"Styles were unable to be assigned to a file" error in Qwik project if used in root route

[EatChangmyeong]

Describe the bug

vanilla-extract fails to extract styles if all of the following conditions are met:

• vanilla-extract is used with Qwik
• dev server has just started with npm run dev or npm start
  • The error disappears with npm run preview or when style is added while dev server is already running
• the route / (i.e. /src/routes/index.tsx or /src/routes/layout.tsx) references vanilla-extract classes in any way
  • The error shows immediately after dev server is ready, even without any browser tabs to trigger it

This bug also affects styled-vanilla-extract, which is how I first discovered it.

The reproduction was created with the following steps:

1. npm create qwik@latest
2. select Empty App (Qwik City + Qwik)
3. npm i @vanilla-extract/css @vanilla-extract/vite-plugin
4. add vanillaExtractPlugin to vite.config.ts
5. add a minimal style in /src/routes/style.css.ts and use it in /src/routes/index.tsx

Reproduction

https://github.com/EatChangmyeong/vanilla-extract-qwik-repro

System Info

System:
    OS: Windows 11 10.0.26100
    CPU: (8) x64 Intel(R) Core(TM) i5-8265U CPU @ 1.60GHz
    Memory: 1.39 GB / 7.86 GB
  Binaries:
    Node: 22.13.1 - C:\Program Files\nodejs\node.EXE
    Yarn: 1.22.22 - C:\Program Files\nodejs\yarn.CMD
    npm: 10.9.2 - C:\Program Files\nodejs\npm.CMD
    pnpm: 10.12.4 - C:\Program Files\nodejs\pnpm.CMD
  Browsers:
    Edge: Chromium (131.0.2903.112)
    Internet Explorer: 11.0.26100.1882
  npmPackages:
    @vanilla-extract/css: ^1.17.4 => 1.17.4
    @vanilla-extract/vite-plugin: ^5.1.0 => 5.1.0
    vite: 5.3.5 => 5.3.5

Used Package Manager

npm

Logs

PS C:\vanilla-extract-qwik-repro> npm run dev                                                 

> dev
> vite --mode ssr

using deprecated parameters for the initialization function; pass a single object instead
(!) Could not auto-determine entry point from rollupOptions or html files and there are no explicit optimizeDeps.include patterns. Skipping dependency pre-bundling.

  VITE v5.3.5  ready in 3033 ms

  ➜  Local:   http://localhost:5173/
  ➜  Network: use --host to expose
  ➜  press h + enter to show help
오전 3:27:37 [vite] Error when evaluating SSR module /src/routes/style.css.ts:
|- Error: Styles were unable to be assigned to a file. This is generally caused by one of the following:

- You may have created styles outside of a '.css.ts' context
- You may have incorrect configuration. See https://vanilla-extract.style/documentation/getting-started
    at Object.getFileScope (C:\vanilla-extract-qwik-repro\node_modules\@vanilla-extract\css\fileScope\dist\vanilla-extract-css-fileScope.cjs.dev.js:35:11)
    at generateIdentifier (C:\vanilla-extract-qwik-repro\node_modules\@vanilla-extract\css\dist\vanilla-extract-css.cjs.dev.js:155:49)
    at Module.style (C:\vanilla-extract-qwik-repro\node_modules\@vanilla-extract\css\dist\vanilla-extract-css.cjs.dev.js:415:19)
    at eval (C:/vanilla-extract-qwik-repro/src/routes/style.css.ts:5:35)
    at async instantiateModule (file:///C:/vanilla-extract-qwik-repro/node_modules/vite/dist/node/chunks/dep-mCdpKltl.js:52650:5)

오전 3:27:37 [vite] Error when evaluating SSR module C:/vanilla-extract-qwik-repro/src/routes/index.tsx:
|- Error: Styles were unable to be assigned to a file. This is generally caused by one of the following:

- You may have created styles outside of a '.css.ts' context
- You may have incorrect configuration. See https://vanilla-extract.style/documentation/getting-started
    at Object.getFileScope (C:\vanilla-extract-qwik-repro\node_modules\@vanilla-extract\css\fileScope\dist\vanilla-extract-css-fileScope.cjs.dev.js:35:11)
    at generateIdentifier (C:\vanilla-extract-qwik-repro\node_modules\@vanilla-extract\css\dist\vanilla-extract-css.cjs.dev.js:155:49)
    at Module.style (C:\vanilla-extract-qwik-repro\node_modules\@vanilla-extract\css\dist\vanilla-extract-css.cjs.dev.js:415:19)
    at eval (C:/vanilla-extract-qwik-repro/src/routes/style.css.ts:5:35)
    at async instantiateModule (file:///C:/vanilla-extract-qwik-repro/node_modules/vite/dist/node/chunks/dep-mCdpKltl.js:52650:5)


  🚧 Please note that development mode is slower than production.

Validations

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