Conditional configuration in vite.config.js breaks prod build

Describe the bug

If your vite.config.js uses conditional configuration, Svelte stops trying to compile components files to JS during SSR, and the resulting build fails because Rollup/Acorn is trying to parse Svelte files as JS.

Reproduction

https://stackblitz.com/edit/sveltejs-kit-template-default-4wrfgp

Logs

❯ npm run build
$ vite build
vite v2.9.13 building for production...
✓ 34 modules transformed.
.svelte-kit/output/client/_app/immutable/assets/svelte-logo-87df40b8.svg                           1.85 KiB
.svelte-kit/output/client/_app/immutable/assets/fira-mono-cyrillic-ext-400-normal-3df7909e.woff2   15.40 KiB
.svelte-kit/output/client/_app/immutable/assets/fira-mono-cyrillic-400-normal-c7d433fd.woff2       8.89 KiB
.svelte-kit/output/client/_app/immutable/assets/fira-mono-greek-ext-400-normal-9e2fe623.woff2      7.33 KiB
.svelte-kit/output/client/_app/immutable/assets/fira-mono-greek-400-normal-a8be01ce.woff2          10.27 KiB
.svelte-kit/output/client/_app/immutable/assets/fira-mono-latin-ext-400-normal-6bfabd30.woff2      11.10 KiB
.svelte-kit/output/client/_app/immutable/assets/fira-mono-latin-400-normal-e43b3538.woff2          15.90 KiB
.svelte-kit/output/client/_app/immutable/assets/fira-mono-all-400-normal-1e3b098c.woff             75.55 KiB
.svelte-kit/output/client/_app/immutable/manifest.json                                             2.67 KiB
.svelte-kit/output/client/_app/immutable/start-ab798b44.js                                         23.25 KiB / gzip: 8.72 KiB
.svelte-kit/output/client/_app/immutable/pages/__layout.svelte-f0707ee1.js                         4.77 KiB / gzip: 1.86 KiB
.svelte-kit/output/client/_app/immutable/error.svelte-c8df2b3e.js                                  1.56 KiB / gzip: 0.75 KiB
.svelte-kit/output/client/_app/immutable/pages/about.svelte-692f0ea0.js                            2.51 KiB / gzip: 1.15 KiB
.svelte-kit/output/client/_app/immutable/pages/index.svelte-471ba9cf.js                            5.47 KiB / gzip: 2.42 KiB
.svelte-kit/output/client/_app/immutable/pages/todos/index.svelte-dda24c9b.js                      6.86 KiB / gzip: 2.89 KiB
.svelte-kit/output/client/_app/immutable/chunks/index-9fe72fd8.js                                  11.81 KiB / gzip: 5.02 KiB
.svelte-kit/output/client/_app/immutable/chunks/index-92d65ea7.js                                  0.43 KiB / gzip: 0.30 KiB
.svelte-kit/output/client/_app/immutable/chunks/singletons-d1fb5791.js                             0.05 KiB / gzip: 0.07 KiB
.svelte-kit/output/client/_app/immutable/assets/pages/__layout.svelte-da7c5ce3.css                 5.08 KiB / gzip: 1.56 KiB
.svelte-kit/output/client/_app/immutable/assets/pages/about.svelte-bf4528fa.css                    0.11 KiB / gzip: 0.10 KiB
.svelte-kit/output/client/_app/immutable/assets/pages/index.svelte-e12bfb09.css                    1.45 KiB / gzip: 0.52 KiB
.svelte-kit/output/client/_app/immutable/assets/pages/todos/index.svelte-a910a02d.css              3.70 KiB / gzip: 1.03 KiB
vite v2.9.13 building SSR bundle for production...
✓ 0 modules transformed.
transforming (1) .svelte-kit/build/index.js[rollup-plugin-dynamic-import-variables] Unexpected token (1:0)
file: /home/projects/sveltejs-kit-template-default-4wrfgp/src/routes/__layout.svelte:1:0
[vite-plugin-svelte-kit] Unexpected token (1:0)
file: /home/projects/sveltejs-kit-template-default-4wrfgp/src/routes/__layout.svelte:1:0

System Info

  System:
    OS: Linux 5.0 undefined
    CPU: (4) x64 Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
    Memory: 0 Bytes / 0 Bytes
    Shell: 1.0 - /bin/jsh
  Binaries:
    Node: 16.14.2 - /usr/local/bin/node
    Yarn: 1.22.10 - /bin/yarn
    npm: 7.17.0 - /bin/npm
  npmPackages:
    @sveltejs/adapter-auto: next => 1.0.0-next.53 
    @sveltejs/kit: next => 1.0.0-next.359 
    svelte: ^3.46.0 => 3.48.0 
    vite: ^2.9.13 => 2.9.13

Severity

blocking an upgrade

Additional Information

No response

[benmccann]

Actually, @benmccann is there a reason that build_server.js and build_service_worker.js try to manually load the Vite config at all? Couldn’t they just be passed the config argument that’s already passed to the config method in the Vite plugin?

Sadly not. An older version did that, which led to issues. See https://github.com/sveltejs/kit/issues/5308

[Conduitry]

Bummer. All right, I’ve opened a PR that keeps the get_vite_config function but now passes it a vite_config_env object.