class RuboCop::Cop::Layout::SpaceAfterMethodName

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

def on_def(node) 

def on_def(node)
  args = node.arguments
  return unless 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.start_with?(' ')
  add_offense(pos_before_left_paren) do |corrector|
    corrector.remove(pos_before_left_paren)
  end
end