Accidental attributes+prototype fix

The program below will correctly print $ with perls 5.16 and above,
but does not get the prototype on earlier perls: (the BEGIN is required)

use strict;
use warnings;
use Attribute::Handlers;
sub Foo :ATTR(BEGIN) {
    my (undef, undef, $referent) = @_;
    print prototype($referent),"\n";
}
sub bar ($) :Foo { }

This does not appear to be documented in any perldelta, so I'm
wondering if this fix is accidental, and more importantly do anyone
know if we have a regression test for it?

• Accidental attributes+prototype fix by Rafael Garcia-Suarez
• Re: Accidental attributes+prototype fix by Father Chrysostomos