## Problem
Relative hash/query handling in `next/link` (e.g. `<Link
href="#hello">`) is broken in App Router, especially if you're on a
nested route.
This wasn't a problem in `/pages` because the href always get fully
resolved in `<NextLink>`; i.e. if you have `<Link href="#hash" />` on
`/hello`, it'll resolve the href to `/hello#hash` and use that
everywhere.
However, in App Router, `<Link>` no longer uses the current location to
resolve the href:
5451564f36/packages/next/src/client/link.tsx (L450-L457)
Therefore navigating with `new URL(href, location.origin)` will skip the
current path and always apply the relative hash/query to the _root_
route:
5451564f36/packages/next/src/client/components/app-router.tsx (L208-L215)
## Solution
Not 100% sure if this is the best solution, but since `app-router` is
already reading `window.location`, I'm using `location.href` as the base
URL to resolve the href.
I grep'd for `location.origin` and checked other callsites; seems like
only `app-router` deals with user specified hrefs.
Fixes https://github.com/vercel/next.js/issues/42157 &
https://github.com/vercel/next.js/issues/44139, and potentially
https://github.com/vercel/next.js/issues/48554 and
https://github.com/vercel/next.js/issues/22838
## Test Plan
```
pnpm testheadless test/e2e/app-dir/navigation
```
---------
Adds support for scrolling based on the [hash
fragment](https://en.wikipedia.org/wiki/URI_fragment) in client-side
navigations for the App Router, mirroring browser behavior.
- `#main-content` → scrolls to `id="main-content"` or
`name="main-content"` property
- `#top` → scrolls to the top of the page, this is a special case in
browsers.
- no hash → default scroll behavior, layout that changed
Fixes NEXT-658
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fixes#44295
---------
Co-authored-by: JJ Kasper <jj@jjsweb.site>
