Catch-all routes do not catch the root index route

Feature Request

Describe the use case

I have a use case where I need all of the following requests to go to the same function:

POST pages/api/users
PATCH pages/api/users/1
DELETE pages/api/users/1

After reading the docs, I was sure I could catch all of those using this:

pages/api/users/[...slug].js

However, this does not catch POST pages/api/users without an explicit /index.js.

To Reproduce

Try the above scenario (even with GET requests)

Expected behavior

This route:

pages/api/users/[...slug].js

Catches all of these:

POST pages/api/users
PATCH pages/api/users/1
DELETE pages/api/users/1

Screenshots

N/A

System information

N/A

Additional context

Next.js 9.2.2-canary.15

[Janpot]

@timneutkens created https://github.com/zeit/next.js/pull/10502

Been thinking a bit more about this issue and I think the requested behavior could make more sense for the following reasons:

1. Conceptually [...slug] looks like array destructuring into an array. Arrays can have zero items, so why can’t slug have zero items? The index route would just receive an empty array as the slug parameter.

2. The solution I proposed is flawed. Let me give an example:

Current situation, imagine we have a catch-all route like:

// /api/posts/[...slug].js
export default function (req, res) {
  res.send(getPost(req.query.slug))
}

And we fetch the following urls:

url	getPost called with
/api/posts	404	wtf? /api/posts/index resolves, so why not this?
/api/posts/index	['index']	ok
/api/posts/something	['something']	ok
/api/posts/something/else	['something', 'else']	ok

Imagine we add a index route:

// /api/posts/index.js
export { default } from './[...slug]';

now this behavior becomes

url	getPost called with
/api/posts	undefined	ok (I guess)
/api/posts/index	undefined	wtf?
/api/posts/something	['something']	ok
/api/posts/something/else	['something', 'else']	ok

Now, imagine /api/posts/[...slug].js would also be called for the index route, like this issue proposes. Then with just the following route

// /api/posts/[...slug].js
export default function (req, res) {
  res.send(getPost(req.query.slug))
}

the behavior would be more predictable and uniform and zen

url	getPost called with
/api/posts	[]	ok
/api/posts/index	['index']	ok
/api/posts/something	['something']	ok
/api/posts/something/else	['something', 'else']	ok

[timneutkens]

I’ll keep the issue open to see if there’s anyone else asking for it.