How to send Rails deprecation warnings to Airbrake

We’re upgrading our Ruby on Rails version from 4.2 to 5.2 this week. A long-awaited change for us. Of course, there are a lot of deprecation warnings that was thrown at us during this process. Rubocop and tests caught the vast majority of those, but we don’t have 100% code coverage, so some of these warnings got into production.

In development Rails send these warnings to the log file:

# Print deprecation notices to the Rails logger.
config.active_support.deprecation = :log

A reasonable default, but I changed it to :raise. It's way faster to find and deal with the warnings this way in development.

For production environment Rails uses ActiveSupport::Notifications:

# Send deprecation notices to registered listeners.
config.active_support.deprecation = :notify

The problem is that nobody listens for it in production. Fortunately, that was easy to fix with Airbrake. I tried to “google” the solution at first but didn’t find anything useful, so I’m sharing my solution for other seeking souls like me :)

# config/initializers/deprecations_notifier.rb

ActiveSupport::Notifications.subscribe('deprecation.rails') do |_name, _start, _finish, _id, payload|
  error = ActiveSupport::DeprecationException.new(payload[:message])
  error.set_backtrace(payload[:callstack].map(&:to_s))

  params = {
    gem_name: payload[:gem_name],
    deprecation_horizon: payload[:deprecation_horizon]
  }

  Airbrake.notify(error, params) do |notice|
    notice[:context][:severity] = 'warning'
  end
end

If you’re using CurrentAttributes and storing request.uuid there it would be a good idea to add current request UUID to the params as well.