rails--rails/activesupport/lib/active_support/deprecation/behaviors.rb

require "active_support/notifications"
require "active_support/core_ext/array/wrap"

module ActiveSupport
  module Deprecation
    class << self
      # Whether to print a backtrace along with the warning.
      attr_accessor :debug

      def behavior
        @behavior ||= DEFAULT_BEHAVIORS[:stderr]
      end

      def behavior=(behavior)
        @behavior = Array.wrap(behavior).map { |b| DEFAULT_BEHAVIORS[b] || b }
      end
    end

    # Default warning behaviors per Rails.env.
    DEFAULT_BEHAVIORS = {
      :stderr => Proc.new { |message, callstack|
         $stderr.puts(message)
         $stderr.puts callstack.join("\n  ") if debug
       },
      :log => Proc.new { |message, callstack|
         logger =
           if defined?(Rails) && Rails.logger
             Rails.logger
           else
             require 'logger'
             Logger.new($stderr)
           end
         logger.warn message
         logger.debug callstack.join("\n  ") if debug
       },
       :notify => Proc.new { |message, callstack|
          ActiveSupport::Notifications.instrument("deprecation.rails",
            :message => message, :callstack => callstack)
       }
    }
  end
end