Python scripts are executed with the wrong path separator in integrated Powershell on Windows

[tsbertalan]

Environment data

• VS Code version: 1.48.2
• Extension version (available under the Extensions sidebar): 2020.08.106424
• OS and version: Windows 10 , 1909, build 18363.1016
• Python version (& distribution if applicable, e.g. Anaconda): Anaconda, 3.7.7
• Type of virtual environment used (N/A | venv | virtualenv | conda | ...): conda
• Relevant/affected Python packages and their versions: N/A
• Relevant/affected Python-related VS Code extensions and their versions: N/A
• Value of the python.languageServer setting: Jedi

Expected behaviour

On Windows, with Powershell as the embedded terminal, the path to the python executable and to the current script being executed should use backslashes.

Actual behaviour

A script command line like this is generated:

(py37) PS C:\Users\tsbertalan\SNIPPED> & C:/Users/tsbertalan/Anaconda3/envs/py37/python.exe "c:/Users/tsbertalan/SNIPPED/SCRIPT.py"

However, invoking workbench.action.debug.start instead generates:

(base) PS C:\Users\tsbertalan\SNIPPED>  & 'C:\Users\tsbertalan\Anaconda3\envs\py37\python.exe' 'c:\Users\tsbertalan\.vscode\extensions\ms-python.python-2020.8.106424\pythonFiles\lib\python\debugpy\launcher' '53300' '--' 'c:\Users\tsbertalan\SNIPPED\SCRIPT.py'

Which was very confusing at first--when I debugged the script, paths which were constructed using os.path.join with os.path.basename(__file__) had homogeneous, all-backslash paths, but when I ran it with python.execInTerminal, the paths were mixed!

Steps to reproduce:

1. Use "Python: Select Interpreter" to launch a file dialog and locate python.exe in C:\Users\USERNAME\Anaconda3\envs\ENVNAME.
2. Use python.execInTerminal (the little play button) to launch a script, with terminal.integrated.shell.windows unset (that is, left to its default of C:\WINDOWS\System32\WindowsPowerShell\v1.0\powershell.exe).
3. Witness the forward-slash generated command in the integrated terminal.

Details

I'm currently working on a script that uses os.path.join, os.path.basename, etc., and in particular uses basename(__file__) to get the path of the current script in a cross-platform way. This does intelligently interprets the forward slashes as path separators, and trims off the SCRIPT.py part, leaving a C:/Users... path. But then, subsequent joins with this path have mixed slashes, since join correctly uses backslash as a path separator on windows.

This isn't a problem for my script at the moment, since all file-access code (for instance, these mixed-slash paths are being passed to glob.glob) seems to be intelligently homogenizing the slashes. But it could become a problem in the future.

[ericsnowcurrently]

@tsbertalan, thanks for letting us know about this. We'll take a look and get back to you as soon as possible.