[SSR] Stop resolving externalized dependencies

Describe the bug

AFAICT, Vite should completely ignore externalize SSR dependencies, including:

• Not trying to resolve the dependency’s module locations
• ~Not read the dependency’s code at all~ (edit: this seems to be the case ✅ )

E.g. https://github.com/vuetifyjs/vuetify/issues/13936; I don’t see a reason why Vite should try to resolve the module vuetify/lib/components.

Proposal: Vite should completely ignore externalized deps.

cc @GrygrFlzr

@aleclarson Do you know why Vite touches externalized deps?

@patak-js I’m thinking maybe we should cue in Evan about this at some point.

Reproduction

Vuetify repro: https://github.com/brillout/vuetify3-ssr

[brillout]

@benmccann

velteKit projects all have type: "module" by default, but users still can’t use unified. If I force unified to be external I get the message Must use import to load ES Module because Vite changed my import statement to require.

If the user has type: "module", then Vite should certainly not transpile import statements to require. That’s part of the ESM plan I described above.

This means that SveleKit users will be able to use unified (since the user’s code does import statements even after transpilation).

The neat thing here is: Vite doesn’t need to resolve externalized SSR dependencies. Vite just looks at the user’s package.json and if there is a type: "module" then it keeps import statements and otherwise transforms them into require statements. That’s it.

To sum up:

• Main propsal: Vite doesn’t need to resolve externalized SSR dependencies.
• ESM proposal: Vite shouldn’t transform import statements to require statements if the user has type: "module".
• Remove custom resolver propsal #4447: for bundling the entire server-side code with all dependencies, Vite needs to resolve all dependencies. But maybe we can use Node.js’s resolver and remove Vite’s custom resolver (for SSR at least; we may still need it for the browser-side).

I believe these three proposals will solve many (if not most…) SSR problems mentioned in https://github.com/vitejs/vite/discussions/4230.

Let me know if there are doubts/questions, I’m happy to elaborate further.

[benmccann]

If a Vite user wants to use unified@10 she has to add type: module to her package.json

SvelteKit projects all have type: "module" by default, but users still can’t use unified. If I force unified to be external I get the message Must use import to load ES Module because Vite changed my import statement to require. I know that’s a loading issue and this thread is about resolving, but I guess the point I’m trying to make is that it’s possible that if we change resolving without fixing loading first it’s possible that we’re going to be hitting these loading issues way more often making SSR even more difficult to use. Not trying to be a cold blanket here because I support your plan. Just trying to keep the larger picture in mind and order things appropriately