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Someone should run /ecosystem-ci run against this PR.

I'm not sure if this is a bug? Like you mentioned, it's using appType: 'custom' so you have to handle HTML requests like in dev too, so I think it's better aligned now. The appType config is top-level instead of nested to server.*.

This should also be covered in the migration guide though which I missed.

EDIT: Unless we say appType: 'custom' has no effect in preview, since it's not common for that in preview especially without middlewareMode there. But it would still be nice to align with dev if there's ever a usecase for custom.

In dev, a page is always SSR'd, regardless of whether the user chooses to pre-render that page.

In preview, when a page is pre-rendered, the page isn't SSR'd and, instead, its HTML is generated at build time and lives in dist/ as a static .html file, for example dist/hello/index.html or dist/hello.html (both ${url}.html and ${url}/index.html are common as some static hosts prefer the one over the other).

From that perspective, the discrepancy between dev and preview is very much expected.

From a technical point of view, I understand this adds an edge case, but I'd argue it's the correct way to do it.

Isn't that Vike specific? In build/preview, you can also choose not to prerender some pages, and handle SSR for the requested pages. Or a hybrid mode where some HTML is prerendered, and some not that goes through SSR. IIUC the discrepancy isn't within Vite.

In build/preview, you can also choose not to prerender some pages, and handle SSR for the requested pages. Or a hybrid mode where some HTML is prerendered, and some not that goes through SSR.

Yes, exactly, and that's precisely why both is needed: the SSR middleware + serving static .html files.

Isn't that Vike specific? [...] IIUC the discrepancy isn't within Vite.

If Vite's preview doesn't serve .html files, then Vike will have to implement/duplicate the whole .html serving logic.

The purpose of Vite's preview server is to alleviate users and framework authors from implementing their own preview server and re-inventing the wheel.

It's specific to Vike and any (future) framework that (will) want to support partial pre-rendering.

This isn't a blocker for Vike and I don't mind re-implementing the .html serving logic in Vike, I just think that this PR is correct way for Vite to do it.

We also talked about this in the meeting and prefer aligning in dev at the meantime. If appType: 'custom' is specified, from a plugin pov if it handles middlewares in dev, it would also do the same in preview.

It also seems like the behaviour you want is the same as appType: 'mpa', however presumably you'd need to know where you're in dev or preview to set it differently, which leads to #12298 (which we also discussed and will comment later).

So since users can specify appType: 'mpa' if they want this today, we don't think this is needed.

It also seems like the behaviour you want is the same as appType: 'mpa'

👍 Makes sense.

I tried to make it work with appType: 'mpa' but couldn't. So I've decided to fallback to what other frameworks do: always use the SSR middleware even for pre-rendered pages. It's a pity because it isn't a faithful preview anymore, but I guess this "cheat" is ok.

Anyways, the decision to reject this PR makes sense, thus closing.