module-subclasses.rb

#!/usr/bin/env ruby

require "bundler/inline"

gemfile do
  source "https://rubygems.org"
  gem "activesupport", "~> #{ENV["AS_VERSION"]}"
end

require "active_support"

p RUBY_VERSION
p ActiveSupport.version.to_s

module C
  extend ActiveSupport::DescendantsTracker
end

p C.subclasses


module M
  extend ActiveSupport::DescendantsTracker
end

p M.subclasses

# $ AS_VERSION=6.1 ruby module-subclasses.rb
# "3.1.0"
# "6.1.4.6"
# []
# []

# $ AS_VERSION=7.0 ruby module-subclasses.rb
# "3.0.2"
# "7.0.2.2"
# []
# []

# $ AS_VERSION=7.0 ruby module-subclasses.rb
# "3.1.0"
# "7.0.2.2"
# []
# /path/to/activesupport-7.0.2.2/lib/active_support/descendants_tracker.rb:83:in `subclasses': super: no superclass method `subclasses' for M:Module (NoMethodError)