Rewrite adds query param when re-appending a matched path param to the destination

Bug report

Describe the bug

A rewrite from /source/:route* to http://my-api-server.example.org/destination/:route* forwards a request sent to /source/foo to http://my-api-server.example.org/destination/foo?route=foo. The extra query param will lead to issues especially with API servers as in REST this might represent a filter criteria.

To Reproduce

1. Create a new next app

2. Create a custom next.config.js:

module.exports = {
  async rewrites() {
    return [
      {
        source: "/api/:route*",
        destination: "https://postman-echo.com/:route*",
      },
    ];
  },
};

1. Start next: yarn next dev

2. Open up http://localhost:3000/api/get

3. The results includes "url":"https://postman-echo.com/get?route=get"

Expected behavior

Params that are added to the destination path should not be included as a query param.

1. The results includes "url":"https://postman-echo.com/get"

Screenshots

n/a

System information

• Version of Next.js: 9.5.0
• Version of Node.js: n/a

Additional context

n/a

[ijjk]

Hi, this is the behavior currently since when rewriting the end-user doesn’t see the query values so we make all params available in the query automatically.

After discussion it looks like it would make sense to not add the params to the query automatically for rewrites if it is already used in the destination so we will be investigating this behavior

[ijjk]

@pratheekhegde the issue you mentioned with the trailing slash and rewrites can be tracked in this issue https://github.com/vercel/next.js/issues/15700