get_adjacent_post: Fix adjacent post navigation for posts with identical dates

[ramonjd]

Note

I came across all these sorting bugs while looking at #10262. I'm not sure if I'm on the right track here, but it seems like a bug that needs to be fixed. 🤷🏻

Problem

When multiple posts have identical post_date values (e.g., when bulk publishing drafts), the next/previous post navigation doesn't work.

The navigation skips posts or behaves unpredictably because the WHERE clause uses strict inequality (> or <) which excludes posts with the same date.

The get_adjacent_post() function's WHERE clause uses:

• Next post: WHERE p.post_date > 'current_date'
• Previous post: WHERE p.post_date < 'current_date'

When posts have identical dates, these conditions never match, causing navigation to fail.

Proposed solution

Modified the WHERE clause to include ID-based fallback for posts with identical dates:

• Next post: WHERE (p.post_date > 'current_date' OR (p.post_date = 'current_date' AND p.ID > current_id))
• Previous post: WHERE (p.post_date < 'current_date' OR (p.post_date = 'current_date' AND p.ID < current_id))

This ensures deterministic ordering when posts have identical dates while maintaining backward compatibility.

Changes

Modified: src/wp-includes/link-template.php - Updated WHERE clause logic in get_adjacent_post()

Added unit tests in tests/phpunit/tests/link/getAdjacentPost.phpandtests/phpunit/tests/url.php`

Test Steps

1. Create test scenario:
   • Publish at least one post (e.g., "Hello World!")
   • Create three draft posts (e.g., "Sample Post 1", "Sample Post 2", "Sample Post 3")
   • Select all three draft posts, then Bulk Actions > Edit
   • Change Status to "Published"
2. Verify navigation:
   • View any of the recently published posts
   • Click "Previous Post" - should navigate to another post published at the same time
   • Click "Next Post" - should navigate to another post published at the same time
   • Continue navigating - should be able to navigate through all posts with identical dates
3. Expected Results:
   • Previous/next navigation works correctly between all posts with identical dates
   • Navigation is deterministic and consistent
   • No posts are skipped during navigation
   • Navigation works in both directions
4. Run tests:
   • npm run test:php -- --filter Tests_Link_GetAdjacentPost
   • npm run test:php -- --filter Tests_URL

Screenshots

Given a post list (noticed the duplicate dates)

Navigate through the posts:

Kapture.2025-10-22.at.18.21.03.mp4

Trac ticket: https://core.trac.wordpress.org/ticket/8107

---

This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

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[westonruter]

This is looking really good. Just a couple nits left from me. It would be good to get someone else's eyes on this, but I really love the thorough tests.

[ramonjd]

Thanks for the quick feedback and help on this one @westonruter 🍺

I can't believe this bug has been alive for so long!

[andrewserong]

This is testing great for me, and the approach looks good and is consistent with the earlier discussions in the trac ticket 👍

but I really love the thorough tests.

Same, it gives a good sense of confidence in the change.

This LGTM, too.

I can't believe this bug has been alive for so long!

Gotta love fixing an ancient bug!

[ramonjd]

Thanks, folks! I'll keep this alive for a couple of days to give other folks a chance to bask in our glory test and review, then I'll get it committed.