From d783f0eca93ad8558af2fd9fe31fa93dc57f7c71 Mon Sep 17 00:00:00 2001
From: JJ Kasper <jj@jjsweb.site>
Date: Wed, 24 Jun 2020 20:00:35 -0500
Subject: [PATCH] Add test case and ensure removal

---
 packages/next/client/index.js                  | 3 ++-
 packages/next/next-server/lib/router/router.ts | 2 +-
 test/integration/basepath/pages/[slug].js      | 2 +-
 test/integration/basepath/test/index.test.js   | 6 ++++++
 4 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/packages/next/client/index.js b/packages/next/client/index.js
index d3a4534f9bea5..9dae7d78ae445 100644
--- a/packages/next/client/index.js
+++ b/packages/next/client/index.js
@@ -9,6 +9,7 @@ import { RouterContext } from '../next-server/lib/router-context'
 import { isDynamicRoute } from '../next-server/lib/router/utils/is-dynamic'
 import * as envConfig from '../next-server/lib/runtime-config'
 import { getURL, loadGetInitialProps, ST } from '../next-server/lib/utils'
+import { delBasePath } from '../next-server/lib/router/router'
 import initHeadManager from './head-manager'
 import PageLoader from './page-loader'
 import measureWebVitals from './performance-relayer'
@@ -48,7 +49,7 @@ envConfig.setConfig({
   publicRuntimeConfig: runtimeConfig || {},
 })
 
-const asPath = getURL()
+const asPath = delBasePath(getURL())
 
 const pageLoader = new PageLoader(buildId, prefix, page)
 const register = ([r, f]) => pageLoader.registerPage(r, f)
diff --git a/packages/next/next-server/lib/router/router.ts b/packages/next/next-server/lib/router/router.ts
index 4babcdd3d4262..063cd653f7af2 100644
--- a/packages/next/next-server/lib/router/router.ts
+++ b/packages/next/next-server/lib/router/router.ts
@@ -21,7 +21,7 @@ import getAssetPathFromRoute from './utils/get-asset-path-from-route'
 const basePath = (process.env.__NEXT_ROUTER_BASEPATH as string) || ''
 
 export function addBasePath(path: string): string {
-  return path.startsWith(basePath) ? path : `${basePath}${path}`
+  return `${basePath}${path}`
 }
 
 export function delBasePath(path: string): string {
diff --git a/test/integration/basepath/pages/[slug].js b/test/integration/basepath/pages/[slug].js
index 7ad5b771f38ac..53205048d0044 100644
--- a/test/integration/basepath/pages/[slug].js
+++ b/test/integration/basepath/pages/[slug].js
@@ -1,3 +1,3 @@
 import { useRouter } from 'next/router'
 
-export default () => <p>slug: {useRouter().query.slug}</p>
+export default () => <p id="slug">slug: {useRouter().query.slug}</p>
diff --git a/test/integration/basepath/test/index.test.js b/test/integration/basepath/test/index.test.js
index d4995dd9da3e7..c9d220b74212d 100644
--- a/test/integration/basepath/test/index.test.js
+++ b/test/integration/basepath/test/index.test.js
@@ -116,6 +116,12 @@ const runTests = (context, dev = false) => {
     })
   }
 
+  it('should update dynamic params after mount correctly', async () => {
+    const browser = await webdriver(context.appPort, '/docs/hello-dynamic')
+    const text = await browser.elementByCss('#slug').text()
+    expect(text).toContain('slug: hello-dynamic')
+  })
+
   it('should navigate to index page with getStaticProps', async () => {
     const browser = await webdriver(context.appPort, '/docs/hello')
     await browser.eval('window.beforeNavigate = "hi"')