Bug report

In Fish, when starting tmux after activating a virtual environment, the deactivate command is not available in the tmux session.

$ python3 -m venv .venv
$ source .venv/bin/activate.fish
(.venv) $ tmux

This starts a tmux session with the virtual environment already activated, and working sort of correctly, but impossible to deactivate:

(.venv) $ echo $VIRTUAL_ENV
~/test/.venv
(.venv) $ which python
~/test/.venv/bin/python
(.venv) $ deactivate
fish: Unknown command: deactivate

Your environment

• CPython versions tested on: Python 3.11.2
• Operating system and architecture: macOS Ventura, M1
• Fish version- 3.6.1
• tmux version- 3.3a

Linked PRs

• gh-103291: Re-activate virtual environments in child processes #103447