class RuboCop::Cop::Style::MultilineBlockLayout

def autocorrect(node)
  @corrections << lambda do |corrector|
    _method, _args, block_body = *node
    first_node = if block_body.type == :begin
                   block_body.children.first
                 else
                   block_body
                 end
    block_start_col = node.loc.expression.column
    corrector.insert_before(first_node.loc.expression,
                            "\n  #{' ' * block_start_col}")
  end
end

def on_block(node)
  end_loc = node.loc.end
  do_loc = node.loc.begin # Actually it's either do or {.
  return if do_loc.line == end_loc.line # One-liner, no newline needed.
  # A block node has three children: the block start,
  # the arguments, and the expression. We care if the block start
  # and the expression start on the same line.
  last_expression = node.children.last
  return unless last_expression
  expression_loc = last_expression.loc
  return unless do_loc.line == expression_loc.line
  expression = last_expression.loc.expression
  range = Parser::Source::Range.new(expression.source_buffer,
                                    expression.begin_pos,
                                    expression.end_pos)
  add_offense(node, range)
end