class SyntaxTree::Parser

def on_block_var(params, locals)

on_block_var: (Params params, (nil | Array[Ident]) locals) -> BlockVar
:call-seq: 
def on_block_var(params, locals)
  index =
    tokens.rindex { |node| node.is_a?(Op) && %w[| ||].include?(node.value) }
  ending = tokens.delete_at(index)
  beginning = ending.value == "||" ? ending : consume_operator(:|)
  # If there are no parameters, then we didn't have anything to base the
  # location information of off. Now that we have an opening of the
  # block, we can correct this.
  if params.empty?
    start_line = params.location.start_line
    start_char =
      (
        if beginning.value == "||"
          beginning.location.start_char
        else
          find_next_statement_start(beginning.location.end_char)
        end
      )
    location =
      Location.fixed(
        line: start_line,
        char: start_char,
        column: start_char - line_counts[start_line - 1].start
      )
    params = params.copy(location: location)
  end
  BlockVar.new(
    params: params,
    locals: locals || [],
    location: beginning.location.to(ending.location)
  )
end