REST API: Return 404 for invalid post ID in Comments update_item().

[dhrupo]

Summary

WP_REST_Comments_Controller::update_item() returned HTTP 403 (Forbidden) when the request targeted a non-existent post ID (e.g. PUT /wp/v2/comments/<id> with post set to a missing post). The correct status is 404 (Not Found): the post is a missing resource, not an authorization failure.

This also makes update_item() consistent with get_item(), which already returns 404 for the same "post does not exist" scenario within the same controller.

Changes

• class-wp-rest-comments-controller.php: change the rest_comment_invalid_post_id error status from 403 to 404 in update_item().
• rest-comments-controller.php (tests): update the test_update_comment_invalid_post_id assertion to expect 404.

The error code (rest_comment_invalid_post_id) is intentionally unchanged to preserve backwards compatibility for clients matching on it. The create_item 403 responses ("Sorry, you are not allowed to create this comment without a post.") are genuine authorization checks and are left untouched.

Relationship to #11529

This completes the work started in #11529 by @saratheonline, which made the code change but left the existing unit test asserting 403, causing CI to fail. @westonruter requested changes noting the test needed updating. This PR includes both the code fix and the corresponding test update so the suite passes.

Testing

Reproduced red → green:

1. With the unpatched code, updating test_update_comment_invalid_post_id to expect 404 fails: Failed asserting that 403 is identical to 404.
2. After the one-line controller fix, the test passes.

Full controller suite green (verified in the local Docker environment):

WP_Test_REST_Comments_Controller: OK (142 tests, 675 assertions)

Manual reproduction:

curl -X POST http://localhost:8889/wp-json/wp/v2/comments/1 \
  -u "admin:<app-password>" \
  -H "Content-Type: application/json" \
  -d '{"post": 9999}'
# Before: 403 Forbidden
# After:  404 Not Found

Trac ticket: https://core.trac.wordpress.org/ticket/65050

Props saratheonline.

Use of AI Tools

AI assistance: Yes
Tool(s): Claude Code
Model(s): Claude Opus 4.8
Used for: Reproducing the failing test, applying the fix and the test update, and running the test suite. All changes were reviewed by me.

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Props dhrupo.

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