update_post_cache() fails when an object is already in the cache

[misterbisson]

The function uses wp_cache_add(), which cannot replace an existing object for the cache key. Should use wp_cache_set(), which happily replaces existing objects or inserts new ones.

Attached patch fixes.

[scribu]

Related: #15452

[ryan]

Despite the name, the update_cache functions aren't meant to update things already in the cache. They are cache primers and typically use add. If some place is using update_post_cache() to update cache values that needs to be fixed.

[mdawaffe]

Looks like every place in core is using this function correctly (to prime).

Closing as invalid. Please reopen with more details if you find somewhere where the function is being used improperly.