Fix missing locale info for middleware data request (#54357)

This ensures we properly populate locale information with `skipMiddlewareUrlNormalize` enabled as we shouldn't provide incorrect values even if we are skipping normalizing. 

Fixes: #53646

Author: ijjk

packages/next/src/shared/lib/router/utils/get-next-pathname-info.ts

@@ -64,9 +64,9 @@ export function getNextPathnameInfo(
     info.pathname = removePathPrefix(info.pathname, basePath)
     info.basePath = basePath
   }
+  let pathnameNoDataPrefix = info.pathname
 
   if (
-    options.parseData === true &&
     info.pathname.startsWith('/_next/data/') &&
     info.pathname.endsWith('.json')
   ) {
@@ -76,21 +76,36 @@ export function getNextPathnameInfo(
       .split('/')
 
     const buildId = paths[0]
-    info.pathname = paths[1] !== 'index' ? `/${paths.slice(1).join('/')}` : '/'
     info.buildId = buildId
+    pathnameNoDataPrefix =
+      paths[1] !== 'index' ? `/${paths.slice(1).join('/')}` : '/'
+
+    // update pathname with normalized if enabled although
+    // we use normalized to populate locale info still
+    if (options.parseData === true) {
+      info.pathname = pathnameNoDataPrefix
+    }
   }
 
   // If provided, use the locale route normalizer to detect the locale instead
   // of the function below.
-  if (options.i18nProvider) {
-    const result = options.i18nProvider.analyze(info.pathname)
+  if (i18n) {
+    let result = options.i18nProvider
+      ? options.i18nProvider.analyze(info.pathname)
+      : normalizeLocalePath(info.pathname, i18n.locales)
+
     info.locale = result.detectedLocale
     info.pathname = result.pathname ?? info.pathname
-  } else if (i18n) {
-    const pathLocale = normalizeLocalePath(info.pathname, i18n.locales)
-    info.locale = pathLocale.detectedLocale
-    info.pathname = pathLocale.pathname ?? info.pathname
-  }
 
+    if (!result.detectedLocale && info.buildId) {
+      result = options.i18nProvider
+        ? options.i18nProvider.analyze(pathnameNoDataPrefix)
+        : normalizeLocalePath(pathnameNoDataPrefix, i18n.locales)
+
+      if (result.detectedLocale) {
+        info.locale = result.detectedLocale
+      }
+    }
+  }
   return info
 }

test/e2e/skip-trailing-slash-redirect/app/middleware.js

@@ -18,6 +18,13 @@ export default function handler(req) {
   console.log(req.nextUrl)
   let { pathname } = req.nextUrl
 
+  if (pathname.startsWith('/_next/data') && pathname.includes('locale-test')) {
+    return NextResponse.json({
+      locale: req.nextUrl.locale,
+      pathname: req.nextUrl.pathname,
+    })
+  }
+
   if (pathname.includes('docs') || pathname.includes('chained-rewrite')) {
     if (pathname.startsWith('/en')) {
       pathname = pathname.replace(/^\/en/, '') || '/'

test/e2e/skip-trailing-slash-redirect/index.test.ts

@@ -16,6 +16,16 @@ describe('skip-trailing-slash-redirect', () => {
   })
   afterAll(() => next.destroy())
 
+  it('should parse locale info for data request correctly', async () => {
+    const pathname = `/_next/data/${next.buildId}/ja-jp/locale-test.json`
+    const res = await next.fetch(pathname)
+
+    expect(await res.json()).toEqual({
+      locale: 'ja-jp',
+      pathname,
+    })
+  })
+
   it.each(['EN', 'JA-JP'])(
     'should be able to redirect locale casing $1',
     async (locale) => {