os.chmod() does not follow symlinks on Windows

[atsuoishimoto]

BPO	15411
Nosy	@atsuoishimoto, @tjguk, @asvetlov, @zware
Files	chmod_symlink_win32.patch chmod_symlink_win32_2.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 = None
created_at = <Date 2012-07-21.08:31:23.124>
labels = ['type-feature', 'library', 'OS-windows']
title = 'os.chmod() does not follow symlinks on Windows'
updated_at = <Date 2019-04-26.19:53:54.688>
user = 'https://github.com/atsuoishimoto'

bugs.python.org fields:

activity = <Date 2019-04-26.19:53:54.688>
actor = 'BreamoreBoy'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)', 'Windows']
creation = <Date 2012-07-21.08:31:23.124>
creator = 'ishimoto'
dependencies = []
files = ['26462', '26464']
hgrepos = []
issue_num = 15411
keywords = ['patch']
message_count = 3.0
messages = ['165996', '166003', '223300']
nosy_count = 4.0
nosy_names = ['ishimoto', 'tim.golden', 'asvetlov', 'zach.ware']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue15411'
versions = ['Python 3.5']

Linked PRs

• gh-59616: Support os.chmod(follow_symlinks=True) and os.lchmod() on Windows #113049

[atsuoishimoto]

os.chmod() should check symlinks if followsymlinks option is True on Windows.

This is a cause of failure of test case

test.test_shutil.TestShutil.test_copymode_follow_symlinks

(bpo-13837)

[atsuoishimoto]

Patch updated. Check symlinks only if supported by platform.

[BreamoreBoy]

Can we have a patch review on this please as it's holding up bpo-13837.

[serhiy-storchaka]

Unfortunately, the patch by @atsuoishimoto is too old and cannot be applied to the current code. The difference is so larger, that it is easier to write a new code from scratch than try to resolve conflicts iteratively.

Which I did. My PR uses a different approach. Instead of resolving the symlink path, it opens a handle and changes file attributes by the handle (it is the recommended way). In future it may be possible to implement also os.fchmod().

[serhiy-storchaka]

Now os.chmod() supports follow_symlinks=True on Windows. But by default it does not follow symlinks. Few versions later (in 3.15 or later) we can change the default. It will allow users to use os.lchmod() or os.chmod(follow_symlinks=False) if they need the old behavior, and it will work in several versions.