Venv activation command leaks into stdin when running tasks on Windows

[samuelefiorini]

Type: Bug

Behaviour

When running a VS Code task, the venv activation command (& c:/path/to/.venv/Scripts/Activate.ps1) leaks into stdin instead of being executed as a shell command. This causes any input() call or stdin-reading command to receive the activation path as input, breaking interactive prompts.

This is probably a regression of #9374.

Steps to reproduce:

1. Create a workspace with a Python venv (I used uv venv .venv)
2. Select the venv interpreter in VS Code
3. Create this debug script (debug_stdin_leak.py):

import msvcrt
import sys

print("Checking stdin buffer for leaked data...")
leaked_chars = []
while msvcrt.kbhit():
    char = msvcrt.getch()
    leaked_chars.append(char)

if leaked_chars:
    leaked_data = b"".join(leaked_chars).decode("utf-8", errors="replace")
    print(f"\n❌ STDIN LEAK DETECTED!")
    print(f"Leaked data ({len(leaked_chars)} chars):")
    print(f"  {repr(leaked_data)}")
else:
    print("\n✅ No data leaked into stdin buffer.")

4. Create a task in .vscode/tasks.json:

{
    "label": "Debug: Check stdin leak",
    "type": "shell",
    "command": "${workspaceFolder}/.venv/Scripts/python.exe",
    "args": ["debug_stdin_leak.py"],
    "presentation": {
        "reveal": "always",
        "panel": "new",
        "focus": true
    },
    "problemMatcher": []
}

5. Run the task (make sure to close any existing terminals first so a fresh one is created)

Expected: stdin should be empty

Actual:

Checking stdin buffer for leaked data...
❌ STDIN LEAK DETECTED!
Leaked data (79 chars):
  '& c:/Users/.../.venv/Scripts/Activate.ps1\r'

Environment:

OS: Windows 11
Shell: PowerShell
venv created with: uv

Workaround: Flush stdin before reading input using msvcrt.kbhit() / msvcrt.getch()

Diagnostic data

Details

2026-01-21 11:35:56.908 [info] Native locator: Refresh started
2026-01-21 11:35:56.999 [info] Native locator: Refresh finished in 673 ms
2026-01-21 11:35:57.437 [info] Native locator: Refresh started
2026-01-21 11:35:57.447 [info] Skipping ActivatedEnv Detection:  process.env.VSCODE_CLI !== '1'
2026-01-21 11:35:57.478 [info] Python interpreter path: .\.venv\Scripts\python.exe
2026-01-21 11:36:01.339 [info] > pyenv which python
2026-01-21 11:36:01.340 [info] cwd: .
2026-01-21 11:36:02.389 [info] > conda info --json
2026-01-21 11:36:03.686 [info] Native locator: Refresh finished in 6249 ms
2026-01-21 11:36:07.857 [info] Starting Pylance language server.
2026-01-21 11:43:34.156 [info] Send text to terminal: & C:/Users/.../.venv/Scripts/Activate.ps1

Extension version: 2026.0.0
VS Code version: Code 1.108.1 (585eba7c0c34fd6b30faac7c62a42050bfbc0086, 2026-01-14T14:55:44.241Z)
OS version: Windows_NT x64 10.0.22631
Modes:

• Python version (& distribution if applicable, e.g. Anaconda): 3.12.9
• Type of virtual environment used (e.g. conda, venv, virtualenv, etc.): Venv
• Value of the python.languageServer setting: Pylance

User Settings

languageServer: "Pylance"

Installed Extensions

Extension Name	Extension Id	Version
amazon-q-vscode	ama	1.107.0
autodocstring	njp	0.6.1
aws-toolkit-vscode	ama	3.93.0
bash-ide-vscode	mad	1.43.0
black-formatter	ms-	2025.2.0
datawrangler	ms-	1.24.0
debugpy	ms-	2025.19.2026011901
docker	doc	0.18.0
even-better-toml	tam	0.21.2
git-graph	mhu	1.30.0
gitblame	wad	11.2.0
gitlens	eam	17.9.0
go	gol	0.52.1
js-debug	ms-	1.105.0
js-debug-companion	ms-	1.1.3
jupyter	ms-	2025.9.1
jupyter-keymap	ms-	1.1.2
jupyter-renderers	ms-	1.3.0
markdown-pdf	yza	1.5.0
pdf	tom	1.2.2
powershell	ms-	2025.4.0
prettier-sql-vscode	inf	1.6.0
pylint	ms-	2025.2.0
python	ms-	2026.0.0
remote-containers	ms-	0.437.0
remote-explorer	ms-	0.5.0
remote-ssh	ms-	0.122.0
remote-ssh-edit	ms-	0.87.0
remote-wsl	ms-	0.104.3
ruff	cha	2026.34.0
rust-analyzer	rus	0.3.2761
rust-syntax	dus	0.6.1
sqltools	mtx	0.28.5
sqltools-driver-mysql	mtx	0.6.6
sqltools-driver-pg	mtx	0.5.7
vscode-containers	ms-	2.3.0
vscode-github-actions	git	0.29.1
vscode-icons	vsc	12.17.0
vscode-js-profile-table	ms-	1.0.10
vscode-jupyter-cell-tags	ms-	0.1.9
vscode-jupyter-slideshow	ms-	0.1.6
vscode-nushell-lang	The	1.10.0
vscode-pylance	ms-	2025.10.4
vscode-python-envs	ms-	1.17.10151015
vscode-typescript-next	ms-	6.0.20260120
vscode-xml	red	0.29.0