[wp-trac] [WordPress Trac] #44467: Ensure meta wrapper functions do not contain additional logic

[WordPress Trac]

#44467: Ensure meta wrapper functions do not contain additional logic
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 Reporter:  flixos90             |      Owner:  (none)
     Type:  defect (bug)         |     Status:  new
 Priority:  normal               |  Milestone:  Awaiting Review
Component:  Options, Meta APIs   |    Version:
 Severity:  normal               |   Keywords:  2nd-opinion
  Focuses:  multisite, rest-api  |
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 WordPress contains numerous wrapper functions for metadata that wrap the
 respective `add_metadata()` / `update_metadata()` / `get_metadata()` /
 `delete_metadata()` calls.

 Those are:
 * `*_post_meta()`
 * `*_term_meta()`
 * `*_comment_meta()`
 * `*_user_meta()`
 * `*_site_meta()` (on multisite)

 These are convenience wrappers that developers are encouraged to use in
 favor of the more low-level functions. However, it has become more and
 more common to also include small pieces of additional logic in the
 wrapper functions that will not be executed when calling the low-level
 functions. This is a problem, because the low-level functions are still
 called in numerous locations in core and also by plugins (usually by areas
 that deal with metadata in a more abstract way). Particularly, the REST
 API meta field classes make use of them, so here it becomes a significant
 problem already. This means that in those cases, crucial functionality
 does not get executed, for example preventing access in case of an old
 database version or clearing the cache. Therefore my suggestion is to
 remove all extra logic from all wrapper functions and instead run it via
 filters that become part of `default-filters.php`. This ensures
 consistency for all metadata functions and their wrappers.

 The following list shows all extra functionality that meta wrapper
 functions in core currently contain:
 * The writing post meta wrappers all ensure the metadata is only changed
 for the root post (not for a revision), and they all clear the cache for
 the respective post ID.
 * All term meta wrappers prevent access to the function if the database
 schema is too old. The writing term meta functions furthermore all clear
 the cache for the respective term ID.
 * The writing comment meta wrappers all clear the cache for the respective
 comment ID.
 * All site meta wrappers prevent access to the function if the database
 schema is too old. The writing site meta functions furthermore all clear
 the cache for the respective site ID.

 All of the above, except for the post revision bit, could easily become a
 filter or action hook:
 * Checks that possibly prevent access to metadata functions can use the
 `add_{$type}_metadata`, `update_{$type}_metadata` and
 `delete_{$type}_metadata` filters.
 * Caches for the respective objects can be cleared by using the
 `added_{$type}_meta`, `updated_{$type}_meta` and `deleted_{$type}_meta`
 actions.

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Ticket URL: <https://core.trac.wordpress.org/ticket/44467>
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