[issue32457] Windows Python cannot handle an early PATH entry containing ".." and python.exe

[Ray Donnelly]

New submission from Ray Donnelly <rdonnelly at anaconda.com>:

Over on the Anaconda Distribution we received a (private) bug report about a crash when trying to use scons. I thought initially it was due to one of our patches but I tested it out with official CPython and also with WinPython and ran into the same crash.

To reproduce this, from cmd.exe on CPython (here I installed CPython as part of Visual Studio 2017, then updated it to the latest 3.6.4 release):

```
set "PATH=C:\Program Files (x86)\Microsoft Visual Studio\Shared\Python36_64\Scripts\..;%PATH%"

python.exe

..

python
Fatal Python error: Py_Initialize: unable to load the file system codec
ModuleNotFoundError: No module named 'encodings'

Current thread 0x00000328 (most recent call first):
```

The trigger for this bug is the following batch code in scons.bat:

https://bitbucket.org/scons/scons/src/c0172db149b1a151eeb76910d55c81746bfede05/src/script/scons.bat?at=default&fileviewer=file-view-default#scons.bat-19

My current thinking is that the best fix here is to modify get_progpath()/get_program_full_path() so that it uses PathCchCanonicalizeEx() at https://github.com/python/cpython/blob/9bee329130aae5a13050c08dab9d349b76e66835/PC/getpathp.c#L558-L559

----------
components: Windows
messages: 309242
nosy: Ray Donnelly, paul.moore, steve.dower, tim.golden, zach.ware
priority: normal
severity: normal
status: open
title: Windows Python cannot handle an early PATH entry containing ".." and python.exe
type: crash
versions: Python 3.6

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue32457>
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