os: Some functions may report bogus errors on Windows

[izbyshev]

BPO	32890
Nosy	@vstinner, @izbyshev, @miss-islington
PRs	bpo-32890: os: Use errno instead of GetLastError() where appropriate #5784 [3.7] bpo-32890, os: Use errno instead of GetLastError() in execve() and truncate() (GH-5784) #9984 [3.6] bpo-32890, os: Use errno instead of GetLastError() in execve() and truncate() (GH-5784) #9985

^{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 2018-10-20.00:53:37.560>
created_at = <Date 2018-02-20.23:54:16.434>
labels = ['3.8', 'type-bug', '3.7']
title = 'os: Some functions may report bogus errors on Windows'
updated_at = <Date 2018-10-22.17:29:14.286>
user = 'https://github.com/izbyshev'

bugs.python.org fields:

activity = <Date 2018-10-22.17:29:14.286>
actor = 'izbyshev'
assignee = 'none'
closed = True
closed_date = <Date 2018-10-20.00:53:37.560>
closer = 'vstinner'
components = []
creation = <Date 2018-02-20.23:54:16.434>
creator = 'izbyshev'
dependencies = []
files = []
hgrepos = []
issue_num = 32890
keywords = ['patch']
message_count = 6.0
messages = ['312446', '328101', '328110', '328113', '328118', '328265']
nosy_count = 3.0
nosy_names = ['vstinner', 'izbyshev', 'miss-islington']
pr_nums = ['5784', '9984', '9985']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue32890'
versions = ['Python 3.6', 'Python 3.7', 'Python 3.8']

[izbyshev]

Demo:

>>> os.execve('', ['a'], {})
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OSError: [WinError 0] The operation completed successfully: ''

The reason is that path_error() used throughout os module always uses GetLastError() on Windows, but some functions are implemented via CRT calls which report errors via errno. It seems that commit 292c835 caused this issue.

[vstinner]

New changeset 8346031 by Victor Stinner (Alexey Izbyshev) in branch 'master':
bpo-32890, os: Use errno instead of GetLastError() in execve() and truncate() (GH-5784)
8346031

[miss-islington]

New changeset 8f53dcd by Miss Islington (bot) in branch '3.7':
bpo-32890, os: Use errno instead of GetLastError() in execve() and truncate() (GH-5784)
8f53dcd

[miss-islington]

New changeset d9a2665 by Miss Islington (bot) in branch '3.6':
bpo-32890, os: Use errno instead of GetLastError() in execve() and truncate() (GH-5784)
d9a2665

[vstinner]

Thanks Alexey Izbyshev!

[izbyshev]

Python 2.7 doesn't have the same issue.

In os.execve(), posix_error() is used, but it is based on errno, which is correct. (A funny bit is that os.execve('', ['a'], {}) crashes in 2.7, probably because of some checks in CRT).

And os.truncate() is not implemented in 2.7 at all.