Fix middleware i18n rewrites (vercel#31174)

Fixes vercel#30897

This PR fixes the linked issue where rewrites are not being applied for locale. It adds the corresponding test but also, as it was added in debugging process, it introduces a helper to read/write into the `request` object.

We are currently writing directly into the request by casting to `any` and then using flags like `_nextRewrote`. Instead, this PR puts all of this metadata under a symbol so it is not directly accessible. This also allows to have a single place where all of this metadata is listed so we can add comments describing the purpose of each flag.

In the same way, there is metadata written in the querystring. This is adding some types for it in order to throw some visibility on where is this metadata accessed. In an upcoming PR we can move all of it to the `request` object if possible to simplify the system.

## Bug

- [x] Related issues linked using `fixes #number`
- [x] Integration tests added
- [x] Errors have helpful link attached, see `contributing.md`

packages/next/build/webpack/loaders/next-serverless-loader/utils.ts

@@ -6,8 +6,9 @@ import { normalizeLocalePath } from '../../../../shared/lib/i18n/normalize-local
 import pathMatch from '../../../../shared/lib/router/utils/path-match'
 import { getRouteRegex } from '../../../../shared/lib/router/utils/route-regex'
 import { getRouteMatcher } from '../../../../shared/lib/router/utils/route-matcher'
-import prepareDestination, {
+import {
   matchHas,
+  prepareDestination,
 } from '../../../../shared/lib/router/utils/prepare-destination'
 import { __ApiPreviewProps } from '../../../../server/api-utils'
 import { BuildManifest } from '../../../../server/get-page-files'
@@ -23,6 +24,7 @@ import { denormalizePagePath } from '../../../../server/denormalize-page-path'
 import cookie from 'next/dist/compiled/cookie'
 import { TEMPORARY_REDIRECT_STATUS } from '../../../../shared/lib/constants'
 import { NextConfig } from '../../../../server/config'
+import { addRequestMeta } from '../../../../server/request-meta'
 
 const getCustomRouteMatcher = pathMatch(true)
 
@@ -99,12 +101,12 @@ export function getUtils({
       }
 
       if (params) {
-        const { parsedDestination } = prepareDestination(
-          rewrite.destination,
-          params,
-          parsedUrl.query,
-          true
-        )
+        const { parsedDestination } = prepareDestination({
+          appendParamsToQuery: true,
+          destination: rewrite.destination,
+          params: params,
+          query: parsedUrl.query,
+        })
 
         Object.assign(parsedUrl.query, parsedDestination.query)
         delete (parsedDestination as any).query
@@ -372,7 +374,7 @@ export function getUtils({
     if (detectedDomain) {
       defaultLocale = detectedDomain.defaultLocale
       detectedLocale = defaultLocale
-      ;(req as any).__nextIsLocaleDomain = true
+      addRequestMeta(req, '__nextIsLocaleDomain', true)
     }
 
     // if not domain specific locale use accept-language preferred
@@ -392,7 +394,7 @@ export function getUtils({
         ...parsedUrl,
         pathname: localePathResult.pathname,
       })
-      ;(req as any).__nextStrippedLocale = true
+      addRequestMeta(req, '__nextStrippedLocale', true)
       parsedUrl.pathname = localePathResult.pathname
     }
 

packages/next/export/worker.ts

@@ -1,3 +1,9 @@
+import type { ComponentType } from 'react'
+import type { FontManifest } from '../server/font-utils'
+import type { GetStaticProps } from '../types'
+import type { IncomingMessage, ServerResponse } from 'http'
+import type { NextConfigComplete } from '../server/config-shared'
+import type { NextParsedUrlQuery } from '../server/request-meta'
 import url from 'url'
 import { extname, join, dirname, sep } from 'path'
 import { renderToHTML } from '../server/render'
@@ -10,15 +16,10 @@ import { getRouteRegex } from '../shared/lib/router/utils/route-regex'
 import { normalizePagePath } from '../server/normalize-page-path'
 import { SERVER_PROPS_EXPORT_ERROR } from '../lib/constants'
 import '../server/node-polyfill-fetch'
-import { IncomingMessage, ServerResponse } from 'http'
-import { ComponentType } from 'react'
-import { GetStaticProps } from '../types'
 import { requireFontManifest } from '../server/require'
-import { FontManifest } from '../server/font-utils'
 import { normalizeLocalePath } from '../shared/lib/i18n/normalize-locale-path'
 import { trace } from '../trace'
 import { isInAmpMode } from '../shared/lib/amp'
-import { NextConfigComplete } from '../server/config-shared'
 import { setHttpAgentOptions } from '../server/config'
 import RenderResult from '../server/render-result'
 import isError from '../lib/is-error'
@@ -39,7 +40,7 @@ interface AmpValidation {
 
 interface PathMap {
   page: string
-  query?: { [key: string]: string | string[] }
+  query?: NextParsedUrlQuery
 }
 
 interface ExportPageInput {
@@ -128,7 +129,7 @@ export default async function exportPage({
       let query = { ...originalQuery }
       let params: { [key: string]: string | string[] } | undefined
 
-      let updatedPath = (query.__nextSsgPath as string) || path
+      let updatedPath = query.__nextSsgPath || path
       let locale = query.__nextLocale || renderOpts.locale
       delete query.__nextLocale
       delete query.__nextSsgPath