Vite produces invalid output paths when rebasing URLs in SCSS files

[VasilyStrelyaev]

Describe the bug

I have a Vite.js application where I import an SCSS file from a dependency. In a CSS bundle produce by Vite, the path is incorrect and invalid.

This issue seems to be specific to the file structure, as I can reproduce it if the SCSS file name matches the target directory name except the leading underscore and the url() argument is built using a variable:

├── foobar
│   └── static.png
└──  _foobar.scss // <- url("foobar/#{$file-name}.png")

In the resulting bundle, the foobar/static.png relative path is rebased to become .../xxx/_foobar.scssstatic.png (see the reproduction repo).

In the real life scenario, although we do control the said dependency, changes to its file structure constitute a breaking change for our customers, that is why it's important for us that this issue is addressed.

This issue may look a bit similar to the existing scss path rebase issues, both fixed and active (#11012, #19058), but I believe it may be a separate problem given that the open issues do not mention distorted file paths.

Reproduction

https://github.com/VasilyStrelyaev/vite-scss-path-rebase-repro

Steps to reproduce

1. npm install
2. npm run build to build a barebone app in packages/client-app
3. Open the build output at packages/client-app/dist/assets/index-XXX.css
4. Search for the url() function and notice its argument. Vite rebased the foobar/react.png relative path so that it became invalid: ../../scss-dep/src/_foobar.scssreact.png

System Info

System:
    OS: macOS 15.4
    CPU: (8) arm64 Apple M1 Pro
    Memory: 499.88 MB / 32.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 22.14.0 - /usr/local/bin/node
    Yarn: 1.22.22 - ~/.yarn/bin/yarn
    npm: 11.2.0 - /usr/local/bin/npm
    pnpm: 9.15.4 - /usr/local/bin/pnpm
  Browsers:
    Chrome: 135.0.7049.42
    Edge: 135.0.3179.54
    Safari: 18.4

Used Package Manager

npm

Logs

No response

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