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

[d-shehu]

This has been driving me nuts. Even if the venv command is in a script within a container that gets launched via tasks.json, I still get the contaminated stdin.

If I run the same command as tasks.json on the CLI and then attach from VScode it works fine. It also seems to occur on Linux irrespective of using shell or process, invoking the script directly or via bash -lc, etc.

[anthonykim1]

The activation command leaking into stdin is caused by the legacy command-based terminal activation mechanism, which sends the activate command as typed text via sendText.

Please try migrating to the Python Environments extension's shellStartup activation, which injects activation into your shell profile instead — no commands are sent via stdin:

1. Set python-envs.terminal.autoActivationType to shellStartup in your settings
2. Add "python.useEnvironmentsExtension": true to your settings.json

See more details here: https://code.visualstudio.com/updates/v1_106#_consolidated-shell-integration-timeout-setting

Also see #25291 for the full migration guide. Please let us know if this resolves the issue!

[samuelefiorini]

Thanks @anthonykim1, following your suggestion resolved the issue. No more leak:

Checking stdin buffer for leaked data...

✅ No data leaked into stdin buffer.