The flag that `ruby2_keywords` uses

ruby2_keywords_flag.rb

# https://twitter.com/josh_cheek/status/1421462056994283521
require 'fiddle'
public def address() = Fiddle.dlwrap(self)
public def pointer() = Fiddle::Pointer.new(address)
public def toggle_keywords!() = (pointer[1] ^= 0b100000)

def m(a:) = a

h = {a: 1}
m *[h] rescue $! # => #<ArgumentError: wrong number of arguments (given 1, expected 0; required keyword: a)>
h.toggle_keywords!
m *[h] rescue $! # => 1
h.toggle_keywords!
m *[h] rescue $! # => #<ArgumentError: wrong number of arguments (given 1, expected 0; required keyword: a)>