Better error logging

[Rich-Harris]

This started out as a PR to address #982 specifically, but I ended up fixing a bunch of adjacent code:

• the SSRRenderOptions type is much neater, with the options passed to app.render separated out
• added SSRRenderState as distinct from SSRRenderOptions — this is used for tracking prerender dependencies and preventing infinite fetch loops. It means that the built app only needs to create the render options object once
• exceptions are always console-logged, whether from endpoints or pages. This fixes More informative error messages in prerendering #982 without adding any additional machinery
• error logging is more readable in dev
• error responses (whether explicit or triggered by exceptions) in prerender will show which page linked to the erroring page, or which page fetched the erroring endpoint. This makes it much easier to find broken links etc

Before submitting the PR, please make sure you do the following

• It's really useful if your PR references an issue where it is discussed ahead of time. In many cases, features are absent for a reason. For large changes, please create an RFC: https://github.com/sveltejs/rfcs
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• Ideally, include a test that fails without this PR but passes with it.

Tests

• Run the tests with pnpm test and lint the project with pnpm lint

Changesets

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[benmccann]

parent_path might be a clearer name? Or could update the JSDoc to clarify that it's a path

[Rich-Harris]

I feel like it's obvious from usage. If you go by the name alone then you might think that the parent_path of /foo/bar was /foo, whereas if you scan down to where it's used, it becomes clear what it does

[benmccann]

Cool!! I wonder if there are any tests we should add for this

[Rich-Harris]

Cool!! I wonder if there are any tests we should add for this

Prerendering tests in general are a bit of a TODO

[datio]

There's a regression when a unicode path is visit'ed because of the following change:

https://github.com/sveltejs/kit/blame/2a1e9795ad9773e04669a7b9d0234caa0b688ade/packages/kit/src/core/adapt/prerender.js#L227

If it's changed, say, to:

await visit(decodeURI(path), parsed.pathname.replace(config.kit.paths.base, ''));

It builds correctly.

[benmccann]

@datio can you file a new issue instead of commenting on a closed PR? this will for sure get lost otherwise