Make the 'dirs' builtin pass the spec tests (#56)

- Fix a bug that caused the wrong directory entry to be pushed onto the directory stack.

core/builtin.py

@@ -483,10 +483,22 @@ def Cd(argv, mem):
  return 0


def PrintDirStack(dir_stack):
  if dir_stack:
    print(' '.join(dir_stack))

WITH_PREFIX = 1
WITHOUT_PREFIX = 2
SINGLE_LINE = 3

def PrintDirStack(dir_stack, mode):
  dirs = [os.getcwd()]
  dirs.extend(dir_stack)
  if mode == WITH_PREFIX:
    for i, entry in enumerate(dirs):
      print('%2d  %s' % (i, entry))
  elif mode == WITHOUT_PREFIX:
    for entry in dirs:
      print(entry)
  elif mode == SINGLE_LINE:
    print(' '.join(dirs))
  sys.stdout.flush()

def Pushd(argv, dir_stack):
  num_args = len(argv)
@@ -498,14 +510,15 @@ def Pushd(argv, dir_stack):
    return 1

  dest_dir = argv[0]
  current_dir = os.getcwd()
  try:
    os.chdir(dest_dir)
  except OSError as e:
    util.error("pushd: %r: %s", dest_dir, os.strerror(e.errno))
    return 1

  dir_stack.append(os.getcwd())
  PrintDirStack(dir_stack)
  dir_stack.append(current_dir)
  PrintDirStack(dir_stack, SINGLE_LINE)
  return 0


@@ -522,7 +535,7 @@ def Popd(argv, dir_stack):
    util.error("popd: %r: %s", dest_dir, os.strerror(e.errno))
    return 1

  PrintDirStack(dir_stack)
  PrintDirStack(dir_stack, SINGLE_LINE)
  return 0


@@ -540,14 +553,11 @@ def Dirs(argv, dir_stack):
  if arg.c:
    del dir_stack[:]
  elif arg.v:
    for i, entry in enumerate(dir_stack):
      print('%2d %s' % (i, entry))
    PrintDirStack(dir_stack, WITH_PREFIX)
  elif arg.p:
    for entry in dir_stack:
      print(entry)
    PrintDirStack(dir_stack, WITHOUT_PREFIX)
  else:
    PrintDirStack(dir_stack)

    PrintDirStack(dir_stack, SINGLE_LINE)
  return 0