shlex: bug in posix mode handling of empty strings

[isoschiz]

BPO	21999
Nosy	@vsajip, @ezio-melotti, @bitdancer, @phmc
Files	shlex.default.patch shlex.2.7.patch

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2016-08-09.14:07:22.926>
created_at = <Date 2014-07-17.16:37:00.766>
labels = ['type-bug']
title = 'shlex: bug in posix mode handling of empty strings'
updated_at = <Date 2016-08-09.14:07:22.924>
user = 'https://bugs.python.org/isoschiz'

bugs.python.org fields:

activity = <Date 2016-08-09.14:07:22.924>
actor = 'python-dev'
assignee = 'none'
closed = True
closed_date = <Date 2016-08-09.14:07:22.926>
closer = 'python-dev'
components = []
creation = <Date 2014-07-17.16:37:00.766>
creator = 'isoschiz'
dependencies = []
files = ['35983', '35984']
hgrepos = []
issue_num = 21999
keywords = ['patch']
message_count = 6.0
messages = ['223348', '223512', '228136', '272083', '272251', '272253']
nosy_count = 6.0
nosy_names = ['vinay.sajip', 'ezio.melotti', 'r.david.murray', 'python-dev', 'pconnell', 'isoschiz']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue21999'
versions = ['Python 2.7', 'Python 3.5']

[isoschiz]

Minimal testcase of the problem situation is tokenising (with posix mode on):

''),

Specifically, an empty string, followed by a non-word character, followed by a non-space character. In this case, the token buffer is empty and due to a missing check for (self.posix and quoted), an extra token is consumed and returned in the wrong order:

>>> s = shlex.shlex("'')abc", posix=True)
>>> s.get_token()
'abc'
>>> s.get_token()
')'
>>> s.get_token()
>>> 

I have patches to fix this issue in both default and 2.7. I've also checked there are no other occurrences of the same typo.

[bitdancer]

Vinay has a patch improving shlex parsing in bpo-1521950, but it doesn't seem to address this case, so I'm adding him as nosy.

[vsajip]

I've updated the patch on bpo-1521950 to address this case, and also added a test there (which is not in this patch). Thanks, RDM, for the notification.

[vsajip]

After the patch for bpo-1521950 was applied, this problem no longer occurs on default/3.6.

Removing 3.4 as it's in "security patches only" mode.

[python-dev]

New changeset cf04243e8d7d by Vinay Sajip in branch '2.7':
Issue bpo-21999: Handled empty strings correctly when in POSIX mode.
https://hg.python.org/cpython/rev/cf04243e8d7d

[python-dev]

New changeset 4f02ad46a0a8 by Vinay Sajip in branch '3.5':
Closes bpo-21999: Handled empty strings correctly when in POSIX mode.
https://hg.python.org/cpython/rev/4f02ad46a0a8

New changeset a8e74448678c by Vinay Sajip in branch 'default':
Closes bpo-21999: (Empty) merge from 3.5.
https://hg.python.org/cpython/rev/a8e74448678c