A trailing comma in a list of attr_reader hijacks the next method definition. How is this not a syntax error?

wat.rb

class Wat
  def initialize(thing)
    @thing = thing
    @foo = 'foo'
  end

  # this ends up creating an attr_reader for foo
  # but shouldn't it throw an error when it
  # sees `def` after a comma?
  attr_reader :thing,

  def foo
    'bar'
  end
end

wat = Wat.new('thing')

puts wat.thing
#-> thing

puts wat.foo
# -> foo