class Rubocop::Cop::Style::SingleLineMethods

It can optionally accept single-line methods with no body.
This cop checks for single-line method definitions.

def allow_empty? 

def allow_empty?
  cop_config['AllowIfMethodIsEmpty']
end

def check(node) 

def check(node)
  start_line = node.loc.keyword.line
  end_line = node.loc.end.line
  if node.type == :def
    empty_body = node.children[2].nil?
  else
    empty_body = node.children[3].nil?
  end
  if start_line == end_line && !(allow_empty? && empty_body)
    convention(node, :expression)
  end
end

def on_def(node) 

def on_def(node)
  check(node)
end

def on_defs(node) 

def on_defs(node)
  check(node)
end