From 755661144979db84e44caa5bb66b62e350f8a107 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=EC=9C=A0=EA=B2=BD=ED=99=94?=
 <51588680+flex-kyunghwa@users.noreply.github.com>
Date: Fri, 16 Sep 2022 07:56:53 +0900
Subject: [PATCH] fix(next/router): Prevent query delete in routing when
 next.config basePath option is truthy (#40566)

## Bug

- [x] Related issues linked using `fixes #number`
    - fixes
        - #38528
        - #40432
- [x] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`

Hi, it is my first pull request in this project.
So... if you need anything more tasks, please tell me.

Co-authored-by: JJ Kasper <22380829+ijjk@users.noreply.github.com>
---
 packages/next/shared/lib/router/router.ts             |  6 +++++-
 .../app/pages/dynamic-routes/[routeName].js           | 11 +++++++++++
 test/e2e/middleware-base-path/app/pages/index.js      |  5 +++++
 test/e2e/middleware-base-path/test/index.test.ts      | 10 ++++++++++
 4 files changed, 31 insertions(+), 1 deletion(-)
 create mode 100644 test/e2e/middleware-base-path/app/pages/dynamic-routes/[routeName].js

diff --git a/packages/next/shared/lib/router/router.ts b/packages/next/shared/lib/router/router.ts
index cf1180fd6766ee0..cda9125962a0719 100644
--- a/packages/next/shared/lib/router/router.ts
+++ b/packages/next/shared/lib/router/router.ts
@@ -1552,7 +1552,11 @@ export default class Router implements BaseRouter {
           query = Object.assign({}, routeInfo.query || {}, query)
         }
 
-        if (routeMatch && pathname !== parsed.pathname) {
+        const cleanedParsedPathname = hasBasePath(parsed.pathname)
+          ? removeBasePath(parsed.pathname)
+          : parsed.pathname
+
+        if (routeMatch && pathname !== cleanedParsedPathname) {
           Object.keys(routeMatch).forEach((key) => {
             if (routeMatch && query[key] === routeMatch[key]) {
               delete query[key]
diff --git a/test/e2e/middleware-base-path/app/pages/dynamic-routes/[routeName].js b/test/e2e/middleware-base-path/app/pages/dynamic-routes/[routeName].js
new file mode 100644
index 000000000000000..1fe4784b683d4e2
--- /dev/null
+++ b/test/e2e/middleware-base-path/app/pages/dynamic-routes/[routeName].js
@@ -0,0 +1,11 @@
+import { useRouter } from 'next/router'
+
+export default function DynamicRoutes() {
+  const { query } = useRouter()
+
+  return (
+    <main>
+      <h1 id="route-name">{query.routeName}</h1>
+    </main>
+  )
+}
diff --git a/test/e2e/middleware-base-path/app/pages/index.js b/test/e2e/middleware-base-path/app/pages/index.js
index bc2fa5dd30667ed..02138dd7460d095 100644
--- a/test/e2e/middleware-base-path/app/pages/index.js
+++ b/test/e2e/middleware-base-path/app/pages/index.js
@@ -27,6 +27,11 @@ export default function Main({ message }) {
             <a>redirect me to about</a>
           </Link>
         </li>
+        <li>
+          <Link href="/dynamic-routes/hello-world">
+            <a id="go-to-hello-world-anchor">Hello World</a>
+          </Link>
+        </li>
       </ul>
     </div>
   )
diff --git a/test/e2e/middleware-base-path/test/index.test.ts b/test/e2e/middleware-base-path/test/index.test.ts
index 2b8ebcb8f87834d..dffe7a1e7963eca 100644
--- a/test/e2e/middleware-base-path/test/index.test.ts
+++ b/test/e2e/middleware-base-path/test/index.test.ts
@@ -35,4 +35,14 @@ describe('Middleware base tests', () => {
     const $ = cheerio.load(html)
     expect($('.title').text()).toBe('About Page')
   })
+  it('router.query must exist when Link clicked page routing', async () => {
+    const browser = await webdriver(next.url, '/root')
+    try {
+      await browser.elementById('go-to-hello-world-anchor').click()
+      const routeName = await browser.elementById('route-name').text()
+      expect(routeName).toMatch('hello-world')
+    } finally {
+      await browser.close()
+    }
+  })
 })