From b6fe1c0b7918582f8b2e7d88a3139f925f094478 Mon Sep 17 00:00:00 2001
From: JJ Kasper <jj@jjsweb.site>
Date: Mon, 26 Oct 2020 18:50:53 -0500
Subject: [PATCH] Make sure to only redirect domain on locale root

---
 .../webpack/loaders/next-serverless-loader.ts |  9 ++++----
 packages/next/next-server/server/config.ts    | 21 +++++++++++++++++-
 .../next/next-server/server/next-server.ts    | 15 ++++++++-----
 .../i18n-support/test/index.test.js           | 22 +++++++++----------
 4 files changed, 44 insertions(+), 23 deletions(-)

diff --git a/packages/next/build/webpack/loaders/next-serverless-loader.ts b/packages/next/build/webpack/loaders/next-serverless-loader.ts
index 33a903cf1b5a5..7ca949a47f82d 100644
--- a/packages/next/build/webpack/loaders/next-serverless-loader.ts
+++ b/packages/next/build/webpack/loaders/next-serverless-loader.ts
@@ -271,8 +271,8 @@ const nextServerlessLoader: loader.Loader = function () {
       // content from multiple domains
       if (detectedDomain) {
         const localeToCheck = localePathResult.detectedLocale
-            ? detectedLocale
-            : acceptPreferredLocale
+          ? detectedLocale
+          : acceptPreferredLocale
 
         const matchedDomain = detectDomainLocale(
           i18n.domains,
@@ -283,9 +283,8 @@ const nextServerlessLoader: loader.Loader = function () {
         if (matchedDomain && matchedDomain.domain !== detectedDomain.domain) {
           localeDomainRedirect = \`http\${matchedDomain.http ? '' : 's'}://\${
             matchedDomain.domain
-          }/\${localeToCheck === matchedDomain.defaultLocale
-            ? ''
-            : localeToCheck
+          }/\${
+            localeToCheck === matchedDomain.defaultLocale ? '' : localeToCheck
           }\`
         }
       }
diff --git a/packages/next/next-server/server/config.ts b/packages/next/next-server/server/config.ts
index 1940286b801c1..cc0b10570ba12 100644
--- a/packages/next/next-server/server/config.ts
+++ b/packages/next/next-server/server/config.ts
@@ -340,7 +340,26 @@ function assignDefaults(userConfig: { [key: string]: any }) {
         if (!item.defaultLocale) return true
         if (!item.domain || typeof item.domain !== 'string') return true
 
-        return false
+        let hasInvalidLocale = false
+
+        if (Array.isArray(item.locales)) {
+          for (const locale of item.locales) {
+            if (typeof locale !== 'string') hasInvalidLocale = true
+
+            for (const domainItem of i18n.domains) {
+              if (domainItem === item) continue
+              if (domainItem.locales && domainItem.locales.includes(locale)) {
+                console.warn(
+                  `Both ${item.domain} and ${domainItem.domain} configured the locale (${locale}) but only one can. Remove it from one i18n.domains config to continue`
+                )
+                hasInvalidLocale = true
+                break
+              }
+            }
+          }
+        }
+
+        return hasInvalidLocale
       })
 
       if (invalidDomainItems.length > 0) {
diff --git a/packages/next/next-server/server/next-server.ts b/packages/next/next-server/server/next-server.ts
index b91b23e8fd106..b6dac836c2685 100644
--- a/packages/next/next-server/server/next-server.ts
+++ b/packages/next/next-server/server/next-server.ts
@@ -347,10 +347,11 @@ export default class Server {
       // If a detected locale is a domain specific locale and we aren't already
       // on that domain and path prefix redirect to it to prevent duplicate
       // content from multiple domains
-      if (detectedDomain) {
-        const localeToCheck = localePathResult.detectedLocale
-          ? detectedLocale
-          : acceptPreferredLocale
+      if (detectedDomain && parsedUrl.pathname === '/') {
+        const localeToCheck = acceptPreferredLocale
+        // const localeToCheck = localePathResult.detectedLocale
+        //   ? detectedLocale
+        //   : acceptPreferredLocale
 
         const matchedDomain = detectDomainLocale(
           i18n.domains,
@@ -358,7 +359,11 @@ export default class Server {
           localeToCheck
         )
 
-        if (matchedDomain && matchedDomain.domain !== detectedDomain.domain) {
+        if (
+          matchedDomain &&
+          (matchedDomain.domain !== detectedDomain.domain ||
+            localeToCheck !== matchedDomain.defaultLocale)
+        ) {
           localeDomainRedirect = `http${matchedDomain.http ? '' : 's'}://${
             matchedDomain.domain
           }/${
diff --git a/test/integration/i18n-support/test/index.test.js b/test/integration/i18n-support/test/index.test.js
index 9b9ef69f6d979..83d22086629be 100644
--- a/test/integration/i18n-support/test/index.test.js
+++ b/test/integration/i18n-support/test/index.test.js
@@ -688,21 +688,19 @@ function runTests(isDev) {
       domain = '',
       locale = ''
     ) => {
-      const res = await fetchViaHTTP(
-        appPort,
-        `/${locale === domainDefault ? '' : locale}`,
-        undefined,
-        {
-          headers: {
-            host: domain,
-          },
-          redirect: 'manual',
-        }
-      )
+      const res = await fetchViaHTTP(appPort, `/`, undefined, {
+        headers: {
+          host: domain,
+          'accept-language': locale,
+        },
+        redirect: 'manual',
+      })
       const expectedDomainItem = domainItems.find(
         (item) => item.defaultLocale === locale || item.locales.includes(locale)
       )
-      const shouldRedirect = expectedDomainItem.domain !== domain
+      const shouldRedirect =
+        expectedDomainItem.domain !== domain ||
+        locale !== expectedDomainItem.defaultLocale
 
       expect(res.status).toBe(shouldRedirect ? 307 : 200)