Simplify trailing slash regex (#15335)

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

@@ -360,13 +360,13 @@ export default async function loadCustomRoutes(
   if (config.trailingSlash) {
     redirects.unshift(
       {
-        source: '/:path*/:file.:ext/',
-        destination: '/:path*/:file.:ext',
+        source: '/:file((?:[^/]+/)*[^/]+\\.\\w+)/',
+        destination: '/:file',
         permanent: true,
       },
       {
-        source: '/:path*/:notfile([^/.]+)',
-        destination: '/:path*/:notfile/',
+        source: '/:notfile((?:[^/]+/)*[^/\\.]+)',
+        destination: '/:notfile/',
         permanent: true,
       }
     )

test/integration/trailing-slashes/test/index.test.js

@@ -258,13 +258,13 @@ describe('Trailing slashes', () => {
         expect.objectContaining({
           redirects: expect.arrayContaining([
             expect.objectContaining({
-              source: '/:path*/:file.:ext/',
-              destination: '/:path*/:file.:ext',
+              source: '/:file((?:[^/]+/)*[^/]+\\.\\w+)/',
+              destination: '/:file',
               statusCode: 308,
             }),
             expect.objectContaining({
-              source: '/:path*/:notfile([^/.]+)',
-              destination: '/:path*/:notfile/',
+              source: '/:notfile((?:[^/]+/)*[^/\\.]+)',
+              destination: '/:notfile/',
               statusCode: 308,
             }),
           ]),