`@sveltejs/kit` and `vite@3` in typescript monorepo fails with `ERR_UNKNOWN_FILE_EXTENSION`

Describe the bug

A pnpm monorepo with symlinked TypeScript packages during development fails with the message ERR_UNKNOWN_FILE_EXTENSION.

@sveltejs/vite-plugin-svelte works fine. Things only break with the kit() plugin from the @sveltejs/kit/vite endpoint.

Reproduction

Here is a minimal(ish) reproduction: https://github.com/ifiokjr/vite3-unknown-file-extension

The readme describes where the error occurs, along with an example of vite handling the typescript package files correctly without @sveltejs/kit.

Logs

Unknown file extension ".ts" for /path/to/root/vite3-unknown-file-extension/packages/simple/src/index.ts
TypeError [ERR_UNKNOWN_FILE_EXTENSION]: Unknown file extension ".ts" for /path/to/root/vite3-unknown-file-extension/packages/simple/src/index.ts
    at new NodeError (node:internal/errors:377:5)
    at Object.getFileProtocolModuleFormat [as file:] (node:internal/modules/esm/get_format:80:11)
    at defaultGetFormat (node:internal/modules/esm/get_format:122:38)
    at defaultLoad (node:internal/modules/esm/load:21:20)
    at ESMLoader.load (node:internal/modules/esm/loader:431:26)
    at ESMLoader.moduleProvider (node:internal/modules/esm/loader:350:22)
    at new ModuleJob (node:internal/modules/esm/module_job:66:26)
    at #createModuleJob (node:internal/modules/esm/loader:369:17)
    at ESMLoader.getModuleJob (node:internal/modules/esm/loader:328:34)
    at async Promise.all (index 0)

System Info

System:
    OS: macOS 12.4
    CPU: (8) x64 Intel(R) Core(TM) i7-7700K CPU @ 4.20GHz
    Memory: 17.79 GB / 64.00 GB
    Shell: 5.8.1 - /bin/zsh
  Binaries:
    Node: 18.3.0 - ~/Library/Caches/fnm_multishells/43378_1657864625724/bin/node
    npm: 8.11.0 - ~/Library/Caches/fnm_multishells/43378_1657864625724/bin/npm
    Watchman: 2022.07.04.00 - /usr/local/bin/watchman
  Browsers:
    Brave Browser: 103.1.40.107
    Chrome: 103.0.5060.114
    Chrome Canary: 105.0.5179.0
    Firefox: 99.0.1
    Safari: 15.5
  npmPackages:
    @sveltejs/adapter-auto: 1.0.0-next.60 => 1.0.0-next.60 
    @sveltejs/kit: 1.0.0-next.375 => 1.0.0-next.375 
    svelte: 3.44.0 => 3.44.0 
    vite: 3.0.0 => 3.0.0

Severity

blocking an upgrade

Additional Information

No response

[ifiokjr]

@benmccann I think you’re right about this being an upstream issue. As a temporary workaround setting your vite config to the following allows it to build.

// vite.config.js
import { sveltekit } from '@sveltejs/kit/vite';
import { defineConfig } from 'vite';

export default defineConfig({
  plugins: [sveltekit()],
+  legacy: { buildSsrCjsExternalHeuristics: true },
});

I found it in the migration guide. https://vitejs.dev/guide/migration.html#ssr-changes

[Mlocik97]

adding another two errors from Discord:

Unknown file extension ".css" for /home/jacek/storage/developSSD/e-poezja-svelte/node_modules/sanitize.css/sanitize.css
TypeError [ERR_UNKNOWN_FILE_EXTENSION]: Unknown file extension ".css" for /home/jacek/storage/developSSD/e-poezja-svelte/node_modules/sanitize.css/sanitize.css
    at new NodeError (node:internal/errors:371:5)
    at Object.getFileProtocolModuleFormat [as file:] (node:internal/modules/esm/get_format:84:11)
    at defaultGetFormat (node:internal/modules/esm/get_format:99:38)
    at defaultLoad (node:internal/modules/esm/load:21:14)
    at ESMLoader.load (node:internal/modules/esm/loader:359:26)
    at ESMLoader.moduleProvider (node:internal/modules/esm/loader:280:58)
    at new ModuleJob (node:internal/modules/esm/module_job:66:26)
    at ESMLoader.#createModuleJob (node:internal/modules/esm/loader:297:17)
    at ESMLoader.getModuleJob (node:internal/modules/esm/loader:261:34)
    at async Promise.all (index 0)

TypeError [ERR_UNKNOWN_FILE_EXTENSION]: Unknown file extension ".svelte" 

(still waiting for second error)