I've seen users struggle with knowing that they sometimes have to do import * as pkg. I wonder if there's some sort of warning we could print in dev mode when they don't do this in order to guide them towards the correct solution?

There's actually an instance of this in Vite you can test out.

Without the * as it reports (Vite emulated error):

SyntaxError: The requested module '@vitejs/test-optimized-with-nested-external' does not provide an export named 'default'
    at Object.get (file:///Users/bjorn/Work/oss/vite/packages/vite/dist/node/chunks/dep-da74c78d.js:56763:23)
    at render (/Users/bjorn/Work/oss/vite/playground/ssr-deps/src/app.js:74:46)
    at async file:///Users/bjorn/Work/oss/vite/playground/ssr-deps/server.js:98:23

We can definitely add more hints/suggestions here, but I think we can improve on that in a later PR.

Yeah, I wasn't sure if users know how to fix it though. The error message could be tweaked a bit to include a solution like The requested module '@vitejs/test-optimized-with-nested-external' does not provide an export named 'default'. Try importing with: import * as pkg from '@vitejs/test-optimized-with-nested-external'

I think we should wait to see how users are often hitting this before adding the hints. I'm afraid to add some suggestions that could be misleading otherwise. Plus there's a lot of resource for that error message on the web that they should be able to find different solutions to what they're hitting.

It would be nice to add this to docs/guide/migration.md.

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