scss paths starting with / on secondary sass modules stopped working on v6 only on Windows, can't solve with custom sass importer.

[miguel-leon]

Describe the bug

main.scss has @use "/src/foo/foo.scss" which works, but the same line in another file errors with [plugin:vite:css] [sass] File URL path must be absolute.
It works on v5 and errors on v6.

Tried to add a sass importer to solve the problem in vite config -> css -> preprocessorOptions -> sass -> importers. But it errors before and doesn't reach the importer.

Reproduction

https://stackblitz.com/edit/vitejs-vite-qnqdkutz

Steps to reproduce

Not reproducible in linux, so the stackblitz link does not error.

After npm create vite add the following files:

vite-project/
└── src/
    ├── main.scss
    ├── foo/
    │   └── foo.scss
    └── bar/
        └── bar.scss

The content of main.scss

@use "/src/foo/foo.scss";
@use "/src/bar/bar.scss";

@debug foo.$foo;

The content of foo.scss

$foo: "hello";

The content of bar.scss

@use "/src/foo/foo.scss";

@debug foo.$foo;

And to index.html add <link rel="stylesheet" href="/src/main.scss" />

Then npm run dev.

System Info

System:
    OS: Windows 11 10.0.26100
    CPU: (12) x64 12th Gen Intel(R) Core(TM) i7-1255U
    Memory: 16.24 GB / 31.83 GB
  Binaries:
    Node: 22.9.0 - C:\Program Files\nodejs\node.EXE
    npm: 10.8.3 - C:\Program Files\nodejs\npm.CMD
    pnpm: 9.14.4 - C:\ProgramData\chocolatey\bin\pnpm.EXE
  Browsers:
    Edge: Chromium (129.0.2792.89)
    Internet Explorer: 11.0.26100.1882
  npmPackages:
    vite: ^6.0.1 => 6.0.3

Used Package Manager

npm

Logs

Click to expand!

  VITE v6.0.3  ready in 222 ms

  ➜  Local:   http://localhost:5173/
  ➜  Network: use --host to expose
  ➜  press h + enter to show help
  vite:html-fallback Rewriting GET / to /index.html +0ms
  vite:time 55.30ms /index.html +0ms
  vite:resolve 30.76ms /src/main.js -> C:/.../vite-project/src/main.js +0ms
  vite:load 5.67ms [fs] /src/main.js +0ms
  vite:resolve 4.51ms ./style.css -> C:/.../vite-project/src/style.css +23ms
  vite:resolve 4.66ms ./javascript.svg -> C:/.../vite-project/src/javascript.svg +0ms
  vite:resolve 4.85ms ./counter.js -> C:/.../vite-project/src/counter.js +0ms
  vite:import-analysis 11.83ms [4 imports rewritten] src/main.js +0ms
  vite:transform 18.19ms /src/main.js +0ms
  vite:resolve 0.54ms /@vite/client -> C:/.../vite-project/node_modules/vite/dist/client/client.mjs +9ms
  vite:resolve 1.44ms /src/main.scss?direct -> C:/.../vite-project/src/main.scss?direct +5ms
  vite:cache [304] /src/main.js +0ms
  vite:time 0.37ms /src/main.js +44ms
  vite:load 20.16ms [plugin] /src/javascript.svg +38ms
  vite:import-analysis 0.28ms [no imports] src/javascript.svg +21ms
  vite:transform 0.84ms [skipped] /src/javascript.svg +19ms
  vite:load 21.46ms [plugin] /vite.svg +1ms
  vite:import-analysis 0.09ms [no imports] /vite.svg +1ms
  vite:transform 0.46ms [skipped] /vite.svg +1ms
  vite:load 22.45ms [fs] /src/style.css +1ms
  vite:hmr [self-accepts] src/style.css +0ms
  vite:import-analysis 0.96ms [0 imports rewritten] src/style.css +2ms
  vite:transform 2.09ms /src/style.css +3ms
  vite:load 19.63ms [fs] /@vite/client +3ms
  vite:resolve 0.10ms @vite/env -> C:/.../vite-project/node_modules/vite/dist/client/env.mjs +28ms
  vite:import-analysis 1.78ms [1 imports rewritten] node_modules/vite/dist/client/client.mjs +15ms
  vite:transform 13.46ms /@vite/client +14ms
  vite:time 35.76ms /@vite/client +28ms
  vite:load 41.39ms [fs] /src/counter.js +16ms
  vite:import-analysis 0.08ms [no imports] src/counter.js +3ms
11:12:09 PM [vite] Internal server error: [sass] File URL path must be absolute
  ╷
1 │ @use "/src/foo/foo.scss";
  │ ^^^^^^^^^^^^^^^^^^^^^^^^
  ╵
  src\bar\bar.scss 1:1  @use
  src\main.scss 2:1     root stylesheet
  Plugin: vite:css
  File: C:/.../vite-project/src/main.scss?direct:1:1
  [sass] File URL path must be absolute
    ╷
  1 │ @use "/src/foo/foo.scss";
    │ ^^^^^^^^^^^^^^^^^^^^^^^^
    ╵
    src\bar\bar.scss 1:1  @use
    src\main.scss 2:1     root stylesheet
      at Object.wrapException (C:\...\vite-project\node_modules\sass\sass.dart.js:2305:43)
      at Object.throwWithTrace0 (C:\...\vite-project\node_modules\sass\sass.dart.js:32304:15)
      at C:\...\vite-project\node_modules\sass\sass.dart.js:87489:19
      at _wrapJsFunctionForAsync_closure.$protected (C:\...\vite-project\node_modules\sass\sass.dart.js:5020:15)
      at _wrapJsFunctionForAsync_closure.call$2 (C:\...\vite-project\node_modules\sass\sass.dart.js:38043:12)
      at _awaitOnObject_closure0.call$2 (C:\...\vite-project\node_modules\sass\sass.dart.js:38037:25)
      at Object._rootRunBinary (C:\...\vite-project\node_modules\sass\sass.dart.js:5437:18)
      at StaticClosure.<anonymous> (C:\...\vite-project\node_modules\sass\sass.dart.js:124040:16)
      at _CustomZone.runBinary$3$3 (C:\...\vite-project\node_modules\sass\sass.dart.js:39496:39)
      at _FutureListener.handleError$1 (C:\...\vite-project\node_modules\sass\sass.dart.js:38260:21)
  vite:time 399.34ms /src/main.scss +51ms

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• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
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• The provided reproduction is a minimal reproducible example of the bug.

[sapphi-red]

Made a fix here: main...sapphi-red:vite:fix/sass-slash-importer-windows
I'll make a PR once sass/sass#3998 has a response and if the fix is needed on Vite side.