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

module ActiveSupport
  module Deprecation
    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})"
      end
      warning
    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