«Rewrite mechanism» transforms array parameters of query of destination link into strings

[lsndr]

What version of Next.js are you using?

10.2.2

What version of Node.js are you using?

14.17.1

What browser are you using?

Safari

What operating system are you using?

macOS

How are you deploying your application?

next start

Describe the Bug

I'm trying to use Next.js' Rewrite feature. But when I put an array in a query part of a destination link string (in next.config.js), a context, that I receive in getServerSideProps, contains only first parameter of the array.

Here is my next.config.js

module.exports = {
...
  async rewrites() {
    return [
      {
        source: '/projects',
        destination: '/?tags=project&tags=проект',
      },
    ]
  },
...
}

When I open /projects in a browser, only first value of tags parameter is passed into context.query of getServerSideProps:

{
    tags: 'project'
}

Expected Behavior

context.query in getServerSideProps must contain all query values.

{
    tags: ['project', 'проект']
}

To Reproduce

• Create a new next.js project with the following next.config.js:

module.exports = {
...
  async rewrites() {
    return [
      {
        source: '/projects',
        destination: '/?tags=project&tags=проект',
      },
    ]
  },
...
}

• Create a page 'index.tsx' with getServerSideProps:

export const getServerSideProps: GetServerSideProps<any> = async (context) => {
    ....
    console.log(context.query);
    ....
};

• Open /projects page in a browser and check the server-side terminal

---

Actually, I've figured out why this happens and i'm ready to create PR. But before, I need to make sure that I understood the problem.

Here is the code, that causes the bug (packages/next/next-server/lib/router/utils/prepare-destination.ts):

export default function prepareDestination(
  destination: string,
  params: Params,
  query: ParsedUrlQuery,
  appendParamsToQuery: boolean
) {
...
  // update any params in query values
  for (const [key, strOrArray] of Object.entries(destQuery)) {
    let value = Array.isArray(strOrArray) ? strOrArray[0] : strOrArray
    if (value) {
      // the value needs to start with a forward-slash to be compiled
      // correctly
      value = compileNonPath(value, params)
    }
    destQuery[key] = value
  }
...

As you can see, it takes only a first item of the query array. I believe we must use.maphere

[balazsorban44]

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