class RuboCop::Cop::Style::ModuleFunction

end
end
# …
class << self
module Test
# good
end
# …
private
# …
extend self
module Test
# bad
end
# …
extend self
module Test
# bad
end
# …
module_function
module Test
# bad
@example EnforcedStyle: forbidden
end
end
# …
class << self
module Test
# good
end
# …
extend self
module Test
# good
end
# …
module_function
module Test
# bad
@example EnforcedStyle: extend_self
end
end
# …
class << self
module Test
# good
end
# …
private
# …
extend self
module Test
# good
end
# …
module_function
module Test
# good
end
# …
extend self
module Test
# bad
@example EnforcedStyle: module_function (default)
and ‘module_function` do not behave exactly the same.
Autocorrection is unsafe (and is disabled by default) because `extend self`
@safety
contains any private methods
- in default mode (`module_function`), the cop won’t be activated when the module
- ‘forbidden` style prohibits the usage of both styles
A couple of things to keep in mind:
Supported styles are: `module_function` (default), `extend_self` and `forbidden`.
Checks for use of `extend self` or `module_function` in a module.

def check_extend_self(nodes) 

def check_extend_self(nodes)
  nodes.each do |node|
    yield node if module_function_node?(node)
  end
end

def check_forbidden(nodes) 

def check_forbidden(nodes)
  nodes.each do |node|
    yield node if extend_self_node?(node)
    yield node if module_function_node?(node)
  end
end

def check_module_function(nodes) 

def check_module_function(nodes)
  return if nodes.any? { |node| private_directive?(node) }
  nodes.each do |node|
    yield node if extend_self_node?(node)
  end
end

def each_wrong_style(nodes, &block) 

def each_wrong_style(nodes, &block)
  case style
  when :module_function
    check_module_function(nodes, &block)
  when :extend_self
    check_extend_self(nodes, &block)
  when :forbidden
    check_forbidden(nodes, &block)
  end
end

def message(_range) 

def message(_range)
  return FORBIDDEN_MSG if style == :forbidden
  style == :module_function ? MODULE_FUNCTION_MSG : EXTEND_SELF_MSG
end

def on_module(node) 

def on_module(node)
  return unless node.body&.begin_type?
  each_wrong_style(node.body.children) do |child_node|
    add_offense(child_node) do |corrector|
      next if style == :forbidden
      if extend_self_node?(child_node)
        corrector.replace(child_node, 'module_function')
      else
        corrector.replace(child_node, 'extend self')
      end
    end
  end
end