getServerSideProps + Link as prop generating incorrect data fetching URL

Bug report

Describe the bug

getServerSideProps with:

• a custom server
• not using NextJS’ builtin dynamic routes
• pretty URLs (using the as prop on Link)

fails to generate a working data fetching URL

To Reproduce

Let’s say we have a couple top-level pages (categories) on our site: /fluff/ and /stuff/. The NextJS page used to render these is category.js

export default Category = ({ category }) => {
  return <div>You are on {category.name}</div>
}

export async function getServerSideProps() {
  return { props: { category: API.getCategory(ctx.query.slug) } }
}

I use Link components like <Link as='/fluff' href='/category?category=fluff'>...</Link>. I’m not using NextJS’ builtin dynamic routing.

The generated data fetching URL is /_next/data/BUILD_ID/fluff.json whereas it should be /_next/data/BUILD_ID/category.json?category=fluff. The former fails, as there’s no page explicitly named “fluff”, the latter works as expected.

It should be noted that if you do not specify the as prop, the URL is generated properly. Also note that that it does not matter if you use { pathname: '/category', query: { category: 'fluff' } } or the syntax specified above.

Our custom server, using express, references these pages like so:

const app = next()
const handler = app.getRequestHandler()

app.prepare().then(() => {
  const server = express()
  server.get('/:category(fluff|stuff)', (req, res) => {
    // note that req.params.category = fluff | stuff and is passed through 
    // to getServerSideProps via ctx.query.category
    app.render(req, res, '/category', { ...req.query, ...req.params })
  })

  server.use((req, res) => handler(req, res))
})

But as mentioned above, data fetching works with a differently generated URL.

Expected behavior

Data fetching should still work using the as prop.

System information

• Version of Next.js: 9.3.2

[Timer]

This should be fixed on canary!

[balazsorban44]

This issue has been automatically locked due to no recent activity. If you are running into a similar issue, please create a new issue with the steps to reproduce. Thank you.