Fix double word hacking test

At present, 'pycodestyle' feeds the following string into the 'tokenizer'
library:

    ["'This is the the best comment'"]

(note the added quotes because this isn't valid Python otherwise)

On previous versions of Python, this tokenizer would parse the string like so:

  (3, "'This is the the best comment'", (1, 0), (1, 30), "'This is the the best comment'")
  (0, '', (2, 0), (2, 0), '')

where (3 = 'STRING', 0 = 'ENDMARKER')

However, with the fix [1] backported to recent versions of Python, this now
resolves to:

  (3, "'This is the the best comment'", (1, 0), (1, 30), "'This is the the best comment'")
  (4, '', (1, 30), (1, 31), '')
  (0, '', (2, 0), (2, 0), '')

where (3 = 'STRING', 4 = 'NEWLINE', 0 = 'ENDMARKER')

Typically, 'pycodestyle' will run physical line checks on each line as it
parses the token:

  https://github.com/PyCQA/pycodestyle/blob/2.5.0/pycodestyle.py#L2036

For the former case above, the line doesn't include a newline which
means we never parse a 'NEWLINE' token with a logical line (the fifth
element of the token tuple) corresponding to our full line. This means
we don't here but that wasn't an issue previously since there's a
fallthrough case that handled tokens remaining at the end of the parse:

  https://github.com/PyCQA/pycodestyle/blob/2.5.0/pycodestyle.py#L2114-L2116

Unfortunately, because we now have an additional newline character to
parse, one that's on a separate line to our test string no less, we run
logical checks on it:

  https://github.com/PyCQA/pycodestyle/blob/2.5.0/pycodestyle.py#L2105-L2107

This is an issue since the logical check wipes stored tokens meaning
we've nothing to check when we get to the fallthrough case:

  https://github.com/PyCQA/pycodestyle/blob/2.5.0/pycodestyle.py#L2012

This fixes changes things so that a newline is included (and also adds
quotes so it's valid Python, but that's mostly unrelated). This means we
end up with the following instead:

  ["'This is the the best comment'\n"]

On both Python without the bugfix and with it, this parses as:

  (3, "'This is the the best comment'", (1, 0), (1, 30), "'This is the the best comment'\n")
  (4, '\n', (1, 30), (1, 31), "'This is the the best comment'\n")
  (0, '', (2, 0), (2, 0), '')

where (3 = 'STRING', 4 = 'NEWLINE', 0 = 'ENDMARKER')

Which triggers things in 'pycodestyle' correctly.

  https://github.com/PyCQA/pycodestyle/blob/2.5.0/pycodestyle.py#L2044-L2046

This isn't _really_ a fix since there's clearly still a bug in either
'pycodestyle' or Python (I think the latter, since it's adding a newline
to a file that explicitly doesn't have one), but the chances of us
hitting this bug in practice are rather low - you'd need to make a
mistake on the very last line of a file without a newline at the end
which is something Vim, for example, won't even let you do without
setting special flags - and therefore it can be reasonably ignored.

[1] https://bugs.python.org/issue33899

Change-Id: Ia597594e0469c0e83d7ad22b0678390aaebaffe7
Signed-off-by: Stephen Finucane <[email protected]>
Closes-Bug: #1804062

Author: stephenfin

nova/tests/unit/test_hacking.py

@@ -16,7 +16,6 @@
 
 import mock
 import pycodestyle
-import testtools
 
 from nova.hacking import checks
 from nova import test
@@ -276,7 +275,7 @@ def __get_msg(fun):
     def _run_check(self, code, checker, filename=None):
         pycodestyle.register_check(checker)
 
-        lines = textwrap.dedent(code).strip().splitlines(True)
+        lines = textwrap.dedent(code).lstrip().splitlines(True)
 
         checker = pycodestyle.Checker(filename=filename, lines=lines)
         # NOTE(sdague): the standard reporter has printing to stdout
@@ -578,19 +577,17 @@ def test_check_config_option_in_central_place(self):
                                    checks.check_config_option_in_central_place,
                                    filename="nova/tests/dummy_test.py")
 
-    # TODO(cdent): Remove when https://bugs.launchpad.net/nova/+bug/1804062
-    # is resolved.
-    @testtools.skip(
-        'tokenize has backwards incompatible behavior from 3.6.7 and 2.7.15')
     def test_check_doubled_words(self):
         errors = [(1, 0, "N343")]
 
-        # Artificial break to stop flake8 detecting the test !
-        code = "This is the" + " the best comment"
+        # Explicit addition of line-ending here and below since this isn't a
+        # block comment and without it we trigger #1804062. Artificial break is
+        # necessary to stop flake8 detecting the test
+        code = "'This is the" + " the best comment'\n"
         self._assert_has_errors(code, checks.check_doubled_words,
                                 expected_errors=errors)
 
-        code = "This is the then best comment"
+        code = "'This is the then best comment'\n"
         self._assert_has_no_errors(code, checks.check_doubled_words)
 
     def test_dict_iteritems(self):