The way that you setup your question seemed to me to be a perfect fit for Method::Specialize and Moose, so I experimented with this. I'll leave it up to you to develop your readsource method:

#!/usr/bin/perl

use strict;
use warnings;
use Method::Specialize;
use Moose::Util;

my $cached = 0;
my $gen = 0;

{
    package RoleA;
    use Moose::Role;

    sub sourceA { print "Testing sourceA\n";}
    sub readsource { print "RoleA contains sourceA\n";}

    package RoleB;
    use Moose::Role;

    sub sourceB { }

    package RoleC;
    use Moose::Role;

    sub sourceC { }

    package Class;
    use Moose;

    with qw(RoleA);

    ::specializing_method source => sub {
        my $class = shift;

        my $meta = Class::MOP::Class->initialize($class);

        my %roles = map { $_->name = undef }
            map { Class::MOP::Class->initialize($_)->calculate_all_rol
+es }
                $meta->linearized_isa;

        ++$gen;

        return sub {
            my ( $class, $role ) = @_;
            ++$cached;
            exists $roles{$role};

        }
    };

    package Method;
    use Moose;

    extends qw(Class);
}
Method->readsource;
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