SASS sourcemaps not working #8656

Describe the bug

SASS sourcemaps don't seem to work correctly.

I've stripped down my project to a few SASS files for reproduction, removed all third-party plugins, etc.

Testing this repro should be as easy as npm ci && npm run dev, then open a browser, open devtools, and inspect any of the elements on screen.

As shown in the screenshot here, sourcemaps do not point to any of the included SASS files in the project - instead, everything points to line numbers in index.scss:

These line numbers do not exist - index.scss is only 6 lines of code.

Reproduction

https://github.com/mindplay-dk/vite-sass-sourcemap-bug

System Info

System:
    OS: Linux 5.10 Ubuntu 16.04.7 LTS (Xenial Xerus)
    CPU: (8) x64 Intel(R) Core(TM) i7-4790K CPU @ 4.00GHz
    Memory: 4.89 GB / 6.13 GB
    Container: Yes
    Shell: 4.3.48 - /bin/bash
  Binaries:
    Node: 16.14.2 - ~/.nvm/versions/node/v16.14.2/bin/node
    Yarn: 1.22.4 - ~/.npm-global/bin/yarn
    npm: 8.5.5 - ~/.npm-global/bin/npm
  npmPackages:
    vite: ^2.9.12 => 2.9.12

Used Package Manager

npm

Logs

No response

Validations

• Follow our Code of Conduct
• 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 https://github.com/vuejs/core instead.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• The provided reproduction is a minimal reproducible example of the bug.