class RuboCop::Cop::Style::MultilineOperationIndentation

d <-- d is indented relative to a
b c { block }. <-- b is indented relative to a
a.
for indentation of all lines following the first. For example:
In a chain of method calls, we regard the top send node as the base

def left_hand_side(receiver)
  lhs = receiver
  while lhs.parent && lhs.parent.type == :send
    _receiver, method_name, *_args = *lhs.parent
    break if operator?(method_name)
    lhs = lhs.parent
  end
  lhs
end