class RuboCop::Cop::Layout::SpaceAfterMethodName

def func(x) … end
# good
def func (x) … end
# bad
@example
Checks for space between a method name and a left parenthesis in defs.

def autocorrect(pos_before_left_paren) 

def autocorrect(pos_before_left_paren)
  ->(corrector) { corrector.remove(pos_before_left_paren) }
end

def on_def(node) 

def on_def(node)
  args = node.arguments
  return unless args.loc.begin && args.loc.begin.is?('(')
  expr = args.source_range
  pos_before_left_paren = range_between(expr.begin_pos - 1,
                                        expr.begin_pos)
  return unless pos_before_left_paren.source =~ /\s/
  add_offense(pos_before_left_paren, pos_before_left_paren)
end