def _TopologicallySortedEnvVarKeys(env):
 regex = re.compile('\\$\\{([a-zA-Z0-9\\-_]+)\\}')
 def GetEdges(node):
  matches = set([v for v in regex.findall(env[node]) if (v in env)])
  for dependee in matches:
   assert ('${' not in dependee), ('Nested variables not supported: ' + dependee)
  return matches
 try:
  order = gyp.common.TopologicallySorted(env.keys(), GetEdges)
  order.reverse()
  return order
 except gyp.common.CycleError as e:
  raise GypError(('Xcode environment variables are cyclically dependent: ' + str(e.nodes)))

def _TopologicallySortedEnvVarKeys ( env ) : regex = re . compile ( '\\$\\{([a-zA-Z0-9\\-_]+)\\}' ) def GetEdges ( node ) : matches = set ( [ v for v in regex . findall ( env [ node ] ) if ( v in env ) ] ) for dependee in matches : assert ( '${' not in dependee ) , ( 'Nested variables not supported: ' + dependee ) return matches try : order = gyp . common . TopologicallySorted ( env . keys ( ) , GetEdges ) order . reverse ( ) return order except gyp . common . CycleError as e : raise GypError ( ( 'Xcode environment variables are cyclically dependent: ' + str ( e . nodes ) ) )
takes a dict |env| whose values are strings that can refer to other keys .