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Gemini's review of all the changes, including the new test:

Here's my review of the changes:

Changes in src/wp-includes/revision.php:

The core change is the introduction of maybe_serialize() before normalize_whitespace():

--- a/src/wp-includes/revision.php
+++ b/src/wp-includes/revision.php
@@ -187,7 +187,7 @@ function wp_save_post_revision( $post_id ) {
                        $post_has_changed = false;
 
                        foreach ( array_keys( _wp_post_revision_fields( $post ) ) as $field ) {
-                               if ( normalize_whitespace( $post->$field ) !== normalize_whitespace( $latest_revision->$field ) ) {
+                               if ( normalize_whitespace( maybe_serialize( $post->$field ) ) !== normalize_whitespace( maybe_serialize( $latest_revision->$field ) ) ) {
                                        $post_has_changed = true;
                                        break;
                                }

• Reasoning: This is an excellent change to address a potential TypeError in PHP 8.0+ when normalize_whitespace() (which internally uses preg_replace()) receives a non-string value (like an array or object). By using maybe_serialize(), any non-scalar values will be converted to a string representation before whitespace normalization, preventing a crash and allowing for consistent comparison.
• Coding Standards: The change adheres to WordPress coding standards regarding formatting and function usage. maybe_serialize() is an idiomatic WordPress function for handling data that might need serialization for storage or comparison.
• PHP 7.2 Compatibility: This change is fully compatible with PHP 7.2 and proactively prevents issues that arise in PHP 8.0+.

Changes in tests/phpunit/tests/post/revisions.php:

A new test method test_wp_save_post_revision_with_array_post_meta() has been added.

• @ticket and @covers Tags: Correctly uses @ticket 64314 and @covers ::wp_save_post_revision.
• Comprehensive Setup: The test cleverly sets up the scenario by:
  • Explicitly setting wp_save_post_revision_check_for_changes to true to ensure change detection is active.
  • Using the wp_post_revision_meta_keys filter to ensure that the custom favorite_things meta key is saved with each revision. This is crucial for the latest_revision to have the correct data for comparison.
  • Using the _wp_post_revision_fields filter to inform wp_save_post_revision that favorite_things should be considered a revisionable field, allowing WP_Post::__get to retrieve the meta value.
• Clear Assertions:
  • The test sets an initial array value, saves a revision, and asserts that the revision was created and that the array was correctly saved to the revision's meta.
  • It then updates the array value, saves a second revision, and asserts that this second revision was successfully created (proving that the change was detected) and that the updated array was saved to its meta.
• Relevance to Fix: This test directly validates the fix by introducing an array into a revisioned field and confirming that wp_save_post_revision works as expected without errors and with proper change detection.
• Nitpicks: The use of anonymous functions for filters is acceptable in unit tests, as WP_UnitTestCase typically cleans up filters between tests. No explicit remove_filter or remove_all_filters is strictly necessary at the end of the test method in this context for robustness.

Conclusion:

Both the code change in src/wp-includes/revision.php and the accompanying unit test in tests/phpunit/tests/post/revisions.php are well-executed. The change is a robust fix for a compatibility issue, and the test provides excellent coverage for the scenario, demonstrating adherence to best practices for extending WordPress revision functionality with custom array-based meta.

The overall quality of the proposed changes is high.

Committed in r61372 (48b2b65)