From PHP 8.2, if someone tries to set a value for a class property which does not have a definitino, a deprecation notice will be emitted. For example:

class User {

    private int $uid;

}

$user = new User();

$user->name = 'Foo';

Deprecated: Creation of dynamic property User::$name is deprecated in ... on line ...

Also from internally:

class User {

    public function __construct() {

        $this->name = 'test';

    }

}

new User();

Deprecated: Creation of dynamic property User::$name is deprecated in ... on line ...

Much more detail here: https://php.watch/versions/8.2/dynamic-properties-deprecated

We should look at writing a sniff for this if possible.

Note: For some legacy code, we may choose to work around this using the AllowDynamicProperties attribute:

 #[AllowDynamicProperties]

 class User {

     private int $uid;

 }

 $user = new User();

 $user->name = 'Foo';

https://php.watch/versions/8.2/dynamic-properties-deprecated#AllowDynamicProperties

Other cases not affected

• stdClass
• classes with a magic __get and __set method

phpstan configuration

I used the following phpstan configuration to genreate the above:

parameters

  # Dynamic properties emits warnings from PHP 8.2 onwards.

  checkDynamicProperties: true

Note: I would recommend generating a baseline first, then adding the above configuration, and then running again against the baseline with the new configuration. This will identify any problem areas.