[wp-trac] [WordPress Trac] #57923: Deprecated notice fired by wp_set_object_terms() with PHP 8.1

[WordPress Trac]

#57923: Deprecated notice fired by wp_set_object_terms() with PHP 8.1
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 Reporter:  Chouby                         |       Owner:  (none)
     Type:  defect (bug)                   |      Status:  new
 Priority:  normal                         |   Milestone:  6.3
Component:  Taxonomy                       |     Version:
 Severity:  normal                         |  Resolution:
 Keywords:  php81 needs-patch 2nd-opinion  |     Focuses:
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Comment (by costdev):

 Thanks for the extra information @Chouby!

 Given that:
 - The documentation in "More Information" explicitly states that `null`
 can be passed.
 - At least 74 that pass `null` for `$terms`, and the documentation
 currently mentions passing `null`.

 I think that officially accepting `null` is the backward compatible
 approach here. The documentation, and loose checking, has somewhat backed
 us into a corner here.

 Based on this, I think we have a few options:

 1. Implicitly accept `null`, by:
   a. Adding `null !== $terms` to the condition
 [https://github.com/WordPress/WordPress/blob/1bf93a87a449a9476d1efd93a0452d7d6ceb3808
 /wp-includes/taxonomy.php#L2728-L2730 here].
     i. This would avoid the deprecation notice, as the `foreach()` uses
 `(array) $terms`, converting `null` to `array()` just for the `foreach()`
 loop.
     ii. This would avoid changing the type of `$terms` passed by the
 `wp_set_object_terms` action, protecting possible explicit `null` checks
 by extenders.
 2. Or, explicitly accept `null`, by:
   a. Adding `null` to the list of types for `$terms`.
   b. Adding `if ( empty( $terms ) ) { $terms = array(); }` before line
 2728.
     i. This would cover more values than `null` but, as far I know, none
 of those values are valid Term IDs/slugs, and it would be consistent with
 the current documentation: "Passing an empty value will remove all related
 terms."
     ii. This would change the type of `$terms` passed by the
 `wp_set_object_terms` action, which would now pass `$terms` as `array()`,
 instead of the current behaviour of `null`.
 3. Or, a mixture of both:
   a. Adding `null` to the list of types for `$terms`.
   b. Adding `null !== $terms` to the condition
 [https://github.com/WordPress/WordPress/blob/1bf93a87a449a9476d1efd93a0452d7d6ceb3808
 /wp-includes/taxonomy.php#L2728-L2730 here].
     i. This would prevent the deprecation notice, and prevent changing the
 type of `$terms` passed by the `wp_set_object_terms` action.

 At the moment, I'm leaning towards option 3.

-- 
Ticket URL: <https://core.trac.wordpress.org/ticket/57923#comment:11>
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