[SingleFetch][basename] root data endpoint is outside basename

[freeman]

Reproduction

You can see the issue on this code sandbox: https://codesandbox.io/p/devbox/zwd9rl

If you hit the "Increment" button you will get an error that is due to vite rejecting the request to /foo.data as it is outside the vite base (== remix basename) which is "/foo/".

I think this was introduced involuntarily by #9792 as it tries to prevent the /.data url format.

System Info

System:
    OS: Linux 6.1 Debian GNU/Linux 12 (bookworm) 12 (bookworm)
    CPU: (2) x64 AMD EPYC
    Memory: 919.50 MB / 4.01 GB
    Container: Yes
    Shell: Unknown
  Binaries:
    Node: 20.9.0 - /usr/local/bin/node
    Yarn: 1.22.19 - /usr/local/bin/yarn
    npm: 9.8.1 - /usr/local/bin/npm
    pnpm: 8.10.2 - /usr/local/share/npm-global/bin/pnpm
  npmPackages:
    @remix-run/css-bundle: ^2.14.0 => 2.14.0 
    @remix-run/dev: ^2.14.0 => 2.14.0 
    @remix-run/node: ^2.14.0 => 2.14.0 
    @remix-run/react: ^2.14.0 => 2.14.0 
    vite: ^5.4.11 => 5.4.11 

Used Package Manager

pnpm

Expected Behavior

I would expect requests for the root/_index data loader when a basename (/foo/ for example) is present to honor it and use either :

• /foo/_root.data
• /foo/.data (though I agree that this format is not great as it may often be blocked as an attempt to access hidden files)

Actual Behavior

When a basename is configured root/index loader data url goes outside of the basename.

[freeman]

I think this impact React Router v7 as well though I have not verified it there.