JSON.on_mixed_keys_hash

# File tmp/rubies/ruby-4.0.0/ext/json/lib/json/common.rb, line 185
def on_mixed_keys_hash(hash, do_raise)
  set = {}
  hash.each_key do |key|
    key_str = key.to_s

    if set[key_str]
      message = "detected duplicate key #{key_str.inspect} in #{hash.inspect}"
      if do_raise
        raise GeneratorError, message
      else
        deprecation_warning("#{message}.\nThis will raise an error in json 3.0 unless enabled via `allow_duplicate_key: true`")
      end
    else
      set[key_str] = true
    end
  end
end