Support unnamed parameters in custom-routes correctly

packages/next/next-server/server/lib/path-match.ts

@@ -16,6 +16,20 @@ export default (customRoute = false) => {
       if (!res) {
         return false
       }
+
+      if (customRoute) {
+        const newParams: { [k: string]: string } = {}
+        Object.keys(res.params).forEach((key, idx) => {
+          if (key === idx + '') {
+            newParams[idx + 1 + ''] = (res.params as any)[key]
+          }
+        })
+        res.params = {
+          ...res.params,
+          ...newParams,
+        }
+      }
+
       return { ...params, ...res.params }
     }
   }

test/integration/custom-routes/next.config.js

@@ -120,6 +120,10 @@ module.exports = {
           source: '/query-redirect/:section/:name',
           destination: '/with-params?first=:section&second=:name',
         },
+        {
+          source: '/unnamed/(first|second)/(.*)',
+          destination: '/:1/:2',
+        },
       ]
     },
 

test/integration/custom-routes/test/index.test.js

@@ -229,6 +229,15 @@ const runTests = (isDev = false) => {
     expect(res.headers.get('x-second-header')).toBe('second')
   })
 
+  it('should support unnamed parameters correctly', async () => {
+    const res = await fetchViaHTTP(appPort, '/unnamed/first/final', undefined, {
+      redirect: 'manual',
+    })
+    const { pathname } = url.parse(res.headers.get('location') || '')
+    expect(res.status).toBe(307)
+    expect(pathname).toBe('/first/final')
+  })
+
   if (!isDev) {
     it('should output routes-manifest successfully', async () => {
       const manifest = await fs.readJSON(
@@ -336,6 +345,15 @@ const runTests = (isDev = false) => {
             source: '/query-redirect/:section/:name',
             statusCode: 307,
           },
+          {
+            destination: '/:1/:2',
+            regex: normalizeRegEx(
+              '^\\/unnamed(?:\\/(first|second))(?:\\/(.*))$'
+            ),
+            regexKeys: [0, 1],
+            source: '/unnamed/(first|second)/(.*)',
+            statusCode: 307,
+          },
         ],
         headers: [
           {