click shell_completion

Oldest completion functions from the argparse/argcomplete days: https://github.com/tmux-python/tmuxp/blob/v1.0.2/tmuxp/cli.py#L185

click-completion

https://github.com/click-contrib/click-completion

0.5.2 is in most package systems

https://repology.org/project/python:click-completion/versions
just got into debian: https://ftp-master.debian.org/new/click-completion_0.5.2-1.html