`ty.interpreter` setting does not expand `${workspaceFolderBasename}` variable (partial variable expansion)

[keuj6]

Description

The ty.interpreter setting only partially expands VS Code variables. While ${env:USERNAME} expands correctly, ${workspaceFolderBasename} remains as a literal string, causing ty to fail finding the Python environment.

Steps to Reproduce

1. Create a project with venv stored outside the project directory using a consistent naming pattern
2. Add to .vscode/settings.json:

   {
     "ty.interpreter": [
       "C:\\Users\\${env:USERNAME}\\venv\\${workspaceFolderBasename}\\Scripts\\python.exe"
     ]
   }

3. Open the project in VS Code
4. Check "ty: Show client logs" (Command Palette → ty: Show client logs)

Expected Behavior

For a project named myproject with username john, the path should expand to:

C:\Users\john\venv\myproject\Scripts\python.exe

Both ${env:USERNAME} and ${workspaceFolderBasename} should be expanded.

Actual Behavior

The path expands to:

C:\Users\john\venv\${workspaceFolderBasename}\Scripts\python.exe

• ✅ ${env:USERNAME} → john (works)
• ❌ ${workspaceFolderBasename} → remains literal (doesn't work)

Log Evidence

Client log:

[error] Unable to find any Python environment for the interpreter path: C:\Users\john\venv\${workspaceFolderBasename}

Use Case / Motivation

Supporting team environments where developers store venvs outside the project directory with consistent naming:

C:\Users\alice\venv\project1\
C:\Users\alice\venv\project2\
C:\Users\bob\venv\project1\
C:\Users\bob\venv\project2\

Current Workaround

Must hardcode the project name in workspace settings (not ideal for shared configs):

{
  "ty.interpreter": [
    "C:\\Users\\${env:USERNAME}\\venv\\myproject\\Scripts\\python.exe"
  ]
}

This requires:

• .vscode/settings.json to be gitignored
• Each team member to manually update their settings with their project name
• Maintaining a .vscode/settings.json.example template

Environment

• ty-vscode version: 2026.4.0
• ty version: 0.0.12
• VS Code version: 1.108.0
• OS: Windows 10
• Python version: 3.13.7

Additional Context

This appears to be a common issue with VS Code extensions. Variable substitution is not automatic and must be implemented by each extension (VS Code issue #46471).

[MichaReiser]

That makes sense.

Very surprisingly, VS Code doesn't provide a standardized API to replace all known environment variables, see microsoft/vscode#46471

There's an NPM package that we could use https://www.npmjs.com/package/vscode-variables

The alternative is to copy paste some of https://github.com/microsoft/vscode-python/blob/b68facc42f684f26c5f83f3cfe895e7aa4bb2bee/src/client/common/variables/systemVariables.ts

[dhruvmanila]

For context, the resolveVariables is mainly coming from https://github.com/microsoft/vscode-python-tools-extension-template/blob/a0dd1f08381ce647c3b7056d405bd36f8d65b12a/src/common/settings.ts#L22-L42 and other Python extensions like vscode-black-formatter, etc.