Specifying the Python interpreter in launch.json using the CONDA_PREFIX environment variable raises an error

[FSpanhel]

Type: Bug

The following configuration launch.json sets the Python interpreter to the Python interpreter of the activated conda environment of the integrated terminal

{
    // Use IntelliSense to learn about possible attributes.
    // Hover to view descriptions of existing attributes.
    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Python: Dynamic path",
            "type": "python",
            "request": "launch",
            "program": "myscript.py",
            "console": "integratedTerminal",
            "cwd": ".",
            "python": "${env:CONDA_PREFIX}/bin/python",
            "justMyCode": true
        },
    ]
}

Wenn I activate the conda environment with the path to the Python interpreter being /conda/envs/my_env/bin/python and then start the debugger of this configuration, I get the following output in the terminal

/usr/bin/env /conda/envs/my_env/bin/python /home/.vscode-server/extensions/ms-python.python-2023.8.0/pythonFiles/lib/python/debugpy/adapter/../../debugpy/launcher 45096 -- myscript.py
-X is reserved for implementation-specific arguments
usage: /bin/python [option] ... [-c cmd | -m mod | file | -] [arg] ...
Try `python -h' for more information.

This is unexpected, because the path /conda/envs/my_env/bin/python to the Python interpreter is correct.
Moreover, I have also followed the steps described in https://code.visualstudio.com/docs/editor/variables-reference#_how-can-i-know-a-variables-actual-value to see that the value of the python field in the configuration is actually the path to the Python interpreter.

When I replace the python field in the configuration by /conda/envs/my_env/bin/python the debugger runs.

Extension version: 2023.5.20
VS Code version: Code 1.78.0 (252e5463d60e63238250799aef7375787f68b4ee, 2023-05-03T20:09:00.748Z)
OS version: Windows_NT x64 10.0.19042
Modes:
Sandboxed: No
Remote OS version: Linux x64 4.4.0-19041-Microsoft
Remote OS version: Linux x64 3.10.0-1160.66.1.el7.x86_64
Remote OS version: Linux x64 4.4.0-19041-Microsoft
Remote OS version: Linux x64 4.4.0-19041-Microsoft

System Info

Item	Value
CPUs	Intel(R) Core(TM) i7-8665U CPU @ 1.90GHz (8 x 2112)
GPU Status	2d_canvas: enabled canvas_oop_rasterization: disabled_off direct_rendering_display_compositor: disabled_off_ok gpu_compositing: enabled multiple_raster_threads: enabled_on opengl: enabled_on rasterization: enabled raw_draw: disabled_off_ok video_decode: enabled video_encode: enabled vulkan: disabled_off webgl: enabled webgl2: enabled webgpu: enabled
Load (avg)	undefined
Memory (System)	15.75GB (1.59GB free)
Process Argv	--crash-reporter-id 0d3cf624-62ed-41e9-9c0e-981ac1406d0e
Screen Reader	no
VM	0%

Item	Value
Remote	WSL: Ubuntu-18.04
OS	Linux x64 4.4.0-19041-Microsoft
CPUs	Intel(R) Core(TM) i7-8665U CPU @ 1.90GHz (8 x 2112)
Memory (System)	15.75GB (1.58GB free)
VM	0%

Item	Value
Remote	SSH: PROD_ADMIN
OS	Linux x64 3.10.0-1160.66.1.el7.x86_64
CPUs	Intel(R) Xeon(R) Gold 5218 CPU @ 2.30GHz (4 x 2294)
Memory (System)	15.51GB (1.41GB free)
VM	100%

Item	Value
Remote	WSL: Ubuntu-18.04
OS	Linux x64 4.4.0-19041-Microsoft
CPUs	Intel(R) Core(TM) i7-8665U CPU @ 1.90GHz (8 x 2112)
Memory (System)	15.75GB (1.58GB free)
VM	0%

Item	Value
Remote	WSL: Ubuntu-18.04
OS	Linux x64 4.4.0-19041-Microsoft
CPUs	Intel(R) Core(TM) i7-8665U CPU @ 1.90GHz (8 x 2112)
Memory (System)	15.75GB (1.58GB free)
VM	0%

A/B Experiments

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vsreu685:30147344
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pythonms35:30701012
pythonfmttext:30731395
pythoncmvfstr:30731969
fixhidewlkth:30730051
hidesbindicator:30730055

[rchiodo]

Thanks for the issue. Pylance does not provide the debugger for python, that would be the python extension. Transferring issue there.

[rchiodo]

According to this: https://code.visualstudio.com/docs/editor/variables-reference#_environment-variables, I believe that syntax should be supported, but the Python extension may not yet support it.

[karthiknadig]

@FSpanhel For this to work correctly, VS Code itself must be started from an activated conda environment.

> cd <your project path>
> conda activate <env>
> code .

[FSpanhel]

@karthiknadig Thank you for your comment.

Unfortunately, this is not what I want. I can achieve the same result by selecting the corresponding Python interpreter in VS Code using the Command Palette and Python: Select Interpreter. This is how I've done it so far when I started debugging with VS Code last week.

However, it would be great if there is a connection between the activated environment in the integrated terminal and the debugger. I tried to achieve this by using the corresponding environment variable in launch.json. As far as I understand the documentation, this should work. And although it appears in my first post that the evaluated path to the Python interpreter is correct, something goes wrong. According to the error message, it appears that somehow the flag -X is passed to the Python interpreter.

Can I somehow investigate what is going on?

[karthiknadig]

@FSpanhel That is kind of the problem. Since VS Code launches the debugger the way VS Code can resolve env:CONDA_PREFIX is if VS Code itself was launched from an activated environment so it sees CONDA_PREFIX. That said, we now have a new terminal activation feature that might be able to help with this. This might be a feature request to resolve such variables, based on the activated terminal.

/cc @karrtikr This should work with the new environment variable API for terminal (i.e, we don't have debugger running with a non-activated python issue). Not sure if env:CONDA_PREFIX style of resolution is handled yet.

[FSpanhel]

@karthiknadig

Okay, so the environment variables of VS Code are determined at startup and are not the environment variables of an integrated terminal that may also change? Is this somewhere documented?

At least to me, reading https://code.visualstudio.com/docs/editor/variables-reference#_environment-variables does not imply such a behavior.

Is there also some documentation about this new "terminal activation feature"?