Expose list of (heading) IDs found on each page at build time

[janosh]

Describe the problem

I'd like to have a nav palette with fuzzy search for all headings with ids anywhere in the app. Here's my current setup listing only pages but not their sections.

Thanks to handleMissingId = 'fail', the build fails when I link to a non-existent id on an existing page:

<a href="existing-page#but-missing-id">will raise at build time</a>

So at least at build time, a list of all IDs on a page must already exist in kit's internals.

Describe the proposed solution

Would be great if that data could be made available for building a better "jump to section" experience on docs pages.

Alternatives considered

No response

Importance

nice to have

Additional Information

No response

[Rich-Harris]

Any thoughts on what an API would look like for this?

How is it that you know what pages exist, but not what headings exist within each page? Presumably any API for this sort of introspection should cover both (though I'm not sure how to make it work in a non-circular fashion). Could be useful in the context of e.g. sitemap generation

[janosh]

I have access to the pages via import.meta.glob(`./**/+page.{svelte,md}`).

vite's import.meta.glob has surprised me multiple times with the amount of features it offers out of the box but I don't think it parses file contents, just imports them. Not sure if a vite plugin could expose markdown and/or HTML headings found in imported files...

How does kit get the IDs at build time? Wherever they come from, maybe they could be added as an immutable property to the $page store. This wouldn't cover dynamically created IDs but that seems like a tall ask anyway.

[Rich-Harris]

How does kit get the IDs at build time?

They come from the crawler when you prerender:

kit/packages/kit/src/core/postbuild/crawl.js

Lines 169 to 172 in 73ccf2d

	} else if (name === 'id') {
	ids.push(value);
	} else if (name === 'name') {
	if (tag === 'A') ids.push(value);

In other words, the app has already been built, so it's too late to add to the $page store (the circularity I referred to).

[janosh]

so it's too late to add to the $page store (the circularity I referred to).

I don't know what I'm talking about here so feel free to ignore. But I'm curious why you can't reach in and update the $page store after build?