Sourcemap is likely to be incorrect: a plugin (undefined) was used to transform files...

Describe the bug

Something changed between 2.5.6 and 2.5.7 in regards to how <style> blocks are processed.

I have a feeling that https://github.com/vitejs/vite/commit/015290a169d5ca3806aa0b2eb417426d61df9b7d is the cause because not much else changed in regards to CSS between 2.5.6 and 2.5.7 releases.

I’ve provided a very minimal repo to reproduce the issue.

Reproduction

https://github.com/bompus/vite-sourcemap-issue

$ npm run build

✓ 10 modules transformed.
rendering chunks (1)...Sourcemap is likely to be incorrect: a plugin (undefined) was used to transform files, but didn't generate a sourcemap for the transformation. Consult the plugin documentation for help

$ npm install vite@2.5.6 $ npm run build no warnings / errors

$ npm install vite@2.5.7 $ npm run build same warning / error appears as above

Edit the App.vue file to change <style lang="scss"> to <style> and the warning still appears, but this time it says a plugin (vite:css) was used instead of a plugin (undefined) was used.

System Info

System:
    OS: Linux 5.11 Ubuntu 20.04.3 LTS (Focal Fossa)
    CPU: (6) x64 AMD Ryzen 9 3950X 16-Core Processor
    Memory: 2.82 GB / 7.74 GB
    Container: Yes
    Shell: 5.0.17 - /bin/bash
  Binaries:
    Node: 16.9.1 - /usr/local/n/bin/node
    npm: 7.23.0 - /usr/local/n/bin/npm
  npmPackages:
    @vitejs/plugin-vue: 1.6.2 => 1.6.2
    vite: 2.5.7 => 2.5.7

Used Package Manager

npm

Logs

No response

Validations

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