`is_object_in_term` object cache uses "set" instead of "add"

[nlemoine]

is_object_in_term should respect [wp_suspend_cache_addition](​https://developer.wordpress.org/reference/functions/wp_suspend_cache_addition/) and use wp_cache_add instead of wp_cache_set as in [get_the_terms](​https://github.com/WordPress/WordPress/blob/c6041fd40a9d499a5d602be791349068699ef695/wp-includes/category-template.php#L1297-L1303)

Blamed line: ​https://github.com/WordPress/WordPress/blob/c6041fd40a9d499a5d602be791349068699ef695/wp-includes/taxonomy.php#L4895

I stumbled upon this building a long running WP-CLI command and noticed a memory leak issue while having object cache suspended. Turns out I had a has_category that filled the whole cache with category_relationships keys.

[nlemoine]

Additional note: term relationships caching is used in multiple functions:

• ​https://github.com/WordPress/WordPress/blob/c6041fd40a9d499a5d602be791349068699ef695/wp-admin/includes/template.php#L357-L361
• ​https://github.com/WordPress/WordPress/blob/c6041fd40a9d499a5d602be791349068699ef695/wp-includes/category-template.php#L1298-L1302
• ​https://github.com/WordPress/WordPress/blob/c6041fd40a9d499a5d602be791349068699ef695/wp-admin/includes/taxonomy.php#L266-L270
• ​https://github.com/WordPress/WordPress/blob/c6041fd40a9d499a5d602be791349068699ef695/wp-includes/taxonomy.php#L4890-L4895

The same code pattern is reused in multiple locations. It may need a central place for handling terms caching.

Use wp_cache_add instead of wp_cache_set to prevent cache additions when wp_suspend_cache_addition has been set to true.

[wildworks]

Sorry for the late reply. I'm checking this ticket in preparation for the 6.9 dry run.

Blamed line: ​https://github.com/WordPress/WordPress/blob/c6041fd40a9d499a5d602be791349068699ef695/wp-includes/taxonomy.php#L4895

At the very least, this issue isn't a new one in an unreleased development version, so we'll remove the version field.