PSR12: should PSR2.Classes.PropertyDeclaration.Underscore be reported as an error?

[rodrigoprimo]

The PSR12 ruleset includes a severity override that promotes PSR2.Methods.MethodDeclaration.Underscore from warning to error and customises the message text from "should not" to "must not", matching the MUST NOT wording in PSR-12 section 4.4.

The equivalent rule for properties in PSR-12 section 4.3 uses identical MUST NOT wording, but no matching override exists for PSR2.Classes.PropertyDeclaration.Underscore. As a result, a property with a leading underscore is reported as a warning, while a method with a leading underscore is reported as an error.

Both were introduced in b7fed6b, but only the method override was applied.

Given the following code sample:

<?php

namespace MyNamespace;

class MyClass
{
    public $_foo;
    protected function _bar()
    {
    }
}

Running phpcs --standard=PSR12 against this file produces:

7 | WARNING | Property name "$_foo" should not be prefixed with an underscore to indicate visibility
8 | ERROR   | Method name "_bar" must not be prefixed with an underscore to indicate visibility

I wonder if there's a reason I'm missing to treat the property rule as a warning or if the PSR12 ruleset should be updated? If the latter, I can open a PR suggesting this change.