Cannot use import statement outside a module

This is a followup on #2161. This issue had been fixed, but it was reintroduced in the latest sveltekit.

As asked, here is a reproduction: https://github.com/lovasoa/SvelteKit-2161

The stacktrace is

Cannot use import statement outside a module

/tmp/SvelteKit-2161/node_modules/@popperjs/core/dist/esm/popper.js:1
import { popperGenerator, detectOverflow } from "./createPopper.js";
^^^^^^

SyntaxError: Cannot use import statement outside a module
    at Object.compileFunction (node:vm:352:18)
    at wrapSafe (node:internal/modules/cjs/loader:1032:15)
    at Module._compile (node:internal/modules/cjs/loader:1067:27)
    at Object.Module._extensions..js (node:internal/modules/cjs/loader:1155:10)
    at Module.load (node:internal/modules/cjs/loader:981:32)
    at Function.Module._load (node:internal/modules/cjs/loader:822:12)
    at ModuleWrap.<anonymous> (node:internal/modules/esm/translators:168:29)
    at ModuleJob.run (node:internal/modules/esm/module_job:195:25)
    at async Promise.all (index 0)
    at async ESMLoader.import (node:internal/modules/esm/loader:337:24)

@lovasoa can you file a new issue with a reproduction? I don’t have a way to reproduce and investigate at the moment

_Originally posted by @benmccann in https://github.com/sveltejs/kit/issues/2161#issuecomment-1085851247_

[Rich-Harris]

This is a bug in @popperjs/core — Node is behaving as it should. Popper should either

• use an .mjs extension for all the modules in dist/esm/**/*.js, or
• create a dist/esm/package.json with {"type":"module"}, or
• (ideally) put {"type":"module"} in the root package.json

It should also declare its exports using the "exports" field in package.json.

As far as I can tell, the package has been superseded by floating-ui, which appears to do things differently, so maybe this is fixed already.

Either way, it can be worked around by populating Vite’s ssr.noExternal config:

/** @type {import('@sveltejs/kit').Config} */
const config = {
  kit: {
    vite: {
      ssr: {
        noExternal: ['@popperjs/core']
      }
    }
  }
};

export default config;

[nstuyvesant]

Dropping the import of the two enums solved the problem but I had to redefine them locally.