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.

++PSR PER 2.0.0 dictates that visibility is declared before the readonly keyword.++

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).

++As this sniff is included in PSR2 and PSR12, the new check will automatically apply the PSR-PER property modifier keyword order rules to PSR2/PSR12.++

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)

[jrfnl]

@gsherwood and me discussed this. This needs checking against PSR-PER.

[jrfnl]

I've verified the current implementation against PSR-PER and the change proposed in this PR is 100% in line with PSR-PER.

4.6 Modifier Keywords

Classes, properties, and methods have numerous keyword modifiers that alter how the engine and language handles them. When present, they MUST be in the following order:

• Inheritance modifier: abstract or final
• Visibility modifier: public, protected, or private
• Scope modifier: static
• Mutation modifier: readonly
• Type declaration
• Name

Ref: https://www.php-fig.org/per/coding-style/#46-modifier-keywords

At this time (PHP 8.2), inheritance modifiers cannot be applied to properties and the static and readonly modifiers are mutually exclusive and cannot be used together.

Based on that, the implementation of the modifier keyword order checks in this PR are sufficient (for now).

Having checked the above, I have now rebased the PR, added a comment to the sniff above the modifier keyword order checks to summarize the above findings and I have removed the exclusions for these new checks from the PSR2 and PSR12 rulesets.

I will also update the PR description to match these findings.

[jrfnl]

Side-note: the example code in PSR-PER for this section contains parse errors/invalid code. I have opened a PR to PSR-PER to fix this: php-fig/per-coding-style#73

[jrfnl]

FYI: this fix is included in today's PHP_CodeSniffer 3.8.0 release.

As per #3932, development on PHP_CodeSniffer will continue in the PHPCSStandards/PHP_CodeSniffer repository. If you want to stay informed, you may want to start "watching" that repo (or watching releases from that repo).