revert method

packages/next/lib/load-custom-routes.ts

@@ -350,19 +350,19 @@ export default async function loadCustomRoutes(
       ? [
           {
             source: '/:path*/:file.:ext/',
-            destination: '/:path*/:file.:ext',
+            destination: config.basePath + '/:path*/:file.:ext',
             permanent: true,
           },
           {
             source: '/:path*/:notfile([^/.]+)',
-            destination: '/:path*/:notfile/',
+            destination: config.basePath + '/:path*/:notfile/',
             permanent: true,
           },
         ]
       : [
           {
             source: '/:path+/',
-            destination: '/:path+',
+            destination: config.basePath + '/:path+',
             permanent: true,
           },
         ])

packages/next/next-server/server/next-server.ts

@@ -65,10 +65,6 @@ import { PagesManifest } from '../../build/webpack/plugins/pages-manifest-plugin
 import { removePathTrailingSlash } from '../../client/normalize-trailing-slash'
 import getRouteFromAssetPath from '../lib/router/utils/get-route-from-asset-path'
 
-function addBasePath(path: string, basePath: string = ''): string {
-  return basePath ? (path === '/' ? basePath : basePath + path) : path
-}
-
 const getCustomRouteMatcher = pathMatch(true)
 
 type NextConfig = any
@@ -513,10 +509,7 @@ export default class Server {
             params,
             parsedUrl.query
           )
-          const updatedDestination = addBasePath(
-            formatUrl(parsedDestination),
-            this.nextConfig.basePath
-          )
+          const updatedDestination = formatUrl(parsedDestination)
 
           res.setHeader('Location', updatedDestination)
           res.statusCode = getRedirectStatus(redirectRoute as Redirect)