CSS file present in src/routes/ breaks production build

[yanneves]

Describe the bug

If a non-empty .css file is present in the src/routes/ directory with the same name as a .svelte file in the same directory, we receive an error in build.

Reproduction

To reproduce using the SvelteKit skeleton project:

1. npm init svelte@next sveltekit-css-repro (select skeleton, no to all options)
2. cd sveltekit-css-repro/
3. npm install
4. npm run build (succeeds)
5. echo "h1 { font-size: 1.5em; }" > src/routes/index.css
6. npm run build (fails, log below)
7. mv src/routes/{index,index-styles}.css
8. npm run build (succeeds)

Logs

$ npm run build

> sveltekit-css-repro@0.0.1 build
> svelte-kit build

vite v2.8.4 building for production...
✓ 13 modules transformed.
.svelte-kit/output/client/_app/manifest.json                    1.15 KiB
.svelte-kit/output/client/_app/layout.svelte-ddbe22e6.js        0.53 KiB / gzip: 0.35 KiB
.svelte-kit/output/client/_app/error.svelte-60b5f229.js         1.56 KiB / gzip: 0.75 KiB
.svelte-kit/output/client/_app/pages/index.svelte-4fdc3974.js   0.80 KiB / gzip: 0.47 KiB
.svelte-kit/output/client/_app/start-0e28adf2.js                23.61 KiB / gzip: 8.09 KiB
.svelte-kit/output/client/_app/chunks/vendor-f0095a1c.js        7.21 KiB / gzip: 2.96 KiB
vite v2.8.4 building SSR bundle for production...
✓ 12 modules transformed.
.svelte-kit/output/server/manifest.json                    0.87 KiB
.svelte-kit/output/server/app.js                           64.10 KiB
.svelte-kit/output/server/entries/pages/layout.svelte.js   0.24 KiB
.svelte-kit/output/server/entries/pages/error.svelte.js    0.72 KiB
.svelte-kit/output/server/entries/pages/index.svelte.js    0.32 KiB
.svelte-kit/output/server/chunks/index-2dc61825.js         2.29 KiB
> Cannot read properties of undefined (reading 'file')
    at file:///home/yann/git/sveltekit-css-repro/node_modules/@sveltejs/kit/dist/chunks/index4.js:78:108
    at Array.map (<anonymous>)
    at generate_manifest (file:///home/yann/git/sveltekit-css-repro/node_modules/@sveltejs/kit/dist/chunks/index4.js:71:14)
    at build (file:///home/yann/git/sveltekit-css-repro/node_modules/@sveltejs/kit/dist/chunks/index3.js:637:46)
    at async file:///home/yann/git/sveltekit-css-repro/node_modules/@sveltejs/kit/dist/cli.js:1054:23

System Info

System:
  OS: Linux 5.10 Debian GNU/Linux 10 (buster) 10 (buster)
  CPU: (8) x64 Intel(R) Core(TM) i7-9700K CPU @ 3.60GHz
  Memory: 8.23 GB / 15.60 GB
  Container: Yes
  Shell: 5.0.3 - /bin/bash
Binaries:
  Node: 17.5.0 - ~/.nvm/versions/node/v17.5.0/bin/node
  Yarn: 1.22.17 - ~/.nvm/versions/node/v17.5.0/bin/yarn
  npm: 8.5.1 - ~/.nvm/versions/node/v17.5.0/bin/npm
npmPackages:
  @sveltejs/adapter-auto: next => 1.0.0-next.17
  @sveltejs/kit: next => 1.0.0-next.278
  svelte: ^3.44.0 => 3.46.4

Severity

serious, but I can work around it

Additional Information

Further discussion in Svelte Discord thread https://discord.com/channels/457912077277855764/944288129114861588. Thanks to nudge#9063 for the help diagnosing!

A workaround is fairly trivial, ensure .css files inside src/routes/**/* do not match the filename of a .svelte file in the same directory.

The error is unclear, though. In a medium to large sized SvelteKit project, this could present a challenge upgrading.

[Conduitry]

I'm on the fence about whether any non-JS/TS and non-Svelte files in the routes folder should be compile time errors or simply ignored. I see arguments in both directions.

[Rich-Harris]

Opened #4185. I don't have a strong opinion about whether it's the right move or not

[Rich-Harris]

Closed via #4197