Posts, Post Types: Unslash tags_input before comparing in wp_update_post().

[abhishekfdd]

wp_update_post() slashes the post array before comparing tags_input against the post's existing tag names. A tag name containing a character that wp_slash() escapes, such as an apostrophe in children's, no longer matches, so tags_input is not discarded and all of the names are passed to wp_set_post_tags(). There, term_exists() can resolve a name like kid+ to a different term whose slug is kid, so a title-only update silently swaps the post's tags.

This also affects the block editor: editing only a post's title sends a REST update without tags, which goes through wp_update_post() and triggers the same swap.

This PR unslashes tags_input before the strict comparison. It also adds a test that creates kid, kid+ and children's tags, assigns kid+ and children's to a post, updates only the title, and asserts that the tags are unchanged. The test fails without the fix (kid+ is replaced by kid) and passes with it.

Trac ticket: https://core.trac.wordpress.org/ticket/62461

Use of AI Tools

AI assistance: Yes
Tool(s): Claude (claude.ai) and Claude Code
Model(s): Claude Opus 5.5
Used for: Claude was used to reproduce and diagnose the bug and to draft the fix and the test. Claude Code applied the patch, ran the tests and lint, and committed. I reviewed and tested the changes.

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[rejaulalomkhan]

Thanks for working on this and diagnosing the root cause so thoroughly, @abhishekfdd! Unslashing tags_input before comparing against the unslashed tag names cleanly resolves the bug where title-only updates silently swapped tags containing slashable characters.

• Verified reproduction locally on trunk: without the fix, test_wp_update_post_should_not_change_tags_with_slashable_names fails as expected (Failed asserting that two arrays are identical: Expected array(3, 4), Actual array(2, 4)).
• With the fix applied, the new unit test passes cleanly (1 test, 2 assertions).
• All 62 tests and 237 assertions in tests/phpunit/tests/post/wpInsertPost.php pass across single-site, multisite, and random order (--order-by=random).
• Verified --group taxonomy (1,085 tests, 2,869 assertions) passes with no regressions.
• PHPCS check on modified lines in src/wp-includes/post.php and tests/phpunit/tests/post/wpInsertPost.php passes with 0 errors and 0 warnings.

Looks good to merge!

AI Review: Antigravity