router: consider href when detecting hash-only changes; add integrati…

[jaydoshi2]

What?

• Fixes a bug where Next.js sometimes treats a navigation as a "hash-only" change and skips data fetching when:
  • href (the internal url) has different query/search params between calls, but
  • as contains the same path + hash (e.g. ...#hash).
• Implementation:
  • onlyAHashChange now accepts an optional url (href) and, when provided, compares the href's pathname+search with the previous asPath so changes in the href's query are considered real navigations.
  • Caller in Router.change() now passes url into onlyAHashChange(...).
• Tests:
  • Adds an integration test that reproduces the bug and asserts:
    • getInitialProps is re-run when href's query changes even if as contains the same #hash.
    • getInitialProps is not re-run for genuine hash-only changes.

Why?

• Bug: calling Router.replace(hrefWithQueryAndHash, asWithHash) previously could be considered “only a hash change” if as stayed identical (including #hash), even when href changed its query string. That made the router skip the full navigation/data-fetch flow (so getInitialProps or data fetching wasn't re-run).
• Fix: include the href (url) in the hash-only check so changes to the href's query/search cause a full navigation/data-fetch as expected.

How?

• Updated logic in packages/next/src/shared/lib/router/router.ts:
  • onlyAHashChange(as: string, url?: string) — if url is provided, parse it with parseRelativeUrl(url) and use the pathname+search when comparing to previous asPath.
  • In change(), call this.onlyAHashChange(cleanedAs, url) instead of this.onlyAHashChange(cleanedAs).
• Left scrollToHash behavior unchanged (still uses onlyAHashChange(as) without url), preserving current scroll optimizations for pure hash navigations.

Files changed

• Modified:
  • packages/next/src/shared/lib/router/router.ts
    • changed onlyAHashChange signature and logic, updated call-site in change().
• Added integration test:
  • test/integration/router-replace-hash-query/pages/index.js
  • test/integration/router-replace-hash-query/test/index.test.js
  • test/integration/router-replace-hash-query/package.json (empty, placeholder test dir)

Tests added

• test/integration/router-replace-hash-query/test/index.test.js
  • Uses next-test-utils + next-webdriver to:
    1. Render /.
    2. Ensure the initial page shows test: undefined.
    3. Trigger Router.replace(route + '?test=123#hash', asPath + '#hash').
    4. Confirm the page updates to test: 123 and getInitialProps ran again.
  • Also validates that pure hash-only changes do not trigger getInitialProps.

Checklist for Contributors (please run before opening PR)

• Run pnpm prettier-fix to fix formatting issues.
• Add related issues with fixes #<issue> if applicable.
• Tests added/updated — included integration test in this PR.

Checklist for Maintainers

• Minimal description added above.
• Notes about the fix logic are in code comments.
• Links to issue trackers / Linear: fill in below if necessary.

Closes NEXT-
Fixes #10900 <-- replace with the appropriate issue number if available

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How to run the test locally (copy/paste)

1. Ensure dependencies and build:

# from repo root
pnpm install
# build the project (the repo uses extensive build/test steps; adjust per your workflow)
pnpm -w build

[ijjk]

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