Add multiroot-workspace variable scoping for `python.defaultInterpreterPath`

[OmeGak]

It's currently not possible to use multiroot-workspace variable scoping to configure python.defaultInterpreterPath, as @kimadeline mentioned in #18207 (comment).

My use case is the following. I have multiple python projects in my workspace but I want them all to use the same virtualenv, existing under one of the workspace folders. The tree structure looks like this:

/
├── python-a/
│  ├── .venv/
│  └── foo.py
├── python-b/
│  └── bar.py

To make it work with python.defaultInterpreterPath I need to configure it like this in the workspace file:

"python.defaultInterpreterPath": "${workspaceFolder}/../python-a/.venv/bin/python"

This is fragile, as it will break if python-b/ workspace folder changes its absolute path. With multiroot-workspace variable scoping it would be possible to express this dependency more robustly like this:

"python.defaultInterpreterPath": "${workspaceFolder:python-a}/.venv/bin/python"

[munro]

@OmeGak I think there may be a bit over overlap here with #18674 (please up vote 😄 )

I don't seem to have this issue specifically, but I have set this in my subworkspace's ./.vscode/settings.json:

{
    "python.defaultInterpreterPath": "${workspaceFolder}/.venv/bin/python"
}

[Samuel-Therrien-Beslogic]

One of the projects I work with is a microservices monorepo
Each service (as well as the common/shared code library/module) have their own .venv
As a workaround I've created a virtual environment at the root of the project and pointed defaultInterpreterPath to it "python.defaultInterpreterPath": ".venv/bin/python", so everything is installed there.
And changed all my debug tasks commands to use the ${workspaceFolder} ("command": "cd backend/services/collect-service; poetry run ${workspaceFolder}/.venv/bin/python run.py",).

But this really isn't the best and is bound to have issues as soon as there's version conflicts between services.
It would be nice if VSCode devs didn't have to do that extra setup and could have scoped virtualenvs (which those using PyCharm don't have an issue with)

[karrtikr]

Note https://code.visualstudio.com/docs/editor/variables-reference#_variables-scoped-per-workspace-folder is currently only supported in tasks.json or launch.json (used while debugging), the use for it in settings.json is discouraged.

@OmeGak In this usecase .venv/ does not belong to the first workspace folder and is something the workspace file owns instead, so I'm wondering if the concept of ${workspaceFile} would work better instead. It can be used to access the path to the .code-workspace file.

[karrtikr]

Thanks for the feature request! We are going to give the community 60 days from when this issue was created to provide 7 👍 upvotes on the opening comment to gauge general interest in this idea. If there's enough upvotes then we will consider this feature request in our future planning. If there's unfortunately not enough upvotes then we will close this issue.