Describe the bug

I have an pre- existing vite project that I am upgrading. Starting in Vite v5.3.5 and going up to the latest v6 release my sass partial files are not loading in the sourcemap, and dev tools only shows the initial imported file (styles.sass). If I revert back to v5.3.4 then my partial sass files are showing again.

I have looked through the changelog but I can't find any API changes that would resolve this issue.

Reproduction

https://stackblitz.com/edit/vitejs-vite-cicjj47e?file=src%2Fsass%2Fvendor%2Findex.scss%3AL98&terminal=dev

Steps to reproduce

npm install && npm run dev

Inspect the select2 element in the middle of the page. The sass selectors report the file as the primary imported file style.scss, when the real file that the styles are coming from is _select2.sass.

If you remove the @import 'select2'; line at src/sass/vendor/index.scss:98 then the partial file will change from style.scss (incorrect) to index.scss (correct).

Reverting to vite 5.3.4 also fixes the problem.

System Info

System:
    OS: Windows 11 10.0.22631
    CPU: (28) x64 Intel(R) Core(TM) i7-14700KF
    Memory: 28.84 GB / 63.83 GB
  Binaries:
    Node: 20.17.0 - C:\Program Files\nodejs\node.EXE
    Yarn: 1.22.22 - C:\Program Files (x86)\Yarn\bin\yarn.CMD
    npm: 10.8.2 - C:\Program Files\nodejs\npm.CMD
    bun: 1.1.3 - ~\.bun\bin\bun.EXE
  Browsers:
    Edge: Chromium (127.0.2651.74)
    Internet Explorer: 11.0.22621.3527

Used Package Manager

npm

Logs

No response

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