custom Webpack Config documentation](https://nextjs.org/docs/api-reference/next.config.js/custom-webpack-config)
+   *
+   */
+  webpack?: NextJsWebpackConfig | null
 
+  /**
+   * By default Next.js will redirect urls with trailing slashes to their counterpart without a trailing slash.
+   * For example /about/ will redirect to /about. You can configure this behavior to act the opposite way,
+   * where urls without trailing slashes are redirected to their counterparts with trailing slashes.
+   *
+   * Refer to complete [Trailing Slash Configuration](https://nextjs.org/docs/api-reference/next.config.js/trailing-slash)
+   */
   trailingSlash?: boolean
+
+  /**
+   * Next.js comes with built-in support for environment variables, which allows you to do the following:
+   *
+   *  - [Use `.env.local` to load environment variables](#loading-environment-variables)
+   *  - [Expose environment variables to the browser by prefixing with `NEXT_PUBLIC_`](#exposing-environment-variables-to-the-browser)
+   *
+   * Refer to complete [Environment Variables documentation](https://nextjs.org/docs/api-reference/next.config.js/environment-variables)
+   */
   env?: { [key: string]: string }
+  /**
+   * Detonation directory
+   */
   distDir?: string
+  /**
+   * The build output directory (defaults to `.next`) is now cleared by default except for the Next.js caches.
+   */
   cleanDistDir?: boolean
+  /**
+   * To set up a CDN, you can set up an asset prefix and configure your CDN's origin to resolve to the domain that Next.js is hosted on.
+   *
+   * See [CDN Support with Asset Prefix](https://nextjs.org/docs/api-reference/next.config.js/cdn-support-with-asset-prefix)
+   */
   assetPrefix?: string
+  /**
+   * By default, `Next` will serve each file in the `pages` folder under a pathname matching the filename.
+   * If your project uses a custom server, this behavior may result in the same content being served from multiple paths,
+   * which can present problems with SEO and UX.
+   *
+   * To disable this behavior set this option to `false`.
+   */
   useFileSystemPublicRoutes?: boolean
+
+  /**
+   * Next.js uses a constant id generated at build time to identify which version of your application is being served.
+   * This can cause problems in multi-server deployments when `next build` is ran on every server.
+   * In order to keep a static build id between builds you can provide your own build id.
+   *
+   * Use this option to provide your own build id.
+   */
   generateBuildId?: () => string | null | Promise<string | null>
+
   generateEtags?: boolean
   pageExtensions?: string[]
   compress?: boolean