On Windows Powershell, venv folders are unexpectedly importable due to how namespace package and venv works

Bug report

PEP420 introduced implicit namespace package, basically by creating a folder without __init__.py, it is treated as namespace package.

For some reasons, in Windows Powershell, venv added the environment's root folder into sys.path (this behavior was not observed in Linux's venv), e.g.

PS C:\Users\TestUser> python -m venv testenv
PS C:\Users\TestUser> . .\testenv\Scripts\activate
(testenv) PS C:\Users\TestUser> python
Python 3.10.5 (tags/v3.10.5:f377153, Jun  6 2022, 16:14:13) [MSC v.1929 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> sys.path
[
    [snip] 
    'C:\\Users\\TestUser\\testenv', 
    'C:\\Users\\TestUser\\testenv\\lib\\site-packages'
]

And because of the way namespace package works, you can import some folders that really aren't intended to be importable:

>>> import Include
>>> Include.__path__
_NamespacePath(['C:\\Users\\TestUser\\testenv\\Include'])
>>>

This was a namespace package created from the Include folder in the root of the testvenv folder:

PS C:\Users\TestUser> ls .\testenv\


    Directory: C:\Users\TestUser\testenv


Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
d-----         7/18/2022   1:15 PM                Include
d-----         7/18/2022   1:15 PM                Lib
d-----         7/18/2022   1:15 PM                Scripts
-a----         7/18/2022   1:15 PM            127 pyvenv.cfg

Similarly, you could have imported Lib and Scripts.

Your environment

Python 3.10.5 (tags/v3.10.5:f377153, Jun 6 2022, 16:14:13) [MSC v.1929 64 bit (AMD64)] on win32

Start by reproducing the Windows PowerShell commands in the report and inspect sys.path after creating and activating a venv. Compare the Windows and Linux venv behavior, then determine how the Include, Lib, and Scripts directories become importable. Done means unintended venv directories are no longer importable without breaking normal environment imports.