Require active_support for `descendants` method

[daichirata]

Hi,

I noticed when using this gem with Rails 5. descendants method is defined by active_support. And when using, we have to require that specifically.

backtrace:

$ bin/rails db:migrate
rails aborted!
Bundler::GemRequireError: There was an error while trying to load the gem 'migration_comments'.
Gem Load Error is: undefined method `descendants' for ActiveRecord::SchemaDumper:Class
Backtrace for gem load error is:
/src/github.com/xxxx/.bundle/ruby/2.3.0/gems/migration_comments-0.4.1/lib/migration_comments.rb:26:in `block in setup'
/src/github.com/xxxx/.bundle/ruby/2.3.0/gems/migration_comments-0.4.1/lib/migration_comments.rb:23:in `each'
/src/github.com/xxxx/.bundle/ruby/2.3.0/gems/migration_comments-0.4.1/lib/migration_comments.rb:23:in `setup'
/src/github.com/xxxx/.bundle/ruby/2.3.0/gems/migration_comments-0.4.1/lib/migration_comments.rb:59:in `<top (required)>'
/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/bundler-1.12.5/lib/bundler/runtime.rb:86:in `require'
/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/bundler-1.12.5/lib/bundler/runtime.rb:86:in `block (2 levels) in require'
/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/bundler-1.12.5/lib/bundler/runtime.rb:81:in `each'
/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/bundler-1.12.5/lib/bundler/runtime.rb:81:in `block in require'
/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/bundler-1.12.5/lib/bundler/runtime.rb:70:in `each'
/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/bundler-1.12.5/lib/bundler/runtime.rb:70:in `require'
/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/bundler-1.12.5/lib/bundler.rb:102:in `require'
/src/github.com/xxxx/config/application.rb:14:in `<top (required)>'
/src/github.com/xxxx/Rakefile:1:in `require_relative'
/src/github.com/xxxx/Rakefile:1:in `<top (required)>'
/src/github.com/xxxx/.bundle/ruby/2.3.0/gems/rake-11.2.2/lib/rake/rake_module.rb:28:in `load'
/src/github.com/xxxx/.bundle/ruby/2.3.0/gems/rake-11.2.2/lib/rake/rake_module.rb:28:in `load_rakefile'
/src/github.com/xxxx/.bundle/ruby/2.3.0/gems/rake-11.2.2/lib/rake/application.rb:686:in `raw_load_rakefile'
/src/github.com/xxxx/.bundle/ruby/2.3.0/gems/rake-11.2.2/lib/rake/application.rb:96:in `block in load_rakefile'
/src/github.com/xxxx/.bundle/ruby/2.3.0/gems/rake-11.2.2/lib/rake/application.rb:178:in `standard_exception_handling'
/src/github.com/xxxx/.bundle/ruby/2.3.0/gems/rake-11.2.2/lib/rake/application.rb:95:in `load_rakefile'
/src/github.com/xxxx/.bundle/ruby/2.3.0/gems/railties-5.0.0/lib/rails/commands/rake_proxy.rb:12:in `block in run_rake_task'
/src/github.com/xxxx/.bundle/ruby/2.3.0/gems/rake-11.2.2/lib/rake/application.rb:178:in `standard_exception_handling'
/src/github.com/xxxx/.bundle/ruby/2.3.0/gems/railties-5.0.0/lib/rails/commands/rake_proxy.rb:10:in `run_rake_task'
/src/github.com/xxxx/.bundle/ruby/2.3.0/gems/railties-5.0.0/lib/rails/commands/commands_tasks.rb:51:in `run_command!'
/src/github.com/xxxx/.bundle/ruby/2.3.0/gems/railties-5.0.0/lib/rails/commands.rb:18:in `<top (required)>'
bin/rails:9:in `require'

[pinnymz]

I appreciate the PR, but I can't reproduce any problem here. I just tested a brand new Rails 5 app on Ruby 2.3, and was able to migrate successfully. Can you post the Gemfile you are using?

[daichirata]

Thank you for me to try. My Gemfile is this.

I investigated conversantly, too. There was cause of the problem in application.rb. action_mailer was unnecessary for my application, so it was excluded.

require_relative 'boot'

# require 'rails/all'
require "rails"
require "active_model/railtie"
require "active_record/railtie"
require "action_controller/railtie"
require "action_view/railtie"
require "sprockets/railtie"
# require "active_job/railtie"
# require "action_mailer/railtie" #=> here
# require "action_cable/engine"
# require "rails/test_unit/railtie"

I think that descendants method in this gem is dependent on require 'active_support/core_ext/class' in action_mailer. https://github.com/rails/rails/blob/v5.0.0/actionmailer/lib/action_mailer.rb#L29