Import scss in node_modules with a Vite resolve.alias fails in Vite 6

[danielelkington]

Describe the bug

I am trying to import Bootstrap Functions from an scss file. In my Vite config I have aliased "@" to the src directory, and I am trying to use the "@" alias when importing the scss file from node_modules. This has worked fine through Vite 5, but breaks in Vite 6 with the error [sass] Can't find stylesheet to import.

Reproduction

https://stackblitz.com/edit/vitejs-vite-y6lwlhpr?file=src%2Fstyle.scss

Steps to reproduce

Open the reproduction link. Note that the app is failing with the error message [sass] Can't find stylesheet to import.
To see it working in Vite 5, in package.json change the Vite version to 5.4.11, and then in the terminal run npm install && npm run dev.

System Info

System:
    OS: Windows 10 10.0.19045
    CPU: (8) x64 Intel(R) Core(TM) i7-8665U CPU @ 1.90GHz
    Memory: 8.90 GB / 31.81 GB
  Binaries:
    Node: 22.10.0 - C:\Program Files\nodejs\node.EXE
    npm: 10.9.0 - C:\Program Files\nodejs\npm.CMD
    pnpm: 8.6.5 - ~\AppData\Local\pnpm\pnpm.EXE
  Browsers:
    Edge: Chromium (127.0.2651.74)
    Internet Explorer: 11.0.19041.4355
  npmPackages:
    @vitejs/plugin-vue: ^5.2.1 => 5.2.1
    vite: ^6.0.5 => 6.0.5

Used Package Manager

npm

Logs

No response

Validations

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• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Make sure this is a Vite issue and not a framework-specific issue. For example, if it's a Vue SFC related bug, it should likely be reported to vuejs/core instead.
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• The provided reproduction is a minimal reproducible example of the bug.

[sapphi-red]

It seems this only happens with modern API (which is the default from Vite 6).

For a workaround, you can set css.preprocessorOptions.sass.api: 'legacy' for now.