PHP 8.1 | PSR2/PropertyDeclaration: add check for visibility before readonly keyword

[jrfnl]

The PSR2.Classes.PropertyDeclaration sniff includes a check to verify that the static keyword is after the visibility in a property declaration.

PHP 8.1 introduced the readonly keyword for properties, but as PSR2/PSR12 were both released before PHP 8.1, no PSR rules have (yet) been defined for the modifier keyword order for readonly properties.

Having said that, all code samples in both the RFC as well as the PHP manual use the visibility - readonly modifier keyword order, so it is likely that this will become the standard modifier keyword order.

A search for PHP projects which have started to use the readonly keyword, also shows these predominantly use the visibility - readonly modifier keyword order.

With that in mind, I'm proposing to add a check for this order to the PSR2.Classes.PropertyDeclaration sniff - this being the only PHPCS native sniff which checks the modifier keyword order for properties.

As PSR2/PSR12 do not formally have rules for the order (yet), the new error code being introduced is excluded for those rulesets (for the time being).

Includes unit tests.

Ref:

• https://wiki.php.net/rfc/readonly_properties_v2
• https://www.php.net/manual/en/language.oop5.properties.php#language.oop5.properties.readonly-properties
• https://sourcegraph.com/search?q=context:global+%5Cs%28public%7Cprotected%7Cprivate%29%5Cs%2Breadonly%5Cs%2B+lang:php+-file:%28%5E%7C/%29%28vendor%7Ctests%3F%29/+fork:no+archived:no&patternType=regexp (searching visibility - readonly order - > 500 results)
• https://sourcegraph.com/search?q=context:global+%5Csreadonly%5Cs%2B%28public%7Cprotected%7Cprivate%29%5Cs%2B+lang:php+-file:%28%5E%7C/%29%28vendor%7Ctests%3F%29/+fork:no+archived:no&patternType=regexp (searching readonly - visibility order - 41 (non false positive) results)