Ability to access original URL after rewrite

[rijk]

Goals

1. Enable using rewrites to reuse a canonical page on alternative URLs
2. Serve one built static page for all alternative URLs
3. Still be able to see which alternative URL was accessed for nav active state etc

Non-Goals

No response

Background

Use case: ecommerce store with multiple collections sharing the same products.

• Product canonical URL is store.com/product/[product]
• Collection URL is store.com/products/[collection]
• Collection product URL is store.com/products/[collection]/[product]

The last URL will be rewritten to store.com/product/[product], so we don't have to duplicate the pages during build time:

const config = {
  async rewrites() {
    return [
      {
        source: '/products/:collection/:product',
        destination: '/product/:product',
      },
    ]
  },
}

This works fine, but it's now impossible to know which [collection] was originally requested (for e.g. highlighting it in the nav).

I've tried to do this with e.g. redirecting to destination: '/product/:product?collection=:collection', but the searchParams aren't passed to either the server or client. Also, this would opt the page out of static mode which defeats the point.

I've also tried looking at window.location manually (because this is the only place still containing the original URL; useParams et al are already returning the rewritten one), but this caused hydration errors.

Proposal

This could be implemented in many ways. One way could be to add a useOriginalPathname() hook.