Comment 10 for bug 1804062

Reviewed: https://review.opendev.org/664940
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=f545a25cc443c41dcd9bdd028064c28b53f56037
Submitter: Zuul
Branch: master

commit f545a25cc443c41dcd9bdd028064c28b53f56037
Author: Stephen Finucane <email address hidden>
Date: Wed Jun 12 15:10:59 2019 +0100

    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 address hidden>
    Closes-Bug: #1804062