Make package (role) initialization depend on metamodel HOW class

[vrurg]

The Problem

The issue is mostly described here: https://stackoverflow.com/questions/53907123/exporthowdeclare-and-role-like-declaration

Briefly: if a package keyword is declared in EXPORTHOW::DECLARE with a Metamodel::PrametricRoleHOW itself or its descendant class then the role created with this keyword wouldn't be initialized properly.

Actual Behavior

This code:

Special.pm6

my package EXPORTHOW {
    package DECLARE {
        # In the following line ParametricRoleHOW could be replaced with a descendant class
        constant special = Metamodel::ParametricRoleHOW;
    }
}

test.p6

use Special;
special Mine { }

class Foo does Mine { }

Results in Could not instantiate role Mine error.

Expected Behavior

Foo ~~ Mine must result in True.

Suggested fix

The inspection of Grammar.nqp and Actions.nqp in src/Perl6 in (45a945b) revealed a couple of lines with the following code:

$*PKGDECL <cmp> 'role' 

where <cmp> is either eq or ne. On IRC Jonathan suggested that this could be replaced with checking of archetypes.

Environment

• Operating system: macOS 10.14
• Compiler version (perl6 -v): This is Rakudo version 2018.12 built on MoarVM version 2018.12