class RuboCop::Cop::Style::DefWithParentheses

end
do_something
def Baz.foo
# good
end
do_something
def Baz.foo()
# bad
def foo()=do_something
def foo() do_something end
# good - without parentheses it’s a syntax error
def foo = do_something
# good
def foo() = do_something
# bad
end
do_something
def foo
# good
end
do_something
def foo()
# bad
@example
class/singleton methods are checked.
that does not take any arguments. Both instance and
Checks for parentheses in the definition of a method,

def on_def(node) 

def on_def(node)
  return unless !node.arguments? && (arguments_range = node.arguments.source_range)
  return if parentheses_required?(node, arguments_range)
  add_offense(arguments_range) do |corrector|
    corrector.remove(arguments_range)
  end
end

def parentheses_required?(node, arguments_range) 

def parentheses_required?(node, arguments_range)
  return true if node.single_line? && !node.endless?
  end_pos = arguments_range.end.end_pos
  token_after_argument = range_between(end_pos, end_pos + 1).source
  token_after_argument == '='
end