[issue34195] test_nt_helpers fails with case difference in drive letter

[Tim Golden]

Tim Golden  added the comment:


New changeset ff64add8d4be2e37c552ba702f629b0b6639cd33 by Tim Golden in branch 
'master':
bpo-34195: Fix case-sensitive comparison in test_nt_helpers (GH-8448)
https://github.com/python/cpython/commit/ff64add8d4be2e37c552ba702f629b0b6639cd33


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[issue34195] test_nt_helpers fails with case difference in drive letter

[Tim Golden]

Tim Golden  added the comment:

Test fixed to ignore case and volume differences between paths

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resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed

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[issue34195] test_nt_helpers fails with case difference in drive letter

[Tim Golden]

Change by Tim Golden :


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keywords: +patch
pull_requests: +7970
stage: needs patch -> patch review

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[issue34195] test_nt_helpers fails with case difference in drive letter

[Eryk Sun]

Eryk Sun  added the comment:

> the directory in which I'm building (c:\work-in-progress) is actually 
> a junction to c:\users\\work-in-progress

That makes sense. GetVolumePathName traverses backwards from the final 
component. If it reaches a reparse point (other than a junction that targets a 
volume name of the form "\??\Volume{GUID}\"), it has to start over from the 
reparsed final path obtained from GetFinalPathNameByHandle. Subsequently it's 
traversing back from "C:\Users\\work-in-progress" down to upper-case "C:\".

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[issue34195] test_nt_helpers fails with case difference in drive letter

[Tim Golden]

Tim Golden  added the comment:

I think I've got down to the determining factor. For info:

PYTHONHOME has nothing to do with it: the same thing happens if I cd into 
PCBuild\win32 and run python_d.exe directly

For historical reasons the directory in which I'm building 
(c:\work-in-progress) is actually a junction to c:\users\\work-in-progress. 
There is some commentary in the API docs about traversing junctions, so 
presumably that's special-cased in some way which results in an uppercase drive 
letter.

If I rebuild in, eg, c:\temp which is a normal directory, I don't see the 
uppercase conversion. So, while I still need to fix the underlying test to be 
case-insensitive, it looks like the Mystery of the Uppercase Drive Letter is at 
least mostly solved.

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[issue34195] test_nt_helpers fails with case difference in drive letter

[Tim Golden]

Tim Golden  added the comment:

@eryksun almost idly I ran your ctypes code in the built interpreter. As 
written, it produces a lower-case c:\\ as yours did.

But...

Running Debug|Win32 interpreter...
Python 3.8.0a0 (heads/master:7a3056f, Jul 23 2018, 08:23:33) [MSC v.1912 32 bit 
(Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import ctypes, sys
>>>
>>> sys.executable
'c:\\work-in-progress\\python\\cpython\\PCbuild\\win32\\python_d.exe'
>>> kernel32 = ctypes.WinDLL('kernel32', use_last_error=True)
>>> path = (ctypes.c_wchar * 4)()
>>> kernel32.GetVolumePathNameW(sys.executable, path, 4)
1
>>> path.value
'C:\\'
>>>

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[issue34195] test_nt_helpers fails with case difference in drive letter

[Tim Golden]

Tim Golden  added the comment:

Thanks, @eryksun. Whatever the reason, it's consistently failing in the way I 
describe. A case-insensitive test is obviously good for that and for the other 
reasons you give, so I'll patch the test anyway.

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[issue34195] test_nt_helpers fails with case difference in drive letter

[Eryk Sun]

Eryk Sun  added the comment:

os__getvolumepathname_impl in Modules/posixmodule.c doesn't directly modify the 
case. So that leaves WinAPI GetVolumePathNameW as the culprit, but, according 
to the following test, apparently not in Windows 10.0.17134:

kernel32 = ctypes.WinDLL('kernel32', use_last_error=True)
path = (ctypes.c_wchar * 4)()
kernel32.GetVolumePathNameW(r'c:\windows', path, 4)

>>> path.value
'c:\\'

On a related note, nowadays we need to be careful to only use a 
case-insensitive comparison for drive letters and other device names. On 
account of WSL, recent versions of NTFS support flagging directories as case 
sensitive [1][2]. For example, a volume may be mounted using a junction in a 
case-sensitive directory. 

[1]: 
https://blogs.msdn.microsoft.com/commandline/2018/02/28/per-directory-case-sensitivity-and-wsl
[2]: 
https://blogs.msdn.microsoft.com/commandline/2018/06/14/improved-per-directory-case-sensitivity-support-in-wsl

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nosy: +eryksun

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[issue34195] test_nt_helpers fails with case difference in drive letter

[Tim Golden]

Tim Golden  added the comment:

import nt, sys; assert 
sys.executable.startswith(nt._getvolumepathname(sys.executable))

This code fails only when run from the python.bat as created by 
pcbuild\build.bat. The obvious difference is that the batch file sets 
PYTHONHOME which, presumably, is used to form sys.executable (haven't checked 
the startup code yet).

The docs for GetVolumePathName [*] don't specify that the drive letter of the 
path returned will be upper-case, but it doesn't seem unlikely.

So... it looks as though the test is unduly sensitive to case-differences in 
the face of something like PYTHONHOME which affects the way in which 
sys.executable is formed.

Phew! I'll put a test patch together later...

[*] 
https://docs.microsoft.com/en-us/windows/desktop/api/fileapi/nf-fileapi-getvolumepathnamew

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[issue34195] test_nt_helpers fails with case difference in drive letter

[Tim Golden]

New submission from Tim Golden :

>From a fresh build on Win10 with VS2017:

python -munittest -v test.test_ntpath.TestNtpath.test_nt_helpers

gives the following error:

==
FAIL: test_nt_helpers (test.test_ntpath.TestNtpath)
--
Traceback (most recent call last):
  File "c:\work-in-progress\python\cpython\lib\test\test_ntpath.py", line 432, 
in test_nt_helpers
self.assertEqual(drive, nt._getvolumepathname(sys.executable))
AssertionError: 'c:\\' != 'C:\\'
- c:\
? ^
+ C:\
? ^


Ad hoc, it appears that:

`sys.executable` gives a lower-case path while `nt._getvolumepathname` gives an 
upper-case drive letter.

While the test could be trivially fixed, it seems worth investigating a little 
further to see what's happening inside `nt._getvolumepathname`

--
assignee: tim.golden
components: Windows
messages: 322185
nosy: paul.moore, steve.dower, tim.golden, zach.ware
priority: normal
severity: normal
stage: needs patch
status: open
title: test_nt_helpers fails with case difference in drive letter
type: behavior
versions: Python 3.8

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