lightningcss fails in scss files on single line comments

[taras-turchenko-moc]

Describe the bug

Lightningcss fails on scss single line comments when using it as a transformer. It's strange because it should be processed by scss to generate valid css comments since it supports only multiline comments. I has another part of an app bundling by rspack and it works fine so it appears a vite bug

Reproduction

https://github.com/taras-turchenko-moc/lightningcss-scss-comments-bug

Steps to reproduce

Reproduction link has a github repo with default vanilla setup, enabled lightningcss, renamed style.css to scss and added a comment

npm install
npm run build

System Info

System:
    OS: macOS 15.1.1
    CPU: (14) arm64 Apple M3 Max
    Memory: 436.25 MB / 36.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 22.11.0 - ~/.nvm/versions/node/v22.11.0/bin/node
    Yarn: 1.22.22 - ~/.nvm/versions/node/v22.11.0/bin/yarn
    npm: 10.9.0 - ~/.nvm/versions/node/v22.11.0/bin/npm
    bun: 1.1.42 - /opt/homebrew/bin/bun
  Browsers:
    Chrome: 131.0.6778.205
    Safari: 18.1.1
  npmPackages:
    vite: ^6.0.5 => 6.0.6

Used Package Manager

npm

Logs

Click to expand!

> [email protected] build
> vite build --debug

  vite:config bundled config file loaded in 16.55ms +0ms
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vite v6.0.6 building for production...
✓ 6 modules transformed.
x Build failed in 22ms
error during build:
[vite:css] [lightningcss] Invalid empty selector
file: /Users/master/Projects/lightningcss-scss-comments-bug/src/style.scss:17:0
SyntaxError: [lightningcss] Invalid empty selector

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• The provided reproduction is a minimal reproducible example of the bug.

[btea]

Problems with the lightningcss side. parcel-bundler/lightningcss#624

[taras-turchenko-moc]

@btea But why lightningcss even trying to process scss files? Shouldn't it be transformed by sass before passing to lightningcss?

[taras-turchenko-moc]

As I said before I have another part of an app that also using lightningcss and it doesnt have any issues with it because rspack/webpack transforms scss file to css before passing it to lightningcss loader

[btea]

@btea But why lightningcss even trying to process scss files? Shouldn't it be transformed by sass before passing to lightningcss?

Because you use lightningcss as transformer.
https://github.com/taras-turchenko-moc/lightningcss-scss-comments-bug/blob/6000ec4ced6e0452cd85d06e52c38335777d6d66/vite.config.js#L4-L6