[wp-trac] [WordPress Trac] #53635: PHP 8.1: various compatibility fixes

[WordPress Trac]

#53635: PHP 8.1: various compatibility fixes
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 Reporter:  SergeyBiryukov  |       Owner:  (none)
     Type:  task (blessed)  |      Status:  new
 Priority:  normal          |   Milestone:  5.9
Component:  General         |     Version:
 Severity:  normal          |  Resolution:
 Keywords:  php81           |     Focuses:  coding-standards
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Comment (by SergeyBiryukov):

 In [changeset:"51517" 51517]:
 {{{
 #!CommitTicketReference repository="" revision="51517"
 Code Modernization: Fix "`JsonSerializable_Object::jsonSerialize()` should
 be compatible with `JsonSerializable::jsonSerialize(): mixed`" error on
 PHP 8.1.

 This relates to the [https://wiki.php.net/rfc/internal_method_return_types
 Return types for internal methods RFC] in PHP 8.1 and in particular, the
 change made in [https://github.com/php/php-src/pull/7051 PHP PR #7051],
 which adds a `mixed` return type to the
 `JsonSerializable::jsonSerialize()` interface method.

 WordPress only contains one (test) class which implements the
 `JsonSerializable` interface and this commit fixes the issue for that
 class.

 As of PHP 8.1, the `jsonSerialize()` method in classes which implement the
 `JsonSerializable` interface are expected to have a return type declared.
 The return type should be `mixed` or a more specific type. This complies
 with the Liskov principle of covariance, which allows the return type of a
 child overloaded method to be more specific than that of the parent.

 The problem with this is that:
 1. The `mixed` return type was only introduced in PHP 8.0.
 2. Return types in general were only introduced in PHP 7.0.

 WordPress still has a minimum PHP version of 5.6, so adding the return
 type is not feasible for the time being.

 The solution chosen for now is to add an attribute to silence the
 deprecation warning. While attributes are a PHP 8.0+ feature, due to the
 choice of the `#[]` syntax, in PHP < 8.0, attributes will just be ignored
 and treated as comments, so there is no drawback to using the attribute.

 Props jrf.
 See #53635.
 }}}

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Ticket URL: <https://core.trac.wordpress.org/ticket/53635#comment:4>
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