@ not working in route paths

Describe the bug

Routes containing @ appear to have been broken in @sveltejs/kit 1.0.0-next.163 and result in a 404 error. 162 is working as expected, 163-165 reproduce the issue.

Reproduction

npm init svelte@next
npm install

create file src/routes/@test.svelte with the following contents:

<h1>@test</h1>

run npm run dev

browsing to this url http://localhost:3000/@test displays 404 Not found: /@test error page.

changing @sveltejs/kit from next to 1.0.0-next.162 in package.json, and then running npm i && npm run dev results in the @test page properly loading.

Logs

No response

System Info

System:
    OS: Linux 5.11 Ubuntu 21.04 (Hirsute Hippo)
    CPU: (4) x64 Intel(R) Core(TM) i5-4690K CPU @ 3.50GHz
    Memory: 7.19 GB / 15.47 GB
    Container: Yes
    Shell: 5.1.4 - /bin/bash
  Binaries:
    Node: 16.9.1 - ~/.n/bin/node
    Yarn: 1.22.5 - /usr/bin/yarn
    npm: 7.23.0 - ~/.npm-global/bin/npm
  Browsers:
    Chrome: 93.0.4577.63
    Firefox: 92.0
  npmPackages:
    @sveltejs/kit: next => 1.0.0-next.165 
    svelte: ^3.34.0 => 3.42.5

Severity

serious, but I can work around it

Additional Information

I am using a src/routes/@[username] path in my application for user profile pages, and they are all resulting in 404 errors now. I can technically work around the issue by refactoring my app to use a different user profile path, but I’d really like to avoid that if possible.

[benmccann]

Making it work correctly for #, @, and / seems challenging. I think we would have to change the pattern from a single pattern to an array of patterns first splitting on / and then matching against each decoded path segment

[benmccann]

Hmm. That doesn’t work.

decodeURIComponent(encodeURI(decodeURI('AC%2fDC'))) returns AC%2fDC while decodeURIComponent('AC%2fDC') returns AC/DC because the first decodeURI leaves the % alone and then it gets encoded again with encodeURI

Maybe what we need to do instead is manually decode the characters that decodeURI doesn’t?