[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:  flixos90
     Type:  defect (bug)                         |      Status:  assigned
 Priority:  normal                               |   Milestone:  5.0
Component:  Options, Meta APIs                   |     Version:
 Severity:  normal                               |  Resolution:
 Keywords:  2nd-opinion has-patch needs-unit-    |     Focuses:  multisite,
  tests                                          |  rest-api
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Changes (by flixos90):

 * keywords:  2nd-opinion => 2nd-opinion has-patch needs-unit-tests
 * owner:  (none) => flixos90
 * status:  new => assigned
 * milestone:  Awaiting Review => 5.0


Comment:

 After talking to @johnjamesjacoby about this, we agreed to proceed with
 this. Let's use this ticket here since it goes a little further than
 #43813. It will likely fix that as well.

 [attachment:"44467.diff"] is the implementation I envision for it. Some
 notes:
 * For posts, terms, comments, and sites updating the cache has been
 removed from the wrapper functions and instead now happens through
 separate actions hooked into the respective `added_{$meta_type}_meta`,
 `updated_{$meta_type}_meta`, and `deleted_{$meta_type}_meta` hooks. Those
 only fire on success, so they replicate the current behavior.
 * For terms and sites, the checks for whether that type of metadata is
 supported has been removed from the wrapper functions and instead now
 happens through separate filters hooked into the respective
 `get_{$meta_type}_metadata`, `add_{$meta_type}_metadata`,
 `update_{$meta_type}_metadata`, and `delete_{$meta_type}_metadata` hooks.
 * In order to catch all possible access to the metadata tables,
 particularly for the point above, four new pre-filters were introduced:
 `get_{$meta_type}_metadata_by_mid`, `update_{$meta_type}_metadata_by_mid`,
 `delete_{$meta_type}_metadata_by_mid`, and
 `update_{$meta_type}_metadata_cache`. Those should be merged in a separate
 commit before the actual changes this ticket is for.
 * With the additional filters, and the pre-filters and post-set-cache-
 actions being hooked in everywhere, it is furthermore ensured that a few
 more cases than before are properly covered.
 * Rerouting the post ID if it is for a revision should remain in the post
 meta wrappers. There is no hook to integrate this directly into the meta
 functions, and more importantly it shouldn't be tied to it as it would
 otherwise prevent plugins to easily implement metadata for post revisions.
 * Checking for whether a term is shared should remain in the term meta
 wrappers. It is really specific, and not as foundational that you would be
 required to prevent access to the term meta database table because of it.

 I will work on unit tests after an initial review once we agree on whether
 this is the approach to proceed with.

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Ticket URL: <https://core.trac.wordpress.org/ticket/44467#comment:2>
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