def getRoot(config):
  if not config.parent:
    return config
  return getRoot(config.parent)

root = getRoot(config)

if 'libdispatch' in root.available_features:
  additional_cflags = ' -fblocks '
  for index, (template, replacement) in enumerate(config.substitutions):
    if template in ['%clang_tsan ', '%clangxx_tsan ']:
      config.substitutions[index] = (template, replacement + additional_cflags)
else:
  config.unsupported = True

if config.host_os == 'Darwin':
  config.environment['TSAN_OPTIONS'] += ':ignore_noninstrumented_modules=1'