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

module ActiveSupport
  module Deprecation
    class << self
      attr_accessor :silenced

      # Outputs a deprecation warning to the output configured by
      # <tt>ActiveSupport::Deprecation.behavior</tt>.
      #
      #   ActiveSupport::Deprecation.warn('something broke!')
      #   # => "DEPRECATION WARNING: something broke! (called from your_code.rb:1)"
      def warn(message = nil, callstack = caller)
        return if silenced
        deprecation_message(callstack, message).tap do |m|
          behavior.each { |b| b.call(m, callstack) }
        end
      end

      # Silence deprecation warnings within the block.
      #
      #   ActiveSupport::Deprecation.warn('something broke!')
      #   # => "DEPRECATION WARNING: something broke! (called from your_code.rb:1)"
      #
      #   ActiveSupport::Deprecation.silence do
      #     ActiveSupport::Deprecation.warn('something broke!')
      #   end
      #   # => nil
      def silence
        old_silenced, @silenced = @silenced, true
        yield
      ensure
        @silenced = old_silenced
      end

      def deprecated_method_warning(method_name, message = nil)
        warning = "#{method_name} is deprecated and will be removed from Rails #{deprecation_horizon}"
        case message
          when Symbol then "#{warning} (use #{message} instead)"
          when String then "#{warning} (#{message})"
          else warning
        end
      end

      private
        def deprecation_message(callstack, message = nil)
          message ||= "You are using deprecated behavior which will be removed from the next major or minor release."
          message += '.' unless message =~ /\.$/
          "DEPRECATION WARNING: #{message} #{deprecation_caller_message(callstack)}"
        end

        def deprecation_caller_message(callstack)
          file, line, method = extract_callstack(callstack)
          if file
            if line && method
              "(called from #{method} at #{file}:#{line})"
            else
              "(called from #{file}:#{line})"
            end
          end
        end

        def extract_callstack(callstack)
          rails_gem_root = File.expand_path("../../../../..", __FILE__) + "/"
          offending_line = callstack.find { |line| !line.start_with?(rails_gem_root) } || callstack.first
          if offending_line
            if md = offending_line.match(/^(.+?):(\d+)(?::in `(.*?)')?/)
              md.captures
            else
              offending_line
            end
          end
        end
    end
  end
end