Detects changes made by an arbitrary chunk of Ruby code that may leak into surrounding code with unpleasant consequences

leakygems.rb

RUBY_PATH = File.expand_path('../../lib/ruby/1.8', `which ruby`)

module Leakygems
  class << self
    def method_metadata(method)
      begin
        file = method.__file__
        line = method.__line__
        if File.expand_path(file).include?(RUBY_PATH)
          type = "ruby"
        else
          type = "custom"
        end
      rescue ArgumentError
        type = "native"
      end
      { :name => method.name, :arity => method.arity, :file => file, :line => line, :type => type }
    end

    def capture_state_of(klass)
      {
        :included_modules => klass.included_modules.map(&:to_s).sort,
        :constants => (klass.constants - klass.included_modules.map(&:constants).flatten).map(&:to_s).sort.map do |name|
          { :name => name, :value => klass.const_get(name.to_sym) }
        end,
        :singleton_methods => (class << klass; self; end).instance_methods(include_super = false).sort.map do |name|
          method_metadata((class << klass; self; end).instance_method(name))
        end,
        :instance_methods => klass.instance_methods(include_super = false).sort.map do |name|
          method_metadata(klass.instance_method(name))
        end
      }
    end

    def diff_state_of(klass, &block)
      before = capture_state_of(klass)
      block.call
      after = capture_state_of(klass)
      after.each_key do |key|
        puts "#{key} added: #{(after[key] - before[key]).inspect}"
        puts "#{key} removed: #{(before[key] - after[key]).inspect}"
      end
    end
  end
end


puts "Crack::XML.parse adds two methods to all instances of String :-"
require 'rubygems'
require 'crack'
Leakygems.diff_state_of(String) do
  Crack::XML.parse(%{
    <element>string</element>
  })
end
puts

puts "Let's see what naughtiness we can detect :-"
Leakygems.diff_state_of(String) do
  module ExtraModule; end
  class String
    include ExtraModule
    def self.extra_singleton_method; end
    def extra_instance_method; end
    EXTRA_CONSTANT = 1
    def self.new(text = nil); "x"; end # redefine existing singleton method
    def squeeze; "y"; end # redefine existing instance method
  end
  String.send(:remove_method, :strip) # remove existing instance method
end

# Crack::XML.parse adds two methods to all instances of String :-
# singleton_methods added: []
# singleton_methods removed: []
# included_modules added: []
# included_modules removed: []
# constants added: []
# constants removed: []
# instance_methods added: [{:type=>"custom", :arity=>0, :file=>"/Users/jamesmead/.rvm/gems/ree-1.8.7-2010.02@mubi-bundler/gems/crack-0.1.8/lib/crack/xml.rb", :line=>85, :name=>"attributes"}, {:type=>"custom", :arity=>1, :file=>"/Users/jamesmead/.rvm/gems/ree-1.8.7-2010.02@mubi-bundler/gems/crack-0.1.8/lib/crack/xml.rb", :line=>85, :name=>"attributes="}]
# instance_methods removed: []

# Let's see what naughtiness we can detect :-
# singleton_methods added: [{:type=>"custom", :arity=>0, :file=>"/Users/jamesmead/Code/leakygems/leakygems.rb", :line=>63, :name=>"extra_singleton_method"}, {:type=>"custom", :arity=>-1, :file=>"/Users/jamesmead/Code/leakygems/leakygems.rb", :line=>66, :name=>"new"}]
# singleton_methods removed: [{:type=>"native", :arity=>-1, :file=>nil, :line=>nil, :name=>"new"}]
# included_modules added: ["ExtraModule"]
# included_modules removed: []
# constants added: [{:value=>1, :name=>"EXTRA_CONSTANT"}]
# constants removed: []
# instance_methods added: [{:type=>"custom", :arity=>0, :file=>"/Users/jamesmead/Code/leakygems/leakygems.rb", :line=>64, :name=>"extra_instance_method"}, {:type=>"custom", :arity=>0, :file=>"/Users/jamesmead/Code/leakygems/leakygems.rb", :line=>67, :name=>"squeeze"}]
# instance_methods removed: [{:type=>"native", :arity=>-1, :file=>nil, :line=>nil, :name=>"squeeze"}, {:type=>"native", :arity=>0, :file=>nil, :line=>nil, :name=>"strip"}]