Rails: Including a Concern with a constant within a Concern - ruby-on-rails

Question

I have concern in which I store constants:
module Group::Constants
extend ActiveSupport::Concern
MEMBERSHIP_STATUSES = %w(accepted invited requested
rejected_by_group rejected_group)
end
And another concern that I wish to use these constants:
module User::Groupable
extend ActiveSupport::Concern
include Group::Constants
MEMBERSHIP_STATUSES.each do |status_name|
define_method "#{status_name}_groups" do
groups.where(:user_memberships => {:status => status_name})
end
end
end
Unfortunately, this results in a routing error:
uninitialized constant User::Groupable::MEMBERSHIP_STATUSES
It looks like the first concern isn't loading properly in the second concern. If that's the case, what can I do about it?

Answer 1

It appears this behavior is by design, as explained nicely over here.
What you'll need to do in this case is not have Group::Constants extend from ActiveSupport::Concern since that will block its implementation from being shared with other ActiveSupport::Concern extending modules (although it will be ultimately shared in a class that includes the second module):
module A
TEST_A = 'foo'
end
module B
extend ActiveSupport::Concern
TEST_B = 'bar'
end
module C
extend ActiveSupport::Concern
include A
include B
end
C::TEST_A
=> 'foo'
C::TEST_B
=> uninitialized constant C::TEST_B
class D
include C
end
D::TEST_A
=> 'foo'
D::TEST_B
=> 'bar'
In short, you'll need to make Group::Constants a standard module and then all will be well.

Answer 2

If you want to keep everything in one file, and if you can stomach a bit of boilerplate, you could break up your module into a "concern" bit and a "non-concern" bit:
module A
FOO = [22]
def self.included base
base.include Concern
end
module Concern
extend ActiveSupport::Concern
class_methods do
def foo_from_the_perspective_of_a_class_method_in_A
{lexical: FOO, instance: self::FOO}
end
end
end
end
module B
extend ActiveSupport::Concern
include A
FOO += [33]
def foo_from_the_perspective_of_an_instance_method_in_B
FOO
end
end
class C
include B
end
C.foo_from_the_perspective_of_a_class_method_in_A
=> {:lexical=>[22], :instance=>[22, 33]}
C.new.foo_from_the_perspective_of_an_instance_method_in_B
=> [22, 33]
C::FOO
=> [22, 33]