monkeypatch.rb

#
# Monkeypatching gem dependencies is a fact of life. But it's dangerous, because *any* update
# to a library might change internals that your patch depends on. This little snippet allows you
# to leave "reminders" in your code that you're relying on a particular version of a gem, and blows
# up if the gem loaded at runtime doesn't fit the requirement.
#
# Example:
#
# monkeypatch('awesome_lib', '1.2.2') do
#   module AwesomeLib
#     def awesome_method
#       self.rely_on_internals_that_could_change_at_any_time(:cowboy => true)
#     end
#   end
# end
#
# Note that the `version_requirement` can be any version specification that RubyGems
# accepts, but if you're relying on any sort of internals in your monkeypatch, you'll
# want to specify an exact version.
#
def monkeypatch(name, version_requirement)
  loaded_gem = Gem.loaded_specs[name]
  raise LoadError, "Monkeypatched gem #{name} is not loaded" unless loaded_gem.present?
  
  unless Gem::Requirement.new(version_requirement).satisfied_by?(loaded_gem.version)
    raise LoadError, "Monkeypatch targets #{name} #{version_requirement}; " \
      "runtime version is #{loaded_gem.version.to_s}. Confirm that monkeypatch works " \
      "with this version and bump monkeypatch version requirement."
  end
  yield
end